NATURAL ATTENUATION FOR GROUNDWATER REMEDIATION

Committee on Intrinsic Remediation

Water Science and Technology Board

Board on Radioactive Waste Management

Commission on Geosciences, Environment, and Resources

NATIONAL ACADEMY PRESS
Washington, D.C.



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Natural Attenuation for Groundwater Remediation NATURAL ATTENUATION FOR GROUNDWATER REMEDIATION Committee on Intrinsic Remediation Water Science and Technology Board Board on Radioactive Waste Management Commission on Geosciences, Environment, and Resources NATIONAL ACADEMY PRESS Washington, D.C.

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Natural Attenuation for Groundwater Remediation NATIONAL ACADEMY PRESS 2101 Constitution Avenue, N.W. Washington, DC 20418 NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. Support for this project was provided by the American Petroleum Institute under contract no. 97-0000-1957, the Chemical Manufacturers’ Association, Chevron, the Lawrence Livermore National Laboratory, the National Mining Association, the Nuclear Regulatory Commission under contract no. NRC-04-97-068, the U.S. Army under contract no. DACA31-97-P-1191, the U.S. Department of Energy under contract no. DE-FC01-94EW54069, the U.S. Environmental Protection Agency under contract no. R-826445-01-0, the U.S. Geological Survey under contract no. 1434-HQ-97-AG-01775, and the U.S. Navy under contract no. N62467-97-M-1009. Library of Congress Cataloging-in-Publication Data Natural attenuation for groundwater remediation / Committee on Intrinsic Remediation, Water Science and Technology Board [and] Board on Radioactive Waste Management, Commission on Geosciences, Environment, and Resources. p. cm. Includes bibliographical references and index. ISBN 0-309-06932-7 (casebound) 1. Hazardous wastes—Natural attenuation—Evaluation. 2. In situ bioremediation—Evaluation. 3. Hazardous waste site remediation—Evaluation. 4. Groundwater—Purification. I. National Research Council (U.S.). Committee on Intrinsic Remediation. TD1060 .N37 2000 628.1′68—dc21 00-008896 Natural Attenuation for Groundwater Remediation is available from the National Academy Press, 2101 Constitution Ave., N.W., Box 285, Washington, DC 20055; (800) 624-6242 or (202) 334-3313 (in the Washington mtropolitan area); Internet <http://www.nap.edu>. Copyright 2000 by the National Academy of Sciences. All rights reserved. Printed in the United States of America

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Natural Attenuation for Groundwater Remediation THE NATIONAL ACADEMIES National Academy of Sciences National Academy of Engineering Institute of Medicine National Research Council The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. William A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. William A. Wulf are chairman and vice chairman, respectively, of the National Research Council.

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Natural Attenuation for Groundwater Remediation COMMITTEE ON INTRINSIC REMEDIATION BRUCE E. RITTMANN, Chair, Northwestern University, Evanston, Illinois MICHAEL J. BARDEN, Geoscience Resources Ltd., Albuquerque, New Mexico BARBARA A. BEKINS, U.S. Geological Survey, Menlo Park, California DAVID E. ELLIS, DuPont Specialty Chemicals, Wilmington, Delaware MARY K. FIRESTONE, University of California, Berkeley (through June 1998) STEPHEN LESTER, Center for Health, Environment, and Justice, Falls Church, Virginia DEREK LOVLEY, University of Massachusetts, Amherst RICHARD G. LUTHY, Stanford University, Stanford, California DOUGLAS M. MACKAY, University of Waterloo, Ontario, Canada EUGENE MADSEN, Cornell University, Ithaca, New York PERRY L. MCCARTY, Stanford University, Stanford, California EILEEN POETER, Colorado School of Mines, Golden ROBERT SCOFIELD, ENVIRON Corporation, Emeryville, California ARTHUR W. WARRICK, University of Arizona, Tucson JOHN T. WILSON, U.S. Environmental Protection Agency, Ada, Oklahoma JOHN ZACHARA, Pacific Northwest National Laboratories, Richland, Washington Staff JACQUELINE A. MACDONALD, Study Director ELLEN A. DE GUZMAN, Senior Project Assistant KIMBERLY SWARTZ, Project Assistant (through June 1999)

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Natural Attenuation for Groundwater Remediation WATER SCIENCE AND TECHNOLOGY BOARD HENRY J. VAUX, Jr., Chair, Division of Agriculture and Natural Resources, University of California, Oakland CAROL A. JOHNSTON, Vice-Chair, University of Minnesota, Duluth RICHELLE M. ALLEN-KING, Washington State University, Pullman GREGORY B. BAECHER, University of Maryland, College Park JOHN S. BOYER, University of Delaware, Lewes JOHN BRISCOE, The World Bank, Washington, D.C. DENISE D. FORT, University of New Mexico, Albuquerque STEVEN P. GLOSS, University of Wyoming, Laramie EVILLE GORHAM, University of Minnesota, St. Paul (through January 2000) WILLIAM A. JURY, University of California, Riverside GARY S. LOGSDON, Black & Veatch, Cincinnati, Ohio RICHARD G. LUTHY, Stanford University, Stanford, California JOHN W. MORRIS, J. W. Morris Ltd., Arlington, Virginia PHILIP A. PALMER, (Retired) E. I. du Pont de Nemours & Co., Wilmington, Delaware REBECCA T. PARKIN, The George Washington University, Washington, D.C. JOAN B. ROSE, University of South Florida, St. Petersburg R. RHODES TRUSSELL, Montgomery Watson, Pasadena, California ERIC F. WOOD, Princeton University, Princeton, New Jersey Staff STEPHEN D. PARKER, Director LAURA J. EHLERS, Senior Staff Officer CHRIS ELFRING, Senior Staff Officer JEFFREY W. JACOBS, Senior Staff Officer WILLIAM S. LOGAN, Staff Officer MARK C. GIBSON, Staff Officer M. JEANNE AQUILINO, Administrative Associate PATRICIA A. JONES, Study/Research Associate ANITA A. HALL, Administrative Assistant ELLEN A. DE GUZMAN, Senior Project Assistant ANIKE L. JOHNSON, Project Assistant

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Natural Attenuation for Groundwater Remediation BOARD ON RADIOACTIVE WASTE MANAGEMENT JOHN F. AHEARNE, Chair, Sigma Xi, The Scientific Research Society, and Duke University, Research Triangle Park, North Carolina CHARLES MCCOMBIE, Vice-Chair, Consultant, Gipf-Oberfrick, Switzerland ROBERT M. BERNERO, Consultant, Gaithersburg, Maryland ROBERT J. BUDNITZ, Future Resources Associates, Inc., Berkeley, California GREGORY CHOPPIN, Florida State University, Tallahassee JAMES H. JOHNSON, JR., Howard University, Washington, D.C. ROGER E. KASPERSON, Clark University, Worcester, Massachusetts JAMES O. LECKIE, Stanford University, Stanford, California JANE C. S. LONG, University of Nevada, Reno ALEXANDER MACLACHLAN, E.I. du Pont de Nemours & Company (retired), Olney, Maryland WILLIAM A. MILLS, Oak Ridge Associated Universities (retired), Olney, Maryland MARTIN J. STEINDLER, Argonne National Laboratory (retired), Argonne, Illinois ATSUYUKI SUZUKI, University of Tokyo, Japan JOHN J. TAYLOR, Electric Power Research Institute, Palo Alto, California VICTORIA J. TSCHINKEL, Landers and Parsons, Tallahassee, Florida MARY LOU ZOBACK, U.S. Geological Survey, Menlo Park, California Staff KEVIN D. CROWLEY, Director ROBERT S. ANDREWS, Senior Staff Officer JOHN R. WILEY, Senior Staff Officer BARBARA PASTINA, Staff Officer SUSAN B. MOCKLER, Research Associate TONI GREENLEAF, Administrative Associate ANGELA R. TAYLOR, Senior Project Assistant LATRICIA C. BAILEY, Project Assistant LAURA D. LLANOS, Project Assistant

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Natural Attenuation for Groundwater Remediation COMMISSION ON GEOSCIENCES, ENVIRONMENT, AND RESOURCES GEORGE M. HORNBERGER, Chair, University of Virginia, Charlottesville RICHARD A. CONWAY, Union Carbide Corporation (retired), South Charleston, West Virginia LYNN GOLDMAN, Johns Hopkins School of Hygiene and Public Health, Baltimore, Maryland THOMAS E. GRAEDEL, Yale University, New Haven, Connecticut THOMAS J. GRAFF, Environmental Defense Fund, Oakland, California EUGENIA KALNAY, University of Maryland, College Park DEBRA KNOPMAN, Progressive Policy Institute, Washington, D.C. BRAD MOONEY, J. Brad Mooney Associates, Ltd., Arlington, Virginia HUGH C. MORRIS, El Dorado Gold Corporation, Vancouver, British Columbia H. RONALD PULLIAM, University of Georgia, Athens MILTON RUSSELL, Joint Institute for Energy and Environment and University of Tennessee (emeritus), Knoxville ROBERT J. SERAFIN, National Center for Atmospheric Research, Boulder, Colorado ANDREW R. SOLOW, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts E-AN ZEN, University of Maryland, College Park MARY LOU ZOBACK, U.S. Geological Survey, Menlo Park, California Staff ROBERT M. HAMILTON, Executive Director GREGORY H. SYMMES, Associate Executive Director JEANETTE SPOON, Administrative and Financial Officer SANDI FITZPATRICK, Administrative Associate

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Natural Attenuation for Groundwater Remediation Preface In 1992, when I chaired the National Research Council’s Committee on In Situ Bioremediation, the committee addressed whether or not microorganisms could clean up contamination of soil and groundwater. The committee’s 1993 report, In Situ Bioremediation: When Does It Work?, concluded that microorganisms are capable of destroying common groundwater contaminants. The report concluded that in situ bioremediation is scientifically valid and technically feasible. The report also stressed that possible biodegradation reactions must be documented clearly with several lines of evidence from the field. One of the important distinctions made in the 1993 report is between engineered bioremediation and intrinsic bioremediation. Engineered bioremediation uses engineered technologies to enhance microbiological activity and increase the rate of biodegradation. Examples include sparging the subsurface with air to supply oxygen and adding nutrients to stimulate microbial growth. On the other hand, intrinsic remediation relies only on the natural supply rates of substances such as oxygen and nutrients that promote contaminant biodegradation. When these supply rates are sufficient, the intrinsic biodegradation capacity of the microorganisms at the site can prevent migration of the contaminants in groundwater and eventually lead to a site cleanup. At the time the Committee on In Situ Bioremediation was deliberating, in situ bioremediation was carried out almost exclusively by engineered approaches. Soon after In Situ Bioremediation: When Does It Work? was published, the pendulum began to swing towards intrinsic bio-

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Natural Attenuation for Groundwater Remediation remediation, which was accepted as a final cleanup remedy at more and more sites. Another important change was taking place in parallel. The term intrinsic bioremediation was slowly being superseded by natural attenuation, an approach having a much broader definition. Besides biodegradation, natural attenuation includes natural physical processes that can immobilize contaminants and natural chemical reactions that can destroy contaminants. It also includes dilution, dispersion, volatilization, adsorption, and other processes that do not destroy or immobilize the contaminants. By 1998, many regulators were happy to “close the books” on sites by accepting a natural attenuation remedy. Responsible parties were relieved to have an approach that seemed to save them money and headaches. The types of sites and contaminants for which natural attenuation was being considered were growing steadily: petroleum hydrocarbons, chlorinated solvents, heavy metals, radionuclides, and more. Clearly the pendulum had swung toward using natural, in situ processes. However, not everyone was so pleased with the rapidly expanding acceptance of natural attenuation as a remedy. Members of communities living near contaminated sites suspected that natural attenuation really meant “do nothing” and “walk away.” Scientists and engineers expert in bioremediation were concerned that natural attenuation was being accepted whether or not it was documented—or even likely—at a site. Perhaps the pendulum had swung too far. The National Research Council (NRC) formed the committee that prepared this report—the Committee on Intrinsic Remediation—in 1997 in order to establish a proper basis for selecting remedies that rely on natural attenuation processes. The committee was charged with the following tasks: assess current knowledge about the natural subsurface processes that play critical roles in intrinsic remediation; outline what intrinsic remediation can and cannot achieve; assess risks associated with leaving contaminants in place; identify the measurements, observations, and monitoring needed when intrinsic remediation is chosen instead of engineered remediation; and evaluate the adequacy of existing protocols for determining whether intrinsic remediation is an appropriate strategy for contaminant management. This report summarizes the findings of the committee, which was made up of 14 experts in the technical and decision-making aspects of natural attenuation. Committee members brought to the table state-of-

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Natural Attenuation for Groundwater Remediation the-art expertise in environmental microbiology, geochemistry, environmental engineering, hydrogeology, soil science, and risk assessment. Academia, industry, government, and community-based institutions were represented. The committee also interviewed a wide range of community activists, researchers, regulators, practitioners, and protocol developers. The findings presented in this report represent the unanimous consensus of the committee. Despite coming from disparate backgrounds and interest groups, all of the committee members agreed with the message that this report delivers. Clearly, the concept that natural attenuation processes can, under the proper conditions, cause the destruction or transformation of contaminants in the environment is valid. However, natural attenuation should never be a default choice. The cause-and-effect link between a decrease in contaminant concentration and the process or processes causing it must be documented before natural attenuation is accepted as a remedy. These processes must continue to occur for as long as is necessary to protect human health and the environment. Furthermore, affected communities need to be part of the decision to accept natural attenuation. Chapter 1 outlines the factors that led the National Research Council to form this committee. Chapter 2 details why community groups have an especially strong stake in decisions involving natural attenuation, and it provides guidance on how community groups can be involved effectively. Chapter 3 reviews the scientific foundation for natural attenuation and summarizes the likelihood that natural attenuation will work for the major classes of contaminants. Chapter 4 describes the steps needed to evaluate whether or not natural attenuation is protecting human health and the environment for a given site; it stresses that many types of information must be integrated to assess natural attenuation potential and provides guidance on the relative level of effort needed to gather and interpret information. Finally, Chapter 5 provides a critical review of the protocols published as of the end of 1998 and offers guidance on topics that protocols developed in the future should address. I want to thank the organizations that sponsored this project for having confidence in the National Research Council process and our committee. In particular, thanks are due to Ken Lovelace and Rich Steimle at the Environmental Protection Agency; Ira May at the Army Environmental Center; Cliff Casey at the Naval Facilities Engineering Command, Southern Division; Herb Buxton and Frank Chapelle of the U.S. Geological Survey; Steve Golian of the Department of Energy; Tom Nicholson and Ralph Cady of the Nuclear Regulatory Commission; Bruce Bauman of the American Petroleum Institute; David Mentall of the Chemical Manufacturers’ Association; Katie Sweeney of the National Mining Association; K. C. Bishop and Tim Buscheck of Chevron USA, Inc.; and David Rice and

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Natural Attenuation for Groundwater Remediation Ellen Raber of Lawrence Livermore National Laboratory. The organizations that these individuals represent provided not only the financial support that made this study possible, but also valuable background information. I sincerely thank each committee member for his or her unique contributions and for being fully invested in the common goal. Being the chair of such a hard-working committee—a true team—has been a most satisfying experience. Finally, I thank our study director, Jacqueline MacDonald, who made the committee’s work go smoothly and who really helped us figure out what “we meant to say,” whether or not we actually had said it. This report has been reviewed, in accordance with NRC procedures, by individuals chosen for their expertise and broad perspectives on natural attenuation issues. This independent review provided candid and critical comments that assisted the authors and the NRC in making the published report as sound as possible and ensured that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The content of the review comments and the draft manuscript remain confidential to protect the integrity of the deliberative process. The committee wishes to thank the following individuals for their participation in the review of this report and their many instructive comments: Charles Andrews, S. S. Papadopulous and Associates Michael Aitken, University of North Carolina Isabelle Cozzarelli, U.S. Geological Survey Paul Hadley, California Department of Toxic Substances Control Michael Kavanaugh, Malcolm Pirnie, Inc. Debra Knopman, Progressive Policy Institute Rebecca Parkin, The George Washington University Medical Center Leonard Siegel, Pacific Studies Center Donald Sparks, University of Delaware Susan Wiltshire, J. K. Associates While the individuals listed above have provided constructive comments and suggestions, it must be emphasized that responsibility for the final content of this report rests entirely with the authoring committee and the institution. BRUCE E. RITTMANN Chair

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Natural Attenuation for Groundwater Remediation Contents     EXECUTIVE SUMMARY   1 1   INTRODUCTION: USING NATURAL PROCESSES IN GROUNDWATER RESTORATION   20      Historical Role of Natural Cleanup Processes,   25      Limitations of Engineered Remediation Systems,   25      Increasing Reliance on Natural Attenuation,   26      Increasing Variety of Contaminants Considered for Natural Attenuation,   31      Increasing Number of Natural Attenuation Protocols,   32      Increasing Public Concerns,   33      Focus of This Report,   34      Summary,   34      References,   35 2   COMMUNITY CONCERNS ABOUT NATURAL ATTENUATION   37      Specific Community Concerns,   38      Basis for Community Concerns,   41      Principles of Community Involvement,   48      Mechanisms for Involving the Community,   53      Conclusions,   58      Recommendations,   60      References,   61

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Natural Attenuation for Groundwater Remediation 3   SCIENTIFIC BASIS FOR NATURAL ATTENUATION   65      Contaminants and Hydrogeologic Settings,   66      Removal of Contaminant Sources,   69      Movement of Contaminants in the Subsurface,   78      Transformation of Contaminants in the Subsurface,   82      Transformation by Microorganisms,   82      Transformation by Chemical Reactions,   106      Integration of the Mechanisms That Affect Subsurface Contaminants,   113      Case Studies of Natural Attenuation,   115      Summary: Appropriate Circumstances for Considering Natural Attenuation,   135      Conclusions,   140      References,   141 4   APPROACHES FOR EVALUATING NATURAL ATTENUATION   150      Footprints of Natural Attenuation Processes,   151      Creating a Conceptual Model,   154      Analyzing Site Data,   172      Monitoring the Site,   203      Conclusions,   204      Recommendations,   207      References,   209 5   PROTOCOLS FOR DOCUMENTING NATURAL ATTENUATION   212      Criteria for a Good Protocol,   213      Overview of Protocols,   219      Adequacy of Protocols,   231      Adequacy of Decision-Making Tools,   241      Adequacy of Training,   244      Adequacy of Policies Concerning Use of Protocols,   248      Conclusions,   250      Recommendations,   252      References,   253     APPENDIXES     A   ACRONYMS   255 B   PRESENTERS AT THE COMMITTEE’S INFORMATION-GATHERING MEETINGS   257 C   BIOGRAPHICAL SKETCHES OF COMMITTEE MEMBERS AND STAFF   259     INDEX   265