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WATER ENCYCLOPEDIA
WATER ENCYCLOPEDIA
Editor-in-Chief
Jay Lehr, Ph.D.
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Jack Keeley
Associate Editor
Janet Lehr
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WATER ENCYCLOPEDIA
GROUND WATER
Jay Lehr, Ph.D.
Editor-in-Chief
Jack Keeley
Senior Editor
Janet Lehr
Associate Editor
Thomas B. Kingery III
Information Technology Director
TheWater Encyclopedia is available online at http://www.mrw.interscience.wiley.com/eow/
Copyright 2005 by John Wiley & Sons, Inc. All rights reserved. Published by John Wiley & Sons, Inc., Hoboken, New Jersey. Published simultaneously in Canada.
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Library of Congress Cataloging-in-Publication Data is available.
Lehr, Jay
Water Encyclopedia: Ground Water ISBN 0-471-73683-X
ISBN 0-471-44164-3 (Set)
Printed in the United States of America 10 9 8 7 6 5 4 3 2 1
CONTENTS
Preface
ix
Contributors
xi
Ground Water
Acid Mine Drainage: Sources and Treatment in
the United States 1
Aquifers 9
Artificial Recharge of Unconfined Aquifer 11 Groundwater and Arsenic: Chemical Behavior
and Treatment 17
Treatment of Arsenic, Chromium, and Biofouling
in Water Supply Wells 22
Artesian Water 29
Modeling Contaminant Transport and
Biodegradation in Groundwater 30
Biofouling in Water Wells 35
In Situ Bioremediation of Contaminated
Groundwater 38
Process Limitations of In Situ Bioremediation of
Groundwater 42
Black Mesa Monitoring Program 48
Brine Deposits 51
Connate Water 54
Consolidated Water Bearing Rocks 55
Sensitivity of Groundwater to Contamination 56 Water Contamination by Low Level Organic
Waste Compounds in the Hydrologic System 60
Darcy’s Law 63
Groundwater Dating with Radiocarbon 64
Groundwater Dating with H–He 65
Dating Groundwaters with Tritium 69
Recharge in Desert Regions Around The World 72 Hydrologic Feasibility Assessment and Design in
Phytoremediation 76
Well Design and Construction 87
Physical Properties of DNAPLs and
Groundwater Contamination 91
Water Dowsing (Witching) 92
Subsurface Drainage 94
Drawdown 101
Water Level Drawdown 102
Water Well Drilling Techniques 105
Groundwater Dye Tracing in Karst 107 Earthquakes—Rattling the Earth’s Plumbing
System 111
In Situ Electrokinetic Treatment of MtBE,
Benzene, and Chlorinated Solvents 116
Field Capacity 124
Groundwater Flow Properties 128
Fluoride Contamination in Ground Water 130
Rock Fracture 136
Geochemical Models 138
Geochemical Modeling-Computer Codes 140 Geochemical Modeling—Computer Code
Concepts 142
Geological Occurrence of Groundwater 145
Geophysics and Remote Sensing 145
Geothermal Water 156
Ghijben–Herzberg Equilibrium 158
Groundwater Balance 162
Hydraulic Head 169
The Role of Heat in Groundwater Systems 172 Groundwater Flow in Heterogenetic Sediments
and Fractured Rock Systems 175
Horizontal Wells 177
Horizontal Wells in Groundwater Remediation 178
Head 180
Well Hydraulics and Aquifer Tests 182 Hydraulic Properties Characterization 184 Mobility of Humic Substances in
Groundwater 188
Assessment of Groundwater Quality in District
Hardwar, Uttaranchal, India 192
Irrigation Water Quality in District Hardwar,
Uttaranchal, India 204
Infiltration and Soil Water Processes 210
Infiltration/Capacity/Rates 212
Infiltrometers 214
Summary of Isotopes in Contaminant
Hydrogeology 216
Environmental Isotopes in Hydrogeology 227 Water-Jetting Drilling Technologies for Well
Installation And In Situ Remediation of
Hydrocarbons, Solvents, and Metals 234
Karst Hydrology 235
Karst Topography 243
Detecting Modern Groundwaters
with85Kr 248
Land Use Impacts on Groundwater Quality 250 Groundwater Contamination From Municipal
Landfills in the USA 253
Metal Organic Interactions in Subtitle D Landfill
Leachates and Associated Ground Waters 258
Leaching 260
Well Maintenance 263
Megawatersheds 266
Mass Transport in Saturated Media 273 Soil and Water Contamination by Heavy
Metals 275
Source, Mobility, and Remediation of Metals 280 Genetics of Metal Tolerance and Accumulation
in Higher Plants 284
In Situ Groundwater Remediation for Heavy
Metal Contamination 290
Methane in Groundwater 293
Fossil Aquifers 294
What is a Hydrochemical Model? 295
Modeling Non-Point Source Pollutants in the
Vadose Zone Using GIS 299
Modeling Techniques for Solute Transport in
Groundwater 305
Ambient Groundwater Monitoring Network
Strategies and Design 313
MTBE 318
vi CONTENTS
Limiting Geochemical Factors in Remediation Using Monitored Natural Attenuation and
Enhanced Bioremediation 319
Nitrate Contamination of Groundwater 322 Treatment for Nitrates in Groundwater 323
Nonpoint Sources 331
Organic Compounds in Ground Water 337
Overdraft 340
Chemical Oxidation Technologies for
Groundwater Remediation 344
Particulate Transport in
Groundwater—Bacteria and Colloids 349
Perched Groundwater 352
Permeability 355
Groundwater Vulnerability to Pesticides: An Overview of Approaches and Methods of
Evaluation 357
High pH Groundwater—The Effect of The
Dissolution of Hardened Cement Pastes 362 Phytoextraction and Phytostabilization:
Technical, Economic and Regulatory
Considerations of the Soil-Lead Issue 365 Phytoextraction of Zinc and Cadmium from Soils
Using Hyperaccumulator Plants 369
Phytoremediation Enhancement of Natural
Attenuation Processes 374
Bacteria Role in the Phytoremediation of Heavy
Metals 376
Phytoremediation of Lead-Contaminated Soils 381 Phytoremediation of Methyl Tertiary-Butyl
Ether 385
Phytoremediation of Selenium-Laden Soils 397
Soil Pipes and Pipe Flow 401
Low Flow Groundwater Purging and
Surging 404
Groundwater Quality 406
Radial Wells 407
Recharge in Arid Regions 408
Sub-Surface Redox Chemistry: A Comparison of
Equilibrium and Reaction-Based Approaches 413
Regional Flow Systems 417
Groundwater Remediation by Injection and
Problem Prevention 421
Groundwater Remediation: In Situ Passive
Methods 423
Groundwater Remediation by In Situ Aeration
and Volatilization 426
Remediation of Contaminated Soils 432 Groundwater Remediation Project Life Cycle 436 Innovative Contaminated Groundwater
Remediation Technologies 438
Resistivity Methods 443
Risk Analysis of Buried Wastes From Electricity
Generation 448
Groundwater Contamination from Runoff 451
Saline Seep 453
Groundwater Sampling Techniques for
Environmental Projects 454
Groundwater Sampling with Passive Diffusion
Samplers 456
Specific Capacity 460
Soil Water 461
Soil and Groundwater Geochemistry and
Microbiology 463
Characterizing Soil Spatial Variability 465
Deep Soil-Water Movement 471
Specific Gravity 473
Hot Springs 475
Squeezing Water from Rock 477
Storage Coefficient 480
Qanats: An Ingenious Sustainable Groundwater
Resource System 483
Lysimeters 487
Steady-State Flow Aquifer Tests 491
Tidal Efficiency 497
Combined Free and Porous Flow in the
Subsurface 498
Groundwater Tracing 501
Hydraulic Conductivity/Transmissibility 507 Groundwater Flow and Transport
Process 514
Reactive Transport in The Saturated Zone: Case
Histories for Permeable Reactive Barriers 518 Transport of Reactive Solute in Soil and
Groundwater 524
Water in The Unsaturated Zone 531
Groundwater and Vadose Zone Hydrology 533 Vadose Zone Monitoring Techniques 538 Vapor Transport in the Unsaturated Zone 543 Applications of Soil Vapor Data to Groundwater
Investigations 548
Groundwater Velocities 554
Viscous Flow 555
Vulnerability Mapping of Groundwater
Resources 561
Water/Rocks Interaction 566
Ground Water: Wells 571
Well Screens 572
Well TEST 574
Safe Yield of an Aquifer 575
Specific Yield Storage Equation 576
Microbial Processes Affecting Monitored Natural Attenuation of Contaminants in the
Subsurface 578
Groundwater Vulnerability to Pesticides:
Statistical Approaches 594
Groundwater—Nature’s Hidden Treasure 599 Pharmaceuticals, Hormones, and Other Organic
Wastewater Contaminants in U.S. Streams 605 The Environmental Impact of Iron in
Groundwater 608
Groundwater and Cobalt: Chemical Behavior
and Treatment 610
Groundwater and Cadmium: Chemical Behavior
and Treatment 613
Groundwater Modeling 619
Groundwater and Benzene: Chemical Behavior
and Treatment 626
Groundwater and Nitrate: Chemical Behavior
and Treatment 628
Groundwater and Perchlorate: Chemical
CONTENTS vii Groundwater and Vinyl Chloride: Chemical
Behavior and Treatment 634
Groundwater and Uranium: Chemical Behavior
and Treatment 640
Groundwater and Mercury: Chemical Behavior
and Treatment 642
Groundwater and Lead: Chemical Behavior and
Treatment 645
Laminar Flow 649
Finite Element Modeling of Coupled Free and
Porous Flow 655
Unconfined Groundwater 662
Modeling of DNAPL Migration in Saturated
Porous Media 668
The Use of Semipermeable Membrane Devices (SPMDs) for Monitoring, Exposure, and
Toxicity Assessment 672
River-Connected Aquifers: Geophysics, Stratigraphy, Hydrogeology, and
Geochemistry 677
Index 689
PREFACE
Throughout history, groundwater has played a major role in providing the resource needs of the world. It accounts for 97% of the world’s freshwater and serves as the base flow for all streams, springs, and rivers. In the United States, one half of the population relies on groundwater for its drinking water and is the sole source of supply for 20 of the 100 largest cities. Well over 90% of rural America is totally dependent on groundwater. An inventory of the total groundwater resources in the United States can be visualized as being equal to the flow of the Mississippi River at Vicksburg for a period of 250 years.
One of the first groundwater scientists was a French engineer who was in charge of public drinking water in Dijon. In 1856, Henri Darcy conducted experiments and published mathematical expressions describing the flow of water through sand filters. His work remains one of the cornerstones of today’s groundwater hydrologists. At about the same time, a Connecticut court ruled that the influences of groundwater movement are so secret, changeable, and uncontrollable that they could not be subject to regulations of law, nor to a system of rules, as had been done with surface streams.
In this volume of the Water Encyclopedia, we have attempted to erase the ignorance that existed in the early years of groundwater science by presenting the most current knowledge on the subject as provided by authors from around the globe. In addition to excellent articles
from many American scholars, equally superb writings from such diverse countries as England, Nigeria, India, Iran, Thailand, and Greece are provided.
As the origins of the selected articles are diverse, so are the subjects of discussion. Along with straightforward descriptions of basic groundwater concepts (drawdown around pumping wells, hydraulic head, field capacity, and flow), the reader is introduced to more complex subjects (isotope technologies, aquifer tests, in situ remediation, tritium dating, modeling, and geophysical properties). There are also articles for more practical applications (well maintenance, subsurface drainage, nitrate contamination, tracer tests, well yields, and drilling technologies). Of course, for the more fanciful reader, we have selected articles that remind us of the way windmills sounded at night, the ancient use of qanats in Persia to provide sustainable groundwater resources, and the development of Darcy’s Law.
In the end, we feel that the information provided will afford an educational home for readers approaching the Water Encyclopedia from a variety of needs as well as different levels of scientific acumen. We are also confident that many readers will simply be expanding their knowledge base by these sets of enjoyable reading.
Jay Lehr Jack Keeley
CONTRIBUTORS
Segun Adelana, University of Ilorin, Ilorin, Nigeria, Summary of Isotopes in Contaminant Hydrogeology, Environmental Isotopes in Hydrogeology Mohammad N. Almasri, An-Najah National University, Nablus,
Palestine, Groundwater Flow and Transport Process
Tom A. Al, University of New Brunswick, Fredericton, New Brunswick,
Canada, River-Connected Aquifers: Geophysics, Stratigraphy,
Hydroge-ology, and Geochemistry
Larry Amskold, University of New Brunswick, Fredericton, New
Brunswick, Canada, River-Connected Aquifers: Geophysics,
Stratigra-phy, Hydrogeology, and Geochemistry
Ann Azadpour-Keeley, National Risk Management Research Laboratory,
ORD, U.S. EPA, Ada, Oklahoma, Microbial Processes Affecting
Monitored Natural Attenuation of Contaminants in the Subsurface, Nitrate Contamination of Groundwater
Mukand Singh Babel, Asian Institute of Technology, Pathumthani,
Thailand, Groundwater Velocities, Groundwater Flow Properties, Water
in The Unsaturated Zone
Philip B. Bedient, Rice University, Houston, Texas, Transport of Reactive Solute in Soil and Groundwater
David M. Bednar, Jr., Michael Baker, Jr. Inc., Shreveport, Louisiana, Karst Hydrology, Karst Topography, Groundwater Dye Tracing in Karst Milovan Beljin, Cincinnati, Ohio, Horizontal Wells
Craig H. Benson, University of Wisconsin-Madison, Madison, Wisconsin, Reactive Transport in The Saturated Zone: Case Histories for Permeable Reactive Barriers
Robert A. Bisson, Alexandria, Virginia, Megawatersheds
William J. Blanford, Louisiana State University, Baton Rouge, Louisiana, Vadose Zone Monitoring Techniques
Thomas B. Boving, University of Rhode Island, Kingston, Rhode
Island, Organic Compounds in Ground Water, Innovative Contaminated
Groundwater Remediation Technologies
Richard C. Brody, UC Berkeley, Berkeley, California, Connate Water Kristofor R. Brye, University of Arkansas, Fayetteville, Arkansas,
Lysimeters, Soil and Water Contamination by Heavy Metals
Gunnar Buckau, Institut f ¨ur Nukleare Entsorgung, Karlsruhe, Germany,
Mobility of Humic Substances in Groundwater
Bureau of Indian Affairs and Arizona Department of Water Resources—U.S. Geological Survey, Black Mesa Monitoring Program
Karl E. Butler, University of New Brunswick, Fredericton, New Brunswick,
Canada, River-Connected Aquifers: Geophysics, Stratigraphy,
Hydroge-ology, and Geochemistry
Herbert T. Buxton, United States Geological Survey, Pharmaceuticals, Hormones, and Other Organic Wastewater Contaminants in U.S. Streams
Natalie L. Capiro, Rice University, Houston, Texas, Transport of Reactive Solute in Soil and Groundwater
Harendra S. Chauhan, G.B. Pant University of Agriculture and
Technology, Uttar Pradesh, India, Steady-State Flow Aquifer Tests,
Subsurface Drainage
Bernard L. Cohen, University of Pittsburgh, Pittsburgh, Pennsylvania, Risk Analysis of Buried Wastes From Electricity Generation
David P. Commander, Water and Rivers Commission, East Perth,
Australia, Water Dowsing (Witching), Artesian Water
Dennis L. Corwin, USDA-ARS George E. Brown, Jr., Salinity Laboratory,
Riverside, California, Characterizing Soil Spatial Variability, Modeling
Non-Point Source Pollutants in the Vadose Zone Using GIS, Groundwater Vulnerability to Pesticides: An Overview of Approaches and Methods of Evaluation
Colin C. Cunningham, The University of Edinburgh, Edinburgh,
Scotland, United Kingdom, In Situ Bioremediation of Contaminated
Groundwater
William L. Cunningham, U.S. Geological Survey, Denver, Colorado, Earthquakes—Rattling the Earth’s Plumbing System
Uwe Dannwolf, URS Australia Pty Ltd., Turner, Australia, Groundwater and Vadose Zone Hydrology
Diganta Bhusan Das, Oxford University, Oxford, United Kingdom, Viscous Flow, Finite Element Modeling of Coupled Free and Porous
Flow, Combined Free and Porous Flow in the Subsurface, Modeling Techniques for Solute Transport in Groundwater
Rupali Datta, University of Texas at San Antonio, San Antonio, Texas, Remediation of Contaminated Soils, Genetics of Metal Tolerance and Accumulation in Higher Plants, Phytoextraction of Zinc and Cadmium from Soils Using Hyperaccumulator Plants, Phytoremediation of Selenium-Laden Soils, Phytoextraction and Phytostabilization: Technical, Economic and Regulatory Considerations of the Soil-Lead Issue
Ali H. Davani, University of Texas at San Antonio, San Antonio, Texas, Remediation of Contaminated Soils
L.C. Davis, (from Phytoremediation: Transformation and Control of
Contaminants, Wiley 2003), Phytoremediation of Methyl Tertiary-Butyl
Ether
Melissa R. Dawe, University of New Brunswick, Fredericton, New
Brunswick, Canada, River-Connected Aquifers: Geophysics,
Stratigra-phy, Hydrogeology, and Geochemistry
Steven A. Dielman, ENVIRON International Corporation, Arlington,
Virginia, Hydraulic Conductivity/Transmissibility
Craig E. Divine, Colorado School of Mines, Golden, Colorado, Ground-water Sampling with Passive Diffusion Samplers, Detecting Modern Groundwaters with85Kr, Groundwater Dating with H–He
Shonel Dwyer, Environmental Bio-Systems, Inc., Mill Valley, California, Groundwater and Perchlorate: Chemical Behavior and Treatment Aly I. El-Kadi, University of Hawaii at Manoa, Honolulu, Hawaii,
Unconfined Groundwater
Environment Canada, Groundwater—Nature’s Hidden Treasure L.E. Erickson, (from Phytoremediation: Transformation and Control of
Contaminants, Wiley 2003), Phytoremediation of Methyl Tertiary-Butyl
Ether
Thomas R. Fisher, Horn Point Laboratory—UMCES, Solomons,
Maryland, What is a Hydrochemical Model?
Craig Foreman, Environmental Bio-Systems, Inc., Mill Valley, California, Groundwater and Cadmium: Chemical Behavior and Treatment Devin L. Galloway, U.S. Geological Survey, Denver, Colorado,
Earth-quakes—Rattling the Earth’s Plumbing System
Lorraine Geddes-McDonald, Environmental Bio-Systems, Inc., Mill
Valley, California, Groundwater and Nitrate: Chemical Behavior and
Treatment
M ´ario Abel Gon ¸calves, Faculdade de Ciˆencias da Universidade de Lisoba,
Lisoba, Portugal, Metal Organic Interactions in Subtitle D Landfill
Leachates and Associated Ground Waters, Geochemical Modeling-Computer Codes, Geochemical Models
Jason J. Gurdak, U.S. Geological Survey, Lakewood, Colorado and
Colorado School of Mines, Golden, Colorado, Groundwater Vulnerability
to Pesticides: Statistical Approaches
Navraj S. Hanspal, Loughborough University, Loughborough, United
Kingdom, Modeling Techniques for Solute Transport in Groundwater,
Viscous Flow, Laminar Flow, Finite Element Modeling of Coupled Free and Porous Flow
Thomas Harter, University of California, Davis, California, Specific Yield Storage Equation, Vulnerability Mapping of Groundwater Resources, Aquifers
Blayne Hartman, H&P Mobile Geochemistry, Solana Beach, California, Applications of Soil Vapor Data to Groundwater Investigations Joseph Holden, University of Leeds, Leeds, United Kingdom,
Infiltrom-eters, Soil Pipes and Pipe Flow, Infiltration and Soil Water Processes, Darcy’s Law, Infiltration/Capacity/Rates
Ekkehard Holzbecher, Humboldt Universit ¨at Berlin, Berlin, Germany, Groundwater Modeling, Ghijben–Herzberg Equilibrium
Paul F. Hudak, University of North Texas, Denton, Texas, Mass Transport in Saturated Media
John D. Humphrey, Colorado School of Mines, Golden, Colorado, Groundwater Dating with H–He
S.L. Hutchinson, (from Phytoremediation: Transformation and Control
of Contaminants, Wiley 2003), Hydrologic Feasibility Assessment and
Design in Phytoremediation
Th.A. Ioannidis, Aristotle University of Thessaloniki, Thessaloniki,
Greece, Phytoremediation of Lead-Contaminated Soils
xii CONTRIBUTORS
Jahangir Islam, City Design Limited, Auckland, New Zealand, Sub-Surface Redox Chemistry: A Comparison of Equilibrium and Reaction-Based Approaches
Irena B. Ivshina, Institute of Ecology and Genetics of Microorganisms
of the RAS, Perm, Russia, In Situ Bioremediation of Contaminated
Groundwater
James A. Jacobs, Environmental Bio-Systems, Inc., Mill Valley,
Cali-fornia, Groundwater and Cobalt: Chemical Behavior and Treatment,
Limiting Geochemical Factors in Remediation Using Monitored Nat-ural Attenuation and Enhanced Bioremediation, The Role of Heat in Groundwater Systems, Horizontal Wells in Groundwater Remediation, Groundwater Flow in Heterogenetic Sediments and Fractured Rock Systems, Groundwater and Cadmium: Chemical Behavior and Treat-ment, Groundwater and Benzene: Chemical Behavior and TreatTreat-ment, Groundwater and Lead: Chemical Behavior and Treatment, Groundwa-ter and Nitrate: Chemical Behavior and Treatment, GroundwaGroundwa-ter and Uranium: Chemical Behavior and Treatment, Groundwater and Mer-cury: Chemical Behavior and Treatment, The Environmental Impact of Iron in Groundwater, Water Well Drilling Techniques, Water-Jetting Drilling Technologies for Well Installation And In Situ Remediation of Hydrocarbons, Solvents, and Metals, Source, Mobility, and Remediation of Metals, Particulate Transport in Groundwater—Bacteria and Col-loids, Groundwater and Arsenic: Chemical Behavior and Treatment,
In Situ Groundwater Remediation for Heavy Metal Contamination,
Groundwater Remediation by In Situ Aeration and Volatilization, MTBE, Phytoremediation Enhancement of Natural Attenuation Pro-cesses, Groundwater Remediation by Injection and Problem Prevention, Chemical Oxidation Technologies for Groundwater Remediation, Phys-ical Properties of DNAPLs and Groundwater Contamination, Process Limitations of In Situ Bioremediation of Groundwater, Water Contam-ination by Low Level Organic Waste Compounds in the Hydrologic System, Applications of Soil Vapor Data to Groundwater Investi-gations, Groundwater Remediation Project Life Cycle, Groundwater Remediation: In Situ Passive Methods, Groundwater and Vinyl Chlo-ride: Chemical Behavior and Treatment, Groundwater and Perchlorate: Chemical Behavior and Treatment, Groundwater Sampling Techniques for Environmental Projects, Low Flow Groundwater Purging and Surging
Hamid R. Jahani, Water Research Institute, Hakimieh, Tehran, Iran, Groundwater Tracing, Resistivity Methods
Chakresh K. Jain, National Institute of Hydrology, Roorkee, India, Assessment of Groundwater Quality in District Hardwar, Uttaranchal, India, Nonpoint Sources, Fluoride Contamination in Ground Water, Irrigation Water Quality in District Hardwar, Uttaranchal, India John R. Jansen, Aquifer Science & Technology, Waukesha, Wisconsin,
Geophysics and Remote Sensing
Anthea Johnson, University of Auckland, Auckland, New Zealand, Bacteria Role in the Phytoremediation of Heavy Metals
Silvia Johnson, Environmental Bio-Systems, Inc., Mill Valley, California, Groundwater and Mercury: Chemical Behavior and Treatment Tracey Johnston, University of Texas at San Antonio, San Antonio,
Texas, Phytoextraction and Phytostabilization: Technical, Economic and
Regulatory Considerations of the Soil-Lead Issue
Jagath J. Kaluarachchi, Utah State University, Logan, Utah, Ground-water Flow and Transport Process
A. Katsoyiannis, Aristotle University of Thessaloniki, Thessaloniki,
Greece, The Use of Semipermeable Membrane Devices (SPMDs) for
Monitoring, Exposure, and Toxicity Assessment
Jack Keeley, Environmental Engineer, Ada, Oklahoma, Nitrate Contam-ination of Groundwater
David W. Kelley, University of St. Thomas, St. Paul, Minnesota, Leaching Lisa Kirkland, Environmental Bio-Systems, Inc., Mill Valley, California,
Groundwater and Lead: Chemical Behavior and Treatment
Dana W. Kolpin, United States Geological Survey, Pharmaceuticals, Hormones, and Other Organic Wastewater Contaminants in U.S. Streams
C.P. Kumar, National Institute of Hydrology, Roorkee, India, Groundwater Balance
Maria S. Kuyukina, Institute of Ecology and Genetics of Microorganisms
of the RAS, Perm, Russia, In Situ Bioremediation of Contaminated
Groundwater
Kung-Yao Lee, Horn Point Laboratory—UMCES, Solomons, Maryland, What is a Hydrochemical Model?
Leo S. Leonhart, Hargis Associates, Inc., Tucson, Arizona, Recharge in Arid Regions, Perched Groundwater
Scott M. Lesch, USDA-ARS George E. Brown, Jr., Salinity Laboratory,
Riverside, California, Characterizing Soil Spatial Variability
Len Li, University of Wisconsin-Madison, Madison, Wisconsin, Reactive Transport in The Saturated Zone: Case Histories for Permeable Reactive Barriers
Keith Loague, Stanford University, Stanford, California, Groundwater Vulnerability to Pesticides: An Overview of Approaches and Methods of Evaluation, Modeling Non-Point Source Pollutants in the Vadose Zone Using GIS
Walter W. Loo, Environmental & Technology Services, Oakland,
California, Treatment for Nitrates in Groundwater, Treatment of
Arsenic, Chromium, and Biofouling in Water Supply Wells, In Situ Electrokinetic Treatment of MtBE, Benzene, and Chlorinated Solvents, Hydraulic Properties Characterization
Kerry T. Macquarrie, University of New Brunswick, Fredericton, New
Brunswick, Canada, River-Connected Aquifers: Geophysics,
Stratigra-phy, Hydrogeology, and Geochemistry
Mini Mathew, Colorado School of Mines, Golden, Colorado, Modeling of DNAPL Migration in Saturated Porous Media
S.C. Mccutcheon, (from Phytoremediation: Transformation and Control
of Contaminants, Wiley 2003), Hydrologic Feasibility Assessment and
Design in Phytoremediation
John E. McCray, Colorado School of Mines, Golden, Colorado, Groundwater Vulnerability to Pesticides: Statistical Approaches M.S. Mohan Kumar, Indian Institute of Science, Bangalore, India,
Modeling of DNAPL Migration in Saturated Porous Media
John E. Moore, USGS (Retired), Denver, Colorado, Well Hydraulics and Aquifer Tests, Drawdown, Groundwater Quality, Hot Springs, Overdraft, Saline Seep, Geological Occurrence of Groundwater
Angela Munroe, Environmental Bio-Systems, Inc., Mill Valley, California, Groundwater and Vinyl Chloride: Chemical Behavior and Treatment Jean-Christophe Nadeau, University of New Brunswick, Fredericton,
New Brunswick, Canada, River-Connected Aquifers: Geophysics,
Stratig-raphy, Hydrogeology, and Geochemistry
NASA Earth Science Enterprise Data and Services, Squeezing Water from Rock
Vahid Nassehi, Loughborough University, Loughborough, United
King-dom, Combined Free and Porous Flow in the Subsurface, Viscous Flow
Sascha E. Oswald, UFZ Centre for Environmental Research,
Leipzig-Halle, Germany, Modeling Contaminant Transport and Biodegradation
in Groundwater
Timothy K. Parker, Groundwater Resources of California, Sacramento,
California, Water Contamination by Low Level Organic Waste
Compounds in the Hydrologic System
Jim C. Philp, Napier University, Edinburgh, Scotland, United Kingdom,
In Situ Bioremediation of Contaminated Groundwater
Laurel Phoenix, Green Bay, Wisconsin, Fossil Aquifers
Nitish Priyadarshi, Ranchi University, Ranchi, Jharkhand, India, Geothermal Water, Rock Fracture, Consolidated Water Bearing Rocks, Groundwater Contamination from Runoff, Groundwater Dating with Radiocarbon, Methane in Groundwater, Permeability
S.N. Rai, National Geophysical Research Institute, Hyderabad, India, Artificial Recharge of Unconfined Aquifer
Todd Rasmussen, The University of Georgia, Athens, Georgia, Head, Deep Soil-Water Movement, Soil Water, Specific Gravity, Tidal Efficiency Hugh H. Russell, CHR2Environmental Services, Inc.,, Oilton, Oklahoma,
Microbial Processes Affecting Monitored Natural Attenuation of Contaminants in the Subsurface
Philip R. Rykwalder, University of Texas at San Antonio, San Antonio,
Texas, Vadose Zone Monitoring Techniques
Bahram Saghafian, Soil Conservation and Watershed Management
Research Institute, Tehran, Iran, Qanats: An Ingenious Sustainable
Groundwater Resource System
C. Samara, Aristotle University of Thessaloniki, Thessaloniki, Greece, The Use of Semipermeable Membrane Devices (SPMDs) for Monitoring, Exposure, and Toxicity Assessment
Dibyendu Sarkar, University of Texas at San Antonio, San Antonio,
Texas, Remediation of Contaminated Soils, Genetics of Metal Tolerance
and Accumulation in Higher Plants, Phytoextraction of Zinc and Cadmium from Soils Using Hyperaccumulator Plants, Phytoremediation
CONTRIBUTORS xiii of Selenium-Laden Soils, Phytoextraction and Phytostabilization:
Technical, Economic and Regulatory Considerations of the Soil-Lead Issue
J.L. Schnoor, (from Phytoremediation: Transformation and Control of
Contaminants, Wiley 2003), Phytoremediation of Methyl Tertiary-Butyl
Ether
Guy W. Sewell, National Risk Management Research Laboratory, ORD,
U.S. EPA, Ada, Oklahoma (formerly with Dynamac Corporation),
Microbial Processes Affecting Monitored Natural Attenuation of Contaminants in the Subsurface
Raj Sharma, University of KwaZulu-Natal, Durban, South Africa, Laminar Flow
Caijun Shi, CJS Technology, Inc., Burlington, Ontario, Canada, High pH Groundwater—The Effect of The Dissolution of Hardened Cement Pastes
Naresh Singhal, University of Auckland, Auckland, New Zealand, Bacteria Role in the Phytoremediation of Heavy Metals, Sub-Surface Redox Chemistry: A Comparison of Equilibrium and Reaction-Based Approaches
V.P. Singh, Louisiana State University, Baton Rouge, Louisiana, Artificial Recharge of Unconfined Aquifer
Joseph Skopp, University of Nebraska, Lincoln, Nebraska, Field Capacity Jeffrey G. Skousen, West Virginia University, Morgantown, West
Virginia, Acid Mine Drainage: Sources and Treatment in the United
States
Ricardo Smalling, Environmental Bio-Systems, Inc., Mill Valley,
California, Groundwater and Uranium: Chemical Behavior and
Treatment
James A. Smith, University of Virginia, Charlottesville, Virginia, Vapor Transport in the Unsaturated Zone
Stuart A. Smith, Smith-Comeskey GroundWater Science LLC, Upper
Sandusky, Ohio, Well Maintenance, Biofouling in Water Wells, Soil and
Groundwater Geochemistry and Microbiology
Michelle Sneed, U.S. Geological Survey, Denver, Colorado, Earth-quakes—Rattling the Earth’s Plumbing System
Roger Spence, Oak Ridge National Laboratory, Oak Ridge, Tennessee, High pH Groundwater—The Effect of The Dissolution of Hardened Cement Pastes
Kenneth F. Steele, University of Arkansas, Fayetteville, Arkansas, Soil and Water Contamination by Heavy Metals
Mark D. Steele, MDC Systems, Inc., Berwyn, Pennsylvania, Water Level Drawdown
P. Takis Elefsiniotis, University of Auckland, Auckland, New Zealand, Bacteria Role in the Phytoremediation of Heavy Metals
Henry Teng, The George Washington University, Washington, DC, Water/Rocks Interaction
Stephen M. Testa, Mokelumne Hill, California, Dating Groundwaters with Tritium, Brine Deposits
Geoffrey Thyne, Colorado School of Mines, Golden, Colorado, Detecting Modern Groundwaters with85Kr, Geochemical Modeling—Computer Code Concepts
Fred D. Tillman, U.S. Environmental Protection Agency, Athens, Georgia, Vapor Transport in the Unsaturated Zone
David J. Tonjes, Cashin Associates PC, Hauppauge, New York, Ground-water Contamination From Municipal Landfills in the USA
Douglas C. Towne, Phoenix, Arizona, Ambient Groundwater Monitoring Network Strategies and Design
Michael D. Trojan, Minnesota Pollution Control Agency, St. Paul,
Minnesota, Land Use Impacts on Groundwater Quality, Sensitivity of
Groundwater to Contamination
Kristine Uhlman, University of Arizona, Tucson, Arizona, Recharge in Desert Regions Around The World
Matthew M. Uliana, Texas State University—San Marcos, San Marcos,
Texas, Regional Flow Systems, Hydraulic Head, Storage Coefficient
David B. Vance, ARCADIS G&M, Inc., Midland, Texas, Groundwater Remediation by In Situ Aeration and Volatilization, Source, Mobility, and Remediation of Metals, Particulate Transport in Groundwater—Bacteria and Colloids, The Environmental Impact of Iron in Groundwater, Groundwater Remediation by Injection and Problem Prevention, Chemi-cal Oxidation Technologies for Groundwater Remediation, PhysiChemi-cal Prop-erties of DNAPLs and Groundwater Contamination, Process Limitations of In Situ Bioremediation of Groundwater, Phytoremediation Enhance-ment of Natural Attenuation Processes, Groundwater and Arsenic: Chemical Behavior and Treatment, Low Flow Groundwater Purging and Surging, The Role of Heat in Groundwater Systems, Horizontal Wells in Groundwater Remediation, Groundwater Flow in Heterogenetic Sed-iments and Fractured Rock Systems, Limiting Geochemical Factors in Remediation Using Monitored Natural Attenuation and Enhanced Bioremediation
Keith Villiers, Environmental Bio-Systems, Inc., Mill Valley, California, Groundwater and Benzene: Chemical Behavior and Treatment Nikolay Voutchkov, Poseidon Resources Corporation, Stamford,
Con-necticut, Well Design and Construction
Atul N. Waghode, Loughborough University, Leicestershire, United
Kingdom, Finite Element Modeling of Coupled Free and Porous Flow
Roger M. Waller, U.S. Geological Survey,, Ground Water: Wells Lise Walter, Environmental Bio-Systems, Mill Valley, California,
Groundwater and Cobalt: Chemical Behavior and Treatment
J.W. Weaver, (from Phytoremediation: Transformation and Control of
Contaminants, Wiley 2003), Hydrologic Feasibility Assessment and
Design in Phytoremediation
Jason J. Wen, City of Downey, Downey, California, Treatment for Nitrates in Groundwater, Treatment of Arsenic, Chromium, and Biofouling in Water Supply Wells
Dennis E. Williams, Geoscience Support Services, Claremont, California, Well TEST, Radial Wells, Well Screens
Eric S. Wilson, E. L. Montgomery & Associates, Inc., Tucson, Arizona, Safe Yield of an Aquifer, Specific Capacity
S.K. Winnike-McMillan, (from Phytoremediation: Transformation and
Control of Contaminants, Wiley 2003), Phytoremediation of Methyl Tertiary-Butyl Ether
Q. Zhang, (from Phytoremediation: Transformation and Control of
Contaminants, Wiley 2003), Phytoremediation of Methyl Tertiary-Butyl
Ether
A.I. Zouboulis, Aristotle University of Thessaloniki, Thessaloniki, Greece, Phytoremediation of Lead-Contaminated Soils
GROUND WATER
GROUND WATER
ACID MINE DRAINAGE: SOURCES AND
TREATMENT IN THE UNITED STATES
JEFFREYG. SKOUSEN West Virginia University Morgantown, West Virginia
Acid mine drainage (AMD) occurs when metal sulfides are exposed to oxidizing conditions. Leaching of reaction products into surface waters pollute over 20,000 km of streams in the United States alone. Mining companies must predict the potential of creating AMD by using overburden analyses. Where a potential exists, special handling of overburden materials and quick coverage of acid-producing materials in the backfill should be practiced. The addition of acid-neutralizing materials can reduce or eliminate AMD problems. Placing acid-producing materials under dry barriers can isolate these materials from air and water. Other AMD control technologies being researched include injection of alkaline materials (ashes and limestone) into abandoned underground mines and into buried acid material in mine backfills, remining of abandoned areas, and installation of alkaline recharge trenches. Chemicals used for treating AMD are Ca(OH)2, CaO, NaOH, Na2CO3, and NH3,
with each having advantages under certain conditions. Under low-flow situations, all chemicals except Ca(OH)2
are cost effective, whereas at high flow, Ca(OH)2 and
CaO are clearly the most cost effective. Floc, the metal hydroxide material collected after treatment, is disposed of in abandoned deep mines, refuse piles, or left in collection ponds. Wetlands remove metals from AMD through formation of oxyhydroxides and sulfides, exchange and organic complexation reactions, and direct plant uptake. Aerobic wetlands are used when water contains enough alkalinity to promote metal precipitation, and anaerobic wetlands are used when alkalinity must be generated by microbial sulfate reduction and limestone dissolution. Anoxic limestone drains are buried trenches of limestone that intercept AMD underground to generate alkalinity. Under anoxia, limestone should not be coated with Fe+3 hydroxides in the drain, which decreases the likelihood of clogging. Vertical flow wetlands pretreat oxygenated AMD with organic matter to remove oxygen and Fe+3, and then the water is introduced into limestone underneath the organic matter. Open limestone channels use limestone in aerobic environments to treat AMD. Coating of limestone occurs, and the reduced limestone dissolution is designed into the treatment system. Alkaline leach beds, containing either limestone or slag, add alkalinity to acid water. At present, most passive systems offer short-term treatment and are more practical for installation on abandoned sites or watershed restoration projects where effluent limits do not apply and where some removal of acid and metals will benefit a stream.
Acid mine drainage (AMD) forms when sulfide minerals deep in the earth are exposed during coal and metal mining, highway construction, and other large-scale excavations. Upon exposure to water and oxygen, sulfide
minerals oxidize to form acidic products, which then can be dissolved in water. The water containing these dissolved products often has a low pH, high amounts of dissolved metals such as iron (Fe) and aluminum (Al), and sulfate.
The metal concentrations in AMD depend on the type and quantity of sulfide minerals present, and the overall water quality from disturbed areas depends on the acid-producing (sulfide) and acid-neutralizing (carbonate) minerals contained in the disturbed rock. The carbonate content of overburden determines whether there is enough neutralization potential or base to counteract the acid produced from pyrite oxidation. Of the many types of acid-neutralizing compounds present in rocks, only carbonates (and some clays) occur in sufficient quantity to effectively neutralize acid-producing rocks. A balance between the acid-producing potential and neutralizing capacity of the disturbed overburden will indicate the ultimate acidity or alkalinity that might be expected in the material upon complete weathering.
Approximately 20,000 km of streams and rivers in the United States are degraded by AMD, but sulfide minerals occur throughout the world causing similar problems. About 90% of the AMD reaching streams originates in abandoned surface and deep mines. No company or individual claims responsibility for reclaiming abandoned mine lands and contaminated water flowing from these sites is not treated.
Control of AMD before land disturbance requires an understanding of three important factors: (1) overburden geochemistry, (2) method and precision of overburden handling and placement in the backfill during reclamation, and (3) the postmining hydrology of the site.
OVERBURDEN ANALYSES, HANDLING, AND PLACEMENT Premining analysis of soils and overburden are required by law (1). Identifying the acid-producing or acid-neutralizing status of rock layers before disturbance aids in developing overburden handling and placement plans. Acid-base accounting provides a simple, relatively inexpensive, and consistent procedure to evaluate overburden chemistry. It balances potential acidity (based on total or pyritic sulfur content) against total neutralizers. Samples containing more acid-producing than acid-neutralizing materials are ‘‘deficient’’ and can cause AMD, whereas those rock samples with the reverse situation have ‘‘excess’’ neutralizing materials and will not cause AMD. Rock layers with equal proportions of each type of material should be subjected to leaching or weathering analyses (2). Kinetic tests such as humidity cells and leach columns are important because they examine the rate of acid-producing and neutralization reactions. This information from kinetic tests can supplement information given by acid-base accounting and help regulators in permitting decisions (3).
The prevailing approach to control AMD is to keep water away from pyritic material. Once overburden materials have been classified, an overburden handling and placement plan for the site can be designed. 1
2 ACID MINE DRAINAGE: SOURCES AND TREATMENT IN THE UNITED STATES Segregating and placing acid-producing materials above
the water table is generally recommended (2,4). Where alkaline materials overwhelm acid-producing materials, no special handling is necessary. Where acid-producing materials cannot be neutralized by onsite alkaline materials, it is necessary to import a sufficient amount to neutralize the potential acidity or the disturbance activity may not be allowed.
Postmining Hydrology
The hydrology of a backfill and its effect on AMD are complex. Generally, the porosity and hydraulic conductivity of the materials in a backfill are greater than those of the consolidated rock overburden that existed before mining, and changes in flow patterns and rates should be expected after mining (5). Water does not move uniformly through the backfill by a consistent wetting front. As water moves into coarse materials in the backfill, it follows the path of least resistance and continues downward through voids or conduits until it encounters a barrier or other compacted layer. Therefore, the chemistry of the water from a backfill will reflect only the rock types encountered in the water flow path, and not the entire geochemistry of the total overburden (6).
Diverting surface water above the site to decrease the amount of water entering the mined area is highly recommended. If it cannot be diverted, incoming water can be treated with limestone to improve water quality. Under certain conditions, pyritic material can be placed where it will be rapidly and permanently inundated, thereby preventing oxidation. Inundation is only suggested where a water table may be reestablished, such as below drainage deep mines (seeWET COVERS).
CONTROL OF AMD
Acid mine drainage control can be undertaken where AMD exists or is anticipated. Control methods treat the acid-producing rock directly and stop or retard the production of acidity. Treatment methods add chemicals directly to acidic water exiting the rock mass. Companies disturbing land in acid-producing areas must often treat AMD, and they face the prospect of long-term water treatment and its liabilities and expense. Cost-effective methods, which prevent the formation of AMD at its source, are preferable. Some control methods are most suited for abandoned mines, and others are only practical on active operations. Other methods can be used in either setting.
Land Reclamation
Backfilling (regrading the land back to contour) and revegetation together are effective methods of reducing acid loads from disturbed lands (7). Water flow from seeps can be reduced by diversion and reclamation, and on some sites where flow may not be reduced, water quality can change from acid to alkaline by proper handling of overburden. Diverting surface water or channeling surface waters to control volume, direction, and contact time can minimize the effects of AMD on receiving streams. Surface diversion involves construction of drainage ditches to move
surface water quickly off the site before infiltration or by providing impervious channels to convey water across the disturbed area.
Alkaline Amendment to Active Disturbances
Certain alkaline amendments can control AMD from acid-producing materials (8–11). All alkaline amendment schemes rely on acid-base accounting or kinetic tests to identify the required alkalinity for neutralization of acidic materials. Special handling of overburden seeks to blend acid-producing and acid-neutralizing rocks in the disturbance/reclamation process to develop a neutral rock mass. The pit floor or material under coal is often rich in pyrite, so isolating it from groundwater may be necessary by building highwall drains (which move incoming groundwater away from the pit floor) or placing impermeable barriers on the pit floor. Acid-forming material can be compacted or capped within the spoil (12). If insufficient alkalinity is available in the spoil, then external sources of alkalinity must be imported (13,14). Limestone is often the least expensive and most readily available source of alkalinity. It has a neutralization potential of between 75% and 100%, and it is safe and easy to handle. On the other hand, it has no cementing properties and cannot be used as a barrier. Fluidized bed combustion ashes generally have neutralizing amounts of between 20% and 40%, and they tend to harden into cement after wetting (15). Other power-generation ashes, like flue gas desulfurization products and scrubber sludges, may also have significant neutralization potential, which make them suitable alkaline amendment materials (16). Other materials, like kiln dust, produced by lime and cement kilns, or lime muds, grit, and dregs from pulp and paper industries contain neutralization products (10). Steel slags, when fresh, have neutralizing amounts from 45% to 90%. Slags are produced by several processes, so care is needed to ensure that candidate slags are not prone to leaching metal ions like Cr, Mn, and Ni. Phosphate rock has been used in some studies to control AMD. It may react with Fe released during pyrite oxidation to form insoluble coatings (17), but phosphate usually costs much more than other calcium-based amendments and is needed in about the same amounts (18).
Alkaline Recharge Trenches
Alkaline recharge trenches (19) are surface ditches or cells filled with alkaline material, which can minimize or eliminate acid seeps through an alkaline-loading process with infiltrating water. Alkaline recharge trenches were constructed on top of an 8-ha, acid-producing coal refuse disposal site, and after 3 years, the drainage water showed 25% to 90% acidity reductions with 70% to 95% reductions in Fe and sulfate (20). Pumping water into alkaline trenches greatly accelerates the movement of alkalinity into the backfill and can cause acid seeps to turn alkaline (21).
Dry Barriers
Dry barriers retard the movement of water and oxygen into areas containing acid-producing rock. These ‘‘water
ACID MINE DRAINAGE: SOURCES AND TREATMENT IN THE UNITED STATES 3 control’’ technologies (4) include impervious membranes,
dry seals, hydraulic mine seals, and grout curtains/walls. Surface barriers can achieve substantial reductions in water flow through piles, but generally they do not control AMD completely. Grouts can separate acid-producing rock and groundwater. Injection of grout barriers or curtains may significantly reduce the volume of groundwater moving through backfills. Gabr et al. (22) found that a 1.5-m-thick grout wall (installed by pumping a mixture of Class F fly ash and Portland cement grout into vertical boreholes near the highwall) reduced groundwater inflow from the highwall to the backfill by 80%, which results in some seeps drying up and others being substantially reduced in flow. At the Heath Steele Metal Mine in New Brunswick, a soil cover was designed to exclude oxygen and water from a tailings pile (23). It consisted of a 10-cm gravel layer for erosion control, 30-10-cm gravel/sand layer as an evaporation barrier, 60-cm compacted till (conductivity of 10−6 cm/sec), 30-cm sand, and pyritic waste rock. This barrier excluded 98% of precipitation, and oxygen concentrations in the waste rock dropped from 20% initially to around 1%. At the Upshur Mining Complex in West Virginia, Meek (12) reported covering a 20-ha spoil pile with a 39-mil PVC liner, and this treatment reduced acid loads by 70%.
Wet Covers
Disposal of sulfide tailings under a water cover, such as in a lake or fjord, is another way to prevent acid generation by excluding oxygen from sulfides. Wet covers also include flooding of aboveground tailings in ponds. Fraser and Robertson (24) studied four freshwater lakes used for subaqueous tailings disposal and found that the reactivity of tailings under water was low and that there were low concentrations of dissolved metals, thereby allowing biological communities to exist.
Alkaline Amendment to Abandoned Mines
Abandoned surface mines comprise huge volumes of spoil of unknown composition and hydrology. Abandoned underground mines are problematic because they are often partially caved and flooded, cannot be accessed, and have unreliable or nonexistent mine maps. Re-handling and mixing alkalinity into an already reclaimed backfill is generally prohibitively expensive.
Filling abandoned underground mine voids with nonpermeable materials is one of the best methods to prevent AMD. Underground mine voids are extensive (a 60-ha mine with a coal bed height of 1.5 m and a recovery rate of 65% would contain about 600,000 m3 of voids), so
fill material and the placement method must be cheap. Mixtures of Class F fly ash and 3–5% Portland cement control subsidence in mined-under residential areas and these slurries are generally injected through vertical boreholes at between 8- and 16-m centers. Pneumatic (air pressure) and slurry injection for placing fly ash in abandoned underground mines can extend the borehole spacing to about 30 m (25). On reclaimed surface mines still producing AMD, researchers in Pennsylvania saw small improvements in water quality after injecting coal combustion residues into buried pods of pyritic materials.
Remining and Reclamation
‘‘Remining’’ means returning to abandoned surface or underground mines for further coal removal. Where AMD occurs, remining reduces acid loads by (1) decreasing infiltration rates, (2) covering acid-producing materials, and (3) removing the remaining coal, which is the source of most of the pyrite. Hawkins (26) found contaminant loads of 57 discharges from remined sites in Pennsylvania to be reduced after remining and reclamation. Short-term loads were sometimes increased during the first six months after remining and reclamation, but reduction in loads after six months resulted from decreased flow rather than large changes in concentrations. Ten remining sites in Pennsylvania and West Virginia were reclaimed to current standards (which included eliminating highwalls, covering refuse, and revegetating the entire area), and all sites had improved water quality (15).
CHEMICAL TREATMENT OF AMD
If AMD problems develop during mining or after reclamation, a plan to treat the discharge must be developed. A water treatment system consists of an inflow pipe or ditch, a storage tank or bin holding the treatment chemical, a valve to control its application rate, a settling pond to capture precipitated metal oxyhydroxides, and a discharge point. At the discharge point, water samples are analyzed to monitor whether specified parameters are being attained. Water discharge permits (NPDES) on surface mines usually require monitoring of pH, total suspended solids, and Fe and Mn concentrations. The type and size of a chemical treatment system is based on flow rate, pH, oxidation status, and concentrations of metals in the AMD. The receiving stream’s designated use and seasonal fluctuations in flow rate are also important. After evaluating these variables over a period of time, the operator can consider the economics of different chemicals.
Six chemicals treat AMD (Table 1). Each is more or less appropriate for a specific condition. The best choice depends on both technical (acidity levels, flow, and the types and concentrations of metals) and economic factors (chemical prices, labor, machinery and equipment, treatment duration, and interest rates). Enough alkalinity must be added to raise pH to between 6 and 9 so insoluble metal hydroxides will form and settle out. Treatment of AMD with high Fe (ferric) concentrations often affords coprecipitation of other metals with the Fe hydroxide, thereby removing them from AMD at a lower pH. Limestone has been used for decades to raise pH and precipitate metals in AMD. It has the lowest material cost and is the safest and easiest to handle of the AMD chemicals. Unfortunately, it is limited because of its low solubility and tendency to develop an external coating, or armor, of Fe(OH)3 when added to AMD. Fine-ground
limestone may be dumped in streams directly or the limestone may be pulverized by water-powered rotating drums and metered into the stream. Limestone has also treated AMD in anaerobic (anoxic limestone drains) and aerobic environments (open limestone channels).
4 ACID MINE DRAINAGE: SOURCES AND TREATMENT IN THE UNITED STATES
Table 1. Chemical Compounds Used in AMD Treatment
2000 Costc $ per Mg or L
Common Name Chemical Name Formula
Conversion Factora
Neutralization
Efficiencyb Bulk <Bulk
Limestone Calcium carbonate CaCO3 1.00 30% $11 $16
Hydrated Lime Calcium hydroxide Ca(OH)2 0.74 90% $66 $110
Pebble Quicklime Calcium oxide CaO 0.56 90% $88 $264
Soda Ash Sodium carbonate Na2CO3 1.06 60% $220 $350
Caustic Soda (solid) Sodium hydroxide NaOH 0.80 100% $750 $970
20% Liquid Caustic Sodium hydroxide NaOH 784 100% $0.06 $0.16
50% Liquid Caustic Sodium hydroxide NaOH 256 100% $0.29 $0.33
Ammonia Anhydrous ammonia NH3 0.34 100% $330 $750
aThe conversion factor may be multiplied by the estimated milligrams acid/yr to get milligrams of chemical needed for neutralization per year. For liquid
caustic, the conversion factor gives liters needed for neutralization.
bNeutralization efficiency estimates the relative effectiveness of the chemical in neutralizing AMD acidity. For example, if 100 Mg of acid/yr was the amount
of acid to be neutralized, then it can be estimated that 82 Mg of hydrated lime would be needed to neutralize the acidity in the water (100(0.74)/0.90).
cPrice of chemical depends on the quantity being delivered. Bulk means delivery of chemical in a large truck, whereas < Bulk means purchased in small
quantities. Liquid caustic prices are for liters. Others in milligrams.
Lime
Hydrated lime is common for treating AMD. As a powder, it tends to be hydrophobic, and extensive mechanical mixing is required for dissolution. Hydrated lime is particularly useful and cost effective in large-flow, high-acidity situations where a lime treatment plant with a mixer/aerator is constructed to help dispense and mix the chemical with the water (27). Hydrated lime has limited effectiveness if a very high pH (>9) is required to remove ions such as Mn. Unfortunately, increasing the lime rate increases the volume of unreacted lime that enters the floc-settling pond.
Pebble quicklime (CaO) is used with the Aquafix Water Treatment System using a water wheel concept (28). A water wheel is turned based on water flow, which causes a screw feeder to dispense the chemical. This system was initially used for small and/or periodic flows of high acidity because CaO is very reactive, but water wheels have been attached to large silos for high-flow/high-acidity situations. Tests show an average of 75% cost savings over NaOH systems and about 20% to 40% savings over NH3systems.
Soda Ash
Soda ash (Na2CO3) generally treats AMD in remote areas
with low flow and low amounts of acidity and metals. This choice is usually based on convenience rather than on chemical cost. Soda ash comes as solid briquettes and is gravity fed into water through bins. The number of briquettes used per day is determined by the rate of flow and quality of the water. One problem is that the briquettes absorb moisture, expand, and stick to the corners of the bin and will not drop into the stream. For short-term treatment, some operators use a much simpler system that employs a wooden box or barrel with holes that allows water inflow and outflow. The operator simply fills the barrel with briquettes on a regular basis and places the barrel in the flowing water. This system offers less control of the amount of chemical used. Caustic Soda
Caustic soda (i.e., lye, NaOH) is often used in remote low-flow, high-acidity situations, or if Mn concentrations
in the AMD are high. The system can be gravity fed by dripping liquid NaOH directly into the AMD. Caustic is very soluble, disperses rapidly, and raises the pH quickly. Caustic should be applied at the surface of ponds because the chemical is denser than water. The major drawbacks of using liquid NaOH for AMD treatment are high cost and dangers in handling.
Ammonia
Ammonia compounds (NH3 or NH4OH) are extremely
hazardous. NH3is compressed and stored as a liquid but
returns to the gaseous state when released. Ammonia is extremely soluble, reacts rapidly, and can raise the pH of receiving water to 9.2. At pH 9.2, it buffers the solution to further pH increases, and therefore very high amounts of NH3must be added to go beyond 9.2. Injection of NH3into
AMD is one of the quickest ways to raise water pH, and it should be injected near the bottom of the pond or water inlet because NH3is less dense than water. NH3is cheap,
and a cost reduction of 50% to 70% is usually realized when NH3 is substituted for NaOH (29). Major disadvantages
of using NH3 include (1) the hazards; (2) uncertainty
concerning nitrification, denitrification, and acidification downstream; and (3) consequences of excessive application rates, which cause toxic conditions to aquatic life.
Costs of Treating AMD
Costs were estimated for five treatment chemicals under four sets of flow and acid concentration conditions [Table 1 from Skousen et al. (30)]. Na2CO3 had the highest labor
requirements (10 hours per week) because the dispensers must be filled by hand and inspected frequently. Caustic had the highest reagent cost per mole of acid-neutralizing capacity, and Na2CO3 had the second highest. Hydrated
lime treatment systems had the highest installation costs of the five chemicals because of the need to construct a lime treatment plant and install a pond aerator. However, the cost of Ca(OH)2was very low, and the combination of
high installation costs and low reagent cost made Ca(OH)2
systems particularly appropriate for long-term treatment of high-flow/high-acidity conditions.
ACID MINE DRAINAGE: SOURCES AND TREATMENT IN THE UNITED STATES 5 For a 5-year treatment, NH3 had the lowest annual
cost for the low-flow/low-acid situation. Pebble quicklime had about the same cost as the NH3 system, but slightly
higher installation costs. Caustic was third because of its high labor and reagent costs, and Na2CO3was fourth
because of high labor costs. Hydrated lime was the most expensive because of its high installation costs. At high-flow/high-acidity, the Ca(OH)2 and CaO systems were
clearly the cheapest treatment systems (annual costs of about $250,000 less than NH3, the next best alternative).
After chemical treatment, the treated water flows into sedimentation ponds so metals in the water can precipitate. All AMD treatment chemicals cause the formation of metal hydroxide sludge or floc. Sufficient residence time of the water (dictated by pond size and depth) is important for adequate metal precipitation. The amount of metal floc generated depends on water quality and quantity, which in turn determines how often the ponds must be cleaned. Knowing the chemical and AMD being treated will provide an estimate of the stability of metal compounds in the floc. Floc disposal options include (1) leaving it submerged indefinitely, (2) pumping or hauling it to abandoned deep mines or to pits dug on surface mines, and (3) dumping it into refuse piles. Pumping flocs onto land and letting them age and dry is a good strategy for disposal, because they become crystalline and behave like soil material.
Each AMD is unique, requiring site-specific treatment. Each AMD source should be tested with various chemicals by titration tests to evaluate the most effective chemical for precipitation of the metals. The costs of each AMD treatment system based on neutralization (in terms of the reagent cost, capital investment, and maintenance of the dispensing system) and floc disposal should be evaluated to determine the most cost-effective system.
PASSIVE TREATMENT OF AMD
Active chemical treatment of AMD is often an expensive, long-term proposition. Passive treatment systems have been developed that do not require continuous chemical inputs and that take advantage of natural chemical and biological processes to cleanse contaminated mine waters. Passive technologies include constructed wetlands, anoxic limestone drains, vertical flow wetlands (also known as SAPS), open limestone channels, and alkaline leach beds (Fig. 1). In low-flow and low-acidity situations, passive systems can be reliably implemented as a single permanent solution for many AMD problems.
Constructed Wetlands
Wetlands are of two basic types: aerobic and anaerobic. Metals are retained within wetlands by (1) formation of metal oxides and oxyhydroxides, (2) formation of metal sulfides, (3) organic complexation reactions, (4) exchange with other cations on negatively charged sites, and (5) direct uptake by living plants. Other beneficial reactions in wetlands include generation of alkalinity caused by microbial mineralization of dead organic matter, microbial dissimilatory reduction of Fe oxyhydroxides and SO4, and dissolution of carbonates.
Aerobic wetlands consist of relatively shallow ponds (<30 cm) with wetland vegetation. Aerobic wetlands promote metal oxidation and hydrolysis, thereby causing precipitation and physical retention of Fe, Al, and Mn oxyhydroxides. Successful metal removal depends on dissolved metal concentrations, dissolved oxygen content, pH and net acidity of the mine water, the presence of active microbial biomass, and detention time of the water in the wetland. The pH and net acidity/alkalinity of the water are particularly important because pH influences both the solubility of metal hydroxide precipitates and the kinetics of metal oxidation and hydrolysis. Therefore, aerobic wetlands are best used in conjunction with water that contains net alkalinity to neutralize metal acidity.
Anaerobic wetlands consisting of deep ponds (>30 cm) with substrates of soil, peat moss, spent mushroom compost, sawdust, straw/manure, hay bales, or other organic mixtures, often underlain or admixed with limestone. Anaerobic wetlands are most successful when used to treat small flows of acidic water. Anaerobic wetlands use chemical and microbial reduction reactions to precipitate metals and neutralize acidity. The water infiltrates through a thick permeable organic subsurface that becomes anaerobic because of high biological oxygen demand. Other chemical mechanisms that occur in situ include metal exchanges, formation and precipitation of metal sulfides, microbial-generated alkalinity, and formation of carbonate alkalinity (because of limestone dissolution). As anaerobic wetlands produce alkalinity, they can be used in net acidic and high dissolved oxygen (>2 mg/L) AMD. Microbial mechanisms of alkalinity production are critical to long-term AMD treatment. Under high acid loads (>300 mg/L), pH-sensitive microbial activities are eventually overwhelmed. At present, the sizing value for Fe removal in these wetlands is 10 gs per day per meter squared (31).
Sorption onto organic materials (such as peat and sawdust) can initially remove 50% to 80% of the metals in AMD (32), but the exchange capacity declines with time. Over the long term, metal hydroxide precipitation is the predominant form of metal retention in a wetland. Wieder (33) reported up to 70% of the Fe in a wetland to be composed of Fe+3oxyhydroxides, whereas the other 30% is reduced and combined with sulfides (34).
Sulfate reducing bacteria (SRB) reactors have been used to generate alkalinity by optimizing anaerobic conditions. Good success has been noted for several systems receiving high and low flows (35,36).
Anoxic Limestone Drains
Anoxic limestone drains are buried cells or trenches of limestone into which anoxic water is introduced. The limestone raises pH and adds alkalinity. Under anoxic conditions, the limestone does not coat or armor with Fe hydroxides because Fe+2does not precipitate as Fe(OH)2at
pH 6.0. Faulkner and Skousen (37) reported both successes and failures among 11 anoxic drains in WV. Failures resulted when ferric iron and Al precipitate as hydroxides in the limestone causing plugging and coating.
6 ACID MINE DRAINAGE: SOURCES AND TREATMENT IN THE UNITED STATES
Figure 1. Diagram of possible passive treatment systems to treat mine water based on water flow and chemistry.
Determine flow rate analyze water chemistry
calculate loading
Net acidic water Net alkaline water
Determine do, ferric iron, al Do < 1 mg/L and ferric < 1 mg/L and al < 1 mg/L Settling pond Net alkaline water Anoxic limestone drain Net acid water Settling pond Sulfate reducing bioreactor Anaerobic wetland Saps Open limestone channel Slag or ls leach bed Settling pond Settling pond Settling pond Settling pond Settling pond Aerobic wetland Meet effluent standards? Meet effluent standards? Re-evaluate design No No Yes Discharge Yes Do > 1 mg/L and ferric > 1 mg/L and al > 1 mg/L
Longevity of treatment is a major concern for anoxic drains, especially in terms of water flow through the lime-stone. Selection of the appropriate water and environmen-tal conditions is critical for long-term alkalinity generation in an anoxic drain. Eventual clogging of the limestone pore spaces with precipitated Al and Fe hydroxides, and gyp-sum is predicted (38). For optimum performance, no Fe+3, dissolved oxygen, or Al should be present in the AMD. Like wetlands, anoxic limestone drains may be a solution for AMD treatment for specific water conditions or for a finite period after which the system must be replenished or replaced.
Vertical Flow Wetlands
In these modified wetlands [called SAPS by Kepler and McCleary (39)], 1 to 3 m of acid water is ponded over an organic compost of 0.2 to 0.3 m, underlain by 0.5 to 1 m of limestone. Below the limestone are drainage pipes
that convey the water into an aerobic pond where metals are precipitated. The hydraulic head drives ponded water through the anaerobic organic compost, where oxygen stripping as well as Fe and sulfate reduction can occur before water entry into the limestone. Water with high metal loads can be successively cycled through additional wetlands. Iron and Al clogging of limestone and pipes can be removed by flushing the system (40). Much work is being done on these wetlands presently, and refinements are being made for better water treatment.
Open Limestone Channels
Open limestone channels are another means of introducing alkalinity to acid water (41). We usually assume that armored limestone ceases to dissolve, but Ziemkiewicz et al. (42) found armored limestone to be 50% to 90% effective in neutralizing acid compared with unarmored limestone. Seven open channels in the field reduced acidity
