Groundwater [Ground water] monitoring handbook for coal and oil shale development

GROUNDWATER MONITORING HANDBOOK FOR COAL AND OIL SHALE DEVELOPMENT DEVELOPMENTS I N WATER SCIENCE, 24 OTHER TITLES I ...

Author: Lorne G. Everett

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GROUNDWATER MONITORING HANDBOOK FOR COAL AND OIL SHALE DEVELOPMENT

DEVELOPMENTS I N WATER SCIENCE, 24 OTHER TITLES I N THIS SERIES

1 G. B U G L I A R E L L O A N D F. GUNTER COMPUTER SYSTEMS AND WATER RESOURCES 2 H.L. GOLTERMAN PHYSIOLOGICAL LIMNOLOGY 3 Y.Y. HAIMES, W.A. H A L L A N D H.T. FREEDMAN MULTIOBJECTIVE OPTIMIZATION I N WATER RESOURCES SYSTEMS: THE SURROGATE WORTH TRADE-OFF-METHOD 4 J.J. FRIED GROUNDWATER POLLUTION

5 N. R A J A R A T N A M TURBULENT JETS 6 D. STEPHENSON PIPELINE DESIGN FOR WATER ENGINEERS

v. HALEK AND J. SVEC 7 GROUNDWATER HYDRAULICS 8 J.BALEK HYDROLOGY A N D WATER RESOURCES I N TROPICAL AFRICA

9 T.A. McMAHON A N D R.G. M E l N RESERVOIR CAPACITY AND Y I E L D 10 G.KOVACS SEEPAGE HYDRAULICS 11 W.H. GRAF A N D C.H. MORTIMER (EDITORS) HYDRODYNAMICS OF LAKES: PROCEEDINGS OF A SYMPOSIUM 12-13 OCTOBER 1978, LAUSANNE, SWITZERLAND 12 W. BACK A N D D.A. STEPHENSON (EDITORS) CONTEMPORARY HYDROGEOLOGY: THE GEORGE BURKE MAXEY MEMORIAL VOLUME 13 M.A. MARIKO AND J.N. LUTHIN SEEPAGE A N D GROUNDWATER 14 D. STEPHENSON STORMWATER HYDROLOGY A N D DRAINAGE 15 D. STEPHENSON PIPELINE DESIGN FOR WATER ENGINEERS (completely revised edition of Vol. 6 in the series) 16 w. BACK AND R. L ~ T O L L E(EDITORS) SYMPOSIUM ON GEOCHEMISTRY OF GROUNDWATER 17 A.H. EL-SHAARAWI (EDITOR) I N COLLABORATION WITH S.R. ESTERBY TIME SERIES METHODS I N HYDROSCIENCES 18 J.BALEK HYDROLOGY AND WATER RESOURCES I N TROPICAL REGIONS 19 D. STEPHENSON PlPEFLOW ANALYSIS 20 I. Z A V O I A N U MORPHOMETRY OF DRAINAGE BASINS 21 M.M.A. SHAHIN HYDROLOGY OF THE N I L E BASIN 22 H.C. RIGGS STREAMF LOW CHARACTER ISTICS

23

M. NEGULESCU MUNICIPAL WASTEWATER TREATMENT

GROUNDWATER MONITORINfi HANDBOOK FOR COAL AND 011SHALE DEVELOPMENT LORNE G. EVERETT Kaman Tempo, 816 State Street, P.O. Drawer 00, Santa Barbara, CA 93102. U.S.A.

ELSEVl E R Amsterdam - Oxford

- New York - Tokyo

1985

ELSEVIER SCIENCE PUBLISHERS B.V. Molenwerf 1 P.O. Box 21 1,1000 AE Amsterdam, The Netherlands

Distributors for the United States and Canada: ELSEVIER SCIENCE PUBLISHING COMPANY INC. 52, Vanderbilt Avenue New York, NY 10017

ISBN 0 4 4 4 4 2 5 1 4 4 (Vol. 24)

I SBN 0-444-41669-2 (Series) 0 Elsevier Science Publishers B.V., 1985 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher, Elsevier Science Publishers B.V./Science & Technology Division, P.O. Box 330, 1000 AH Amsterdam, The Netherlands. Special regulations for readers in the USA - This publication has been registed with the Copyright Clearance Center Inc. (CCC), Salem, Massachusetts. Information can be obtained from the CCC about conditions under which photocopies of parts of this publication may be made in the USA. All other copyright questions, including photocopying outside of the USA, should be referred to the publisher, Elsevier Science Publishers B.V., unless otherwise specified. Printed in The Netherlands

To my parents whose lives began in a mining town in Canada

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LORNE G. EVERETT Dr. Everett is Manager of the Natural Resources Program for Kaman Tempo, formerly General Electric's Center for Advanced Studies, Santa Barbara, California. His current hydrology interests are related to the design of groundwater quality monitoring programs for coal strip mining, oil shale extraction, uranium mine abandonment, and hazardous waste disposal areas. In addition, he oversees programs relating to minerals, industrial, and agricultural development.

After completing his Ph.D. in Hydrology at the University of Arizona in 1972, Dr. Everett was invited to join the faculty in the Department of Hydrology. Prior to his current position, Dr. Everett was the Manager of Tempo's Water Resources Program and a principal investigator in developing a national groundwater quality monitoring methodology for the U.S. Environmental Protection Agency. Dr. Everett recently completed a major EPA contract to develop groundwater quality monitoring guidelines for all western coal strip mine operations and for surface and in situ extraction of shale oil. He has written fundamental EPA manuals on soil core monitoring and soil pore-liquid monitoring at hazardous waste disposal sites. Dr. Everett was asked to develop and present training programs to all 10 EPA regions on groundwater monitoring permit requirements for hazardous waste sites. Dr. Everett has worked under contract to the U.S. Department of Justice in managing testimony relative to water resource decisions. He has testified before Congress on national legislation relative to water monitoring. Dr. Everett was invited by the American Water Resources Association to be the Technical Chairman of a special symposium on water quality monitoring. He has published over 85 professional papers, book chapters, and reports. He is the principal author of the book Establishment of Water Quality Monitorins Programs and his handbook entitled Groundwater Monitoring is in its third printing. His handbook entitled Vadose Zone Monitorinq for Hazardous Waste Sites has received wide application. His recent publications include a Soil Gas Sampling Manual and a USEPA national guideline document on soil-core and soilpore liquid monitoring 'of hazardous waste sites.

vii

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ACKNOWLEDGMENTS Appreciation is extended to several members of the Tempo Geohydrologic staff who contributed to Part I of this book: Mr. Daniel B. Kimball, Mr. Michael B. Bishop, Mr. Kevin E. Kelly, and Mr. Edward W. Hoylman. Engineering aspects of the document were reviewed by Tempo engineers Mr. Donald C. Carlson, Mr. William E. Green, and Mr. George W. Quinn. Field investigations related to the document were conducted by Mr. James D. Brown and Mr. Michael G. Kuntz. The document was externally reviewed extensively by Ms. Margery A. Hulburt, former Chief Hydrologist, Wyoming Department of Environmental Quality: Mr. Wayne Van Voast, Senior Hydrologist, Montana Bureau of Mines and Geology; Dr. L. Graham Wilson, Professor of Hydrology, University of Arizona: and Dr. David B. McWhorter, Professor of Engineering, Colorado State University. Dr. Guenton C. Slawson, Jr., Mr. Kevin E. Kelly, and Mr. Edward W. Hoylman were principal contributors to Part I1 of this book. Dr. Slawson's involvement with the book ceased when he joined the Rio Blanco Oil Shale Company as Manager of Environmental Affairs. His insight into monitoring requirements is highly appreciated. Technical consultation and review for this study were provided by Mr. Glen A. Miller, U.S. Geological Survey, Conservation Division, Area Oil Shale Supervisor's Office. In addition, Kaman Tempo wishes to acknowledge the support and cooperative interaction of representatives of Tract C-a and C-b developers: Ms. Rosalie Gash and Ms. Marla Moody of the Rio Blanco Oil Shale Company, and Mr. R.E. Thomason and Mr. C.B. Bray of the C-b Oil Shale Venture. Special recognition is given to Mr. Leslie G. McMillion, EPA project officer, under whom this research was developed (EPA Contract No. 68-03-2449). His invaluable insights are reflected in the many recommendations which were developed over the 5 years of research required to prepare for this book.

ix

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PREFACE This handbook contains specific information on the application of a widely accepted groundwater monitoring methodology, which has been applied to coal and oil shale developmental sites. The original methodology described a chronological procedure for implementing a groundwater quality monitoring program. Activities of different steps within the methodology will, in practice, overlap to make sufficient use of personnel and time. The original steps include: Groundwater Monitorinq Methodolow Step

1 2 3 4

5 6

7 8 9 10 11 12 13 14 15

Select area or basin for monitoring Identify pollution sources and causes and methods of waste disposal Identify potential pollutants Define groundwater usage Define hydrogeologic situation Study existing groundwater quality Evaluate infiltration potential of wastes at the land surface Evaluate mobility of pollutants from the land surface to water table Evaluate attenuation of pollutants in the saturated zone Prioritization of sources and causes Evaluate existing monitoring programs Establish alternative monitoring approaches Select and implement the monitoring program Review and interpret monitoring results Summarize and transmit monitoring information.

This methodology, which has been endorsed by the U . S . Environmental Protection Agency as "establishing the state of the art used by industry today," is fully developed in the handbook entitled Groundwater Monitorinq by L.G. Everett and is published by the General Electric Company, Technology Marketing Operation, 120 Erie Boulevard, Schenectady, New York 12305. A complete review of groundwater monitoring techniques and pollution migration in the saturated zone can be found in this handbook. An exhaustive review of vadose (unsaturated zone) monitoring techniques and unsaturated flow characteristics can be found in the handbook entitled Vadose Zone Monitorinq for Hazardous Waste Sites by L.G. Everett, which can be purchased through Kaman Tempo, 816 State Street, Santa Barbara, California 93102.

The monitoring techniques in both the saturated and unsaturated zone identified in the above two books are used as the basis upon which the groundwater monitoring recommendations in this handbook are developed for coal and oil shale sites.

xi

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TABLE OF CONTENTS ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . PREFACE . . . . . . . . . . . . . . . . . . . . . .

.......... ..........

ix xi

PART..I GROUNDWATER MONITORING FOR SURFACE COAL MINES SECTION 1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . Groundwater Monitoring Methodology . . . . . . . . . . . . . . . Surface Coal Mining Technologies . . . . . . . . . . . . . . . . General Characteristics of Surface Mining . . . . . . . . . . Planning and Exploration . . . . . . . . . . . . . . . . . . . . Mining and Reclamation . . . . . . . . . . . . . . . . . . . . . Relation of Surface Mining to Potential Groundwater Pollution . Mine-Related sources of Potential contaminants . . . . . . . Relative Contamination Potential of Sources . . . . . . . . . Groundwater Pollution Model . . . . . . . . . . . . . . . . . Groundwater Pollution Pathways . . . . . . . . . . . . . . . . . Transportation/Mobility . . . . . . . . . . . . . . . . . . . . . Application to Western Surface Coal Mining . . . . . . . . . . . SECTION 2. PROJECT DEFINITION . . . . . . . . . . . . . . . . . . . . The Project Monitoring Area . . . . . . . . . . . . . . . . . . . . Generic Monitoring Steps . . . . . . . . . . . . . . . . . . . . . . Step 1 . Select Area or Basin for Monitoring . . . . . . . . . step 2. Inventory Potential Pollution Sources . . . . . . . . Step 4 . Define Groundwater Usage . . . . . . . . . . . . . .

.. .. ..

.. .. .. .. .. .. .. .. ..

SECTION 3 . MONITORING RECOMMENDATIONS FOR ACTIVE MINE SOURCES OFPOLLUTION . . . . . . . . . . . . . . . . . . . . . .. Stockpiles . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Topsoil . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Overburden .. Coal. Coal Refuse. and Coaly Waste . . . . . . . . . . . . . . . Step 3 . Identify Potential Pollutants.. Topsoil . . . . . . . . . Step 3 . Identify Potential Pollutants.. Overburden and Interburden . . . . . . . . . . . . . . . . . . . . . .. Step 3 . Identify Potential Pollutants..Coal. Coal Refuse. and Coaly Waste . . . . . . . . . . . . . . . . . . . . . .. Step 5. Evaluate Infiltration Potential . . . . . . . . . . . . . Step 6 . Mobility of Potential Pollutants in the Vadose Zone . . . Step 7 . Mobility in the Saturated Zone .. Pit Water .. Step 3 . Identify Potential Pollutants.. Pit Water . . . . . . . . Step 3 . Identify Potential Pollutants.. Impoundments . . . . . . . Step 5. Evaluate Infiltration Potential .. .. Step 6 . Evaluate Mobility in the Vadose Zone Step 7 . Evaluate Attenuation of Pollutants in the Saturated Zone . . . . . . . . . . . . . . . . . . . . .

..........................

...........

...........................

........... ........

xiii

1 2 3 3 5 5 6 6 8 8 9 9 9

12 12 12 12 15 16 20 20 20 20

21 22 26

31 36 39

42 44 44 49 53 55 60

SECTION 4.

MONITORING RECOMMENDATIONS FOR RECLAIMED MINE SOURCES OFPOLLUTION . . . . . . . . . . . . . . . . . . . .

... ............................ ... .. .......... .. .. ... .. .. .. ... ..

Spoils Step 3. Identify Potential Pollutants . . . . . . . . . . . . Step 5 . Evaluate Infiltration Potential . Step 6. Evaluate Pollutant Mobility in the Vadose Zone . . . Step 7. Evaluate Pollutant Mobility in the Saturated Zone . Reclamation Aids . . . . . . . . . . . . . . . . . . . . . . . . . Step 3. Identify Potential Pollutants . . . . . . . . . . . . Step 5. Evaluate Infiltration Potential . . . . . . . . . . . Step 6. Mobility in the Vadose Zone . . . . . . . . . . . . Step 7. Mobility in the Saturated Zone . . . . . . . . . . .

65 65 68 87 91 95 101 101

103 103 106

SECTION 5 .

MONITORING RECOMMENDATIONS FOR MISCELLANEOUS SOURCES OF POLLUTION . . . . . . . . . . . . . . . . . . . . . . . Spills and Leaks . . . . . . . . . . . . . . . . . . . . . . . . . . Step 3. Identify Potential Pollutants . . . . . . . . . . . . . . Step 5. Evaluate Infiltration Potential Step 6. Evaluate Pollutant Mobility in the Vadose Zone . . . . . Step 7. Evaluate Pollutant Mobility in the Saturated Zone . . . . Solid Wastes for Road Construction . . . . . . . . . . . . . . . . . Step 3 . Identify Potential Pollutants Step 5 . Evaluate Infiltration Potential Step 6 . Evaluate Pollutant Mobility in Vadose Zone . . . . . . . Step 7. Evaluate Pollutant Mobility in Saturated Zone . . . . . . LiquidShopWastes. . . . . . . . . . . . . . . . . . . . . . . . . Step 3. Identify Potential Pollutants Step 5. Evaluate Infiltration Potential . . . . . . . . . . . . . Step 6. Evaluate Pollutant Mobility in Vadose Zone Step 7. Evaluate Pollutant Mobility in Saturated Zone Explosives step 3. Identify Potential Pollutants . . . . . . . . . . . . . . . Mine Sanitary and Solid Wastes

.............

.............. .............

REFERENCES APPENDIX A. APPENDIX B.

.............. ....... ...... ............................. ................... .............................. CONVERSION FACTORS . . . . . . . . . . . . . . . . . . . . ACID-NEUTRALIZATION CALCULATIONS FOR SPOILS . . . . . . .

108 108 108 109 110 110 110 110 112 113 114 115 115 116 117 117 117 117 119 120

128 130

PART 11--GROUNDWATER MONITORING FOR OIL SHALE DEVELOPMENT

....................... ............................. ............... ........................... ........................... SECTION7. SUMMARY.. . . . . . . . . . . . . . . . . . . . . . . . . Hydrogeologic Characterization . . . . . . . . . . . . . . . . . . . Geophysical Methods . . . . . . . . . . . . . . . . . . . . . . . SECTION 6. INTRODUCTION Background Federal Prototype Lease Development Previous Work Present Study

xiv

145 145 145 146 147 150 150 150

........................ .......................... .....................

Hydraulic Methods sampling Methods Well Design . . . . . . . . . . . . . . . . . . . . . . . . . . . Monitor Well Placement Sample Collection Methods . . . . . . . . . . . . . . . . . . . . Sampling Frequency . . . . . . . . . . . . . . . . . . . . . . . Sample Preservation and Handling Selection and Preservation of Constituents for Monitoring . . Sample Analysis . . . . . . . . . . . . . . . . . . . . . . . . . Interpretation of Water Quality Data . . . . . . . . . . . .

................

..

.. SECTION 8. HYDROGEOLOGIC CHARACTERIZATION METHODS . . . . . . . . . . General Basin Hydrogeology . . . . . . . . . . . . . . . . . . . . . Lower Aquifer . . . . . . . . . . . . . . . . . . . . . . . . . . upper Aquifer . . . . . . . . . . . . . . . . . . . . . . . . . . Alluvial Aquifers . . . . . . . . . . . . . . . . . . . . . . . . Geophysical Methods . . . . . . . . . . . . . . . . . . . . . . . . Temperature Log . . . . . . . . . . . . . . . . . . . . . . . . . CaliperLog . . . . . . . . . . . . . . . . . . . . . . . . . . . Gamma-Ray Log . . . . . . . . . . . . . . . . . . . . . . . . . . spinner Log . . . . . . . . . . . . . . . . . . . . . . . . . . . Radioactive Tracer Log . . . . . . . . . . . . . . . . . . . . . Three-Dimensional Velocity Log . . . . . . . . . . . . . . . . . Acoustic Log . . . . . . . . . . . . . . . . . . . . . . . . . . Density Log . . . . . . . . . . . . . . . . . . . . . . . . . . . Electric Logs . . . . . . . . . . . . . . . . . . . . . . . . . . Seisviewer Log . . . . . . . . . . . . . . . . . . . . . . . . . Hydraulic Test Methods . . . . . . . . . . . . . . . . . . . . . . . Drill Stem Tests . . . . . . . . . . . . . . . . . . . . . . . . Single Packer Tests . . . . . . . . . . . . . . . . . . . . . . . Dual Packer Tests . . . . . . . . . . . . . . . . . . . . . . . . Long-Term Pump Tests . . . . . . . . . . . . . . . . . . . . . . Evaluation of Mine Development Data . . . . . . . . . . . . . . . . SECTION 9. SAMPLING METHODS . . . . . . . . . . . . . . . . . . . . . Well Construction Factors . . . . . . . . . . . . . . . . . . . . . Well Construction . . . . . . . . . . . . . . . . . . . . . . . . Well Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . Annular Seal . . . . . . . . . . . . . . . . . . . . . . . . . . Casing Material . . . . . . . . . . . . . . . . . . . . . . . . . Well Security and Protection . . . . . . . . . . . . . . . . . . Well Design and Sampling Costs . . . . . . . . . . . . . . . . . . . Well Design Costs . . . . . . . . . . . . . . . . . . . . . . . . Sampling costs . . . . . . . . . . . . . . . . . . . . . . . . . Monitor Well Placement . . . . . . . . . . . . . . . . . . . . . . . Sample Collection Methods . . . . . . . . . . . . . . . . . . . . . Bailing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pumping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Swabbing . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sampling Frequency . . . . . . . . . . . . . . . . . . . . . . . . . Sample Handling and Preservation . . . . . . . . . . . . . . . . . . Field Data Collection . . . . . . . . . . . . . . . . . . . . . . xv

151 151 152 155 155 158 159 160 162 162 164 164 166 166 167 168 171 172 176 176 180 182 183 187 196 202 205 206 210 216 220 227 229 229 229 233 233 234 236 236 236 238 239 239 241 249 258 259 260 260

............. ........... ......................... ........................ .............. ....................... ..................... ......................... ..................... ......................... ......................... ..................... ................ .......................... ........................ ........... ..............................

Field Notes and Records. Sample Labels Field Handling and Preservation Techniques Sample Shipment Chain of Custody selection of constituents for Monitoring Enrichment Factors Indicator Constituents Stable Isotopes Sample Analysis and Costs Trace Elements Organic Methods Other Inorganic Species Interpretation of Water Quality Data Data Analysis Data Presentation Data Interpretation and Reporting . . . . . REFERENCES

xvi

264 265 267 272 273 273 286 288 289 289 293 294 296 296 298 300 301

LIST OF ABBREVIATIONS AND SYMBOLS ABBREVIATIONS AND SYMBOLS bPd

barrels per day

MDP

mine development phase

OC

degrees Centigrade

meq

milliequivalent

cfs

cubic feet per second

mg/ 1

milligrams per liter

EPA

U.S. Environmental Protection Agency

MIS

modified in situ

ml

milliliter(s)

EMF

electromotive force PVC

polyvinyl chloride

OF

degrees F RBOSC

Rio Blanco Oil Shale Company

ft/min

feet per minute SP

ft

foot, feet

spontaneous potential, self-potential

ft2

square foot, square feet

SPI

secondary porosity index

g

gram( s1

USGS

U.S.

gm/cc

grams per cubic centimeter

pmho/cm micromhos per centimeter

gpm

gallons per minute

psec

microsecond(s)

3-D

three dimensional

gal/ ton gallons per ton

Geological Survey

CHEMICALS, IONS, CONSTITUENTS co2

carbon dioxide

I

iodine

cuso4

copper sulfate

MBAS

methylene blue active substances

DOC

dissolved organic carbon NaHC03

nahcolite

H2SO4

sulfuric acid NaOH

sodium hydroxide

H3PO4

phosphoric acid NTA

nitrilotriacetic acid

HNo3

nitric acid TDS

total dissolved solids

FORMULAE ABBREVIATlONS A

length of test section

S

storage coefficient

C

hydraulic resistance

SP

inflection point

xvii

cu

conductivity coefficient, unsaturated

cs

conductivity coefficient, saturated

T

t ransmissivity

Te

effective transmissivity

ti

flow time for each change in rate

hl

static water column head

tn

total flow time

h2

applied pressure

Tn

transmissivity in the direction (e+a) with the x-axis

H

effective head

k

hydraulic conductivity

K

permeability coefficient

kD

aquifer transmissivity

KO

Bessel function

L

leakage factor

m

slope

Q

constant recovery ( drawdown1 discharge

qi

ith flow interval

U

porosity

qn

last flow interval

X

percentage of unsaturated strata

r

distance from pumping well

d

porosity

S

drawdown

time corresponding to Sp transmissivity on major flow axis transmissivity on minor flow axis change in slope interval transit time fluid interval transit time matrix interval transit time change in pressure

xviii

PART I

GROUNDWATER MONITORING FOR SURFACE COAL MINES

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SECTION 1 INTRODUCTION

In recent years the nation has become increasingly dependent on imported foreign oil to meet its energy requirements. With rapidly escalating costs and decreasing security of domestic petroleum resources, many Government officials have advocated a shift from the use of foreign oil to the use of domestic coal. coal in the Western United States may represent an important part of the solution to the nation's energy problems. In many areas, these coal beds are relatively shallow, thick, and flat-lying and, therefore, may be readily mined by rapid and economical surface mining methods. Although coals of the Western United States are distant from the established energy-consumptive industrial areas of the East and have a lower energy content than eastern coals, the lower mining costs and reduced sulfur content of western coals tend to make them an acceptable and, in many cases, advantageous energy source. The low sulfur content of western coal tends to minimize air quality impacts at locations where it is consumed. As in the development of most earth resources, however, mining operations have the potential for contaminating water supplies by disturbing the local environmental equilibrium. In the Western United States water is generally scarce and usually represents a limiting factor in local and regional development. Therefore, while obtaining needed coal supplies, these valuable water resources must be conserved and protected from damage. Accordingly, this book is oriented toward conservation and protection of groundwater by development and presentation of a groundwater monitoring methodology. The objective of this study is to develop an exhaustive set of source-specific groundwater quality monitoring recommendations to guide government and industry representatives concerned with western coal strip mine programs. This book is a compendium of potential groundwater monitoring activities. The identified list of monitoring activities is not envisioned as universally applicable to western surface coal mine sites. It should serve as a reference to assist in the development of groundwater monitoring programs for specific site conditions, characteristics of the mining operation, and types of potential groundwater quality contamination. The book is structured to permit selecting from the table of contents specific potential pollution sources that may be present at a given mine site. Monitoring recommendations for each source are independently developed in the book to allow the user to quickly obtain those recommendations that are relevant t o his mine site. Because this listing of sources is presented in a handbook style, it does not lend itself to continuous reading. Each source 1

description is independent by design and, consequently, the methodology is repeated for each source. No overall summary or conclusion section is included since the book is composed of sections that are complete within themselves. GROUNDWATER MONITORING METHODOLOGY The U . S . Environmental Protection Agency (EPA) is responsib'le under the Federal Water Pollution Control Act Amendment of 1972 (Public Law 92-500) and the safe Drinking Water Act of 1974 (Public Law 92-523) to prevent, reduce, and eliminate groundwater quality degradation. In view of this responsibility, the EPA developed a methodology to monitor the effects of human activities on groundwater quality (Todd et al., 1976). The methodology was applied to two types of energy-related activities in the Western United States--oil shale extraction and surface coal mining. The monitoring recommendations presented in this book follow a systematized 8-step methodology that has evolved from an earlier 15-step version (Todd et al., 1976). The methodology is partially based on characterization of the hydrologic system involved and is described later under the heading "Groundwater Pollution System." The eight steps used here are shown in Table 1. TABLE 1. GROUNDWATER MONITORING METHODOLOGY Step 1.

Select study area for monitoring

Step 2. Inventory potential pollution sources and methods of disposal Step 3 .

Identify potential pollutants

Step 4.

Identify groundwater usage

step 5.

Evaluate infiltration potential

Step 6. Evaluate pollutant mobility in vadose zone Step 7. Evaluate pollutant mobility in saturated zone Step 8. Prioritize sources a.

Potential pollutant amounts and concentration

b.

c.

Amounts infiltrating Mobility of infiltrating pollutants in vadose zone

d.

Mobility of pollutants reaching saturated zone

step 1 is directed toward the selection of study areas for groundwater monitoring based on certain administrative and physiographic considerations. These considerations are used to divide a State (or area under consideration) into manageable study units. Once these are established, study area priorities should be evaluated using available information on the types and numbers of potential pollution sources present in each area. In some instances, sufficient information may be available in order to arrive at priorities. In 2

many instances, only limited information will be available, and Step 2 of the methodology will assist in obtaining the necessary information. In instances where the monitoring methodology is to be applied to a particular mining operation, the study area is initially known and site and operations information may be sufficient to prioritize study areas. Step 2 of the methodology includes a detailed inventory of potential sources of pollution and methods of waste disposal in the study area. During Step 2, a comprehensive priority listing of potential groundwater pollution sources should be attempted. Results of this initial evaluation will be enhanced by knowledge of case histories of groundwater contamination that have resulted from similar sources in similar environments. Since this book is intended to present monitoring recommendations for a series of generic groundwater pollution sources related to coal strip mining, no reference is made to any specific mine site. Step 8 is the priority ranking scheme presented in Everett (1979) and requires mine-specific data for each of the Steps 1 through 7. Potential sources of pollution are ranked in terms of the four substeps of Step 8. Steps 3 , 5, 6, and 7, however, are fully discussed for each of the pollution sources. A coal mine operator planning to use the monitoring methodology would select those potential sources associated with his operation from the list given in Table 2. Funds allocated to each potential source for development of an appropriate monitoring program would be based on relative significance. To develop this program, Steps 3 through 8 of the methodology would be applied to each source in order of the source's priority or importance at the particular mine site. The priority of the pollutant source can be established by identifying the individual potential pollutants involved (Step 31, the intended uses of the water (Step 4 1 , the infiltration rate of the pollutants (Step 5 1 , the rate of movement of the pollutants in the vadose zone (Step 6 1 , and the rate of pollutant movement in the saturated zone (Step 7 ) . The primary goal is to evaluate the effectiveness of monitoring for each of the existing sources and determine the potential for groundwater contamination from each source based on the priority established in Step 8. SURFACE COAL MINING TECHNOLOGIES General Characteristics of Surface Mining Important advantages usually cited for the surface mining of coal are relatively high rates of production and low cost. Generally, the greatest effort and largest cost factor in surface mining is stripping and replacing overburden. Thus, for a given thickness and quality of coal, optimal mining conditions exist where geologic conditions facilitate stripping (e.g., where the coal deposits are large and flat-lying with thin, uniform overburden that is easily fragmented). Irregular topography causes undesirable and sometimes locally restrictive variations in thickness of overburden. With dipping beds, the thickness of overburden increases in a down-dip direction to a point where

3

TABLE 2.

RANKING OF POTENTIAL SOURCES OF GROUNDWATER POLLUTION FROM SURFACE COAL MINING OPERATIONS (after Everett, 1979)

1.

spoils

2.

Pit water

3.

Sedimentation ponds

4.

Explosives

5.

Mine solid waste and shop liquid wastes

6.

Sanitary waste

7.

Spills 8. Leaks 9.

Stockpiles a.

Topsoil

b.

Overburden

c.

Coal

d.

Coal refuse

10.

e. Partings Reclamation aids

11.

Solid waste from road construction

continued mining is uneconomical. Under present equipment limitations, it is difficult to mine at depths much greater than 200 feet.* The type of geological material in the overburden, whether it is solid bedrock that is difficult to break up and load or soft or fractured rock, is an important cost factor. The quality of the overburden and the degree to which selective handling is necessary must also be considered. The ratio of overburden thickness to recoverable coal thickness may provide a rough rule of thumb for mining feasibility. A low ratio, in many instances, is advantageous in terms of recovery, grade control, flexibility of operation, safety, and general working environment. Various other economic factors, including availability of markets, market value, distance of transport, and, more recently, the cost of environmental protection, are included as factors in such a rule of thumb, as well as in other more detailed economic evaluations of the coal and its development potential.

* See Appendix A for conversion to metric units. English units are generally used in this book because of their current usage and familiarity in industry and the hydrology-related sciences. Certain units, expressed in commonly used metric units (e.g., concentrations), are expressed as milligrams per liter or similar units. 4

commonly used surface mining and reclamation procedures and sequences of operation vary among different areas and mines because of physical and economic conditions, local availability of equipment, and other conditions. The following brief outline is broadly representative of western surface coal mining procedures, including those that may affect groundwater. Planninq and Exploration In planning for mining and reclamation of a coal property, a number of geographic and geologic factors must be considered. climatic conditions, including rainfall, temperature, and other weather conditions, may affect the physical characteristics of the earth materials that must be handled, the types of equipment required, annual working days, general efficiency of the operation, and reclamation practices. Geologic and surface topography influence the design of the pit as well as equipment type and mining and reclamation procedures. Topographic and geologic mapping and exploratory drilling are usually needed to obtain information on the thickness, character, dip, and strike of the overburden and coal and on subsurface water conditions. Systematic coring of the overburden and coal throughout a proposed mine yields samples for detailed physical and chemical analyses. Mininq and Reclamation An initial step in uncovering the coal seam that is to be mined is removal of topsoil and subsoil from the area and stockpiling for replacement over spoils or other disturbed areas during reclamation. Scrapers are used for removing soil. Overburden that lies between the soil and the 'coal seam is removed or stripped to expose the coal, using combinations of shovels, draglines, scrapers, and bulldozers. Typically, stripping and subsequent removal of the exposed coal occur in alternating sequence along a series of elongated, parallel 'cuts" designed to uncover the area of proposed mining. The overburden is progressively removed along one cut at a time. The waste overburden (or spoil) is dumped into t.he adjacent parallel cut from which coal had been previously removed. Toxic or acid-forming materials with a high potential for causing environmental contamination are selectively removed, stored, and ultimately placed in the spoils or on the surface in a location and manner to minimize future leaching or mobility of the potential contaminants. The exposed coal is drilled and fractured with explosives, as necessary, thereby facilitating loading of coal by mechanical shovels. From the pit, the coal is hauled by truck or conveyor belt to the preparation plant where, commonly, it is crushed, screened, sized, and graded, and then loaded on railroad cars or trucks for transport to a more distant point for further processing and/or usage. Western coals are very seldom washed. Upon completion of coal removal, overburden is graded, surface drainage patterns restored, and topsoil and subsoil respread and seeded.

5

RELATION OF SURFACE MINING TO POTENTIAL GROUNDWATER POLLUTION Mine-Related Sources of Potential Contaminants Surface mining operations may result in basic environmental changes which, in turn, can cause or contribute to groundwater pollution. These changes can be classified as: (1) disturbances of the solid earth materials, (2) disturbances of the surface water and groundwater, and ( 3 ) introduction of miscellaneous foreign liquid and solid materials into the local environment. Discussions of specific "sources" of potential pollutants (as shown in Figure 1) resulting from mining follow. Excavation of solid materials, which may have been protected from chemical and physical interaction with circulating water and air, and the storage or deposition of these materials on the surface may lead to release of pollutants to the hydrologic environment. Depending on the particular mining operation, these stored or deposited materials may consist of constituents of the coal and overlying zones, such as soils, overburden from between the soil and coal zones, rider coal seams or coal stringers, coal waste, coal refuse, and partings. Most of the overburden that overlies the coal seam and must be removed to expose the coal for mining is immediately placed in an adjacent or nearby part of the pit from which coal has been removed. As soon as practicable, the rough surface of these "spoils" is reclaimed (i.e., recontoured, soils replaced, and seeded). This tends to minimize the release of potential contaminants from the spoils by reducing infiltration and exposure to water, air, and wind erosion. In many instances, earth materials and wastes from the general mining operations that are potentially toxic, acid forming, or otherwise environmentally threatening are selectively placed at protected locations within the spoils zone. Although permanently buried spoils are better protected from the elements than those displaced materials that are temporarily or permanently placed on the surface, they are major potential contributors to groundwater contamination because of their large volume and geohydrologic characteristics. Also, because of their subsurface location, spoils above or below the water table may more readily transmit contaminants directly to the groundwater zone. In comparison, only limited contaminants released from surface sources may reach the groundwater zone, due to possible diversions to other surface locations and greater attenuation along the generally more lengthy and circuitous route to the groundwater zone. Air entrapped during backfilling of the spoils or moving into the spoils through available openings may appreciably increase the potential for oxidation and dissolution of certain mineral constituents in the spoil material. In addition to the disturbed solid earth materials, several other minerelated sources of potential groundwater contaminants exist. The most important of these are pit water and sedimentation pond water. Pit water is composed of surface water and groundwater that collects in open pits from which the coal and overburden have been removed. Water in sedimentation ponds is collected from surface runoff and pit sources. Both pits and sedimentation 6

Figure 1

Potential pollution source interrelationships--western surface coal mining Operations

ponds may collect water that is already naturally or artificially contaminated, or the water may become contaminated by contact with coal or rock materials in the pit or pond. Concentrations of dissolved solids also may increase due to evaporation. Subsequently, seeps or other discharges from the pit or pond may enter and contaminate groundwater zones. Under most conditions, the chemical quality of waters in pits and ponds is not sufficiently poor so as to damage the hydrologic balance. However, miscellaneous byproducts or wastes from mine operations may be released to the environment and become potential groundwater contaminants. These wastes include explosives, shop wastes, sanitary wastes, spills, leaks, and reclamation aids. Relative contamination Potential of Sources The schematic cross section of a surface coal mine in Figure 1 shows the interrelations of various contaminant "sources," the disturbed environment, and the undisturbed environment. As indicated in Table 2, spoils are ranked as having the highest groundwater pollution potential at typical mining operations because, at most locations, they comprise a large volume of disturbed earth material that is subject to leaching by water in the vadose and saturated zones (Everett, 1979). The priority ranking for specific mines should be based on a sequence of data compilation and the evaluation steps of Table 1. The three basic criteria used to develop a site-specific source pollutant ranking include: Potential mobility Waste characteristics, i.e., volume, persistence, toxicity, and concentration Usability. Guidelines for monitoring these sources of potential groundwater pollution are presented in Section 3 , Monitoring Recommendations for Active Mine Sources of Pollution, and Section 4 , Monitoring Recommendations for Reclaimed Mine Sources of Pollution. Groundwater Pollution Model Effective counteraction against potential or existing groundwater pollution requires an understanding of the sequences of processes and conditions involved in the transport of pollutants from a source to the groundwater zone. Through analysis of the potential pollutants, the local environmental conditions, and their possible interactions at a m i n e site, it is possible to develop a diagrammatic model of part of the total hydrologic cycle of groundwater pollution. Since the hydraulics of water movement from the land surface to the saturated zone are of secondary interest, this model emphasizes the physical, chemical, and biological processes that contribute to or limit the potential for groundwater pollution. It assists in visualizing the movement and effects of pollutants in the hydrologic cycle as they relate to the various steps in the methodology.

8

Figure 2 illustrates the sequence of hydrologic processes and conditions considered by the model. With the model, it may be possible to identify critical stages in the contamination process where countermeasures that prevent, minimize, or mitigate pollution are necessary. The component processes and conditions will vary in detail from one mine site to another. Total knowledge of the groundwater system is not likely to be available at any location. HOWever, the available information, augmented by reasonable hypotheses, is often sufficient to provide a workable model, or possibly several alternative ones, that can be used as a starting point in countering pollution. Even where data are grossly inadequate, it is worthwhile to construct one or several best-possible alternative conceptual models of the probable and possible local groundwater contamination systems for use in planning an initial data collection program. In all situations, the accuracy of the model and its use fulness in designing pollution countermeasures are upgraded as additional data are gathered and evaluated. The groundwater pollution system has a number of basic component processes and conditions, each with a particular function in the overall system (Figure 2). After examination oE the components of the system and their functions, it becomes apparent that pollutant transport is analogous to a conventional transportation system. Steps 3 through 7 in the monitoring methodology, which relate to the pollutants and their interaction with the earth environment, correlate with components of the pollution system, as indicated in Figure 2. Thus, by following the steps of the methodology, an understanding of the pollutant-environment interrelations and of other factors needed in monitoring design is achieved. GROUNDWATER POLLUTION PATHWAYS Transportation/Mobility As further illustrated in Figure 2, the pollution system diagram (which also shows the steps for the groundwater monitoring methodology) shows the source of pollutants to be on the land surface. With the exception of the "infiltration" component, however, the diagram is equally applicable to underground sources. In a typical case of groundwater pollution, there is a "source" (origin) OE the polluting material, a "vehicle" for transport of the pollutant, and one or more "routes" along which the pollutant is transported to a groundwater "destination." Typically, the transporting agent is water in which the pollutant is suspended or dissolved. Wind is an important transporting agent in some instances. In less common instances, animals, vegetation, or even gravity (e.g., earth slides) may act as transporting agents. In the case of water transport, gravity is usually the force moving pollutants from a higher to a lower elevation. Under some relatively unusual conditions, subsurface pollutants might be transported by artesian groundwater flow from a lower to a higher location. Under unsaturated conditions, water solutions can be moved either upward or downward by capillary forces. APPLICATION TO WESTERN SURFACE COAL MINING As a means to illustrate how the groundwater monitoring methodology may be applied to western surface coal mining operations, Campbell County, Wyoming 9

MONITORING METHODOLOGY STEP 1

STEP

IDENTIFY SOURCES OF POLLUTANTS

STEP

IDENTIFY POTENTIAL POLLUTANTS

1

t

GROUNDWATER US1

INFILTRATIO

t

I

II1 h’obility o! pollutants in the vadose zone is a ‘unction of conditions and processes including the openings (site. continuity. directsons.permeabilitiesl. gradients Ihvdraulic, capillary. thermal, salinity], dildtion. evapnratlrm. tiin exchange. adsiirption, prmpltatiun and other plrvsical. chemlcalhological conditions and processes.

VADOSE ZONE

V

WATER‘TABLE

PROJECT AREA]

DO

SURFACE FCOW

LAND SURFACE

ISELECT

--1

A

\

I

EVALUATE STEP 6 POLLUTANT MOBILITY IN VADOSE ZONE

I

--

L>

POLLUTION OF GROUNDWATER

SATURATED ZONE

Mobility of pollutants In the saturated zone 8s a function of the phvsicallchernml: biological characteristics of the aquifer. the pollutant, the exlrtmg groundwatpt qualrty, Qmdof the general hvdrologv

PRlORlTlZE SOURCES STEP 8

Figure 2.

Pollution model diagram.

I

(not part of pollution system)

I

has been chosen as an example study area. However, the recommendations outlined in this document are intended to apply to individual mine sites throughout the western states. Potential sources of groundwater pollution from surface coal mining have been identified through research, interviews, and site visits to mines in the Powder River Basin. Each of these potential pollution sources is presented separately. A source-specific monitoring program is developed for each source by following Steps 3 through 7 of the methodology. Under each step, existing data for the study area are examined, monitoring methods are identified, possible alternative monitoring approaches are discussed, and a monitoring scheme is recommended. Once Steps 3 through 7 are completed, recommended monitoring approaches for each step are integrated into an overall monitoring program (Step 8) for a specific mine. A computer interactive systems version of the EPA groundwater quality monitoring methodology given in Everett and Rasmussen (1982) can be used to assist in this process. By following the format presented in this guideline, a user will be able to develop a groundwater monitoring program that is tailored to a specific mine. Information included in this book is based on: (1) field studies and monitoring at coal mine sites located throughout the western coal-producing states, ( 2 ) background acquired during continuing studies of groundwater pollution and monitoring over a period of 10 years, and ( 3 ) the accumulated personal experience of a number of specialists who contributed to this study.

11

SECTION 2 PROJECT DEFINITION THE PROJECT MONITORING AREA Although the example project area used in this book is located in campbell County, Wyoming (see Figure 3 ) , the groundwater monitoring recommendations have been expanded to include all western coal strip mining operations. Campbell County is the largest producing coal field in the Western United States and contains about 50 percent of Wyoming's coal resources and approximately 84 percent of its known strippable coal. At least 20 billion tons lie within 200 feet of the surface and are recoverable by surface mining methods (Breckenridge et al., 1974). Within the project area (Figure 4), several coal mines at various levels of production were identified. The majority of the examples used in this book are taken from the seven mines identified in Figure 4. The majority of the potential pollution problems associated with coal strip mining were assumed to be represented by the seven mines; therefore, the monitoring recommendations have been generalized to cover all western coal strip mine development. GENERIC MONITORING STEPS Before evaluating monitoring needs for individual sources of potential pollution from surface coal mining activities, Steps 1, 2, and 4 of the methodology must be addressed. Step 1. Select Area or Basin for Monitorinq The selection of areas to be monitored (on an areawide basis) will be made within a State by a designated monitoring agency (DMA). The DMA may be a Federal or State agency charged with developing the monitoring program. The basis for selecting areas will be governed, in general, by a combination of administrative, physiographic, and priority considerations. For a coal mining operation, the operator is required to monitor the hydrologic balance within the "mine plan and adjacent areas" of the mine. These monitoring areas are defined in the OSM Permanent Regulatory Program at 30 CFR 701.5 (and approved State regulatory programs) and include the area to be disturbed by mining and the surrounding lands where surface or groundwaters may be adversely affected by coal mining and reclamation operations. The operator's identification of the mine plan (or permit) and adjacent areas fulfills the requirements of Step 1 of the methodology.

12

Administrative ConsiderationsThe initiation of an areawide groundwater monitoring program requires specification of a local DMA. In many situations, the requisite agency with the necessary technical staff will be the designated coal regulatory authority in the State (possibly cooperating with other county, district, or regional organizations). The size of a particular area may vary from a few square miles to thousands of square miles. Size alone is less important than the ready assessibility of all portions of the area t o the DMA as well as hydrogeologic knowledge of the area by the DMA.

0

50

a & a

100

M MILES

MAJOR COAL BEARING AREAS STRIPPABLE COAL PROJECT AWEA

Figure 3. Major coal fields of Wyoming (adapted from U.S. Geological Survey, 1974).

13

LEGEND BOUNDARY LINE A BETWEEN EPHEMERAL AND INTERMITTENT STREAMS

A

WATERSHED BOUNDARY EPHEMERAL OR INTERMITTENT STREAM INTERMITTENT OR P E R E N N I A L STREAM

.....

MONITORING AREA PROJECT COAL LEASE AREAS

1

CARTER N O R T H RAWHIDE

2

A M A X EAGLE BUTTE

3

WYODAK

4

A M A X BELLE AYR SUN O I L CORDER0 KERR McGEE JACOBS RANCH

?

I

T41N RJ5W

j

I Figure 4.

1

1

I

1

A R C 0 BLACK THUNDER

T41N R69W

Map of project monitoring area, Campbell County, Wyoming (after Everett, 1979).

14

Political boundaries frequently create water management problems. such a boundary may cross a major groundwater basin so that, for example, pollutants from an adjoining area may be entering from sources not subject to monitoring by the DMA. Clearly, such situations should be minimized as much as possible. Alternatively, cooperation among DMAs sharing common groundwater pollution problems will be essential to the success of their respective monitoring programs. Physiographic Considerations-The physiographic basis for selecting monitoring areas includes the recognition that groundwater basins are distinct hydrographic units containing one or more aquifers. Such basins usually, but not always, coincide with surface water drainage basins. By establishing a monitoring area related to a groundwater basin, total hydrologic inflows to and outflows from the basin are fully encompassed. This permits all pollution sources and their consequent effects on groundwater quality to be monitored. Where basins are extensive, monitoring areas become impractically large. Boundaries should then be drawn parallel to groundwater flows or where crossElow components are insignificant. Most groundwater basins in the United States have been mapped, based on hydrogeologic investigations, and information is available from State water agencies and/or the U . S . Geological Survey. Priority Considerations-Establishment of a national program to assess the impact of coal activities on groundwater quality will develop gradually because of administrative, budgetary, and personnel constraints. Since it is the stated intent of the EPA to rely on the States to select the areas to be monitored and to conduct the appropriate monitoring activities, any national program that evolves will, consequently, be built upon the data and information generated by these State monitoring activities. A first consideration of a State will be to select and rank aquifers subject to the greatest pollution threat. This first level of priority ranking is a necessary starting point for application of the groundwater monitoring methodology. Rarely will sufficient data and information be initially available for anything but a gross appraisal of the threat. To apply the methodology most effectively on a spatial basis, areas that have the largest number of identified or potential pollution sources and a high utilization of groundwater should be ranked and sectioned off as areas within which to apply the monitoring methodology. By utilizing the above two criteria in combination with the administrative and physiographic considerations previously set forth, the total area of a State can be divided into areas that may require monitoring programs.

Step 2. Inventory Potential Pollution sources The design of a monitoring program requires identification of the potential sources of waste disposal within an area. Important mine-related sources of contaminants are listed in Table 3 and classified in order of their 15

potential for contaminating groundwater at typical mine sites. Priority lists for individual mines may differ in sequence. As indicated in Table 3, the sources may also be classified by whether they are most closely related to active mines, reclaimed mines, or miscellaneous contamination sources. Recommendations for monitoring active mine sources are presented in Section 3 and those for reclaimed mine sources are presented in Section 4. Recommendations for miscellaneous sources are discussed in section 5. Sources in all three categories, however, may exist at an operating mine. TABLE 3. Active Mine Pit water Impoundments Stockpiles

CATEGORIES OF POTENTIAL POLLUTION SOURCES Reclaimed Mine

Miscellaneous Sources

spoils Reclamation aids

Mine solid wastes Liquid shop wastes Sanitary waste spills Leaks Solid waste from road construction Exp 10s ives

Step 4. Define Groundwater Usaqe While Steps 3 , 5, 6, 7, and 8 must be developed for each potential source of pollution, Step 4 applies to each source and need not be discussed in Sections 3, 4 , and 5. Groundwater contamination is the principal subject of concern in this study because of its effect on the usefulness of water. Water quality standards generally define water pollution in terms of its use. For each use, a standard may specify separate mandatory and recommended limits for certain physical characteristics and for concentrations of certain constituents. Thus, in evaluating the groundwater contamination potential of specific sources and development of related monitoring programs, groundwater use must be considered. Existing or potential uses most likely to be affected are those located downgradient along the paths of groundwater flow. In addition to being a potential target of contamination, groundwater also can be a contributor to the contamination process. For example, it may act as a loading and transporting agent when in contact with spoil materials either in the unsaturated or saturated zone. Usage may also cause consumptive losses that increase dissolved solids concentrations in the remaining water. Groundwater withdrawals and uses may change the water table elevation within the spoil zone and affect the types and magnitude of pollutants being released from the spoils. For certain potential contaminants (e.g., iron sulfide minerals such as pyrite and marcasite which are below the water table), the protective presence of groundwater (with an oxygen diffusion coefficient four times less than for sulfides in air) may exclude oxygen and thereby retard the 16

contaminating effects of sulfide oxidation (Pionke and Rogowski, 1979). Other potential contaminants, such as soluble salts, are more subject to release below the water table. While most western spoils contain sufficient soluble salts to buffer groundwater against acid production through the oxidation of pyrites, the oxidation of sulfide minerals can cause liberation of elevated levels of dissolved solids, primarily in the form of sulfates. Ultimately, source-related pollutants may deleteriously affect various groundwater uses (e.g., municipal, agricultural, and industrial) if leachate from the source occurs. An inventory of types of uses, including the volume and location of pumping centers, is an integral component of a monitoring design and is required under the OSM Permanent Regulatory Program (30 CFR 779.15). shallow wells apparently are not used for domestic groundwater in the vicinity of the project mines. Almost all water used for domestic purposes is pumped from the deeper Fort Union or Fox Hills aquifers. However, shallow wells in the study area are used for agricultural water. Most of the groundwater used on the mine sites in the study area comes from pit discharges (averaging about 100,000 gallons per day). Dust suppression is the primary use of pit discharge water, requiring up to 80,000 gallons per day during summer months. Deep wells at mine sites supply potable water for drinking, bathing, and cleanup. Potable water consumption varies depending on mine equipment, maintenance, shop cleaning, and bath house capacity. A suitable supply of groundwater to irrigate spoils for vegetation establishment is a spoils reclamation concern. The benefits of temporary irrigation to assist in revegetation of mined areas have been studied by several researchers throughout the semiarid coal mining region (Gould, Rai, and Wierenga, 1975; Ries, Power, and Sandoval, 1976; Ries and Day, 1978; Depuit, Coenenberg, and Dollhopf, 1979; and Young and Depuit, 1981). This research indicates that temporary irrigation extends the period for successful seeding, suppresses weed invasion, enhances stand diversity, and generally assists in the establishment of perennial grasses. With the benefits that have been demonstrated by numerous researchers, temporary irrigation may become a common reclamation practice in the semiarid West. Thus, irrigation demands on existing or new wells may occur. The application of irrigation water, however, may also lead to additional percolation through the spoils, thereby increasing the potential for groundwater contamination.

Monitoring Information Needs-A monitoring program designed to identify groundwater usage in a potential pollution area should include the following background information: 0

Potable water requirements for domestic purposes

0

Variations in pit discharge quantity over time

0

Volume of water used for dust suppression over time

17

Sources of supplemental water for dust suppression, fire protection, and coal preparation Volume of water used for shop, office, and sanitary purposes Locations of water supply wells, springs, and seepage areas relative to potential pollution sources Irrigation requirements for vegetation reestablishment Stock and wildlife watering requirements Volume of streamflow used for stock and irrigation downgradient of the mine area(s). Alternative Monitoring Approaches-Nonsamplinq methods-Several alternatives are available for characterizing groundwater use: Determine Furrent efforts by the mine to quantify groundwater use for various needs and collect available water use data. Count truckloads of water sprayed on roads for dust control and obtain the capacities of the trucks. Obtain locations of pumping centers and uses of well water through discussions with mine personnel. Estimate domestic usage from the number of mine employees. Locate water supply wells on a base map by contacting the mine operator or the State engineer. Obtain data on the capacities of on-site wells. Estimate pumpage from power consumption data. Assess anticipated use of groundwater for irrigation of reclaimed land through discussions with mine personnel. (If irrigation is being used, the quantity of water can be monitored with metering devices installed in the supply lines. The volume of water needed for irrigation can also be estimated by using the Thornthwaite (1948), Blaney-Criddle (1950), or other similar method in conjunction with monthly precipitation records.) Obtain data on groundwater uses by discussions with mine personnel and local residents; by review of mine plans, hydrologic and geologic reports, and maps; and by field observations. For each of the foregoing categories, some estimates of the percentages of consumptive and nonconsumptive water use are desirable. 18

Samplinq methods--No sampling methods are required to determine groundwater usage under this step. Recommended Monitoring Approach-All the nonsampling methods should be employed as a function of relative levels of concern. The costs will include little or no capital expenditures and will be limited essentially to manpower rates.

19

SECTION 3 MONITORING RECOMMENDATIONS FOR ACTIVE MINE SOURCES OF POLLUTION This section develops Steps 3 , 5 , 6 , and 7 of the groundwater monitoring methodology for each of the active surface coal mine pollution sources. These sources include: stockpiles (topsoil, overburden/interburden, coal, coal refuse, coaly waste, partings), pit water, and impoundments. The discussion and recommendations for impoundment monitoring are detailed and cover sedimentation ponds , evaporation ponds , sewage lagoons, and permanent impoundments. Step 8 is a mine-specific application of the methodology and is developed in Everett ( 19 7 9 ) . STOCKPILES Stockpiles can act as groundwater pollution sources when precipitation percolates through the stored material, dissolving pollutants and transporting them to the groundwater system. They are also subject to leaching from ponded surface waters or irrigation. Classes of material that may be stored in stockpiles during the active mining phase are topsoil, overburden, coal, coal refuse, coaly waste, and the partings that occur between coal seams. Stockpiles may be very temporary or they may exist for the life of a mine. Topsoil At all the Powder River Basin coal mines, some topsoil is selectively removed and stockpiled before being replaced on top of regraded overburden. Commonly, topsoil from the first area to be mined is stockpiled because no place to use it yet exists. For example, at one mine the topsoil removed from the first area to be mined will remain stockpiled until used to cover the final area to be mined in about the year 2000. Topsoil might also be stockpiled for blending to upgrade the quality of reclamation soil cover.

Overburden Overburden is that material lying between the topsoil and the mineable coal beds. In the study area, the mineable coal lies at or near the top of the Fort Union Formation and the overburden is sandstone, shale, carbonaceous shale, and thin or impure coal beds of the Wasatch or uppermost Fort Union Formations. In local areas, along the outcrops of coal beds, a unique rock type has been formed by the baking of shale and siltstone by burning coal beds. The baked material is commonly called scoria or clinker and may also be 20

incorporated in the overburden. An additional type of overburden is the alluvium found in the stream valleys. It consists of gravel, sand, silt, and clay derived from the bedrock units. Overburden thickness in operating and proposed mines ranges from none at the outcrop of the mineable coal up to perhaps 300 feet as the coal beds are traced westward into the Powder River Basin. The thickness of the overburden that can be removed at a mine is based on economics and available technology. During mining, the overburden is removed, the coal extracted, and the overburden then replaced and graded to the desired topography. Overburden removed during early development of a mine is stockpiled because there is no previously mined area in which to place it. Toxic or acid-forming material should be stockpiled separately. Materials suitable for aquifer reconstruction may also be handled separately. goal, Coal Refuse, and Coaly Waste Coal, coal refuse, and coaly waste are geologically and chemically similar. Coal refuse is the fine coal and waste material removed during the coal preparation process. Coaly waste describes the thin coal seams, impure coal, and carbonaceous shale that may occur in the overburden and within the partings between coal seams. Despite their geological and chemical similarity, these materials are identified separately because they are handled differently and, therefore, have differing water pollution potentials. Coal, the commercial product, is handled carefully. It is mined soon after exposure by stripping and is not allowed to weather. After mining, it is usually processed in some manner. Common steps in coal processing include crushing, screening, and washing. Coal from Powder River Basin mines is usually only crushed. After crushing, it is temporarily stored in silos, bunkers, or open piles (used only occasionally, limiting their potential for pollution from infiltration). Coaly waste is considered separately from the remainder of the overburden because it usually has a different type and amount of water pollution potential. Its geochemical properties also affect its potential as a soil-forming material. Such materials commonly form toxic soils and are thus segregated from the other overburden during mining. Western coaly waste commonly has elevated levels of sulfides. The oxidation of sulfides and associated dissolution of carbonate minerals can be responsible for elevated levels of TDS (totally dissolved solids, specifically sulfates). A frequent method of handling is to attempt to place the coaly waste at or near the bottom of the spoils. The State of Wyoming has two philosophies for handling coaly wastes high in sulfides. One is to bury the waste above the water table in an area where minimal deep percolation can move through the material. The second is to bury the waste in the saturated zone, thereby limiting the potential for oxidation of the sulfides (personal communication, D. Fransway of Wyoming Department of Environmental Quality, 1982). In order to selectively place the coaly waste, it may be necessary to stockpile it temporarily. The three types of stockpiles may yield different potential groundwater pollutants. Therefore, the identification of potential pollutants (Step 3) is discussed separately for each material. The remaining Steps (5 through 7 ) are discussed for stockpiles in general. 21

Step 3 . Identify Potential Pollutants--Topsoil Potential groundwater pollutants in stockpiled topsoil may be due to (1) the natural poor quality of soils that are stockpiled, (2) fertilization and irrigation of the stockpiled soils, and ( 3 ) physical and chemical changes in the soils after they have been stockpiled for long periods of time. Poorquality soils are generally treated as spoils. If vegetation is not immediately established on topsoil stockpiles, they may contribute excessive sediment to sedimentation ponds. Many topsoil stockpiles are surrounded by ditches or berms to reduce the sediment problem. If the stockpiles are fertilized and irrigated, however, leaching could occur by water percolating through the root zone. Compounds of nitrogen and potassium could be potential pollutants, with nitrates being of principal concern. Gradual physical and chemical changes may occur in stockpiles of long duration, primarily from leaching in the surface layer. Leaching of nitrates and other readily soluble salts turned over from lower soil layers may occur from mixing during stockpiling operations. If the stockpiles are deep, the lack of oxygen will result in a diminished number of microorganisms at the lower levels, particularly in the soils underlying the stockpiles. Because of the reduced oxygen availability, an increase in ammonium-nitrate could be expected in the deeper layers. Topsoils in the Powder River Basin may contain certain trace elements that can be significant groundwater pollutants. Summary analyses of trace elements in near-surface materials in the Powder River Basin are given by the U.S. Geological Survey (Keefer and Hadley, 1976). Most trace element analyses in mining and reclamation plans use rigorous extraction procedures (e.g., organic chelates, DTPA acid method, or hot water) that remove more constituent from a soil sample than that readily available to percolating water under field conditions. The extraction methods do not remove constituent from the mineral structure but do strip ions from exchange sites, thereby indicating available plant concentrations for particular parameters (personal communication, D. Fransway, 1982). Therefore, topsoil and overburden trace element analyses that are readily available in mining and reclamation plans can be used to identify zones with high concentrations of constituents that may cause water quality problems. After these readily available analytical data have been used to identify a zone with potential to cause groundwater degradation, additional analyses using distilled water extracts are appropriate. The distilled water extracts are more representative of water soluble concentrations of constituents that may be expected in water percolating through the topsoil with the potential to reach groundwater systems. Dollhopf et al. (1979) found that the results of column leach tests produce trace metal concentrations that are generally similar to concentrations observed in spoil wells in the Colstrip, Montana area. Dollhopf et al. concluded that column leaching methods may be promising for predicting trace element concentrations in spoil groundwaters, although additional work is necessary on this topic. Major soil series on the AMAX Eagle Butte lease were analyzed for boron, cadmium, lead, and mercury concentrations (see Table 4 ) . In another analysis, boron was found to range from zero to 1.01 ppm with an average of 0 . 4 7 ppm on 22

Sun Oil's Corder0 Mine. Selenium found at the Wyodak Mine ranges from less than 0.01 to 0.06 ppm (averaging 0.01 ppm), with boron concentrations between 0.2 and 2.0 ppm averaging 0.81 ppm. Trace element analyses were not available for many of the mines. TABLE 4.

Soil Series

CONCENTRATIONS (ppm) OF TRACE ELEMENTS BORON, CADMIUM, LEAD, AND MERCURY IN SOILS ON THE EAGLE BUTTE MINE PROPERTY B

Cd

Pb

H9

Terry

0.18

0.52

1.95

0.27

Vona

0.12

0.52

1.99

0.31

Maysdorf

0.08

0.50

2.36

0.39

Renohill

0.29

0.66

2.65

0.38

Bidman

0.25

0.53

2.00

0.18

Goshen

0.48

0.57

1.81

0.32

Arvada

1.94

0.56

3.28

0.40

Shingle

0.13

0.54

2.44

0.58

Topsoil characteristics summarized in Table 5 for four Wyoming mines give ranges for sodium adsorption ratio (SARI, electrical conductivity (EC), and pH along with the number of samples analyzed. The S A R is defined as: Na

where the concentrations of the constituents are expressed in milliequivalents per liter. EC refers to the conductance of a cube of the saturated paste, 1 centimeter on a side and measured at 25OC. These parameters are commonly measured on saturation paste extracts that are considered close to field conditions. Monitoring Needs-Monitoring needs include identification and characterization of soils on the mine plan (permit) area, estimates of the locations, volumes and anticipated duration of topsoil stockpiles, and characterization of physical and chemical changes in soils that have been stockpiled for an extended period of time

.

Alternative Monitoring Approaches-A preferred monitoring approach for characterizing potential pollutants in topsoil stockpiles includes both nonsampling and sampling methods. Possible alternative approaches are given below. 23

TABLE 5.

SITE-SPECIFIC TOPSOIL CHARACTERISTICS

Sodium Adsorption Ratio

Conductivity (mmho/cm)

PH

Number O€

Mine

Min

Max

Avg

Min

Max

AVg

AMAX Belle Ayr South

0.2

7.5

2.62

0.13

1.53

0.81

--

1.04

7.6

8.2

7.95

20

21.3

5.68

6.2

8.2

7.6

58

0.052

7.3

9.2

8.4

43

AMAX Eagle Butte

0.3

5.1

2.19

0.13

Sun Oil Cordero

0.18

16.18

5.62

0.13

Wyodak

0.5

8.9

5.0

a

2.18

Min

Max

Avg

7.2

8.1

7.6

Samples 86

Note: aData missing.

Nonsamplinq methods--One of the first steps is to obtain soil inventory maps for the lease area. These maps can be used to identify soils that may be stockpiled and their chemical characteristics. Plans for topsoil removal can be compared with soil inventory maps for a closer estimate of the future volume of stockpiled topsoil and the expected life of individual stockpiles. The volume of existing stockpiles can be estimated in three ways: (1) from mine engineering and production records and mine plans, ( 2 ) the stockpiles can be measured and the volumes computed, and ( 3 ) aerial photography. Mine records may also yield information on the use of irrigation and fertilizers on stockpiles. The amounts of potential pollutants in the stockpiles can be estimated from the volume of stockpiled material and information on potential pollutants in the topsoil. The costs include: 0

Labor: review of soil maps: computation of stockpile volume from measurements; and review of aerial photographs, mine records, and plans.

0

Operation:

any possible field transportation.

Samplinq methods and method of analyses--Existing soil chemistry information should be sufficient to identify topsoil with the potential for causing groundwater degradation. If high concentrations of a constituent are found using the standard extract methods, additional analyses using distilled water extracts can be used to better characterize amounts of the constituent available in water-soluble form to contaminate groundwaters. Topsoil stockpiles that remain in place for extended periods of time (e.g., a year or more) may undergo physical as well as chemical changes. To evaluate these, stockpiles should be sampled at 2-foot vertical intervals at

24

more than one point per acre of stockpiled material. lyzed annually for:

Samples should be ana-

0

pH (determination on paste)

0

Electrical conductivity (EC; rnillimhos per centimeter on SatUrated extract)

0

saturation percentage

0

calcium (ppm)

0

Magnesium (ppm)

0

Sodium (pprn)

0

Sodium adsorption ratio

0

Nitrogen (sum of nitrate-nitrogen [N03-N] and ammonium-nitrogen [NH4-N] in Soil)

0

Phosphorous (ppm)

0

Potassium (ppm)

0

Trace metals (ppm)

(SAR)

Total salts (ppm). Costs of the sampling approach will depend upon the areal extent and volume of stockpiled topsoil. The types of monitoring costs have been identified and are: 0

Labor: review of soil maps: interview of mine personnel; and sample handling, preparation, quality control, etc.

0

Operational costs: chemical analysis of samples and air freight, refrigeration, packing, etc. for samples.

0

Capital costs: containers, labels, chemicals, etc. for samples and hand-driven soil sampler.

Recommendations-A nonsampling approach is often preferable to the sampling approach because it may indicate that further monitoring activities are unwarranted. Where stockpiles have been in place for a year or more, sampling methodology is the best approach. This approach will enable assessment of physical and chemical changes occurring over time to determine if pollutants are present in amounts that warrant more intensive or continued monitoring. The use of

25

aerial photography is not recommended for mines with small numbers of closely spaced stockpiles due to the expense involved. Step 3. Identify Potential Pollutants--Overburden and Interburden As with topsoil, a potential water pollutant in overburden is soluble salts. For example, the soluble salt content of six overburden samples from the Sun Oil Company Corder0 mine ranged from 0.04 to 0.88 percent by weight (Dames and Moore, 1974). using these values and an assumed dry weight of 1.5 tons per cubic yard for overburden, there would be from 1.2 to 26.4 pounds of soluble salt per cubic yard. Because an acre-foot of overburden contains 1,613 cubic yards, each acre-foot of overburden would contain 1,936 to 42,580 pounds of soluble salts. Table 6 summarizes analyses of conductivity, sodium adsorption ratio, cation exchange capacity, pH, and trace elements from cores of the overburden taken from selected mines. Trace element analyses are also available for the ARC0 Black Thunder mine and the Wyodack mine. The rigorous extraction procedures (as mentioned for topsoils) generally show higher trace element concentrations than are water soluble and available for transport into groundwater systems. The trace element data, obtained using plant-available extraction techniques, can be used to identify zones with higher concentrations of trace elements, which may have potential for groundwater degradation. Zones found to have higher concentrations of a particular element should be reanalyzed using a distilled water extract to better characterize the amount of constituent available to move to the groundwater system. Maximum electrical conductivity (EC) values range from 4.2 to 8.0 millimhos per centimeter (mmho/cm) throughout the study area. Values less than 8.0 mmho/cm indicate only moderately saline conditions (Wiram, no date). High EC values are found for samples taken within 5 feet of the surface on the Belle Ayr South Mine. For deeper overburden, salt concentrations are usually less than 2.0 mmho/cm which is considered to be insignificant (Wiram, no date) and would have negligible effect on plant growth. The major anions responsible for the observed EC values on the Eagle Butte lease are, in order of abundance: sulfate, chloride, bicarbonate, and nitrate. The major source of sulfate is gypsum (CaS04-2H20) and epsomite (MgSO4-7H20). Palmer and Cherry (1979) describe two processes, including the oxidation of organic matter (production of C02) and dissolution of carbonate minerals, responsible for the presence of HC03 in groundwaters. Soluble nitrates may be formed by the nitrification of exchangeable ammonium nitrogen (Power et al., 1974). High SAR values were also found in the uppermost 5 feet. The maximum value was 17.6. For deeper overburden, S A R values averaged 3.5, indicating that the clay minerals are saturated with calcium and magnesium. Shales and mudstones, in general, were found to have slightly higher SAR values than associated sandstones. Almost all of the overburden samples were found to have a pH greater than 7 , with the values ranging from 3.6 to 8.7.

26

TABLE 6.

Nunbef

SITE-SPECIFIC OVERBURDEN CHARACTERISTICS

Conductivity (mho/cm)

CECa (rneq/100 q )

SAU

Elementsb (ppm)

PH

Of

Mine

Samples

AMAX Belle Ayr South

I

AV9

Min

Pb

Zn

Ni

Cu

__

5.3

8.2

0.23

0.08

1.0

--

--

27.5

5.0

8.5

0.05

0.43

--

--

__

-.

-.

--

__

__

..

-

__

0.17 3.44

0.12

__

__

--

--

--

13.0

33.0

--

7.4

8.7

--

--

_-

__

--

--

--

11.0

32.0

22.7

7.8

8.4

__

__

33.8

-_

-_

-_

--

--

0.3

7.2

--

3.9

48.4

--

3.6

--

0.1

0.07

4.3

14.8

.-

__

__

--

. -

--

--

__

--

11

0.7

4.2

1.9

Kerr-McGee Jacobs Ranch

55

0.5

5.5

--

89

0.5

8.0

..

..

‘Trace element analysis only.

Hg

16.8

__

bAveraqe concent rat ions.

Cd

36.0

~.-.

aCation exchange capacity.

AVq

30.0

..

Notes:

Min Max

--

41c

7c

Avq

12.8

ARC0 Black Thunder Carter North Rawhide Oil Cordero

Max

3.3

6.5

Sun

Min

3.5

6.2--

--

Wyodak

Avg

__

--

92

Eagle Butte

Max 17.6

74

ANAX

h,

Min Max

__

_.

__

__

. .

35

__

__

2.1

__

1.7 0.88

__ 0.47

S

As

Se

Five overburden samples from Belle Ayr South were found to have a total sulfur content greater than 1.0 percent, with the others rarely exceeding 0.3 percent. Of the five samples, two contained fine-grained pyrite and others had large amounts of gypsum and carbonaceous matter. Gypsum crystals (selenite; CaS04-2H20) and soluble sulfate salts are the major sources of sulfur in the overburden. Sulfate concentrations were found to range from 20 to 40 meqlliter, primarily in the form of selenite. The overburden trace element analyses of Table 6 show cadmium concentrations of 0.1 to 3.44 ppm and mercury concentrations of 0.05 to 0.12 ppm. Arsenic found at Black Thunder ranged from less than 0.05 to 7.75 ppm, averaging 0.8 ppm. selenium was found in concentrations less than 0.1 ppm for all samples taken at Wyodack. Chemical analyses of partings and interburden have been more limited than those for overburden, but those that have been done tend to confirm that the same elements are present. The U.S. Bureau of Land Management (1974) states that chemical analyses were run on two samples of parting material between coal seams at the Carter North Rawhide mine. Electrical conductivity values were found to be 2.4 and 0.8 mmho/cm. Both parting samples were found to be acidic, with pH values of 4.9 and 6.8. Values for sulfur content were 200 and 39 ppm and the copper content was 8.2 and 1.6 ppm. Recommendations for calculating net acidity (potential acidity and neutralization potential) can be found in Section 4. According to the U . S . Bureau of Land Management (1974), chemical analyses were run at the Kerr-McGee Jacobs Ranch mine on three samples from the parting between the Upper Wyodak and Lower Wyodak 1 coal seams. All three samples were taken from a single drill hole and showed little variation. The average electrical conductivity value was 0.83 mmho/cm. All of the samples had basic pH values of 7.9, 8.1, and 8.2. The sulfur content in all three samples was greater than 200 ppm. The average copper content was 1.57 ppm. Existing monitoring on the AMAX Belle Ayr South lease includes in-place overburden samples that have been collected from eight drill holes on a 1/2mile grid over three--fourthsof the mining area. In these holes, the upper 10 feet have been sampled on 1-foot intervals and the remainder of each hole has been sampled at 10-foot intervals to the top of the coal. Electrical conductivity measurements indicate the materials in general to be slightly saline. Sodium adsorption ratios taken in the upper 5 feet also indicate moderately saline soils. Monitoring NeedsData related to undisturbed overburden materials may be useful in characterizing overburden stockpiles; however, it will also be necessary to monitor stockpiled overburden materials to determine if any appreciable changes in their overall composition have resulted from mining and stockpiling. Monitoring needs include the chemical composition of in-place overburden using distilled water extracts; the volume, composition, and expected life of overburden stockpiles; and changes that occur in the overall chemical makeup of stockpiled overburden from exposure to a new environment. 28

Alternative Monitoring Approaches-. A recommended monitoring approach for characterizing potential pollutants in overburden stockpiles can be selected from the following nonsampling methods or sampling methods.

Nonsamplinq methods--The primary nonsampling method is to obtain, review, and interpret the existing data on the chemical characteristics of the inplace overburden. The next step is to determine the volume of overburden stockpiled for any appreciable time (1 year or more). From this information, the chemical nature and volume of potential pollutants in the stockpiled overburden can be estimated. The use of low-altitude aerial photography is inappropriate because of its cost. If adequate, engineering and production records for the mining operation can be used to estimate the volume and duration of the material stockpiled. The costs of this approach are for labor only; they include: Review of existing data on in-place overburden (e.g., water well or core hole lithologic logs, geophysical logs, core sample analysis, etc.) Review of engineering production records or aerial photographs for volume determination Review of mine engineering and production records for determining estimated stockpile durations. Samplinq methods and methods of analysis-Overburden stockpiles expected to remain in place for a year or more should be sampled to determine if exposure causes any changes in their overall chemical makeup. For a reconnaissance level investigation, samples can be obtained at 10-foot intervals vertically through the stockpile. One sample hole per 10 acres of surface area should be sufficient. If serious chemical changes are documented, such as high levels of nitrates resulting from oxidation of ammonia (NHq+), greater sampling intensity is warranted. Sampling densities on 30--meter grids have been used for research level efforts where the intent was to locate inhibitory zones in spoil materials (Dollhopf et al., 1981). Unless some means is devised to hold the hole open while taking the samples, sampling the material will most likely be difficult because of its unconsolidated nature. All samples should be analyzed for the parameters listed in Table 7. The costs for this approach include: 0

Labor: compilation of volumetric and chemical data from field and laboratory analysis; sampling of new and old (more than 1 year) stockpiles to determine chemical change; and sample handling, preparation, quality control, etc. Operational: chemical analysis; air freight, refrigeration, packing, etc.; and field transportation.

29

TABLE 7 .

MONTANA DEPAKTMENT OF STATE LANDS LIST OF PARAMETERS FOR SOIL AND OVERBURDEN MONITORING

Quantity

Methods of Analysisa

PH

Paste

Conductivity

Saturation extract

SAR

Saturation extract

Texture

Hydrometer

selenium

b Distilled water extract b Distilled water extract b Distilled water extract b Distilled water extract b Distilled water extract b Distilled water extract b Distilled water extract b Distilled water extract b Distilled water extract b Distilled water extract

Zinc

Distilled water extract

Boron Cadmium Copper Iron Lead Manganese Mercury Molybdenum Nickel

b

C

Ammonium-nitrogen C

Nitrate-nitrogen

b

Distilled water extract b Distilled water extract

Notes: a

The recommended methods of analysis are based on recent research for determining potential impact to groundwaters and are not necessarily recommended by the State of Montana.

bPossibly using leach columns. C

The significance of ammonium and nitrate stems from the water pollution potential of nitrate. The Federal drinking water standard is 10 ppm nitrate-nitrogen and a recommended maximum concentration for livestock is 100 ppm nitrate plus nitrate-nitrogen. Ammonium can be biologically oxidized to nitrate if conditions are suitable.

30

0

Capital: sample containers, labels, chemicals, preservatives, etc., and hand-driven soil sampler.

Recommended Monitoring Approach-The preferred approach for monitoring the potential pollutants in stockpiled overburden is: 1.

Review existing data on chemistry of in-place overburden.

2.

Determine the volume measurement.

3.

Sample the stockpile at 10-foot vertical intervals (a minimum of two samples per location, with one hole every 10 acres).

4.

Analyze annually for parameters listed in Table 7. Overburden should not be analyzed using DTPA acid techniques; column leach extracts have provided concentrations most similar to spoil groundwaters (Dollhopf et al., 1981). Analyses of column leach extracts using distilled water are recommended at this time although more research is needed in this area.

of

overburden

stockpiled by

direct

Step 3 . Identify Potential Pollutants--coal, Coal Refuse, and Coaly Waste One of the characteristics of the project area coals is the low sulfur content. Elevated concentrations of sulfides and organic sulfur, however, are commonly associated with carbonaceous materials such as coal stringers, carbonaceous shale, and top or bottom coal that is wasted (personal communication, N. Harrington, Montana Department of State Lands; D. Fransway, Wyoming Department of Environmental Quality; and J. Rogers, Front Range Laboratories [Fort Collins, Colorado]). Palmer and Cherry (1979) acknowledge the oxidation of pyrites and organic sulfur and the subsequent dissolution of carbonate minerals as one of the p.rimary reactions influencing spoil groundwater quality changes. The concern in the West is not acid spoil waters but, rather, significantly elevated TDS. More specifically, sulfates are increased as a result of this process and this, coupled with sulfates already present in the spoils, can significantly increase spoils sulfate concentrations to the point that waters will not be suitable for postmining stock or domestic uses. Section 4 and Appendix B (taken directly from Smith et al., 1974) contain a discussion of calculations used to predict the net acid-neutralization potential of spoils when acid waters are a real concern. Acid that is found might also dissolve some trace metals before it is neutralized although, as the pH is neutralized, metals soluble in acid conditions will precipitate. According to the U . S . Geological Survey (19751, a representative coal sample at the AMAX Belle Ayr South mine had a sulfur content of 0 . 6 percent. Sulfate content was given as 0.02 percent, pyrite sulfur as 0.17 percent, and organic sulfur as 0 . 4 4 percent. Coal, coal refuse, and coaly waste probably contain some soluble salts. However, no analysis of the soluble salt content of these materials has been 31

found in the literature or in unpublished reports. The soluble salts are expected to be principally in the form of gypsum crystals or similar minerals formed in open fractures. Intergranular pores are not present in the coal and coaly strata as they are in the rest of the overburden. Sulfur is universally found in coal and carbonaceous strata but in different forms and varying amounts. The two general forms of sulfur that occur in and with coal are inorganic and organic. Inorganic sulfur occurs primarily as pyrite or marcasite, which are both iron disulfide (FeS2). As far as is known, no studies have been made of the amount and fate of acid formed in Powder River Basin strata as a result of coal strip mining. Sulfur- and iron-oxidizing bacteria are present at existing mines, however, and probably do generate small amounts of acid. Olson and McFeters (1978) found Thiobacillus ferrooxidans at numerous sites at the Decker (Montana) and Big Horn (Wyoming) mines. They concluded, however, that acid produced by & ferrooxidans is quickly neutralized by bicarbonate in the mine waters and therefore is not evident in mine effluents. A number of measurements have been made of the trace elements in Powder River Basin coals. Keefer and Hadley (1976) present a summary of analyses of 15 coal samples from Wyodak mine and 11 samples from Belle Ayr mine. A few trace elements are present in coals in amounts greater than in the overburden and the earth's crust as a whole, but these trace elements have not yet been identified as actual water pollutants. Table 8 summarizes trace element and sulfur content of coal samples.

Mon toring Needs-All mining companies analyze coal seam samples before mining. Usually, the proximate analyses include moisture content, volatile matter, fixed carbon ash, Btu, softening, grindability, and specific gravity. The ultimate ana yses may also include hydrogen, carbon, nitrogen, oxygen, chlorine, sulfur sulfate, pyrite, and organic content. Ash analyses should include the fol owing:

A1203

Fe203

M9O

S io2

Ti02

p2°5

so3

Na20

cao

K20

These elements have also been measured in Powder River Basin coals. Suffi-cient information is available to characterize coals in the project area in terms of the potential pollutants they contain, except soluble salts. This does not appear to be the case for coaly waste: no records have been found to indicate any attempts to characterize it. This waste is usually lumped with the overburden core analysis which requires sampling at discrete depths to the coal. Stockpiles of coaly waste should be sampled to determine if, in fact, soluble salts are present in sufficient amounts to present a problem. Uncertainty exists about the location of coaly waste stockpiles and methods of disposal for this material on most mining sites. In many instances, it is mixed indiscriminately with overburden materials and backfilled. Stockpiles of coaly waste need to be located and grab samples acquired for chemical analyses to identify any potential groundwater pollutants. 32

TABLE 8. SULFUR AND TRACE ELEMENT CONCENTRATIONS IN COAL SAMPLES Average Trace Elements (ppm) Sulfur (percent)

Mine a AMAX Belle Ayr South b AMAX Eagle Butte C

ARC0 Black Thunder

0.14-1.0

e

Carter North Rawhide

0.1

e

0.09-0.59 C

w w

0.25-0.6

Cd

e

0.28-0. 52e

-0.36

__

Hg

Pb

0.13

AS

Se

2.7

2.5

0.1

1.0

0.19 0.1

--

11.62

0.15

__

1.5

--

1.0

1.1

0.13

1.09

--

__

0.002

--

--

0.09

9.12

1.0-2.0f

0.86

0.88

--

0.59

0.1-0.16

e Range of sulfur concentrations. f Range of trace element concentrations.

1.1

0.44

Wyodak'

U.S. Bureau of Land Management (1974). d u . S . Geological Survey (1976b).

0.31

2.1

0.66

bU.S. Geological Survey (1976a).

1.1

2.1

0.30

C

_-

0.1

<0.001

Geological Survey (1975).

1.0

0.02

<0.001

U.S.

1.1

--

1.06

a

CU

--

Kerr-McGee Jacobs RanchC d Sun Oil Cordero

Notes:

U

Alternative Monitoring Approaches-Alternative sampling and nonsampling approaches for monitoring the potential pollutants in coal, coal refuse, and coaly waste are discussed below. Nonsamplinq methods--A primary nonsampling method is to determine the volume of coal, coal refuse, and coaly waste stockpiled. The manner in which these materials are stockpiled will, to a large degree, determine if they present a threat to groundwater quality. For example, coal stored in open bunkers with concrete floors may not present a problem. Two alternatives for estimating the volume of these materials are: (1) directly measure the areal extent of the stockpiles and periodically update this information, or (2) work directly from mine engineering and production reports. Any available data on the chemical characteristics of the stockpiled materials can be obtained from mine operators and used to estimate the total volume of potential pollutants in the stockpiles. The labor costs of this approach include determining the method and duration of stockpiling from mine engineering and production records, and determining potential coal pollutants from existing chemical data. Samplinq methods--If the stockpiles weathering and possible leaching may take at or near the surface OE the stockpiles. locations on the stockpiles. The sainples water extracts for the following:

are exposed to the elements, some place. Most weathering will occur Grab samples can be taken at a few should be analyzed using distilled MO

B

As Ge

Be

V

F

A9 cu

Pb Cd

se Mn

H9

Ni

zn

cr

U

These elements should be analyzed with an accuracy of +_20 percent of the actual population concentrations. Therefore, at least three replications will be necessary for each stockpile. More may be required to achieve an acceptable accuracy. Analyses-. The analysis should include all identifiable trace elements, although only the foregoing 18 require an accuracy of 220 percent. Spark-source mass spectrometry is recommended as the most accurate method. Other methods, such as neutron activation analyses, may also be used. However, wet chemical methods are satisfactory and are used by most laboratories. Analyses by wet chemical methods should be performed as follows: Ag - atomic absorption spectrometry Cu - atomic absorption spectrometry Ni - atomic absorption spectrometry Pb - atomic absorption spectrometry 34

Cd - atomic absorption spectrometry Zn - atomic absorption spectrometry Se - atomic absorption spectrometry Mn - atomic absorption spectrometry Cr - atomic absorption spectrometry Hg - double gold amalgam flameless atomic absorption

B

- emission spectrometry

Be - emission spectrometry As - colorimetric Ge - colorimetric V

-

colorimetric

Mo - colorimetric U

-

fluorometric

F

-

specific ion electrode.

Additional analyses will include hydrogen, carbon, nitrogen, oxygen, chlorine, sulfur, and sulfate pyrite. Annual measurements should be adequate to follow any changes in the chemical characteristics of stockpiled coal, coal refuse, or coaly waste. Stockpiling of coal for such long periods of time will be unusual. Stockpiles usually will be augmented or depleted on a regular basis. The cost of this monitoring approach includes: Labor: determining method of stockpiling, location, and volume from field surveys; collection of grab samples: and sample handling, preparation, quality control, etc. Operational: chemical analyses of grab samples; air freight, refrigeration, packing, etc.; and field transportation. Capital: sample containers, labels, chemicals, etc., and handdriven soil sampler. Recommendations-The preferred monitoring approach is to determine the volume of stockpiled material by direct measurement and use this information, along with available data on the chemical characteristics of the stockpiled materials, to estimate the volume of potential pollutants in the stockpiles. Samples should be collected and analyzed as needed to fill data gaps.

35

Step 5. Evaluate Infiltration Potential The purpose of determining the infiltration potential of a source is to quantify the volume of water and associated pollutants moving into the underlying vadose zone. Information must be obtained on precipitation, irrigation rates, runoff rates, evapotranspiration, and soil water content at field capacity and at the permanent wilting point. This information can be used for a water balance calculation to determine if significant amounts of water are percolating through the stockpiles to cause groundwater degradation. Monitoring Needs-A need exists to determine if water can move through stockpiles in sufficient quantities to carry potential pollutants into the vadose zone. Although infiltration from precipitation will be high to moderately high on the loose materials of stockpiles, infiltrating water is unlikely to penetrate deeply enough under the natural precipitation regime or irrigation to contribute significantly to groundwater. This must be established, however, particularly for stockpile areas near natural stream channel areas with shallow groundwater.

Deep percolation of water (below the root zone) is the mechanism necessary to transport pollutants from stockpiles. McWhorter (personal communication, 1981) recommends using a water balance method to calculate the amount of water moving through stockpiles. The following method is recommended as a calculation to determine if significant volumes of water are available for transport of pollutants (before a detailed field monitoring program can be justified). The surface water balance on a stockpile can be expressed as: P - Q = I

(1)

where P = precipitation Q

=

direct runoff

I

=

infiltration.

Precipitation (P) values can be obtained from climatological records. Determination of Q using the Soil Conservation Service curve number approach is recommended for individual storms where only those storms exceeding the initial abstraction produce a value for Q. Infiltration capacity as determined from double-ring infiltrometer tests is useful for assisting in the determination of initial abstraction by the SCS procedure. (This is done directly by curve number.) Experience with data from Colorado and Arizona indicates that the number of storms exceeding the initial abstraction that must be considered is generally less than 10. The value of I determined from the above calculation is considered to be the temporal distribution of infiltration into stockpiles.

36

A monthly water balance for the root zone, assuming an average precipitation year, can be calculated by: I - Et - W t AS

where I

=

infiltration (from Equation 1)

Et

=

potential evapotranspiration

W

=

percolation below the root zone

(2)

= 0

AS = the change in soil water storage in the root zone.

Determination of potential evapotranspiration (Et), assuming water availability is not limiting,. can be done using the Blaney-Criddle (1950) equation. The Blaney-Criddle equation is considered more acceptable for arid or semiarid regions than the Thornthwaite (1948) method, which is generally used for humid and subhumid regions. The actual evapotranspiration (Eta) is calculated as part of the water balance in the following example, where Eta is limited by the amount of water available each month in the soil profile. The volumetric water content at permanent wilting and at field capacity is obtained from laboratory measurements. Calculation of the maximum available water capacity that can be stored in the soil profile is:

where AWC

=

maximum available water capacity

ofc = volumetric water content at field capacity Opw = volumetric water content at the permanent wilting point D

=

depth of the root zone.

The change in soil water storage (AS) can also be determined by accounting for all the inputs and outputs of moisture from the soil profile according to the following example. The parameter of greatest concern, percolation below the root zone (W), is the end product of the calculations in the following exarnple. The volume of moisture lost to deep percolation is the amount of water available to carry pollutants from stockpiles. A. Determine the maximum available water capacity (AWC) when the difference between the field capacity and permanent wilting point water contents (Ofc - Opw) is known to be 0.7 in/in with a root zone (D) 36 inches deep. AWC = (0.07 in/in) (36 in) B. month.

= 2.52

inches.

(4)

Calculate the amount of water lost to deep percolation (W) for each

37

1 AW

2 Deficit

3 4 5 -6 -7 I

Et

Eta

AS

W

+2.12

0.40

April

0.40

2.12

4.04

1.52

1.52

May June

2.52 2.52

0

4.81

3.26

3.26

0

1.23

4.87

3.75

July

0

2.52

1.29

5.23

1.29

0

0

August

0

2.52

1.90

4.01

1.90

0

0

September

0

2.52

1.52

2.28

1.52

0

0

October

0

2.52

1.49

1.50

1.49

0

0

November

0

2.52

0.40

0

16 -68

1.55

0

-2.52

0

0 +0.40 0 -

14.73

0

1.95

where 1. AW = the initial available water stored in the root zone at the beginning of each month. The initial value at the beginning of the growing season (April) can be assumed to be zero, or the residual moisture stored from the previous year may be used. In the example, the value (0.40) calculated for AS for November was used for the April initial available water value. 2. Deficit = the net storage capacity remaining in the root zone after all inputs and losses have been accounted for, for the month. The deficit cannot exceed the value of the maximum available water capacity, AWC (2.52 inches in this example). 3. I = infiltration values determined from previous calculation (Equation l). 4. Et ,= potential calculation.

evapotranspiration

determined

from

previous

5. Eta = actual evapotranspiration allowed, limited by moisture availability in the root zone. This is the net gain or loss of moisture for the months that have been accounted for.

6. AS = change in storage in the root zone.

7. W = amount of water lost to deep percolation that is available for transporting pollutants from the stockpile. Percolation can occur only when the initial moisture in the root zone (AW) plus the amount of water gained by infiltration (I) exceeds the current moisture deficit plus the actual evapotranspiration for the month. Alternative Monitoring Approaches-Laboratory determinations of saturated conductivity on disturbed samples are of doubtful value for indicating infiltration characteristics. Infiltrometer tests in the field, however, are useful for establishing relative rates 38

of water penetration at the soil surface. A double-ring infiltrometer can be used for field tests on the stockpiles. Data can be analyzed to determine the probable penetration of water under natural rates of precipitation or under applied irrigation schedules. Several methods are available for determining infiltration under conditions of unsteady application of water at the surface. These methods can be used with climatic records to determine maximum expected depth of water penetration. In addition, laboratory determinations of moisture content at field capacity and permanent wilting point are necessary for the water balance calculation. Costs include labor for conducting and analyzing the infiltration tests and capital costs for infiltrometers. Standardized methods are available for determining soil moisture contents at field capacity and at the permanent wilting period. Laboratory costs are associated with this determination. Recommendations-Double-ring infiltrometer tests can be run. No fewer than three runs should be made on each stockpile, and more should be made if considerable variation is found in the materials. Step 6 . Mobility of Potential Pollutants in the Vadose Zone Potential pollutants for stockpiled material include inorganic chemical, organic chemical, and radiological types. The major inorganic chemical groundwater constituents that can enter the vadose zone are calcium, magnesium, sodium, potassium, carbonates, chlorides, sulfates, boron, fluoride, iron, manganese, nitrogen oxides, and phosphorous oxides. Inorganic trace elements are barium, chromium, copper, lead, lithium, nickel, strontium, vanadium, zinc, zirconium, arsenic, cobalt, cadmium, mercury, beryllium, selenium, molybdenum, titanium, bromine, tin, tellurium, and silver. Organic chemical compounds (total organic carbon, or TOC) can also migrate through the vadose zone, as can the radiological compounds of uranium, thorium, and radium-226. Organic acids can be expected in the vadose zone and their presence is highly important. The organic acids mobilize trace metals through chelation, thus increasing their potential migration in the hydrologic system. Of the major inorganic chemical constituents, sodium and chloride are relatively mobile. Calcium, magnesium, bicarbonate, and sulfate may be precipitated in the vadose zone. These and other constituents may be dissolved from minerals by water percolating through the vadose zone. Nitrate is relatively mobile and iron and manganese are generally immobile under aerobic conditions. The bacteriological content of water leaving the vadose zone should be low due to pollutant attenuation in the vadose zone. At least three major sources of data can be used to assess trace element mobility in the vadose zone. First, numerous leaching studies have been performed for specific elements applied to specific soils. Second, the general geochemical behavior for many trace elements in natural water systems is fairly well defined. Third, the occurrence of selected trace elements in groundwater is generally known.

39

Keeney and Wildung ( 1 9 7 7 ) summarize soil interactions with trace metals. Fuller ( 1 9 7 7 ) presents a detailed discussion of trace element mobility in soils. He states that numerous factors control pollutant mobility but, in general, the following are most significant: Soil texture or particle size Pore space distribution in the soil Content and distribution of iron, aluminum, and manganese oxides and hydroxides in the soil pH of the soil and percolating waters Oxidation-reduction potential in the soil Organic matter content of soils and percolating waters Concentration of trace elements. Selenium was found to be relatively mobile under aerobic conditions such as might be present in the vadose zone. Iron, zinc, lead, copper, and beryllium were moderately mobile. Arsenic, cadmium, chromium, and mercury were slowly mobile. Hem ( 1 9 7 0 ) discusses the occurrence of a number of trace elements in natural waters. Beryllium is generally not present in dissolved form in such waters because of its low solubility. strontium contents are greatly limited by sulfate contents as high as those in the groundwater of the Gillette area. Barium can also be adsorbed by metal oxides or hydroxides and, thus, generally occurs in only small concentrations in groundwater. Titanium is not present in high concentrations in natural water because of the low solubility of its oxides and hydroxides. Vanadium appears to be soluble in groundwater under anaerobic conditions and may be present in significant concentrations if a source is present. Numerous instances of chromium contamination of groundwater have been documented. The anionic species are apparently relatively stable in many groundwater systems. Molybdenum is predominantly present in the anionic form in groundwater. There appears to be no effective solubility control over molybdenum concentrations and, thus, large values may be found if a source is present. Cobalt content in groundwater is likely controlled by manganese or iron oxides and hydroxides and generally is low in groundwater. The general geochemical behavior of nickel is similar to that of cobalt. The solubility of copper oxide and hydroxy-carbonate minerals tends to limit the content of copper in groundwater to low values. Silver content is limited by the solubility of silver oxide and silver chloride. In dilute aerated water, the equilibrium concentration of silver should be less than 0.01 ppm. Concentrations of zinc exceeding 1 ppm can be in groundwater. Cadmium contents in groundwater are generally very low. However, some cases of cadmium contamination have been documented for groundwater. Very few natural waters contain detectable concentrations of mercury. 40

Lead content is controlled by bicarbonate and sulfate contents. Lead sulfate is relatively insoluble, particularly in aerobic situations. Arsenic can be present in the anionic form over the pH range of most natural waters. Numerous occurrences of arsenic in groundwater under anaerobic conditions have been documented. The sorption of arsenate on ferric hydroxide or other active surfaces is likely an important factor, limiting arsenic contents in natural waters. The stable form of selenium in aerobic groundwater is the anion form but little information is available on selenite solubility. Bromide has a geochemical behavior similar to chloride and, thus, can occur in relatively high contents in groundwater. Groundwater quality studies throughout the United States indicate that the trace elements chromium, vanadium, arsenic, cadmium, selenium, molybdenum, and bromine have been found in high concentrations in certain geohydrologic situations. All of these elements readily form anions in the soil-groundwater system and may be mobile in the vadose zone. Studies of hazardous waste disposal summarized by the U . S . Environmental Protection Agency ( 1 9 7 6 ) indicate that the results of soil-leaching studies are consistent with these observations. These constituents should thus be given priority over other trace elements in a monitoring program. Organic chemicals may move with percolating water through the vadose zone. However, the organic chemicals to be expected in water that contacts materials such as coaly waste have not been well defined. Leenheer and Huffman ( 1 9 7 6 ) have proposed a classification scheme for organic solute characterization. The scheme begins with dissolved organic carbon and is further divided on the basis of soluble sorption and acid-base characteristics. Little is known about the mobility of the organic chemical fraction of the stockpile wastes. Monitoring Needs-Information on the mobility of pollutants in the vadose zone within or beneath present or future topsoil and overburden stockpiles is not currently available. A need exists to first determine if water is moving in significant quantities through the stockpiles according to the water balance calculation recommended previously. If so, monitoring those pollutants that contribute contaminants in excess of background levels will be necessary. Alternative Monitoring Approaches-The greatest amount of water movement in the vadose zone will occur as unsaturated flow. Although the soil surface may become saturated after heavy precipitation or prolonged irrigation, subsequent movement will occur at pressures less than atmospheric along gravitational and soil matrix potential gradients. One way of documenting unsaturated flow is through the installation of neutron probes in the stockpile. These could extend several feet into the spoils or underlying native soil. Monthly measurements could be made with the neutron probe and more frequently after heavy precipitation events or extended irrigation.

41

Tensiometers can be installed to measure pressure differentials with depth and thereby determine the rate and volume of flow. Under ideal conditions, tensiometers are only effective at moisture contents equivalent to negative pressure of less than 1 bar. Porous cups installed within the stockpile at the same depths as the tensiometers can be used to extract soil solution to test for pollutants if the moisture content is sufficiently high. The cups will fail to function at -0.8 atmosphere of soil-water pressure. Samples can initially be analyzed (using distilled water extracts) for calcium, magnesium, sodium, potassium bicarbonate, chloride, sulfate, phosphate, silica, ammonia-nitrogen, nitrate-nitrogen, total nitrogen, pH, and electrical conductivity. Subsequent monitoring can be limited to the constituents that appear to exceed 20 percent of the background levels. Costs for Step 6 include labor costs for conducting and analyzing neutron probe measurements; operational costs for installing access tubes; and capital costs for the neutron logger, steel pipe, and miscellaneous materials for construction of the access tubes. Recommendations-Appreciable quantities of water are unlikely to flow through stockpiled materials, even with irrigation. This concern can initially be evaluated by the water balance calculation. The results can be calibrated by conducting field infiltrometer tests. If little water movement is found, monitoring will not be necessary. If appreciable water movement is indicated, then monthly measurements with a neutron probe and the alternative methods can be implemented at a later date. The monitoring methods will document the occurrence of deep percolation and the associated quality of the leachate. These methods are not sensitive enough for determining volumes of water percolating through the stockpiles. Step 7. Mobility in the saturated Zone The general purpose of this step is to measure or estimate the attenuation of source pollutants during migration in the zone of saturation. The pollutants of concern are those that have not been completely attenuated during movement through the vadose zone. Some constituents in liquids moving through all or part of the vadose zone may be substantially attenuated. Numerous pollutants, however, will likely be picked up by the percolating water and become introduced into the saturated zone. Once in the saturated zone, the mobility of these pollutants depends greatly on the aquifer transmissivity, porosity, and the hydraulic gradient. King (1974) notes that hydraulic gradients in the more permeable aquifers of the Gillette area range from 10 to 25 feet per mile and for consolidated rock aquifers are probably about 4 0 to 50 feet per mile. The University of Wyoming (1976) reported on extensive groundwater monitoring at ARCO's Black Thunder mine. The hydraulic gradient for the coal aquifer ranges from 15 to 40 feet per mile.

42

Porosities for different aquifer materials are not well known. However, an independent analysis of groundwater flow rate can be obtained from the results of carbon-14 age dating of groundwater at Black Thunder mine. Ages in the range of 11,000 to 34,000 years for groundwater within several miles of the recharge point indicate very slow travel times, in the range of only several feet per year. Assuming a porosity of 0.10 for fractured consolidated rock, a groundwater flow rate of about 35 feet per year is calculated, based on average values for transmissivity and hydraulic gradient. The rate of groundwater flow in the consolidated rock aquifers implies that polluted groundwater entering these aquifers would generally move very slowly. Thus, monitor wells would have to be located very close to a potential source of pollution. A thousand years might be required for such water to flow only a quarter of a mile. The key conclusion is that little effect on groundwater quality would be noticeable over the short term except in the immediate proximity of the stockpile. Flow rates in the alluvial aquifers (underflow) could be much greater. These are generally unknown, however, due to lack of data on aquifer characteristics and hydraulic gradients. Land surface and vadose zone monitoring can provide information on travel times to the saturated zone and indicate when polluted water might be expected to reach the water table. The chemical aspects of pollutant transportation and attenuation are not considered further because of the relatively slow groundwater flow rates, which exert the controlling factor on pollutant mobility in the saturated zone. Monitoring NeedsWhether monitoring is justified to determine attenuation of stockpile pollutants in the saturated zone will depend entirely upon whether water will penetrate through the piles and the underlying materials to groundwater and, if it does, whether it would carry quantities of pollutants significantly exceeding those existing in the natural groundwater system. Both possibilities are unlikely. The stockpiled material may be highly permeable, but the underlying soil will probably be less so due to scraping and compaction. If the stockpile is placed on compacted mine spoils with a characteristically large, shale-derived component, penetration of water to the saturated zone will be greatly restricted. Furthermore, the only pollutants other than those that occur naturally or through oxidation would come from fertilizer applications, principally nitrates. Since fertilizer will only be used to assist development of a protective vegetative cover and not for agricultural production, application will be light. Costs associated with Step 7 are those measuring or estimating the likelihood of pollutants infiltrating to the water table.

Recommendations-No monitoring during Step 7 unless indicated by the results of previous steps.

43

PIT WATER

Step 3 . Identify Potential Pollutants--Pit Water Water entering coal mine pits can originate from a number of sourcesl each of which may contribute pollutants. Sources of this pit water include: 0

Groundwater in the coal seam

0

Groundwater percolating from nearby stream channels through alluvium beneath the flood plain

0

Groundwater in the overburden

0

Groundwater in the interburden and underburden

0

Groundwater in spoils

0

Direct precipitation

0

Surface runoff into the pit

0

Waste disposal, such as sewage treatment facility effluent.

A

number of potential sources of pollutants may be in the pit water, such

0

Coal

0

Overburden, interburden, and underburden

0

Explosives

0

spoils

0

Solid waste

0

Liquid waste

0

Polluted streamflow

0

Airborne pollutants and polluted precipitation

0

Spills and leaks

0

Natural sources, as a result of hydrogeologic modifications.

as :

All of the potential pollutants from explosives--ammonium-nitrogen, nitrate-nitrogenl fuel oil, and trace organics--can be in the pit discharge. Most of the major inorganic chemical constituents and some trace elements can originate from groundwater percolating through the coal, overburden, and underlying beds. A t Decker mine in Montana, high contents of sodium, bicarbonate, and sulfate, and occasional very high contents of nitrate, were found in 44

pit discharge (Van Voast and Hedges, 1975). Calcium, magnesium, chloride, boron, and fluoride are additional potential pollutants. At Big Horn mine, high contents of iron, manganese, zinc. and copper were found in pit discharge. Cadmium, chromium, arsenic, lead, molybdenum, vanadium, uranium, thorium, radium, and selenium are additional potential pollutants. Organic materials from the coal and related beds are also potential pollutants. Gasoline and oil can be introduced by heavy equipment working in the pit. Bacteriological pollutants can be introduced from domestic waste water, runoff, and solid wastes disposed of in or near the pits. Monitoring Needs-In areas where mining operations are above the groundwater table, any water accumulating in the pit may percolate downward and pollute the groundwater. Pit water then acts as a potential source of pollution. Conversely, when operations are situated at or below the groundwater table, pit waters serve as receiving waters for potential pollutants. Usually, this water must be disposed of by pumping to evaporation ponds or used in dust control operations. Therefore, determination of the quality of water in the pit is needed. Secondarily, if water quality concerns are revealed in the pit waters, determination of the discrete origin of pollutants in the pit water is needed, which will likely entail additional monitoring beyond the pit. Alternative Monitoring Approaches-Nonsamplinq methods--A water budget approach using existing data and field measurements can be used to determine the amount of water in the pit. Pit water discharge can be measured by installing a continuously recording flow meter in the discharge lines and keeping an account of the number of truckloads of water hauled for dust suppression. Precipitation falling on the water surface can be.measured by installing a continuously recording rain gauge near the pit bottom. Evaporation can be measured indirectly by installing a floating evaporation pan. For both precipitation and evaporation determinations, the area of water surface in the pit must be known. This can be determined by periodic surveys. Aerial photographs can also be taken periodically to document the location of water bodies in the pit. The volume of water entering the pit is more difficult to determine, because the water may come both from discrete sources, such as leakage at one location from a stream channel, and diffuse sources, such as seepage. For discrete sources, flumes or weirs can be installed near the point of entrance to the pit. Groundwater seepage into the pit from diffuse sources can be calculated if gradients and aquifer characteristics are known. The groundwater seepage can be characterized by a network of monitoring wells surrounding the pit. Aquifer tests and water level measurements would be necessary to determine the transmissivity and hydraulic gradient, respectively.

45

Items other than pit inflow and discharge can be measured, such as changes in water storage in the pit. A staff gauge used in conjunction with aerial photographs or water surface area surveys can be employed. Additionally, leakage from the pit can be estimated after other water budget items are determined. Samplinq methods--Water samples should be collected from pit water and discrete sources of water entering the pit. F o r water in the pit, samples should be taken at various depths since water quality may vary substantially. A depth-integrated sampler can be used from a small boat to sample various parts of the pit pond. A composite sampler can be used to continuously monitor the quality of water discharged from the pit. Grab samples can be collected from any discrete sources of inflow to the pit. Sediments beneath the pit water can also be collected for sampling. Wells can be installed at the periphery of the pit to collect groundwater samples in the coal seam, overburden, underburden, and spoils. Changes in water quality along flow paths can be determined as groundwater approaches the pit. Generalized data from operating mines indicate that the effects of pit dewatering do not extend outward more than a few miles. Thus, any monitor wells should be placed within one-quarter mile or less from the pit. For groundwater percolating from streams, water samples can be collected from streamflow. Wells can also be installed to allow sample collection from the alluvium and to determine changes in water quality during percolation as groundwater approaches the pit. Both solid and liquid wastes that might affect the quality of pit water can be sampled for chemical analyses. In general, the latter type of monitoring would have the lowest priority, unless sampling of pit water suggests the necessity for this approach. Water entering the upper part of a pit can traverse significant distances before joining the pit water body, in which case the water could pick up a number of pollutants from spills, native or disturbed materials, and other sources. Sampling this water at different locations along the traverse may prove helpful. Monitor well construction should allow pump testing for optimal determination of aquifer transmissivity. Transmissivity values are a key input for calculating the rate of groundwater flow. A 4-inch-diametercasing is recommended to allow room for a submersible pump plus an electric sounder. Testing pumps are not permanently installed and, since PVC is the preferred casing material, it should be large enough to avoid damage during pump installation and removal. Also, €or depths exceeding 100 feet or s o , most casing strings are not perfectly straight, making extra space advisable. A 4-inch-diameter casing is generally adequate for pumping lifts of up to 300 feet, assuming the range of well yields normally encountered in coal regions. A 3-inch-thick gravel pack is generally recommended, but a 2-inch gravel pack would suffice for shallow wells in alluvium. For monitor wells that are not to be pump tested, where water levels are to be measured and water quality samples collected, a 2-inch-diameter PVC casing can be used. Such a diameter would be feasible for monitoring groundwater quality in alluvium. In many cases, however, use of a somewhat

46

larger-diameter casing is the least expensive procedure in the long term. Larger-diameter wells are easier to develop, easier to sample, and provide maximum use flexibility. For example, a water-level recorder can be more easily installed in a larger well. An annular seal should be placed at the upper 10 to 20 feet of wells. Wells should be properly developed upon completion to remove drilling mud and other foreign materials. The top of the casing should extend several inches above the ground surface and a locking cap should be installed. Barriers should be constructed to prevent damage. obviously, as the pit moves, some monitor wells will have to be abandoned and new ones drilled. Thus, it may be advisable to construct them with provisions for retrieval of the casing at a later date. For deep wells, air rotary drilling is the usual method for overburden or coal above the water table. When saturated conditions are encountered, mud is added and drilling is by direct rotary, with a circulating drilling fluid. Bentonite is cornmonly used for drilling below the water table. Clinker is a special case and may be rather easily drilled above the water table. Circulation loss commonly occurs below the water table, however, even when drilling mud is used. Thus, bran, fiber, cement, or other materials are sometimes added. Bran, fiber, and other organic lost-circulation materials are themselves pollutants and their use in potable groundwater conditions should be restricted. The State of Montana forbids the use of these materials in drilling and plugging coal exploration holes. For alluvium, a common procedure is to drill an 8-inch-diameter hole with a flight auger and install a 4-inchdiameter PVC casing with a 2-inch-thick gravel pack. Annular well seals are usually bentonite.

Considerable attention should be given to well development. Monitor wells can be swabbed and bailed, air or water jetted, and finally pumped and surged. Use of a larger-diameter casing enhances proper well development. Upon completion of a well, a pump should be installed, pumping commenced, and water samples collected at frequent intervals during the first few hours of pumping. For alluvium, test durations of about 24 hours are usually adequate. The duration of tests in bedrock and clinker wells should depend upon the transmissivities and storativities of the aquifers, the types of tests, and the types of results desired. Where transmissivities are low and storativity is not being determined, single-well tests for 3 or 4 hours are generally sufficient. Where storativity is a desired result, longer tests with one or more observation wells are necessary. If directional permeability or aquifer boundaries are also to be evaluated, several observation wells and pumping for as long as a week may be required. Continuous water-level recorders installed at observation wells give the most dependable drawdown data. A step-drawdown test is advisable during the first part of the test to determine well losses. Water should be piped a sufficient distance from the pumped well to ensure that no recirculation occurs during the test. A 1-inch-diameter sounding line should be installed for water-level measurements in the pumping well by electric sounder if a transducer is not utilized. Totalizing propeller-type flow meters or orifice plates should be used to measure the flow. Electrical conductivity, pH, and temperature of 47

discharged water should be periodically measured during the pump test. About six water samples should be collected at different times during the test for chemical analysis of parameters to be monitored. Field determinations of pH, electrical conductivity, oxidation potential, and other parameters can be conducted simultaneously with pump testing to avoid duplication. From such data, the optimum duration of pumping before water sample collection can be determined. Sample collection procedures are given by Brown, Skougstad, and Fishman (1970) and Thatcher, Janzer, and Edwards (1977). Pumping is the preferred method of sampling where well yields exceeding about 1/2 gpm can be obtained. Airlifting is commonly used in the Gillette, Wyoming area and may be the most feasible approach where wells yield less than 1/2 gpm. Consideration must be given, however, to changes in chemical composition that may be induced by the airlifting process. Grab samples of pit water initially should be collected weekly. Before initiation of a routine sampling program, the variability in pit-water composition with depth and location should be determined. Results of this survey can be used to determine the number of samples required for each sampling round. The sampling frequency may be increased or decreased depending on results of the first several months of sampling. A composite sampling device may be necessary if grab samples prove inadequate. The date and time of sample collection should consider climatic conditions and operational procedures at the mine that might affect the quality of water sampled. A quarterly sampling frequency is adequate for overburden and coal and semiannual sampling is adequate for deeper materials. In Wyoming, the Department of Environmental Quality specifies sampling monitor wells quarterly. The greatest constraint to more frequent sampling in many western coal regions is adverse weather conditions.

The most complete analysis should be performed on the pit water. Samples of water should be examined for the major inorganic chemical constituents, including pH, electrical conductivity, and total dissolved solids (residue at 18OOC). Selected samples should be examined for TDS (ignition at 60O0F). Such determinations allow comparison of cation-anion sums, TDS versus electrical conductivity, and calculated TDS versus residue. Boron, phosphorus, and fluoride should be determined on all samples. Proper sample treatment and filtration techniques should be used (Brown, Skougstad, and Fishman, 1970). The various nitrogen forms should occasionally be determined. Trace elements that are recommended for frequent determinations include iron, manganese, cadmium, chromium, arsenic, lead, molybdenum, vanadium, cyanide, and selenium. An extensive list of trace elements should be determined early in the program and annually thereafter. A gross indication of the organic chemical composition can be obtained by total organic carbon and dissolved organic carbon determinations. Oil, grease, gasoline, and selected pesticides should be determined early in the program and annually thereafter. For radiological composition, uranium and thorium contents and gross alpha activity, gross beta activity, and radium-226 activity should be determined. For bacteriological composition, total coliform and fecal coliform should be determined. 48

For solid materials accumulated at the bottom of the pit water, the nitrogen forms, trace elements, and total organic carbon should be determined on saturated extracts. Proper quality control procedures for laboratory analyses should be used.

Labor costs include inventorying and characterizing discrete and diffuse sources and field checking water quality and sample collection. Capital expenditures for sampling equipment are not required if these instruments have been obtained to sample sedimentation ponds. Grab samples of solid waste materials found in the pit water will not require additional equipment. Operating costs include those for analysis and transportation and storage of samples. Recommendations-A recommended general procedure is to perform the most complete analyses on water. Existing information on discrete and diffuse sources should be compiled and reviewed. Water entering the pit will not require complete analysis once it is characterized.

Grab samples of pit water initially should be collected weekly. Before initiation of a routine sampling program, the variability in pit-water composition with depth and location should be determined. Results of this survey can be used to determine the number of samples required for each sampling round. The sampling frequency may be increased or decreased depending on results of the first several months of sampling. A composite sampling device may be necessary if grab samples prove inadequate. The date and time of sample collection should consider climatic conditions and operational procedures at the mine that might affect the quality of water sampled. Step 3 . Identify Potential Pollutants--Impoundments Potential sources of pollution within impoundments include pit discharge, sewage effluent, and surface runoff. Pit discharge may contribute a large amount of,suspended solids, some or all of the major inorganic chemical constituents (calcium, magnesium, potassium, sodium, bicarbonate, carbonate, chloride, sulfate, sulfide, phosphate, etc.), and trace contaminants (including iron, manganese, zinc, copper, cadmium, chromium, arsenic, lead, molybdenum, vanadium, uranium, thorium, radium, and selenium). Among the potential pollutants in ammonium-nitrate/fuel oil ( A N F O ) , used as an explosive for overburden removal, are nitric oxide, nitrogen dioxide, nitrous oxide, ammonia, hydrogen cyanide (0.10 pound of hydrogen cyanide is produced for each 120-ton charge of ANFO), fuel oil, and trace organics. Gasoline, diesel fuel, and oil may be introduced by heavy equipment working in the pit. Pollutants introduced into impoundments from an onsite package plant include major inorganics and trace contaminants, organics (measured by total organic carbon [TOC], chemical oxygen demand [COD]), and microorganisms (Everett, 1979). Surface runoff into the pit includes both sediment and wastes deposited on the ground surface, such as oils, chemical spills, salts, etc., as well as salts, organics, and microorganisms flushed from the soil surface.

49

Monitoring Needs-Monitoring needs include characterization of the sources of possible pollutants entering the impoundments, identification of potential pollutants entering the ponds, and determination of the chemical characteristics of the water in the ponds themselves. Alternative Monitoring Approaches-Nonsamplinq methods--One method of characterizing potential pollutants is to collect pollutant-specific information on monitoring activities relating to an impoundment. For example, water quality data may be requested, together with information on the status of a National Pollutant Discharge Elimination System permit for the basin. The NPDES permit also usually requires monitoring of flow, pH, total suspended solids (TSS), magnesium, and iron. Alternatively, the quantities of water discharging into ponds from the main sources of potential pollution can be measured or otherwise characterized. For example, flow meters can be installed within pipelines used to transport pit water to ponds. Similarly, a Palmer-Bowlus flume or a weir can be placed in the line from a package plant. The watershed area above a pond can be characterized, and a rainfall-runoff relationship developed using techniques in the SCS National Engineering Handbook (soil Conservation Service, 1972).

Another nonsampling method is to inventory sources contributing possible pollutants to the impoundments. For example, the mass of ANFO used in overburden removal and coal fracturing can be determined. Sources contributing to the package plant can be inventoried during a parallel program. The surface runoff area above ponds can be examined for surface stockpiles (e.g., topsoil, coal refuse, oil drums, etc.) containing potential pollutants. The sources can be located on a suitable base map. Measurement of overflow from the ponds is required for an NPDES permit and these flow data may be used as part of the nonsampling program. To obtain overflow measurements, appropriate weirs or flumes can be installed in a well-defined reach of the river into which ponds discharge or as close as possible to the ponds. An automatic stage recorder can be installed for continuous measurement.

Samplinq methods--Water samples for characterizing pollutants within the impoundment and downstream runoff can be obtained from a number of locations. For example, pit water discharging into the impoundment can be sampled directly at the pipeline discharge point. Similarly, samples of package plant effluent and surface runoff into ponds can be obtained within the ponds and from the outfall to determine water quality transformations in transit. Finally, pond surface runoff can be sampled at a number of downstream locations. Water sampling methods include grab sampling, automatic composite sampling, and automatic discrete sampling. Grab samples are obtained to determine instantaneous water quality. Composite samplers are used to obtain 50

blended water samples over an appropriate time interval. Discrete samplers are used to extract water samples at timed intervals. The relative advantages and disadvantages of these techniques for wastewater sampling are reviewed by Harris and Keefer (1974). Three alternative methods are possible for analyzing water samples. First, all samples may be submitted to a laboratory for complete analyses, including suspended sediment; major inorganics (calcium, magnesium, sodium, potassium, chlorine, HCO3, SO4, PO4, Si02, NH3-N, total-N, pH, and EC); trace constituents (iron, manganese, zinc, copper, chromium, arsenic, molybdenum, vanadium, thorium, rubidium, and selenium); hydrogen cyanide (possible byproduct of ANFO); organics (oils, grease); and microorganisms (total and fecal coliform). Recommended quality control measures (e.g., submitting duplicate samples to other EPA-audited laboratories) should be an integral part of this approach. A second technique is to analyze completely the first few water samples collected during the program. Trace constituents found to be present in low concentrations can be excluded from further analyses. Similarly, cyanide, low-level organics, and microorganisms can be deleted from routine analyses. It is recommended, however, that each sample be completely analyzed for the major organics. Similarly, package plant effluent should always be checked for biochemical oxygen demand (BOD) and coliforms. Quality control measures should be implemented. A third method is to analyze samples in the field for constituents such as total dissolved solids (TDS), pH, cloride, and nitrate. This approach requires the purchase of a portable field kit. When the results of such checks indicate a substantial change between tests, samples should be collected for laboratory analysis.

Selecting a sampling frequency to characterize the waterborne pollutants in a source such as a sedimentation pond is generally a trial-and-error process. One method is to sample frequently (e.g., every hour using a 24-hour discrete sampler) until time trends in the quality of the source are characterized. 'Subsequently, samples can be obtained by periodic grab sampling (e.g., weekly or monthly). An increase in sampling frequency may be warranted by unusual circumstances. For example, a spill of toxic substances on the watershed area draining into the ponds may justify an increase in sampling frequency. Sampling frequency is also related to analytical costs. Thus, complete laboratory analyses of 24 samples collected during the 24-hour cycle of a discrete sampler may be prohibitively expensive and dictate 6 - or 12-hour discrete samples or a single 24-hour composite sample. The overall costs of Step 3 are high initially because of the need to completely analyze source samples. Later, the sampling frequency and requisite analyses can be reduced. Using field checks to determine sampling frequency is another cost-reducing technique.

51

Labor costs include inventorying and characterizing sources, installing and operating water sampling equipment, field checking quality, and collecting and transporting samples. Capital costs include purchasing composite or discrete samplers and for equipment for field-checking quality. These items are capital items available for an overall monitoring program. Consequently, the proportionate charges against this source would be low. Initial operating costs for analyzing samples are high but will drop as the list of constituents to examine is narrowed and field checks are used to guide sampling. Recommendations-All of the above methods are important in a program to identify potential pollutants. However, source characterization, e.g., package plant discharge, will be included in parallel monitoring programs and is not considered here. Similarly, inflow-outflow rate relationships will be considered as a sampling item under Step 5, Evaluate Infiltration Potential. Consequently, the following preferred monitoring approach is recommended: Obtain available water quality data, including information on the National Pollutant Discharge Elimination System permit. Collect samples of pit water, runoff from disturbed areas, and sewage effluent discharging into the detention basin via composite or discrete samplers. These samples can be used to characterize incoming quality trends and to assist in determining water quality transformations during transit through the basin. In addition, time trends in certain quality parameters (e.g., biological oxygen demand, or BOD) may be warranted from results of parallel studies on the package plant. Subsequently, when trends are apparent, discrete grab samples can be collected. 0

Grab--samplesurface runoff flowing into the ponds at the inlet point. Grab-sample water at two or three locations within each pond and at two or three depths at each location to characterize quality transformations during transit of water through the ponds. Grab-sample pond discharge at the outfall point and at two or three downstream locations.

~ l water l samples should be collected, preserved, and transported using recommended procedures (see Brown, Skougstad, and Fishman, 1970). The following approach is recommended for analyses of water samples collected from sedimentation ponds:

52

Completely analyze the first five water samples from each sampling location for all constituents using rigorous quality con-trol measures. Analyze field samples for representative constituents (e.g., TDS, pH, nitrate, chloride). Collect samples for complete analysis if substantial changes in concentrations of these parameters occur during the nonsampling period. Analyze water samples collected on the basis of results under the second step only for those constituents found during the first step to be present in above-permissible concentrations. The major inorganics, however, should be completely analyzed and package plant effluent checked for BOD and microorganisms using rigorous quality control measures. A preferred approach to sampling frequencies for sampling points related to sedimentation ponds includes:

Sampling pit water and package plant effluent at their respective discharge points on a 6- and 12-hour basis, using discrete samplers, three or four times a week for 4 weeks, or until time trends in quality are characterized. Thereafter, obtain grab samples on a semimonthly basis, unless more frequent sampling is warranted (e.g., discharge of toxic chemicals from the pit). Grab-sampling surface runoff at the inlet point to the pit during one or two snowmelt runoff events and during one or two summer discharge events. Collecting water samples at two locations in both pit and sedimentation ponds at weekly intervals until quality trends are established. Thereafter, water can be sampled monthly. Collecting water samples at the outfall point from the detention basin at the same frequency and at the time that inflow discharges are sampled: that is, collect samples on a 6- or 12-hour basis, three or four times a week, until quality trends become apparent. Thereafter, discrete samples can be collected twice a month. Water samples should be obtained when available from the outflow channel. If flows are sustained, samples should be taken twice a month. Step 5. Evaluate Infiltration Potential Monitoring Needs-The primary monitoring need is to determine the quantity of water seeping into the subsurface from the impoundment and outflow channel.

53

Alternative Monitoring Approaches-Two methods are possible for estimating pond seepage: the water budget method and a seepage matrix. The water budget method requires determining inflow rates from all sources, outflow rates, evaporation-rainfall rates, and changes in storage. Inflow rates from the pit and package plant can be determined via weirs or flow meters. Runoff from the watershed draining into the ponds can be estimated from rainfall data and suitable rainfall-runoff relationships, such as developed by Craig and Rank1 (1977). Outflow rates may also be determined via weirs or flow meters. The amount of water removed from the ponds for road spraying can be estimated from the capacity and number of truckloads utilized for dust suppression. Evaporation and rainfall rates can be determined by installing rain gauges and evaporation pans in the vicinity of the pond, by using meteorological data from an onsite station, or by using such data from a nearby station. The most cost-effective approach is to use data from an onsite station. Data from other areas may not be strictly applicable. Changes in storage can be determined by installing either staff gauges or an automatic stage recorder. The latter unit requires a stilling well and possibly a platform. Staff gauges offer the most cost-effective approach unless rapid changes in water levels are expected.

When all the above components of the water budget have been determined, seepage rates are calculated by differences. Seepage meters provide point information on seepage. Such meters may be difficult to install and operate in sedimentation ponds. In addition, many observations are required in order to ensure meaningful results. Infiltration in the outflow channel from pond overflow can be determined by using existing flumes, by installing flumes between measuring points, or by current metering of different outfall reaches. Water budget determinations can be made on a continuous or intermittent basis. Continuous determinations require the installation of recording flow meters, automatic stage, recorders, etc. Alternatively, the measurements required to compute a water balance can be obtained on a monthly or seasonal basis. In addition, measurements can be obtained before and after sedimentation removal. The surface mining reclamation and enforcement provisions require that sediment be removed from sedimentation ponds when the volume of sediment accumulates to 6 0 percent of the sediment storage required. After sediment removal, seepage rates will probably increase. The principal costs for this effort include: Labor costs: conducting water balance studies, i.e., for installing weirs and flow meters: installing staff gauges on automatic stage records: collecting rainfall-evaporation data (or installing associated equipment): determining rainfall-runoff relationships for the contributing watershed; analysis and interpretation of data: and determining seepage in the outflow channel.

54

0

Capital costs: weirs or flow meters, water stage recorders or staff gauges, and gauging station in the outflow channel. Operating funds for travel, chart paper, etc.

The foregoing capital items are general project items and costs would be apportioned to usage. RecommendationsThe water budget approach is recommended. Although the initial cost of determining seepage rates via a water budget may be greater than by installing seepage meters, the results will be more accurate. In addition, capital items (e.g., weirs) may be general project items, reducing the cost apportioned to the impoundments. A cost-effective approach for monitoring infiltration through the outflow channel is to utilize existing gauging stations, where possible, supplemented with an additional station in an upstream or downstream locat ion. The preferred approach to conducting a water balance for impoundments is to obtain measurements on a monthly basis, until a seepage curve is obtained,

and thereafter on a semiannual basis. before and after sediment removal.

Measurements should also be obtained

Seepage rates in reaches of the outflow channel can be determined via an existing or project gauging station on a frequency dependent on pond overflow. If overflow is continuous, monthly measurements should be obtained. If overflow is periodic, measurements should also be periodic. Seepage rates should also be obtained during precipitation runoff. Step 6 . Evaluate Mobility in the Vadose Zone Mobility and attenuation of potential pollutants in the vadose zone will depend entirely on the quantity of infiltration water, defined in Step 5, that enters the zone. Thus, this and subsequent monitoring steps will be implemented only when preceding studies indicate a need for further evaluation. Monitoring Needs-Data gaps exist in knowledge of the factors tending to attenuate pollutants within the vadose zone (i.e., dilution, filtration, sorption, chemical precipitation, buffering, oxidation-reduction, volatilization, and biological degradation and assimilation) and field data on transformations in waterborne pollutants during flow in the vadose zone. Alternative Monitoring Approaches-The potential attenuation of pollutants in the vadose zone can be depicted by constructing a table comprising attenuating factors (rows) versus specific pollutants (columns). Each location in the matrix specifies the relative potential of a factor (e.g., sorption) to attenuate a specific pollutant (e.g., zinc). Each position in the table may be filled in by subjective 55

evaluation or on the basis of actual measurement. Subjective evaluation involves examining available data and estimating the effect on the mobility of a specific pollutant. Actual values from attenuating factors can be obtained from field measurements. For example, drill cuttings obtained during construction of wells can be analyzed to characterize cation exchange, pH, particle size, Eh, etc. Obviously, completion of the matrix will be complicated by the interaction (synergistic or antagonistic) of attenuating factors. In addition, some factors may not be easily determined or estimated (e.g., volatilization). Consequently, the recommended approach is to use a mix of subjective estimates supplemented, when possible, with actual data. Access wells through the vadose zone and a neutron moisture logger can be used to obtain water-content profiles. The vertical movement of water can be inferred by periodically logging in single wells. For example, water-content changes between daily logs show moisture accretion to, or drainage from, vertical segments of the vadose zone. In addition, the growth and dissipation of perched groundwater may be manifested on logs. The rate of lateral movement of perched groundwater can be inferred by monitoring water-content profiles in a transect of wells. Several construction methods are possible for installing access wells (e.g., rotary percussion, cable tool). However, the method providing the tightest fit should be selected. Access wells can be constructed of steel, PVC, or aluminum. PVC moderates the thermal neutrons used in moisture detection and results in poor resolution. Aluminum wells deteriorate under highly saline conditions. Water movement in the vadose zone underlying impoundments can also be estimated by installing tensiometers and using methods described by Bouwer and Jackson (1974). Such units can be installed in several depths below the impoundment. Since tensiometers fail to function at water pressures less than -0.8 atmosphere, moisture blocks that function at lower pressures could be inst a1led. In order to characterize water movement beneath the outflow channel during pond overflow or natural discharge, access wells and/or tensiometers and moisture blocks can be installed at two or three locations. To supplement the nonsampling program, field activities can be initiated to monitor the actual movement of pollutants in the vadose zone. Alternative methods include collecting drill or auger samples for laboratory analysis, installing suction cups, and installing sampling wells within perched groundwater bodies.

Collection of samples of vadose zone sediments entails using hand or power augers or core samplers. Depending on the physical composition of sediments underlying the ponds, hand-augered samples can be obtained to a depth of about 10 feet. If deeper samples are required, power equipment is needed. Samples may be collected (if possible) within the pond and in a transect away from the pond. Similarly, hand or power auger samples can be collected in the outflow channel and analyzed in the laboratory.

56

Suction-cup lysimeters can be installed throughout the vadose zone if the region consists of alluvium. Installations of cups in shale or standstone might cause postoperational difficulties. Suction cups can be installed as individual units, in depth-wise increments, or as multiple units in a common borehole. The cheapest approach is to install separate units to a depth of about 5 to 10 feet, say in 1-foot increments. Beyond 10 feet, borehole installation would be a more efficient alternative. For illustration of suction-cup lysimeter installations and operation procedures, see Fenn, Hanley, and DeGeare (1975). Perched groundwater can be detected from neutron moisture logs. Perched groundwater regions may yield water in sufficient volume to permit sampling. In this case, PVC wells can be constructed to the perched regions and samples extracted by hand bailing or by pumping. Water samples collected from suction-cup lysimeters can be analyzed completely or partially. Ideally, a complete analysis includes the major inorganics, trace constituents, and organics listed under Step 3, Identify Potential Pollutants. (The ceramic suction cups may filter out microorganisms.) Upon examination of the results of complete analysis, subsequent samples may be analyzed only for those trace constituents found present in greater-than-permissible concentrations. An initial complete analysis for major constituents is always recommended. Solid samples can be used to obtain saturated extracts and particle-size distribution via techniques in Methods of Soil Analysis (Black, 1965). Saturated extracts can be employed to determine cation exchange capacity, EC, pH, and specific major and trace constituents, including boron, calcium, magnesium, potassium, chlorine, sodium, C02, HCO3, and SO4. Additional techniques are available for determining other trace constituents, such as copper, zinc, fluorine, selenium, cobalt, and molybdenum (Black, 1965). organics can be determined using procedures described by Dunlap et al. (1977). Water samples taken from PVC wells within perched layers can be analyzed. Alternatives include complete analysis of each sample: complete analysis of the first five to ten samples, until the water quality is characterized: partial analysis for those constituents found in excessive concentrations: and field checks. Sampling frequency in suction-cup lysimeters depends on the water pressure within the surrounding porous matrix. If the matrix is very dry, water will enter the cups at a very slow rate. A week or more may be required to collect sufficient samples for analyses. In the extreme case, the cups become inoperable when water pressure is less than -0.8 atmosphere and samples may be available only once or twice a year. In contrast, if the porous system is very wet, samples may be extracted on a daily basis. The sampling frequency cannot be explicitly defined until field units are installed and operating. For a wet system, it may be desirable to collect samples on a more frequent basis (e.g., weekly) until quality trends are established. Later, samples can be obtained monthly.

57

Perched groundwater may be available only on a cyclic basis. Samples must then be obtained whenever possible. If perched groundwater is available continuously, samples can be obtained frequently (say, once a week) until quality trends are established. Later, samples can be collected monthly. Costs associated with the recommended approach for monitoring in the vadose zone include: 0

Labor costs: constructing an attenuation factor versus pollutant matrix and interpreting results; overseeing the installation of access wells and, subsequently, logging the wells; installing tensiometers and moisture blocks and collecting and interpreting results; obtaining and examining data from neutron moisture logs and tensiometer data to determine the flux of water (and pollutants) in the vadose zone; installing suction-cup lysimeters; collecting solid samples from the vadose zone; collecting water samples from the suction cups and PVC wells (if constructed); and conducting field checks on pH, EC, chloride, and nitrate.

0

capital costs: access wells; neutron moisture logger; tensiometers; suction-cup lysimeters; PVC wells; pH meter, EC bridge, and field kit for measuring chloride and nitrate (these items are general project items and associated costs for this step will be apportioned according to usage); and hand augers or power augers (again, these are project items).

0

Operating costs: analytical costs for water samples (this cost is reduced when field checks are used to determine the need for laboratory analysis, and the number of requisite analyses is reduced throughout the program) ; analytical costs for analysis of auger samples; and transportation costs, sample bottle costs, etc.

Recommendations--The preferred approach for estimating pollutant movement in the vadose zone comprises: 0

Constructing a matrix of attenuation factors versus specific pollutants using available data when possible, supplemented with intuition.

0

Installing three access wells laterally away from the impoundment into the uppermost aquifer.

0

Installing two networks of shallow tensiometers and moisture blocks in each pond with individual units terminating in 1-foot increments to 5 feet beneath the base of the ponds.

0

Installing a network of shallow access wells, tensiometers, and moisture blocks at three locations along the outflow channel.

58

Installing suction-cup lysimeters in 1-foot increments to a depth of 10 feet below the base of the pond and in the outflow channel alluvium. Three sets of suction-cup lysimeters should be installed, one set within or immediately next to the pond, and the remaining sets at appropriate intervals along the outflow channel. If suction-cup samples show deep percolation of water, additional units should be installed at greater depths. 0

Collecting solid samples for laboratory analysis of pollutants during installation of suction-cup lysimeters and PVC wells.

0

Collecting additional auger samples of solids only as deemed necessary, or when suction cups are inoperable.

0

Installing one PVC well within each perched groundwater body detected by neutron logging and sampling via a submersible pump.

A preferred approach for analyzing solid and water samples collected from the vadose zone comprises:

Analyzing solid samples for major and trace constituents and organics. Particular attention should be paid to determining those pollutants found in excessive concentrations in the source during the program (Step 3, Identify Potential Pollutants). Analyzing the initial five to ten water samples from the suctioncup lysimeters completely for major trace constituents. Subsequent analyses should include all major constituents, but only those trace constituents found in excessive concentrations. Examining perched groundwater samples completely for major and trace constituents, organics, and microorganisms in the first five samples. Subsequently, only those trace constituents, organics, and microorganisms found in excessive concentrations should be determined. After the initial characterization, pH, EC, chloride, and nitrate concentrations can be field-checked. When substantial changes occur in these constituents, samples should be collected for partial analysis, as described above. A preferred approach to sampling frequency is:

Sampling suction cups whenever possible during very dry conditions. For wet conditions, sampling weekly until quality trends are established: thereafter, sampling monthly. Obtaining and analyzing solid samples only during installation of suction cups and PVC wells. Sampling PVC wells at a frequency depending upon availability of free, perched groundwater.

59

Step 7. Evaluate Attenuation of Pollutants in the Saturated Zone As pointed out by Todd et al. (1976), the principal processes involved in attenuating pollutants in the saturated zone include decay, physical-chemical reactions, and dilution. For pollutants in a source, such as a sedimentation pond, physical-chemical processes and dilution may be of prime significance. Included in the physical-chemical processes are adsorption, precipitation, volatilization, oxidation-reduction reactions, etc. Dilution is through hydrodynamic dispersion resulting from such effects as convection diffusion and flow tortuosity. Dispersion (or dispersivity) within an aquifer is difficult to determine without careful, extensive field experimentation. A qualitative notion of dilution resulting from dispersion may be obtained from knowledge of the following (see Todd et al., 1976): volume of wastewater reaching the water table, the waste loading, areal-head distribution, transmissivity values, vertical hydraulic-head gradients and permeabilities, groundwater quality, quantity and quality of recharge from other sources, and pumpage volumes and patterns. Monitoring Needs-Information gaps currently exist in predicting the effects of dilution and physical-chemical reactions on pollutant attenuation within aquifers underlying impoundments. Alternative Monitoring Approaches-The relative effect of various physical-chemical mechanisms for attenuating pollutants within the saturated zone can be estimated by constructing a matrix similar to that for the vadose zone, consisting of attenuating mechanisms (rows) versus pollutants (columns). Attenuating mechanisms consist of physical-chemical factors: sorption, precipitation, volatilization, oxidation-reduction (Eh), decay, and dilution. The completed table will show, in a mixed qualitative-quantitative sense, the pollutants that should be monitored. Knowledge of geochemical processes naturally active in the system can be valuable in predicting the transport and attenuation of pollutants. For example, Thompson and Van Voast (1981) describe processes of salt dissolution, cation exchange, and sulfate reduction as being highly active in the flow system southwest of Decker, Montana. Pollutants entering that system are subject to these processes and attenuated or transported accordingly. Completion of the matrix for the physical-chemical items requires specific information on exchange capacity of aquifer materials, on the Eh and pH of groundwater, and on the specific pollutants entering the zone of saturation. Many of the physical-chemical parameters can be quantified from analyses of drill cuttings obtained during well construction and from field analyses of Eh and pH. Identification of pollutants must await the results of mobility studies in the vadose zone. Estimating the effect of dilution on pollutant attenuation requires data on items listed previously, i.e., volume of wastewater reaching the water 60

table, the waste loading, areal-head distribution, aquifer transmissivity, vertical hydraulic-head gradients and permeabilities, groundwater quality, quantity and quality of recharge from other sources, and pumpage volume and patterns. The volume of pond water reaching the water table may be estimated from data on seepage rates (see Step 5 , Evaluate Infiltration Potential), assuming that steady-state seepage has been reached and that the water content of vadose sediments equals or exceeds field capacity. Water content data from access wells installed earlier is useful in verifying these assumptions. Similarly, neutron moisture logging data in a transect of access wells may indicate the lateral spread of pond water within the vadose zone and, consequently, the waste loading rate. Installation of additional access wells may be necessary to obtain adequate resolution. Areal head distributions in the aquifer can be obtained via a set of wells. Similarly, piezometer clusters may provide data on vertical hydraulic gradients and possibly on vertical hydraulic conductivity. Aquifer transmissivity values may also be obtained as a result of earlier pumping tests on wells. Groundwater quality can be quantified as a result of activities during Steps 5 through 7. The quantity and quality of recharge from other sources may be the most difficult items to identify. Use of available data, e.g., on seepage rates in the outflow channel, may be possible. Similarly, information on pumping rates in existing wells can be solicited from mine managers. In lieu of constructing an attenuation matrix, an alternative method is to initiate tracer studies to estimate the spread and attenuation of pollutants. For example, a conservative tracer, such as chloride, could be injected in one of the upstream wells installed earlier and water samples extracted periodically from downstream wells. In light of possible low transmissivity values in shallow aquifers, however, the time to obtain a tracer breakthrough in downstream wells could be excessive. Groundwater samples can be obtained for analysis and ensuing data examined to characterize pollutant attenuation. A network of wells can be used in such a program. In actuality, a special sampling program should not be required, because of available samples from these wells. Obtaining vertical samples within the water-bearing strata being examined is imperative. The rationale for this necessity is stated by Mooji and Rovers (1976): In the past it was frequently assumed that the monitoring of the upper few feet of an aquifer was adequate as it was assumed that the contaminants migrated vertically to the water table followed by lateral migration in the upper zone of the aquifer. In fact, recent research studies show that the contaminants can migrate to the bottom of the aquifer prior to extensive lateral migration taking place .... Therefore the preferred method is to install piezometers at varying depths throughout the thickness of the aquifer. In lieu of, or to supplement, piezometer clusters, alternative methods for obtaining depthwise samples from a given water-bearing formation include multilevel samplers and groundwater profile samplers. Details of a multilevel 61

sampling well designed by Pickens et al. (1977) are illustrated in Figure 5 . This well consists of PVC or steel well casing, openings at desired incremental depths, screened coverings on openings, and polypropylene tubing sealed onto the openings, extending to the surface. According to Pickens et al. (1977), this unit may be used to depths of 100 to 130 feet. Its advantages are that depthwise sampling is facilitated and overall construction costs may be lower than for piezometers. A suitable pumping unit may be the type used to purge tensiometer units (available from Soil Moisture Equipment Company, Santa Barbara, California).

MULTI- L E V E L GROUND-WATER SAMPLER CR0 SS - S ECT 10N 0 F SAMPLING POINT-TYPE P

FIELD INSTALLATION

CROSS-SECTION OF iAMPLlNG POINT-TYPE B

END CAP- - M A L E 8 FEMALE GROUND p u P L l NGS SURFACE WATER TABLE -

I

- - PVC

PV c PIPE

SAMPLER PIPE

SCREEh +-COUPLING I

>

SAMPLING POINTS

I

END CAP

Figure 5 .

Multilevel groundwater sampler (after Pickens et al., 1977).

An alternative depthwise sampler was designed by Hansen and Harris (1974). The unit, called a "groundwater profile sampler," is shown in Figure 6 . Basically, the sampler consists of a 1.25-inch-diameter well point, of op-tional length, with isolated chambers containing fiberglass probes. The individual chambers are filled with sand and separated by caulking compound. Small-diameter tubing provides surface access to the probes. The positioning of probes is optional, depending on aquifer materials, desired sampling 62

frequency, etc. In operation, a vacuum is applied to the sampling flasks. Hansen and Harris (1974) recommend simultaneous extraction of all samples at the same rate to minimize variation in aquifer thickness sampled by the individual probes. Water tables as deep as 30 feet may be sampled by the unit.

P

"

b Figure 6. Groundwater profile sampler (after Hansen and Harris, 1974).

63

The costs for the proposed approach consist of: Labor costs for obtaining data to prepare and interpret the attenuation mechanisms versus pollutant matrix Capital costs for additional wells. Recommendations-A preferred monitoring approach includes:

Constructing an attenuating mechanism versus pollutant matrix, using available data whenever possible. Conducting tracer studies if two monitor wells are deemed to be sufficiently close that short-time studies are possible. Using monitor wells installed during previous steps and installing additional piezometer clusters as necessary to obtain samples for characterizing the vertical distribution of quality (the other methods, multilevel samplers or groundwater profile samplers, are not recommended unless the water table is very shallow).

64

SECTION 4 MONITORING RECOMMENDATIONS FOR RECLAIMED MINE SOURCES OF POLLUTION Steps 3, 5, 6 , and 7 of the groundwater quality monitoring methodology have been developed for reclaimed mine sources of pollution as identified in Table 2. The reclaimed surface coal mine sources of potential pollution include spoils and reclamation aids. Step 8 is a mine-specific application of the methodology and is presented in Everett (1979). SPOILS Spoils are largely composed of overburden and interburden materials that have been removed from the zone between coal seams and between the coal and soil removed before stripping the coal. Minor amounts of material from the coal and soil zones, as well as artificial wastes, may also be present. The spoil materials are generally replaced in the pit area from which they were removed. They are physically disturbed, however, as compared to the original generally stratified sedimentary deposits of the premining overburden. This physical disturbance of the geologic strata results in a corresponding disturbance of the premining chemical equilibrium between the earth material and its surrounding environment. Various leaching processes acting over geologic time remove most of the readily soluble constituents that are exposed or accessible to leaching in the undisturbed overburden. Thus, most of the readily soluble materials have been removed from the strata that are permeable to water,,while a considerable quantity of soluble constituents may still remain in the relatively impermeable strata, such as finer-grained clastic rocks including clay, silt, and shale. Dislodging and mixing of the natural geologic stratigraphy, however, exposes new lithologic surfaces and mineral constituents that may be susceptible to chemical-physical interaction with the water, air, biological, and mineral components of the environment. Fracturing of the rock structure may also increase permeability to water and, in some instances, to air, thereby facilitating these interactions. Through dissolution, ion exchange, and other chemical interactions, certain minerals are released and may then be transported in solution to downgradient locations above or below the water table. From there, they may continue along flow paths to points of surface discharge. In contrast, some of the minerals that are released from their parent materials at depths of several feet or less may be subject to upward capillary movement into soil zones.

65

Potential pollutants may be generally defined as being those constituents of spoil materials that are likely to go into water solution under local geological, hydrological, climatic, or other physical-chemical processes and conditions and that might adversely affect usefulness of the water resources by man, animals, or plants. Water pollution is normally thought of as being a condition that results when undesirable materials are added to water, but can be even more broadly defined to include the removal of certain desirable chemical constituents (e.g., as by ion exchange) or by changing physical characteristics (e.g., temperature and color). The potential pollutants may differ with geographic location and stratigraphic depth of the mining and reclamation activity. They may also change with time after emplacement of the spoils in response to changes in the physical-chemical processes and the availability of certain pollutants. Although the potential pollutants tend to be site-specific, generalized information on pollutant conditions and processes observed in other regions, at other coal operations, and in laboratory research can be useful in predict-. ing and identifying local potential pollutants. Palmer and Cherry (1979) have evaluated the chemical composition of groundwater and undisturbed overburden in the Fort Union Coal Region of Western North Dakota, Montana, Wyoming, and Saskatchewan and have concluded that the chemical evolution of groundwater is governed by the processes involving oxidation of organic material in the soil zone, dissolution of calcite and dolomite, oxidation of pyrite, precipitation of gypsum, dissolution of gypsum, cation exchange, and sulfate reduction. In the western United States, the primary groundwater contamination problem associated with surface coal mining is the elevation of total dissolved solids (TDS) levels in spoil groundwaters. The soluble salts observed to be the principal constituents responsible for the elevated TDS levels are the salts of sodium, calcium, magnesium, and sulfate. Column leach experiments conducted by several researchers indicate that the salinity of spoil groundwaters will decrease over time as successive volumes of water leach the spoils mass. The time frames necessary for TDS levels to approach baseline levels are highly dependent upon the degree of TDS contamination and site-specific conditions responsible for groundwater flow rates that will leach the spoils. For example, leaching experiments in conjunction with groundwater calculations at the Yampa River Coal Company's Energy #2 mine in northwest Colorado indicated that the return to baseline TDS levels would take approximately 75 years At (Mining and Reclamation Plan, Energy #1, #2, and Eckman Park mines). nearby Edna mine (Pittsburg and Midway Coal Company), similar testing and calculations estimated that approximately 700 years of leaching are necessary at that site (Edna Mining and Reclamation Plan) in order for water quality (TDS) to return to levels observed in undisturbed areas. Spoil leaching tests do not account for the time element and associated weathering rates that can cause an unknown amount of groundwater degradation. The processes involved in elevating TDS levels in spoil groundwaters is a topic of debate. The principal processes responsible for spoil-water degradation reported by Palmer and Cherry (1979) are the oxidation of pyrite and associated dissolution of carbonate minerals. Recent work conducted by Koob 66

(personal communication, 1982) at North Dakota State University, however, indicates that insufficient amounts of sulfide (or organic sulfur) are present in the spoils to be responsible for the manyfold increase in sulfates seen in spoil groundwaters. He theorizes that in undisturbed overburden, an equilibrium is reached between the oxidation of sulfides (and organic sulfur) near the land surface with a slow migration of the byproducts of this process (salts, primarily sulfates) to groundwaters. The large quantities of sulfates already present in the overburden are made available for dissolution in spoil groundwaters aEter the mining process relocates these materials in the saturated zone or in locations where the materials can be leached. Van Voast, Hedges, and McDermott (1978) concluded from their leaching experiments that the rapidity of dissolution strongly indicates that the salts are readily available in soluble form in the overburden and that the reactions creating them had occurred long before the overburden was disturbed. Premining overburden sampling is essential to identify overburden zones that may contribute significantly to levels of TDS and sulfates in spoil groundwaters. Dollhopf et al. (1978) mention that during an extensive program to delineate overburden inimical zones at Rosebud mine (Area B) in Montana, the materials high in soluble salts (measured by electrical conductivity) are usually found within a few meters of the surface. Harrington (Montana Department of State Lands, personal communication, 1982) has also noticed in his review of overburden data from several mines in Montana that materials with high salinity are generally quite shallow (less than 15 meters). The normal dragline strip mining operation would generally place the near surface overburden at the base of the pit resulting from the previous mine cut. This mining practice places the more saline materials in the resaturated zone and may be responsible for the most significant groundwater degradation observed in spoil groundwaters (i.e-, elevated TDS, particularly sulfates). Any program designed to characterize the geochemistry of overburden materials should acknowledge the importance of measurements of electrical conductivity (on saturated paste extracts). When saline overburden materials are observed, care should be taken to determine the extent of the saline zone and a decision made whether or not to selectively place the materials out of the resaturated zone and out of zones where percolation of moisture through the saline material is likely. When sulfates are the primary component of the saline zone, particular consideration should be given to what the addition of sulfates to the postmining groundwaters will mean to potential water users. The levels of sulfates in groundwaters may be the most limiting parameter to be affected by surface coal mining because concentrations as low as 500 mg/l can affect livestock (McKee and Wolf, 1963). Dollholf et al. (1981) mention that during a research project involving selective burial of saline materials conducted at Rosebud mine in Montana, detailed measurements of deep percolation revealed topography. In semiarid areas, then, the logical location for placement of spoils high in soluble constituents would be beneath surface landforms that would enhance runoff and minimize infiltration.

67

Step 3 . Identify Potential Pollutants In identifying potential pollutants at a proposed mine site, it is desirable to have an understanding of the local geological, hydrological, chemical, physical, biological, and other environmental conditions and processes that may determine whether certain mineral species are present and might reasonably become groundwater contaminants. In many parts of the West, the more soluble salts contribute most to the initial mineralization of groundwater. These include salts of sodium, magnesium, calcium, and sulfate. These highly soluble pollution sources tend to be depleted with time, but not necessarily at the same rates. Typically, as leaching continues, the salinity of the water decreases as the more soluble sodium and magnesium cation source materials are depleted. Concurrently, the relative concentration of the calcium cation increases in the leachate. For example, Yampa Rivers Coal Company's Mining and Reclamation Plan for the Energy #1, #2, and Eckman Park mines in northwest Colorado presents the results of leaching tests indicating spoil-water quality levels (in terms of TDS) will be elevated above the baseline water quality levels. The leaching study further indicates that the readily soluble constituents are removed and the TDS levels gradually decrease over time. The volumes of water relative to spoil mass used in the leaching tests when compared with the field hydrologic conditions indicate spoil water qualities could return to baseline levels in less than 100 years. Similar leaching tests and associated calculations conducted for the Pittsburg and Midway Edna mine indicate that baseline water quality would be approached 700 years following mining. In all studies of this type, the effect of time as it may relate to weathering and release of additional soluble constituents cannot be assessed. Researchers agree, however, that an initial slug of soluble constituents introduced to the spoil groundwater system upon resaturation will decrease over time . Over a longer term, the presence of sulfide mineral sources (e.g., pyrite) in the spoils may exert a relatively strong influence on groundwater quality. Abundant pyrite in the presence of oxygen will oxidize to produce large amounts of sulfate, resulting in acid water unless excess carbonate minerals are present. Even though the pH may be kept neutral or slightly basic by the dissolution of carbonates, salinity can increase to higher levels as the pyrite oxidizes and the carbonates dissolve (Moran et al., 1979). A mitigating factor in semiarid western mine settings is a general paucity of infiltration from precipitation. Most hydrologists who have studied these settings agree that significant recharge occurs only in specific locales where precipitation accumulates or is retained long enough to penetrate beneath the root zone. Identification of potential pollutants should be considered as a data collection process that can effectively begin before the mining period and extend through the mining and postmining phases. In the West, spoil waters are rarely acidic. Commonly, sufficient carbonate minerals and alkaline salts are available to neutralize any acid 68

production resulting from the oxidation of sulfides (pyrites) and organic sulfur. However, the oxidation of pyrite and organic sulfur causes an elevated level in TDS caused by the dissolution of alkaline materials such as the carbonate minerals. The result can be elevated levels of TDS, particularly sulfate, that could render groundwater unsuitable for livestock use. The opportunity exists during the mining process to minimize the oxidation of pyrites and production of sulfates by burying localized pyritic zones in the postmining saturated zone. Pionke and Rogowski (1979) state that water has an oxygen diffusion coefficient four magnitudes less than for sulfides in air and, therefore, limits the oxidation reaction rate. Another method to limit the groundwater degradation from sulfate production associated with oxidation of pyrites is to bury the pyritic material where it will not be transported into the groundwater. In areas of little, if any, deep percolation, burial of the pyritic zone above the saturated zone would not slow the oxidation of pyrites but would effectively limit groundwater degradation by isolating the sulfates that are produced. Dollhopf et al. (1981) found at Rosebud mine in Montana that very little deep percolation occurred at a selective burial monitoring site that was overlain by a hillslope landform. Dollhopf et al. suggest that selective burial of spoils high in soluble constituents should be done above the resaturated zone under sloping landforms that will minimize percolation of moisture. Concentrations of pyrites are not uncommon in carbonaceous materials such as rider coal seams or carbonaceous shales overlying coal seams, as well as in other isolated strata (personal communication, D. Fransway, 1982). Table 9 is an example of overburden data taken from a mine near Gillette, Wyoming (personal communication, D. Fransway, 1982) showing a zone high in pyrites and/or organic sulfur as evidenced by the high total concentrations. Selective burial of zones such as in Table 9 showing high pyrite levels would help minimize degradation of spoil groundwaters. Research is being conducted at Montana State University on an appropriate calculation for assessing the acid-neutralization potential of spoil materials. Dollhopf (personal communication, 1982) has found that sulfur detected by total sulfur analyses has been as much as 70 percent organic sulfur. In contrast, total sulfur analyses in the eastern United States generally show less than 1 percent organic sulfur. The significance of this finding is that the potential activity associated with the organic form of sulfur has not been accounted for in acid-neutralization potential calculations in the West. According to Dollhopf, organic sulfur when oxidized produces approximately onethird less acid than the sulfide forms of sulfur. Therefore, calculations regarding the acid-neutralization potential of spoils such as that described by Smith et al. (1974) should account for the potential acidity associated with the organic and sulfide forms of sulfur in the spoils. A disparity of opinions exists on the appropriate density of overburden samples. Overburden sampling in Montana, Wyoming, and North Dakota is required on a grid spacing ranging from 600 to 1,500 meters. These states have the most demanding overburden characterization requirements of the western states. A recommendation was made by the Department of the Interior, Bureau 69

TABLE 9. OVERBURDEN ANALYSES FROM A SURFACE COAL MINE NEAR GILLETTE, WYOMING, SHOWING NET POTENTIAL ACIDITY ASSOCIATED WITH ISOLATED STRATA (D. Fransway, Wyoming Department of Environmental Quality) Tons CaC03/1,000 Tons Material

Sample Number

Depth (feet)

Total sulfur (percent)

SO4-S (percent1

Maximum Required

Present Neutralization Potential

Amount Needed for Neutralization

Hole #200

0-10 10-13 13-20 20-30 30-35 40-45 45-55 55-56 65-73 73-80 87-95

0.37 0.28 0.20 0.18 0.70 0.66 0.62 1.00 0.30 0.54 0.60

0.11 0.02 0.02 0.06 0.21 0.08 0.06 0.12 0.02 0.10 0.05

8.13 8.13 5.63 3.75 15.31 18.13 17.50 27.50 8.75 13.75 17.19

9.56 -12.00 -4.00 -3.50 -5.50 3.75 43.13 22.25 2.75 14.25 5.13

17.6ga 20.13a 9.63a 7.25a 20.81a 14.3aa -25.63 5.25a 6.DOa -0.50 12.06a

Hole #203

0-5 5-10 10-20 20-29 20-35 35-41 41-49 51-59

0.76 0.23 0.10 0.04 0.05 0.05 0.12 0.10

0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01

23.44 6.88 2.81 0.94 1.25 1.25 3.44 2.81

-46.25 -7.88 30.25 3.75 47.00 4.50 29.38 5.75

69.6ga 14.76a -27.44 -2.81 -45.75 -3.25 -25.94 -2.94

Note: a Zones showing net acidity requiring CaCo3 for neutralization calculated according to methods in Smith et al., 1974. Calculations used do not account for any difference in potential acidity associated with the forms of sulfur (sulfides versus organic sulfur).

of Land Management ( 1 9 7 7 ) , "For a limited amount of sampling and analysis of overburden in the Fort Union Region ... the rock material is homogeneous and ... the concentrations of potentially harmful elements are not high. We feel that it is not justifiable to spend large amounts of money for a slight increase in the confidence that minor zones of high concentration have not escaped detection." In contrast, Dollhopf et al. ( 1 9 8 1 ) conducted a research project using high-density overburden sampling to delineate chemical migration inhibitory zones.

The salient point is that groundwater degradation should be minimized whenever possible. The site-specific harm that may come from introducing a localized chemical migration inhibitory zone into the groundwater versus the economic cost of selective burial of such material is a regulatory matter that cannot be resolved in this document. Dollhopf et al. ( 1 9 8 1 ) evaluate the accuracy of varying drilling intensities while attempting to delineate chemical migration inhibitory overburden zones at the Rosebud mine in Montana with regard to elevated soluble salts, nickel, and clay contents: Of course, there is one inescapable conclusion.

That is, as drilling intensity increases, our ability to accurately define overburden inhibitory zones increases [Figure 71. Ideally, in biological-environmental systems, we would like to make correct evaluations at least nine times out of ten (i.e., with 90% accuracy). If we apply this criterion to the regression equations presented in Figure 7 to clay and soluble salt prediction, then we see the required drilling intensity would approach a 43 m grid. Our ability to characterize unsuitable overburden with drill holes 600 to 1500 m apart as recommended by States has an accuracy of only 45 to 60%. This means that it is probable that a typical premine overburden assessment program missed detecting half of the unsuitable materials in the project area. Since our ability to predict inhibitory (or noninhibitory) status of overburden between two boreholes approaches a 50% accuracy, our ability to predict the presence of absence of inhibitory material between such boreholes is very limited. Therefore, when reconnaissance overburden sampling is performed, it may very likely be a false interpretation to assume noninhibitory overburden will be present between two adjacent boreholes which did not intercept inhibitory material. Considering that western states sample overburden in a 600 to 1500 m grid fashion, it is likely that incorrect interpretations are being made resulting in inhibitory materials being unknowingly deposited either in the future aquifer zone or root zone. Dollhopf et al. acknowledge that intensive sampling could become prohibitively expensive. They suggest a two-phase approach that begins with a wide grid spacing (i.e., 600 meters). Following the initial overburden analyses, only the parameters that occurred above or near inhibitory levels would be considered in the second phase of sampling. The second intensive drilling and

71

1 oa OBSERVED DATA

0

PREDICTED VALUES SOLUBLE SALTS

9c

-----

NICKEL

A

CLAY

8C

I

I

c

al

->$

7c

-\ 1

Q

Ya

60 0

Q

50

40 y=1

30

I

I

I

200

1

I

400

+ 0.562 ( 1 ? ~ . ~ ~ ~R~2 =- 0.9 1 ) ,

I

h

600

1 2.000

OVERBURDEN SAMPLING INTENSITY (m)

Figure 7 .

Accuracy in characterizing unsuitable overburden zones as a function of drilling intensity for soluble salts, nickel, and clay at Rosebud mine near Colstrip (Area B), Montana (Dollhopf et al., 1981).

sampling program would be designed to attain a characterization accuracy of 80 to 90 percent of a chemical migration inhibitory zone. To attain that accuracy, a 60-meter drilling would be necessary. Another way to save drilling costs and yet maintain the characterization accuracy would be to couple the overburden sampling with the drilling of the highwall for blasting. This suggestion has problems because frequently insufficient time is available between the drilling, blasting, and removal of the overburden to allow the mine operator to react to the results of the geochemical analyses. Drilling and sampling of the mine highwall, however, may be best utilized to guide subsequent drilling ,(back from the highwall) and delineation of potential inhibitory zones. 72

The recommended drilling intensities should be considered site-specific and, while they provide insight to acceptable drilling intensities for other mine sites, the recommendation should not be considered absolute. In many instances, it may be relatively simple to identify or predict potential pollutants during the premining stage while they are confined to their natural positions within the geologic strata. At this time, correlation of data from test holes in the proposed mining area may be sufficient to show the three-dimensional distribution of rock types, thickness, and elevation throughout the proposed mining zone. These stratigraphic data, in combination with information on potential pollutants in each respective stratum acquired by sampling during drilling and subsequent field or laboratory analyses, provide a corresponding three-dimensional picture of potential pollutant distributionIn the postreclamation period, detecting, identifying, and locating potential pollutants after they are highly scattered at possibly unknown locations and depths in the spoil mass may be considerably more difficult and expensive than it would have been at earlier stages. It would be preferable

to: 1.

Identify during the planning/exploration period the types of potential pollutants in the undisturbed overburden and their stratigraphic position, with particular attention to those types that may be especially toxic, acid forming, or otherwise troublesome (e.g., zones high in pyrite). Reliable extrapolation of information for great distances from a test hole drilled in undisturbed stratified overburden may be possible, whereas a later sample from the spoils consisting of the same but highly mixed materials may not reflect conditions existing more than a few feet from the hole.

2.

Observe and record the general locations at which the different stratigraphic levels are emplaced in the spoil zone during the mining/reclamation period and, in particular, the location and method of protective emplacement of the highly noxious materials.

3.

Determine or estimate the sources and qualities of waters (e.g., infiltration, runoff, groundwater) expected to reenter the spoil zone.

4.

Continuously plan for monitoring during the premining, operational, and postmining periods.

This "before-during-after" approach is applicable to proposed mining operations. However, for many existing mines with little or no monitoring history, only the "after" approach is applicable. The methodology presented here is applicable to either of these general approaches, depending on whether the potential pollution sources under consideration are predicted for the future at a proposed mine or are actually present at an existing mine.

73

Even without drilling, sampling, and analysis, tentative prediction of types of pollutants and associated pollution problems may be possible if information is available on the stratigraphic sequence of rock types that will be encountered during mining. Sedimentary rock types that overlie or are interlayered with the coal seam and portions of the coal seam itself are likely to become part of the spoils. Therefore, knowledge of the overburden rock types and their stratigraphic distribution is a general indicator of the types and perhaps relative importance of certain potential contaminants that will exist in the future spoils. In general, each rock type has a characteristic positive or negative pollution potential. Each rock type has characteristic mineral or chemical constituents, permeability, solubility, and other properties that tend to contribute pollutants. Each rock type also has characteristic properties such as adsorption, ion exchange, and filtration that tend to remove pollutants from water solutions. Without drilling, determining or predicting the types and stratigraphic (vertical and horizontal) distribution of the rock and associated pollution potentials is often possible by local geologic reconnaissance in combination with a review of available geologic reports and maps. The sedimentary rock types that are commonly in sequence with coal seams are clay, silt, sandstone, and 1imestone. As examples, limestone (caco3) and dolomite (CaMg(CO3)2) may be highly soluble depending on pH and carbonate content (and saturation state) of the water. Where carbonate minerals are present in appreciable quantity relative to sulfide minerals (e.g., pyrite and marcasite), the sulfide minerals are less likely to go into solution.

Several special classes of earth materials associated with coal typically become part of the spoils. These include partings, coal, coal refuse, and coaly waste. Partings are the generally lenticular-shaped, stratified inclusions of noncoal material within coal seams. They are primarily shale and carbonaceous shale. Coal, coal refuse, and coaly waste are geologically and chemically similar. Coal refuse is the fine coal and waste material removed during the coal preparation process. Coaly waste includes the thin coal seams, impure coal, and carbonaceous shale that may occur in the overburden and in partings between coal seams. In some instances, these materials contain concentrations of toxic- or acid-forming constituents and, therefore, should be selectively emplaced in the spoils and perhaps specially protected to discourage mobility of potential pollutants. Protection against mobilization may consist of isolation from contact with water or air and possibly the use of clays with high ion-exchange or adsorption capacity to remove any mobilized pollutants from solution. In addition to being in or adjacent to the coal seams being mined, these coalrelated potential contaminants may also include associated thin coal or carbonaceous seams in the overburden. Such thin or impure zones are uneconomic or impracticable to mine. During mining, they may be backfilled with other over-burden material as part of the mixed spoil material. Test drilling, sampling, and analyses before mining will indicate which of these coal-related materials should be segregated and protected within the spoil zone. 74

In some instances where these coaly materials are stripped, they are stockpiled as byproducts of coal handling and processing. The stockpiles may be temporarily placed before disposal in the spoils of the active mine, or permanently located on the surface. These temporary or permanent stockpiles are another potential source of pollutants and are discussed at the beginning of Section 3 in the subsection titled Stockpiles. This discussion should be consulted for additional information on the pollution potential of partings, coal, coal refuse, and coaly waste. Coal wastes buried within the spoils can become sources of trace element pollution, depending upon the minerals contained in the coal. Potential pollutants may include soluble salts with sulfates of calcium, magnesium, and sodium predominating. Most spoils in the West also contain appreciable quantities of calcium carbonate. Normally, very few readily soluble chlorides, carbonates, or bicarbonates are present. Also, concentrations of phosphorous in forms available to plants are normally low in the spoils and overburden. Shales commonly contain appreciable exchangeable ammonium nitrogen when weathered. Nitrifying organisms are scarce at depths of about 8 to 10 meters because of lower soil temperatures. Consequently, nitrate forms of nitrogen predominate in the upper levels and ammonium-nitrogen predominates at the lower levels. Methods for Predicting Spoil Groundwater Quality-The literature reviewed concerning spoil-water quality prediction techniques involved site-specific studies at coal mines in Montana, Colorado, and North Dakota. The studies reviewed revealed two general trends in spoil-water quality predictive methods. One approach involves measuring water-soluble constituents in the spoils and relating these values to observed spoil-water quality at the respective mine. This method assumes that spoil-water quality is largely a function of the readily soluble constituents in the spoils that are easily leached by groundwater. Research efforts reviewed that followed this approach are Dollhopf et al. (1979, 19811, Van Voast, Hedges, and McDermott (19781, and McWhorter et al. (1979). Work done by each of these research teams is summarized in this section. This spoil-water quality prediction method is the procedure most frequently used in the western United States. The second approach to predicting spoil-water quality is based on an understanding of the chemical processes responsible for the evolution of spoilwater quality, which is the basis for calculating the ultimate water quality. The researchers involved in developing this predictive method are convinced that the saturation extract method estimates only the short-term spoil-water quality. Their calculations include the long-term salt generation capacity of spoil waters (Fred C. Hart Associates, 1981). The work on this prediction method is primarily being conducted within the Fort Union Region of Western North Dakota by numerous researchers. Their research work is also summarized in this section. Van Voast et al. (1978) evaluated data obtained from column leach tests and saturation paste extracts of spoil materials to determine if a method could be established for predicting spoil-water quality. The constituents that were observed in the data collection phase were specific conductance, 75

sulfate, magnesium, sodium, and calcium. Comparison of column leach test data with saturated paste extract data indicated that concentrations of major ions in saturated paste extracts were very similar to the values obtained for the first pore volume of extract obtained from column leach tests. The cost of column leach tests is much greater than obtaining saturated paste extracts. Therefore, with the similar concentrations and disparity in cost , Van Voast et al. recommend using saturated paste extracts for continued work on the prediction of spoil water quality. Also, analysis of saturated paste extracts is a commonly required overburden analytical technique in the western United States with data already available at various mine sites. Van Voast et al. (1978) utilized saturated paste extract analyses and spoil-water analyses from Big Sky and Decker mines for the continued search for a spoil-water quality predictive tool. Van Voast et al. note that, "The overburden values were equally or more diverse than those of the spoil waters but were generally of similar chemical type." With the large range in the data, statistical methods were used to determine if a relationship could be developed between the overburden saturated paste data and the observed spoilwater quality for each mine site. The mean cation concentrations observed in spoil wells and from saturated paste extracts from overburden samples at Big Sky and Decker mines have been graphically summarized. Van Voast et al. (1978) state: Because of the diversities of spoils-water and extract qualities. statistical methods were employed toward comparisons that might lead to use of extract chemistry for predictions of spoils-water quality. Nomographs comparing idealized statistical distributions of calcium, magnesium, and sodium in overburden extracts and in spoils waters at the Big Sky and Decker Mines were generated during the study. From these, probable ranges of log-normal mean concentrations of calcium, magnesium, and sodium may be predicted for spoils waters at proposed mines where saturated-paste-extract analyses have been conducted on overburden. A similar attempt toward predicting specific conductance through statistical correlations did not appear successful. The nomographs provide a very general means at cation predictions. Additional data such as sulfate analyses of paste ex-tracts, more spoils-water quality analyses from the Big Sky and Decker Mines, and similar data from other mines may allow refinement of the nomographs toward greater precision. In later attempts to predict s p o i l water quality, Van Voast and Thompson (1982) have utilized saturated paste extract concentrations (major constituents) as direct additions to concentrations in nearby groundwaters, assuming that salinities of reentering groundwaters would also contribute to spoil water quality. In current research, Van Voast and Thompson (personal communication, 1982) are comparing saturated paste analyses using distilled water with paste analyses using water from coal field aquifers.

76

Dollhopf et al. (1979, 1981) conducted research at Rosebud mine in Montana in an attempt to develop a predictive technique for trace metal concentrations in spoil groundwaters. Overburden geochemical data from extracts using DTPA acid and column leach methods were evaluated during the study. All DTPA extract trace metal concentrations were greater (sometimes 1,000 times greater) than values produced from column leach extracts. This was expected because the DTPA extraction technique is more rigorous than water leach extraction and the DTPA method is intended to evaluate the concentrations of elements available to plants (the western states generally require overburden trace metal analyses on extracts using the DTPA methodology). When the overburden trace metal analytical data from both extraction techniques were compared with spoil-water quality observations in the area, the column leach data were found to be most similar to the values observed in the spoil groundwaters. Table 10 compares trace metal concentrations from column leach and spoil water at Rosebud mine. Dollhopf et al. (1981) summarize the study effort to develop a technique for predicting trace metal concentrations in spoil waters as follows: Examination of the water column extracted chemistry and corresponding water well chemistry indicate that leachates from columns may provide predictions of postmine water quality. It should be clearly noted that the statistical means and ranges for these comparisons between column leachates and waters from wells often differed by as much as a factor of ten [Table 1 0 1 . Part of this difference can be attributed to sampling and lab error. Certainly, the leaching column technique is not a perfect simulation of the in situ groundwater system, so the technique itself introduces error. However, trace element concentrations in column leachates were comparable to concentrations in waters from wells to a degree which indicates the potential exists to judge which overburden materials would be most suitable for aquifer reestablishment. However, comparisons of water leachate metal concentrations and in situ groundwater quality would have to be correlated at many mines with contrasting chemical conditions to verify the usefulness of this method. Column leaching techniques are slow, expensive, and may not be practical for premine studies. An investigation should be initiated to determine whether a water saturated paste extract, which is performed on a routine basis, could provide similar trace metal levels as those attained from column leachates. McWhorter et al. (1979) examined the relationships of the chemical composition of spoils to the observed quality of spoil waters at Edna mine in Colorado. In their study, McWhorter et al. used saturated paste and one-to-one dilution extracts to characterize the soluble constituents in spoils available for leaching by groundwaters. Table 11 shows the results of determinations of specific electrical conductance (EC) on saturation extracts prepared from drill cuttings and spoil 77

TABLE 10.

COMPARISON OF TRACE ELEMENT CONCENTRATION (pprn) IN LABORATORY COLUMN LEACHATES AND IN WATERS FROM WELLS IN OVERBURDEN AND SPOILS AT THE WESTERN ENERGY ROSEBUD MINE NEAR COLSTRIP, MONTANA (after Dollhopf et dl., 1981)

Range

Recommended Maximum Permissible Concentration in Public Water Supplies

(0.272-0.710)

0.05

(<0.005-0.020)

0.01

Observation Well Data Soil Water Column Leachate Concentration (n = 25)a Trace metal

Mean f S 0.10

Mn

f 0.22

Overburden (n

Range (<0.01-1.09)

Mean f 0.077

S

Range

f 0.074

(0.055-0.252)

Cd

C

(<0.001-0.043)

C

CU

0.021 f 0.022

(<0.01-0.04)

0.023 f 0.010

(0.005-0.038)

Pb

C

(<0.001-0.003)

C

(<0.01-0.025)

Zn Ni

0.009

f 0.005

0.040 f 0.047

spoils (n = 10)

= 16)

Mean f S 0.424

(<0.005-0.014)

(0.002-0.026)

0.093

+_

0.112

(<0.005-0.377)

(<0.01-0.23)

0.013

f 0.006

(<0.01-0.018)

2 0.129 C

0.033

0.220

f 0.019

(0.012-0.075)

1.0

C

(<0.01-0.01)

0.05

f 0.241

(0.022-0.712)

5.0

C

(<0.01-0.01)

__

Notes: n'

=

number of samples.

bU.S. Department of Health, Education, and Welfare ( 1 9 6 2 ) .

'many values were reported as less than sensitivity.

(<)

the indicated range, indicating a concentration less than technique

samples compared to drainage from spoils issuing from drains and at monitoring point C5. The values indicate a strong similarity between the average EC values measured on the saturated paste extracts and the values observed for spoil waters. The standard deviations for each set of analyses indicate quite a range of observations. This suggests that the use of EC values from spoils or cuttings would only be valid as an indicator of average spoil-water quality and that multiple EC measurements of the spoils or overburden are also necessary. Table 11.

COMPARISON OF ELECTRICAL CONDUCTIVITY OF SPOIL, OVERBURDEN, AND SUBSURFACE WATER (after McWhorter et al., 1979)

0

Average EC (pmho/cm at 25 C)

Spoil

Drill Cuttings

Drains

c5 Monitoring Point

3,100

3,000

3,400

3,400

Number of Samples

14

Standard Deviation

930

5a 430

58

720

31b 430

Notes: a Samples were prepared by compositing, by depth interval, samples from four locations along an active highwall. bRegular monthly samples from October 1973 to June 1976 from C5 monitoring point. McWhorter et al. (1979) evaluated the accuracy of measuring EC on 1:l extracts for predicting the specific electrical conductance of spoil waters. They found.measurementsof EC on 1:l dilution extracts much less reliable than saturated paste extracts. McWhorter et al. (1979) also evaluated the relationship of measurements of the dominant constituents (sodium, calcium, magnesium, potassium, HCO3, chlorine, and SO4) on 1:l dilution and saturated paste extracts with values observed for spoil waters. Table 12 compares the analytical data obtained from the two spoil extract methods and actual spoil-water quality values. The data indicate an excellent relationship between the relative composition of the major constituents and the conclusion may be drawn that, for Edna mine, either extraction method (1:l or saturated paste) would provide an acceptable prediction of spoil-water quality. The hydrogeologic circumstances at Edna mine are such that all recharge to the spoils is from vertical deep percolation, with no horizontal component of groundwater flow into the spoils. ses

In summary, the spoil-water quality prediction technique involving analyof specific electrical conductance (EC) and the major ions on saturated

paste extracts appears to be the easiest and quickest way to estimate average 79

spoil-water quality. Although this method has been successful at several mine sites, there have also been problems. Researchers should use large sample sizes and acknowledge that, at best, these data will only give an average estimate of spoil-water quality. Whenever possible, the results of saturated paste analyses should be compared to spoil-water quality values from similar geohydrologic environments in the area to assure that a valid relationship exists between analyses of saturated paste extracts and spoil waters. TABLE 12. COMPARISON OF COMMON ION CONTENTS IN EXTRACTS AND MINE DRAINAGE (after McWhorter et al., 1979) Percent of Total ca

Mg

Na

K

HCO3

C1

SO4

3.3

18.8

2.4

15.4

1.3

55.2

1:l Extract - Spoil

14.3

8.3

3.5 2.3

--

5.3

0.4

69.4

Subsurface Drains

12.6

8.9

3.1

0.8

10.0

0.1

64.4

C5 Monitoring Point

12.1

8.5

3.8

0.6

6.7

0.2

68.2

Saturation Extract - Spoil

The following discussion of groundwater quality projection techniques is taken from a report to the Office of Surface Mining, Region V (Fred C. Hart Associates, 1981). Research in and around the Fort Union Coal Region of Western North Dakota relating to the impacts of surface coal mining on the land and water resources of the area has been extensively studied by Moran and Cherry (1977); Moran, Groenewold, and Cherry (1978a); Moran et al. (1978b, 1979); Groenewold (1979); Groenewold et al. (1980); Palmer and Cherry (1979); and M.G. Croft and his coworkers (personal communication, 1981). Croft's research for the USGS involved Gascoyne mine near Bismarck, North Dakota, while the remaining researchers investigated five other sites in North Dakota. The overall objective of the work performed by Moran, Groenewold, Palmer, and coworkers is to aid in the reclamation of surface-mined lands by developing a basis for predicting their soil and groundwater chemistry. The term "engineered cast overburden" (ECO) has been coined to refer to an approach to reclamation of surface-mined lands and is defined as reconstruction of the entire landscape rather than just its surface form and soil (Moran, Groenewold, and Cherry, 1978a). This approach to assessment of postmining groundwater chemistry requires a thorough understanding of several geochemical and mining processes as well as the development of a number of analytical techniques. Materials comprising the overburden had to be identified and evaluated. The inventory involved soil mapping, geologic mapping, development of a threedimensional materials framework, geohydrological studies, and geochemical studies to delineate the properties of the materials. Understanding the form 80

and internal structure of material deposited by various types of mining equipment and techniques was necessary to determine which equipment and procedures could be used to obtain desired physical and chemical characteristics at desired locations within the cast overburden. In the study by Moran, Groenewold, and Cherry (1978a1, the chemistry of overburden core and cutting samples was analyzed at five mine sites. The constituents evaluated included texture, oxidation state, pH, electrical conductivity (EC), and carbonate content. Over 500 saturation extracts were analyzed. Additionally, the quality of the groundwater was evaluated. Water quality parameters that were analyzed included pH, EC, TDS, alkalinity, hardness, and the eight major cations and anions. Relationships between overburden type and water quality were evaluated. Four significant chemical property trends of overburden materials were identified from the analyses: (1) materials having a higher clay content have a greater tendency to be sodic; ( 2 ) the proximity of the materials to the land surface, regardless of texture, has a strong influence on their chemical characteristics; ( 3 ) the direction of groundwater movement in the near-surface zone in large part controls the chemical characteristics of the materials; and (4) it is very likely that geochemical variations in the materials of the original environment of deposition and interaction with groundwater flow have a strong influence on the chemical characteristics of the overburden materials (Moran, Groenewold, and Cherry, 1978a). To determine the postmining quality of groundwater, the authors based their analysis on the assumption that "an interpretive framework that adequately accounts for the observed water chemistry in the natural overburden will have some applicability in the analysis of salt generation and accumulation in reclaimed land" (Moran, Groenewold, and Cherry, 1978a). To be valid, this framework must account for several variables, including the existence and variation of the predominant ions in the subsurface water, the pH of the water, variation in the concentration of total dissolved solids of the groundwater, and the partial pressure of dissolved carbon dioxide in the water (Moran, Groenewold, and Cherry, 1978a). It must also account for changes in water chemistry that occur as the water infiltrates and migrates through the underlying vadose zone into the groundwater zone.

Several important reactions that can determine the postmining groundwater quality were found (Moran, Groenewold, and Cherry, 1978a): 1.

Production of carbon dioxide in the soil zone by oxidation of organic matter

2. Oxidation of pyrite 3.

Dissolution of carbonate minerals

4.

Precipitation of gypsum

81

5.

Dissolution of gypsum

6.

Cation exchange

7. Sulfate reduction. The most common groundwater composition in tertiary deposits in Western North Dakota (water with dominant concentrations of Na+, HCOS, and S 0 i 2 ions) is generated by various sequences of the seven geochemical processes indicated above. Additionally, in cast overburden, the release, transport, and accumulation of Na+ depends on the occurrence of calcite and gypsum in the overburden and the cation exchange capacity of the overburden. The occurrence of gypsum depends primarily on the occurrence of pyrite and the rate and frequency at which water containing dissolved oxygen contacts pyrite and then evaporates or transpires. All of the important geochemical processes that determine the chemistry of groundwater in the study areas are primarily operative above the groundwater; the chemistry of the groundwater, regardless of the age and distance that the water has traveled, is determined by the geochemical processes that occur during recharge (Moran, Groenewold, and Cherry, 1978a). During exceptional recharge events, gypsum and other soluble salts are transported to the water table, resulting in high concentrations of sulfates. The existence of gypsum is the result of the concentration of calcium sulfate due to evapotranspiration of groundwater in the unsaturated zone. The existence of the calcium and sulfate can be primarily attributed to the oxidation of pyrite and the dissolution of calcite (Groenewold et al., 1980). The important result from studies by the authors was the following conclusion: " ... an understanding of the runoff-infiltration relationships within the landscape combined with a knowledge of the distribution of nearsurface permeability and mineralogical constituents such as pyrite, calcite, gypsum, clay minerals with Na+ adsorbed on the exchange sites provides an adequate basis to evaluate EC and SAR of the cast overburden. In order to predict how the materials will behave in a reconstructed landscape, it is necessary to know where in the landscape each type of material will be placed and what the configuration of the landscape will be. In this way, the subsurface hydrologic regime can be projected and the resulting liberation of available ionic constituents by weathering and transport or nontransport of these constituents can be estimated" (Moran, Groenewold, and Cherry, 1978a). The major limitation to understanding the postmining groundwater quality in this type of analysis is accurate determination of the amount of carbonate, pyrite, and gypsum in the overburden. Although existing analytical techniques may show an absence of carbonate, pyrite, or gypsum, this cannot be taken as positive evidence of the absence of these minerals. Thus, long-term postmininq groundwater quality prediction is extremely speculative, at best, with respect to these minerals and their relationship to total dissolved solids concentrations. Several areas of additional research must be explored before the EC geochemical model can be confidently used as a predictive practical tool in designing reclamation programs to protect groundwater quality from surface mining impacts. One is the development of analytical techniques to 82

evaluate the amount of potentially soluble calcite and gypsum and potentially oxidizable sulfide (pyrite) present. In addition, a methodology needs to be developed to adequately evaluate cation exchange capacity and to determine which cations are available for exchange. The model itself needs to be further tested, modified, and sharpened as a predictive tool (Moran, Groenewold, and Cherry, 1978a). Also, the composition of the gas phase in the spoils must be determined to evaluate the extent of pyrite oxidation (Palmer and Cherry, 1979). Currently, a computer model is being developed by Groenewold et al. (1980) to predict the postmining water quality. This model uses an iterative technique to determine the equilibrium distribution of the aqueous and solid phases. The reactions described above are used in the model (Groenewold et al., 1980). Research that has been conducted by Croft and coworkers is similar to that of Moran and coworkers. Croft has been working at Gascoyne mine in North Dakota. The existing groundwater hydrology at Gascoyne mine is very complex, as it is at the other North Dakota mines that were studied. Croft and coworkers are also attempting to quantify the existing, undisturbed geohydrologic system at the mine to determine what reactions are occurring between the groundwater and the various constituents of the strata. This allows them to understand the reactions that are occurring naturally and extrapolate these mechanisms to reactions in overburden material. Groundwater quality in the undisturbed recharge area at Gascoyne is extremely variable. The water has a very low sulfate and total dissolved solids content. As the water migrates southeast toward the mine, both of these constituents increase dramatically until the sulfate content reaches a few thousand parts per million upgradient of the mine. In one area where the lignite outcrops and a marshy area has formed, a sulfate content of up to 16,000 parts per million has been found. This is beyond any influence of the mining operation. The high sulfate concentration has been hypothesized to be from the dissolution of gypsum (D. Fisher, USGS, personal communication, 1981) or the oxidation .of pyrite in the lignite along with cation exchange (R. Houghton, USGS, personal communication, 1981). In general, the evolution of the groundwater is thought to be a result of the same processes identified by Moran, Groenewold, and Cherry (1978a). In addition, two other reactions have been found to have significant effect in the Gascoyne area. These are the high cation exchange capacity of the Gascoyne lignite, which is one to two orders of magnitude greater than the exchange capacity of the clays, and carbon dioxide production from the lignite (D. Fisher and R. Houghton, USGS, personal communication, 1981). The high CEC has the same effect as before, removal of calcium from the system so that the saturation limit of gypsum is not reached. The carbon dioxide production limits pyrite oxidation because oxygen is displaced from the system. At one testing site, the gas phase consisted of 18 percent carbon dioxide and almost 80 percent nitrogen. In this situation, pyrite oxidation is negligible. Houghton (USGS, personal communication, 1981) has hypothesized that the carbon dioxide is produced from the lignite and from organic material in the strata below. As the water in the lignite (which is high in carbon dioxide) moves laterally into the spoil material, carbon dioxide is released and moves up through the spoil material, displacing oxygen 83

entrapped during mining. Again, pyrite oxidation is reduced. Only the pyrite in the lignite seams, or highly carbonaceous shales that underlie the lignite, appears to be susceptible to extensive oxidation. Pyrite in the overburden, which has been found near the surface subsequent to disturbance, has shown no signs of oxidation over a period of up to a year (R. Houghton, USGS, personal communication, 1981). To attempt to project the postmining water quality at Gascoyne mine, the foregoing reactions and considerations are being incorporated into a computer model. This model will attempt to predict what the quality of the postmining groundwater will be, based upon equilibrium of these reactions in the system (R. Houghton, USGS, personal communication, 1981). Nothing has yet been published on the postmining groundwater quality at Gascoyne because the exact nature of the geohydrochemical system remains uncertain.

In summary, the ongoing research in North Dakota has centered on a more indepth understanding of the geochemical reactions that could occur in the overburden. These reactions and interreactions that occur during the evolution of the postmining groundwater quality are extremely complex. The system is dynamic and no single equation can define it. Changes in sulfate levels will occur in the groundwater in response to recharge from major precipitation events. If piping in the overburden occurs as the overburden settles, increased oxygen levels in the spoils may result in increased oxidation of pyrite. This process has been found to occur up to 5 years after mining was completed (Palmer and Cherry, 1979). No analytical technique has been developed to assess the long-term impacts to the groundwater system by mining. However, the ongoing research in North Dakota should yield extensive insight into quantifying these impacts. The geohydrological setting is complex and no simple answer will suffice to quantitatively assess postmining impact. Monitoring Needs-Knowledge of the general chemical characteristics of the regraded soil is needed. Information is especially needed on the type, concentration, and distribution of elements and compounds that can become sources of groundwater pollution, particularly for those zones of regraded spoils in contact with free underground water, whose leachate possibly could contribute pollutants to the groundwater system. Alternative Monitoring Approaches-The preferred, or recommended, monitoring approach is to be selected from nonsampling and sampling alternatives. Nonsamplinq methods--Records of the location and amount of spoils that are emplaced during the monitoring program are desirable. Special attention should be given in these records to disposition of materials that have significant pollution potential and to any protective measures taken to isolate certain potentially toxic or acid-forming materials from water, air, and other conditions or processes that may tend to introduce contaminants to the hydrologic system.

84

Maps can be compiled on a monthly basis indicating both the location and elevations of spoil material in the reclaimed area. Gross volumes or weights of material can be estimated. A photographic record of the face of the spoils in the pit can be maintained. Such a record can substantiate, for example, that more consolidated formations with few contaminants are selectively placed in the bottom of the spoils. Samplinq methods--It would be highly advantageous to identify and locate poten;ial pollutants and their in-place stratigraphic position during the premining exploration phase and then, based on this information, formulate and execute a systematic reclamation plan including special emplacement or protective isolation in the spoil zone of materials with high potential for contamination. This effort can minimize later pollution. A l s o , the resulting records on material types and their systematic placement in the spoil zone probably will be less complex and more informative than information obtained solely by postmining probing in the heterogeneous spoil mass. The composition of materials contained in the spoils should be determined. Random composite samples can be taken at points on a grid covering the entire spoil area. The spacing of the points on a second sampling pass should be determined by the variability and toxicity of material encountered during initial sampling. Such a system has an advantage of simplicity but would be time consuming and costly. Alternatively, a priority sampling scheme can be employed. The objective would not be to characterize the entire area of spoils by one or more elements or compounds, but rather to delineate selected zones containing pollutants that due to their location or toxicity have a relatively high potential for introducing new pollutants or increasing existing concentrations of pollutants in the groundwater system. These selected areas can first be delineated on the basis of their relation to existing or predicted water table elevations within the spoil materials. Potential contaminants that are readily water-soluble are more likely to be released from the spoils if they are in the saturated zone. In contrast, those potential pollutants that are mobilized by oxidation processes are more likely to be released in the vadose zone above the water table. The potentially saturated and unsaturated zones that are delineated can be sampled in two stages. Initially, grid points spaced about 300 feet apart can be sampled. Samples should be taken at each point throughout the entire depth of spoils at no less than 5-foot vertical intervals (M. Hulbert, personal communication, 1980). Sampling can be at closer intervals if particularly toxic materials are encountered. The subject of spoils sampling in areas of potentially toxic material placement has not been addressed by State regulations. The sampling frequency of solids in spoils is difficult to specify. In part, it depends on the variability of materials encountered in the pit, including overburden, partings, and coaly waste. Part of this variation will be known at the time of mining due to the quality of coal desired and for purposes of reclamation. The frequency of sampling can be related to this variability. During the first year, monthly grab samples should be collected.

85

After the first year, the frequency can be adjusted based on past experience and the dynamic chemical characteristics of regraded spoils. Spoil samples should be analyzed for pH, electrical conductivity, total soluble salts, soluble cations, base saturation, sulfate, nitrate, total nitrogen, and total organic carbon. Tests should be run on saturation extracts for powdered samples. In addition, boron and fluoride levels should be determined. The content and character of pyrite or other forms of iron sulfide largely control the potential acidity of water contracting spoils and should be evaluated. The soluble calcium content of the spoils also exerts a controlling influence on the pH. Drever, Murphy, and Surdam (1977) discuss trace elements associated with the Wyodak coal seam at Black Thunder mine. Vanadium, manganese, nickel, copper, zinc, arsenic, selenium, lead, barium, cadmium, chromium, iron, molybdenum, and silver should receive groundwater quality monitoring priority due to their importance for water use and their probable relative mobility in soilaquifer systems. Organic chemical content of certain materials in the spoils can be substantial. This is particularly true for coaly waste and shales. A gross indication of the composition can be obtained by determining the total carbon and total nitrogen content. If specific organic chemical constituents are found in spoil groundwater, then solid spoil materials can be sampled for specific constituents later. The radiological content of spoils should be grossly evaluated periodically by determining the uraniurn and thorium contents. samples can also be analyzed for alpha, beta, and radium-226 activity. Changes in water quality may be the first detectable indication of release of contaminants from the spoil materials and of the particular contaminant species being released. Thus, it may be desirable to sample and analyze water from zones within the spoils and immediately downgradient along spoil flow paths. Costs for Step 3 include labor for gathering existing information, mapping spoils, and sampling; operational costs for mapping and sampling supplies and spoil analyses; and capital costs for soil samples. Recommendations-For proposed mining sites, information should be obtained on the distribution of in-place geologic strata that will be disturbed and replaced during mining and reclamation. During conventional exploratory drilling, the respective strata and their lateral and vertical distribution, including overburden, coal, and adjacent underburden zones, should be sampled, tested, observed, and chemically analyzed to obtain a three-dimensional appreciation of potential pollutant types. As many of the samples as possible should be obtained by coring. Appropriate plans for systematic removal and emplacement in the spoil zone should be incorporated in the mining plan. In particular, selective

86

protective emplacement in the spoil zone should be planned for any previously identified constituents that may be highly contaminating. For monitoring programs that start after the premining exploratory period, exploration information should be reviewed and interpreted in terms of potential pollution type and location of materials that have been emplaced in the spoil zone. Existing information on the location and nature of backfilled spoil material should be obtained and arrangements should be made with the mining company to receive ongoing information of this type. If such data are not being gathered, backfilled areas should be mapped and photographed, including items such as spoil location, elevation, and composition. These maps should be updated frequently, possibly monthly. The composition of spoil materials should be determined using a priority sampling scheme with sampling frequency depending on the variability of spoil material and the rate at which an area is backfilled. Samples should be analyzed for the constituents discussed earlier. Step 5 . Evaluate Infiltration Potential Monitoring Needs-Infiltration is the combined process of the entrance of water at the soil surface and its subsequent downward movement through near-surface soil media. Water that infiltrates the land surface and passes the near-surface zone, where it may be subject to return to the surface by capillary action, evapora-tion, root capture, or other processes, will subsequently percolate generally downward toward the groundwater zone. The infiltrating water may carry contaminants from surface sources and as it percolates through the vadose zone, it is subject to various processes that either increase or decrease its contaminant load. Infiltration is affected both by the condition of the surface and the nature of the soil material. A large portion of the spoils at the mine sites in the study area is fine-textured (excluding large rock fragments) material derived from shale and siltstone with a high clay fraction (often above 20 percent). Furthermore, the characteristically rapid decomposition of shale when exposed to weathering releases salts that tend to inhibit flocculation and the formation of soil structure. If the materials have an exchangeable sodium percentage greater than 15 (i.e., sodic), as they often do, they may form a soil surface essentially impermeable to water. Infiltration rates on spoil materials may vary from as high as 20 inches per hour (alluvial material) to 0.2 inch per hour (shale material). An average infiltration of about 0.5 inch per hour is common in spoils with high shale and clay components (M. Bishop, personal communication, 1981). Reclamation regrading and surface treatments (pits, furrows, berms, etc.) create depressions for surface water retention, resulting in a trapped supply of water at the soil surface that might sustain infiltration for long periods. 87

Retention basins, however, often become sealed by fine material washed in by surface runoff. Their effective life may be only a few years under the best conditions. In areas where underground fires have occurred, infiltration may be greatly influenced by cracking and caving at the surface that allow the entry of free water. If the mining operation is efficient, these areas are small and short-lived and occur infrequently. Stream channels reconstructed across spoil material are an important source of possible groundwater pollution from infiltrating waters. Creeks that are ephemeral in their natural state will probably also become reestablished as such and will have a high potential for contributing significant amounts of surface water to the groundwater system. Infiltration capacity is important in characterizing the hydrologic behavior of spoils. Information on infiltration is needed to supplement other data such as precipitation, snowmelt, evaporation potential, and geochemistry necessary to classify the potential of spoil materials to pollute the groundwater system. Alternative Monitoring Approaches-Nonsamplinq methods--Infiltration capacity should be estimated with double-ring infiltrometers or sprinkler-type infiltrometers. Field infiltrometer tests are useful for comparing differences of magnitude between sites and for irrigation purposes, where the supply of water at the soil surface is steady, but they cannot be relied upon for quantitative representation of actual infiltration of natural precipitation. Sprinkler-type infiltrometers are generally preferred over the ring type for field tests. They more closely approximate natural rainfall, provide a measure of surface runoff potential, and with some devices give estimates of erosion potential. They are also difficult to operate, however, require considerable auxiliary equipment, and are expensive. The ring devices are very simple and are a quick means of obtaining relative values of infiltration capacity for different sites. Measurement sites can be chosen randomly or selected on the basis of previous information. Ideally, sampling should be completely random or systematic with random starts, but this requires inordinate effort to characterize a large area. Interpretation is complex because of point-to-point variability. Stratification would help reduce variability if an average were sought for an entire area. Representative sites for infiltration studies can be based on chemical and physical characteristics. For example, a representative balance might be used in distributing sites between sodic areas and saline areas, which are more permeable. Sufficient testinq should be done to achieve a reasonable degree of precision: 10 percent of the mean final infiltration rate (fc) at the 95-percent confidence level is desirable. For most spoil materials, the final rate is obtained within 2 hours (U.S. Bureau of Reclamation, 1977). 88

Infiltrometer data can be used with precipitation measurements and historic records of precipitation to estimate the maximum probable infiltration under the prevailing climatic conditions at a mine site. Samplinq methods--Infiltration capacity can be estimated by laboratory tests of spoil permeability. These tests, however, are of doubtful value because of the disturbed nature of the samples, their small size, and the associated difficulty of obtaining representative samples. Recommendations-Infiltration capacity should be determined using a double--ringinfiltrometer because of economics and ease of obtaining data quickly from a large number of sites. Sites should be selected on the basis of information gathered in Step 3 , Identify Potential Pollutants. Precipitation data can be obtained from existing records for the area. Costs for Step 5 include labor for infiltration measurements and data collection and capital costs for ring infiltrometers.

Infiltration is the net downward movement from the surface. Water that returns to the surface rather than percolating through the topsoil and spoils is not included in this definition. Continuous application of water to the spoils surface, such as from a pond or stream, may establish saturated flow, which is a measure of the rate that water will percolate downward through the spoils to the water table or to a saturated zone that drains the spoils mass. Assuming that the storage capacity of the spoils has been met, in unsaturated conditions the water moves under the force of gravity. Typically, however, in the water-deficient areas of the West, water is not continuously applied to spoils. Thus, during dry periods, water that has not penetrated beyond shallow, near-surface zones may return to the surface or to the atmosphere due to upward capillary movement, evaporation, plant consumption, or other processes. Much research has been done on agricultural soil infiltration, but relatively little on spoils infiltration. The following review of research on soil-water relations in spoils, quoted from Schafer et al. (1979), describes infiltration, runoff, erosion, and other interrelated variables that may be useful in monitoring contamination from spoil resources: Low infiltration rates on mine spoils cause increased runoff which can reduce plant available water, remove applied topsoil, and create sedimentation problems. Erosion and reduced infiltration are therefore major problems in arid mine land reclamation. Gilley and others (1976b, 1977a) measured runoff and erosion on native range, and topsoiled, and nontopsoiled spoils in North Dakota using a large rainfall simulator. Two storms of 1-hour duration and 2.5-inch/hour intensity were simulated. Soil loss on native range was 200 kg/ha; only 12% of the applied water ran off the plots. Water from both events moved deeply into the profile (>18 inches). 89

Soil loss on raw spoils was 15,000 kg/ha and 21,000 kg/ha on cultivated and uncultivated erosion plots. Runoff consisted of 66 to 74% of the applied water. Water did not penetrate significantly into uncultivated spoils and increased only in the upper 6 inches of cultivated plots. Cultivation of the topsoil/spoil interface did not increase percolation into the spoils. As slope was decreased from 17 to 6%, soil loss was reduced by about 30%. Differences in spoil texture had little influence on soil loss. Gilley and others (1976a) found that topsoiled spoils had higher infiltration than raw spoils. However, water did not penetrate the topsoiUspoi1 interface. Cultivation of the interface to increase contact did not influence percolation into the spoils. Restricted percolation of water below the topsoil zone was also observed by Dollhopf and others (1977). It was suggested that physical and chemical treatments to decrease compaction and minimize clay dispersion would be necessary to increase deep percolation. Henning and Affleck (1977) in Iowa found that deep tillage of compacted spoil sublayers increased infiltration, deep water movement, and initial corn growth. Erosion was greatest on topsoiled spoils at 74,000 kg/ha. As topsoil thickness of the treatments was increased from 25 to 61 cm, runoff decreased but erosion increased. Water content of the topsoil zone increased after the rainfall events, but no water entered the underlying spoils. Application of straw mulch decreased erosion on topsoiled and nontopsoiled plots by 93 and 84%, respectively. Erosion was less on spoils without topsoil because a surface crust formed on the clayey sodic materials which slowed erosion. Topsoil materials on spoils were more erodible than similar undisturbed soil in part due to a loss of soil structure during the handling process (Gee and others, 1976). Water content of topsoil increased rapidly during the rainfall events. Miyamoto and others (1977, 1978) reported that some spoils in New Mexico were nonwettable and, as a result, had slow infiltration rates. High-grade coal was identified as the source of the hydrophobic substance. Addition of ethyl alcohol significantly increased infiltration into coaly spoil by decreasing the contact angle, thus increasing capillary adsorption. Infiltration into sodic, noncoaly spoils was not affected by addition of ethyl alcohol, but was increased by adding CaC12 to the irrigation water. Arnold and Dollhopf (1977) found that minesoils in Southeastern Montana had slower 30-minute infiltration rates than undisturbed soils. The presence of vegetation or application of topsoil signficantly increased infiltration into spoils, however. Dollhopf and others (1977) found a similar result on 90

spoils at Colstrip and Savage, Montana; and Beulah, North Dakota. Infiltration on selected surface soil treatments decreased in the order topsoil/chiseled > nontopsoil/chiseled > topsoil/dozer basin. The dozer basin treatment removed topsoil from the basin area, and in addition compacted the underlying spoil. Therefore, infiltration was highly influenced by the surface material and decreased from topsoil to spoil to corn-pacted spoil. Wyatt (1978), working with data from this study, found that infiltration rates on native range, oil spoils, and new spoils were not significantly different. Spoils and soils were predominantly sandy loam in texture and were nonsodic. Application of topsoil derives its maximum benefit when the spoils are clayey, sodic, or high in coal content. Although topsoil often increases infiltration, and can store more water than spoils, it is very erodible with a small amount of runoff and therefore must be protected during the early stages of reclamation. Arnold and Dollhopf (1977) found that the hydraulic conductivity (K) of native range soils (4.9 cm/day) was greater than all spoils studied (1.3 cmlday). Topsoiled spoils had higher K values in the topsoil zone than in the underlying soil. Drainage below the root zone of fallow native range and spoils was calculated. Assuming the soil was recharged to field capacity in the spring, 2.5 to 4.0 cm would drain in one year from spoils and native range, respectively. Schafer et al. (1979) found in their studies in the Colstrip, Montana area that infiltration into minesoils was not slower than into natural soils as had been shown by other studies in the region (Gilley et al., 1977b; Dollhopf et al., 1977; Arnold and Dollhopf 1977; Miyamoto, 1978). Differences in infiltration rates between different sites are highly correlated with surface sand and silt content. Moderately rapid infiltration rates can apparently be attained quickly in minesoils by using nonsodic, coarse-textured surface material. Impermeable subsoil layers would be expected to eventually decrease infiltration rates (Gilley et al., 1977b). Step 6. Evaluate Pollutant Mobility in the Vadose Zone Monitoring Needs-After infiltration through the near-surface zone of soils and shallow spoils to a depth below which they are not returned to the surface, pollutants, in water solution, are subject to continued downward percolation through the spoil vadose zone toward the water table. Mobility in this zone involves rates and routing of pollutant movement and changes in heads and concentration. Mobility of waterborne pollutants through the vadose zone is relatively complex because of both unsaturated and saturated flow and storage conditions and numerous conditions that may alter the chemical characteristics of the pollutant load being carried in solution. Conditions that influence direction and rates of flow, storage, and chemical characteristics in the 91

vadose zones of spoils are likely to be more complex than average because of the heterogeneity of spoils. Monitoring of the mobility of pollutants in the vadose zone of mine spoils may be correspondingly difficult. Whether or not waterborne pollutants remain in solution, or either temporarily or permanently drop out of solution at some location along the path of flow, is a function of various chemical-physical interactions of the pollutants and their changing environment along the flowpaths. Thus, in attempting to evaluate the mobility of pollutants, both the mobility of the water component of the solution that is the transporting agent and the mobility of the pollutant components must be considered. Although a major concern of a monitoring program may be the movement of water in the vadose zone, accounting for the stoppage or lack of movement that relates to storage capabilities of the zone, which may be large, is also important. Spoils consist of solid material and the intervening pore space that may retain water in storage. Porosity is a measure of the volume of water that can be stored under saturated conditions. specific retention is the water volume content of a particular geologic material after drainage has occurred for a specified time. (Field capacity is the essentially analogous term, expressed on a weight basis, for soil.) Specific yield, or effective porosity, of geologic material is the difference between porosity and specific retention. Low infiltration rates and the presence of restrictive soil or deeper strata have caused water deficiencies in subsurface zones in many areas of the West. Spoils that are dry or that develop water deficiencies have a potential for storage of additional water. The greater the thickness of a deficient zone, the greater the storage potential. Figure 8 shows the relationship between specific retention, porosity, specific yield, and grain size of different geologic materials. Specific retention and porosity, both measures of storage capacity, are greater for finer-grained materials. In monitoring the quantity and quality of water moving through the vadose zone of spoil to groundwater, particular attention needs to be given to sites with high infiltration capacities and/or high permeability situated in a low topographic position, extended periods of water availability at the surface, shallow depth of spoil water above the water table, and concentrations of potential pollutants within the spoils. Pollutant constituents of the water solution move with the water but may be removed from solution by contact with certain types of rock surfaces, by intermixing with other waters, or by filtration through certain earth materi-als. Such reductions in dissolved load and concentration may be caused by processes that include adsorption or ion exchange, precipitation, and oxidation-reduction. The diversions and changes in rate of water movement, including storage, can also occur without accompanying changes in load or concentration of contained pollutants. 92

45

POROSITY

40w

35-

$ 309

25-

a3 I-

20-

> W

ya

\ \ \

SPECIFIC YIELD

15-

10-

/

SPECIFIC RETENT ION

5-

Figure 8. Relationship between median grain size and water-storage properties of alluvium from large valleys (after Davis and Dewiest, 1966). Load and concentration of contaminants can be increased by removal of water from the water-contaminant solution. Water can be removed by processes that include evaporation, consumption by vegetation, filtration, and osmosis. Load and concentration of percolating solution also can be increased by dissolution of solids from the surfaces of spoil material. Materials previously removed fromsolution are potentially subject to redissolution when the chemical environment changes. Further, simple mixing with more concentrated solutions can increase load and concentration. Although some of the foregoing processes may cause proportional changes in concentrations of the chemical constituents of the solution, disproportionate changes in which constituents leave or enter solution at different rates can be expected in most instances. Alternative Monitoring Approaches-Nonsamplinq methods--Development of a monitoring program for the vadose zone will require site-specific information on where monitoring is needed, what methods to use, and the intensity of sampling required. Regraded spoil areas can be surveyed and mapped to delineate their potential for contributing water and/or pollutants to groundwater. Hydrologic, geologic, and geochemical data collected before and during the mining and reclamation phases can be evaluated. The survey requires information on 93

hydrologic characteristics (high, medium, and low infiltration capacities), topographic position (swales, depressions, drainage channels, etc.), predominant types of material (alluvium, shale, siltstone, sandstone, etc.), chemical characteristics of the material (sodic, alkaline, normal, etc.), depth to existing or predicted future water tables, and anomalies (excessive amounts of partings, unrecovered coal, other toxic and acid-forming materials, wastes, and underground combustion). In addition to topography and spoil type, maps should include delineations of free water surfaces (existing and future possibilities), the results of soil sampling and analyses, infiltration characteristics, and the existence and depth of water table. Using overlays or computer graphics, critical areas of spoils can be delineated and ranked for their potential to contribute to groundwater problems. For example, an area with potentially pollutant spoil material , surface concentrations of water, and high infiltration capacity that overlies a shallow water table would be given a high priority and warrant intensive monitoring. samplinq methods- Since water movement and any pollutants it might carry to the groundwater system will occur as unsaturated, unsteady flow, it will be necessary both to sample changes in water content and measure the pressure changes with time and depth. The following methods can be used to determine if movement of water is occurring from a pollutant source. The three most common means of measuring moisture changes are gravimetric, electrical resistance, and neutron scattering. Changes in pressure (negative head) can be measured with pressure plates, tensiometers, and psychrometers. For measuring moisture content, electrical resistance methods are difficult, if not impossible, to quantify with confidence. Gravimetric methods give good results but eventually destroy the sampling site and are time-consuming and labor intensive. Neutron probes and loggers also present technical and logistic problems but are a satisfactory compromise. Tensiometers, although simple, require diligent maintenance and will not give reliable results below moisture contents corresponding to pressure of about 3 . 4 bar. At lower moisture contents, soil psychrometers can be used instead of, or to augment, tensiometers. These devices require skill and experience to interpret accurately. They are ineffective in wet soils but give good results at lower moisture contents.

In theory, simulation of moisture flux in soil media is also possible using field- and laboratory-determined values of the necessary parameters. Models have been developed to date, however, only for homogeneous and simple layered systems and have little application to mine spoils because of the inhomogeneities in most spoils and the difficulty of obtaining the parameters required by the models. Costs for Step 6 include labor for installation of access wells and tensiometers and for sampling; operational costs for installation; and capital

94

costs for wells, tensiometers, a neutron logger, and chemical analyses of soil and spoil moisture. Recommendations-Surveys should be collected and evaluated with previously collected data to delineate and rank critical spoil areas. Based on the preceding considerations, neutron probe access wells extending through the spoil well into existing or predicted future saturated zones are recommended at critical sites. Tensiometers should be installed adjacent to access wells at three depths above the capillary fringe region of the water table at intervals of no more than 2 feet apart. Since moisture flow will be negligible at pressures less than 1 bar, psychrometers will not be necessary. The data from this monitoring can be used to document movement of water out of critical pollutant source zones. Sampling should be conducted in two stages. Initially, all sites delineated in the survey should be instrumented with an access tube extending through the entire depth of spoil. Monthly monitoring throughout the first year will allow the most obvious nonproblem sites to be eliminated from subsequent monitoring. Questionable sites should be monitored as long as necessary to determine if they present problems or may be eliminated. The final number of problem areas is not expected to be large. Significant flow of water, under conditions of low precipitation, will occur only in the most permeable and shallow materials. Monitoring should be intensified on sites that exhibit a high potential for contributing to the groundwater system. Additional access tubes in a second stage are recommended for critical sites. Moisture contents are assumed to be high where problems exist. Therefore, tensiometers should be installed adjacent to the access tubes to measure pressure differences for the determination of flow volumes. The number of installations will depend upon cost, the variability encountered, and the precision desired. Standard sampling analyses that incorporate these variables should be used to establish the sampling intensity. Step 7 . Evaluate Pollutant Mobility in the Saturated Zone Water that percolates downward through the spoils normally will enter a saturated zone below a water table that forms at some depth in the spoils. Relatively impermeable materials below the spoils support the saturated zone and limit further downward percolation. Thus, in the saturated zone, the water generally moves laterally in the direction of the hydraulic gradient. In some instances, leakage into underlying aquifers may occur. Premining geologic strata usually contain groundwater. Coal seams are important water-bearing aquifers in many areas. After removal of overburden and coal and backfilling of spoils, the original aquifers are not present in the spoil zone. In the nonmined zone abutting the spoils, however, extensions of the original aquifers in their natural undisturbed condition are likely. Water will tend to enter the spoils from undisturbed zones. Thus, water in

95

the saturated part of the spoil zone may be derived not only from percolating surface water, but also from undisturbed adjacent areas. Because of their heterogeneity and lack of stratification to serve as confining layers, spoils tend to contain unconfined groundwater only. Van Voast, Hedges, and McDermott ( 1 9 7 8 ) found, however, that at dragline operations in Southern Montana coarse rubble tends to roll down the sides of spoil piles during backfilling and form a permeable basal aquifer. Tests indicated that these stratified aquifers that are formed at the level of the lowermost mined coal seam are confined under artesian pressure. In such situations the spoils may contain both a confined, basal aquifer and an overlying unconfined aquifer. Water percolating downward through the spoils from the surface is not likely to enter the confined aquifer. Instead, water enters the confined strata from corresponding undisturbed aquifers in adjacent areas. Thus, the separated aquifers may contain water of considerably different quality due to different sources. Moran et al. ( 1 9 7 9 ) report that data presented by Rahn ( 1 9 7 6 ) indicate that spoil aquifers at the sites of two pumping tests in Wyoming are under water table conditions. At locations where coal to be mined is above the water table, relatively little opportunity exists for appreciable lateral recharge into the spoils from adjacent undisturbed areas.

To facilitate mining, pit water is usually maintained at a low level by pumpage that commonly causes a drawdown of the water table in adjacent areas. Considerable time may be required after mining ceases before the water table recovers in the spoils to a level that is in appropriate equilibrium with recharge and discharge conditions. As the water level changes, the amount of soluble materials available for solution changes, affecting postmining water quality . Below the water table, less oxygen may be available than in the overlying unsaturated vadose zone, resulting in less sulfide oxidation-reduction increases in salinity or acidity of water. In fact, sulfide-reduction rather than oxidation may be the predominant process below the water table. Dockins et al. ( 1 9 8 0 ) found substantial populations of sulfate-reducing Desulfovibrio desulfuricans bacteria in 25 of 26 groundwater samples (including spoil waters) from Southeastern Montana. Fluctuation of the water table may tend to increase dissolved solids concentrations in the saturated zone by alternating leaching and weathering processes in the overlying vadose zone as the water table rises and falls. As the water table lowers, weathering processes tend to increase in the dewatered zone; as it rises, leaching and transport of dissolved and soluble constituents may increase the dissolved solids concentrations in the saturated zone. Such changes in water level may correspond to discontinuous precipitation, snowmelt, soil freezing and thawing, and rninerelated application of water to the surface. During flow in the saturated zone, pollutant concentrations in groundwater may increase or decrease due to chemical, physical, biological and/or radioactive processes. The particular processes that occur depend on the 96

respective conditions of the water solution and its environment. Typical processes that affect groundwater concentration in the saturated zone include adsorption, ion exchange, dissolution, chemical precipitation, oxidationreduction, physical dispersion, dilution, various biological processes, radioactive decay, and evapotranspiration. Monitoring Needs- -Two types of saturated zone monitoring can be done. One type can be done during pit dewatering adjacent to a specific area of spoils. In this case, pit water, water from wells tapping nearby coal seams and overburden, and monitor wells in the spoils can be sampled. The second type is for spoils beyond the influence of pit dewatering. In this case, monitoring pit discharge is unnecessary; however, monitoring is still necessary for groundwater in coal seams and overburden adjacent to the spoils. Monitoring needs for the saturated zone include aquifer tests on saturated spoils, determination of the extent of saturated spoils, definition of groundwater flow direction in the spoils, and analysis of spoil groundwater quality, including trace elements, organic chemical constituents, and radiological parameters. All of these parameters are important in characterizing mining-related impacts to the groundwater system and verifying the suitability of the spoil aquifer for postmining uses. It is essential to consider the effects of mining on groundwater system hydraulics as well as water quality impacts.

In the Gillette, Wyoming study area, wells in the Wasatch Formation, coal seam, and underlying Fort Union Formation are needed in close proximity to the spoils to provide background water quality. Groundwater conditions in undisturbed materials adjacent to the spoils must be understood to interpret the results of monitoring groundwater in the spoils. Monitoring and testing wells in spoils should be completed at diverse depths in the saturated zone, since basal spoils can be much more permeable. Monitoring, spoil water quality in the most permeable zones will provide insight into possible off-site consequences of pollutant transport. Alternative Monitoring Approaches-Nonsamplinq methods--Collection of existing data to characterize the hy-drogeology of the mine area is the major nonsampling method. Samplinq methods--The composite contribution of contaminants to the groundwater by mine spoils and other upgradient sources, including mine-related activities at the surface, may be measured by monitoring the saturated zone. In some instances, approximate identification of the relative contributions of several contributing water sources may be possible by comparing time and space distributions of the quantity and quality of water changes in the saturated zone with observable time and space variables of potential sources. Because of the hidden and complex nature of the spoils zone, the contribution of the spoils is likely to be less amenable to direct measurement than the contributions of other more observable sources at the surface. Under such 97

conditions, estimating the contribution of other sources and the influx to the saturated zone in a water balance calculation may be feasible. Monitoring and knowledge of the geologic framework and related groundwater hydrology will indicate the routing of groundwater flow and any entrained contaminants from the spoils zone into downstream areas. The aquifer characteristics for, and water levels in, the emplaced spoils need to be determined. Also, the site-specific geohydrologic framework for undisturbed materials adjacent to the spoils must be developed, including subsurface geology, water levels, aquifer characteristics, and groundwater quality. Much of this information can be gathered in the course of monitor well construction. A number of new wells should be drilled in the spoils after emplacement. These can be constructed while pit dewatering is still occurring nearby. These wells should be 10-inch-diameter boreholes equipped with 6-inch-diameter PVC casing to allow proper pump tests. The casing would be perforated at the depth of expected eventual saturation when pit dewatering ceases. The wells should be packed opposite the perforations with gravel of known composition. The upper 10 to 20 feet of annulus around the well casing should be sealed. The wells should be properly developed upon completion to remove drilling mud or other foreign material. The top of the casing should extend several feet above the ground surface, have a locking cap, and be protected by barriers.

Wells in the spoils can be test pumped to determine aquifer characteristics once water levels have recovered from pit dewatering. Conducting tests with the maximum possible saturated thickness is advisable. Interpreting the results of groundwater monitoring in saturated spoils requires additional groundwater monitoring in materials adjacent to the spoils. For example, in the Campbell County, Wyoming area, this would include Wasatch Formation overburden, coal, scoria, alluvium, and Fort Union Formation underburden, depending on the particular area. Existing monitor wells can indicate regional groundwater conditions in the coal seam overburden, but regional groundwater conditions are poorly known for alluvium and the Fort Union Formation beneath the coal. In the early stages of mining, pit discharge near emplaced spoils can be monitored, as well as additional wells in native materials adjacent to the spoils, particularly upgradient. This requires several monitoring wells in the coal seam, several additional monitoring wells in the overburden, and possibly additional wells in the alluvium and underburden. Both solid and liquid samples should be collected from the saturated zone. Solid material should also be sampled during well drilling. solids penetrated by the monitor well should be sampled to allow interpretation of the results of groundwater quality monitoring. Since some of the spoil materials are well consolidated, the optimal drilling method is uncertain, but drill cuttings could be collected in any case. Solids sampling data may be valuable for evaluating factors such as trace metal migration in groundwater. Additional holes should be periodically drilled into spoils near monitor wells to allow sampling and analysis of solids to correlate with the results of groundwater quality sampling.

98

When the optimal pumping duration for collecting representative water samples has been determined, samples should be collected monthly for the first year. These results can be used to determine the proper sampling frequency for the duration of the monitoring program. Climatic factors, such as precipitation events, should be considered in determining sample collection dates. Pumping tests in spoils should allow ample opportunity to collect samples for chemical analyses over several days or weeks. Results may be available from existing pit discharge monitoring programs. Pit discharge is monitored at the point of discharge to surface for a few parameters. Weekly grab samples can be collected for l year and the frequency adjusted thereafter. specific pollutant sources of pit discharge samples are difficult to interpret, however, unless a complete monitoring program exists for all sources of pit recharge. At some mine sites, gravity discharge from the spoils zone might be monitored before mixing with other pit waters, simplifying interpretations. Solids beneath the water table should be analyzed for determinations similar to those specified for spoils as discussed under Step 3 , Identify Potential Pollutants. For water, major inorganic chemical constituents should be determined in addition to pH, total dissolved solids (residue at 18OoC), and electrical conductivity. Such determinations allow comparison of cation-anion sums, total dissolved solids versus electrical conductivity, and calculated total dissolved solids versus residue. Occasional samples should have total dissolved solids (ignition at 600°F) determined. Boron, fluoride, and various nitrogen forms should also be determined on occasion. An exhaustive suite of trace elements should be determined for at least one sample of water taken from each well near the end of the pump test. This will aid in selecting parameters to be routinely determined. Iron, manganese, arsenic, selenium, cadmium, chromium, lead, molybdenum, and vanadium, if pertinent, should be determined frequently. Also, the results of the pollutant-source sampling program should be used to choose trace elements of importance in groundwater quality monitoring. Federal regulations specify that total suspended and dissolved solids, total iron, pH, and total manganese should be determined for groundwater. State regulations may require analyses for additional parameters. The gross organic chemical composition of groundwater can be determined through analysis of dissolved organic carbon. More detailed determinations can be recommended if results obtained from the gross determinations indicate their desirability. Uranium and thorium content and gross alpha activity, gross beta activity, and radium-226 activity should be determined on several water samples from each well and the pit discharge early in the program. Similar analyses should be made of water samples from monitor wells in undisturbed materials near the spoils. Water levels in spoi.ls wells shodd be monitored at least monthly. Continuous water level recorders should be installed in key wells. Annual fluctuations and long-term trends of water levels may be critical for controlling spoil water quality.

99

Costs for Step 7 include labor for drilling supervision, sampling, and interpretation of results; operational costs for drilling, miscellaneous sampling equipment, and analyses of water and solid samples; and capital costs for wells, pumps, etc. Recommendations-The approach for monitoring pollutant mobility in the saturated zone should be custom designed for each mine site. An estimated 50 to 100 acres of spoils at each mine will be reclaimed each year. About six monitor wells should be constructed annually in the spoils. These wells will average 100 feet deep and be equipped with 6-inch-diameter PVC casing. Each well should be carefully surveyed to document location and land-surface elevation. Each of the wells installed during the first year should be pump-tested and water levels recorded. Approximately three water samples should be analyzed from each test. An average of three samples of solid materials penetrated by the monitor wells should be analyzed for each well. samples of pit water can be obtained from the pit sump pump or, if possible, from representative spoil discharge before it mixes with other water in the pit. Individual aquifers within and downgradient from the spoils should be monitored for pollution from the spoils zone and potential for affecting downstream water uses. A monthly sampling and water level measurement frequency based upon average groundwater flow and discharge rates is initially recommended for monitor wells and pit discharge. If flow rates and sample parameter values vary widely, increased sampling may be required. A portable submersible pump, generator, tripod, winch, pump column, discharge line, and electric cable will be necessary. A two-technician team probably will be required; it should be able to sample several wells per day. Sampling of pit discharge wil.1 not require extra time. Water from below the water table can be analyzed for the same constituents specified for solids under Step 3 , Identify Potential Pollutants. Procedures for preservation of samples and chemical analyses are presented in Manual of Methods for Chemical Analysis of Water and Wastes ( U . S . Environmental Protection Agency, 1974).

For water samples, the following should be determined routinely: 0

Calcium

0

Boron

0

Magnesium

0

Fluoride

0

Sodium

0

Total nitrogen

0

Potassium

0

Silica

0

Carbonate

0

Iron

0

Bicarbonate

0

Manganese

0

Sulfate

0

Arsenic

0

Chloride

0

Selenium

100

Nitrate PH

0

0

Lead Cadmium

0

Total dissolved solids (residue at 18OoC)

0

Chromium

0

Electrical conductivity

0

Dissolved organic carbon.

0

Several samples collected early in the program, such as during the pump tests, should be analyzed for: 0

Total dissolved solids (ignition at 316OC)

0

Antimony

0

Iodide

0

Titanium

0

Bromide

0

Rubidium

0

Vanadium

0

Strontium

0

Nickel

0

Aluminum

0

Copper

0

Cobalt

0

Zinc

0

Cesium

0

Barium

0

Uranium

0

Molybdenum

0

Thorium

0

Silver

0

Tungsten

Alpha activity 0

Beta activity

0

Radium-226 activity.

RECLAMATION AIDS Step 3. Identify Potential Pollutants Fertilizer sources most likely to affect the quality of water within reclaimed areas include the major mineral nutrients nitrogen and phosphorus and certain micronutrients, if applied in relatively large amounts. Ammonium-nitrate is entirely soluble in water when used as a fertilizer. Nitrate-nitrogen (NOS) is immediately available to plants, as this is the form that plants primarily absorb, though some plants have the ability to absorb small amounts of ammonia-nitrogen (NHi) by direct cation exchange. Because ammonia- and nitrate-nitrogen have the ability to move up and down in the soil solution, both should be included in the monitoring effort. The cationic nature of ammonia-nitrogen permits its absorption and retention by soil colloidal material if the cation exchange capacity of the soil is sufficiently high: otherwise, it will be removed in percolating water. Nitrate is highly subject to leaching as it is completely mobile in soils. Hence, its inclusion in the monitoring effort is highly justified.

101

Because the phosphate ion is almost immobile in soil, phosphorus moves very slowly from the point of placement. Also, the activity of phosphorus is lower in alkaline or calcareous soils due to the high calcium cation (Ca2+) activity, a large amount of finely divided calcium carbonate, and a large amount of calcium-saturated clay, all of which contribute to the precipitation of phosphate on solid phase calcium carbonate. Therefore, phosphorus is a doubtful source of groundwater contamination and need not be included in the monitoring effort. Monitoring Needs-Nutrients being applied to reclaimed areas must quantified.

be

identified and

Alternative Monitoring Approaches-Pollutant-specific information on monitoring activities by a coal company on fertilizer application to reclaimed areas should be collected. For example, any existing water quality data should be requested together with information on fertilizer application. Alternatively, the fertilizer application areas and its rate should be clearly delineated. Water samples for characterizing pollutants associated with fertilizer application should be obtained from surface waters adjacent to reclaimed areas. Samples should be collected before and after fertilization, with any increases in the concentration of particular constituents being noted. These alternative methods are possible for analyzing surface water samples. First, all samples may be submitted for complete analyses including the major inorganics (nitrate-nitrogen, ammonia-nitrogen, calcium, magnesium, sodium, potassium, bicarbonate, chloride, sulfate, phosphate, silica, total nitrogen, pH, and electrical conductivity) and trace constituents (iron, manganese, zinc, copper, cadmium, chromium, arsenic, molybdenum, vanadium, and selenium). A second technique is to completely analyze the first few water samples collected during the program. Subsequently, analysis for known fertilizer constituents should be continued, while those not applied as fertilizer could be excluded.

selecting a sampling frequency to characterize the waterborne pollutants in a source, such as applied fertilizer, is generally a trial-and-error process. One method is to sample every few days or weekly until time trends in the quality of the source are characterized. Subsequent samples can be obtained by sampling weekly, monthly, or quarterly. An increase in sampling frequency may be warranted by unusual circumstances. For example, a spill of fertilizer on the watershed area draining into surface water might justify an increase in sampling frequency. Costs for Step 3 include labor for data collection and sampling, operational costs for analyses, and capital costs for miscellaneous sampling equipment.

102

Recommendations---A l l areas receiving fertilizer should be delineated, along with the nature of the application and its rate. Surface water in the area should be sampled before and after fertilization to characterize water quality and quantity trends. Initial water samples should be analyzed completely, with later sample analyses only for those constituents present in the fertilizer.

Step 5 . Evaluate Infiltration Potential The purpose of determining the infiltration potential of a source is to quantify the volume of water and associated pollutants moving to the underlying saturated zone. The priority ranking report (Everett, 1979) indicates that the soil material used for surface dressing is expected to have a higher infiltration than the spoil material but lower, after settlement, than the structured natural soils. Monitoring Needs-The primary monitoring need is the quantity of water that infiltrates the fertilized reclaimed soil. Alternative Monitoring Approaches-Infiltration capacity can be determined by laboratory tests of spoil permeability, ring infiltrometers, or sprinkler-type infiltrometers. These techniques are discussed in the monitoring design for infiltration capacity of spoils. Costs for Step 5 include labor for infiltration measurements and data collection and capital costs for ring infiltrometers. These costs will be similar to those for spoils (Step 5, Evaluate Infiltration Potential). Recommendations-Infiltration capacity can be determined using a single-ring infiltrometer. Site selection should be based on information collected during identification of potential pollutants for spoils. Step 6. Mobility in the Vadose Zone The general purpose of this step is to estimate or measure the movement of pollutants in the vadose zone underlying a source or sources. Pollutants associated with fertilizers will be specified upon implementation of Step 3 , Identify Potential Pollutants. Similarly, the potential for pollutants to move into the vadose zone from the point of application will be determined during Step 5, Evaluate Infiltration Potential. Because ammonium-nitrate is completely soluble if sufficient moisture exists to solubilize it, the two types of nitrogen salt that compose this 103

fertilizer have the ability to move up and down in the soil solution. Tisdale and Nelson (1975) discuss the retention of nitrate-nitrogen in soil. Nitrified ammonia is subject to leaching. Nitrate-nitrogen is completely mobile in soils and, within limits, moves largely with the soil water. Under conditions of excessive rain, it is leached out of the upper horizons of the soil. During extremely dry weather, upward capillary movement of water is possible. Under such conditions, nitrates will accumulate in the upper horizons of the soil or even on the soil surface. Figure 9 illustrates the pattern of nitrate distribution in some soil columns that differ in their particle-size distribution. The percentage of large pore space and the amount of coarse sand decrease from sample A to sample H, although the total pore space is relatively constant (Tisdale and Nelson, 1975).

C

B

A

o r

L

L Y = 579

112E

Y = 567

G

F

X

I-

n.

56 Y =

84

341

L Y =

0

0

20

329

Y =

230

20

0

20

D Y = M E A N MOVEMENT OF NITRATE Icm)

Y =

563

H

L Y =

0

20

155

40

60

80

NITRATE AS PERCENT OF TOTAL EXTRACTED

Figure 9. Distribution of nitrates through columns of coarse-textured soils after adding 3.29 cm of water (after Tisdale and Nelson, 1975). Monitoring Needs-Data gaps exist in knowledge of the factors tending to attenuate pollutants within the vadose zone (i-e., dilution, filtration, sorption, chemical precipitation, buffering, oxidation-reduction, volatilization, and biological 104

degradation and assimilation) and field data on transformations in waterborne pollutants during flow in the vadose zone. Alternative Monitoring Approaches-The potential attenuation of pollutants in the vadose zone can be depicted by constructing a matrix comprising attenuating factors (rows) versus specific pollutants (columns). Each location in the matrix should specify the relative potential of a factor (e.g., sorption) to attenuate a specific pollutant (e.g., ammonia-nitrogen). Each position in the table may be filled in by subjective evaluation or on the basis of actual measurement. Subjective evaluation involves examining available data and estimating the effect on the mobility of a specific pollutant. Some actual attenuating factor values may be obtainable from field measurements. For example, spoil sample analyses in a previous step may yield analytical data on pollutant mobility. A second method is to use previously installed instruments to determine water and pollutant movement in the vadose zone, such as neutron moisture logging access wells and tensiometers. Field activities can be initiated to monitor the actual movement of pollutants in the vadose zone. Methods include collecting drill or auger samples for laboratory analysis and installing suction-cup samplers. Collection of samples of vadose zone sediments will entail using hand or power augers or core samplers, depending on physical composition and depth of the underlying spoil. Suction-cup samplers can be installed within the fertilized areas at depths corresponding to tensiometer locations. Collection bottles and the vacuum supply should be located in buried shelters, with vacuum and discharge lines from the suction-cup and tensiometer units protected by conduits. During sampling, vacuum equivalent to water-content pressure in tensiometers is applied to the suction cups. Water samples collected from suction cups can be analyzed completely or partially.. A complete analysis includes the major inorganics and trace constituents listed under Step 3 , Identify Potential Pollutants. Upon examination of the results of a complete analysis, subsequent samples may be analyzed only for those constituents found in greater-than-permissible concentrations and for those present in applied fertilizer. solid samples can be used to obtain saturated extracts via techniques in Methods of Soil Analysis (Black, 1965). Sampling frequency with suction-cup samplers depends on the water pressure within the surrounding porous matrix. If the system is very dry, water will enter the cups very slowly. A week or more may be required to collect a sufficient sample for analysis. In the extreme case, the cups become inoperable when water pressure is less than -0.8 atmosphere, and samples may become available only once or twice a year. sampling frequency cannot be explicitly defined until field units are installed and operating. For a wet system, it may be desirable to collect weekly samples until quality trends are established. Later, samples might be obtained monthly. 105

Solid sample collection schedules can be adjusted as appropriate after initial testing to establish quality levels and trends. Costs for Step 6 include labor for constructing an attenuation factor versus pollutant matrix and interpreting results, installing suction-cup samplers, and collecting liquid and solid samples; operational costs for analyses; and capital costs for suction-cup samplers. Recommendations-The monitoring program should include construction of a matrix of attenuating factors versus specific pollutants using available data when possible, supplemented with intuition. Water movement in the vadose zone underlying fertilized areas should be determined using facilities developed during previous steps. A few suction cups should be installed at depths corresponding to tensiometer locations, with sample analysis frequency dependent on soil moisture conditions. Suction cups should be sampled whenever possible during very dry conditions. For wet conditions, suction cups can be sampled more frequently until quality trends are established. Thereafter, samples can be analyzed monthly. Step 7. Mobility in the Saturated Zone The purpose of this step is to estimate or measure the attenuation of source pollutants during flow in the zone of saturation. The pollutants of concern will be those that have not been completely attenuated during flow through the vadose zone. As pointed out by Todd et al. (1976), the principal processes involved pollutant attenuation in the saturated zone include physical-chemical reactions or dilution. For pollutants in a source such as fertilizer, physical-chemical processes are sorption, precipitation, volatilization, and oxidation-reduction reactions. Dilution is affected by hydrodynamic dispersion resulting from such effects as convection, diffusion, and flow tortuosity. Monitoring Needs-Information gaps currently exist in predicting the effect of physicalchemical reactions and dilution on pollutant mobility within aquifers underlying fertilized areas. Alternative Monitoring Approaches-The relative effect of various physical-chemical mechanisms for attenuating pollutants within the saturated zone can be estimated by constructing a matrix similar to that for the vadose zone; i.e., a table consisting of attenuating mechanisms (rows) versus pollutants (columns). Attenuating mechanisms consist of physical-chemical factors (i-e., sorption, precipitation, volatilization, pH, oxidation-reduction [Eh], and decay) and dilution. When completed, the table will show, in a mixed qualitative-quantitative sense, the pollutants that should be monitored.

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Completion of the matrix for the physical-chemical items requires specific information on exchange capacity of aquifer materials and the Eh and pH of groundwater, as well as on the specific pollutants entering the saturated zone. Many of the physical-chemical parameters can be quantified from analyses of drill cuttings obtained during well construction and from field analyses of Eh and pH. Identification of pollutants must await results of mobility studies in the vadose zone. Groundwater samples can be obtained for analysis and ensuing data examined to characterize pollutant attenuation. Data from existing wells and wells installed during previous monitoring steps can be used in the matrix. In actuality, a special sampling program should not be required because samples should be available from these steps. Recommendations-The recommended approach includes all of the methods discussed above. Costs for Step 7 include only labor for construction of the attenuation mechanism versus pollutant matrix.

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SECTION 5 MONITORING RECOMMENDATIONS FOR MISCELLANEOUS SOURCES OF POLLUTION Steps 3 , 5, 6 , and 7 of the groundwater monitoring methodology have been developed for miscellaneous sources of potential pollution related to surface coal mining activities. These sources include spills and leaks, solid wastes for road construction, liquid shop wastes, explosives, and mine sanitary and solid wastes. Step 8 has been developed for specific mines and is presented in Everett (1979). SPILLS AND LEAKS Step 3 . Identify Potential Pollutants Mining operations require the movement and storage of a large number of substances that can be spilled or leaked from their containers. Gasoline, diesel fuel, oils, and lubricants are used in the shop area. Ammonium-nitrate and fuel oil (ANFO) are used for blasting. Herbicides are used to clear rights-of-way, and pesticides, fertilizers, and soil amendments are used in reclamation. Topsoil, overburden, parting materials, and coaly waste are transported to stockpiles and, of course, coal is transported from the mine pit to storage facilities. Monitoring Needs-Monitoring needs include characterizing the types of substances transported and stored on the lease area and their quantities. The current extent of monitoring for spills and leaks at active mines is unknown. Alternative Monitoring Approaches-Nonsamplinq methods--Substances transported and stored at the mine can be determined through discussions with mine personnel and field observation. Storage locations and transportation routes can be checked for evidence of spills or leaks. Accident records or past spills can be reviewed for potential problem areas that should be watched more closely. The costs include: Labor costs: interviews with mine personnel to determine quantities and transportation requirements or substances stored on the lease area, review of accident reports and records of previous

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spills or leaks, and field checking storage locations and transportation routes for potential pollutants resulting from spills or leaks. Operational costs: field transportation. Samplinq methods--Substances for which analyses do not exist can be sampled and analyzed. Grab samples can be taken if field monitoring personnel are present at a spill or discover a leak. The costs include: Labor costs: discussions with mine personnel and field observation, review of existing records and analyses, and sampling sub-stances for which analyses are not available. Operational costs: transportation.

analysis, sample bottles, etc., and field

Recommended Monitoring Approach-Nonsampling methods are recommended for monitoring spills and leaks. Step 5. Evaluate Infiltration Potential Infiltration potential depends greatly upon the location of leaks or spills. Although certain areas may be identified as susceptible to a large number of leaks or spills, in most cases it is not cost-effective to try to characterize the infiltration potential of ground materials in local areas because of the possibility of a spill. Monitoring Needs-The following needs are associated with monitoring infiltration potential: storage locations, areas where spills are likely to occur, procedures for checking tanks and pipelines for leaks, and emergency procedures. Alternative Monitoring Approaches-The following nonsampling monitoring methods are available: 0

Obtain information from field observations and discussions with mine personnel on storage locations and areas where spills may occur Review records of past spills for information on likely spill areas Check tanks and pipelines periodically for leaks using a dipstick or pressure-sensitive devices and visually check aboveground facilities for signs of leaks

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Review emergency cleanup procedures and check for preparedness of employees and equipment. Costs for this include: Labor costs: field observations and discussions with mine personnel, review of past records, checking tanks and pipelines for leaks, and review of emergency procedures. Operational costs:

field transportation.

Capital costs: possibly, dipsticks or other devices for checking tanks and pipelines for leaks. Recommendation-The nonsampling approach is preferred for determining the infiltration potential of spills and leaks. Step 6 . Evaluate Pollutant Mobility in the Vadose Zone Because of the wide range of locations at which spills and leaks might occur, vadose zone monitoring is not recommended. Step 7. Evaluate Pollutant Mobility in the Saturated Zone Monitoring the saturated zone is not recommended unless a particularly bad spill or leak occurs. SOLID WASTES FOR ROAD CONSTRUCTION Access and haul roads are constructed on a variety of surfaces, including coal, unmined ground, and reclaimed spoils. Roadbeds are often constructed of overburden and most roads are surfaced with scoria. Pit water is continuously applied to some roads to reduce dust. Dust suppressants such as calcium chloride and lignin sulfonate are also sprayed on roads, particularly at mines where water supplies are limited. The extent to which roads may constitute a pollution source depends upon construction materials, the quality and quantity of water or dust suppressant used, and the total land area covered by roads. Step 3 . Identify Potential Pollutants Potential pollutants from road construction include: Major and trace inorganics leached from road construction overburden materials Major and trace inorganics from pit discharge water applied to the roads for dust suppression Major inorganics from calcium-based dust suppressants

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Organics due to application of other dust suppressants such as Coherex, a cold water emulsion of petroleum resins mixed with water and applied to the roads. Major inorganics include calcium, magnesium, potassium, sodium, chlorine, carbonates, nitrates, sulfates, hydrogen sulfide, silica, etc. Trace inorganics include iron, manganese, zinc, copper, cadmium, chromium, arsenic, lead, molybdenum, vanadium, uranium, thorium, ruthenium, and selenium. Alternative Monitoring Approaches-Nonsamplinq methods--Potential pollutants are a function of the materials used to construct the roads. Information on roadbed materials can be obtained by : Discussions with mine personnel Review of road construction records Field observation Review of geophysical logs of overburden materials Requesting a complete analysis of commercially available calcium or organic-based dust suppressants. Any costs incurred for these activities are minimal and only represent the time necessary to obtain the information. Samplinq methods--When roads are heavily watered for dust control, pit water quality partially determines potential pollutants due to road construction. Pit discharge can be sampled and analyzed. An alternative method for determining potential pollutants is to install a series of monitoring wells perpendicular to the road. Samples from these wells can be analyzed and compared to determine if any contaminants are associated with the roadbed. Wells can be completed in the saturated zone or suction-cup samplers can be installed for sampling in the vadose zone. Both the wells and samplers can be used for monitoring later stages of the program, such as groundwater quality, mobility in the vadose zone, and attenuation in the saturated zone. Any existing wells near access and haul roads can be sampled individually or incorporated into a series of sampler wells. A well series can be installed in one localized area along a road, or several such areas can be chosen to represent different roadbed materials, construction practices, and local geohydrology. Pit discharge and monitoring well samples should be analyzed to determine pollutants initially present. Complete monthly analyses can then be run to determine the presence of new pollutants in the system. This frequency may be altered as initial results indicate. Discussions with mine personnel regarding road construction should also be held monthly. 111

A complete analysis for major inorganics, trace constituents, organics, and microorganisms should be performed. Followup analyses can be made to coincide with analyses required for other sections of the overall monitoring program.

The costs include:

Labor costs: inventory of roadbed materials, review of overburden geophysical logs, sampling of pit discharge, and installation and sampling of monitoring wells and lysimeters. Capital costs: lysimeters.

samplers, monitoring wells, and suction-cup

Operational costs: water quality analysis, sample bottles, and operation and maintenance expenses. Step 5. Evaluate Infiltration Potential Potential pollutants must infiltrate the roadbed or ditches and the ground surface beneath to reach the vadose zone. Infiltration potential depends very heavily on: Roadbed materials and construction practices Types of underlying materials Amount of water coming in contact with the road surface. Monitoring Needs-Assuming existing monitoring of infiltration parameters is unknown, the following items are monitoring needs: Water balance, including precipitation, evaporation, and amount of water applied to the roads for dust control Total road area Types of surface materials Permeability of roadbed materials Types of underlying materials Presence of streams and ponds near roads, including seasonal flows Direction and character of ditch flow along or under roads.

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Alternative Monitoring Approaches-Bpnsamplinq methods--Water balance information can be obtained from rain gauges and evaporation pans at the site. from weather data, or possibly from mine personnel. Truckloads of water applied to the roads can be counted as described in Step 4 , Identify Groundwater Usage. The amount of chemical dust suppressants used and methods of application can be obtained by discussions with mine personnel or estimated from mine maps and road specifications. The type and infiltration potential of road surface or ditch materials can be determined through field observations, discussions with mine personnel, and/or leaching studies on similar materials. Similarly, roadbed materials can be characterized by discussions with mine personnel, review of overburden geophysical logs, and/or leaching studies of similar materials. Information on underlying materials can be obtained from discussions with mine personnel and/or leaching studies. Soil infiltration data may be available from the Soil Conservation Service. Locations of streams and ponds can be determined by discussions with mine personnel and field observation. bor.

Costs involved in nonsampling methods of monitoring are primarily for laThey include:

Obtaining precipitation and evaporation data Counting truckloads of water applied to roads Discussions with mine personnel regarding road area and construction material and underlying materials Leaching studies Locating streams and ponds. Capital costs may include some leaching studies. Recommendat ions--If potential pollutants are identified, infiltration rates should be estimated. Step 6 . Evaluate Pollutant Mobility in Vadose Zone Monitoring Needs-The objectives of monitoring in the vadose zone are to determine the following: Direction and velocity of water movement Presence of perched layers Movement of pollutants. 113

Alternative Monitoring Approaches-Nonsampling methods--Nonsampling methods include neutron moisture logging in access wells and installation and operation of tensiometers and moisture blocks. Moisture logging and tensiometer data can be used to determine flux. Moisture logging can also be used to identify perched layers. samplinq methods--Several sampling methods can be used to monitor the movement of pollutants through the vadose zone. Split-spoon samples of vadose zone sediments can be analyzed in the laboratory for organics. Even though the cost of obtaining samples with split-spoon samplers is more expensive than with augers, the method is often preferred because of the better accuracy gained in estimating the vertical position of the sample. Samples from suction-cup lysimeters can be analyzed periodically for changes. Lysimeters and perched water table wells should be sampled weekly, or as frequently as possible, until quality trends are established. Monthly samples can then be taken. Sediment should be sampled monthly until a trend is established, then sampled every 6 months. Initially, all samples should be analyzed completely for major inorganics, trace constituents, and organics. Subsequent analyses can include only major inorganics and trace constituents and organics that have been found in excessive concentrations. The costs include: Labor costs: neutron moisture logging, installation and operation of tensiometers and moisture blocks, collection of sediment samples, and sampling wells and lysimeters. Capital costs: neutron moisture logger, tensiometers, moisture blocks, and auger. Operational costs: sediment analysis, water quality analysis, and sample bottles, etc. Recommendations-Nothing should be done unless pollutants are indicated and a high infiltration potential is found. Step 7. Evaluate Pollutant Mobility in Saturated Zone Monitoring Needs-Source-specific monitoring of mobility and attenuation is necessary to collect information on: 0

Aquifer characteristics

0

Direction and velocity of water movement 114

a Direction and velocity of pollutant movement.

Recommendations-Nothing should be done unless pollutants are indicated and a high infiltration potential is found. LIQUID SHOP WASTES Liquid shop wastes include fluids such as oils and lubricants, which are used in the repair and maintenance of mining equipment, and detergents and wash water used for cleaning trucks and machinery. Waste oils are probably stored either for recycling or disposal away from the shop area. Other waste products and water may enter some type of a sewer system. Oillwater separators are usually employed. Water from equipment washing will probably run onto the ground in a designated equipment washing area. Step 3. Identify Potential Pollutants Potential pollutants include oils, lubricants, gasoline, wash water, and detergents, or other substances that may be mixed with these fluids. Monitoring Needs-Current monitoring for pollutants in the shop area at coal strip mines is unknown. The following information gaps exist: types and quantities of liquid wastes, quantity of wash water used, location of washing areas, and use of detergents, etc. in wash water. Alternative Monitoring Approaches-Eonsamplinq methods--Several nonsampling methods for identifying potential pollutants include discussions with mine personnel on types and quantities of liquid wastes produced, quantity of wash water used, location of washing areas, use of detergents, etc. All of the above can be confirmed through field observation. Quantities of liquid wastes and wash water used can be measured and wastes can be inventoried regularly. sampling methods--Several sampling methods exist for identifying potential pollutants. The wastes themselves can be sampled and analyzed completely. Lysimeters can be installed in the vadose zone beneath the shop area and sampled for potential pollutants. Wells can be installed in perched layers and sampled. Piezometer clusters can be installed for sampling from the saturated zone. Samples should be taken on a weekly basis until potential pollutants have been identified. Subsequent samples can be taken once a month or as necessary to identify any new contaminants entering the system. All initial samples should be analyzed completely for major inorganics, trace constituents, organics, and microorganisms until potential pollutants have been identified. 115

Costs include: Labor costs: discussions with mine personnel, field observation of liquid waste disposal practices, measurement of liquid waste quantities, inventory of wastes, sampling of liquid wastes, and installation and sampling of lysimeters, perched water table wells, and piezometer clusters. Capital costs: clusters.

lysimeters, water table wells, and piezometer

Operational costs: etc.

water quality analysis and sample bottles,

Recommendations-Use of all the monitoring approaches in the foregoing categories is the overall preferred monitoring approach for identification of potential pollutants due to liquid shop wastes. Step 5. Evaluate Infiltration Potential The infiltration potential of liquid shop wastes depends in large part on how these wastes are disposed of or stored. Oils, for example, if carefully stored for recycling will have a much lower probability of reaching the subsurface than wash water poured onto the ground. Monitoring Needs-Information should be obtained on: Storage and disposal methods of liquid wastes Amount of maintenance and equipment washing done outdoors Type of surface materials in shop area. Alternative Monitoring Approaches-NOnSamPlinq methods--Monitoring methods include: 0

Obtaining information on storage and disposal methods through discussions with mine personnel and field observation Checking storage tanks and shop area for evidence of spills andl or leaks Determining infiltration of ground surface by conducting leaching studies of similar materials.

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Costs include:

Labor costs: discussions with mine personnel and field observation, checks for spills or leaks, and leaching studies. Capital costs:

leaching studies.

Step 6. Evaluate Pollutant Mobility in Vadose Zone Monitoring needs are to obtain information on: Direction and velocity of water movement in the vadose zone Presence of perched layers Movement of pollutants. Step I . Evaluate Pollutant Mobility in Saturated Zone Monitoring needs are to obtain information on: Aquifer characteristics Direction and velocity of water movement Direction and velocity of pollutant movement. EXPLOSIVES At mining sites with well-consolidated overburden and coal seams, explosives are used to dislodge the materials before their removal. The principal explosive used is an ammonium nitrate-fuel oil mixture known as ANFO. The water pollution potential of explosives used for surface coal mining has not been studied in detail in the West. In an incomplete explosion, some ammonium-nitrate and fuel oil residual will occur. Also, spillage of explosives can create a pollution potential. Such materials could directly affect the quality of pit water. Stockpile and spoils may also contain these materials and affect groundwater quality. Step 3 . Identify Potential Pollutants The primary potential pollutants from explosives appear to be ammonianitrogen, nitrate-nitrogen, fuel oil, and possibly trace organics. Monitoring Needs-Records are kept of blasting operations at western coal strip mines. No direct monitoring of explosives in relation to water pollution potential, however, is assumed to be performed. Determination of the approximate amounts of residual ammonium-nitrate and fuel oil from explosives is needed. Spills of these materials should also be monitored.

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Alternative Monitoring Approaches-Nonsamplinq methods--Much of the required information for nonsampling monitoring is available because of provisions of the Surface Mining and Control and Reclamation Act and State Regulatory Programs. Specifically, locations, dates, and times of blasting, types of material blasted, number of holes and spacing, depth and diameter of holes, and type and weight of explosives used are recorded. From this information, maps can be prepared illustrating patterns in the use of explosives, such as hole density or tonnage of explosives. Records should also be maintained on location, amounts of spills of explosives, and cleanup measures. Samplinq methods--Both overburden and coal should be sampled before and after blasting and before removal from the pit. Although the blasted materials are eventually removed from the area, water may contact the materials and drain into the pit before their removal. Also, after the overburden is removed and before blasting the coal, the uppermost layers of coal should be sampled for explosives or residual materials. After the coal is removed, the uppermost layers of underburden should be sampled for explosives or residual materials. Water may run over both of these surfaces and pick up potential pollutants. Because explosives may be used near the pit water body, sampling water in the pit and its disposal tributaries is recommended. In general, the direction of groundwater movement in the coal and overburden in areas where explosives are used will be toward the pit water body. Water could pick up residuals from explosives or spilled materials during flow over the surface of the pit. Based on present data, this is the most likely mechanism for pollutants from explosives to enter the pit water. Thus, the optimal situation is to monitor the amount and type of explosives and pit water at the same mine, a procedure followed in this monitoring program design. Water flowing across the pit a significant distance before entering the pit water body can be sampled along the flow path, as recommended in Section 3 . At the same time, samples of solid materials beneath the flowing water can be sampled for residuals or spilled explosives. If any pollutant transport by groundwater is occurring, the recommended monitoring for groundwater seepage for pit water will detect it (see Pit Water, Steps 5, 6 , and 7). Samples of overburden and coal should initially be collected weekly for determination of explosives and residuals. When water is running over the surface of the pit and into the pit water body, monthly traverses should be made along the flow path. Both the water and the underlying materials should be sampled. The nitrogen forms and fuel oil residuals from ANFO, however, should be determined at least weekly. Analyses for explosives and residuals can apparently be limited to the nitrogen forms, fuel oil, and possibly total organic carbon. Future studies, however, may detect pollutants unknown earlier but formed as residuals. If the inventory of type of explosive indicates additional potential pollutants, then they would also be determined in the water analyses. Saturation extract can be used for chemical determination of solid materials.

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The costs involved will be related to the following considerations: manhours required to review data collected in accordance with the Surface Mining Control and Reclamation Act and State Regulatory Programs: man-hours required to sample the overburden, coal pit water, and explosives throughout the mining operations: man-hours required to review the analyses of the explosives; and the chemical determinations from the solid material saturation extracts. MINE SANITARY AND SOLID WASTES Three methods of disposal are commonly used for sanitary wastes generated at the mine. They are: septic tank and leach field systems Oxidation ponds and lagoons Package sewage treatment plants. In addition, the sludge accumulation from the package sewage treatment plants must be disposed of. Solid waste disposal techniques may involve: On-site landfill Off-site disposal facility Incorporation in mine spoils Incineration followed by land disposal of residue. The monitoring recommendations for mine sanitary and solid wastes are adequately presented in Everett and Hoylman (1980). At most coal strip mines, these sources of pollution are minor and require minimal monitoring programs.

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REFERENCES Abruna, F., and J. Vicente, 1955. Refinement of a Ouantitative Method for Determining the Lime Requirements of Soils, J. Aqric. Univ. (Puerto Rico), 39(1), 41-45. Arnold, F.B., and D.J. Dollhopf, 1977. Soil Water and Solute Movement in Montana Stripmine Spoils, Res. Rpt. 106, Montana Agric. Exp. Sta. Beaton, J.D., G.K. Burns, and J. Platon, 1968. Determination of sulphur in Soil and Plant Materials, Technical Bulletin #14. Sulphur Institute, Washington, D.C. Black, C.A. (ed). 1965. Methods of Soil Analysis, Part 2, Chemical and Microbioloqical Properties, in Agronomy, Series 9, Amer. SOC. of Agron., Madison, Wisconsin. Blaney, H.F., and W.D. Criddle, Aug 1950. Determininq Water Requirements in Irriqated Areas from Climatoloqical and Irriqation Data, SCS TP-96, U.S. Dept. Agric., Div. Irrig. and Water Conserv. Bouwer, H., and R.D. Jackson, 1974. Determining Soil Properties, in Drainaqe for Aqriculture, J. van Schilfgaarde (ed), Agronomy No. 17, 611-675, iier. SOC. of Agron., Madison, Wisconsin. Breckenridge, R.M., G.B. Glass, F.K. Root, and W.G. Wendell, Dec 1974. Campbell county, Wyominq Geoloqic Map Atlas and Summary of Land, Water, and Mineral Resources, County Resource series No. 3 , Geol. Surv. of Wyoming, Laramie. Brinkman, R., and L.J. Pons, 1972. Recognition and Prediction of Acid Sulphate Soil Conditions, Proc. Internat. Symp. on Acid Sulphate Soils, Wageningen, The Netherlands. Brown, E., M.W. Skougstad, and M.J. Fishman, 1970. Methods for Collection and Analysis of Water Samples for Dissolved Minerals and Gases, in Techniques of Water-Resources Investiqations, Book 5, Chapt. Al, U . S . Geol. Surv. Craig, G.S., Jr., and J.G. Rankl, Sep 1977. Analysis of Runoff from Small Drainaqe Basins in Wyominq, Open File Rpt. 77-727, U.S. Geol. surv. Dames and Moore, Inc., 1974. Preliminary Reclamation Feasibility Study, Proposed Belle Fourche Coal Mine Near Gillette, Wyoming, prepared for Sun Oil Co., Denver, Colorado. 120

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Dewiest, 1966. Hydroqeoloqy, John Wiley and Sons, New

Depuit, E.J., J.G. Coenenberg, and D.J. Dollhopf, 1979. Salt Translocation in Saline-Sodic Mine Spoils, Res. Rpt. 136, Montana Agric. Exp. Sta. Dockins, W.S., G.J. Olson, G.A. McFeters, S.C. Turbak, and R.W. Lee, 1980. Sulphate Reduction in Groundwater of Southeastern Montana, Water Resources Invest. 80-9, U . S . Geol. Surv. Dollhopf, D.J., J.D. Goering, C.J. Levine, B.J. Bauman. and R.L. Hodder, Jul 1979. Selective Placement of Coal Strip Mine Overburden in Montana, IV. Hydroqeologic Studies, Interim Report: July 1978 to June 1979, contract No. H0262032, Montana Agric. Exp. Sta. Dollhopf, D.J., J.D. Goering, C.J. Levine, B.J. Bauman, D.W. Hedberg, and R.L. Hodder, Jun 1981. Selective Placement of strip Mine Overburden in Montana, V. Summary Report, Final Report: July 1976 to June 1981, Contract No. H0262032, Montana Agric. Exp. Sta. Dollhopf, D.J. W.D. Hall, C.A. Cull, and R.L. Hodder, JUn 1977. Selective Placement of Coal Stripmine Overburden in Montana, 11. Final Field Demonstration, Interim Report: January 1976 to June 1977, Contract No. H0262032, Montana Agric. Exp. Sta. Dollhopf, D.J., W.D. Hall, W.M. Schafer, E.J. DePuit, and R.L. Hodder, Mar 1978. Selective Placement of Coal Stripmine Overburden in Montana, I. Data Base, Interim Report: January 1976 to June 1977, Contract No. H0262032, Montana Agric. Exp. Sta. Drever, J.I., J.W. Murphy, and R.C. Surdam, 1977. The Distribution of As, Be, Cd, Ca, Hg, Mo, Pb, and U Associated with the Wyodak Coal Seam, Powder River Basin, Wyoming, Contrib. to GeOl., U. of Wyoming, 15(2), 93-101. Dunlap, W.J., J.F. McNabb, M.R. Scalf, and R.L. Cosby, 1977. Sampling for Organic Chemicals and Microorqanisms in the Subsurface, EPA-600/2-77-176, U . S . Environmental Protection Agency, Robert S . Kerr Environmental Research Laboratory. Everett, L.G., 1980. Groundwater Monitorinq, Guidelines and Methodoloqy for -. Developinq and Implementinq a Groundwater Quality Monitoring Proqram, General Electric, Technology Mktg. Oper., Schenectady, New York. Everett, L.G. (ed), Jan 1979. Groundwater Ouality Monitorinq of Western Coal strip Mininq: Identification and Priority Rankinq of Potential Pollution Sources, EPA-60017-79-024, U.S. Environmental Protection Agency, Monitoring and Support Laboratory, Las Vegas, Nevada. Everett, L . G . , and E.W. Hoylman, Jan 1980. Groundwater Quality Monitoring of Western Coal Strip Mininq: Preliminary Desiqns for Active Mine Sources of Pollution, EPA-600/7-80-110, U.S. Environmental Protection Agency, Las Vegas, Nevada. 121

Everett, L.G., and W.O. Rasmussen, Aug 1982. A Prototype Computer Interactive Ground Water Monitdring Methodology for Surface Water Impoundments, Water Resources Bulletin, 18(4). Everett, L.G., K.D. Schmidt, R.M. Tinlin, and D.K. Todd, May 1976. Monitorinq Groundwater Quality: Methods and Costs, EPA-60014-76-023, U.S. Environmental Protection Agency, Las Vegas, Nevada. Fenn, D.G., K.J. Hanley, and T.V. DeGeare, 1975. Use of the Water Balance Method for Predictinq Leachate Generation from Solid Waste Disposal Sites, EPA/530/SW-168, U.S. Environmental Protection Agency, Cincinnati, Ohio. Fuller, W.H., 1977. Movement of Selected Metals, Asbestos, and Cyanide in Soil: Applications to Waste Disposal Problems, EPA-60012-77-020, U.S. Environmental Protection Agency. Gee G.W., and A. Bauer, 1976. Physical and Chemical Properties of stockpiled Materials at a Mine Site in North Dakota, North Dakota Farm Res., 34:44-51. I

Gilley, J.E., G.W. Gee, and A. Bauer, 1976a. Particle Size Distribution of Eroded Spoil Materials, North Dakota Farm ReS., 34:35-36 Gilley, J.E., G.W. Gee, W.O. Willis and R.A. Young, 1976b. Water Infiltration at Surface Mined Sites in Western North Dakota, North Dakota Farm Res., 34:32-34. Gilley, J.E. and A. Bauer, 1977a. Effects of Tillaqe on Water Movement into -. Surface-Mined Materials, North Dakota Farm Res., 34(4), 22-29. Gilley, J.E., G.W. Gee, A. Bauer, W.O. Willis and R.A. YOUng, 1977b. Runoff and Erosion Characteristics of surface-mined Sites in Western North Dakota, Trans. Am. SOC. Agric. Eng., 20(4), 697-704. Gould, W.L., D. Rai, and P.J. Wierenga, 1975. Problems in Reclamation of Coal Mine Spoils in New Mexico, in Practices and Problems of Land Reclamation in Western North America, M.K. Wall (ed), U. of North Dakota Press, Grand Forks. Groenewold, G.H., 1979. Hydrologic and Hydrochemical Characteristics of Selected Strip Mine Spoils in Western North Dakota, in Ecology and Coal Resources Development, Symposium Proceedinqs, M.K. Wali (ed), Pergamon Press, 685-692. Groenwold, G.H., B.W. Rehm, J.A. Cherry, R.D. Koob, S.R. Moran, C.D. Palmer, and W.M. Peterson, 1980. Potential Hydrogeochemical Impacts of Surface Mining in the Northern Great Plains, Symposium on Surface Minins Hydrol%y, Sedimentoloqy, and Reclamation, December 1-5, U. of Kentucky. Hansen, E.A., and A.R. Harris, 1974. Resources Research, lO(2).

A Groundwater Profile sampler," Water

122

Harris, D.J., and W.J. Keefer, 1974. Wastewater Samplinq Methodoloqies for Flow Measurement Techniques, EPA-907/9-74-005, U . S . Environmental Protection Agency, Kansas City, Kansas. Fred C. Hart Associates, Nov 1981. A Review of Techniques for Projecting Lost-Mine Groundwater Quality at Western Surface Mine Sites, Draft Interim Report, Contract No. J5101071, Task Order 18. Hem, J.D., 1970. Study and Interpretation of the Chemical Characteristics of Natural Water, Water-supply Paper 1473, U . S . Geol. Surv. Henning, S.J. and S.B. Affleck, 1977. utilization and Movement of Water in Deep-Tilled Soils of Reclaimed Surface-Mined Land, Agron. Abstr. Jackson, M.L., 1958. New Jersey.

Soil Chemical Analysis, Prentice Hall, Englewood Cliffs,

Keefer, W.R., and R.F. Hadley, 1976. Land and Natural Resource Information and Some Potential Environmental Effects of Surface Mininq of Coal in the Gillette Area, wyominq, circular 743, U.S. Geol. surv. Keeney, D.R., and R.E. Wildung, 1977. Chemical Properties of Soils, Soils for Manaqement of Orqanic Wastes and Waste Water, Soil Science, Amer. SOC. Agron., Crop Sci. SOC. of Amer., Madison, Wisconsin. King, N.I., 1974. Maps Showinq Occurrence of Ground Water in the Gillette Area, Campbell County, Wyoming, Misc. Invest. Series Map I-848-E, U.S. Geol. Surv. Leenheer, J.A., and E.W.D. Huffman, Jr., 1976. Classification of Organic Solutes in Water by Using Macroreticular Resins, J. Res. of the U.S. Geol. w, 4(6), 737-751 McKee, J.E., and H.W. wolf, 1963. water Quality Criteria, Pub. 3-A, california State Water Quality Control Board. McWhorter, D.B., J.W. Rowe, M.W. Van Liew, R.L. Chandler, R.K. Skogerboe, D.K. Sunada, and G.V. Skogerboe, Aug 1979. Surface and Subsurface Water Quality Hydroloqy in Surface Mined Watersheds, Part I: Text, EPA-600/7-79193a, U . S . Environmental Protection Agency, Industrial Environmental Research Laboratory, Cincinnati, Ohio. Miyamoto,S., 1978. Effects of Wetting Agents on Water Infiltration into Water Repellent Coal Mine Spoils, Soil Sci., 125:184-187. Miyamoto, S . , A. Bristol, and W.L. Gould, 1977. Wettability of Coal-Mine Spoils in Northwestern New Mexico, Soil Sci., 123:258-263. Mooji, H., and F.A. Rovers, 1976. Recommended Groundwater and Soil Samplinq Procedures, Rpt. EPS-4-EC, 76-7, Environmental Protection Service, Canada.

123

Moran, S.R., and J.A. Cherry, 1977. Subsurface-Water Chemistry in Mined-Land Reclamation: Key to Development of a Productive Post-Mining Landscape, Proc. Second Ann. Gen. Meetinq Canadian Land Reclam. ASSOC., Auqust 1977, Paper No. 4, Edmonton, Alberta. Moran, S.R., G.H. Groenewold, and J.A. Cherry, 1978a. Geologic, Hydroloqic and Geochemical Concepts and Techniques in Overburden Characterization for Mined-Land Reclamation, Rpt. of Invest. No. 63, North Dakota Geol. surv. Moran, S.R., J.A. Cherry, P. Fritz, W.M. Peterson, M.H. Somerville, S.A. Stancel, and J.H. Ulmer, 1978b. Geology, Groundwater Hydroloqy and Hydroqeochemistry of a Proposed Surface Mine and Liqnite Gasification Plant Site Near Dunn Center, North Dakota, Rpt. of Invest. No. 61, North Dakota Geol. Surv. Moran, S.R., J.A. Cherry, B. Rehm, and G.H. Groenewold, 1979. Hydrologic Impacts of Surface Mining of Coal in Western North Dakota, Proc. Symp. on Surface Mininq Hydrology, Sedimentology, and Reclamation, December 4-7, 57-65, U . of Kentucky. Nelson, W.L., A. Mehlich, and E. Winters, 1953. The Development, Evaluation and Use of Soil Tests for Phosphorus Availability, in Soil and Fertilizer Phosphate in Crop Nutrition, Agronomy Monograph 4, W.H. Pierre and A.G. Norman (eds), 153-188. Olsen, S.R., and L.A. Dean, 1965. graph 9, C.A. Black (ed).

Methods of Soil Analysis, Agronomy Mono-

Olsen, S.R., C.V. Cole, F.F. Watanabe, and L.A. Dean, 1954. Estimation of Available Phosphorus in Soils by Extraction with Sodium Bicarbonate, Circular 939, U . S . Geol. Surv. Olson, G.J., and G.A. McFeters, 1978. Microbial Sulfur Cycle Activity at a Western Coal Strip .Mine, Rpt. No. 98, Montana U. Joint Water Resources Res. Center. Palmer, C.D., and J.A. Cherry, Aug 1979. Hydrogeochemical Concepts Applied to to Mined Land in the Fort Union Coal Region, in Proc., 4th Ann. Meetinq Canadian Land Reclam. Assoc., Regina, Saskatchewan. Pickens, J.F., J.A. Cherry, G.E. Grisak, W.F. Merrit, and B.A. Risto, 1977. A Multi-Level Device for Ground-Water Sampling and Piezometric Monitoring, Ground Water_, 15(3). Pionke, H.B., and A.S. Rogowski, Aug 1979. How Effective Is the Deep Placement of Acid spoil Materials? in Proc., 4th Ann. Meetinq Canadian Land Reclam. Assoc., Regina, Saskatchewan. Power, J.F., J.J. Band, F.M. Sandoval, and W.O. Willis, 15 Mar 1974. cation of Paleocene Shale, Science, 183(4129), 1077.

124

Nitrifi-

Rahn, P., 1976. Potential of Coal Strip Mine Spoils as Aquifers in the Powder River Basin, Proj. No. 10470025, Old West Regional Council. Ries, R.E., and A.D. ~ a y ,1978. Use of Irrigation in Reclamation in Dry Regions, in Reclamation and DrasticaLlY Disturbed Lands, F.W. Schaller and P. Sutton (eds), Amer. SOC. of Agron., Madison, Wisconsin Ries, R.E., J.F. Power, and F.M. Sandoval, 1976. Potential Use of Supplemental Irrigation for Establishment of Veqetation on Surface-Mined Lands, North Dakota Farm Res., 34:21-22. Schafer, W.M., G.A. Nielsen, D.J. Dollhopf, and K. Temple, 1979. Soil Genesis, Hydroloqical Properties, Root Characteristics and Microbial Activity of 1- to 250-Year-Old Strip Mine Spoils, 600/7-779-100, U . S . Environmental Protection Agency, Cincinnati, Ohio. Smith, R.M., W.E. Grube, Jr., T. Arkle, Jr., and A. Sobek, Oct 1974. >M Spoil Potentials for Soil and Water Quality, EPA-670/2-74-070, EPA Technology Series, U.S. Environmental Protection Agency, Nat. Env. Res. Center, Off. of Res. and Dev., Cincinnati, Ohio. Soil Conservation Service, 1972. Soil Conservation Service Enqineerinq Handbook, Section 5, U . S . Dept. of Agric. Thatcher, L.L., V.J. Janzer, and K.W. Edwards, 1977. Methods for Deterrnination of Radioactive Substances in Water and Fluvial Sediments, in Techniques of Water-Resources Investiqations, Book 5, Chapt. A5, U . S . Geol. surv . Thompson, K.S., and W.A. Van Voast, 1981. Hydroloqy of the Lower squirrel Creek Drainaqe, Southeastern Montana, with Special Reference to Coal Mininq, Open File Rpt. 84, Montana Bur. of Mines and Geol. Thornthwaite, C.W., 1948. An Approach Toward a Rational classification of Climate, Amer. Geographical Rev., Vol. 38. Tisdale, S.L., and W.L. Nelson, 1975. Soil Fertility and Fertilizers, MacMillan Publishing Co. Todd, D.K., R.M. Tinlin, K.D. Schmidt, and L.G. Everett, 1976. Monitorinq Groundwater Quality: Monitorinq Methodolow, EPA-60014-76-026, U.S. Environmental Protection Agency, Monitoring and Support Laboratory, Las Vegas, Nevada, 1976.

University of Wyoming, Oct 1976. Atlantic Richfield Co., Black Thunder Mine, Final Environmental Assessment, Vols. I1 and 111. U.S.

Bureau of Land Management, 1974. Final Environmental Assessment, Eastern Powder River Coal Basin, FES-74-75.

U.S.

Bureau of Land Management, 1977. Hanqinq Woman Creek Study Area, Resource and Potential Reclamation Evaluation, EMRIA Rpt. No. 12. 125

U.S.

Bureau of Reclamation, 1977. rior, Washington, D.C.

Ground Water Manual,

U.S.

Department of Health, Education, and Welfare, 1962. Public Health Service Drinking Water Standards, U.S. Public Health Service Publication 756.

U.S.

Environmental Protection Agency, 1974. Manual of Methods for Chemical Analysis of Water and Wastes, EPA-625115-75-003, Meth. Dev. and Qual. Assur. Res. Lab., Nat. Env. Res. Center, Cincinnati, Ohio.

U.S.

Environmental Protection Agency, 1976. Residual Management by Land Disposal, Proc. Hazardous Waste Res. Symp., EPA-600/9-76-105, Tucson, Arizona, February 1976, Munic. Env. Res. Lab., Cincinnati, Ohio.

U.S.

Geological Survey, Jan 1974. Surv. Bull. 1412.

U.S.

Geological Survey, 1975. Final Environmental Statement, Proposed Plan of Plininq and Reclamation, Belle Ayr South Mine, AMAX Coal Company, Coal Lease W-0317682, Campbell County, Wyoming, FES 75-86.

U.S.

Geological Survey, 1976a. Draft Environmental Statement, Proposed Mininq and Reclamation Plan, Eagle Butte Mine, AMAX Coal Company, Coal Lease W-0313773, Campbell County, Wyominq, DES 76-36.

U.S.

Geological survey, 1976b. Final Environmental Statement, Proposed Plan of Mininq and Reclamation, Corder0 Mine, Sun Oil Company, Coal Lease w-8385, Campbell County, Wyoming, FES 76-22.

U.S.

Dept. of Inte-

Coal Resources of the United States, Geol.

Van Voast, W.A., and R.B. Hedges, 1975. Hydroqeoloqic Aspects of Existinq and Proposed strip Coal Mines Near Decker, Montana, Bull. No. 97, Montana Bur. of Mines and Geol. Van Voast, W.A., and K.S. Thompson, 1982. Estimates of Post-Mininq Water Quality for the Upper Tonque River, Montana and Wyominq, Hydrogeologic Map NO. 5, Montana Bur. of Mines and Geol. Van Voast, W.A., R.B. Hedges, and J.J. McDermott, 1978. Strip Coal Mininq and Mined-Land Reclamation in the Hydrologic System, Southeastern Montana, old West Regional Commission, Billings, Montana. West Virginia University, 1971a. Mine Spoil Potentials for Water Quality and controlled Erosion, Water Poll. Cont. Res. series 1401OEJE, U.S. Environmental Protection Agency, Washington, D.C. West Virginia University, 1971b. soil Development of Mine Spoils, west virginia U. Agric. Exp. Sta. Bull. 604T. Wiram, V.P., no date. Evaluation of Overburden within the Belle AYr Mine Property of AMAX Coal Co., Gillette, Wyoming.

126

Woodruff, C.M., 1948. Testing Soils for Lime Requirement by Means of a Buf-fered Solution and the Glass Electrode, Soil Sci., 66:53-66. Wyatt,J.W., 1978. Soil Water and Root Characteristics of 1- to 53-Year Old Stripmine Spoils in Southeastern Montana, unpublished MS thesis, Montana State U., Bozeman. Young, S . A . , and E.J. Depuit, 1981. Response of seeded Species to Temporary Irrigation and Seeding Date, Symp. on Surface Mininq Hydroloqy, Sedimentoloqy and Reclamation, December 7-11, U. of Kentucky

127

APPENDIX A CONVERSION FACTORS U.S. Customary to SI (Metric)

U.S. customary unit

Name

SI

Abbreviation

Multiplier

Symbol

Name

acre

acre

0.405

ha

hectare

acre-foot

acre-ft

1,234

m3

cubic metre

cubic foot

ft3

28.32 0.0283

1 m3

litre cubic metre

cubic feet per second

ft3/s

28.32

11s

litres per second

degrees Fahrenheit

OF

0.555(OF-32)

OC

degrees Celsius

feet per second

ft / s

0 -305

m/ s

metres per second

foot (feet)

ft

0.305

m

met re ( s)

gallon( s)

gal

3.785

1

litre ( s )

gallons per acre per day

gallacre-d

9.353

l/ha d

litres per hectare per day

gallons per day

gal/d

4.381 x

l/s

litres per second

gallons per minute

gal/min

0.0631

l/s

litres per second

horsepower

hP

0

kW

kilowatt

inch( es )

in.

2.54

cm

centimetre(s1

inches per hour

in./hr

2.54

cm/h

centimetres per hour

mile

mi

1.609

km

k ilomet re

- 746

(continued) 128

CONVERSION FACTORS (continued)

U.S.

customary unit

Name

Abbreviation

SI

Multiplier

Symbol

Name

miles per hour

mi/h

0.45

m/ s

metres per second

million gallons

Mgal

3.785

M1

3,785

m3

megalitres (litres x 106) cubic metres

million gallons per acre

Mgal/acre

a, 353

m3/ha

cubic metres per hectare

million gallons per day

Mgal/d

43.8

l/s

litres per second

0.044

m3/s

cubic metres per second

mg/ 1

milligrams per litre

parts per million

PPm

1

pound ( s1

lb

0.454 453.6

pounds per acre per day

lb/acre-d

1.12

kg/ha-d kilograms per hectare per day

pounds per square inch

lb/in.2

0.069

kg/cm2

0-69

N/cm2

,.

kilograms per square centimetre Newtons per square centimetre

square foot

ft2

0.0929

mL

square metre

square inch

in.2

6.452

cm2

square centimetre

square mile

mi2

2.590 259

km2 ha

square kilometre hectare

129

APPENDIX B ACID-NEUTRALIZATION CALCULATIONS FOR SPOILS SULFUR DETERMINATION Among the various chemical analyses to which overburden and minesoil samples have been subjected, pyritic sulfur content is most important when considering toxicity or potential toxicity from acidity. Pyritic sulfur content, knowledge of which allows calculation of the maximum amount of acid that might be produced during the weathering of a rock, is estimated from the total sulfur content after the sample has been leached to remove sulfates. The LECO Induction Furnace with Automatic Sulfur Titrator is used for the sulfur analyses (Beaton, Burns, and Platon, 1968; West Virginia University, 1971a). The stepby-step procedure used in the instrument operation follows. Simplified procedure for determination of total sulphur usinq the LECO model 521-400 Induction Furnace with Variable Temperature Control Transformer and Timer and model 532-000 Automatic Sulfur Tit rator General Considerations a.

For coal or very high carbon shale samples, sandwich sample (0.100 gram) between two scoops of MgO to prevent splashing of sample. A longer time of running may be expected with such samples.

b.

Some samples, e-g., coal, when first placed in the furnace may change the color of the solution in the titration vessel to pink or purple (probably from organic matter being driven off the sample). Some samples may contain halogens (I, C1, F), which darken the solution in the titration vessel and will therefore produce S results that are low. This problem, if encountered, may be eliminated by the use of antimony in a trap between the furnace and titration assembly.

c.

Generally, with low chroma samples (shale) or other types where high sulfur content might be present, either 0.2500- or 0.1000-gram samples should be run first. If sulfur is not detectable or more accurate values are desired in this sample weight, increase sample size to 0.5000 gram and rerun.

130

Sample Preparation

-.

a.

Place one 0.2 ml scoop, level full, of iron chips in crucible, then

b.

Weigh exactly 0.500 gram of 6 0 mesh sample into the crucible. (For samples such as shale and coal that contain or are suspected to contain over I.% sulfur, use only 0.100 gram.)

c.

Add 1 scoop of MgO, about 0.5 mm3.

d.

Add 2 scoops of Fe powder and one Cu ring.

e.

After adding each component, gently shake the crucible to evenly cover the bottom.

f.

Place porous cover on the crucible (cover may be turned over and reused).

solution Preparation a.

Potassium iodate titrant: (1) 1.110 grams KIO3/l, multiply buret reading by 5 (0.5-gram sample: 0.005 - 1-00 % S range) (2) 0 . 0 4 4 4 gram KIO3/l, multiply buret reading by 0.200 (0.5-gram sample; 0.0002 - 0.040 % S range).

b.

Hydrochloric acid solution:

C.

Starch solution: Use only arrowroot starch. Add 2 grams of Arrowroot starch to 50 ml H20; stir well. Separately boil 150 ml H20 and to this slowly add the 2-gram starch solution, stirring constantly. Cool and add 6 grams of potassium iodate to the solution; pour this solution into the polyethylene starch dispenser. Do not use starch over 5 days old.

15 ml concentrated HC1/1 H20.

Instrument Operation a.

Read entire manuals on Titrator.

both

LECO

b.

Turn ON "Filament Voltage"; grid tap to high position.

C.

Turn on titrator--upper left switch (above "Endpoint Adjust")

d.

Set timer switch to ON, adjust timer to 8 minutes, or a time sufficient to satisfy instructions p. and q.

e.

Set "Titrate-Endpoint" switch to its middle position.

f.

Slosh carboys containing HC1 and KI03 to mix the condensate on the unfilled walls of the container.

4-

Fill iodate buret. 131

Induction Furnace and Automatic

h.

Fill titrating chamber to mark; add one measure of Starch; bottom of meniscus shall be 2 3/8" below top of chamber.

i.

Turn on oxygen; set pressure to 15 psi, flow rate to 1.0 minute.

j.

Turn "high voltage" ON.

k.

Place sample crucible on pedestal, making sure it is centered; carefully raise sample fully and close switching level. Make sure sample platform makes airtight contact when closed, as evidenced by vigorous bubbling in top of titration cell.

1.

Turn switch to "Endpoint".

m.

After a few seconds when titrant level has stopped falling and titrating chamber is a deep blue color, refill buret or note and record initial buret reading; turn switch to "Titrate" (see instruction x. also).

n.

Push RED button on timer to start analysis.

0.

While a sample is being titrated, add the final quantities of iron and tin and copper to the next crucible.

P-

Plate current must go to 300-350 mA for at least 15 seconds during the analysis; if not, rerun sample.

4-

Adjust to prevent Plate Current from exceeding 350 mA.

r.

When buret does not change reading for 2 minutes, and Plate Current has achieved 300 to 350 mA, it can be assumed that all of the sulfur has been driven from the sample. If buret is still changing when timer shuts off instrument, set Timer Switch to OFF, which restarts furnace, leave furnace on until buret is stable for 2 minutes, then turn Timer Switch to ON.

S.

Set "Titrate-Endpoint" to middle position (IMPORTANT).

t.

Lower sample platform, remove crucible using tongs, place fresh sample crucible in place, but do not close sample chamber.

U.

Drain titrating chamber and refill every third sample, or more if a large quantity of titrant was used by the previous sample. Slightly drain titrating chamber to maintain original level.

V.

Refill KI03 buret.

W.

Close sample chamber, making sure it is tight.

X.

Switch to "Titrate", or, if it is known that sample will evolve SO2 slowly, leave switch at Endpoint - this acts as a "Fine" control allowing buret valve to discriminate smaller increments. 132

liter per

y.

Continue from "n" above.

To Shut Down a.

Turn "Titrate-.Endpoint"switch to mid position.

b.

Turn off main 0 2 valve on top of tank.

c.

Turn off "High Voltage".

d.

Turn off automatic titrator.

e.

Drain titration chamber: flush once with a chamber full of HC1 solution or water, cover and leave stand.

f.

If 0 2 has stopped bubbling knurled valve on gage outlet.

g.

Turn off "Filament Voltage".

in

H2SO4

solution,

turn

off

small

Maintenance Periodically clean titration chamber and associated glassware with acetone or concentrated HC1. Sulfate removal from minesoil and overburden samples before total sulfur determination in LECO furnace Materials a.

28-nun ID polyethylene funnel.

b.

5.5-cm glass fiber filter paper.

c.

Acid-inert filter funnel holder (polyethylene).

d.

2:3 HC1.

e.

Mariotte bottle, at least 500-ml capacity, with height of outlet capillary adjustable to regulate outflow rate.

Procedure a.

Taking care to not sharply crease the glass fibers, fold a filter to fit the polyethylene funnel.

b.

With filter assembly on a suitable holder (small plastic vial), place onto pan of a balance and weigh 0.500 f 0.001 gram of 60 mesh sample into the filter.

c.

Place sample and filter onto funnel holder in sink or other suitable pan which can receive outflow from funnel. 133

d.

Charge Mariotte bottle with 50 ml of 2:3 HC1; start siphon and adjust flow rate into funnel to avoid funnel overflow.

e.

After sample has been leached with the acid, rinse out feed bottle and fill with 500 ml of distilled water: leach sample with water.

f.

After leached sample has dried (overnight airdry or 5OoC oven) , carefully fold glass fiber filter paper around the sample and transfer to a ceramic crucible for total sulfur analysis in the LECO furnace.

9.

Determine sulfur using standard LECO procedure, however add one extra scoop of Fe chips or powder.

POTENTIAL ACIDITY WITH PEROXIDE Direct oxidation of reduced sulfur to acid with hydrogen peroxide and subsequent titration with a standard base has been suggested as the most attractive method of evaluating the acid potential of "acid sulfate soils" (Brinkman and Pons, 1972). Although they also advocate the use of peroxide oxidation to detect "net potential acidity" in acid sulfate soils containing carbonates, oxidative efficiency is greatly reduced at pH of 5.8 and above (Jackson, 1958). Earlier investigations (West Virginia University, 1971a) showed a close relationship between total sulfur content of fresh overburden samples and the amount of acid measured after the samples were treated with hydrogen peroxide. When the samples consisted of minesoils or weathered overburden materials, sulfate-sulfur, organic content, and calcium carbonate content unpredictably influenced the amount of acidity generated by peroxide treatment. The relationship between sulfur content and generated acidity for 49 minesoil and weathered overburden samples, where the samples had been treated with acid to remove sulfates and carbonates before both the sulfur determination and the peroxide treatment, has been statistically confirmed. Correlation between the acidity produced, and the pyritic plus organic sulphur content, was significant at the 0.001 level, with an r2 value of 0.970. Acidity could be related to percent sulfur by the equation: Y = 4.93

+ 52.29 X

where Y is total potential acidity, expressed as milliequivalents of hydrogen per one hundred grams, and X is percent pyritic plus organic sulphur. Procedure Note: If the sample contains no carbonates and no sulfates, and the pH is less than 5.5 in a 1:l soil-water suspension, then Step 1 can be eliminated. 1.

Place 3 grams of sample (< 60 mesh) into a funnel fitted with filter paper (11.0 cm., Whatman No. 41). Leach sample with 300 ml of 2:3 HC1 (HC1:water) in funnel-full increments, followed by distilled water (in funnel-full increments) until effluent is free from chloride as detected by 10% silver nitrate. Airdry filter paper and sample overnight, or place in 5OoC forced-air oven until dry.

134

2.

Carefully scrape dried sample from paper surface and mix.

3.

Weigh out accurately 2.00 grams of sample into a 300-ml tall form beaker. Add 24 ml of ACS Reagent Grade 30% H202 and heat beaker on hotplate until solution is approximately 40OC. Remove beaker from hotplate and allow reaction to go to completion, or for 30 minutes, whichever comes first. Three blanks for each batch of samples should be handled in the same manner. Caution: initial reaction may be quite turbulent when samples contain 0.1% sulfur or greater.

4.

Add an additional 12 ml of reagent grade H202 (30%) to beaker and allow to react for 30 minutes, then place beaker on hotplate at approximately 90 to 95OC, solution temperature, for 30 minutes to destroy any unreacted H202 left in beaker. Do not allow to go to dryness.

5.

Wash down the sides of the beaker with distilled water and make the volume of solution to approximately 100 ml.

6.

Place beaker on the hotplate or over a Bunsen burner and heat the solution to boiling to drive off any dissolved C02, then cool the solution to room temperature.

7.

Titrate the solution, with 0.0100 g NaOH that is free of C02 and protected from the atmosphere, to pH 7.0 using a glass electrode pH meter. Note: The NaOH must be standardized precisely with KHC8H40q to obtain its exact Normality which will be used in the calculation.

8.

Calculations: a.

(ml of NaOH) x (Normality of NaOH) x (50)

b.

meq H+/100 g x 0.01 = tons H'/thousand

c.

One ton of H+ requires 50 tons of CaCO3 equivalent to neutralize i.t.

=

meq (H+)/~oog.

tons of material.

NEUTRALIZATION POTENTIAL The natural base content of overburden materials is important in evaluating potential minesoils. Quantization of neutralizing bases, including carbonates, present in a rock was accomplished by treating the sample with a known excess of hydrochloric acid, heating to insure complete reaction, and determination of the unconsumed acid by titration with standardized base. This is a modification of the procedure used to measure the neutralizing equivalence of agricultural limestone (Jackson, 1958). Procedure for Minesoil or Overburden Material 1.

Weigh 2.00 grams of sample, ground to pass a 60 mesh (0.25 nun) sieve, into a 250-ml Erlenmeyer flask.

135

2.

Carefully pipet 20.00 ml of 0.1 g HC1 (the normality of which is known exactly) into the flask.

3.

Heat nearly to boiling until reaction (acid plus carbonates) is complete: 5 minutes is usually sufficient.

4.

Add H20 to a total volume of 150 ml, boil 1 minute: cool.

5.

Titrate using 0.1 g NaOH (concentration exactly known), to pH 7.0 using an electrometric pH meter. a.

If the pH of the suspension is greater than 7.0 before beginning the back titration with NaOH, a CaC03 equivalent of over 50 tons per thousand tons of material can be assumed.

b.

If less than 3 ml of the 0.1 N NaOH is required to obtain a pH of insufficient addition of acid to neutralize all of the base present is likely. Therefore, to obtain the most reliable results, the sample should be rerun using a greater amount of acid initially added to the sample. 7.0,

c.

6.

If an exact value of this high neutralizing capacity is desired, rerun the sample using a greater amount of acid initially, or using above procedure but substituting 1.0 g HC1 and 1.0 N NaOH.

Calculate neutralization potential (NP) using equations a. through c. a.

Millilitres of acid consumed by sample = millilitres of acid added to sample, minus millilitres of base required to neutralize sample times g l of acid (only) in a flask

ml of base required to neutralize it

b.

Parts CaC03 equivalent/million parts of soil consumed by sample) times g of acid times 100 10,000 grams of sample used X 1

c.

d.

=

(millilitres of acid

50 grams of CaCO 3

+-

1 gram of H

For a 2.0-gram sample:

1.

Tons of CaCO3 equivalent/1000 tons = millilitres of acid consumed by sample times 25,000/1,000 times g of acid

2.

Tons of CaC03 equivalent/thousand tons of soil times 25.0 times N of acid

=

millilitres

Maximum CaC03 requirement for neutralization of acid developed from total sulfur = %S times 31.24 (assuming all sulfur occurs as pyrite or marcasite). 136

The soil test analyses discussed in Smith et al. (1974) for pH, lime requirement, available phosphorus, potassium, calcium, and magnesium were carried out on overburden rock material pulverized to pass a 60-mesh sieve and, in the case of minesoils, crushed material passing a 2--mmsieve. The analytical procedures for available phosphorus and potassium are essentially those instituted by the North Carolina Agricultural Experiment Station (Nelson, Mehlich, and Winters, 1953) and used by several Eastern states. Available calcium and magnesium were determined in this same extract. The lime requirement test was that proposed by Woodruff (1948). Analyses for available phosphorus by the sodium bicarbonate extraction, as discussed in smith et al. (1974), were carried out using the method of Olsen et al. (1954) as described by Olsen and Dean (1965). The step-by-step procedure for this method follows. PROCEDURE FOR DETERMINING AVAILABLE PHOSPHORUS IN MINESOILS. (MODIFIED METHOD O F OLSEN et al., 1954)

Materials 1.

50-ml Erlenmeyer flasks with stoppers, or similar containers for phosphorus extraction step.

2.

Funnels, 60-mm diameter, with funnel rack to hold several.

3.

Whatman #40 or S i

4.

50-ml beakers to receive filtrate after extraction.

5.

Decolorizing equivalent.

6.

Balance, capable of 20.01-gram accuracy.

7.

Shaking machine, Burrell Wrist-Action Shaker, or reciprocating shaker adjustable from about 50-200 excursions/minute.

8.

25-1111volumetric flasks.

9.

Colorimeter or spectrophotometer, with filter or adjustment to provide 660-mu incident light.

10.

Cuvettes or matched test tubes to fit above colorimeter.

11.

Sodium bicarbonate (NaHCO3) solution, 0.5 M, adjusted to pH 8.5 with 1 g NaOH. Mineral oil added to avoid exposure to the air; stored in a polyethylene container and made fresh every 2 months.

12.

4H20, solution: dissolve 15 grams in Ammonium molybdate, (NH4)6 M07O24 300 ml of warm distilled water. Filter if cloudy and allow to cool. Gradually add 342 ml of concentrated HC1 and mix. Dilute to 1 liter.

S

589-white, filter paper, 110-mm diameter.

charcoal,

Darco

G-60

-

137

(J.T.

Baker

Chemical

Co.)

or

-

13. Concentrated SnC12 2H20 solution: 10 grams of large crystals dissolved in 25 ml concentrated HC1. Store refrigerated in a brown glass bottle. Prepare fresh every 2 months. a.

Dilute SnC12: Add 0.5 ml of the concentrated SnC12 solution to 66 ml distilled water. Prepare the dilute solution for each set of determinations.

14. standard P solution: Weigh 0.4393 g. KH2P04 into a 1-liter volumetric flask. Add 500 ml distilled water and dissolve the salt. Dilute to 1 liter, and add 5 drops of toluene to reduce microbial growth. 15. Dilute P solution: Dilute 20 ml (pipet) of the P solution from step 14 to 1 liter with distilled water. This solution contains 2 pg of P per ml. Procedure 1.

Add 1.00 gram of < 60-mesh rock or soil sample, 1.7-cm decolorizing carbon, and 20 ml of NaHC03 solution to the 50-1111Erlenmeyer flask. Stopper the flask.

2.

Shake for 30 minutes, at 2OoC, using a shaking speed of 2 on a Burrell wrist-action shaker, or 120 excursions per minute on a reciprocating shaker.

3.

Filter through filter paper specified; shake flask before pouring suspension into filter funnel.

4.

Pipet 10 ml of filtrate into a 25-ml volumetric flask. interrupt work, stop here.)

5.

a.

slowly add, with a pipet or calibrated dispenser, 5 ml of ammonium molybdate solution. Shake gently to mix well (pH of the solution after adding molybdate should be between 3.0 and 4.0. With some alkaline soils addition of more acid may be necessary to assure the indicated pH for consistent color development. With minesoils studied, however, 5 ml of molybdate has been sufficient and has avoided excess acidity with extremely acid samples).

b.

Wash down neck of flask with a small amount of water and dilute to about 22 ml.

(If necessary to

6.

Pipet 1 ml of the dilute SnCL2 solution into the flask, dilute to volume, and mix immediately holding the top of the volumetric flask tightly closed (gases are generated during this mixing); be sure solution is thoroughly mixed before releasing hand pressure on the cap of the flask.

7.

Ten minutes but less than 20 minutes after adding the dilute SnCL2 to the flask and mixing, measure the transmittance (%TI of the blue solution, using the colorimeter or spectrophotometer at 660 mu. Be sure to understand instructions for operating the instrument correctly. 138

8.

Obtain P concentration from standard curve prepared as follows: a. Pipet aliquots, containing from 2 to 25 pg of P (this gives a range of from 0.08 to 1.0 pg/ml in the 25 ml flask), of the dilute P solution into 25 ml volometric flasks and add 5 ml of the NaHC03 extracting solution to each flask. b.

Develop the color as in step 4.

c.

Plot the %T vs P concentration in the 25 ml flask on single-cycle, semilog graph paper, or Absorbance (A) vs P concentration on linear graph paper.

Calculations If a 1.0-gram sample is extracted with 20.0 ml of extractant, and a 10.0-ml aliquot of the filtered extractant is taken into a 25-ml volumetric flask for color development then: ppm available P in the soil = ppm P in sample, taken from standard curve x 50. IMMEDIATE LIME REQUIREMENT DETERMINATIONS Determinations of the lime requirement of minesoils by Ca(0H)Z titration are discussed in West Virginia University (1971b1, and further interpretations appear in Smith et al. (1974). A further study, involving 32 minesoil samples selected from an Upper Freeport coal mining area, was undertaken to investigate the suitability of the 5-minute-boiling modification of the Ca(OH)2 incubation reported by Abruna and Vicente (1955). Their method, slightly modified for minesoils, follows. Procedure Place lO-gram samples of sieved (10 mesh) air-dry soil in beakers. Dilute with 50 cm of distilled water and add varying increments of 0.03 N Ca(OH12 solution, depending on the expected exchange capacity and base saturation of the soil. Boil on a hot plate for 5 minutes (intermittent stirring of the samples may be necessary to avoid excessive foaming). Cool in a water tray to 25OC and determine the pH of the suspension using a glass electrode. Buffer curves relating pH values to quantity of lime prepared from these data are then used to determine the lime required to raise the soil pH to any desired level. Figure B-1 compares the two methods for determining lime requirement by titration. The results compare favorably and considerable time is saved by the 5-minute-boiling method. By boiling the solution for 5 minutes, the time for reaching equilibrium was reduced from 100 hours to 1 hour. Certain theoretical considerations in addition to a limited study of data accumulated to date suggest that some relationship exists between the lime requirement of soils as determined by the various buffer methods, and the 139

a A

Y =0.7565 x+1*3795 r = 0.9875

A

Y

* PREDICTED V A L U E OF

L I N E REOUIREMENT C O R R E L A T I O N COEFFICIENT

r

I

I

I

I

I

I

I

1

2

3

4

5

6

7

pH (after 5-minute boiling)

Figure B-1.

Comparison of lime requirements of 32 upper minesoil samples by direct Ca(OH12 titration using a rapid 5-minute-boiling method and the standard 4-day incubation (Smith et al., 1974).

titratable acidity as detected in the neutralization potential (NP) measurement discussed earlier. Figure B-2 indicates that Soiltest Lime Requirement (modified Woodruff buffer method) and neutralization potential are closely correlated. In these predominantly sandstone minesoil samples positive and negative values of the neutralization potential were used. The high correlation shows that it is possible to predict lime requirement from neutralization potential. SOIL ACIDITY

Several constituents contribute to the development of minesoil acidity. These sources (humus, alumino-silicates, hydrous oxides, pyritic materials and soluble salts) may contribute independently or by interaction. The more common methods of measuring acidity are pH, electrometrically by means of glass electrode, exchangeable acidity using unbuffered KC1, and titratable acidity, using unbuffered solution.

140

-

A

Y E PREDICTED V A L U E OF L I N E REQUIREMENT r C O R R E L A T I O N COEFFICIENT

I

I

I

I

I

-3

-2

-1

0

1

2

-3

NEUTRALIZATION POTENTIAL

(tons CaC03 equivalent/l ,000 tons of material)

Figure B-2.

Relationship between soiltest lime requirement-and neutralization potential (Smith et al., 1974).

Two important factors affecting soil pH measurements are (1) the soillwater ratio and (2) the presence of soluble salts. The "suspension effect" results in a different pH reading when the electrode is placed in the sediment as opposed to the supernatent liquid. The pH of the sediment is usually lower for acid soils. Ideally, pH measurements should be taken in a "thin paste". At West Virginia university's soil testing laboratory a 1: 1 soil/water ratio is used, which gives an ideal thin paste or slurry with some soils. With sandy soils and many coarse or medium textured minesoils the 1:l mixture must be agitated while the pH is being determined in order to assure suspension. A satisfactory alternative is to use less water relative to minesoil. Soluble salts may have a pronounced effect on soil pH. As the salt concentration increases, the measured pH commonly decreases because the cation of the salt replaces the exchange acidity on the soil colloid releasing the acidity to the soil solution and decreasing the pH.

Two procedures have been used to overcome the salt effect. One method is leaching out the soluble salts with water and then measuring the pH. The second method is to add a salt solution instead of distilled water to the soil before measuring pH. One tenth normal K C 1 and 0.01 M CaCL2 are the salts normally used. The salts in the soil solution are assumed negligible compared to the salt solution added to the soil. The more common approach in the United States is to determine pH in a distilled water slurry, realizing that significant soluble salts may be present, depending on character of the sample.

141

The pH measurements of the 1:1, soil/water slurry (agitated to assure soil suspension) were all higher than those of the 1:1, soil/salt solution (Table B-1). The relationship between the two methods was good, resulting in a correlation coefficient of 0.858; however, when the pH measurements in water and salt solution were correlated with the extractable aluminum, the correlation coefficients were 0.0319 and 0.0954 respectively. There are two reasons for these poor relationships: (1) all the pH measurements were below 3.7, where acidity is dominantly from mineral acids in the soil solution and the range of pH from 4.0 to 5.5 is where soil acidity is dominated by exchangeable aluminun, and ( 2 ) the range of pH values (2.9 to 3.6 for water slurry and 2.4 to Table B-1.

COMPARISON OF TOTAL ACIDITY AND pH BY TWO DIFFERENT METHODS ALONG WITH EXTRACTABLE ALUMINUM ON 3- TO 8-YEAR OLD UPPER FREEPORT MINESOILS (Jackson, 1958). PH

Ba C12-TEA pH 8.2

Sample

meq H+/100 g

lNKC1 meq H+/100 g

lHKC1 meq A1+++/100 g

H20

lNKCl

1:l

1:l

3.87 3.87 3.51 2.50 2.85 2.55 4.89 3.26 5.09

2.75 3.00 2.56 1.89 1.72 1.99 4.22 2.39 4.81

2.9 2.1 3.1 3.2 2.9 3.3 3.3 3.2 3.4

2.4 2.5 2.6 2.6 2.5 2.7 2.6 2.5 2.7

QQ QQ QQ QQ QQ QQ

2-1 2-2 2-3 3-1 3-2 3-3

12.26 11.28 10.79 8.34 9.48 8.01 13.73 10.46 13.24

RR RR RR RR RR RR RR RR RR

1-1

11.61

1-2 1-3 2-1 2-2 2-3 3-1 3--2 3-3

11.77 12.59 10.79 9.81 10.95 10.63 11.45 9.16

3.36 3.62 4.02 3.62 3.26 3.67 3.46 3.87 3.05

2.70 2.92 3.17 3.11 3.00 3.00 2.50 2.92 2.22

3.2 3.0 3.1 3.2 3.2 3.2 3.1 3.0 3.1

2.7 2.7 2.7 2.7 2.8 2.7 2.7 2.6 2.7

ss 1-1 ss 1-2

5.72 7.52 7.68 10.95 7.57 11.77 7.19 6.38 6.70

1.99 2.70 2.65 3.87 2.85 3.77 2.65 2.34 2.04

1.61 2.22 2.22 3.36 2.22 3.31 2.22 1.83 1.67

3.6 3.5 3.5 3.3 3.5 3.4 3.5 3.5 3.6

3.0 2.9 2.9 2.8 2.9 2.8 2.9 2.9 3.1

QQ 1-1 QQ 1-2 QQ 1-3

SS 1-3

ss 2-1 ss 2-2 S S 2-3 SS 3 - 1 SS 3-2

ss 3-3

3 . 1 for the salt solution slurry) is so small that other uncontrolled variables dominate. The exchange acidity of a soil is thought of as acidity that can be replaced by a neutral, unbuffered salt such as KC1. The titratable acidity is that amount of acidity which is neutralized at a selected pH such as 8.2 for the BaC12-triethanolamine (TEA) method. The latter has the rationale of measuring the many different components of soil acidity, and corresponds to the definition of a calcium-saturated soil.

The soil acidity measurements (Table B-1) indicate that the BaC12-TEA method results are higher than those from the 1N KC1 method by a factor of approximately 3:O; however, both methods are closely related as evidenced by a correlation coefficient of 0.945. When data of both methods were compared with exchangeable aluminum, the 1N KC1 method correlated more closely (r=0.948) than the BaC12-TEA method (r=0.840), indicating that the latter measures acidity other than just that contributed by the exchangeable aluminum.

143

PART I1

GROUNDWATER MONITORING FOR OIL SHALE DEVELOPMENT

SECTION 6 INTRODUCTION BACKGROUND Synthetic petroleum products recovered from western oil shales are expected to play an important part in supplying energy needs of the United States during the later part of the 1900's. Various estimates of the magnitude of western oil shale reserves have been made. The U.S. Geological Survey estimates that an equivalent of about 4,000 billion barrels* of oil are contained in the oil shales of the Green River Formation of Utah, Colorado, and Wyoming. These oil shale resources account for 80 percent of the known world resources but, of course, are not completely recoverable. Recoverable resources are a function of mining and retorting technology and economics, but may amount to about 1,800 billion barrels of oil (Hendricks and Ward, 1976). A s the estimated remaining world ultimate oil resources are about 2,000 billion barrels (Tiratsou, 1976), of which less than 150 billion barrels are in the United States, western oil shale is clearly a significant energy resource. Federal Prototype Lease Development The current Federal Prototype Oil Shale Leasing Program, administered by the U.S. Department of Interior, was initiated in 1969. Program planning and environmental evaluation efforts by various government interagency and industry groups culminated in preparation of a draft environmental impact statement in 1971. .Informational core hole drilling by firms interested in obtaining oil shale leases was conducted in the 1971 through 1973 period. This led to nomination of 20 potential lease tracts in Colorado, Utah, and Wyoming. The Department of Interior selected six tracts for the prototype leasing program. The environmental impact statement was finalized in 1973. Later in 1973, the first lease sale was initiated. In January 1974, successful bidders for the two Colorado lease tracts (c-a and C-b) and for two Utah tracts (U-a and U-b) were announced. No bids were received on the proposed Wyoming lease tracts. Environmental baseline and operation design studies were conducted over the two years following the lease initiation. In 1976, Detailed Development Plans (DDP) were submitted for both Tracts C-a and C-b. The initial DDP for Tract C-a called for open pit mining, surface retorting, and off-tract locations for processing facilities, overburden, and processed shale disposal. A

* See Appendix A in Part I for conversion to metric units. 145

number of serious problems, in particular approval for off-tract disposal of wastes, could not be resolved and a lease suspension was requested. This suspension was granted in September 1976. During this suspension, a revised DDP for Tract C-a was prepared calling for modified in situ (MIS) development plus surface retorting of the oil shale mined from development of the MIS retorts. This revised DDP was submitted in May 1977 and was subsequently approved by the Area Oil Shale Supervisor (AOSS). Initial development plans on Tract C-b (by Ashland Oil, Inc. and Shell Oil Company) were submitted in February 1976. This plan called for a deep mining and surface retorting (and disposal) operation. Development was suspended later in 1976. In November of that year, Shell withdrew from the C-b Oil Shale Project and Ashland formed a new venture with Occidental Oil Shale, Inc. A revised DDP proposing MIS operations was submitted in February 1977. Site development was initiated in the fall of 1977. Shale deposits in the Piceance Basin that can potentially be exploited by in situ technologies underlie an area of considerable topographic variation that is largely undeveloped. A wide range in both hydrologic and geologic conditions occurs throughout the area containing the deposits. Several in situ technologies are available, each of which could have characteristic impacts. There has not been sufficient experience with the various retorting methods to determine which is the most suitable in terms of minimizing environmental harm in the Piceance Basin. It may appear at first glance that in situ retorting has less potential for impact to the environment than surface retorting; however, the long-term impact to the subsurface environment may prove this assumption to be wrong. Monitoring of groundwater quality impacts associated with in situ oil shale development will be difficult. Retort waters produced by small-scale in situ operations have resulted in the identification of a wide spectrum of potential pollutants. Research to date indicates that many of these pollutants have only recently been classified, while others are still under investigation. It is not clear if the quality of the retort waters from small-scale in situ retorting will be similar to those waters produced by large--scalecommercial in situ retorts. The Federal Water Pollution Control Act Ammendments of 1972 (P.L. 92-500) and the Safe Drinking Water Act of 1974 (P.L. 92-523) provide for protection of groundwater quality. These mandates call for programs to prevent, reduce, and eliminate pollution of both navigable waters and groundwater and for particular protection of drinking water resources. Similar goals are embodied in the Toxic Substances Control Act of 1976 and the Resource Conservation and Recovery Act of 1976. The national responsibility for these various activities is given to the U . S . Environmental Protection Agency (EPA). Various State agencies also have similar responsibilities via State enabling legislation. PREVIOUS WORK A companion report to this study, developed at Tempo and prepared by Slawson (1980b), presents the results of a groundwater monitoring design study

146

of in situ oil shale development. The approach used in that study is the general monitoring methodology developed by Tempo as follows: MOnitOrinq Step

Description

1

Select Area for Monitoring

2

Identify Pollution sources, Causes, and Methods of Disposal

3

Identify Potential Pollutants

4

5

Define Groundwater Usage Define Hydrogeologic Situation

6

Describe Existing Groundwater Quality

7

Evaluate Infiltration Potential of Wastes at the Land Surface

8

Evaluate Mobility of Pollutants from the Land Surface

9

Evaluate Attenuation of Pollutants in the Saturated Zone

10

Prioritize Sources and Causes

11

Evaluate Existing Monitoring Programs

12

Identify Alternative Monitoring Approaches

13

Select and Implement the Monitoring Program

14

Review and Interpret Monitoring Results

15

Summarize and Transmit Monitoring Information

In particular, the companion report focused on modified in situ development as proposed for Federal Prototype Lease Tracts C-a and C-b in Colorado by developing data required for an initial pass through methodology Steps 1 through 13, although Step 13 is not fully implemented. The methodology, in general, and its application to monitoring design problems are described in several other reports (Everett, 1979, 1980; Todd et al., 1976; slawson, 1979) and will not be presented here in detail. A preliminary monitoring design/implementation framework has been developed for M I S retorts in the companion report. This work lead to the identification of areas of uncertainty with regard to implementation of groundwater quality monitoring programs for in situ facilities. These uncertainties were found to be primarily within (1) hydrogeologic characterization and (2) sampling methods utilized at the MIS retorts.

PRESENT STUDY This study addresses the two primary groups of uncertainties regarding the implementation of a groundwater quality monitoring program for M I S oil shale development such as proposed for Federal Prototype Lease Tracts C-a and C-b (see Figure 10). Hydrogeologic characterization, an essential element in siting monitor wells and for the design of the wells to obtain consistent and representative samples, is discussed in terms of geophysical and hydraulic methods that are employed on the Federal Tracts. These methods are also

147

148

v

h

3

a

v)

U

V

I

.n

5

a

I

(II

V

w 0

c

0

-rl

appropriate for other areas with oil shale stratigraphy. Geophysical and hydraulic methods are evaluated and ranked relative to cost, potential effec-tiveness, and availability of testing equipment in the oil shale region. Sampling methods are discussed, covering a wide variety of monitoring elements including: (1) well design, ( 2 ) monitor well placement, (3) sample collection methods, ( 4 ) sampling frequency, (5) sample preservation and handling, (6) selection and preservation of constituents for monitoring, (7) sample analysis, and ( 8 ) interpretation of water quality data. A discussion of these monitoring elements is presented in the following paragraphs with detailed information provided throughout the text.

149

SECTION 7 SUMMARY HYDROGEOLOGIC CHARACTERIZATION A program designed to characterize the hydrogeology of an o i l shale tract prior to designing a groundwater quality monitoring program should include a proper suite of geophysical logs and appropriate aquifer testing methods. This book discusses these subjects and presents recommendations for their use in the design and implementation of groundwater quality monitoring programs for MIS retorting areas. Geophysical Methods Several logs were evaluated in this study to determine their overall effectiveness in providing environmentally pertinent and reliable hydraulic data. Those logs evaluated include: Temperature

Velocity

Caliper

Sonic (acoustic)

Gamma-ray

Density

Spinner

Electric

Radioactive tracer

Seisviewer.

With the exception of the seisviewer log, all the logs listed above were found to be comparable to each other in cost. Accordingly, recommendation of geophysical logs is based on effectiveness in obtaining reliable hydraulic data. The following log suite is recommended for its utility for hydrogeologic characterization: temperature, caliper, sonic, and electric logs. Of more limited value and receiving secondary, or lower, priority ranking are gammaray, velocity, density, and spinner logs. The radioactive tracer and seisviewer logs are not recommended for obtaining hydraulic data for the design of groundwater monitoring strategies at oil shale development sites.

150

gdraulic Methods Tempo's previous study (Slawson, 1980a) indicated a need for aquifer testing and recommended that selected exploration and core holes be converted to serve as testing wells. Existing wells can be conditioned or new wells constructed to be of sufficient size to accommodate pumps for aquifer testing. Four general methods of hydraulic testing procedures have been evaluated and are classed as follows: Drill stem tests Dual packer tests Long-term pump tests Single packer tests. Review of the testing procedures, equipment costs, and utility of the resulting data has produced the following priority ranking: 1.

Dual Packer Tests provide specific hydrologic data at a minimal cost when multiple tests are conducted in a single borehole. Down-hole test equipment assembly allows for pumping, injection tests, and discrete water quality sampling.

2.

Lonq-Term Pump Tests produce the most representative data on boundary conditions and flow patterns and are especially effective for determining regional groundwater conditions. Longterm pump tests should be carefully planned and positioned to provide maximum data per test because their use is limited by the rather large expense of implementation.

3.

Sinqle Packer Tests provide horizon specific data similar to the dual packer method. However, for each test, the packer must be inserted and removed from the borehole. This labor intensive activity can significantly increase the cost of data acquisition.

4.

Drill Stem Tests are commonly run during drilling operations. They are of value when single, well-defined aquifer systems are penetrated. However, when multiple aquifers are encountered during drilling, interpretation of data resulting from drill stem tests becomes extremely difficult. Drill stem tests are therefore not recommended for determining hydraulic parameters in complex hydrologic environments.

SAMPLING METHODS The objective of a groundwater monitoring strategy in the o i l shale region where MIS retort development could be selected as the mining methodology is to (1) provide baseline groundwater quality data, (2) detect and measure 151

groundwater flow within the abandoned retort interval, and ( 3 ) detect changes induced by waste residuals (e.g., spent shale, retort water) within the abandoned retort zone. Compilation of baseline data and accurate evaluation of the latter two aspects require collection of representative groundwater quality samples. However, a number of factors can influence the representative nature of the groundwater samples collected. These factors include well design, sample collection methods, and sample handling procedures. Well Desiqn The Upper and Lower Aquifer zones present in the Piceance Basin, Colorado, are composed of numerous layers, each of which can possess variable water quality and quantity characteristics. Since numerous wells are open or perforated over the entire Upper or Lower Aquifer interval, the water quality data collected from these wells represent a composite of all penetrated layers. On the other hand, a layer exhibiting greater hydrostatic head than adjacent layers can influence portions of the well bore, resulting in collection of a water quality sample that represents the high head layer and not a composite of the entire open interval. Under both of these conditions, baseline water quality data collected may not be adequately measured in detail, and for operation/abandonment phase monitoring, groundwater flow through abandoned retorts may not be adequately represented. Furthermore, any trace constituents or potential contaminant present may be sufficiently reduced below detection limits due to the composite nature of the well design if mixing does occur. A network of multiple completion wells is the recommended approach for a groundwater monitoring program near the retort fields. Multiple completion well design will enable the collection of representative data from each of the intervals potentially affected by the oil shale retorting operation. The suggested specifications for this type of well are: 0

Steel casing and polyvinyl chloride (PVC) well construction mate-rial. Although the structural properties of PVC may preclude its use as a casing material, the inert characteristics of PVC make it ideal as a well construction material. PVC is also inexpensive when compared with other materials.

0

The diameter of the PVC should be large enough to accommodate a submersible pump. The recommended diameter and wall thickness of the PVC is 6 inches OD and schedule 40 (19/64 inch), respectively.

0

Each well of the multiple completion should be completed in a different interval using cement grout to prevent the interconnection of different intervals.

0

Wells should be developed thoroughly, i.e., fresh water circulated in the well bore, to remove any traces of drilling fluid or other materials that may affect water quality samples.

It appears that wells completed over the entire Upper or Lower Aquifer are suitable for groundwater monitoring in areas removed from the retort

152

field(s1. This open type of well design will provide general information on the regional water quality and does not require the finer levels of completion It is recommended that the necessary for wells close to the retort field(s). same specifications suggested for the multiple completion wells be utilized for the more regional wells if samples are to be collected via a submersible Pump

-

The recommended specifications presented above are designed to allow for sampling with a submersible pump. Although pumping samples is the best approach from a technical standpoint, there are some distinct trade-offs with respect to the construction costs associated with the larger diameter wells. There are also some significant trade-offs with respect to sampling costs. The approximate costs for the well development are:

Approximate Cost per Well (dollars)a

Design b Large Diameter (6-inch) Well Upper Aquifer single completion

18,000 - 20,000

Lower Aquifer single completion

35,000 - 38,000

Multiple completion

53,000 -- 58,000 C

Smaller Diameter (2-5/8-inch tubing strings) Wells Dual completion (i-e., two completion strings with one open over the entire Upper Aquifer and one open over the entire Lower Aquifer Mu 1t iple complet ion

35,500 - 38,000

39,000 - 44,000

Notes: a These costs include drilling, development, casing material, etc. in 1980 dollars. bSubmersible pump can be utilized for sample collection. C

Bailer can be utilized for sample collection.

These cost data show that large-.diametersingle and multiple completion wells are more expensive than smaller diameter dual and multiple completion wells, respectively. In addition, the cost for an entire groundwater monitoring pro-gram would be substantially higher and equal to the cumulative cost of all wells in the system. The approximate costs of an entire groundwater monitoring program, including sampling, are presented in Table 13 of this section.

153

TABLE 13. WELL CONSTRUCTION AND SAMPLING COSTS FOR DEEP AQUIFER WELLS (1980 dollars)

Item

Well Construction

Fixed Submersible Portable Submersible PUP Pump (USGS)

Bailing (Tract c-a)

Swabbing (Tract C-b) 39,000-44,000

53,000-58,OOOa

53,000-58,000

35,500-38,000

61,800-79,800

55,000-60,000

8,000-10,000

200-400

1,400-1,700

200-400

16,000-18,000

135-200'

d 11,200-14,000

135-200'

3,500-4,300e

Sampling costs Capital Requirements Operational Requirements (Quarterly) Labor (quarterly)

N/Ab

P

4 cn

Five-year Total (including construction of 12 monitoring well sites)

704,500-78'7,800

943,000-1,072,000

440,700-478,000 858,000-974,000

Notes: a Assumes similar well construction for fixed pump as with portable pump. bTract C-b contracts swabbing rig, thereby eliminating capital requirements. C

Assumes sampling eight wells per day.

dAssumes sampling one well per day. e Assumes sampling three wells per day.

Monitor Well Placement One of the goals of hydrogeologic characterization efforts is to allow description of groundwater flow patterns within and near a retort field. The purpose of this description is to locate monitoring wells so as to sample flow through and from the retort field area. Monitor wells should be located as follows: 1.

Near retort field (within a few hundred feet) and within the field

2.

Oriented downgradient of the MIS retorts along fracture lines and major axis of anisotropy as defined by geologic testing program

3.

Accessible for sampling equipment.

Construction of new wells may be required for operation/abandonment monitoring. Wells constructed for hydrogeologic testing may not be appropriately located for inclusion in the monitoring program. sample Collection Methods Sampling of deep aquifer wells on Federal Lease Tracts C-a and C-b reviewed in this study is accomplished by bailing and swabbing, respectively. Although these techniques obtain the desired results of collecting a sample, there is some question as to the representative nature of the sample collected. Some factors contributing to the problem of collecting a representative sample using these techniques follow. Problems associated with bailing are: The water column chemistry can become stratified due to variations in water quality and hydrostatic head in the different layers .penetrated by the well. Although this is a function of well design, nonrepresentative samples will be bailed from this well if the samples are collected inconsistently with respect to depth. Water quality data are more representative if samples are collected consistently adjacent to the water-producing intervals. The water present in the well casing above the open, or perforated, section can be isolated from the aquifer water. Samples collected from this portion of the well will be nonrepresentative of the aquifer water chemistry. Small deviations in the sample collection depth can significantly affect the data when a bailer is being employed. The potential magnitude of this effect is apparent from the profile sampling data presented in this book.

155

These potentially negative influences can be alleviated if correct bailing procedures are exercised. The recommended procedure for bailing groundwater samples is as follows: 1.

Use a flow-through type bailer (e.g., Kemmerer sampler). Bailers that are open at the top and sealed at the bottom do not have this flow-through characteristic and will generally be filled with the first water encountered in the well (i.e., water near the static water level).

2.

Compile well completion data. Of particular importance is the well diameter, depth to aquifer, aquifer thickness, and total depth.

3.

For shallow wells with very slow groundwater movement, estimate

the well volume from the well completion data and extract at least one well volume previous to sample collection. For both shallow and deep wells with rapid groundwater movement, select a sampling point adjacent to the aquifer. 4.

Consistently sample from the same depth and adjacent to the aquifer during every sampling effort.

5.

Measure temperature, specific conductance, and pH in the field.

If these guidelines are followed, bailing is a very effective method for collecting groundwater quality samples. In addition, bailing is the most cost-effective approach (see Table 13).

Swabbing a well is a more representative sampling technique than bailing in that a well volume can be removed prior to sample collection. However, this technique is very expensive to employ and presents a potential for contamination. The following problems are associated with swabbing: 0

There is high potential for introducing organics into the sample when oil-field equipment is used. Care must be taken to clean the swabbing equipment thoroughly.

0

The amount of water swabbed from a well is difficult to determine, and can result in obtaining inconsistent and nonrepresentative samples. If possible, the discharge should be carefully measured to provide the necessary data for collecting consistent and representative data.

0

Swabbing may accelerate plugging of perforations in the well.

0

Swabbing is extremely expensive and time-consuming.

Due to these factors, swabbing should not be employed as a sampling met hod. 156

For the deep wells to be utilized for monitoring modified in situ re-torts, pumping is the recommended sampling approach from a technical standpoint. Pumping allows a greater portion of the aquifer to be sampled, minimizes the effects well casing or water stratification may have on the sample representativeness, and reduces the potential for missing or delaying the observation of mobile pollutant constituents. In addition, a submersible pump can be fixed in the well or be used as a mobile unit, alternatives which can be very beneficial to a sample collection program. However, on a cost-effective basis, the fixed submersible pump is suggested for deep aquifer wells (see Table 13).

The following procedure is recommended for collecting a representative sample from a well when using a submersible pump: 1.

Compile well construction data, including well diameter, total depth, and perforated interval, or aquifer interval in an open well.

2.

Measure static water level and estimate well volume.

3.

The pump intake should be placed approximately 5 feet above the open, perforated, or screened aquifer interval.

4.

The discharge rate should be maintained at a moderately low rate to prevent excessive drawdowns in the aquifer and well, as well as minimizing turbulent mixing in the annulus.

5.

At least one well volume should be extracted from the well before sampling.

6.

The parameters most easily monitored in the field are specific conductance, pH, and temperature. These parameters should be measured continuously throughout the pumping period. Continuously monitoring these parameters is particularly important for infrequently sampled monitor wells.

7.

A sample should be collected only after the field parameters have stabilized for a period of time. The data provided in the text indicate that conductivity is the most representative parameter of infusion of aquifer water in the well bore or casing. However, it is suggested that all of the parameters (i.e., pH, temperature, and specific conductance) be utilized to determine representative aquifer water to prevent premature sample collection due to the failure of field apparatus.

8.

The sample should be collected as close to the well head as possible to avoid potential contamination, precipitation of solutes, and the loss of dissolved gases.

In addition to providing consistency with respect to pump placement, field measurements, etc. among the different sampling dates, these recommendations also provide a means for establishing the sampling protocols for each 157

well. This is an important aspect in that the data presented in Section 8 indicate the duration of pumping required for an equilibrated discharge may vary substantially from well to well. Therefore, the individual testing of each well is critical to representative sample collection. In addition, these protocols should be updated periodically for each well, particularly for wells with large open intervals. In addition to the technical aspects, there are some cost considerations that need to be evaluated. Table 13 provides the approximate sampling costs for four different sampling methods and corresponding well design necessary for the sampling tool. The sampling methods evaluated were a fixed submersible pump, portable submersible pump, bailing, and swabbing. For comparison purposes, the costs for each sampling method were developed under a quarterly sampling frequency of 12 Upper and Lower Aquifer wells for a 5-year period. Based on the data presented in Table 13, it is apparent that the bailing method is the best approach from a cost perspective. The portable submersible pump and swabbing methods are very expensive compared with the bailing method and, therefore, are not recommended. Although the fixed submersible pump clearly has some economic trade-offs when compared with bailing, there are some technical advantages to using this approach and the fixed pump should not be ruled out. The data comparing samples collected by bailing with samples collected by pumping for deep aquifer wells indicate that more representative samples are collected via a pump. Therefore, it is recommended that each method be evaluated according to the type of well design and the overall monitoring strategy. It appears that the bailing method works well for the "nearretort" type of well designs (i.e., wells with fine levels of completion), whereas a fixed submersible pump provides better results in wells that are completed over a large interval. Sampling Frequency Proper selection of well sampling frequency is a function of potential pollutant mobility, and when hard data are not available, the selection is often made by trial and error. Shallow groundwater systems commonly display response to seasonal or otherwise cyclic events of recharge and infiltration of dissolved constituents from the surface. Regional pumping patterns can also affect the variability of water quality in both deep and shallow wells. Such variability would necessitate relatively greater sampling frequencies. The aquifers to be monitored for the impacts of abandoned MIS retorts are relatively deep and not subject to great variability from recharge events. Such influence of cyclic events is usually attenuated during slow passage through the aquifer. Hence, a somewhat low sampling frequency is appropriate. Another consideration is the sequence of events leading to abandonment, namely, mine-retort operation, termination of retorting, termination of dewatering, and recovery of aquifer water levels in the mine-retort area. During the operational phase, particularly when dewatering is appreciable, no releases would be anticipated from the M I S retorts. Thus, low-frequency sampling (e.g., annual) would be adequate. If dewatering is via wells (rather than strictly from the mine itself), the dewatering wells (sampled 158

individually) may be an acceptable location for sampling. Any groundwater flow within the retort field during this dewatering phase would be dominated by and directed toward the dewatering wells. Thus, any appreciable groundwater movement in the retort interval would be effectively sampled by these wells. During the time from cessation of dewatering through stabilization of water levels, the groundwater system would be in a state of flux and rapid changes in water quality may occur. During this period, more frequent sampling is recommended. Initially, monthly sampling is appropriate to establish patterns of temporal variability. This frequency can then probably be diminished to semiannual and then perhaps to annual as time trends are established. Several years may pass before these low frequencies are appropriate.

Sample Preservation and Handlinq Delayed receipt of samples at the analytical laboratory and incorrect preservation techniques can significantly adversely affect sample chemistry. To prevent any potential sample modification, the following sample preservation and handling procedures are recommended: Sample volumes, preservatives, and containers should be selected according to the EPA-recommended procedures presented in Methods for Chemical Analyses of Waters and Wastes ( U . S . Environmental Protection Agency, 1979). The samples should be filtered in the field through a 0.45-micron filter before preservation. Data on past water quality trends should be consulted to detect any anomalous data during the sampling effort. Specific conductance, pH, and temperature should be measured in the field at the time of sample withdrawal. This also applies to oxidation-reduction potential and dissolved oxygen determinations. if desired. Accurate field notes should be maintained for future data evaluation. These notes should include: specific times and dates the activities were performed, water levels, source of sample, weather conditions, well completion data, sample collection method, field observations, reason for sampling, field measurements, problems encountered, and the sample collector's identity. The samples should be shipped each day from the field to the analytical laboratory via commercial plane or bus. Both methods are reliable and inexpensive, and provide reasonable assurance against prolonged sample storage. If the samples cannot be shipped and received at the laboratory within 24 hours, on-site analytical facilities should be provided.

159

a The chain of custody for the sample should be recorded and be as limited as possible to prevent excessive sample handling, which can result in shipment and analysis delays. Individuals should be designated both in the field and at the laboratory to maintain adequate quality control with respect to sample handling and analysis activities.

If these procedures are followed, sample handling and preservation techniques should not affect the analytical results. Selection and Preservation of Constituents for Monitorinq Recommended monitoring constituents for general water quality, major inorganics, organics, and trace metals are given below. Sample preservation and handling requirements for these water quality parameters are dictated by the nature of the constituents to be analyzed. For the recommended constituents, the holding times listed below are recommended by U.S. EPA (1974). Bottle requirements (plastic versus glass) are also provided in this reference. Filtering of samples immediately after collection is recommended with addition of chemical preservatives in the field at the time of collection or addition of preservatives to sample bottles prior to initiation of field activities. Preservation techniques include:

Preservative

Maximum holding time

General water quality constituents 7 days

Total dissolved solids (filterable residue)

cool. 4%

Conductance PH

cool, 4oc Determine on site

24 hours 6 hours

Alkalinity

Cool, 4%

24 hours

Major inorganics Calcium, magnesium, potassium, and sodium

Nitric acid to pH < 2

Bicarbonate

Cool, 4%"

24 hours*

Carbonate

cool, 4oc*

24 hours*

Chloride

None required

6 months

7 days (continued)

* Assumed same as alkalinity. 160

Preservative

Maximum holding time

Major inorganics (continued) Nitrate

Cool, 4%

24 hours

Sulfate

cool, 4%

24 hours

Fluoride

cool, 4%

7 days

Ammonia

Cool, 4OC. sulfuric acid to pH < 2

24 hours

Phosphate

Cool. 4%

24 hours

Dissolved organic carbon

Cool, 4OC. sulfuric acid to pH < 2

24 hours

Kjeldahl nitrogen

cool, 4OC, sulfuric acid to pH < 2

24 hours

organics

Trace metals Arsenic

Nitric acid to pH < 2

6 months

Selenium

Nitric acid to pH < 2

6 months

Vanadium

Nitric acid to pH < 2

6 months

Molybdenum

Nitric acid to pH < 2

6 months

Mercury

Nitric acid to pH < 2

38 days

(glass container) The short holding times listed here will be difficult, if not impossible, to accomplish in the -remoteness of the oil shale region unless on-site laboratory facilities are developed. Such an approach is recommended for the following: Conductance PH Alkalinity Carbonate Bicarbonate Chloride

161

Ammonia (electrode method) e Fluoride (electrode method).

Since it may not be feasible to meet the listed holding time requirements for many of the constituents listed (e.g., TDS, nitrate, sulfate, phosphate, DOC, and Kjeldahl nitrogen), it is recommended that testing be initiated so that more suitable holding times for the waters in question can be defined and the nature and significance of errors evaluated. Sample Analysis Recommendations for sample analysis are as follows: 1. Routine monitoring of recommended constituents listed in the preceding discussion of sample preservation and handling 2. More extensive sample collection and analysis (such as unique indicators discussed in Slawson, 1980a, Section 10) should the routine sampling program indicate an impact of MIS retorts on groundwater quality 3.

Use of standard analytical methods.

The constituents listed in the preceding discussion of sample preservation were selected for routine monitoring because high levels are expected should materials leach from MIS retorts. In addition, constituents include those which allow data checks (TDS-conductivity, cation-anion balance, etc.) to be performed as a quality control measure. Should this routine monitoring program indicate an impact of MIS retorts on groundwater quality, more extensive analysis of samples is recommended. This analysis should include the sets of possible unique indicators presented in Slawson, 1980a, Section 10. This recommended list of constituents includes fewer constituents than the analysis sets of presently implemented monitoring programs, such as outlined in Slawson, 1980a, Section 9. This shortened list should allow detection of groundwater quality impacts due to MIS retorts while economizing on analytical needs. Other sets of constituents, such as various organic fractionations and stable isotope ratios, need to be evaluated further, particularly the interpretation of such data with regard to indicating the impact of oil shale byproducts. Standard analytical methods, such as presented by U.S. EPA (1974) or in standard Methods (American Public Health Association, 1976), should be employed. Interpretation of Water Quality Data The purpose of interpreting water quality data is to define quality trends, identify new pollution problems or regions of improvement, and assess the effectiveness of pollution control activities. To ensure the utility of the water resource information collected, data analysis procedures include 162

(1) checks on data validity and (2) methods of presenting the resulting information so it is useful for environmental description or control purposes. Data checking procedures include: 0

Cation-anion balance

0

TDS-conductivity comparison

0

Conductivity-ion comparison (meq/l)

0

Diluted-conductance method.

Data presentation and interpretation are key aspects of monitoring for environmental detection and control. Several methods are available for organization and presentation of water quality data. These include tabulation and graphical tabulation of appropriate water quality criteria or standards, providing a format for screening data, and identifying important sites or pollutant constituents. Presentation of ionic concentration as milligrams per liter or milliequivalents per liter and segmentation of contributing components, such as total and noncarbonate hardness or phenolphthalein and methyl orange alkalinity, are useful techniques for data correlation and evaluation. Further discussion of data analysis procedures is provided in Section 8.

163

SECTION 8 HYDRCGEOLOGIC CHARACTERIZATION METHODS Much descriptive information and data have been published on the geologic and hydrologic characteristics of the oil shale regions of Colorado, Utah, and Wyoming. These studies, however, have been largely regional in scope, leading to a generalized focus on developmental groundwater quality monitoring plans, rather than environmental protection site- and source-specific orientations. The goal of this study has been to develop support information that will provide a procedure for obtaining valid groundwater quality data to provide an evaluation and decision-making framework for design of monitoring programs to protect the environment and water quality at specific development sites. This study is intended to be a planning document that will provide a technical basis and a methodology for the design of groundwater quality monitoring programs for industrial oil shale developers and the several governmental agen-. cies concerned with environmental planning and protection. The Piceance Creek Basin of Colorado, where the richest oil shale deposits lie and where it is expected that most future leasing and industrial development will occur, is discussed in this study. The general procedures and framework for environmentally sound hydrogeologic characterization, however, are valid for other oil shale regions. Most of the hydrogeologic characterization methods described in this study will be employed during the initial exploration/resource evaluation phase of industrial development. Some methods will be employed during the mine development phase, while others, such as sample collection for ongoing water quality monitoring, will be conducted over the entire life of the project, including the postclosure period.

To plan, design, and conduct a hydrogeologic characterization program as a basis for designing a groundwater monitoring strategy, a general understanding of basin hydrogeology is necessary. The following subsections describe the Piceance Basin hydrogeology. GENERAL BASIN HYDROGEOLOGY The area contains three important aquifer systems: the Lower Aquifer, the Upper Aquifer, and the alluvial aquifers. The Lower Aquifer occurs in the Parachute Creek Member below the Mahogany Zone, and the Upper Aquifer is above the Mahogany Zone (see Figure 11). The alluvial aquifer system occurs in the stream valley bottoms.

164

9,000 NORTH

SOUTH

8.000

-

-

4,000 -

I

3,000-

2

0

0

2

4

4

I

'.--,'

Wasatch Formation

I

GMILES

GKILOMETRES

V E R T I C A L E X A G G E R A T I O N X 21 D A T U M IS M E A N SEA L E V E L

Figure 11.

Geologic section through Piceance Basin along north-south line between Tracts C-a and C-b (Weeks et al., 1974).

Lower Aquifer The Lower Aquifer is bounded generally on the top by the Mahogany Zone and on the bottom by the shales of the Garden Gulch Member. Porosity is mostly secondary, resulting from fracturing and jointing of the marlstone and oil shale of the lower Parachute Creek Member. Porosity also results from the solution of the evaporite minerals in the saline section at the base of the Parachute Creek Member. Removal of these soluble minerals by groundwater has created a zone of high permeability (known as the leached zone) at the top of the saline section. The saline section below the leached zone still contains its original salts. Because of the high electrical resistivity of the salts, which characterizes this zone on geophysical logs, it is called the "high resistivity" (?€I?) zone. Inasmuch as both the high-kerogen-content oil shales and the saline minerals of the NR zone are rather ductile, the I-IR zone has experienced little fracturing and has a low permeability. Because of these characteristics, in the center of the basin the HR zone forms the lower confining stratum. The fracture-solution of this confined aquifer results in heterogeneous hydraulic characteristics. In general, transmissivity increases with the soluble mineral content from the margins to the center of the basin. The degree of fracturing, resulting from deformation, increases toward the structural axis of the basin, and northwest along the axis. Weeks et al. (1974) estimated that the average transmissivity varies from 130 ft2/day near the southeastern corner of the basin, to 670 ft2/day in the area between Yellow and Piceance Creeks. They estimated the storage coefficient to be on the order of and the specific yield to be 10-l. We11 yields of 200 to 400 gallons per minute (gpm) are typical. Upper Aquifer The Upper Aquifer is separated from the Lower Aquifer by the Mahogany Zone. Although no interaquifer response was observed during vertical permeability tests, Weeks et al. (1974) have concluded that considerable movement of water between the aquifers does occur. They base this conclusion on the fact that the water level in the two aquifers rarely differs by more than 100 feet over the 1,20O-~foot head drop of the two aquifers across the basin. The Upper Aquifer zone is composed of the Parachute Creek Member above the Mahogany Zone and the Uinta Formation. The lower portion of the Uinta Formation is divided by numerous tongues of the Green River Formation. Although the primary porosity of the sandstones is greater than that of the marlstones, the sandstone porosity has been decreased by precipitates from groundwater, while fracturing has increased the permeability of the marlstones, which are more susceptible to fracturing than the Uinta sandstones. The sandstones, therefore, tend to form confining layers for the marlstone aquifers. The Upper Aquifer is generally confined but is unconfined in many locations, depending on the relationship of the water level and the lithology. Strata containing nahcolite (NaHC03) solution cavities, which occur in the southern part of the basin, should form transmissive layers.

166

The transmissivity (T) varies with saturated thickness, degree of fracturing, degree of solution, and location of wells with regard to fractures. Calculated T values range from 8 to 1,000 ft2/day. The saturated thickness, degree of solution, and transmissivity increase toward the basin center. Weeks et al. (1974) considered representative values to be 70 ft2/day around the rim, 130 ft2/day in the area around the center, and 270 ft2/day in the center. Porosity ranges from 10 percent to 1 percent. It is highest in the center, where solution cavities are present, and least around the edges. The calculated storage coefficient is on the order of indicating confined conditions. The total storage is probably somewhat less than that in the Lower Aquifer due to lower saturated thickness and porosity. Since the difference in water level between the two aquifers is rarely more than 100 feet, the potentiometric map of either the Upper or Lower Aquifer should not differ greatly. The potentiometric configuration is determined by the transmissivity distribution and the recharge and discharge characteristics. Recharge occurs around the rim of the basin, the gradual infiltration of snowmelt in the spring probably being the major source. The downward potential difference between the two aquifers around the rim of the basin indicates that most of the recharge is to the Upper Aquifer and that the Lower Aquifer is recharged by leakage from the Upper Aquifer through the Mahogany Zone. The water migrates toward the center of the basin, where it discharges to Piceance and Yellow Creeks at some locations. Here, the head of the Lower Aquifer is higher than the Upper, and Lower Aquifer discharge is through the Upper Aquifer.

Alluvia: Aquifers Alluvial sediments line most of the major stream valleys and are usually saturated at their base. They are thickest along Piceance and Yellow Creeks. Near the confluence with the White River, there may be 100 feet or more saturated alluvium underlying Piceance Creek. All of these aquifers follow the slope of their stream valleys. They are recharged in their upper reaches from streams and from snowmelt. In the lower sections, they are recharged from the deep aquifers and, in turn, discharge to the streams, maintaining the base flow* The hydraulic conductivity of these unconsolidated alluvial deposits is high, reflected in transmissivities of 2,700 to 20,000 ft2/day. Their unconsolidated nature also results in high specific yields, on the order of 20 percent. In spite of these favorable aquifer parameters, the alluvial aquifers are not desirable areas for large-scale water development because of the small total storage and boundary effects created by the aquifer morphology. In addition, withdrawal from the aquifers is sure to affect the stream base flow adversely, and with it agricultural interests, wildlife habitat, and existing water rights allocations.

167

GEOPHYSICAL METHODS Phase I study efforts are documented in Slawson (1980b) and summarize geophysical methods that may be appropriate in defining the hydrogeologic characteristics in oil shale environments. This comprehensive review includes a wide range of geophysical well-logging techniques available through major logging companies. The utility of these geophysical tools for defining hydraulic properties in typical oil shale stratigraphy was not addressed in the Phase I study. This appraisal was conducted as part of the following Phase I1 efforts. Suites of geophysical logs run during the post-leasing exploration stud-ies on the Federal oil shale tracts in the Piceance Basin have been reviewed. Log suites for oil shale Tracts C-a and C-b are given in Tables 14 and 15, respectively. These tables show that while similar suites of logs are run on both of the Colorado tracts, specific logs are emphasized. For example, the engineering production (spinner) logs perform well and are commonly run on Tract C-a but seldom, if ever, on Tract C-b. Sonic logs are used extensively on Tract C-b but only infrequently used on Tract C-a, where three-dimensional velocity logs provide much of the same acoustic information. Use of alternate logging tools reflects, in part, individual log response, the information desired from their interpretation, the preference of the geophysical program coordinator, the logging service company selected to perform the work, and specific data-gathering requirements externally imposed on the exploration effort. Therefore, the most commonly run logs indicated in Tables 14 and 15 may not reflect the most appropriate suite for defining the hydrogeology in any one oil shale region. Exploration studies on the Federal tracts are primarily interested in resource characterization. Defining the hydrogeologic framework, while important to the mine design, is initially of secondary importance. In the Phase I1 studies, Tempo reevaluated the geophysical exploration data with definition of the hydrogeologic framework as a primary focus. Following a review of these geophysical data and discussions with the major well-logging companies, a suite of logs has been selected to evaluate the hydrologic characteristics of test holes in an oil shale environment. This does not imply that a single suite of logs would be best suited for all boreholes. Unique borehole conditions must be dealt with on a site-specific basis. However, it is instructive to select a suite of geophysical logs and evaluate their effectiveness in defining the hydrogeologic framework in an oil shale environment. The following suite of logs has been selected for this purpose: 0

Temperature log

0

3-D velocity log

0

Caliper log

0

sonic/acoustic log

0

Gamma-ray log

0

Density l o g

0

spinner log

0

Electric log

0

Radioactive tracer log

0

Seisviewer log.

168

TABLE 14. GEOPHYSICAL DATA COLLECTION, TRACT C-a Well designations Gulf-Standard core holes Geophysical logs

1 2-3 4-5

6 '7

x x

x x x x x x x x x

8 9

10

Monitor holes

11 12 13

14 15

1

2

3

4

x

x

x

x

x

x

x

x x x

x x x

x x x

x x x

x x x

x x x

x x x

x

x x

x x

x

x

x

x

x

x

x

x

x

x

x

Schlumberger Dual Induction Laterolog Compensated Neutron Formation Density Borehole Compensated Sonic-Gamma Ray

x x X

Engineered Production (Spinner-Temp)

X

X

Continuous Directional P

m

X

Bi rdwe11

\D

Electric Gamma-Ray Density Neutron Three-Dimensional Velocity

X

Spinner Caliper (only)

X

Nuclear (Gamma-Ray-Neutron) Gamma-Ray Density Continuous Directional Inclinometer

x x

x

x X

x x x

x x x

x x x

x x x

x x

x

x

x

X X

X

X

x x x

X

x x X

Seisviewer Density

x

X

x x

Temperature

x

X

X X

TABLE 15.

GEOPHYSICAL DATA COLLECTION, TRACT C-b Well Designation

Geophysical logs

AT-1

AT-la

AT-lb

AT-ld

SG-l

Borehole, Compensated Sonic

X

X

X

Laterolog

X

X

X

Formation Density

X

X

x

X

X

X

X

SB-la

SB-8

SB-9

x

x x x

x x x

x

x

SG-10

SG-11

SG-17

SG-18

SG-19

SG-20

SG-21

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

Cb-1

Cb-2

Cb-3

Schlumberger

Nuclear Formation Density Temperature

x

x

X

x

X

X

Birdwell Three-Dimensional Velocity

X

X

Electric

X

X

Dens it y

X

X

Nuclear

X

X

Ca 1 ipe r

X

X

X

X

-Temperature

x

x

x

A discussion of each of these logs has been developed for its specific use in defining hydraulic parameters of interest. As with all geophysical studies, conjunctive use of the individual logs is important in improving the accuracy of the interpretation. In addition, alternative data sources, e.g., water production tests and computer analogs that complement the geophysical record, are used wherever possible.

In compiling the information on current logging methods and sonde instrumentation, the logs from four major logging service companies were evaluated: Birdwell Division of Seismography Service Corporation, Schlumberger Well Services, Dresser Atlas, Inc., and Welex, A Halliburton Company. Data developed during the study was drawn from interviews with logging company personnel, information sheets and catalogs provided by the companies, and a review of logs run in wells on Federal Oil Shale Tracts C-a and C-b. Cost data for logging services was taken from the most current Rocky Mountain price schedules for the respective companies. Current prices may vary from those quoted in the text. Temperature Loq Principle of Operation-Temperature logs were run on nearly every test hole during exploration efforts on the Federal oil shale tracts. Temperature logs are made by passing a temperature electrode down a cased or an uncased hole. Temperature logs use a sonde with a resistance-type thermocouple or a wire calibrated to correlate resistance variations with temperature variations. In the former, a junction of two dissimilar metallic conductors is housed in a protective cage. An electromotive force is inducted at the junction when the conductors are maintained at different temperatures. This force is measured and recorded on strip charts or a magnetic tape at the surface. In the latter, the sonde uses a length of platinum wire that rapidly assumes the temperature of the borehole fluid. Variations in the temperature of the wire produce changes in resistance that are detected at a bridge circuit in the sonde. These signals are transmitted.to a recording device at the surface. The diameter of temperature sondes range from 1 to 3-5/8 inches and can be run down boreholes 2 to 20 inches in diameter. The temperature tool is used in a wide variety of borehole environments including water, mud, oil, or air. Two passes of the temperature sonde should be recorded for each test hole studied. Both runs are made down the borehole. The first measurement should be made immediately after pulling the drill string and before natural circulation becomes established. The second run should be made at the end of the logging program. If the drilling fluids have been well circulated, the first run will provide an indication of the natural geothermal gradient, which can be used as a reference to compare anomalies from the second pass. Temperature anomalies show up at varying times after circulation has ceased, depending on the thermal conductivity of the formation penetrated, the flow rates within the well bore, and the diameter of the well.

171

On the oil shale tracts, temperature logs provide indications of fluid entry and exit from the well bore. In subsequent hydraulic studies they can be used to locate formation waters leaking through casing, which could create a contamination problem for water quality evaluations. During retorting, temperature logs can be used to detect and monitor excursion events. Figure 12 is a computer plot of a typical temperature log from Federal Oil Shale Tract C-a. The log shows the effect of cooler formation water entering the well bore through small permeable zones between 580- and 850-foot depths. This water flows down the borehole, depressing the natural geothermal gradient to a depth of 1,420 feet. Below 1,420 feet, the sharp increase in fluid temperature suggests that the cooler waters have entered a "thief zone" and are no longer depressing the temperature of the borehole fluid. Cost Data-Costs for running temperature logs are computed based on per foot depth and operation charges. Minimum costs per test hole are based on 2,000 feet of logged hole. Current price schedules for the four major logging service companies are given in Table 1 6 . Evaluation--Temperature logs are useful in providing indications of fluid movement in well bores and are essential in establishing baseline temperature data. Such inforrLiation is utilized in subsequent pollutant migration evaluations or geochemical studies. Temperature anomalies found on Tract C-a are primarily the result of well developed flow patterns from the Upper to the Lower Aquifer systems. These conditions are favorable for deducing hydraulic data from temperature logs. Tract C - b wells show l e s s anomalous conditions, with many plots reflecting the natural geothermal gradient of the area. These logs are less instructive. Ca 1iperLog Principle of OperationCaliper logs provide a continuous record of the variation in the diameter of the uncased drill hole. Several sonde configurations are available, e.g., two-, three-, four-, and six-arm devices. The average diameter of the hole is described by the tips of the arms of the device, which, when extended, contact the sides of the drill hole. The independent action of each arm, when grouped into pairs of opposed arms spaced 120 degrees apart, provides a direct measurement of up to three specific borehole diameters. These can be recorded simultaneously on a strip chart, with or without the calculated average hole diameter. The caliper log is run by lowering the sonde to the bottom of the test section, actuating the arms, and pulling the tool out of the hole. It is commonly run with a temperature device or other logging tools.

172

------4040-

Figure Figure 12. 12.

Computer Computer plot plot of of aa typical typical temperature temperature log log from from Tract Tract C-a. C-a.

TABLE 16.

COST SCHEDULE FOR TEMPERATURE LOGS (dollars)

Company/Service ~

Depth

Operation

a per foot minimum

per foot minimum

Total a a minimum

~~

b B irdwe11 Temperature

0.22

440.00

0.19

380.00

820.00

Differential temperature

0.22

440.00

0.19

380.00

820.00

0.26

520.00

0.21

420.00

940-110

0.28

560.00

___

750.00

1,310.00

0.25

500 - 0 0

0.20

400.00

900.00

C

Schlumberger

High resolution temperature

d Dresser Atlas Differential temperature e Welex Precision temperature log Notes:

a

All the service companies have a 2,000-foot minimum.

bBirdwell Rocky Mountain Price Schedule, June 1980. C

Schlumberger Rocky Mountain Price Schedule, October 1979.

dDresser Atlas Rocky Mountain Price Schedule, July 1980. e Welex Rocky Mountain Price Schedule, January 1980. Caliper logs are primarily used to determine the volume of the drill hole and thus the annular space between the casing and the well. They are useful in identifying and permitting the correlation of nonround boreholes from well to well. In hydraulic testing, caliper logs are useful in the selection of competent beds required for setting packers. In general, determination of accurate borehole diameters is essential for quantitative interpretation of production engineering (spinner), electric, acoustic, density, and radiation logs. In oil shale stratigraphy, they are useful in locating soft, friable, or fractured zones, which are associated with porous and permeable beds. The caliper sonde ranges in diameter from 1-5/8 to 3-5/8 inches for the three- and the six-arm tool, respectively. The smaller tool can be operated in a 3- to 30-inch-diameter borehole, while the larger tool requires a minimum hole diameter of 6 inches. They operate equally well in air-, mud-, oil-, and water-filled holes.

174

Cost DataService company costs for running the caliper log is computed based on a per foot depth and operation charge. Minimum charges, based on 2,000 feet of logged hole, are given in Table 17. TABLE 17.

COST SCHEDULE FOR CALIPER LOGS (dollars) Depth

Operat ion minimuma

Total minimuma

0.19

380.00

820.00

440.00

0.17

340.00

780.00

0.26

520.00

0.21

420.00

940- 0 0

0.26

520.00

0.21

420.00

940.00

0.20

400.00

0.18

360.00

760.00

per foot

minimuma

caliper (3-arm)

0.22

440.00

Caliper (6-arm)

0.22

Company/service b Birdwe 11

per foot

C

Schlumberger

caliper (all) d Dresser Atlas

caliper (4-arm) e We lex Caliper (4-arm)

Notes: a All service companies have a 2,000-foot minimum. b Birdwell Rocky Mountain Price Schedule, June 1980. C

Schlumberger Rocky Mountain Price Schedule, October 1979.

dDresser Atlas Rocky Mountain Price Schedule, July 1980. e Welex Rocky Mountain Price Schedule, January 1980. Evaluation-In the dense, tight, oil-shale stratigraphy, fracture patterns control the secondary porosity and permeability within the formation. These fractured areas lead to zones of weakness in the borehole that may be subject to caving or raveling. Caliper logs are designed to detect these out-of-gage portions of the drill hole and therefore provide indirect information on porosity and permeability in oil shale environments. To evaluate this relationship, pump tests and spinner logs were compared to caliper logs. Below the static water level in the Federal oil shale tract wells, permeable zones correspond well with borehole enlargement due to caving (see Figure 14, page 185); i.e, lower permeabilities were found throughout in-gage sections of the holes, while 175

large washouts, in general, corresponded to zones of higher permeability. A l though the comparative evaluation is only qualitative, caliper logs are useful in directing hydraulic test programs to potential zones of permeability for further injection or production testing. Gamma-Ray Log Principle of Operation-Gamma--raylogs measure emissions from natural radioactive materials found in all rocks. When the gamma rays emitted from the formation penetrate the sonde detector, usually a scintillometer, an electrical pulse is produced and transmitted to the surface recorder through electrical cables. The gamma-ray log is thus a curve relating depth to the intensity of natural radiation. Because clays and shales are considerably more radioactive than carbonates, i.e., limestone or dolomite, and sandstone, this geophysical tool is especially useful in "fingerprinting" lithologic sequences that are correlatable across well fields. The gamma-ray sonde measures 1-518, 2-314, and 3-518 inches in diameter, depending on the company and tool selected, and can be used in a 2- to 15inch-diameter borehole. The gamma-ray tool operates in all test hole environments and is effective in cased and uncased holes. In cased holes, it is combined with a casing collar locator for depth control while measuring complementary parameters and providing information on the cased lithology. In uncased holes, it can be combined with temperature, density, caliper, and other types of neutron logs. Cost Data-Service company costs for gamma--ray logging are divided into depth and operation charges with minimum fixed prices per hole. Price schedules for the four major logging companies are given in Table 18. Evaluation-The gamma-ray log is run separately or in combination with other logging tools on nearly every test hole on the Federal oil shale tracts. It is primarily used for lithologic correlation between tract wells and for depth control. Detailed core analysis for tract wells provides a better source for lithologic information, however, and supersedes the data from gamma-ray logs. The shale correction factor determined from the gamma-ray log is the key parameter in the petroleum industry but is not useful to the oil shale industry. Spinner Loq Principle of Operation--The spinner, or engineering production, log measures vertical flow in the borehole. The sonde consists of a propeller-type blade mounted to rotate about a vertical axis. Rotation of the blade is measured in counts per minute as a magnetic coupling passes a fixed reference point on the shaft, sending an 176

TABLE 18. COST SCHEDULE FOR GAMMA-RAY LOGS (dollars) Oper ation

Depth Company/Service b Birdwell SchlumbergerL d Dresser Atlas e Welex

per foot

a minimum

per foot

a minimum

Total a minimum

0.22

440.00

0.19

380.00

820.00

0.26

520.00

0.21

420- 0 0

940.00

0.26

520.00

0.22

440.00

960.00

0.20

400.00

0.18

360.00

760.00

Notes: a All service companies have a 2,000-foot minimum. b13irdwell Rocky Mountain Price Schedule, June 1980. C

Schlumberger Rocky Mountain Price Schedule, October 1979.

dDresser Atlas Rocky Mountain Price Schedule, July 1980. e - - Welex Rocky Mountain Price Schedule, January 1980. electrical pulse to a surface recording station. Counts per minute are converted to flow past the sonde based on hole diameter, blade size, configuration etc. Measurements can be recorded with the sonde in a fixed position or while it is being lowered into or pulled out of the borehole. When recordings are made in the fixed position, the vertical flow rate in the hole must be sufficient to overcome the mechanical friction of the tool. This minimum flow rate will vary depending on the configuration and general condition of the sonde, the size of the blade, and the diameter and degree to which the hole is in gage. For example, experience has shown that a sonde with a 4-inch diameter blade inserted in a 5-inch hole requires a flow rate of approximately 5 ft/min t o overcome mechanical friction, and give an accurate measurement in a fixed position. To minimize the effect of friction and measure small flow rates, the sonde is moved up and down the well at a constant rate. Unlike temperature, caliper, or gamma-ray logs discussed earlier, the spinner log is a qualitative rather than a quantitative tool, requiring careful calibration for each test hole. Calibration charts can be developed by plotting counts per minute (cpm) versus logging speed. Figure 13 shows a calibration plot for a hypothetical 5-inch-diameter hole. Data for construction of the plot were gathered as follows: gaged section of the borehole is selected, based on the caliper log

0 A

0

Preliminary up- and down-hole spinner measurements are made to ensure that there is no vertical flow in the test section

177

0

Three or more passes up and down the test section are made at varied logging speeds and the cpm readings recorded for each pass Counts per minute versus logging speed plot is constructed as shown in Figure 13.

0

10

20

30

40

50

60

70

80

90

100

110

LOGGING SPEED ( f t h i n )

Figure 13.

Spinner log calibration plot.

Calibration plots can also be made for specific out-of-gage borehole conditions if significant fluid production is suspected from a given stratigraphic horizon. In this case, a static test section with similar borehole characteristics can be used for construction of the calibration plot. In general, sections with high rugosity produce turbulent flow in the well bore and are extremely difficult to accurately calibrate. Following construction of the calibration plot(s), a single run of the spinner tool should be sufficient to determine vertical flow velocity in the well. However, if the sonde is moved in the same direction and at approximately the same rate as the borehole, fluid mechanical friction of the tool will not be overcome and inaccurate flow measurements will result. This can be overcome by recording flow rates while moving the tool both up and down the hole at a constant rate. Comparison of the two velocity versus depth logs would show the velocity and direction of fluid movement more clearly. Cost Data-costs for running a spinner survey are calculated based on the depth, operation expenses, and the number of passes that are made up and down the hole. These costs are given in Table 19. 178

TABLE 19.

COST SCHEDULE FOR SPINNER SURVEYS (dollars) Depth

Company/Service

per foot

a minimum

Operation per foot

a minimum

Total minimuma

b Birdwe11 C

Spinner survey

d Schlumberger e continuous flowmeter Second pass (in combination)

f Dresser Atlas Spinner Flolog Additional runs

350.00

790.00

- ._

740.00

- .-

620.00

1,280.00 1,060.00

560.00

- ._

750.00

1,310.00

0.19

380.00

-

550.00

930.00

0.20

400.00

0.20

400.00

800.00

0.22

440.00

-.

0.27 0.22

540.00 440.00

0.28

._

.-

welexg h spinner Notes: a All service companies have a 2,000-foot minimum. b Birdwell Rocky Mountain Price Schedule, June 1980. C

Includes one recorded run down and one recorded run up. For additional recordings at different logging speeds, add $0.07/ft, $105.00 minimum.

dSchlumberger Rocky Mountain Price Schedule , October 1979. e If more than one descent is made into a well with the same tool, each descent is considered a separate service and charged at the single service rate. fDresser Atlas Rocky Mountain Price Schedule, July 1980. 'Welex

Rocky Mountain Price Schedule, January 1980

hAvailable in limited areas. Evaluation-Semiquantitative information can be developed from spinner surveys on a site-specific basis when calibration plots are carefully constructed. However, these data are dependent on the hydraulic head relationship and therefore on the dynamic flow characteristics of the permeable beds penetrated and interconnected by the well bore. For example, quantitative flow data can be derived from spinner logs run in boreholes that intercept two permeable zones with sufficiently different hydraulic heads to allow flow from one zone to 179

another. This condition exists on Tract C-a, where water flows in response to potential differences from the upper to the lower permeable zones. The flow measured, however, does not necessarily reflect the true ability of an aquifer to produce or accept fluid from the borehole, but rather provides information on the existing flow system and provides lower limits of permeability and water production. Likewise, if two highly permeable beds are interconnected by a well and have nearly equal hydrostatic heads, the spinner survey provides little information on the aquifer hydraulics since no flow would occur in the well. This is perhaps one reason why spinner surveys are not as useful nor as commonly run on Tract C-b wells as on Tract C-a wells. Radioactive Tracer Loq Principle of Operation-The radioactive tracer sonde consists of an ejector that extrudes a short-lived radioactive source (1131, 1192) into the borehole and one or two detecting elements. If a single-element sonde is used in logging, the radioactive source is emitted and the detecting element is moved through the source to determine its location in the borehole. After a short period of time, the detecting element is again moved up or down the hole to locate the source, and from the time-distance relationship the flow rate in the well can be calculated. With two detecting elements at fixed distances on the sonde, the source material is ejected and detected at the same time, and the tool does not have to be moved, thus reducing dispersion of the source and increasing the peakedness of the log trace, hence providing greater accuracy in locating the radioactive material in the well. With this type of tool, the source ejector can be located at either the top or bottom of the sonde to measure flow up or down the borehole. The borehole instrument comes in 1- and 1-5/8-inch diameters and can be run in 1-1/2- to 12-inch-diameter wells. It will operate in all fluid-filled holes. Cost Data-Service charges for running radioactive tracer logs are given in Table 20. These include standard per foot and operating costs, as well as radioactive material ejector fees. Evaluation-The accuracy of the radioactive tracer log depends on the peakedness of the source-detection-versus-depth plot. This is primarily a function of knowing where the source is in the borehole. While tracer logs do ,not have the mechanical friction problems inherent in the spinner tool, extremely low borehole velocities provide time for diffusion of the source material and spread of the radiation-versus-depth plot, thereby limiting the accuracy of the measurements. Also, turbulence associated with higher flow rates tends to disperse the source material, especially in permeable areas where rugosity is often a significant characteristic of the borehole.

180

TABLE 20.

COST SCHEDULE FOR RADIOACTlVE TKACER LOGS (dollars)

Company/Service b Birdwe11 C

Radioactive tracer profile

Depth

Ope rat ion

a per foot minimum

a per foot minimum

Total minimuma

0.22

440.00

0.19

380.00

820.00

e,f Radioactive tracer

0.27

540.00

_ _-

740.00

1,280.00

Second run

0.22

440.00

_-_

520.00

1,080.00

Dresser Atlas9 h Tracelog

0.28

560.00

750.00

1,310.00

0.19

380.00

550.00

930.00

0.20

400.00

280.00

680.00

d Schlumberger

Additional runs Welex

i

Radioactive tracerj

0.14

Notes: a All service companies have a 2,000-foot minimum. bBirdwell Rocky Mountain Price schedule, June 1980. Radioactive material ejector charge:

$150.00 for the first ten stations and

$0.11 per station thereafter.

d Schlumberger Rocky Mountain Price Schedule, October 1979. e With radioactive tracer logging, an added charge of $112.00 per ejection of radioactive material is applied when a down-hole ejector tool is used.

f

Radioactive material is charged at cost plus 10 percent handling charge.

'Dresser

Atlas Rocky Mountain Price Schedule, July 1980.

hTracer dump bailers $130.00 per run. iWelex Rocky Mountain Price Schedule, January 1980. 'Radioactive material not included in price. A significant disadvantage of the tracer log is the inherent danger in handling and the consequence of losing the radioactive source material (thereby contaminating the well). This is especially acute when working with shallow-water supply wells or in areas where groundwater may be transmitted directly into underground mine works. Attempts have been made to minimize this problem by using radioactive substances with a relatively short half-life (I131 half-life = 8 days). In general, the potential danger versus the

181

qualitative or semiquantitative information gained does not warrant the use of radioactive tracer logs in groundwater wells. Laboratory or supplier preparation of the source material requires time, which can result in delays in the field. If this method is used, careful planning must be made to coordinate drilling schedules and running other logs. Three-Dimensional Velocity Loq Principle of Operation-Birdwell's single-receiver velocity sonde provides a record of the complete acoustic wave train as propagated along the fluid-borehole boundary of the well. The total wave train is displayed as variable density, black lines (legs) on a strip chart and includes the compressional, shear, and boundary waves. The sonde contains a magnetostrictive-type transmitting transducer that generates pulses at a rate of 20 per minute. The ceramic receiving transducer (a barium titanate crystal) converts the signals transmitted along the borehole to electrical impulses that are transmitted to a receiver at the surface and recorded. The three-dimensional (3-D) velocity l o g is used in fracture studies, porosity determinations, cement bond evaluations, and in the study of dynamically determined elastic properties of rocks. In the latter, compressional and shear waves are used in the calculation of elastic moduli (shear, bulk, and Young's) and in determining Poisson's ratio. Elastic properties are use-ful in oil shale mine design and are also used extensively in other types of construction projects. The sonde diameter varies from 1-3/4 to 3-3/4 inches and can be utilized in test holes from 3 to 18 inches in diameter. The tool requires a fluid formation boundary to transmit the acoustic wave train: water, mud, or oil mediums are acceptable. Cost Dataservice company costs for running 3-D velocity logs, or equivalent, are given in Table 21. Welex's fracture-finder microseismogram log provides formation information similar to Birdwell's 3-D velocity log. The cement bond/ variable density log is Schlumberger's closest equivalent to the 3-D velocity log, but is specialized to determine the effectiveness of the cement seal in the casing-formation annulus and does not give comparable information. Dresser Atlas did not have a 3-.D velocity log listed in its wireline service catalog. Evaluation--The 3-D velocity log provides valuable information on the elastic properties of rocks useful in mine design, and it is one of the few down-hole geophysical tools that provides a complete record of the acoustic wave train. However, in hydrology studies where porosity determinations are of primary importance, shear and boundary waves are not required. Variation in the 182

TABLE 21. COST SCHEDULE FOR 3-D VELOCITY LOGS (dollars) Operat ion

Depth Company/Service b Birdwell 3-D velocity

per foot

minimuma

Total a minimum

580.00

0.25

500.00

1,080.00

0.26

520.00

0.25

500.00

1,020.00

0.27

540.00

0.23

460.00

1 ,000.00

per foot

minimum

0.29

a

C

Schlumberger Cement bond/ variable density log d We lex Fracture-finder Microseismogram log Notes:

a All service companies have a 2,000-foot minimum. bBirdwell Rocky Mountain Price Schedule, June 1980. C

Schlumberger Rocky Mountain Price Schedule, October 1979. e Welex Rocky Mountain Price Schedule, January 1980. interval transit time (At) of the compressional wave along the fluid-formation boundary provides the At value needed for porosity calculations. This travel time is a function of the rock and fluid properties in the borehole as well as the distance between the detectors. While the detector spacing in the sonde is fixed, the overall travel distance depends on the rugosity of the well bore. Smooth in-gage sections produce the shortest travel distances, while washouts or out-of-gage sections produce longer travel distances for a fixed set of receivers. The 3-D velocity log is not designed to compensate for this variation in travel distance and thus will introduce error into the At values and hence the porosity measurements calculated from these data. Therefore, in hydrology studies where porosity determinations are of primary interest, specially designed, compensated acoustic logs are recommended. This type of log is discussed below. acoustic Loq Principle of Operation-The acoustic, or sonic, sonde consists of two sections. The upper section houses the electronic equipment necessary to control and activate the transmitting transducers that convert electrical impulses to acoustic pulses. Pressure waves created by the acoustic pulses radiate out from the sonde, are refracted through the formation, and return to the borehole instrument through the drilling fluid. The lower section contains both transmitting and 183

receiving transducer component in a rigid, slotted metal sleeve. The sleeve is specially designed to separate acoustic energy transmitted through the instrument from signals received from the formation. For a single compensated sampling point, At is computed through selectively combined time signals from the receiving transducer array. Changes in borehole diameter and misalignment of the instrument axis have signification implications on the accuracy of the acoustic sonde. For limited variations in borehole diameter or instrument misalignment, multiple transducer arrays have been developed to ensure accurate measurement recordings. This is accomplished through a surface panel capable of combining and averaging signals from two transducer arrays, inverted with respect to one another, for the same borehole interval. The diameter of the sonde varies from 3-3/8 to 3-3/4 inches, depending on the tool selected. It is run in fluid-filled, open holes ranging from 6 to 18 inches in diameter at logging speeds of 30 to 80 ft/min. Measurement of interval transit time is the primary purpose of the compensated acoustic log. Interval transit time may be used to determine porosity using the following equation: At - Atma

9 = where :

Atf - Atma

9

(5)

is porosity (dimensionless) At is interval transit time (usec/ft)

Atrna is matrix interval transit time (psec/ft)

Af is fluid interval transit time (psec/ft). Service companies provide automatically computed and recorded porosity values given the desired fixed matrix and fluid velocities using the above relationship. The utility of the porosity measurements for hydrology studies and their correlation to permeable zones has been evaluated for a test section located on Federal Oil Shale Tract C-b. The test zone includes 800 feet of oil shale stratigraphy penetrated by Tract C-b Well 32x-12 (see Figure 14). Water production from pump and spinner tests and borehole enlargements from caliper logs are presented with a porosity analog developed from Equation 5 . The test zone was selected for its geophysical logs, varied lithology, and water production data. Stratigraphic features included in the section are as follows: 0

220 feet at the base of the Uinta Formation (2800 to 1,020 feet)

0

Top of Parachute Creek (+_1,020 feet)

0

Four Senators Zone (21,100 feet) 184

240 .O

loo

[

E>

I

I-: t

180.0

AQUIFER PRODUCTION ZONES FROM PUMP/SPINNER TESTS (gpm) BOR EHOL E EN L A RG EM ENT IN EXCESS OF 4 inches (FROM CALIPER LOG)

74 .O

II il

38.0

I I

[

I

800

!BED2

900

BED3

1,000

BED 4

1,100

BEE

1,200

cI

/

I

'

I:

BED 8

1,300

-_

.... BED 9

10

1.400

DEPTH [bet)

Figure 14.

68.0

64.0

50.0

L I L I

BED1

220.o 7-

Acoustic porosity analog and aquifer production zones for Tract C-b Well 32x-12.

L

,

11

1,500

B E D 12

1,600

0

A-groove (f1,310 feet)

e Mahogany Zone (f1,400 feet) 0

B-groove (+1,500 feet)

0

Top part of R-6 Zone (t1,520 to 1,600 feet).

The porosity analog was developed from interval transit times taken from a Birdwell acoustic/borehole compensated log. The matrix interval transit time, taken from a graph of oil shale yield versus time developed by Birdwell, was set at 59 psec/ft. Varying this parameter shifted the porosity axis (yaxis of the analog plot) but did not affect the relative magnitude of the porosity values. As can be seen in Equation 5, decreasing the matrix interval transit time will increase the porosity values when the other variables are held constant. The fluid interval transit time was set at 198 psec/ft, an average value for fluids in oil shale test holes (oral communication with Mr. Asher Atkinson, Rocky Mountain Regional Manager for Birdwell Division). Increasing this parameter increases the denominator of the porosity equation, thus decreasing porosity values. Again, the shift in the axis does not affect the relative magnitude of the calculated porosity values. Porosity values for the upper part of the test hole (between 400 and 800 feet; not shown on Figure 14) are uniform, averaging about 32 percent void ratio. These values appear to be high and are probably the result of a relatively low average Atma value (held constant in Equation 5) for the Uinta Formation and the uniform, but oversized, borehole diameter. Below a depth of 880 feet, the caliper log shows the hole returning to gage (10-314 inches) and more variation in the porosity is observed. The prominent spike between Beds 1 and 2 is a washout of probable high porosity that was too large for accurate measurements, even with the averaging of signals from the transducer arrays. Narrower washout features (shown at the base of the y-axis) are for the most part eliminated from the porosity analog through transit-time signal averaging. Some of the features may represent solution cavities that cause high rugosity, which, with a continuous matrix framework, will transmit the acoustic energy as if through solid rock. The correlation between permeable production zones and the porosity analog is complex. High water production from Bed 9 (between 1,393 and 1,450 feet) corresponds to a relatively wide band of high porosity values. The apparent porosity appears to be a combination of the rich oil shale beds (Mahogany Zone) and true secondary porosity created by solution breccia zones and fracture breccia, or "rubble" beds. The rich grades of oil shale tend to increase At, thus increasing the calculated porosity when Atma remains constant. The three prominent porosity peaks within and slightly above Bed 9 correspond to washout zones on the caliper log and solution or breccia horizons on the lithologic log. Here, partings and solution cavities must contribute significantly to the void space in the rock matrix. Based solely on the relatively low porosity calculations, Bed 7 (between 1,222 and 1,247 feet) cannot be expected to produce the large quantities of water shown in Figure 14. The caliper log for Bed 7, however, shows three narrow washout zones, two correIn addition, the rock sponding to fracture "rubble" breccia horizons. 186

fracture and partings log shows a large number of major fractures within the bed. In this case, the permeability may be created by partings that are not large enough to significantly increase the void ratio of the matrix, or the partings may be oriented vertically and do not influence the speed of the acoustic waves. An alternate explanation could be that solution cavities are interconnected through an otherwise consolidated matrix. Bed 5 (between 1,135 and 1,145 feet) is producing from a narrow, highly fractured zone, with no core recovery found within the bed (represented by a spike in the porosity analog 1 . In general, the porosity analog shows high porosity values for the entire test section. This is probably due to the relatively low fixed matrix travel time for the varying grades of oil shale. cost Data-Service company price schedules for running acoustic/sonic logs are given in Table 22. These costs are broken down into depth and operation charges. Evaluation-Porosity calculations from acoustic/sonic log interval transit times should be considered semiquantitative and used with an understanding of the parameters that interact to yield these data. The matrix interval transit time, held constant in constructing the porosity analog, can vary significantly with a change in oil shale yield from 10 to 35 gal/ton. This could cause a large error in the porosity calculation. Fluid interval transit time, held constant in Equation 5, will also vary with temperature, pressure, and amount of dissolved salts in the well fluid. However, these parameters produce less change in Atf in shallow borehole conditions and can generally be disregarded. In addition, the interval transit time can be affected by extreme borehole rugosity, as shown in Figure 14, even with the compensating receiving arrays of the acoustic sonde. Of the parameters discussed above, changes in the grade of the oil shale are believed to produce the largest single variation in the computed porosity. Utilizing Fischer analysis to determine oil shale grade, and hence an approximate interval transit time, more quantitative porosity calculations can be made by varying Atrna with depth in Equation 5. Unfortunately, Fischer analyses for Well 32x-12 and most of the other test holes on the Federal tracts are confidential information and therefore were not available for study. It may be of interest to tract developers who have access to Fischer analysis to calculate porosity values varying Atma with depth and compare this analog with water production in the well bore. Density Log Principle of operation-The density sonde consists of a gamma-ray source (usually cesium-1371, two gamma-ray detectors, a caliper arm used to force the source/detector against the well bore, and electronic equipment required to transmit data to 187

TABLE 22. COST SCHEDULE FOR ACOUSTIC/SONIC LOGS (dollars) Depth Company/service b Birdwe11 Acoustic/borehole compensated

Operation

per foot

minimuma

per foot

a minimum

Total a minimum

0.29

580.00

0.25

500.00

1,080.00

0.29

580.00

0.27

540.00

1,120.00

0.20

580.00

0.27

540.00

1,120.00

0.27

540.00

0.23

460.00

1,000.00

C

Schlumberger

Sonic/borehole compensated d Dresser Atlas Borehole compensated acoustilog-caliper e Welex Compensated acoustic velocity Notes:

a All service companies have a 2,000-foot minimum. bBirdwell Rocky Mountain Price Schedule, June 1980. Schlumberger Rocky Mountain Price Schedule, October 1979. d

Dresser Atlas Rocky Mountain Price Schedule, July 1980. e Welex Rocky Mountain Price Schedule, January 1980. the surface panel. The source and detectors are shielded with heavy metal to ensure that the signal received is primarily from gamma rays that have traveled through the formation. The count rate of gamma rays reaching the detectors is inversely proportional to the number of electrons per unit volume of the formation between the source and detectors. Therefore, the number of gamma rays per second reaching the detector is a function of the bulk density of the formation. A compensating effect of the sonde is the short and long spacing of the detector relative to the gamma-ray source, which reduces error caused by borehole rugosity, and a perturbation created by the change in density of the mud cake relative to the formation on the borehole wall. The density log is primarily used to measure formation porosity. Logging service companies provide automatically computed and recorded porosity values from the compensated bulk density measurements. The relationship used to calculate porosity is as follows: 188

+ =

where:

C$

- Qb Qma - Qp

is the porosity

kma is the density of the formation matrix

kb is the bulk density measured by the logging tool Qp is the density of the formation interstitial fluid.

The utility of these porosity data and their correlation with permeable zones has been evaluated for a test section on Tract C-b Well 32x-12. This is the same section used to study calculated porosity values from the acoustic log. Figure 15 shows the density porosity analog, aquifer production zones from pump/spinner tests, and borehole enlargements (washouts) from a caliper log in a format similar to Figure 14. This analog was developed using 2.52 gm/cc as the fixed matrix density and 1.00 gm/cc for the interstitial fluid density. The matrix density was derived from a graph developed by Birdwell relating oil shale yield in gallons per ton to matrix density in grams per cubic centimeters. The value of 2.52 gm/cc represents the extrapolated density of oil shale rock with a yield of zero gallons per ton. This is an equivalent density value to the matrix transit time used in computation of the acoustic porosity analog. Like the acoustic porosity analog, varying the numerical value of the matrix density does not alter the relative calculated porosity values, it simply shifts the porosity (y-axis) of the plot, other parameters held constant. Thus, increasing the matrix density will increase the porosity for a given bulk density reading. In general, the density-derived porosity analog appears to reflect secon-dary porosity and its associated permeability more closely than the acoustic analog. Nearly all the poorly consolidated fracture/rubble zones, indicated by washouts on the caliper log, or zones of poor core recovery have been recorded as porosity peaks on the analog. These peaks correspond with beds of high water production and suggest alternate horizons that should be considered for inclusion in the permeability testing. For example, the prominent porosity peak beween Beds 8 and 9 (Figure 1 5 ) should have been included in a packer permeability test as it appears to have the potential of producing a significant quantity of water. Smaller, less prominent peaks between Beds 1 and 2 and Beds 11 and 12 should also have been considered for inclusion in the hydrology testing program. In the dense, tight, oil shale rocks, secondary porosity (vuggy solution cavities or fraction zones) produces the principal groundwater flowpaths. In sections where secondary porosity exists, a density or neutron porosity analog should read higher than the acoustic porosity analog. The difference between the two porosity values has been defined as the secondary porosity index (SPI). This index exists because acoustic logs ignore vuggy solution porosity since a continuous path for the acoustic energy exists through the solid formation matrix. In comparison, density or neutron logs respond to bulk-volume 189

P

W 0

F i g u r e 15.

Density porosity analog and a q u i f e r production zones for Tract C-b Well 32x-12.

porosity. For secondary fracture porosity, the bulk-volume porosity added by the fracture system is small unless the zone is extensively rubblized, and the SPI will not provide useful information. Porosity analogs (density and acoustic) for the test section in We1.1 32x12 were computed with equivalent matrix characteristics so that the SPI could be evaluated. Comparison of Figures 14 and 15 shows that the acoustic porosity values are, in general, higher than the density porosity values. This relationship is more clearly shown in Figure 16 for section 1 of a Birdwell elastic property log for Well 32x-12. The computed porosity values in Figure 16 will not correspond with Figures 14 and 15 because porosity in Figure 16 was calculated with apparent sandstone unit parameters as follows: matrix density, 2.62 gm/cc; fluid density 1.00 gm/cc; matrix interval transit time, 192 psec/ft. However, the same general trends occur when the acoustic porosity is greater than the density porosity. This is an anomalous situation, for porosity calculations from density logs should represent the total matrix porosity and be greater than the acoustic porosity. It appears that for the rich oil shale rock, the large volume of organic material included in the matrix increases the bulk density readings and thus reduces the calculated porosity more than it affects the transit travel times used in the acoustic porosity determinations. Porosity from density measurements are larger than acoustic porosity in breccia zones (washouts on the caliper log), where secondary porosity is extremely high (see Figure 16). Hence, the S P I values (shaded areas in Figure 16) correspond to production test beds rather well and suggest where additional packer permeable tests might have been run, i.e., shaded zone above Bed 7. A porosity analog was computed from bulk density measurements taken in Tract C-a, Well CE-705A. Apparent limestone unit parameters (ama equal to 2.69 gm/cc, and llf equal to 1.00 gm/cc) were used in the porosity calculations. Figure 17 shows the resulting analog along with a spinner survey for the same section. The spinner survey was constructed so that the step-like incremental change in water production or intake was positioned at the first increase in slope of the log trace for water production and at the base of the slope for thief zones. For this log presentation, water production zones will be located down-hole from the step-wise increase in the spinner log or up-hole from a step-wise decrease, given the established flow direction down-hole. Qualitative evaluation of these logs shows a partial correlation between water production/thief beds and high porosity values. However, a nearly perfect correlation (except for Zone R-6) is found when porosity values are compared to rich oil shale zones shown at the base of the y-axis. Again, it is well known that the porosity analog is strongly influenced by oil shale grade. Cost Data-Cost information from four major logging companies that run formation density logs is given in Table 23.

Evaluation-Bulk density measurements taken from the density log can be used directly for cross-correlation of wells or test holes throughout the exploration phase of an oil shale mine development program. Porosity analogs developed from the 191

Figure 16.

Birdwell elastic properties log for Well 32x-12, Tract C-b.

Fiaure 17

Density porosity analog and spinner survey for Tract C-a Well CE-705A.

TABLE 23. COST SCHEDULE FOR DENSITY LOGS (dollars)

company/service b Birdwell Density/borehole compensated

Depth

Operat ion

a per foot minimum

per foot minimuma

Total a minimum

0.27

540.00

0.23

345.00

885.00

0.29

580.00

0.27

540.00

1,120.00

0.29

580.00

0.27

540.00

1,120.00

0.27

540.00

0.23

460.00

1,000.00

C

Schlumberger Formation density d Dresser Atlas Compensated densilog-caliper e Welex Compensated density log Notes: a

All service companies have a 2,000-foot minimum.

bBirdwell Rocky Mountain Price Schedule, June 1980. C

Schlumberger Rocky Mountain Price Schedule, October 1979.

dDresser Atlas Rocky Mountain Price Schedule, July 1980. e Welex Rocky Mountain Price Schedule, January 1980. density logs can be used to define the hydrogeologic framework: however, these data should be considered semiquantitative and used in conjunction with other geophysical logs, i.e., caliper, fracture, lithologic, etc.

In constructing porosity analogs from density data, oil shale grade will affect the porosity calculations. This is shown in Figure 17, where rich oil shale zones correspond to high porosity values, and is a direct result of the method used in constructing the analog. The matrix density, held constant in computer routines used by logging companies to construct porosity analogs, can vary 19 percent with a change in oil shale grade from 10 to 35 gallton. This would produce a change in porosity of up to 25 percent if values of the other parameters in Equation 6 are held constant, reflecting, in part, a real change in the primary porosity of the oil shale with pore spaces filled with less dense organic material. This type of primary porosity would not serve as a conduit for groundwater and therefore would not correlate with permeable zones important to hydrogeologic studies. In an attempt to illuminate the effect of oil shale grade on porosity calculations, another analog was developed for the same test section in Well CE-705A and is shown in Figure 18. This porosity analog was constructed with bulk density measurements taken from the same 194

80

I

60 c

t-

W

ul

40F 20

0

DEPTH (feet)

Figure 18.

Variable matrix density-porosity analog and spinner survey for Tract C-a Well CE-705A.

Birdwell density/borehole compensated log used to construct Figure 17. In Figure 18, matrix densities were varied with depth based on Fischer analysis and on the relationship of oil yield to specific gravities of Colorado oil shale developed from a nearby test hole on Tract C-a. A problem in constructing the analog developed in a few cases where bulk density measurements were found to be higher than corresponding matrix densities based on the Fischer analysis. In these cases, the numerator of Equation 6 became negative and negative porosity values resulted. These values were set equal to zero in the computer routine used to calculate the analog. An explanation for this phenomenon may lie in errors, nonrepresentative Fischer analysis (2-foot varied lithologic sections described by a single analysis), or calibration errors in the density log. In addition, a discrepancy was noted in the density values for the varying grades of oil shale. Birdwell plots shows density varying from 2.49 to 1.66 gm/cc with a corresponding change in oil shale grade from 2 to 80 gal/ton. A table developed by the Department of Energy shows density varying from 2.66 to 1.58 gm/cc for the same change in oil shale grade. This latter range of densities was used to set matrix values for construction of Figure 19. Comparison of Figures 15, 16, and 17 with Figure 18 show marked differences. Figure 18 appears to provide a more realistic range of porosity values but shows little correlation with water production from the spinner log. The generally high porosity values correlating with rich oil shale zones have been eliminated, leaving isolated porosity peaks. Unfortunately, alternate logs instructive in evaluating these peaks (caliper, fracture, and lithologic, etc.) were not available for review; thus, the utility of Figure 18 could not be fully determined. In theory, porosity analogs developed by varying the matrix density to reflect the true lithologic conditions should provide a better measure of porosity and should lead to correlation methods to equate permeable and porous zones in the oil shale stratigraphy. Additional analogs should be developed to evaluate this tool in defining the hydrogeologic framework. Electric L o q s Principle of Operation-Electric logs measure the electrical properties of the formation and drilling fluids that penetrate the borehole wall. These properties include electric potential and resistivity o r , conversely, conductivity. The electric log is primarily used for the construction and correlation of stratigraphic and structural cross sections and in delineating permeable beds. Multiple-track log presentations, including measurements of electric potential and resistivity/conductivity, are commonly used. The dual-induction laterolog discussed here consists of a correlation log, including spontaneous potential, resistivity. and conductivity measurements on a log scale of 2 inches per 100 feet, and a detail log (5 inches per 100 feet) developed from deep- and medium-reading induction devices and a shallow-investigation, focused resistivity tool. The detail log is recorded on a logarithmic grid along with a standard spontaneous potential curve. Portions of the correla-tion and detail logs from Tract C-a Well CE-705A are shown in Figures 19 and 20, respectively. The three types of electric logs (spontaneous potential, induction, and focused current resistivity) are usually run simultaneously. 196

+

SPONTANEOUS POTENTIAL mV

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1

100

I

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001

001

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Spontaneous potential--The naturally occurring electric potential of a formation penetrated by a borehole is called the spontaneous potential, selfpotential, or simply SP. It is generally printed on the left track of the log as shown in Figures 19 and 20. Two phenomena (electromechanical and electrokinetic) are thought to produce the potential current recorded in the SP log. The amplitude of the current is the cumulative effect of these phenomena taking place between the drilling fluid and the formation. For an SP current to be recorded, the well must be filled with a conductive fluid that can provide electrical continuity between the SP electrode and the formation. Furthermore, if this conductive fluid and the formation water have essentially equal resistivities the SP currents will be quite small and the log trace rather Eeatureless. The existence of the SP current is also dependent on a certain minimum permeability that will allow ion migration between the drilling fluid and the formation. The electromotive forces (EMF) of electrochemical origins are believed to be the largest contributor to the SP deflection. These are generated by differences in solution concentration between the drilling fluid and the formation water. For example, if the salinity of the drilling,Eluid is lower than that of the formation water, electric current flows into the formation opposite to the permeable zones, producing a negative (left) deflection on the SP log. Conversely, if the drilling fluid has a higher salinity than the formation water, a positive (right) deflection is recorded. Thus, the SP log is theoretically useful in the detection of permeable beds and in defining the location of their boundaries. This phenomenon may contribute to the shaded SP response shown in Figures 19 and 20. These negative deflections appear to define permeable beds in the Lower Aquifer system. The spinner log indicates significant fluid loss from the borehole that corresponds to the three upper deflections. However, no change in vertical flow velocity is found opposite the lowest stratigraphic SP deflection, nor do similar log anomalies up-hole indicate a change in water production on the spinner log. This may be caused by limitations inherent in the spinner log measurements or it may reflect relatively low permeability of the beds. Whether the beds are permeable or not, there is no direct relationship between the magnitude of the SP deflection and the permeability of the formation, nor is there any direct relation to porosity. Supplemental information from alternative geophysical logs is required for an accurate interpretation in this case. The electrokinetic portion of the SP log is generated when the drilling fluid (an electrolyte) flows through a porous, nonmetallic medium (the mud cake) into the formation. The EMF is primarily produced opposite permeable formations where the pressure differential is maximum. Flow from the well bore into the formation produces a negative (left) SP deflection, and flow from a bed to the borehole produces a positive (right) deflection. The magnitude of the recorded potential is related to the velocity of the flow, resistivity of the electrolyte in the mud cake or formation, as well as several other factors. In general, the SP deflection generated by this electrofiltration is small and commonly considered negligible except for special situations that are comparatively rare. Induction--The induction sonde consists of several receiver and transmitter coils. Constant intensity, high-frequency, electromagnetic waves are 199

emitted from the transmitter coils, inducing secondary currents in the formation from the alternating magnetic fields set up by these waves. The eddy currents flowing through the formation produce their own magnetic fields that generate signals in the receiver coils. These induced signals are essentially proportional to the conductivity of the formation or inversely proportional to the resistivity. Variations of the transmitter/receiver coil spacing in the sonde produce deep- and medium-reading tools. Focused-current resistivity--The focused current sonde consists of a central electrode symmetrically surrounded by additional pairs of interconnected electrodes. The potential difference of the surrounding (guard) electrodes is maintained at zero to focus the formation current into a thin sheet, which flows horizontally into the borehole wall. Focused-current devices provide better resolution than conventional resistivity tools in thin to moderately thick, highly resistive beds. Focusing sondes are available for use in deep, medium, and shallow depths of investigation. The separation of deep and shallow resistivity measurements, whether induction- or focused-current-derived, is an indication of invaded or permeable zones. This separation occurs when the resistivity of the drilling fluid and the water in the invaded bed are sufficiently different to alter the resistivity of that bed near the borehole. Thus, if the resistivity of the drilling fluid is greater than that of the formation water, the shallow investigation tool should read higher than the deep-reading device. In Figure 19 , separation of the short-normal and induction-resistivity reading opposite the four negative SP deflections cannot be determined since both are off the linear scale. The logarithmic grid used in Figure 20 shows generally high resistivity values for the same section with no discernible separation between the deep- and shallow-reading tools. This suggests that invasion is so deep that it extends beyond the limits of the deep-reading tool. Water chemistry data indicate that a salinity difference exists between the borehole fluid and formation water, and the spinner survey shows a large quantity of water intake for this zone. An order-of-magnitude change in the resistivity occurs below a depth of about 1,150 feet. Fischer analysis and lithologic records show no significant change in the oil shale stratigraphy at this depth, suggesting that the reduction in resistivity (increase in conductivity) can be related to more saline formation water below the Lower Aquifer system. Cost Data--Several combinations of resistivity log presentations are available from logging service companies. Two representative resistivity logs have been selected from each service company. The cost schedules for running these logs are given in Table 24. Evaluation-In general, shallow, fresh-water aquifer test holes in oil shale stratigraphy provide a poor working environment for electric logging devices. The 200

TABLE 24.

COST SCHEDULE FOR VARIOUS RESISTIVITY LOGS (dollars)

company/service

Depth

operation

a per foot minimum

per foot minimuma

Total minimuma

b

Birdwell

Induction electric

0.25

500.00

0.24

360.00

860.00

FS guard log

0.25

500.00

0.24

360.00

860.00

Induction electrical

0.29

580.00

0.25

500.00

1,080.00

Dual-induction laterolog

0.30

600.00

0.25

500.00

1,100.00

Induction electric

0.29

580.00

0.25

500.00

1,080.00

Dual-induction focused

0 -30

600.00

0.25

500.00

1,100.00

Induction electric l o g

0.26

520.00

0.24

480.00

1,000.00

Dual-induction guard log

0.27

540.00

0.23

460.00

1,000.00

SchlumbergerL

d Dresser Atlas

welexe

Notes: a All service companies have a 2,000-foot minimum. bBirdwell Rocky Mountain Price Schedule, June 1980. C

Schlumberger Rocky Mountain Price Schedule, October 1979.

dDresser Atlas. Rocky Mountain Price Schedule, July 1980. e Welex Rocky Mountain Price Schedule, January 1980. highly resistive (clear water) drilling fluids and oil shale rock mask or distort the normal SP and induction/focused current resistivity tool response, complicating the quantitative interpretation of these data. Specific conditions or observed log responses that hinder the utility of these data are given below: spontaneous Potential -- SP curves undergo gradual

transition at bed boundaries in highly resistive o i l shale environments. Therefore, permeable beds cannot be accurately located using the SP curve.

- - The highly resistive drilling fluids provide poor electrical

continuity between the SP electrode and the formation.

201

-- Borehole fluids are used during drilling operations: therefore, the resistivity differences between formation waters and drilling fluids is small, reducing the character of the SP deflections. -- Drilling muds are not always used during exploration studies; therefore, the pressure differential caused by the mud cake between permeable beds and the borehole may not develop, reducing the electrokinetic component of the SP curve. --

Fluid motion common in Tract C-a wells tends to mask the true SP response.

Induction/Focused Current Logs --

Resistivity logs have not produced a clear separation between deep and shallow investigation tools for known permeable beds in the oil shale environment.

-- Conductivity measurements have a high degree of uncertainty in the nonconductive oil shale rock due primarily to instrument sensitivity at the low end of the scale. --

Invasion of permeable zones will be extremely deep due to minimal mud cake development, masking true formation water resistivity determinations used in several alternative quantitative log interpretation techniques (not discussed here).

Bearing in mind the difficulties of using resistivity logging devices in oil shale environments, they are still useful in construction and the correlation of cross sections. However, information derived from log interpretation should be considered qualitative in nature. Seisviewer Loq Principle of OperationThe seisviewer sonde consists of a transmitter and receiver transducer mounted on a vertical axis that is rotated at a uniform rate during logging. In this configuration, the transmitting transducer emits a narrow-band acoustic signal to the entire inside diameter of the borehole as the instrument is lowered into the hole. The acoustic energy is transmitted through the drilling fluid, strikes the fluid formation boundary, and is reflected back to the receiving transducer. The amount of energy returned to the sonde is a function of the scatter caused by the physical properties of the borehole wall and attenuation in the borehole fluid. This signal is subsequently sent to the recording oscilloscopes at the surface via the wireline. , A flux-gate magnetometer is mounted on the vertical axis with the transducers and senses the earth's magnetic field. The sonde is then oriented by magnetic direction, as shown at the top right of Figure 21.

202

N

E

S

W

N -1,110

.1,120

c

0 0 c

1,140

1,150

Figure 21.

A

portion of a seisviewer log for Tract C-b Well 32x-12.

203

The diameter of the sonde is 3-3/8 inches and can be operated in a 4- to 12-inch borehole. It is run in fluid-filled (water, mud, or oil base), cased or uncased holes. The log presentation is an acoustic picture of the fluid formation boundary as if the borehole had been vertically dissected and layed out flat. The magnetic orientation of the log is given at the top of each log trace. Figure 21 shows a 40-foot section of a seisviewer log of Well 32x-12. Some of the features of the borehole wall depicted on the log are the sinusoidal curves at 1,122 and 1,125 feet. These are low angle fractures dipping to the north and south, respectively. Dark patches on the log are areas of weak signal return and represent vugs or beds that have eroded during drilling or completion operations. The sections from 1,115 to 1,120 feet and 1,145 to 1,150 feet are in-gage, competent rock with a strong signal return. Water production test zones 4 and 5 for Well 32x-12 are shown to the left of the log. cost Data-Birdwell Division is the only logging company of those reviewed that has the facilities to operate a seisviewer. However, this logging tool has been pulled out of general use and can only be obtained by special request to the Birdwell office in Tulsa, Oklahoma. Although cost quotes were not developed for the seisviewer,it will be expensive to obtain this type of borehole imagery. A logging program involving several shallow oil shale exploration holes would be required to bring the unit cost per log into a comparable price range with other geophysical logging methods. Evaluation-Seisviewer logs are used to define vugs, fractures, breccia zones, washouts, and bedding planes in open holes. In the shallow, clear water, oil shale exploration holes, resolution of these physical features is excellent when the hole is close to the gage. These field data are extremely useful when production testing directly follows the logging operation. In this case, the seisviewer log can help guide the selection of hydrologic zones to be tested and aid in the placement of the testing equipment. In Figure 21, for example, water production for Bed 5 (between 1,135 and 1,145 feet) was recorded at 180 gpm, which was the third most productive zone tested in Well 32x-12. From the imagery in Figure 21 it appears that the upper test limit of Bed 5 does not conform to the upper part of the production zone. Based on the seisviewer log, the upper packer for a production test for Bed 5 should have been set in the more competent rock at a depth of 1,125 feet. This would have included the potentially permeable vugs and eroded bedding planes shown in the log, providing a more representative picture of the production to be expected from a mine shaft penetrating this horizon. As indicated earlier, the seisviewer is no longer in widespread use. The electronic equipment for this labor-intensive logging method is costly to run and maintain. Viscous drilling fluids (mud or oil) and oblong or over-gage borehole diameters attenuate the signal, thus reducing resolution. The logging speed for high resolution is slow, about 5 ft/min, creating excessively long logging runs for deep wells. A combination of these factors has limited

204

t h e usefulness of this logging method in the oil industry, thus reducing its werall utility and marketability. This is probably the primary reason why Birdwell has elected to provide the service on a limited basis.

HYDRAULIC TEST METHODS Geophysical methods of determining hydrogeologic parameters in oil shale stratigraphy rely on direct or indirect measurements of the borehole wall, the surrounding rock, and the formation fluid to deduce the hydraulic parameters important to the development of an oil shale project. These methods, however, do not include a significant class of direct hydraulic testing procedures that provide detailed hydrology data through an evaluation of the response of the test well to the injection and removal of fluids. Hydraulic test methods are discussed in this subsection. Well pump and injection tests range from simple, rather informal procedures conducted during a period of a few hours, to sophisticated hydraulic tests conducted over a continuous operational period of several weeks and involving numerous observation wells. To simplify the profusion of methods, testing procedures have been grouped into four general classes as follows: 1.

Drill stem tests

2.

Single packer tests

3.

Dual packer tests

4.

Long-term pump tests.

The groups are not intended to be inclusive, yet they provide a sufficiently large range of testing methods to meet the needs of most oil shale development projects. Each group is divided into three components including (1) test procedures, equipment, and costs, (2) analytical methods used to interpret test data, and ( 3 ) remarks. Actual test data from the Federal oil shale tracts are utilized wherever possihle. Review of the testing procedures, equipment, costs, and utility of the esulting data has led to the following priority ranking of the four general lasses of tests: 0

Dual packer tests provide horizon-specific hydrologic data at a minimal cost when multiple tests are conducted in a single borehole. Down-hole test equipment assembly allows for pumping, injection tests, and discrete water quality sampling.

0

Lonq-term pump tests of aquifer systems produce the most representative regional data on boundary conditions and flow patterns. However, these tests are expensive and should be conducted by personnel knowledgeable in hydrologic principles.

205

Sinqle packer tests generate good-quality, bed-specific hydrologic information at about three to four times the cost of similar data gathered by dual packer tests (assuming a single-hole, multiple-test application). Field operation and procedures are simplified over the dual packer assembly. Drill stem test data is of limited value due to its nonspecific nature, high cost relative to the data return, and difficult interpretation. Drill stem tests are now seldom used in the development of o i l shale tracts. Drill Stem Tests Test Procedures, Equipment, and Costs-In conjunction with early exploration efforts, drill stem tests were IOU-tinely performed in core holes to define the hydrology of the Federal oil shale tracts. This kind of test includes the "informal pump tests" conducted on Tract C-a and the "jetting tests" performed on Tract C-b. Similar procedures were followed for both testing methods with some minor differences in the equipment utilized. Drill stem tests are performed in an open hole as f0 1 lows: The borehole is drilled to the desired depth An air line is lowered down the drill stem to a point near the bottom of the string Air is blown or jetted through the air line, lifting the fluid in the drill string to the surface Discharge is measured as changes in water level through a Parshall flume or similar device and converted to a flow rate in gallons per minute Airlift pumping at a constant rate is maintained for a predetermined length of time ( 2 hours for Tracts C-a and C-b) Immediately following shutdown of the air compressor, a waterlevel measuring device is lowered down the drill string (depth sounder or water-pressure recorder) Recovery of the water level following shutdown is recorded If an observation tube is installed in the well, both drawdown and recovery-water-level measurements can be compiled. On Tract C-a, drill stem tests were conducted after penetration of the B-groove and at the bottom of the borehole. This testing program was intended to provide hydrologic data on the Upper Aquifer system and on a combination of the Upper and Lower Aquifer systems. The majority of these tests are described in Rio Blanco Oil Shale Report (1974). On Tract C-b, from three to 206

six drill stem tests were conducted on site wells and core holes. Test zones included top of Parachute Creek, top of mining zone, base of mining zone, and total depth of the hole. Raw data for these tests are given in C-b Shale Oil Venture, 1974. Equipment required to perform a drill stem test, in addition to that commonly available on drill rigs, include an air compressor of sufficient capacity to overcome the pressure developed from the column of water within the drill string and a water-level measuring device. A geologist or hydrologist should be present to supervise the test. Costs for each test are based on the total rig time, equipment cost or rental, labor for supervision, and the number of tests conducted. Individual tests should run from $600 to $750 for the short (4- to 5-hour) tests. Longer tests are more expensive, depending on the amount of additional labor and rig time involved. Analytical Techniques-The time-recovery data compiled during the drill stem tests are used to calculate transmissivity (T) and specific capacity. T is the rate at which water will flow through a unit width of aquifer fully penetrating the saturated thickness under a unit hydraulic gradient. T has dimensions of length squared per unit of time because it represents flow through a vertical strip of unit width. Specific capacity is yield per unit drawdown expressed in gal-lons per minute per foot or gallons per day per foot. Analytical methods for determining these parameters are derived from Theis' nonequilibrium formula (Theis, 1935). A straight-line, or graphical, solution for a modified Theis equation was discussed by Cooper and Jacob (1946) and has been used by both tract developers to calculate T. A concise description of this graphical solution is presented in Miller (1973). The general method is as follows: Time-recovery da.ta are plotted on semilog paper, recovery (in feet) on the arithmetic scale and time (in minutes) on the log scale The slope (As) is determined by the change in water level (recovery) through one log cycle of time Transmissivty (T) is then calculated from the following formula: T =

(264)(Q) f

AS

where:

Q is the constant recovery (drawdown) discharge (gpm) As

is the slope (feet)

T is the transmissivity (gpdlft).

207

The success of the straight-line solution is based on the assumption that the recovery time is long and the radius of the observation point to the pumping (recovering) well is small such that the straight-line approximation coincides with the Theis-type curve. This constraint is met within the first few minutes of recovery (pumping) when measurements of the water level are taken in the pumping well. Relatively few, if any, of the aquifers in fractured oil shale stratigraphy will conform to the basic hydrologic assumption of infinite extent in all directions from the pumping well used by Theis to develop the flow equations. Geologic and hydrologic boundaries affect the slope of the time-recovery (drawdown) plot. Impervious boundaries limit the flow of water to the pumping well, causing a more rapid deepening on the cone of depression and steepening the slope of the. time-drawdown curve. Conversely, impervious boundaries increase the rate of recovery and steepen the slope of the timerecovery curve when calculated recovery (drawdown extended through the recovery period minus residual drawdown) is plotted against time. Recharge boundaries have the reverse effect on the slope in the straight-line solution. Recharge water entering the well flattens the slope of the curve. Qualitative evaluation of boundary conditions from the graphical solution are useful in defining the hydrogeologic framework of the study area and in planning more detailed hydraulic testing programs. A more detailed discussion of boundary conditions on well hydraulics is given in Chapter 6 of Johnson (1975). More sophisticated approaches are available to define T from confinedaquifer, unsteady-state drawdown/recovery data. These include Theis' straight-line recovery method (Theis, 1935), Theis' curve-fitting method (Jacob, 19401, and Chow's nomogram method (Chow, 1952). However, the additional time required to interpret the data from these methods is difficult to justify in that the data sets are from thick, complex aquifer sequences that are not adequately represented by the simplified models used to develop the interpretational theory. Remarks---Review of the drill stem test data submitted to the Area Oil Shale Supervisor indicated that the "informal pump tests" provided ranges for T based on the straight--line solution to the time-recovery data. Noting a change in slope oE the plot and the implicated boundary condition, T values were calculated using Jacob's method with As values derived from the primary and secondary slopes of the graph (Figure 22). This is not consistent with standard methods derived from the Theis nonequilibrium formula. The following is stated in Johnson (1975), p. 118, regarding such an interpretation: It should be pointed out in passing that calculation of the transmissibility, T , of the water-bearing formation must be made from the value of A, corresponding to the slope of the first part of the time-drawdown (recovery) graph. Beyond the point where a change in slope occurs, a numerical value that may represent the slope oE the second part of the graph is of no significance in analyzing the pumping (recovery) test data. No attempt should be

208

made to use any such value in either the Theis non-equilibrium or modified non-.equilibriumformulas. Therefore, T values calculated in this manner have no theoretical basis and can be extremely misleading to tract developers.

350

I

I I IIIII

I

I

I I I Ill

I

I I IIIII-

STATIC WATER LEVEL

400 -

-a

I

-

L

.a

L

450

INFORMAL RECOVERY TEST

w

5

T i = 264(240)/200 = 320gpd/ft

0 IS

t

T2 = 264(240)/38 = 1,670 gpd/ft

500

w

n

SC = 240/210 = 1.1 gpm/ft

550 SOURCE

600

I

I

I1111

I 10

I

I 1 1l111

RIO BLANCO O I L SHALE PROJECT, HOLE C 7 PRESSURE BOMB TEST, DEPTH 1.200 feel IWRIGHT WATER ENGINEERS. AUGUST 19741

I

I

I111111

100

I

1,000

1

I

I I Ill1

I

10,000

TIME SINCE PUMP OFF (minutes)

Figure 22.

Jacob's straight-line solution for T.

Well completion reports (drill stem tests) for eight core holes on Tract C-a show that boundary conditions usually affected the time-recovery plots within the first 20 to 30 minutes of recovery. Without exception, impermeable boundary conditions were indicated by these time-recovery curves. This is to be anticipated in an aquifer where permeability is fracture-controlled because of the low permeability of the unfractured matrix rocks. The tests should have been conducted for a long enough period of time to observe if recharge water had broken into the well in response to the head difference in the fracture system created by pumping: thus the true nature of the boundary could have been determined. Raw data for 55 drill stem tests are given in Table 11 B-4, C-b Shale Oil Venture (1974). These data have not been plotted to check the analytical procedures used to calculate T values. A serious disadvantage of the drill stem test, and rendering less value to the calculated parameters, is that T is obtained for the entire open portion of the borehole and no zone-specific information is obtained. In

209

addition, when combined (Upper and Lower Aquifer systems with differing pressure heads that create production and "thief" zones) drill stem tests are conducted, it is unlikely that the straight-line solution will adequately model the well conditions from which T values are to be calculated. For these and other reasons, drill stem tests on both Tracts C-a and C-b were discontinued early in the exploration/data-gathering phase of development. Sinqle Packer Tests Test Procedures, Equipment, and Costs-Testing methods included here are single packer drawdown/recovery and injection-pressure permeability tests. Test procedures for the former are similar to those discussed for drill stem tests except that a packer is lowered on drill pipe to a point above the bottom of the hole (approximately 50 feet on Tract C-b), water is lifted or jetted from the packed-off section, and waterlevel measurements are compiled. The packer is then removed, the hole deepened to the next zone of interest, and the test repeated. Equipment for the packer test includes an air compressor, a string of drill pipe, and a packer. Inflatable packers, as opposed to compression or leather cups, are recommended because they seal better on rough walls or in irregular shaped holes, reduce testing time, and are therefore more economical. Costs for running a single packer drawdown/recovery test requires rig time to set the packer in addition to labor and equipment for a standard drill stem test. The cost (in 1980 dollars) is estimated to be $1,800 to $2,000 per test. The injection-permeability test is run by drilling the borehole to the desired depth, pulling the drill string, and seating the packer at the desired depth above the bottom of the hole. The section is flushed out to remove drilling fluid and water is pumped under pressure into the test zone. The constant pump discharge .(Q) and applied pressure (Hz) are recorded. Following completion of the test, the hole is deepened to the next test horizon and the procedure repeated. Pressure-permeability tests on Tract C-b were run in conjunction with drawdown/recovery tests. The procedure varies slightly from the injection test in that after the packer is set, a valve is opened to allow formation fluid to flow into the drill pipe, thus reducing the hydrostatic pressure in the test section. The valve is then closed and data on the pressure recovery are recorded. A pump test is performed following recovery of the hydrostatic pressure. The injection pressure test is then conducted by pumping water at a constant rate into the test section and observing the pressure change in the drill pipe. Commonly, several different injection rates are used during the test. Single packer injection-permeability tests require substantially more equipment than pump tests, including a centrifugal test pump, a water meter to measure injection flow rates, connection pipes, a swivel plug valve, a 210

pressure gage and sub for the gage, etc. Further details on equipment requirements and arrangement for testing are given in Bureau of Reclamation (1977). In addition to the above equipment, a clear source of water is required for testing. This can be discharge from local wells or springs but should be of equal or better quality (lower TDS) than the formation fluid in the test zone. In arid areas this water may have to be trucked to the test site and can become a substantial cost item. The injection pump is the primary piece of test equipment. Tests are usually run using the rig's mud pump. These multiple-cylinder-type pumps usually have a maximum capacity of from 25 to 30 gpm and provide acceptable test results only when low permeabilities or short test sections allow development of back pressure on the formation. In addition, since the fluctuating pressure through this type of pump is difficult to read accurately, it is recommended that a suitable centrifugal pump be obtained for testing. Tests should be run for 20 minutes or longer with readings of injection rates (gpm) and applied pressure (psi) taken at 5-minute intervals. Pressure can be increased during the test to determine rock characteristics but, to prevent blowouts or fracturing the borehole wall, it should not be taken too high. As a general rule-of-thumb, safe pressure in consolidated rock is 0.5 psi per foot of depth from the ground surface to the upper packer. Costs for the injection test vary with injection fluid and the cost of obtaining the mated (in 1980 dollars) that $2,200 to $2,600 ment, operation, and labor costs incurred permeability test.

the availability of a suitable surface equipment. It is estiper test would cover the equipby a single packer injection

Analytical Techniques-T values can be calculated from a single packer drawdown/recovery test using methods discussed under "Drill Stem Tests" in this section. Injectionpermeability tests are discussed in Ahrens and Barlow (1951). Figure 23 is a reproduction from this book that shows the setup for the single packer permeability test. Parameters measured during testing are as follows:

1.

Elevation of the ground surface at the test site (feet)

2.

Radius of the hole, R (feet)

3.

Length of the test section (the distance between the packer and the bottom of the hole), A (feet)

4.

Depth from ground surface to bottom of the hole (feet)

5.

Distance of swivel above ground surface (feet)

6.

Applied pressure of head, H2 (psi or feet)

7.

Steady flow into well at 5-minute intervals, Q (gpm)

211

SWlV GROUND SURFACE

P

K

ZONE I

= A Cu r H

BASE OF ZONE I

ZONE I I

c

2r

WATER TABLE

I S

ZONE I l l

+

TOP OF IMPERMEABLE ZONE LIMITATIONS: O h K

< 0.10, S > 5A.

= Coefficient of permeability

Q

= Steady flow into wall lcfsl

H

= Effective head = h l

A

> 101

lftliecl under unit gradient

+ h t - L lftl

h l = In test above water table, distance between swivel and bottom of hole in tests below water table lftl: distance between swivel and water table lkl h2 = Applied pressure a t collar

L

lftl: 1 psi = 2.31 feet

= Head loss in pipe due t o friction: for quantities less than 4 gpm in 1%" pipe, it may be ignored lft)

x =

Percent of unsaturated strata l X = HIT")

A

= Length of test section lkl

r

=

Radius of t e s t hole lftl

C" = Conductivity coefficient. unsaturated bed

Cr = Conductivity coefficient. saturated bed U = Thickness of unsaturated material lft)

S

= Thickness of saturated material lft)

Tu = U - D I H D

= Distance from ground surface to bottom of hole

a

=

lftl

Surface area of test section lftl: in Method I area of wall plus area of bottom: in Method I1 area of wall

Figure 23.

Single packer injection test setup (after Ahrens and Barlow, 1951).

212

8.

Nominal size of pipe (inches) and length of pipe (feet) between swivel and packer

9.

Thickness of saturated material above a relatively impermeable bed, S (feet).

In addition to these measurements, head l o s s in the drill pipe due to friction (L), saturated bed conductivity coefficients ( C s ) , and a definition of boundary conditions between Zones 1 and 2 are required to interpret test results. Graphs required to determine these parameters and numerical examples are provided in Ahrens and Barlow (1951).

Multiple scribed above equal steps. safe pressure

pressure injection tests are performed in the same manner as deexcept that the pressure is applied in more than one essentially The applied pressure can be estimated by determining the maximum and dividing by the number of pressure steps desired.

Synthetic test results of multiple pressure tests for varying formation conditions have been postulated in Bureau of Reclamation (1977). These are given in Figure 24. Circled numbers on Figure 24 denote the following probable conditions: 1.

Probably very narrow, clean fractures: laminar flow: low permeability with discharge directly proportional to head

2.

Firm, practically impermeable material; tight fractures: little or no intake regardless of pressure

3.

Highly permeable, relatively large open fractures indicated by high rates of water intake and no back pressure (pressure shown on gage due entirely to pipe resistance)

4.

High permeability with open and permeable fractures containing filling material that tends to collect in traps and retard flow: turbulent flow

5.

High permeability: contains fracture filling material that washes out and increases permeability with time: fractures probably are relatively large: turbulent flow

6.

Similar to (4) but tighter fractures and laminar flow

7.

Packer failed or fractures are large and have been washed clean -- highly permeable: turbulent flow (test takes capacity of the pump with little or no back pressure)

8.

Fairly wide and open fractures filled with clay gouge material that tends to pack and seal under water pressure (takes full pressure with no water intake near end of test)

9.

Open fractures with filling that tends to block and then break under increased pressure: probably permeable: turbulent flow. 213

PRACTICALLY IMPERMEABLE; NO INTAKE,

P A C K E R BROKE LOOSE; TOOK CAPACITY

EFFECTIVE

Figure 24.

VERY PERMEABLE; TAKES CAPACITY OF PUMP; NO BACK PRESSURE

PLUGGED TIGHT WITH NO MEASURABLE INTAKE AT MAXIMUM PRESSURE

DI F F E R ENTlA L PR ESSU R E (psi 1

Plots of simulated, multiple pressure, permeability tests (after Bureau of Reclamation. 1977).

Tract C-b developers used a technique presented by Horner (1951) to analyze the pressure-recovery data from the single packer tests. This method is essentially the same as Jacob's straight-line solution except that pressure in psi is plotted against time on semilog paper instead of water levels in feet. A drawdown analysis presented by Odeh and Jones (1965) on Tract C-b was used to analyze the multiple-pressure, single packer injection tests. Although developed primarily for formation evaluation from oil and gas wells flowing at variable rates, this technique has had wider application. Analysis of field data is conducted as follows (for greater detail, see Odeh and Jones, 1965):

Production in barrels per day is plotted on regular graph paper versus time in appropriate units (minutes) Average flow rates for specific time increments are calculated

214

The change in pressure, Ap, (original formation pressure minus flowing bottom--hole pressure) is determined and divided by the average flow rate (9,) for each increment, Ap/qn The summation of the different flow rates divided by the last flow rate is calculated as a function of time from the following expression and plotted against Ap/qn n- 1

where:

qn is the last flow interval (bpd) qi is the ith flow interval (bpd) tn is the total flow time (minutes)

ti is the flow time for each change in rate (minutes) The slope (m> of the resulting straight-line plot is determined T is calculated from the formula T = 7.06 the viscosity of the fluid in centipoise).

p/m (where

p

is

T values and permeability for single packer tests in Well SG-17 were calculated as described above. Computer plots from the analysis are given in the C-b Shale Oil Venture (1979).

Remarks-Single packer tests have performed well in the oil shale stratigraphy on the Federal tracts. Analytical methods for data interpertation are readily available. Detailed information was compiled for Tract C-b, borehole SG-17, where 40 single packer tests were performed. These data provided a composite picture of horizontal transmissivity through the lithologic section penetrated by the well. These data were the primary input parameters for a computer model specifically designed for the Tract C-b mining and reinjection program. As such, the accuracy of these parameters is extremely important to the oil shale project. These computer-derived permeabilities are not consistent with values for the same test sections presented to the area oil shale office in February of 1975 (C-b Shale Oil Venture, 1975). In addition, test results would be more easily evaluated if they were presented in generally accepted water supply units (gpd/ft2) rather than Darcy units adopted in petroleum engineering. The primary drawback in using the single packer test method is that it is very costly. Setting up the pump for injection and the "round trip" for the rig to set and remove the packer is time-intensive. Because the tests are run

215

prior to completing the well or core hole, geophysical logs useful in directing the hydrologic program by defining test beds cannot be utilized. These drawbacks are in part overcome through hydraulic testing using the dual packer method described below.

_Dual _ Packer Tests Procedures, Equipment, and Costs-Dual packer tests have been run on Tract C-b and are referred to as "mini-pump tests" in the C-b Shale Oil Venture (1979). In general, the test procedure is to drill the borehole to its final depth. The drill string i s then removed and geophysical logs can be run in the open hole at this point if they are part of the overall testing program. The dual packer assembly is lowered to the bottom of the borehole and testing proceeds upward through the zones of interest. The packer assembly is set straddling the test zone and the desired test(s) are run. The packers are then deflated and moved up the hole to the next test horizon. The equipment utilized in dual packer testing includes the packers, a submersible pump, a multipurpose valve, and pressure transducers. The straddle packers should be gas-inflatable so they can be deflated and reinflated without requiring a return to the surface for redressing. This allows testing of all zones during one trip into and out of the hole. A submersible pump should be installed between the packers so that water samples and pump test data can be collected. The multiple-purpose valve installed between the packers and above the pump provides access to the packed-off zone for fluid injection and can be sealed off during pump testing. Pressure transducers installed above, below, and in the packed-off zone are used to measure pressure changes and detect packer failure. Surface equipment is be similar to that described for the single packer test. In 1978, the U.S. Geological Survey (USGS) developed a custom packer assembly for hydrologic testing and hydrofracturing by modifying a production injection packer manufactured by Lynes, Inc., of Houston, Texas. This equipment was tested in the Piceance Basin. Study results are documented in U . S . Geological Survey (1978). The USGS tests show that the dual packer assembly requires from onequarter to one-third less time than a standard single packer assembly for the same hydrologic test because several tests can be performed on one round trip. Costs are cut in nearly direct proportion to the time saved, resulting in costs of about $500 for a 4- to 5-hour pump test and about $650 for an injection test (if water is trucked to the test site). Analytical Techniques-Dual packer tests on Tract C-b were conducted in 1975 in twin holes SG-1 and SG-1A. Equivalent test zones with rich oil shale beds were isolated in each well with straddle packers and pump and injection tests performed. Semiconfined, unsteady-state conditions described by Hantush and Jacob (1955) were 216

used to model the aquifer. solutions for the unsteady-state flow have been described by Walton (1962) and Hantush (1956). These analytical methods are discussed below. Walton's method is a curve-fitting procedure from which transmissivity, storage coefficient, hydraulic resistance of a semipervious layer, and leakage factor of the water-bearing stratum can be determined. The reasoning used to develop the solution is similar to Theis' method except there are several type curves instead of one. This family of curves can be drawn from data published by Hantush (1956) or found in Walton (1962). The analytical procedure of Walton is as follows: A

family of type curves is developed on double-logarithmic paper

Drawdown versus time is plotted on double-log paper of the same scale as that used for the family of curves Observed data is superimposed over the family of type curves and the best fit is found keeping the x- and y-axes parallel match point on the superimposed observed data sheet is selected and the four corresponding parameters are read

A

These values are substituted into the appropriate equations and the hydrologic parameters of interest calculated. Hantush's Method I (Hantush, 1956) solution uses the inflection point of the time-drawdown data plotted on semilogarithmic paper. To determine the inflection point, the steady-state drawdown (maximum drawdown) is required and should be known through direct observation or by extrapolation. This method uses data from a single observation piezometer. The solution is developed as f01lows: 0

plot on semilogarithmic paper of drawdown versus time (time on the logarithmic scale) is prepared and the best fit curve is drawn through the plotted points A

Determine the value of the maximum drawdown by extrapolating the plotted points through time Calculate the inflection point (Sp) on the curve using the formula (see Hantush, 19561, sp =

4nkD

Ko(r/L)

where Q is the discharge k is the hydraulic conductivity D is the saturated thickness

217

r is the distance from the pumping well to the observation well L is the leakage factor of the water-bearing layer KO is the Bessel function 0

Read the value of time (tp) that corresponds to Sp

0

Determine the slope of the best fit curve at the inflection point (Asp) by the change in slope over one log cycle that includes the inflection point, or by the tangent to the curve at the inflection point.

0

Substitute the values at Sp and Asp in the formula, 2 - 3 0 sp = erlL Ko(r/L)

,

ASP and determine the value of r/L by extrapolation from tables in Hantush (1956) 0

Transmissivity (kD) is then calculated using the equation, Asp

=

L Z L W er/L, 4nkD

and a table of values for eWx (Hantush, 1956) 0

The storage coefficient lowing equation:

(S)

can then be calculated using the fol-

s = 0

4kD(tp) 2rL

Hydraulic resistance (c) of the semipervious layer is then found from the relation, c = L2/kD.

Injection permeability tests can be analyzed using the method of Odeh and Jones (1965) described earlier. An alternative injection test is presented in Ahrens and Barlow (1951) for steady flow conditions. Figure 25 is a diagram of the test setup and equations used to calculate the permeability coefficient (K). Measurements taken during testing are the same as those for a single packer test (see page 211) with the following exceptions: 3. Length of test section, A, is the distance between the packers (feet)

4. Depth, D, is measured from the ground surface to the uppermost part of the lower packer.

218

SWlVELi GROUND SURFACE

K

=

L

ZONE I

Cu r H

________----BASE OF ZONE I

K = (Cr r ) (Tu+H-A)

ZONE II

WATER TABLE

ZONE 111

K = O/CrrH

TOP OF IMPERMEABLE ZONE LIMITATIONS: Qla C 0.10,

S > 5A.

A

> 10 r; in Method ll, thickness of each packer must be > 10 I

K

= Coefficient of permeability (fthec) under unit gradient

Q

= Steady flow into wall lcfsl

H

= Effective head = hl

hl

+ hp - L (ftl

= In test above water table, distance between swivel and bottom of hole in tests

below water table lft); distance between swivel and water table

(ftl

h2 = Applied pressure at collar Iftl; 1 psi = 2.31 feet L = Head loss in pipe due to friction; for quantities less than 4 gpm in 1%" pipe, it may be ignored Iftl X

= Percent of unsaturatedstrata I X = HIT")

Length of test section lftl

A

=

r

= Radius of test hole (ft)

Cu = Conductivity coefficient, unsaturatedbed Cr

= Conductivity coefficient, saturated bed

U

= Thickness of unsaturated material (ftl

S

= Thickness of saturated material (ft)

Tu = U - D + H D

= Distance from ground surface to bottom of hole Iftl

a

=

Surface area of t e s t section Iftl;in Method I area of wall plus area of bottom: in Method IIarea of wall

Figure 25.

Dual packer steady flow injection test (after Bureau of Reclamation, 1951).

219

Remarks-Dual packer tests were conducted in only two holes, SG-1 and SG-1A on Tract C-b. In each of these holes a single, interconnected horizon was isolated and tests run without moving the packers. This testing method did not utilize the primary economic advantage of the dual packer assembly, namely, the ability to run several tests from one round trip in the borehole. Analysis of the pump test data from the same section using Walton's method shows large variations in T values. This variation could be caused by inaccuracies in the water level, pressure measures (pressure measurements are only accurate to +1/4 foot), or significant leakage through the semipervious layer during testing, which makes a unique fit to the family of curves difficult. T values calculated by the Walton and Hantush methods show relatively close agreement but are low in relation to other test results for the same bed. The accuracy of Hantush's method depends on precision water-level measurements and the estimation of the steady-state (maximum) drawdown. Fortunately, an independent check of T, S , and L can be made by substituting these parameters into equations presented by Hantush and Jacob (1955) and calculating drawdown and time values that should fall within the observed data points. The equations utilized in this check are as follows:

and

4kDt where s = drawdown in the observation piezometer a distance r from the pumping well kD = aquifer transmissivity

s

=

coefficient of storage

t = time since pumping started

and w(u,r/L) is the "well function" for a specific piezometer with distance r from sampling well and leakage factor L. Lons-Term Pump Tests procedures, Equipment. and Costs-Long-term pump tests have been conducted on both Tracts C-a and C-b. Procedures for performing this type of test are given in numerous hydrology texts. Chapter 10, Bureau of Reclamation 1977 Ground Water Manual provides an in-depth discussion of acceptable methods, instrumentation, and required equipment for pump testing.

220

Cost items are similar to those for a dual packer pump test (with or without the packers) and include labor, operation, and equipment. Total costs can range from $3,000 up to $10,000 for a more sophisticated long-term test with multiple observation wells.

Analytical Techniques-Long-term pump tests provide the most representative information on aquifer characteristics and boundary conditions. Analytical methods used by tract developers are similar to those discussed earlier and include curve fitting, calculation, and straight-line solutions. These methods have been developed for isotropic aquifers and therefore provide average values of the hydraulic parameters in anisotropic systems. Little information is developed for the maximum and minimum flow directions or rates that are important in mine design and developing dewatering programs. Anisotropic aquifer solutions that address these shortcomings are discussed below. Fracture-controlled aquifers in oil shale stratigraphy are prone to exhibit anisotropic flow with the principal axis parallel to the strike of the primary fracture system. The shape of the drawdown cone for the Upper Aquifer on Tract C-a, as defined by Weeks et al. (1974), is elliptical, indicating a strongly anisotropic aquifer. Several solutions to unsteady-state flow in confined or unconfined anisotropic aquifers have been presented by Hantush (1966) and Hantush and Thomas (1966). Alternate analytical methods are used based on available information for the anisotropic system. This information can be grouped into three cases: Principal direction of anisotropy known Principal direction of anistropy not known 0

Drawdown ellipse for test well known.

Solutions for these cases will be discussed in turn. Principle direction of anisotropy known (Hantush method)--Geological and geophysical surveys of Oil Shale Tract C-a evaluated surface fault and joint systems. These data have been condensed into rose diagrams showing principal and subset joint and fracture systems. Figure 26 shows surface joint strikes from the outcrops in the vicinity of the mine development plan (MDP) area, Tract C-a. The primary joint set ranges from N40-70% with N52% as the average strike direction. Secondary and tertiary joint sets are also shown in the diagram and both have a joint frequency of two to five relative to the primary system. Figure 27 shows a rose diagram of photolinear strikes within the MDP area, Tract C-a, from work conducted by R.A. Hodgson (1979). The primary linear sets ranges from N45-75% with N61% as the average strike direction. Alternate joint systems are also presented in Figure 27. These data are in agreement with the surface geologic study and suggest the principal anisotropic flow axis should be about N57%. Assuming that these data accurately define the principal direction of anisotropic flow (field data show principal flow direction more to the east), and that information from at least two groups of observation wells on different radial lines from the pumped well 221

JOINT SET

RANGE

WTD. AVE."

JOINTS M E A S U R E D

JOINT FREOUENCY

PRIMARY

N40°-700W

N5Z0W

54

5

SECONDARY

NZ0°-600E

N350E

19

2

TERTIARY

N10°-200W

NlPW

19

2

92 'WTD. AVE. - W E I G H T E D A V E R A G E S T R I K E (COMPASS D I R E C T I O N ) O F A L L JOINTS W I T H I N T H E SET. SOURCE: DATA FROM R I O BLANCO OIL SHALE COMPANY

Figure 26.

Rose diagram of s u r f a c e j o i n t s t r i k e s i n v i c i n i t y of MDP a r e a , Tract C-a (based on e i g h t nearby outcrop s t a t i o n s ) .

222

71.750 feet

=

TOTAL OF LINEAR LENGTHS WITHIN MAP AREA ( A )

47,495 feet TREND NW 166.4%l 24.075 feet TREND NE 133.6%)

r

I-

cy 3 0 W

STRIKE (B) LINEAR SET

RANGE

PRIMARY SECONDARY SUBSET SUBSET TERTIARY SUBSET SUBSET FOURTH FIFTH

N45-75OW N5-30°W N20-30°W N5-15'W N65-90°E N80.90°E N65-75OE N80-85'W N50-60"E

WTD. AVG. IC)

PERCENT OF T O T A L LINEAR LENGTHS MEASURED ID)

N61°W N19OW N26'W NlPW N79OE N85'E N71°E NWOW N56OE

22.8

APPROXIMATE LINEAR LENGTH F R EOUE NCY (El

I

6

5

22.7

2 2

10.8 10.3 19.2

4

2

9.5 7.4

1-2

5.9

1

4.9 -

1

80.9 NOTES I A I MAP AREA OF RBOSC FIGURE M I 114 I B I REFERENCED FROM GRID NORTH 12"W OF TRUE NORTH1 ICI WEIGHTED BY LENGTHS OF A L L LINEARS WITHIN THE SET OR SUBSET

ID1 PERCENT OF T O T A L LINEAR LENGTHS WITHIN MAP AREA 1123 LINEARS WHOSE COMBINED LENGTH I S 71.510 feed IEl

LINEAR SET PERCENTAGE COLUMN INDICATES APPROXIMATE RELATIVE LINEAR LENGTH FRERUENCY FOR EVERY 1 foot OF LINEAR L E N G r H I N THE FOURTH A N D FIFTH SETS, 6.5, A N D 4 lee! ARE I N THE PRIMARY, SECONDARY, A N D TERTIARY SETS, RESPECTIVELY

SOURCE

Figure 27.

R A HODGSON. GULF R & D . 19791

Rose diagram of photolinear strikes within MDP area, Tract C-a (data from R.A. Hodgson, Gulf R&D, 1979).

223

is available, then the transmissivity parallel to the major flow axis (Tx), minor flow axis (Ty), and the storage coefficient ( S ) can be determined (see Figure 28). The procedure and equations developed by Hantush are as follows: 0

Isotropic methods (Theis, Chow, Jacob) are used on each of the observation well rays to determine values for the effective transmissivity (Te), S/T1, and S/T2, Te = d m .

0

Parameters S/T1 and S/T2 are combined in Equation 7 to provide values of a and subsequently in Equation 8 to yield T, and TY a

= -~1

- cos2(e+an)

Tn where:

t

m sin2 (e+an)

C d e t

Tn is the transmissivity with the x-axis (Figure 28)

(7)

m sin% in

the

direction

(€)+a)

m is equal to T,/T~

=

(T~/T~)~ . )

If an = 1, then Equations 7 and 8 can be combined: an C O S ~8 - Cos2 (8+an) m = -Te- sin2 (etan) - an sin2 Ty and m can be calculated because 8, a, a, and Te are known. Substituting m into Equation 8 provides values of Tx and Ty0

Values of T1 and T2 can be found by substituting m, 8, and a into Equation 10 and T1 into Equation 7 to find T2: -

T1 0

is determined from the relationship SIT1 and should be essentially the same.

S

S/T2 and

Principal direction of anisotropy not known (Hantush method)--If the principal direction of anisotropy is not known and there are at least three groups of observation stations on radial lines from the pumped well, then T,, Ty, and S can be determined for the aquifer system. Figure 29 shows the required observation wells and some of the parameters used in the solution. The method presented by Hantush is as follows: 0

Isotropic methods are used to determine Te, S/Tl, S/T2, and SIT3 as discussed above.

224

Figure 28.

Illustration of parameters used by Hantush (1966) (known direction of anisotropy).

/o$ /Q

<&

4+ /OQ'

/$ /+$

4v \

-t\ 9+$

+A 9 d 0 \

Qq\

04kQ\\ CC

+04\

\ K

OBSERVATION WELL 41

?

Figure 29.

Illustration of parameters used by Hantush (1966) (unknown direction of anisotropy).

225

S/Tl, S/T2, and SIT3 are combined in Equation 7 to deter8 can be calculated from the following mine a2 and a3. equation because a2 and a3 are known. tan(28)

-2 (a3-1) sin2 a2 - (a2-1) sin2 a3

=

(7)

(a3-1) sin2 a2 - (a2-1) sin2 a3 Substituting a2, "2, 8, and Te into Equation 9 yields m, and Tl, T2, and T3 are found by substituting T,, 8, rn, a2, "3, and a1 into the following formula: 2 2 Tn = T / cos (€)+an) + m sin (8+an) X

(8)

S is then calculated from the relationship(s) S/Tl, S/T2, and S/T3 and should be essentially the same value.

Equal drawdown ellipse known (Hantush-Thomas)--Hantush and Thomas (1966) have shown that if the effective transmissivity (Te), the length of the major flow axis (a2), and the length of the minor flow axis (bs) are known for an anisotropic aquifer, then S , Tx, and Ty can be calculated. To utilize this method, sufficient observation stations are required such that equal drawdown ellipses can be constructed about the test well. Analytical methods and equations presented by Hantush and Thomas are as follows: Isotropic methods are used to determine Te and S/t for each ray containing observation well(s). Te is substituted into the formula(s) presented by Hantush (1966) and drawdown ( s ) is calculated for any distance along a given radii for the desired time.

from Equation 8, TX and TY can be determined. where

u'

=

r2S/4t(Tn)

r is the radius from the test well t is the desired time

W(u') is the "well function" From the s values, one or more equal drawdown ellipses are constructed and as and b, are determined (note: if there are sufficient observation points, the equal drawdown ellipses can be constructed from field data).

226

T,,

Ty, and Tn are calculated using the following relationships:

The "well function" of W(u') is found using Te, a specific drawdown ( s ) ellipse, and a modification of Equation 13 W(U') =

4ns(Te)

Q

(13)

Corresponding values of u' are found in tables presented by Walton (1962) and S is computed from the following relationship:

Vertical hydraulic conductivity (leakage) for the Federal tracts has been calculated through a computer solution for the Neuman-Witherspoon leaky aquifer equation (Neuman and Witherspoon, 1969). If individual permeable zones within the Upper or Lower Aquifer systems are being evaluated (single or dual packer tests), leakage becomes a more important parameter and semiconfined aquifer conditions more accurately model field conditions. The analytical methods can be modified for semiconfined conditions by including the leakage factor (L). This is accomplished by modifying Equation 7 as follows:

where Ln = Tnc (c is a constant). The procedure is the same as above except that Equation 19 replaces Equation 7 and isotropic semiconfined methods are used to calculate Te and S/Tn. Remarks-Anisotropic flow patterns controlled by major fracture systems have been analyzed by tract developers using the R.E. Glover method and reevaluated by Kaman Tempo using a technique described by Kruseman and Ridder (1976). This analysis is discussed in Slawson (1980b). The long-term pump tests conducted on Tract C-b, the analytical methods, and recommendations for test modifications are also documented therein. EVALUATION OF MINE DEVELOPMENT DATA The third category of methods to obtain hydrogeologic data is evaluation of mine development data. Primary data sources contained within this category

227

consist of those compiled from the existing monitoring program and ongoing mine construction. The results of baseline data collection programs on Lease Tracts C-a and C--bare presented in Sections 5 and 6 (pages 51-128) of a companion report entitled Monitorinq Groundwater Quality: The Impact of In Situ Oil Shale Retortinq (EPA-600/7-80-132). Evaluation of the existing monitoring program and data compiled therein is discussed in detail in Section 9 (pages 150-185) of that report. As mine workings are developed, a perspective of the rock fracture and/or solution cavity system(s) can be gained, which can greatly supplement the data obtained in the two previous categories (geophysical methods and well testing procedures). For example, detailed surface geological surveys and analysis of photolinear strikes have been used to define anisotropic conditions that will affect long-term pump tests. These data are presented earlier in this section. Additional information can be gained by examining and mapping fracture surfaces encountered during mine development, observing and recording relative amounts of water entering the mine in different zones and areas, and sampling the quality of such water encountered. The concept of mine development activities done in conjunction with hydrogeologic assessment offers a unique opportunity to conduct studies such as the dewatering and reinjection programs conducted at Federal Tracts C-a and C-b. Unfortunately, no record was kept of the quantities or quality of waters transported during these programs and therefore assessment of their utility in defining the hydrogeologic framework could not be made.

228

SECTION 9 SAMPLING METHODS This section addresses the sampling methods currently being utilized in the oil shale region. Factors that influence the sampling methods are also discussed. These factors include well Construction, sample handling, and preservation techniques. WELL CONSTRUCTION FACTORS The groundwater hydrology in the oil shale region can be significantly affected by the stratigraphy and structure of the area. Therefore, it is important to develop a site-specific characterization of the hydrogeology prior to the development of well specifications for a groundwater quality monitoring program. The purpose of this characterization work is to identify intervals of distinct water quality and hydraulic character. It is cost-effective to coordinate this hydrogeologic analysis with the preliminary resource exploration and evaluation efforts. In addition to the hydrogeologic considerations, monitoring needs are an important consideration. Each well should be located and designed according to the objectives of an overall monitoring strategy. For instance, wells needed exclusively for piezometric measurements require accessibility only for water-level measuring instruments and should be designed with a minimum inner diameter. The need to collect water quality data or to conduct pump or injection tests dictate a different well design, as do wells monitoring two or more aquifers (i-e., multicompletion wells). Preliminary site-specific characterization of the hydrogeology and objective analysis of the data requirements are essential to proper well design procedures. If this type of approach is utilized, both costly and timely well recompletion efforts will be avoided. Discussed below are some aspects of well design and construction that should also be considered prior to implementation of a groundwater quality monitoring program. Well construction Open Well or Perforated Over Entire Aquifer-This type of well construction is common in the oil shale region. When the rock is well consolidated and competent, such in as the Lower Aquifer, the 229

well is left open. In the Upper Aquifer wells, where tubing is usually perforated over the entire interval to maintain accessibility, caving is still a problem when semiconsolidated rock is intercepted by the well. Both types of well construction are designed to monitor a single vertical interval, in this case the entire Lower or Upper Aquifer. Although this type of construction is commonly utilized for groundwater quality monitoring in the Piceance Basin, there are some disadvantages associated with the design. The regional hydrogeologic concept of a dual aquifer system (i-e., Upper and Lower) separated by the relatively impermeable Mahogany Zone has resulted in this design. However, on a smaller scale, the groundwater hydrology is more complicated. It has been shown that the deep aquifer of the oil shale region is actually composed of numerous fractures and cavities (i.e., secondary porosity) that will contribute variable water quality to a well completed over the entire interval. A sample collected from this well may reflect the composite water quality of the entire section or the water quality of a high head interval. In any case, the sample may not represent the true groundwater quality for a given aquifer. A potential pollutant of low concentration present in this situation may become diluted below detection limits in a composite sample, or it may not be detected at all in samples collected from an aquifer dominating the open section (i-e., a high head interval). In addition, a well completed over the entire section may not provide any information on the source of the contaminant. In addition to water quality considerations, the hydraulic characteristics (e.g., transmissivity) of the different aquifer intervals are difficult to determine with this type of well design. Although an aquifer test will provide composite information on all of the aquifer intervals, the test procedure, without elaborate and costly modification, would be inconclusive for specific aquifer intervals. Furthermore, the interconnection of these different aquifer intervals can result in the collection of water quality samples from a layer exhibiting greater head rather than a composite including the adjacent layers. Multiple Completion Wells-Multiple completion wells are designed to monitor more than one aquifer interval (see Figure 30). The wells of this type in the Piceance Basin have two to four tubing strings per well, each of which are perforated in a specific aquifer interval. Potential interconnection among the different aquifers is prevented by the placement of cement grout in the annulus above and/or below the perforated zone and in some cases by bridging plugs used in conjunction with cement. This type of well construction is designed to minimize the problem of nondelineation of the vertical distribution of groundwater quality and hydraulic characteristics exhibited by the different layers within the Lower and Upper Aquifer zones. Although this type of well construction provides for more representative sample collection from the various horizons, there are some problems associated with the present design utilized in the region. These problems include:

230

C

p:;:.,.,:. . ,,. , .:

c4-

4---

8-5/8-inch CASING AT 156 feet CEMENTED TO SURFACE

7-7/8-inch HOLE DRILLED TO 1,036 feet 6-3/4-inch HOLE DRILLED TO 1,710 feet

STRING No. 4: 2-3/8-inch tubing OPEN-ENDED AT 550 feet 50(

I

+---TOP

c a

-

OF CEMENT 792 feet BY CBL

Y0

I n

+

W

n

-

-

STRING No. 3: 2-3/8-inch TUBING CEMENTED AT 1,040 feet PERFORATED 820 to 1,005 feet

-

-

1 ,OO(

STRING No. 2: 2-3/8-inch TUBING CEMENTED AT 1,501 feet PERFORATED 1,050 to 1,480 feet

-

-

-

1,500 STRING No. 1 : 2-3/8-inch TUBING CEMENTED AT 1,709 feet PERFORATED 1,530 to 1,680 feet

1.710

'OTAL DEPTH

Figure 30.

An example of multiple completion well, Tract C-b Well SG-21.

23 1

From a technical standpoint, pumping is the preferred method for assuring the collection of representative samples. Because the diameter of the tubing strings in these multiple completion wells will not accommodate a submersible pump, this type of well design is not recommended in the groundwater monitoring network. Although cement grout and bridging plugs are utilized, it is difficult to completely ensure that interconnection will not occur between different aquifer intervals using these techniques. If interconnection does occur, water quality samples collected from the well may be nonrepresentative and costly recompletion efforts may be required. The structural properties of the small-diameter tubing strings are, in some settings, insufficient at the depths required for monitoring deep aquifers. Failure of a tubing string can result in very expensive and time-consuming replacement. It should be noted that the above referenced groundwater monitoring system was derived from a well recompletion effort conducted on a tract in the Piceance Basin. Many of the problems cited are due to the well design prior to recompletion (e.g., the 2-5/8-inch tubing strings). It is strongly recommended that future multiple completion designs be modified to allow for 6--inch diameter wells. This aspect would not only provide for sample collection by pumping but also signiEicantly reduce potential failure of a well at depth. To accommodate a submersible pump for sample collection, larger-diameter boreholes are required for installation of the larger diameter, multiple completion wells. The borehole should be drilled large enough to accommodate the casing, 6--inch-diameterwell strings, and cement grout. These proposed well specifications require an annulus of 10 to 12 inches. The cost implications (In 1980 dollars) of this increase in diameter are substantial during the initial drilling operation, on the order of $26 to $30 per foot. Casing costs are estimated (in 1980 dollars) to be in the range of $10 to $13 per foot. Drilling, casing, and equipment costs can be obtained for comparison purposes in Everett et al. (1976). In Everett et al. (19761, a methodology for updating the 1976 costs is provided.

Although the costs are substantially higher for the multiple, 6-inch well design, the sampling approach is more effective compared to the smaller diameter tubing strings. The common procedure for sampling these smaller diameter wells is a bailer, which represents a passive method of groundwater quality monitoring. The effectiveness of a well in providing baseline water quality data and/or detecting potential pollutant excursions using bailing techniques is dependent upon the location of the well and the hydrologic gradient. In comparison to pumping, the passive nature of a monitoring program utilizing bailing as a sample collection method requires an additional number of wells to be incorporated in the network. The larger diameter wells allow samples to be collected by pumping. Since pumping samples a larger cross-sectional area of the aquifer, €ewer wells are required in the monitoring program. The active nature of this sampling approach will also allow the detection of any

232

potential pollutants present in the zone of groundwater flow intercepted by the pumping. Well Size The diameter of the monitoring well should be large enough to accommodate the sampling tool. Where a submersible pump is to be utilized in deep aquifers, the well diameter should be at least 6 inches. For shallower alluvial wells, a 4-inch-diameter well is adequate to accommodate a submersible pump. Wells from which water-level measurements are required need only be 1 inch in diameter. The diameter of the borehole into which the casing is placed must be at least large enough for proper casing placement. It is recommended that the borehole be at least 2 inches larger than the casing in the multiple completion wells to permit proper placement of the cement grout around the casing and adjacent to the layers or aquifers that are to be sealed from the well. The approximate costs of drilling, casing, grout placement, etc. are provided in the discussion on well construction above. Annular Seal The annular space consists of the area between the casing material and the borehole. This space is unavoidable regardless of the drilling method or casing installation. To prevent contamination of the well from surface drainage or from formations other than the aquifer to be monitored, this annular space should be sealed. The most common material used in providing an annular seal is cement grout. Cement grout is a fluid slurry composed of a mixture of Portland cement and water. The ratio of water to cement for a suitable grout mixture is 5 to 6 gallons of water per 90 pounds of cement (Johnson Division, 1966). Mixtures of more than 6 gallons of water to 90 pounds of cement should not be used because the amount of shrinkage upon settling increases with water content, producing an inadequate annular seal. In addition, the water used for the grout should be free of oil or other organic material, dissolved solids content should be less than 2,000 mg/l, and the sulfate content should be kept to a minimum. The correct placement of the cement grout is equally as important as its composition. To assure that the grout will provide a satisfactory seal against potential pollutants from the surface or aquifers not to be incorporated in the monitoring well, implacement should be continuous with the cement slurry introduced through a pipe 2 to 4 inches in diameter. Introducing the grout through a pipe to the desired depth will prevent any gravitational separation of the cement due to "free falling." This aspect is particularly important in the deep aquifer wells where the grout may have to be placed at great depths to prevent aquifer interconnection.

233

Casinq Material Well casing materials can play a critical role in a groundwater quality monitoring well. The potential influence of the casing material on groundwater chemistry, the structural properties of the well, and economics of the monitoring program are all important considerations. In general, the proper selection of casing requires site-specific evaluation of the monitoring objectives, groundwater characteristics, and the anticipated well specifications. Some properties of various well casing materials that should be considered and evaluated prior to installation are presented below. Plastic Casing and Screens-Plastic well casing is widely utilized in groundwater monitoring wells, particularly at shallow depths. The most common type of plastic casing used is polyvinyl chloride (PVC). The primary advantages associated with PVC casing include: Nonconducting - - electrochemical reactions will not be a factor affecting the groundwater quality Inert -- resists chemical attack (with the exception of ketones, esters, and aromatics (U.S. EPA, 1977) Lightweight -- easy to handle and install Inexpensive when compared to other casing materials (i.e., steel and stainless steel) if the previous recommendations are followed (i-e., 6-5/8-inch-diameter wells), the PVC should be at least schedule 40 (19/64 inch) in thickness: with these specifications the PVC would cost approximately $2.50 to $3.00 per foot (Everett et al., 1976). The disadvantages associated with PVC casing include: The structural properties of PVC may be inadequate at depth. Given the well consolidated rock in the oil shale region, this should not be a great problem provided the casing is installed correctly and the pipe schedule is selected properly. If PVC is cemented together, organic solvents will be introduced into the groundwater system, resulting in anomalous trace organic determinations. To alleviate this problem, it is suggested that pressure joints be used for PVC connections. PVC possesses a hydrophobic surface when initially introduced into the groundwater system, causing trace organics to be extracted from the groundwater until equilibrium between the PVC and the groundwater system is reached.

234

Steel Casing and Perforated Tubing--Steel casing and perforated tubing is widely used in the deep aquifer wells of the Piceance Basin. The basic disadvantages of utilizing steel materials in a well are: Steel casing and tubing materials are active conductors and will be involved in electrochemical reactions, in most cases causing the plating of iron (although iron can go into solution as well). Steel materials can contaminate water quality samples collected from the well through the introduction of trace metals derived from the casing or tubing. A l s o , the sorption of trace metals or organic constituents may occur due to metal oxides. 0

In the Piceance Basin, perforated steel tubing commonly has to be replaced due to the corrosive groundwater environment, which is a costly procedure. Excessive corrosion can result in nonrepresentative samples being collected from the well.

0

The structural properties of the small, 2-518-inch perforated tubing strings are, in some cases, not sufficient to withstand deep aquifer conditions. In this situation, the tubing will fail and accessibility to the well will not be maintained. Steel materials cost approximately $1 to $1.75 more per foot than PVC .

0

Steel materials can be more difficult to handle.

Many of these disadvantages are due to the restricted well diameters. If the inner diameter of the wells were expanded to 6 inches, nonpumping sampling techniques could be discontinued. In addition, the collection of groundwater samples that reflect the effects of the steel casing material would be minimized, provided the well is flushed prior to sample collection. Failure of the wells can also be significantly reduced, if not completely eliminated, with the increased diameter. Stainless Steel Casing and Screens-Stainless steel materials technically surpass any material for groundwater quality monitoring purposes. They are inert to all chemical reactions and will not contaminate the groundwater environment. Furthermore, stainless steel materials are structurally stable under any conditions if selected properly . The major detriment to installing stainless steel materials in monitoring wells 1s the cost. Stainless steel screen generally costs between $25 and $35 per foot, significantly more than other casing materials. The advantages of the stainless steel material do not compensate for the economics, particularly when the disadvantages associated with the other materials can be mitigated if correct sampling procedures are followed. 235

Well Security and Protection As with any well, proper procedures should be taken to ensure the protection and security of the monitoring well after installation. These procedures will prevent the inadvertent or deliberate introduction of materials into the well. Proper protection will also deny accessibility to small rodents. These foreign materials can notably affect the groundwater quality data obtained from the well, particularly if nonpumping sampling techniques are practiced. Well security can be best acquired by placing a locking cap on the well. If continuous monitoring equipment (e.g., Stevens Water Level Recorder) is employed, it should be protected as well. This can usually be done by welding a metal box with hinges onto the well casing and installing a lock on the metal box. WELL DESIGN AND SAMPLING COSTS Well Desiqn Costs Approximate costs for each well design are provided below. These costs assume that 24 sites were selected for each well design. This assumption provides for a per-well distribution of the base costs that are accrued by a multiple drilling operation. Such base costs include capital requirements for mobilizing drilling equipment to the region, contracting geophysical equipment on a monthly basis, and delivery of materials (i-e., tubing strings, casing, packers, etc.) to the site. The costs provided below assume that the number of wells were evenly distributed among the Upper and Lower Aquifer. For instance, the Tract c-a design would have 12 dual completion wells montoring both the Upper and Lower Aquifer (see Figure 31), whereas the U.S. Geological Survey (USGS) approach is to construct 2 wells per site (see Figure 321, one in the Upper Aquifer and one in the Lower Aquifer. This distribution will assure comparable well costs for each approach since there are the same number of wells in each aquifer. The approximate costs of each well design are as follows:

Design

Approximate cost per well (dollars)

Approximate cost per site (dollars)

USGS Upper Aquifer well

18,000-20,000

Lower Aquifer well

35,000-38,000

53,000-58,000

Tract C-a Dual completion well

35,500-38,000

35,500-38,000

39,000-44,000

39,000-44,000

Tract C-b Multiple completion well

236

7

. _... ...

DEPTH (ft)

.,.~-

:.;-.;,

8-5/8-inch SURFACE CASING

.!+:

..._ *...’.. .:.> % ,[’,

i .l.....

........:....: -.,

CEMENT

:

.:,

.,. -.:.y

11-inch HOLE SIZE

J r.:!.

(....

150

25-fOOt CEMENT (TO =850 feet)-\

HALLIBURTON SPEED E-LINE BRIDGE PLUG

-

PACKER (TENSION) --.-.-/ CEMENT4-1/2-inch LINER

6-3/4-inch BOREHOLE

-

1,097

LOWER AQUIFER

HORIZONTALSCALE: 1 ” = 1’ VERTICAL SCALE: 1 ” = 200’

Figure 31.

1,800

Typical recompleted Upper Aquifer monitoring well for Tract C-a (derived from Rio Blanco Oil Shale Co., March 1979).

237

DISTANCE BETWEEN UPPER AQU I FER WELL

8-518-inch OD STEEL SURFACE CASING

LOWER AQUl FER WELL

AQUIFER 6-3/4-inch BORE HOLE-6-5/8-inch OD STEEL CASING

5-1/2-inch BORE HOLE

G R E E NR I V E R FORMATION LOWER AQUIFER

HORIZONTAL SCALE

Y! Figure 32.

VERTICAL SCALE

1"=

1'

l " = 250'

USGS Upper and Lower Aquifer monitoring well design.

Samplinq C o s , The approximate sampling costs for each well design and corresponding sampling method are presented in the subsection that follows ("Sample Collection Methods"). In addition to the sampling methods currently being utilized in the oil shale region (i-e., bailing, swabbing, and portable submersible pump), a Eixed submersible pump was analyzed as a sampling approach. For comparison purposes, the costs for each sampling method were developed under the assumption of a quarterly sampling frequency of 12 Upper and Lower Aquifer wells for a 5-year period. Sampling costs include the wages for personnel, the materials utilized, and equipment capital requirements.

238

The sampling costs and corresponding well design costs (derived from well design cost data presented above) are given in Table 25. Based on the data presented in Table 25, it is apparent that the bailing method is the best approach from a cost perspective. The portable submersible pump and swabbing methods are very expensive compared to the bailing method and, therefore, are not recommended. Although the fixed submersible pump is more expensive to utilize than bailing, this method should not be ruled out due to the technical advantages of the approach. Each method is discussed further in the discussion of "Sample Collection Methods" (below). The initial step in developing the well construction costs was to identify the specifications for each design. The costs for the drilling operations, geophysical logging, and materials relative to each of the design specifications was provided by companies dealing in these areas. Three companies were contacted for each of these areas and average costs were developed. These construction costs were then reconfirmed by the respective designers (i.e., USGS, Tract C-a developers, and Tract C-b developers). In most cases, the sampling costs were provided through correspondence with USGS, Tract C-a developers, and Tract C-b developers. The costs that were not included in this correspondence were developed in a similar manner to the well construction costs. MONITOR WELL PLACEMENT The placement and design of monitoring wells is defined by the design of the MIS operation, the site-specific hydrogeology, and by the potential mobility of the constituents from the MIS retorts. An earlier companion report (Slawson, 1980a) examined proposed monitoring programs for Federal Oil Shale Tracts U-a and U-b to identify information deficiencies and to develop a monitoring design program. Monitor well program designs are developed for different aspects of the MIS mining operations. specific examples are presented that show monitor well placement for proposed and existing alluvial, Bird's Nest, and Douglas Creek aquifers. Additional wells are identified in the saturated zone of the Uinta and Green River Formations above the Bird's Nest aquifer. Source specific monitoring systems for spent shale landfills include observation wells and multiple completion wells, as well as geophysical and unsaturated sediment monitoring devices. For greater detail on monitor well placement, see Slawson (1980a), entitled Groundwater Quality Monitorinq of Western Oil Shale Development: Monitorins Proqram Development. SAMPLE COLLECTION METHODS Three predominant methods of sample collection are commonly utilized in the oil shale region: bailing, swabbing, and pumping. Each of these sampling procedures is discussed below with respect to advantages and disadvantages of the methodology, as well as the approximate costs for initiating and conducting each procedure. Related issues, i.e., quality and custody control of the water quality samples obtained, are discussed by Everett (1980) and slawson (1980b).

239

TABLE 25.

Item Well construction

SAMPLING COSTS

Fixed Submersible Portable Submersible Pump (USGS) PUP

Bailing (Tract c-a)

Swabbing (Tract C-b) 39,000-44,000

53,000-58,OOOa

53,000-58,000

35,500-38,000

61,800-79,800

55,000-60,000

8,000-10,000

200-400

1,400-1,700

Sampling Costs Capital Requirements Operational Requirements (Quarterly) Labor (quarterly) N

la 0

Five-year Total (including construction of 12 monitoring well sites)

135-200'

704,500-787,800

d

11,200-14,000

943,000-1,072,000

200-400

16,000-18,000

135-200'

3,500-4,300e

440,700-478,000 858,000-974,000

Notes: All costs in 1980 dollars. a Assumes similar well construction for fixed pump as with portable pump. bTract C-b contracts swabbing rig, thereby eliminating capital requirements. Assumes the sampling of eight wells per day. dAssumes sampling of one well per day. e Assumes the sampling of three wells per day.

b N/A

Ba i1inq Bailing involves introducing a hollow cylinder that is supported from the surface into the well. Figure 33 portrays the features of a Kemmerer sampler, a commonly used bailer. The cylinder can be tripped to close at any desired depth thereby collecting a sample. The important aspect of the Kemmerer sampler is that it allows the water to flow through the cylinder, thus permitting samples to be collected from any depth. Samplers that are open at the top and sealed at the bottom do not have this flow-through characteristic and should not be used because the sampler is generally filled with the first water encountered in the well, i.e., the water near the static water level.

ch

Chain t h a t anchors upper valve to upper i n t e r i o r guide

dh Rubber d r a i n t u b e dt

Brass d r a i n t u b e

g h

I n t e r i o r guide fastened to i n n e r surface of sampler Rubbertube

j

Jaw of release

is

Jaw spring

Iv

L o w e r valve

m

Messenger

o

Opening i n t e r i o r of d r a i n t u b e

p

Pinch c o c k

s

Upper release spring operating on h o r i z o n t a l pin, one end of w h i c h f i t s i n t o groove o n central r o d

spr Spring fastened t o l o w e r internal guide a n d operating in groove on central r o d to provide l o w e r release st

S t o p on central r o d

uv

Upper valve

L e f t : V i e w of complete sampler w i t h valves o p e n

Top Right: A n o t h e r t y p e of construction of upper valve and t r i p p i n g device Bottom Right: A n o t h e r t y p e o f c o n s t r u c t i o n of l o w e r valve and d r a i n t u b e

Figure 33.

Features of the modified Kemmerer bailer ( P . S . Welch, Limnoloqical Methods, p . 200, Figure 59).

241

The major advantage of utilizing the bailing method is that it allows samples to be collected from small-diameter wells that have relatively deep static water levels, a situation that generally restricts the use of other sampling methods. Bailing is also very simple to use and does not require a large number of personnel for operation. It is also fairly inexpensive, with capital requirements (i.e. , bailer, winch, power source, truck, etc.) of $8,000 to $10,000 (in 1980 dollars). There are a number of potential problems associated with bailing water quality samples. Extreme variations in the water quality data can be observed when the depth selected for sampling is inconsistent. This is pronounced when the well is completed in an aquifer possessing multiple permeable intervals, which may contribute dissimilar water quality. The groundwater in such wells can be stratified, resulting in noticeable vertical changes in water quality. Schmidt (1977) attributes this stratification to the distinct water quality in each permeable zone penetrated by the well. Schmidt (1977) also suggests that variations in the composition of aquifer materials with depth and possible differences in the sources of recharge can modify groundwater quality in wells penetrating these intervals. An additional problem is the nonrepresentative nature of the sample collected. Water standing in the well bore above the screened or open interval will be isolated and have little or no mixing with natural groundwater. This stagnation effect is particularly pronounced in little-used or nonpumping wells. Samples collected from this stagnant zone are not indicative of the groundwater quality and will result in unrepresentative data. Factors contributing to the unrepresentative nature of the samples collected from the well bore include the introduction of unnatural constituents through the interaction between the casing with the groundwater system, as well as foreign material entering the well from the surface. Furthermore, changes in pH, and subsequently in water quality, can be induced through the variations in pressure and C02 dissolution in the well bore (Summers and Brandvold, 1967). The magnitude of the vertical variations that can be observed during sampling a well is shown in Figures 34, 35, and 36. These vertical profiles were compiled by collecting samples from specific depths via a bailer and performing specific conductance and temperature measurements for each sample. The results of the detailed water chemistry analysis for selected samples are shown in Table 26. The temperature and conductivity profile for Well GS-13 (well diagrammed in Figure 37) show a declining level of conductivity over the approximately 375 feet of water standing in the well bore. The conductivity measurement obtained near the static water level was 2,300 pmho/cm, compared to a measurement of 1,600 pmho/cm obtained near the bottom of the open interval (see Figure 34). Temperature measurements were much more uniform with depth. Appreciable increases in conductivity with depth were also noted in Wells D-17 and D-18 (Figures 35 and 36, respectively). In Well D-18, an order-ofmagnitude increase in conductivity was observed in a very small interval near the bottom of the well. Above this level the conductivity was very stable. The decline in conductivity with depth noted in Well GS-13 is also seen in the 242

DEPTH (ft)

OL 100

200

'

300 .-

400 .-

900

16

POTENTIOMETRIC SURFACE 425 ft

17

18

19

20

21

22

SPECIFIC CONDUCTANCE (pnhos/cm @ 25°C) X l o 2

Figure 34.

23

13

14

15

16

17

TEMPERATURE ("C)

Variation in specific conductance and temperature with depth, Upper Aquifer Well GS-13, Tract C-a.

243

DEPTH (ft)

300 373 f t

' SPECIFIC CONDUCTANCE (prnhodcrn 621 25°C) X lo2

Figure 35.

18

19

20

4TURE ("C)

Variation in specific conductance and temperature with depth, Lower Aquifer Well D-17, Tract C-a.

244

DEPTH f t ) -34 ft

0

10

20

30

40

50

60

SPECIFIC CONDUCTANCE (pmhos/cm @ 25°C) X lo2

Figure 3 6 .

-

19

'

20

21

22

23

24

TEMPERATURE ("C)

Variation in specific conductance and temperature with depth, Lower Aquifer Well D-18, Tract C-a.

245

TABLE 26.

VARIATION IN WATER QUALITY WITH DEPTH IN SELECTED DEEP AQUIFER WELLS, TRACT C-a Depth (feet) Well D-17

Well GS-13 Constituent

a

450 7.3

515

725

7.5

7.5

475 9.1

875 9.0

Well D-18 990

1,400

8.6

8.2

1,500 8.1

PH Specific conductance

1,940

1,559

1,344

1,344

1,790

2,210

3,856

64,794

Total dissolved solids

1,409

1,140

1,160

1,093

1,174

1,524

2,954

37,839

calcium

3.9

67

46

42

Magnesium

118

89

82

32

30

24

sodium

28 1

213

194

312

417

557

Pot ass ium Bicarbonate

0.8

0.5

0.4

115

551

637

<1

<1

<1

610

466

262

3.4

1.9

6 86

2.6 898

5.0

2.3 1,355

2.2

2.8

6.6

6.8

1,224 2.3 3,089

16,816 14.2 45,682

N I&

m

Carbonate Sulfate Chloride Fluoride Ammonia Arsenic Boron

13.4 0.48

<0.1 0.01 0.29

8.8 304

13.1 170

4.8 118

<1

97

220 480

11.4

357:

28.2

53.6

59.0

47.2

10.1

<0.1

1.6

2.6

5.6

9.3

<0.1

<0.1

<0.1

10.1

<0.1

<0.1

<0.01

<0.01

<0.01

<0.01

0.01

10 . 1

3.9 <0.01

0.31

0.31

0.53

0.73

0.79

0.87

<0.001

<0.001

<0.001

<0.001

<0.001

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

30.6

21.2

24.1

35.0

25.7

12.4

21.0

0.31

Mercury

<0.001

Selenium

<0.01

Dissolved organic carbon

28.6

001

Note: a

<1

Constituent units are mg/l except €or pH units and specific conductance in pmhos/cm at 25oC.

DEPTH ( f t )

UPPER AQUIFER

BRIDGE PLL

+

CEMENT

...... . ...

>

, :.

<

>

Figure 37.

1751

well diagram of Upper Aquifer Well GS-13, Tract C-a.

247

water chemistry data (Table 26). The largest changes with depth were observed for the major inorganic ions. The trace constituents and DOC were generally more stable with depth. The general ionic composition is fairly consistent at all three depths in Well GS-13, although sulfate concentrations decreased with depth to a greater extent than most other ions. The increases in conductivity with depth observed in Wells D-17 and D-18 are also consistent with water chemistry analysis (Table 26). Most of the conductivity increase in Well D-17 can be attributed to increased sodium bicarbonate concentration. Magnesium, carbonate, and sulfate levels decline with depth. Thus, the salinity of the water increased and the ionic composition of the well water changed. The variation in water quality with depth, as indicated in Figures 34, 35, and 36 and Table 26, demonstrate the importance of consistent sample collection depths. This is a very critical area and essential to accurate data interpretation. The depth selected for sample collection is of equal importance. It is obvious that a sample collected near the static water level or in the cased section above the aquifer is unrepresentative of the groundwater system. Therefore, it is recommended that samples be collected from the portion of the well that is screened or open and adjacent to the aquifer. To collect a representative sample using the bailer method and to assure the above-cited effects are minimal, at least one well volume of water should be evacuated from shallow wells in which the groundwater movement is very slow. This is particularly important because stagnation effects can greatly influence the water quality of these low-yielding wells. Once one well volume has been removed, a representative sample can be obtained. In very-low-yielding wells where the evacuation process has resulted in dryness, the well should be allowed to recover prior to sample withdrawal.

Removal of one well volume is very impractical for eliminating stagnant water in a deep well with the bailer method because of the quantity of water obtainable from the well on each down-hole trip. Attempting to evacuate one or more well volumes would be very time-consuming and inefficient for the field personnel. As previously demonstrated, representative samples of the natural groundwater system can be obtained by sampling adjacent to the open or perforated section. Marsh and Lloyd (1980) have indicated that this is particularly true for wells that monitor aquifers where significant groundwater movement is occurring. If this type of approach is to be utilized, the hydraulic characteristics of the aquifer to be monitored should be determined. These characteristics can be best determined during the initial drilling operations. However, if postdrilling determinations are necessary, down-hole flowmeter surveys and other geophysical methods can be beneficial. Additional modification of the sample chemistry can occur when transferring the sample from the bailer to the sample container. Precipitation of easily oxidized constituents by introducing atmospheric oxygen during the transfer and altering the natural oxidation-reduction potential is of primary concern. The loss of dissolved gases is also a potential problem during the transfer process. To alleviate the effects of the sample transfer, sample

248

contact with the air should be minimized. Furthermore, caution should be taken when transferring the sample in order to prevent unnecessary agitation. An additional consideration when sampling is the number of samples necessary to determine the difference among data collected during different sampling periods. To accurately address this consideration, the variability of the data needs to be established. To identify this variability, four replicate samples were collected from selected depths in four wells. The sampling program involved the (1) collection of field data (i-e., specific conductance, temperature, and pH) and (2) collection of samples for detailed chemical analysis. The results of the statistical analysis indicate that only one sample is necessary for accurately determining a difference among data sets for the major constituents (e.g., bicarbonate, sodium, TDS). This is also true for con-stituents that are intermediate in concentration (e.g., sulfate, chloride). For the constituents that are low in concentration (e.g., calcium, magnesium, fluoride, etc.), an extremely high number of samples appears to be required. However, this aspect can be attributed to the statistical procedure and it is therefore not necessary to collect more than one sample to characterize these constituents. In summary, the following procedure is recommended for collecting samples from a well when using a bailer: 1.

Use a flow-through type of bailer (e.g., Kemmerer sampler)

2.

Compile well completion data; of particular importance is well diameter, depth to aquifer, aquifer thickness, and total depth

3.

For shallow wells with very slow groundwater movement, estimate the well volume from the well completion data and extract at least one well volume previous to sample collection.

4.

For both shallow and deep wells, select a sampling point adjacent to the aquifer

5.

Consistently sample from the same depth and adjacent to the aquifer during every sampling effort

6.

It is necessary to collect only one sample from the well

7.

Measure temperature, specific conductance, and pH in the field.

Pumping The use of a submersible pump is a common procedure for sample collection from the alluvial wells on Tract C-b and the deep wells monitored by the USGS. For this sampling method, the submersible pump is introduced to the desired depth and a sample collected from the discharge line. A typical pumping apparatus configuration is shown in Figure 38.

249

110-V POWER

ELECTRIC POWER CORD DISCHARGE PIPE

STATIC WATER LEVEL

DRILL HOLE

Figure 38.

Typical pump apparatus configuration (after Slawson, 1980b).

The use of the submersible pump for sample collection is the superior sampl.ing approach. submersible pumps can be used to collect samples from any depth provided the pump is properly selected and the well is conducive to pumping. Submersible pumps can efficiently extract sufficient volumes of water and eliminate the stagnant well bore water, thereby allowing representative sample collection. Extraction can be performed in a relatively short period of time. Additional advantages of submersible pumps include: 0

Easy installation and withdrawal. from a shallow well (although a great deal of effort may be required for a deep well)

0

Little maintenance is required

250

They can be used as portable or fixed pumps: both Tract C--b and USGS personnel have designed a truck-portable pump capable of efficiently servicing a suite of wells The well discharge can be easily controlled and both very low or very high discharges can be obtained They have relatively little effect on the native aquifer water quality (nitrogen and airlift methods, however, can substantially alter the iron content and pH of the water and, therefore, are not recommended). Although these characteristics make the submersible pump the preferred sampling approach, some aspects may preclude its use. The primary disadvantage of the submersible pump is the minimum size requirements of the well annulus. Submersible pumps generally require a minimum 4-inch-diameter well for shallow sampling efforts and a 6 - to 8-inch-diameter well for deeper sampling. As most of the wells in the study area have 2-518-inch tubing in the deep wells, the use of a submersible pump in the sampling program is limited. An additional disadvantage of this approach is the capital requirement, which can be significantly higher than other sampling devices. The Tract C-b truck-portable pump, which is capable oE sampling at depths up to 100 feet, costs $10,000 to $12,000 in 1980. However, the USGS portable pump rig, which is designed to be set at depths of 500 to 600 feet (i-e., Upper Aquifer wells), requires an initial expenditure of $50,000 to $60,000. Rigs designed to sample Lower Aquifer wells require a capability of pumping from depths of 1,000 to 1,500 feet and require an initial expenditure (in 1980 dollars) in excess of $70,000, substantially more than the capital requirements for bailing. In addition, the time required for pump placement and withdrawal at these depths is about 7 to 12 hours, depending on the depth of the pump placement (i.e., sampling Upper or Lower Aquifer). As pointed out above, a mobile pumping rig for sampling deep wells (i.e., Upper and Lower Aquifers) is very time-consuming and expensive, particularly on a frequent sampling basis. A more feasible approach may be a fixed pump in each well and a mobile generator for a power source. This approach requires substantially less manhours because the time for pump placement and withdrawal is eliminated. The approximate initial expenditure for a submersible pump in each well, capable of pumping from up to 1,600 feet at 40 gpm, is $6,600 to $7,800 (in 1980 dollars). Additional expenditures of $950 to $1,980 (in 1980 dollars) are required for each well for discharge pipe, power line, etc., depending on the depth of the pump. To employ this sampling method efficiently, some expertise in the following areas is required: pump placement, discharge rate, duration of discharge, and representative sample collection. Although the submersible pump represents the most reliable method for collecting representative groundwater samples, incorrect procedures can produce inaccurate data. In addition, applying consistent procedures during each sampling event allows better comparison among the data collected on different dates.

251

Before establishing the sampling procedures for each well (i.e., pump placement , discharge rates, etc. 1, the wells need to be individually evaluated. Samples for water quality analysis should be collected only after the discharge has equilibrated. Additional factors to be considered during this evaluation include local hydrogeology, well construction, and well location, all of which can affect the time associated with obtaining a stable or equilibrated well discharge. The importance of testing wells individually prior to establishing sampling protocols is apparent from the data presented in the following figures and tables. These data were collected from three wells installed by the USGS in the Piceance Basin. The typical well construction for these wells is shown in Figure 32. The objective of this sampling program was to evaluate the variability of the water quality with pumping time. The types of data collected during this survey included continuous pH, temperature, and specific conductance measurements. Samples for detailed chemical analysis were also collected at selected intervals. As Figures 39 through 43 indicate, the conductivity can vary substantially with pumping time. In the case of Well 75-1A (Figure 391, a very large and rapid change in conductivity was initially observed. After approximately one well volume, the conductivity stabilized and remained fairly constant for the duration of the test.

1.o

0

1.91

I USGS WELL 75-1A -

-

E > c

-

1600"-

-E, >

Z !

2

-

1400 --

+ V

-

3

n

=

8

- -

-

-

11

1200

-

-

1000

-

-

800

I

I

10

20

I

30

I 40

I

50

252

I 60

I

70

1

80

I

90

100

Variation in specific conductance with continued pumping, USGS Colorado Core Hole #3, 1980.

Figure 40.

1.o

0.5

1

I

70,000°

USGS WELL TH 75-16

60,000

-

-

I

E -

-

E,

t

k

2 I-

40.000

-

-

-

8 20,000

-

-

10.000 1

Figure 41.

1

I

I

I

I

1

10

I

I

I

I 100

I 140

Variation in specific conductance with continued pUmping, USGS Well TH75-1Bt 1980.

253

CUMULATIVE NUMBER OF WELL VOLUMES 1 .o

0.5

0

30

I

I

USGS WELL TH 75-16

I

I

I

I

I

I 10

I

I

l

l

I 140

100

TIME SINCE START ( m i d

Figure 42. Variation of temperature of pumped discharge, Well TH75-1B. 1980.

10.0

I USGS WELL 75-1A

-

PH

-

A

=

=

-

-

-

-

8.0 -

7.0

d l

I

I

I

I

I

I

I

I

I

The conductivity data collected for Colorado Core Hole #3 (Figure 401, steadily declined throughout the entire test. Conductivity values obtained toward the end of the test were about 20 percent of the initial measurements. Although more than one well volume was discharged from this well, the test was obviously not long enough for obtaining an equilibrated discharge. An increasing trend in conductivity was observed for Well TH75-1B (Figure During the test performed on this well, the conductivity was fairly stable at around 30,000 pmho/cm, until approximately three-quarters of a well volume had been discharged. At this point, the conductivity increased abruptly to around 58,000 pmho/cm, where it stabilized for the duration of the test. 41).

The other constituents measured in the field also changed during the tests. The temperature of the discharge of Well TH75-1B (Figure 42) initially declined steadily and then appeared to increase slightly. The pH of Well 254

(Figure 43) initially increased one pH unit and stabilized after about 10 minutes of pumping.

75-1A

These patterns of changes in the constituents measured in the field are also reflected in the water chemistry analysis (Table 27). For instance, the large change in conductivity for Well 75-1A is repeated for several major inorganic ions (potassium, sodium, bicarbonate, chloride, and sulfate), alkalinity, TDS, and fluoride concentrations. Most of the trace constituents (arsenic, boron, mercury, and selenium) were largely unchanged for the duration of the pumping. The data collected during this survey and presented above point out the need for the individual testing of each well. It is obvious that a sample collected during the first few minutes of pumping and before conductivity has stabilized will not be representative. It is also obvious that the extraction of one well volume previous to representative sample collection is not a completely accurate rule-of-thumb, since the data for Colorado Core Hole #3 never stabilized, even after more than one and one-fourth volumes had been extracted. In regard to pump location, it is recommended that the pump intake be placed approximately 5 feet above the open, perforated, or screened aquifer interval. The rationale for placing the pump in this location is as follows: structurally unstable aquifer interval could fail due to the excessive stresses created by the pump if it were placed directly opposite the open, perforated, or screened interval

A

If the well is not developed properly, the pump can produce sufficient turbulence in the aquifer interval to produce sand, etc. If the pump is placed in the aquifer interval and the discharge is too high, excessive drawdown may create cascading conditions that can produce sufficient turbulence to modify easily oxidized constituents

Humenick et a l . (1980) have pointed out that this pump location significantly reduces the volume of water necessary for extraction before representative aquifer water is obtained. Figure 44 (from Humenick et al., 1980) illustrates two wells. Well A, with the pump intake 5 feet above the open aquifer interval, requires 12 gallons of discharge before formation water is produced. For Well B, the pump intake is 35 feet above the open interval and requires 77 gallons of discharge before representative formation water is produced. In short, the following procedure defining sampling protocols is recommended for collecting representative samples from a well when using a submersible pump:

255

TABLE 27.

WATER CHEMISTRY OF SAMPLES COLLECTED AFTER DISCHARGE OF VARYING WELL VOLUMES, USGS WELLS, PICEANCE BASIN, 1980 Well volumes discharged ~~~

Well 75-1A

a Constituent

1

0

Core Hole # 3 2

1

0

~

Well TH75-18 0

0.2

1 ~~

Total dissolved solids Calcium Magnesium Sodium Potassium Bicarbonate Carbonate Sulfate

1,1'76 4.3 32 429 1.2

816

836

7,148

3,276

22,880

22,400

45,220

13.8

11.7

1.8

3.2

3.6

2.0

1.5

54.9

52.5

24.6

29.3

4.4

2.2

2.8

235 0.4

225 0.4

944

695

708

<1

5

<1

184

149

144

2,910 21.3 3,496 39.5

1,320 13.6 1,719 14.1

10,200

22.5 23,300 32.5

229

228

131

2,236

852

1,540

9,900 22.1

19,650 32.5

23,640

48,560

<1

<1

87.2

61.7 3,730

Chloride

85.7

10.7

12.3

Fluoride

0.6

0.2

0.2

0.4

0.2

17.3

17.2

18.4

Ammonia

0.4

0.3

0.2

5.6

2.3

8.0

8.3

8.2

Arsenic

<0.01

<0.01

<0.01

0.02

0.02

0.01

0.3

0.3

0.4

0.5

0.4

0.8

0.8

Boron Mercury

<1

<1

<1

Selenium

<0.01

<0.01

<0.01

Dissolved organic carbon

10.1

13.1

34.5

<1 0.01

26.3

<1 0.01

24.0

1,670

<1

<1

<0.01

<0.01

23.4

26.9

24.4

Note: a

0.9 <1

Constituent units are mg/l except for pH units and specific conductance in pmhos/cm at 25OC.

77 gallons

12 gallons

/-+

/+

STATIC WATER L E V E L

7 +DRAWDOWN

(3 feet)

7

DRAWDOWN (17 feet)--

PUMP I N T A K E 35 feet ABOVE OPEN H O L E

PUMP I N T A K E 5 feet

N

VOLUME OF STATIC WELL-BORE WATER VOLUME OF STATIC WATER DISCHARGED BEFOHE FORMATION WATER IS PRODUCED

Figure 44.

Comparison of pump locations and the volume of water necessary for extraction before representative aquifer water is obtained (modified from Humenick et al., 1980).

257

1.

Compile well construction data, including well diameter, total depth, and perforated interval or aquifer interval in an open well.

2.

Measure static water level and estimate well volume.

3.

The pump intake should be placed approximately 5 feet above the open, perforated, or screened aquifer interval.

4.

The discharge rate should be maintained at a moderately low rate to prevent excessive drawdown in the aquifer and well and minimize turbulent mixing in the annulus.

5.

Extract at least one well volume from the well.

6. Continuously monitor and measure specific conductance, pH, and temperature in the field throughout the pumping period. Continuously monitoring these parameters is particularly important for little-used groundwater quality monitoring wells. 7.

Collect the sample only after the field parameters have stabilized for a period of time. Although the data indicate that the conductivity is the most conclusive of aquifer water, it is suggested that all of the parameters be monitored to indicate representative aquifer water to prevent premature sample collection.

8. Collect the sample as close to the well head as possible to avoid potential contamination, precipitation of solutes, and the loss of dissolved gases. It is recommended that these protocols be recharacterized periodically for each well, particularly for wells with large, open intervals.- Once these protocols are defined or redefined and consistency among items such as discharge rate, time of col.lection,and pump placement is established, representative samples can be collected. However, to produce comparable data for establishing water quality trends, these procedures (i.e., pump placement, discharge rate, etc.) should be followed during each sampling effort.

swabbing The swabbing method is utilized by Cathedral Bluffs Shale Oil Company (operators of Tract C-b) for sampling deep aquifer wells. This methodology is a common procedure used in oil field operations and has been adapted for use on Tract C-b as a sampling procedure. The swabbing technique involves introducing a swabbing cup into the well, which is supported from the surface by a pipe, and removing a portion of the water from the 2-5/8-inch-diameter well. The water extracted from the well is discharged through a line to the place where the water quality samples are collected. This sampling method requires a capitalization cost (in 1980 dollars) of approximately $50,000 to $55,000 and requires four personnel for operation. Tract C-b contracts the equipment

258

and personnel for each sampling effort, performed quarterly, at a cost of about $20,000. The sampling approach applied by Tract C-b personnel is to completely evacuate a well volume of water. After this evacuation process has been performed, the well is allowed to recover for at least 24 hours. After this period, the swabbing equipment is returned to the site and the process is re-peated and a sample is collected. Parameters measured in the field include specific conductance, pH, and temperature. The advantages of swabbing are as follows: 0

Swabbing can be used where the depth to water is relatively great and well diameters are relatively small

0

At least one well volume can be obtained from the well, allowing

for representative sample collection. The disadvantages of this method include: 0

Difficulty in regulating the volumes of water obtained from the well and the discharge rates

0

Well contamination can occur when oil-field equipment is used for deep aquifer sampling; also, there is a potential for cross-con-taminating the samples

0

Very difficult to employ

0

Accelerated plugging of the piezometer perforations is a potential problem, particularly with the small diameter of the piezometers

0

Consistent water quality sample collection is difficult to achieve due to the vertical mixing of the well water upon extraction of the water; consistent swabbing depth during each sampling effort would help alleviate this problem.

In general, the use of swabbing is not recommended as a sampling technique. SAMPLING FREQUENCY Defining an appropriate sampling frequency is a complex issue influenced by location of sampling sites, monitoring goals, climatological factors, and characteristics of groundwater flow. As a result, sampling frequency should be defined on a case-by-case and likely trial-and-error basis. One of the key factors is groundwater flow rate. If flow from a potential pollution source to a monitoring well is expected to be on the order of decades (assuming a release occurs), then very frequent sampling does not seem warranted and perhaps annual sampling for a few indicator constituents would suffice.

259

The complexity of the hydrogeology of the oil shale region makes estimation of groundwater flow rate difficult at best and the actual flow rates highly site specific. Table 28 lists some estimates of travel time in the Upper Aquifer zone of the Piceance Creek Basin. The wide variation in results reinforces the care needed in design of monitoring programs, as our understanding of the system is incomplete. TABLE 28.

FLOW RATES OF THE UPPER AQUIFER, PICEANCE CREEK BASIN, ESTIMATED BY THREE STUDIES

Study reference

Flow velocity (feet per day)

Lawrence Berkeley Labs, 1978 (data from Weeks et al., 1974) U.S.

Atomic Energy Commission,

Travel time (years to travel 1 mile)

0.05

300

0.36 - 0.78a

20 - 40

11.7

1.2

1972 KnutSOn, 1973 Note: a Range for representative gradient and maximum gradient cases. SAMPLE HANDLING AND PRESERVATION Proper methods of sample handling and preservation should be exercised to minimize the changes in the geochemical environment from which the sample is extracted. The chemical qualities of some samples can change within a few hours or minutes following withdrawal. Other constituents can be preserved and stabilized for a limited period of time, whereas still other constituents have a shelf life of up to 6 months. In addition to sample time constraints, the sampler should be aware of potential problems that may arise from improper selection of sample volumes, containers, and preservatives, as well as inadequate field records and chain-of-custody preparations. Field Data Collection Parameters that should be measured in the field include pH, temperature, and specific conductance. If dissolved oxygen and oxidation-reduction potential measurements are required, these should also be determined in the field. Although some of these parameters have holding times of up to 24 hours (see Table 291, it is recommended that these determinations be made in the field with the appropriate apparatus to prevent inaccurate results Erom delay in receipt of the samples at the analytical laboratory. In addition to holding times Table 29, derived from U.S. EPA (19741, contains information regarding the recommended choice of preservatives and sample containers and volume requirements for various constituents.

260

TABLE 29.

RECOMMENDATION FOR SAMPLING AND PRESERVATION OF SAMPLES ACCORDING TO MEASUREMENTa

~~

Parameter Measured

Volume Required (ml)

b Container

Preservative

Holding TimeC

Acidity

100

None required

24 hours

Alkalinity

100

Cool, 4OC

Arsenic

100

HNO

24 hours d 6 months

3

1,000

BOD Bromide

100

Chloride

50

Chlorine

200

to pH < 2

Cool, 4OC

6 hours

Cool, 4OC

24 hours

None required

7 days

Determine on site

No holding

to pH < 2

COD

50

H

Color

50

C o o l , 4OC

SO

2 4

7 days 24 hours

500

Cool, 4O; NaOH to pH 12

Probe

300

Determine on site

Winkler

300

Fix on site

4

Fluoride

300

None required

7 days

Hardness

100

Cool,

4OC;

Iodide

100

Cool.

4OC

24 hours

MBAS

250

Cool.

4OC

24 hours

Filter on site:

6 monthsd

Cyanides Dissolved Oxygen

HNO to pH < 2 3

None

to 8 hours

d 6 months

Metals Dissolved

200

HNO3 to pH < 2

Suspended

200

Filter on site

Total

100

HN03 to pH < 2

Dissolved

100

Filter: HNO3 to pH < 2

38 days (glass); 13 days (hard plastic)

Total

100

HNO3 to pH < 2

38 days (glass): 13 days (hard plastic )d

Ammonia

400

Cool,

4OC;

Kjeldahl, total

500

Cool,

4OC;

Nitrate

100

Cool, 4O

24 hours

Nitrite

50

Cool,

4OC

48 hours

6 months d 6 months

Mercury

Nitrogen H2SO4 to pH < 2 H2S04 to pH < 2

24 hours 24 hourse

C o o l , 4OC

24 hours

and grease

1,000

Cool, 4oc; HC1 or H2SO4 to pH < 2

24 hours

Organic carbon

25

Cool, 4%; HC1 or H2SO4 to pH < 2

24 hours

25

Determine on site

6 hours

50

NTA Oil

(continued)

26 1

TABLE 29 (continued)

Constituent Phenolics

Volume Required (ml) 500

b Contdiner G only

Preservative

Holding TimeC

Cool, 4OC; H3PO4 to pH < 4 ; 1.0 g CUSO4/l

24 hours

24 hours

Phosphorus Orthophosphate. dissolved

50

P.G

Filter on site; cool

Hydrolyzable

Cool, 4OC; H SO to pH < 2 2 4 Cool, 4OC; H SO to pH < 2 2 4 Filter on site; cool, 4% H2SO4 to pH < 2

24 hourse

~ O C

50

P.G

Total

50

P,G

Total, dissolved

50

P.G

100

P.G

Cool. 4OC

7 days 7 days

24 hourse 24 hour+

Residue Filterable Nonfilterable

100

P.G

Cool, 4OC

Total

100

P.G

Cool, 4OC

7 days

volatile

100

P,G

Cool, 4OC

7 days

Settleable matter Silica Specific conductance

None required

24 hours

50

P only

Cool, 4OC

7 days

100

P.G

Cool, 4OC

f 24 hours 7 days

1,000

P,G

Sulfate

50

P,G

Cool. 4OC

SulEide

50

P.G

2 ml zinc acetate

24 hours

sulE i te

50

P.G

Determine on site

No holding

P,G

Determine on site

No holding

P.G

Cool, 4OC

7 days

Temperature Tur bid i t y

1, 000

100

__

Notes: aMore specific instructions for preservation and sampling are found with each procedure as detailed in U.S. EPA (1974). A general discussion on sampling water and industrial wastewater may be found in ASTM, Part 31, p. 72-82 (1976). Method D-3370. bPlastic (P) or glass(G): for metals polyethylene with a polypropylene cap (no liner) is preferred. CIt should be pointed out that holding times listed above are recommended for properly preserved samples based on currently available data. It is recognized that for some sample types, extension oE these times may be possible, while for other types, these times may be too long. Where shipping regulations prevent the use of the proper preservation technique or the holding time is exceeded, such as the case of a 24-hour composite, the final reported data for these samples should indicate the specific variance. dWhere HNO3 cannot be used because of shipping restrictions, the sample may be initially preserved by icing and immediately shipped to the laboratory. Upon receipt in the laboratory, the sample must be acidified to a pH < 2 with HNO3 (normally 3 ml 1:l HN03/l is sufficient). At the time of analysis, the sample container should be thoroughly rinsed with 1:l HNO3 and the washings added to the sample (volume correction may be required). eData obtained from National Enforcement Investigations center, Denver, Colorado, support a 4-week holding time for this parameter in sewerage systems (SIC 4952;. fIf the sample is stabilized by cooling. it should be warmed to 25OC for reading, or temperature correction made and results reported at 25OC.

262

Today, field studies are supported by some fairly precise, portable, analytical equipment that furnish accurate data, thus eliminating any effects delayed sample shipment may have on the validity of water chemistry analysis performed at the laboratory. Furthermore, these determinations can be easily measured and provide valuable on-site information regarding aquifer characteristics of aid in the collection of representative aquifer water. Specific Conductance-Specific conductance is a measure of the ability of a solution to transmit an electrical current. In water samples, the specific conductance is an The indication of the concentration of dissolved solids (i.e., salinity). unit of measurement for specific conductance is the inverse of the resistivity and is typically expressed in micromhos per centimeter. Specific conductance is an important measurement that should always be made in the field during sample collection. This parameter is very useful in determining when aquifer water has been obtained and thereby aids in the collection of representative samples. The recommended holding time is only 24 hours (U.S. EPA, 19791, which may present problems in obtaining accurate results from the analytical laboratory if sample shipment is delayed. Temperature-Temperature should always be measured immediately after sample withdrawal. It is a very easy measurement to obtain, and the equipment used for its determination should be accurate to within fO.l°C to allow for future geochemical evaluations of equilibrium thermodynamics. Also, field determinations of aquifer water temperatures prevent inaccurate measurements due to the modification of the sample temperature during sample preservation and transportation. pH-Wood (1976) provides the following description for pH: "The pH of a solution is a measure of effective hydrogen-ion concentration or, more accurately, it is the negative logarithm of the hydrogen-ion activity in moles per The pH of an aqueous solution is typically conlitre: pH = -log (H+)." trolled by the disassociation of acids, bases, and hydrolysis. The pH of a groundwater sample is further controlled by the carbonate system, including dissolved carbon dioxide, bicarbonate, and carbonate ions. The pH of an aqueous solution can be measured precisely and quickly with mechanical instruments. Some researchers have found that pH is the best parameter for determining that representative aquifer water has been obtained from a well (Brown et al., 1970; wood, 1976; and Humenick et al., 1980). The holding time for pH is 7 hours ( U . S . EPA, 1979), however, which can affect analytical determinations if sample shipment is delayed. Therefore, it is highly recommended that pH be measured in the field at the time of sample withdrawal.

263

Dissolved Oxygen and Oxidation-Reduction PotentialGeochemical evaluations of a groundwater system may require dissolved oxygen and oxidation-reduction potential measurements. If this is the case, these measurements should be conducted in the field at the time of sample collection for accurate results. Particular care must be exercised during these measurements to prevent atmospheric aeration of the sample during collection and analysis. Many companies produce precise, portable, easily used, analytical equipment for these measurements. Field Notes and Records, sample Labels The following notes and records for sample collection should be maintained for future data evaluation: Time and date of arrival, sample collection, and departure from the well site The water level of the well Description of the sample source, including well number and location and the following additional information (if applicable): --

Depth of bailing)

sample collection

(of critical

importance for

--

Duration of pumping previous to sample collection

--

Well volumes extracted previous to sample collection

--

Pump placement

Well data information pertaining to well construction and completion and the aquifer(s1 or section of aquifer in which the well is completed, including:

-- Length and depth to screened interval, open interval, and/or casing interval

-- Well annulus -- Total depth of well Water quality data for specific conductance, pH, temperature, water level, et.c. Sampling specifications, particularly the procedures previously employed for sample collection, that will establish consistent sampling methods for each sampling effort, including: --

Pump placement

26 4

Discharge rate --

Time of sample collection, etc.

0

The type of sampling methodology utilized for sample withdrawal

0

Field observations pertinent to sample collection, including color, sediment, turbidity, etc.

0

The reason for the sampling effort

0

The results of field determinations performed at the time of sample collection (e.g., temperature, specific conductance, pH, oxidation-reduction potential, dissolved oxygen, etc.)

0

Any problems encountered in the field during sample collection.

0

The identity of the sample collector.

Sample labels should be prepared before the sampling effort and affixed to the sample container. If possible, the information should be duplicated on the sample container itself to prevent errors resulting from label detachment during sample handling and shipment. In addition, waterproof pens should be used by the sampler to prevent dissipation. The following information should be included on the sample label and container: 0

Time and date of sample collection (if multiple samples are to be collected from the same well, the hierarchy or succession of the samples collected should also be noted)

0

The well number and location

0

The preservative (if any) utilized

0

If the sample has been filtered in the field or been sent to the analytical laboratory unfiltered.

_. Field

Handling and Preservation Techniques

Preservation of samples through the use of techniques currently available and easily applied in the field can only retard the chemical or biological changes that take place after the sample has been withdrawn from the well. Methods of preservation are relatively limited and are intended to: (1) retard biological activity, (2) retard hydrolysis of chemical compounds and complexes, ( 3 ) reduce volatility of constituents, and ( 4 ) reduce absorption effects (U.S. EPA, 1979). In general, preservation techniques include pH control, chemical addition, refrigeration, and freezing. The following preservatives are used to retard sample changes after collection (U.S. EPA, 1977):

26 5

Preservative

Applicable To

Action

HgC12

Bacterial inhibitor

Nitrogen forms, phosphorus. forms

Acid (HNO3)

Metals solvent, prevents prec ipitat ion

Metals

Acid (H2SO4)

Bacterial inhibitor

Organic samples (COD, oil and grease, organic carbon)

Acid (H2SO4)

Salt formation with organic bases

Ammonia, amines

Alkali (NaOH)

Salt formation with volatile compounds

Cyanides, organic acids

Refrigeration

Bacterial inhibitor

Acidity-alkalinity , organic materials, BOD, color, odor, organic P, organic N, carbon, etc., biological organisms (coliform, etc.)

Containers used for sample collection should be selected for their nonreactivity with the particular analytical parameter to be measured. Depending on the constituent(s1, the containers typically consist of either glass or plastic. Table 29 provides the recommended sample container for the particular analysis of interest. In addition, it is generally advantageous to prepare the sample containers with the appropriate preservative prior to sample collection. This procedure may be very time-consuming since separate bottles and chemical preservatives are required for certain parameters, which may result in several containers for each sample collected. However, this preparation will result in the elimination of laborious effort in the field during sample collection. Determination of dissolved concentrations will require the sample to be filtered through a 0.45-micron filter prior to acidification. If the sample is not filtered and acid is added as a preservative, much of the particulate matter will be dissolved by the acid resulting in anomalously high concentrations of dissolved constituents. It is also recommended that the sample be filtered as soon as possible after withdrawal, preferably in the field. However, samples to be used for on-site temperature, dissolved oxygen, pH, and/or oxidation-reduction potential measurements should not be filtered before these determinations have been made. After the sample has been filtered and preserved, the recommended procedure is to place the samples on ice for further preservation during shipment. The use of an ice chest is the preferred approach for sample shipment since ice chests are easy to handle and are insulated such that a temperature between Oo and 10°C can be maintained for a limited period of time. 266

Sample Shipment The relative remoteness of the oil shale region can result in some delay in receipt of the groundwater quality samples at commercial analytical laboratories. To evaluate the effects of this potential problem on the results of chemical analysis, a testing program was initiated by Tempo. The program was conducted in conjunction with Cathedral Bluffs Shale Oil Company personnel on Federal Lease Tract C-b. The field effort involved the sampling of three alluvial wells with a portable, submersible pump. At each well, the samples were collected after the field parameters (i.e., specific conductance, pH, and temperature) had stabilized. The sample collected from each well was handled as follows: The sample was split three ways and preserved with EPA-recommended preservatives (see Table 29) Samples were refrigerated or cooled as recommended by EPA (see Table 29) The samples were then shipped to the analytical laboratory for analysis in the following sequence: --

First sample split was analyzed within 24 hours of sample collection

-- Second sample split was

analyzed

7

days

after

sample

15

days

after

sample

collection

-- Third

sample collection.

split

was

analyzed

This sequence of sample analysis was intended to simulate circumstances that can arise during field sampling efforts. The initial split represents the optimum situation for sample shipment, i.e., immediately after sample collection. The second sample split represents the situation where samples collected during the week are shipped to the laboratory for analysis at the end of the week. The third sample split represents either a lengthy field survey resulting in a shipment of samples at the end of two working weeks or a significant delay in the receipt of the samples at the laboratory due to shipping problems. The chemical analyses presented in Tables 30 through 32 represent samples collected from alluvial wells A-6, A-9, and A-12. respectively. The constituents of the chemical analyses consisted of specific conductance, pH, total dissolved solids (TDS), bicarbonate, carbonate, chloride, ammonia, sulfate, nitrate, and dissolved organic carbon (DOC). The constituents chosen were based on the following EPA holding-time recommendations:

267

TABLE 30.

CHEMICAL ANALYSIS OF SAMPLES TAKEN FROM ALLUVIAL WELL A-6 T I M E S OF ANALYSIS Within 24 hours

Constituent

Repl 1

specific conductancea 1,270 PHb Bicarbonate Carbonate sulfate Chloride TDS Ammonia

7.8

Repl 2 1.260 7.75

Repl 3 1,280 7.8

mean 1,270 7.8

706

710

709

<1

<1

<1

<1

189

208

195

197

888 <0.1

15.8 880 <0.1

15.8 884 <0.1

15 days

7 days

712

16.2

FOR THREE DIFFERENT

15.9 884 <0.1

Std. Dev. 8.2

Repl 1 1,220

0.02

2.5 0

7.9 0.2 3.3 0

'7.70

Repl 2 1,210 7.80

Repl 3 1,205 7.70

mean 1,212

702

699

702

<1

<1

<1

<1

249

233

243

242

918 10.1

12.9 912 <0.1

12.8 920 <0.1

6.2

7.730.05

706

12.4

Std. Dev.

12.7 917 <0.1

2.9 0 6.6

0.22 3.4 0

Repl 1 1,250 7.70

Rep1 2 1,260

7.80

Repl 3 1,255 7.79

Mean 1.255

699

699

697

<1

<1

<1

<1

234

242

240

239

928 <0.1

12.6 920 <0.1

12.9

920 <0.1

12.9 923

t0.1

Nitrate

0.20

0.20

0.20

0.20

0

0.20

0.20

0.30

0.23

0.5

0.20

0.20

0.20

0.20

Fluoride

0.33

0.34

0.33

0.33

0

0.40

0.40

0.41

0.40

0

0.39

0.40

0.40

0.40

DOC

16

14

14

15

1

Notes: a Measured 1.350 in the Eield. units umhos/cm at 25OC.. bNeasured 7.5 in the field, pH units. Repl -- Replicate Sampling: Std. Dev. -- Standard Deviation.

46

52

49

Constituent units mq/l.

49

2.4

63

61

56

4.1

7.760.05

693

12.8

Std. Dev.

60

2.8

0 3.4

0.1 3.8

0 0 0 2.9

TABLE 31.

CHEMICAL ANALYSIS OF SAMPLES TAKEN FROM ALLWIAL WELL A-9 TIMES OF ANALYSIS Within 24 hours

Constituent

Repl 1

specific Conductancea 1,110 PHb Bicarbonate Carbonate sulfate Chloride

7.97 482

1,100

7.99 486

Repl 3 1,095 7.85 486

7 days Mean 1,102 7.94 485

<1

<1

<1

299

296

305

300

7.22 784

TDS

Repl 2

7.59 784

1.6 776

7.47 781

Ammonia

<0.1

<0.1

<0.1

Nitrate

1.0

0.9

1.0

0.97

Fluoride

0.20

0.18

0.19

Doc

8

7

10

Std. Dev. 6.2 0.06 1.9 0

3.'7 0.26 3.8

1,050 7.93 489

Repl 2 1,055 7.90 493

Repl 3 1,055 7.82 492

1,053 7.88 491

<1

<1

<1

<1

315

322

320

319

4.90 796

5.32 800

5.30 804

5.17 800

2.4 0.05 1.7 0

2.9 0.19 3.3

<0.1

<0.1

0.04

1.0

0.9

1.0

0.97

0.04

0.19

0

0.19

0.21

0.20

0.20

0

8

1.3

34

42

37

a SpeciEic conductance measured 1.170 in the field. units pmhos/cm at 25OC. bpH measured 7.6 in the field, pH units.

--

Mean

Std. Dev.

<0.1

<0.1

0

Repl 1

15 days

Notes:

Repl

FOR THREE DIFFERENT

Replicate Sampling: Std. Dev. -- Standard Deviation. Constituent units m g / l .

<0.1

38

0

3.3

Repl 1 1,085 8.05 492

Rep1 2 1,110 8.05 489

Repl 3 1,115 7.98 492

Mean 1,103 8.03 491

<1

<1

<1

355

325

329

330

5.20 812

5.65 804

5.26 816

5.37 811

Std. Dev. 13.1 0.04 1.4 0

4.1 0.17 5.0

<0.1

<0.1

1.0

0.9

1.0

0.97

0.04

0.19

0.20

0.20

0.20

0

<0.1

45

51

50

<0.1

49

0

2.6

TABLE 32. CHEMICAL ANALYSIS OF SAMPLES TAKEN FROM ALLWIAL WELL A-12 FOR THREE DIFFERENT TIMES OF ANALYSIS Constituent Specific Conductancea PHb Bicarbonate Carbonate Sulfate Chloride TDS Ammonia

Repl 1 1,410 7.8 598

Within 24 hours Repl 2 1,400 7.85 596

Repl 3 1,400 7.8 596

Mean 1,403 7.82 597

<1

<1

<1

<1

398

418

402

406

9.11 1,052 <0.1

10.10

1,040 <0.1

9.31 1,056 <0.1

15 days

1 days

9.71 1,049 <0.1

Std. Dev. 4.7 0.02 1.0 0

8.6 0.32 6.8 0

Repl 1 1,385 7.81 596

Repl 2 1,390 7.86 606

Repl 3 1,315 1.85 602

Mean 1,380

601

<1

<1

<1

<1

441

450

455

1,116 <0.1

1.31 1,116

8.17 1,100 <0.1

4.1

'7.84 0.02

469 7.22

Std. Dev.

7.51 1.111 <0.1

4.1

u 9.1 0.43 7.5 0

Repl 1 1.405 7.83 609

Repl 2 1,395 '7.84 596

Repl 3 1,400 7.85 602

Mean 1,400 1.84 602

<1

<1

412

465

451

462

1.56 1,136 <0.1

1.56 1.156

<0.1

1.41 1,056 <0.1

1.53 1,116 <0.1

Nitrate

0.30

0.20

0.20

0.23

0.05

0.20

0.20

0.30

0.23

0.05

0.20

0.20

0.20

0.20

Fluoride

0.20

0.18

0.18

0.19

0.01

0.23

0.20

0.19

0.21

0.02

0.20

0.20

0.20

0.20

Doc

15

15

19

16

1.9

31

35

34

Notes: a SpeciEic conductance measured 1,350 in the field, units pmhos/cm at 25W. bpH measured 1.5 in the field. pH units. Repl -- Replicate Sampling: Std. Dev. -- standard Deviation. constituent units mg/l.

35

1.3

57

56

55

56

Std. Dev. 4.1 0

5.3 0

8.9 0.04 43.2 0

0 0 0.8

EPA Recommended

Constituent

Holdinq Time 24 hours

Specific conductance PH

6 hours

Total dissolved solids

6 months

Bicarbonate

24 hours

Carbonate

24 hours

Chloride

7 days

Fluoride

7 days

Ammonia

24 hours

Nitrate

24 hours

sulfate

7 days

Dissolved organic carbon

24 hours 6 months

Trace metals

Due to the long shelf life of the trace metals (i.e., 6 months), these constituents were not incorporated in the chemical analysis. The constituents that display changes in concentration during the holding periods are specific conductance, pH, sulfate, chloride, and DOC. TDS concentrations also vary somewhat between holding periods. The other constituents either had concentrations below detection limits (e.g., ammonia and carbonate) or maintained fairly uniform concentrations throughout the entire 15-day period (e.g., bicarbonate, nitrate, and fluoride). In every sample, the specific conductance and pH data differ somewhat between the field and the analyses performed after 24 hours. After this period, the next two analyses indicate that the pH remains fairly constant. The specific conductance does vary slightly during the latter two analyses. The TDS data do not reflect the trend observed for specific conductance but instead generally increase slightly during the 15-day period. The sulfate and chloride concentrations were also variable, particularly between the 24-hour analysis and the 7-day analysis. In general, sulfate increased in concentration during the holding periods, whereas the chloride concentration decreased during the same interim. In some instances, such as the decrease in chloride concentration during the initial 7-day period for the sample collected from Well A-6, the changes were considerable. The constituent that displayed the most appreciable variability was DOC. In all three well samples, the DOC concentration increased significantly over the 15-day period. However, the polyethylene sample containers may have contributed somewhat to this trend. It has been demonstrated that polyethylene can contribute contaminating organics to the sample and affect the DOC concentrations.

271

Summers (1972) has demonstrated that changes in pH, specific conductivity, and the carbonate-bicarbonate system are all indicative of sample aging. Typically, the following reaction will control these changes: CaC03 + H20 + COi + Ca2 + 2HC03. Changes in the C02 concentration can also influence these constituents. The data collected by this survey do not reflect appreciable increases in the bicarbonate concentration during the 15-day period. However, in that the greatest increase in pH occurred during the first 24 hours, perhaps the samples achieved equilibrium before the first analysis by the laboratory. If such were the case, a significant increase in the bicarbonate would require immediate analysis for detection and probably could not be observed after a period of time, in this case 24 hours. The data also indicate that chloride and sulfate may be the most sensitive parameters with respect to sample holding-time considerations. Although the EPA-recommended holding time for these constituents is 7 days, it is apparent from the data that the most significant changes in the concentrations of these constituents occurred during the first 7 days. Due to the potential contamination of the DOC by the polyethylene sample container, the effects of the holding times on this constituent are inconclusive. It is apparent that correct and quick sample shipment is critical for accurate analytical results. In the oil shale regions, time constraints may prevent field personnel from delivering the samples to the laboratory, particularly if the sampling effort extends beyond 24 hours. In this case, the most efficient procedure is to ship the samples via commercial bus or plane. This procedure is very inexpensive (on the order of $2 to $10 per ice chest) and will eliminate unnecessary trips to the analytical laboratory by field person-nel. Furthermore, transportation by these methods is very reliable and provides reasonable assurance against changes in sample chemistry due to prolonged sample storage. Chain of Custody The typical chain of custody in the oil shale region includes the Sam-pler, the individuals involved in the transportation, and the individuals handling the sample at the analytical laboratory. The proper procedures that should be followed during this chain of custody are: Include as few people as possible in the chain of custody. Collect, preserve, and ice the samples according to the recommended procedures Label each sample container according to the recommendations previously presented indicating the analysis required on the sample labels if preparations have not previously been made Maintain a field notebook or logbook during each survey and store it in a safe place, with all entries signed by the individual responsible for the field effort

272

Assign complete responsibility for the collected samples (including those delivered by field personnel) to the individual conducting the effort, including overseeing all transportation activities (including timely delivery of the samples to the busline or airline facility and their receipt at the analytical laboratory) and maintaining a record of these activities as follows: time and date of deliveries, method of transportation, and the individual(s) performing the transportation. Furthermore, effort should be made to have the laboratory performing the chemical analysis retain a custodian to maintain a record indicating: Time and date of sample receipt The person receiving the sample The sample number The number assigned to each sample by the laboratory. This custodian should provide for proper handling and storage of the samples prior to analysis. In addition, the custodian should be responsible for distribution of the samples to the individual performing the analysis, recording the individual's identity, and assuring that immediate analysis is conducted to avoid water chemistry changes due to prolonged sample storage. SELECTION OF CONSTITUENTS FOR MONITORING The proper location of monitoring points is largely determined by the locale and character of the potential sources of groundwater quality impact and the local source hydrogeology. The constituents for monitoring are selected so as to provide a cost-effective indication of the nature and extent of impact on groundwater quality. Assessment of enrichment factors (or concentration change above ambient), specific indicator constituents, and stable isotopes are possible approaches for selection of constituents for chemical analysis. Enrichment Factors In this subsection, enrichment factors, EF, will be calculated for major possible sources of groundwater impact according to the expression: EF

=

concentration from potential pollution source concentration in aquifer

For this assessment, representative baseline water quality levels were selected (Table 3 3 ) . Concentrations from the more saline sections of the Lower Aquifer are included principally in Table 33 in order to most clearly demarcate the differences in enrichment factors. Representative concentrations of constituents in retort water and in spent shale leachate were used in this preliminary analysis.

273

TABLE 33.

REPRESENTATIVE CONCENTRATIONS IN GROUNDWATERS ADAPTED FOR THIS STUDY.

Springs, seeps and alluvial aquifer Gross Parameters (mg/l) Conductance (pmho/cm)

1,300

upper Aquifer

1,500

7

-

Saline Lower Aquifer

7,000 8

PH TDS Ammonia

6 - 8

Bicarbonate

500

500

4,000

70

50

200

Carbonate

3

3

20

Chloride

10

10

20

Calcium

Cyanide Magnesium

900

8.5

1,000

0.4

0.5

0.01

0.01 70

70

Lower working limit of detection, Denver a Laboratory

2

---

6,000

1

10

100

0.01 20

5 0.05

5 0.2 - 1

0.002 50

Nitrate

2

1.0

Potassillm

2

2

20

0.1

Silica

20

20

10

1

Sodium

150

200

2

2

350

350

Strontium Sulfate Phosphate

0.5

2,500

___ 60

0.02

0.1 0.01 3 - 10

<0.1

<0.1

<0.1

0.1

Kjeldahl nitrogen

2

___

___

0.1

Nitrite

0.2

sulfide

0.2

0.02 0.6

0.6

0.1

Minor and Trace Elements Aluminum Arsenic Barium Beryllium Boron Bromine

300

200

250

100

2 - 50

5

10

10

50

100

800

<10

500

1,000

40,000

50

20

50

500

2,000

50

5

(continued)

274

TABLE 33 (continued)

Springs, seeps and a 1luvial aquifer

Upper Aquifer

Saline Lower Aquifer

Lower working limit of detection, Denver a Laboratory

2

Minor and Trace Elements ( p g / l ) (continued) Cadmium

17

10

5

Chromium

11

2 - 300

10

3

5

Coba1t

8

5

10

-

10

30

70

70

10

Fluoride

400

7,000

20,000

100

Iron

500

800

10

Lead

50

Copper

Manganese Mercury

500

Molybdenum

40

Nickel

5,000

10 - 100

30 - 500 0.4 - 3

-

100

0.4 - 3

50

5 10

30

20

5

5

20

Radiation, beta (pCi/l)

4

4

20

20

70

<10

110

10

10

---

-__

10 4

selenium

<10

silver Thallium Titanium

<1 - - _.

100

100

<30

<20

5

2

16

200

200

200

200

Uranium

___

vanadium zinc Lithium

0.02

50

Radiation, alpha (pCi/l)

scandium

5

100

0.4 - 2

10

Rubidium

1 - 10

100

5 0.05 5

-

10

-

50

300

___

Gross Organic Parameters

TOC (mg/l)

5

3

10

1

Phenol (pg/l)

3

3

1 - 10

DOC (mg/l)

5

8

20

__-

COD (mg/l)

16

18

13

10

Note: a Using standard methods.

275

1

Also shown in Table 33 are the lowest concentrations typically reported by a Denver water quality laboratory employing standard methods. As can be seen, the average concentrations of P, V, Ti, As, Se, Ni, Co, Cu, Cd, Br, Be, Ba, and As are close to or below these lower limits. It is therefore likely that many of these trace element species were determined by spark source mass spectroscopy which resulted in the improvement in detectability. This, however, resulted i.n a degradation in precision in comparison to standard met hods. Table 34, which lists enrichment factors for the Lower Aquifer, is pertinent to the contamination of the Upper Aquifer, springs, and seeps by the Lower Aquifer. As can be seen, NH4, K, Na, B, and Br are enriched at least 10 times in the Lower Aquifer compared to either the Upper Aquifer or spring waters. In addition, Ba and F are enriched in the Lower Aquifer compared to spring waters. It is likely, therefore, that these species would be indicators of intrusion of waters from the Lower Aquifer. TABLE 34.

SPECIES ENRICHED IN THE LOWER AQUIFER Enrichment factors

Conductance TDS

Lower Aquifer

Lower Aquifer

Upper Aquifer

Springs and seeps

4.6

5.4

6

6.6

20

25

Bicarbonate

8

8

Calcium

4

4

Potassium

10

10

Sodium

13

17

Barium

8

16

Boron

40

80

Bromine

10

25

Ammonia

Fluoride

2.9

Phenolics

0.3 - 10

50 0.3 - 10

Table 35 lists enrichment factors for leachates and shows that the parameters pH, TDS, C1, Na, SO4, Mo, Se, and TOC are likely indicators (i-e., tracers) of contamination in the Lower Aquifer. Although carbonate appears to be enriched in leachate, this reflects an increase in pH rather than an increase in total HCO3 + CO3.

276

TABLE 35.

ENKICHMENT FACTORS ESTIMATED FOR SPENT MIS OIL SHALE LEACHATE

-

Enrichment factors

Gross

Leachate

Leachate

Upper Aquifer

Lower Aquifer

Parameters (mg/l)

Conductance (umhos/cm)

2.5 - 52

PH TDS

0.6 - 2 6

0.6

- 140

0.2

Bicarbonate

-.

0.54 - 11

0.4

- 1.5

1 - 23

--_

Calcium

0.2 - 60

Carbonate

330 - 1,000

Chloride

6.4 - 310

3.2 - 160

Cyanide

--_

---

Magnesium

0.01 - 67

---

Nit rate Potassium

2.5 - 70

Silica

0.5 - 1.0

Sodium

0.37 - 180

---

S t ront ium

sulfate Kjeldahl nitrogen

0.51 - 260

Sulfide

0.05 - 16 50 - 150

0.05 - 235

--0.25 - 7 1.0 - 2.0 0.03 - 14

--3 - 1,500

---

---

1.6 - 3.3

1.6 - 3.3

Minor and Trace Elements (pg/1)

---

Aluminum Arsenic Barium Beryllium

0.20 - 20

0.20 - 20

0.6 - 1.0

0.08 - 0.13

---

--(continued)

277

TABLE 35 (continued) Enrichment factors Leachate

Leachate

Upper Aquifer

Lower Aquifer

Minor and Trace Elements (pg/l) (continued) Boron

0.4 - 12

0.01 - 0.3

Bromine

___

--_

Cadmium

0.3 - 0.6

0 6 - 1.2

Chromium

0.01 - 4

Fluoride Iron

0.14 - 2.9

Mercury

0. 4 - 2.9

0.001 - 11

0 - 4

0.12 - 6

0.8 - 3.8

--_

-__

Lead Manganese

---

--_

Cobalt Copper

0 4 - 130

0.6 - 5

- 0.8

0.10

0.6 - 5 0.15 - 0.8

-

Molybdenum

1.5 - 4,000

4

Nickel

2.5 - 30

5 - 60

1,500

Scandium

-_---

Selenium

0.5 - 200

0.5 - 200

___

Thallium

___ -_-

T'itanium

---

Uranium

---

Vanadium

1.5 - 50

0.19 - 6.3

Zinc

0.1 - 15

0.1 - 15

Rubidium

Silver

Gross Organic Parameters

- 550 ---

TOC

10

Phenolics

278

3 - 170

---

The uncertainty in the enrichment factors reflects variations in the original oil shale, methods of retorting, methods of analysis, and emphasizes the necessity of preliminary controlled experiments prior to finalizing monitoring programs. Enrichment factors for those elements which are present in concentrations near the detection limit, such as Se, would also be expected to give variable enrichment factors. Table 36 presents enrichment factors for retort waters and is relevant to the extent that an in situ retort is not completely burned and retains a fraction of the retort water. Most notably enriched in the retort water are NH;, Cog, As, Br, Co, Hg, Se, V, U, and TOC, and possibly NO?, PO:-, and Ni. The sulfur species shown at the bottom of the table will be discussed in the next subsection. Although CO? is enriched in retort waters, it is unlikely that this species would successfully pass through a spent retort because of the reaction: 2+ ca + C O ~= cacog

In fact, Parker et al. (1977) have shown that spent shale does, in fact, remove carbonate from surface waters. N H ~ ,on the other hand, is likely a highly mobile Species, possibly after conversion to nitrate. In addition, the more hydrophilic portions of the TOC may also travel with leachate and prove indicative of groundwater contamination. As in leachates from spent shale, retort waters appear enriched in those species forming soluble anions, such as As, Br, Se, and U. The origin of Co, Hg, and V in the retort waters is less clear, although V is known to form organic complexes with organic compounds found in crude petroleum oils, and Hg is known to vaporize from a simulated in situ retort and to recondense later (Fox et al., 1978).

In summary, the water quality parameters pH, TDS, C1, Na, SO4, Mo, Se, NH4, Br, Se, V, U, and TOC should be considered as potentially valuable indicators of groundwater contamination, both for their elevated enrichment factors and for chemical reasons. The utility of enrichment factor estimates is the identification of chemical species likely to be detected in groundwater which indicate the impact of a known source. To evaluate this possible monitoring approach, the enrichment factors calculated above were categorized (arbitrarily) as follows: Re lat ive likelihood of detection of impact

Table 37 category

Enrichment factor range

1

>500

2

50 - 500

Moder at e

3

10 - 50

LOW

279

High

TABLE 36.

ENRICHMENT FACTORS FOR RETORT WATERS Enrichment factors Leachate

Leachate

Upper Aquifer

Lower Aquifer

Gross Parameters (mg/l)

Conductance Alkalinity

-

10 - 130

2.1

19 - 130

2.4 - 17

27

PH

1.0 - 1.6

1.0 - 1.2

TDS

1.8 - 25

0.3 - 4

Ammonium

3,400 - 26,000 34

Bicarbonate

170 - 10,000

Carbonate

0.002

-

80

40

-

90

Cyanide Magnesium

62

0.01 - 1.2

calcium Chloride

-

0.001 - 5

0.17 - 120

Nitrate

1.5 - 35

Potassium silica

0.02 - 8

sodium

0.001 -- 22

0.06 - 5.4

Sulfate

0.8 - 1,000

Phosphate Kjeldahl nitrogen

1,700

Sulfide

0.17

170

-

1,300

4 - 8 0.002 25

-

0.31 1,600

0.001 - 40

40 - 90 0.01 - 20

0.34

-

240

0.15 - 3.5 0.04 -0

- 15 - 1.7

0.3 - 30 0.8 - 1,000

__0.17

Minor and Trace Elements (vg/l) Aluminum

-__

Arsenic

2.4 - 600

Barium

0.2 - 7

-

600

-__

Beryllium Boron

2.4

0.003 - 0.9

0.26 - 9

0.01 - 0.22

Bromine

0.4 - 50

0.04 - 5

Cadmium

0.1 - 1.6

0.20

Chromium Cobalt

0.07 - 60 0.4 - 130

-

3.2

2.0 - 12 0.7 - 220 (continued)

280

TABLE 36 (continued)

Enrichment factors Leachate

Leachate

Upper Aquifer

Lower Aquifer

Minor and Trace Elements (pg/l) (continued) Copper Fluorine Iron Lead Manganese Mercury

0.04 - 1.3

0.05 - 9 0.00001 - 15

- 10 0.23 - 1.4 0.05

3.3 - 1,000

Molybdenum

2 - 11

Nickel

3

Radiation, beta

9 - 35

- 50

0.04 - 1.3 0.02 - 3 0.001

-

100

0.4 - 10

- 1.4 - 1,000 2 - 11

0.23

5

6 - 100

1.8 - 7

Scandium

---

---

Selenium

>0.5 - >170

>0.5 - >170

Silver

---

Thallium

---

Titanium uranium

2 >0.33

2 - 5,500

Vanadium Zinc

- 21 - >150

0.20 - 25

_-_

Lithium

---_2 - 21 >0.50 - 230 0.25 - 700 0.20 - 25 ---

Organic Parameters 10,000

3,000

- 20a b 1,200 - 6,400

- 120a b 1,200 - 6,400

TOC Unusual Sulfur Species Total sulfur Thiosulfate

6

Tetrathionate

400b b 65 - 2,000

Thiocyanate

35

400b

65

-

b 2,000

Notes: a Calculated by assuming that all S in groundwaters is present as sulfate. bCalculated by assuming background concentrations equal to a detection limit of 0.5 mg/l.

281

TABLE 37.

RELATIVE LIKELIHOOD OF DETECTION OF MOBILITY FROM VARIOUS SOURCES TO UPPER AND LOWER AQUIFERS AND SPRINGS BASED ON ESTIMATED ENRICHMENT FACTORS~ In situ leachate to Upper Aquifer

to Lower Aquifer

Conductivit y

2

3

3

Total dissolved soiids

2

3

___

___

___

3

Constituent

Lower to Upper Aquifer

Lower Aquifer to springs

In situ leachate

Retort water to Upper Aquifer

Retort water to Lower Aquifer

General water quality measures

Alkalinity Major inorganic ions Calcium

2

Magnesium

2

Potassium

2

3

Sodium

2

3

Chloride

2

2

Sulfate

2

___

3

___

Fluoride Bicarbonate Carbonate

_. -

1

2

1

Ammonia

___

1

Nitrate

.

__

2

Phosphate Silica

1 -__

Organics Total organic carbon

1 -__

___

Kjeldahl nitrogen

1

_--

Cyanide

2

2

Phenolics

1

(continued)

TABLE 37 (continued)

Constituent

Lower to Upper Aquifer

Lower Aquifer to springs

In situ leachate to Upper Aquifer

In situ leachate to Lower Aquifer

Retort water to Upper Aquifer

Retort water to Lower Aquifer

Sulfur species Total sulfur Th iosu1 fate Tetrathionate Thiocyanate Trace elements Arsenic

3

Barium

3

Boron

2

Bromide

3

Chromium

..

.__

1

1

-__

___

___ 3

-

2

3

Cobalt

2

2

Iron

3

2

Lead

3

3

Mercury

1

1

Molybdenum

1

1

3

3

Nickel

3

2

3

2

selenium

2

2

2

Titanium

___

___

2

3

3

2

2

Urariium Vanadium

3

Zinc

3

3

1

1

3

3

Radiological Gross beta

3

Note: 'Enrichment factor (EF) categories: 1 = high likelihood of detection (EF = > 5 0 0 ) : 2 = moderate likelihood (EF = 50 to 500); relatively low likelihood (EF = 10 to 5 0 ) .

The results of this categorization are shown in Table 37. For monitoring in the Upper'Aquifer for the impact from two major in situ sourcesl consider the following listing: Water quality constituent Potential source of impact Retort water

Enrichment factor >500

Enrichment factor 50 - 500

Carbonate

Conductivity

Ammonia

Alkalinity

Phosphate

Chloride

TOC (or DOC) Kjeldahl N

Bicarbonate

Thiosulfate

Cyanide

Thiocyanate

Tetrathionate

Arsenic

Chromium

Mercury

Cobalt

Vanadium

Selenium

Nitrate

Uranium In situ spent shale leachate

Carbonate

Conductivity

TOC (or DOC)

TDS Calcium Magnesium

Molybdenum

Potassium Chloride Sulfate Selenium Examination of this listing indicates that the following constituents may be unique indicators of the impact of retort water or spent shale leachate on the Upper Aquifer. A unique indicator is one which is in the above listing for one sourcel but not for the other:

284

Possible unique indicators Retort water

In situ spent shale leachate

Alkalinity

TDS

Bicarbonate

calcium

Ammonia

Magnesium

Phosphate Nitrate

Potassium Sodium

Kjeldahl N

sulfate

Thiosulfate

Molybdenum

Thiocyanate Tetrathionate Cyanide Arsenic Chromium Cobalt Mercury Uranium Vanadium Following the same procedure for consideration of monitoring in the Lower Aquifer, the following listing was extracted from Table 37: Water quality constituent Potential source of impact Retort water

Enrichment factor >500

Enrichment factor 50 - 500

Carbonate

Nitrate

Ammonia

Cyanide

Phosphate

Total sulfur

TOC

Tetrathionate

Thiosulfate

Cobalt

Thiocyanate

Iron

Arsenic

Nickel

Mercury

selenium

Vanadium

uranium (continued)

285

Water quality constituent Potential source of impact

Enrichment factor >500

In situ spent shale leachate

Enrichment factor 50 - 500

Molybdenum

Chloride Carbonate TOC Chromium Nickel Selenium

Possible unique indicators were then identified from this listing: Possible unique indicators Retort water

In situ spent shale leachate

Ammonia

sulfate

Phosphate

Magnesium

Nitrate

Chloride

Tetrathionate

Chromium

Thiosulfate

Molybdenum

Thiocyanate Arsenic Cobalt Iron Mercury Uranium Vanadium Indicator Constituents

In addition to those water quality parameters for which baseline values have been established, additional species have been measured on a random basis in oil shale effluents. These species will be discussed in this subsection. Inorganic SpeciesData presented earlier suggest that those trace elements forming stable, soluble anions under basic, oxidizing conditions are most likely to be enriched in leachates from a spent in situ retort. It is thus interesting to speculate whether additional elements not discussed above may behave similarly. Other trace elements which form anions under basic, oxidizing 286

conditions include Te, Sb, Bi, Po, W, Re, and I, and their monitoring may prove valuable. However, a more complete investigation of the geochemistry of these species is beyond the scope of this book and their potential mobility remains speculative. Species such as SCN-, S 2 0 3 , and '5402 are normally not detectable in groundwater and should, therefore, form excellent indicators of groundwater contamination. Since background concentrations of these species have not been measured, enrichment factors (Table 3 3 ) were calculated using estimated detection limits as background concentrations, based on the assumption that their concentrations were less than the detectable limit. The enrichment factors shown in Table 33 for these species recommend them as possible tracers of groundwater contamination, especially if even lower detection limits can be achieved. Organic Species-The enrichment factors for TOC (or DOC) for both leachates and retort water suggest organic matter as a valuable indicator. However, the baseline organic content of groundwater actually varies widely; Leenheer and Huffman (1976), €or example, indicate levels of DOC of 30,700 mg/l for trona water collected near Eden, Wyoming. Few measurements in the Piceance Basin have been greater than about 10 mg/l. Leachates from raw shale may contain more organic acids than leachates from spent shale. For these reasons, individual organic compounds (or compound classes) which are absent in natural groundwater, but which are produced by the retorting process, should prove to be more sensitive probes of groundwater movement. For this reason, organic (DOC) fractionation methods, such as those described by Leenheer and Huffman ( 1 9 7 6 ) , may provide a set of useful indicators for monitoring.

One such type of organic compound could be aromatic acids, which are enriched in leachate from spent shale compared to raw shale. In addition, the smaller (lower molecular weight) aromatic acids should be highly soluble in the basic conditions expected and should, therefore, follow water movement closely. The larger acids, although ionized, could be more readily sorbed and, therefore, migrate less slowly. Polynuclear aromatic hydrocarbons, which are products of combustion, may also increase during combustion. Another likely organic tracer would be in hydrophilic bases. Much interest has focused on such compounds lately because of their biological activity and unusually large occurrence in oil shale products. Fruchter et al. (19771, for example, have found that indoles, substituted pyridines, quinolines, and acridines are highly enriched in shale oil as compared to coal-derived syncrude. Sievers and Denny (1978) have also detected numerous organic bases, many of which could not be readily identified, in retort waters. To the extent that such organic bases are retained by groundwater, they should provide sensitive and unusual indicators of groundwater contamination.

287

Stable Isotopes It is well established that variations in isotopic abundances--especially for the light elements--occur naturally through such processes as diffusion, evaporation, dissolution, and chemical reaction. For example, 13C is about 3 percent more abundant in ocean bicarbonate than in terrestrial petroleum (Roboz, 1968).

similar variations in the isotopic ratios of other light elements, such as H, N, 0 and S , suggest this measurement as a probe for studying the migration of groundwater. As an example, suppose the 2H/1H ratio is slightly higher in kerogen than in natural groundwater. Water produced by combusting kerogen will thus be labeled with a higher 2H/1H ratio and could be distinguished from natural groundwater. Similar considerations should be given to natural and combustion--producedNH;, CO: , and SO;. The variation in stable isotope abundances is normally reported as parts per thousand variation from a standard: (I /I 1

6 =

- (I

sample (I /I

/I standard

)

standard where 12 and I1 refer to the minor and major isotope, respectively. Variations in isotope ratios are measured almost exclusively by mass spectrometry. Although any mass spectrometer is capable of measuring isotope ratios, the measurement of naturally occurring variations requires highly specialized instruments. Indeed, many isotope ratio mass spectrometers are dedicated to a single element. Consequently, such instruments are found almost exclusively in research laboratories and are numerically absent from commercial laboratories. Isotope ratio mass spectrometers are characterized by dual detector systems which are designed to collect both isotopes simultaneously, thereby minimizing errors due to ion current instability. Detector electronics are specifically designed to yield the isotope ratio directly, and ion sources typically include a means of switching rapidly between the sample and a standard of known isotopic composition. The precision with which d may be measured in a routine matter is about l mil for H and 0.1 mil for C, 0, and N. The precision of d j s typically limited by isotope fractionation which occurs during sample preparation and introduction into the mass spectrometer. Although studies of isotope ratios in the Green River Formation have not been found in the literature, other relevant investigations deserve mention. Friedman et al. (19641, for example, discuss the natural variations of deuterium in the hydrologic cycle, including the theory of the fractionation processes which occur during evaporation, transport, and deposition. They also report the results of over 1,000 determinations of 2H in waters of North America. Dansgaard (1964) also discusses both the theory and the measurements of 2H and l80 in precipitation. 288

Holt et al. (1972) and Jensen and Nakai (1961) both discuss natural variations of 34S in environmental samples. Holt et al. (1972) observed perturbations of 634s in surface waters due to rainfall, earth-surface disturbances, and effluents from sewage treatment plants. N isotopic ratios have been studied widely, principally as a means of identifying pollutant sources and characterizing the atmospheric N cycle (Moore, 1977; Moore, 1974; Hoering and Moore, 1958; Wada et al., 1975). Naturally occurring values of 615N ranging from -15 to +25 have been observed. Possible problems which may be encountered in the application of the sta-~ ble isotope technique to the Green River Formation include lack of background data, insufficient difference in 6 for natural and contaminated groundwater, and exchange reactions such as the following: H' HO + 2 H2I80 + HC

1 HCO 3

16 O3

-f

1 2 H20 + HC03 18 16 -

-f

H l60 + HC 0 O2 2

.

Thus, to the extent that carbonates and bicarbonates exchange with, or precipitate as solid materials, the isotopic composition of certain elements may be altered. SAMPLE ANALYSIS AND COSTS This discussion is meant to aid the reader in the efficient selection of analytical techniques suitable for monitoring groundwater movement. Both survey and element-specific techniques are discussed. Trace Elements The most common techniques which are used for trace element analysis are instrumental neutron activation analysis (INAA), inductively coupled plasma emission spectroscopy (ICP), spark source mass spectroscopy (SSMS), and atomic Each technique has spectroscopy with its various modifications ( A A ) . strengths and weaknesses which should be recognized. Table 38 compares these techniques on the basis of their abilities to detect trace levels of 44 elements. Although not shown on the table, the limit for SSMS is typically 1 pg/l for most elements. The detection limits for ICP were obtained from a recent review of an ICP spectrometer in use at a DOE synfuels laboratory, and were determined with artificial, multielement standards. The detection limits shown for a flameless (carbon rod) and flame AA were taken from the manufacturer's literature. The limits for INAA were for a routine survey available on a commercial basis. The working limits shown in the table are the lowest concentrations typically reported by a routine analytical services laboratory located in Denver. In this case, the working limits are typically several times the detection limit, since the method of choice in an analytical services laboratory is determined by regulatory requirement, 289

TABLE 38. COMPARISON OF ANALYTICAL TECHNIQUES FOR TRACE ELEMENT DETERMINATIONSa

Working limit, Denver Laboratory

Detection limits

AA

AA

Instrumental Neutron Activatio 6 Analysis

(vg/l)

(vgll)

(vgll)

Flameless ICP Element

(vg/l)

A9

3

0.03

A1

3

2

As B Ba

16

15

2

Be

1

0.2

Bi

80

1.4

ca

2

15

20 100, 2

0.06 0.02

20

0.7 46

2

(pg/l)

0.5

2

2,000

15 1

Cd

Flame

100

100

d

0.5

NA

0.8

7

C1

___

___

B C

A A

NA

500

A

50

A

2

A

10

A

500

200

C

10

A

0.5

5

2 50

5

0.7

---

A

50

1,000

Cr

3

0.5

5

2

CU

4

0.4

2

300

10

A

-70

---

___

___ ---

Ga Ge Fe F

30

2

20

___

5

-__

0.5 -_-

40

NA

100

(vgll)

B

NA

100

0.10

co

0.05

Method'

Colorado water quality standards cleanest classification

6

200

lo

A

___

200

100

D (continued)

TABLE 38 (continued)

Working limit, Denver Laboratory

Detection limits

Flame less Element

ICP (pg/l)

Flame

AA

AA

(pg/l)

(vg/l)

12

0.4

Hg K

600

50

0.2

2

Li

50

0.4

2 0.2

Mg Mn

1

0.006

5

0.04

Mo

7

0.6

Na

90

0.02

Nb

30

---

Ni

9

Instrumental Neutron ACtiVatiO Analysis (pg/l)

t:

b

0.5

300

NA 5,000

(pg/l)

Method

100

A

5

A

50

A

2

20

5

A

30

3

5

B

70

100

0.3

3,000

-25,000

A

---

---

8

NA

lo

A

30

---

---

NA

100

C

Pb

20

0.3

15

NA

1

B

Sb

60

3

40

0.5

50

A

d 250, 2

5

B

1,000

C

500

A

Se

20

6

si

30

7

sn sr

12

1

S

1

200

NA

30

80 2,000

10

0.8

2

_-_

-_-

---

NA

(pg/l)

d

0.02

1

P

Colorado water quality standards cleanest classification

10

A

---

--(continued)

TABLE 38 (continued)

Detection limits

AA

AA

Instrumental Neutron Activatio I: Analysis

(pg/l)

(lJg/l)

(pg/l)

F1ame less

ICP Element

Th

(pg/l)

-_ -

F 1ame

___

___

0.6

13

(pg/l)

0.2

NA

Method

___

___

5

B

T1

200

U

500

1,000

60,000

1

2

E

V

2

10

50

1

5

A

Zn

10

0.02

W

_--

Br

___

--__-

I

___

___

1

___ ___ ___

Colorado water quality standards cleanest classification

Working limit, Denver Laboratory

10

5

A

30

_-_

--___ ___

1 30

_-_ ___

C

(lJg/l)

___ ___ ---

Notes: a Detection limits correspond to approximately 20 times the background noise level. Working limits typically correspond to several times the background noise level and are based on a wide variety of groundwater and surface water using equipment in a routine fashion. bNote INAA not approved EPA method. LA E

- flame atomic absorption: B - fluorometric.

- carbon rod atomic absorption; C - colorimetric: D - electrode:

dVapor generation. NA - not available under normal circumstances or very insensitive.

economics, and ease of operation. It should be recognized that data in Table 38 represent a common basis for discussion; however, detection limits are often degraded in complex samples or improved by special pretreatment processes. In addition to the detection limits, the precision and importance interferences should be considered. ICP is relatively free oE matrix interferences, but is subject to spectral interferences. For example, the DOE operators have reported poor accuracy Eor U, Co, As, and Cd on complex samples, presumably because of spectral interferences. A A has fewer spectral interferences, but special corrections may be needed for background or matrix interferences. The precision of AA or ICP spectroscopy is typically + l o percent when used by trained personnel. INAA is often considered a reference method for trace elements because of its relatively high precision at trace levels and freedom from matrix interferences. SSMS is typically subject to fewer interferences than either ICP or AA, but the routine precision for this technique is about 5 4 0 percent, although precisions of +3 percent have been reported in the literature using electrical detection under tightly controlled conditions. Since samples for SSMS must be dried onto a graphite substrate and placed in a vacuum, volatile elements such as Hg, s, and Se may be lost, especially under acidic conditions. It is obvious that no single method is a panacea. INAA is attractive because of its detectability for the potential low-level indicators A s , Sb, Se, Te, U, and V. SSMS is favored as a survey technique because it provides uniformly low detection levels and broad elemental coverage. The other methods listed in Table 38 are attractive as monitoring tools because of their adequate precision and detectability for many elements. -Organic Methods

Common techniques which are available for the determination of trace organic species in complex mixtures include gas chromatography (GC), combined gas chromatography/mass spectroscopy (GC/MS), high-pressure liquid chromatography (HPLC), and thin-layer chromatography (TLC). Recent advances in controlling the variables in TLC are also giving rise to high-performance, thin-layer chromatography (KPTLC). Standardized methods are not normally available for specific organic compounds since operating parameters are optimized for each substrate and analyte . For more tractable species, literature references may be found for similar substrates, although as a general rule a significant effort will be re-quired for implementing, adapting, and "debugging" methods for groundwater in the oil shale area. Organic bases are a particular problem since they readily decompose and since analytical methods are poorly developed.

Instrumentation should include a GC, GC/MS, and HPLC as a minimum, along with other standard analytical equipment. The GC/MS should be capable of operating with capillary columns and be capable of peak switching and single ion monitoring. A specific nitrogen detector on the GC should be considered essential for the determination of organic bases (Sievers and Denny, 1978). 293

Nonspecific separation schemes are also available for classifying the types of organic compounds in water (Hamersma et al., 1976; Leenheer and Huffman, 1976). Such schemes can provide a first warning of the groundwater changes and can indicate otherwise unsuspected changes. The procedures by Leenheer and Huffman may be of special interest since it was originally conceived as an aid in understanding the movement of organic materials in groundwater. The procedure operates by separating hydrophilic and hydrophobic acidic, basic, and neutral compounds based on their adsorptive characteristics on artificial resins. In this scheme, the hydrophilic fractions should be most mobile in groundwater, while the hydrophobic fractions should most readily be retained by sorptive clays and minerals. Other Inorganic Species For a wide variety of commonly occurring inorganic species, standard methods have been developed and tested which are reliable when applied to typical surface water or groundwater and which can be performed with a minimum of equipment (U.S. EPA, 1974; American Public Health Association, 1976; U.S. Geological Survey, 1970). Although standard methods must not be applied blindly to oil shale waste water (or to other waste water), it is believed that many standard methods can be modified slightly in order to produce more reliable results. In any case, a carefully designed quality assurance program is highly recommended.

This subsection first discusses several representative standard analytical procedures, analytical problems which occur, and possible solutions. A discussion of possible additional procedures which could be used to better or more eEficiently analyze oil shale waste waters then follows. Total Suspended and Dissolved Solids-Normally, these are determined by drying an aliquot of water at 103O to 105OC. In retort waters, this may cause the loss of ammonium carbonate and result in an artificially low result. A possible solution is evaporation at a different pressure and temperature to more selectively remove the water, or complete evaporation of ammonium carbonate, which is then determined separately. Alkalinity-Normally, alkalinity is measured by titrating with dilute acid. Results are typically interpreted as total bicarbonate and carbonate. In retort waters, dissolved ammonia and organic acids are also titrated so that the results should be interpreted as "total titratable base." Another method is to determine carbonate and bicarbonate by measuring total inorganic carbon in a TOC analyzer and adjusting the pH and ionic strength. Other options include acidification of the sample and determination of the evolved C02 titremetrically, colorimetrically, or by hydrogenation and the detection of methane.

294

ChlorideChloride is of ten determined by the subsequent reactions in a continuous flow system: 2C1- + Hg(SCNl2

-+

HgC12 + 2SCN-

+

Fe(SCN)x

-

SCN + Fe3+

.

The colored ferric thiocyanate complex is then detected colorimetrically. In retort water, thiocyanate is thus detected as chloride. This problem should be removed by chemically oxidizing the thiocyanate prior to analysis. Alternatively, analyzing subsequent samples with and without the addition of Hg(SCN)2 may provide a determination for both chloride and thiocyanate. pH- pH electrodes are subject to fouling by oils. This common problem can be overcome by frequent standardization or a cross check with a series of pH indicators, which are certainly as accurate, if not as convenient. Nitrate-Often nitrate is determined by the automated Cd reduction method. A common problem is the fouling of the Cd reduction column by organic materials. A possible solution is extraction of the organic material prior to analysis, or the use of an alternate reducing agent, such as hydrazine. BOD--

In our experience, the normal BOD determination is not reproducible unless acclimated seed is used. m o n ia--Often ammonia is determined with a selective ion electrode (which is subject to fouling by organic materials). A likely solution is removal of the organic materials by extraction, by filtration with a hydrophilic filter, or by the use of macroreticular resins. Other Constituents-It is likely that similar problems and relatively straightforward solutions may exist for other assays, such as fluoride and sulfate. Such minor modifications may be simple and, indeed, are often practiced by the alert analytical chemist. There are, of course, requirements for entirely new or greatly improved analytical methods. Possible analytical schemes are discussed below as examples.

295

Determination of the complex mixture of sulfur and nitrogen species in retort waters is an unresolved problem. In addition, S , S205, S3Oz, S o i l SCN-, and CN- can interlact and thereby change their chemical SCN- can further react with oxidizing agents, which might be used in treatment, to form the highly toxic cyanogen chloride.

found SqO:,

form. water

One approach which has been used (Stuber et al., in press) for this problem is the cyanolysis of the various sulfur oxides with selective catalysts (Kelly et al., 1 9 6 9 ) . The resulting SCN- was detected colorimetrically as the ferric thiocyanate complex. However, it has not yet been shown that the catalysts are sufficiently selective or that they do not occur naturally in sufficient quantities in waste waters. There are several possible approaches to this problem which would be considered: Ion chromatography The development of coloring agents specific for thiosulfate, thiocyanate, tetrathionate, etc. Polarographic techniques which distinguish between the various and N species on differing oxidation potentials

S

Surrogate tests. The latter tests assume that speciation of the various forms of S and N is not essential. As an example, S20%, S3O%, and S4Oz could be determined as a group using the cyanolysis procedure of Kelly et al. ( 1 9 6 9 ) . An especially attractive technique for such complex waters is ion chromatography. Because it is a separatory technique, complex and selective reactions are not required. Ion chromatography holds the possibility of chromatographically determining cyanide, thiocyanate, sulfate, thiosulfate, trithionate, tetrathionate, sulfide, as well as phosphate, fluoride and nitrate, minutes after sample collection. Because ion chromatography detects ions nonselectively, the presence of unexpected peaks alerts the analysts to unknown ions. Thus, the analyst can often detect previously unexpected compounds. At the other extreme are tests which would measure, for example, total sulfur in all forms. Such a technique could be used to alert the analysts to the need for a more detailed analysis of sulfur species.

INTERPRETATION OF WATER QUALITY DATA Data Analysis Data analysis procedures include (1) checks on data validity, and (2) methods for presenting data for interpretation for environmental description or control purposes. Data checking procedures include:

296

0

Cation-anion balance

0

TDS-conductivity comparison

0

Conductivity-ion comparison (meq/l)

0

Diluted-conductance method.

The cation-anion balance check involves considering the theoretical equivalence of the sum of the cations [expressed in milliequivalents per liter (meq/l)] and the sum of the anions (in meq/l). Because of variations in analysis which may be unavoidable, exact equivalence is seldom achieved. In general, the inequality observed can be expected to increase as the total ionic concentration increases. When using this method, it is assumed that analyses of all significant ions have been included and that the nature of the ionic species is known. In addition, it should be noted that compensating analytical errors can fortuitously produce a close ion balance. Hence, a combination of quality control (e.g., replicate analyses, use of standard references, spiked samples, etc.) and data checking procedures should be employed. For other analysis checks, samples can be evaporated to dryness at and the weight compared to the total solids determined by calculation. This check is approximate because losses may occur during drying by volatilization and other factors may cause interference (Brown, Skougstad, and Fishman, 1970). Another recommended check on analyses involves multiplying specific conductance (pmhos/cm) by a factor ranging from 0.55 to 0.75. The product should approximately equal total dissolved solids, in mg/l, for water samples with TDS below 2,000 to 3,000 mg/l. Also, the specific conductance divided by 100 should approximately equal the meq/l of anions or cations. This relationship is useful in deciding on which sum, cations or anions, is in error. A more refined method for checking TDS by the electrical conductivity relationships, called the diluted-conductance method, may also be employed. 180°C

Proper design OE the monitoring program with regard to selection of monitoring sites, sampling frequency and analytical methods, and implementation of quality control measures will alleviate such data interpretation problems. Good monitoring design can deal effectively with sources of data variability, such as operational variability of field instrumentations and errors in calculations or analysis. Other significant sources of data variability are events such as in-plant spills, poor in-plant housekeeping practices, temporary process or control equipment failure or modification, and other in-plant events. These events may be entirely random (e.g., spills) or somewhat cyclic (e.g., equipment maintenance) in nature. Effectively dealing with these sources of data variability requires liaison with facility operators. Ideally, this communication should be of two types, namely to assure that (1) monitoring personnel have adequate knowledge of facility operations (and deviations), and (2) that plant developers have access to monitoring data and the evaluations made of that data. Such intercommunication can enhance data interpretation efforts.

297

Data Presentation Data presentation and interpretation are key aspects of monitoring for environmental detection and control. Several methods are available for organization and presentation of water quality data. These include tabulation and graphical tabulation of appropriate water quality criteria or standards, providing a format for screening data and identifying important sites or pollutant constituents. Ionic concentrations can be expressed as milligrams per liter or milliequivalents per liter. Other water quality measures may be segmented into contributing components, such as total and noncarbonate hardness or phenolphthalein and methyl orange alkalinity. Graphic representations of analyses of the chemical quality of water are useful for display purposes, for comparing analyses, and for emphasizing similarities and differences. Graphs can also aid in detecting the mixing of waters of different composition and in identifying chemical processes occurring as water moves through the hydrologic regime of the monitoring area. A variety of graphic techniques is available: some of the more useful ones are described in the following paragraphs. A widely used method of data presentation is the bar graph. On a bar graph, each sample analysis appears as a vertical bar whose total height is proportional to the total concentration of anions and cations, expressed in milliequivalents per liter. One-half of the bar represents cations and the other half anions. These segments are divided horizontally to show the concentrations of major ions or groups of closely related ions, which are shown by distinctive patterns. Variations include the addition of individual bar graphs to express levels of other water quality measures, such as hardness or un-ionized solutes such as silica.

Water quality data can also be plotted as a set of radiating vectors (Figure 4 5 ) . Related methods of showing concentrations as linear vectors result in constructions of polygons. These approaches are useful in displaying changes in water quality as changes in, for example, the shape of these polygons. Trilinear diagrams are another useful method for representing and comparing water quality analyses (Figure 4 6 ) . Here, cations, expressed in percentage of total cations (as milliequivalents per liter), plot as a single point on the left triangle. Anions, similarly expressed as a percentage of total anions, appear as a point in the right triangle. These points are then projected into the central, diamondshaped area parallel to the upper edges of the central area. This single point is thus uniquely related to the total ionic quality, and at this point a circle can be drawn with an area proportional to the total dissolved solids concentration. The trilinear diagram is a convenient way to distinguish similarities and differences among various water samples as waters with similar qualities will tend to plot together as groups. Also, simple mixtures of waters can be identified as the mixture data will plot at locations intermediate between the mixture component waters.

298

NatK

10

Na + K

lZ6

17-3

Na+K

15.1

CI

tic03

so4 MILLIEQUIVALENTS PER LITER

Water quality data display using vectors.

Figure 45.

a UI k U 0 0

Lu

0 0 0.

O X H

9

SCALE OF DIAMETERS

i -

I

C.3

CI

CATIONS

ANIONS PERCENT OF TOTAL MILLIEQUIVALENTS PER LITER

.gure 46.

Trilinear diagram for displaying water quality data. 299

Other graphic methods include time series plots, plots of variation in water quality constituents with distance or depth, area or cross-section plots of equal water quality lines, and plane maps. The choice of data presentation is determined by the goals of the monitoring program and the type of audience to which the data are to be presented. The goal of data presentation is to provide a clear portrayal of the data for evaluation of environmental quality. Data Interpretation and Reportinq Water quality data from monitoring should be analyzed and interpreted so as to define quality trends, identify new pollution problems or regions of improvement, and assess the effectiveness of pollution control activities. Assessments include such things as identifying segments of the groundwater systems not meeting water quality standards and projections of impact on various water uses. The monitoring program should incorporate pertinent data from all agencies and organizations involved in the monitoring region. The final result of a monitoring program organized in an area is information on water quality. The final task of the monitoring program is to dissem-inate the information gained in usable forms to the agencies and organizations concerned with such information. Monitoring should be summarized in appropriate forms for convenient study before wide distribution outside of the monitoring agency. This may involve preparation of tables showing averages and/or changes in water quality. Similarly, graphs prepared to readily display long-term trends may be helpful, as described previously. Maps showing, for example, locations of major known sources of pollution, areal distribution of concentrations of key pollutants, and regions having groundwater with qualities not meeting some water quality criterion can also be shown to be both useful and effective. Monitoring information should be distributed regularly to appropriate public agencies---local, State, and Federal. Major industries in the area should also receive the material as well as cooperating agencies and organizations that contribute monitoring data, Finally, the monitoring agency would have the responsibility to alert action and enforcement agencies of critical problems or situations which are discovered within the monitoring program. This may involve, for example, detection of hazardous or toxic pollutants which could affect water users. Prompt reporting of such instances is essential, as is following up with specialized monitoring efforts for documenting and controlling emergency situations.

300

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