Groundwater Remediation E-Book

Nicholas P. Cheremisinoff

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 609

Veröffentlichungsjahr: 2017

Beschreibung

Written by one of the world's foremost authorities on the subject, this is the most comprehensive and in-depth treatment available to environmental engineers and scientists for the remediation of groundwater, one of the earth's most precious resources. Groundwater is one of the Earth's most precious resources. We use it for drinking, bathing, and many other purposes. Without clean water, humans would cease to exist. Unfortunately, because of ignorance or lack of caring, groundwater is often contaminated through industrialization, construction or any number of other ways. It is the job of the environmental engineer to remediate the contaminated groundwater and make what has been tainted safe again.Selecting the proper remediation strategy and process is the key to moving forward, and, once this process has been selected, it must be executed properly, taking into consideration the costs, the type of contaminants that are involved, time frames, and many other factors. This volume provides a broad overview of the current and most widely applied remedial strategies. Instead of discussing these strategies in a generic way, the volume is organized by focusing on major contaminants that are of prime focus to industry and municipal water suppliers. The specific technologies that are applicable to the chemical contaminants discussed in different chapters are presented, but then cross-referenced to other chemical classes or contaminants that are also candidates for the technologies. The reader will also find extensive cost guidance in this volume to assist in developing preliminary cost estimates for capital equipment and operations & maintenance costs, which should be useful in screening strategies. The eight chapters cover all of the major various types of contaminants and their industrial applications, providing a valuable context to each scenario of contamination. This is the most thorough and up-to-date volume available on this important subject, and it is a must-have for any environmental engineer or scientist working in groundwater remediation.

Leseprobe

Contents

Cover

Title page

Copyright page

Preface

About the Author

Chapter 1: Conducting Groundwater Quality Investigations

1.1 Introduction

1.2 Evolution of Site Assessments

1.3 Technology Limitations and Cleanup Goals

1.4 Conceptual Models

1.5 Risk Assessment Concepts

1.6 Institutional Controls

1.7 Risk-Based Cleanup Goals and Screening Level Evaluations

1.8 Assessing Plume Migration Potential

Recommended Reference Sources

Chapter 2: The Family of DNAPLs

2.1 Defining DNAPL

2.2 Chemicals and Origins

2.3 DNAPL Behavior

2.4 Overview of Remediation Strategies

Chapter 3: Hydrocarbons

3.1 Fate and Transport

3.2 Gasoline Compounds

3.3 Pump and Treat

Chapter 4: 1,4-Dioxane

4.1 Overview

4.2 Properties, Fate and Transport

4.3 Health Effects and Regulations

4.4 Remediation Technologies

References Consulted

Chapter 5: Perfluorinated Compounds (PFCS)

5.1 Overview

5.2 Origins of the Contaminants

5.3 PFAs Properties and Structures

5.4 Environmental Fate and Transport

5.5 Groundwater Contamination

5.6 Water Treatment

5.7 Estimating Carbon Treatement Costs

References

Chapter 6: Chlorinated Solvents

6.1 Physico-Chemical Properties of Chlorinated Solvents

6.2 Origins of Groundwater Contamination

6.3 Fate and Transport

6.4 Groundwater Remediation Strategies

6.5 Costs

References Consulted

Chapter 7: Mineral Ions and Natural Groundwater Contaminants

7.1 Overview

7.2 Secondary Drinking Water Standards

7.3 Irrigation Water Quality Standards

7.4 Water Treatment Membrane Technologies

7.5 Ion Exchange

7.6 Crystallization

Other References Consulted

Chapter 8: Heavy Metals and Mixed Media Remediation Technologies for Contaminated Soils and Groundwater

8.1 Nature of the Problem

8.2 Toxic Metal Chemical Forms, Speciation and Properties

8.3 Remedial Technology Strategies

8.4 Cost Data

References Consulted

Index

End User License Agreement

Guide

Cover

Copyright

Contents

Begin Reading

List of Illustrations

Chapter 2

Figure 2.1

Conceptual illustration of a migration of DNAPL released to ground surface.

Figure 2.2

Illustrates DNAPL distribution in soil and water matrix.

Figure 2.3

Cross-section of spatial variability of groundwater concentration in a plume.

Figure 2.4

Illustrates smoothly varying distribution of concentration based on contouring.

Figure 2.5

Illustrates DNAPL pooling at base of overburden; normally unlikely.

Figure 2.6

Illustration identifying various site parameters that may be tested when characterizing a site.

Chapter 3

Figure 3.1

Pathway for aerobic biodegradation of benzene, o-, and m-xylene. Source: After Source: Lawrence, S.J., 2006, Description, properties, and degradation of selected volatile organic compounds detected in ground water — A Review of Selected Literature: Atlanta, Georgia, U.S. Geological Survey, Open-File Report 2006-1338, 62 p., a Web-only publication at http://pubs.usgs.gov/ofr/2006/1338/

Figure 3.2

Various aerobic biodegradation pathways of toluene. After Lawrence.

Figure 3.3

Aerobic biodegradation pathways of

p

-xylene. After Lawrence.

Figure 3.4

Aerobic biodegradation pathways of ethylbenzene. After Lawrence.

Figure 3.5

Anaerobic biodegradation pathways of BETX compounds – benzene, ethylbenzene and xylene. After Lawrence.

Figure 3.6

Aerobic biodegradation pathways of methyl

tert

-butyl ether. After Lawrence.

Figure 3.7

Aerobic biodegradation pathways of

m

-cresol. After Lawrence.

Figure 3.8

Aerobic biodegradation pathways of styrene. After Lawrence.

Figure 3.9

Plot of concentration versus pumping duration or volume illustrating tailing and rebound effects.

Figure 3.10

Plot illustrating effect of groundwater velocities on dissolved phase contaminant concentration.

Figure 3.11

Illustrates funnel-and-gate configurations of permeable

in situ

reactive barriers to treat a contaminant plume. Source: U.S.EPA, Pump-and-Treat Ground-Water Remediation, EPA/625/R-95/005, July 1996

Chapter 4

Figure 4.1

Reported manufacturing data for 1,4-Dioxane in pounds (Lbs)

Figure 4.2

TRI reported discharges to all media.

Figure 4.3

Number of facilities reporting 1,4-dioxane discharges to the TRI.

Figure 4.4

Total TRI reported 1,4-dioxane discharges to all media by region of country.

Chapter 5

Figure 5.1

Chart reporting inventories of AFF by sector. Data obtained from a report by Darwin

6

. Sector Key: 1 - Military & Other Federal; 2 - Civil Aviation (Aircraft Rescue and Fire); 3 - Oil Refineries; 4 - Other Petro-Chem; 5 - Civil Aviation (Hangars); 6 - Fire Departments; 7 – Miscellaneous

Figure 5.2

Examples of PFAS classes of compounds.

Figure 5.3

Shows chemical structures of major PFCs.

Figure 5.4

3M Company reported estimates of global PFOS use in 2000. Refer to Figure 2.8 for details of market applications.

Figure 5.5

Capital and O&M costs (2004 U.S. dollars) for GAC systems. Source: U.S.EPA, Remediation Technology Cost Compendium – Year 2000, EPA 542-R-01-009, Sept. 2001.

Chapter 6

Figure 6.1

Degradation pathways of 1,1,2,2-tetrachloroethane; 1,1,2-trichloroethene; and 1,1,2-trichloroethane. Sources: Chen, Chun, J.A. Puhakka, and J.F. Ferguson, 1996, Transformation of 1,1,2,2-tetrachloroethane under methanogenic conditions:

Environmental Science and Technology,

v. 30, no. 2, p. 542–547; McCarty, P.L., 1997, Biotic and abiotic transformations of chlorinated solvents in ground water, in

Proceedings of the Symposium on Natural Attenuation of Chlorinated Organics in Ground Water

, Dallas, Tex., September 11–13, 1996: U.S. Environmental Protection Agency, EPA/540/R-97/504, p. 7–11; and Grostern, Ariel, and E.A. Edwards, 2006, Growth of

Dehalobacter

and

Dehalococcoides

spp. during degradation of chlorinated ethanes:

Applied and Environmental Microbiology,

v. 72, no. 1, p. 428–436.

Figure 6.2

Biodegradation pathways of 1,1,1-trichloroethane for the abiotic, aerobic, and anaerobic mechanisms. Source: After Ibid Lawrence, S.J.

Figure 6.3

Aerobic biodegradation pathway of 1,2-dichloroethane. After Lawrence.

Figure 6.4

Aerobic biodegradation pathway of tetrachloromethane (carbon tetrachloride). After Lawrence.

Figure 6.5

Biodegradation pathways for trichloroethene. After Lawrence.

Figure 6.6

Anaerobic biodegradation pathways for tetrachloroethene (PCE). After Lawrence.

Figure 6.7

Aerobic and anaerobic biodegradation pathways for 1,2,4-trichlorobenzene. After Lawrence.

Figure 6.8

Aerobic biodegradation pathway for 1,4-dichlorobenzene. After Lawrence.

Figure 6.9

Aerobic biodegradation pathway for chlorobenzene and 1,2-dichlorobenzene. After Lawrence.

Figure 6.10

Illustrates components of SVE system. Source: After EPA (https://frtr.gov/matrix2/section4/4-7.html).

Figure 6.11

Conceptual schematic of

in situ

AS. Source: U.S.EPA Power Point Presentation titled In-situ Air Sparging, https://clu-in.org/download/techfocus/air-sparging/AABR09-4-AS.pdf

Figure 6.12

Illustrates reductive degradation of chlorinated ethenes.

11

Figure 6.13

Average total costs for excavation (2004 dollars) using EPA data. (Source: U.S.EPA, Remediation Technology Cost Compendium)

Figure 6.14

Relative cost breakdown reported by Los Alamos.

Figure 6.15

Los Alamos cost comparison evaluations. Refer to Table 6.13 for VOC removal data and assumptions.

Chapter 7

Figure 7.1

Example of water quality test lab report for an agricultural irrigation case.

Figure 7.2

Illustrates basic concept of reverse osmosis.

Figure 7.3

Basic schematic of an RO system.

Figure 7.4

Illustrates an asymmetric RO membrane.

Figure 7.5

Illustrates a thin-film RO membrane.

Figure 7.6

Illustrates major RO system components.

Figure 7.7

Illustrates spiral-wound and hollow-fiber RO membrane modules.

Figure 7.8

Example of a skid-mounted RO unit for water treatment. Units are compact and have small footprints.

Figure 7.9

Illustrates an ion exchange resin column.

Figure 7.10

Comparative capital cost data reported for 550 m

3

/day (145,200 gpd) produced water capacity. Nitrate raw water for the comparison is 85–120 mg/L for all three processes. Source: Thorne and Segal (2014)

Figure 7.11

Dried waste stream of water treatment processes. After Thorne and Segal.

Figure 7.12

Annual power operating costs, and chemical & maintenance cost comparisons. After Thorne and Segal.

Figure 7.13

Illustrates process of crystallization from standpoint of reactor parameter behavior.

Figure 7.14

Illustrates solid-liquid phase behavior.

Figure 7.15

Shows a forced-circulation crystallizer. This type of configurations uses evaporation of adiabatic cooling without the use of a heat exchanger to generate supersaturation.

Figure 7.16

Illustrates a draft-tube crystallizer.

Figure 7.17

Illustrates a surface-cooled baffle crystallizer which employs an external heat-exchnager surface to generate supersaturation by cooling.

Figure 7.18

Illustrates an Oslo crystallizer.

Figure 7.19

Shows a fluidized bed crystallizer.

Figure 7.20

Process scheme for zero-waste desalination process. After Geisen

et al.

Chapter 8

Figure 8.1

Illustrates features of a capped landfill.

Figure 8.2

Illustrates features of a subsurface barrier.

Figure 8.3

Simplified process flow sheet of WAO process. Adapted from U.S. Army Chemical Materials Agency (Provisional) Program Manager for Elimination of Chemical Weapons, FY03 Technology Evaluation for Chemical Demilitarization, Wet Air Oxidation Technology Assessment, Contract: DAAD13-01-D-0007, Task: T-03-S-002, April 2003, Science Applications International Corporation.

Figure 8.4

Heterogeneous Catalytic WAO Process.

Figure 8.5

Process flow sheet of DAF.

Figure 8.6

Estimated operating costs for remediation strategies of metal-contaminated soils (after Evanko and Dzombak, 1996). Data are based on computing relative value of 1996 U.S. dollar amount to 2015 based on Consumer Price Index.

Figure 8.7

Capital costs in 2004 millions of dollars for site capping. Key: A – Simple soil and vegetative cap constructed using on-site stockpiled soil; B – Simple soil and vegetative cap constructed using off-site fill; C – Subtitle C composite cap constructed using on-site clay for compacted clay; D – Subtitle C composite cap constructed using off-site clay for compacted clay liner. (Source: U.S.EPA, Remediation Technology Cost Compendium).

Figure 8.8

Annual O&M Costs in 2004 dollars. Key: A – Simple soil and vegetative cap annual O&M costs. No cost differential between use of on-site stockpiled soils and off-site fill: B – Total Annual O&M costs for Subtitle C Composite Cap Constructed Using On-site Clay for Compacted Clay Liner; C – Total Annual O&M costs for Subtitle C Composite Cap Constructed Using Off-site Clay for Compacted Clay Liner. (Source: U.S.EPA, Remediation Technology Cost Compendium).

Figure 8.9

EPA reported costs (2004 million dollars) as a function of total volume of waste/contaminated soil for

in situ

solidification. Key: A – In-Situ Solidification of Gravel/Gravel-Sand to Sand/Gravelly-Sand Soil; B – In-Situ Solidification of Sand-Silt/Sand-Clay Soil; C – In-Situ Solidification of silt/silty-clay soils. (Source: U.S.EPA, Remediation Technology Cost Compendium).

Figure 8.10

EPA cost trends (2004 million dollars) for Ex-Situ Solidification/Stabilization. Assumed batch sizes based on following: 500–1,000 cy waste volume 2 Batch Plant Sizes; >1,000–5,000 cy waste volume 5 Batch Plant Sizes; >5,000–20,000 cy waste volume 10 Batch Plant Sizes; >20,000–100,000 cy waste volume 15 Plant Batch Sizes. Key: A- Ex-Situ Solidification of Incinerator Ash; B – Ex-Situ Solidification of Solids/Soils; C – Ex-Situ Solidification of Sludges. (Source: U.S.EPA, Remediation Technology Cost Compendium).

Figure 8.11

EPA cost trends (2004 million dollars) for soil washing. Key: A – Costs based on a 25 TPH Plant; B – Costs based on a 50 TPH Plant; C – Costs based on a 100 TPH Plant. (Source: U.S.EPA, Remediation Technology Cost Compendium).

Figure 8.12

Capital costs in dollars (2004 dollars) for slurry walls. Key: A – 20 ft depth wall; B – 50 ft depth wall; C – 80 ft depth wall. (Source: U.S.EPA, Remediation Technology Cost Compendium).

Figure 8.13

Annual O&M costs in dollars (2004 dollars) for slurry walls. Costs are same regardless of depth. (Source: U.S.EPA, Remediation Technology Cost Compendium).

List of Tables

Chapter 2

Table 2.1

Properties of creosote.

Table 2.2

Major components and typical compositions of chemicals in creosote.

Table 2.3

Chlorine levels in aroclors.

Table 2.4

Composition and properties of different aroclors.

Table 2.5

Select physical and chemical properties of some chlorinated solvents.

Table 2.6

Typical parameters and their relevance to the characterization of a site.

Chapter 3

Table 3.1

Physical properties of some of the gasoline VOCs.

Table 3.2

Summary of pump-and-treat technologies and their applicability to different contaminants (source u.S.Epa, pump-and-treat ground-water remediation, epa/625/r-95/005, july 1996).

Table 3.3

Examples of Pump-and-Treat sites with fully defined costs data. Source U.S.EPA, Remediation Technology Cost Compendium, EPA-542-R-01-009

Chapter 4

Table 4.1

Properties of 1,4-dioxane.

Table 4.2

U.S. Statutory guidelines for 1,4-dioxane in water.

Table 4.3

U.S.EPA and State guidance for dioxane in soil and water.

Chapter 5

Table 5.1

Examples of pfass. Highlighted chemicals are in biomonitoring studies.

Table 5.2

Common derivatives and their chemical formulas.

Table 5.3

3M reported properties of PFOS.

Table 5.4

Chemical and physical properties of PFOA (EPA (2016)).

Table 5.5

Drinking water guidelines for PFOA and PFOS.

Table 5.6

Administrative guidelines in μg/L.

Chapter 6

Table 6.1

Common chlorinated (VOC) compounds found in groundwater.

Table 6.2

Henry’s Law constants (H

1

) at 25 °C for compounds in order of decreasing tendency to move from water phase to vapor phase when in equilibrium with pure water.

2

Table 6.3

Diffusion coefficients of chlorinated solvents. (Source general literature sources)

Table 6.4

Water Solubility data (at 25 °C) of compounds detected in groundwater. Data reported in order of decreasing amount of non-aqueous phase liquid that can dissolve in water.

3

Table 6.5

Densities (at 20 °C) of compounds detected in groundwater.

4

Table 6.6

Octanol-water partition coefficients for compounds detected in groundwater. Data reported in order of decreasing affinity for organic matter and lipids.

5

Table 6.7

Soil-sorption partition coefficients for compounds detected in groundwater. Data reported in order of decreasing affinity for soil organic matter.

6

Table 6.8

Half-lifes of selected compounds.

Table 6.9

Average total costs for backfill (2004 dollars) using EPA data. (Source U.S.EPA, Remediation Technology Cost Compendium).

Table 6.10

Costs for in-situ SVE for different levels of remediation. Source 4.8 Soil Vapor Extraction -

In Situ

Soil Remediation Technology; https://frtr.gov/matrix2/section4/4-7.html

Table 6.11

EPA cost data (2004 dollars) for SVE. (Source U.S.EPA, Remediation Technology Cost Compendium).

Table 6.12

Los alamos cost data.

Table 6.13

Case studies and assumptions applied to developing the comparisons reported in figure 6.15. values are in Lbs VOC removed per day.

Chapter 7

Table 7.1

Primary, secondary, and trace constituents in natural groundwater.

4

Table 7.2

U.S.EPA secondary drinking water standards.

2

Table 7.3

Typical salts normally found in groundwater.

Table 7.4

Useful parameters and conversions for understanding water quality analyses reports.

3

Table 7.5

Irrigation water and soil tolerance levels, where x is conductivity in mmhos/cm – Best fits to data reported by Fipps (Irrigation Water Quality Standards and Salinity Management, Texas A&M AgriLife Extension, Publication B-1667, 4-03).

Table 7.6

Cost data for RO reported by Yeo (2010).

Table 7.7

approximate costs of membrane technologies (after fedler,

et al.

)

Table 7.8

suitability of membrane technologies and selection criteria.

Chapter 8

Table 8.1

Forms and speciation of major toxic heavy metals (Information compiled and/or quoted from Evanko and Dzomak

3

).

Table 8.2

Geomembrane types (Materials) and their intended applications.

Table 8.3

Chemical resistance comparison (source survey of manufacturer’s literature on WWW).

Table 8.4

Effectiveness and use of solidification/stabilization strategies. (source review of EPA publications and fact sheets)

Table 8.5

Site and soil characterization parameters for treatment technology evaluation. (Source U.S.EPA, Treatment of Lead-Contaminated Soils, Superfund Engineering Issue, EPA540/2-91/009, April 1991)

Table 8.6

Comparative costs for different heavy metal soil remedial actions.

Table 8.7

Additive-mix ratios applied by EPA to develop costs.

Table 8.8

EPA assumed waste volumes (cy) after treatment based on the default mix ratio used to generate cost estimates.

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Scrivener Publishing100 Cummings Center, Suite 541JBeverly, MA 01915-6106

Publishers at ScrivenerMartin Scrivener ([email protected])Phillip Carmical ([email protected])

Groundwater Remediation

A Practical Guide for Environmental Engineers and Scientists

Edited by

Nicholas P. Cheremisinoff

This edition first published 2017 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA © 2017 Scrivener Publishing LLC For more information about Scrivener publications please visit www.scrivenerpublishing.com.

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Library of Congress Cataloging-in-Publication Data ISBN 978-1-119-40757-7

Preface

Clean, healthy groundwater is essential to sustaining civilization. Groundwater is relied on as the major source of drinking water and as a source for agricultural activities; it interacts with surface water bodies which support aquatic and other natural species that mankind relies on. Out of both ignorance and poor practices, historical industrial activities have caused groundwater quality in many industrialized countries to become impaired, placing significant populations at risk, and causing water sources to become either restricted or unusable for long periods of time, and in some cases inaccessible for future generations. Properly addressing and managing groundwater contamination problems can be complex, costly, and depending on the nature of the chemical contaminants and hydrogeological conditions, can take many years to address. Each affected site oftentimes poses a unique set of challenges, generally requiring several technologies to be tried, tested and evaluated before effective strategies are implemented. Addressing groundwater contamination commands the integration of several branches of science and engineering, as well as policy specialists; among these are the branches of hydrogeology, specialists in conducting site investigations, risk assessment tools and models, an understanding of chemistry and in particular natural biodegradation factors, cost estimating, analytical tools, and many other fields. The subjects and fields of science, as well as the analytical tools required to address groundwater problems are many, and oftentimes require significant effort and costs to be invested prior to selecting strategies and technologies appropriate to address a site. Because of the comprehensive nature of this field, this volume was prepared to provide a primer for students, as well as environmental engineers, scientists and property managers who are faced with dealing with these issues early in their careers. The volume is written with the intent of providing a broad overview of the elements essential to conducting investigations and in the selection of strategies and technologies for remedial action. At the same time, considerable practical information is included in the volume along with guidance on costs and levels of effort needed to address groundwater quality problems.

Selecting the proper strategy needs to be based first and foremost on understanding whether pathways to human and other sensitive receptors are open and therefore present risks. Risks may in fact be both present and future – as an example, today’s commercial or industrial property that has a groundwater quality problem may not have an open pathway to human exposure, but it could if the land were to be redeveloped at some future time. Therefore, institutional controls may play a very large part in selection of the remedial strategy. An additional concern is that in the past, the costs for addressing remediation became open ended because conceptual site models were not properly developed and a clear understanding and documentation of groundwater plume behavior and chemistry were lacking. Many times it has been assumed that the technology that was applicable to remediating the groundwater at one site is equally applicable to another site with the same or similar set of chemical contaminants – only to find that insufficient planning and technology vetting contributed to ineffective cleanup with timeframes that were unrealistic.

This volume provides a broad overview of the current and most widely applied remedial strategies. Instead of discussing these strategies in a generic way, the volume is organized by focusing on major contaminants that are of prime focus to industry and municipal water suppliers. The specific technologies that are applicable to the chemical contaminants discussed in different chapters are presented, but then cross-referenced to other chemical classes or contaminants that are also candidates for the technologies. The reader will also find extensive cost guidance in this volume to assist in developing preliminary cost estimates for capital equipment and operations & maintenance costs, which should be useful in screening strategies.

There are eight chapters. Chapter 1 provides an overview of the concepts and important factors to consider when conducting site and groundwater quality investigations. Chapter 2 provides an overview of an important class of groundwater contaminants known as DNAPLs (dense non-aqueous phase liquids) which are extremely challenging from the standpoint of remediation. Chapter 3 address technologies suitable for addressing the cleanup of common hydrocarbons like VOCs and gasoline. Chapter 4 addresses a particular chemical contaminant (1,4-Dioxane), which many municipal water suppliers are concerned about due to emerging regulations as a contaminant of concern. Chapter 5 focuses on perfluorinated compounds. These chemical contaminants are extremely stable and persistent in the environment and are of major concern because of world health advisories which link exposures to trace amounts in the parts per trillion range to health problems. Chapter 6 discusses chlorinated solvents. These toxins have been found at almost every Superfund site in the United States and at numerous industrial complexes around the world because of the extensive use of these solvents in industrial cleaning and degreasing operations. The biodegradation properties of these contaminants is better understood today than a mere decade ago, and hence for some sites groundwater management strategies may be based on natural attenuation and careful monitoring. Chapter 7 addresses mineral ions and natural groundwater contaminants with a focus on ensuring good-quality irrigation sources. Finally Chapter 8 tackles the subject of heavy metals and mixed media remediation technologies for contaminated soils and groundwater.

The author extends heartfelt gratitude to Scrivener Publishers for their efforts in producing this volume.

Nicholas P. Cheremisinoff, Ph.D.

About the Author

Nicholas P. Cheremisinoff is a chemical engineer with more than 40 years of industry, R&D and international business experience. He has worked extensively in the environmental management and pollution prevention fields, while also representing and consulting for private sector companies on new technologies for power generation, clean fuels and advanced water treatment technologies. He is a Principal of No Pollution Enterprises. He has led and implemented various technical assignments in parts of Russia, eastern Ukraine, the Balkans, South Korea, in parts of the Middle East, Nigeria, and other regions of the world for such organizations as the U.S. Agency for International Development, the U.S. Trade & Development Agency, the World Bank Organization, and the private sector. Over his career he has served as a standard of care industry expert on a number of litigation matters. As a contributor to the industrial press, he has authored, co-authored or edited more than 160 technical reference books concerning chemical engineering technologies and industry practices aimed at sound environmental management, safe work practices and public protection from harmful chemicals. He is cited in U.S. congressional records concerning emerging environmental legislations, and is a graduate of Clarkson University (formally Clarkson College of Technology) where all three of his degrees – BSc, MSc, and PhD. – were conferred.

Chapter 1Conducting Groundwater Quality Investigations

1.1 Introduction

The volume is intended as a primer to address groundwater contamination often caused by legacy pollution or unintentional releases of chemicals to the subsurface. When groundwater has been adversely impacted, a variety of sciences, strategies, technologies and actions are needed to assess human and ecological risks from the contamination. The first step in assessing impacts requires a body of good practices that are recognized by industry on the whole and is referred to as the environmental site assessment.

Environmental site assessment practices are also commonly referred to as environmental audits. The practices for conducting an environmental site assessment began evolving in the United States in the 1970s. Throughout the 1980s environmental site assessment practices evolved further with the promulgation of the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) and the Resource Conservation and Recovery Act (RCRA), which required commercial facilities to identify, report and remediate recognized environmental conditions. Throughout the 1990s environmental site assessment practices were enhanced with more precise tools that aided in site characterization and quantification of recognized environmental conditions. Over the years additional analytical tools have evolved to aid environmental site assessment practices.

The goal of an environmental site assessment is to identify recognized environmental conditions. The term recognized environmental conditions means “the presence or likely presence of any hazardous substances or petroleum products on a property under conditions that indicate an existing release, a past release, or a material threat of a release of any hazardous substances or petroleum products into structures on the property or into the ground, groundwater, or surface water of the property.”1

1.2 Evolution of Site Assessments

The control of hazardous substances and the prevention of the entry of these substances into the environment is the objective of several acts of U.S. Congress. Rules regulating various aspects of hazardous waste can be attributed to the Toxic Substances Control Act (TSCA); the Clean Water Act (CWA); the Clean Air Act (CAA); the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA); the Safe Drinking Water Act (SDWA); the Resource Conservation and Recovery Act (RCRA); and the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). RCRA and CERCLA are the two that are most often associated with environmental site assessments.

RCRA was passed to control industrial and municipal solid wastes, including sludges, slurries, etc. The act also called for a tracking system to document the generation, transport, and disposal/storage of solid wastes. The discovery of a large number of uncontrolled and abandoned hazardous waste sites, such as at Love Canal, New York, prompted a much greater emphasis on the hazardous nature of the wastes. In the 1980s the regulations and resources of RCRA were primarily devoted to the control of hazardous wastes, with a lesser emphasis on nonhazardous solid wastes.

In 1980, legislation aimed at providing federal money for the cleanup of inactive waste disposal sites was enacted. The Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), often called the “Superfund Act”, provides regulatory agencies with the authority to deal with inactive sites, funds to deal with hazardous waste emergencies and a means to assign the liability of cleanup to the responsible parties. It also provides monies (Superfund) to pay for the mitigation of hazards from abandoned sites when no responsible party can be found or when the responsible party refuses to take action. In addition, it empowers the government to seek compensation from responsible parties to recover funds used in mitigation actions.

Section 105 of the CERCLA requires that the National Contingency Plan (NCP), developed under the Clean Water Act, be revised to include procedures and standards for responding to releases of oil and hazardous substances. The revised plan reflected and effectuated the responsibilities and powers created by the act.

Subpart F of the NCP, Hazardous Substance Response, establishes a seven-phase approach for determining the appropriate extent of a response authorized by CERCLA “when any hazardous substance is released or there is a substantial threat of such a release into the environment, or there is a release or substantial threat of a release of any pollutant or contaminant which may present an imminent and substantial danger to the public health or welfare”2. Each phase sets specific criteria to establish the need for further action. The phases are:

Phase I – Discovery and Notification

Phase II – Preliminary Assessment

Phase III – Immediate Removal

Phase IV – Evaluation and Determination of Appropriate Response – Planned Removal and Remedial Action

Phase V – Planned Removal

Phase VI – Remedial Action

Phase VII – Documentation and Cost Recovery

This phased approach is the basis for implementation of all CERCLA-authorized Hazardous Substance Responses with which industry is obligated to comply.

The practice of conducting environmental site assessments began in the 1970s in the United States. These practices evolved over time, which is why it is important to place them within a historical context. As early as the 1970s specific property purchasers in the United States undertook studies resembling current Phase I ESAs, to assess risks of ownership of commercial properties which had a high degree of risk from prior toxic chemical use or disposal. Many times these studies were preparatory to understanding the nature of cleanup costs if the property was being considered for redevelopment or change of land use.

The evolution of best practices in conducting site assessments was driven by an expanding knowledge base on the fate and transport of harmful chemicals. Until the early 1960s, the question of whether or not groundwater was significantly affected by organic wastes was generally addressed by observing the subsurface breakdown of sewage and similar matter. There was a general belief that the easiest way to eliminate contamination was through the natural processes of separation, filtration, dilution, oxidation and chemical reaction. Soils were believed to serve the purpose of filtration, aid in chemical reaction by adsorbing some chemicals, while groundwater was generally believed to be an infinite medium, thereby diluting any harmful chemicals. Not until the mid-1960s did organic contaminants begin to receive attention.

Some properties are associated with groundwater contamination that can be characterized as being comprised of Dense Non-Aqueous Phase Liquids (DNAPLs). DNAPLs are characterized by their lack of noticeable taste or odor and their higher density relative to water. These properties render them difficult to detect and monitor. In contrast, petroleum spills float atop the water table and are usually volatile with distinctive tastes and odors. The rare discovery of DNAPL contamination before the development and ready availability of analytical techniques allowing the measurement of organic contaminants on the ppm to ppt level is not surprising.

Although appropriate analytical methods actively existed and were relied on by industry since the mid-1950s, there was no drive to investigate groundwater for the presence of chlorinated solvents. Analytical chemists instead concentrated efforts on alkyl benzene sulphonate (ABS) detergents and organic pesticides such as DDT and aldrin. The surreptitious nature of DNAPLs led them to be disregarded as groundwater contaminants until much later. Dissolved plumes caused by DNAPLs were not discovered until the 1970s. DNAPL (the free phase, not dissolved phase) was not discovered until the mid-1980s. This was partially because monitoring wells was not understood, as it is now, to be a poor method to detect DNAPL (i.e., it has rarely been reported in wells).

The discovery of DNAPLs was prompted by legislation introduced during the previous decade: Safe Drinking Water Act (1974), Resource Conservation and Recovery Act (RCRA, 1976) and the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA, 1980). These legislations required sampling of municipal wells specifically for chlorinated solvents, which were discovered in some drinking water systems. Unlike some other contaminants, such as methyl tert-butyl ether (MTBE), chlorinated solvents have high taste and odor thresholds, meaning that people don’t taste or smell the compounds in water until there is a relatively high concentration. Chlorinated solvents have taste thresholds around several hundred μg/L (i.e., ppb) whereas MTBE is nearly two orders of magnitude lower. Furthermore, taste thresholds are highly dependent on the individual.

The 1980s ushered in a vast cache of knowledge supported by reports and peer reviewed publications concerning groundwater investigations and DNAPLs. During this time period the evolution of vapor intrusion pathway (VIP) science also took place.

VIP refers to the migration of vapors from the soil zone into structures. The pathway starts from the groundwater to soil gas pathway. The origins of VIP may be traced back to the 1930s when petroleum exploration by soil gas analysis for hydrocarbons was first understood, but not from an environmental aspect. From the 1950s onward it was common practice to use volatile chemicals as root zone fumigants. This application added to the general knowledge of VIP, but there was no link to environmental concerns. In the 1960s vapor intrusion began to be understood as a risk associated with acute exposure or fire/explosion, mostly from petroleum wells. The American Petroleum Institute (API) published warnings, guidelines and best practices to reduce these risks associated with well drilling and exploration activities.

Beginning in the early 1960s and onward landfill gas surveys and radon surveys were steadily reported in the industry and in the scientific literature. In the 1970s VOC plume mapping by soil gas surveys began to evolve. By the late 1980s VOC plume mapping by soil gas surveys was a well-established and standard technique used in environmental investigations.

Throughout the 1980s vapor intrusion risk from acute exposure and chronic risks began to be considered in tandem where acute chemical risks were identified. Chronic exposure and risks via the VIP was recognized in the late 1970s/early 1980s which gave rise to OSHA’s focus on VOCs as inhalation carcinogens (1970s); and then in the early 1980s it was recognized as a mainstream topic of concern for residential indoor air quality. The most significant topic of VIP in the early 1980s concerned radon intrusion.

Along with the evolution of science, best practices and tools for industry, statutory evolution took place. In 1980 RCRA 261.31 F001 listing of spent degreasing solvents became an obligation. The U.S.EPA defined TCE and PCE mobility in groundwater along with the properties of volatility and carcinogicity, and further acknowledged the pathway of vapor intrusion into the basements of buildings as a human health risk.

In 1984 the U.S.EPA published a nationwide strategy for groundwater protection3. It stated that “ground water contamination looms as a major environmental issue of the 1980’s. The attention of agencies at all levels of government, as well as that of industry and environmentalists, is now focused on this vital resource. As contamination has appeared in well water and wells have been closed, the public has expressed growing concern about the health implications of inappropriate use and disposal of chemicals. As concern has increased, so have demands for expanded protection of the resource.”

In 1985 through Love Canal Enforcement actions the well-known, so-called Murphy Models were applied to assessing VIP into basements as part of performing risk assessments; and in 1986 RCRA OSWER4 Corrective Action directives required that investigations be conducted in environmental site assessments in order to characterize subsurface gasses from buried waste and hazardous constituents found in groundwater.

In 1989, RFI Guidance for Conducting RI/FS5 noted inter media transfer from groundwater to soil gas to air. In 1992 Air/Superfund guidance and best practices were published (U.S.EPA - “Assessing Potential Indoor Air Impacts for Superfund Sites”). This document includes case studies. In 1993 a further Air/Superfund guidance document was published (“Options for Developing and Evaluating Mitigation Strategies for Indoor Air Impacts at Superfund Sites”). This publication includes examples, case studies and best practices.

From the mid-1990s onward several states began to require VIP evaluations when conducting an environmental site assessment. These states were Massachusetts, Michigan, Connecticut, and Rhode Island. In later years more states added such requirements. In 1994 and again in 1995 the ASTM developed separate but complementary guidelines for conducting general Phase I and Phase II site assessments. In 1996 U.S.EPA published the NPL (National Priority List) Guidance document titled “Soil Screening Guidance User’s Guide.”

The ASTM developed the RBCA standard for petroleum releases that includes VIP. RBCA stands for Risk-Based Corrective Action, which is a generic term for corrective action strategies that categorizes a site according to risk and moves the site toward completion using appropriate levels of action and oversight. The most recent ASTM standard provides a framework for implementing a RBCA strategy. With this process, regulators and investigators can make sound, quick, consistent management decisions for a variety of sites using a three-tiered approach to data collection and site review contained in ASTM’s E1739 standard guide for “Risk-Based Corrective Action applied at Petroleum Release Sites.”

The RBCA helps to categorize sites according to risk, allocate resources for maximum protection of human health and the environment, and provide resources for appropriate levels of oversight. These actions are intended to assist sites to move forward quickly towards defining risks and mitigating them.

The ASTM RBCA standard, like the early ones established by the U.S.EPA in 1985, is intended to identify exposure pathways and receptors at a site; determine the level and urgency of response required at a site; determine the level of oversight appropriate for a site; incorporate risk analysis into all phases of the corrective action process; and enable selection of appropriate and cost-effective corrective action measures. RBCA is not a substitute for corrective action, but a tool for determining the amount and urgency of action necessary.

The ASTM standard (E1739) is based on a “tiered” approach to risk and exposure assessment, where each tier refers to a different level of complexity. The goal of all of ASTM’s tiers is to achieve similar levels of protection. The difference is that, in moving to higher tiers, more efficient and cost-effective corrective action results because the conservative assumptions of earlier tiers are replaced with more realistic site-specific assumptions. Additional site assessment data may be required as sites move to higher tiers. In contrast to earlier approaches to conducting site assessments which tend to be executed in steps, the approach taken today is more streamlined.

In 2001/2002 the U.S.EPA published “Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway From Groundwater and Intrusion to Indoor Air Pathway from Groundwater and Soils.”

Beginning circa 1980, the U.S.EPA began to steadily develop best practices for conducting environmental site assessments. These best practices were widely published and accessible to industry. By 1985 well-defined best practices were established, constituting the foundation for further refinements over the next decade. From about 1995 onward, further refinements to both technologies that aid in site assessments as well as more refined best management practices were devised and published by the American Society of Testing Materials (ASTM) and later further refined by such organizations as the World Bank Organization (WBO), ANSI, ISO, and others.

In 1985 U.S.EPA published a three-volume manual of best practices for industry to follow when conducting environmental site assessments. The first volume was titled: Characterization of Hazardous Waste Sites: A Methods Manual, Volume I – Site Investigations6. The following are excerpts from the publication, annotated in some instances with my comments. Overall the statements and recommended good industry practices are self-evident.

“At the first meeting of the Agency-Wide Steering Group for the Development of a Methods Manual for Characterization of Hazardous Waste Sites in August 1981, the scope of the planned Available Methods Manual was expanded from sampling and analysis to site characterization. The steering group agreed that

sampling and analysis of hazardous wastes must be closely tied to sampling and analysis strategy. Before methods can be useful, they must be related to the purposes and objectives of sampling and analysis. Such an association leads to the necessity of considering all aspects of hazardous waste site characterization.

”

As early as 1981 the U.S.EPA recognized and recommended that proper site characterization requires that a strategy with clearly defined objectives be established in order to properly identify and characterize the environmental conditions of a property.

“The objective of this manual is to provide field and laboratory managers, investigators, and technicians with a consolidated source of information on the subject of hazardous waste site characterization. The manual covers the range of endeavors necessary to characterize hazardous waste sites, from preliminary data gathering to sampling and analysis.”

“Because of the large number of subjects covered in this manual and the need to provide detailed methodology in the areas of sampling and sample analysis, this manual comprises three volumes: Volume I - Site Investigations; Volume II - Available Sampling Methods; Volume III - Available Laboratory Analytical Methods.”

U.S.EPA’s 1985 multi-volume manual of practices provides guidance on information-gathering activities in support of the requirements specified in the National Oil and Hazardous Substances Pollution Contingency Plan. “The National Contingency Plan contains a seven-phase approach to implementing the authority of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). Each phase represents a level of response dependent upon the situation. Information must be obtained to determine the appropriate level of environmental response. Both

remedial and enforcement actions under CERCLA require reliable site information.

This volume describes approaches to obtaining this information and follows a semi-chronological order through subsequent phases of the National Contingency Plan. These steps range from

preliminary data gathering

,

to site inspections

,

to large field investigations

.

”

U.S.EPA’s manual described policies and procedures common to all data-gathering efforts, such as personal conduct, document control, and quality assurance. Sections included in the manual provided a framework for gathering the required information. U.S.EPA detailed what information is necessary, where that information can be found and how the information can be acquired in an environmental site assessment. Its manual presented topics such as investigative conduct, documentation and recordkeeping, quality assurance, site entry, etc., from the viewpoint of Agency policy. It stated that although its discussions were based on EPA policy, they were intended to “serve as a guideline for anyone conducting a hazardous waste site investigation.”

U.S.EPA stated that the following requirements constitute good practices: Persons conducting hazardous waste site investigations must “develop and report the facts of an investigation completely, accurately, and objectively.”

On p. 2–3 of EPA’s document control practices are discussed. “The purpose of document control is to assure that all project documents issued to or generated during hazardous waste site investigations will be accounted for when the project is completed. The purpose is achieved through a program which makes all investigation documents accountable.This should include serialized document numbering, document inventory procedures, and an evidentiary filing system. Accountable documents used or generated during investigations include: Project Work Plans, Project Logbooks, Field Logbooks, Sample Data Sheets, Sample Tags, Chain-of-Custody Records and Seals, Laboratory Logbooks, Laboratory Data, Calculation, Graphs, etc., Sample Checkout, Sample Inventory, Internal Memos, External Written Communication, Business Confidential Information, Photographs, Drawings, Maps, Quality Assurance Plan, Litigation or Enforcement Sensitive Documents, and Final Report.”

EPA recognized that site investigations have the potential to generate large volumes of information and reports and that document control is an essential element to controlling information, and in support of any analysis applied towards remediation. It recommended that each document be assigned a “serialized number” and be “listed, with the number, in a project document inventory assembled at the project’s completion.” Volume II, Appendix D, provides further discussion of Document Control/Chain-of-Custody Procedures.

Beginning on p. 2–17 of Volume I U.S.EPA recommended good practices to be applied in environmental site assessments to ensure high quality and reliability throughout the assessment and in developing remedial actions.

Section 4 (beginning p. 4–1) of EPA’s 1985 good practices manual provides practices, protocols and stepwise procedures for data gathering in order to perform a proper environmental site assessment. EPA recommended that a task should be “initiated to collect and review available information about the known or suspected hazardous substance site or release.” EPA’s recommended practices constitute what is commonly referred to as a Phase I environmental audit.

In Section 5 beginning on p. 5–1 EPA provided detailed procedures, protocols and best practices for conducting site inspections. It defined these as being important components of Phase II, Preliminary Assessment and Phase IV, Evaluation and Determination of Appropriate Response - Planned Removal and Remedial Action. It stated that the “major objective of a site inspection is to determine if there is any immediate danger to persons living or working near the facility.” It explained in great detail the recommended practices, protocols and procedures for conducting these activities and stated that the primary items addressed during the site inspection are:

“A determination of the need for immediate removal action”;

“An assessment of the amounts, types and location of stored hazardous substances”;

“An assessment of the potential for substances to migrate”; and

“Documentation of immediate threats to the public or environment”.

The section covers various topics and best practices for conducting preliminary site investigations, Phase I site investigations, Phase II site investigations, and conducting remedial investigations. The recommended practices are detailed and stepwise. It stated for examples (p. 5–6) that “Inspections of basins and vessels should verify structural dimensions and note the number and location of input or discharge lines. Any manways, hatches, or valve pits should be identified and monitored with the survey instruments. If the structures contain a material, an estimate of percent full (look for staff gauges or site glasses) and a description of the material should be noted. A general assessment of structural condition also should be included…. The presence of buried vessels is often only apparent upon discovery of small standpipes or vents protruding above the ground surface. All such pipes should be noted and marked with colored tape and/or flags. Closer investigation of the immediate vicinity of the vents often uncovers hatches or valve pits. Further investigation during the inspection should be limited to screening the vents and hatch seals with an OVA, HNu or other monitors …”

On p. 5–7 EPA recommended that “information regarding population size and distribution should be available from the preliminary assessment. In many instances this information, if obtained from state or regional agencies will be somewhat dated. It is important therefore to tour the area assessing the likelihood of significant demographic changes. Recently constructed housing developments, apartments, schools and public buildings may indicate that changes have occurred since the information was published.” Such practices were recommended in order for the environmental site assessment to define the potential risks of hazardous substances on-site to neighboring off-site receptors.

Beginning on p. 6–1 EPA addressed the need and best practices for data evaluation. It wrote that “a data assessment is performed to ultimately assist in formulating response management decisions affecting later stages of the investigation. The data evaluation may also indicate data gaps which need to be filled either by further background research or additional site inspections (or an initial inspection if one has not yet been conducted) … The evaluation should encompass the scope detailed below:

the existence (or nonexistence) of a potential hazardous waste problem;

probable seriousness of the problem and the priority for further investigation or action; and

the type of action or investigation appropriate to the situation.”

In 1996 the ASTM published its standard Designation: E 1528 – 96: Standard Practice for Environmental Site Assessments: Transaction Screen Process. It wrote, “The purpose of this practice, as well as Practice E 1527, is to define good commercial and customary practice in the United States of America for conducting an environmental site assessment of a parcel of commercial real estate with respect to the range of contaminants within the scope of the Comprehensive Environmental Response Compensation and Liability Act (CERCLA) and petroleum products …” It further defined the term Recognized Environmental Conditions: “In defining a standard of good commercial and customary practice for conducting an environmental site assessment of a parcel of property, the goal of the processes established by this practice is to identify recognized environmental conditions. The term recognized environmental conditions means the presence or likely presence of any hazardous substances or petroleum products on a property under conditions that indicate an existing release, a past release, or a material threat of a release of any hazardous substances or petroleum products into structures on the property or into the ground, groundwater, or surface water of the property. The term includes hazardous substances or petroleum products even under conditions in compliance with laws. The term is not intended to include deminimis conditions that generally do not present a material risk of harm to public health or the environment and that generally.”

It further wrote, “Objectives guiding the development of this practice and Practice E 1527 are (1) to synthesize and put in writing good commercial and customary practice for environmental site assessments for commercial real estate, (2) to facilitate high quality, standardized environmental site assessments, (3) to ensure that the standard of appropriate inquiry is practical and reasonable …”

It also wrote, “This practice and Practice E 1527 are designed to assist the user in developing information about the environmental condition of a property and as such has utility for a wide range of persons, including those who may have no actual or potential CERCLA liability and/or may not be seeking the innocent landowner defense.“

In 1997 the ASTM published its standard Designation: Designation: E 1903 – 97: Standard Guide for Environmental Site Assessments: Phase II Environmental Site Assessment Process. It wrote “The primary objectives of conducting a Phase II ESA are to evaluate the recognized environmental conditions identified in the Phase I ESA or transaction screen process for the purpose of providing sufficient information regarding the nature and extent of contamination to assist in making informed business decisions about the property …”

ASTM further stated in E 1903 – 97 “At the completion of a Phase II ESA, the environmental professional should be able to conclude, at a minimum, that either (a) the ESA has provided sufficient information to render a professional opinion that there is no reasonable basis to suspect the presence of hazardous substances or petroleum products at the property associated with the recognized environmental conditions under assessment, or (b) the ESA has confirmed the presence of hazardous substances or petroleum products at the property under conditions that indicate disposal or release. If the information developed in the ESA is insufficient for the environmental professional to reach either of these conclusions, the environmental professional may recommend additional iterations of assessment if warranted to meet the objectives of the user. If the environmental professional reasonably suspects that unconfirmed hazardous substance or petroleum releases remain but concludes that further reasonable assessment is not expected to provide additional information of significant value, he may recommend that further assessment is not warranted. In such circumstances, the recommendation for no further assessment should be accompanied by an explanation why a reasonable suspicion of releases remains and why further reasonable assessment is not warranted.”

In 1998 the necessity of performing a Phase I ESA was underscored by congressional action in passing the Superfund Cleanup Acceleration Act of 1998. This act requires purchasers of commercial property to perform a Phase I study meeting the specific standard of ASTM E1527: Standard Practice for Environmental Site Assessments: Phase I Environmental Site Assessment Process. The most recent standard is “Standards and Practices for All Appropriate Inquiries” 40 Code of Federal Regulations, Section 312 which drew heavily from ASTM E1527-05 which has become known as ‘All Appropriate Inquiry’ (AAI). Previous guidances regarding the ASTM E1527 standard were ASTM E1527-97 and ASTM E1527-00.

1.3 Technology Limitations and Cleanup Goals

The basis of any groundwater remediation strategy needs to take into consideration the risks to receptors, current technology, regulatory requirements and trends, and cost considerations. Today, the EPA and many state regulatory agencies acknowledge there are limitations of existing technologies to completely remediate some impacted sites. This awareness has resulted in U.S. regulatory changes which are favorable to more site-specific and risk-based remediation objectives for industrial sites. As an example, in 1994, the EPA published guidance that allows for Technical Impracticability waivers for sites where complete remediation is impossible due to the site conditions or the presence of inaccessible DNAPLs. This guidance describes what technical evidence is required and what regulatory procedures exist for establishing more realistic remediation objectives for chlorinated solvent contaminated sites.

The EPA “Brownfields” initiative encouraged local governments, environmental regulators, and land developers to work together to establish realistic cleanup goals for contaminated industrial properties. Using risk assessment tools, the actual exposure pathways and receptors are identified for the proposed land use and cleanup goals and remediation activities are tailored to eliminate these risks. Both RCRA and CERCLA contain provisions for establishing alternate concentration limits or remediation goals based on industrial land use assumptions. It is not always reasonable nor practical to apply drinking water maximum contaminant levels (MCLs) as the basis for cleanup goals in all situations where there is little chance of human exposure to groundwater.

Many if not most state agencies now publish risk-based cleanup criteria for industrial sites and recognize “mixing zone” concepts which allow stable contaminated plumes to attenuate in place so long as surface water and drinking water resources are protected. ASTM has also been developing a risk-based corrective action (RBCA) standard for chlorinated solvents that is similar to the standard developed for fuel.

1.4 Conceptual Models

The nature and extent of a site’s groundwater contamination must be defined in part with a conceptual model. The investigator needs to develop a useful conceptual site model or update an existing one and determine what human or ecological receptors may be at risk and how to limit their exposure to the contamination.

An accurate conceptual site model is critical to evaluating the true risk of contamination, as well as the possibilities and limitations of site remediation strategies. A complete model should include a visual representation of contaminant source and release information, site geology and hydrology, contaminant distribution, fate and transport parameters, and risk assessment features such as current and future land use and potential exposure pathways and receptors.

The conceptual site model should be developed as a part of the site investigation or feasibility study phase of site remediation. Many interim remedial systems have been installed and are operating without a well-defined model, oftentimes leading to major cost overruns or inability to achieve cleanup goals within reasonable time periods. Some remedial systems were designed based on an initial model that requires updating based on recent operations and monitoring data. Changes in land use, or changes in the enforcement of institutional controls, can also alter the exposure and risk assumptions of the model. It is important to recognize that the conceptual site model is intended to be a dynamic representation of site conditions based on a continual influx of information from the site. The following are important elements of a conceptual site model.

1.4.1 Source and Release Information