Barrier systems for environmental contaminant containment and treatment [1 ed.] 0849340403, 9780849340406, 9781420037319

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BARRIER SYSTEMS for ENVIRONMENTAL CONTAMINANT CONTAINMENT and TREATMENT

BARRIER SYSTEMS for ENVIRONMENTAL CONTAMINANT CONTAINMENT and TREATMENT Edited by

Calvin C. Chien • Hilary I. Inyang Lorne G. Everett

Boca Raton London New York

A CRC title, part of the Taylor & Francis imprint, a member of the Taylor & Francis Group, the academic division of T&F Informa plc.

Published in 2006 by CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2006 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group No claim to original U.S. Government works Printed in the United States of America on acid-free paper 10 9 8 7 6 5 4 3 2 1 International Standard Book Number-10: 0-8493-4040-3 (Hardcover) International Standard Book Number-13: 978-0-8493-4040-6 (Hardcover) Library of Congress Card Number 2005047215 This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. No part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC) 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe.

Library of Congress Cataloging-in-Publication Data Barrier systems for environmental contaminant containment and treatment / contributing editors, Calvin C. Chien, Hilary I. Inyang, Lorne G. Everett ; prepared under the auspices of U.S. Department of Energy, U.S. Environmental Protection Agency, DuPont. p. cm. Includes bibliographical references and index. ISBN 0-8493-4040-3 (alk. paper) 1. In situ remediation. 2. Sealing (Technology) I. Chien, Calvin C. II. Inyang, Hilary I. III. Everett, Lorne G. IV. United States. Dept. of Energy. V. United States. Environmental Protection Agency. VI. E.I. du Pont de Nemours & Company. TD192.8.B375 2005 628.5--dc22

2005047215

Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com Taylor & Francis Group is the Academic Division of Informa plc.

and the CRC Press Web site at http://www.crcpress.com

Contributing Editors Calvin C. Chien, Ph.D., P.E. DuPont Fellow DuPont Wilmington, Delaware Hilary I. Inyang, Ph.D. Duke Energy Distinguished Professor and Director, Global Institute for Energy and Environmental Systems University of North Carolina, Charlotte, North Carolina Lorne G. Everett, Ph.D., D.Sc. President L. Everett and Associates, LLC Santa Barbara, California Prepared under the auspices of U.S. Department of Energy U.S. Environmental Protection Agency DuPont With contributions by renowned experts on waste containment and waste treatment science and technology 2005

Technical Review Board David E. Daniel, Ph.D., Overall Book Reviewer University of Illinois Urbana-Champaign, Illinois Skip Chamberlain U.S. Department of Energy Washington, DC Calvin C. Chien, Ph.D., P.E. DuPont Wilmington, Delaware

Lorne G. Everett, Ph.D., D.Sc. L. Everett and Associates, LLC Santa Barbara, California Brent E. Sleep, Ph.D. University of Toronto Toronto, Ontario, Canada Craig H. Benson, Ph.D., P.E. University of Wisconsin Madison, Wisconsin

Annette M. Gatchett U.S. Environmental Protection Agency Washington, DC

Ernest L. Majer, Ph.D. Lawrence Berkeley Laboratory Berkeley, California

Hilary I. Inyang, Ph.D. University of North Carolina Charlotte, North Carolina

David J. Borns, Ph.D. Sandia National Laboratories Albuquerque, New Mexico

Special Contributors Jada M. Kanak, Special Technical Assistant DuPont Wilmington, Delaware Kathy O. Adams, Contract Technical Writer DuPont Wilmington, Delaware

Introduction Significant advances in subsurface containment technology occurred in the 1990s, both with the improvement of the technology and the broader acceptance and applications as a measure for environmental remediation. Since 1995, the U.S. Department of Energy (USDOE), U.S. Environmental Protection Agency (USEPA), and DuPont have collaborated on a series of organized efforts to advance this technology. In that year, these collaborators sponsored an international expert workshop that led to the publication of the first major book on containment technology. Two international conferences were held by the same three partners in 1997 and 2001, with individuals from all over the world attending. Although subsurface containment technologies are becoming increasingly acceptable and popular in the environmental remediation field, questions remained on the prediction and verification of long-term barrier performance and this subject began to gain interest from the public, government agencies, and the U.S. Congress. With funding provided by USDOE, an executive committee, consisting of Skip Chamberlain (Chairperson, USDOE), Calvin C. Chien (DuPont), and Annette M. Gatchett (USEPA), was formed in October 2001 to plan and organize an expert workshop. Sixty invited international experts participated. The meeting was held between June 30 and July 2, 2002 in Baltimore, Maryland, and consisted of five discussion panels — three on prediction and two on verification. Each panel was led by a panel leader and a co-leader to address particular technical topics in a designated area. A designated graduate fellow, a graduate student whose research was related to these topics, recorded detailed notes for the panel discussions. The graduate fellow group was coordinated and supervised by Jada M. Kanak (DuPont). Each panel leader, assisted by the co-leader, was responsible for writing a chapter for this book, using the information generated from the panel discussions and the detailed notes recorded by the graduate fellows. The prediction chapters were reviewed and edited by Hilary I. Inyang, and Lorne G. Everett reviewed and edited the verification chapters. Calvin Chien had the responsibility for planning, coordinating, and editing the book, ensuring consistency and completeness, and resolving differences in opinions. Skip Chamberlain provided technical input and crucial support in working with experts from the national laboratories on critical issues during the preparation of the book. David E. Daniel (University of Illinois) conducted an initial review of the first draft and provided high-level comments, which were useful in performing subsequent revisions. Dr. Daniel also wrote the preface for the book, which provides an outstanding introduction of containment technology history and book structure. Relevant new information that became available during the period of preparation

and editing was identified, evaluated, and added to the book to ensure that the information is as up-to-date as possible. In addition to organizing and leading the graduate fellow group, Jada Kanak also served as a special technical assistant for book preparation. Her detailed and patient efforts in reviewing and checking all of the references, figures, and tables contributed greatly to the quality of this book. Ms. Kathy O. Adams, a long-time DuPont in-house contract technical writer, was responsible for ensuring the grammatical accuracy of the book, and did an excellent job polishing the final draft. The team from Florida State University, consisting of Norbert Barszczewski, Sheryl A. Grossman, Loreen Y. Kollar, J. Michael Kuperberg, and Laymon L. Gray, were responsible for the workshop planning and contributed greatly to the success of the meeting.

Preface The containment of buried waste, contaminated soil or groundwater, refers to in situ (in place) management of contaminants in the subsurface. Containment is achieved with individual barriers or control technologies that, together, provide a system of engineered control. Containment is potentially applicable to any circumstance in which contaminants exist in the subsurface (e.g., uncontrolled landfills or dumps, chemical spills or leaks, pond or lagoon contaminant seepage) and can provide a safe and highly cost-effective mechanism for environmental control. Containment is accomplished using physical, hydraulic, or chemical barriers that prevent or control the outward migration of contaminants. Containment has come full circle as an acceptable environmental control technology over the past 30 years. Prior to the 1980s, containment was virtually the only technology available for managing subsurface contamination. Although some wastes were exhumed and treated, more often than not, if the pollution problem was recognized at all, the problem was managed via containment. During the 1980s, new environmental regulations emphasized treatment rather than containment. Research and development during this time dramatically expanded the portfolio of options available for treating or destroying contaminants at polluted sites. Technologies such as vapor extraction, oxidation, bioremediation, surfactant flushing, and heat-induced treatment became viable, though often expensive, treatment alternatives. In the 1990s, a dose of reality swung the pendulum back toward containment. It became apparent that it was not technically feasible to return contaminated sites to pristine condition. Further, as a nation, the United States came to realize that it could not afford, nor did it need, the most sophisticated treatment technology available to manage pollution problems at every site effectively and safely. In addition, further research clearly showed that the subsurface has advantages in addressing contamination problems — natural processes such as adsorption and biodegradation can serve to contain or degrade contaminants. For certain materials such as radioactive wastes, it became apparent that the exposure risks associated with exhuming contaminants might be far greater than risks associated with managing the wastes in situ with containment. Thus, for many reasons, interest in containment was revived in the 1990s. Today, containment thrives as a viable environmental management technology, and is often the preferred choice for protecting human health and the environment. But a price was paid for putting containment “on hold” during the 1980s, when emphasis was placed on developing sophisticated treatment technologies: little research and development on containment technologies was achieved during

this time. As interest shifted back toward containment in the 1990s, the industry found itself relying largely on pre-1980s technology. Fortunately, in the past 10 years, important advances have occurred in several areas of containment, most notably in the area of permeable reactive barriers, which transform containment barriers into a passive treatment installation. In the early 1990s, the need to define the state of the art for containment was understood by three visionary organizations: DuPont, the U.S. Environmental Protection Agency, and the U.S. Department of Energy. The DuPont Corporate Remediation Group (CRG) initiated the trio’s first collaborative effort in 1992. Experts from four nations experts were invited by DuPont to work with a team at the State University of New York at Buffalo to conduct a comprehensive review of the containment technology, the technology gaps, and future direction. The product of the work, a 1993 internal report, was published in 1995 by John Wiley & Sons, New York, titled Barrier Containment Technologies for Environmental Remediation Applications, and edited by Ralph R. Rumer and Michael E. Ryan. The principal chapters of the book focused on vertical barriers (walls), bottom barriers (floors), and surface barriers (caps). The three organizations joined again and organized an expert workshop on containment technology in 1995, inviting 115 international experts. The book, Assessment of Barrier Containment Technologies: A Comprehensive Treatment for Environmental Remediation Applications, was edited by Ralph R. Rumer and James K. Mitchell and was published the next year. With the rapidly increasing use of barrier technology in remediation, the need for better understanding, prediction, and monitoring of the performance of barriers emerged. The trio organized another expert workshop on the topic in 2002, which led to the development of this book. The workshop planning committee invited many of the world’s most knowledgeable researchers and practitioners to discuss the current state of the art and debate the appropriate applications and directions for containment. The participants then went home and collectively created this book from their knowledge and exchanges. This book is essentially a diary of those discussions and assessments, recast into the form of an easily readable, comprehensive book that is rich with discussion and references to literature, as well as further detail on specific topics of interest. The first two chapters address prediction issues, Chapters 3 and 4 address monitoring techniques, and Chapter 5 addresses the largely undeveloped field of verification. The discussions in the first four chapters address caps, vertical walls, and permeable reactive barriers. Chapter 1, “Damage and System Performance Prediction,” sets the stage for how contaminants can get into the subsurface. This is an important chapter, because one cannot understand how to contain something unless one knows how the contaminants got into the subsurface in the first place, and how they might spread and threaten the environment without containment. This chapter not only describes pathways, but also introduces the essential concept of risk. No control technology is without risk. Ultimately, a low risk of adverse environmental impact

should be maintained in a way that uses resources as wisely as possible. Chapter 1 draws from concepts in reliability of structures, and couples barrier structural failure to functional failure. Relevant quantitative frameworks are presented for use in assessing the long-term performance of containment systems. Chapter 2, “Modeling of Fluid Transport through Barriers,” addresses the basis for predicting the transport of water and contaminants through barrier components. This chapter focuses on modeling the inflow of moisture to the buried waste (e.g., caps), or modeling the release of contaminants through subsurface barriers. Fluid transport rate prediction is essential to the design process, because predictions can be integrated into the overall containment system performance assessment scheme presented in Chapter 1. Chapter 2 provides details on the current state of the art for performance prediction, but also clearly delineates the limitations in modeling specific situations. Chapter 3, “Material Stability and Applications,” addresses the materials used in barriers, defining the properties of barrier materials and exploring how materials perform in the field. The materials used for barriers include a myriad of natural and man-made materials, such as natural soil, stones and cobbles, impermeable plastic lining materials, man-made filter fabrics, and chemical agents designed to sorb or degrade contaminants that might come in contact with the material. Factors such as clogging, deterioration, or alteration of physical, chemical, or hydraulic properties are explored, not only to define what is known about these materials, but also to provide a learned and balance sense of what is not known. Chapter 4, “Airborne and Surface Geophysical Method Verification,” provides a thorough description of the application of geophysical methods to subsurface barriers. Geophysical methods have been used widely to assist in identifying potential mineral resources deep within the subsurface, and in more recent years, in the shallow environment, to help with identifying contaminant plumes and other anomalies. When applied to subsurface barriers, geophysical methods are challenged beyond their traditional role of identifying gross features that might warrant more detailed exploration (e.g., via a borehole), toward identifying more subtle features, such as a leak in a subsurface barrier. The techniques described in this chapter include both near- and far-field devices, spanning equipment deployed in aircraft flying above a site to devices placed on the ground surface that probe the subsurface directly with electromagnetic or other sources of energy. The first half of this chapter describes the technologies that are available, and the second half addresses their applications to various types of barriers. The subject of Chapter 5, “Subsurface Barrier Verification,” tackles perhaps the most challenging aspect of waste containment technology, i.e., validation of field performance. Traditionally, monitoring has consisted of sampling of groundwater or soil gas from wells. Although sampling soil, water, and air can provide information about the general performance of a system, it does not provide immediate, specific information about how a particular barrier component is meeting its design goals. Further, there is little to motivate stakeholders to spend money

for performance verification, unless required for compliance with regulations. This chapter provides a comprehensive review of sensors and examples of how sensors can be used to document system performance, addressing the basic questions: where, what, how, and what-if? Ultimately, the performance verification scheme should be linked to the performance prediction process. It is perhaps this linkage that is our most important end point, and one that requires more work, particularly in terms of assessing reliability and risk associated with the use of waste containment as a technique for managing waste in the subsurface. The two well-known case studies in the United States that are presented in this chapter provide particular value to this need. That which is buried in the subsurface, out of sight and out of mind, is that which in some respects is the most challenging. Nature has placed geologic materials in the subsurface in rather unpredictable and unknowable locations, with properties that are difficult to discern. Individual barriers are constructed in more controlled and documented ways, but still with considerable uncertainty in actual characteristics. Systems comprised of multiple barriers enjoy considerable redundancy and tend not to rely on any single component for success. Scientists and engineers strive to understand, predict, design, and verify safe containment schemes, both in terms of individual barriers and more complex containment systems. This book provides a comprehensive report on the science and technology of waste containment, with a balanced presentation of what is and is not known. Subsurface containment will continue to be a widely used environmental control technology in the years ahead. This book will provide a valuable reference, helping to chart the way to successfully managing many contaminated sites. David E. Daniel University of Illinois Urbana, Illinois

Editors Calvin C. Chien is a DuPont Fellow, one of only 13 individuals serving in this capacity in DuPont. He has been working in the area of groundwater investigation and remediation since 1975. Since 1991, he has been responsible for evaluating and developing transport modeling and containment technologies. As such, Dr. Chien has played a leading role in improving the understanding of containment technology for use in environmental remediation. He orchestrated the First International Expert Workshop (1995) and the publication (based on the workshop) of the first comprehensive containment book: Assessment of Barrier Containment Technologies: A Comprehensive Treatment for Environmental Remediation Applications (1996). In 1997, he spearheaded another effort to advance the technology: the First International Containment Technology Conference. Through these efforts, he has been recognized as a leading contributor to improving the science of containment technology as well as its acceptance at the regulatory level. He has authored and co-authored many technical papers for peer-reviewed journals and books. Currently, Dr. Chien provides technical environmental support and oversight for existing and new DuPont operations in the Asia-Pacific region. His contributions in the region led the Chinese Ministry of Science and Technology to invite him to evaluate candidates for the 2005 State Natural Science Award of the People’s Republic of China. This award is the most prestigious award for scientists and engineers in China. Hilary I. Inyang is the Duke Energy Distinguished Professor of Environmental Engineering and Science, Professor of Earth Science (GIEES), and Director of the Global Institute for Energy and Environmental Systems at the University of North Carolina–Charlotte. From 1997 to 2001, he was the Chair of the Environmental Engineering Committee of the U.S. Environmental Protection Agency Science Advisory Board, and also served on the Effluent Guidelines Committee of the National Council for Environmental Policy and Technology. He has authored and co-authored more than 170 research articles, book chapters, federal design manuals, and the textbook Geoenvironmental Engineering: Principles and Applications published by Marcel Dekker (ISBN: 0-8247-0045-7). Dr. Inyang is an associate editor and editorial board member of 17 refereed international journals, and contributing editor of three books, including the United Nations Encyclopedia of Life Support Systems (Environmental Monitoring Section). He has served on more than 85 international, national, and state science/engineering panels and committees. Since 1995, he has co-chaired several international conferences on waste management and related topics, and given more than 100 invited

speeches and presentations on a variety of technical and policy issues at institutions and agencies globally. Professor Inyang holds a Ph.D. with a double major in Geotechnical Engineering and Materials, and a minor in Mineral Resources from Iowa State University, Ames; a M.S. and B.S. in Civil Engineering from North Dakota State University, Fargo; and a B.Sc. (Honors) in Geology from the University of Calabar, Nigeria. His research has been sponsored by several agencies and corporations. Dr. Inyang’s research accomplishments and contributions to geoenvironmental science and engineering have been rewarded with honors by various national and international agencies among which are Fellow of the Geological Society of London; 2001 Swiss Forum Fellow selection by the American Association for the Advancement of Science; 1991 Chancellor’s Medal for Distinguished Public Service awarded by the University of Massachusetts Lowell; and the 1992/93 Eisenhower Fellowship of the World Affairs Council to commemorate the international achievements of the late U.S. President Dwight Eisenhower. In 1999, Prof. Inyang was appointed to Concurrent Professorship of Nanjing University, China and subsequently selected as an Honorary Professor of the China University of Mining and Technology, Jiangsu, China. He is the President of the International Society of Environmental Geotechnology (ISEG) and the Global Alliance for Disaster Reduction (GADR). Lorne G. Everett is the 6th Chancellor of Lakehead University in Canada, President of L. Everett and Associates LLC, Santa Barbara, a Research Professor in the Bren School of Environmental Science & Management at UCSB (Level VII), and Past Director of the University of California Vadose Zone Monitoring Laboratory. The University of California describes full professor Level VII as “reserved for scholars of great distinction.” He has a Ph.D. in Hydrology from the University of Arizona in Tucson, and is a member of the Russian Academy of Natural Sciences. In 1996, he received a Doctor of Science Degree (Honoris Causa) from Lakehead University in Canada for Distinguished Achievement in Hydrology. In 1997, he received the Ivan A. Johnston Award for Outstanding Contributions to hydrogeology. In 1999, he received the Kapitsa Gold Medal — the highest award given by the Russian Academy for original contributions to science. In 2000, he received the Medal of Excellence from the U.S. Navy, and the Award of Merit, the highest award given by American Standards and Testing Materials (ASTM) International. In 2002, he received the C.V. Theis Award, the highest award given by the American Institute of Hydrology (AIH) for major contributions to groundwater hydrology. In 2003, he received the Canadian Golden Jubilee Medal for “Significant Contributions to Canada.” He is an internationally recognized expert who has conducted extensive research on subsurface characterization and remediation. Dr. Everett has published over 150 technical papers, holds several patents, developed 11 national ASTM vadose zone monitoring standards, and authored several books, including Vadose Zone Monitoring for Hazardous Waste Sites and Subsurface Migration of Hazardous Waste. His book, entitled Handbook of Vadose Zone Characterization and Monitoring, is a

best seller. His book Groundwater Monitoring was endorsed by the U.S. Environmental Protection Agency as establishing “the state-of-the-art used by industry today,” and is recommended by the World Health Organization for all developing countries.

Table Of Contents Chapter 1 Damage and System Performance Prediction.................................1 Hilary I. Inyang and Steven J. Piet 1.1 1.2

1.3

1.4

Overview......................................................................................................1 Long-Term Performance Analysis Framework...........................................7 1.2.1 Concepts and Analytical Framework ..............................................8 1.2.2 Types of Performance Prediction Approaches..............................11 1.2.2.1 Empirical Prediction Approaches ..................................11 1.2.2.2 Semi-Empirical Prediction Approaches.........................12 1.2.2.3 Less Empirical (Theoretical) Modeling Approach........14 Relationship of Structural Failure to Functional Failure..........................15 1.3.1 Economic or Pseudo-Economic Criteria.......................................18 1.3.2 Regulatory Criteria ........................................................................19 1.3.3 Prescriptive Design Criteria ..........................................................19 1.3.4 Risk Criteria...................................................................................20 1.3.5 Demonstrating Compliance: The Safety Case Concept ...............22 1.3.6 Mixed Criteria ...............................................................................23 1.3.7 Qualitative and Indexing Analyses................................................23 Quantification of Long-Term Damage Scenarios, Events, and Mechanisms ...............................................................................................24 1.4.1 Categories of Degradation Mechanisms .......................................24 1.4.1.1 Slow Physico-Chemical and Biological Processes........24 1.4.1.2 Intrusive Events..............................................................29 1.4.1.3 Transient Events .............................................................30 1.4.1.4 Cyclical Stressing Mechanisms .....................................32 1.4.2 Quantitative Linkage of Contaminant Release Source Terms to Risk Assessment and Compliance Limits ................................37 1.4.3 Frameworks for Assessment of Event Consequences and Connectivities Among Causes of Failure......................................42 1.4.3.1 Fault Trees......................................................................42 1.4.3.2 Event Trees.....................................................................42 1.4.4 Estimation of Long-Term Failure Probabilities ............................42 1.4.4.1 System Failure Probability.............................................43 1.4.4.2 Component Failure Probability......................................44 1.4.4.3 Random Resistance ........................................................47 1.4.4.4 Simplifications of Theory ..............................................48 1.4.4.5 The Multi-Dimensional Case.........................................51 1.4.5 Component and System Failure in Containing Contaminants .....53 1.4.6 Relating Probable Contaminant Concentrations to Risks ............54

1.5

Use of Barrier Damage and Performance Models for Temporal Scaling of Monitoring and Maintenance Needs .......................................59 1.5.1 Updating ........................................................................................59 1.5.2 Effect of Updating on System Management.................................60 1.6 Life-Cycle Decision Approach and Management.....................................61 References ...........................................................................................................62 Chapter 2 Modeling of Fluid Transport through Barriers .............................71 Brent E. Sleep, Charles D. Shackelford, and Jack C. Parker 2.1 2.2

2.3

Overview....................................................................................................71 Caps ...........................................................................................................72 2.2.1 Features, Events, and Processes Affecting Performance of Caps ...............................................................................................72 2.2.1.1 Hydrologic Cycle ...........................................................72 2.2.1.2 Layers and Features .......................................................74 2.2.2 Current State of Practice for Modeling Performance of Caps.....75 2.2.2.1 Water Balance Method...................................................75 2.2.2.2 HELP ..............................................................................81 2.2.2.3 UNSAT-H .......................................................................82 2.2.2.4 SoilCover........................................................................82 2.2.2.5 HYDRUS-2D .................................................................83 2.2.2.6 VADOSE/W ...................................................................84 2.2.2.7 TOUGH2 ........................................................................84 2.2.2.8 FEHM.............................................................................85 2.2.2.9 RAECOM.......................................................................85 2.2.3 Modeling Limitations and Research Needs for Caps...................86 2.2.3.1 Role of Modeling ...........................................................86 2.2.3.2 Data Needs .....................................................................86 2.2.3.3 Code Quality Assurance and Quality Control...............87 2.2.3.4 Verification, Validation, and Calibration........................88 2.2.4 Unresolved Modeling Challenges .................................................89 2.2.4.1 Time-Varying Material Properties and Processes..........89 2.2.4.2 Infiltration at Arid Sites .................................................90 2.2.4.3 Role of Heterogeneities .................................................90 PRBs ..........................................................................................................90 2.3.1 Features, Events, and Processes Affecting Performance of PRBs ..............................................................................................91 2.3.1.1 Groundwater Hydraulics ................................................91 2.3.1.2 Geochemical Processes ..................................................92 2.3.1.3 Reaction Kinetics ...........................................................98 2.3.2 Impacts on Downgradient Biodegradation Processes...................98 2.3.2.1 Enhancement of Geochemical Conditions Conducive to Anaerobic Biodegradation .........................................98 2.3.2.2 Overall Contaminant Concentration Reduction ............99

2.3.2.3 Production of Hydrogen.................................................99 2.3.2.4 Electron Donor Production ..........................................100 2.3.2.5 Direct Addition of Dissolved Organic Carbon............100 2.3.3 PRB System Dynamics ...............................................................101 2.3.4 Geochemical Modeling ...............................................................104 2.3.4.1 Speciation Modeling ....................................................105 2.3.4.2 Reaction Path Modeling...............................................106 2.3.4.3 Reactive Transport Modeling.......................................107 2.3.4.4 Inverse Modeling..........................................................108 2.3.5 Modeling Limitations and Research Needs of PRBs .................109 2.4 Walls and Floors......................................................................................110 2.4.1 Vertical Barriers...........................................................................110 2.4.2 Horizontal Barriers ......................................................................110 2.4.3 Current State of Practice for Modeling Performance of Walls and Floors ....................................................................................111 2.4.4 Contaminant Transport Processes ...............................................112 2.4.4.1 Aqueous-Phase Transport ............................................112 2.4.4.2 Coupled Solute Transport ............................................117 2.4.4.3 Modeling Water Flow through Barriers.......................119 2.4.4.4 Analytical Models ........................................................120 2.4.5 Modeling Limitations and Research Needs of Walls and Floors ...........................................................................................123 2.4.5.1 Input Parameters and Measurement Accuracy ............123 2.4.5.2 Time-Varying Properties and Processes ......................125 2.4.5.3 Influence of Coupled Solute Transport........................125 2.4.5.4 Membrane Behavior in Clay Soils ..............................126 2.5 Complicating Factors...............................................................................128 2.5.1 Constant Seepage Velocity Assumption......................................128 2.5.2 Constant Volumetric Water Content Assumption .......................128 2.5.3 Anion Exclusion and Effective Porosity.....................................129 2.5.4 Nonlinear Sorption ......................................................................129 2.5.5 Rate-Dependent Sorption ............................................................130 2.5.6 Anion Exchange ..........................................................................130 2.5.7 Complexation...............................................................................131 2.5.8 Organic Contaminant Biodegradation.........................................131 2.5.9 Temperature Effects.....................................................................132 References .........................................................................................................132 Chapter 3 Material Stability and Applications ............................................143 Craig H. Benson and Stephan F. Dwyer 3.1

Overview..................................................................................................143 3.1.1 The Role of Barrier Material Mineralogy and Mix Composition on Performance......................................................144 3.1.2 Approaches to Material Evaluation and Selection .....................147 3.1.3 Geosynthetics and their Durability in Barrier Systems..............149

3.2

Material Performance Factors in Caps....................................................153 3.2.1 Material Performance Factors in Composite Barriers ................155 3.2.2 Material Performance Factors in Water Balance Designs ..........160 3.2.3 Coupling of Vegetation and Material Performance Factors .......163 3.3 Material Performance Factors in PRBs ..................................................167 3.3.1 Approach to Selection of PRB Materials ...................................168 3.3.2 Evaluation of Field Performance Using Pilot Testing................170 3.3.3 Effects of Hydraulic Considerations on Reactive Material Performance.................................................................................172 3.3.4 Structural Stability Factors in Performance................................178 3.3.5 Material Durability Factors .........................................................183 3.3.5.1 Effect of Mineral Precipitation on Porosity and Hydraulic Conductivity ................................................185 3.3.5.2 Effect of Mineral Precipitation on Reactivity .............186 3.3.6 Applications of Geochemical Models in Reaction Tracking .....187 3.4 Material Performance Factors in Cutoff Walls .......................................191 3.4.1 In Situ Hydraulic Conductivity ...................................................193 3.4.2 Design Configuration ..................................................................196 3.4.3 Geosynthetics in Vertical Cutoff Walls .......................................198 3.4.4 Permeant Interaction Effects .......................................................199 References .........................................................................................................201 Chapter 4 Airborne and Surface Geophysical Method Verification............209 Ernest L. Majer 4.1

4.2

Geophysical Method Application and Use .............................................209 4.1.1 Characterization and Geophysics ................................................210 4.1.2 Performance Monitoring and Geophysics ..................................212 4.1.3 Geophysical Methods for Site Characterization and Monitoring of Subsurface Processes...........................................214 4.1.3.1 Seismic .........................................................................214 4.1.3.2 Electrical and Electromagnetic ....................................214 4.1.3.3 Natural Field and Magnetic .........................................215 4.1.3.4 Remote Sensing............................................................216 Specific Methods .....................................................................................216 4.2.1 Seismic Methods .........................................................................216 4.2.1.1 Conventional and Advanced Ray and Waveform Tomography..................................................................220 4.2.1.2 Guided/Channel Waves ................................................221 4.2.1.3 Scattered and Reflected Energy ...................................221 4.2.1.4 Cross-Well/VSP/Single Well Imaging .........................222 4.2.1.5 Summary ......................................................................224 4.2.2 Electrical and Electromagnetic Methods ....................................224 4.2.3 Natural Field and Magnetic Methods .........................................227 4.2.4 Airborne Geophysical Methods ..................................................228

4.2.5

4.3

4.4

4.5

State-of-the-Practice Remote Sensing Methods .........................231 4.2.5.1 Aerial Photography ......................................................232 4.2.5.2 Multi-Spectral Scanners ...............................................232 4.2.5.3 Thermal Scanners.........................................................233 4.2.6 State-of-the-Art Remote Sensing Technologies..........................233 4.2.6.1 Hyperspectral Imaging Sensors ...................................234 4.2.6.2 LIDAR Systems ...........................................................235 4.2.6.3 Laser-Induced Fluorescence (LIF)...............................236 4.2.6.4 Radar Systems..............................................................237 4.2.6.5 Fused Sensor Systems/Data Streams...........................238 PRBs ........................................................................................................239 4.3.1 Requirements, Site Characterization, Design Verification, and Monitoring ............................................................................239 4.3.1.1 Site Characterization ....................................................240 4.3.1.2 PRB Construction Verification.....................................241 4.3.1.3 Short-Term Monitoring ................................................242 4.3.1.4 Long-Term Monitoring ................................................242 4.3.2 Case Histories..............................................................................243 4.3.2.1 Electrical Imaging of PRB Construction and Installation (Kansas City, Missouri) ............................243 4.3.2.2 Cross-Hole GPR Investigations (Massachusetts Military Reservation, Massachusetts)..........................245 Vertical Barriers.......................................................................................246 4.4.1 Requirements, Site Characterization, Design Verification, and Monitoring ............................................................................249 4.4.1.1 Design...........................................................................249 4.4.1.2 Installation/Verification ................................................249 4.4.1.3 Short-Term Monitoring ................................................254 4.4.1.4 Long-Term Monitoring ................................................254 4.4.2 Case Studies ................................................................................254 4.4.2.1 Cross-Hole GPR...........................................................255 4.4.2.2 Seismic .........................................................................259 4.4.2.3 ERT...............................................................................260 Caps and Covers......................................................................................261 4.5.1 Requirements, Site Characterization, Design Verification, and Monitoring ............................................................................262 4.5.2 Case Histories..............................................................................263 4.5.2.1 EMI and GPR...............................................................263 4.5.2.2 Apparent Conductivity Maps.......................................267 4.5.2.3 Electromagnetic Radar for Monitoring Moisture Content .........................................................................269 4.5.2.4 Aerial Photography ......................................................272 4.5.2.5 Multi-Spectral Scanners ...............................................273 4.5.2.6 Thermal Scanners.........................................................273 4.6.2.7 HIS Imagery .................................................................274

4.6

Summary..................................................................................................274 4.6.1 Primary Needs for Advancement ................................................275 4.6.1.1 Integration ....................................................................275 4.6.1.2 Processing and Interpretation.......................................275 4.6.1.3 Code Development.......................................................276 4.6.1.4 Instrumentation.............................................................276 4.6.2 Future Developments...................................................................276 References .........................................................................................................278 Chapter 5 Subsurface Barrier Verification ...................................................287 David J. Borns, Carol Eddy-Dilek, John D. Koutsandreas, and Lorne G. Everett 5.1 5.2 5.3

5.4 5.5

5.6

5.7

Overview..................................................................................................287 Goals ........................................................................................................288 Verification Monitoring ...........................................................................289 5.3.1 Methods .......................................................................................292 5.3.1.1 Moisture Change Monitoring Methods .......................292 5.3.1.2 Moisture Sampling Methods........................................294 5.3.1.3 Vadose Zone Monitoring Considerations ....................295 Verification System Design .....................................................................296 Moving from State of the Practice to State of the Art...........................297 5.5.1 System Approach.........................................................................298 5.5.1.1 Links to Modeling and Prediction ...............................298 5.5.1.2 Optimization.................................................................299 5.5.1.3 Decision and Uncertainty Analysis..............................299 5.5.2 Smart Structures ..........................................................................300 5.5.2.1 Long-Term, Post-Closure Radiation Monitoring Systems (LPRMS)........................................................302 5.5.2.2 Environmental Systems Management, Analysis, and Reporting (E-SMART™) Network..............................304 5.5.2.3 Direct Push Technologies ............................................305 5.5.2.4 Nanotechnology Sensors..............................................307 5.5.3 Advanced Environmental Monitoring System (AEMS).............307 5.5.4 A New DOE Barrier Design Code .............................................308 Drivers for Implementation of New Approaches....................................309 5.6.1 Costs ............................................................................................309 5.6.2 Enabling Desired End States.......................................................309 Covers ......................................................................................................310 5.7.1 Moving from State of the Practice to State of the Art...............310 5.7.1.1 Methods ........................................................................310 5.7.1.2 Verification Measurement Systems..............................311 5.7.1.3 Barrier Cap Monitoring ...............................................311 5.7.2 Case History: Mixed Waste Landfill...........................................312 5.7.2.1 Cover Infiltration Monitoring ......................................313 5.7.2.2 Neutron Moisture Monitoring......................................313

5.7.2.3

Fiber Optics Distributed Temperature Moisture Monitoring....................................................................314 5.7.2.4 Shallow Vadose Zone Moisture Monitoring................314 5.7.3 Case History: Fernald On-Site Disposal Facility .......................315 5.7.4 Verification Needs .......................................................................318 5.7.4.1 Optimization and Trend Analysis ................................319 5.7.4.2 Sensors and Other Hardware .......................................320 5.8 PRBS........................................................................................................321 5.8.1 Regulatory Framework ................................................................324 5.8.2 Moving from State of the Practice to State of the Art...............325 5.8.2.1 Flow Characterization and Monitoring........................325 5.8.2.2 Verification of Geochemical Gradients and Zones......327 5.8.3 Case History: Subsurface Monitoring.........................................329 5.8.4 Verification Needs .......................................................................329 5.8.4.1 Spatial and Temporal Flow Monitoring Considerations ..............................................................330 5.8.4.2 Geochemical and Hydrological Process Monitoring Considerations ..............................................................331 5.8.4.3 Acoustic Wave Devices................................................331 5.9 Walls and Floors......................................................................................332 5.9.1 Moving from State of the Practice to State of the Art...............337 5.9.1.1 Neutron Well Logging .................................................337 5.9.1.2 Perfluorocarbon Tracer (PFT) Monitoring/ Verification ...................................................................338 5.9.2 Case History: Colloidal Silica Demonstration............................341 5.9.3 Case History: Barrier Monitoring at the Environmental Restoration Disposal Facility (ERDF) ........................................343 5.9.3.1 Study Conclusions........................................................345 5.9.3.2 Study Recommendations..............................................345 5.9.4 Verification Needs .......................................................................346 5.9.4.1 Adequacy of the Containment Region ........................347 5.9.4.2 Long-Term Performance of the Containment .............347 5.10 Conclusions..............................................................................................348 References .........................................................................................................349 Appendix A Workshop Panels .........................................................................353 Panel Panel Panel Panel Panel

1 2 3 4 5

Prediction: Materials Stability and Application.................................353 Prediction: Barrier Performance Prediction.......................................353 Prediction: Damage and System Performance Prediction.................354 Verification: Airborne and Surface/Geophysical Methods ................355 Verification: Subsurface-Based Methods ...........................................355

Index..................................................................................................................357

1

Damage and System Performance Prediction Prepared by*

Hilary I. Inyang University of North Carolina at Charlotte, Charlotte, North Carolina

Steven J. Piet Idaho National Engineering and Environmental Laboratory, Idaho Falls, Idaho 1.1 OVERVIEW Long-term hazardous waste containment using physical barriers such as caps demands the estimation of system reliability, system deterioration rate, and consequences of system failure. The use of a systematic approach and a set of sequential analytical steps, such as those included in Figure 1.1, enables opportunities for system improvement to be identified. Barrier systems for buried waste or migrating contaminants are subjected to various physical, physico-chemical, and biological phenomena. The synergistic action of these phenomena ultimately damages barrier systems and produces or enlarges flow channels through which pollutants can escape. The observation that the degradation of constructed facilities increases with service life is not unique to containment systems: deterioration characterizes all constructed facilities, from roadways to pyramids. Current uncertainties pertain to the establishment of reasonably valid deterioration rates for various barrier designs, waste types, management systems, climatic and geohydrologic environments, site stability, and barrier construction materials for time frames that range from hundreds to thousands of years. The diversity of waste types and desirable service lives for facilities under various regulatory programs are summarized in Tables 1.1 and 1.2, respectively. * With contributions by James H. Clarke, Vanderbilt University, Nashville, Tennessee; John B. Gladden, Westinghouse Savannah River Company, Aiken, South Carolina; Horace K. Moo-Young, Villanova University, Villanova, Pennsylvania; Priyantha W. Jayawickrama, Texas Tech University, Lubbock, Texas; W. Barnes Johnson, U.S. Environmental Protection Agency, Washington, DC; Robert E. Melchers, University of Newcastle, Callaghan, NSW, Australia; Mark L. Mercer, U.S. Environmental Protection Agency, Washington, DC; V. Rajaram, Black and Veatch Corporation, Overland Park, Kansas; and, Paul R. Wachsmuth, University of North Carolina at Charlotte, Charlotte, North Carolina.

1

2

Barrier Systems for Environmental Contaminant Containment & Treatment Define Context social, individual, organizational, political, technological

Define System

Hazard Scenario Analysis • what can go wrong? • how can it happen? • what controls exist?

Estimate Consequences (magnitude)

Estimate Probability (of occurrence of consequences)

Define Risk Scenarios

Sensitivity Analysis

Risk Assessment compare risks against criteria

Monitor and Review

Risk Treatment • avoidance • reduction • transfer • acceptance

FIGURE 1.1 Flow chart for risk-based decision making. (From Stewart, M.G. and Melchers, R.E., 1997. Probabilistic Risk Assessment of Engineering Systems, Chapman & Hall, London. With permission.)

Estimation of the long-term deterioration pattern of barriers is necessary to improve the reliability of estimates of long-term contaminant release source terms for input into human health and ecological risk assessments, as well as facility monitoring and maintenance planning. Monitoring of barrier performance provides useful but inadequate data for performance predictions, because of limited field experience with barriers of various configurations in many environments, and because epochal events such as floods and earthquakes produce transient effects that cause deviations from performance patterns. The majority of quantitative methods that are currently used to estimate longterm barrier performance have time-invariant material characteristics and load/fluid application rates. The use of these fate and transport models, most of

3

Damage and System Performance Prediction

TABLE 1.1 Types of Hazardous Materials

Type

Typically Found in Nature?

Importance of Chemical Form to Toxicity

Does Hazard Decay Naturally?

Radioactive isotopes

Yesa

Can affect the level of exposure to the hazard by altering the ingestion or inhalation uptake of isotopes

Natural decay is fixed for each isotope

Toxic organic compoundsb

No

Affects ingestion and inhalation uptake

Decay generally slow (years, decades) and often dependent on specific chemical environment, e.g., trichloroethylene

Determines toxicity level

Toxic metals

Yes, although sometimes not in the more hazardous chemical forms

Can affect ingestion or inhalation uptake

Generally affects toxicity

Metals won’t decay, but the chemical form may naturally change into less toxic forms

Do We Know How to Destroy Hazard? Negligible prospects for in situ destruction or treatment Ex situ treatment may be practical to separate longlived isotopes from short-lived isotopes In situ decay may be deliberately enhanced by microbes

Ex situ destruction generally possible, but the associated risks and costs of transportation and destruction are high Destruction is not practical

In situ alteration of chemical form can sometimes be enhanced by microorganisms

4

Barrier Systems for Environmental Contaminant Containment & Treatment

TABLE 1.1 (continued) Types of Hazardous Materials

Type

Typically Found in Nature?

Importance of Chemical Form to Toxicity

Does Hazard Decay Naturally?

Toxic metals

Do We Know How to Destroy Hazard? Ex situ destruction generally possible, but with associated risks and costs during transportation and destruction

a

However, the specific radioactive isotopes are typically are not the specific isotopes found in nature. b There are also some toxic compounds that are neither organic nor metals, e.g., asbestos. Source: INEEL (2000). Environmental Laboratory Report INEEL/EXT-2000-01094; Piet et al. (2001). INEEL technical report INEEL/EXT-2001-01485.

TABLE 1.2 Time frames for Waste Containment Performance under Various U.S. Regulatory Programs Time Frame

Regulatory Program

10,000 years

Nuclear Regulatory Commission and EPA regulations for high-level and transuranic waste (10 CFR 60, 10 CFR 63, 40 CFR 191, 40 CFR 197) EPA regulations for near-surface uranium and thorium mill tailings (40 CFR192) and DOE policy for new land burial (DOE M 435.1) NRC regulations for near-surface burial of low-level waste (10CFR61) Baseline EPA RCRA time period for near-surface burial chemical hazards (40 CFR264); EPA can increase or decrease this value for each case Baseline EPA CERCLA time period for residual hazards (CERCLA requires a 5-year review to ensure the remedy is still protective of human health and the environment and is still performing as predicted)

1000 years 500 years 30 years Indefinite

which are based on one-dimensional differential equations, for describing contaminant advection-dispersion has simplified barrier performance analyses but does not address long-term barrier system performance adequately. As the performance

Damage and System Performance Prediction

5

analyses time frames extend from one or two decades to hundreds of years, changes in barrier material characteristics; cyclic changes, waning, or growth of stressing events; and possible exhaustion of initially present parent contaminants and/or generation of daughter contaminants combine to decrease the reliability of contaminant release estimates. Long-term performance modeling of waste containment systems and individual barriers within such systems require identifying possible damage mechanisms and assessing the system resistance in all possible ways in which the system might fail. Various techniques have been developed in practice (in different industries) and, hence, with different names, including the following: • Preliminary hazard analysis (PHA) (nuclear industry) • Walk-down analysis consisting of on-site visual inspection, particularly of pipe work (nuclear industry) • Failure modes and effects analysis (FMEA), which uses generic terms as prompts (various applications) • Failure modes, effects, and criticality analysis (FMECA), which also assesses criticality of consequences • Hazard and operability studies (HAZOP), which uses guide words as prompts (primarily chemical industry) • Incident data banks, which contain data such as accident data and nearmiss data For the range of barrier applications available now and in the future, there is a need for improved capacity to predict containment barrier damage and system performance. Damage and system performance models must be: • Responsive to the needs of a diverse set of decision makers (i.e., designers of new barriers, managers of barriers in service, regulators, funding agencies, and the public) • Integrative of the most important mechanisms of failure (i.e., both spatially uniform degradation and localized degradation; both continuously acting and discrete in time) • Comprehensive with regard to the range of performance measures relevant to a given barrier design that solves a particular problem at a particular location • Stochastic to allow evaluation of the sensitivities of parameter uncertainties compared to performance measures • Probabilistic in consideration of failure scenarios and mechanisms that may or may not occur during the service life • Validated by data to the extent practical • Adaptive to new information obtained during barrier service

6

Barrier Systems for Environmental Contaminant Containment & Treatment

• Informative regarding barrier degradation to guide barrier surveillance and maintenance, justification for reduction of surveillance and maintenance, barrier lifetime extension while in service, and future barrier designs • Graded in its implementation according to the severity and longevity of the associated risks (barriers with lower severity or shorter duration hazards do not need all of the above) Attempts to provide satisfactory system performance demands that one or more criteria be available against which to measure system performance. The setting or derivation of performance criteria is a problem with a fascinating and complex history, much of it based originally on issues associated with the nuclear industry. This history includes some deep philosophical questions, including “Who is to bear what level of risk, who is to benefit from risk-taking, and who is to pay? Where should the line be drawn between risks that are to be managed by the state and those that are to be managed by individuals, groups, or corporations? Who evaluates success or failure in risk management and how? Who decides what should be the desired trade-off between different risks?” (Hood et al., 1992). The decisions about these matters are influenced by judgments about the following (Stewart and Melchers, 1997): • Anticipation of system failure and resilience against unexpected catastrophe • Assumptions used to compute a numerical estimate of system risks • Size of uncertainties in estimating system risks • Organizational vulnerabilities to system failure • Cost of risk reduction • Size and composition of groups involved in decision-making processes • Aggregation of individual preferences (i.e., distribution of benefits and risks) • Counter-risks (i.e., alternatives may have other societal risks) Psychological aspects, such as risk perception and risk aversion, social and cultural preferences, as well as political processes and risk communication also play a part. The term “failure” can mean a variety of structural conditions or lack of capacity to meet expected performance functions when it is applied to containment systems. Structural failure of a system component or the entire system should be differentiated from functional system failure as described by Inyang (1994) and Inyang et al. (1995). Structural failure of a containment system may not necessarily lead to immediate functional failure because the former is often indexed in terms of parameters that define the stability and hydraulic characteristics of the containment system, whereas functional failure is assessed in terms of the risk of environmental and human exposure to contaminants that may be released from the system. More broadly, for a given initial hazard inventory, the

7

Damage and System Performance Prediction

Hazard halflife

Rates inventory mobilizes per year Delay time in transport through environmental media

Hazard inventory

Exposed individuals

Escaping inventory

Time barrier starts to degrade

Rate barrier degrades per year

FIGURE 1.2 Simplistic illustration of processes that influence exposure to individuals.

exposure generally depends on the five factors listed below and illustrated in Figure 1.2. Eventually, hazard either decays (with some half-life) or escapes. 1. Hazardous half-life 2. Mobilization rate/year (e.g., leaching, diffusion in the absence of a barrier) 3. Time at which barrier begins to degrade 4. Barrier degradation rate/year 5. Transport time of escaped materials between barrier and recipients Factors 2, 3, and 4 control when and how fast the hazard escapes. Factor 5 controls how much time (with additional hazard decay) will elapse before the escaped hazard impacts human health and the environment. With reference to the range of time horizons in various regulations, there is no systematic connection between the hazard timescales and regulatory timescales that are summarized in Table 1.2. Different regulations were established at different times by different legislation in response to different issues. Thus, the appropriate framework for predicting barrier system performance is not always clear: the time frames can differ greatly and the appropriate assumptions on how long to monitor and manage the barrier system can also differ.

1.2 LONG-TERM PERFORMANCE ANALYSIS FRAMEWORK It is necessary to formulate a long-term performance analysis framework that enables the consideration of factors that are significant for a given class of containment systems. The failure states of the constructed system in terms of both structural failure and functional failure need to be defined. Also, the performance assessment

8

Barrier Systems for Environmental Contaminant Containment & Treatment

framework should incorporate nodes to which pre-failure performance models can be linked.

1.2.1 CONCEPTS

AND

ANALYTICAL FRAMEWORK

Several concepts and analytical frameworks have been proposed for use in assessing the long-term performance of containment systems. The concepts pertain to the performance pattern of containment systems during service lives and postclosure time frames that can range from 30 years to thousands of years. The focus of the analyses is the formulation and use of performance prediction models that are capable of determining contaminant release rates as a function of estimated, measured, or designed magnitudes of containment system design parameters, waste characteristics, stressing events and processes, and site/hydrological conditions. The factors that need to be considered are numerous, as exemplified by the case of a near-surface barrier illustrated in Figure 1.3. Several attempts have been made to establish the expected general pattern of barrier performance over long service lives. Figure 1.4a shows the containment system performance model that is implicit to current practice. The facility is assumed to provide a constant level of service, or to be structurally sound until external monitoring data indicate the release of contaminants at unacceptable Natural boundary conditions (weather, climate, biota)

Engineered boundary conditions (design, maintenance, repair) Plants

Temperature

Dimensions, materials configuration

Wind/water erosion Precipitation Surface ecology (especially evapotranspiration barriers) Ecological

Plant/animal intrusion Soil type and thickness

Interfacial ecology (especially capillary barriers) Biochemical changes?

Structure

Plugging and surface tension

Water

Hydrology (including micropores, capillaries)

Erosion

Compaction Waste zone Subsidence

Output: Contaminant flow to the vadose zone

FIGURE 1.3 An illustration of the interaction among various processes and parameters that influence the long-term performance of near-surface containment systems.

Damage and System Performance Prediction

9

Current Methodology

Performance

Design Life

Detect only after failure (leakage through barrier)

Time

Realistic Performance

Performance

(a)

Uncertain long-term performance

Uncertain how to manage barriers & resistance to new materials and designs

Time (b)

FIGURE 1.4 Conceptual pattern of long-term performance of containment systems (a) abrupt failure pattern implicit to current practice (b) gradual degradation pattern that is more realistic.

concentrations. Figure 1.4b shows a more realistic performance pattern in which the performance degrades gradually during the immediate post-implementation period and then decays abruptly. After abrupt decay, the performance decreases much more gradually in a period that is characterized by large uncertainties. The reader should note that system damage vs. time plots have configurations that are the reverse of those of system performance (or effectiveness) vs. time plots. Thus, Figure 1.5 shows an increase in the risk of containment system failure with time. It should be noted that although the system deterioration pattern may be represented by a smooth curve, the performance pattern of a particular component of the containment system could exhibit temporal fluctuations in response to transient stressing mechanisms, the passage of contaminant fronts, and maintenance activity. In developing the conceptual framework for estimating the longterm performance pattern of containment systems, Inyang (1994) identified the various stages illustrated in Figure 1.6. Curve 1 shows the barrier degrading via continuous deterioration mechanisms. The branching to Curve 2 shows a barrier suffering from a discrete (in time) negative perturbation, such as a flood or an earthquake. The branching to Curve 3 reflects a barrier being upgraded or repaired. In the illustration, following Curve 1, the containment system effectiveness decays from an initial level of Eto, to a minimum acceptable level of Etr at time, tr . Etr corresponds to the functional performance level that is typically

10

Barrier Systems for Environmental Contaminant Containment & Treatment

Risk of failure

Acceptable risk level Particular structure deterioration Expected deterioration

Time (age of structure)

FIGURE 1.5 Conceptual degradation-time function of a containment system. (Illustrated by Melchers, R.E., 2001. Reliability Engineering and System Safety, 71(2), 201–208. With permission.)

Curve 1

System effectiveness, E (fraction)

Eto

Curve 3

Etm E1 E2 Etg Etr

Curve 2

to

tg

t2 tm

tr

Time, t (years)

FIGURE 1.6 A conceptual long-term deterioration pattern and maintenance scheme for waste containment system. (From Inyang, H.I., 1994. Proceedings of the First International Congress on Environmental Geotechnics, Calgary, Canada, pp. 273–278. With permission.)

specified by regulators or other authorities. If the facility is repaired at a time, tm, the effectiveness can abruptly increase to Etm so that an improved performance (described by Curve 3) results. Essentially, repairs postpone the attainment of Etr

11

Damage and System Performance Prediction

by slowing down the deterioration of the repaired component(s) and, hence, the system. The system can also degrade abruptly, as at tg, such that its effectiveness falls to Etg and system performance follows Curve 2 to failure at t2 (much sooner than would result from the regular deterioration pattern).

1.2.2 TYPES

OF

PERFORMANCE PREDICTION APPROACHES

In order to serve practical purposes, performance patterns need to be quantified, requiring the development of rating systems and models. Approaches to performance prediction can be categorized as empirical, semi-empirical, and less empirical (theoretical modeling). 1.2.2.1 Empirical Prediction Approaches Empirical prediction approaches involve the extrapolation of current knowledge of system behavior and/or similar system behavior to long-term system behavior. Such knowledge can also be acquired through accelerated testing in intensified environments. Another example of an empirical approach is performance indexing. In most cases, indexing criteria do not explicitly include time functions with performance factors. Table 1.3 shows the ratings of single components and composite configurations of barriers (Piet et al., 2001). In general, the scores on

TABLE 1.3 Overall Benefit of Each Barrier Configuration of Cover/Liner Materials Design Alternate

Description

Overall Benefit

Estimated Cost (dollars/ft2)

Benefit/Cost Ratio

Ranking in Group

A B C

CCL GM GCL

One-Barrier 36 64 46

Layer 0.70 0.70 0.70

51 91 66

3 1 2

D E

GM/CCL GM/GCL

Two-Barrier Layer 58 1.40 66 1.40

41 47

2 1

F G

GM/CCL/GM GM/GCL/GM

Three-Barrier Layer 71 2.10 77 2.10

34 37

2 1

CCL, single compacted clay liner; GM, single geomembrane; GCL, single geosynthetic clay liner; GM/CCL, two-component composite; GM/GCL, two-component composite; GM/CCL/GM, three-component composite liner; GM/GCL/GM, three-component composite liner. Source: Adapted with modification from Koerner, R.M. and Daniel, D.E. (1992). Civil Engineering, pp. 55–57.

12

Barrier Systems for Environmental Contaminant Containment & Treatment

TABLE 1.4 Estimated Long-Term Effectiveness of Selected Waste Containment Measures Indexing Time Increments (t years) Effectiveness, Et (%)

t0

t10

t30

Clay cap Synthetic cap Clay plus synthetic cap RCRA C composite liner system Clay liner Synthetic liner HDPE wall Slurry wall

80 90 95 98 70 85 65 70

75 85 92 95 60 75 60 60

60 75 80 85 40 35 50 20 (70e)

a b c d e

Assumes Assumes Assumes Assumes Assumes

t100 20 15 35 60 5 0 25 0

(85a) (90b) (98c)

(65d)

addition of new clay cap at 100 years. addition of new synthetic cap at 100 years. addition of new composite clay and synthetic cap at 100 years. addition of new HDPE at 100 years. addition of new slurry wall at 30 years.

Source: Inyang, H.I. and Tomassoni, G. (1992). Indexing of long-term effectiveness of waste containment systems for a regulatory impact analysis. A technical guidance document. Office of Solid Waste, U.S. Environmental Protection Agency, Washington, DC.

overall benefit or utility of a particular design increase with the number of components. Inyang and Tomassoni (1992) indexed the long-term performance pattern of waste covers for use in regulatory impact analysis. The scores are presented in Table 1.4. The reader should note that these scores are general indices and are not precise estimates of the performance of the components scored. Other researchers exemplified by Hagemeister et al. (1996) developed detailed performance indexing systems that incorporate ratings of barrier components, contaminant transport pathway factors, and human exposure potential. 1.2.2.2 Semi-Empirical Prediction Approaches These approaches involve the use of semi-empirical models to estimate the damage time functions or deterioration pattern of containment systems or specific containment system components. Using adaptations from product reliability analyses, a parameter that is generically referred to as the “failure rate” is used to quantitatively describe the effectiveness or reliability of a barrier or containment system with time. The magnitude of the failure rate is the significant determinant of the barrier degradation rate in the absence of transient events. It is tempting

13

Damage and System Performance Prediction

to erroneously assume that failure rates for containment systems are constant. In practice, the failure rates of most engineered systems are not constant with time. Generally, λ(t ) = λ 0 exp(β t )

(1.1)

where λ(t) is the time-variable failure rate of the containment system; λ0 is the initial failure rate of the containment system; β is an exponent that describes the variation (usually decay) of the failure rate with time, t. Equation (1.1) represents the general exponential form of the decay equation. The linear and Weibull forms of the equation are presented below as Equations (1.2) and (1.3), respectively. The parameters are as defined for Equation (1.1). The time parameter, t0, is the time corresponding to the origin of the initial failure, λ0. λ(t ) = λ 0 (1 + β t ) ⎛ t⎞ λ(t ) = λ 0 ⎜ ⎟ ⎝ t0 ⎠

(1.2)

β

(1.3)

For Equations (1.1) through (1.3), the value of the constant β determines the shape of the failure rate function. The failure rate is increasing with time if β > 0, it is constant if β = 0, and it is decreasing if β < 0. For more information, the reader is referred to Wolford et al. (1992), who used this approach to estimate the aging pattern of nuclear power plant equipment. Such techniques have already been successful in extending the license of 10 United States nuclear power plants by 20 years. Inyang (1994) observed that the Weibull format of failure analysis provides the curve geometries that match the expected deterioration pattern of most containment systems and proposed the use of Equation (1.4) with shape parameters ranging from 2 to 5. The use of Equation (1.4) enables long-term performance to be addressed within the context of system reliability. ⎡ ⎛ t − t ⎞β ⎤ 0 Rt = exp ⎢ − ⎜ ⎟⎠ ⎥⎥ n ⎝ ⎢ ⎦ ⎣

(1.4)

where Rt is the reliability of the containment system at a future time of reference, t is the future time of reference, and n is the scale or normalization parameter that corresponds to the time duration at which the failure probability is 0.632. Generally, the larger the magnitude of β, the greater the deterioration rate. Considering that there is a complimentary relationship between the probability of failure, Pt , and reliability, Rt , of a component or system as indicated by Equation (1.5), initial values of reliability can be established.

14

Barrier Systems for Environmental Contaminant Containment & Treatment

Rt = 1 − Pt

(1.5)

The damage functions for each system component can be generated from current knowledge, testing, and extrapolations, and can be used to determine the probability that barrier characteristics will meet specified standards at specified future times. 1.2.2.3 Less Empirical (Theoretical) Modeling Approach This approach involves modeling the stresses, deterioration processes, waste transformations and release, barrier material durability, and flaw evolution for a barrier component or system. In this approach, the failure probabilities of system components and the system itself are modeled. Interactions among various parameters that promote or negate effects are considered. Considering that various stressors and their impacts have different probabilities of occurrence within different timescales, the challenge of deciphering the interactions among parameters is quite great. Therefore, an innovation within this modeling approach is the use of modeling frameworks that enable the incorporation of various models and the establishment of dynamic linkages among them. This technique is nested in the subdiscipline of system dynamics. System dynamics is the study of dynamic feedback systems using computer modeling and simulation (Forrester, 1961). Unlike other scientists, who study the world by breaking it up into smaller and smaller pieces, system dynamicists look at things as a whole. The central concept of system dynamics is understanding how all objects in a system interact with one another. Visualization of the system is one of the assets of this modeling technique. However, beneath the visual exterior is a series of differential equations that define the behavior of the system over time. An example of software that can be used in this modeling exercise is Stella Research (Stella, 2001). The calculations are performed using numerical integration. Although the interface makes the modeling look superficial and almost trivial, a sophisticated mathematical engine performs the calculations. Using this modeling technique, it is possible to model complicated systems. A thorough understanding of the structure of these complex systems can lead to an explanation of their performance, both over time and in response to internal and external perturbations. By understanding the underlying system structure, predictions can be made relative to how the system will react to change. System dynamics models are descriptive in nature. The elements in the models must correspond to actual entities in the real world. The decision rules in the models must conform to actual practice and real-world phenomena. A new project at the Idaho National Engineering and Environmental Laboratory (INEEL) is addressing barrier degradation dynamics (Piet and Breckenridge, 2002). One component of the effort is the use of relatively simple but flexible system dynamics models to explore possible interactions of processes. These models provide a tool to explore uncertainties in scenarios and mechanisms, whereas more sophisticated models are tools for exploring sensitivities to parameter uncertainties.

Damage and System Performance Prediction

15

To illustrate the necessity of addressing interactions among various parameters, the effects of the burrowing of covers by animals on evapo-transpiration are considered. During the summer months, more water is lost from plots with animal burrows than from plots where no animal burrows are present. During the winter months, both the plots with animal burrows and the control plots gain water. In addition, water does not infiltrate below approximately 1 meter (m), even though burrow depths always exceed approximately 1.2 m. The lack of significant water infiltration at depth and the overall water loss in the lysimeter plots are occurring despite the following worst-case conditions: No vegetative cover (no water loss through transpiration) No water run off (all precipitation is contained) Burrow densities in lysimeters greater than those in natural settings Extreme rainfall events applied frequently (i.e., three 100-year storm events in three months) • Animals burrowing deeper in the lysimeters than in natural settings As part of the conclusion of the study described in the preceding paragraph, the investigators noted that “the overall water loss from soils with small-small burrows appears to be enhanced by a combination of soil turnover and subsequent drying, ventilation effects from open burrows, and high ambient temperatures” (Gee and Ward, 1997). Thus, in this case, animal intrusion had a net positive effect. Indeed, earlier work shows that soils were more dry beneath burrows than elsewhere (Cadwell et al., 1989; Link et al., 1995). Link et al. (1995) report that the increased moisture in burrows facilitated vegetation response that increased plant transpiration as plants took advantage of the moisture and sent roots to use it, leading to dry zones under the burrows. Indeed, Link et al. (1995) note that “ecologically, it is expected that a local abundance of a limiting resource, in this case moisture, would be rapidly and therefore depleted.” • • • •

1.3 RELATIONSHIP OF STRUCTURAL FAILURE TO FUNCTIONAL FAILURE In real-world situations, defining satisfactory system performance can be difficult. It is a vector with many components, governed by different criteria, and driven by different and perhaps interacting processes. These processes may not be well understood and, hence, can be represented analytically only with considerable uncertainty. This situation is not too different from that in other spheres and disciplines. It is usual in risk analysis to consider the consequences of failure, hence the recent focus of performance assessments has been on readily measurable barrier characteristics (e.g., barrier permeability) with limited focus on various combinations of outflows and inflows. Because the system properties and processes are uncertain, failure consequences can be described only with uncertainty. Moreover,

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Barrier Systems for Environmental Contaminant Containment & Treatment

the consequences usually are the critical outcome(s) of the system because the larger community seldom has particular interest in the structural system itself. The foregoing discussion leads to the need to examine the performance factors necessary to evaluate containment systems. These factors are divided into the following two categories: • Total system (parameters that define functional performance) • Concentration of hazardous materials in surface/aquifer water • Exposure to humans (e.g., water, air, intrusion pathways) • Risk to humans • Risk to ecologies • Barrier and barrier subsystems (parameters that define structural performance) • Resistance to human intrusion • Water flux through barrier • Gas flux through barrier • Hazardous material flux through barrier • Measures of individual degradation mechanisms (e.g., erosion, subsidence) The satisfaction of both functional and structural design functions of the composite containment system requires that the various system components meet specific design functions that contribute to overall system performance. The variability in the combination of various containment system components implies that long-term performance under a given set of applied stresses will also be different. Inyang (1999) suggested the following nonexclusive criteria as indices of containment system and component performance: • Ability of the system to reduce the concentrations of aqueous phase contaminants to acceptable levels through one or more contaminant attenuation processes (e.g., sorption, precipitation) • Ability of the system to reduce the volume of contaminants that is released into protected media to acceptable levels • Ability of the system to reduce the leaching of bound contaminants from stabilized media to acceptable levels • Ability of near-surface system components to attenuate radiation to nondamaging levels Often, the locations at which measurements of contaminant volumes or release rates will be obtained are specified in documents that are used to establish the compliance of a component or system at specified time intervals. As an example, in Table 1.5, Ho et al. (2002a) summarized the design performance objectives for the Monticello Mill Tailings Repository in which performance standards are specified in terms of specific quantities of contaminants that must not be exceeded.

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Damage and System Performance Prediction

TABLE 1.5 Summary of Performance Objectives Applicable to the Monticello Mill Tailings Repository Media All pathways

Atmosphere

Atmosphere

Standard