Natural and Enhanced Remediation Systems - Chapter 1 doc

Suthersan, Suthan S. “Frontmatter”

Natural and Enhanced Remediation Systems

Edited by Suthan S. Suthersan
Boca Raton: CRC Press LLC, 2001

©2001 CRC Press LLC

Natural and Enhanced Remediation Systems

by
Suthan S. Suthersan

©2001 CRC Press LLC

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Library of Congress Cataloging-in-Publication Data

Suthersan, Suthan S.
Natural and enhanced remediation systems / by Suthan S. Suthersan.
p. cm. — (Arcadis Geraghty & Miller science and engineering)
Includes bibliographical references and index.
ISBN 1-56670-282-8
1. Soil remediation. 2. Groundwater–Purification. 3. Hazardous wastes–Natural
attenuation. 4. Bioremediation. I. Title. II. Geraghty & Miller environmental science and
engineering series.
TD878.S873 2001
628.5—dc21 2001029566
CIP

©2001 CRC Press LLC

Sincere Thanks To:

Sumathy, Shauna, and Nealon for their enthusiastic
support and unending patience.
STP, MTP, MLM, and SBB for their insight, support,
inspiration, and trust.
Dedicated with utmost humility to the heroes and heroines of
Eelam who have put their lives in the line of fire to express
their intellectual freedom.

©2001 CRC Press LLC

Foreword

I have worked with Dr. Suthersan for the past 13 years and have seen firsthand
the impact he has had on the evolution of our business. Over this period, environ-
mental remediation has moved from a world of standard operation and application
of proven technology to one where more innovative concepts can be applied, tested,
and developed for the benefit of the environment, the regulatory community, and
industry. Dr. Suthersan has worked assiduously to develop new remediation tech-
nologies, move them to pilot testing in cooperation with industry, and make them
demonstrated techniques.
As our industry has matured, the pressures on all parties have increased: pressure
to assure protection of human health and the environment, to remediate faster, to
rapidly return sites to beneficial use, to reduce costs, etc. Finding a solution to these
competing objectives has become more and more intricate and must include the
impacts of social, economic, business, and environmental factors. Dr. Suthersan is
one of the most talented purveyors of remediation technology as a tool to solve these
complex problems in a world where competing priorities are the rule not the excep-
tion. The author has focused on finding these total business solutions for our industry,
using the innovative technical solutions he or others have created. Finding total
business solutions to multifaceted environmental problems is one of the hallmarks

of Dr. Suthersan’s career.
In this book, Dr. Suthersan explains some of the pioneering remediation tech-
nologies developed over the past few years. The focus is on those techniques that
modify or enhance the natural environment to aid in the remediation of contaminants.
When applied correctly, these engineered, natural systems have proven to be more
efficient and cost effective than their more intrusive predecessors. Assuring that these
techniques are applied correctly and tailored to each particular setting is a key
component of any system’s success. The impact of biological, chemical, and hydro-
geologic settings on these technologies is thoroughly discussed. Dr. Suthersan
describes each technique in detail: its processes, the science behind it, its application,
and the constraints. This book will be an invaluable resource to the practicing
remediation engineer, the regulatory community charged with evaluating these tech-
niques, and the industry applying them.
It has been a privilege to have worked with Dr. Suthersan for these past years
and to have seen the influence of his knowledge and skill in our industry. I believe
that those who read this book will gain from his wisdom.

Steve Blake

Executive Board, ARCADIS, N.V.
Denver, Colorado

©2001 CRC Press LLC

Preface

Remediation of hazardous wastes present in the subsurface has evolved with
time and has been influenced by various factors over the years. During the early
years, direction and efforts were mostly influenced by the regulations in place and
the need for compliance and protection of human health and environment. The

contaminants primarily focused upon during this time were the petroleum-related
contaminants stemming from leaking underground storage tanks (USTs).
In later years, remediation efforts were driven by a combination of economic
and regulatory factors. During this time contaminants that caught most of the atten-
tion were the chlorinated solvents, heavy metals, and chlorinated and nonchlorinated
polynuclear aromatic hydrocarbons (PAHs). The current focus seems to be taking a
different direction: instead of focusing on the type of contaminants, emphasis is on
evaluating the damage to the environment (and thus the risk) and repairing that
damage in a cost-effective manner.
Evolution of remediation technologies was influenced not only by changing
regulatory and economic factors, but also by the type and chemical characteristics
of contaminants under focus. An example is the shift in emphasis from engineered
aerobic bioremediation systems of the 1980s to engineered anaerobic bioremediation
systems of the 1990s. Significant reliance and dependence on natural remediation
systems have increased as a result of recent acceptance that landfills behave as
bioreactors and the very recent focus on dealing with ecological risks and natural
resources damage (NRD) assessments. Ever increasing understanding of the behav-
ior of most contaminants in the natural environment has also led to the effort of
maximizing the remediation potential of natural systems.
The thematic focus of this book is to highlight the current phase in the evolution
of remediation technologies. All the technologies discussed in the book utilize or
enhance the natural biogeochemical environment for remediation of hazardous con-
taminants. The discussion throughout the book is focused towards helping practitioners
of remediation to engineer remediation systems utilizing the natural environment.
These natural systems or reactors still have to be properly designed and engineered to
optimize the performance and maximize contaminant removal efficiencies.
The basic understanding of environmental and contaminant characteristics
required to design these systems is provided in Chapter 2. I had just coined the
phrase “

in situ

reactive zones (IRZ)” when I wrote my previous book in 1996 and
was able to provide only an introduction of the technology. I have made a signif-
icant effort in Chapter 4 to describe the IRZ technology and its various modified
applications. The manner in which the application of this technology is exploding
may justify a book of its own. I am proud to see the advances and expansion of
this technology pioneered by my colleagues and me at ARCADIS G & M, Inc.
Due to the shortage of space I could not present data from all the successful sites
using this technology. Technical advances and theoretical insights on the applica-
tion of

in situ

chemical oxidation are also presented in Chapter 4 (special thanks
to Dr. Fred Payne).

©2001 CRC Press LLC

I also had the privilege of being involved in some of the earliest phytoremediation
and phyto-cover applications. Some contributions to the science of designing phyto-
covers are presented in Chapter 7 (special thanks to Dr. Scott Potter). I have provided
only a summary on the current state of the science of phytoremediation in Chapter
5. Basic concepts of treatment wetlands are provided in Chapter 6. I truly believe
that this technology will have more applications in the field of hazardous waste
remediation.
I wrote this book to reach a wide audience: remediation design engineers,
scientists, regulatory specialists, graduate students in environmental engineering,
and people from the industry who have general responsibility for site cleanups. I
have tried to provide a general, basic description of the technologies in all chapters

in addition to detailed information on basic principles and fundamentals in most
chapters. Readers who are not interested in basic principles can skip these passages
and still receive the general knowledge they need.

Suthan S. Suthersan

Yardley, Pennsylvania

©2001 CRC Press LLC

Acknowledgments

First and foremost, I would like to thank members and colleagues from the
Innovative Strategies Group (ISG) of ARCADIS — Frank Lenzo, Mike Hansen, and
Jeff Burdick — for their enthusiasm and hard work in trying to experiment with
innovative and cutting edge technologies in the field. Insights and advice provided
by Drs. Scott Potter and Fred Payne in formulating the theoretical and mathematical
foundations behind the technical concepts are immense. In addition, the patience
and excitement exhibited by Chris Lutes and David Liles during the laboratory
“proof of concept” experiments always boosted my confidence to proceed to the
next level in implementing many of the technologies. Taking these technologies
from the conceptual level to field scale applications would not have been possible
without these individuals.
I have to thank Eileen Schumacher and Ben Tufford for patiently drafting all
the figures and Amy Weinert and Gail Champlin for typing the manuscript. The
management of my employer ARCADIS G & M, Inc. deserves special mention for
all the support given to me over the years. The opportunities and encouragement
provided to me in order to “think out of the box” are a reflection of the company’s
culture. I owe a special debt to all the engineers and project managers who helped
me to implement many innovative and challenging remediation projects. This list is

a long one, but special mention is due to the following: Mike Maierle, Don Kidd,
Gary Keyes, Steve Brussee, Jack Kratzmeyer, Mark Wagner, Jim Drought, Tina
Stack, Eric Carman, Al Hannum, John Horst, Kurt Beil, Dave Vance, Nanjun Shetty,
and Pat Hicks.
The encouragement, support, and feedback on the state of the science approaches
in phytoremediation by Drs. Steve Rock and Steve McCutcheon, of the USEPA, are
very much appreciated.

©2001 CRC Press LLC

The Author

Suthan S. Suthersan

, Ph.D., P.E., is senior vice president
and director of Innovative Remediation Strategies at
ARCADIS G & M, Inc., an international environmental
and infrastructure services company. In his 12 years with
the company, Dr. Suthersan has helped make AG&M one
of the most respected environmental engineering compa-
nies in the U.S., specifically in the field of

in situ

remedi-
ation of hazardous wastes. Many of the technologies he
pioneered have since become industry standards. His big-
gest contribution to the industry, beyond the technology
development itself, has been to convince the regulatory
community that these innovative technologies are better

than traditional ones, not only from a cost viewpoint, but also for technical effec-
tiveness. His experience is derived from working on at least 500 remediation projects
in design, implementation, and technical oversight capacities during the past 15
years.
Dr. Suthersan’s technology development efforts have been rewarded with seven
patents awarded and more pending. His most important recent contributions are
reflected by the following patents: Engineered

In Situ

Anaerobic Reactive Zones,
US Patent 6,143,177; In Well Air Stripping, Oxidation, and Adsorption, US Patent
6,102,623;

In Situ

Anaerobic Reactive Zone for

In Situ

Metals Precipitation and to
Achieve Microbial De-Nitrification, US Patent 5,554,290;

In Situ

Reactive Gate for
Groundwater Remediation, US Patent 6,116,816.
Dr. Suthersan has a Ph.D. in environmental engineering from the University of
Toronto, a M.S. degree in environmental engineering from the Asian Institute of
Technology, and a B.S. degree in civil engineering from the University of Sri Lanka.

In addition to his consulting experience Dr. Suthersan has taught courses at several
universities. He is the founding editor in chief of the

Journal of Strategic Environ-
mental Management

and is a member of the editorial board of the

International
Journal of Phytoremediation

.

©2001 CRC Press LLC

Contents

Chapter 1

Hazardous Wastes Pollution and Evolution of Remediation
1.1 Introduction
1.2 The Concept of Risk
1.2.1 The Decision Making Framework
1.3 Evolution of Understanding of Fate and Transport in
Natural Systems
1.4 Evolution of Remediation Technologies
References

Chapter 2

Contaminant and Environmental Characteristics
2.1 Introduction
2.2 Contaminant Characteristics
2.2.1 Physical/Chemical Properties
2.2.1.1 Boiling Point
2.2.1.2 Vapor Pressure
2.2.1.3 Henry’s Law Constant
2.2.1.4 Octanol/Water Partition Coefficients
2.2.1.5 Solubility in Water
2.2.1.6 Hydrolysis
2.2.1.7 Photolytic Reactions in Surface Water
2.2.2 Biological Characteristics
2.2.2.1 Cometabolism
2.2.2.2 Kinetics of Biodegradation
2.3 Environmental Characteristics
2.3.1 Sorption Coefficient
2.3.1.1 Soil Sorption Coefficients
2.3.1.2 Factors Affecting Sorption Coefficients
2.3.2 Oxidation-Reduction Capacities of Aquifer Solids
2.3.2.1 pe and pH
2.3.2.2 REDOX Poise
2.3.2.3 REDOX Reactions
References

Chapter 3

Monitored Natural Attenuation
3.1 Introduction
3.1.1 Definitions of Natural Attenuation
3.2 Approaches for Evaluating Natural Attenuation

3.3 Patterns vs. Protocols

©2001 CRC Press LLC

3.3.1 Protocols for Natural Attenuation
3.3.2 Patterns of Natural Attenuation
3.3.2.1 Various Patterns of Natural Attenuation
3.4 Processes Affecting Natural Attenuation of Compounds
3.4.1 Movement of Contaminants in the Subsurface
3.4.1.1 Dilution (Recharge)
3.4.1.2 Advection
3.4.1.3 Dispersion
3.4.2 Phase Transfers
3.4.2.1 Sorption
3.4.2.2 Stabilization
3.4.2.3 Volatilization
3.4.3 Transformation Mechanisms
3.4.3.1 Biodegradation
3.5 Monitoring and Sampling for Natural Attenuation
3.5.1 Dissolved Oxygen (DO)
3.5.2 Oxidation–Reduction (REDOX) Potential (ORP)
3.5.3 pH
3.5.4 Filtered vs. Unfiltered Samples for Metals
3.5.4.1 Field Filtration and the Nature of
Groundwater Particulates
3.5.4.2 Reaasons for Field Filtration
3.5.5 Low-Flow Sampling as a Paradigm for Filtration
3.5.6 A Comparison Study
References

Chapter 4

In Situ

Reactive Zones
4.1 Introduction
4.2 Engineered Anaerobic Systems
4.2.1 Enhanced Reductive Dechlorination (ERD) Systems
4.2.1.1 Early Evidence
4.2.1.1.1 Biostimulation vs. Bioaugmentation
4.2.1.2 Mechanisms of Reductive Dechlorination
4.2.1.3 Microbiology of Reductive Dechlorination
4.2.1.3.1 Cometabolic Dechlorination
4.2.1.3.2 Dechlorination by Halorespiring
Microorganisms
4.2.1.4 Electron Donors
4.2.1.4.1 Production of H

2

by Fermentation
4.2.1.4.2 Competition for H

2

4.2.1.5 Mixture of Compounds on Kinetics
4.2.1.6 Temperature Effects
4.2.1.7 Anaerobic Oxidation

©2001 CRC Press LLC

4.2.1.8 Electron Acceptors and Nutrients
4.2.1.9 Field Implementation of IRZ for Enhanced Reductive
4.2.1.10 Lessons Learned
4.2.1.11 Derivation of a Completely Mixed System for
Groundwater Solute Transport of Chlorinated Ethenes
4.2.1.12 IRZ Performance Data
4.2.2

In Situ

Metals Precipitation
4.2.2.1 Principles of Heavy Metals Precipitation
4.2.2.2 Aquifer Parameters and Transport Mechanisms
4.2.2.3 Contaminant Removal Mechanisms
4.2.3

In Situ

Denitrification
4.2.4 Perchlorate Reduction
4.3 Engineered Aerobic Systems
4.3.1 Direct Aerobic Oxidation
4.3.1.1 Aerobic Cometabolic Oxidation
4.3.1.2 MTBE Degradation
4.4

In Situ

Chemical Oxidation Systems

4.4.1 Advantages
4.4.2 Concerns
4.4.3 Oxidation Chemistry
4.4.3.1 Hydrogen Peroxide
4.4.3.2 Potassium Permanganate
4.4.3.3 Ozone
4.4.4 Application
4.4.4.1 Oxidation of 1,4-Dioxane by Ozone
4.4.4.2 Biodegradation Enhanced by Chemical
Oxidation Pretreatment
4.5 Nano-Scale Fe (0) Colloid Injection within an IRZ
4.5.1 Production of Nano-Scale Iron Particles
4.5.2 Injection of Nano-Scale Particles in Permeable Sediments
4.5.3 Organic Contaminants Treatable by Fe (0)
References

Chapter 5

Phytoremediation
5.1 Introduction
5.2 Chemicals in the Soil–Plant System
5.2.1 Metals
5.2.2 Organics
5.3 Types of Phytoremediation
5.3.1 Phytoaccumulation
5.3.2 Phytodegradation
5.3.3 Phytostabilization
5.3.4 Phytovolatilization
Dechlorination

©2001 CRC Press LLC

5.3.5 Rhizodegradation
5.3.6 Rhizofiltration
5.3.7 Phytoremediation for Groundwater Containment
5.3.8 Phytoremediation of Dredged Sediments
5.4 Phytoremediation Design
5.4.1 Contaminant Levels
5.4.2 Plant Selection
5.4.3 Treatability
5.4.4 Irrigation, Agronomic Inputs, and Maintenance
5.4.5 Groundwater Capture Zone and Transpiration Rate
References

Chapter 6

Constructed Treatment Wetlands
6.1 Introduction
6.1.1 Beyond Municipal Wastewater
6.1.2 Looking Inside the “Black Box”
6.1.3 Potential “Attractive Nuisances”
6.1.4 Regulatory Uncertainty and Barriers
6.2 Types of Constructed Wetlands
6.2.1 Horizontal Flow Systems
6.2.2 Vertical Flow Systems
6.3 Microbial and Plant Communities of a Wetland
6.3.1 Bacteria and Fungi
6.3.2 Algae
6.3.3 Species of Vegetation for Treatment Wetland Systems
6.3.3.1 Free-Floating Macrophyte-Based Systems

6.3.3.2 Emergent Aquatic Macrophyte-Based Systems
6.3.3.3 Emergent Macrophyte-Based Systems with Horizontal
Subsurface Flow
6.3.3.4 Emergent Macrophyte-Based Systems with Vertical
Subsurface Flow
6.3.3.5 Submerged Macrophyte-Based Systems
6.3.3.6 Multistage Macrophyte-Based Treatment Systems
6.4 Treatment-Wetland Soils
6.4.1 Cation Exchange Capacity
6.4.2 Oxidation and Reduction Reactions
6.4.3 pH
6.4.4 Biological Influences on Hydric Soils
6.4.5 Microbial Soil Processes
6.4.6 Treatment Wetland Soils
6.5 Contaminant Removal Mechanisms
6.5.1 Volatilization
6.5.2 Partitioning and Storage
6.5.3 Hydraulic Retention Time

©2001 CRC Press LLC

6.6 Treatment Wetlands for Groundwater Remediation
6.6.1 Metals-Laden Water Treatment
6.6.1.1 A Case Study for Metals Removal
6.6.2 Removal of Toxic Organics
6.6.2.1 Biodegradation
6.6.3 Removal of Inorganics
6.6.4 Wetland Morphology, Hydrology, and Landscape Position
References

Chapter 7

Engineered Vegetative Landfill Covers
7.1 Historical Perspective on Landfill Practices
7.2 The Role of Caps in the Containment of Wastes
7.3 Conventional Landfill Covers
7.4 Landfill Dynamics
7.5 Alternative Landfill Cover Technology
7.6 Phyto-Cover Technology
7.6.1 Benefits of Phyto-Covers over Traditional RCRA Caps
7.6.2 Enhancing

In Situ

Biodegradation
7.6.3 Gas Permeability
7.6.4 Ecological and Aesthetic Advantages
7.6.5 Maintenance, Economic, and Public Safety Advantages
7.7 Phyto-Cover Design
7.7.1 Vegetative Cover Soils
7.7.2 Nonsoil Amendment
7.7.3 Plants and Trees
7.8 Cover System Performance
7.8.1 Hydrologic Water Balance
7.8.2 Precipitation
7.8.3 Runoff
7.8.4 Potential Evapotranspiration — Measured Data
7.8.5 Potential Evapotranspiration — Empirical Data
7.8.6 Effective Evapotranspiration
7.8.7 Water Balance Model

7.9 Example Application
7.10 Summary of Phyto-Cover Water Balance
7.11 General Phyto-Cover Maintenance Activities
7.11.1 Site Inspections
7.11.2 Soil Moisture Monitoring
7.11.2.1 Drainage Measurement
7.11.3 General Irrigation Guidelines
7.11.4 Tree Evaluation
7.11.4.1 Stem
7.11.4.2 Leaves
7.11.5 Agronomic Chemistry Sampling

©2001 CRC Press LLC

7.11.6 Safety and Preventative Maintenance
7.11.7 Repairs and Maintenance
7.12 Operation and Maintenance (O&M) Schedule
7.12.1 Year 1 — Establishment
7.12.2 Years 2 and 3 — Active Maintenance
7.12.3 Year 4 — Passive Maintenance
7.13 Specific Operational Issues
7.13.1 Irrigation System Requirements
7.13.2 Tree Replacement
References

Appendix A

Physical Properties of Some Common Environmental Contaminants

Appendix B

Useful Information for Biogeochemical Sampling

Appendix C

Common and Scientific Names of Various Plants

©2001 CRC Press LLC

CHAPTER

1
Hazardous Wastes Pollution and
Evolution of Remediation

CONTENTS

1.1 Introduction
1.2 The Concept of Risk
1.2.1 The Decision Making Framework
1.3 Evolution of Understanding of Fate and Transport in Natural Systems
1.4 Evolution of Remediation Technologies
References

The earth was made so various that the mind of desultory man, studious of
change and pleased with novelty, might be indulged.

1.1 INTRODUCTION

Among the many environmental problems that have received attention in recent

decades is subsurface contamination caused by hazardous wastes. This has been due
to the growing concern over short and long term health and environmental effects
of toxic substances released into the environment.
The public policy maker is faced with particular difficulties in regulating haz-
ardous pollutants, most notably because of the high levels of uncertainty surrounding
the issue. Such uncertainty exists in determining the precise impacts in relation to
both human health effects and long term effects on the environment, especially with
recalcitrant pollutants, or pollutants with extremely slow degradation rates. Never-
theless, policy makers have been required to formulate environmental regulations
using some dependable basis. While theoretical methods of decision making such
as dose-response and risk-benefit analysis may be employed to assist regulators,

©2001 CRC Press LLC

they are still faced with conflicting pressures — for example, between political and
economic priorities or between public demands and technical expertise.
Estimating the damage function of a pollutant is an exercise that underpins
regulatory formulation for hazardous waste management. Figure 1.1 outlines the
basic steps involved in this estimation. Determining the transfer function of a haz-
ardous pollutant raises several problems. Persistent, nondegradable substances will
tend to accumulate in the environment often becoming concentrated in the food
chain. In the past, the potential life span of persistent substances in the subsurface
was considered to be decades or even centuries. Research performed and scientific
advancements, specifically in the last decade, indicate that compounds deemed to
be persistent or nondegradable in the past are considered to be less persistent or at
least partially degradable under natural conditions.

1.2 THE CONCEPT OF RISK

Many of the problems associated with hazardous waste management, such as uncer-

tainty, irreversibility, and persistence make the concept of risk relevant to this discussion.
From an engineering or scientific standpoint, “risk” may be defined in quantitative terms
by applying probabilistic measures. If “hazard” is defined as the potential for adverse
consequences of some event, then “risk” may be defined as the chance of a particular
hazard occurring. It combines two aspects — the probabilistic measure of the occurrence
of the event with a measure of the consequences of the event (in this case the level of
toxicity of the pollutant). Further aspects of risk are highlighted by social scientists who
examine risk perception in recognition that a particular risk or hazard may mean
different things to different people in different contexts.
The concept of risk is not without problems, particularly in relation to the issue
of hazardous pollutants. For example, an initial problem is determining the proba-
bility of such risks; there have been only a few decades of experience in dealing
with many pollutants. Their effects on human beings had been largely unknown,
and thus the probabilistic calculations of risk on exposure and associated health and
ecological impacts were mostly conservative.
In relation to the assumed, perceived, or calculated risks associated with haz-
ardous pollutants until recently, it is important to highlight two significant features:
1) the subjective probability of the hazard (caused by toxicity of the released
pollutant) occurring may be very low, but, 2) the consequence of the hazard was
assumed or perceived to be very high, often as irreversible because of assumptions

Figure 1.1

Evaluation of pollution damage.
Release of
Pollutants
Rate and Mass
at a Particular
Place and Time
Ambient

Conditions
Concentrations
of Pollutants in
Different Media
Damage
Effects
Physical, Ecological,
Health, Property,
Natural Resources
Exposure
Pathways
Dose-Response
Function
Transfer
Function
Monetary

©2001 CRC Press LLC

of persistence and negligible degradation of many pollutants in the natural environ-
ment. Thus the low probability tends to cancel out the assumed or perceived impacts
associated with the risk.
Recent research shows that pollutants and other organic chemicals present in the
subsurface become less available or create lesser levels of hazard (in other words
become less toxic) due to interactions between the compound and the subsurface
environment. This drop in availability and toxicity lowers the risk of these chemicals
to human and ecological receptors. Furthermore, the availability of an organic
chemical in the subsurface is not a function of its measured concentration; rather,
it depends upon the geologic and biogeochemical characteristics of the subsurface,
the physicochemical properties of the chemical itself, and the time of contact between

the chemical and the subsurface media, i.e., aging, as well as the type and extent of
treatment, natural or anthropogenic, to which it has been subjected.

1.2.1 The Decision Making Framework

In the face of the many uncertainties surrounding hazardous waste management
with respect to the assumed, perceived, or calculated risks, the regulatory authorities
are faced with an initial decision about the appropriate framework for decision-
making: should it be a balancing approach such as cost-benefit or risk-benefit
analysis, or should it be an approach which emphasizes the protection of human
health and natural resources regardless of costs?
Three types of approaches have been utilized to implement hazardous waste
management policies in the U.S. during the past three decades:

1. Health-based approaches — zero risk, significant risk, or acceptable risk
2. Balancing approaches — cost-benefit, risk-benefit, or decision analysis
3. Technology-based approaches — best available technology, risks as low as rea-
sonably practicable

Environmental threats, rather than the scientific evidence and theory from which
they may be deduced, have been ill-defined during the past three decades. The
evidence from which a threat is deduced has been challenged by conflicting evidence
or placed into a context of associations which heightens its significance. A scenario
for an exposure pathway typically used in the past, where a kid climbing an eight-
foot fence and eating a few grams of soil every day for a decade is an example of
such an association. For many years, there was a widespread but unfounded assump-
tion that some toxic pollutants stemming from industrial releases and/or accidents
and landfills would not be degraded in the natural environment. The measurement
of damage, and thus the risk, requires an understanding of the physical processes
of transportation and of the distribution and deposition of pollutants, including their

chemical and biological transformations on the way.
The creation of new knowledge usually involves institutions very different from
those concerned with its acceptance, application, and dissemination. A genuine
science-based environmental policy should be a dynamic one and evolve via con-
tinuous monitoring of pollutants in many media, as well as of their impacts on the
ecosystem and human health (or any other selected target organisms). The technical

©2001 CRC Press LLC

means for such monitoring must, of course, be available, as must the baselines for
the establishment of a time series so that change can be observed over time in the
natural environment. There must be agreement on which pollutants to monitor and
how to synthesize and use the masses of data that will accumulate.
Even complete understanding of how the subsurface works as a bio-geo-physi-
co-chemical system cannot give ready answers as to the proper regulatory response,
i.e., how to use the earth in the common interest of humanity and without degrading
it for future generations. This is probably why the government, more out of frustra-
tion than intent, has come to rely less on science, engineering, and economics and
more on caution and law.
Figure 1.2 describes the shortcomings of the health-based, conservative approach
of the past and the more credible, balanced approach still evolving. Understanding
the contribution by Mother Nature towards a natural remediation process has had a
significant influence on this evolution.

1.3 EVOLUTION OF UNDERSTANDING OF FATE AND
TRANSPORT IN NATURAL SYSTEMS

Predicting the hazard of an organic contaminant to humans, animals, and plants
requires information not only on its toxicity to living organisms but also on the
degree of exposure of the organisms to the compound. The mere release or discharge

of a pollutant does not, in itself, constitute a hazard; the individual human, animal,
or plant must also be exposed to it. In evaluating exposure, the transport of the

Figure 1.2

A hypothetical analysis of cost to risk reduction beneÞt ratios during remediation
activities.
Remediation expenditure
which justifies reasonable
risk reduction
Cost of Remediation ($)
Associated Risk
10
-7
-6
10
-5
10
-4
10
-3
10

©2001 CRC Press LLC

chemical and its fate must be considered. A molecule that is not subject to environ-
mental transport is not a health or environmental problem except to species at the
specific point of release.
Information on dissemination of the chemical from the point of its release to the
point where it could have an effect is of great relevancy for risk calculations.

However, the chemical may be modified structurally or totally destroyed during its
transport, and the fate of the compound during transport, that is, its modification or
destruction, is crucial to defining the exposure. A compound modified to yield
products that are less or more toxic, or totally degraded to harmless end products,
or bio-magnified — factors associated with the fate of the molecule — represents
greater or lesser hazard to the species potentially exposed to injury.
At the specific site of discharge or during its transport, the pollutant molecule
or ion may be acted on by abiotic mechanisms. Photochemical transformations occur
in the atmosphere and at or very near the surfaces of water, soil, and vegetation,
and these processes may totally destroy or appreciably modify a number of different
types of organic chemicals. Nonenzymatic, nonphotochemical reactions are also
prominent in soil, sediment, and surface and groundwater, and these may bring about
significant changes; however, such processes rarely, if ever, totally convert organic
compounds to harmless end products or mineralized compounds in nature. Many of
these nonenzymatic reactions only bring about a slight modification of the molecule
so that the product is frequently similar in structure, and often in toxicity, to the
precursor compound.
However, biological processes may modify organic molecules at the site of their
release or during their transport. Such biological transformations, which involve
enzymes as catalysts, frequently bring about extensive modification in the structure
and toxicological properties of pollutants or potential pollutants. These biotic pro-
cesses may result in the complete conversion of the organic molecule to inorganic
products, cause major changes resulting in new organic products, or occasionally
lead to only minor modifications. The available body of information suggests that
the major agents causing the biological transformations in soil, sediment, surface
and groundwater, and many other sites are the microorganisms that inhabit these
environments.
The earth is thought to be about 4.6

¥

10

9

years (4.6 eons) old.

2

The original
atmosphere surrounding the earth was reducing and probably included the gases
CH

4

, CO

2

, CO, NH

3

and H

2

O. Although abiotic organic synthesis probably occurred
since the earth’s beginnings, life probably did not appear until about 0.5–1 billion
years later, according to present thinking.

The first form of life that was established on the “infant” earth was anaerobic.

1

As anaerobic life became more firmly established, the organic nutrients must have
begun to be depleted at a faster rate than they could be replenished by abiotic
synthesis. Hence, an alternative mechanism for producing organic matter was
required to sustain life. The subsequent evolutionary developments led to the emer-
gence of photosynthesis and eventually resulted in the emergence of aerobic het-
erotrophic organisms. These aerobic organisms ended up much more efficient than
their anaerobic counterparts in sustaining life.

©2001 CRC Press LLC

Billions of years of evolution by Mother Nature have shown that the natural
communities of microorganisms in the various habitats have an amazing physiolog-
ical versatility. These communities are adaptable, flexible, versatile, and robust. They
are able to metabolize and often mineralize an enormous number of organic mole-
cules. Probably every natural product, regardless of its complexity, is degraded by
one or another species in some particular environment; if not, this long after the
appearance of life on earth, such compounds would have accumulated in enormous
amounts.
The compounds that caught the most attention in the remediation industry,
initially during the 1970s and 1980s, were the BTEX compounds released via
petroleum spills — natural products formed as the result of decomposition of plants
and other organic materials over millions of years. It has been proven during the
last decade that the BTEX compounds will naturally attenuate in the groundwater
through microbial degradation. Although certain bacteria and fungi act on a broad
range of organic compounds, no organism known to date is sufficiently omnivorous
to destroy a very large percentage of the natural chemicals.

2

Bioremediation is now a widely accepted technique for contaminant cleanup.
But a few short decades ago, its use for anything as effective as the

in situ

cleanup
of groundwater contamination was considered laughable. “At that time, there was a
myth, widely held by the geological and hydrological community, that the subsurface
was sterile, that there were no bacteria, and therefore no biological processes of
consequence”.

3

This thinking was mainly due to the information available from the
textbooks at that time.
Microbial ecology is the study of interrelationships between different microor-
ganisms; among microorganisms, plants, and animals; and between microorganisms
and their environment. Microbial biogeochemistry is the study of microbially cata-
lyzed reactions and their kinetics with emphasis on environmental mass transfer and
energy flow.
In subsequent chapters, this book summarizes and systematizes current under-
standing of abiotic and biotic transformations of organic and inorganic pollutants in
the natural environment. Knowledge of abiotic transformations can provide a con-
ceptual framework for understanding biologically mediated transformations. Most
abiotic transformations are slow, but they can still be significant within the time
scales commonly associated with groundwater movement. In contrast, biotic trans-
formations typically proceed much faster, provided the biogeochemical environment

is conducive to mediate such transformations.
The ability to predict the behavior of a chemical substance in a biological or
environmental system largely depends on knowledge of the physical-chemical prop-
erties and reactivity of that compound or closely related compounds. Chemical
properties frequently used in environmental fate assessment include melting/boiling
temperature, vapor pressure, various partition coefficients, water solubility, Henry’s
Law Constant, sorption coefficient, and diffusion properties. Reactivities by pro-
cesses such as biodegradation, hydrolysis, photoysis, and oxidation/reduction are
also critical determinants of environmental fate. Unfortunately, measured values
often are not available and, even if they are, the reported values may be inconsistent
or of doubtful validity. In this situation it may be appropriate or even essential to

©2001 CRC Press LLC

use estimation methods. The evolution of understanding of half-lives of chlorinated
aliphatic compounds and the refinement of those values by precisely measured values
have been remarkable during the last decade. Half-lives which were estimated to be
in the two to three year range have been measured in the field to be in the range of
three to six months. Later chapters describe the marked difference in the accepted
half-lives during the last decade.

1.4 EVOLUTION OF REMEDIATION TECHNOLOGIES

Remediation technologies have undergone many changes over the last two decades
during which they have been applied to clean up subsurface and hazardous waste
contamination problems. These changes have occurred at a relatively rapid pace; during
this period some of the most profound changes have occurred in how we apply remedial
technologies as a result of pressure from the industry to continuously improve technical
efficiency and cost effectiveness of the preferred technologies.
Initially contaminated groundwater was a driving concern because it was mobile

and, as a result, transported the liability off site. Also, the need to contain the
contamination on site led to universal application of pump and treat systems for
source control and mass removal. A decade of experience has taught that pump and
treat is not the solution and, in fact, is an inefficient technology for fast and cheap
site cleanup.
The realization that mass removal efficiencies can be significantly enhanced
using air as an extractive media instead of water led to the development and appli-
cation of

in situ

extractive technologies such as soil vapor extraction and

in situ

air
sparging. While it can be argued that the initial motive for applying these technol-
ogies has been one of saving money, the end result is much quicker cleanup times
to more acceptable cleanup levels (Figure 1.3). This win-win situation for the entire
remediation industry fostered continuous innovation, which led to 1) faster, cheaper
solutions, 2) less invasive

in situ

technologies, and 3) technologies complementary
to the natural environment which took advantage of nature’s capacity to degrade the
pollutants. Thus holistically, environmentally, and economically sound and sustain-
able solutions were provided.
Figure 1.4 illustrates the evolutionary reduction in remediation costs from the
late 1970s to the present time.

Ex situ

extractive techniques such as pump and treat
systems were replaced by

in situ

extractive techniques, namely, soil vapor extraction
(SVE) and

in situ

air sparging. Subsequently these

in situ

extractive techniques gave
way to

in situ

nonextractive techniques such as funnel and gate systems and, even-
tually, to

in situ

mass destruction techniques such as

in situ

reactive zones (IRZ) as
the preferred remediation technologies. This evolutionary pattern has focused
towards more natural solutions and/or enhancing existing subsurface biogeochemical
conditions that contribute to remediation.
The most recent shift occurred approximately 5 years ago, with the recognition
and demonstrated value of natural mechanisms that contributed towards the contain-
ment, control, and mass reduction of contaminants in soil and groundwater. Under a
host of names — including natural attenuation, bioattenuation, natural remediation,

©2001 CRC Press LLC

monitored natural attenuation (MNA) — this remediation approach has taken root as
a viable remediation approach at the appropriate site and under the right biogeochem-
ical conditions. Used in conjunction with already ongoing remediation systems or as
a stand-alone remedy, MNA can increase significantly the probability of a successful,
cost-effective, and well-documented restoration of a contaminated site.
The development of

in situ

reactive zones (IRZ), which are engineered

in situ

anaerobic or aerobic systems, is essentially an outgrowth of the efforts to enhance the
natural processes which contribute towards degradation of many contaminants. For
example, the use of an engineered IRZ to reductively dechlorinate chlorinated aliphatic
hydrocarbons, such as PCE and TCE, in essence, enhances the rate of natural degra-
dation by providing the optimum biogeochemical conditions (Figure 1.5).

At many contaminated sites, the bulk of the contaminant mass may still be
present in what remediation professionals call “source areas.” Even though the plume
length has reached a stable equilibrium and the contaminant concentrations have
reached steady or declining concentrations at the compliance points, it may be
desirable to enhance the rates of natural degradation if the plume has crossed the
property boundary (Figure 1.6a). Surgical reduction of the mass at the source areas
and enhancement of natural degradation along the property boundary will enable
such properties to be restored within a reasonable time frame (Figure 1.6b). The
duration of the containment IRZ at the property boundary will be significantly longer
if mass removal is not accomplished at the source area.

Figure 1.3

Evolution of

in situ

remediation technologies and improvements in efÞciencies.
Clean-Up Standards
Only When
Contaminants
Are Aerobically
Biodegradable
Time
Concentration
MNA with Source Reduction
Conventional Pump and Treat
In Situ Reactive Zones (IRZ)
In Situ Air Sparging
MNA - Monitored Natural Attenuation

©2001 CRC Press LLC

Figure 1.4

Evolution reduction in remediation costs.

Figure 1.5

Implementation of an IRZ for enhanced biodegradation has an impact on the time
towards closure in comparison to reliance on MNA.
Ex Situ Extractive
Techniques
Late 1970s - Early 1980s
Cost ($)
Capital Costs
O&M Costs
Monitored Natural Attenuation
In Situ Extractive
Techniques
Early 1980s - Late 1980s
In Situ Extractive
Techniques
Early 1990s - Present
In Situ Mass Destruction
Techniques
Mid 1990s - Present
MNA
Current
MNA

Cost ($)
Time
In Situ
Reactive Zones
Monitored Natural Attenuation
IRZ
MNA
Creation of IRZ
Natural Rate of Decline
Enhanced Rate of Decline

©2001 CRC Press LLC

Figure 1.6a

Implementation of a containment IRZ and a source reduction IRZ to reduce the
cleanup time.

Figure 1.6b

Reduction in cleanup time as a result of enhanced rate of mass removal.
Engineered IRZ
Stable Plume
Compliance
Points
Property Boundary
Source Area
In Situ
Reactive Zones
IRZ

Concentraation at Compliance Point(s)
Time
In Situ
Reactive Zones
IRZ
Creation of IRZ