vvEPA
            United States
            Environmental Protection
            Agency
            Risk Reduction
            Engineering Laboratory
            Cincinnati OH 45268
EPA/540/2-90/002
January 1990
            Superfund
Handbook on In Situ
Treatment of Hazardous
Waste-Contaminated
Soils

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                                       EPA/540/2-90/002
                                          January 1990
     Handbook on In Situ Treatment
of Hazardous Waste-Contaminated Soils
                    „*»! Protection
         U g. Enviroraaeatftl wo
         ?..:*lon 5,       WL ,o
       Risk Reduction Engineering Laboratory
       Office of Research and Development
       U.S. Environmental Protection Agency
             Cincinnati, Ohio 45268

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                                         Notice


This material has been funded wholly or in part by the United States Environmental Protection Agency
under contract 68-03-3413 to PEI Associates, Inc.  The document has been subjected to the Agency's
peer and administrative review, and it has been approved for publication as an EPA document.  Mention
of trade names or commercial products does not constitute endorsement or recommendation for use.

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                                        Contents

                                                                             Page
Executive Summary                                                              v
Acknowledgments                                                                xi
1.  Introduction                                                                    1
       1.1 Purpose                                                              1
       1.2 Background                                                           1
       1.3 Special Considerations for In Situ Treatment                               2
       1.4 Overview of Handbook                                                 2

2.  Legislative and Regulatory Overview                                              3
       2.1 Comprehensive Environmental Response, Compensation,
           and Liability Act                                                        3
       2.2 Superfund Amendments and Reauthorization Act                          3
       2.3 National Contingency Plan                                              4

3  Technologies for In Situ Treatment                                                7
       3.1 Soil Flushing                                                           7
              3.1.1 Status of the Technology                                       8
              3.1.2 Secondary Impacts                                           10
              3.1.3 Equipment, Exogenous Reagents, and Information
                    Required                      .                              10
              3.1.4 Advantages  of Soil Flushing                                   11
              3.1.5 Disadvantages of Soil Flushing                                 11
       3.2 Solidification and Stabilization                                           11
              3.2.1 Solidification/Stabilization Techniques                          12
              3.2.2 In Situ Vitrification                                            17
       3.3 Degradation                                                          19
              3.3.1 Chemical Degradation                                        19
              3.3.2 Biological Degradation                                        36
              3.3.3 Photolysis                                                   68
       3.4 Control of Volatile Materials                                             78
              3.4.1 Soil Vapor Extraction                                          78
              3.4.2 Radio Frequency Heating                                     83
              3.4.3 Soil Cooling                                                  85
       3.5 Chemical and Physical Separation Techniques                           86
              3.5.1 Permeable Barriers                                           86
              3.5.2 Electrokinetics                                               90
              3.5.3 Ground Freezing                                             93
                                              in

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                                    Contents (continued)
                                                                                Page
4.  Delivery and Recovery Systems                                                  96
       4.1 Hydraulic Fracturing                                                    96
       4.2 Radial Well Drilling                                                     97
       4.3 Ultrasonic Methods                                                     98
       4.4 Kerfing                                                                99
       4.5 Jet-induced Slurry Method                                               99
       4.6 Carbon Dioxide Injection                                               100
       4.7 Hot Brine Injection                                                     101
       4.8 Cyclic Pumping                                                       102

References                                                                      103
Bibliography                                                                     125
Appendix A. Modification of Soil Properties                                          143
Index                                                                           152
                                               IV

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                                    Executive Summary

 Purpose and Scope

        This handbook comprises an update of Volume 1 of the 1984 USEPA document entitled "Review
 of In-Place Treatment Techniques for Contaminated Surface Soils." The purpose of this handbook is the
 same as that of the original document - to provide state-of-the-art information on in situ treatment tech-
 nologies for contaminated soils. Like the previous document, this handbook is written for the use of a
 varied audience with diverse technical backgrounds.

        The information presented herein is detailed enough to provide the reader with adequate data for
 an initial evaluation of the applicability of a technology in certain situations, yet general enough to be
 useful and informative to those whose backgrounds are not highly technical.  Extensive references are
 provided for the reader's use in obtaining additional details on these technologies.

        An in situ treatment technology is defined as one that can be applied to treat the hazardous
 constituents of a waste or contaminated environmental medium where they are located and is capable of
 reducing the risk posed by these contaminants to an acceptable level or completely eliminating that risk.
 In situ treatment implies that the waste materials are treated without being physically removed from the
 ground.

        The handbook is divided into four sections. Section 1 provides an introduction and background
 for the handbook. Section 2 provides a general overview of the legislation and regulations pertaining to
 Superfund site remedial activities that have been instrumental in promoting the development of in situ
 treatment technologies. Section 3 presents state-of-the-art information on in situ treatment technologies.
 It includes a description of each technology process; the wastes amenable to treatment; the ease of
 application; potential level of treatment available; reliability of the  method; current status of the technol-
 ogy; secondary impacts; equipment, exogenous reagents, and information required; and sources of
 information.  Section 4 addresses delivery and recovery technologies.  A brief discussion of techniques
 for the modification of soil properties is presented in the appendix.

        The 1984 document consisted of two volumes.  Only Volume 1 is being updated by this hand-
 book. The reader can refer to Volume 2, however, for a still current and comprehensive discussion of the
 fundamental properties of soil/waste systems.

 Legislative and Regulatory Overview

        Methods for cleaning up hazardous waste sites  have changed since 1980 when the Comprehen-
 sive  Environmental Response, Compensation, and Liability Act (CERCLA), or Superfund, was enacted.
 Early remedial actions for contaminated soils consisted primarily of excavation and removal of the con-
taminated soil from the  site and disposal at a landfill. Congress has recently enacted legislation that
prohibits the land disposal of hazardous wastes unless the USEPA determines otherwise [i.e., Hazardous
and Solid Waste Amendments (HSWA)] and encourages permanent treatment of contaminated sub-
stances [i.e., Superfund Amendments and Reauthorization Act (SARA)]. In many cases, in situ treatment
of contaminated soils and hazardous waste can effect permanent and significant reductions in the vol-
ume, toxicity, and mobility of hazardous substances.

        Remediation of hazardous waste sites requires striking a  balance between the desire to charac-
terize site risks quickly and to analyze alternative remedial approaches to begin the cleanup while still
meeting all the CERCLA mandates.  In the proposed revision of the National Contingency Plan (NCP)

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EPA fulfills both of these requirements through an approach that examines the characteristics of sites and
evaluates alternative methods for remediation in a streamlined remedial action process.
       Treatment alternatives are subjected to detailed analysis consisting of a complete assessment of
each alternative as it relates to nine criteria encompassing the recommendations and mandated require-
ments of CERCLA as amended by SARA. These criteria are as follows:
       1)  Overall protection of human health and the environment
       2)  Compliance with applicable or relevant and appropriate requirements (ARARs)
       3)  Long-term effectiveness and permanence
       4)  Reduction of toxicity, mobility, or volume
       5)  Short-term effectiveness
       6)  Implementability
       7)  Cost
       8)  State acceptance
       9)  Community acceptance
In Situ Treatment Technologies
       Detailed information on specific in situ treatment technologies in the following categories is
provided:
       •  Soil flushing
       •  Solidification/stabilization
       •  Degradation
       •  Control of volatile materials
       •  Chemical and physical separation techniques
       Table ES-1 summarizes the in situ treatment technologies discussed in the handbook in relation
to the waste amenable to treatment and the status ol the technology development.
Soil Flushing
       Soil flushing is the washing of contaminants  from the soil with a suitable solvent such as water or
other aqueous or nonaqueous solutions. The method is potentially applicable to  all types of soil contami-
nants.  Several bench- and pilot-scale studies have been completed on the effectiveness of soil flushing.
Soil flushing in conjunction with bioremediation may  be a cost-effective means of soil remediation at
certain sites. Soil flushing enables permanent  removal of contaminants from the soil and is most effective
in permeable soils. The technology can introduce potential toxins into the soil system. An effective col-
lection system is required to prevent contaminant migration.
Solidification and Stabilization
       Solidification and stabilization refer to treatment processes that are designed to accomplish one
or more of the following:
       •  Improve handling and physical characteristics of the waste by producing a solid from liquid or
         semiliquid wastes.
       •  Reduce contaminant solubility in the treated waste.
       •  Decrease the  exposed surface area  across which transfer or loss of contaminants may occur.
                                              VI

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 Table ES-1.  Summary Matrix of Treatment Technologies

 Technology	Wastes amenable to treatment
                                                      Status
 Soil Flushing

 Solidification/stabilization
  Pozzolan-portiand cement
  Lime-fly ash pozzolan
  Thermoplastic microencapsulation
  Sorption
  Vitrification

 Degradation

 Oxidation
  Soil catalyzed reactions
  Oxidizing agents

 Reduction
  Organics

  Chromium
  Selenium
  Dechlorination

 Polymerization
 Biodegradation
  Colloidal gas aphrons
  Soil moisture
  Soil oxygen - aerobic
  Soil oxygen - anaerobic
  Soil pH
  Nutrients
  Temperature

 Nonspecific organic amendments

 Cometabolism
  Analogue enrichment
  Nonanalogue enrichment
  with methane
  Other nonanalogue
  hydrocarbon substrates

 Exogenous acclimated or
  mutant microorganisms

 Cell-free enzymes

 Photolysis
  Proton donors
 Enhanced volatilization

Control of volatile materials
 Soil vapor extraction
 Radio frequency heating
 Soil cooling

Chemical and physical  separation
 Permeable barriers
 Electrokinetics
 Ground freezing	
 Soluble organics and inorganics
 Inorganics
 Inorganics
 Inorganics, organics
 Inorganics
 Metals, inorganics, organics
Aliphatic organics, other organics
Various organics
Chlorinated organics,
 unsaturated aromatics, ahphatics
Hexavalent chromium
Hexavalent selenium
PCB, dioxin, halogenated compounds

Aliphatics, aromatics, oxygenated organic
 compounds
Organics
Organics
Organics
Halogenated organics
Organics
Organics
Organics

Organics, arsenite wastes
Some organics with analogues
Chlorinated solvents

Organics
Various organics


Organics
Some organics, including TCDD, kepone, PCB
Specific organics
Volatile, semivolatile organics
Solvents and fuels
Volatile organics
Organics and inorganics
Ionic metal species
Volatile organics	
 Pilot scale
 Pilot scale
 Pilot scale
 Laboratory
 Pilot scale
 Pilot scale
Limited field
Field scale
Field scale

Limited field
Limited field
Limited field

Limited field
Bench and pilot
Field scale
Field scale
Conceptual
Field scale
Field scale
Field scale

Laboratory
Laboratory
Laboratory

Laboratory
Field scale
Laboratory
Field scale
Laboratory
Field scale
Pilot scale
Bench scale
Bench, pilot scale
Pilot scale
Bench scale
                                                         vii

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       Solidification techniques eliminate the free liquid, increase the bearing strength, decrease the
surface area of the waste material, and produce a monolithic solid product of high structural integrity.
Solidification may involve encapsulation of fine waste particles (microencapsulation) or large blocks of
wastes (macroencapsulation). Chemical interactions do not necessarily occur between the wastes and
the solidifying agents, but the waste material is mechanically bound within the solidified matrix in such a
way that hazardous substances cannot be released upon exposure to air, water, soil, or mild acidic
conditions.

       Stabilization refers to the process of reducing the hazardous potential of waste material by
converting the contaminants into their least soluble, mobile, or toxic form. This technique does not
necessarily change the physical characteristics of the waste.

       Solidification/stabilization techniques have been widely used in low-level radioactive waste
disposal. Their application to hazardous wastes is becoming more common, however, and many vendors
are studying and developing processes that are directly applicable to  hazardous waste-contaminated soils
and sludges.

       Waste solidification/stabilization systems that are potentially useful in remedial action activities
are as follows:

       • Pozzolan-portland cement systems

       • Lime-fly ash pozzolan  systems

       • Thermoplastic microencapsulation

       • Sorption

       • Organic binding

       In situ vitrification is a thermal treatment process by which contaminated soils are converted into
chemically inert and stable glass and crystalline materials.  Large electrodes are inserted into contami-
nated soils, and heat (up to 3600°C) is generated by passing electric  current through the electrodes.  In
situ vitrification has been used to stabilize low-level radioactive wastes.

Degradation

       Chemical degradation, biodegradation, and photolysis may be effective in situ treatment
technologies.

Chemical Degradation

       Oxidation, reduction, dechlorination, and polymerization reactions may be carried out in situ to
transform soil contaminants into  less toxic or less mobile products.

       Chemical oxidation increases the oxidation state of an atom by removing electrons or adding
oxygen to the atom. Oxidation may cause a substance to be transformed, degraded, or immobilized in
soil.  Oxidation reactions within the soil matrix may occur through management of the natural processes
in a soil or through addition of an oxidizing agent to the soil-waste complex.

       Chemical reduction is a process in which the oxidation state of an atom is decreased. Reducing
agents are electron donors, and  reduction is accomplished by the addition of electrons to the atom.
Reduction of chemicals may occur naturally within the  soil system. Certain compounds are more suscep-
tible to reduction than others  because they will accept  electrons. The addition of reducing agents to soil
to degrade reducible compounds can be used as an in situ treatment technology.

       Chemical dechlorination processes use specially synthesized chemical reagents to destroy
hazardous chlorinated molecules or to detoxify them to form other compounds that  are considered less
harmful.  In recent years, several dechlorination processes using different reagents have been developed
                                                VIM

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to detoxify PCBs and many chlorinated organic compounds. These processes were first developed for
the treatment of PCB-containing oils, but several have potential application to in situ treatment of contami-
nated soils.

       A polymerization reaction is the conversion of a particular compound to a larger chemical multiple
of itself. The resulting polymer often has physical and chemical properties different from the initial unit,
and it could be less mobile in the soil system.  Chemical polymerization is most effective for immobiliza-
tion of organic constituents, preferably those with more than one double bond. General categories of
constituents suitable for polymerization include aliphatic, aromatic, and oxygenated monomers such as
styrene, vinyl chloride, isoprene, and acrylonitrile.

Biodegradation

       Biodegradation refers to the breakdown of organic compounds in soils by the action of microor-
ganisms such as bacteria, actinomycetes, and fungi. Treatment generally consists of optimizing condi-
tions of pH, temperature, soil moisture content, soil oxygen content, and nutrient concentration to stimu-
late the growth of microorganisms that will feed on the particular contaminants present. Alternatively,
genetically engineered organisms may be added to the soil system and conditions established within the
soil to optimize their growth.  Some of the hazardous constituents present in a contaminated soil may be
most readily biodegraded under aerobic conditions, whereas others are more readily degraded under an-
aerobic conditions. Treatment might, therefore, consist of alternate aerobic and anaerobic cycles.

Photolysis

       Photochemical reactions require the absorption of light energy, generally from sunlight in natural
systems. Because light does not penetrate very far into soils, photodegradation of soil contaminants is
limited to soil surfaces. The addition of proton donors in the form of polar solvents such as methanol can
enhance surface photodegradation of soil contaminants.

Control of Volatile Materials

       Concentrations of volatile materials can be reduced by the use of various vapor extraction sys-
tems. Vapor extraction systems involve the recovery of volatile contaminants by injecting air or steam
into the soils and extracting the air (in which volatile chemicals have partitioned) in a vapor-recovery well.

       Radio frequency (RF) heating is a technique for rapid and uniform in situ heating of large volumes
of soil. It can be used to volatilize materials such as chlorinated solvents and the aliphatic and aromatic
fractions of jet fuels and gasoline.  The volatilized  materials are then collected and treated.

       Soil cooling may be used to decrease soil temperatures as a means of reducing the vapor
pressure of volatile constituents and thus their volatilization rates.  Cooling agents are applied, such as
dry ice cr liquid nitrogen. This technology is currently in the bench-scale stage of development.

Chemical and Physical Separation Techniques

       Chemical contaminants can be removed from soil particles by physical and chemical means.
This subsection discusses three such techniques:  1) permeable barriers, 2) electrokinetics, and 3)
ground freezing.  (Although permeable barriers are not directly used for soil treatment, the technology is
an important in situ method for treating hazardous waste landfill leachate and is thus presented here.)

       Migration of leachate from hazardous waste deposits (i.e., landfills) presents a significant ob-
stacle in attempts to remediate hazardous waste sites. Permeable barriers, which may be used to retain
contamination within site boundaries, represent a potentially effective method of in situ treatment.  The
technology incorporates the use of readily available materials to adsorb contaminants from ground water
as the contaminated plume migrates through the permeable barrier unit.

       Electrokinetics has been used for more than 50 years to dewater and stabilize soils.  It is hoped
that it will produce similar results at hazardous waste sites.  An electrokinetic phenomenon referred to as
electroosmosis occurs when a liquid migrates through a charged  porous medium under the influence of a
                                               IX

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charged electrical field. The charged medium is usually some kind of clay, sand, or other mineral par-
ticles that characteristically carry a negative surface charge. When the charged particles come into
contact with water molecules, they attract positive ions, which effectively neutralize their negative surface
charge.  As a result, cations predominate in the layer of water next to the surfaces of the particles and
create what is referred to as a "diffuse double layer."

       If an electric field is applied to the saturated medium through anodes, cations bound in the diffuse
double layer will migrate toward the negatively charged cathode. The viscous drag of water molecules
due to the migration of the cations produces a net flow of water toward the cathode.  The application of an
electrical field induces the water to flow.

       Artificial ground freezing has been shown in laboratory studies to be a potentially effective
method of driving volatile organic contaminants from soil matrices. Artificial ground freezing was used to
facilitate decontamination of soils and the dewatering of slurries in the bench-scale demonstration.
Contaminants are removed from soils by utilizing the differences in physical and chemical properties of
the water and contaminants within the soil.

Delivery and Recovery Systems

       Delivery and recovery technologies refer to methods that facilitate the transport of materials either
into or out of the subsurface.  Delivery and recovery techniques are integral to some of the in situ treat-
ment technologies such as biodegradation, vapor extraction, and solidification/stabilization.  Delivery and
recovery technologies have been developed largely by the petroleum and mining  industries. Research is
currently under way to adapt some of these techniques to the treatment of  hazardous wastes.

Time Frame

       This report covers  a period from May 1988 to  July 1989, and work was completed as of Novem-
ber 1989.

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                                   A cknowledgments


       This handbook was prepared for the U.S. Environmental Protection Agency, Office of Research
and Development, Risk Reduction Engineering Laboratory, Cincinnati, Ohio by PEI Associates, Inc. and
the University of Cincinnati under Contract No. 68-03-3413.  The authors were Catherine D. Chambers,
Jeffrey Willis, Steve Giti-Pour, and Janet L. Zieleniewski of PEI and Janet F. Rickabaugh,
Maria I. Mecca, and Berna Pasin of the University of Cincinnati. Other PEI staff contributing were
Martha H. Phillips, technical editor, Laura E. Biddle, information processing, and Joy Wallace, lay-out.

       Ms. Naomi P. Barkley served as the EPA Technical Project Monitor for Phase I of this work and
Dr. Michael Roulier served as the EPA Technical Project Monitor for Phase II. Mr. Herbert R. Pahren of
EPA provided direct technical guidance throughout the development of the document. Technical
reviewers were Dr. Ronald C. Sims of the Utah State University and Dr. Danny R. Jackson of Radian
Corporation.
                                            XI

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                                         Section 1
                                        Introduction


1.1  Purpose

       This handbook comprises an update of Volume 1 of the 1984 document entitled "Review of In-
Place Treatment Techniques for Contaminated Surface Soils" (Sims and Bass 1984). The purpose of
the original document was to provide state-of-the-art information on in situ treatment technologies for
contaminated soil.  Like the previous document, this handbook is written for the use of a varied audi-
ence with diverse technical backgrounds, such  as On-Scene Coordinators (OSCs), Remedial Project
Managers (RPMs), State and local regulatory personnel, and others involved in the selection of reme-
dial actions for soils contaminated by hazardous substances.

       The information presented herein is detailed enough to provide the reader with adequate data
for an initial evaluation of the applicability of a technology in certain situations, yet general enough to be
useful and informative to those whose backgrounds are not highly technical.  Extensive references are
provided, and the reader is encouraged to seek additional details from these sources.

       For purposes of this handbook, an in situ treatment technology is defined as one that can be
applied to treat the hazardous constituents of a contaminated environmental medium where they are
located and is capable of reducing the risk posed by these contaminants to an acceptable level or
completely eliminating that risk. In situ treatment implies that the waste materials (i.e., contaminated
soils) are treated without being physically removed from the ground. In situ removal, that is removing
contaminants without removing the soils, is also discussed in this handbook.

       The technologies presented in this handbook have been demonstrated at various levels ranging
from bench or laboratory scale to field implementation.  Although some of the technologies addressed
have not been tested in situ, they are presented here because their in situ application may be feasible in
the future.

1.2  Background

       Legislation, recently promulgated regulations, and the high costs associated with treating large
volumes of contaminated soils have prompted the development of technologies for the in situ treatment
of contaminated soils and other hazardous wastes.  The original report (Sims and Bass 1984) described
large numbers of chemical and physical processes (e.g., oxidation, reduction, precipitation, ion ex-
change) that have potential for in situ application to immobilize or detoxify contaminants in the soil.
Many of these technologies were conceptual in nature or had been tested only at the bench scale. Most
of the technologies involve aqueous solution chemistry, and it was  hoped that workable in situ treatment
would be developed along these lines.  Instead, major developments have involved biodegradation, so-
lidification/stabilization, and removal of contaminants.

       Another area of significant research concerns delivery and recovery technologies, i.e., proc-
esses that facilitate the transport of materials either into or out of the subsurface. Murdoch et al. (1988)
define delivery technologies as involving "the transport of materials into the subsurface.  Liquids are the
principal phase used in most delivery operations, although some of the new techniques will allow either
vapor or solid phases to be delivered as well."  Similarly, recovery technologies are described as
including "any process used to remove materials from the subsurface. The principal recovery technolo-

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gies used for remediation are associated with fluid flows driven by hydraulic gradients."  Also used are
"... technologies driven by other types of processes, such as thermal methods, as well as processes that
expedite recovery by chemical reactions that alter the behavior of contaminants."

        Delivery and recovery techniques are integral to some of the in situ treatment technologies,
such as bioremediation, vapor extraction, and solidification/stabilization. Delivery and recovery tech-
nologies have been developed largely by the petroleum and mining industries. Research is currently
under way to adapt some of the delivery/recovery techniques to the treatment of hazardous wastes.
The preliminary research is discussed in this document.

1.3 Special Considerations for In Situ Treatment

        The mechanism of in situ treatment may be physical, chemical, thermal, biological, or a combi-
nation of these. The location of treatment (i.e., in situ), however, imposes unique constraints on the
application and effectiveness of the treatment process. Thorough site characterization is critical to the
proper evaluation of the feasibility of applying any in situ treatment technology. The site characteriza-
tion (i.e., physical, chemical, and biological characteristics) should be tailored to the specific technology
under consideration. Bench- and pilot-scale treatability studies should be designed and conducted with
site characteristics in mind. There are several guidance documents available concerning site charac-
terization and treatability testing (USEPA 1985; Amdurer et al. 1986; USEPA 1988) that should be
referred to during the remedial action process to ensure a rational approach  to the selection, design,
and implementation of specific in situ treatment technologies.

        Monitoring the effectiveness of the in situ treatment process also requires special consideration
and planning and could have a major impact on the overall cost of implementing an in situ treatment
technology.  Subsurface geologic and hydrologic conditions may cause treatment agents to be diverted
away from target areas and thus limit treatment effectiveness.  Numerous samples  may need to be
collected and analyzed to verify the uniformity and successfulness of treatment. A carefully developed
sampling strategy will be necessary as part of the technology implementation.

1.4 Overview of the Handbook

        The handbook is divided into four sections.  Section 2 provides a general overview of the
legislation and regulations pertaining to Superfund site remedial activities that have been instrumental in
promoting the development of in situ treatment technologies. Section 3 presents state-of-the-art infor-
mation on in situ treatment technologies.  It includes a description of each technology or process; the
wastes amenable to treatment; the ease of application; potential level of treatment available; reliability of
the method; current status of the technology; secondary impacts; equipment, exogenous reagents,
and information required; and sources of information.  Section 4 addresses delivery and recovery
technologies. A brief discussion of techniques for the modification of soil properties is presented in the
appendix.

        The 1984 document consisted of two volumes. Only Volume 1 is being updated by this hand-
book. The reader can refer to Volume 2 (Sims 1984), however, for  a still current and comprehensive
discussion of the fundamental properties of soil/waste systems. The discussion includes physical soil
properties, soil sorption, soil microbiology, and volatilization and degradation as related to hazardous
waste treatment in soil systems.

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                                       Section 2
                        Legislative and Regulatory Overview


       Methods for cleaning up hazardous waste sites have changed since 1980 when the Compre-
hensive Environmental Response, Compensation, and Liability Act (CERCLA), or Superfund, was
enacted.  Early remedial actions for contaminated soils consisted primarily of  excavation and removal
of the contaminated soil from the site and disposal at a landfill. This, in effect, moved the problem from
one location to another. Subsequent findings of leaking landfills and heightened public concern about
the problem have resulted in a shift in public policy concerning cleanup of hazardous waste sites.
Specifically, Congress has enacted legislation that prohibits the land disposal of hazardous wastes
unless EPA determines otherwise [i.e., Hazardous and Solid Waste Amendments (HSWA)] and encour-
ages permanent treatment of contaminated substances [i.e., Superfund Amendments and Reauthoriza-
tion Act (SARA)].

       In many cases, in situ treatment of contaminated soils and hazardous waste can effect perma-
nent and significant reductions in the volume, toxicity, and mobility of hazardous substances.  The U.S.
Environmental Protection Agency (EPA) Office of Research and Development, through several research
studies such as the Superfund Innovative Technology Evaluation (SITE) Program and the SARA Best
Demonstrated Available Technology (BOAT) Program, is investigating promising treatment technologies
for contaminated Superfund site soils. In  situ treatment technologies are also  being developed and
tested in Europe and Japan. A NATO/CCMS program has been instituted to study technologies for the
treatment of contaminated ground water and soils.

       The following sections present a general overview of the legislation and regulations that have
influenced the development of some of the in situ treatment technologies for the treatment of hazardous
waste.

2.1 Comprehensive Environmental Response,  Compensation, and Liability Act

       In 1980, Congress enacted CERCLA, the first comprehensive Federal law addressing releases
of hazardous substances into the environment.  The primary goal of CERCLA (or Superfund), was to
establish an organized cost-effective mechanism for responding to releases of hazardous substances or
to abandoned or uncontrolled hazardous waste sites that posed a serious threat to human health and
the environment. To accomplish this goal, CERCLA mandated two types of response capabilities:
1) an emergency response action for handling major chemical spills or incidents requiring immediate
action, and 2) a remedial response capability for undertaking the long-term cleanup of abandoned
hazardous waste disposal sites. The regulatory framework developed to guide these responses be-
came the new National Contingency Plan (NCP). Revised in 1982 and again in 1985, the NCP first
outlined the level of cleanup necessary at a Superfund site and established basic procedures to be
followed for discovery or notification, response,  and remediation of a hazardous waste site (Hall and
Bryson 1985).

2.2 Superfund Amendments and Reauthorization Act

       The Superfund Amendments and Reauthorization Act of I986 (SARA)  added several important,
new dimensions to CERCLA, such as increased emphasis on health assessments  and consideration of
air releases.  One of the most far-reaching provisions, however, Section 121, Cleanup Standards, which

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stipulates rules for the selection of remedial actions, provides for a review of those actions, describes re-
quirements for the degree of cleanup, and mandates conformance with the National Contingency Plan
whenever practicable. It strongly recommends that remedial actions use onsite treatment that
"... permanently and significantly reduces the volume, toxicity, or mobility of hazardous substances ..."
and requires selection of a remedial action that is"... protective of human health and the environment,
that is cost-effective, and that utilizes permanent solutions and alternative treatment technologies or re-
source recovery technologies to the maximum extent practicable" (PL 99-499).

       Another SARA requirement is that remedial actions meet all applicable  or relevant and appropri-
ate (ARAB) Federal standards and any more stringent State standards. "Applicable requirements" refer
to those standards, requirements, criteria, or limitations that specifically address a hazardous sub-
stance, pollutant, contaminant, remedial action, location, or other circumstance  at a CERCLA site.
"Relevant and appropriate requirements" refer to those cleanup  standards that,  although not applicable,
address problems or situations sufficiently similar to those encountered at the site so that their use is
suitable.

       As amended by SARA, CERCLA sets rigorous remedial-action cleanup standards.  It empha-
sizes achieving protection that will endure by mandating the use of permanent solutions, and it ex-
presses a clear preference for achieving this protection through  the use of treatment technologies as the
principal element of remediation.  Clearly, the most permanent solution is attained by remedies that do
not rely heavily on long-term operation and maintenance; however, because of  the variety of releases
and threats encountered at hazardous waste sites, specific remedial actions and cleanup levels must
be determined on a site-by-site basis. The function of the National Contingency Plan is to delineate how
such site-specific decisions will be made.

2.3  National Contingency Plan

       Remediation of hazardous waste sites requires striking  a balance between the desire to charac-
terize site risks quickly and to analyze alternative remedial approaches to begin the cleanup while still
meeting all the CERCLA mandates.  In the proposed revision of the National Contingency Plan
(USEPA1988),  EPA fulfills both of these requirements through an approach that examines the charac-
teristics of sites and evaluates alternative methods for remediation in a streamlined remedial action
process.  The five steps  involved  in this process are as follows:

       1) Project scoping
       2) Remedial investigation
       3) Feasibility study
       4) Selection of an action
       5) Documentation

       The first step, project scoping, is the development and planning phase  of the project. It involves
defining the appropriate type and extent of investigative and analytical studies that should be under-
taken. During this phase, the remedial investigation and feasibility studies  are planned and a prelimi-
nary site characterization is developed.  Both the quality and the quantity of data necessary for a full site
evaluation should be determined, and studies that will result in these data should be selected.  Potential
ARARs are identified, and preliminary remediation objectives for the protection  of human health and the
environment are formulated.

       The purpose of a remedial investigation, the second step, is to gather sufficient data to charac-
terize the site conditions and to assist in the selection of an appropriate response action. Of particular
interest are any data that will affect the type and extent of possible treatment or recycling approaches.
Preliminary treatability studies should be performed to make a better evaluation of potential technolo-
gies.  A site-specific baseline risk assessment consisting of an exposure assessment and a toxicity as-
sessment is also initiated during the remedial investigation.  Chemical-specific toxicity information is
analyzed along with critical assumptions and uncertainties so that all significant risks can be identified.

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        The third step, the feasibility study, is the real heart of the remedial action process. During this
phase, viable remedial alternatives are analyzed based on nine criteria related to CERCLA's mandates.
In the selection of these alternatives, the lead agency must first refine the remedial action objectives
developed during the planning stage. Contaminants and media of concern, potential exposure path-
ways, and remediation goals should be specified.  Risks associated with potential alternatives are
assessed based on a reasonable maximum exposure scenario that will insure that exposure levels are
both protective and attainable. Once these objectives have been established, potential technologies are
identified, briefly evaluated to verify their suitability, and assembled into remedial alternatives.

        The range of alternatives selected for detailed analysis should represent distinct, promising
approaches to managing site problems. In view of the statutory preference for treatment remedies, this
range should include alternatives that feature treatments that will reduce the toxicity, mobility, or volume
of the hazardous substance at the site. Included in CERCLA is the flexibility to examine and select
technologies not yet proven in practice to promote the development of new methods of hazardous waste
treatment. Thus, innovative technologies may also be selected for detailed analysis if these technolo-
gies are believed to offer significant advantages over other options being considered.

        The number and type of remedial alternatives should be tailored to fit the site and the remedial
action objectives. The variety of options considered should not be limited simply because of quantity.
Should a preliminary screening become necessary to reduce the number of alternatives analyzed in
detail, however, the primary factors for consideration are effectiveness, ease of implementation, and
cost. Effectiveness refers to the overall potential of a technology to eliminate, reduce, or control current
and potential risks; ease of implementation includes technical, administrative, and logistical problems.
Cost should be considered in conjunction with other factors to determine whether an option is likely to
yield cost-effective results.

        Viable treatment alternatives that have  fulfilled the aforementioned requirements are subjected
to a detailed analysis, i.e.,  a complete assessment of each alternative as it relates to nine criteria
encompassing the  recommendations and mandated requirements of CERCLA as amended by SARA.
These criteria are as follows:

        1) Overall protection of human health and the environment. Mandated by CERCLA, this is the
          primary goal of any remediation program. A selected remedy must adequately eliminate,
          reduce, or control all current and potential risks.

        2) Compliance with applicable or relevant and appropriate requirements (ARARs). Also as
          mandated by CERCLA, Federal and State agencies must cooperate to identify ARARs early
          in the remediation process. Remedial actions must be in compliance with other environ-
          mental and public health laws.

       3) Long-term effectiveness and permanence.  Analysis should focus on the residual risks that
          will remain at the site after completion of the remedial action. Consideration should be given
          to any long-term management requirements, the reliability of any necessary controls, and the
          potential need for replacement of the remedy.

       4) Reduction of toxicity,  mobility, or volume. The reduction potential of treatment methods
          should be compared in terms of magnitude, significance, and  irreversibility.  Persistence,
          toxicity,  mobility, and bioaccumulation tendencies of any residuals must be considered.

       5) Short-term effectiveness. The environmental impact of implementing  a treatment must be
          evaluated, including the effectiveness and reliability of mitigative measures used to
          protect the health and welfare of workers and the  community.

       6) Implementability.  The technical and administrative feasibility of treatment alternatives must
          be analyzed. Items such as seasonal constraints, availability of materials, equipment, or
          services, and operational reliability are all factors that must be weighed.

       7) Cost. Cost considerations encompass all construction and operation and maintenance costs
          incurred over the life of the project.  A remedy must be cost-effective in that its overall effec-
          tiveness is proportionate to its total costs.

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       8) State acceptance.  Substantial and meaningful State involvement is a statutory requirement.
          States should be involved in all phases of the remediation process, including initiation, devel-
          opment, and selection of a remedial action.

       9) Community acceptance. Although difficult to assess before the public hearings, considera-
          tion must be given to any issues that might concern the community. Groups specifically af-
          fected by a site have the statutory right to participate in the selection of a remedy.

       These criteria fall  into three groups: threshold, balancing, and modifying criteria.  Protection of
human health and the environment and compliance with applicable or relevant and appropriate require-
ments (ARARs) are threshold requirements that must be met. Long-term effectiveness and perma-
nence; reduction of toxicity, mobility, or volume; short-term effectiveness; implementability; and cost are
balancing factors used to weigh major tradeoffs between viable strategies. State and community accep-
tance are modifying considerations.

       To complete the fourth step in the process, the lead agency must consider the advantages and
disadvantages of each treatment alternative and balance the major tradeoffs to select the method that
offers the best combination of attributes and is most appropriate for a given site. The proposed plan
issued for public comment and review will identify the alternative selected, summarize the decision-
making process, and allow for  public participation.

       The final phase of the  remedial action process involves documenting the assessment (particu-
larly how the nine criteria were used to select the  remedy) and results in a record of decision  (ROD).

       Thus, the entire remedial action process follows the natural progression of investigation, analy-
sis, and remediation, with  the protection of human health and the environment  kept foremost  in all
decisions.

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                                           Section 3
                            Technologies for In Situ Treatment
        This section presents detailed information on specific in situ technologies that were selected for
their potential or demonstrated ability to augment natural soil processes. The discussions are divided
into the following treatment categories: soil flushing, solidification/stabilization, degradation, control of
volatile materials, and physical and chemical separation techniques.

        Remediation of hazardous waste sites can involve implementing several treatment technologies
in series or what is called a treatment train. This approach may allow for a more comprehensive
remediation than a single technology could provide.  An example of this is product recovery by pumping
free product to the surface, followed by soil flushing and pumping and treating on the surface, and sub-
sequent in situ treatment of the residual materials by biodegradation.

3.1  Soil Flushing

        The use of soil flushing to remove soil contaminants involves the elutriation of organic and/or
inorganic constituents from soil for recovery and treatment.  The site is flooded with the appropriate
washing solution, and the elutriate is collected in a series of shallow wellpoints or subsurface drains.
The elutriate is then treated and/or recycled back into the site.  During the elutriation process, contami-
nants are mobilized into the flushing solution  by way of solubilization, formation of emulsions, or a
chemical reaction with the flushing solution (USEPA1985).  Collection of elutriate is required to prevent
uncontrolled contaminant migration through uncontaminated soil and into receiver systems, including
ground and surface waters. Figure 1 presents an example of a soil flushing system with elutriate
recycling.

        Flushing solutions may include water, acidic aqueous solutions (sulfuric, hydrochloric, nitric,
phosphoric, and carbonic acid), basic solutions (e.g., sodium hydroxide), and surfactants (e.g., alkylben-
zene sulfonate). Water can be used to extract water-soluble or water-mobile constituents. Acidic
solutions are used for metals recovery and for basic organic constituents (including amines, ethers,

Figure 1. Schematic of an elutriate recycle system.
                                   Spray
                                Application
                                                   Pump
                                                                                Q
            Water
            Table
          Storage
Waste      pond
                                                                             Well
               Leachate

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and anilines); basic solutions for metals (including zinc, tin, and lead); and basic solutions for some
phenols, complexing and chelating agents, and surfactants (USEPA 1985).

        The addition of any flushing solution to the system requires careful management and knowledge
of reactions that may adversely affect the soil system.  For example, a sodium addition as sodium
hydroxide to soil systems may adversely affect soil permeability by affecting the soil sodium absorption
ratio.  It is not only important to understand the chemical reaction(s) between the solvent and solute, but
also between the solvent and the site/soil system.

        At a site contaminated by organic constituents, recycling the elutriate  back through the soil for
treatment by biodegradation may be possible.  Proper control of the application rate, based on hazard-
ous waste land treatment principles (USEPA 1983), would provide for effective in situ treatment at soil
concentrations that would allow controlled biodegradation of the waste constituents. This approach
could eliminate the need for separate processes for treatment and disposal of the collected waste
solution, or at least provide for a combination of pretreatment/land application that may be considerably
more economical than the  use of unit operations alone for treatment of elutriate.

        For soils contaminated with inorganic and organic constituents, a combination of pretreatment
that reduces or eliminates the metal constituent(s) in the elutriate by precipitation, followed by a land
application of the elutriate, may be a feasible cost-effective method of treatment.

        Soil flushing and elutriate recovery may also be appropriate in situations where chemical
oxidizing or reducing agents are used to degrade waste constituents chemically and result in the
production of  large amounts of oxygenated, mobile, degradation products. The most conservative and
safest approach may be to flush the soil after treatment to recover and possibly to reapply the elutriate
in a controlled manner to the soil surface.

        Both inorganics and organics are amenable to soil flushing treatment  if they are sufficiently
soluble in an inexpensive solvent that can be obtained in large volumes. Surfactant can be used for
hydrophobic organics.  Studies have been conducted to determine appropriate solvents for mobilizing
various classes and types of waste constituents.  The  characteristics of various surfactants and their
environmental and chemical properties are listed in Table 1. Laboratory testing on site-specific soils
should be undertaken to verify surfactant properties (Amdurer et al. 1986).

        Success or failure  also depends on the retention or inactivation of the solvent by the soil.  The
soil overlying the contaminated zone will need to be completely saturated before the solvent reaches the
zone  of contamination. The interaction of the solvent with the soil must be considered for successful ap-
plication of the treatment.

        The level of treatment that can be achieved will vary depending on the contact of the flushing
solution with waste constituents, the appropriateness of the solutions for the wastes, the soil adsorption
coefficients of the waste(s), and the hydraulic conductivity of the soil.  This technology should produce
the best treatment results in highly permeable soils with low organic content.  Despite the varying level
of treatment accomplished by soil flushing, however, once the waste components have been removed
from the soil,  results are not reversible and no retreatment is necessary.

3.1.1 Status of the Technology

        Several bench- and pilot-scale studies have been completed on the effectiveness of extraction
as an in situ treatment technology.  Nash (1988) used soil flushing with surfactants to demonstrate
contaminant reduction at the Volk Air National Guard Base in Camp Douglas, Wisconsin. The contami-
nation consisted primarily as medium-weight oil (2,000-25,000 mg/kg) with some volatile organics (5 to
10 mg/kg). After applying surfactants on small areas of contamination at a rate of 77 Urn2 per day for 7
days, no statistically significant reduction of contamination was observed.  Nash concluded that in situ
soil flushing with aqueous surfactants would be ineffective at sites that have contaminants with relatively
high soil-sorption values (K>10"3).

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                     Table 1. Surfactant Characteristics*
CO
                     Surfactant
                      type
                                                                     Selected
                                                                     properties
                                                                     and uses
                                                                                                            Solubility
                                                                                Reactivity
Anionic          1)  Carboxylic acid salts

                 2)  Sulfunc acid ester salts

                 3)  Phosphoric and polyphosphonc acid esters

                 4)  Perfluorinated aniomcs

                 5)  Sulfonic acid salts

Cationic          1)  Long-chain amines

                 2)  Diammes and polyammes

                 3)  Quaternary ammonium salts

                 4)  Polyoxyethylenated long-chain amines

Nonionic         1)  Polyoxyethylenated alkylphenols
                    alkylphenol ethoxylates

                 2)  Polyoxyelhylenated straight-chain
                    alcohols and alcohol ethoxylates

                 3)  Polyoxyethylenated polyoxypropylene glycols

                 4)  Polyoxyethylenated mercaptans

                 5)  Long-chain carboxyiic acid esters

                 6)  Alkylamme "condensates", alkanolamides

                 7)  Tertiary acetylenic glycols

Amphoterics      1)  pH-sensitive

                 2)  pH-insensitive
                                                                                       Good detergency

                                                                                       Good wetting agents

                                                                                       Strong surface tension reducers



                                                                                       Good oil-m-water emulsifiers

                                                                                       Emulsifying agents

                                                                                       Corrosion inhibitor
Emulsifying agents


Detergents


Wetting agents

Dispersents

Foam control
                                                                                       Solubilizmg agents

                                                                                       Wetting agents
                                       Generally water-soluble
                                       Soluble in polar organics
                                       Low or varying water solubility
                                                                                                                             Water-soluble
                                                                                                                             Generally water-soluble
Electrolyte-tolerant

Electrolyte-sensitive

Resistant to biodegradation

High chemical stability

Resistant to acid and alkaline hydrolysis

Acid-stable



Surface adsorption to  silicaeous materials



Good chemical stability
                                                                                                                             Water-insoluble formulations        Resistant to biodegradation
                                                                                                                                                               Relatively nontoxic
                                                                                                                                                               Subject to acid and alkaline hydrolysis
                                       Varied (pH-dependent)              Nontoxic

                                                                         Electrolyte-tolerant

                                                                         Adsorption to negatively charged surfaces
                     *  Source   Amdurer  et al.   1986

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       Dworkin et al. (1988) indicate that in situ soil flushing, in combination with a biodegradation
process, could be a cost-eftective means of soil remediation at sites contaminated with creosote.
Specifically, soil flushing may be used to remove high concentrations of the polycyclic aromatic hydro-
carbons associated with creosote contamination, and the process may be followed by in situ biodegra-
dation.  They report that this system of flushing/biodegradation would result in significant reduction or
possibly elimination of the health risks and environmental impacts associated with the migration of
PAHs into ground water and surface water.

       Kuhn and Piontek (1989) proposed using in situ soil flushing combined with biodegradation to
remediate a contaminated wood-preserving site. During screening tests to determine a potentially effec-
tive combination of alkaline agents, polymers, and surfactants for treatment, several combinations were
discovered to be effective for the site-specific remedial action necessary.  As a final test, flood tests
were conducted on soil  cores to select the most effective combination of polymer, alkaline agents, and
surfactants and to predict the degree of contaminant removal potentially achievable with the combina-
tion. In the laboratory testing, 98 percent contaminant removal was achieved on the core samples
representing ideal field conditions. Based on the results of the testing program, in situ soil flushing
followed by in situ biodegradation was determined to be a cost-effective method of site remediation.

       Soil flushing has been used to effect several full-scale remedial actions.  Truett et al. (1982)
reported the use of water flushing for 5 to 6 years to reclaim a former herbicide factory site  in Sweden.
A wellpoint collection and recharge system was installed at the Goose  Farm Site, Plumstead, New
Jersey (USEPA 1984).  Water was used to flush the/contaminants from the soil.  Bench-scale leaching
tests indicated that 10 complete soil rinses (1.1 x 10  gallons of water) would be required for complete
soil flushing of total organic carbon
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        The following information is needed for application of this in situ treatment:
        • Characterization and concentration of waste constituents.
        • Depth, profile, and areal distribution of contamination.
        • Partitioning of waste constituents between solvent(s) and soil.
        • Effects of washing agent (solvent) on physical, chemical, and biological properties of soil.
        • Suitability of site for flooding and installation of wells or subsurface drains.
        • Site-specific ground-water flow rate and direction.
        • Trafficability of soil and site.
 3.1.4 Advantages of Soil Flushing
        Advantages of using this treatment technology for site remediation include:
        • Removal of contaminants is permanent, no additional treatments are necessary if the soil
          flushing process is successful.
        • The technology is  easily applied to permeable soils.
        • Costs are moderate, depending on the flushing solution chosen.
 3.1.5 Disadvantages of Soil Flushing
        Disadvantages of using soil flushing are as follows:
        • The technology introduces potential toxins (the flushing solution) into the soil system.
        • Physical/chemical properties of the soil system may be altered because of the introduction of
          the flushing solution.
        • A potential exists for solvents to transport contaminants away from the site into uncontami-
          nated areas.
        • A potential exists for incomplete removal of contaminants due to heterogeneity of soil
          permeability.
 3.2 Solidification and  Stabilization
        Solidification and stabilization refer to treatment processes that are designed to accomplish one
 or more of the following:
        • Improve  handling and physical characteristics of the waste by producing a solid from liquid or
          semiliquid wastes.
        • Reduce contaminant solubility in the treated waste.
        • Decrease the exposed surface area across which transfer or loss of contaminants may occur.
        Solidification techniques eliminate the free liquid, increase the bearing strength, decrease the
 surface area of the waste material, and produce a monolithic solid product of high structural integrity.
 Solidification may involve encapsulation of fine waste  particles (microencapsulation) or large blocks of
wastes (macroencapsulation).  Chemical interactions do not necessarily occur between the wastes and
the solidifying agents, but the waste material is mechanically bound within the solidified matrix in such a
way that the release rate of hazardous substances is significantly decreased upon exposure to air,
water, soil, or mild acidic conditions.
        Stabilization refers to the process of reducing the hazardous potential of waste material by
converting the contaminants  into their least soluble, mobile, or toxic form.  This technique does not
necessarily change the physical characteristics of the waste.
                                               11

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3.2.1  Solidification/Stabilization Techniques

       Solidification/stabilization techniques have been widely used in low-level radioactive waste
disposal. Their application to hazardous wastes is becoming more common, however, and many
vendors are studying and developing processes that are directly applicable to hazardous waste-con-
taminated soils and sludges. Table 2 identifies several in situ applications of this technology.

       Waste solidification/stabilization systems that are potentially useful in remedial action activities
are as follows:

       • Pozzolan-portland cement systems

       • Lime-fly ash pozzolan systems

       • Thermoplastic microencapsulation

       • Sorption

       • Organic binding

       Cullinane et al. (1986) describe the first four of the systems as follows:

       • Pozzolan-portland systems used portland cement and pozzolan materials (e.g., fly ash) to
         produce a structurally stronger waste/concrete composite. The waste is contained in the con-
         crete matrix by microencapsulation (i.e., physical entrapment).

       • Lime-fly ash pozzolanic processes use a finely divided, noncrystalline silica in fly ash and the
         calcium in lime to produce low-strength cementation. The waste containment is produced by
         microencapsulation in the pozzolan concrete matrix.

       • Thermoplastic microencapsulation involves blending fine paniculate waste with melted
         asphalt or other matrix. Liquid and volatile phases associated with the wastes are driven off,
         and the wastes are isolated in a mass of cool hardened asphalt.

       • Sorption involves adding a solid to soak up any liquid present. The major use of sorption is to
         eliminate all free liquid. Typical examples of nonreactive, nonbiodegradable sorbents are
         activated carbon, clays, zeolites, anhydrous sodium silicate, and various forms of gypsum.

       Many of these additives are  not effective in immobilizing organic contaminants. Recent studies,
however, indicate that modified clays can be used to immobilize organic contaminants (Gibbons and
Soundararajan 1988). Clay particles are platy-shaped minerals that have  negative charges on their
surfaces as a result of isomorphous substitution. To achieve neutrality in their structure, clay particles
attract cationic metals such as Li*, Na*, Ca*, and Mg* on their surfaces. These cations might be further
replaced by quarternary ammonium ions such  as [R4N ]. Introduction of these organic cations into clays
increases the interplanar distance between the clay particles and provides more suitable conditions for
bonding of organic contaminants (Gibbons and Soundararajan 1988).

       An extensive discussion of these and other solidification/stabilization techniques is presented in
the document entitled "Handbook for Stabilization/Solidification of Hazardous Wastes" (Cullinane et al.
1986). Also, Malone et al. (1979 and 1980) present detailed information concerning the solidification/
stabilization of hazardous wastes. Physical and chemical testing and technology evaluation procedures
are discussed in another report (PEI Associates, Inc. and Earth Technology Corp. 1989).

       The most significant challenge in applying solidification/stabilization treatment in situ for con-
taminated soils is achieving complete and uniform mixing of the solidifying/stabilizing agent with the
soils.  In situ mixing of solidifying/stabilizing agents with contaminated sludges in a lagoon is typically
                                               12

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Table  2.   Selected In Situ Solidification  Case  Studies*
                                     Treatment
Site/
contractor
Midwest, U.S.
Plating Co.,
Envirite
Unnamed,
ENREOO
Hialea, FL,
Geo-Con,
Inc.
Unnamed,
Kentucky,
ENREOO
N.E. Refinery,
ENREOO
Velsicol Chem.,
Memphis
Env. Centre

Vickery, OH,
Chemical Waste
Management
Wood Treating,
Savannah, GA,
Geo-Con, Inc.
Metalplating, Wl,
Geo-Con, Inc.
Contaminant
(concentration)
Cu, Cr, Ni
Pb/soil
(2-100 ppm)
PCBs (0 BOO
ppm)
Vinyl chloride
ethylene
dichloride
Oil sludges,
Pb, Cr, As
Pesticides
and organics
(resins, etc.)
up to 45%
organic
Waste acid
PCBs (<500
ppm), dioxins
Creosote
wastes
Al (9500 ppm)
Ni (750 ppm)
Cr (220 ppm)
Cu (2000 ppm)
volume, cubic
yards (ex-
cept as noted)
16,000
7,000
300
(7,000
total)
180,000
100,000
20,000,000
gallons

235,000
12,000
3,000
Physical
form
Sludge
Solid/
soils
Wet soil
Sludges,
variable
Sludges,
variable
Sludges,
variable

Sludges
(viscous)
Sludges
Sludges
Pre-
treat Binder
No Portland
cement
No Portland
cement and
proprietary
No HWT-20TM
(cement-
based)
Yes Portland
cement and
proprietary
No Kiln dust
(high CaO
content)
No Portland
cement and
kiln dust,
proprietary

Yes Lime and
kiln dust
Yes Kiln dust
No Lime
Percentage
bmder(s) Treat-
added ment
20 In situ
Cement In situ
(15-20)
proprietary
- 5
1 5 In situ
Varied In situ
25 +
Varied, In situ
1 5-30
Varied In situ
(cement
5-15)

15 CaO In situ
5 kiln
dust
20 In situ
25-Oct In situ
Disposal
On site
Landfill
On site
On site (two
secure cells
built on site)
On site
On site

On site
(TSCA cells)
On site
(lined cells)
On site
landfill
Volume
increase,
%
>0
Mass >20
(volume
>30-35)
>Small
>7-9
>Vaned,
-20
average
>Vaned
-10
or less

>-9 +
>-14
>4-10
Scale of
operation
Full-scale
Full-scale
Pilot (full-
scale plan-
ned)
Full-scale
Full-scale
Full-scale

Full-scale
Full-scale
Full-scale
"Source:  PEI Associates, Inc. and Earth Technology Corp  1989

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accomplished by use of a backhoe, clamshell, or dragline (Cullinane et al. 1986). Depending on the
depth of contamination, however, these implements may not be useful for mixing in the subsurface.

       This factor becomes more significant when multiple-constituent wastes have been buried and
intermixed with soils of various textures and properties. Uniformity of the waste-reagent matrix is also
important when the waste constituents are directly involved in the chemical reactions of the solidifica-
tion/stabilization process (e.g., water required for the hydration process in portland cement-pozzolanic
reactions) or when more than one additive is being used in the treatment of the wastes. Proper mixing
or degree of contact between the waste, soil, and solidification/stabilization reagent depends on the
following parameters (Truett et al. 1983):

       • Viscosity of the agent.

       • Permeability of the waste materials and the soils surrounding them.

       • Porosity of the waste materials and soils.

       • Special distribution of the wastes in the  surrounding material (i.e., soils, rocks).

       • Rate of reactions.

       Truett et al.  (1983) describe three  methods for applying solidifying/stabilizing agents to the
subsurface:

       • Injection method. Solidifying/stabilizing agents can be injected into the waste material in
         liquid or slurry form.  Injection can  be achieved by flow of the solidifying/stabilizing reagent
         inside a porous tube to the required depth.

       • Surface application.  When the  waste material is sufficiently shallow and permeable, stabiliz-
         ing agents can be applied in a solid or liquid form onto the surfaces and allowed to penetrate.
         This application technique is especially appropriate for rendering a specific waste component
         less toxic. This method is not commonly used, however.

       • Application of electrical energy.  Electrical energy can be applied to the ground  to melt the
         soils and rocks that  contain hazardous material.  This method involves the application of the
         electrical energy through electrodes placed into the ground to increase the temperature of the
         landfill material above the fusion point and to stabilize the waste components. A thin layer of
         graphite is usually placed between the electrodes to act as a starter to melt the  soil. Before
         this process is applied, a cover may be placed over the fused area to capture the released
         gases during the process and to direct them to the treatment unit.

3.2.1.1 Status of the Technology

       An in situ solidification/stabilization process involving a proprietary solidifying/stabilizing agent
and a unique mixing system has been evaluated through the SITE Program (USEPA 1988). The pro-
prietary agent, developed by International  Waste Technologies (IWT), is claimed to bind with ions and
neutral organics present in the soil and eventually to form macromolecules. The method for injecting
the chemical into the soil, which was developed by Geo-Con, Inc., utilizes a hollow drill with an injection
point at the bottom of the shaft. The drill is advanced into the ground to the desired depth.  The chemi-
cal additive is then injected at low pressure to prevent excessive spreading and is blended with the soil
as the drill rotates. The treated soil forms a  solid vertical column.  Soil columns overlap to insure that all
the soil is adequately treated.  The soil surface may then be covered with a layer of asphalt to protect
the solidified mass from rain and water erosion. The technology was evaluated on PCB-contaminated
soils at the General Electric Superfund Site in Hialeah, Florida. Two test sectors, 10 x 20 ft, were reme-
diated to a depth of 18 ft in one sector and 14 ft in the other.  Samples of untreated and treated soil
were taken from the same locations in each  test sector, and laboratory analyses were performed to
obtain a comparison of physical properties and contaminant mobilities  before and after soil treatment.
The results are summarized here (USEPA 1989):
                                              14

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       • Based on TCLP analyses, the PCBs appear to be immobilized.  Because the PCB concentra-
         tions measured in the soil and leachates were very low, this finding was not conclusive.

       • The physical test results were satisfactory (except for the freeze/thaw tests) which indicates a
         potential for long-term durability of the hardened mass. The results were as follows:

         - High unconfined compressive strength (average about 410 psi).

         - Treatment improved soil permeability four orders of magnitude, to an average of
            4 x 107 cm/s.

         - Wet/dry weathered samples showed satisfactorily low weight losses.

         - Treatment increased volume by 8.5 percent.

         - Freeze/thaw weathered samples showed unsatisfactorily large weight losses.

         - Microstructural studies  showed the treated soil to have a dense, homogeneous structure of
            low porosity, which might give long-term  durability

3.2.1.2 Secondary Impacts

       The permeability of the treated area is significantly reduced and could prohibit subsequent use
of the area for construction or revegetation. Runoff controls may be required.

3.2.1.3 Equipment, Exogenous Reagents, and Information Required

       The equipment required for  preparing, mixing, and applying solidification/stabilization reagents
depends on the reagent, the process, and the depth of contamination.  Application methods were dis-
cussed previously.

       Knowledge of the waste composition is required for the selection of the proper reagent to
stabilize waste components.  Such knowledge is also needed to determine whether waste constituents
will interfere with the setup of the solidifying agents in different processes (i.e., crystallization, polymeri-
zation, gelling, adhesion, or other setting mechanisms).  In addition, information regarding the character-
istics of the soils and other geologic materials and the rates and directions of ground-water movement
are essential for a good assessment of the applicability of each solidification/stabilization process.  This
information can be obtained by various established methods and sampling techniques (Fenn 1980).
Table 3 provides a summary of the compatibility of selected waste types with different solidification/
stabilization techniques.

       The reagents required depend on the particular solidification/stabilization process being imple-
mented. For physical entrapment (microencapsulation), portland cement and a pozzolanic material
such as fly ash are the principal reagents.  Another microencapsulation technique involves the use of
lime and fly ash. Asphalt or bitumen is  used to effect thermoplastic microencapsulation. For sorption
processes, the adsorbents can include activated carbon, clays, zeolites, anhydrous sodium silicate, or
gypsum.  Organophilic clays and portland cement are  necessary for binding of organic contaminants.
                                             15

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Table 3. CompatlbllHy of Selected Waste Categories WHh Different Stabilization/Solidification Techniques*




                                                                       Treatment type
Waste component
Organics
Organic solvents and oils

Solid and organics e g.,
plastics, resins, tars)
Inorganics
Acid wastes

Oxidizers

Sulfates


Halides

Heavy metals
Radioactive
materials
Cement-based

May impede setting, may
escape as vapor
Good-often increases
durability.

Cement will neutralize acids.

Compatible

May retard setting and cause
spelling unless special
cement is used.
Easily leached from cement,
may retard setting.
Compatible
Compatible

Pozzolan-based

May impede setting, may
escape as vapor
Good-often increases
durability

Compatible, will neutralize

Compatible

Compatible


May retard set, most are easily
leached.
Compatible
Compatible

Thermoplastic
microencapsulation

Organics may vaporize on
heating
Possible use as binding agent
in this system

Can be neutralized before
incorporation
May cause matrix breakdown,
fire
May dehydrate and rehydrate,
causing splitting.

May dehydrate and rehydrate

Compatible
Compatible

'Source:  Maloneetal.  1980.

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3.2.1.4 Advantages of Solidification/Stabilization

        The advantages of this treatment technique are as follows:

        •  Additives and reagents are widely available and relatively inexpensive.

        •  The resulting solidified material may require little or no further treatment if proper conditions
          are maintained.

        •  Leaching of contaminants is greatly reduced.

3.2.1.5 Disadvantages of Solidification/Stabilization

        The disadvantages of this treatment technology are as follows:

        •  Volume of treated material may increase with the addition of reagents.

        •  Delivering reagents to the subsurface and achieving uniform mixing and treatment in situ may
          be difficult.

        •  Volatilization and emission of volatile organic compounds may occur during mixing proce-
          dures.

3.2.2 In Situ Vitrification
        In situ vitrification is a thermal treatment process by which contaminated soils are converted into
chemically inert and stable glass and crystalline materials (Fitzpatrick et al. 1987). Field application
requires the insertion of large electrodes into contaminated soils containing significant levels of silicate
material and the generation of heat (up to 3600°C) by passing electric current through the electrodes.
Because dry soils are not electrically conductive, a layer of flaked graphite and glass frit is placed
between the electrodes; this transfers electrical energy and acts as a starter to increase the tempera-
ture of the soil and waste material. At this temperature, any soil or rock components of the waste
material will melt (melting temperature of soils is 2000° to 2500°F), organic compounds will be pyrolyzed
in the glass matrix, and many metallic materials will either fuse or vaporize.  Any gases and vapors pro-
duced can be collected by placing a hood above the treating area to draw them for further treatment
(Fitzpatrick 1988).  After  the process is terminated and the ground has been cooled, the fused waste
material will be dispersed into a chemically inert and stable crystalline form that has very low teachability
rates and almost the same  chemical stability of granite. Figure 2 presents different processing stages of
in situ vitrification techniques.

Figure 2. The in situ vitrification operating sequence.
 "|             Support
     Off-gas Cover >
   Starter
                             Waste Burial Trench
                                                                                      Backfill
                                                                              Vitrified Soil/Waste
                                               17

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       Table 4 presents the different scales of testing conducted in the development of the in situ
vitrification technique (Fitzpatrick et al. 1987).  The in situ vitrification technique was originally used to
stabilize radioactive wastes, and it has only recently has been considered for the treatment of hazard-
ous material. The process destroys nitrates and partially decomposes sulfate compounds in the wastes.
Fluoride and chloride compounds are dissolved into the glass materials up to their limits of solubility
(PEI 1988).  Wastes containing heavy metals,  PCBs, process sludges, and plating wastes are amenable
to treatment by this vitrification process.

Table 4. In Situ Vitrification Test System Characteristics*
System
scale
Bench
Engineering
Pilot
Large
Power,
kW
10
30
500
3750
Electrode
spacing, ft
036
0 75 to 1 2
40
11 5 to 180
Vitrified mass
per setting
2 to 5 Ib
0 05 to 1 0 ton
1 0 to 50 tons
400 to 800 tons
Number of
tests
5
26
15
5
'Source Fitzpatrick 1988

3.2.2.1'  Status of the Technology

       To date, no Superfund site has been treated by this technology in the field.

3.2.2.2 Secondary Impacts

       The resulting vitrified mass is effectively inert and impermeable; therefore, it could not support
vegetative growth unless covered by fill and topsoil.

3.2.2.3 Equipment, Exogenous Reagents, and Information Required

       Operation of the in situ vitrification process requires an adequate power supply.  A full-scale,
four-electrode system requires a 4160-volt, 3000-kW source provided by a multitap transformer
(Johnson and Cosmos 1989).  Glass trit and graphite are necessary as starter materials for the melting
processs. An off-gas hood is required for the entire treatment area. Off-gas treatment equipment may
include quenchers, tandem nozzle scrubbers, separators, condensers, or high-efficiency paniculate air
(HEPA) filters.
       Soil moisture is an important factor in the operation of the in situ vitrification process.  More
power and time are required to evaporate the water as soil moisture increases. Engineered barriers
may be required to vitrify soils below the water table.

3.2.2.4 Advantages of In Situ Vitrification

       The potential advantages of this technology are as follows:

       •  This process eliminates excavation, processing, and reburial of the hazardous compounds.

       •  The process minimizes exposure to contaminants.
       •  The process produces glassified materials that are long-lasting and highly durable.

       •  The treatment efficiency rate is relatively high (3 to 5 tons/h).

       •  Additives are relatively inexpensive.
       •  The products of this  process have an extremely tow leach rate (USEPA1985).
                                               18

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3.2.2.5  Disadvantages of In Situ Vitrification
        The potential disadvantages of this technology are as follows:
        • The process is energy-intensive and often requires temperatures up to 2500°F for fusion and
          melting of the waste-silicate matrix.
        • Special equipment and trained personnel are required.
        • Water in soils affects operational time and increases the total cost of the process.
        • The technology has the potential to cause contaminants to migrate to the outside boundaries
          of the treatment area instead of to the surface for collection.
3.3 Degradation
3.3.1 Chemical Degradation
        Chemicals naturally undergo reactions in soil that may transform them into more or less toxic
products or that may increase or decrease their mobility within the soil system.  Chemical treatment of
contaminated soils entails the reaction of pollutants with reagents, which  results in products that are less
toxic or that  become immobilized in the soil column. These reactions are classified as oxidation reac-
tions, reduction reactions, and polymerization reactions.
3.3.1.1  Chemical Oxidation
        In general, chemical oxidation entails the loss of electrons by an  atom or group of atoms. A
broader definition of oxidation entails an increase in oxidation  number of one reactant accompanied by a
corresponding decrease in oxidation number of the other (reduced) reactant. Adding oxygen to a simple
alkene (e.g., ethene) entails oxidation because electrons from ethene are "lost" to the oxygen atom.
Oxidation reactions can occur within the soil matrix, and the rate of such  reactions can be increased
through management of the natural processes in a soil or through the addition of an oxidizing agent to
the soil-waste complex.  Certain compounds are more susceptible to oxidation than are others. The
rate of oxidation depends on several factors, including temperature, oxygen concentration in the liquid,
impurities present, and the concentration and chemical properties of the oxidizable component.
        The following discussion primarily concerns the chemical oxidation of organics. Oxidation of
heavy metals usually is not effective as a treatment method because the  higher the oxidation state, the
more mobile the heavy metal tends to be. Two approaches are applicable to in situ oxidation of hazard-
ous waste materials in contaminated soils: 1) soil-catalyzed reactions, and 2) the addition of oxidizing
agents.
        The following information is required prior to the implementation of in situ treatment techniques
for soil oxidation:
        • Characterization and concentration of wastes, particularly organics at the site.
        • Potential for oxidation of waste constituents (half-potentials, Ei/2).
        • Oxidation products (particularly hazardous products).
        • Solubility of organics.
        • Depth, profile, and areal distribution of contamination.
        • Soil moisture.
        • Soil type and profile.
        • Catalysts for oxidation present in soil.
        • Trafficability of soil and site.
                                              19

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Soil-Catalyzed Reactions

        Iron, aluminum, trace metals within layered silicates, and adsorbed oxygen have been identified
as catalysts that promote free-radical oxidation of constituents in soil systems (Page 1941, Solomon
1968, Theng 1974, Furukawa and Brindley 1973, and Hirschler 1966). General characteristics of the
organic chemicals likely to undergo oxidation include 1) aromaticrty, 2) fused ring structures, 3) exten-
sive conjugation, and 4) ring substituent fragments.

        For oxidation to occur in soil systems, the redox potential of the solid phase must be greater
than that of the organic chemical contaminant. Therefore, the half-cell potentials, Ei/z, of chemical
contaminants need to be below the redox potential, 0.8V of a well-oxidized soil (Dragun and Baker
1979).

        Another characteristic that is significant with respect to soil-catalyzed oxidation is the solubility
of the organic contaminant. The oxidation reaction site is the hydrophilic clay mineral surface, and
sorption to the surface precedes soil-catalyzed oxidation.  Therefore,  highly water-soluble compounds
should be readily  oxidized  in clay-catalyzed systems.

        Organic wastes that are water-soluble and have half-cell potentials below the redox potential of
a well-oxidized soil are amenable to this treatment. Table 5 lists chemicals that do not undergo free-
radical oxidation at soil and clay surfaces. This group of chemicals includes the aliphatic class of
compounds.

Table 5.  Some Chemicals That Do Not Oxidize At Soil And Clay Surfaces*

                                       Chemical Name
                       Acetamide                      5-Carotene
                       Acetone, anisihdene-              Cyclohexylamine
                        -, dianisilidene-                 Monoethanolamme
                        -, dicinnamylidene-               Triethylamine
                        -, dibenzylidene-

                       *Source- Dragun and Helling 1982

        The water content of the soil (degree of saturation) also may play an important role in control-
ling, and therefore managing, soil-catalyzed oxidation.  Greater oxidation of chemical contaminants is
expected in less-saturated soils (Dragun and Helling 1982).  Therefore, the technique for immobilization
by control of soil moisture is completely compatible with this treatment technique.

        Immobilization techniques that involve controlling soil moisture or incorporating or adding
uncontaminated soil should not only augment sorption, but should also augment clay-catalyzed reac-
tions in the soil B-horizon where the clay fraction of soil is predominant. Thus, a physical-chemical and
biological treatment system may be used in a layered system through the soil where sorption of hydro-
phobic constituents occurs in the upper soil layers or where  organic matter content is high, and where
chemical reactions for hydrophilic constituents occur in lower soil  layers where the clay fraction predomi-
nates.  Biological activity may be expected to increase  the extent  of degradation of constituents as the
retention time of constituents is increased through sorption.

        Hydrolysis refers to the reaction of water with an organic or inorganic compound where a
hydrogen atom, an oxygen atom, and/or a hydroxide group from the water is incorporated into the
products that result from the reaction:

                              R-X + HaO      ^   R-OH +  HX                           (3-1)

where R is the organic moiety and X is the leaving group.

        Hydrolysis reactions are influenced by pH, temperature, degree of sorption, and the presence of
other compounds that might act as catalysts. The rate of hydrolysis can be increased  up to one order of
magnitude for a change of 1 standard unit in pH (Amdurer et al. 1986). Hydrolysis of parathion occurs
                                               20

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rapidly in alkaline solution at a pH value greater than 9. The hydrolysis rate also increases with increas-
ing temperature.

       Generally, organophosphorus pesticides and carbamate pesticides can be degraded by hy-
drolysis under alkaline conditions.  Malathion, parathion, methyl parathion, 2,2-dichlorovinyl dimethyl
phosphate, and carbaryl have been degraded by alkaline hydrolysis.  Dimethoate, another organo-
phosphorus pesticide, can be destroyed by alkaline hydrolysis, but the toxicity of mercaptoacetic acid,
one of the reaction products, is almost as great as that of dimethoate itself (Tucker and Carson 1985).

       Classes of compounds with potential for in situ treatment by hydrolysis include esters,  amides,
carbamates, phosphoric and phosphonic acid esters, and pesticides.

       If required, clay may be applied to the soil surface and thoroughly incorporated through the
depth of contamination.  Drainage systems may have to be installed on the site to reduce soil moisture.
Tillage may be used to dry and aerate the soil. Increasing soil temperatures may enhance soil drying
and increase the rate of reaction. This treatment technology requires aerobic soil conditions to be
maintained, which may be easy or difficult, depending on the site and the depth of contamination as it
affects the ability to incorporate clays.

       The level of treatment achievable will vary, depending on the oxidation potential of the waste
constituents and the aeration of the soil.

       Status of the Technology.  Soil-catalyzed oxidation reactions have been verified in the  field for
several chemical classes, including s-triazines and organophosphate compounds. Some other com-
pounds have been verified in the laboratory.

       A site near Phoenix Arizona, contaminated with parathion was treated in situ. Laboratory and
field feasibility studies showed that the combination of sodium hydroxide and water degraded ethyl and
methyl parathion quickly by alkaline hydrolysis (King et al.  1985).  Concentrations of the ethyl parathion
were decreased by more than 50 percent in 15 days, and 76 percent after 69 days.  Concentrations of
methyl parathion decreased more rapidly; 81 percent after 15 days and 98 percent after 69 days.

       Secondary Impacts. Drainage systems may have to be installed on the site to reduce soil
moisture. Because tillage may  be needed to dry and aerate the soil, wind erosion could occur.

       Equipment, Exogenous Reagents, and Information Required.  Equipment may be needed to set
up a drainage system. If clay is added, applicators and tillers will be required to incorporate the clay.
The information required prior to implementation is the  same for all in situ treatment techniques for soil
oxidation.

       Advantages of Soil-Catalyzed Reactions.  The  advantages of soil-catalyzed oxidation reactions
are as follows:

       • Organophosphorus pesticides and carbamate pesticides can be  degraded by  hydrolysis
         under alkaline conditions.

       • The process has been verified in the field for several chemical classes, including s-triazines
         and organophosphate compounds.

       • Toxic concentrations  may also be reduced by attenuation with the added soil.

       Disadvantages of Soil-Catalyzed Reactions. The disadvantages of this process are as follows:

       • Oxidation of the waste can produce substances  more problematic than the parent compounds
         in the waste.

       • Decreased soil moisture could result in retardation of microbial activity or increased ventiliza-
         tion of volatile waste  constituents.  (Volatilization may present a  public health  hazard, but  it
         also may reduce toxic concentrations to soil  microorganisms.)
                                             21

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       • Depth of treatment may be limited by feasible depth of tillage.

       • Tillage may increase the susceptibility of the soil to erosion.

Addition of Oxidizing Agents

       Oxidizing agents can be used to degrade organic constituents in soil systems. The application
of oxidizing reactions is usually limited because of their substrate specificity and pH dependence. Two
powerful oxidizing agents considered for in situ treatment are ozone and hydrogen peroxide.  The
relative oxidizing ability of these chemicals compared with that of other well known oxidants is shown in
Table 6. A serious potential limitation to the use of oxidizing agents for soil treatment is the additional
consumption of the oxidizing agent(s) by nontarget constituents in the soil organic matter.

Table 6. Relative Oxidation Power of Oxidizing Species*

        Species               Oxidation potential volts            Relative oxidation power
Fluorine
Hydroxyl radical
Atomic oxygen
Ozone
Hydrogen peroxide
Perhydroxyl radicals
Hypochlorous acid
Chlorine
306
280
242
207
1 77
1.70
1 49
1 36
225
205
1 78
1 52
1 30
1.25
1.10
1 00
       'Source  Rice 1981

       Ozone is an oxidizing agent that may be used to degrade recalcitrant compounds directly, to
create an oxygenated compound without chemical degradation, or to increase the dissolved oxygen
level in water for purposes of enhancing biological activity. Ozone is a colorless gas characterized by a
pungent odor and very high oxidation potential.  It cannot be shipped or stored; therefore, it must be
generated on site  prior to application. Ozone rapidly decomposes, and its half-life in ground water is
only 18 minutes (Sanning and Black  1987).

       The rate of decomposition of ozone is strongly influenced by pH.  Ozone reactions are believed
to be of two fundamental types: 1) direct reaction of ozone with the organic compounds; and 2) free
radical reaction of ozone, which involves a hydroxyl free radical intermediate. Direct reaction of ozone
with solute achieves the most rapid decomposition of the solute. At high pH, the hydroxyl free-radical
reactions tend to dominate over the direct ozone reactions. Thus, the relative rate of ozone reaction can
be controlled by adjusting the pH of the medium.

       If the specific organic constituents present in contaminated soil are relatively biodegradable,
ozone treatment may be very effective as an enhancement of biological activity.  If a large fraction of the
matrix is relatively biorefractory, however, the amount of ozone required for direct treatment of the waste
by chemical destruction will be a function of the  organic matter present in the solution and in the soil;
this will greatly increase the cost of treatment. The presence of natural soil organic matter will greatly
increase the ozone dosage and consumption needed to treat the target constituents.

       Ground water contaminated with oil products was treated with ozone to reduce the dissolved
organic carbon (DOC) concentration  (Nagel 1982).  Dosages of 1  gram ozone per gram of dissolved
organic carbon resulted in an ozone concentration of  0.1 to 0.2 ppm in the residual water. The treated
water was then infiltrated into the aquifer through injection wells. The dissolved oxygen (DO) in the
contaminated water increased. This  increase in DO increased the microbial activity in the saturated soil
zone, which stimulated microbial degradation of the organic contaminants. Ozone has also been used
in the treatment of soils and ground water at the Karlsruhe site in Germany (Rice 1984).

       Hydrogen peroxide is an oxidant that has been successfully used in wastewater treatment to
degrade compounds that are resistant to biological treatment (recalcitrant). It has also been used to
modify the mobility of some metals.
                                              22

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       Hydrogen peroxide can react in three major ways:

        1) Direct reaction with substrate as shown in Equation 3-2, where the peroxide reacts with
          silver nitrate to form elemental silver and nitric acid:

                      2AgNO3 + H2O2        ^i    Ag + O2 + 2HNO3                     (3-2)

       2) Can be degraded by UV light to form hydroxyl free radicals, as shown in Equation 3-3:

                           + UV (2.53A)             2OH~                                (3-3)
       3) Can undergo auto-decomposition in the presence of a metal catalyst, as shown in
          Equation 3-4.                 .,   ,
                                       Metal
                             GHzOz   — ^^-   6H2O + 3O2                          (3-4)

Hydrogen peroxide has also been used in conjunction with ozone to degrade compounds that are
refractory to either material individually (Nakayama 1979).

       Peroxide, as demonstrated in Equations 3-2 and 3-4, can be used to increase oxygen levels in
the soil. In a previous study, Nagel (1982) found that increasing the oxygen content in soil/ground-water
systems increased the microbial activity and microbial degradation of organic contaminants.

       Because hydrogen peroxide is a strong oxidant, it is nonselective. If this material is added to
the soil, it will react with any oxidizable material present in the soil.  This is a major concern because the
concentration of natural organic material in the soils may be lowered, which would result in a decrease
in the sorption capacity of some organics.

       Hypochlorite, generally available as potassium, calcium, or sodium hypochlorite, has never
been used in the treatment of contaminated ground water or soils (Sanning and Lewis 1987). Tolman et
al. (1978) described the conceptual design and in situ detoxification of cyanide with sodium hypo-
chlorite. The reactions of many organics with hypochlorite result in the formation of chlorinated organics
that can be equally or more toxic than the original contaminant.

N^-  - Some hazardous compounds are known to be  nonreactive with ozone. Nonreactive chemical
species are usually  inorganic compounds in which cations and anions are in their highest oxidation
state, or organic compounds that are highly halogenated. No information currently exists concerning the
susceptibility of many hazardous chemicals to ozone oxidation.

       The following are some general rules concerning chemical destruction of organic constituents:

       • Saturated aliphatic compounds that do not contain easily oxidized functional groups are not
         readily reactive with ozone. Examples include saturated aliphatic hydrocarbons, aldehydes,
         and alcohols.

       •  For aromatic compounds, reactivity with ozone is a function of the number and type of
         substituent(s).  Generally, substituents that withdraw electrons from the ring deactivate the
         ring toward ozone. Examples are halogens, nitro, sulfonic acid, carbonyl, and carboxyl
         groups. Substituents that release electrons activate the ring toward ozone.  Examples are
         alkyl, methoxyl, and hydroxyl.

       The following general patterns have been identified with regard to reactivity with ozone:

       1) Phenol, xylene > toluene > benzene

       2) Pentachlorophenol < dichloro-, trichloro-, tetrachlorophenol

       Ozonation of hazardous pesticides may actually be detrimental in many instances. Table 7
presents specific examples in which reactions of ozone with parent compounds result in the production
of hazardous products that are often degraded very slowly by ozone.
                                              23

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Table 7. Hazardous Products of Ozone Reactions*
                                                              Oxidation
                                                              of product
                Parent compound         Reaction product           with ozone


                Aldrin                  Dieldrm                  Very slow
                Heptachlor              Heptachlor epoxide         Stable to further
                                                              oxidation
                DDT                   DDE
                Parathion               Paraoxon                Nitrophenols,
                                                              phosphoric acid
                Malathion               Malaoxon


               'Source  Sims and Bass 1984


       Hydrogen peroxide has been demonstrated to be effective for oxidizing cyanide, aldehydes,
dialkyl sulfides, dithionate, nitrogen compounds, phenols, and sulfur compounds (FMC Corp. 1979).

       The reaction of peroxide with many chemical classes increases the mobility of the products
(Amdurer et al. 1986).  Table 8 shows chemical groups that react with peroxides and form more mobile
products.

Table 8. Chemical Groups That React With Peroxides To Form More Mobile Products*
               Acid chlorides and anhydrides               Cyanides
               Acids, mineral, nonoxidizing                 Dithio carbamates
               Acids, mineral, oxidizing                    Aldehydes
               Acids, organics                           Metals and metal compounds
               Alcohols and glycols                       Phenols and cresols
               Alkyl halides                            Sulfides, inorganic
               Azo, diazo compounds, hydrazine             Chlorinated aromatics/alicycles


               'Source:  Sims and Bass 1984.

        Several oxidants for the treatment of PCB-contaminated wastes have been evaluated (Carpen-
ter and Wilson 1988; Arienti et al. 1986) with the following results. Potassium permanganate plus
chromic acid and nitric acid cannot destroy PCBs with 5 to 7 chlorine atoms per molecule.  When
chloroiodides are used,  products of partial degradation may be toxic. No commercial application of this
process exists. Additional bench-scale testing is needed for further optimization of the process, including
the possibility of in situ decontamination of contaminated soil. Oxidation with ruthenium tetroxide
(RuCM) has been applied on a laboratory scale; however, the reaction end products from TCDD degra-
dation have not been identified  (Ayres et al. 1985).

        The oxidizing agents may be applied in water solutions directly onto the soil surface, injected
into the subsurface, or applied through injection wells, depending on the depth and location of contami-
nation.  Loading rates can be determined in short-term treatability studies.

        Status of the Technology. A formaldehyde spill at Ukiah, California, was treated successfully by
in situ chemical oxidation and biological treatment techniques.  Alkaline hydrogen peroxide was used to
lower the formaldehyde  concentration to levels where biological oxidation could be used.  At the end of
two days, the concentration dropped from 30,000 to 50,000 ppm to about 500 to 1000 ppm. At this
point, a biological treatment process was used, and one last peroxide treatment was applied at the end
of the biological treatment after confirmation of <42 ppb residual formaldehyde. The purpose of this
treatment was to sterilize the  area. (Sikes et al. 1984).
                                               24

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        Secondary Impacts.  Oxidizing agents may result in violent reactions with certain classes of
compounds (e.g., metals) and may be corrosive to application equipment. Their use may also affect soil
hydraulic properties (e.g., infiltration rate), especially in structured soils. Oxidation of soil organic matter
may decrease sorption sites for nonoxidizable waste constituents.  Oxygenated degradation products
are expected to be more polar than the parent compounds and therefore potentially more mobile.  The
chemical reaction may produce a large quantity of potentially mobile constituents in a relatively short
period of time and necessitate the installation of recovery wells. The oxygenated products may also be
toxic to soil systems, human health, and the environment.  Some products may be more refractory than
the parent compounds. The use of oxidizing agents may also increase the mobility of some metals.

        Equipment, Exogenous Reagents, and Information Required.  Power implements are  required.
If ozone is used, an ozone generator is necessary.  Depending on the  application method, an  irrigation
system, applicators, or injection wells may be needed.  Exogenous reagents needed are oxidizing
agents, ozone, or hydrogen peroxide. In addition to the general information requirements, the soil and
water pH must be known, along with the selectivity of oxidizing agents for specific wastes present  at the
site.

        Advantages of the Addition of Oxidizing Agents. The advantages of this technique are as
follows:

        • The achievable level of treatment is potentially high for wastes susceptible to oxidation,  in
         soils that do not contain large quantities of competing oxidizable substances, and for limited
         areas of contamination.

        • Oxidizing agents may have beneficial effects on microbial degradation processes by adding
         Oz to the soil-water solution.

        Disadvantages of the Addition of Oxidizing Agents. The disadvantages of this technique are as
follows:

       • The effectiveness of peroxide may be inhibited because it simultaneously increases mobility
          and decreases possible sorption sites.

       • The reactions of many organics with hypochlorite results in the formation of chlorinated
         organics that can be equally or more toxic than the  original contaminant.

       • Presence of reduced Fe2*  in soil will lower the efficiency of the process because of oxidation.

       • Ozonation of hazardous pesticides may actually be detrimental  in many instances.

       • Because ozone and hydrogen oxide are very strong oxidizers, they are not particularly dis-
         criminating in the substances they will oxidize in the soil. Thus,  much of the oxidant will  be
         wasted on oxidizing nontarget compounds.

       • Treatment may have to be repeated if initial applications prove to be insufficient.

3.3.1.2 Chemical Reduction

       Chemical reduction is a process in which the oxidation state of an atom is decreased. Reducing
agents are electron donors, and reduction is accomplished by the addition of electrons to the atom.
Reduction of chemicals may occur naturally within the soil system.  Certain compounds are more
susceptible to reduction than  others because they will accept  electrons. The addition of reducing agents
to soil to degrade reducible compounds can be used as an in situ treatment technology.

        Reducing agents and conditions of reduction vary with organics and with metals.  The following
discussion is divided into organics, chromium, and selenium for ease of organization of the information.
                                              25

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       Information needed before the implementation of reduction technologies is as follows:

       • Characterization and concentration of wastes, particularly organics at the site.

       • Potential for reduction of waste constituents.

       • Reduction products.

       • Depth, profile, and areal distribution of contamination.

       • Soil and waste pH.

       • Soil moisture.

       • Selectivity of reducing agent(s) for specific wastes present at the site.

       • Trafficability of soil and site.

Addition of Reducing Agents to Treat Organic Chemicals

       Chemical reduction through the use of catalyzed metal powders and sodium borohydride has
been shown to degrade toxic organic compounds. Reduction with catalyzed iron, zinc, or aluminum
effect treatment through mechanisms such as hydrogenolysis, hydroxylation, saturation of aromatic
structures, condensation, ring opening, and rearrangements to transform toxic organics to innocuous
forms.  Reductive dehalogenation of a variety of chlorinated organics, unsaturated aromatics, and
aliphatics has been demonstrated in laboratory studies in which catalyzed metal powders were used.
The treatment reagents are costly, and the effectiveness of chemical reduction in soils has yet to be
demonstrated (Sanning and Lewis 1987).

       Catalyzed metal powders have been used successfully for aqueous solutions passed through
beds of reactant diluted with an inert solid  (Sweeney 1981). This process may be adaptable to terres-
trial application; however, it has not yet been directly demonstrated. It has been used successfully on
the following specific constituents:

              Hexachlorocyclopentadiene           PCBs
              p-Nitrophenol                        Chlordane
              Trichloroethylene                    Chlorinated phenoxyacetic acid
              Chlorobenzene                       Di-and tri-nitrophenols
              Kepone                             Atrazine

       Iron powders are not only preferred for soil systems, they are also the most cost-effective and
readily available. Reactions of iron with some organic constituents are as follows:

       Removal of halogen atom and replacement by hydrogen in halogenated organic species:

                      Fe + H2O + RCI    ^  ^    RH + Fe2* + OH" + Cl"               (3-5)

       An example is the transformation of DDT to DDA.

       Replacement of a halogen by a hydroxyl group:

                       Fe + 2H2O + 2RCI^>"^  2RQH + R>2* + 2CA~  + H2            (3-6)

       Saturation of an aromatic structure:

                      Fe + 2H2O + RCH = CHR   ^  ^  RCH2CH2R + Fe2* + 2OH"     (3-7)

       An example is the transformation of Chlorobenzene to cyclohexanol.

       Condensation of species:

                      Fe + 2RCI   ^  ^     RR + 2CI"  + Fe2*                        (3-8)

   An example is the condensation of DDT to TTTB.
                                             26

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       Consumption of metal occurs through the preceding reactions and also through reactions of the
active metal with water:
                     Fe + 2H2O
                      Fe2+  + 2OH"   + H2
                                     (3-9)
       The total consumption of metal from these reactions in aqueous solutions of industrial waste-
waters produces 1 to 5 mg/L of metal (Fe2*) in the solution when low toxicant levels are treated.

       Organic chemical constituents in soil may also be chemically reduced through the use of
sodium borohydride and zinc. These chemicals have been successful for in situ, small-scale, field
experiments with soils (Staiff et al. 1981). Table 9 presents results of reductive treatment for degrada-
tion of paraquat in soil. The results indicate that sodium borohydride and powdered zinc/acetic acid
combinations effectively degraded paraquat in soil and sand media.  Toxic products and other bypro-
ducts that may result from reductive treatment were not investigated to any significant extent in this
study.

Table 9. Chemical Reductive Treatment For Degradation of Paraquat in Soil*
Chemical treatment
        Paraquat in soil, ppm
Initial (1 day)             4 months
                      Comment
None


NaBH4-soil


NaBH4-sand


Powdered Zn/
 acetic acid
9590


None detected


None detected



60
6300


None detected


None detected



69
Violent foaming


No foaming



Some bubbling
'Source: Staiff etal 1981.


       The soil should not be disturbed prior to treatment so dilution of contaminants in the soil can be
avoided.  For metal-catalyzed powders, stoichiometric excess of the reducing powder should be applied
to the soil surface and mixed with the contaminated soil to achieve maximum contact. For chemical
reducing  agents, a sodium borohydride stabilized water solution should be applied to the soil at 50
percent stoichiometric excess. A solution used in a small-scale study contained the following:
                      Sodium borohydride
                      Sodium hydroxide
                      Water
                      12 ±0.5%
                      42 ± 2%
                      Balance
       Iron may be more desirable than zinc or aluminum because it  is naturally present in most soils.
Aluminum is toxic to biological systems and contributes to soil acidity.  The soil pH must be maintained
at 6 to 8 for maximum treatment effectiveness.  Soil water should be controlled at less than saturated
conditions (60 to 80 percent of field capacity) to provide an aqueous environment in which reductive
reactions can occur while leaching is prevented.

       The achievable level of treatment is potentially high for wastes susceptible to reduction and for
limited areas of contamination.  If the soil contains large quantities of competing constituents susceptible
to reduction, the level of treatment may be greatly decreased.  If the reducing agents are not sufficient,
treatment may have to be repeated because of high levels of naturally occurring reducible compounds
in the soil.
                                               27

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       Status of the Technology.  In Phoenix, Arizona, a site contaminated with toxaphene was chemi-
cally treated with NaOH; the mechanism is believed to be dechlorination (King et al. 1985).  An area of
1.7 acres was treated, and the site was tilled to a depth of 1.5 to 2.0 feet prior to cleanup. An irrigation
system was installed, and 35,000 Ib of sodium hydroxide was added to the soil. No change was noted
in the concentration after 15 days; however, the average concentration decreased by 21 percent after
36 days and by 45 percent after 69 days. In situ treatment did not reduce toxaphene concentrations as
well as the laboratory and field pilot studies did.  After the Phase I chemical treatment, the site was
prepared for the Phase II anaerobic treatment.  Results are not yet available.

       Fresh manure was applied to a soil-waste mixture (2 percent manure dry weight) contaminated
with toxaphene to lower the redox potential of the soil (McLean et al. 1988). Toxaphene was collected
from a site where spent toxaphene dipping solution used in cattle operations had been disposed of on
the soil.  The application of manure was not effective in stimulating degradation of the toxaphene
residues over the time period of the study.

       Secondary Impacts. The addition of reducing agents as a treatment for organics in soil may
have the following secondary impacts:

       • The use of reducing agents may also degrade soil organic matter.

       • The products of reduction may present problems  with respect to toxicity,  mobility, and degra-
         dation.

       • The addition of metals to soils adds to the metal contaminant load.

       • The addition of metals with acetic acid could increase metal mobility by decreasing soil pH.

       • Aluminum is toxic to biological systems and contributes to soil acidity.

       • The addition of sodium borohydride may have an adverse impact on soil permeability.

       Equipment, Exogenous Reagents, and Information  Required. Power implements, tillers, and
applicators are needed. Also needed is an irrigation and drainage system. Controls for run-on and
runoff management may also be needed. The possible exogenous reagents include catalyzed iron,
zinc, or aluminum and sodium borohydride. The information requirements are those listed for all
reduction treatments.

       Advantages of the Addition of Reducing Agents to Treat Organic Chemicals in Soil. The
achievable level of treatment is potentially high for wastes susceptible to reduction and for limited areas
of contamination.

       Disadvantages of the Addition of Reducing Agents. The disadvantages of using this process for
treating organic chemicals in soil are as follows:

       • The treatment reagents are costly.

       • The effectiveness of chemical reduction in soils has not yet been demonstrated.

       • If soil contains large quantities of competing constituents susceptible to reduction, treatment
         may  have to be repeated.

Addition of Reducing Agents to Treat Chromium

       Hexavalent chromium is highly  toxic and mobile in soils. Treatment consists of reducing Cr(VI)
to Cr(lll), which is less toxic and is readily precipitated by hydroxide over a wide pH range.  In a study  of
the relative mobility of metals in soils at pH 5, Cr(lll) was found to be the least mobile (Griffin and Shimp
1978).

       Acidification agents (such as sulfur) and reducing agents (such as leaf litter, acid compost, or
ferrous iron) may help to convert Cr(VI) to Cr(lll) (Grove and Ellis 1980).  Because hexavalent chromium
itself is a strong oxidizing agent under acidic conditions, Cr(VI) will be readily reduced to Cr(lll) even
without the addition of strong reducing agents.  After the reduction, liming of the soil will precipitate
                                              28

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Cr(lll) compounds. Precipitation of Cr(lll) occurs at pH 4.5 to 5.5, so little soil pH adjustment is neces-
sary.  Caution is required, however, because Cr(lll) can be oxidized to Cr (VI) under conditions preva-
lent in many soils; e.g., under alkaline and aerobic conditions in the presence of manganese.

       Acidification requirements for a particular soil need to be determined. Three moles of ferrous
sulfate will reduce one mole of Cr(VI).  More than this amount will probably be needed to account for
other reduction  reactions occurring in the soil.  The quantity of organic material cannot be predicted from
stoichiometric considerations. After the acidification and reducing steps, liming materials are applied to
raise the pH to greater than 5.

       Leaf litter and compost are easily applied to soils by standard agricultural methods if site/soil
trafficability is suitable.  Ferrous sulfate may be applied directly to the soil or through an irrigation
system. Reduction of Cr(VI) must occur under acidic conditions and be followed by liming to precipitate
Cr(lll). Acidification and liming are standard agricultural practices.

       The pH of the system must be maintained  at greater than 5.  Periodic reliming may be neces-
sary to ensure that the chromium is immobilized in the soil.

       Status of the Technology. Laboratory data support the theory of this treatment method. Soils
have been treated  under field conditions. The  in situ reduction of hexavalent chromium to trivalent
chromium has been accomplished in Arizona well water by using minute quantities of a reducing agent
(Banning and Black 1987).

       In Japan, remedial action was  taken at  sites contaminated by the disposal of chromite roast
residues from the manufacture of sodium bichromate.  The primary contaminated areas were exca-
vated, and secondary contaminated areas were treated with the reducing agent ferrous sulfate.  The
soluble hexavalent chromium was reduced to insoluble trivalent chromium (Sanning and Black 1987).

       Secondary Impacts. Tillage increases the susceptibility of a  site to water and wind erosion, and
organic materials may have many effects on soil properties, including the following:

       • Degree of structure.

       • Water-holding capacity.

       • Bulk density.

       • Immobilization of nutrients, which hinders degradation of organic wastes.

       • Reduction in soil erosion potential.

       • Soil temperature.

       Organic materials may also cause excessive nitrate levels in receiving waters, depending on the
nitrogen content and degree of mineralization of the material.

        Equipment, Exogenous Reagents, and Information Required. Power implements, tillers,
applicators, and an irrigation system are  necessary to apply reducing, acidifying, and liming materials.
Run-on and runoff  controls may have to be installed to prevent erosion and drainage problems.  Rea-
gents used include acidification agents (e.g., sulfur) and  reducing agents (leaf litter, acid compost, or
ferrous sulfate). Liming  materials are also used. Additional information requirements prior to implemen-
tation are as follows:

       • Characterization and concentration of metals, particularly Cr(VI), arsenic, mercury, and other
         constituents whose treatment requirements  may be incompatible.

       • Acidification, reduction, and  liming reaction rates.
                                               29

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        Advantages of the Addition of Reducing Agents to Treat Chromium.  The advantages of this
technique are as follows:

        •  Ease of application by standard agricultural methods.

        •  Has been demonstrated in the field.

        Disadvantages of the Addition of Reducing Agents to Treat Chromium. This technique has the
disadvantage that reliming may be necessary at intervals to ensure that the chromium is immobilized in
the soil.

Addition of Reducing Agents to Treat Selenium

        Hexavalent selenium [as selenate (SeO2)], the dominant form of selenium in calcareous soils,
is highly mobile in soils.  Elemental selenium and selenite [Se(IV)] are less mobile in soils.  Hexavalent
selenium can be reduced to Se(IV) or Se under acid conditions.  Reduction of selenium occurs naturally
in soils. Elemental selenium is virtually immobile in soils.  The Se(IV) will participate in sorption and pre-
cipitation reactions, but unlike the metals discussed previously, selenite is an anion (SeOa2), and its po-
tential leachability will increase with increasing pH. Therefore, at a site that contains selenium as well
as other metals, selenium could not be treated if increased pH were required as part of the treatment for
the other metals.

        Selenium reduction studies have been limited to those involving the basic chemistry of selenium
in soils. Wastes containing hexavalent selenium (SeO*2)  but no significant amounts of other metallic
constituents are the most amenable to treatment by reduction. Before treatment, the soil must be
acidified to pH 2 or 3  with sulfur or another agricultural acidifying agent. Acidification requirements for
the particular soil must be determined experimentally.  If site trafficability is suitable, leaf litter or com-
post are easily applied to soils by standard agricultural methods. Ferrous sulfate may be applied
directly to the soil or through an irrigation system. Two moles of ferrous sulfate will reduce one mole of
Se(IV).  More than this amount should be added, however, to account for other reduction reactions that
may occur in the soil. The quantity of organic material cannot be predicted from stoichiometric consid-
erations.

        The addition of reducing agents speeds up the natural process of selenium reduction in soils.
Thus, the  potential level of treatment should be high. Once reduction has occurred, however, the soil
must be kept acidic.  Reapplication of an acidifying agent may be necessary as required to maintain the
pH at between 2 and  3.

        Secondary Impacts. Low pH will adversely affect microbial activity and the degradation of
organic waste constituents. Tillage may increase the susceptibility of the site to water and wind erosion.
Organic materials may have many effects on soil properties, including:

        •  Degree of structure.

        •  Water-holding capacity.

        •  Bulk density.

        •  Immobilization of nutrients, which hinders degradation of organic wastes.

        •  Reduction of soil erosion potential.

        •  Soil temperature.

        Organic matter may also result in excessive nitrate levels in receiving waters, depending on the
nitrogen content and the degree of mineralization of the material.

        Equipment, Exogenous Reagents, and Information Required.   Power implements, tillers, and
applicators are needed to prepare the site and to apply the acidifying agent and reducing agent. Runoff
and run-on controls may be necessary to prevent erosion and drainage problems. Exogenous reagents
required are sulfur or some other agricultural acidifying agent and ferrous sulfate.  Additional information
                                              30

-------
requirements prior to implementation of in-place treatment techniques for reduction of selenium are as
follows:
       • Characterization and concentration of metals, particularly selenium. (Treatment of selenium
         is incompatible with treatment of all other metals.)

       • Oxidation state of metallic ions.

       • Clay content of soil.

       • Acidification and reduction reaction rates.

       Advantages of Adding Reducing Agents to Treat Selenium. The advantages of this technique
are as follows:
       • Particularly amenable to the treatment of wastes containing hexavalent selenium but no
         significant amounts of other metals.

       • Ease of application of reagents by standard agricultural methods.

       • Potential level of treatment should be high.
       Disadvantages of Adding Reducing Agents to Treat Selenium. The disadvantages of this
technique are as follows:
       • Not suitable for sites where an increased pH is required as part of the treatment for other
         metals.

       • Acidification requirements must be determined experimentally.

       • After reduction has occurred, soil must be kept acidic, which can entail reapplication of an
         acidfying agent.

       • Organic matter can cause excessive nitrate levels in receiving waters.

3.3.1.3 Chemical Dechlorination Reactions

       Chemical dechlorination processes use specially synthesized chemical reagents to destroy
hazardous chlorinated molecules or to detoxify them to form other compounds that are considered less
harmful and environmentally safer.  In recent years, several dechlorination processes using different
reagents have been developed to detoxify PCBs and many chlorinated organic compounds.  The
residue structures are generally nontoxic or lower in toxicity than the original compound. These proc-
esses were first developed for the treatment of PCB-containing oils, but several have potential applica-
tion to in situ treatment of contaminated soils.

       The reaction mechanism is nucleophilic substitution. Nucleophilic substitution removes chlorine
from aromatic compounds by two mechanisms: the intermediate complex mechanism and the benzyne
mechanism (Wilson 1987). Discussions of the dechlorination reactions in the following subsections are
based on the reagent used in the process.

Acurex Process
       The Acurex process is a two-step procedure. First, the organics are extracted from the soil with
a special blend of solvents. The solvents are then treated with a proprietary sodium-based reagent to
destroy the contaminants, in transformer oil, 2,3,7,8-TCDD has been reduced from 200 to 400 ppt to
40 ± 20 ppt by the Acurex process.  The process has only been demonstrated to be applicable to
treatment of PCB-contaminated oils. A commercial unit designed to treat soil is in the development
stage (USEPA 1986). This process is  not applicable to aqueous waste. The residues from the process
include sodium chloride in sodium hydroxide solutions. It was noted that the sodium-based reagent
process developed by Acurex Corporation should never be used in the field because of its explosive
nature  (Arienti et al. 1986).
                                              31

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PPM Process

       The PPM process uses a proprietary sodium reagent to dechlorinate organic molecules. A solid
polymer is generated (on the average about one 55-gallon barrel for every 10,500 gallons of oil treated).
This substance (although regulated) can be more easily disposed of than the chlorinated organics.
PPM currently has under development a dechlorination process designed to work on soils; however, no
information is available on the process (Arienti et al. 1986).

Alkali Polyethylene Glycolate (APEG) Process

       These processes use polyethylene glycols (PEG) or their derivatives that have been reacted
with alkali (usually potassium) metals or their hydroxides to dechlorinate. When alkali metals are used,
the reagents are susceptible to decomposition by water.  The use of alkali metal hydroxides may solve
this problem.

       Dioxin and PCBs can be destroyed in soil by using reagents prepared from potassium and
polyethylene glycols (KPEG). Moisture adversely affects the rate of the reaction. The APEG reaction
with PCBs proceeds rapidly (from 10 minutes to several hours) under mild conditions in a nonpolar
medium such as transformer oils or in hydrophobic solvent, such as toluene or hexane (Kornel and
Rogers 1985).

       In 1978, the Franklin Research Institute began studies to develop a dechlorination reagent. The
research identified a compound that can be synthesized  from sodium, polyethylene glycols, and oxygen.
This reagent, called NaPEG, was formulated by mixing molten sodium  (60 g) with 1 liter of polyethylene
glycol having an average molecular weight of 400. It was first applied to the dechlorination of dielectric
fluids containing  PCBs.  Later, this reagent (generally referred to as APEG) was also proven to be
effective for the detoxification of dioxin-contaminated soils.

       In the 1982 research performed by the U.S. EPA and Wright State University, actual dioxin-
contaminated soils were effectively dechlorinated under laboratory conditions (Arienti et al. 1986).

       Laboratory research conducted in 1985 by the U.S. EPA and Galson Research Corporation
using 1,2,3,4-tetrachlorodibenzo-p-dioxin (TCDD) demonstrated that chlorinated dioxin levels in soil may
be chemically reduced by applying APEG-type reagents (Arienti et al.  1986). In situ and slurry testing,
with potassium hydroxide/polyethylene glycol 400/dimethyl sulfoxide (KOH/PEG/DMSO) and potassium
hydroxide/2-(2-methoxy ethoxy ethanol)/dimethyl sulfoxide (KOH/MEE/DMSO) reagents on contami-
nated soils containing an initial concentration of 2000 ppb showed quite favorable results, which are
presented in Tables 10 and 11. Several key factors were uncovered during these experiments:

       • Temperature increases from 20° to 70°C during the in situ process indicated a dramatic
         improvement in reaction efficiency, i.e., an increase from 50 to 90 percent.

       • No difference between reagent formulations was noted at 70°C during in situ testing.

       • Dilution of the reagent with water was not effective in reducing the amount of reagent required
         during the in situ process.
       • A removal efficiency of 99.5 percent TCDD (from 2000 ppb to 1 ppb) was realized after 12
         hours at 70°C during the slurry processing.

        Formulations of APEG containing polyethylene glycols having  a molecular weight of 400 to 600
form biphasal systems with polar solvents and require agitation for intimate raagent-pollutant contact. In
static systems, the reagent at the interphase is depleted, products will  build up, and the reaction rates
decrease. Although viscous reagents such as APEG-400 or 600 function quite well in biphasal agitated
reactions, they are quite slow to penetrate and decontaminate soils that contain PCBs.  Results of the
study performed by EPA indicate promise for in situ application of the KPEG-350M reagent formulations
(Kornel and  Rogers 1985). A nonpolar solvent for PCB dissolution was used in the investigations of
APEG-PCB  reactions, and a reagent that is completely miscible with the hydrophobic and hydrophilic
                                             32

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solvent was formulated. This reagent is based on polyethylene glycol monomethyl ether (average mo-
lecular weight of 350) and formulated with potassium hydroxide in either the pellet form or as a 60
percent solution.  It is miscible with water as well as with hydrocarbons such as toluene, hexane, and
other nonreactive solvents, and its viscosity is lower than the APEG 400 and 600 reagents. The
characteristics of this reagent (called APEGM) indicate that it may be a useful candidate for in situ
application.

Table 10. Summary of Results of In Situ Processing • All Soils Initially At 2000 ppb*


Reagent
1.1:1 KOH/PEG/DMSO
1 1 1 KOH/PEG/DMSO
1-1:1 KOH/PEG/DMSO
2:221 KOH/MEE/DMSO/WATER
2 2 2.1 KOH/MEE/DMSO/WATER
222:1 KOH/MEE/DMSO/WATER
2:221 KOH/MEE/DMSO/WATER
2 2 26 KOH/MEE/DMSO/WATER
222:30 KOH/MEE/DMSO/WATER
22230 KOH/MEE/DMSO/WATER

Wt% in
soil
20
20
20
20
20
20
20
20
50
20

Temperature,
°C
20
70
70
70
70
70
70
70
70
70

Time,
days
7
7
1
1
1
4
7
7
7
7
Final TCDD
average
concentration,
ppb
980
<1
53
2.8
3.3
21
1.2
21
18
50
Blanks - All
'Source.  Peterson et al  1985
Table 11.  Results of Slurry Processing*
Reagent
1.1:1 KOH/PEG/DMSO
1:1:1 KOH/PEG/DMSO
1:1:1 KOH/PEG/DMSO
1:1-1 KOH/PEG/DMSO
1:1:1 KOH/PEG/DMSO
1:1:1 KOH/PEG/DMSO
Temperature,
°C
180-260
180
150
70
70
25
Reaction
time, h
4
2
2
2
05
2
Final TCDD
concentration, ppb
<1
<1
<1
<1
15
36






        Blanks - all <1 ppb TCDD
        Spikes - % recovery in soil - 0.1 -5 9

        'Source: Peterson et al.  1985.

        This study investigated the effect of the APEG concentration and dilution in water and organic
 solvent on the dehalogenation of Aroclors 1242 and 1260 with potential application for the in situ
 destruction of PCBs in soil (Kernel and Rogers 1985). Polyethylene glycol monomethyl ether of aver-
 age molecular weight [350 daltons (PEG-350M)], potassium hydroxide, toluene, and a proprietary
 solvent were used. The proprietary solvent was dimethyl sulfoxide (DMSO), patented by the Galson
 Research Corporation.  It has been demonstrated that even dilution with H2
-------
several feet deep over a selected area with minimal energy. Thus, a combination of the reagent,
proprietary solvent, and radio frequency heating is promising for the in situ treatment of heavily contami-
nated soils.

       Brunelle and Singleton (1985) reported that the more highly chlorinated PCS mixtures (e.g.,
Aroclor 1260, Aroclor 1254) react readily with PEG/KOH or PEGM/KOH at temperatures as low as -6°C,
and contaminated soil samples may be effectively treated with this reagent.

       In a two-step process reported by Novinson (1985) polychlorinated biphenyls are first reduced
to unsubstituted biphenyl by using a mild reducing agent such as sodium borohydride in methanol/
water. This is followed by oxidation with potassium permanganate to yield simpler, less-toxic, and
more-biodegradable organic carboxylic acids.  This process can be used on site to treat contaminated
soils; however, no data are available.

       Whereas laboratory studies investigated in situ applications of APEG to contaminated soils,
recent research has focused on slurry application of the reagent to dioxin-contaminated soils and
wastes.  The APEG process has been tested in the laboratory on 2,3,7,8-TCDD-contaminated soils
(USEPA 1986). In a laboratory-scale slurry process, PCDD- or PCB-contaminated soil (2000 ppm) was
reacted with the KPEG reagent, and the concentration was reduced to below 1 ppb after being heated
to 75°C and being mixed for 2 hours. The reagent was removed for reuse (>90 percent).  A 1 to 10 ton/
day slurry process is being prepared for field verification on actual waste.

       The results obtained by using the IT/SEA Marconi reagent (a polyethylene glycol-based mix-
ture) to treat a PCB-contaminated concrete floor indicate the reagent is effective in reducing the concen-
tration of PCBs on the surface or contained within the upper 1/2 inch of concrete (Taylor et al. 1989).

       Status of the Technology.  Chemical dechlorination with different reagents has been tested both
as a batch reactor process and an  in situ process. To date, the batch reactor process has been more
successful in terms of destruction efficiency. The estimated cost of the batch  process is less because
the chemical reagent can be recovered under  enclosed and controlled conditions, whereas a chemical
reagent that is added directly to the soil in the  field cannot be recovered. In general, an in situ process
is desirable when a large quantity of contaminated soil  is involved in which the level of contamination is
not extremely high (10 tolOO ppb).  In these cases, the quantity of soil that would have to be excavated
to destroy a small quantity of contaminant may not be justified (Arienti et al. 1986).

       Secondary Impacts.  Heating the soil,  which is  necessary for the reaction to occur, may cause
increased microbial activity in the area as well as changes in other soil properties. The  application of
reagent to the soil surface may cause the formation of reaction byproducts that are not well understood
and may be more toxic than the contaminants being treated.
       Equipment, Exogenous Reagents, and Information Required. Methods for heating the soil,
delivering the reagent to the contaminated subsurface, and mixing the reagent and the soil are required.
An alkali metal hydroxide (e.g., KOH) and polyethylene glycol (PEG) are the required reagents. A
solvent and water may also be necessary depending on the specific  reaction.

       The following information is required before implementation of this technique:

       • Vertical and area! extent of contamination.

       • Soil physical characteristics (percentage clay, sand, etc.).

       • Types of chemical contaminants.

       • Soil moisture content.

       Advantages of the APEG Process.  The advantages of the APEG process for in situ treatment
of soils are as follows:
       • The process is effective  for treating  PCBs, TCDDs, and other chlorinated hydrocarbons.

       • The reagents are readily available.
                                              34

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       Disadvantages of the APEG Process. The disadvantages of the APEG process are as follows:

       • Water can adversely affect the rate of reaction.

       • Reaction byproducts are currently not well understood.

       • The need to deliver, mix, and heat the reagent and the soil in situ may limit the applicability of
         the technology.

3.3.1.4 Polymerization

       A polymer is a large molecule built up by the repetition of small, simple, chemical units. A
polymerization reaction is the conversion of a particular compound to a larger chemical multiple of itself
(Kirk Othmer 1982). The resulting polymer often has physical and chemical properties different from the
initial unit, and it could be less mobile in the soil system.

       Demonstration has shown that naturally occurring iron and sulfates in contaminated soil may
catalyze initial polymerization of contaminants. Treatment solutions containing sulfate-related constitu-
ents have been used successfully in polymerization reactions in the soil (Williams 1982).

       While working with grouting materials and polymeric agents, Mercer et al. (1970) found the
process of in situ immobilization with these agents expensive and complicated  by the logistics of obtain-
ing widespread coverage without  an excessive number of injection wells.

       Chemical polymerization  is most effective for immobilization of organic constituents, preferably
those with more than one double  bond. General categories of constituents suitable for polymerization
include aliphatic, aromatic, and oxygenated monomers such as styrene, vinyl chloride, isoprene, acrylo-
nitrile, etc. When used for multiorganic contamination, the catalysts and activators necessary to achieve
polymerization may interact with one another.

       A 2:1 ratio of the volume of  catalyst and activator to the volume of contaminant is used. Two
applications  of the catalyst and activator are required, and they should be applied separately to prevent
reactions before they contact with wastes. A wetting agent is added to promote rapid and uniform
dispersion of solutions throughout the contaminated area. If ground temperature falls below 50°F, it
may be necessary to warm the treatment solution to 50°F before its use.  Because of the acidic nature
of treatment reagents, corrosion-resistant application equipment is required.

       If the surficial zone is too  shallow to tolerate sufficient injection pressure for dispersing catalyst
and activator solutions, installation of exfiltration galleries is required (e.g., a 2-inch-diameter perforated
PVC casing, buried in trenches below ground surface across the contaminated zone).  A riser pipe and
manifold  header connect each gallery to solution tanks containing the catalyst and the activator.

       This technology is moderate to difficult to apply. In a field study, it was found that obtaining
widespread coverage was difficult without an excessive number of injection wells.

       The level of treatment achievable varies and depends on waste and soil conditions. The poten-
tial for long-term immobilization is unknown at this time.

       The polymerized area may exhibit decreased infiltration and permeability.  Catalysts and
activators are needed. Vendors should be consulted as to equipment needs.

       Boyd and Mortland (1985) describe the formation of dibenzo-p-dioxin radical cation and polym-
erization  on a simple clay mineral [Cu(ll)-smectite] under mild conditions.  The  radical cation  polymer-
ized to form dimers and trimers.  Radical cations of 1- and 2-chlorodibenzo-p-dioxin were also formed
on Cu(ll)-smectite.  The results of this work suggest the possibility for detoxification of dioxins through
catalysis by a simple mineral material.

       In situ polymerization was successfully performed to remedy a 4200-gallon acrylate monomer
leak from a corroded underground pipeline into a glacial sand and gravel layer (Sanning and Black
1987).  Soil borings indicated that as much as 90 percent of the monomer had  been polymerized by
injection of a catalyst, an activator, and a wetting agent.
                                               35

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Status of the Technology
       The reliability of the treatment is unknown because no information exists regarding its long-term
effectiveness.  In situ polymerization is suitable mostly for ground-water cleanup after land spills or
underground leaks of the pure monomer. Applications to uncontrolled hazardous waste sites are
limited.
Secondary Impacts
       The polymerized area may exhibit decreased infiltration and permeability.
Equipment, Exogenous Reagents, and Information Required
       Corrosion-resistant application equipment is needed because of the acidic nature of the treat-
ment reagents. In some cases, exfiltration galleries are also required.  A riser pipe and manifold header
connect each gallery to solution tanks containing the exogenous reagents (catalyst and activator)  used.
Wetting agents are also required.
       The following information is needed before the implementation of polymerization techniques.
       • Characterization and concentration of wastes, particularly organics, at the site.
       • Potential for polymerization of waste constituents.
       • Polymerization products.
       • Depth, profile, and areal distribution of constituents.
       • Iron and sulfate content in soil.
       • Catalysts  and activators present in  soil.
       • Trafficability of soil and site.
Advantages of Polymerization
       Polymerization offers the following advantages:
       • Effective for immobilization of aliphatic, aromatic,  and oxygenated monomers (e.g., styrene,
         vinyl chloride, isoprene, acrylonitrile).
       • May be suitable for detoxification of dioxins through catalysis by a simple mineral material.
Disadvantages of Polymerization
       This technology has the following disadvantages:
       • The treatment can be expensive and complicated by the logistics of obtaining widespread
         coverage  without an excessive number of injection wells.
       • Technology can be difficult to apply.
       • The reliability and long-term effectiveness of this treatment are unknown.
       • Limited application and difficulty of  initiating sufficient contact between the catalyst and  the
         dispersed monomer are major disadvantages.
3.3.2. Biological Degradation
       Biodegradation is an important environmental process that causes the breakdown of organic
compounds.  The ultimate goal of biodegradation is to convert organic  wastes into biomass and harm-
less byproducts of microbial  metabolism such as CO2, ChU, and inorganic salts.
        Microorganisms (principally bacteria,  actinomycetes, and fungi) make up the  most significant
group of organisms  involved in biodegradation, and soil environments contain a diverse microbial
population. Two types of parameters influence the rate of biodegradation:

                                              36

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        1) Those that determine the availability and concentration of the compound to be degraded or
           that affect the microbial population site and activity.
        2) Those that control the reaction rate.
        Some of the important parameters affecting biodegradation  include pH, temperature, soil
moisture content, soil oxygen content, and nutrient concentration (Bonazountas and Wagner 1981).
        Table 12 lists rate constants of organic compounds in soil. Table 13 presents rates in anaerobic
systems.
Table 12.  Biodegradation Rate Constants For Organic Compounds In Soil*
                                               Test Method
Compound
Aldnn, dieldnn
Atrazine
Bromacil
Carbaryl
Carbofuran
Dalapon
DDT
Diazmon
Dicamba
Fonofos
Glyphosate
Heptachlor
Lindane
Linuron
Malathion
Methyl parathion
Paraquat
Parathion
Phorate
Picloram
Simazme
TCA
Terbacil
Tnfluralm
2,4-D
2,4,5-T
Die-Away
(day1 )
0013
0019
00077
0037
0047
0047
000013
0023
0022
0012
0 1
0011
00026
00096
1 4
016
00016
0029
00084
00073
0014
0059
0015
0008
0066
0035
1<1CO2 Evolution
(day1 )

00001
00024
00063
00013


0022
00022

00086








00008


00045
00013
0051
0029
               'Sources Lyman et al  1982, USEPA 1988, Dragun 1988
Table 13. Biodegradation Rate Constants For Organic Compounds In Anaerobic Systems'
Compound
Carbofuran
DDT
Endrin
Lindane
PCP
Trifluralin
Mirex
Methoxyclor
2,3,5,6-Tetrachlorobenzene
Bifenox
In Soil
Die-Away 14CO2 Evolution
(day1 ) (day1 )
0026
0.0035
0.03
00046
007
0025




In
sludge
(day1 )






0.0192
9.6
1272
6.27
               "Source: Lyman etal. 1982
                                               37

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       Prior to the implementation of in situ treatment techniques for modifying the soil properties, the
following information is required:

       • Characterization and concentration of wastes, particularly organics at site.

       • Microorganisms present at site.

       • Biodegradability of waste constituents (half-life, rate constant).

       • Biodegradation products (partially hazardous byproducts).

       • Depth, profile, and areal distribution of constituents.

       • Soil properties for biological activity (such as pH, oxygen content, moisture and nutrient
         contents, organic matter, temperature, etc.).

       • Soil texture, water-holding capacity, degree of structure, erosion potential of the soil.

       • Trafficability of soil and site.

       Four approaches are used or evaluated for in situ biological treatment of hazardous waste
materials in contaminated soils:

       1) Enhancement of the biochemical mechanisms for detoxifying or decomposing the soil
          contaminants.

       2) Augmentation with exogenous acclimated or specialized microorganisms (mutants).

       3) Application of cell-free enzymes.

       4) Vegetative uptake.

       Although it cannot be considered an in situ treatment, soil extraction/excavation followed by
onsite biological treatment is one of the technologies most frequently used in bioremediation of hazard-
ous waste sites.

3.3.2.1. Enhancement of Biochemical Mechanisms

       Microorganisms (principally bacteria, actinomycetes, and fungi) are important in decomposition
or detoxification processes.  Therefore, treatments applied to the soil to enhance biological processes
must not alter the physical environment in such a way that it would severely restrict microbial growth or
biochemical  activity. Based on these restrictions, treatments that may enhance microbial activity
(biochemical mechanisms) in hazardous-waste-contaminated soil are discussed in the following  subsec-
tions.

Colloidal Gas Aphrons

       The  introduction of microscopic bubbles of gas (gas aphrons) into the soil can enhance aerobic
biodegradation of dissolved and dispersed organic contaminants by delivering gases at greater than
their solubility limits. In laboratory experiments, colloidal gas aphrons have been shown to increase the
concentration of gases present within the soil matrix.

       Microscopic dispersions of a gas in water are referred to as colloidal gas aphrons (CGAs),
which typically exist as 25- to 50-u.m gas bubbles with the characteristics  of a free-floating soap bubble.
In the microdispersion media, CGAs have a film-like surface of sufficient strength to prevent their
coalescence, even when pressed together (Michaelsen et al. 1984).  Because they do not coalesce, the
microscopic  bubbles have a very large surface area. One liter of CGA containing 60 percent gas as 24-
u.m-diameter bubbles represents a total bubble surface area of 150 m2  (Michaelsen et al. 1984). Any
water-soluble surfactant and a gas of limited solubility (e.g., oxygen, carbon dioxide, or  nitrogen) can  be
used to generate CGAs.
                                              38

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       Because they are so small, CGAs can remain in suspension and flow through channels such as
those that exist in sandy soils. They may also be pumped with positive displacement pumps without
losing their integrity or characteristics (Michaelsen et al. 1984).

       Sebba and Barnett (1981) describe how CGAs are formed. A rapid stream of dilute surfactant
solution is passed through a Venturi throat, where a restricted orifice is located. At this point, gas
(usually air) is sucked into the stream under an excess pressure of about 1 atmosphere.  As a result of
the turbulent jet and the slow entry of the gas, the solution enters in the form of microbubbles. For a
shell-encapsulated bubble to be generated, the gas must break through (at least twice) an aqueous-gas
surface that has a surfactant monolayer at the surface. The turbulence ensures that, in contact, a
'"bubble" introduced by sparging through a fitted disc or by gas precipitation is likely to be gas sur-
rounded by the bulk water and have only one interface; therefore, it essentially is a gas-filled hole.  A
high concentration of  CGA bubbles is obtained  by recycling the suspended gas bubbles in solution
through the CGA generator a few times.

       In situ  laboratory degradation studies (Michaelsen et al. 1984) have shown that injecting a
combination of CGAs and Pseudomonas putida plus microbial nutrients into an anaerobic sand matrix
spiked with 300 u,g/L phenol degraded 60 percent of the phenol in 24 hours.  The CGAs converted the
anaerobic matrix into  an aerobic environment, which allowed the P. putida to degrade the contaminant.

       The use of CGAs at uncontrolled hazardous waste sites depends on the microdispersion as a
source of oxygen for in situ bioreclamation.  The contaminated medium retains the CGAs for much
longer periods  of time than it does air directly injected into the contaminated matrix because directly
injected air moves rapidly toward the unsaturated zone and allows little oxygen retention.

       This technology is applicable to waste sites contaminated with biodegradable chemicals.
Potential treatment levels range from low to medium, depending on the waste types present. Treatment
levels also depend on the soil type and condition and the  accessibility of the contaminated area.

       This technology may be applied with relative ease, depending on soil parameters.  It is best
suited for sandy soils.

       Status of the  Technology. Applications of colloidal gas aphrons have been limited to bench-
and pilot-scale studies.  This technology has not been demonstrated in field-scale studies.

       Secondary Impacts. This technology increases soil oxygen levels dramatically , and the  intro-
duction of bacteria may cause other species present to decline in numbers. Also,  certain wastes may
be degraded into precursor species, which may or may not be less hazardous than the original
contaminant(s).

       Equipment, Exogenous Reagents, and Information Required. An injection plow is needed to
inject CGAs into the soil matrix. The exogenous reagents needed include the CGA microdispersion,
appropriate bacteriological species for the waste type to be decomposed, and nutrients to sustain the
microbes during the decontamination process.

       The following information is needed for effective application of this technology:

       •  Soil characteristics, e.g., particle size distribution and porosity.

       •  Bacterial species conducive to degrading waste(s)  at the contaminated site.

       •  Area of contamination.

       Advantages of CGA. The advantages of using this technology for hazardous waste site reme-
diation are as follows:

       •  The cost of application is low.

       •  It enhances biodegradation of waste products.

       •  A wide variety of surfactants can be used to create the microdispersion.
                                             39

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        Disadvantages of CGA. The disadvantages of this technology are as follows:

        • Waste product can degrade into unknown compounds.

        • Its application is limited because it is most appropriate for use in sandy soils.

        • It does not completely degrade the waste products; wastes remain after the technology has
         been applied.

        • Additional treatment is required for permanent remediation of a site.

Modification of Soil Properties to Optimize Environmental Conditions

        Because the activity of microorganisms depends greatly on soil conditions, modification of soil
properties such as moisture content, oxidation-reduction (redox) potential, pH, nutrient content, and
temperature is a viable method for enhancing the microbial activity in the soil. Studies have shown that
soil temperatures should be between 50° and 60°C (Atlas and Bartha 1981); soil potential should be
greater than -15 bars (Sommers et al. 1981); pH should be between 5 and 9 (Alexander 1977, Atlas and
Bartha 1981); and redox potential should be between pe + pH of 17.5 to 2.7 (Baas Becking et al. 1960).
Soil pH and redox boundaries should be carefully monitored when chemical and biological treatments
are combined. (Details of application methods for soil modification techniques are discussed in
Appendix A.)

        So/7 Moisture.  Moisture control may take the form of supplemental water to the site (irrigation),
removal of excess water (drainage, wellpoints), a combination of techniques for greater moisture
control, or other methods (e.g., soil additives).  Furthermore, the addition of vegetation to a site will
increase evapotranspiration of water and therefore assist in retarding the downward migration of water
(i.e., leaching).

        In a review of how soil water affects the decomposition processes in soils, including pesticide
degradation, Sommers et  al. (1981) suggested that, in pesticide degradation, the water alters general
microbial activity and affects the kinds of microorganisms that are metabolically active in the soil.  Ou et
al. (1983) observed rapid mineralization of methyl  parathion in soils at -0.1 and -0.33 bar soil moisture
tension and the formation of bound residues. The ratio of the degradation products (p-nitrophenol to  p-
aminophenol) increased as the soils became drier. In dry soil (-15 bar), mineralization of methyl  para-
thion and bound residue formation were slower. Limited experimentation indicates that degradation
rates are highest at soil tensions between 0 and -1  bar.

        The degradation of hazardous organic compounds can be accelerated by optimum soil mois-
ture, and this approach may be sufficient to bring about the required degradation.  For constituents
relatively easy to degrade, however, more rapid treatment of the contaminated soil can be achieved
when moisture control is used in combination with other techniques.

        Various additives  are available to enhance moisture control.  For example, the water-retaining
capacity of the soil can be enhanced by adding water-soluble substances. Nimah et al. (1983) evalu-
ated three such synthetic substances for use in soils in arid areas and found that two of them increased
the water content of the soil. Water-repelling agents that diminish water absorption by soils are also
available.  Conversely, water-repelling soils can be treated with surf ace-active wetting agents to  improve
water infiltration and percolation.  Other soil characteristics that have been modified by surface-active
agents include acceleration of soil drainage, modification of soil structure, dispersion of clays, and
making soil more compactable. Evaporation retardants are also available to retain moisture in a soil.

        Status of Technology.  Moisture control practices are widely implemented  in agriculture and are
generally applicable to hazardous waste sites with certain precautions taken for leachate collection.

        Secondary Impacts.  Secondary impacts of some of these amendments or additives on soil
biological activities, other soil physical properties, soil chemical properties, and environmental effects,
(e.g., teachability and degradability) are discussed by Brandt (1972). Leaching of soluble hazardous
                                              40

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compounds also may occur, especially when the soil-water partition coefficient is less than 10. There-
fore, caution must be exercised at a hazardous waste site to ensure that drainage water disposed of off-
site is not contaminated with hazardous substances.  Provisions must be made to collect, store, treat, or
recycle water that is not acceptable for offsite release. The drainage system should be managed to
prevent or minimize contamination problems. Erosion may also be a problem.

        Equipment, Exogenous Reagents, and Information Required. When natural precipitation is
insufficient to maintain soil moisture within a near optimal range for microbial activity, irrigation may be
necessary.  Water can be applied by standard irrigation methods, i.e., subirrigation or overhead (sprin-
kler) irrigation. Irrigation should be applied frequently in relatively small amounts that do not exceed
field capacity so as to minimize leaching (Fry and Grey 1971).

        The ease of controlling moisture depends on how easily water is controlled at the site and on
the availability of a suitable water source (e.g., transport distance, drilling of new wells, availability, and
cost of energy for pumping). Controls for erosion and proper drainage to handle runoff are also neces-
sary.

        A properly designed drainage system either removes excess water or lowers the ground-water
level to prevent waterlogging.  Surface drainage is accomplished by a system of open ditches and
buried tube drains into which water seeps by gravity.  The collected water is conveyed to a suitable
disposal point. Subsurface drainage may also be accomplished by pumping water from the wells to
lower the water table.  Like subsurface drains, wellpoints can be used to lower the table in shallow
aquifers.

        Information concerning the depth to the water table and the permeability of the soils is neces-
sary. Vertical and horizontal hydraulic conductivities are also useful information.

        Advantages of Moisture Control. Moisture control is a standard and relatively easy technique to
implement.  The required equipment and reagents are inexpensive and commonly available.

        Disadvantages of Moisture Control. There is the possibility of generating drainage or leachate
that is contaminated. Care must be taken to control drainage of this material.

        Control of Oxygen for Aerobic Biodegradation. One reason for the common agricultural prac-
tices of tilling and draining the soil is to stimulate the decomposition of organic matter in an aerobic
environment so that nutrients will be mineralized and made available for plant assimilation. Aerobic
metabolism  is more energy-efficient, and microbial decomposition processes are generally more rapid
under aerobic conditions. Although the decomposition of some xenobiotic organic compounds appears
to require anaerobic metabolism, most soil organisms shown to be active in the decomposition of
pesticides and other xenobiotic compounds are aerobic (Alexander 1977; Pal et al. 1980, Baker and
Mayfield 1980; Brunner and Focht  1983; Sims and Overcash 1981).  Therefore, assuring the aerobiosis
of the soil will often enhance the rate of biological decomposition.

       Aerobiosis can also be maintained by the addition of air, oxygen, or other oxidants or oxygen
sources (such as hydrogen peroxide, ozone, and nitrates). Gas injection or infiltration of water contain-
ing these alternative oxygen sources is being used for the  reclamation of soil contaminated with hazard-
ous wastes.  Both ozone and hydrogen peroxide have been demonstrated to enhance dissolved oxygen
levels in soil/ground-water systems and, consequently, to stimulate microbial activity. Ozone and
hydrogen peroxide can also chemically degrade (oxidize) the contaminants completely or partially.
Table 14 summarizes the advantages and disadvantages of some of these oxygen sources.

       Yaniga and Smith (1986) observed an increase in the number of bacteria and  in the degradation
of gasoline with increasing  oxygen concentration  in soil columns treated with four different oxygen/air
mixtures, a nitrogen and pure oxygen mixture, a pure oxygen, and a stabilized hydrogen peroxide
solution.
                                              41

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Table 14. Oxygen Supply Alternatives*

                       Application
   Substance             method
                 Advantages
                                                                    Disadvantages
Air
Oxygen-enriched
 or pure oxygen


Hydrogen peroxide
                       In-line           Economical
In situ wells      Constant supply
                of oxygen possible

In-line           Provides considerably
                higher O2 solubiluty
                 than does aeration

In-line           Moderate cost

               Intimate mixing with
                ground water

               Greater oxygen
                concentrations can
                be supplied to the
                subsurface (100 mg/L
                HzOa provides 50 mg/L
                02)

               Helps to keep well free of
                heavy biogrowth
 Not practical except for trace con-
 tamination <10 mg/L COD

Wells subject to blowout
Not practical except for low levels of
contamination <25 mg/L COD
HzO2 decomposes rapidly upon contact
 with soil, and oxygen may bubble out
 prematurely unless properly stabilized

HzO2 is cytotoxic, however, organisms
 can be acclimated to high concentrations
"Source Wagner and Kosin 1985


       The applicability of microdispersion of air colloidal gas aphrons (CGAs) for treatment of liquid
hazardous wastes by using 60 to 65 percent dispersion of air (or possibly oxygen, ozone, etc., as an
oxygen source) has been tested in laboratory and in situ pilot studies. In situ biodegradation laboratory
tests showed that the injection of a mixture of CGAs,  Pseudomonas putida, and microbial nutrients into
a saturated anaerobic sand matrix containing 300 mg/L of phenol solution  resulted in 60 percent degra-
dation of the phenol in 24 hours (Michelsen et al. 1984).

       Tilling the soil for aeration, a common practice in agriculture, has been recommended for the
reclamation of soil contaminated with hazardous wastes by practitioners and researchers (Arthur D.
Little, Inc. 1976; Thibault and Elliott 1979). Rickabaugh (1988) reported that biodegradation of soil
contaminants was favored by soil conditions similar to those obtained by tilling, i.e., mixing and aerobi-
osis followed by limited oxygen. Soils with high water tables that restrict aeration also may be drained
by common agricultural techniques.

        If the site is too wet, a drainage system must be installed.  The soil can be tilled  periodically to
achieve aeration, and controls are necessary to prevent run-on and runoff of precipitation.

       Achievable treatment levels range from low to high, depending on the biodegradability of the
waste constituents and the suitability of the site and soil for maintenance of aerobic conditions. Retreat-
ment at periodic intervals is necessary to assure that the soil oxygen is at a sufficiently high level.

       Status of the Technology.  The application of soil venting technology to increase aeration of
subsurface soil has been investigated at field scale at the U.S. Air Force Engineering and Services
Laboratory, Eglin AFB, Florida;  by the Naval Civil Engineering Laboratory, Port Hueneme,  California;
and at Hill AFB, Ogden, Utah.  Field-scale results obtained at Hill AFB indicated that soil  venting stimu-
lated biodegradation and that biodegradation may have resulted in 25 percent or more of the remedial
action (Hinchee et al.1987).
                                                42

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       Secondary Impacts. Tillage increases the susceptibility of the site to erosion. The use of
oxidizing agents requires special treatment because they can react violently with certain compounds
and can cause corrosion of the application equipment. They can also oxidize nontarget organic com-
pounds and thus reduce the sorptive capacity of the soil  being treated.  Both hydrogen peroxide and
ozone have two major limitations: they are toxic to bacteria and they may produce gas bubbles that
block the pores in the soil matrix (Lee and Ward 1984).  Hydrogen peroxide can also mobilize metals
(Pb, An) (Wilson et al. 1986).

       Equipment, Exogenous Reagents, and Information Required. A variety of equipment is avail-
able for aerating surface soils, all grouped under the category of tillers. Aeration of soils deeper than
about 2 feet can be accomplished by air injection through wellpoints; however, aeration through well-
points has been used and shown to be effective, primarily for saturated soils.

       Hydrogen peroxide can be infiltrated through surface irrigation systems, shallow infiltration
galleries, or ponds, or be injected into the subsurface through drains or injection wells, depending on the
depth of the contaminated soil layers.

       Advantages of Control of Oxygen for Aerobic Biodegradation. Oxidation can be achieved
through the introduction of such additives as ozone and hydrogen peroxide as well as through tilling.

       Disadvantages of Control of Oxygen for Aerobic  Biodegradation.  Delivery of the reagent to the
subsurface is sometimes difficult. Extensive monitoring may be necessary to ensure uniform application
of oxidizing agents.

       Control by Oxygen for Anaerobic Biodegradation. There is increasing evidence that some
halogenated xenobiotic compounds may be dehalogenated or completely degraded under anaerobic
conditions (Suflita et al. 1982; Suflita and Tiedje 1983; Horowitz et al. 1983; Suflita et al. 1983;
Kobayashi and Rittman 1982; Pfaender and Alexander 1972). Therefore, manipulation of contaminated
soil to create an anaerobic reducing environment that enhances the decomposition of certain hazardous
waste constituents should be considered. Apparently, the redox potential (Eh) of the environment must
be below 0.35V for significant reductive dechlorination to take place, but exact requirements depend on
the individual compounds being reduced (Kobayashi and Rittman 1982).  Reductive reactions may be
catalyzed by both abiotic and biochemical means  in anaerobic environments.

       When a recalcitrant compound has been altered by reductive reactions under anaerobic condi-
tions, it may be more amenable to decomposition  under aerobic conditions. For example, Munnecke et
al. (1982) described the reductive dechlorination of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) under
anaerobic conditions to 2,4-dichlorophenoxyacetic acid (2,4-D), which is readily degraded in the soil
under aerobic conditions.  Laboratory experimentation may show that anaerobic soil conditions followed
by aeration enhances biological decomposition of  some hazardous waste constituents; however, weekly
alternations between anaerobic and aerobic conditions for enhancement of biodegradation of trichlo-
robenzenes in soil were evaluated, and no improvement  in the mineralization rates was found (Mar-
inucci and Bartha 1979). The trichlorobenzenes were mineralized most rapidly under continuous
aerobic conditions. Other classes of compounds may not follow this pattern, however, and more
research  is needed for further evaluation of the potential  for treatment by using alternating anaerobic
and aerobic conditions.  Longer periods between alternations may be appropriate.

       Biodegradation can also be stimulated by  adding other electron acceptors, such as nitrates.
Microorganisms using nitrates as electron acceptors can degrade some phenols and cresols (Wilson et
al. 1986)  and some low molecular-weight polycyclic aromatic hydrocarbons (Luthy and Mihelcic 1987).
Kuhn et al. (1985) also reported that microorganisms present in river alluvium were able to respire
nitrate that was degrading xylene. Although methanes and carbon tetrachloride can be degraded by
nitrate-respiring microorganisms, chloroform and stable chlorinated ethylenes or ethanes (i.e., in oxy-
genated water) cannot (Bouwer and McCarty 1985). Based on their studies, Major et al. (1988) con-
cluded that the addition of nitrate to gasoline-contaminated ground water might be a more economical
and effective remedial action than aeration.  Batlermann  and Werner (1984) also used nitrate as an
alternative oxygen source for decontamination of  an oil spill in the upper Rhine catchment. By adding
                                             43

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nitrate (50 Ib) and nutrients to recovered ground water (in-line) and then injecting it back into the satu-
rated zone, they were able to remove 16.6 tons ot hydrocarbon retained in the pore volume of the
formation in about 300 days.  Laboratory column studies have shown that m-xylene is rapidly mineral-
ized in the absence of molecular oxygen and with nitrate as electron acceptor (Zeyer et al. 1986). In
general, the results from these anoxic column studies (e.g., ground-water infiltration zones, sludge di-
gestors) seem to indicate that aromatic hydrocarbons may be mineralized in the absence of molecular
oxygen. Suflita and Gibson (1984) reported reductive dehalogenation, but not degradation, of naturally
occurring aromatics in environments where the levels of sulfate were relatively high and where sulfate
respiration was taking place.

       Arthur D. Little, Inc. (1976) reported that a proven method of creating anaerobic conditions is to
dike and flood the soil in a fashion similar to that used to grow rice. They cite unpublished work by W.
Farmer at the University of California at Riverside, in which a 1.5-acre DDT-contaminated field was
amended with organic matter and flooded and the soil temperature was increased. The DDT was
completely transformed into ODD in 18 days.  They suggest that, without this treatment, the transforma-
tion to ODD would have taken more than 2 years. Because flooding the soil presents opportunities for
leaching hazardous materials from contaminated soil, it is probably not advisable in most soils contami-
nated with hazardous wastes.  It should be possible to lower the redox potential of the soil, however, by
adding excessive amounts of readily biodegradable organic matter, compacting the soil to reduce oxy-
gen diffusion through large soil pore spaces, keeping the soil wet without exceeding the gravitational
water potential (field capacity), and perhaps deep mulching to impair oxygen diffusion to the soil
surface.

       Reductive dehalogenations or other reductive reactions that lead to decomposition or detoxifica-
tion of specific  hazardous waste constituents should be verified in the literature or through  experimenta-
tion before this treatment is used.

       Depending on the degradative pathway of the constituents, the treatment levels achieved may
range from low to high. This technology may result in only partial degradation,  and aerobic conditions
may have to be established to complete the treatment.  Retreatment may be required to maintain
anaerobic conditions. This treatment may range from moderate to difficult to apply.  Run-on and runoff
controls are necessary.

       Status of the Technology.  Few applications of this method of inducing  anaerobiosis, either in
the field or under laboratory conditions, have been reported (McLean et al. 1988).

       Secondary Impacts.  Inducing anaerobic conditions may result in the formation of toxic volatile
forms of metals (e.g., methylated mercury and arsines), hydrogen sulfide, and other nuisance odor
compounds. Leaching of hazardous constituents may also occur if water addition  is  not carefully
controlled.  Organic materials may affect soil properties such as degree of structure,  water-holding
capacity, bulk density, and temperature. They can  also immobilize nutrients, which hinders the degra-
dation of organic wastes and reduces soil erosion potential. Organic materials can also cause exces-
sive nitrate levels in receiving waters, depending on the nitrogen content and degree of  mineralization of
the material. In the field, the addition of organic materials to create anaerobic conditions is only concep-
tual.
        Equipment and Exogenous Reagents Required. Power implements, compactors, and an
irrigation system are necessary. The exogenous materials required are irrigation water and organic
materials (e.g., mulches).

        Irrigation water for inducing anaerobiosis can be applied by use of standard irrigation practices.
Mulches also may be applied to act as a barrier to oxygen diffusion into the soil. Surface soil may be
compacted to reduce porosity.  Reducing pore size and restricting reaeration will increase the anaerobic
microsite frequency in the soil.  Compaction helps to draw moisture to the soil surface, which lessens
the problems of leaching that can occur if anaerobiosis is achieved by water addition. If the compaction
itself should prove  inadequate to achieve the required degree of anaerobiosis,  water could be added.
                                               44

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Because less water should be required in a compacted soil than in an uncompacted soil, the leaching
potential would be minimized. Readily biodegradable organic materials are applied and incorporated
into the soil so that the soil microbial population will rapidly deplete the oxygen and create anaerobic
conditions while degrading these materials.

        Advantages of Control of Oxygen for Anaerobic Biodegradation. Some recalcitrant aromatic
hydrocarbons can be degraded under anaerobic conditions.

        Disadvantages of Control of Oxygen for Anaerobic Biodegradation. Creating anaerobic condi-
tions in the soil involves manipulating the soil in a complex manner (i.e., moisture control, organic
amendment, compaction, and mulching). Flooding, one method of inducing anaerobiosis, presents
opportunities for leaching hazardous materials from the soil.

        Soil pH.  Depending on the nature of the hazardous waste components contaminating the soil,
it may be advantageous to optimize the soil pH for a particular segment of the microbial community
because both structure and activity are affected by the soil pH (Gray 1978, Alexander 1977). Some
fungi have a competitive advantage at slightly acidic pH, whereas actinomycetes flourish at slightly
alkaline pH (Alexander 1977). Soil pH has also been  shown to be an important factor in determining the
effect various pesticides have on soil microorganisms (Anderson 1978). Near neutral pH values are
probably most conducive to microbial functioning in general. The discovery that fungal  metabolism of
polynuclear aromatics hydrocarbons (PAHs) is qualitatively similar to mammalian metabolism in that
mutagenic arene oxides (epoxides)  are produced as initial oxidation  products (Cerniglia and Gibson
1979, Cerniglia et al.  1979) suggests that fungal degradation of  PAHs in the environment should be
discouraged.  Although the effect of soil pH on the formation of epoxides from PAHs has not been
demonstrated, it may be advantageous to maintain the pH near 7 to  encourage a relatively higher
bacterial activity in soils contaminated with these compounds. Laboratory studies have shown that
increasing soil pH values from acidic to neutral results in an increased biodegradation rate for
benzo(a)pyrene and that mutagenic characteristics for metabolites 7,12-dimethylbenz(a)anthracene
formed in acidic and neutral soil were similar (Park et  al.  1988). Laboratory studies also have shown
that soil pH values higher than those found at the Chem-Dyne Site enhanced the decomposition of
some contaminants of interest (Rickabaugh 1988). This investigation also demonstrated that although
adjusting the soil moisture content to 20 percent and the pH to about 8 resulted in a greater decline of
chlorinated hydrocarbons (compared with the controls), maintaining this high pH appeared to retard this
decline (Rickabaugh 1988).

        In agriculture, the application of fluid lime is becoming more  popular, especially when it is mixed
with fluid nitrogen fertilizer. The combination results in fewer trips across the soil, and the lime counter-
acts the acidity produced by the nitrogen. Limestone  has also been  applied successfully through a
spray irrigation system to a land treatment facility where pharmaceutical wastewaters are treated. Thus,
this technique would be suitable  at hazardous waste sites. Contaminated soil may have to be treated
with crushed limestone or lime products to  raise the pH to the desired range, or with acid-producing
materials or sulfur to lower the pH.

        Lime treatment for soil pH adjustment is dependent on several soil factors, including soil texture,
type of clay, organic matter content, and exchangeable aluminum (Follett et al. 1981). The buffering
capacity of the soil reflects the ability of the soil components to hold a large number of ions in adsorbed
or reserve form. Thus, adsorption or inactivation of H* ions or the release of adsorbed ions to neutralize
OH-ions provides protection against abrupt changes in pH when acidic or basic constituents are added
to the soil. The varying buffering capacity among soils reflects differences in the soil cation  exchange
capacities and will directly affect  the amount of lime required to adjust soil pH. The amount  of lime
required is also a function of the depth of contamination at the site (i.e., the volume of soil to be treated).
Because no guidelines for adjusting soil pH are readily available, the amount of lime required to effect a
pH change in a particular site/soil/waste system must  be determined by a soil-testing laboratory in short-
term treatabilrty studies or soil-buffer tests (McLean 1982).
                                             45

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       The achievable level of treatment is high, depending on the biodegradability of the wastes and
the suitability of the site and the soil. Lime and acidification requirements for a particular soil have to be
determined experimentally.  The buffering capacity of the waste also must be considered. Thorough
mixing is required in the zone of contamination to effect pH change. Because the soil is tilled, runoff
and minor controls are necessary to control drainages and erosion. This technology ranges from easy
to difficult to apply, depending on the trafficability of the  soil and the depth of contamination. Reliming or
reacidification is necessary as treatment progresses.

       Status of the Technology.  Soil pH control is commonly practiced in agriculture and in pollution
control processes to neutralize toxic substances. In agriculture, acidification is practiced much less
commonly than liming. Adjustment of pH is often reported in laboratory tests, but less information is
available on the application of this technique in  pilot-scale studies or in the field.

       Secondary Impacts. Changes in soil pH affect dissolution or precipitation of materials within the
soil. Care must be taken to assure that raising or lowering of soil pH does not increase the mobility of
hazardous materials. Tillage increases the susceptibility of the site to erosion.

       Equipment and Exogenous Reagents Required. Applicators, tillers, and power implements are
required.  Depending on the wastes and the soil characteristics, liming or acidifying material is required.

       Advantages of Soil pH Control. The technology is widely practiced with positive  results. The
required additives are readily available.

       Disadvantages of Soil pH Control. Because thorough mixing is required, extensive disturbance
of contaminated soils may occur. Proper personnel health and safety protections must be implemented.

       Soil Nutrients.  As in the case of all living organisms, microorganisms must have specific
inorganic nutrients (e.g., nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, and trace
metals) and a carbon and energy source to survive. The organic contaminants present in the soil may
provide the carbon and energy source and serve as primary substrates. If the compound of interest is
only degraded cometabolically, however, a primary substrate must be made available for the microbial
population. The primary source of carbon may already  be present in the soil or it may be added (e.g.,
glucose,  acetate, citrate). Carbon sources also could be added if the concentration of contaminants
present in the soil are not sufficient to support an active microbial population; however, the addition of
these compounds could inhibit the biodegradation of the compound(s) of interest as a result of preferen-
tial degradation. Laboratory anaerobic studies performed with 4-nitrophenol-contaminated topsoil have
shown that adding glucose (50 mg/kg) reduced the half-life of the 4-nitrophenol from 12 to 6 days
(Lokke 1985).

       Although most microorganisms can efficiently extract inorganic nutrients from their environment,
their activity may be limited by the availability of nutrients.  This is especially true if  available carbon is
excessive relative to the amount of nitrogen or phosphorus the microorganisms need to degrade it. If
the soil organic carbon, organic nitrogen, and organic phosphorus are determined,  the C:N:P ratio can
be  determined and nutrient availability can be evaluated.  If the ratio of organic C:N:P is wider than
about 300:15:1 and available (extractable) inorganic forms of N and P do not narrow the ratio to within
these limits, supplemental nitrogen or phosphorus should be added (Alexander 1977, Kowalenko 1978).
Lokke (1985) reported that adding 50 mg/kg of nitrate-N under anaerobic conditions to soil concentrated
with 4-nitrophenol could reduce the half-life of this compound from 12 to 10 days. Thorton-Manning et
al.  (1987) found that whereas the addition of nitrate and phosphate resulted in faster and more exten-
sive mineralization of phenol in subsurface horizons, it did not stimulate degradation in the upper
horizons of contaminated soil.  Excesses or deficits of nitrogen or phosphorus brought about by the
addition of any organic amendments should be taken into account, and commercial fertilizers can be
used to make up any deficit.
                                              46

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        In agriculture, fertilizer is added to hasten the decomposition of crop residues (Alexander 1977);
 this procedure also has been used in the treatment of soil contaminated with hazardous wastes as a
 result of an oil spill (Thibault and Elliott 1980). Skujins et al. (1983) studied the biodegradation of waste
 oils at a disposal site where soils were amended with calcium hydroxide, phosphate, and urea.  Within 4
 years, 90 percent of the applied oil was degraded.

        Standard agricultural methods are used to add fertilizers to the soil.  Depending on the nutrient
 type, physical state, solubility of the fertilizer, and depth of contamination, the fertilizer is incorporated
 into the soil as necessary.  Power implements, tillers, and applicators are required to apply the fertilizer
 to the soil. If nutrient availability is limiting or retarding microbial degradation or detoxification of organic
 hazardous waste constituents, the achievable level of treatment could be increased by making the
 nutritional characteristics of the site and soil more suitable.

        Sufficient nitrogen and phosphorus must be reapplied to ensure that these nutrients do not limit
 the microbial and metabolic activity. Controls to manage the run-on and runoff at the site are necessary
 to prevent drainage and erosion problems. This technology ranges from easy to difficult to apply,
 depending on the trafficability of the site.

        Status of the Technology.  Commonly used in agriculture, this technology has been used in the
 bio re medial ion of contaminated ground water and in the treatment of oil wastes. Commercially avail-
 able nutrient solutions are especially formulated to prevent precipitation of the  chemical nutrients.

        Secondary Impacts. Nitrogen must be applied to the soil cautiously  to avoid excessive nitrate
 formation. Nitrate or other forms of nitrogen in the soil that oxidize to nitrate  may be leached to ground
 water. Also, some nitrogen fertilizers tend to lower the soil pH, which necessitates a liming program to
 maintain an optimum pH for biological activity. Tillage will increase the susceptibility of the site to
 erosion.

        Equipment and Exogenous Reagents Required.  Power implements, tillers, and applicators are
 required to apply the fertilizer containing inorganic nutrients (nitrogen, phosphorus, potassium, calcium,
 magnesium, sulfur, iron, and trace metals) to the soil. Carbon in the form of  glucose, acetate, citrate,
 etc., also may have to be added. Lime may also be required.

        Advantages of Soil Nutrient Addition. This technique is extremely effective in enhancing
 microbial activity resulting decomposition of organic contaminants.  Equipment and additives are readily
 available.

        Disadvantages of Soil Nutrient Addition. Retreatment may be necessary at intervals as nutri-
 ents are used up in the process.  Also, liming and reliming may be necessary to maintain optimal pH  for
 biological activity.

        Soil Temperature. Soil temperature is one of the most important factors controlling microbio-
 logical activity and the rate of decomposition of organic matter. It also influences the rate of volatiliza-
 tion of compounds from soil. Soil temperature can be modified by regulating the oncoming and outgoing
 radiation or by changing the thermal properties of the soil (Baver et al. 1972). Laboratory studies have
 shown that the rate and extent of low-molecular-weight PAHs removed from  agricultural soils can be
 significantly enhanced by increasing the soil temperature. Conversely, temperature  had little effect on
 the removal of five- and six-ring PAHs (Coover and Sims 1987a).

        Thorton-Manning et al. (1987) evaluated the importance of soil temperature  and inorganic
 nutrient  availability in the stimulation of phenol biodegradation in surface and subsurface soils. These
 researchers found that, the effect of temperature on mineralization was a function of the soil type. They
 also found that, whereas the addition of nitrate and phosphate resulted in faster and more extensive
 mineralization of phenol in the subsurface horizons, it did not stimulate degradation in the upper hori-
zons. Bachmann et al. (1988) reported that temperatures in the 20° to 30°C  range were the most
favorable for biological degradation of alpha-hexachlorocyclohexane (HCH) in contaminated soil. At
temperatures below 4°C and above 40°C, they were unable to detect biological degradation of alpha-
HCH.
                                              47

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       Because of the insulating properties of plant cover, vegetation plays a significant role in soil
temperature.  Bare soil unprotected from the sun's direct rays becomes very warm during the hottest
part of the day; it also loses its heat rapidly during colder seasons.  A well-vegetated soil, however, does
not become as warm as a bare soil during the summer, and the vegetation acts as an insulator to
reduce heat toss from the soil in the winter. Frost penetrates more rapidly and deeper in bare soils than
in soils under a vegetative cover.

       Mulches can affect soil temperature in several ways.  Mulches generally reduce diurnal and
seasonal fluctuations in soil temperature.  In the middle of the summer, mulched and bare plots differ
very little; however, mulched soil is cooler in the winter and fall and warms up more slowly in the spring.
Because mulches with low thermal conductivities decrease heat flow both into and out of the soil, soil
will be cooler during the day and warmer during the night.  White paper, plastic, or other types of white
mulch increase the reflection of incoming  radiation, which  reduces excessive heating during the day.  A
transparent plastic mulch transmits solar energy to the soil and produces a greenhouse effect.  A black
paper or plastic mulch absorbs radiant energy during the day and reduces heat loss.

       Irrigation increases the heat capacity of the soil, raises the humidity of the air, lowers air tem-
perature over the soil, and increases thermal conductivity; the result is a reduction of daily soil tempera-
ture variations (Baver et al. 1972). Sprinkle irrigation, for example, has been used for temperature
control (specifically, frost protection in the winter and cooling in the summer) and for the reduction of
wind erosion of the soil (Schwab et al. 1981).  Drainage  decreases the heat capacity and thereby raises
the soil temperature. Elimination of excess water in the  spring results in a more rapid temperature rise.
The addition of humic substances improves soil  structure,  which improves soil drainability and results
indirectly in higher soil temperature.

       Several physical characteristics of the soil surface can be modified to alter soil temperature
(Baver et al. 1972).  Compaction of the soil surface increases the density and thus the thermal conduc-
tivity.  Tillage, on the other hand, creates  a surface mulch that reduces the  heat flow from the surface to
the subsurface. The diurnal temperature  variation in a cultivated soil is much greater than that in an
untilled soil.  A loosened  soil is cooler at night and more susceptible to frost.

       Mulches not only modify the soil temperature, they also protect the soil surfaces from erosion
and reduce water and sediment runoff. Because this prevents surface compaction or crushing and
conserves moisture, the achievable level  of treatment could be high when site and soil characteristics
are suitable.

       Status of the Technology.  Application of mulches to soil to increase soil temperature is com-
monly used in agriculture. No laboratory or field studies, however, have been reported in which this
technique has been used in the treatment of soils contaminated with hazardous wastes. Nevertheless,
application of mulches may be useful for controlling soil  temperature at contaminated  sites.  Also, the
techniques used to modify soil characteristics (irrigation, tillage, etc.) indirectly modify the soil tempera-
ture.

       Secondary Impacts.  Few secondary impacts have been identified for this technique.

       Equipment and Exogenous Reagents Required. The type of mulch required determines the
application method.  Commercial  machines are available for spraying mulches. Hydromulching is a
process in which seed, fertilizer, and  mulch are applied as a slurry.  Plastic mulches are applied me-
chanically with equipment that is towed behind a tractor; the plastic strips are sealed at the edges with
soil. For treatment of large areas, special machines are available that glue polyethylene strips together
(Mulder 1979).  If irrigation or drainage is  used to modify the heat capacity of the soil,  appropriate
irrigation/drainage systems are needed. Power implements, tillers, and applicators are usually required
to apply this technique.
       Advantages of Soil Temperature  Control.  Optimal soil temperature greatly enhances biodegra-
dation and affects volatilization of organics.

       Disadvantages of Soil Temperature Control.  The techniques of temperature  control commonly
practiced do not allow for minute changes in temperature.
                                               48

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 Addition of Nonspecific Organic Amendments

        Stimulating general soil microbial activity and population size through the addition of organic
 matter increases the opportunity to select organisms that can degrade hazardous waste components.
 High microbial activity allows cometabolic processes to act on recalcitrant hazardous waste compo-
 nents. The addition of manures, plant materials, or wastewater treatment digestor sludge at levels
 characteristic of composting may prove valuable to biological treatment of soil contaminated with
 hazardous wastes (Kaplan and Kaplan 1982a, Doyle and Isbister 1982).

        Extensive laboratory research has shown that supplemental carbon and energy sources can
 stimulate the metabolism of xenobiotic, often recalcitrant compounds.  The breakdown or transformation
 of these compounds can be through cometabolism (Alexander 1981; Keck et al. 1989; Sims 1986), or
 metabolism of the compound may simply be stimulated by the supplemental carbon and energy source
 (Yagi and Sudo 1980). Bachmann et al. (1988), however, reported that adding an auxiliary carbon
 source (variable acetate/glucose mixtures) showed inhibitory effects on alpha-hexachlorocyclohexane
 biomineralization in contaminated soils.  Coover and Sims (1987b) indicated that manure addition had
 no apparent effect on the rate of disappearance of benzo(a) pyrene in soil. Based on the results of their
 laboratory studies, Schmidt and Alexander (1985) concluded that second substrate and uncharacterized
 dissolved organic carbon might play an important role in controlling not only the rate, but also the extent,
 of microbial degradation of organic contaminants present at low concentrations.

        Composting of contaminated soil has been shown to degrade hexahydro-1,3,5-trinitro-1,3,5-
 triazine (RDX), whereas the ring structure of 2,4,6-trinitrotoluene (TNT) was not mineralized. The TNT
 residues were apparently strongly sorbed to the compost (Doyle and Isbister 1982). Camoni et al.
 (1982) demonstrated that adding organic compost to soil had no significant effect on the half-life (1 year)
 of 2,3,7,8-TCDD in soil. The degradation of pentachlorophenol  and pentachloronitrobenzene in a
 laboratory composting system  has also been studied (Sikora et  al. 1982). Laboratory studies (Wilson
 1987) have shown that aerobic composting of PCB-contaminated soils resulted in greater PCB removal
 than did anaerobic composting; the concentration decreased an average of 60 percent in 4 weeks.
 Several problems encountered during these studies and the fact that it is impossible to control weather
 conditions in a field situation have led to the conclusion that composting of PCB-contaminated soils is
 an uncertain technology.

        Laboratory experimentation may be needed to determine the biochemical fate of given hazard-
 ous compounds in organically enriched soil or compost and to evaluate the environmental hazards
 associated with any  residues and byproducts (Kaplan and Kaplan 1982b, Isbister et al. 1984). Residues
 may be more or less toxic than the parent compounds. Residues of hazardous compounds may not be
 extractable from organically enriched soil by use of ordinary solvents, which suggests the existence of a
 strong binding to organic matter or other soil constituents (Doyle and Isbister 1982, Khan 1982,
 Wallnofer et al. 1981, Bartha 1980, Stevenson 1972). Enzymatic activities of soil microorganisms can
 be responsible for coupling xenobiotic compounds and their breakdown products to soil humic materials
 (Bollag 1983, Bollag et al. 1983, Sjobland and Bollag 1981, Liu et al. 1981, Suflita and Bollag 1980,
 Bollag et at. 1980, Bollag et al. 1978).  Careful monitoring for bound hazardous organic compounds,
 including toxic metabolites of hazardous parent compounds, should be performed.  Humus-bound xeno-
 biotic compounds may be slow to mineralize or be transformed to innocuous forms (Khan 1982, Cho-
 wdhury et  al. 1981).  In such cases, increasing the humic content of the soil may not be the method of
 choice.

       Because pesticides and other residues have been shown to form stable chemical linkages with
 humic material in the process of humification, the incorporation of hazardous chemicals into soil humic
 material could  represent a method for decontamination of soil. The binding and detoxification of hazard-
 ous chemicals are discussed by Bollag (1989).

       Microbial decomposition of humic matter that contains bound hazardous organic compounds
can release these compounds  to the soil solution, where they are subject to leaching, vc latilization, or
                                             49

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reattachment to soil organic matter.  This potential mobility of bound hazardous compounds suggests
that treatment is not complete until their absence or safe level in the soil can be demonstrated (Bartha
1980, Saxena and Bartha 1983, Khan and Iverson 1982).

       No examples of field trials of this treatment technique are available. Doyle and Isbister (1982)
observed 55 percent degradation in  6 weeks of RDX in compost incubated in a greenhouse.  In the
same study,  TNT levels were reduced by more than 99 percent within 3 weeks, but very little  decompo-
sition (mineralization) was observed. Field pilot-scale  studies conducted at the Skrydstrup Chemical
Waste Disposal Site (Denmark) are  discussed in Section 3.3.2.5.

       With the consumption of Oz, aerobic heterotropic bacteria oxidize arsenite (As*3) to arsenate
(As<6). An available reserve of organic matter must be present in the soil for the oxidation to  occur.
Therefore, when arsenite contaminates a soil in concentrations that are below toxic levels for soil
heterotrophs, the arsenite can be oxidized to arsenate by amending the soil with readily available
organic matter and maintaining aerobic conditions in the soil. Quastel and Scholefield (1953) described
the oxidation of arsenite in laboratory soil perfusion systems. Alexander (1977) and Konetzka (1977)
have reviewed the microbial biochemistry of arsenic. Further treatment with ferrous sulfate will form
highly insoluble FeASO4.  Biodegradable organic compounds as well as arsenite wastes  are amenable
to this treatment.

       The  potential achievable level of treatment ranges from low to high, depending on the solubility,
sorption, and biodegradability of the organic constituents in the waste.  Some arsenite may be bound to
the soil and will not be available for oxidation.  Available (extractable) arsenite  should be quickly and
completely oxidized.  Hazardous constituents may initially be bound to organic materials, but  they may
later be released as organic materials decompose.

       The  quantity of organic material required must be determined in treatability studies. Nonspe-
cific, readily biodegradable, organic  matter should be present, and frequent mixing is required to main-
tain aerobic conditions. Run-on and runoff controls are required. This technology can be easy or
difficult, depending on the trafficability of the soil and site and the depth of contamination. This technol-
ogy may require reapplications for complete treatment.

       Under anaerobic conditions, the added organic matter may result in the reduction and methyla-
tion of arsenic to volatile forms. Although anaerobic conditions must be avoided, anaerobic microsites
are known to exist even in well-aerated soil, and some volatile metal compounds may be produced even
in carefully managed soils.

       Status of the Technology. Although extensive laboratory research has shown that supplemental
carbon and energy sources can stimulate the metabolism of even recalcitrant compounds, no field trials
have been run. Experimental soil systems have demonstrated the microbial oxidation of arsenite to
arsenate, however.

       Secondary Impacts. Organic materials may affect several of the soil properties (degree of
structure, water-holding capacity, bulk density, etc.). Organic materials may also result in excessive
nitrate levels in receiving waters, depending on the nitrogen content and degree of mineralization of the
material.  Tillage may increase the susceptibility of the site to erosion.

       Equipment and Exogenous  Reagents Required. Power implements, tillers,  applicators,  and
proper drainage systems are required. The exogenous reagent required is organic material.

Cometabolism

       Thomas and Ward (1989) define cometabolism as the biodegradation  of an organic substance
by a microbe that cannot use the compound for growth and hence must rely on other compounds for
carbon and energy.  Three mechanisms of cometabolism are discussed in the  subsections that follow:
1) analogue enrichment;  2) nonanalogue enrichment with methane; and 3) other nonanalogue  hydro-
carbon substrates.
                                              50

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        Analogue Enrichment.  Adding a chemical analogue of a hazardous compound to a contami-
 nated soil or to culture media can accomplish cometabolism of the hazardous compound (Keck et al.
 1989; Sims and Overcash 1981; Pal et al. 1980; Furukawa 1982; Focht and Alexander 1970).  Appar-
 ently, enzymes proliferated by microorganisms to metabolize an energy-yielding substrate structurally
 similar to a recalcitrant xenobiotic compound can sometimes transform the recalcitrant molecule com-
 etabolically (Alexander 1981). For compounds in which the transformation product of the cometabolic
 process is not hazardous or is degradable by other organisms in the soil microbial community, analogue
 enrichment may be an effective treatment for contaminated soil. Sims and Overcash (1981) used
 analogue enrichment with phenanthrene to increase the rate of degradation of benzo(a)pyrene, which
 decreased the half-life by 35 percent.  Biphenyl has been used to stimulate  cometabolic degradation of
 PCBs (Furukawa 1982).  Wilson and Wilson (1985) reported that exposing unsaturated soil columns to
 a mixture of air and natural gas for 3 weeks can stimulate trichloroethylene (TCE) biodegradation.
 Ninety percent of the applied TCE was mineralized (confirmed by the recovery of 14C label).  Whereas
 acclimation of sandy soil to an air/natural gas mixture has been shown to stimulate mineralization of
 chloroform, the addition of acetylene and methane inhibited chloroform oxidation (Strand and Shipper!
 1987).

        Because chemical analogues to hazardous compounds or their degradation  products may be
 hazardous, care must be taken in the selection and use of analogues for treatment.

        Organic waste containing constituent(s) with analogues that have high rates  of degradation by
 organisms without producing toxic products are amenable to treatment. The level  of treatment may
 range from tow to high, depending on the susceptibility of the hazardous constituent to cometabolism.

        Analogue compounds are added in amounts large enough to stimulate microbial activity, but not
 large enough to be toxic to microbial functions or to have an adverse effect on public health and the
 environment.  Treatability studies are needed to determine the feasibility,  loading rate, and effectiveness
 of the analogue(s). The analogues may be applied as solids, liquids, or slurries and mixed thoroughly
 with the contaminated soil. Fertilization may be necessary to maintain microbial activity. Controls may
 be required to prevent drainage and erosion problems. Tillage will increase the susceptibility of the site
 to erosion.

        No information is available on field application. Laboratory studies have shown that analogue
 enrichment can accomplish cometabolism. The reliability of this technology is unknown.

        Nonanalogue Enrichment With Methane.  Chlorinated alphatic solvents such as 1,1,1-trichlo-
 roethane and trichloroethylene, which are common contaminants of aerobic aquifers, appear to be
 biologically recalcitrant in the presence of oxygen; however, cometabolism of these compounds has
 been observed in environmental samples through enrichment with natural gas or methane and air
 (Thomas and Ward 1989).  Methanotrophs, or methane-utilizing microorganisms, are selected as the
 microbial population when methane and air are introduced in soil samples. Colby et al.  (1977) found
that Methyloccus capsulatus produces a soluble, nonspecific monooxygenese that oxidizes methane as
well as several alkanes, alkenes, and halogenated methanes.  Several investigators have noted the
cometabolism of such compounds as tetrachloroethylene, trichloroethylene, 1,1,1-trichloroethane, 1,1,2-
trichtoroethane, 1,1-dichloroethane, 1,2-dichloroethane, cis- and trans-1,2-dichloroethylene, 1,1-dichlo-
roetnylene, vinyl chloride, dichloromethane, carbon tetrachloride, and chloroform (Wilson and Wilson
 1985; Fogel et al. 1986; Strand and Shippert 1986; Little et al. 1988). Fogel et al. (1986) found that the
more heavily chlorinated compounds are degraded more slowly than the less chlorinated analogues and
sometimes not at all.

       Other Nonanalogue Hydrocarbon Substrates. Specific and nonspecific hydrocarbon substrates
can be used to enhance cometabolism and specifically cooxidation (Keck et al. 1989). A soil isolate,
Nocardia Strain 107-332, was found to cooxidize alkyl-substituted aromatic hydrocarbons to the corre-
sponding acid while growing on n-hexadecane with no ring cleavage (Davis  and Raymond 1961).
Cooxidation studies by Raymond et al. (1967) identified several Nocardia species capable of aromatic
ring dihydroxylation but not ring cleavage.
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       An increase in microbial numbers and the induction of the production of extracellular oxygenase
may result in cooxidation of recalcitrant compounds in soil following the addition of nonspecific hydrocar-
bons (Keck et al. 1989). Bossert and Bartha (1984) noted that the addition of hydrocarbon substrates,
such as oil to soil, can result in an overall increase in  microbial activity if other nutrients are not limiting.

3.3.2.2. Augmentation With Acclimated or Mutant  Microorganisms

       Biological treatment methods described thus  far have relied on the stimulation of microbial
activity in the soil or on the natural selection of populations of microorganisms capable of degrading
toxic waste constituents. Although these approaches show considerable promise for treating many
kinds of organic hazardous waste constituents, the metabolic range of the natural soil microbiota may
not be capable of degrading certain compounds or classes of compounds. Also, microbial metabolic
specialists may not develop large enough populations under limited substrate conditions to degrade
xenobiotic compounds rapidly enough to meet treatment criteria. In situations such as these, it may be
advisable to add exogenously grown microorganisms to the soil. These microorganisms can be se-
lected by enrichment culturing or genetic manipulation,  and they can be acclimated to the degradation of
different organic contaminants by repeatedly exposing them to the compound of interest. Microbial
inoculants with a broad range of metabolic capabilities are available commercially, and experience
with their use in both soil and aquatic systems contaminated with waste chemicals is expanding  (Thi-
bault and Elliot 1979,1980; Walton and Dobbs 1980). Table 15 lists suppliers of biological products
that have been or may be used to treat soils contaminated with hazardous wastes. Frequently, the
application of microbial amendments to the soil is combined with other treatment techniques such as
soil moisture management, aeration, and fertilizer addition.

       Laboratory trials have demonstrated the potential of exogenously grown bacteria to degrade
xenobiotic compounds quickly. Edgehill and Finn (1983) inoculated soil with Arthrobacterfor the
degradation of pentachlorophenol (PCP) and observed rapid degradation (ti/2 <1 day) when the soil
was incubated at 30°C.  In soil treated  under a roof where temperatures ranged from 8° to 16°C, PCP
degradation was much slower, but it was much faster in mixed inoculated soil than in the control soil.
Focht and Shelton (1987) found that although 3-chlorobenzoate was not degraded by the soil-indige-
nous microflora, it was completely metabolized in the presence of relatively  small amounts of inoculum
of Pseudomonas alcaligenes C-0 (102 cells/g).

        Laboratory tests have shown that inoculation of soil columns with native microbial culture along
with recycled effluent resulted in higher removals of chlorinated hydrocarbons than did  inoculation with
commercially available cultures (Sybron and Hydrobac) acclimated to these compounds (Rickabaugh
1988).

       Chakrabarty (1987) used repeated applications of a "genetically engineered" Pseudomonas
cepacia with the ability to mineralize 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and obtained 90 percent
to essentially complete removal of 2,4,5-T from contaminated soil within 6 weeks.  When the 2,4,5-T
was exhausted, the population of P. cepacia became undetectable.

       Thirty-four bacterial and five fungal PCB degraders have been discovered; however, none of the
species could individually metabolize PCB and PCB isomers.  Therefore, it may be necessary to use a
consortium of more than two bacterial or fungal strains or a mixture of them to mineralize PCB and its
isomers effectively  (Wilson 1987).

       Research involving white rot fungus (Phanerochaete chrysosporium) performed in  recent years
has demonstrated the ability of this fungus to degrade halogenated organic compounds, especially to
dehalogenate and degrade chlorobenzene derivatives and to cleave aromatic rings (des Rosiers 1987).
Laboratory studies  of pentachlorophenol and related  polyaromatic hydrocarbons seem to indicate that
P. chrysosporium shows promise for in situ treatment of soils contaminated by wood-preserving materi-
als. Field tests are planned for this year (Glaser et al.1989).
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Table 15.  Commercial Microblal  Augmentation  Products or Processes  Used  to  Treat Hazardous-
           Waste-Contaminated Soils*
Vendor
  Address
Product
name(s)
  Product description
Treatment
Flow Laboratories
 Environmental
 Cultures Division
General
 Environmental
 Science
Groundwater
 Decontamination
 Systems, Inc.
Ingelwood, CA
Beachwood, OH
Waldwick, NJ
Polybac/Cytox
 Corporation
Allentown, PA;
 San Francisco,
 CA; Gonzales,
 FL
                    ed.
DBC Plus;     Formulated from specifically
Types A,       cultured bacteria preserved
A-2,B,F        by freeze drying and air dry-
 and H-1        ing techniques.

LLMO         Mixture of seven bacterial
               strains (Bacillus, Pseudo-
               monas, Nitrosomonas,
               Nitrobacter, Cellulomonas,
               Acrobacter, Rhodopseudo-
               monas) in liquid suspension.

GDS          Technique involves circulat-
 process       ing water from the soil into
               an environmentally controlled
               tank. Nutrients are  added,
               and the water is aerated.
               Treated water is returned
               to the soil.  Air may be
               injected  into the soil to
               stimulate further biodegra-
               dation.

Polysoil       Mutant bacterial formula-
 process       tion, nitrogen and phosphorus
               fertilizer, and biodegradable
               emulsifier.
Sybron
 Biochemical
Birmingham, NJ;
 Salem, VA
                                        Chemical
                                         biological
                                         augmenta-
                                         tion process
Detoxsol
Uses chemical treatment
 ahead of biological treat-
 ment to shorten treatment
 time (currently in experi-
 mental and demonstration
 stages).

Formulation of mutant
 bacteria, buffer nutrients,
 growth stimulator, and de-
 toxifying agent.
                                 25 to/acre
                                  (Site
                                  depen-
                                  dent)
                                  (Site
                                  depen-
                                  dent)
                                  100 Ib or-
                                  ganism
                                  plus 400
                                  Ib fertil-
                                  izer and
                                  emubifer
                                  if need-
 363b/
  acre
'Source: Sims and Bass 1984
                                                53

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        Augmentation of biological systems with exogenous microbes (bioaugmentation) may be most
effective against one compound or closely related compounds. Toxicity or the inability of the microor-
ganisms to metabolize a wide range of substrates may limit the effectiveness of the treatment.

        Table 16 lists compounds or classes of compounds that may be degraded by mutant or sel-
ected bacterial cultures that are available commercially.

Table 16.  Classes of Compounds That Can Be Degraded by Commerically Available Microbial Augmentation
         Productions*


               Alcohols                                       Esters
                 n-Butyl alcohol                                    Methacrylates
                 Dimethylaminoethanol
                                                             Ketones
               Alkyl halides                                      Acetone
                Ethylene dichloride (1,2-dichloroethane)
                 Methylene chloride (dichloromethane)                Nitnles
                 Propylene dichloride (1,2-dichloropropane)             Acrylonitrile

               Amines                                         Phenols
                 Dimethylaniline                                   Phenol
                 Trimethylamme                                   Metachlorophenol
                                                               Orthochlorophenol
               Aromatic hydrocarbons                              Pentachlorophenol
                 Divinyl benzene                                   Resorcinol (1,3-benzenediol)
                 Polynuclear aromatic hydrocarbons (PAHs)               t-Butylcatechol
                 Styrene (vinyl benzene)
                                                             Crude and refined oils
               Chlorinated aromatics
                 Polychlonnated biphenyls (PCBs)                   Emulsifiers

                                                             Detergents

               * Source  Sims and Bass 1984

        The potential level of treatment achievable with bioaugmentation is high if the waste constitu-
ents are susceptible to degradation by the added microorganisms  and site and soil conditions are
conducive to microbial activity.

        Application methods are determined in consultation with the vendor of the microorganisms.
They may be applied in liquid suspension or with a solid carrier.  Depending on the method  of applica-
tion, run-on and runoff controls may  be required.  The ease of application depends on the trafficability of
the site and the depth of contamination.

        Treatment may require relatively long periods of time to complete.  Excessive precipitation may
"wash out" the inoculum and necessitate retreatment. If tillage is used, the susceptibility of the site to
erosion will increase.

        This technology has been demonstrated in the laboratory and used in several full-scale decon-
tamination operations. Thibault and Elliot (1979,1980)  and Walton and Dobbs (1980)  reported case
histories of successful treatment at chemical spill sites (oil spill, orthochlorophenol spill, and acrylonitrile
spill).  Nevertheless, some hazardous waste cleanup practioners are skeptical about the use of this
technology because of the importance of the soil environment in determining microbial activity and,
hence, the success of applying exogenous organisms.  More information is needed on the ability of
exogenous organisms to survive, grow, and function in the soil environment.
                                                54

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Secondary Impacts
       If tillage, is used, the site's suspectibility to erosion may increase.
Equipment, Exogenous Reagents, and Information Required
       The equipment required for bioaugmentation varies according to the microorganisms used and
as recommended by the vendor.  Microorganisms are usually supplied by the vendors. The following
information is required prior to augmentation:
       • Characterization and concentration of wastes, particularly organics at site.
       • Microorganisms present at site.
       • Pathogenicity to susceptible populations.
       • Biodegradability of waste constituents (half-life,  rate constant).
       • Biodegradation products (particularly hazardous products).
       • Depth, profile, and areal distribution of constituents.
       • Soil properties (pH, soil moisture, nutrients, oxygen content, organic matter, temperature,
         etc.).
       • Trafficability of soil and site.
       • Climate, particularly precipitation.
       • Ability of the added microorganisms to survive in a foreign and possibly hostile environment
         and to compete for nutrients with indigenous microbial population.
       • Ability of the exogenous microorganisms to move from the injection point to the location of the
         contaminant in the  subsurface materials (saturated and unsaturated zones).
       • Ability of the added microorganisms to retain their selectivity for metabolizing those contami-
         nants for which they were initially adapted.
Advantages of Augmentation With Acclimated or Mutant Microorganisms
       The advantages of this technology are as follows:
       • The potential level of achievable treatment is high.
       • Microbial inoculants with a broad range of metabolic capabilities are available commercially.
       • Experience with this approach in both soil and aquatic systems contaminated with waste
         chemicals is expanding.
Disadvantages of Augmentation With Acclimated or Mutant Microorganisms
       The disadvantages of this technology are as follows:
       • Toxicity or the inability of the microorganisms to metabolize a wide range of substrates may
         limit their effectiveness.
       • Excessive precipitation may "wash out" the inoculum and necessitate retreatment.
       • Competition by other microorganisms and stress of soil environmental conditions may limit the
         longevity of the microorganisms.
                                              55

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3.3.2.3. Application of Cell-Free Enzymes

       Enzymes produced by microorganisms, which can transform hazardous compounds to
nonhazardous or more labile products, could be harvested from cells grown in mass culture and
applied to contaminated soils.  Industry commonly uses crude or purified enzyme extracts, either in
solution or immobilized on glass beads, resins, or fibers, to catalyze a variety of reactions, including
the breakdown or transformation or carbohydrates and proteins.  Munnecke et al. (1982) discussed the
enzymology of selected pesticide degradation and suggested that extracted (cell-free) enzymes might
be used for the quick transformation of pesticides in soils. They pointed out that a bacterial enzyme
preparation has been used to detoxify organophosphate pesticide waste from containers (Munnecke
1980) and that the enzyme parathion hydrolase hydrolyzed 1 percent parathion or diazinon within 24
hours in contaminated soil.

       The use of gene-engineered, eukaryotic, cytochrome P-450 monooxygenase is another impor-
tant  new approach to dehydroxilation  and detoxification of recalcitrant compounds such as polychlori-
nated aromatic hydrocarbons.  Battelle, which is conducting  studies on the production of enzymes, has
stated that it is possible to produce enzymes to which an engineered protein sequence is attached at
strategic locations. These introduced protein sequences will allow efficient immobilization of enzymes
on inexpensive substrates or provide a means for microencapsulating the enzyme. Although tech-
niques for producing and recovering the enzymes from bioengineered cells (Bacillus subtilis) have
been refined somewhat, work on a process for the application of the enzymes for the destruction of
hazardous wastes is still in progress.

       Enzyme activity can often be preserved in environments that are not hospitable to microorgan-
isms. Enzymes could possibly be used in soils with extreme pH and temperature, high salinity, or high
solvent concentrations, i.e., in soils where microbial growth may be restricted. In  milder soil environ-
ments, enzymatic hydrolysis or oxidation of a compound may make it more susceptible to decomposi-
tion by the soil microbiota (Munnecke et al. 1982).

       To function outside the cell in the soil environment, an enzyme must not require cofactors or
coenzymes, as such a requirement limits the application of many enzymes. Enzymes may also be
chemically or  biologically degraded.  They may be leached out of the treatment zone, and they may be
inactive or have lower activity if they are bound to clay or humus in the soil.  Outside of biochemical
and environmental constraints, logistics and costs for producing enzymes in large enough quantities
may limit their use. Given the appropriate enzyme, if the enzyme remains active in the soil, the
potential achievable treatment level is high.

       Theoretically, enzymes would quickly transform hazardous compounds if they remained active
in soil. After transforming the contaminants, the enzymes, being biochemical molecules, could be
degraded easily and leave no hazardous byproducts in the soil.  Laboratory experiments have been
performed with parathion hydrolase. Paulson et al. (1984) demonstrated that complete degradation of
2000 ppm diazinon (97 percent) could be achieved in 3 weeks by using parathion hydrolase and high
moisture control (actual field conditions were tested in greenhouse soil, and no leaching occurred).

Status of the  Technology

       Little  information is available on the use of this technique in soil. No information is available on
its use in the field. The reliability of this technology is unknown.

Secondary Impacts

       Enzymatic degradation products may not be less hazardous than the parent compound(s).
Products may be more water-soluble or mobile in the soil. If required, tillage will increase the suscepti-
bility of the  site to erosion. Depending on the application method, controls may be needed to prevent
run-on and runoff.
                                          56

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 Equipment, Exogenous Reagents, and Information Required
       Power implements, tillers, and applicators are needed for application of this treatment.  En-
zymes are sprayed on the soil in solution or suspension or are spread with a solid carrier by use of
sprayers or fertilizer spreaders.
       In addition to the general information required for all the preceding biodegradation enhancement
techniques, the following information is required prior to enzyme utilization:
       •  Cell-free enzymatic activity for transformation of the compound(s) of interest.
       •  Cofactor requirement of enzymes.
       •  Stability of enzyme under soil environmental conditions.
Advantages of the Application of Cell-Free Enzymes
       The advantages of this technology are as follows:
       •  Offers a possible means of quick detoxification of pesticides.
       •  Enzyme activity can often be preserved in environments that are not hospitable to
         microorganisms.
Disadvantages of the Application of Cell-Free Enzymes
       The disadvantages of this technology are as follows:
       •  Enzymes may be chemically or biologically degraded.
       •  They may be leached out of the treatment zone.
       •  If bound to clay or humus in the soil, their activity may decrease or stop entirely.
       •  Logistics and costs for producing enzymes in large enough quantities may limit use of this
         approach.
3.3.2.4. Vegetation Uptake
       The ability of higher plants (i.e., seed-producing) to remove and accumulate compounds from
the soil has resulted in studies for their potential use as an in situ treatment technique for both organic
and inorganic compounds. The potential method of treatment by plants may occur through bioaccumu-
lation, transformation  (i.e., metabolizing the compound to nontoxic metabolites), or by adsorbing to plant
roots for microbial degradation.  Plant uptake of both organics and inorganics in the soil environment is
influenced by numerous physical and chemical  factors, including pH, clay content, cation exchange
capacity,  soil texture and compaction, organic matter content, plant species, and toxicity of the com-
pound.
       Uptake of compounds by plants occurs through chemical partitioning onto the external root
surfaces leading to accumulation into the root with subsequent access to the vascular system of the
plant (Bell 1988). In general, plant uptake of  a chemical in the soil can be accomplished through the
following  main pathways  (Topp et al. 1986):
       •  Root uptake into conduction channels.
       •  Uptake of vapor in the surrounding air by the vegetative parts of the plant.
       •  Uptake by external contamination of shoots by soil and dust, followed by retention in the
         cuticle or penetration through it.
       •  Uptake and transport in the oil cells of oil-containing plants (carrots, parsnips).
                                             57

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Most uptake by the plant will occur through the first two pathways, although the second two pathways
may apply under specific conditions (e.g., uptake and transport of highly lipophilic compounds into the
oil cells of oil-containing plants).

       Several differences occur between the plant uptake of organic versus inorganic compounds.
Uptake of elements can take place if the element exists as either a cation or anion (Ryan 1976).  Sev-
eral variables may influence the concentration of metals found in plants, including species, cultivar,
maturity,  and plant part. Bingham et al. (1975,1976) have shown that leafy vegetables (lettuce, cress)
accumulate significantly greater amounts of cadmium than do plants such as corn or wheat.

       A major consideration to be addressed when assessing the uptake of inorganics is toxicity.
Plant species differ significantly in their tolerance of metals, which could affect their use as an in situ
treatment technique.

       Plant uptake of organic compounds has also been investigated. Nonionic (organic) adsorption
in the soil is largely to the organic matter that coats most particles in the soil.  Several studies have
shown  that plant roots adsorb high levels of lipophilic pollutants from the soil which compete with
existing soil organic matter. Bell (1988), Kew et al. (1989), and Facchetti et al. (1987) have shown that
there is substantial accumulation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in plant roots and
tubers. This ability to collect and hold TCDD offers potential as a soil cleanup technique.

       The half-life of a compound also affects ultimate  plant uptake. Ryan  et al. (1988) have shown
that chemicals with short half-lives (less than 10 days) are removed from the  system before they can be
taken up  by the plant.  Compounds with longer half-lives  (greater than 6 months or longer than the
growing season) persist long enough to have potential for plant uptake.

       To date, several other studies on plant uptake of pollutants have been attempted, including:

       • Biotransformation of TNT (Palazzo et al. 1986).

       • Uptake of organics by aerial plant parts to predict air-to-aerial vegetative transfer of organic
         chemicals (Travis and Hattemeyer-Frey 1988).

       • Uptake of organic compounds by rice plants using  C (Bahadir and Pfister 1987).

       • Inverse affects of Kow on uptake and bioconcentration of compounds (Travis and Arms  1988).

Status  of Technology

       Use of this technology for cleanup has been investigated, primarily at the laboratory level.
Several studies (Bell 1988, Dowdy and Larson 1975, Shauer et al. 1980) have investigated plant uptake
of organics and metals under field conditions. Further investigations of rates  of uptake, toxicity, and
transformation of pollutants are warranted.

Secondary Impacts

       Substantial uptake of pollutants could produce toxic effects on the plant and  result in harmful
effects  on both the plant and any animals ingesting the plant.

Equipment, Exogeneous Reagents, and Information Required

       This technology would require basic agricultural techniques for growing crops. Knowledge of
plant tolerances and their ability to take up and accumulate the pollutant in question would be neces-
sary.
                                               58

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Advantages of Vegetation Uptake

       Advantages of this treatment technique include:

       • Soils can be treated without excavating large quantities of material.

       • Worker exposure is minimized.

       • Cost of this technology would be relatively low.

Disadvantages of Vegetation Uptake

       The disadvantages of this treatment method are as follows:

       • Toxicity of pollutants may have adverse effects on the plant or on animals eating the plant.

       • Plants will, in most cases, only remove small amounts of the contaminant.

       • Plants would need to be disposed of (e.g., incinerated) after uptake of the contaminants.

3.3.2.5. Case Histories of Bioremediation

       Most large-scale bioremedial actions involve more than one of the technological approaches
described in this subsection or comprise a combination of chemical/physical/biological in situ or onsite
treatments.  The biological treatment is often used as a polishing step. Selected examples of full-scale
bioremediation projects reported in the literature are described herein.  Several EPA documents contain
additional descriptions of in situ applications of biodegradation and should be consulted (EPA 1984,
1986, 1988).

Formaldehyde Rail Car Spill, Ukiah, California (Sikes et al. 1984)

       A strong formaldehyde solution (20,000 gallons) drained from a rail car and seeped into and
through the ballast and into a drainage system. A heavy rainfall washed most of the remaining formal-
dehyde into the drainage system. The following mitigation operations were developed and imple-
mented:

       1) Isolation of the spill site and removal of more than  3,000,000 gallons of contaminated
          rainwater for offsite treatment.

       2) In situ chemical oxidation of the contaminant with alkaline hydrogen peroxide (pH 9 to10),
          followed by biological oxidation with exogenous acclimated microorganisms.

Figure 3 presents a schematic diagram of the treatment system.

       After chemical treatment, the rail ballast was converted into a trickling filter.  The commercially
available Hydrobac inoculum (Polybac, Inc.) was used because it was certified to contain no human
pathogens.  The inoculum, nitrogen-phosphate nutrients, and chemicals for pH control (sulfuric acid
and soda ash) were mixed in an aboveground aeration tank, and the mixture was sprayed over the
system periodically (inoculum at 3 Ib/day, chemicals as needed).

       After 8 days of operation, weather conditions and water evaporation in the aeration tank and
spray system had dropped the low sump temperature to about 10°C.  Because low temperatures could
slow down the biological activity, a 1.5-million Btu/h steam-cleaning unit had to be used to maintain the
optimum temperature.

       After 17 days of treatment, the formaldehyde concentration at the spill site had been reduced
from approximately 700 ppm to less than 1  ppm. The biological treatment was discontinued after the
formaldehyde concentration was 1 ppm or less for several days, and 200 gallons of 35 percent peroxide
solution was then added to the holding tank and pumped through the soil system to sterilize it.

       Based on the data collected during the entire operation, it was concluded that biological oxida-
tion was the major mechanism of formaldehyde removal at the spill  site.
                                             59

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Figure 3. Diagram of the biological treatment process at the spill site.
        Natural
       Drainage
                                           Return Pump      Air Compressor
  Power
Generator
                         Sump excavated
                          under original
                           rail car spill
                                               Under Bed Drainage Tile (sandbag sealed)
        Natural
        Drainage
Phenol-Contaminated Site in Michigan (Walton and Dobbs 1980)

       The soil and ground water at this site were highly contaminated with a mixture of phenol and its
chlorinated derivatives.  A combination of aboveground and in situ biological treatment was selected as
the remedial action.

       Ground water was pumped out of the aquifer, circulated through activated carbon filters (to
remove contaminants), and injected into the soil.

       The natural soil microbial population was augmented with mutant bacteria. These bacteria were
injected into the soil and in a containment pond holding surface runoff.

       Phenol was rapidly degraded, whereas the degradation or o-chlorophenol was slower. Al-
though the data presented did not conclusively link the degradation of contaminants to the bioaugmen-
tation technique, a correlation between removal of contaminants and inoculation of mutant bacteria
seemed to be indicated.

Biocraft Site, Waldwick, New Jersey (Jhaveri and Mazzacca 1985)

       Soil and ground water at the  Biocraft Site (4.5 acres) were contaminated with methylene
chloride, n-butyl alcohol, dimethylaniline, and acetone. These compounds had leaked into the ground
from an underground pipeline and contaminated approximately 1.75 acres. Based on the information
obtained in laboratory and field studies (and with the approval of the New Jersey Department of Envi-
ronmental Protection), Groundwater Decontamination Systems, Inc., designed and successfully oper-
ated a biorestoration program.  The program consisted of 1)  recovery of ground water downgradient of
the contaminated plume  by use of a collection trench and two dewatering wells; 2) aboveground aerobic
biological treatment of contaminated  ground water; 3) injection of air along the major pathway of the
ground-water flow (by use of nine wells)  to maintain aerobiosis; and 4) injection of the treated ground
water upgradient of the contaminated plume by use of two infiltration trenches.  The aboveground
biological treatment operated as a conventional activated sludge system. In the first tank (aeration unit),
                                              60

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air, water, nutrients, and acclimated microorganisms were mixed and maintained at the optimum tem-
perature with a steam coil.  The treated ground water then flowed to a second tank (settling tank), where
the bulk of the microorganisms were settled out. The settled biomass could either be recycled to the
aeration tank or discarded. The effluent, which contained residual microorganisms,  nutrients, and dis-
solved oxygen, was infiltrated into the ground. Figure  4 presents a schematic diagram of the in situ
bioreclamation system.
       Water and soil analyses (COD, GC, CCfe) showed that, in 3 years, this biostimulation-degrada-
tion system had reduced the size of the original contaminated plume by 90 percent.  A tenfold increase
in COa production in the contaminated area compared with background levels confirmed that in situ
biodegradation had occurred at the Biocraft site. Although at the time of the Jhaveri and Mazzacca
publication (1985), detectable levels of methylene chloride, acetone, n-butyl alcohol, and dimethylaniline
still remained in the contaminated area, evidence indicated these contaminants were being rapidly
degraded.
Naval Air Engineering Center (NAEC) Site, Lakehurst, New Jersey (Flathman and Caplan 1986)

       An estimated 4000 gal of cooling water (25 parcent ethylene glycol) leaked from a lined surface
storage lagoon and contaminated the soil and ground  water with ethylene glycol.

       Because feasibility study data indicated that biological treatment was a viable option for reme-
diation of this site, O.H.  Materials, Co. (Findlay, Ohio)  designed and implemented a program consisting
of three phases:
       1) Operational:  Fourteen days to achieve maximum recovery and treatment of ground water
         and maximum enhancement of bacterial growth in the soil/ground-water system.

       2) Monitoring: Three months to evaluate the effect of nutrient addition (nitrogen and phos-
         phate), pH adjustment, and bioaugmentation on the ethylene glycol degradation rate in the
         ground water.
       3) Maintenance: Nine months to provide the optimum environmental conditions for biological
         degradation of any ethylene glycol residues remaining in the soil/ground-water system.

       Ground water was recovered for aboveground treatment in an activated sludge unit. Superna-
tant from the settling tank was reinjected into the subsurface environment, which established a closed-
loop system. Before reinjection, nutrients and chemicals were added to the treated ground water to
adjust the pH so as to enhance subsurface microbial activity.

Figure 4. Schematic diagram of biological treatment system for in situ  treatment of contaminated ground water at the
         Biocraft site.
                                                           Settling
                                                            Tank
Activating
  Tank
                                              61

-------
       Three injection systems were used: 1) a lagoon (to flush the contaminants from the unsaturated
zone to the extraction wells), 2) a plume-injection system (to enhance bacterial growth and to create a
gradient from the fringe of the contaminated plume toward the recovery wells located at the center of the
plume), and 3) a surface-application system (to enhance microbial activity in the contaminated soil).

       After 26 days of treatment, 85 to 93 percent of the ethylene glycol had been removed from the
ground water; and by the end of the program, the level of contaminant in all production wells had been
reduced to below detection limit (< 50 mg/L).

Gasoline-Contaminated Site (Yaniga and Smith 1986)

       Soil and ground water at this site were contaminated with gasoline-type hydrocarbons (ben-
zene, toluene, xylene — from less than 10 u.g/L to more than 15 mg/L) and certain associated inorganic
compounds (Fe, 0.1 to 6.7 mg/L; Mn, 0.2 to 12  mg/L) as a result of leakage from an underground
storage tank.  In this case, a 3-year combined physical/chemical/biological abatement program was
implemented to treat hydrocarbons adsorbed/dissolved into the ground-water system.

       Preliminary research indicated that field and laboratory Nocardia and Pseudomonas cultures
were degrading the organic contaminants.  Therefore, the in situ aquifer restoration program involved
stimulation of the growth of the indigenous hydrocarbon degraders by adding nutrients and oxygen to
the ground-water system and physical/chemical treatment to neutralize and remove metallic com-
pounds. Ground water was pumped from a well located in the center of the contaminated plume to
force the water to flow radially from the periphery.  The ground water was then air-stripped to remove
volatile organics and to supply oxygen. Nutrients were added to the oxygenated water before it was
injected into the contaminated soil and ground water. An infiltration gallery located at the periphery of
the plume (30,000 to 50,000 gal/day) was used to deliver the water.  Initially, air was also injected to the
peripheral areas of the plume outside the infiltration gallery by using air lines and down-well diffusers.
This air-sparging system,  however, was able to induce  only a limited quantity of oxygen (10 mg/L) to the
ground-water system, which is approximately the solubility of oxygen in water at 18°C. Also, frequent
mechanical cleaning was  required to eliminate fouling at the sparging points, caused by thick bacterial
growth.

       After 11 months of operation, this cleanup system reduced organic contaminants by 50 to 85
percent.  Despite these results, the low rate of oxygen transfer was limiting the microbial growth rate
and, consequently, the rate of degradation of contaminants, which lengthened the overall biorestoration
time.  Laboratory and field studies were conducted to find a more effective oxygen-delivery system.
These studies showed that using a hydrogen peroxide  solution could increase the dissolved oxygen
concentration from 0.5 to  8.0 mg/L in the soil/ground-water system in a 24-hour period. When a 100
mg/L  solution of hydrogen peroxide was added to the soil/ground-water system at the infiltration gallery
and air sparging wells, this solution not only yielded a dissolved oxygen concentration of 50 mg/L (avail-
able for the microorganisms), but also helped to control undesirable biological growth at the well bores.
The abatement program reduced the overall hydrocarbon concentration levels in the initially most con-
taminated area of the plume. The data collected at the site also indicated that degradation was still
taking place in five of the  homeowner wells in which contaminants had been detected.

Kelly Air Force Base (KAFB) Waste Disposal Site, Texas (Wetzel  et al. 1986; 1987a, b, c)

       The KAFB site was originally used to dispose of chromium sludges and other electroplating
wastes and later as an evaporation pit for chlorinated solvents, cresols, chlorobenzenes, and other
chemicals. The effectiveness of the in situ biological treatment of  the organic contaminants was tested
in a small-scale field soil and ground-water system.

        The design and implementation of this field demonstration project demanded extensive investi-
gations 1) to characterize the site (site stratigraphy and hydrology); 2) to determine the extent and
nature of the contamination; 3) to confirm the existence of viable bacterial population at the site and to
evaluate possible correlations between the number of bacteria present and the soil type, location, and
contaminant concentrations; and 4) to determine (by use of microcosms) which compounds would be
degraded under which treatment conditions, and which compounds were the intermediate metabolites
and metabolic products of such a degradation process.
                                              62

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       The cleanup project involved circulation of ground water by extraction/infiltration.  Ground water
was pumped from the pumping wells to a central surge tank, from which it was released at a controlled
rate to a distribution pipe. Along the pipe, hydrogen peroxide and specially formulated nutrient solutions
were added to the circulating water to enhance biodegradation (Restore 105, Stabilized HzCte, and
Restore 375 K Microbial Nutrients from FMC Aquifer Remediation Systems, Princeton, New Jersey).
The ground water was then sent to a central distribution box, where the flow was divided for gravity
injection. Figure 5 shows the configuration of the pumping and injection systems.

       The results reported by Wetzel et al. (1986) were inconclusive concerning the effectiveness of
the biodegradation for treating organic contaminants at the KAFB site, primarily because of the short
study period (3 months). Although preliminary bench-scale investigations showed that enhancing the
biochemical activity of native microorganisms could make biodegradation a feasible alternative for the
KAFB site,  the site stratigraphy and hydrology limited the effectiveness of such an in situ biological re-
mediation program.  Subsurface heterogeneity appeared to decrease the rate of transport of nutrients
and hydrogen peroxide (oxygen source) at certain areas of the demonstration site.

Figure 5. Configuration of pumping injection system at the Kelly Air Force Base site.
                    Power
                     Line
                               •o
Circuit
 Box
                                                                    Site
                                                                   Office
                                            FP2
                                         Surge Tankr
                                                          'P3
                                                                        'P4
                          s\ Distribution Box
                          v       ^
                                       P5
                                      Overflow Tanks
                                                \
                                                  O
                                            rP8
                                                          FP7
                                                                        'P6
 Skrydstrup Chemical Waste Disposal Site, Denmark (Christiansen and Vedby 1988)

        A refrigerator factory used the Skrydstrup site (approximately 15,000 m2) to dispose of 200 tons
 of drums containing paint sludge and foam waste from refrigerator insulation (xylenes, butanols,
 oxytoles, and acetone) and drums containing sludge from the degreasing bath (oil waste), waste
 packaging materials, and chemical residues (chlorinated solvents such as trichloroethylene, etc.; acid
 residues such as hydrochloric and sulfuric acids), plastic waste from faulty refrigerators (burnt boxes),
 and other production waste. Severe soil and ground-water contamination was detected, especially from
 chlorinated solvents and some haloalkyl phosphates (from foam waste). In general, the site remediation
 consisted of 1) removal of drums, 2) excavation of the most contaminated spots until removal of any
 visible contamination, and 3) cleanup of the remaining contaminated unsaturated zone and ground
 water. For the accomplishment of the last step, four full-scale development  projects were established to
 evaluate different in situ and onsite remediation technologies:
                                               63

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        1) Biodegradation of chlorinated solvents in soil.

        2) Aerobic degradation of chlorinated solvents in ground water by the addition of natural gas
          through activated carbon adsorption in columns.

        3) Aerobic degradation in the unsaturated zone with cometabolism by oxidation of methane or
          propane gas.

        4) Anaerobic biodegradation of chlorinated solvents in the  contaminated aquifer by the addition
          of sodium acetate.

        Only the in situ treatment of the residual chlorinated solvents in the unsaturated zone is de-
scribed herein.

        Although most of the source of the contamination at this site had been removed by other tech-
niques, some chlorinated solvents remained in the soil under the site.  Extracted and treated ground
water was to be recycled through the excavation site to accelerate the  leaching of the remaining chlorin-
ated solvents (and other pollutants). Also, laboratory and field tests were designed to evaluate in situ
aerobic biodegradation of the contaminants. The  laboratory tests consisted of batch and column studies
to assess the effect of 1) biostimulation (addition of nutrients), 2) augmentation (with adapted bacteria
instead of natural soil bacteria), and 3) cometabolism (with different gases — methane, propane, and
natural gas). Various gas/air ratios and frequencies of application (continuous vs. intermittent injection)
were also evaluated. Information and principles obtained from the column studies were used in the
design and conducting of the field tests.  In general, the tests consisted of injection of air/gas through
the unsaturated zone and infiltration of water with  and without nutrients and naturally acclimated micro-
organisms.  Gas catchment devices were installed on the soil surface to collect samples for analysis of
injected gases and chlorinated solvents.  Biodegradation was to be monitored during the period of the
field tests (2 years).  Water samples were to be taken at different depths in the unsaturated zone, and
soil samples were to be taken before and after the test. No data have  been reported at this writing.

Petrol Station, Asten, The Netherlands (van der Berg et al. 1987)

        At this petrol station, the soil (approximately 1500 m )  is contaminated with gasoline (approxi-
mately 30,000 liters)  and a small quantity of diesel oil from a leaking tank.

        Laboratory studies were conducted of the soil contaminated with gasoline and diesel  oil to
assess the possibility of  stimulating the biological  degradation of such contaminants by changing the
abiotic and biotic conditions. The  following parameters were evaluated:  nutrient content (C-N-P ratio),
nitrogen source, bioagumentation with oil degraders, addition of sodium acetate, moisture control, pH,
and alternative oxygen sources (hydrogen peroxide and nitrate).  In summary, the laboratory studies
showed that the biological activity in the soil could be enhanced by 1) inoculation of acclimated oil-
degrading bacteria, 2) maintaining saturated and neutral pH conditions, and 3) the addition of nitrate
and phosphate.  Mass balance calculations indicated that the rate of degradation of the gasoline in the
site soil was determined by the rate at which the gasoline became available (via dissolution and volatili-
zation processes). Soil column leaching experiments were set up for the investigation of the bioavaila-
bility problem and the effects of percolation rate, gasoline concentration in the soil, and the addition of
detergents when available.  These experiments showed that 1) the leaching of gasoline was hardly af-
fected by the gasoline concentration in the soil, 2) a linear relationship existed between the total amount
of organic carbon leached and the flow rate, and 3) leachability of gasoline was not promoted by deter-
gents.

        The column tests also indicated that injection of aerated water would not provide sufficient
oxygen and that hydrogen peroxide could be used as an alternative oxygen source.  Nitrate, on the
other hand, did not appear to be a reasonable prospect.  Although considerable biodegradation seems
to have taken place, the actual biodegradation of  contaminants and cleanup of the soil will be deter-
mined from analysis of the soil after the columns are dismantled. Based on the above results, it was
estimated that the site could be cleaned up in 1.5 years by stimulating biodegradation (a degradation
                                              64

-------
rate of 10 mg C/kg per day was measured under laboratory conditions).  A daily throughput of approxi-
mately 1850 m3 of water for a 625-m2 area was also calculated and used for the design of the site re-
mediation operation.  The water will be infiltrated through drains and recovered by pumping wells (rate
of withdrawal > rate of infiltration).  These findings and the preliminary hydrological investigation have
led the investigators in charge of the remediation program to conclude that the proposed remedial
actions are technically feasible and that "in situ biological treatment offers a good alternative and some
advantages over excavation combined with physical, chemical, or biological treatment."

Jet-Fuel Spill Site, Eglin Air Force Base, Florida (Downey 1988)

       Approximately 100,000 liters of jet fuel leaked from an underground pipeline in the base petro-
leum storage area and contaminated 4000 to 5000 m3 of soil and shallow ground water. The first
cleanup operations involved removal of the free fuel by use of a series of shallow trenches filled with
gravel and removal of 30,000 additional liters of fuel by use of skimmer pumps.

       Because the  hydraulic properties of the site and the soil characteristics were suitable for in situ
bioremediation, the Air Force Engineering and Service Laboratory conducted a full-scale investigation at
the site to assess techniques for enhancing biological degradation of the fuel residuals in the soil and
ground water. Total petroleum hydrocarbons (TPH), TOC, and a set of representative  fuel components
were selected to characterize the soil and water and to monitor the degradation process. Prior to
operation of the field system, laboratory studies were performed to determine the viability of the soil and
ground-water microorganisms, their response to the addition of nutrients and oxygen,  and their ability to
degrade jet fuel.

       The 2- to 3-year field study was designed primarily to evaluate the following:

       1) The use of several phosphate compounds (soil conditioners)  to prevent destabilization of the
          hydrogen  peroxide used as an alternative oxygen  source in the aerobic treatment.

       2) Optimum  nutrient and oxygen concentrations and  delivery system.

       3) Rate of degradation of certain components of jet fuel.

       A control area upgradient of the site was used to determine natural degradation of the jet fuel.
Figure 6 shows the three delivery systems used in this project.

       After 3 months of applying nutrients and hydrogen peroxide, no conclusive signs of biodegrada-
tton of the jet fuel were observed (based on soil and ground-water analysis).  The most important
information obtained from the first 4 months of operation of the system was that, in spite of having
pretreated the soil with phosphates to  increase the hydrogen  peroxide half-life (from 1  to 2 hours), little
peroxide was being transported to the aquifer.  Another report was planned for  publication after 8
months of operation of the bioremediation system.

Phenolic Resin Plant, U.S.A. (Rozich and Zitrides 1988)

       Over the years, soil and ground water at this site were contaminated with accidental spills of
stored solvent and other chemicals. Toluene,  xylene, phenol, methyl ethyl ketone, and other monomers
and solvents were detected in the ground water (100 to 200 mg/L). A biostimulation system (Figure 7)
was developed and operated to clean  up the contaminated soil and associated  ground water. The
system consisted of extraction of ground water, aboveground biotreatment, and infiltration  (spray appli-
cation) of a portion of the bioreactor effluent containing active biomass to clean the contaminated soil.
The surface biological treatment (fixed-film aerobic system) was sometimes complemented with a
physical or chemical treatment to remove those pollutants that could not be removed by microorganisms
(e.g.,  heavy metals).

       The site was delisted under State regulations after 2 years of treatment.

Trichtoroethane Spill Site, New Jersey (Boyer et al. 1988)

       The soil and ground water at this site had been contaminated with several hundred kilograms of
1,1,1-trichloroethane  (TCA) that was accidentally spilled.
                                              65

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Figure 6.  Flow diagram of the jet-fuel spill site at Eglin Air Force Baae.
                                    Input from Recovery Wells

                                                I
Upgradient ]
Control Area

Gallery i
' /AtMcuiun ctnu
f Settling Tanks
^N (Iron removal)
-^ — Nutrients and H2O2
F«er 1 1
Injection
\A/allc
                              Spray
                          Irrigation Area
                                                       QEA-2
                                                                Recovery
                                                                  Wells
Figure 7.  Schematic of a blostimulation bloremediation system.


                                  Physical/
                                  Chemical
                                   System    Biotreater
                                                              Clarifier
                                                                               Discharge
                                                                                        Water
                                                                        Contaminated   Table
                                                                            Zone       v   s
                                                                          Plume
                                                  66

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       Based on the results obtained in laboratory studies, a pilot-scale plant was designed and con-
structed to evaluate an in situ aerobic/anaerobic biodegradation system. The design of the pilot plant,
which was installed in the most heavily contaminated area of the site, was based on the soil column
used in laboratory investigations. Figure 8 presents a flow diagram of the pilot plant.  The two lysime-
ters were packed with contaminated soil and granular activated carbon (GAG) (5 percent).  The GAG
was added to facilitate flow control and to mimic the behavior of the loam at the site. Contaminated
ground water was introduced into the lysimeters through surface and subsurface feed lines. While the
surface feed/aerobic reaction zone prevented downward oxygen diffusion and protected the lower an-
aerobic zone, the subsurface feed prevented TCA losses to the atmosphere. A drainage system was
used to collect the lysimeter effluents, which were then pumped into a holding tank or discarded if TCA
concentrations were less than 20 ppb. The units were regularly fed with 1) a nutrient solution (nutri-
ents, chemicals for pH control, and trace metals); 2) a surface and subsurface feed composed of
glucose and ammonium sulfate (to maintain a carbon/nitrogen ratio of 10:1); and 3) a mixture of waste
secondary sludge and anaerobic digester sludge microorganisms as seed.  After approximately 15 days
of operation, the  subsurface feed was changed to contain ethanol and ammonium sulfate (C/N ratio of
10:1).  Later on, and until the end of the pilot study (6 months), a solution containing calcium nitrate, glu-
cose or ethanol, ammonium chlorine, and monobasic potassium phosphate was used as feed.  During
the pilot-plant operation, some modifications in the design of the lysimeters were introduced to over-
come mechanical blockage in the effluent lines. Although one of the lysimeters did not achieve accept-
able flow rates, both units were equally effective in removing TCA to levels below detection (20 ppb) in
the effluent at feed flow rates greater than 189 liters/day (50 gal/day).  The effluents did not contain
other hydrocarbons, volatile compounds, or priority organic pollutants.  Based on these results, Boyer et
al. (1988) concluded that "anaerobic degradation is a viable process for remediation of soil and ground
water contaminated with TCA."

Figure 8. Pilot-plant flow diagram of an in situ aerobic/anaerobic biodegradation system.
                Surface
                Nutrient —
                Solution

               Subsurface
                Nutrient
                Solution
 Sample
Port No. 1
                             Sample
                            Port No. 3
  Surface
  Nutrient -
  Solution

Subsurface
  Nutrient
 Solution
^X_X\   Sample
               Port No. 2
                          Sample
                         Port No. 4
                                              67

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3.3.3 Photolysis

       Photolysis (or photodegradation) is a process that breaks down a chemical by light energy,
usually in a specific wavelength range. Ultraviolet (UV) radiation is defined as electromagnetic radia-
tion with a wavelength shorter than visible  light but longer than x-ray radiation.  The energy content of
light increases as the wavelength decreases.  The energy of the wavelengths in the UV region is
sufficient to break down chemical bonds and cause rearrangement or dislocation of molecular struc-
tures. Table 17 lists the dissociation energies of common chemical bonds and the wavelength corre-
sponding to the energy at which UV photons will cause dissociation.

       Ultraviolet radiation combined with a reducing environment can dechlorinate PCBs in 1.5 to 2
hours (Wilson 1987). Because the photochemical reaction is initiated by the absorption of light energy,
the irradiation wavelength must match the  absorption band associated with the chemical bond of
interest in the molecule, and significant absorption of the solvent must not occur at the irradiation
wavelength. For PCBs, low-pressure mercury lamps that emit approximately 95 percent of their energy
at 253.7 nm provide adequate irradiation (Wilson 1987).

       Use of the lower atmosphere as a treatment medium requires an analysis of both the pho-
toreaction potential and the volatility of the compounds of interest.  An adequate assessment of the
potential for the use of photodegradation requires information regarding the compound's atmospheric
reaction rate (log KOH°) and anticipated reaction products. This information is available for a selected
number of compounds (Cupitt 1980,  Lemaire et al. 1980); however, much more data are needed if
photodegradation is to become a viable treatment option.

       If a compound is determined to be poorly photoreactive (i.e.,  a ti« in the atmosphere greater
than 1 day), volatilization may have to be suppressed to maintain safe ambient air concentrations at the
site.

       Photodegradation involves the use of incident  solar radiation to carry out photoreaction proc-
esses. Both direct photolysis (photoreactions due to direct light absorption by the substrate molecule)
and sensitized photooxidation (photoreactions mitigated by an energy-transferring sensitizer molecule)
are possible under environmental conditions.  Sensitized photoreactions are characteristically ones of
photooxidation  that result in substrate molecule oxidation rather than substrate isomerism, dehaloge-
nation, or dissociation, which are characteristic of direct photolysis reactions.

       Studies on macroscopic sunlight attenuation at the soil surface suggest that the photolysis
zone is restricted to the upper 1 to 2 mm of the soil surface.  Nevertheless, field studies have shown
that photochemical loss of organic chemicals may be rapid and substantial, especially in the case of
hydrophobic or cationic organics that tightly sorb to the soil surface (Miller et al. 1986).

       The photoreaction rate is influenced by the nature of light reaching the reaction medium, the
absorption spectrum of the reacting species of the sensitizer, the concentration of reacting species, the
energy yield produced upon light energy absorption, the nature of the media in which the reaction is
taking place, and the interactions between the contaminant and its surroundings. Reactions are a
complicated function of all these characteristics.  Understanding of the photolysis reaction rates and
breakdown products is very limited.

       Although the soil phototreaction of adsorbed chemicals is known to occur, the importance of
this reaction compared with aqueous or vapor photoreactivity has not been established. Soil photode-
composition will be of concern if the compound or compounds remain relatively stationary within the
contaminated soil, e.g., high values of KD (soil:water partition coefficient) and high values of Kw
(airwater partition coefficient). Soil characteristcs, including  soil organic content (Spencer et al. 1980),
transition metal content (Nilles and Zabik 1975), and soil pigment content (Hautala 1978) affect
photochemical reactions within soil systems.  Moisture content and its effect on chemical partitioning
within the air/water/soil matrix of a soil system also may have a great impact on soil photoreactions
(Burkhardand Guth 1979, Hautala 1978).
                                              68

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Table 17. Dissociation Energies for Some Chemical Bonds'
Bond
C-C
C=C
C=C
C-CI
C-F
C-H
C-N
C=N
C=N
C-O
C=O (aldehydes)
C=O (ketones)
C-S
c=s
Hydrogen
H-H
Nitrogen
N-N
N=N
N=N
N-N
N-H(NH3)
N-0
N=O
Oxygen
O-O(O2)
-O-O-
O-H (water)
Sulfur
S-H
S-N
S-O
Dissociation
energy,
kcal/mol
826
1458
199.6
81.0
116.0
987
728
1470
2126
850
1760
1790
650
166.0
104.2
52.0
600
2260
85.0
1020
480
162.0
119.1
47.0
117.5
83.0
1150
1190
Wavelength
to break bond,
nm
346 1
196.1
1432
353.0
2465
2897
3927
194.5
1345
3345
1624
1597
4399
1722
274.4
5408
476.5
1266
3364
280.3
5956
1765
240 1
6083
243.3
3445
248.6
240.3
               'Source March 1985, Gray 1973, Weast and Astle 1982
       Because of the relatively high volatility of pesticides and the concern for their transport via the
air medium, information regarding the photolysis of pesticides in air is generally available.  The major
photoreaction that occurs with pesticides in the atmosphere is oxidation (Crosby 1971, Plimmer 1971)
involving the OH radical or ozone, of which the OH radical is the species of greater reactivity (LeMaire et
al. 1982).  Based on a first-order rate of reaction of vapor phase reactions with the OH radical, the half-
life of a specific chemical species can be estimated by the following equation if its OH reaction rate
constant is known:
                      ti/2 = 0.693/(KoH[OH°])

where  ti/z= Time to decrease component concentration by 50 percent, s

     KOH = OH radical reaction rate constant, cm3/molecule-s

    [OH°] = Atmospheric OH radical concentration, (4 x 105 molecules/cm3
                  (3-10)
6645 x10'13moles/cm3)
                                              69

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       Table 18 presents several OH radical reaction rate constants as presented by Klopffer (1980)
and Cupitt (1980). Table 19 presents additional constants as given by Cupitt (1980) and an estima-
tion of the likelihood of a photolysis reaction occurring within the ambient atmosphere. Cupitt (1980)
indicated that of all the atmospheric removal mechanisms (physical, chemical, and photochemical), the
photochemical reactions are of greatest significance for most classes of hazardous compounds and
should be investigated further as a viable treatment option.

       Using photochemical reactions to enhance compound biodegradation is an area of interest for
the mitigation of hazards at hazardous waste sites. Because photolysis reactions are oxidative in
nature, they would be expected to aid in  microbial degradation through the oxidation of resistant
complex structures (Crosby 1971, Sims  and Overcash 1983). Photoreactions are limited to soil
surfaces because of the light extinction within the soil system; however, coupled with soil mixing, they
may prove to be an effective in situ treatment technique for relatively immobile chemical species.

       Exner (1984) proposed photolysis as a treatment option for dioxin-contaminated sites in
Missouri.  Experiments were carried out with mercury vapor-lamps. Within 48 hours, the dioxin in the
soil was reduced by more than 90 percent.  This application can be useful for decontaminating road
shoulders where depth of contamination  ranges from 1 to 30 cm and concentrations of dioxins range
from 1 to 20 ppb.  This treatment consists of the following steps:

       •  Disking and raking the contaminated area with agricultural equipment and using dust-
         supression techniques.

       • Spraying the soil with a biodegradable solvent by use of a boom sprayer.

       •  Passing a mobile UV irradiation train over the area.

       • Continuing the work until the appropriate dioxin reduction is achieved.

       A photochemical treatment process was evaluated for decontamination of PCB-tainted sur-
faces.  In a field test on concrete contaminated with Aroclor 1260 about 10 years  ago, the prototype
reactor destroyed 47 percent of the PCB residue after 21 hours of treatment (Draper et al. 1987). The
prototype surface photoreactor was constructed of a Flexiform aluminum frame, and Westinghouse
FS40 fluorescent lamps irradiated a 1.5-nf surface with a light intensity of 4600 u-W/cm2. Before treat-
ment, the concrete floor was contaminated with 81  ± 31 ng Aroclor 1260/100 cm2; this was reduced to
43 ±13 u.g/100 cm2. The destruction efficiency on concrete could be improved by the following:

       1) Increasing the interception of  light.

       2) Using a photoreactor with  increased light output.

       3) Using hydrogen or electron-donating solvents or photochemical sensitizers.

       Photochemical reactions make up an important part of the reactions used to degrade the
hazardous compounds and should be investigated further as a viable treatment option.  Effectiveness
of this treatment depends on the amount of tillage possible at the site, trafficability of the site, and the
depth of contamination.

       Various compounds can be produced by photolytic reactions, and each product must be inves-
tigated with respect to its health and environmental effects.  Production of hazardous compounds from
the photodegradation of pesticides has been documented, i.e., dieldrin formation  from aldrin, paraoxon
formation from parathion, phosgene formation from chloropicrin (Crosby 1971), and the formation of
PCBs from the photoreaction of DDT (Woodrow et al. 1983).
                                            70

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Table 18.   Rate Constants for the Hydroxide Radical Reaction In Air  With  Various Organic
           Substances*

                           Substance                             Logajr koH°t
                          Acetaldehyde                              9.98
                          Acrolein                                  10.42
                          Acrylonitrile                                9.08
                          Allyl chloride                               10.23
                          Benzene                                   8.95
                          Benzyl chloride                             9.26
                          Bis(chloromethyl)ether                      9.38
                          Carbon tetrachloride                        <5.78
                          Chlorobenzene                             8.38
                          Chloroform                                 7.78
                          Chloromethyl methyl ether                   9.26
                          Chloroprene                               10.44
                          o-.m-.p-Cresol*                            10.52
                          p-Cresol                                  10.49
                          Dichlorobromobenzene                      8.26
                          Diethyl ether                                9.73
                          Dimethyl nitrosamine                       10.37
                          Dioxane                                   9.26
                          Epichlorophydrin                            9.08
                          1,2-Epoxybutane                            9.16
                          Epoxypropane                              8.89
                          Ethanol                                    9.28
                          Ethyl acetate                               9.06
                          Ethyl propionate                            9.03
                          Ethylene dibromide                          8.18
                          Ethylene dichloride                          8.12
                          Ethylene oxide                              9.08
                          Formaldehyde                              9.78
                          Hexachlorocyclopentadiene                 10.55
                          Maelic anhydride                           10.56
                          Methanol                                   8.78
                          Methyl  acetate                              8.04
                          Methyl chloroform                            6.86
                          Methyl  ethyl ketone                          9.32
                          Methylene chloride                          7.93
                          Methyl propionate                            8.23
                          Nitrobenzene                               7.56
                          Nitromethane                               8.81
                          2-Nitropropane                             10.52
                          n-Nitrosodiethylamine                       10.19
                          Nitrosoethylurea                            9.98
                          n-Propylacetate                             9.41
                          Perchloroethylene                           8.01
                          Phenol                                     10.01
                          Phosgene                                Nonreactive
                          Polychlorinated biphenyls                   <8.78
                          Propanol                                   9.51
                          Propylene oxide                             8.89
                          Tetrahydrofuran                             9.95
                          Toluene                                    9.52, 9.56
                          Trichloroethylene                            9.12
                          Vinylidene chloride                          9.38
                          o-,m-p-Xylene                               9.98
                          'Source: Adapted from Lemaire et al. (1980) and Cupitt (1980).

                          t KQH° 'n un'ts o' (mole-s)~1
                                                       71

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Table  19.  Atmospheric Reaction Rates and Residence Times of Selected Organic Chemicals*
(cm^ Direct
molecule"^ photolysis
Compound s"1 ) probability
Acetaldehyde
Acrolein
Acrylonitrile
Allyl chloride
Benzyl chloride
Bis (chloromethyl)
ether
Carbon tetrachloride
Chlorobenzene
Chloroform
Chloromethyl
methyl ether
16 Probable
44a Probable
2
28a Possible
3a Possible
4a Possible
<0.001
0.4a Possible
0.1
3a Possible
Physical
removal
probability
Unlikely
Unlikely
Unlikely
Unlikely
Unlikely
Probable
Unlikely
Unlikely
Unlikely
Probable
Residence
time,
days
0.03-0.7°
0.2
5.6
0.3
3.9
0.02-2. 9d
>1 1,000
28
120
0.004-3.9d
Anticipated
photoproducts
H2CO, CO2
OCH-CHO, H2CO, HCOOH, CO2
H2CO, HC(O)CN, HCOOH, CN°
HCOOH, H2CO, CICH2CHO,
chlorinated hydroxy carbonyls,
CICH2COOH
OCHO, Cl; ring cleavage products
chloromethylphenols
HCI+H2CO, CIHCO, chloromethyl-
formate
CI2CO, CIO
Chlorophenols, ring cleavage
products
ci2co, cr
Chloromethyl and methyl formate,
CIHCO
Chloroprene
o,m,p-Cresole
46a
55
Probable
Unlikely      0.2
Dichlorobenzene6      0.3a      Possible


Dimethyl nitrosamine   39a      Probable

Dioxane              3a
             Unlikely


             Unlikely




             Unlikely
            0.2


            39


            <0.3

            3.9
H2CO, H2C=CCICHO, OHCCHO,
 CICOCHO, H2CCHCCIO, chloro-
 hydroxy acids, aldehydes

Hydroxynitrotoluenes, ring
         cleavage products

Chlorinated phenols, ring cleavage
 products

aldehydes, NO

OHCOCH2CH2OCHO, OHCOCHO
 oxygenated formates
Dioxin
          Probable
(continued)
                                                  72

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 Table 19. (continued)
kQHx1°12
(cm3
molecule"^
Compound s"^ )
Epichlorohydrin
Ethylene dibromide
Ethylene dichloride
Ethylene oxide
Formaldehyde
Hexachlorocyclo-
pentadiene
Maleic Anhydride
Methyl chloroform
Methylene chloride
Methyl iodide
Nitrobenzene
2-Nitropropane
N-Nitrosodi-
ethylamine
Nitrosoethylurea
Nitrosomethylurea
Nitrosomorpholine
Perchlorethylene
Phenol
2a
0.25
0.22
2a
10
59a
60a
0.012
0.14
0.0043
0.06a
55a
26a
13a
20a
28a
0.17
17a
Direct
photolysis
probability
Possible
Possible
Possible
-
Probable
Probable
Possible
Possible
Possible
Possible
Possible
Possible
Probable
Possible
Possible
Possible
Possible
-
Physical
removal
probability
Unlikely
Unlikely
Unlikely
Unlikely
Unlikely
-
Possible
Unlikely
Unlikely
Unlikely
Unlikely
Unlikely
-
-
-
-
Unlikely
Possible
Residence
time,
days
5.8
45
53
5.8
0.1-1.2°
0.2
0.1
970
83
2900
190
0.2
<0.4
<0.9
<0.6
<0.4
67
0.6
Anticipated
photoproducts
H2CO, OHCOCHO,
CICH2O(O)OHCO
Bi, BrCH2CH2CHO, H2CO, Br HCO
CIHCHO, H2CCICOCI, H2CO,
H2CCICHO
OHCOCHO
CO, CO2
CI2CO, diacyclchlorides, ketones,
Cl.
CO2, CO; acids, aldehydes and
esters which should photolyze
H2CO, CI2CO, Cl.
CI2CO, CO, CIHCO, Cl.
H2CO, l°, ICHO, CO
Nitrophenols, ring cleavage
products
H2CO, CHaCHO
Aldehydes, nitroamines
Aldehydes, nitroamines
Aldehydes, nitroamines
Aldehydes, ethers
CI2CO, CI2CI(OH)COCI, CIO
Dihydroxybenzenes, nrtrophenols,
                                                                         ring cleavage products
(continued)
                                                   73

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Table 19. (continued)
Compound
Phosgene*
Polychlorinated
biphenyls
POM (benzo(a)-
pyrene)
Propylene oxide
Toluene
Trichloroethylene
Vinyllidene
chloride
o-,m-,p-Xylene
(cm3
molecule"1
s'1)
~0
<1a
-
1.3
6
2.2
4a
16
Direct Physical
photolysis removal
probability probability
Possible
Possible Unlikely
Possible Probable
Unlikely
Unlikely
Possible Unlikely
Possible Unlikely
Unlikely
Residence
time,
days
-
>11
8
8.9
1.9
5.2
2.9
-0.7
Anticipated
photoproducts
CO2, CIO, HCI
Hydroxy PCB's, ring cleavage
products
B(a)P-1,6-quinone
CH3C(O)OCHO, CH3C(O)CHO,
H2CO, HC(0)OCHO
Benzaldehyde, cresols, ring
cleavage products, nitro com-
pounds
CI2CO, CIHCO, CO, Cl-
H2CO, CI2CO, HCOOH
Substituted benzaldehydes,
hydroxy xylenes, ring cleavage
products nitro compounds
' Source:  Cupitt(1980)

a Rate constant by method of Hendry and Kenley,(1979).

b Material is not expected to exist in vapor phase at normal temperatures. Residence time calculation assumes the
  chemical is substantially absorbed on aerosol particles and that the aerosol particles have a residence time of
  approximately 7 days.

c The shorter residence time includes a photolysis rate as given in Graedel (1978).

^ Decomposition in moist air is expected. The shorter residence time includes the cited decomposition rate.

6 Values given are averages for the various isomers.

* Reaction with O('D) is possible; k = 3.6 x 10~10 cm3/molecule/s, and [O('D)] = 0.2 molecules/cm^ implies a
  tropospheric lifetime of 440 years.  In addition,  slow hydrolysis is expected.
                                                   74

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       Also, the effectiveness of this treatment depends on the amount of tillage possible at the site
and the effect of any contaminants produced by photolytic reactions. A major drawback in treating soil
via photolysis is the lack of penetration depth of ultraviolet radiation.  In some cases, cultivators have
been suggested and used to expose the contaminated material to UV light.  Treatment of soil not
exposed to sunlight has been attempted with banks of low-pressure mercury lights in conjunction with a
surface pretreatment consisting of the application of a hydrogen donor. Run-on and runoff controls may
be necessary to manage the drainage and erosion.

       Photolysis of soil contaminants may be enhanced in two ways: 1) by adding photoenhancement
agents, and 2) by enhancing volatilization leading to photodegradation.

3.3.3.1 Addition of Photoenhancement Agents

       Certain compounds (e.g., ozone and hydrogen peroxide) are degraded to form reactive radical
species (hydroxyl, peroxy, and hydroperoxy radicals and singlet oxygen) and thus enhance photochemi-
cal reactions. Gohre and Miller (1986) reported that singlet oxygen is a likely reactant in the photooxida-
tion of sulfur-containing pesticides on soil  surfaces because it is produced on both irradiated inorganic
metal oxides and irradiated soils (e.g., alumina and silica gel).

       Photodegradation of soil contaminants may be enhanced by adding various proton donor
materials to the contaminated soils.  Solvents used as hydrogen donors include alcohols, water, and
hydrocarbons. In heavy hydrocarbons, polymerization of the  biphenyl radicals to yield polyphenylenes
Is the major PCS reaction. In basic alcohol solutions, a stepwise dechlorination of the molecule occurs.
These photochemical reactions yield only  biphenyl and sodium chloride as the final  products.

       Crosby et al. (1971) reported photolysis of tetrachlorodibenz-p-dioxin (TCDD) on soil surfaces in
the presence of suitable hydrogen sources in the form of polar solvents. Plimmer and Klingebiel (1973)
indicated that methanol used as a solvent for TCDD photooxidation also acted as a  hydrogen donor in
the photolysis reaction.

       Several authors have reported on investigations of feasible in situ treatment methods for
contaminated areas  surrounding a TCDD  release that occurred near Seveso, Italy, in 1976. Wipf et al.
(1978) investigated the use of alternative hydrogen donors for the photooxidation of TCDD. Solutions of
80 percent olive oil and 20 percent cyclohexane at 350 L/ha and 40  percent aqueous emulsion with 4
percent biodegradable emulsifying agent at 400 L/ha were found to produce a thin film on vegetation
and other smooth surfaces suitable for maximum reaction of TCDD photolysis.  Within 48 hours after
treatment, TCDD reductions in excess of 60 percent were observed. Under laboratory conditions, the
oil and emulsion solutions reduced the half-life of TCDD by a factor of 25 upon  irradiation with simulated
sunlight.

       Liberti et al.  (1978) reported the use of a 1:1 solution of ethyl oleate and xylene as hydrogen
donors also resulted in complete degradation of TCDD on building surfaces in approximately 1  hour at 2
mW/cm2 light intensity  and 72 hours at 20 jiW/cnf  light intensity.
       Dehalogenation of kepone (Dawson et al. 1980) and  enhanced PBB (Christensen and  Weimer
1979) photolysis  have  been reported when hydrogen donors  in the form of amino groups were  added to
contaminated soils prior to irradiation with sunlight; however,  no observable degradation of  PCBs in soil
was found with amine-enhanced soil (Meuser and Weimer 1982).

       Occhiucci and Patacchiola (1982) reported soil photodecomposition of  PCBs. This photode-
composition was shown to be enhanced by the addition of a proton donor, triethylamine, to the waste/
montmorillonite system. Adding triethylamine resulted in a 2.5- to 5-fold increase in PCB degradation
over a  100-hour irradiation period and provided 4 to 18 percent decomposition of the various chlorinated
species tested.

       These dechlorination reactions  result from hydrogen  abstraction by organic radicals formed
upon irradiation (Bunce1982).  This process has not yet been optimized for soil systems, but it  appears
to  have potential for  use in the in situ treatment of stable, nonmobile compounds.
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       Activated carbon adsorption of organics at hazardous waste sites followed by chemical addition
and photolysis was reported (Sims et al. 1986). This technology involves impregnating the site with
activated carbon and then sampling the soils.  The most highly contaminated materials are physically
removed, packaged, and disposed of in an approved hazardous waste disposal facility. The remaining
material is mixed with sodium bicarbonate to increase soil pH and then allowed to react photochemi-
cally, which results in the photolysis of the parent material. The level of treatment achieved is expected
to be high to medium.

       Semiconductor powders and colloids,  which are inexpensive, nontoxic, and recyclable, have
been shown to enhance photodegradation  (Sukol 1987).  Titanium dioxide is the best of these photocat-
alysts because it can absorb a wide range of solar spectrum wavelengths more efficiently than organic
contaminants can  by direct photolysis.

       Minerals rich in manganese,  iron, and titanium oxides can be relatively abundant in soils.
Transformation of  certain types of xenobiotics  are affected by the redox reactions  on the surface of
these metal oxides.

       Natural sediments and clays  have  also been studied for their application as photosensitizing
agents, and it has been reported that low levels of humic substances actually catalyze photodegradation
by UV/ozonation.

       Surfactants may  improve photodegradation rates by enhancing the solubility of the compounds.
Exner (1984) showed that irradiation  of dioxin-contaminated soil in the presence of surfactants can
reduce the concentration of dioxin by 90 to 99 percent within 24 hours.

       Photodegradable organic wastes are amenable to this treatment. Generally, these include
compounds with moderate to strong absorption in the >290-nm wavelength range. Such compounds
generally have an extended conjugated hydrocarbon system or a functional  group with an unsaturated
hetero atom (e.g., carbonyl, azo, nitro). Groups that typically do not undergo direct photolysis include
saturated aliphatics, alcohols,  ethers, and amines. Tetrachlorodibenz-p-dioxin (TCDD), kepone, and
PCBs have been treated with this method.

Status of the Technology

       Some field testing and evaluation of the use of photoenhancement agents to promote photode-
gradation is ongoing (Sims et al. 1986). In addition, research is being conducted on an in situ diffusion
method for enhancing the mobility of haloaromatics in the soil and increasing their movement to the soil
surface for subsequent photodegradation.  Investigations are continuing  on the use of ethyl oleate and
hexadecane for this application, and  the preliminary results are encouraging (Overcash et al. 1986).

        Exner (1984) reported preliminary  experiments (no field study) of in  situ detoxification of dioxin-
contaminated soil by irradiation with UV light in the presence of organic solvents and aqueous surfactant
emulsions. Spraying the soil with 0.5 to 3 percent w/w of organic surfactants and irradiation with a
mercury vapor lamp reduced the dioxin concentration from 671 ng/g to 11 ng/g (a 98 percent reduction)
within 31 hours. The results show that solubilization of dioxin is the primary step for in situ photolysis of
the soil. Also, it was reported  that the use  of organic solvents is not necessary; aqueous surfactant
solutions can be used instead.

        A method that uses light generated by ordinary incandescent light bulbs, which is absorbed by a
common dye sensitizer, has been developed for the photoreduction of PCBs to biphenyls. The dye
molecules can promote a chemical reaction between polychlorinated biphenyls and a  hydrogen gas
such  as propane (Stallard 1988). In this reaction, hydrogen is abstracted from the hydrocarbon mole-
cule and is substituted for chlorine on the PCB molecule, which yields the reaction product biphenyl.
The reaction occurs in polar aprotic solvent at room temperature and in the presence of an alkali metal
hydroxide.  This process could be applied to the treatment of PCB-contaminated transformer oils,  soils,
and landfill leachates.
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Secondary Impacts
        The addition of photoenhancement agents (i.e., proton donors) may change the soil pH and
affect the natural microbial populations.  Soil pH controls may need to be applied.
Equipment, Exogenous Reagents, and Information Required
        Cultivators, equipment for diking and raking, boom sprayers, or some other sprinkling system
may be required to apply the photoenhancement agents to the soil. Reagents may include singlet
oxygen and hydrogen donor solvents, such as water, methanol, ethyl oleate, xylene, amino groups, and
triethylamine; semiconductor powders; natural sediments and clays; metal oxides (e.g., manganese,
iron, and titanium oxides); and surfactants.
        The following information is required prior to the use of photoenhancement agents to effect pho-
todegradation:
        • Characterization and concentration of wastes, particularly organics, at site.
        • Absorption spectra of waste constituents (at wavelengths >290  nm, molecular absorptivities,
         absorption maxima, quantum yield).
        • Atmospheric reaction rate of compounds (log  KOH°).
        • Photolysis rate constant(s).
        • Products of photolysis and expected reaction  products (particularly hazardous products).
        • Volatility of organics (vapor pressure, Henry's law constant)
        • Depth, profile, and areal distribution of contamination.
        • Light intensity at site.
        • Trafficability of soil and site.
Advantages of Applying Photoenhancement  Agents
        The advantages of this technique for the in situ treatment of soils are as follows:
        • Reagents are inexpensive and recyclable.
        • The treatment is effective on relatively immobile organic chemical species, such as a
         dioxin- or PCB-contaminated soil.
Disadvantages of Applying Photoenchancement Agents
        The disadvantages of this technique  are as follows:
        • The depth of treatment is limited to approximately 1 to 3 mm below grade.
        • Understanding of the photolysis reaction rates and breakdown products is limited.
3.3.3.2  Enhancement of Volatilization
        Enhancing volatilization of compounds from the  soil that are susceptible to photodegradation
may be a potential treatment technique.  This technique involves increasing the bulk density or drying of
the soil system to increase soil vapor pore spaces and, subsequently, the  vaporization rate of the
desired compounds, followed by their photodegradation  in air.
        Unlike photoreactions in solution, the photolysis rate constants of  hydrophobia organics sorbed
on soil surfaces show a decrease with increasing irradiation. This behavior has been observed in  the
volatilization of pesticides from soil surfaces.  This unusual behavior in kinetics may be partly due to the
                                              77

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intraparticle transport of a portion of the organic substrate into aggregate interiors, where it is protected
from sunlight or from volatilization. These results indicate that it is probably meaningless to describe the
loss of PCDD or other hydrophobic organics in soils in terms of a first-order half-life (Miller et al. 1986).

       Some important factors that influence volatilization of organics from the soil surface are concen-
tration of the chemicals in the soil, chemical properties such as solubility and vapor pressure, soil water
content, and water evaporation rate.  Henry's law constant, Kh, which denotes the ratio between the
vapor pressure of a compound and its solubility in water at a given temperature, gives an indication of
the ease with which  a compound may be stripped from the soil or water.

       Temperature strongly affects volatilization at the soil surface. Studies of the soil temperature
profiles have shown that the top few centimeters undergo pronounced diurnal and seasonal variations.
In experiments with well-mixed dioxin-contaminated soil from Times Beach, Missouri, significant loss of
the compound was observed within the top 3 mm from the soil surface, especially when the soil was
damp. It has been proposed that these results indicate that evapotranspiration processes are important
for moving PCDDs to the surface, where they undergo surface photolysis or volatilization (Miller et al.
1986).

       The technique is applicable to compounds of low water solubility, with low KD values  and  low
Kw values, and those that are highly photoreactive and that, once within the lower atmosphere, would
have a relatively short life (on the order of hours or preferably minutes).

       Techniques for enhancing contaminant volatilization are discussed in detail in Section 3.4.

3.4 Control of Volatile Materials

       Controlling volatilization of contaminants from a hazardous waste site is often necessary  to
prevent or reduce air emissions.  In situ treatment technologies suitable for this purpose include reduc-
ing the rate of volatilization through physical and/or chemical means and increasing the rate of volatiliza-
tion for more efficient and effective management of vapors that could be released into the atmosphere.

       Volatilization from a hazardous waste site may have to be controlled to reduce air emissions.
Three technologies may be used to reduce volatilization or volatile materials from a contaminated site:
1) soil vapor extraction (including vacuum extracting and steam stripping), 2) radio frequency heating,
and 3) soil cooling.

3.4.1 Soil Vapor Extraction

       Concentrations of volatile materials can be reduced by the use of various vapor extraction
systems. Vapor extraction systems involve the recovery of volatile contaminants by injecting air into
contaminated soils and extracting the air (in which volatile chemicals have partitioned) in a vapor
recovery well. A vacuum apparatus is typically used to extract the volatilized contaminants.
3.4.1.1 Vacuum Extraction

       Vacuum extraction processes have proved to be an effective method of controlling fugitive
emissions of vaporized contaminants from uncontrolled hazardous waste sites, and are the most
commonly used in situ remedial technology (Murdoch et al. 1988). Soil vapor extraction systems
involve the extraction of air containing volatile contaminants from unsaturated soils. Clean air is injected
into the contaminated soils, and a vacuum apparatus is used to extract the vapor-filled air from recov-
ery or extraction wells (Hutzler et al.  1989). The operation involves the  use of an air blower,  and  the
inducted air flows come into equilibrium with extracted air. The established air flows are a function of
the equipment used and soil characteristics, including soil air permeability (Hutzler et al. 1989).

       The pore space of unsaturated soils is composed of liquid and vapor phases in equilibrium.
Contaminants with high vapor pressures partition into the vapor phase in the air-filled pore spaces.
With vapor extraction systems, these partitioning characteristics of volatile contaminants are used to
facilitate their extraction when a vacuum is applied to the soil. This results in the liquid-phase contami-
nants being volatilized to  maintain the liquid-vapor phase equilibrium present in the soil strata.
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        The use of vapor extraction systems is typically limited to permeable unsaturated soils such as
 sands, gravels, and coarse silts; diffusion rates through dense soils, such as compacted clays, are
 much lower than through sandy soils (USEPA 1988).  Clayey soils usually lack the conductivity neces-
 sary for effective vapor extraction, unless they are first fractured. Hydraulic fracturing, a method used to
 increase fluid flow within the subsurface, may increase the effectiveness of vapor extraction (Murdoch
 1989). Hydraulic fracturing is discussed in Section 4.1.

        Vapor extraction systems may be designed to have flexible operational parameters. These
 include air extraction rates, extraction-well spacing and configuration, control of water infiltration, and
 pumping deviations (Hutzler et al. 1989).  Higher flow  rates increase vapor removal, as more air is
 forced through the permeable soil layers. Although additional wells allow a greater measure of air flow
 control, they also increase costs.  Temporarily stopping the flow of air from the air-forcing blowers allows
 time for chemicals to diffuse into the vapor phase, and venting will subsequently remove higher concen-
 trations of volatile contaminants (Hutzler et al. 1989).

       Glynn and Duchesneau (1988) assessed the soil vapor extraction system used  at a Belleview,
 Florida, site with leaking underground storage tanks (USTs). The soil had been contaminated with
 gasoline and other hyrocarbons and with gasoline components, including benzene, xylene, ethyl ben-
 zene, and toluene.  The  contaminants at this approximately 50-acre site had migrated to and contami-
 nated the city well field, which the city subsequently abandoned. A vapor extraction system was imple-
 mented to reduce the concentrations of gasoline and gasoline components in the soils surrounding the
 USTs responsible for the contamination.

       In a 25-day period, the vacuum extraction system removed 90 kg of total hydrocarbons from the
 contaminated area.  The soil gases extracted from the site showed decreasing concentrations of volatile
 organics as time passed, which indicates that concentrations of gasoline components were being
 decreased. Glynn and Duchesneau (1988) found that the concentration ratio between each gasoline
 component tested (benzene, toluene, ethyl benzene, and xylene) varied over the 25-day field demon-
 stration of the soil vapor extraction system. Because of their high volatility, benzene and toluene
 concentrations  in the extracted gasses decreased faster than the other compounds. This led to the
 conclusion that highly volatile compounds are removed at a faster rate than less volatile compounds.

       In situ vacuum extraction by a process developed by Terra Vac, Inc., has been demonstrated
 and evaluated as part of the Superfund Innovative Technology Evaluation (SITE) Program.  Figure 9, a
 process diagram for this in situ vacuum extraction process, shows the extraction well,  vapor/liquid
 separation, and the vapor treatment train. Recovery rates ranging from 20 to 2500 pounds  per day are
 said to be obtained from the Terra Vac system; they are a function of the volatility of the organic com-
 pound recovered (USEPA 1988).  During the SITE Program demonstration at Groveland, Massachu-
 setts, approximately 1300 pounds of volatile organic compounds were extracted during a 56-day operat-
 ing period (USEPA 1989).

 Status of the Technology

       In situ vacuum extraction is being implemented in many locations across the United States.
 One example is the Verona Wells Superfund Site in Battle Creek, Michigan, in EPA Region V. This site
 contains trichloroethylene contamination (USEPA 1988). The technology has also been demonstrated
 at a Superfund site in Puerto Rico, where carbon tetrachloride had leaked from an underground storage
 tank.  The SITE Program demonstration of the Terra Vac process was conducted at the  Valley Manufac-
 tured  Products Company, Inc. property, which is part of the Groveland Wells Superfund Site in Grove-
 land, Massachusetts (USEPA 1989).  Trichloroethylene was the main contaminant at that site.
 Secondary Impacts

       This technology has very few secondary impacts, as only blower-induced air is introduced into
the contaminated soils.
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Figure 9. Process diagram of an in situ vacuum extraction process.
                                                      Primary
                                                     Activated
                                                      Carbon
                                                     Canisters
Equipment, Exogenous Reagents, and Information Requirements

        Equipment required for soil vapor extraction systems includes air blowers, injection wells,
extraction wells, a vacuum apparatus, and a carbon adsorption system to adsorb extracted vapors.  No
exogenous reagents are required for soil vapor extraction systems.

        The following information is needed to operate this technology:

        •  Characterization of wastes, primarily volatile organics.

        •  Volatility of organic contaminants (vapor pressure, Henry's law constant, air/water partition
          coefficient, solubility).

        •  Depth, profile, and areal distribution of contamination.

        •  Soil matrix properties (permeability, porosity, organic carbon content, soil moisture content,
          and particle size distribution).

        •  Accessibility  of soil and site.

Advantages of Vacuum Extraction

        One advantage of a soil vapor extraction system is that it does not require the addition of
reagents that must be delivered to and subsequently recovered from the contaminated area.  The ex-
traction system is used to remove contaminated vapor only.  Also, this technology provides permanent
remedial action; i.e., the contaminated soils are actually cleaned, not just contained along with the
hazardous contaminants.
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 Disadvantages of Vacuum Extraction

        A disadvantage of this technology is that the soils must be permeable and fairly homogeneous
 for it to be most effective. Impermeable soil lenses within more permeable soils could adversely affect
 the recovery of volatile soil contaminants.

        Another disadvantage is that a single site containing wastes of varying volatility may require
 additional technologies for remediation, as vapor extraction techniques are most amenable for highly
 volatile compounds.

 3.4.1.2  Steam Stripping

        In situ steam stripping of contaminants from soil involves injecting steam into the soil beneath
 the contaminated zone. When assisted by a vacuum at the ground surface, steam stripping brings the
 contaminants to a collection point for further treatment. Lord et al. (1989) conducted a field test of this
 technology that included a unique geosynthetic cap and a geomembrane for containment of the steam
 and contaminant.

        Steam stripping is particularly effective on alkanes and on alkane-based alcohols such as
 octanol and butanol (Lord et al. 1989).  The vapor pressure and polarity of the compounds are important
 in determining the amenability of the compound to steam stripping; however, the exact correlation is not
 fully understood (Lord et al. 1989).

 Status of the Technology

        Bench- and field-scale studies have been conducted of in situ steam stripping of contaminated
 soil (Lord et al. 1989; Lord et al. 1988; Hilberts 1985; Baker et al. 1986).  Further investigation of the
 technology is needed for a better understanding of its applicability to various chemicals and soil types.

       A portable treatment unit called a "Detoxifier" is used for in situ steam and air stripping. This
 unit is being evaluated as part of EPA's SITE Program  (Ghassemi 1988). The drills are modified to
 allow the injection of steam and air into the soil through the cutting blades.  The ground area being
 drilled is covered by a containment system to trap and recover the stripped volatiles.

       In this process, steam is piped to the top of  the drills and injected through the cutting blades.
 The steam heats the ground being remediated, which increases the vapor pressure of the volatile con-
 taminants and the rate at which they can be stripped.  Both the air and the steam serve as carriers to
 convey these contaminants to the surface. The shroud, a metal box designed to seal the process area
 above the rotating cutter blades from the outside environment, collects the volatile contaminants and
 ducts them to the process train. In the process train, the volatile contaminants and the water vapor are
 removed from the off-gas stream by condensation.  The condensed water is separated from the organ-
 ics by distillation, filtered through activated carbon beds, and subsequently used as makeup water in a
 cooling tower.  Figure 10 presents a process flow diagram of this treatment system.

 Secondary Impacts

       The introduction of steam to the subsurface increases the temperature of the soil, which may
 either increase microbial activity or destroy some microbial populations.

 Equipment, Exogenous Equipment, and Information Required

       In situ, vacuum-assisted, steam stripping requires steam injection pipes, a vapor containment
system (geomembrane), and a vacuum collection system. A steam generator is also required.
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Figure 10. Process flow diagram of an in situ steam stripping process.
        VV
                        Off
                        Gas
                       Shroud
                                Suction
                                Blower
      Counter-rotating
           Drills

Scrubbing
System

Water
Purification
Water <
r
Evaporative
Cooler



A

Gas
Cooling

Hydrocarbon
Separator
+
Recovered
Hydrocarbons

Contaminant
Condenser
	 *



        Information necessary for the effective design and application of an in situ steam-stripping
system includes the following:
        •  Depth and areal extent of contamination.
        •  Depth to ground-water table.
        •  Vapor pressure and polarity of organic contaminants.
        •  Subsurface stratigraphy, including the presence of clay lenses.
Advantages of Steam Stripping
        Steam stripping to extract contaminants from the soil has the following advantages:
        •  Alkanes and alkane-based alcohols are effectively extracted from soils.
        •  The treatment time can be as short as several hours, depending on the extent and amount of
          contamination.
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Disadvantages of Steam Stripping

        Steam stripping has the following disadvantages:

        • The increase in soil temperature may adversely affect other soil properties.

        • Not all the mechanisms of the technology are fully understood.

3.4.2 Radio Frequency Heating

        Many Superfund sites are contaminated with various solvents and fuels. Aliphatic and aromatic
fractions of jet fuels and gasoline, chlorobenzene, trichloroethylene, dichloroethane, and tetrachloroeth-
ylene are some of the contaminants found at contaminated sites. These compounds pose a consider-
able environmental threat, as they could migrate from the site and contaminate drinking water supplies.
Materials that typically volatilize in the temperature range of 80° to 300°C (such as those just listed)
may be more easily recovered in extraction systems if the soil temperature is raised to increase the
volatilization rates.  Radio frequency heating is one method of soil heating for contaminant removal.

        Radio frequency (RF) heating is a technique for rapid and uniform in situ heating of large
volumes of soil (Dev et al. 1988).  This technique heats the soil to the point where volatile and semivola-
tile contaminants are vaporized into the soil matrix.  Vented electrodes are then used to recover the
gases formed in the soil matrix during the heating process.  The concentrated extracted gas stream that
is recovered can be incinerated or subjected to other treatment methods.

        Radio frequency heating is accomplished by the use of electromagnetic energy in the radio
frequency band (Dev et al. 1988). The energy is introduced into the soil matrix by electrodes inserted
into drilled holes. According to Dev et al.  (1988), the mechanism of heat generation is similar to that of
a microwave oven. The heating process does not rely on the thermal conductivity of the soil. A modi-
fied radio transmitter serves as the power source, and the industrial, scientific, and medical (ISM) band
provides the frequency at which the modified transmitter operates. The exact operational frequency is
obtained from an evaluation of the areal extent of contamination and the dielectric properties of the soil
matrix (Devetal. 1988).

        The frequencies used during RF heating remedial work may be as low as 45 Hz or as high or
higher than 10 GHz. The frequency range for most RF heating applications at hazardous waste sites is
between 6.78 MHz to 2.45 GHz (Dev et al. 1988).

        Full implementation of an RF heating system at a contaminated hazardous waste site requires
four major subsystems: 1) an RF energy deposition array; 2) RF power generating, transmitting,
monitoring, and control systems; 3) a vapor barrier and contaminant system; and 4) a gas and liquid
condensate handling and treatment system.  The electrode array (also  known as the exciter array)
design is the critical system that determines the design and operational parameters of the other sys-
tems.

        During installation of RF heating systems, electrodes are placed in three parallel rows that form
two outer walls and a single central conductor. Demonstration has shown that appropriate spacing of
the electrodes within each row and the rows themselves allow the applied electromagnetic field to be
contained within the outer "walls" of electrodes (Dev et al. 1988).

        A field demonstration test was conducted at the Volk Air National Guard Based at Camp
Douglas, Wisconsin. For more than 25 years this site had been used as a fire-fighting training area,
where waste oils, fuels, and other hydrocarbons were dumped into a pit and ignited to simulate aircraft
fires.  An estimated 50,000 gallons of waste hydrocarbons had migrated into the soil in and around the
pit (USDOE 1988).  This site offered the homogeneous waste and soil characteristics necessary for a
controlled test of the RF heating technology.  The complete system included a cooler/condenser, a gas-
liquid separator, and a carbon adsorption unit for trapping the vented gas stream. Condensed liquids
were collected and saved for later analysis.
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       The soil temperature reached 100°C after 2 days of inducting the radio frequency waves into
the soil, and 150°C after 8 days of RF heating (Dev et al. 1988).  The test was completed after 12.5
days of RF heating.  The results presented in Table 20 show that RF heating decreased the relative
levels of contamination at this site. The method was especially effective for removal of volatile organics.
As shown, this technology is suitable for treating both volatile and semivolatile organic contaminants in
soils.  Treatment levels are potentially high, depending on the waste characteristics and the homogenity
of the contaminated soil. The best treatment levels could be expected in predominantly sandy soils.
Application of this technology could be hindered if the soil characteristics caused the drilling of soil
borings to be difficult.

Table 20. Percent Reduction of Contaminants From RF Heating of Soil*
Depth interval,
inches
6-72
6-12
30-42
60-72
Moisture
97.2
96 1
961
989
Aliphatics
Volatile Semivolatile
993
982
997
998
943
881
976
985
Aromatics
Volatile Semivolatile
996
992
996
999
991
98.1
99.6
999
       * Source Dev et al 1988

3.4.2.1 Status of the Technology
       Radio frequency heating is a new technology for cleanup of hazardous waste sites.  It is cur-
rently in the pilot- and field-scale demonstration stage and has been tested at the Volk Field ANGB,
Wisconsin in cooperation with the U.S. Department of Defense, U.S. EPA, and the Illinois Institute of
Technology Research Institute.
3.4.2.2 Secondary Impacts
       The high soil temperatures associated with this technology would inhibit or destroy existing
colonies of microbes in the soil matrix. The high temperatures could also have an adverse effect on
humic matter within the soil matrix.
3.4.2.3 Equipment, Exogenous Reagents, and Information Required
       Equipment requirements include a transmitter, a power source, electrodes, ancillary equipment
for gas extraction and containment, and soil boring devices. No exogenous reagents are required for
this technology.
       The following information is needed to implement this technology:

       • Type and homogenity of soils.
       • Types of contaminants present.
       • Dielectric properties of the soil matrix.
       • The size of the area requiring treatment.

       • Accessibility of the soil and the site.

3.4.2.4  Advantages of Radio Frequency Heating
       The advantages of using this technology for remediation of hazardous waste sites are as
follows:
       • It offers a potentially high level of treatment.
        • No other treatments are necessary if the contamination consists solely of volatile and
         semivolatile organics.
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        •  It is economically feasible if soil consists primarily of sand and loams.

        •  It provides permanent remediation.

 3.4.2.5  Disadvantages of Radio Frequency Heating

 This technology has the following disadvantages:

        •  Has limitations related to various soil types and contaminants.

        •  Could be difficult to apply.

        •  Does not remediate nonvolatile organics, metals, or other inorganic contaminants.

        •  Must be supplemented with other treatment methods if nonvolatile contaminants are present.

        •  Very deep contamination would require more costly solutions.

 3.4.3 So/7 Cooling

        Soil cooling is a technique for decreasing soil temperatures so as to reduce the vapor pressure
 of volatile  constituents and thus their volatilization rates. One way to lower soil temperature is to apply
 cooling agents to the soil surface.  Greer and Gross (1980) found solid carbon dioxide (dry ice) to be
 more effective than liquid carbon dioxide, liquid nitrogen, or ice in reducing ethyl ether vaporization from
 a liquid pool.  Ethyl ether vapor concentrations were reduced from 8300 to 96 ppm by the addition of dry
 ice.  The dry ice resulted in a liquid pool temperature of -85°C for 80 minutes at an application rate of 95
 kg/m3.  Liquid nitrogen produced -120°C temperatures, but 1025 kg was required to reduce atmospheric
 concentrations from 93,000 to 116 ppm.  Also, liquid nitrogen was more difficult to work with than was
 dry ice.  Because of the effectiveness of solid carbon dioxide and the minimal risks it  poses for response
 personnel during its application, it was the cooling agent of choice (Greer and Gross  1980).

        Ground freezing is another means of immobilizing contaminants. Ground freezing involves
 injecting a cooling agent (e.g., ethylene glycol brine or liquid nitrogen) into pipes located within the soil
 matrix, which cools the soil to far below the freezing point of water (0°C) (Iskandar and Jenkins 1985).
 Artificial ground freezing is typically accomplished by the Poetsch method (Sullivan et al. 1984), which
 entails using uniformly spaced black-iron pipes within soils contaminated by volatiles.  The coolant is
 injected and withdrawn in an open loop within each pipe to provide continuous recycling.  Ground
 freezing to separate contaminants from water in a soil  system is discussed in Section 3.5.3.

        Sullivan et al. (1984) have determined that liquid nitrogen is the best coolant for quickly freezing
 contaminated soils.  This fast freezing immobilizes volatile chemicals as the soil water (containing
 contaminants) freezes in situ.

       This technology is apparently most suitable for immobilizing volatile organics  at uncontrolled
 hazardous waste sites. The potential level of treatment is high; however, how effective the technology
 is depends on the degree of temperature reduction possible.  Cooling agents are more effective than
 soil modifications, but cost  may make their use impractical.

       Cooling agents may be applied to the soil surface or  circulated in a piping system below the
 surface. The  soil characteristics and accessibility of the site determine the ease of application of this
technology.

3.4.3.1 Status of the Technology

       This technology is currently in the laboratory- and bench-scale stage. A literature search
produced no reports indicating soil cooling or ground freezing had been demonstrated for soil vapor
mitigation.  Experimentation has been limited to certain types of contaminants. Laboratory studies of
this technology have dealt specifically with liquid volatile organic compounds.
                                              85

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3.4.3.2 Secondary Impacts

       Low temperatures may decrease or inhibit microbial activity. Extremely low temperatures may
severely decrease microbial numbers or activity.

3.4.3.3 Equipment, Exogenous Reagents, and Information Required

       Equipment requirements include machinery for creating vertical drill holes, piping, and recycling
equipment. Cooling agents are the only exogenous reagents involved.

       The following information is necessary for successful application of this technology:

       • Characterization and concentration of wastes, particularly organics, at the site.

       • Volatility of organic constituents (vapor pressure, Henry's law constant, air/water partition
         coefficient, solubility, and especially their dependence on temperature).
       • Sorption of organics in soil (Koc).

       • Depth, profile, and areal distribution of contamination.
       • Soil moisture.

       • Effectiveness of cooling agents.
       • Accessibility of soil and site.

3.4.3.4 Advantages of Soil Cooling

       The primary  advantage of applying this technology in situ is that no additional contamination (or
chemicals for treatment purposes) would be added to the contaminated site, which precludes the need
to recover such contaminants or additives.

3.4.3.5 Disadvantages of Soil Cooling

       This technology has several inherent disadvantages.

       • It is essentially a temporary remediation method, as the contaminants are bound only by the
         frozen water in the soil.

       • It provides no degradation or removal of contaminants from hazardous waste sites.

       • Although this technology has been shown to be effective against the migration of volatile
         organics, its effects on other types of contaminants (e.g., nonvolatile organics, metals, acids)
         have not been demonstrated.

       • The use of cooling and freezing agents would  not be reliable for large areas or for long
         periods of time.

3.5  Chemical and Physical Separation Techniques

       Chemical contaminants can be removed from soil particles by physical and chemical means.
This subsection discusses three such techniques: 1) permeable barriers; 2) electrokinetics; and 3)
ground freezing. (Although permeable barriers are not directly used for soil treatment, the technology is
an important in situ method for treating hazarous waste landfill leachate, which is why it is presented
here.)

3.5.1 Permeable Barriers

       Migration of leachate from hazardous waste deposits (i.e., landfills) presents a significant
obstacle in attempts to remediate hazardous waste sites. Permeable barriers, which may be used to
retain contamination within site boundaries, represent a potentially effective method of in situ treatment.
The technology incorporates the  use of readily available materials to adsorb contaminants from ground
water as the contaminated plume migrates through the permeable barrier unit.
                                              86

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       Permeable barriers may be used effectively to remove contaminants from leachate and to
allow the treated leachate to migrate away from the contaminated source. There are several chemi-
cal and physical means of remediating hazardous waste sites by removal of contaminants from the
leachate. Permeable barriers typically incorporate precipitation, physical and chemical adsorption, ion
exchange, and filtration.

       Commonly available and relatively inexpensive materials may be used to construct permeable
barriers around hazardous waste sites. An example is activated carbon, which is widely used and is a
strong sorbent for certain classes of chemicals. It is especially effective for removal of hydrophobic,
high-molecular-weight organic compounds from liquid waste.

       Activated carbon has been used to reduce the phytotoxicity and the crops' uptake of pesti-
cides from the soil (Ahrens and Kring 1968, Anderson 1968, Lichtenstein et al. 1968, Coffey and
Warren 1969, Gupta 1976, Weber and Mrozek 1979, Strek et al. 1981). For pesticide chemicals,
activated carbon proved to be more effective on nonionic compounds; however, desorption may be
significant.

       Park (1986) has conducted bench-scale studies to quantify the remedial capabilities of
materiasl such as coal, limestone, fly ash, and soils containing clay.  Combinations of these materials
in various sequences were tested to determine the optimum treatment barrier configuration. Because
no individual material has the capacity to remove all the contaminants found at many hazardous
waste sites, combinations of layers of materials possessing the qualities needed to retain the various
contaminants at waste sites are needed. The bench-scale experiment was conducted to determine
retentive capabilities of these materials and to evaluate the optimum layer depth and order of several
common adsorptive materials.

       Park (1986) used two connected units, each possessing six  columns with a surface area of
412 cnf.  Each of these columns was packed to a depth of 36 cm with various combinations of soils,
limestone, fly ash, and coal.  The four materials used in the bench-scale analysis were chosen
because they were locally available, which would be a cost-minimizing attribute for such materials at
hazardous waste sites.  A simulated hazardous waste leachate consisting of municipal landfill
leachate spiked with phenol and dichlorobenzene was developed.  During subsequent runs the
simulated leachate consisted of various organic compounds listed in Table 21.

Table 21.  Priority Pollutants Utilized in Permeable Barriers Experiment.*
Pollutant
Bis(2-ethylhexyl)phthalate
Di-n-butyl phthalate
1 ,4-Dichlorobenzene
2,4-Dichlorophenol
Ethylbenzene
Fluoranthene
Isophorone
Pentachlorophenolf
Phenanthrenef
Phenol
Pyrene
Naphthalene
Actual
concentration,
Hg/liter
163
128
192
109
261
129
120
136
115
135
137
                      'Source-  Park 1986

                      t These two compounds could not be distinguished
                        in the analytical procedure .
                                             87

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       The simulated hazardous waste leachate was run through each of the columns packed with
adsorptive materials. The order of the materials placed into each of the 12 columns is shown in Figure
11.  The thinnest layers were 6 cm thick, and the intermediate and thickest layers were 10 cm and 20
cm, respectively. Two of the columns were dedicated to fly ash and coal only, because these two
materials were expected to exhibit the greatest adsorptive capacity (Park 1986).

       Effluent and interfacial samples were collected daily and analyzed for total organic carbon
(TOC) content.  As the simulated hazardous waste leachate passed through the columns, constituents
of the leachate mixture were retained on the various components of the permeable barrier columns.
Instead each individual retentive action (e.g., adsorption,  ion exchange, precipitation, filtering, and
chemical bonding) being measured, the cumulative  effect of all of these mechanisms was measured to
quantify the retentive capabilities of the permeable materials.

       The results of the bench-scale study showed that coal retained more organics than did the other
materials. Limestone retained very little TOC in both runs, which indicates its usefulness in treatment of
organic-contaminated ground water may be limited. Table 22 lists the results for each of the permeable
flow columns in Run No. 1 (leachate spiked with phenol/dichlorobenzene). Table 23 presents the
results of the bench-scale study for the simulated leachate used in Run No. 2 (various organic com-
pounds).

Figure 11.  Schematic of permeable barrier bench-scale design.
                                                               10 cm
                                                               20cm
                                                               6 cm
             '        '        'Rflunnts'       '        I
                                           Recycle
                  Coal


                  Soil


                  Limestone


                  Fly Ash
                                                          Liquid Level
         Influent
10

                                                            Effluents
                                              88

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Table 22. Run No. 1 Column Performance
Column
1
2
3
4
5
6
7
8
9
10
11
12
Total
flow, liter
7.18
6.66
6.79
393
8.95
774
6.47
922
621
9.23
8.08
892
Total TOO
retained,
mg
6337
7839
5709
5247
7299
6103
5177
10493
6567
11683
7900
12274
Days to
50% break
through
16
18
9
19
11
12
7
11
12
18
19
7
Linear
velocity,
cm/day
193
17.2
102
7.5
188
124
92
21 4
278
23.5
94
222
Permeability,
cm/day
078
0.73
0.96
0.41
098
085
091
1.01
0.68
0.95
0.84
0.97
Overall
ranking
8
6
11
10
4
9
12
2
7
1
5
3
            •Source Park 1986
Table 23. Run No. 2 Column Performance*
Column
1
2
3
4
5
6
7
8
9
10
11
12
Total
flow, liter
15.86
12.38
2578
11.86
23.99
24.02
26.12
28.40
14.35
16.12
17.00
2944
Total TOC
retained,
mg
4448
3857
7064
4310
6146
7525
6810
7006
3796
3911
4374
6533
Days to
50% break
through
26
39
30
47
16
37
19
20
13
14
28
15
Linear
velocity,
cm/day
345
21.7
138
88
605
41 2
14.8
16.0
233
259
31 1
8.2
Permeability,
cm/day
0.84
0.52
1.12
0.50
1 47
1 01
1.10
1.19
1.36
1.00
0.77
1.23
Overall
ranking
5
9
3
8
2
1
7
4
13
12
6
10
            •Source: Park 1986


       Park (1986) developed three conceptual designs for use in the treatment of contaminated
ground water:  1) a boundary treatment barrier, 2) a flushable barrier, and 3) a modular treatment
system. Each design uses the most appropriate (based on test results) ordering of the permeable
materials studied. Coal is used as the primary retaining material. Fly ash is used to moderate leachate
flow and to reduce channeling into the coal.  Limestone is used to adjust the pH after the leachate
contacts with the layer of coal.

       Three scenarios are described briefly (Park 1986):

       • The boundary treatment barrier is designed to intercept the contaminated ground water from a
          site with a vertical wall of permeable materials for a given length of time.

       • The flushable barrier is designed to make use of the ability of fly ash to elute all the organ-
          ics retained when flushed with CaSCk  After flushing, the fly ash will remain in place
          and be reused. Limestone will serve to precipitate cations and adjust pH.
                                              89

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       • The modular treatment system is used when it is desirable to remove and properly dispose of
         the spent permeable materials. The rationale behind this design is to use the most
         appropriate orderings ot permeable materials in modular, series-operated systems to allow
         easy replacement of spent treatment materials.
3.5.1.1 Status of the Technology
       This technology is currently in the bench- and pilot-scale stage.  It has not been tested at un-
controlled hazardous waste sites.
3.5.1.2 Secondary Impacts
       The use of this technology requires that a treatment trench be constructed such that the perme-
able barrier may be installed.  Also, the permeable barrier may become clogged with paniculate matter
and alter the rate of ground-water flow.
3.5.1.3 Equipment, Exogenous Reagents, and Information Required
       No  special equipment is required for implementing this technology; however, a backhoe may be
necessary to construct the treatment trench for installing the permeable barrier. Permeable materials
such as coal, fly ash, limestone, and activated carbon are required.  Materials for installing drainage
systems may be necessary.  Information needed to implement this technology includes:
       • Areal extent of contamination.
       • Direction and rate of ground-water flow.
       • Vertical location of ground-water table (and the extent of seasonal fluctuations of the
         ground-water table).
       • Local availability of permeable retentive materials.
       • Type(s) of contamination present.
3.5.1.4 Advantages of Permeable Barriers
       This technology offers the following advantages:
       • Use of commonly available retentive materials.
       • Removal of contamination (i.e., permanent treatment).
3.5.1.5 Disadvantages of Permeable Barriers
       Disadvantages of using this technology are as follows:
       • Potentially tow treatment levels.
       • Possible migration of contamination offsite (if retentive capacities of permeable materials are
         reduced by flow rates or variable contaminant concentrations).
       • Need to treat or dispose of contaminated permeable materials.
3.5.2 Electrokinetics
       Electrokinetics has been used for more than 50 years to dewater and  stabilize soils (Spangler
and Hardy 1973).  It is hoped that it will produce similar results at hazardous waste sites.
       An electrokinetic phenomenon referred to as electroosmosis occurs when a liquid migrates
through a charged porous medium under the influence of a charged electrical  field (Murdoch et al.
1988). The charged medium  is usually some kind of clay, sand, or other mineral particles that charac-
teristically carry a negative surface charge.
                                             90

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       When the charged particles come into contact with water molecules, they attract positive ions,
which effectively neutralize their negative surface charge. As a result, cations predominate in the layer
of water next to the surfaces of the particles and create what is referred to as a "diffuse double layer."

       If an electric field is applied to the saturated medium through anodes, cations bound in the
diffuse double layer will migrate toward the negatively charged cathode.  The viscous drag of water
molecules due to the migration of the cations produces a net flow of water toward the cathode.  The
application of an electrical field induces the water to flow (Murdoch et al. 1988).

       The chemical reaction inherent in electroosmosis produces a cathodic reaction, specifically the
electrolysis of water.  Subsequently, hydrogen is reduced to form hydrogen gas. The removal of
hydrogen ions from the soil solution increases the soil pH, and soils have been known to have pH
values in excess of 13 (Murdoch et al. 1988).

       If the electrolysis is continued, concentration gradients in the soil solution are established
between the cathode and anode (Murdoch et al. 1988).  The concentration gradients cause diffusion
from areas of low concentrations to areas of high concentration.  This diffusion may be in the same
direction as the ion conductance transport, or it may occur in the opposite direction (Murdoch et al.
1988)

       The Helmholtz-Smoluchowski model is a widely used theoretical description of electrokinetics.
The basis of this model is similar to that of Darcy's law, which uses solutions to groundwater flow
problems to estimate electroosmotic flow rates (Murdoch et al. 1988).  The major difference between the
Helmholtz-Smoluchowski model and Darcy's law  is the independence of Ke (the electroosmotic permea-
bility constant) from hydraulic conductivity. Soil porosity and the zeta potential of the capillary walls
apparently exert the most influence on electroosmotic potential (Murdoch et al.  1988).

       Ionic metal species that are subject to ionic reaction and migrate in the soil system appear to be
the types of contaminants that can be effectively treated with electrokinetics.

       The potential treatment levels achievable with electrokinetics range from low to medium,
depending on soil and site characteristics and the waste type(s) present.  This technology may be
difficult to demonstrate in the field. The fact that it is easy to apply could make the electrical power
requirements excessive for the level of cleanup achieved in large areas of contamination.

3.5.2.1 Status of the Technology

       Horng and Banerjee (1987) investigated the use of electrokinetics for the remediation of a haz-
ardous waste site (the United Chrome Superfund site near Corvallis, Oregon). The area selected for
testing consisted of approximately 0.6 hectare of level ground, which was enough for the electrokinetics
experimentation. The investigators determined that this area! extent, a nearly static ground-water
regime, and saturated moderately permeable soils at a shallow depth are favorable conditions for
applying electrokinetics as a remedial technology.

       Contamination at the United Chrome site includes inorganics that exist in the soil system as
tons. The most important of the contaminants, hexavalent chromium (Cr VI), exists primarily in the
anionic forms CrOz4, HCrCV, or CrzGv2", depending on the concentration of the individual chromium ions
and the pH of the soil system.  The removal of the toxic forms of chromium was the goal of remedial
action testing at this site. Because chromates, which do not react with soils,  are a major ionic constitu-
ent in the soil, transportation of the ions through the soil matrix at this site was achievable with high-
efficiency and relatively low power consumption (Horng and Banerjee1987).

       After conducting several tests on the soils at the United Chrome site, Horng and Banerjee
(1987) concluded that a treatment combination of hydraulic leaching and electrokinetics can accelerate
chromium removal compared with the use of hydraulic leaching alone. They also concluded that the
possible methods of action involved in the use of electrokinetics are dispersion due to hydraulic flow, ton
migration, water electrolysis, adsorption/desorption, and chromium  reduction resulting from the applied
electrical field.
                                             91

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3.5.2.2 Secondary Impacts
       This technology may raise the soil pH to levels that result in the mobilization of metallic contami-
nants.  The high pH levels could also inhibit or destroy the microbial population present within the soil
matrix.
3.5.2.3 Equipment, Exogenous Reagents, and Information Required
       The schematic presented in Figure 12 shows the equipment used by Horng and Banerjee
(1987). No exogenous reagents are required for this technology.  The following information is needed
to implement this technology:
       • Hydraulic conductivity of the contaminated soil.
       • Areal extent of contamination.
       • Ground-water flow rates.
       • Ground-water depth characteristics, including seasonal changes in the depth.
       • Permeability of soils.
Figure 12.  Diagram of a typical electrokinetic operation.
                                            Cathode
                                         (extraction well)
                                              92

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3.5.2.4 Advantages of Electrokinetics

       This technology offers the following advantages:

       • The remediation of contaminated sites is permanent.

       • The contaminated soil solution is easily extracted from the point of collection.

3.5.2.5 Disadvantages of Electrokinetics

This technology has the following disadvantages:

       • The technology is confined to sites contaminated with metals.

       • Electrical power requirements could be excessive; thus the technology might not be cost-
         effective.

       • The effects on the soil matrix itself are unknown.

       • Further treatments  would be required for sites contaminated with organics or other waste
         types.

       • Precipitation of salts and secondary minerals could decrease the effectiveness of this
         technology.

3.5.3  Ground Freezing

       Laboratory studies have shown artificial ground freezing to be a potentially effective method of
driving volatile organic contaminants from soil matrices (Iskandar et al. 1986). Contaminants can be
removed from soils by  using the differences in the physical and chemical properties of the water and
contaminants within the soil.  When the temperature of soil is gradually lowered below 0°C, ice nuclea-
tion starts in the soil water and ions are rejected.  As the dissolved chemicals in the soil solution are ex-
cluded from the ice, they become more concentrated in the remaining liquid. As the temperature drops
further, the  amount of ice becomes larger and the amount of unfrozen water decreases (Iskandar and
Houthoofd 1985, Iskandar and Jenkins 1985). The concentrated solution is pushed ahead of the ice
lense  in a desired direction, as determined by the location of the cooling system.  This large bulb of
concentrated contaminated soil may then be treated separately without treating the entire soil mass.

       If a situation requires the contaminants to be immobilized, the temperature should be dropped
rapidly rather than gradually.  In this case, the ions and salts are entrapped between the ice particles
and the separation process will not be complete (Iskandar and Houthoofd 1985).  This concept was dis-
cussed in Section 3.4.3.

       Iskandar et al.  (1986) used 80-cm high plexiglass columns filled with a dredged sludge satu-
rated with a solution modified with four metals (Cd, Zn, Cu, and Ni) and four volatile organics (chloro-
form, benzene, toluene, and tetrachloroethylene). Six separate treatments (and two controls) were
compared; one column was used for each treatment.  During each treatment, soils were gradually
frozen from the bottom up. Thermocouples were used to measure soil temperatures at various depths.
Soil temperatures ranged  from -1.8°C to  -16.0°C, and frost penetration rates varied from 15 to 50 cm
per day. After each episode of freezing, the soil columns were permitted to thaw and leachate was
allowed to drain from the soil  columns. The leachate was analyzed for the metals and volatile organics
used to spike the soils.

       Using such freeze/thaw cycles reduced the volumes of the soil columns.  The consolidation of
the soils resulted from the physical effects of the freeze/thaw cycles. Iskandar et al. (1986) concluded
that freezing and thawing  saturated sediments can decrease the amount of time necessary to remove
water relative to natural processes. The  rate of water migration through the treated columns was
enhanced to approximately 3 times the magnitude of natural drainage because of the formation of ag-
gregates and cracks in the soil matrix as a result of repeated freeze/thaw cycles.
                                             93

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       The effects of freezing/thawing cycles on the recovery of the volatile organics used to spike the
soils was inconsistent (see Table 24). The one- and three-cycle treatments had similar effects on the
amount of volatile organics recovered from the soil and leachate.  The two- and five-cycle treatments,
however, had a much lower percentage recovery compared with the other treatments. The volatile
organics were believed to have volatilized from the experimental apparatus, which reduced the recovery
rate for the volatile compounds. Apparently, increased numbers of freeze/thaw cycles had little effect on
the amount of volatile organics recovered from the columns, even though the cycles enhanced the rate
of volatilization.
Table 24. The Effects of Freeze/Thaw Cycle* on Contaminant Recovery*
Column
number
1 (control)
2 (control)
3
4
5
6
7
8
Freeze/thaw
cycles
0 (frozen)
0 (unfrozen)
1
1
2
3
3
5
Time,
days
50
125
12
70
22
27
41
50
% Volume
reduction
34
36
28
34
37
36
37
35
Total VOC
recovery, %
80
36
NDa
62
33b
70
ND
16
Average metals
recovery, %
97
84
94
94
91
ND
ND
ND
'Source:  Iskandar et al. 1986.
 aND - Not determined.
 bDoes not include recovery of toluene (not determined).

        Metal concentrations were also analyzed in the leachate and column sections. Unlike the
reduction in concentrations of volatile organics, some metals concentrations increased in the treated
columns as a result of the volume reduction and the high retention of metals in the sediment. Therefore,
as the amount of metals present (on a mass basis) remains fairly constant (freezing from the bottom up
prevented metal leaching) and volume  is reduced, metals concentrations increase.

        Artificial ground freezing may enhance water percolation through soils as a result of aggregate
and channel formation (which could be used in conjunction with delivery/recovery systems). It may also
provide a barrier to the input of volatile organics and metals entering the ground water when soils are
frozen from the bottom to top, and enhance the ability to remove volatile organics from contaminated
soils.

3.5.3.1  Status of the Technology

        Artificial ground freezing is currently in the bench-scale stage.  Ayorinde et  al. (1989) have
reported preliminary results from a laboratory study to evaluate the possibility of mobilizing different
types of contaminants by freezing. Two types of contaminants were studied: explosives and volatile
organic compounds (VOCs).  Preliminary data indicate a certain degree of movement of both explosives
and VOCs when the soil columns spiked with these contaminants were frozen unidirectionally from the
bottom up. For given freezing rates, freeze-thaw cycles, soil types, and moisture contents, it appears
that the ability to move any contaminant by freezing depends on the type and initial concentration of the
contaminant, and the interaction of the soil and the contaminant (Ayorinde et al. 1989).

3.5.3.2  Secondary Impacts

        Low temperatures may decrease or inhibit microbial activity. Extremely low temperatures  may
 severely decrease microbial numbers or activity.
                                               94

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3.5.3.3 Equipment, Exogenous Reagents, and Information Required
       Equipment requirements include machinery for creating vertical drill holes, piping, and recycling
equipment. Cooling agents are the only exogenous reagents involved.  The following information is
necessary for successful application of this technology:
       • Characterization and concentration of wastes, particularly organics, at the site.
       • Volatility of organic constituents (vapor pressure, Henry's law constant, air/water partition
         coefficient, solubility, and especially their dependence on temperature).
       • Sorption of organics in soil (Koc).
       • Depth, profile, and areal distribution of contamination.
       • Soil moisture.
       • Effectiveness of cooling agents.
       • Accessibility of soil and site.
3.5.3.4 Advantages of Ground Freezing
       The advantages of ground freezing are as follows:
       • No additional chemicals are added to the contaminated soils.
       • The size of the area to be treated can be reduced by concentrating the contaminants in
          one location.
       • Permeability of the soils increases.
       • Contaminants can be separated from the soil mass.
3.5.3.5 Disadvantages of Ground Freezing
       This technology has several inherent disadvantages:
       • It concentrates metals in the soil and allows organic vapors to enter the air around
          the site.
       • The use of cooling agents and piping systems to deliver freezing agents through the
          site may not be cost effective.
       • The use of freezing agents to immobilize contaminants would not be reliable for large areas or
          for long time periods.
                                             95

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                                          Section 4
                             Delivery and Recovery Systems


       Delivery/recovery systems refer to technologies that either deliver remediating materials into
environmental compartments or recover contaminating materials from these compartments. Delivery
technologies generally involve the transport of remediating materials into soils or ground water. The
delivered materials are usually liquids; however, newer technologies involve the delivery of solids,
gases, and vapors as well. Recovery technologies generally remove contaminants from these same
environmental compartments. This latter category includes technologies that expedite removals by
altering the physical or chemical attributes of contaminants or pathways. Recovery technologies
typically involve fluid flows driven by hydraulic gradients, thermal methods, or chemical reactions.

       Delivery/recovery technologies have been used in hazardous waste site remediation for several
years.  Most of these technologies involve pumping ground water from recovery wells, treating it, and
then reintroducing it at injection wells. Such "pump and treat" technologies vary in effectiveness with
variations in site and contaminant properties.  In addition, dense soil formations (with hydraulic conduc-
tivities of less than 10"4 cm/s) severely limit the application of recovery techniques to contaminated haz-
ardous waste sites.

       Other problems associated with the implementation of delivery and recovery systems at waste
sites include the presence of contaminants with low solubilities; adsorption of contaminants onto clayey
soils; the existence of fractured soils or rocks, which create pathways of high conductivity separated by
a matrix block of low conductivity; and the absence of an underlying impermeable layer to preclude the
possibility of delivered materials migrating into the ground water.

       Delivery/recovery technologies include some of the technologies described in other sections of
this document; for example, although vapor extraction is a recovery technique, it is described in the sub-
section dealing with the control of volatile materials. Table 25 lists other delivery/recovery technologies
that are described elsewhere in this report.

Table 25. Delivery/Recovery Technologies Cross-Reference

               Delivery/Recovery Technology         Included in this report under

               Colloidal gas aphrons                         Section 3.3
               Vapor extraction                              Section 3.4
               Steam stripping                              Section 3.4
               Radio frequency heating                       Section 3.4
               Electrokinetics                               Section 3.5
               Ground freezing                              Section 3.5

       Discussed in this section are several delivery  and recovery technologies (hydraulic fracturing,
radial drilling, kerfing, and cyclic pumping) and technologies  identified as recovery only (ultrasonic
methods, jet slurrying, COz injection, and hot brine injection).

4.1  Hydraulic Fracturing

       Hydraulic fracturing,  a technology widely used in the petroleum industry, stimulates the recov-
ery of hydrocarbons from low-permeability reservoirs and enhances the delivery of fluids used to
                                               96

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displace petroleum in sweeping operations (Murdoch et al. 1988).  The technology involves the injection
of a fluid (typically water) at pressures exceeding the confining pressures at the bottom of a borehole.
This process generates a single fracture (either horizontal or vertical) that propagates away from the
borehole.  Sand is introduced into the formed fracture to hold it open and to create a highly permeable
channel suitable for either the delivery of remediating materials or the recovery of contaminants.

        Preliminary investigations consisting of theoretical calculations and comparative investigations
on applications developed by the energy industry suggest that this technology can be used with soil and
rock types commonly found at contaminated waste sites. Possible applications include increasing the
efficiency of pump and treat systems, stimulating the extraction of vapor phases from dense soils, or
forming a horizontal drain to capture leachate (Murdoch et al. 1988).

        Murdoch (1989) conducted theoretical analyses of ground-water flow that indicated hydraulic
fractures could significantly increase the yields of recovery wells. Immediately after the fracturing, the
yields could increase tenfold or more. Over time the yield from a fractured well will diminish, but can
eventually maintain a yield of two times  that of an unfractured well.

        Volumes of ground water extracted from contaminated aquifers can be estimated theoretically
as a function of time (Murdoch et al. 1988). The recovered volume obtainable by using hydraulic
fracturing at well sites also depends on the length, width, and conductivities of the fractures and the
enveloping formation.  Application of the theory to the expected values of the preceding variables indi-
cates that the volume of water recovered from a well intersecting a hydraulic fracture could be an order
of magnitude greater than the volume obtainable from an unfractured well.

        Murdoch (1989) conducted a field test to evaluate the  characteristics of fractured soils. Un-
lithified glacial  till (hydraulic conductivity ranging from 1.5x10'6 to 1.9x10 "7cm/s) was fractured by in-
jecting a mixture of water, sand, and chemicals (a gel and a dye) into 11 separate boreholes with depths
ranging from 1.64 to 3.81 m.

        The fractures formed by the process typically vented to the surface. The largest fracture
covered 90 m2  and extended 13.5 m from the borehole when it vented to the surface. A typical fracture
covered approximately 20 m2 and extended 5 to 8 m from the borehole. A maximum thickness of 1  cm
of sand was observed in the fractures.

        The following conclusions were  drawn from the field test conducted at a contaminated site
(Murdoch 1989):

        • Hydraulic fractures can be created at shallow depths in glacial till. The fractures are elon-
         gated in plan and dip gently toward the parent borehole.

        • Injection pressure can be used to determine the onset of hydraulic fracturing in till.  Tilt meters
         can be used to monitor growth of hydraulic fractures at shallow depths.  Electrical geophysical
         methods may be useful as monitoring tools.

        • Equipment used to create hydraulic fractures at oil wells can be used to create hydraulic
         fractures at contaminated sites. Equipment designed for creating hydraulic fractures at
         shallow depths should perform better than that used by the oil industry.

4.2  Radial Well Drilling

        Radial (horizontal) wells drilled outward from a central borehole may be used to enhance
access to a contaminated soil system or ground-water aquifer. Multiple wells may be placed at the
same or various levels within the same borehole. Potential applications of this technology include
ground-water extraction and delivery of in situ remediating materials.

        Initial applications of this technology involved drilling a central downward core sufficiently wide
to allow a worker to descend into the borehole and to drill radially outward.  Recent developments made
by the petroleum industry have dramatically improved the method of drilling horizontal wells. This new
system includes a jet nozzle fixed to 1.25-inch-diameter tubing (used to create the horizontal well) and a
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whipstock, which is placed at the bottom of the vertical borehole to redirect the jet nozzle and tubing
horizontally into the formation (Dickinson et at. 1987).  Radial wells are created by pumping high-velocity
water out of the jet nozzle. The water for this process is supplied from the surface through steel tubing.
This equipment cuts a borehole with a diameter several times larger than the tubing (Dickinson et al.
1987). In addition, static pressure on the inside of the nozzle results in a force that pulls the nozzle and
attached tubing down the drill stem, through the whipstock, and into the radial well. This force is re-
sponsible for keeping the radial progressing in a straight line.

       The  whipstock is erected in a 24-inch-diameter cavity. This device consists of a series of slides
and wheels that redirect the tubing from a vertical plane in the main borehole through a 90-degree bend
to a horizontal plane. This redirection occurs within a 9- to 12-inch bend radius (Dickinson et al. 1987).

       A wireline system has been developed to locate each radial produced by the jet nozzle. The
wireline, which is quite flexible and thin, is run through the 1.25-inch tubing.  The device logs the
horizontal and vertical location and records the length of the radial (Dickinson et al. 1987).

       For completion of the radial well, techniques have been developed that will electrochemically
perforate and cut off the tubing within each radial, place a slotted liner within the perforated tube, and
gravel-pack the tube. The gravel packing is accomplished in two separate steps:  1) gravel is pumped
out of the end of the 1.25-inch tube and forced toward the borehole, and 2) gravel is forced from the
borehole into the radial well (Murdoch et al. 1988).

       In the petroleum industry this technology has been applied  to both consolidated rock and
unconsolidated soils. As can be expected, the rate of placement in  rock is much less than the rate of
placement in soils. Murdoch et al. (1988) report that drilling rates in unconsolidated materials range
from 5 to 120 feet per minute. Rates in consolidated, hard, and homogeneous basalt range from 0.10 to
0.50 foot per minute.

       Radial wells applied to hazardous waste sites can be positioned in both saturated and unsatu-
rated media  and can facilitate the remediation of contaminated sites by increasing the available delivery/
recovery routes for delivering remediating materials or recovering contaminated ground water.  The
technology, although not fully demonstrated at hazardous waste sites, is the focus of current research
and is being  refined for that purpose.

4.3  Ultrasonic Methods

       Ultrasonic methods (ultrasonic vibrations) can be used to increase the efficiency of recovery
wells. Extrapolations from current applications of ultrasonic methods can be used to describe the mode
of action at sites requiring remediation. At least three potential applications to hazardous waste sites
have been identified: 1) the dispersion or disaggregation of clay particles during cleaning of pores or
well screens by enhancing the removal of chemicals adhered to solid particles (which could improve re-
covery efficiency), 2) the sterilization of wells, and 3) the elimination of microbes that clog pore  spaces.
This technology could  eliminate the need for antibacterial agents in the cleaning of wells used in biore-
clamation.

       Soil scientists  have used this technology extensively to disperse clay and silt particles.  Ultra-
sonic methods have also proved to be effective for removing mineral films and clay aggregates from
sand grains (Busacca et al. 1984).

       Laboratory tests involving the use of ultrasonic methods have shown that they often reduce the
time required to extract humic acids (Ramunni and Palmieri 1985), to leach various metallic ions from
soils (Tamari et al. 1982), and to clean MoS2 from steel surfaces (Bertrand and Vuleasovich 1977).

       Ultrasonic methods may be used to increase recovery volumes from wells clogged with clay
particles or microorganisms and to separate contaminants from clay particles near well sites.

       Murdoch et al. (1988) describe a laboratory-scale test of an ultrasonic method.  An experiment
was conducted to determine the effect of ultrasonic vibrations on a mixture of sand and clay in a rigid-
wall permeameter. Several falling-head permeability tests conducted on the mixture showed consistent
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results of 3.8x10"4 cm/s for the hydraulic conductivity of the sample. The permeameter was then placed
in an ultrasonic cleaning chamber used to clean samples in the laboratory. A falling-head permeability
test was conducted while the cleaning apparatus was turned on for 30 seconds. The hydraulic conduc-
tivity abruptly increased one order of magnitude to 1.8x10"3 cm/s, and the effluent changed from clear
water to a turbid mixture of clay and water.  The results show that this  method effectively dislodged clay
particles and caused them to be removed by flow through the permeameter.

4.4 Kerfing

       Kerfing (or borehole notching) is currently used to produce a slot either perpendicular or parallel
to the axis of a previously drilled borehole. This technology has aroused interest as a possible method
for preventing the migration of pollutants from hazardous waste sites; however, kerfing may also have
applications as a recovery technique (Murdoch et al. 1988).

       Kerfing was developed in the United States and Europe; however, Huck et al. (1980) indicate it
was first applied in Japan. Kerfing is used primarily as a method of placing barriers of low permeability
beneath hazardous waste sites to intercept leachate and to prevent further ground-water con-
tamination (Huck et al. 1980).

       This technique uses a high-pressure water jet and and an abrasive material (e.g., sand) to cut a
slit in the wall of a borehole. The high-pressure water jet is placed in an existing borehole, where it is
rotated to cut a disk-shaped cavity, moved along the axis of the hole to create an axial slit, or kept in
place  to cut a cylindrical hole. The water jet advances  the kerf at a rate of several centimeters per
second, and the final slit or hole  is 1 to 3 m long. The slot created is subsequently filled with a perme-
able material to create a drain, an impermeable material to create a barrier, or a remediating material to
facilitate cleanup (Huck et al. 1980).

       Two methods are currently used to construct impermeable barriers with this technology. One
method involves implacing a floor by kerfing a series of disk-shaped cavities and filling them with
bentonite slurry.  This method has been referred to as "pancake slurry jetting" (Murdoch et al.  1988).
The other method uses this technique to initiate hydraulic fractures.  Two adjacent boreholes are
concurrently pressurized with a fracturing fluid (a cement/grout mixture), and fractures are propagated
outward from the kerfs. As the fractures approach each other, the stresses at their tips tend to cause
the fractures to intersect (Huck et al. 1980). Continued injection of the grout forms a continuous imper-
meable layer. This method was  used to form an impermeable barrier at a Whitehouse, Florida, site
(Brunning 1987).

       Kerfing may also be suitable as a technique for improving recovery processes. A potential
method of improving recovery would be to fill the kerf with a highly permeable material (much  as a
hydraulic fracture is filled with sand), which would improve the yield of  a recovery well.

       As a recovery technique, kerfing appears to be most applicable to materials of low permeability,
such as clay, silt, or rock, where most contaminants would be immobile (Murdoch et al. 1988). Using
kerfing to increase the rate of recovery from recovery wells is undocumented.  The rate could  be ex-
pected to increase by a factor of 2 to 10 compared with the rate before fracturing (Murdoch et al. 1988).

       Kerfing is widely used in the petroleum industry (where it is referred to as borehole notching) to
initiate hydraulic fractures. Some oil field service companies provide borehole notching services.

4.5 Jet-induced Slurry Method

       The jet-induced slurry method is a mining industry technique used to excavate an ore formation
by fragmenting the subsurface ores with a high-velocity hydraulic jet and then pumping the slurry to the
surface through a borehole (Murdoch et al. 1988). This technology enables solid ores to be recovered
from the the subsurface at any depth without presenting the disposal problems of overburden.

       The use of high-pressure water jets to slurry ore-bearing rock is not a new technique; it has
been used for more that 100 years to mine placer gold and gilsonite at the ground surface.  The applica-
tion of this technology to subsurface formations, however, has only occurred within the past few years
(Kasperetal. 1979).
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       The jet-induced slurry method (called "in situ borehole slurry mining" by the mining industry) is
facilitated by drilling an 18-inch borehole to roughly 6 feet below the bottom horizon of an ore-bearing
formation and installing a sump pump at the bottom of the borehole, below the hydraulic jet. The jet
slurries the rock in the ore zone and the slurry flows to the sump, where it is pumped to the surface for
processing. The tailings from the processing are used to backfill the cavity left by the excavation
(Kasperetal. 1979).

       Solid materials may be removed up to 75 feet away from the borehole, depending on the
properties of the ore body and the jet system. Typically, the jet is rotated through an arc of about 300
degrees, which leaves a portion of the ore body unmined for roof support (Murdoch et al. 1988). For
complete mining of an ore formation, wells are aligned so that adjacent wells slurry and remove the roof
supports from previous wells.

       Although no documented applications of the jet-induced slurry method for remediation of
hazardous waste sites were found, this technique should be applicable to any soil or rock formation that
could be fragmented by a hydraulic jet. Lithified sediments, including pebble phosphate deposits in
Florida and North Carolina and uranium-bearing sandstones in Wyoming and Texas,  have all been
successfully mined with this technology (Kasper et al. 1979).  Ore bodies located both above and below
the water table have been mined by the jet-induced slurry method, but fewer complications arise during
the mining of ore bodies  above the water table (Kasper et al. 1979).

4.6  Carbon Dioxide Injection

       Implementation of this technology in the petroleum industry involves injecting carbon dioxide
(CCk) into oil-bearing rock formations to maintain pressure and to displace the oil. The  two principal
mechanisms for mobilizing the oil by carbon dioxide injection  are the reduction of the oil viscosity upon
solution of the gas into the oil and an increase in the volume of the reservoir (Holm 1987; Donaldsen et
al. 1985; Morrow and Heller 1985).

       Use of this technology for the recovery of ground-water contaminants probably  would be limited
to applications where CCfe is either dissolved in water or contained in aphrons.  In either case, the
injection of carbon dioxide could decrease the viscosity and increase the recovery of hydrocarbons
(Murdoch et al. 1988). It has been reported that injecting CO2 at high pressures (approximately 1200
psi) increased its solubility in oil and dramatically reduced the  viscosity of the oil (Grogan and
Pinczewski 1987; Holm 1987, Collins and Wright 1985; Latil 1980). The feasibility of applying this
technique to a site where contamination is near the surface is  questionable. The pressure exerted by
the injection stream may be  sufficient to displace (with great force) the soil overburden.

       Reduction of the viscosity of the oil results in two phenomena that should increase recovery. A
decrease in viscosity results in an increase in mobility and thereby decreases the head  gradient re-
quired to sustain flow.  A decrease in the difference in the viscosities of the oil and the fluid used to
displace it tends to minimize the formation of viscous instabilities or fingers (Holm 1987).

       The most effective method for introducing CCfe involves following a CC-2 slug with alternating
water and COs injections. Other methods involve the injection of water saturated with CCk and the ap-
plication of high-pressure injections of the gas itself (Holm 1987).

       Successful COz injection programs have been implemented in limestones and dolomites with 10
to 15 percent porosity and 5 to 25 mD permeability (Pittaway et al. 1987; Albright 1986, Pittaway et al.
1985; Ader and Stein 1984).  Homogeneous permeability is preferred, but not necessary (Collins and
Wright  1985).

       The volumetric ratio of the COz injected to the oil recovered ranges from 0.1 to several hundred
(Williamson et al.  1986; Desch et al. 1984; Ehrlich et al.  1984; Boiling 1985; Boyer 1985). Reservoirs
depleted to less than 10 percent of the original oil in place have overall injection-to-recovery ratios of
0.09 to 0.1 (Williamson et al. 1986; Desch et al. 1984).
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       Carbon dioxide flooding is one of the major enhanced oil-recovery processes in the United
States (Holm 1987). It has been applied successfully in many large and small oil reservoirs around the
world.  Sophisticated computer simulations of specific reservoirs permit oil companies to estimate the
optimal rates and pressures for gas injection and the corresponding rates of oil recovery.  Laboratory
studies have concentrated primarily on substitute gases and alternate gas-fluid or gas-gas injection
mechanisms (Holm 1987).

4.7  Hot Brine Injection

       Natural gas deposits typically occur as liquids or solids at existing pressures in  many reservoirs.
Because extraction of these liquid or solid deposits is more difficult than extraction of the gas in vapor
phase, petroleum engineers have developed methods for converting the gas from the solid or liquid
phase to the vapor phase (Kamath and Godbole 1987).

       The hot brine injection method for recovering natural gas hydrates appears to be  limited to
depths greater than 150 m because the hydrate equilibrium curves indicate lower dissociation tempera-
tures are needed than the ambient earth temperatures that occur at shallow depths (Kamath and
Godbole  1987). The dissociation temperature could be reduced through the artificial increase of salinity
of the pore solution, however, to facilitate the recovery of contaminating chemicals with a  dissociation
temperature exceeding the temperature at shallow depths.  For this method to be used  successfully, the
dissociation temperature of the contaminant to be recovered must have a salinity dependence.

       At depths of approximately 150 to 1000 meters, the temperature of hydrate dissociation from a
solution with no salinity exceeds the ambient temperature of the surrounding earth by almost 10°C
(Kamath  and Godbole 1987).  Increasing the salinity of the pore solution to  15 weight percent reduces
the temperature of hydrate dissociation by about 11°C.  The relationship between  salinity  and dissocia-
tion temperature reduction is approximately  linear within the range of 0 to15 weight percent salinity
(Kamath  and Godbole 1987).

       The amount of thermal energy required to dissociate gas hydrates into a pure gas vapor phase
and liquid water decreases as  dissociation temperatures decline. Increasing the salinity of the pore
solution from 0 to 15 weight percent reduces the energy of hydrate dissociation by nearly  8 percent
(Kamath  and Godbole 1987).

       The principal mechanism of hot brine injection is the reduction  in dissociation temperature
resulting  from an increase in salinity.  Reducing the dissociation temperature decreases the thermal
energy required during recovery .

       A minimum porosity of 15 percent is required for effective use of this technology.  At  lower
porosities, gas production declines rapidly. At porosities greater than 15 percent, gas production does
not change significantly.  Because hydrate dissociation  energy is directly proportional to porosity,
excessive porosity (greater that about 50 percent) is also undesirable (Kamath and Godbole 1987).

       A minimum thickness of 7 m at the hydrate zone is required for effective use of  this technology.
This thickness minimizes heat  loss to surrounding rock or earth, especially to overlying  material. The
energy efficiency of this technology increases significantly with increases in the thickness of the hydrate
zone up to about 100 m.  Beyond 100 m, the increase in energy efficiency is small (Kamath and
Godbole  1987).

       Salt  precipitation may cause pore occlusion over extended periods  of time, which would hamper
gas recovery (Murdoch et al. 1988). The optimal temperature range is between 120° and 200°C. The
use of very high brine temperatures may cause severe heat loss and reduce the energy efficiency ratio.
When very low injection temperatures are used, high brine input rates are required to increase gas pro-
duction (Kamath and Godbole  1987).

       Theoretically, the efficiency of gas production via hot brine injection ranges from 150 to 200
standard cubic meters of gas extracted per cubic meter of hot brine  injected.  In general, the higher the
salinity of the injected brine is the higher the rate of  return of extracted gas.
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       The ratio of heat injected to the heat value of the gas produced (the energy efficiency ratio)
ranges from 5 to 11.  It increases with porosity, reservoir layer thickness and burial depth, brine injec-
tion rate, salinity, and temperature (Kamath and Godbole 1987).

       The proposed stimulation of contaminant removal by use of hot brine is based on the results of
theoretical analyses.  The technique has not yet been tested in the laboratory or field.

4.8  Cyclic Pumping

       Cyclic pumping (both a delivery and recovery technique) varies the rates of either injection or
extraction in an effort  to minimize pumping costs .  Optimizing pumping activities could conceivably
reduce remediation costs at contaminated waste sites (Murdoch et al. 1988).

       In typical pump and treat operations, the pumping rates are usually held constant, as opposed
to a cyclic pumping operation, in which the rates are variable and the pumps are turned on during active
cycles and turned off during rest cycles.  Pumping in this manner (active and rest cycles) can be accom-
plished for either the injection of  treating solutions or the extraction of contaminated ground water (Keely
et al. 1987).

       The purpose of a rest cycle is to permit sufficient time to elapse for diffusion between high-
permeability channels (fractures or large pores) and the comparatively low-permeability blocks between
them. Pumped treatment solutions diffuse from the pathways into the low-permeability areas, and
contaminants diffuse from these  areas to the high-permeability channels during a rest cycle.  The active
cycle of cyclic pumping is designed to deliver the necessary volume of reactants or to recover the nec-
essary volume of reaction products (Keely et al. 1987).

       Because no applications of cyclic pumping at contaminated hazardous waste sites are docu-
mented, no information on appropriate site conditions is available. It appears, however, that cyclic
pumping would be most effective in soils composed of preferred high-permeability channels and low-
permeability blocks.

       The petroleum industry uses this technique to enhance oil recovery. Techniques include cyclic
water flooding and steam stimulation (cyclic injection). Cyclic water flooding involves an injection of
water to restore reservoir pressure, followed by an extended period of oil extraction. When production
rates decline, water is again injected  and the cycle is repeated (Aguilera 1980).

       These techniques are designed to increase the efficiency of pump and treat systems by increas-
ing the concentration  of contaminants recovered (or reactants delivered) per volume of ground water
(Murdoch et al. 1988). The diffusion that occurs during the rest cycle between the  low-permeability
blocks and the preferred high-permeability channels is the rate-limiting step in the cyclic pumping
technique and may limit the use  of this technology. The time required for a sufficient quantity of con-
taminants to diffuse into the channels may increase the time it takes for complete remediation of a site
and thus render the technology economically infeasible.

       This technology has been proposed for use at contaminated waste sites, and EPA is initiating
research on this subject.
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                                      References

 Section  1  Introduction

 Amdurer, M., R. T. Fellman, J. Roetzer, and C. Russ. 1986. Systems to Accelerate In Situ Stabilization
     of Waste Deposits. EPA/540/2-86/002. U.S. Environmental Protection Agency, Cincinnati, OH.

 Murdoch, L, B. Patterson, G. Losonsky, and W. Harrar. 1988. Innovative Technologies of Delivery or
     Recovery: A Review of Current Research and a Strategy for Maximizing Future Investigations.
     Report for Contract No. 68-03-3379.  U.S. EPA Risk Reduction Engineering Laboratory,
     Cincinnati, OH.

 Sims, R. C. 1984.  Review of In-Place Treatment Technologies for Contaminated Surface Soils - Volume
     2: Background Information for In-Situ Treatment. EPA-540/2-84-003b. U.S. Environmental
     Protection Agency, Cincinnati, OH.

 Sims, R.C. and J. Bass.  1984. Review of In-Place Treatment Technologies for Contaminated Surface
     Soils - Volume 1: Technical Evaluation. EPA-540/2-84-003a. U.S. Environmental Protection
     Agency, Cincinnati, OH.

 U.S. Environmental Protection Agency   1985. Handbook: Remedial Action at Waste Disposal Sites
     (Revised) EPA/625/6-85/006. Hazardous Waste Engineering Research Laboratory, Cincinnati, OH
     and Office of Emergency and Remedial Response, Washington, DC.

 U.S. Environmental Protection Agency.  1988. Guidance for Conducting Remedial Investigations and
     Feasibility Studies Under CERCLA.  EPA/540/G-89-004. Office of Emergency and Remedial
     Response, Washington, DC.


 Section 2  Legislative  and  Regulatory Overview

 Hall, R. M., Jr. and N. S. Bryson, 1985. Comprehensive Environmental Response, Compensation, and
     Liability Act (Superfund). In: Environmental Law Handbook, 8th Edition.  Edited by Gordon J.
     Arbuckle. Government Institutes, Inc., Rockville, MD.

 Public Law 99-499. 1986.  Superfund Amendments and Reauthorization Act  of 1986.

 U.S. Environmental Protection Agency.  1988. National Oil and Hazardous Substances Pollution
     Contingency Plan; Proposed Rule. 53 FR 51394, December 21.


 Section 3   Technologies for In Situ  Treatment

3.1  Soil  Flushing

Amdurer, M., R. T. Fellman, J. Roetzer,  and C. Russ.  1986. Systems to Accelerate In Situ Stabilization
     of Waste Deposits.  EPA/540/2-86/002. U.S. Environmental Protection Agency, Cincinnati, OH.
                                        103

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Dworkin, D., D. J. Messinger, and R. M. Shapot. 1988. In Situ Flushing and Bioreclamation
    Technologies at a Creosote-Based Wood Treatment Plant. In:  Proceed, of the 5th National
    Conference on Hazardous Waste and Hazardous Materials - April 19-21,1988 - Las Vegas, NV.
    Hazardous Materials Control Research Institute, Washington, DC.

Kuhn, R. C., andK. R. Piontek. 1989.  A Site-Specific In Situ Treatment Process Development Program
   for Wood Preserving Site.  Presented at Robert S. Kerr Technical Assistance Program - Oily Waste
   Fate, Transport, Site Characterization and Remediation.  May 17-18,  Denver, CO.

Nash, J. H. 1988.  Project Summary: Field Studies on In Situ Soil Washing  EPA/600/S2-87/110, U.S.
    EPA Hazardous Waste Engineering Research Laboratory, Cincinnati, OH.

Stief, K. 1984. Remedial Action for Groundwater Protection Case Studies Within the Federal Republic
    of Germany. In: the 5th National Conference on Management of Uncontrolled Hazardous Waste
    Sites. November 7-9. Washington, DC.

Truett, J. B., R. L. Holberger, and D. E. Sanning. 1982.  In Situ Treatment of Uncontrolled Hazardous
    Waste Sites, Proceedings  of the 3rd National Conference. The  Hazardous Materials Control
    Research Institute, Silver Springs, MD. pp. 451-457.

U.S. Environmental Protection Agency. 1983. Hazardous Waste  Land Treatment.  SW-874 (Revised
    Edition).  Washington, DC.

U.S. Environmental Protection Agency. 1984. Case Studies 1-23: Remedial Response at Hazardous
    Waste Sites.  EPA/540/2-84/002B.  Municipal Environmental Research Laboratory, Cincinnati, OH.

U. S. Environmental Protection  Agency.  1985.  Handbook: Remedial Action at Waste Disposal Sites
    (Revised) EPA/625/6-85/006. Hazardous Waste Engineering Research Laboratory,  Cincinnati,
    Ohio and Office of Emergency and Remedial Response, Washington, DC.


3.2    Solidification/Stabilization

Cullinane, M. J., Jr., L. W. Jones, and P. G. Malone.  1986.  Handbook for Stabilization/Solidification of
    Hazardous Waste.  EPA/540/2-86/001.  U.S. EPA Hazardous Waste Engineering Research
    Laboratory, Cincinnati, OH.

Fenn, D. 1980. Procedures Manual for Ground Water Monitoring at Solid Waste Disposal Facilities.  SW-
    611. U.S. Environmental  Protection Agency, Washington, DC.

Fitzpatrick, V. F. 1988. In Situ  Vitrifications an Innovative Melting Technology for the Remediation of
    Contaminated Soil. In:  Contaminated Soil 1988 Volume 1, Proceedings of the 2nd International
    TNO/BMFT Conference on Contaminated Soil, April 11-15, Hamburg, Federal Republic of
    Germany, K. Wolf, J. van den Brink, F. J. Colon, eds., Kluser Academic Publishers, The
    Netherlands,  pp. 857-859.

Fitzpatrick, V. F., C. L. Timmerman and J. L. Buelt. 1987. In Situ Vitrification - An Innovative Thermal
    Treatment Technology.  In: Proceedings, Second International Conference on New  Frontiers for
    Hazardous Waste Engineering Research Laboratory, Cincinnati, OH, EPA/600/9-87/018F, pp.
    305-322.

Gibbons, J. J. and R. Soundararajan, 1988. The Nature of Chemical Bonding Between Modified Clay
    Minerals and Organic Waste Materials. American Laboratory, July, pp. 38-46.
                                         104

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Johnson, N. P. and M. G. Cosmos.  1989.  Thermal Treatment Technologies for Hazardous Remedia-
     tion.  Pollution Engineering, 20(11):66-85.

Malone P. G., and L. W. Jones.  1979.  Survey of Solidification/Stabilization Technology for Hazardous
     Industrial Waste.  EPA/600/2-79/056.  U.S. Environmental Protection Agency, Cincinnati, OH.

Malone, P. G., L. W. Jones, and R. J. Larson.  1980. Guide to the Disposal of Chemically Stabilized and
     Solidified Waste.  SW-872, U.S. Environmental Protection Agency, Washington, DC.

PEI Associates, Inc. 1988. Lessons Learned at Hazardous Waste Sites, Solidification/Stabilization
     Processes. Prepared under Contract No.68-03-3413 for the U.S. Environmental Protection
     Agency, Hazardous Wastes Engineering Research Laboratory, Cincinnati, OH.

PEI Associates, Inc. and Earth Technology Corporation. 1989. Stabilization/Solidification of CERCLA
     and RCRA Wastes: Physical Tests, Chemical Testing Procedures, Technology Screening, and
     Field Activities. Prepared under Contract No. 68-03-3413.  USEPA, Center for Environmental
     Research Information, Cincinnati, OH.

Truett, J. B., R. L. Holberger, and K. W. Barrett.  1983.  Feasibility of In Situ Solidification/Stabilization of
     Landfilled Hazardous Wastes.  Prepared under Contract No. 68-02-3665 by MITRE Corporation for
     the U.S. Environmental Protection Agency, Municipal Environmental Research Laboratory,
     Cincinnati, OH.

U. S. Environmental Protection Agency.  1985. Handbook: Remedial Action at Waste Disposal Sites
     (Revised) EPA/625/6-85/006.  Hazardous Waste Engineering Research Laboratory, Cincinnati,
     Ohio and Office of Emergency and Remedial Response, Washington, DC.

U. S. Environmental Protection Agency. 1988.  The Superfund Innovative Technology Evaluation
     Program:  Technology Profiles. EPA/540/5-88/003. Office of Solid Waste and Emergency
     Response and Office of Research and Development, Washington, DC.

U. S. Environmental Protection Agency. 1989. Technology Evaluation Report: SITE Program
     Demonstration Test, International Waste Technologies, In Situ Stabilization/Solidification, Hialeah,
     Florida, Volume 1.  EPA/540/5-89/004a.  Risk Reduction Engineering Laboratory, Cincinnati, OH.


3.3    Degradation

3.3.1   Chemical Degradation

Amdurer, M., R. T. Fellman, J. Roetzer, and C. Russ. 1986. Systems to Accelerate In Situ Stabilization
     of Waste Deposits. EPA/540/2-86/002. .Hazardous Waste Research Laboratory, U.S.
     Environmental Protection Agency, Cincinnati, OH.

Arienti, M., L. Wilk, M. Jasinski, and  N. Prominski, 1986. Technical Resource Document: Treatment
     Technologies for Dioxin-Containing Waste, EPA/600/2-86/096.  Office of Research and
     Development, Cincinnati, OH.

Ayres, D. C., D. P. Levy, and C. S. Greaser. 1985. Destruction of Chlorinated Dioxins and Related
     Compounds by Ruthenium Tetroxide.  In: Chlorinated Dioxins and Dibenzofurans in  the Total
     Environment II - Butterworth Publishers, Stoneham, MA.

Boyd, S. A., and M. M. Mortland, 1985.  Dioxin Radical Formation and Polymerization on Cu(ll)-Smectite
     Nature 316:532-535.
                                         105

-------
Brunelle, D. J., and D. A. Singleton, 1985.  Chemical Reaction of Polychlorinated Biphenyls on Soils
    With Poly (Ethylene Glycol)/KOH. Chemosphere, 14(2):173-181.

Carpenter, B. H. and D. L. Wilson, 1988. Technical/Economic Assessment ot Selected PCB
    Decontamination Processes, J. Hazard Materials 17, pp. 125-148.

Dragun, J., and D. E. Baker.  1979.  Electrochemistry, pp. 130-135. In The Encyclopedia of Soil
    Science. Parti: Physics, Chemistry,  Biology, Fertility, and Technology. Dowden Hutchinson, and
    Ross, Inc., Stroudsburg, PA.

Dragun, J., and C. S. Helling.  1982. Soil-and Clay-catalyzed Reactions: I. Physicochemical and
    Structural Relationships of Organic Chemicals Undergoing Free-Radical Oxidation. In Land
    Disposal of Hazardous Waste. Proc.  Eighth Annual Research Symposium.  EPA-600/9-82-002.

FMC Corporation. 1979. Industrial Waste  Treatment with Hydrogen Peroxide. Industrial Chemicals
    Group,  Phil., PA.

 Furukawa, T., and G. W. Brindley. 1973.  Adsorption and Oxidation of Benzidine and Aniline by
    Montmorillonite and Hectorite.  Clay Miner. 21:279-288.

Griffin, R. A., and N. F. Shimp. 1978.  Attenuation of  Pollutants in Municipal Landfill Leachate by Clay
    Minerals. EPA/600/2-78/157.  U.S. Environmental Protection Agency Municipal Environmental
    Research Laboratory, Cincinnati, OH.

Grove, J. H., and B. G. Ellis.  1980. Extractable Chromium as Related to Soil pH and Applied Chromium.
    Soil Sci. Soc. Am. J. 44:238-242.

Hirschler, A. E.  1966.  Proton Acids and Electron Acceptors on Aluminosilicates.  J. Catalysis 5:196-
    197.

King, J., T.Tinto, and M. Ridosh. 1985. In Situ Treatment of Pesticide Contaminated Soils. In:
    Proceed, of the 6th National Conference on Management of Uncontrolled Hazardous Waste Site -
    Nov. 4-6, Washington, DC., pp. 243-248.

Kirk Othmer Encyclopedia of Chemical Technology.  1982. Vol. 18. John Wiley & Sons, New York, NY.

Kernel, A., and C. Rogers, 1985. PCB Destruction:  A Novel Dehalogenation Reagent, J. Hazard
    Materials, 2:161-176.

McLean, J. E., R. C. Sims, W. J. Doucette, C. R. Caupp, and W. J.  Grenney.  1988. Evaluation of Mobility
    of Pesticides in Soil Using U.S. EPA  Methodology. Journal of Environmental Engineering
     114(3):689-703, American Society of Civil Engineering.

Mercer, B. W., A. J. Shuckrow, and L. L. Ames.  1970. Fixation of Radioactive Wastes in Soil and Salt
    Cores With Organic Polymers. BNWL-1220.

Nagel, G. 1982. Sanitation of Groundwater by Infiltration of Ozone  Treated Water. GWF-
    Wasser/Abwasser 123(8):399-407.

Nakayama,  S., 1979.  Ozone. Science and Engineering 1(2):119-132.

Novinson, T. 1985. Chemical Detoxification of Polychlorinated Biphenyls (PCBs), Department of the
     Navy, AD-D012072.
                                          106

-------
Page, J. B.  1941.  Unreadability of the Benzidine Color Reactions as a Test for Montmorillonite. SoilSci.
    51:133-140.

Peterson, R. L, E. Milicic, C. J. Rogers, 1985. Chemical Destruction/Detoxification of Chlorinated
    Dioxins in Soils.  In: Proceedings of the 11th Annual Research Symposium, Incineration and
    Treatment of Hazardous Waste, Cincinnati, OH.  EPA/600/9-85/028.

Rice, R. G.  1981.  Ozone for the Treatment of Hazardous Materials. Water-1980 Symposium Series.
    American Institute of Chemical Engineers, 29(77) :79-l 07.

Rice, R. G.  1984.  Purification and Recycling of Groundwater Contaminated with Petroleum Products
    and Cyanide - The Karlsruhe (Federal Republic of Germany) Drinking Water Treatment Plant. In:
    The 5th National Conference on Management of  Uncontrolled Hazardous Waste Sites, November
    7-9, Washington, DC.

Sanning, D. E., and M. I. Black, 1987.  Protecting the Environment at Superiund Sites Through
    Chemistry.  EPA/600/D-87/222. USEPA, Hazardous Waste Engineering Research Laboratory,
    Cincinnati, OH.

Sanning, D. E., and R. F. Lewis. 1987.  Technologies for In Situ Treatment of Hazardous Waste.
    EPA/600/D-87/014.  USEPA, Hazardous Waste Engineering Research Laboratory, Cincinnati, OH.

Sikes, D. J., M. N. McCullough, and J. W. Blackburn, 1984. The Containment and Mitigation of a
    Formaldehyde Rail Car Spill Using Novel Chemical and Biological In Situ Treatment Techniques. In:
    Proceed, of the 1984 Hazardous Materials Spills  Conference:  Prevention, Behavior, Control and
    Cleanup of Spills and Waste Sites. April 9-12, Nashville, TN, pp. 98-103.

Sims, R. C.  and J. Bass. 1984.  Review of In Place Treatment Technologies for Contaminated Surface
    Soils -  Volume 1, Technical Evaluation.  EPA-540/2-84-003a. U.S. Environmental Protection
    Agency, Cincinnati, OH.

Solomon, D.H. 1968.  Clay Minerals as Electron Acceptors and/or Electron Donors in Organic
    Reactions.  Clay Miner.  16:31-39.

Staiff, D.C.,  L.C. Butler, and J. E. Davis.  1981. A  Field Study of the Chemical Degradation of Paraquat
    Dichloride Following Simulated Spillage on Soil.  Bull. Environ. Contam. Toxicol. 26:16-21.

Sweeney, K. 1981. Reductive Treatment of Industrial  Wastewaters. I. Process and Description and II.
    Process Application, pp. 67-78. In Water 1980. G. F. Bennett (ed.). American Institute of
    Chemical Engineers Symposium. Series 209 (77).

Taylor, M. L., M. A. Dosani, J. A. Wentz, T. Kling, R. B.  Sukol, J. S. Greber, and N. P. Barkley.  1989.
    Assessment of Chemical and Physical Methods for Decontaminating Buildings and Debris at
    Superfund Sites. In: Remedial Action, Treatment and Disposal of  Hazardous Waste, Proceedings
    of the Fifteenth Annual Research Symposium, Cincinnati, OH.

Theng, B. K. G.  1974. The Chemistry of Clay-Organic Reactions. Adam Hilger, London.

Tucker, S. P., and G. A. Carson, 1985.  Deactivation of Hazardous Chemical Wastes, Environmental
    Science and Technology, Vol. 19, No. 3.

U.S. Environmental Protection Agency.  1986. Hazardous Waste Treatment Technology. EPA/600/D-
    86/006. Office of Research and Development, Cincinnati, OH.
                                         107

-------
Williams, E.B. 1982.  Contamination Containment by In Situ Polymerization.  Second National
    Symposium on Aquifer Restoration and Groundwater Monitoring. National Water Well Association.
    Worthington, OH.
Wilson, D. L, 1987.  Report on Decontamination ot PCB-Bearing Sediments.  EPA/600/2-87/093,
    USEPA Hazardous Waste Engineering Research Laboratory, Cincinnati, OH.
3.3.2  Biological  Degradation
Alexander, M. 1977.  Introduction to Soil Microbiology. Second Edition. John Wiley and Sons.  New
    York, NY. 467 p.
Alexander, M. 1981. Biodegradation of Chemicals of Environmental Concern.  Science 211:132-138.
Anderson, J. R.  1978.  Pesticide Effects on Non-Target Soil Microorganisms, pp. 313-533.  In Pesticide
    Microbiology. Hill,  I. R. and Wright, S. J. L. (eds) Academic Press, New York, NY.
Arthur D.  Little, Inc.  1976.  State-of-the-Art Survey of Land Reclamation Technology. EC-CR-76-76.
    Department of the Army, Edgewood Arsenal, Aberdeen Proving Ground, MD.
Atlas, R.M., and R. Bartha. 1981. Microbial Ecology, Fundamentals, and Applications. Addison-Wesley
    Publishing Company,  Reading, MA. 560 p.
Baas  Becking, L. G. M., I. R. Kaplan, and D. Moore. 1960. Limits of the Natural Environment in Terms of
    pH and Oxidation-Reduction Potentials. J. Geology 68:243-284.
Bachmann, A., P. Walet, P. Wijnen, W. de Bruin, J. L. M. Huntjens, W. Roelofsen,  and A. J. B. Zehnder,
     1988.  Biodegradation of Alpha- and Beta-Hexachlorocyclohexane in a Soil Slurry Under Different
     Redox Conditions. Appl. Environ. Microbiol., 54(1):143-149.
Baker, M. D., and C.  I. Mayfield, 1980. Microbial and  Non-biological Decomposition of Chlorophenols
    and  Phenol in Soil. Water Air Soil Poll.  13:411-424.
Bartha, R. 1980. Pesticide Residues in Humus. ASM News 46:356-360.
Batterman, G. and P. Werner.  1984. Grundwasser-forscung-Wasser/Abwasser.  125:366-373.
Baver, L.  D., W. H. Gardner, and W. R. Gardner. 1972. Soil  Physics.  Fourth Edition. John Wiley and
     Sons, Inc., New York, NY. 498 p.
Bahadir, M., and G. Pfister. 1987.  Uptake of Carbofuran 14C by Rice Plants After Root Zone Application
     as a Controlled  Release Formulation.  Chemosphere, 16(6) :1273-1279.
Bell, R. M.  1988. Higher Plant Accumulation of Organic Pollutants From Soils.  Final Report Under
     Cooperative Agreement CR812845-01. USEPA, Hazardous Waste Engineering Research
     Laboratory, Cincinnati, OH.
Bingham, F. T., A. L.  Page, R. J. Mahler, and T. J. Granje. 1975. Growth and Cadmium Accumulation of
     Plants Grown on a Soil Treated with a Cadmium-Enriched Sewage Sludge. J. Environmental
     Quality, 4:207-211.
Bingham, F. T., A. L.  Page, R. J. Mahler, and T. J. Granje. 1976. Yield and Cadmium Accumulation of
     Forage Species in Relation to Cadmium Content of Sludge-Amended Soil. J. Environmental
     Quality, 5:57-59.
                                         108

-------
 Bollag, J. M.  1989.  Decontamination of the Environment Through Binding of Pollutants to Humic
     Materials. In: Chemical and Biochemical Detoxification of Hazardous Waste. (J. A. Glaser, ed).
     Lewis Publishers, Inc. (In Press).

 Bollag, J. M. 1983. Cross-Coupling of Humus Constituents and Xenobiotic Substances,  pp. 127-141.
     In Aquatic and Terrestrial Humic Materials.  Christman, R. F., and Gjessing, E. T. (eds.).  Ann Arbor
     Science Publishers, Ann Arbor, Ml.

 Bollag, J. M., R. M. Minard, and S. Y. Liu.  1983.  Cross-Linkage Betwen Anilines and Phenolic Humus
     Constituents.  Environ. Sci. Tech. 17:72-80.

 Bollag, J. M., S  Y. Liu, and R. D. Minard.  1980.  Cross-Coupling of Phenolic Humus Constituents and
     2,4-dichlorophenol. Soil Sci. Soc. Am. J. 44:52-56.

 Bollag, J. M. , P. Blattman, and T. Laanio.  1978. Adsorption and Transformation of Four Substituted
     Anilines in Soil   J. Agric. Food Chem. 26:1302-1306.

 Bonazountas, M., and J. Wagner.  1981. SESOIL - A Seasonal Compartment Model. Arthur D. Little.,
     Inc., Cambridge, Mass. Prepared for U.S. Environmental Protection Agency Office of Toxic
     Substances, Washington, DC.

 Bossert, I. and R. Bartha.  1984. The Fate  of Petroleum in Soil Ecosystems. In Atlas R. M. (ed.):
     Petroleum Microbiology, pp. 553-577.  MacMillan Publishers, New York, NY.

 Bouwer, E. J., and P. L. McCarty, 1985. Ethylene Dibromide Transformation Under Methanogenic
     Conditions.  Appl.  Environ. Microbiol., 50(2):527-528.

 Boyer, J.D., R. C. Ahlert, and D.S. Kosson. 1988. Pilot Plant Demontration Of In Situ Biodegradation Of
     1,1,1-Trichloroethane. J. Wat. Pollut. Control  Fed., 60(10):1843-1849.

 Brandt, C. H. 1972. Soil Physical Property Modifiers. In Organic Chemicals in the Soil Environment.  Vol.
     2. Goring, C.A.I., and Hamaker J.W. (eds.) Marcel Dekker, Inc., New York, NY.  pp 691-729.

 Brunner, W., and D. D. Focht. 1983. Persistence of Polychlorinated Phenyls (PCB) in Soils Under
     Aerobic and Anaerobic Conditions. In:  Abstracts of the Annual Meeting of the ASM.  American
     Society for Microbiology, Washinton, DC.  p. 266.

 Camoni, I., A. DiMuccio, D. Pontecovo, F. Taggi, and L. Vergoni.  1982.  Laboratory Investigation for
     Microbiological Degradation of 2,3,7,8-TCDD in Soil by Addition of Organic Compost. In
     Chlorinated Dioxins and Related Compounds Impact on the Environment. Hutzinger, O. (ed.)
     Pergamon Press, New York, NY.

 Cerniglia, C. E., and D. T. Gibson. 1979. Oxidation of Benzo(a)pyrene by the Filamentous Fungus
     Cunninghamella elegans. J. Biol. Chem. 254(23):12174.

 Cerniglia, C.  E., R. L. Herbert, R. H. Dodge, P. J. Szaniszlo, and D. T. Gibson. 1979.  Some Approaches
     to Studies on the Degradation of Aromatic Hydrocarbons by Fungi.  In Proceedings of the
     Workshop:  Microbial Degradation of Pollutants in Marine Environments.  Bourquin, A. L., and
     Pritshard, H. (eds.). EPA-600/9-79-012, Pensacola Beach, FL.

Chakrabarty, A.M. 1987. Microbial Degradation of 2,4,5-T And Chlorinated Dioxins.  EPA/600/M-
     86/025, Environmental Reserach Brief.  USEPA, Hazardous Waste Engineering Laboratory,
     Cincinnati, OH.
                                         109

-------
Chowdhury, A., D. Vockel, P. N. Moza, W. Klein, and F. Korte. 1981. Balance of Conversion and
    Degradation of 2,6-Dichlorobenzonitrile - 14c in Humus Soil. Chemosphere 10:1101-1108.

Christiansen, K, and S. Vedby.  1988.  SKRYDSTRUP Chemical Waste Disposal Site. In: Report on First
    International Workshop of the NATO/CCMS Pilot Study, "Demonstration of Remedial Action
    Technologies for Contaminated Land and Groundwater", Washington, D.C.

Colby, J., D. F.Stirling, H. Dalton.  1977.  Biochemistry Journal.  165:395-402.

Coover, M. P., and R. C. Sims. 1987a. The Effect of Temperature on Polycyclic Aromatic Hydrocarbon
    Persistence in an Unacclimated Agricultural  Soil. Hazardous Wastes & Hazardous Materials,
    4(1):69-82.

Coover, M. P., and R. C. Sims. 1987b. The Rate of Benzo(a)pyrene Apparent Loss in a Natural and
    Manure Amended Clay Loam Soil. Hazardous Waste and Hazardous Materials, 4(2):151-158.

Davis, J. B. and Raymond, R. L. 1961. Oxidation of Alkyl-Substituted Cyclic Hydrocarbons by a Nocardia
    During Growth on n-Alkanes.  Applied  Microbiol. 9:383-388.

des Rosiers, P.  1987. Evaluation of Technology for Wastes and Soils Contaminated With Dioxins,
    Furans, and Related Substances. J. Hazard Materials, 14:119-133.

Dowdy, R. H., and W. E.  Larson.  1975.  The Availability of Sludge-Borne Metals to Various Vegetable
    Crops.  J. Environmental Quality, 4:278-282.

Downey, M. 1988. Enhanced Biodegradation of Jet Fuel - Eglin AFB, U.S.A.  In:  Report on First
     International Workshop of the NATO/CCMS Pilot Study, "Demonstration of Remedial Action
    Technologies for Contaminated Land and Groundwater," Washington, DC.

Doyle, R.  C., and J. D. Isbister. 1982. Treatment of TNT and RDX Contaminated Soils by Composting.
     pp. 209-213. In Managing Uncontrolled Hazardous Waste Sites.  Hazardous Materials Control
     Research Institute, Silver Spring, MD.

Dragun.J. 1988.  The Soil Chemistry  of Hazardous  Materials. Hazardous Materials Control Research
     Institute, Silver Spring, MD.  458 pp.

Edgehill, R. U., and  R. K. Finn. 1983. Microbial Treatment of Soil to Remove Pentachlorophenol. Appl.
     Environ. Microbiol.  45:1122-1125.

Facchetti, S., A. Balasso, C. Fichtner, G. Frare, A. Leoni, C. Mauri, and M. Vasconi.  1987. Studies on
     the Absorption  of TCDD by Plant Species,  pp. 225-336. In: Chlorinated Dioxins and
     Dibenzofurans  in Perspective. C. Rappe, G. Choudhary, L. H. Keith (eds.). Lewis Publishers, Inc.,
     Chelsea, Ml.

 Flathman, P. E., and J. A. Caplan.  1986. Cleanup of Contaminated Soil and Groundwater Using
     Biological Techniques. In: Proceedings of the National Conference on Hazardous Wastes and
     Hazardous Materials, March 4-6,1986. Atlanta, GA.  pp.110-119.

 Focht, D. D., and D. Shelton. 1987. Growth Kinetics of Pseudomonas alcaligenes C-O Relative to
     Innoculation and 3-ChlorobenzDate Metabolism in Soil. Appl. Environ. Microbiol., 53(8):1846-
     1849.

 Focht, D. D., and M. Alexander. 1970. DDT Metabolites and Analogs: Ring Fission by
     Hydrogenomonas.  Science 170:91-92.
                                          110

-------
 Fogel, M. M., A. R. Taddeo, and S. Fogel.  1986.  Biodegradation of Chlorinated Ethenes by a Methane-
     Utilizing Mixed Culture.  Appl. Environ. Microbiol., 51(4):720-724.

 Follett, R. H., L. S. Murphy, and R. L. Donahue. 1981. Fertilizers and Soil Amendments.  Prentice-Hall,
     Inc., Englewood Cliffs, NJ.

 Fry, A. W., and A. S. Grey.  1971.  Sprinkler Irrigation Handbook.  Rain Bird Sprinkler Mfg. Corporation.
     Glendora, CA.

 Furukawa, K. 1982. Microbial Degradation of Polychlorinated Biphenyls (PCBs). pp. 33-57.  In
     Biodegradation and Detoxification of Environmental Pollutants.  Chakrabarty, A. M., (ed.), CRC
     Press, Boca Raton, FL.

 Glaser, J. A., R. Lamar, D. Dietrich, and T. K. Kirk.  1989. Treatment of Wood Preserving Soil
     Contaminants by White Rot Fungus.  Presented at:  15th Annual Research Symposium on
     Remedial Action, Treatment and Disposal of Hazardous Waste. April 10-12, Cincinnati, OH.

 Gray, T.R.G. 1978.  Microbial Aspects of the Soil,  Plant, Aquatic,  Air, and Animal Environments: Soil and
     Plants,  pp. 19-38.  In Pesticide Microbiology. Hill, I. R., and  Wright, S. J. L. (eds.) Academic Press,
     New York, NY.

 Hinchee, R., D. C. Downey, and E. J. Coleman. 1987. Enhanced Bioreclamation, Soil Venting and
     Ground-water Extraction: A Cost-Effective and Feasibility Comparison, pp. 147-164, In:
     Proceedings of Petroleum Hydrocarbons and Organic Chemicals in Ground Water: Protection,
     Detection, and Restoration. November 17-19, Houston, TX.

 Horowitz, A., J. M. Sulflita, and J. M. Tiedje. 1983. Reductive Dehalogenation of Halobenzoates by
     Anaerobic Lake Sediment Microorganisms. Appl. Environ.  Microbiol. 45:1459-1465.

 Isbister, J. D., G. L. Anspach, and J. F. Kitchens.  1984. Composting for Degradation of PCBs in Soil.
     In: Proceed, of the 1984 Hazardous Materials Spills Conference:  Prevention, Behavior, Control,
     and Cleanup of Spills and Waste Sites. April 9-12, Nashville, TN, pp. 104-109.

Jhaveri, V., and A. J. Mazzacca. 1985. Bioreclamation of Ground and Groundwater by In Situ
     Biodegradation:  Case History.  In:  Proceed,  of the 6th National Conference on Management of
     Uncontrolled Hazardous Waste Sites -1985, Washington, DC., pp. 239-242.

 Kaplan, D. L, and A. M. Kaplan. I982a. Thermophilic Biotransformations of 2,4,6-Trinitrotoluene Under
     Simulated Composting Conditions. Appl. Environ. Microbial. 44:757-760.

 Kaplan, D. L., and A. M. Kaplan 1982b.  Composting Industrial Wastes -  Biochemical Consideration.
     Biocycle May/June:42-44.

Keck, J., R. C. Sims, M. Coover, K. Park, and B. Symons.  1989.  Evidence for Cooxidation of
     Polynuclear Aromatic Hydrocarbons in Soil. Water Research (In Press).

Kew, G. A., J. L. Shaum, P. White, and T. T. Evans. 1989.  Review of Plant Uptake of 2,3,7,8-TCDD
     From Soil and Potential Influence of Bioavailability. Chemosphere, 18(8):1313-1318.

Khan, S. U.  1982.  Studies on Bound 14C-prometryn Residues in Soil and Plants.  Chemosohere
     11:771-795.

Khan, S. U.,  and K. C. Iverson. 1982. Release of Soil Bound (non-extractable) Residues by Various
     Physiological Groups of Microorganisms.  J. Environ. Sci. Health 17:737-749.
                                         111

-------
Kobayashi, H., and B. E. Ritlman. 1982. Microbial Removal of Hazardous Organic Compounds.
    Environmental Science and Technology 16:170A-183A.

Konetzka, W. A. 1977.  Microbiology of Metal Transformations. In Microorganisms and Minerals.
    Weinberg, E.D. (ed.).  Marcel Dekker, Inc., New York, NY. pp. 317-342.

Kowalenko, C. G. 1978. Organic Nitrogen, Phosphorus and Sulfur in Soils, pp. 95-135.  In Soil Organic
    Matter. Schnitzer, M. and Khan, S. U. (eds.) Esevier Scientific Publishing Co., New York, NY.

Kuhn, E. P., P. J. Colberg, J. L. Schnoor, O. Wanner,  A. J. B. Zehnder,  and R. P. Schwarzenbach.
    1985. Microbial Transformation of Substituted Benzenes During Infiltration of River Water to
    Groundwater:  Laboratory Column Studies.  Environmental Science and Technology, 19(10):961-
    968.

Lee, M. D., and C. H. Ward. 1984. Reclamation of Contaminated Aquifers:  Biological Techniques. In:
    Proceed, of the 1984 Hazardous Materials Spills Conference:  Prevention, Behavior, Control and
    Cleanup of Spills and Waste Sites. April 9-12.  Nashville, TN, pp. 98-103.

Little, C. D., A. V. Palumbo, S. E. Herbes, M. E. Lidstrom,  R.  L. Tyndall, and P. J. Gilmer. 1988.
    Trichloroethylene Biodegradation by a Methane-Oxidizing Bacterium.  Appl. Environ. Microbil.,
    54(4):951-956.

Liu, S. Y., R. D., Minard, and J. M. Bollag.  1981.  Coupling Reactions of 2,4-dichlorophenol with Various
    Anilines.  J. Agric. Food Chem. 29:253-257.

Lokke, H. 1985. Degradation fo 4-Nitrophenol in Two Danish Soils.  Environ. Pollut. (Series A) 38:171-
    181.

Luthy, R. G., and J. R. Mihelcic.  1987. Microbial Degradation of Acenaphthene and Naphthalene under
    Denitrification Conditions in Soil-Water Systems:  Annual Report. DOE/FC/10619-2519.  October.
    p. 33.

Lyman, W.J., W. F.  Reehl, and D. H. Rosenblatt.  1982.  Handbook of Chemical Property Estimation
    Methods. McGraw-Hill Book Company, New York, NY.

Major, D. W., C. I. Mayfield, and J. F. Baker. 1988. Biotransformation of Benzene by Denitrification in
    Aquifer Sand.  Ground Water, 26(1): 8-14.

Marinucci, A. C., and R. Bartha.  1979. Biodegradation of 1,2,3- and 1, 2,4-trichlorobenzene in Soil and
    in Liquid Culture.  Appl. Environ. Microbiol.  38:811-817.

McLean, E. 0.1982. Soil pH and Lime Requirement,  pp. 199-224. In Methods of Soil Analysis.  Part 2 -
    Chemical and Microbiological Properties.  Second Edition. Page, A. L. (ed.). American Society of
    Agronomy, Inc., Madison, Wl.

McLean, J. E., R. C. Sims, W. J. Doucette, C. R. Caupp, and W. J. Grenney. 1988. Evaluation of Mobility
    of Pesticides in Soil Using U.S. EPA Methodology. Journal of Environmental Engineering
    114{3):689-703, American  Society of Civil Engineering.

Michelsen, D. L., D. A. Wallis, and F. Sebba. 1984. In Situ Biological Oxidation of Hazardous Organics.
    Env. Prog. 3:103-106.

Mulder, D. (ed.)- 1979.  Soil Disinfection.  Elsevier Scientific Publishing Co., Amsterdam.
                                          112

-------
Munnecke, D. M.  1980.  Enzymatic Detoxification of Waste Organophosphate Pesticides. J. Agric.
     Food Chem. 28:105-111.

Munnecke, D. M., L. M. Johnson, H. W. Talbot, and S. Barik. 1982. Microbial Metabolism and
     Enzymology of Selected Pesticides,  pp. 1-32. In Biodegradation and Detoxification of
     Environmental Pollutants. Chakrabarty, A. M. (ed.).  CRC Press, Inc., Boca Raton, FL.

Nimah, M. H., J. Ryan and M. Chaudry. 1983. Effect of Synthetic Conditioners on Soil Water Retention,
     Hydraulic Conductivity, Porosity, and Aggregation.  Soil. Sci. Soc. Am. J. 47:742-745.

Ou, L. T., P. S. C. Rao, and J. M. Davidson.  1983.  Methyl Parathion Degradation in Soil:  Influence of
     Soil-Water Tension. Soil Biol. Biochem.  15:211-215.

Pal, D., J. B. Weber, and M. R. Overcash.  1980.  Fate of Polychlorinated Biphenyls (PCBs) in Soil-Plant
     Systems.  Residue Reviews 74:45-98.

Pallazo, A. J., and D. C. Leggett. 1986. Effect and Disposition of TNT in a Treatment Plant. Journal of
     Environmental Quality, 15(1):49-52

Park, K. S., R. C. Sims, W. J. Doucette, and J. E.  Matthews. 1988.  Biological Transformation and
     Detoxification of  7,l2-dimethylbenz(a)anthracene in Soil Systems. Journal Water Pollution Control
     Federation.  60(10):1822-1825.

Paulson, D. L. Jr., R. Honeycutt, H. Lebaron, and V. Seim.  1984. Degradation of High Concentrations
     of Diazinon in Soils by Parathion Hydrolase.  In: Proceed, of the 1984 Hazardous Materials Spills
     Conference: Prevention, Behavior, Control, and Cleanup of Spills and Waste Sites.  April 9-12,
     Nashville, TN, pp. 92-97.

Pfaender, F. K., and M. Alexander.  1972.  Extensive Microbial  Degradation of DDT in Vitro and DDT
     Metabolism  by Natural Communities. J. Agric. Food Chem. 20:842-846.

Quastel, J. H., and P. G. Scholefield. 1953.  Arsenite Oxidation in Soil.  Soil Sci. 75:279-285.

Raymond, R. L., V. W. Jamison, and J. O.  Hudson. 1967. Microbial Hydrocarbon Co-oxidation.
     Oxidation of Mono- and Dicyclic Hydrocarbons by Soil Isolates of the Genus Nocardia. Applied
     Microbiol. 15,857-365.

Rickabaugh, J. 1988. Chemical and Microbial Stabilization Techniques for Remedial Action Sites. Final
     Report for U. S. EPA Contract No. 68-03-3210-01, Cincinnati, OH.

Rozich, A. F., and T. G. Zitrides, 1988.  Practical Approach for the Biological Remediation of Hazardous
     Waste Sites. In:  Proceedings of the 5th National Conference on Hazardous Waste and Hazardous
     Materials, Las Vegas, NV.

Ryan, J. A.  1976. Factors Affecting Plant Uptake of Heavy Metals From Land Application of Residuals.
     Presented at the National Conference on Disposal of Resides on Land. September 12-15.
     St. Louis, MO.

Ryan, J. A., R. M. Bell, J. M. Davidson,  and G. A.  O'Conner. 1988. Plant Uptake of Non-Ionic Organic
     Chemicals From Soils.  Chemosphere, 17(12):2299-2323.

Saxena, A., and R. Bartha.  1983. Microbial Mineralization of Humic Acid - 3,4-dichloroaniline complexes.
     Soil Biol. Biochem., 15:59-62.
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Shauer, P. S., W. R. Wright, and J. Pelchat. 1980. Sludge-Borne Heavy Metal Availability and Uptake by
    Vegetable Crops Under Field Conditions.  J. Environmental Quality, 9:69-73.

Schmidt, S. K., and M. Alexander. 1985. Effects to Dissolved Organic Carbon and Second Substrates
    on the Biodegradation of Organic Compounds at Low Concentrations. Appl. Environ. Microbiol.,
    49(4):822-827.

Schwab, G. O., R. K. Frevert, T. W. Edminster, and K. K. Barhes. 1981. Soil and Water Conservation
    Engineering. Third Edition. John Wiley and Sons, New York,  NY.

Sebba, F., and S. M. Barnett.  1981.  Separation Using Colloidal Gas Aphrons.  In Proceedings of the
    2nd International Congress of Chemical Engineers, IV. p  27-31.

Sikes, D. J., M. N. McCullough, and J. W. Blackburn, 1984. The Containment and Mitigation of a
    Formaldehyde Rail Car Spill Using Novel Chemical and Biological In Situ Treatment Techniques. In:
    Proceed, of the 1984 Hazardous Materials Spills Conference: Prevention, Behavior, Control and
    Cleanup of Spills and Waste Sites.  April 9-12.  Nashville, TN,  pp. 98-103.

Sikora, L. J., D. D. Kaufman, M. A. Ramirez, and G. B. Wilson.  1982.  Degradation of Pentachlorophenol
    and Pentachloronitrobenzene in a Laboratory Composting System.  In Proc. Eighth Ann. Symp. on
    Disposal of Hazardous Wastes.  U. S. Environmental Protection Agency, Cincinnati, OH.

Sims, R. C. and J. Bass.  1984.  Review of In Place Treatment Technologies for Contaminated Surface
    Soils  - Volume 1, Technical Evaluation. EPA-540/2-84-003a. U.S. Environmental Protection
    Agency, Cincinnati, OH.

Sims, R. C., and M. R. Overcash.  1981. Land Treatment of Coal Conversion Wastewaters. In
    Environmental Aspects of Coal  Conversion Technology VI, a  Symposium on Coal-based Synfuels.
    EPA-600/9-82-017. U. S. Environmental Protection Agency, Washington, DC.

Sims, R. C., D. L. Sorenson, W. J. Doucette, L. L. Hastings, and J.  L. Sims. 1986. Waste/Soil
    Treatability Studies for Four Complex Industrial Wastes: Methodologies and Results, Vol. 2, Waste
    Loading Impacts on Soil Degradation, Transformation.  EPA/600/6-86/003B. U.S. EPA, Robert S.
    Kerr Environmental Research Laboratory, Ada, OK.

Sjobland, R. D., and J. M. Bollag.  1981.  Oxidative Coupling of Aromatic Compounds by Enzymes from
    Soil Microorganisms, pp. 113-152. In Slil Biochemistry. Vo. 5.  Paul, E. A., and Ladd, J. N. (eds.).
    Marcel Dekker, Inc. New York, NY.

Skujins, J., S. O. McDonald, and W. G. Knight.  1983. Metal Ion Availability During Biodegradation of
    Waste Oil in Semi-arid Soils. Environmental Biogeochemistry 35:341-350.

Sommers, L. E., C. M. Gilmour, R. E. Wildung, and S. M. Beck.  1981. The Effect of Water Potential on
    Decomposition  Processes in Soils, pp. 97-117. In Water Potential Relations in Soil Microbiology.
    SSA Special Publication  Number 9.  Soil Sci. Soc. of Ameri., Madison, Wl.

Stevenson, F. J. 1972.  Role and Function of Humus in Soil With Emphasis on Adsorption of Herbicides
    and Chelation of Micronutrients. Bioscience 22(11):643-640.

Strand, S. E. and L. Shipper!. 1987. Oxidation of Chloroform in an Aerobic Soil Exposed to Natural Gas.
    Appl. Environ. Microbiol., 52(1)203-205.

Suflita, J. M., and J. M. Bollag. 1980. Oxidative Coupling Activity in Soil Extracts.  Soil Viol. Biochem.
     12:177-183.
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Suflita, J.M., A. Horowitz, D. R. Shelton, and J. M. Tiedje. 1982. Dehalogenalion: A Novel Pathway for
    the Anaerobic Biodegradation of Haloaromatic Compounds.  Science, 218:1115-1117.

Suflita, J. M., J. A. Robinson, and J. M. Tiedje. 1983.  Kinetics of Microbial Dehalogenation of
    Haloaromatic Substrates in Methanogenic Environments. Appl. Environ. Microbial. 45:1466-1473.

Suflita, J. M., and J. M. Tiedje. 1983. The Anaerobic Degradation fo 2,4,5-trichlorophenoxyacetic Acid
    by a Dehalogenating Bacterial Consortium. In Abstracts of the Annual Meeting of the ASM. Amer.
    Soc. for Microbiol., Washington, DC. p. 266.

Suflita, J. M. and S. A. Gibson. 1984. Biodegradation of Haloaromatic Substrates in a Shallow Anoxic
    Ground Water Aquifer. In: Proceed, of the Second International Conference on Ground Water
    Quality Research, Stillwater, OK., pp. 30-32.

Thibault, G. T., and N. W. Elliott. 1980. Biological Detoxification of Hazardous Organic Chemical Spills.
    In Control of Hazardous Material Spills. Vanderbilt University, Nashville, TN. pp. 398-402.

Thibault, G. T., and N. W. Elliott. 1979. Accelerating the Biological Clean-Up of Hazardous Materials
    Spills.  In Oil and Hazardous Material Spills: Prevention, Control, Cleanup, Recovery, Disposal.
    Information Transfer, Inc., Silver Spring, MD.  pp. 115-120.

Thomas, J.  M. and C. H. Ward. 1989.  In Situ  Biorestoration of Organic Contaminants in the Subsurface.
    Environment Science and Technology.  23(7):760-766.

Thornton-Manning, J. R., D. D. Jones, and T.  W. Federle.  1987.  Effects of Experimental Manipulation
    of Environmental Factors on Phenol Mineralization in Soil.  Environ. Toxicol. & Chem., 6:615-621.

Topp. E., I.  Scheunert, A. Attar, and F. Korte.  1986. Factors  Affecting the Uptake of 14C-Labeled
    Organic Chemicals by Plants From Soil.  Ecotoxicology and Environmental Safety, 11:219-228.

Travis, C. C., and A. D. Arms. 1988. Bioconcentration of Organics in Beef, Milk and Vegetation.
    Environmental Science and Technology, 22(3) :271-274.

Travis, C. C., and H. A. Hattemeyer-Frey. 1988. Uptake of Organics by Aerial Plant Parts: A Call for
    Research.  Chemosphere, 12(2)-.277-283.

U.S. Environmental Protection Agency. 1984. Case Studies 1-23:  Remedial Response at Hazardous
    Waste Sites.  EPA/540/2-84/002B. Municipal Environmental Research Laboratory, Cincinnati, OH.

U.S. Environmental Protection Agency. 1986. Mobile Treatment Technologies for Superfund Wastes.
    EPA/540/2-86/003(F).  Office of Emergency and Remedial Response, Washington, DC.

U.S. Environmental Protection Agency. 1988. Treatment  Potential for 56 EPA Listed Hazardous
    Chemicals in Soil.  EPA/600/6-88/001. Robert S. Kerr Environmental Research Laboratory,
    Ada, OK.

van der Berg, R., E. Soczo, J. Verheul, and D. Eikelboom, 1987. In Situ Biorestoration of a Subsoil
    Contaminated with Oil. In: Report of First International Workshop of the NATO/CCMS Pilot Study,
    "Demonstration of Remedial Action Technologies for Contaminated Land and Groundwater",
    Washington, DC.

Wagner, K., and Z. Kosin. 1985.  In Situ Treatment. In:  Proceed, of the 6th National Conference on
    Management of Uncontrolled Hazardous Waste Sites - Nov. 4-6. Washington, DC., pp. 221-248.
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Wallnofer, P. R., W. Ziegler, and G. Engelhardt. 1981. Bacterial Oxidation of 4-methylthio-substituted
    Veratrylglycerol-B-aryl-ethers, Model Compounds for Soil Bound Pesticide Residues.
    Chemosphere 10:341-346.

Walton, G.C., and D. Dobbs. 1980. Biodegradation of Hazardous Materials in Spill Situations,  pp. 23-
    29. In:  Control of Hazardous Material Spills. Vanderbilt University, Nashville, TN.

Wetzel, R. S., D. H. Davidson, C. M. Durst, and D. J. Sarno.  1987a.  Effectiveness of In Situ Biological
    Treatment of Contaminated Groundwater and Soils at Kelly Air Force Base, Texas. In: Proceed, of
    the National Conference on Hazardous Wastes and Hazardous Materials - March  16-17,1987,
    Washington, DC.

Wetzel, R. S., C. M. Durst, D. H. Davidson, and D. J. Sarno.  1987b.  In Situ Biobgical Treatment Test at
    Kelly Air Force Base, Volume II: Field Test Results and Cost Model.  (ESL-TR-85-52-II). U.S. Air
    Force Engineering & Services Center, Tyndall Air Force Base, FL 32403  170p.

Wetzel, R. S., C. M. Durst, D. H. Davidson, and D. J. Sarno.  1987c. In Situ Biological Treatment Test at
    Kelly Air Force Base, Volume III:  Appendices.  (ESL-TR-85-52-III) U.S. Air Force  Engineering &
    Services Center, Tyndall Air Force Base, FL 32403 215p.

Wetzel, R. S., C. M. Durst, P. A. Spooner, W. D. Ellis, D. J. Sarno, B. C. Vickers, J. R. Payne, M. S. Floyd,
    and Z. A. Saleem. 1986.  In-Situ Biological Degradation Test at Kelly Air Force Base, Volume 1:
    Site Characterization, Laboratory Studies, and Treatment System Design and Installation. ESL-TR-
    85-52.  Air Force Engineering and Services Center, Tyndall Air Force Base, FL.

Wilson, D. L., 1987. Report on Decontamination of PCB-Bearing Sediments.  EPA/600/2-97/093.
    USEPA Hazardous Waste Engineering  Research Laboratory, Cincinnati, OH.

Wilson, J. T., and B. H. Wilson. 1985.  Biotransformation of Trochlorethylene in Soil.  Appl. Environ.
    Microbiol., 49(1).'242-243.

Wilson, J. T., L. E. Leach, M. Henson,  and J. N. Jones. 1986. In Situ Biorestoration as a Groundwater
    Remediation Technique.  Ground Water Monitoring Res., Fall, pp. 56-64.

Yagi, O., and R. Sudo. 1980.   Degradation of Polychlorinated Biphenyls by Microorganisms. J. Water
    Poll. Control Fed. 52:1035-1043.

Yaniga, P. M., and W. Smith.  1986. Aquifer Restoration Via Accelerated In Situ Biodegradation of
    Organic Contaminants. In:  Proceed, of the 7th National Conference on Management of
    Uncontrolled Hazardous Waste Sites, Dec. 1-3, Washington DC.

Zeyer, J., E. P. Kuhn, and R. P. Schwarzenbach. 1986. Applied Environmental Microbiology.
    52:944-947.

3.3.3  Photolysis

Bunce.N.J. 1982. Photodechlorination of PCB's: Current Status. Chemosphere 11(8)701-714.

Burkhard, N., and J. A, Guth.   1979. Photolysis of Organophosphorus Insecticides on Soil Surfaces.
    Pest. Sci. 10:313.

Christensen, D. C., and W. C.  Weimer. 1979. Enhanced Photodegradation of Persistent Halogenated
    Organic Materials.  Presented at the 34th Annual Purdue Industrial Waste Conference, Purdue
    University, Lafayette, IN., pp 160-166.
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Crosby, D. G. 1971. Environmental Photooxidation of Pesticides,  pp 260-290.  In Degradation of
    Synthetic Organic Molecules in the Biosphere.  National Academy of Science. Washington, DC.

Crosby, D. G., A. S. Wong, J. R. Plimmer, and E. A. Woolson. 1971. Photodecomposition of
    Chlorinated dibenzo-p-dioxins. Science 73:748.

Cupitt, L. T. 1980. Fate of Toxic and Hazardous Materials in the Air Environment.  EPA-600/53-80-084.
    U.S. Environmental Protection Agency, Athens, GA.

Dawson, G. W.,  B. W. Mercer, and C. H. Thompson,1980.  Strategy for the Treatment of Spills on Land.
    National Conference on Control of Hazardous Waste Materials Spills.

Draper, W. M., F. D. Stephens, and L. O. Ruzo, 1987. Photochemical Surface Decontamination:
    Application to a Polychlorinated Biphenyl Spill Site, In  Solving  Hazardous Waste Problems, Exner,
    J. H. ed., ACS Washington DC.

Exner, J. H. 1984.  Options for Missouri Dioxin Sites,  In:  Hazardous Material Spills Conference,
    Disposal, Treatment, and Mitigation pp. 245-248.

Graedel, T. E. 1978. Chemical Compounds in the Atmosphere. Academic Press, New York, NY.

Gray, H. B. 1973. Chemical Bonds: An Introduction to Atomic and Molecular Structure.  W.A.Benjamin,
    Inc.,  Philippines.

Gohre,  K., and G. C. Miller, 1986.  Photooxidation of Thioether Pesticides on Soil Surfaces, J. Agric.
    Food Chem., 34(4)709-713.

Hautala, R.  1978.  Surfactant Effects on Pesticide Photochemistry  in Water and Soil. EPA-600/3-78-
    060. U.S. Environmental Protection Agency, Athens, GA.

Hendry, D. G., and R. A. Kenley. 1979. Atmospheric Reaction Products of Organic Compounds.
    Environmental Protection Agency Report EPA 560/12-79-001.  USEPA, Office of Toxic
    Substances, Washinton, DC.

Klopffer, W., 1980. Rapid Test for Simulation of Photo-oxidative Degradation in the Gas Phase. In Int.
    Workshop on Test Methods and Assessing Procedures for the Determination of the
    Photochemical Degradation Behavior of Chemical Substances, Berlin.

Lemaire, J., I. Campbell, H. Hulpke, J. A. Guth, W. Merz, L.  Phillip, and C. Von Waldow. 1980. An
    Assessment of Test Methods for Photodegradation of Chemicals in the Environment.
    Chemosphere 11(2):119-164.

Liberti, A., D. Broco, A. Allegrini, and G. Bertoni.  1978.  Field Photodegradation of TCDD by Ultra-Violet
    Radiation,  pp. 195-200. In Dioxin: Toxilogical and Chemical Aspects. Cattabeni, F., Cavallero, A.,
    and Galli, G. (eds.). Spectrum Publications,  Inc., New York, NY.

March, J.  1985. Advanced Organic Chemistry:  Reactions, Mechanisms and Structure, Third Edition,
    John Wiley  and Sons.  New York, NY.

Meuser, J. M. and W. C. Weimer.  1982. Amine-Enhanced Photodegradation of  Polychlorinated
    Biphenyls.  EPRI Research Project 1263-6.  Battelle Pacific Northwest Laboratories.

Miller, G. C., V. R. Hebert, R. G. Zepp. 1986. Chemistry and Photochemistry of  Low-Volatility Organic
    Chemicals on Environmental Surfaces,  Environmental Science and Technology, 21(12):1164-
    1167.
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Nilles, G. P., and M. J. Zabik. 1975. Photochemistry of Bioactive Combasagran. J. Agr. Food Chem.
    23:410.

Occhiucci, G., and A. Patacchiola. 1982. Sensitized Photodegradation of Adsorbed Polychloro-
    biphenyls (PCBs). Chemisphere 11(3):255-262.

Overcash, M. R., J. B. Webber, and W. P. Tucker.  1986.  Toxic and Priority Organics in Municipal Sludge
    Land Treatment Systems.  EPA/600/2-86/010.  U.S. EPA, Water Engineering  Research
    Laboratory, Cincinnati, OH.

Plimmer, J. R. 1971. Principles of Photodecomposition of Pesticides, pp. 279-290. In Degradation of
    Synthetic Organic Molecules in the Biosphere.  National Academy of Sciences, Washington, DC.

Plimmer, J. R., and U. I. Klingebiel.  1973. Photochemistry of dibenzo-p-dioxins pp. 44-54. In
    Chloroodioxins - Origin and Fate.  Blair, E. H. (ed.). American Chemical Society, Washinton, DC.

Sims, R. C. and M. Overcash. 1983. Fate of Polynuclear Aromatic Compounds (PNAs) in Soil-Plant
    Systems.  Residue Reviews, 88:1-68.

Sims, R. C., D. L. Sorenson, W. J. Doucette, L. L. Hastings, and J. L. Sims.  1986. Waste/Soil
    Treatability Studies for Four Complex Industrial Wastes: Methodologies and Results, Vol. 2, Waste
    Loading Impacts on Soil Degradation, Transformation.  EPA/600/6-86/003B.  U.S. EPA, Robert S.
    Kerr Environmental Research Laboratory, Ada, OK.

Spencer, W. F., J. D. Adam, T. D. Shoup, and R. C. Spear. 1980.  Conversion of Parathion to Paraoxon
    on Soil Dusts and Clay Minerals as Affected by Ozone and UV Light. J. Agri. Food Chem.  28:369.

Stallard, M. L. 1988.  Dye-Sensitized Photochemical Reduction of PCBs, Journal of Environmental
     Engineering, Vol. 114, No.  5.

Sukol, R. 1987.  Guide to Commercially Available Bioremediation Processes. Report under Contract
     No. 68-03-3413. USEPA, Hazardous Waste Engineering Research Laboratory, Cincinnati, OH.

Weast, R. C. and M. J. Astle (eds.). 1982. CRC Handbook of Chemistry and Physics, CRC Press, Inc.
     Boca Raton, FL.

Wilson, D. L. 1987.  Report on Decontamination of  PCB-Bearing Sediments, EPA/600/2-87/093.
     USEPA,  Hazardous Waste  Engineering Research Laboratory, Cincinnati,  OH.

Wipf, H. K., E. Homberger, N. Nuener, and F. Schenker. 1978. Field Trials on Photodegradation of
     TCDD on Vegetation  After Spraying with Vegetable Oil. pp. 201-217. In Dioxin:  Toxilogical and
     Chemical Aspects. Cattabeni, F., Cavallero, A., and Galli,  G. (eds.).  Spectrum Publications, Inc.,
     New York, NY.

Woodrow, J. E., D. G. Crosby, and J. N. Seiber.  1983. Vapor-phase Photochemistry of Pesticides.
     Residue  Reviews 85:111-125.

3.4   Control  of Volatile  Materials

Baker, R., J. Steinke, F. Manchak, Jr., and M. Ghassemi. 1986. In Situ Treatment for Site Remediation.
     Proc. of Third Annual Conference on Hazardous Waste Law and Management, Seattle, WA.
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Dev, H., G.C. Sresty, J. E. Bridges, and D. Downey. 1988. Field Test of the Radio Frequency In Situ
     Soil Decontamination Process.  In: Superfund '88, Proceedings of the 9th National Conference.
     The Hazardous Materials Control Research Institute, Silver Spring, MD. pp. 498-502.

Ghassemi, M. 1988. Innovative In Situ Treatment Technologies for Cleanup of Contaminated Sites.
     Journal of Hazardous Materials, 17:189-206.

Glynn, W. and M. Duchesneau, 1988. Assessment of Vacuum Extraction Technology Application:
     Belleview, Florida LUST Site. Prepared under Contract No. 68-03-3409 for U.S. EPA Risk
     Reduction Enginneering Laboratory, Cincinnati, OH.

Greer, J. S., and S. S. Gross. 1980. The Practicality of Controlling Vapor Release From Spills of Volatile
     Chemials Through Cooling, pp. 130-133. In National Conference on Control of Hazardous Material
     Spills.

Hilberts, B.  1985. In Situ Steam Stripping. Assink, J. W. and W.  J. van den Brink (eds), Contaminated
     Soil. Proceedings of 1st International TNO Conference on Contaminated Soil, Utrecht, The
     Netherlands.

Hutzler,  N. J., B. E. Murphy, and J. S. Gierke 1989. State of Technology Review - Soil Vapor Extraction
     Systems, EPA 600/2-89/024, USEPA,  Risk Reduction Engineering Laboratory, Cincinnati, OH.

Iskandar, I.K., and T. F. Jenkins 1985.  Potential Use of Artificial Ground Freezing for Contaminant
     Immobilization. In:  Proceedings, International Conference on New Frontiers for Hazardous Wastes
     Management, EPA/600/9-85/025. U.S. EPA Hazardous Wastes Engineering Research
     Laboratory, Cincinnati, OH. pp. 128-137.

Lord, A.  E., Jr., R. M. Koerner, and V. P. Murphy. 1988. Laboratory Studies of Vacuum-Assisted Steam
     Stripping of Organic Contaminants From Soil.  In:  Land Disposal, Remedial Action, Incineration and
     Treatment of Hazardous Waste, Proceedings of the Fourteenth  Annual Research Symposium,
     EPA/600/9-88/021, U.S. EPA Risk Reduction Engineering Laboratory, Cincinnati, OH.  pp. 65-92.

Lord, A.  E., Jr. R. M. Koerner, D. E. Hullings, and J. E. Brugger.  1989. Laboratory Studies of Vacuum-
     Assisted Steam Stripping of Organic Contaminants from Soil.  Presented  at the 15th Annual
     Research Symposium for Land Disposal, Remedial Action, Incineration, and Treatment of
     Hazardous Waste, U.S. EPA Risk Reduction Engineering Laboratory, Cincinnati, OH.

Murdoch, L., B. Patterson, G. Losonsky, and W.  Harrar, 1988.  Innovative Technologies of Delivery or
     Recovery: A Review of Current Research and a Strategy for Maximizing Future Investigations.
     University of Cincinnati/U.S.  EPA Risk  Reduction Engineering Laboratory, Cincinnati, OH.

Murdoch, L. C., 1989.  Innovative Delivery and Recovery Systems: Hydraulic Fracturing - A Field Test.
     Presented at the  U.S. EPA Research Symposium, March 15, Cincinnati, OH.

Sullivan, J. M., D. R. Lynch, and I. K. Iskandar. 1984. The Economics of Ground Freezing for
     Management of Uncontrolled Hazardous Waste Sites. U.S.  EPA, U.S. Army Cold Regions
     Research and Engineering Laboratory  and  Dartmouth College, 5th National Conference on
     Management of Uncontrolled Hazardous Waste Sites, Nov.  7-9,  Washington, DC.

U.S. Department of  Energy. 1988. The Interagency Work Group on Hazardous Waste Technologies.
     Prepared under Contract No. DE-AC05-84OR21400 by Martin Marietta Energy Systems, Inc.
     Oak Ridge, TN.
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U. S. Environmental Protection Agency. 1988. The Superfund Innovative Technology Evaluation
    Program: Progress and Accomplishments - A Report to Congress. Office of Research and
    Development, Washington, DC.

U.S. Environmental Protection Agency. 1989. Technology Evaluation Report: SITE Program
    Demonstration Test, Terra Vac In Situ Vacuum Extraction System, Groveland, Massachusetts.
    EPA/540/5-89/003a. Risk Reduction Engineering Laboratory, Cincinnati, OH.


3.5   Chemical  and  Physical Separation  Techniques

Ahrens, J. F., and J. B. Kring. 1968. Activated Carbon Adsorbs Pesticides.  Front.  Plant Sci. 20:13.

Anderson, A. H. 1968.  The Inactivation of Simazine and Liuron in Soil by Charcoal. Weed Res. 8:58-60.

Ayorinde, O. A., L. B. Perry, and I. K. Iskandar. 1989.  Use of Innovative Freezing Technique for In Situ
    Treatment of Contaminated Soils.  In: Third International Conference on New Frontiers for
    Hazardous Waste Management, Proceedings. Pittsburgh, PA. EPA/600/9-89/072. U.S. EPA
    Risk Reduction Engineering Laboratory, Cincinnati, OH.

Coffey, D. L., and G. F. Warren.  1969.  Inactivation of Herbicides by Activated Carbon and Other
    Adsorbents. Weed Sci. 17:16-19.

Gupta, O. P. 1976. Adsorbents and Antidotes.  World Crops. 28:134-138.

Horng, J., and S. Banerjee  1987.  Evaluating Electro-Kinetics as a Remedial Action Technique. In:
    Proceedings, Second International Conference on New Frontiers  for Hazardous Waste
    Management.  EPA/600/9-87/018F.  U.S. EPA Hazardous Wastes Engineering Research
    Laboratory, Cincinnati, OH. pp. 65-77.

Iskandar, I.  K., and J. M. Houthoofd. 1985.  Effect of Freezing on the Level of Contaminants in
    Uncontrolled Hazardous Waste Sites. Part 1. Literature Review and Concepts.  In: Land Disposal
    of Hazardous Wastes, Proceedings of  the Eleventh Annual Research Symposium, EPA/600/9-
    85/013. U.S. EPA Hazardous Wastes  Engineering Research Laboratory Cincinnati, OH.  pp. 122-
    129.

Iskandar, I.K., and T. F. Jenkins 1985.  Potential Use of Artificial Ground Freezing for Contaminant
    Immobilization.  In: Proceedings, International Conference on New Frontiers for Hazardous Wastes
    Management, EPA/600/9-85/025. U.S. EPA Hazardous Wastes  Engineering Research
    Laboratory, Cincinnati, OH. pp. 128-137.

Iskandar, I.  K., L. B. Perry, T. F. Jenkins, and J. M. Houthoofd. 1986.  Effect of Freezing on the Level of
    Contaminants in Uncontrolled Hazardous Waste Sites - Part II:  Preliminary Results. In:
    Proceedings of the 12th Annual Research Symposium, Land Disposal, Remedial Action,
    Incineration, and Treatment of Hazardous Wastes. EPA/600/9-86/002. U.S. EPA Hazardous
    Waste Engineering Research Laboratory. Cincinnati, OH.

Lichtenstein, E. P., T. W. Fuhremann, and K. R. Schulz. 1968.  Use of Carbon to Reduce the Uptake of
    Insecticidal Soil Residues by Crop Plants. J. Agr. Food Chem. 16:348-355.

Murdoch, L., B. Patterson, G. Losonsky, and W. Harrar, 1988. Innovative Technologies of Delivery or
    Recovery: A Review of Current Research and a Strategy for Maximizing Future Investigations.
    University of Cincinnati/U.S. EPA Risk  Reduction Engineering Laboratory, Cincinnati, OH.
                                         120

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Park, J. E., 1986. Testing and Evaluation of Permeable Materials for Removing Pollutants from
    Leachates at Remedial Action Sites.  EPA/600/2-86/074.  U.S. Environmental Protection Agency,
    Cincinnati, OH.
Spangler, M. G., and R. L. Hardy. 1973.  Soil Engineering, Intext Educational Publishers, New York, NY.
Strek, H. J., J. B. Weber, P.  J. Shea, E. Mrozek, Jr., and M. R. Overcash.  1981.  Reduction of
    Polychlorinated Biphenyl Toxicity and Uptake of Carbon-14 Activity by Plants Through the Use of
    Activated Carbon. J. Agr. Food Chem. 29:288-293.
Weber, J. B., and E. Mrozek, Jr.  1979.  Polychlorinated Biphenyls: Phytotoxicity, Adsorption, and
    Translocation by Plants, and Inactivation by Activated Carbon.  Bull. Environ. Contam. Toxicol.
    23:412-417.
Section 4   Delivery and Recovery  Systems
Ader, J. C., and M. H. Stein, 1984. Slaughter Estate Unit Tertiary Miscible Gas Pilot Reservior
    Description.  Jour. Petrol. Tech., May.
Aguilera, R. 1980. Cyclic Water Flooding. In: Naturally Fractured Reserviors.  Petroleum Publishing
    Company, Tulsa, OK.
Albright, J. C.  1986. Use of Well Logs to Characterize Fluid Flow in the Maljamar CO2 Pilot. Jour. Petrol.
    Tech.,  August.
Bertrand, R. G., and M. S. Vukasovich, 1977.  Cleaning of MoS2 Soils from Steel Surfaces. Lubrication
    Engineering,  p. 538-543.
Boiling, J. D. 1985. A Full Field Model Study of the East Velma West Block, Sims Sand Unit Reservoir.
    Journal of Petroleum Technology.  August,  pp. 1429-1440.
Boyer, R. C. 1985. Geologic Description of East Velma West Block, Sims Sand Unit, for an Enhanced
    Oil Recovery Project. Journal of Petroleum Technology.  August, pp. 1420-1428.
Brunning, T.  1987. The Block Displacement Method Field Demonstration and Specifications.
    EPA/600/S2-87/023.  U.S. EPA Hazardous Waste Engineering Laboratory, Cincinnati, OH.
Busacca, A. J., J. R. Aniku, and M. J. Singer, 1984. Dispersion of Soils by and Ultrasonic Method that
    Eliminates Probe Contract. Soil Sci. Am. J., 28:125-1129.
Collins, A. G., and C. C. Wright, 1985.  Enhanced  Oil  Recovery Injection Waters. In: Donaldson and
    others (eds.), Enhanced Oil Recovery,  I. Elsevier, NY.
Desch, J. B., W. K. Larsen, R. F. Lindsay, and R. L. Nettle. 1984.  Enhanced Oil Recovery by CO2
    Miscible Displacement in the Little Knife Field, Billings County, North Dakota.  Journal of Petroleum
    Technology.  September, pp. 1592-1602.
Dickinson, W., R. W. Dickinson, P. A. Mote,  and J. S. Nelson. 1987. Horizontal Radials for Geophysics
    and Hazardous Waste Remediation. In:  Superfund '87, Proceedings of the 8th National
    Conference.  The Hazardous Materials Control Research Institute, Silver Spring, MD. pp.  371-375.
Donaldson, E. C., G. V. Chilingarian, and-T.  G. Yen (eds.).  1985.  Enhanced Oil Recovery, I,
    Fundamentals and Analyses. Elsevier, Amsterdam, p. 357
                                         121

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Ehrlich, R., J. H. Tracht, and S. E. Kaye. 1984. Laboratory and Field Study of the Effect of Mobile Water
    on CO2 Flood Residual Oil Saturation. Journal of Petroleum Technology.  October, pp. 1797-
    1809.

Grogan, A. T., and Pinczewski, 1987.  The Role of Molecular Diffusion Processes in Tertiary CO2
    Flooding.  Jour. Petrol. Tech.  May.

Holm, L. W., 1987.  Evolution of the Carbon Dioxide Flooding Processes.  Jour. Petrol. Tech  p 1337-
    1342.

Huck, P., M. Waller, and S. Shimondle. 1980. Innovative Geotechnical Approaches to the Remedial In
    Situ Treatment of Hazardous Materials Disposal Sites. Proceedings of the 1980 National
    Conference of Control of Hazardous Materials Spills,  May 13-15, Louisville, KY.

Kamath, V. A.,  and S. P. Godbole.  1987. Evaluation of Hot-Brine Stimulation Technique for Gas
    Production from Natural Gas Hydrates. Journal of Petroleum Technology.

Kasper,  D. R., H. W. Martin, and L. D.  Munsey. 1979. Environmental Assessment of In Situ Mining.
    Bureau of Mines OFR  101-80.

Keely, J. F., R. L. Johnson, and C.D. Palmer.  1987. Innovations in Delivery and Recovery Techniques
    for  In Situ Remediations.  USEPA, Hazardous Waste Engineering Research Laboratory,
    Cincinnati, OH.

Latil, M., 1980.  Enhanced Oil Recovery. Gulf Publ. Co., Houston, TX.  236 pp.

Morrow, N. R.,  and J. P. Heller, 1985.  Fundamentals of Enhanced Recovery.  In: Donaldson and others
    (eds.), Enhanced Oil Recovery, I. Elsevier, New York.

Murdoch, L., B. Patterson, G. Losonsky, and W. Harrar.  1988. Innovative Technologies of Delivery or
    Recovery: A Review of Current Research and  a Strategy for Maximizing  Future Investigations.
    Report for Contract No. 68-03-3379.  U.S. EPA Risk Reduction Engineering Laboratory,
    Cincinnati, OH.

Murdoch, L. C. 1989. Innovative Delivery and Recovery Systems: Hydraulic Fracturing - A Field Test.
    Presented at the 1989 U.S. EPA  Research Symposium, March 15. U.S. EPA  Risk Reduction
    Engineering Laboratory, Cincinnati, OH.

Pittaway, K. R., Albright, J. C., Hoover, J. W., and Moore J. S.  1987. The Maljamar CO2 Pilot: Review
    and Results.  Jour. Petrol. Tech., October, p.  1256-1260.

Pittaway, K. R., Hoover, J. W., and Deckert, L. B., 1985.  Development and Status of the Maljamar CO2
    Pilot. Jour. Petrol. Tech., March.

Ramunni, A. U. and F. Palmieri.  1985.  Use of Ultrasonic Treatment for Extraction of Humic Acid with
    Inorganic  Reagents from Soil. Org. Geochem. 8 (4):241-246.

Tamari, Y., Y. Inonue, H. Tsuji, and Y.  Kusaka, 1982. Ultrasonic Extraction of Several Cations with Dilute
    Nitric Acid Solutions from Soils.  31:409-412.

Williamson, A.  S., M. Gondouin, E. J. Pavlas, J. E. Olson, L. W. Schnell, and R. R. Bowen.  1986. The
    Planning of a Large-Scale Miscible Flood at Prudhoe Bay. Journal of Petroleum Technology.
    October, pg.  1103-1110.
                                         122

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Appendix  A   Modification  of Soil Properties

Baver, L. D., W. H. Gardner, and W. R. Gardner. 1972. Soil Physics.  John Wiley and Sons, Inc., New
    York, NY.

Brandt, C. H. 1972. Soil Physical Property Modifiers, pp. 691-729. In:  Organic Chemicals in the Soil
    Environment. Vol. 2. C. A. Goring, and J. W. Hamaker, eds., Marcel Dekker, Inc., New York, NY.

Donnan, W. W., and G. O. Schwab. 1974.  Current Drainage Methods in the U.S.A.  pp. 93-114.  In:
    Proceedings of the First International Symposium on Acid Precipitation and the Forest Ecosystem.
    U.S. Forest Service General Technical Report NE-23, USDA - Forest Service, Upper Darby, PA.

Ehrenfeld, J. R. and J. M. Bass.  1983.  Handbook for Evaluating Remedial Action Technology Plans.
    EPA-600/2-83-076, USEPA Municipal Environmental Research Laboratory, Cincinnati, OH.

Finck, A. 1982.  Fertilizers and Fertilization. Verlog Chemic, Deerfield Beach, FL

Follett, R. H., L. S. Murphy, and R. L. Donahue. 1981. Fertilizers and Soil Amendments. Prentice-Hall,
    Inc.  Englewood Cliffs, NJ.

Frink, C. R., and G. K. Voight. 1976. Potential Effects of Acid Precipitation on Soils in the Humid
    Temperature Zone. pp. 685-709.  In:  Proceedings of the First International Symposium on Acid
    Precipitation and the Forest Service General Technical Report NE-23, U.S. Department of
    Agriculture - Forest Service, Upper Darby, PA.

Fry, A. W., and A. S. Grey. 1971.  Sprinkler Irrigation Handbook. Rain Bird Sprinkler Manufacturing
    Corporation, Glendora, CA.

McLean, E. O. 1982. Soil pH and Lime Requirement,  pp. 199-224. In: Methods of Soil Analysis. Part
    2 - Chemical and Microbiological Properties.  A. L. Page ed. American Society of Agronomy, Inc.,
    Madison, Wl.

Mulder, D. (ed.)  1979.  Soil Disinfection. Elsevier Scientific Publishing Company, Amsterdam.

Nimah, M. H., J.  Ryan, and M. A. Chaudhry. 1983. Effect of Synthetic Conditioners on Soil Water
    Retention, Hydraulic Conductivity, Porosity, and Aggregation. Soil Sci. Soc. Ams. J. 47:742-745.

Raymond, J. L., V. W. Jamison, and J. O. Hudson. 1976. Beneficial Stimulation at Bacterial Activity in
    Groundwaters Containing Petroleum Products.  AICHE, (73)166:390-404.

Schilfgaarde, J. V. 1974. Drainage for Agriculture. Monograph No. 17, Amer. Soc. of Agron., In.,
    Madison, Wl.

Schwab, G. O., R. K. Frevert, T. W. Edminster, and K. K.  Borbes. 1981. Soil and Water Conservation
    Engineering. John Wiley and Sons, New York, NY.

Sims, R. C. and J. Bass. 1984. Review of In Place Treatment Technologies for Contaminated Surface
    Soils - Volume 1, Technical Evaluation.  EPA-540/2-84-003a. U.S. Environmental Protection
    Agency, Cincinnati, OH.
                                         123

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Soil Conservation Service.  1979.  Guide for Sediment Control on Construction Sites in North Carolina.
    U. S. Department of Agriculture, Soil Conservation Service, Raleigh, NC.

Tisdale, S. L, W. L. Nelson, and J. D. Beaton.  1985. Soil Fertility and Fertilizers, 4th Edition.  MacMillan.
    New York, NY.

Turner, J. H., and C. L. Anderson, 1980.  Planning for an Irrigation System.  American Association for
    Vocational Instruction  Materials, Athens, GA.
                                           124

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                                      Bibliography


Alther, G. R., J. C. Evans, and S. E. Pancoski. 1988. Organically Modified Clays for Stabilization of
     Organic Hazardous Wastes.  In:  Superfund '88, Proceedings of the 9th National Conference. The
     Hazardous Materials Control Research Institute, Silver Spring, MD. pp. 440-445.

Anastos, G., M. H. Corbin, andM. F. Coia.  1986. In Situ Air Stripping: A New Technique for Removing
     Volatile Organic Contaminants From Soils.  In: Superfund '86, Proceedings of the 7th National
     Conference on Management of Uncontrolled Hazardous Wastes Sites (HMCRI), Silver Spring, MD.
     pp. 322-324.

Anderson, J. J.,  and J. J. Dulka. 1985. Environmental Fate of Sulfometuron Methyl in Aerobic Soils.  J.
     Agric. Food Chem. 33(4):596-602.

Applegate, J., J. K. Gentry, and J. J. Malot. 1987.  Vacuum Extraction of Hydrocarbons from Subsurface
     Soils at a Gasoline Contamination Site.  In:  Superfund '87, Proceedings of the 8th National
     Conference.  The Hazardous  Materials Control Research Institute, Silver Spring, MD.  pp. 273-279.

Baarschers, W.H., and H. S. Hetiland.  1986.  Biodegradation of Fenitrothion and Fenitrooxon by the
     Fungus Trichoderma Viride. J. Agric. Food Chem.  34(4):707-709.

Bachmann, A., W. de Bruin, J. C. Jumelet, H. H. N. Rijnaarts, and A. J. B. Zehnder. 1987. Aerobic
     Biomineralization of Alpha-Hexachlorocyciohexane in Contaminated Soil. Appl. Environ. Microbiol.
     54(2):548-554.

Barbeni, M., E. Pramauro, and E. Pelizzetti.  1985.  Photodegradation of Pentachlorophenol Catalyzed by
     Semiconductors Particles, Chemosphere.  14(2):195-208.

Barbeni, M., E. Pramauro, and E. Pelizzetti. 1986. Photochemical Degradation of Chlorinated Dioxins,
     Biphenyls Phenols and Benzene on Semiconductor Dispersion, Chemosphere.  15(9-12):1913-
     1916.

Barrio-Lange, G., F. Z. Parsons, R. S. Nassar, and P. Lorenzo.  1986.  Sequential Dehalogenation of
     Chlorinated Ethenes. Environmental Science and Technology.  20(1):96-99.

Barton, M. R., and R. L. Crawford.  1987. Novel Biotransformations of 4-Chlorobiphenyl by  a
     Pseudomonassp. Appli. Environ. Microbial.  54(2):594-595.

Bedard, D. L., R. E. Wagner,  M. J. Brennan, M. L. Haberl, and J. F.  Brown Jr.  1987. Extensive
     Degradation of Aroclors and Environmentally Transformed Polychlorinated Biphenyls  by Alcaligenes
     eutrophusH&SQ. Appl. Environ.  Microbiol. 53:1094-1102.

Behki, R. M., and S. U. Khan. 1986. Degradation of Atrazine by Pseudomonas:  N-Dealkylation and
     Dehalogenation of Atrazine and its Metabolites.  J. Agric. Food. Chem. 34(4):746-749.

Berry, D. F., and S. A. Boyd.  1985. Decontamination of Soil Through Enhanced Formation of Bound
     Residues.  Environmental Science and Technology.  19(11):1132-1133.
                                         125

-------
Bogue, R. H.  1955.  The Chemistry of Portland Cement. 2nd ed., Reinhold Publishing Corp.

Bollag, J. M., and S. Y. Liu.  1983.  Incorporation of Pentachlorophenol Into Humic Acid Polymers by a
    Fungal Laccase. p. 273. In: Abstracts of the Annual Meeting of the ASM. Amer. Soc. Microbiol.,
    Washington, DC.

Bollag, J. M., R. D. Minard, and S. Y. Liu. 1983. Cross-Linkage Between Anilines and Phenolic Humus
    Constituents. Environmental Science and Technology.  17:72-80.

Sort, M.J. 1985.  In Situ Stabilization of Viscoelastic Polymer Waste. In. Management of Uncontrolled
    Hazardous Waste Sites. The Hazardous Materials Control Research Institute, Silver Spring, MD.  pp.
    152-156.

Borup, M. B., and E. J. Middlebrooks. 1986.  Photocatalyzed Oxidation of Organic Wastestreams, In:
    Proceedings of the 18th Mid-Atlantic Waste Conference Boardman, G. D. ed.

Borup, M. B. and  E. J. Middlebrooks.  1987.  Photocatalyzed Oxidation of Toxic Organics.  Wat. Sci. Tech.
    19:381-390.

Bossert, I., W. M.  Kachel, and R. Bartha. 1984. Fate of Hydrocarbons During Soily Sludge Disposal in
    Soil. Appl. Environ. Microbiol.  47(4)763-767.

Bossert, I. D., and L. Y. Young. 1986.  Anaerobic Oxidation of p-Cresol by a Denitrifying Bacterium. Appl
    Environ. Microbiol.  52(5):1117-11120.

Botre, C., A. Memoli, and F. Alhaique. 1978. TCDD Solubilization and  Photodecomposition in Aqueous
    Solutions. Environmental Science and Technology. 12(3):335-336.

Bouwer, E. J., J. P. Wright, and G. D. Cobb.  1986.  Anoxic Transformation of Trace Halogenated
    Aliphatics. In:  Toxic and Hazardous Waste-Proceeding from the 18th Mid-Atlantic Industrial Waste
    Conference. Boardman, G. D. (Ed ).  Technomic Publishing Co., Inc., Lancaster, PA.

Boyd, S. A., C. W. Kao, and J. M. Suflita. 1984. Fate of 3,3'-Dichlorobenzidine In  Soil: Persistence And
    Binding. Environ. Toxicol. Chem. 3:201-208.

Boyer, J.D., R. C. Ahlert, and D.S. Kosson.  1987.  Degradation of 1,1,1-Trichloroethane in Bench-Scale
    Bioreactors. Hazardous Waste  & Hazardous Materials. 4(3):241-260.

Brady, N.C.  1974. The Nature and Properties of Soil. 8th ed.  Macmillan Publishing Company, Inc., New
    York, NY.

Brown, E. J., J. J. Pignatello, M. M. Martison, and R. L. Crawford.  1987. Pentachlorophenol Degradation:
    A Pure Bacterial Culture and an Epilithic Microbiol Consortium. Appl. Environ. Microbiol.  52:92-97.

Brunner, W., F. H. Sutherland, and D. D. Focht. 1984.  Enhanced Biodegradation of Polychlorinated
    Biphenyls in Soil by Analog Enrichment and Bacterial Inoculation. J. Environ. Qual. 14(3):324-328.

Bumpus, J. A., and S. D. Aust. 1985.  Studies on the Biodegradation of Organopollutants by a White Rot
    Fungus. In: Proceed. International Conference on New Frontiers for Hazardous Waste
    Management.  EPA/600/9-85/025, Pittsburgh, PA.

Bumpus, J. A., M. Tien, D.S.Wright.  1985.  Biodegradation of Environmental Pollutants by the White
     Rot Fungus Phanerochaete chrysosporium. In: Proceed, of the 11th Annual Research Symposium
    on Incineration and Treatment of Hazardous Waste. EPA/600/9-85-028, Cincinnati, OH.
                                          126

-------
Bumpus, J. A., and S. D. Aust. 1986. Biodegradation of Chlorinated Organic Compounds by
     Phanerochaete chrysosporium, A Wood-Rotting Fungus. In:  ACS Symposium Series 338:  Solving
     Hazardous Waste Problems, Learning from Dioxins (191st Meeting of the ACS, April 1986). Exner, J.
     H. (Ed.).  ACS, Washington, DC.

Bumpus, J. A., and S. D. Aust. 1987. Mineralization of Recalcitrant Environmental Pollutants by a White
     Rot Fungus.  In:  Proceed, of the National Conference on Hazardous Wastes and Hazardous
     Materials. Hazardous Materials Control Research Institute, Washington.  DC.

Bumpus, J. A., F.Tudor, G. J. Mileski,  and S. D. Aust. 1987. Biodegradation of Organopollutants by
     Phanerochaete chrysosporium: Practical Considerations.  In: Proceed, of the  13th Annual Research
     Symposium on Land Disposal, Remedial Action, Incineration, and Treatment of Hazardous Waste.
     EPA/600/9-87/015, Cincinnati, OH.

Bumpus, J. A., and S. D. Aust. 1987. Biodegradation of DDT [1 ,1 ,1-Trichloro-2,2-Bis(4-
     Chlorophenyl) Ethane] By the White Rot Fungus Phanerochaete chrysosporium. Appl. Environ.
     Microbiol. 53(9):2001-2008.

Bunce, N.J. 1982. Photodechlorination of PCB's:  Current Status. Chemosphere. 11(8):701-714.

Camper, N. D., M.  M. Fleming,  and H. D . Skipper. 1987. Biodegradation of Carbofuran in Pretreated and
     Non-Pretreated Soils. Bull. Environ. Contam. Toxicol. 39:571-578.

Chakrabarty, A. M. 1980. Plasmids and Dissimilation of Synthetic Environmental Pollutants, pp. 21-30.
     In:  Plasmids  andTransposons, Environmental Effects and Maintenance Mechanisms. Stuttard, C.,
     and Rozee, K. R. (eds.). Academic Press, New York, NY.

Chakrabarty, A. M. 1982.  Genetic Mechanisms in the Dissimilation of Chlorinated Compounds, pp. 127-
     139.  In:  Biodegradation and Detoxification of Environmental Pollutants. Chakrabarty, A. M. (ed.).
     CRC  Press, Inc.,  Boca Raton, FL.

Chanmugathas, P., and J. Bollag. 1987. Microbial Mobilization of Cadmium in Soil Under Aerobic and
     Anaerobic Conditions.  J. Environ. Qual.  16(2):161-167.

Chapman, R. A., C.R.Harris, P. Moy, and K. Henning.  1986.  Biodegradation of Pesticides in Soil: Rapid
     Degradation of Isofenphos in a Clay Loam After a Previous Treatment. J. Environ. Sci. Health.
     21(3):269-276.

Chapman, R. A., C.R.Harris, and C. Harris. 1986. Observations on the  Effect of Soil Type, Treatment
     Intensity, Insecticide Formation, Temperature and Moisture on the Adaptation  of Subsequent
     Activity of Biological Agents Associated with Carbofuran Degradation in Soil.  J. Environ. Sci. Health.
Chaudry, R. G., A. N. Ali, and W.B. Wheeler. 1987. Isolation of a Methyl Parathion-Degrading
    Pseudomonas . That Possesses DNA Homologous to the OPD Gene From A Flavobacterium . Appl.
    Environ. Microbiol.  54(2):288-293.

Chaudry, R.G., and A.N. Ali. 1988.  Bacterial Metabolism of Carbofuran. Appl. Environ. Microbiol.
    54(6):1414-1419.

Choudhry, G. G. and B. G. R. Webster.  1985.  Environmental Photochemistry of PCDDs. Part I.  Kinetics
    and Quantum Yields of the Photodegradation of 1,2,3,4,7,8-Hexachlorodibenzo-p-dioxin in
    Aqueous Acetonitrile, Chemosphere.  14(1):9-26.
                                         127

-------
Choudhry, G. G., and G. B. Webster. 1986. Photochemical Quantum Yields and Sunlight Half-Lives of
    Polychlorodibenzo-p-Dioxins in Aquatic Systems, Chemosphere.  15(9-12):1935-1940.

Clapes, P., 1986. Degradation of MCPA by Photochemical Methods, Chemosphere. 15(4):395-401.

Crow, W. L, E. P. Anderson, and E. M. Minugh.  1987. Subsurface Venting of Vapors Emanating from
    Hydrocarbon Production Ground Water. Ground Water Monitoring Review, 7(l):5l-55.

Dev, H., P. Condorelli, J. Bridges, C. Rogers, and D. Downey.  1986.  In Situ Radio Frequency Heating
    Process for Decontamination of Soil. In: Solving Hazardous Waste Problems Learning From Dioxins.
    Division of Environmental Chemistry at the 191 Meeting of the American Chemical Society, New
    York, NY. April 13-18, 1986, pp. 329-339.

DeWeerd, K. A., A. Saxena,  D. P. Nagel Jr., and J. M. Suflita.  1988.  Metabolisms of the 19O-Methoxy
    Substituent of 3-Methoxybenzoic Acid and Other Unlabeled Methoxybenzoid Acids.  Appl. Environ.
    Microbiol.  54(5):1237-1242.

Dial, C. J. 1985. Hazardous Waste Treatment Research, EPA/600/M-85/027, U.S. Environmental
    Protection Agency, Cincinnati, OH.

Dial, C. J., and J. A. Glaser.  1987. Hazardous Waste Detoxification-Science and Technology.
    EPA/600/D-87/291, U. S.  EPA, Cincinnati, OH.

Dial, C. J. 1988. Alternative Treatment Methods for Hazardous Wastes.  In: 1988 Spring Meeting
    American Institute of Chemical Engineers-New Orleans, Louisiana, March 6-10, 1988.

Dobbins, D. C., J. R. Thornton-Manning, D. D. Jones, and T. W. Federle. 1987.  Mineralization Potential
    for Phenol in Subsurface Soils. J. Environ.  Qual. 16(1):54-58.

Dobbs, R. A., and J. M. Cohen. 1980.  Carbon Adsorption Isotherms for Toxic Organics. EPA/600/8-80-
    023. Municipal Environmental Research Laboratory, U.S. Environmental Protection Agency,
    Cincinnati,  OH.

Doelman, P., L. Haanstra, E. de Ruiter, and J. Slange. 1985.  Rate of Microbial Degradation of High
    Concentrations of Alfa-Hexachlorocyclohexane in Soil Under Aerobic and Anaerobic Conditions.
    Chemosphere. 14(5):565-570.

Doyle, R. D. 1979. Use of an Extruder/Evaporator to Stabilize and Solidify Hazardous Wastes.  In: Toxic
    and Hazardous Waste Disposal, Vol.  1, Pojasek, R. B. (ed.).  Ann Arbor Science Publishers, Ann
    Arbor, Michigan, pp. 65-91.

Draper, W. M., and D. G. Crosby.  1984. Solar Photooxidation of Pesticides in Dilute Hydrogen Peroxide,
    J. Agric. Food Chem.  32:231-237.

Drechsler, W. D. 1986.  Destruction of PCDD/PCDF by Non-Thermal Methods, Chemosphere. 15(9-
     12):1529-1534.

Dworkin, D., and M. W. Cawley. 1988.  Aquifer Restoration: Chlorinated Organics Removal
    Considerations in Proven vs. Innovative Technologies.  Environmental Progress. 7(2):99-103.

Eaton, R. G., and M. V. Glaze.  1986.  Gasoline Recovery in Southern Michigan. In: Proceed, of the 41st
     Industrial Waste Conference, May 1986, Purdue University, West Lafayette, Indiana,  pp. 313-318.

Edwards, B. H., J. N. Paullin, K. Coghlan-Jordan.  1985. Emerging Technologies for the Control of
     Hazardous Wastes, J.  Hazard. Materials, 12:201-205.
                                          128

-------
Eisenberg, T. N., E. J. Middlebrooks, and V. D. Adams.  1986. Sensitized Photooxidation of Bromacil: A
    Dye Survey of Potential Photosensitizing Agents, In:  41st Purdue University Industrial Waste
    Conference Proceedings, pp. 325-332.

Electric Power Research Institute. 1987.  Remedial Technologies for Leaking Underground Storage
    Tanks (EPRI CS-5261). Electric Power Research Institute, Palo Alto, CA. p. 288.

Epling, G.  A. and E. Florio. 1986. Enhanced Photodehalogenation of Chlorobiphenyls, Tetrahedron
    Letters. 27(6):675-678.

Epling, G. A., W. McVicar, and A. Kumar.  1987. Accelerated Debromination of Biphenyls by Photolysis
    With Sodium Borohydride, Chemosphere. 16(5):1013-1020.

Fairbanks, B. C., N. E. Schmidt, and G. A. O'Conner.  1985.  Butanol Degradation and Volatilization in
    Soils Amended With Spent Acid or Sulfuric Acid. J. Environ. Qual.  14(1):83-86.

Fathepure, B. Z., J. P. Nengu,  and S. A. Boyd.  1987. Anaerobic Bacteria That Dechlorinate
    Perchloroethene.  Appl.  Environ. Microbiol.  53(11):2671-2674.

Faust, B.C., M. R. Hoffman. 1986. Photoinduced Reductive Dissolution of Alpha-FE2C>3 by Bisulfite.
    Environmental Science and Technology.  20(9):943-948.

Federle, T. W., D. C. Dobbins,  and J. R. Thornton-Manning. 1986. Microbiol Biomass, Activity, and
    Community Structure in Subsurface Soils.  Ground Water. 24(3):365-374.

Fedorak, P. M.,  D. J. Roberts, and S. E. Hrudey.  1986. The Effects of Cyanide on the Methanogenic
    Degradation of Phenolic Compounds. Wat. Res.  20(10):1315-1320.

Flathman,  P. E., and J. A. Caplan. 1986. Cleanup of Contaminated Soil and Groundwater Using Biological
    Techniques.  In: Proceedings of the National Conference on Hazardous Wastes and Hazardous
    Materials-March 4-6,1986. Atlanta, Georgia, pp. 110-119.

Fliermans, C. B., T. J. Phelps, D. Ringelberg, A. T. Mikell, and D. C. White. 1988. Mineralization of
    Trichloroethylene by Heterotrophic Enrichment Cultures. Appl. Environ. Microbiol.  54(7) :1709-
    1714.

Fogel, S.,  R. L. Lancione, and A. E. Sewall. 1982. Enhanced Biodegradation of Methoxychlor in Soil
    Under Sequential Environmental Conditions. Appl. Environ. Microbiol.  44:113.

Francis, A. J., and C. J. Dodge. 1986. Anaerobic  Bacterial Dissolution of Lead Oxide. Arch. Environ.
    Contam. Toxicol.  15:611-616.

Francis, A. J., and C. J. Dodge.  1988.  Anaerobic Microbial Dissolution of Transition and Heavy Metal
    Oxides. Appl. Environ. Microbil.  54(4):1009-1014.

Frankemberger, W. T. Jr., and W. A. Dick.  1988. Use of Urea as a Nitrogen Fertilizer in Bioreclamation of
    Petroleum  Hydrocarbons in Soil.  Bull. Environ. Contam. Toxicol. 40:66-68.

Franklin Institute Research Laboratory, Inc. 1981. The  Franklin Institute Chemical Method for Detoxifying
    Polychlorinated Biphenyls (PCBs) and Other Toxic Waste. Philadelphia, PA.
                                          129

-------
Fu, J. K., and J. R. Smith.  1987.  Evaluation of an Engineered Biodegradation Land Treatment System for
     Soil Decontamination at a Wood Preserving Site. In:  Proceedings of the Second International
     Conference on New Frontiers for Hazardous Waste Management-Sept. 27-30, Pittsburgh, PA.
     EPA/600/9-87/018F.

Furman, C., and S. R. Cochran.  1985.  Case Study Investigations of Remedial Response Programs at
     Uncontrolled Hazardous Waste Sites.  In:  Proceedings of the 11th Annual Research Symposium on
     Incineration and Treatment of Hazardous  Waste.  EPA/600/9-85-028, pp.107-121.

Geldner, P. 1987. Stimulated In Situ Biodegradation of Aromatic Hydrocarbons.  In: Proceed. Second
     International Conference on New Frontiers for Hazardous Waste Management-Sept. 27-30, 1987 -
     Pittsburgh, PA. - EPA/600/9-87/018F.

Gibbs, H. J.  1966, "Research on Electro-reclamation of  Saline-Alkali Soils," Trans. ASAE. 9:164-169.

Gibson,  S. A., and J. M. Suflita.  1986.  Extrapolation of Biodegradation Results to Groundwater Aquifers:
     Reductive Dehalogenation  of Aromatic Compounds.  Appl. Environ. Microbiol. 52(4):681-688.

Glaser, J. A., and P. R. Sferra. 1987. White Rot Fungus Detoxification Research: Status and Directions.
     In:  Proceed. Second International Conference on New Frontiers for Hazardous Waste Management -
     Sept. 27-30, 1987 - Pittsburgh, PA. -  EPA/600/9-87/018F.

Glaser, J. A., and P. R. Sferra. 1988. Biological Detoxification Research:  Potential Uses for a Fungal
     Species.  EPA/600/12 - To be published in the United Nations Environmental Program Newsletter.

Godsy, E. M., D. F. Goerlitz, and G. G. Ehrlich.  1986. Effects of Pentachlorophenol on Methanogenic
     Fermentation of Phenol. Bull. Environ. Contam. Toxicol.  36:271-277.

Gohre, K., R. Scholl, and G. C. Miller.  1986. Singlet Oxygen Reactions on Irradiated Soil Surfaces.
     Environmental Science and Technology.   20(9):934-938.

Goldstein, R. M., L. M. Mallory, and M. Alexander.  1986. Reasons for Possible Failure of Inoculation to
     Enhance Biodegradation. Appl. Environ.  Microbiol.  50(4):977-983.

Grady, C.  P. L. 1985. Biodegradation: Its Measurement and Microbiological Basis. Biotechnology and
     Bioengineering. 27:660-674.

Grady, C.  P. L. Jr. 1986. Biodegradation of Hazardous Wastes by Conventional Biological Treatment.
     Hazardous Waste & Hazardous Materials.  3(4):333-365.

Graveel, J. G., L. E. Sommers, and D. W. Nelson. 1985. Decomposition of Benzidine, Naphthylamine,
     and p-Toluidine in Soils. J. Environ. Qual. 15(1):53-59.

Grbic-Galic, D., and L. Y. Young. 1985. Methane Fermentation of Ferulate and Benzoate: Anaerobic
     Degradation Pathway.  Appl. Environ.  Microbiol. 50(2).-292-297.

Grbic-Galic, D., and T. M. Vogel. 1987. Transformation of Toluene and Benzene by Mixed Methanogenic
     Cultures.  Appl. Environ. Microbiol.  53(2):254-260.

Grosjean, D.  1985.  Reactions of o-Cresol and Nitrocresol with NOX in Sunlight and With Ozone-Nitrogen
     Dioxide Mixtures in the Dark. Environmental Science and Technology. 19(10):968-974.

Guerin,  W. F., and G. E. Jones.  1987.  Mineralization of Phenanthrene by a Mycobacterium. Appl.
     Environ. Microbiol. 54(4):937-944.
                                          130

-------
Gurol, M. D. and R. Vatistas. 1987.  Photolytic Oxidation of Phenols, Wat. Sci. Tech.  19:1177-1180.

Haag, W. R., and T. Mill. 1987. Direct and Indirect Photolysis of Water-Soluble Azodyes: Kinetic
    Measurements and Structure-Activity Relationships, Environmental Toxicology and Chemistry.
    6:359-369.

Haag, W. R.  1984.  Singlet Oxygen in Surface Waters - Part II:  Quantum Yields of its Production by Some
    Natural Humic Materials as a Function of Wavelength, Chemosphere.  13(5/6):641-650.

Haggblom, M. M., J. H. A. Apajalahti, and M. S. Salkinoja-Salonen. 1988.  Hydroxylation and
    Dechlorination of Chlorinated Guaiacols and Syringols by Rhodococcus Chlorphenolicus. Appl.
    Environ. Microbil. 54(3):683-687.

Haigler, B. E., S. F. Nishino, and  J. C. Spain.  1988.  Degradation of 1,2-Dichlorobenzene by a
    Pseudomonas . Appl. Environ. Microbil.  54(2):294-301.

Harsh, K.M. 1978.  In Situ Neutralization of an Acrylonitrile Spill.  In: Proceedings of 1978 Conference on
    Control of Hazardous Materials Spills, April 1978. Miami, FL, Information Transfer Inc., Rockville,
    Maryland pp. 187-189.

Hartman, J. R., C. R. Lange,  M. R. Matsumoto, and A. S. Weber. 1986. Effects of Bioaugmentation of
    Hazardous Waste Treatment. In: Toxic and Hazardous Wastes - Proceedings from the 18th Mid-
    Atlantic Industrial Waste Conference. Bordman, G. D. (ed.), Technomic Pub. Co., Inc. Lancaster, PA.

Harwood, C. S., and J. Gibson. 1988. Anaerobic and Aerobic Metabolism of Diverse Aromatic
    Compounds by the Photosynthetic Bacterium Rhodopseudomonas palustris.  Appl. Environ.
    Microbiol. 54(3) :712-717.

Haugland, R. A., U. M. X. Sangodkar, A. M. Chakrabarty,  P. H. Tomaske,  and P.  R. Sferra.  1987.
    Microbial Degradation of Synthetic Chlorinated Compounds. In:  Proceed, of the  13th Annual
    Research Symposium on Land Disposal, Remedial Action, Incineration and Treatment of Hazardous
    Waste.  EPA/600/9-87/015, pp. 388-394.

Heitkamp, M. A., J. P. Freeman,  and C. E. Cerniglia.  1986.  Biodegradation of tert-Butylphenyl Diphenyl
    Phosphate.  Appl. Environ. Microbiol. 51(2):316-322.

Heitkamp, M. A., J. P. Freeman, and C. E. Cerniglia.  1987.  Naphthalene Biodegradation in
    Environmental Microcosms:  Estimates of Degradation Rates and Characterization of Metabolites.
    Appl. Environ. Microbiol. 53(1):129-136.

Heitkamp, M. A., and C. E. Cerniglia. 1988. Mineralization of Polycyclic Aromatic  Hydrocarbons by a
    Bacterium Isolated from Sediment Below an Oil Field. Appl. Environ. Microbiol. 54(6):1612-1614.

Helsel R. 1987. Technology Demonstration of a Thermal Desorption-UV Photolysis Process for
    Decontaminating Soils Containing Herbicide Orange, In: Solving Hazardous Waste Problems, Exner,
    J. H. ed., ACS Washington,  DC.

Herrmann, J. G. 1989. Status Report on Electro-Kinetics Technology. January 23,1989. Memorandum
    from J. G. Herrmann, U.S. EPA Risk Reduction Engineering Laboratory, Cincinnati, OH to J.
    Kingscott, U.S. EPA Office of Solid Waste and Emergency Response, Washington, DC.

Hill, R. D.  1984. Promising Site Cleanup Technology. EPA/600/D-84-006. U.S. EPA, Cincinnati, OH.
                                         131

-------
Hill, R. D. 1987. The SITE Program: Superfund Innovative Technology Evaluation - New Approaches to
    Cleaning Up Hazardous Waste Sites.  EPA/600/D-87/238, U.S. Environmental Protection Agency,
    Cincinnati, OH.

Hoogendoorn, D. 1984.  Review of the Development of Remedial Action Techniques for Soil
    Contamination in The Netherlands. In:  Proceed, of the 5th National Conference on Management of
    Uncontrolled Hazardous Waste Sites - Nov. 7-9, 1984, Washington, D. C.

laconianni, F. J.,  1985.  Destruction of PCBs-Environmental Applications of Alkali Metal Polyethylene
    Glycolate Complexes. EPA/600/2-85/108.

IT Enviroscience, Incorporated.  1983.  Survey of Industrial Applications of Aqueous-phase Activated
    Carbon Adsorption for Control of Pollutant Compounds from Manufacture of Organic Compounds.
    Prepared for U.S. Environmental Protection Agency.  EPA/600/2-83-034.

Jain, R. K., G. S. Sayler, J. T. Wilson, L. Houston, and D. Pacia. 1987.  Maintenance And Stability of
    Introduced Genotypes in Groundwater Aquifer Materials.  Appl. Environ. Microbiol. 53(5):996-1002.

Jerger, D.E., and P. E. Flathman.  1988. In Situ Bioremediation of Methylene Chloride-Contaminated
    Groundwater Following Physical Treatment. In:  Superfund '88 Proceedings of the 9th National
    Conference. The Hazardous Materials Control Research Institute, Silver Spring, MD.

Jhaveri, V., and A. J.  Mazzacca. 1986. Bio-Reclamation of Ground and Groundwater by In Situ
    Biodegradation.  In: Groundwater Hydrology, Contamination, and Remediation. Khanbilvardi Reze
    M., and John Fillos (Eds.), Scientific Publications Co., Washington, D. C.

Johnson, J. B.; and S. G. Robinson. 1984. Genetic Engineering and New Pollution Control
    Technologies.  Pollution Technology Review No. 106 - Biotechnology Review  No. 3,  Noyes Data
    Co., Park Ridge, N.J.  EPA/600/2-84-037.

Jones, B. M., R. H. Sakaji, and G. C. Daughton. 1985. Effects of Ozonation and Ultraviolet Irradiation on
    Biodegradability of Oil Shale Wastewater Organic Solutes, Wat. Res.  19(11):1421-1428, 1985.

Kaplan, D. L., and A. M. Kaplan.  1985.  Biodegradation of N-Nitrosodimethylamine  in Aqueous and Soil
    Systems.  Appl. Environ. Microbiol. 50(4) :1077-1086.

Kaplan, D. L., P. A. Riley,  D. J. Emerson, and A. M. Kaplan. 1984. Degradation of Ammonium Nitrate
     Propellants in Aqueous and Soil Systems. Environmental Science and Technology.  18(9):694-699.

Khan, S., C. R. Huang, and J. W. Bozzelli.  1985. Oxidation of 2-Chlorophenol Using Ozone and
    Ultraviolet Radiation. Environ. Progr.  4(4):229-238.

Kilbane, J. J., D. K. Chatterjee, and A. M. Chakrabarty. 1983. Detoxification of 2,4,5-
    trichlorophenoxyacetic Acid From Contaminated Soil by Pseudomonas cepacia. Appl. Environ.
     Microbiol.  45:1697-1700.

Kim, C. J., and W. J. Maier. 1986.  Biodegradation of Pentachlorophenol in Soil Environments.  In:
     Proceed, of the 41st Industrial Waste Conference May 13-15,1986 - Purdue University, West
     Lafayette, Indiana.

Kim, C. J., and W. J. Maier. 1986.  Acclimation and Biodegradation of Chlorinated Organic Compounds in
    the Presence of Alternate Substrates. J. Wat. Pollut. Control. Fed.  58(2):157-164.

Kingsbury, G. L. and P. M. Ray.  1986. Reclamation and Redevelopment of Contaminated Land Volume I.
     U.S. Case Studies. EPA/600/2-86/066. U.S. Environmental Protection Agency, Cincinnati, OH.
                                          132

-------
Kleofher, R. D., D. M. Easley, B. B. Mass, Jr., T. G. Deihl, D. E. Jackson, and C J. Wurrey. 1985.
    Anaerobic Degradation of Trichloroethylene in Soil.  Environmental Science and Technology.
    19(3):277-280.

Ko, W. H., and J. L. Lockwood.  1968.  Accumulation and Concentration of Chlorinated Hydrocarbon
    Pesticides by Microorganisms in Soil.  Can. J. Microbiol. 14:1075-1078.

Koltuniak,  D. L.  1986.  In Situ Air Stripping Cleans Contaminated Soil. Chem. Eng.  August 18, pp. 30-
    31.

Kosson, D. S., E. A. Dienemann, and R. C. Ahlert. 1984.  Characterization and Treatability Studies of an
    Industrial Landfill Leachate (KIN-BUC I). In:  Proceed, of the 39th Industrial Waste Conference - May
    8-10, 1984.  Purdue University, West Lafayette, Indiana, pp.  329-341.

Kosson, D. S., and R. C. Ahlert. 1985.  In Situ and On-Site Biodegradation of Industrial Landfill Leachate.
    Environmental Progress.  3(3):176-183.

Kosson, D. S., E. A. Dienemann, and R. C. Ahlert. 1986.  Field Studies  on In Situ Extraction and Soil
    Based Microbial Treatment of an Industrial Sludge Lagoon. In:  Proceed, of the National Conference
    on Hazardous Wastes and Hazardous Materials. Atlanta, Georgia, pp. 102-109.

Kosson, D. S., I. A. Legiec, and R. C. Ahlert. 1987. Remediation of an Industrial Dump Site - A Case
    Study, Part II.  In: Proceed, of the 13th Annual Research Symposium on Land Disposal,  Remedial
    Action, Incineration and Treatment of Hazardous Waste, May 6-8,  1987. EPA/600/9-87/015, pp.
    105-112.

Krause, A., W. G. Hannock, R. D. Minard, A. J.  Freyer, R. C. Honeycutt, H. M. LeBaron, D. L. Paulson,
    Shu-Yen Liu, and J. Bollag. 1985.  Microbial Transformation of the  Herbicide Metolachlor by a Soil.
    J. Agric.  Food Chem. 33(4):584-589.

Kyles, J. H., K. C. Malinowski, and T. F. Stanczyk. 1987.  Solidification/Stabilization of Hazardous Waste.
    A Comparison of Conventional and Novel Techniques.  In:  Toxic and Hazardous Wastes,
    Proceedings of the 19th Mid Atlantic Industrial Waste Conference.  June 21-23, 1987. J. C. Evans,
    ed.

Lai, R., S.  Lai, and S. Shivaji.  Use of Microbes for Detoxification of  Pesticides. CRC Critical Reviews in
    Biotechnology. 3(lssue  1):1-16.

Lamar, R.  T., M. J. Larsen, T. K. Kirk, and J. A. Glaser. 1987. Growth of the White Rot Fungus
    Phaneroschaete chrysosporium in Soil. In:  Proceed, of the 13th Annual Research Symposium on
    Land Disposal, Remedial Action, Incineration and Treatments of Hazardous Waste. EPA/600/9-
    87/015, pp. 419-424.

La Mori, P. N. 1987. In Situ Treatment Process for Removal of Volatile Hydrocarbons From Soils: Results
    of Prototype Test.  In: Proceedings, Second International Conference on New Frontiers for
    Hazardous Waste Management.  EPA/600/9-87/018F, pp. 503-509.  U.S. EPA Hazardous Waste
    Engineering Research Laboratory, Cincinnati, OH.

Lee, M. D., J.  M. Thomas,  R. C. Borden, P. B. Bedient, J. T. Wilson, C. H. Ward. 1988.  Biorestoration of
    Aquifers  Contaminated with Organic Compounds. CRC Critical Reviews in Environmental Control.
    18(lssue 1):29-89.

Lee, M. D., J.  T. Wilson and C. H. Ward. 1987. In Situ Restoration Techniques for Aquifers Contaminated
    with Hazardous Waste. J. Hazard Materials, 14:71-82.
                                          133

-------
Lepore, J. V., D. S. Kosson, and R. C. Ahlert. 1986. Development of an In Situ Biodegradation Process
    for Remediation of a Gasoline Spill.  In: Proceed, of the National Conference on Hazardous Wastes
    and Hazardous Materials, Washington, D. C. pp. 38-43.

Lewis, D. L, and D. K. Gattie.  1988. Prediction of Substrate Removal Rates of Attached Microorganisms
    and of Relative Contributions of Attached and Suspended Communities at Field Sites. Appl.
    Environ. Microbiol. 54(2):434-440.

Liang, L. N., J. L. Sinclair, L. M. Mallory, and M. Alexander.  1982.  Fate in Model Ecosystems of Microbial
    Species of Potential Use in Genetic Engineering. Appl.  Environ. Microbial. 44:708-714.

Lickly, T. L., W. L Rinehart, P. G. Murphy, and C. G. Mendoza. 1984.  Aerobic and Anaerobic Soil
    Degradation of a Hexahalocyclohexane Mixture. Environmental Toxicology and Chemistry, 3:503-
    510.

Lisiecki, J. B. and F. C.  Payne.  1988. Enhanced Volatilization: Possibilities, Practicalities, and
    Performance. Presented At:  The Engineering Foundation Conference, Mercersburg, PA.

Litz, N., H. W. Doering, M. Thiele, and H. P. Blume.  1987. The Behavior of Linear Alkylbenzenesulfonate
    in Different Soils:  A Comparison Between Field and Laboratory Studies. Ecotoxicology and
    Environmental Safety. 14:103-116.

Loper, J. C., C. Chen, and C. R. Dey. 1985. Gene Engineering of Yeast for the Biodegradation of
    Hazardous Wastes. In: Proceed, of the 11th Annual Research Symposium on Incineration and
    Treatment of Hazardous Waste - April 29, May 1, 1985.  EPA/600/9-85-028, pp. 112-119.

Loper, J. C. 1988. Gene Engineering of Yeasts for the Degradation of Hazardous Waste.  Environmental
    Research Brief. EPA/600/M-88/001, U.S. EPA, Cincinnati, OH.

Mahmood, R., and R. C. Sims.  1984. Management of Toxic Organic Compounds in Soil Systems.
    Dissertation Prepared for Utah State University, Dept. of Civil and Environmental Engineering.

Mahmood, R.J. 1989.  Enhanced Mobility of Toxic Organic Compounds in Soil Systems. Ph.D
    Dissertation.  Department of Civil and Environmental Engineering, Utah State  University, Logan, UT.

Marley, M.C. and G. E.  Hoag.  1984. Inducted Soil Venting for Recovery/Restoration of Gasoline
    Hydrocarbons in the Vadose Zone. In:  Proceedings of the NWWA/API Conference on  Petroleum
    Hydro-Carbons and Organic Chemicals in Groundwater. Houston, TX. pp. 473-503.

Materon, L. A., R. M. Weaver,  and F. W. Plapp,  1987. Qualitative Evaluation of the Effect of a Soil
    Detoxicant on Aldicarb Persistence. Bull. Environ.  Contam. Toxicol.,  38:104-108.

Mattigod, S. W., and G. Sposito, and A. L. Page. 1981.  Factors Affecting the Solubility of Trace Metals in
    Soils. In: Chemistry in the Soil Environment.  ASA  Special Publication 40.

McArdle, J. L., M. M. Arozarena, and W. E. Gallagher. 1987. A Handbook  on Treatment of Hazardous
    Waste Leachate.  EPA/600/8-87/006, U. S. EPA, Cincinnati, OH.

McLean, E. O., S. W. Dumford, and F. Coronel.  1966. A Comparison of Several Methods of Determining
    Lime Requirements of Soil. Soil Sci. Soc. Am. Proc. 30:26-30.

Metzer, N., M. Corbin, S. Cullinan.  1987.  In Situ Volatilization (ISV) Remedial System Cost Analysis.
    (AMXTH-TE-CR-87123) U.S. Army Toxic and Hazardous Materials Agency, Edgewood,  Area,
    Aberdeen Proving Ground, MD 21010.
                                         134

-------
Michel, L. J., L E. Macaskie,  and A. C. R. Dean. 1986. Cadmium Accumulation by Immobilized Cells of a
     Citrobacter Using Various Phosphate Donors. Biotechnology and Bioengineering.  28:1358-1365.

Michelsen, D. L., D. A. Wallis,  and F. Sebba.  1984. The Use of a Microdispersion of Air in Water for In Situ
     Treatment of Hazardous Organics.  In:  Proceed,  of the 5th National Conference on Management of
     Uncontrolled Hazardous Waste Sites, Nov. 7-9, 1984, Washington, D. C.

Michelsen, D. L., D. A. Wallis, and S. R. Lavinder.  1985. In Situ Biodegradation of Dispersed Organics
     Using Microdispersion of Air in Water. In:  Management of Uncontrolled Hazardous Waste Sites. The
     Hazardous Materials Control Research Institute, Silver Spring, MD.  pp. 291-298.

Michelsen, D. L., Wallis, D. A. and Sebba, F.  1984.  In Situ Biological Oxidation of Hazardous Organics.
     Env. Prog.  3:103-106.

Michelsen, D. L., A. Foss, and J. W. Smith. 1988.  Microbubble Applications for Hazardous Waste
     Treatment.  In: Superfund '88, Proceedings of the 9th National Conference. The Hazardous
     Materials Control Research Institute. Silver Spring, MD. pp. 455-461.

Michelsen, D. L., J. W. Smith, and J. A. Suggs.  1988.  Use of Colloidal Gas Aphrons for In Situ
     Biodegradation of Contaminated Ground Water.  In: Proceedings of the Fourteenth Annual
     Research Symposium, EPA/9-88/021, May 9-11, 1988. U.S. EPA  Risk Reduction Engineering
     Laboratory, Cincinnati, OH. pp. 203-217.

Mihelcic, J. R., and R. G. Luthy.  1988.  Microbial Degradation of Acenaphthene and Naphthalene Under
     Denitrification Conditions in Soil-Water Systems.  Appl. Environ. Microbiol.  64(5):1188-1198.

Mihelcic, J. R., and R. G. Luthy.  1988.  Degradation of Polycyclic Aromatic Hydrocarbon Compounds
     Under Various Redox Conditions in Soil-Water Systems  Appl. Environ. Microbiol. 54(5):1188-
     1198.

Mikesell, M. D., and S. A. Boyd.  1988.  Enhancement of Pentachlorophenol Degradation in Soil Through
     Induced Anaerobiosis and Bioaugmentation With Anaerobic Sewage Sludge. Environmental
     Science and Technology.  22(12):1411-1414.

Mischgofsky, F. H. and R. Kabos. 1988 General Survey of Site Clearance Techniques:  Trend Towards In
     Situ Treatment.  In: Contaminated Soil '88 Volume 1, Proceedings  of the Second International
     TNO/BMFT Conference on Contaminated  Soil, Hamburg, Federal Republic of Germany, K. Wolf, J.
     van den Brink, F. J. Colon, eds., Kluser Academic Publishers, The  Netherlands, pp. 523-533.

Mitchel, W. R. 1987. Biodegradation of Guanidinium Ion in Aerobic Soil Samples. Bull. Environ. Contam.
     Toxicol. 39:974-981.

Mitchell, J. K. 1976.  Fundamentals of Soil Behavior, John Wiley and Sons, Inc., New York, NY.

Muir, D. C. G., A. L. Yarechewski, R. L. Corbet,  G.  R. Webster,  and A. E. Smith. 1985.  Laboratory and
     Field Studies on the Fate of 1,3,6,8-Tetrachlorodibenzo-p-dioxin in  Soil and Sediments.  J Agric
     Food Chem.  33:518-523.

Mulle, G. J. 1981. Chemical Decomposition of PCBs in Transformer Fluids.  The Acurex Process.  Acurex
     Waste Technologies, Inc., Mountain View, CA.
                                         135

-------
Nadin, L. M., M. J.Schocken,  F. K. Higson, and D. T. Gibson. 1987. Bacterial Oxidation of
    Polychlorinated Biphenyls.  In: Proceed, of the  13th Annual Research Symposium on Land
    Disposal, Remedial Action, Incineration and Treatment of Hazardous Waste. EPA/600/9-87/015,
    pp. 395-402.

Nelson, M. J., S. O. Montgomery, E. J. O'Neill, and P. H. Pritchard. 1986.  Aerobic Metabolism of
    Trichloroethylene by a Bacterial Isolate. Appl. Environ. Microbiol.  52(2):383-384.

Nelson, M. J., S. O. Montgomery, and P. H. Pritchard.  1988. Trichloroethylene Metabolism by
    Microorganisms That Degrade Aromatic Compounds. Appl. Environ. Microbiol.  54(2):604-606.

Nelson, R. C., J. B. Lawson, D. R. Thigpen, and G. L. Stegemeier.  1984. Cosurfactant-Enhanced
    Alkaline Flooding. Fourth Symposium on Enhanced Oil Recovery.  April 15-18, 1984. Tulsa,
    Oklahoma.

Novak, J. T., C. D. Goldsmith, R. E. Benoit, and J. H. O'Brien.  1985.  Biodegradation of Methanol and
    Tertiary Butyl Alcohol in Subsurface Systems. Wat. Sci. Tech. 17:71-85.

Olexsey, R. A., and D. W. Grosse. 1987. EPA's Pilot Scale Studies for Hazardous Wastes. In: Proceed.
    Second International Conference on New Frontiers in Hazardous for Waste Management.
    EPA/600/9-87-018F, U.S. Environmental Protection Agency, Cincinnati, OH.

Olfenbuttel, R.  F., E. Heyse, D. C. Downey, and T. L. Stoddart.  1988. Lessons Learned:  A Basis for
    Future Success. In:  Contaminated Soil '88 Volume 1, Proceedings of the Second International
    TNO/BMFT Conference on Contaminated Soil,  Hamburg,  Federal Republic of Germany, K. Wolf, J.
    van den Brink, F. J. Colon, eds., Kluser Academic Publishers. The Netherlands, pp. 471-479.

Ou, L. T., J. E.  Thomas, K. S.  V. Edvardsson,  P. S. C. Rao, and W. B. Wheeler. 1986. Aerobic and
    Anaerobic Degradation of Aldicarb  in Aseptically Collected Soils. J. Environ. Qual. 15:356-363.

Ou, L. T. 1987. Microbial Degradation of Hydrazine. Bull. Environ. Contam. Toxicol. 39:78-85.

Ou, L. T., and J. J. Street. 1987. Microbial Enhancement of Hydrazine Degradation in Soil and Water.
    Bull. Environ. Contam. Toxicol. 39:541-548.

Oudot, J., P. Fusey, D. E. Abdelouahid,  S. Haloui and M. F. Roquebert.  1987. Degradation Capability of
    Bacteria and Fungi Isolated From a Fuel Contaminated Soil. Can. J. Microbiol. 33:323-243. (In
    French).

Overcash, M. R., and D. Pal.  1979. Design of Land Treatment Systems for Industrial Wastes - Theory and
    Practice.  Ann Arbor Science, Ann Arbor, Ml.

Paris, D. F., and N. L. Wolfe.  1987.  Relationship Between Properties of a Series of Anilines and Their
    Transformation by Bacteria. Appl.  Environ. Microbiol. 53(5):911-916.

Parker, L. V., and T. F. Jenkins.  1986. Removal of Trace-Level Organics by Slow-Rate Land Treatment.
    Wat. Res. 20(11):1417-1426.

Payne, F. C., C. P. Cubbage,  G. L. Kilmer and L. H. Fish. 1986.  In Situ Removal of Purgeable Organic
    Compounds from Vadose Zone Soils. Presented at Purdue Industrial Waste Conference
    Proceedings, West Lafayette, Indiana. May 14. pp. 365-369.

Pennington, D. 1985. Overview of Chemical In Situ Treatment.  In: Management of Uncontrolled
    Hazardous Wastes Sites. The Hazardous Materials Control Institute, Silver Spring, MD. pp. 253-254.
                                          136

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Pignatello, J. J. 1986. Ethylene Dibromide Mineralization in Soils Under Aerobic Conditions. Appl.
    Environ. Microbiol. 51(3):588-592.

Pillie, R. J., R. E. Baier, R. C. Ziegler, R. P. Lenard, J. C. Micholovic, S. L. Pek, and P. H. Bock. 1975.
    Methods to Treat, Control, and Monitor Spilled Hazardous Materials.  EPA/670/2-75/042.

Podoll, R. T., H. M. Jaber, T. Mill.  1986.  Tetrachlorodibenzodioxin:  Rates of Volatilization and Photolysis
    in the Environment.  Environmental Science and Technology. 20(5):490-492.

Puglinonesi, P. S., J. Kesari, M. H. Corbin, and E. B. Hangeland. 1987. Heavy Metals-Contaminated Soils
    Treatment. In:  Supertund '87, Proceedings of the 8th National Conference. The Hazardous
    Materials Control Research Institute, Silver Spring, MD.  pp. 380-384.

Rajagopal, B. S., S. Panda, and N. Sethunathan.  1986. Accelerated Degradation of Carbaryl and
    Carbofuran in a Flooded Soil Pretreated with Hydrolysis Products, 1-Naphthol and Carbofuran
    Phenol. Bull. Environ. Contam. Toxicol. 36:827-836.

Regalbuto, D. P., J. A. Barrera and J. B. Liziecki. 1988. In Situ Removal of VOC by Means of Enhanced
    Volatilization. In:  Proceedings of the Conference on Petroleum Hydrocarbons and Organic
    Chemicals in Ground Water: Prevention, Detection, and Restoration.  Houston, Texas. National
    Water Well Association Dublin, OH.

Rice, C. W., P.  E. Sierzega, J. M. Tiedje, and L. W. Jacobs. 1988. Stimulated Denitrification in the
    Microenvironment of a Biodegradable Organic Waste Injected Into Soil.  Soil Sci. Soc. Am. J.  52:102-
    108.

Rosenberg, A.  1984. 2,3,6-Trichlorophenylacetic Acid (FENAC) Degradation in Aqueous and Soil
    Systems.  Bull.  Environ. Contam. Toxicol. 32:383-390.

Roulier, M. 1989. In Place Treatment of Contaminated Soil at Superfund Sites: A Review. In: Remedial
    Action, Treatment and Disposal of Hazardous Waste, Proceedings of the Fifteenth Annual Research
    Symposium, Cincinnati, OH.

Roux, P. H. 1985.  Impact of Site Hydrogeology on In Situ Remediation Strategies. In:  Proceeding-
    HAZPRO '85, Young, R. A., ed., Pudvan Publishing, Northbrook, III.

Roy, D., and S. Mitra. 1986. Biodegradation of Chlorophenoxy Herbicides.  In: Proceed, of the 12th
    Annual Research Symposium on Land Disposal, Remedial Action, Incineration and Treatment of
    Hazardous Waste. EPA/600/9-86/022, pp. 454-461.

Saber, D. L., and R. L. Crawford. 1986. Isolation and Characterization of Flavobacterium Strains That
    Degrade Pentachlorophenol. Appl.  Environ. Microbiol.  50(6):1512-1518.

Sanning, D. E.  1985. In Situ Treatment (Chapter 4). In: Contaminated Land: Reclamation and Treatment
    - Smith, M. A. (Ed.), NATO/CCMS, Vol. 8, Plenum Press, New York, NY.

Sanning, D. E., and R. D. Hill. 1988.  NATO/CCMS Pilot Study on Demonstration of Remedial Action
    Technologies for Contaminated Land and Groundwater - August 1988 Update of Activities.
    Presented at UNESCO Workshop on "Impact of Waste Disposal on Groundwater and Surface Water."
    Copenhagen, Denmark.

Santillan-Medrano, J., and J. J. Jurinak. 1975. The Chemistry of Lead and Cadmium in Soil  Solid Phase
    Formation. Soil Sci. Soc. Am. J. 39:851-856.
                                         137

-------
Scheunert, I., D. Vockel, J. Schmitzer, and F. Koerte.  1987.  Biomineralization Rates of 14C-Labeled
    Organic Chemicals in Aerobic and Anaerobic Suspended Soil. Chemosphere.  16(5):1031-1041.

Scheunert, I., D. Vockel, M. E. Bahig, and F. Korte.  1987.  Influence of Atrazine on the Mineralization of
    n-Docecylbenzene-Sulfonate '14CinSoil. Chemosphere.  16(7):1521-1526.

Schroeff, J. Avander.  1985.  Rehabilitation of a Waste Dump Site. Wat.  Sci. Tech. 17(8-L):1399-1402.

Schwefer, H. J.  1988.  Latest Development of Biological !n Situ Remedial Action Techniques, Portrayed
    by Examples from Europe and USA. 1988. In:  Contaminated Soil '88 Volume 1, Proceedings of the
    Second International TNO/BMFT Conference on Contaminated Soil, Hamburg, Federal Republic of
    Germany, K. Wolf, J. van den Brink, F. J. Colon, eds., Kluser Academic Publishers, The Netherlands,
    pp. 687-694.

Scow, K. M., S. Simkins, and M. Alexander. 1986. Kinetics of Mineralization of Organic Compounds at
    Low Concentrations in Soil.  Appl. Environ. Microbiol.  51(5):1028-1035.

Segall, B. A., C. E. O'Bannon, and J. A Mathias.  1980. Electroosmosis Chemistry of Water Quality, J. of
    Geotechnical Division, ASCE.  106(GT10):1148-1152.

Shanker, R., C. Ramakrishna and P. K. Seth. 1985.  Degradation of Some Phthalic Acid Esters in Soil.
    Environmental Pollution (Series A) 39:1-7.

Shannon, M. J. R., and R. Bartha.  1988.  Immobilization of Leachable Toxic and Soil Pollutants by Using
    Oxidative Enzymes. Appl. Environ. Microbiol. 54(7):1719-1723.

Shin, Y., J. J. Chodan, and A. R. Wolcort. 1970. Adsorption of DDT by Soils, Soil Fractions, and Biological
    Materials. J. Agr. Food Chem.  18:1129-1133.

Shuckrow, A. J., A. P. Pajak, and C. J. Touhill. 1986.  Groundwater and Leachates Treatability Studies at
    Four Superfund Sites.  EPA/600/92-86/029.  U. S. EPA, Cincinnati, OH.

Sims, G. K., and L. E. Sommers.  1985. Degradation of Pyridine Derivatives in Soil. J. Environ. Qual.
    14(4):580-584.

Sims, G. K.,  and L. E. Sommers.  1986. Biodegradation of Pyridine Derivatives in Soil Suspensions.
    Environ. Toxicol. & Chem. 5:503-509.

Sims, G. K.,  L. E. Sommers, and A. Konopka. 1986.  Degradation of Pyridine by Micrococcus luteus
    Isolated From Soil. Appl. Environ. Microbiol.  51(5):963-968.

Sims, R. C.,  1986.  Waste/Soil Treatability Studies for Four Complex Industrial Wastes: methodologies
    and Results, Vol. 2, Waste Loading Impacts on Soil Degradation, Transformation. EPA/600/6-
    86/003b.  U. S. EPA, Cincinnati, OH.

Sims, R. C.,  and J. L Sims.  1986.  Cleanup on Contaminated Soils. In: Proceed, of the Workshop on
     Utilization, Treatment, and Disposal of Waste  on Land,  Chicago, IL. Soil Sci. Soc. of America, Inc.,
     Madison, Wl.,  pp. 257-277.

Sinton, G. L., L. E. Erickson, and L. T. Fan. 1987. The Effect of pH on 2,4-D Biodegradation.  In:
     Proceed. Second International Conference on New Frontiers for  Hazardous Waste Management.
     EPA/600/9-87/018F, Pittsburgh, PA.

Skinner, J. H.  1987.  Innovative Technologies Get Superfunds.  Waste Age, Oct. 1987, pp. 34-42.
                                          138

-------
Smith, J. A., and J. T. Novak.  1987.  Biodegradation of Chlorinated Phenols in Subsurface Soils. Water,
    Air, and Soil Pollution. 33:29-42.

Smith, J. W., and L. W. Moore. 1984. Biological Detoxification of Hazardous Wastes.  Tennessee Water
    Resources Research Center, Knoxville, Tennessee, USGS, Reston VA.

Smith, R. L., D.T. Musser and T.J. DeGrood.  1985.  In Situ Solidification/Fixation of Industrial Wastes.  In:
    Management of Uncontrolled Hazardous Waste  Sites. The Hazardous Materials Control Research
    Institute, Silver Spring, MD.  pp. 231-233.

Soczo, E. R., J. J. M. Slaps.  1988.  Review of Biological Soil Treatment Techniques in The Netherlands.
    In:  Contaminated Soil '88 Volume 1.  Proceedings of the Second International TNO/BMFT
    Conference on Contaminated Soil, 11-15 April 1988, Hamburg, Federal  Republic of Germany, K.
    Wolf, J. van den Brink, F. J. Colon, eds., Kluser Academic Publishers, The Netherlands, pp. 663-
    670.

Spain, J. C., and S. F. Nishino. 1987. Degradation of 1,4-Dichlorobenzene by a Pseudomonas . Appl.
    Environ.  Microbiol. 53(5):1010-1019.

Spain, J. C., and D. T. Gibson. 1988. Oxidation of Substituted Phenols by Pseudomonas putida F1 and
    Pseudomonas . Strain JS6.  Appl. Environ. Microbiol.  54(6):1399-1404.

Stanczyk, T. F., B. C. Senfelder, and J. H. Clarke.  1982.  Solidification/Stabilization Process Appropriate
    to Hazardous Chemicals and Waste Spills. In: 1982 Hazardous Materials Spills Conference,
    Government Institute Inc., Rockville, Maryland,  pp. 79-84.

Stinson, M. K., and S. Sawyer. 1988. In Situ Treatment of PCB-Contaminated Soil. In: Superfund'88.
    Proceedings of the 9th National Conference. The Hazardous Materials Control Research Institute,
    Silver Spring, MD. pp. 504-507.

Stoddart, T. L. 1986. Demonstration of Innovative Remedial Action Technologies at United States Military
    Dioxin Contaminated Sites, Chemosphere.  15(9-12):1535-1541.

Stow, S. H., C. S. Hasse, and  H. O. Weeren. 1985. Waste Disposal by Hydrofracture and Application of
    the Technology to the Management of Hazardous Wastes.  International Conference on New
    Frontiers for Hazardous Waste Management. EPA/600/9-85/025 p. 138. RREL, ORD, Cincinnati,
    OH.

Subba-Rao, R. V. and M. Alexander. 1985. Bacterial and Fungal Cometabolism of 1,1,1-Trichloro-2,2-
    bis(4-Chlorophenyl)Ethane (DDT) and its Breakdown Products. Appl. Environ. Microbiol.  49(3):509-
    516.

Suflita, J. M. and S. A. Gibson. 1984. Biodegradation of Haloaromatic Substrates in a Shallow Anoxic
    Ground Water Aquifer. In:  Proceed, of the Second International Conference on Ground Water
    Quality Research -1984, Stillwater, OK., pp. 30-32.

Suflita, J. M., J. Stout, and J.  M. Tiedje.  1984. Dechlorination of (2,4,5-Trichlorophenoxy) Acetic Acid by
    Anaerobic Microorganisms. J. Agric. Food Chem. 32:218-221.

Suflita, J. M. 1985. Development of  Microbial Dehalogenating Enzymes for the Detoxification of Industrial
    Wastes.  DOE/CB40658-T1 Final Report.

Sundstrom D. W. 1986. Destruction of Halogenated  Aliphatics by Ultraviolet Catalyzed Oxidation with
    Hydrogen Peroxide, Hazardous Waste & Hazardous Materials, Volume 3, Number 1.
                                         139

-------
Swindell, C. M., C. M. Aelion, and F. K. Pfaender. 1988. Influence of Inorganic and Organic Nutrients on
    Aerobic Biodegradation and on the Adaptation Response of Subsurface Microbial Communities.
    Appl.  Environ. Microbiol.  54(1):212-217.

Taeger, K., H. J. Knackmuss, and E. Schmidt. 1988. Biodegradability of Mixtures of Chloro- and Methyl-
    substituted Aromatics:  Simultaneous Degradation of 3-Chlorobenzoate and 3-Methylbenzoate.
    Appl.  Microbiol. Biotechnol.  28:603-608.

Tames, R.  S., and R. J. Hance. 1969.  The Adsorption of Herbicides by Roots.  Plant and Soil. 30:221-
    226.

Terry, R. E., and J. M. Duxbury. 1985.  Acetylene Decomposition in Soils.  Soil Sci. Soc. Am. J. 49:90-94.

Thomas, J. M., M. D. Lee, P. B. Bendient,  R. C. Borden, L. W. Canter, and C. H. Ward. 1987. Leaking
    Underground Storage Tanks:  Remediation With Emphasis on In Situ Biorestoration.  EPA/600/2-
    87/008.

Tittlebaum, M. E. 1985. State of the Art on Stabilization of Hazardous Organic Liquid Wastes and
    Sludges. CRC Critical  Reviews in Environmental Control, 15(2):  191-193.

Tobin, J. M., D. G. Cooper, and R. J. Neufeld. 1984. Uptake of Metal Ions by Rhizopus arrhizus Biomass.
    Appl.  Environ.  Microbiol.  47(4):821-824.

Tomasek,  P. H. and A. M. Chakrabarty. 1985. Bacterial Degradation of Chlorinated Compounds. In:
    Proceed, of the 11th Annual Research Symposium on Incineration and Treatment of Hazardous
    Waste.  EPA/600/9-85-028, pp. 127-134.

Tundo, P.  1985. Chemical Degradation of 2,3,7,8-TCDD By Means of Polytheyleneglycols in the
    Presence of Weak Bases and an Oxidant, Chemosphere.  14(5):403-410.

Unterman, R., D. L.  Bedard, L. H. Bopp, M. J. Brennan, C. Johnson, and M. L. Haberl.  1985.  Microbia!
    Degradation of Polychlorinated Biphenyls. In: Proceed. International Conference on New Frontiers
    for Hazardous  Waste Management.  EPA/600/9-85-025, Pittsburgh, PA.

Unterman, R., F. J. Mondello, M. J. Brennan, R. E. Brooks, D. P. Mobely, J. B. McDermott, and C. C.
    Schwartz.  1987. Bacterial Treatment of PCB-Contaminated Soils:  Prospects for the Application of
    Recombinant DNA Technology. In:  Proceed. Second International Conference on New Frontiers for
    Hazardous Waste Management.   EPA/600/9-87/018F, Pittsburgh, PA.

Urlings, L.  G. C. M., V. P. Ackerman, J. C. v. Woudenberg, P. P. v.d. Pijl, and J. J. Gaastra.  1988. In Situ
    Cadmium Removal - Full-Scale Remedial Action of Contaminated Soil.  In:  Contaminated Soil '88
    Volume 1, Proceedings of the Second International TNO/BMFT Conference on Contaminated Soil,
    Hamburg, Federal Republic of Germany, K. Wolf, J. van den Brink, F. J. Colon, eds., Kluser Academic
    Publishers, The Netherlands, pp. 911-920.

U. S. Environmental Protection Agency.  1988. Assessment of International Technologies for Superfund
    Applications: Technology Review and Trip Report Results. EPA/540/2-88/003.  U.S. EPA Office of
    Solid Waste Emergency Response, Cincinnati, OH.

U. S. Environmental Protection Agency. 1988. Cleanup of Releases from Petroleum USTs: Selected
    Technologies.  EPA/530/UST-88/001.  U.S. EPA Office of Underground Storage Tanks,
    Washington, DC.

U. S. Environmental Protection Agency. 1988. Technology Screening Guide for Treatment  of CERCLA
    Soils and Sludges.  EPA/540/2-88/004. OSWER/OERR, Washington, DC.
                                         140

-------
U. S. Environmental Protection Agency.  1989. Demonstration Bulletin:  In Situ Soil Stabilization,
    International Waste Technology. EPA/540/M5-89/004.  RREL, Cincinnati, OH.

U. S. Environmental Protection Agency.  1989. SITE Demonstration Bulletin:  In Situ Vacuum Extraction,
    Terra Vac. Inc. EPA/540/M5-89/003.  RREL, Cincinnati, OH.

U. S. Environmental Protection Agency.  1989. Superfund Technology Evaluation (SITE) Program.
    EPA/540/8-89/002, Cincinnati, OH.

Van Olphen, H. 1963. An Introduction to Clay Colloid Chemistry, John Wiley and Sons, New York.

Van Tassel, R., and P. N. LaMori. 1987. Innovative In Situ Soil Decontamination System. In:  Superfund
    '87, Proceedings of the 8th National Conference. The Hazardous Materials Control Research
    Institute, Silver Spring, MD.  pp. 396-402.

Vernese, F. J., A. P. Schechter, and T. Helgason. Design and Installation of a Groundwater
    Interceptor/Collection Trench and Treatment System. In: International Conference on New Frontiers
    for Hazardous Waste Management. USEPA-HWERL, Cincinnati, OH. EPA/600/9-85/025, p. 145.

Verhuel, J. H. A. M., R. van den Berg, and D. H. Eikelboom. 1988. In  Situ Biorestoration of a Subsoil
    Contaminated With Gasoline. In: Contaminated Soil '88 Volume 1, Proceedings of the Second
    International TNO/BMFT Conference on Contaminated Soil, Hamburg, Federal Republic of Germany,
    K. Wolf, J. van den Brink, F. J. Colon, eds., Kluser Academic Publishers, The Netherlands, pp. 705-
    715.

Vogel, T. M., and P. L McCarty. 1985. Biotransformation of Tetrachloroethylene to Trichloroethylene,
    Dichloroethylene, Vinyl Chloride, and Carbon Dioxide Under Methanogenic Conditions.  Appl.
    Environ. Microbiol. 49:1080-1083.

Vogel, T. M., and P. L. McCarty.  1986. Abiotic and Biotic Transformations of 1,1,1-Trichloroethane
    Under Methanogenic Conditions. Environmental Science  and Technology.  21(12):1208-1213.

Wang, Y., M. T. Suidan, and J. T. Pfeffer. 1984. Anaerobic Biodegradation of Indole to Methane. Appl.
    Environ. Microbiol. 48(5):1058-1060.

Wang, Y., M. T. Suidan,  J. T. Pfeffer,  and I. Najm. 1988. Effects of Some Alkyl Phenols on
    Methanogenic Degradation of Phenol. Appl. Environ. Microbiol. 54(5):1277-1279.

Weber, S. A., and M.  R. Matsumoto.  1986.  Feasibility of Intermittent Biological Treatment for Hazardous
    Wastes. Environmental Progress.  6(3):166-171.

Weber, S. A., and M.  R. Matsumoto.  1985.  Intermittent Biological Treatment of Hazardous Waste
    Biotreatment-Proceedings of the 17th Mid-Atlantic Industrial Waste Conference.  Kugelman, I. J.
    (Ed.). Technomic Pub. Co.,  Inc.  Lancaster, PA.

Weber, S. A., M. R. Matsumoto, and J. G. Goeddertz. 1986.  Effect of Extended Idle Periods on
    Hazardous Waste Biotreatment.  In: Toxic and Hazardous Wastes-Proceedings of the 18th Mid-
    Atlantic Industrial Waste Conference.  Boardman, G. D. (Ed.).  Technomic Pub. Co., Inc.

Weir, B. A., D. W. Sundstrom, and H. E.  Klei. 1987.  Destruction of Benzene by Ultraviolet Light-
    Catalyzed Oxidation with Hydrogen  Peroxide,  Hazardous Waste and Hazardous Materials. 4(2):165-
    176.
                                         141

-------
Wentz, J.A. 1989. Results and Preliminary Economic Analysis of An KPEG Treatment System for
    Degrading PCBs in Soil. In: Remedial Action, Treatment and Disposal of Hazardous Waste,
    Proceedings of the Fifteenth Annual Research Symposium, Cincinnati, OH.

Werner,  P. and H. J. Brauch. 1988. Aspects on the In Situ and On Site Removal of Hydrocarbons From
    Contaminated Sites by Biodegradation.  In: Contaminated Soil '88 Volume 1, Proceedings of the
    Second International TNO/BMFT Conference on Contaminated Soil, Hamburg, Federal Republic of
    Germany, K. Wolf, J. van den Brink, F. J. Colon, eds., Kluser Academic Publishers, The Netherlands,
    pp. 695-704.

White, D. C., J. R. Dunckel and T. D. Van Epp.  1986.  Applying Alternative Technologies at Superfund
    Sites.  In:  Management of Uncontrolled Hazardous Waste Sites.  The Hazardous Materials Control
    Research Institute, Silver Spring, MD. pp. 361-364.

Wiles, C. 1987. Perspectives on Solidification/Stabilization Technology for Treating Hazardous Waste.
    EPA 600/D-87/027.  U.S. Environmental Protection Agency, Hazardous Wastes Engineering
    Research Laboratory, Cincinnati, OH.

Yong, R. N., and D. Mourato.  1987. Stimulation of Microbial Degradation in a Jet Fuel Contaminated Soil
    In:  Proceed. Second International Conference on New Frontiers for Hazardous Waste Management -
    Sept. 27-30, 1987.  Pittsburgh, PA. EPA/600/9-87/018F. Washington DC.

Zeyer, J., P. R. Lehrbach, and K. N. Timmis.  1986.  Use of Cloned Genes of Pseudomonas Tol Plasmid to
     Effect Biotransformation of Benzoates to cis-Dihydrodiols and Catechols by Escherichia co//Cells.
    Appl. Environ. Microbiol.  50(6):1409-1413.
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                                        Appendix A
                             Modification of Soil Properties
Introduction
       Implementation of in situ treatment techniques for contaminated soils often involves the modifi-
cation of soil properties.  Biological degradation, for example, can be enhanced by the addition of
nutrients, and immobilization of heavy metals may require adjustment of soil pH. Soil properties dis-
cussed in this section include
       • Oxygen content
       • Moisture content
       • Nutrient content
       • pH
       • Temperature

This section emphasizes the mechanics of soil property modification, independent of the treatment
technology.  Table A-1 lists the technologies of Section 3, indicating which soil properties may require
modification as a part of treatment.

Control of Oxygen Content
       Oxygen content in surface soils can be  increased primarily through the use of tillage equipment
which breaks, mixes, and aerates the soil.  Alternatively, oxygen content can be decreased by compac-
tion or increased moisture content. Aeration of subsurface soils not accessible to tillage equipment can
be accomplished using construction equipment, such as a backhoe, or using a well point injection
system.

       A variety of tilling equipment is available to aerate surface soils. Tilling equipment can also be
used to mix wastes or reagents into the soil. Choice of equipment depends on the amount of soil
disturbance or mixing desired, and on site characteristics such as the rockiness of the soil.

       For some processes, such as anaerobic biological degradation, surface soil compaction may be
desirable.  By reducing pore sizes and restricting reaeration, anaerobic microsite frequency in the soil
will increase. Compaction helps  draw moisture  to the soil surface. Thus, the problems of leaching that
may occur if anaerobiosis were achieved by water addition would be lessened.  If the compaction itself
were not adequate to achieve the required degree of anaerobiosis, water could be added.  Less water,
however, should be required in a compacted soil than in an uncompacted soil; thereby minimizing the
leaching potential. Volatilization may also be suppressed by surface soil compaction.

       Aeration of soils deeper than about 2 feet can be accomplished by air injection through well
points. In one case, air was injected into a series of 10 wells using diffusers attached to paint sprayer-
type compressors. They delivered about 2.5 cfm to enhance microbial degradation.  Various nutrients
were added simultaneously. The diffusers were positioned 5 feet from the bottom of the well and below
the water table (Raymond et at. 1976).  Aeration through well points has been primarily used for satu-
rated soils and has been shown to be effective.  Applicability of the technique for unsaturated soils is not
certain.
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Table A-1.  Soil Modification Requirements For Treatment Technologies*
Oxygen Moisture Nutrient
Technology content content content
Soil flushing
Solidification/stabilization
Pozzolan-portland cement - x
Lime-fly ash - x
Thermoplastic microencapsulation - x
Sorption - x
Vitrification - x
Degradation
Chemical degradation
Oxidation
Soil-catalyzed reactions x
Oxidizing agents x
Reduction
Reducing agents x x
Chromium x
Selenium x
Dechlonnation - x
Polymerization
Biodegradation
Colloidal gas aphrons x
Soil moisture - x
Soil oxygen-aerobic x
Soil oxygen-anaerobic x x
SoilpH - - x
Nutnents - - x
Temperature - x
Nonspecific org
amendments
pH
x
x
X
X
X
X
X
X
X
-
-

Tempera-
ture
x
-
-
X
-
X
X
 Cometa holism
  Analogue enrichment              -                 -                 x                 -                 x
  Nonanalogue enrichment
    with methane                    x                 -                 x                 -                 x
  Other nonanalogue hydro-
    carbon enrichment               -                 -                 x                 -                 x

 Exogenous acclimated
  or mutant microorganism            -                 -                 x                 -                 x

 Cell-free enzymes                  -                 -                 -                 -                 x

 Photolysis
  Proton donors                    -
  Enhanced volatilization             -                 x                 -                 -                 -

Control of volatile materials

Soil vapor extraction                 -                 x                 -                 -                 -
Radio frequency heating              -                 x                 -                 -                 -
Soil cooling                         -                 x                 -                 -                 x

Chemical and physical
 separation
  Permeable barriers                 -                 -                 -                 x                 -
  Electrokinetics                    -                 x                 -                 x                 -
  Ground freezing                                      x                 -                 -                 x
                                                       144

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Moisture Control

       Control of moisture content of soils at an in situ treatment site may be essential for control and
optimization of some degradative and sorptive processes, as well as for suppression of volatilization of
some hazardous constituents.  Moisture control may take the form of supplemental water to the site
(irrigation), removal of excess water (drainage, well points), and a combination of techniques for greater
moisture control, or other methods, such as soil additives.

Irrigation

       Irrigation may be accomplished by  subirrigation, surface irrigation, or overhead (sprinkler)
irrigation (Fry and Grey 1971).

       With subirrigation, water is applied  below the ground surface and moves upward by capillary
action. If the water has high salinity, salts may accumulate in the surface soil, resulting in an adverse
effect on soil microbiological activity. The site must be nearly level and smooth, with either a natural or
perched water table, which can be maintained  at a desired elevation. The ground water is regulated by
check dams and gates in open ditches, or jointed perforated pipe to maintain the water level in soil. The
use of such systems  is limited by the restrictive site criteria. There may be situations in which a subirri-
gation system may be combined with a drainage system to optimize  soil moisture content. However, at
a hazardous waste site, raising the water table might result in undesirable ground-water contamination.

       Trickle irrigation is a system of supplying filtered water directly on or below the soil surface
through an extensive pipe network with low flow-rate outlets only to areas which require irrigation. It
does not give uniform coverage to an area, but with proper management, does reduce percolation and
evaporation losses. For most in situ treatment sites, this method would probably not be appropriate, but
it may find application in an area where only "hot spots" of wastes are being treated.

       Surface irrigation includes flood, furrow, or corrugation irrigation. Since the prevention of off-site
migration of hazardous constituents to ground or surface waters is a primary restraint on in situ treat-
ment technology, the use of surface irrigation should be viewed with  caution.  Contaminated water may
also present a hazard to on-site personnel.

       In flood irrigation, water covers the surface of a soil in a continuous sheet.  Theoretically, water
should stay at every point just long enough to apply the desired amount,  but this is difficult or impossible
to achieve under field conditions.

       In corrugation irrigation, as with furrow irrigation, water is applied in small furrows from a head
ditch. However, in this case, the furrows are used only to guide the water, and overflooding of the
furrows can occur.
       In general, control and uniform application of water is difficult with surface irrigation. Also, soils
high in clay content tend to seal when water floods the surface, limiting water infiltration.

       The basic sprinkler irrigation system consists of a pump to move water from the source to the
site, a pipe or pipes leading from the pump to the sprinkler heads, and the spray nozzles. Sprinkler
irrigation has many advantages. Erosion and runoff of irrigation water can be controlled or eliminated,
application rates can be adjusted for soils of different textures, even within the same  area, and water
can be distributed more uniformly. Irrigation is also possible on steep, sloping land and irregular terrain.
Usually less water is  required than with surface flooding methods, and the amount  of water applied can
be controlled to meet the needs of the  in situ treatment technique.

       There are several types of sprinkler irrigation systems:

       •  Permanent installation with buried main and lateral lines.

       •  Semi-permanent systems with fixed  main lines and portable laterals.

       •  Fully portable systems with portable main lines and laterals, as well as portable pumping
         plant.
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The first two types (especially the first) would likely not be appropriate nor cost-effective for a hazardous
waste site because of the required land disturbance for installation and the limited time period for
execution of the treatment.

       The fully portable systems may have hand-moved or mechanically moved laterals. To eliminate
movement by hand, the system may have enough laterals to cover the whole area (a solid set system).
Portable systems can be installed in such areas as forests in pattern such as to avoid interfer
ence with trees.  Mechanically moved laterals may be divided into three categories: side-roll wheel
move; center pivot systems; and traveling sprinklers.  The amount of labor is considerably reduced com-
pared to portable systems, but the cost of the equipment is higher. The health and safety of workers,
however, must be considered as well as cost in the choice of an appropriate system.

       The side-roll wheel move is a lateral suspended on a series of wheels.  The unit is stationary
during operation  and is moved while shut off by an engine mounted at the center of the line or an
outside power source at one end of the line.  A variation of this system is a continuous travel wheel with
a flexible hose, which remains in operation as the wheel moves across the field.

       The center pivot system is a pipeline suspended above ground with various sized sprinklers
spaced along its  length.  The system is self-propelled and continuously rotates around a pivot point.

       The traveling sprinkler consists of a single gun sprinkler mounted on a portable, wheeled unit
which is self-propelled up and down the length  of the field.

       The choice of an appropriate irrigation  system depends on site conditions, costs, and health  and
safety considerations for both on-site personnel and off-site populations. The system should be de-
signed by a qualified specialist such as an agricultural engineer. Preliminary guidelines for designing an
irrigation system can  be found in the Sprinkler Irrigation Handbook (Fry and Grey 1971) and  Planning
for an Irrigation System (Turner and Anderson  1980). The latter publication discusses sources of water,
including legal rights, and methods of determining irrigation costs, in addition to technical aspects of
irrigation.

Drainage

        A properly designed drainage system removes excess water and lowers the ground-water level
to prevent waterlogging. Surface drainage is accomplished by open ditches and lateral drains, while
subsurface drainage is accomplished by a system of open ditches and buried tube drains into which
water seeps by gravity. The collected water is  conveyed to a suitable disposal point. Subsurface
drainage may also  be accomplished by pumping from wells to lower the water table. Caution is required
at a hazardous waste site to ensure that drainage water disposed off site is  not contaminated with
hazardous substances.  Provision must be made to collect, store, treat, and or recycle water that is not
acceptable for offsite release.  The drainage system should be managed to  prevent or minimize con-
tamination problems.

        The design of a drainage system is affected by the topography, soil properties, and water
source factors of a site.  The two types of drainage systems are (Donnan and Schwab 1974):

        • Surface drains - used where subsurface drainage is impractical (e.g., impermeable soils,
         excavation difficult), to remove surface water or lower water table.

        • Subsurface drains - used to lower the water table.  Construction materials include clay or
         concrete tile, corrugated metal pipe,  and plastic tubing. Selection depends on strength
          requirements, chemical compatibility, and cost considerations.

For the design and construction of a drainage system, a drainage engineer  should be consulted. The
American Society of Agromony monograph, Drainage for Agriculture (Schilfgaarde 1974) contains a
complete discussion of drainage.
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Well Points

       Well points, like subsurface drains, can be used to lower the water table in shallow aquifers.
They typically consist of a series of riser pipes screened at the bottom and connected to a common
header pipe and centrifugal pump. Well point systems are practical up to 10 meters (33 feet) and are
most effective at 4.5 meters (15 feet). Their effectiveness, however, depends on site-specific condi-
tions, such as the horizontal and vertical hydraulic conductivity of the aquifer (Ehrenfeld and Bass
1983).

Additives

       Various additives are available to enhance moisture control.  For example, the water-retaining
capacity of the soil can be enhanced by adding water-storing substances.  Three such synthetic sub-
stances were recently evaluated by Nimah et al. (1983) for use in arid area soils. They found that
available soil water content was increased by two of the products. Water-repelling agents are available
which diminish water absorption by soils. On the other hand, water-repelling soils can be treated with
surface-active wetting agents to improve water infiltration and percolation.  Other soil characteristics
which have been modified by surface active agent include acceleration of soil drainage, modification of
soil structure, dispersion of clays, and soil made more compactable.  Evaporation retardants are also
available to retain moisture in a soil.  Secondary effects of some of these amendments on soil biological
activities, other soil physical properties, soil chemical properties and environmental effects, e.g., leach-
ability and degradability, are discussed by Brandt (1972).

Nutrient Additions To The Soil

       Degradation of organic compounds at a hazardous waste site requires an active population of
microorganisms. Among other environmental factors (e.g., temperature, moisture, pH, etc.), adequate
nutrition is vital to maintain the  microbial population at an optimum level. The hazardous wastes being
degraded may contribute some necessary nutrients, but may not supply all that are required or that may
be beneficial (e.g., silicon and sodium).  If the soil does not contain an adequate supply of nutrients, the
soil must be supplied with the appropriate elements in the form of fertilizers. A fertilizer is any sub-
stance added to the soil to supply those elements required in plant nutrition.

       The number of substances suitable as fertilizers is very large, and their compositions and
origins differ considerably. Classification systems incorporating many aspects of fertilizer origin, use,
and characteristics are presented in Finck (1982).  Because of the variety of possible classifications, the
choice of an appropriate fertilizer can be complicated, and an agronomist should be consulted to
develop a fertilization plan at a  hazardous waste site.  A plan may include types and amounts of nutri-
ents, timing and frequency of application, and method of application.  The nutrient status of the soil and
the nutrient content of the wastes must be determined to formulate an appropriate fertilization plan.
Basic textbooks on fertilization  include So/7 Fertility and Fertilizers (Tisdale et al.  1985), Fertilizers  and
Fertilization (Finck 1982), and Fertilizers and Soil Amendments (Follett et  al. 1981).

       The development of a fertilization program not only includes the proper selection of fertilizer
form and determination of correct fertilizer quantities, but also the selection of an application method.
Fertilizers must be transported, stored, and applied so that no chemical or physical changes occur to
decrease dispersibility and effectiveness.  Improper handling during transportation and storage may
result in the creation of safety hazards due to moisture absorption, such as increased flammability,
explosiveness, and corrosiveness, or the formation of noxious gases. Improper mixing of fertilizer types
before or after application may  result in nitrogen losses, immobilization of water-soluble phosphate, or
deterioration of distribution properties due to moisture absorption (Finck 1982).

       In agricultural application, fertilizers are either applied evenly over an area or concentrated at
given points, such as banded along roots. At a hazardous waste site, however, fertilizer will  likely be
applied evenly over the whole contaminated area and incorporated by tilling, if necessary.  Nutrients can
also  be injected through well points below the plow layer.
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       With broadcast fertilization, the fertilizer can be left on the surface or incorporated with a harrow
(2 to 3 cm deep), a cultivator (4 to 6 cm deep), or a plow (a layer at bottom of furrow, e.g., 15 cm deep).
The depth of incorporation depends on the solubility of the fertilizer and the desired point of contact in
the soil. In general, nitrate fertilizers move freely, while ammonia nitrogen  is adsorbed by soil colloids
and moves little until converted to nitrate. Potassium is also adsorbed and moves little except in sandy
soils. Phosphorus does not move in most soils. Therefore, potassium and phosphorus need to be
applied or incorporated to the desired  point of use.

Control  of Soil pH

       Control of soil pH at an in situ hazardous waste treatment site is a  critical factor in several
treatment techniques (e.g., metal immobilization, optimum microbial activity). The goal of soil pH
adjustment in agricultural application usually is to increase the pH to near neutral values, since natural
soils tend to be acidic.
       The areas of the country in which the need for increasing soil pH is greatest are the humid
regions of the East, South, Middle West, and Far West States.  In areas where rainfall is  low and
leaching is minimal, such as parts of the Great Plain States and the arid, irrigated saline-alkali soils of
the Southwest, Intermountain, and Far West States, pH adjustment is usually not necessary. Some
soils, especially those high in carbonates, do require the pH to be lowered. However, a hazardous
waste-contaminated soil may have substances high in pH, thus necessitating soil acidification.

       The most common method of controlling pH is liming. Liming is the addition to the  soil of any
calcium or calcium- and magnesium-containing compound that is capable  of reducing acidity (i.e.,
raising pH).  Lime  correctly refers only to calcium oxide, but is commonly used to refer to calcium
hydroxide, calcium carbonate, calcium-magnesium carbonate, and calcium silicate slags (Tisdale et al.
1985).
       There are several benefits of  liming to biological activity.  At higher pH values, aluminum and
manganese are less  soluble.  Both of these compounds are toxic to most plants. In addition, phos-
phates and most micro-elements necessary for plant growth (except molybdenum) are more available at
higher pH. Microbial activity is greater at or  near neutral pH, which enhances mineralization and
degradation processes and nitrogen transformations (e.g., nitrogen fixation and nitrification).

       A summary of commonly used liming materials is presented in Table A-2. The choice of liming
material depends upon several factors.  Calcitic and dolomitic limestones are the most commonly used
materials. To be  effective quickly, however, these materials must be ground, because the  rate of
reaction is dependent on the surface  in contact with the soil.  The finer they are ground, the more rapidly
they react with the soil. A more finely ground limestone product, however, usually contains a mixture of
fine and coarse particles to effect a pH change rapidly and to still be relatively long-lasting  as well as
reasonably priced. Many states require that 75 to 100 percent of the limestone pass an 8- to 10-mesh
sieve and that 20 to 80 percent pass  anywhere from an 8- to 100-mesh sieve (Tisdale et al. 1985).
Calcium oxide and calcium hydroxide are manufactured as powders and react quickly.

        Other factors to consider in the selection of a limestone are neutralizing value, magnesium
content, and cost per ton applied to the land.
        Lime requirement for soil pH  adjustment is dependent on several factors, including soil texture,
type of clay, organic matter content, and exchangeable aluminum (Follett  et al.  1981). The buffering
capacity of soil reflects the  ability of soil components to hold a large number of ions in adsorbed or
 reserve form. Thus, adsorption or inactivation of H+ ions, or the release of adsorbed ions to neutralize
 OH- ions provides protection against  abrupt changes in pH when acidic or basic constituents are added
to the soil. Differences among soils in their buffering capacity reflect differences in the soil cation
 exchange capacities and will directly  affect the amount of lime required to adjust soil pH. The amount of
 lime required is also a function of the depth  of incorporation at the site, i.e., volume of soil to be treated.
 The amount of lime required to effect a pH change in a particular site/soil/waste system  is  determined
 by a state experimental or commercial soil testing laboratory in short-term treatability studies or soil-
 buffer tests (McLean 1982).
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        Lime requirements may also be affected by acid precipitation and acid-forming fertilizers.  A
field study in Connecticut showed that each year the acidity generated by acid precipitation would
require 36 kg/ha (32 Ib/A) of pure calcium carbonate for neutralization (Frink and Voight 1976).
Table A-2.  Liming Materials*
Liming material
Description
 Calcium
carbonate
equivalent!
Comments
Limestone, caltitic
Limestone, dolomitic
Lime, unslaked
 lime, burned lime,
 quick lime
Hydrated lime,
 staked lime,
 builder's lime

Marl
Blast furnace
 slag

Waste lime
 products
CaCOs, 100% purity        100
65% CaCOs + 20%         89
 MgCOs, 87%
 purity ^

CaO, 85% purity           151
Ca(OH)2, 85% purity        120



CaCOs, 50% purity         50


CaSi2 Os                 75-90
Extremely variable
in composition
            Neutralization value usually between 90-98%
            because of impurities; pulverized to desired
            fineness

            Pure dolomite (50% MgCOs and 50% CaCOs)
            has neutralizing value of 109%; pulverized to
            desired fineness.

            Manufactured by roasting calcitic limestone,
            purity depends on purity of raw materials,
            white powder, difficult to handle - caustic,
            quick acting, must be mixed with soil or will
            harden and cake

            Prepared by hydrating CaO, white powder,
            caustic, difficult to handle; quickly acting
           Soft, unconsolidated deposits of CaCOa,
           mixed with earth, and usually quite moist

           By-product in manufacture of pig iron,
           usually contains magnesium
* Source: Follett et al. 1981, Tisdale et al. 1985.
t Calcium carbonate equivalent (CCE): neutralizing value compared to pure calcium carbonate, which has a
  neutralizing value defined as 100.
tt State laws specify a calcium carbonate equivalent averaging 85%.

        Lime is usually applied from a V-shaped truck bed with a spinner-type propeller in the back
(Follett et al. 1981). Uniform spreading is difficult with this equipment, and wind losses can be signifi-
cant. A more accurate but slower and more costly method is a lime spreader ( a covered hopper or
conveyor) pulled by a tractor.  Limestone does not migrate easily in the soil since it is only slightly
soluble, and must be placed where needed.  Plowing and/or discing surface-applied lime into the soil
may therefore be required.
        The application of fluid lime is becoming more popular, especially when mixed with fluid nitro-
gen fertilizer. The combination results in less trips across the soil, and the lime is available to counter-
act acidity produced by the nitrogen.  Also, limestone has been applied successfully to a pharmaceutical
wastewater land treatment facility through a spray irrigation system.

Modification of Soil Temperature

        Soil temperature is one of the more important factors that controls microbiological activity and
the rate of organic matter decomposition. Soil temperature is also important in influencing the rate of
volatilization of compounds from soil. Soil temperature can be modified by regulating the oncoming and
outgoing radiation, or by changing the thermal properties of the soil (Baver et al.  1972).
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       Vegetation plays a significant role in soil temperature because of the insulating properties of
plant cover.  Bare soil unprotected from the direct rays from the sun becomes very warm during the
hottest part of the day, but also loses its heat rapidly during colder seasons.

       However, a well-vegetated soil during the summer does not become as warm as a bare soil,
and in the winter, the vegetation acts as an insulator to reduce heat lost from the soil. Frost penetration
is more rapid and deeper under bare soils than under a vegetative cover.

       Mulches can affect soil temperature in several ways.  In general mulches reduce diurnal and
seasonal fluctuations in soil temperature.  In the middle of the summer, there is little difference between
mulched and bare plots, but mulched soil is cooler in spring, winter, and fall, and warms up more slowly
in the spring. Mulches with low thermal conductivities decrease heat flow both  into and out of the soil;
thus, soil will be cooler during the day and warmer during the night. White paper, plastic, or other types
of while mulch increase the reflection of incoming radiation, thus reducing excessive heating during the
day. A transparent plastic mulch transmits solar energy to the soil and produces a greenhouse effect.
A black paper or plastic mulch adsorbs radiant energy during the day and reduces heat loss at night.
Humic  substances  increase soil temperature by their dark color, which increases the soil's heat adsorp-
tion.

       The  type of mulch required determines the application method. Mulches, in addition to modifi-
cation of soil temperature, are also used to protect soil surfaces from erosion and to reduce water and
sediment runoff, prevent surface compaction or crusting, conserve  moisture, and help establish plant
cover (Soil Conservation Service  1979).  A summary of mulch materials is presented in Table A-3.
Commercial  machines for spraying mulches are available.  Hydromulching is a  process in which seed,
fertilizer, and mulch are applied as a slurry. To apply plastic mulches, equipment which is towed behind
a tractor mechanically applies plastic strips which are sealed at the edges with  soil. For treatment of
large areas,  special machines that glue polyethylene strips together are available (Mulder  1979).

       Irrigation increases the heat capacity of the soil, raises the  humidity of the air, lowers air tem-
perature over the soil, and increases thermal conductivity, resulting in a reduction of daily soil tempera-
ture variations (Baver et al. 1972). Sprinkle irrigation, for example, has been used for temperature
control, specifically frost protection in winter and cooling in tn summer and for reduction of soil erosion
by wind (Schwab et al. 1981). Drainage decreases the heat capacity, thus raising the soil temperature.
Elimination of excess water in spring causes a more rapid temperature increase.  The addition of humic
substances improves soil structure, thus improving soil drainability, resulting indirectly in increased soil
temperature.

       Several physical characteristics of the soil surface can be modified to alter soil temperature
(Baver et al. 1972). Compaction of the soil surface increases the density and thus the thermal conduc-
tivity. Tillage, on the other hand, creates  a surface mulch which reduces heat flow from the surface to
the subsurface. The diurnal temperature variation in a cultivated soil is much greater than in an unfilled
soil. A loosened soil is colder at night and more susceptible to frost.
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Table A-3. Mulch Materials*

Organic materials
         Quality
         Notes
Small grain straw or
 tame hay
Corn stalks chopped
 or shreded

Wood excelsior
Wood cellulose fiber


Compost or manure



Wood chips and bark



Sawdust



Pine straw


Asphalt emulsion
Gravel or crushed
 stone
Wood excelsior
 mats
Jute, mesh or net
Undamaged, air dry threshed
straw, free of undesirable
weed seed
Air dried, shredded into 6" to
12" lengths

Burred wood fibers approx-
mately 4" long

Air dry, non-toxic with no
growth inhibiting factors

Shredded, free of clumps
or excessive coarse
material

Air dried, free from objec-
tionable coarse material
Free from objectionable
coarse material
Air dry  Free of coarse
objectionable material

Slow setting
SS-1
Blanket of excelsior
fibers with a net back-
ing on one side

Woven jute yarn with
3/4" openings
Spread uniformly - at least 1/4 of ground should
be visible to avoid smothering seedling. Anchor
either during application or immediately after
placement to avoid loss by wind or water.  Straw
anchored in place is excellent on permanent
seedings.

Relative slow to decompose. Resistant to wind
blowing

A commercial product packaged in 80-90 Ib bales.
Apply with power equipment Tie down usually.

Must be applied with  hydraulic seeder.
Excellent around shrubs.  May create problems
with weeds
Most effective as mulch around ornamentals, etc.
Resistant to wind blowing.  May require anchoring
with netting to prevent washing or floating off

More commonly used as a mulch around orna-
mentals, etc.  Requires anchoring on slopes
Tend to crust and shed water.

Excellent around plantings  Resistant to wind
blowing

Use as a film  on soil surface for temporary pro-
tection without seeding  Requires special equip-
ment to apply

Apply as mulch around woody plants.  May be used
on seeded areas subject to foot traffic.  (Approxi-
mate weight - 1 ton per cu. yd)

Roll 36" x 30 yards covers 161/2 sq. yds. Use with-
out additional mulch.  Tie down as specified by
manufacturer.

Roll 48" x 75 yds weighs 90 Ib and covers 100 sq
yds.
'Source:  Soil Conservation Service 1979.
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                                       Index
Acetaldehyde, 711, 72t
Acetamide, 20t
Acetone, 20t, 60
Acetylene, 50
Acids,
    mineral and oxidizing, 24t
    organic, 24t
Acrobacter, 53t
Acrolein, 71t, 72t
Acrylonitrile, 35, 54t, 71-72t
Actinomycetes, 36-38
Activated carbon,
    filters, 60
    granular, 65-67
    use in permeable barriers, 86-90
Acurex dechlorination process, 31
Aerobic systems,  38-40, 41-43, 59-67
Air, 42t
Alcohols, 24t, 54t
    and glycols, 24t
Aldehydes,  24t
    oxidation of, 23
Aldrin, 24t, 37t
Alkali polyethylene glycolate
    dechlorination process
        (APEG), 32-35
Alkaline agents, use as flushing
    agents,  9t, 10
Alkenes, 19
Alkyl halides,24t,  54t
Alkylbenzene sulfonate, 7
Allyl chloride, 711, 73t
Aluminum, 13t, 20, 26, 27
    effects on biological  systems, 27
Amides, 21
Amines, 7, 54t
Ammonium chloride,67
Ammonium sulfate, 67
Anaerobic biodegradation, 37t, 43-45
Anaerobic digester, 67
Analytical studies, 4
Analines, 7
Analogue enrichment, 51
APEG,  32-35
Aqueous solution chemistry, 1
ARARs, 4-6
Aroclors (also see PCBs), 31-35
Aromatic hydrocarbons, 54t
    chlorinated, 24t
Arsenic, 13t
Arsenite, oxidation of, 49-50
Arthrobacter, 52
Asphalt, 14
Atrazine, 26, 37t
Azo compounds, 24t
Bacillus subtilis, 53t, 56
Bacterial inoculation, 59
Baseline risk assessment, 4
Bearing strength, 11
Bench-scale treatability studies, 2
Benzene, 23, 62, 71t, 76
Benzo(a)pyrene, 50,  711, 73t
Benzyl chloride, 72t
Benzyne mechanism, 32
Bifenox, 37t
Bioaugmentation, 52-55
Biochemical mechanisms, enhancement
    of, 38-52
Biodegradation, 37t
    case studies, 59-67
Biological oxidation, 60-61
Biological treatment system (fig.), 61
Bioremediation,
    for organic contamination, 59-67
    for phenol contamination, 60
    formaldehyde spill, 59-60
Biostimulation, systems for, 62-63
Biphenyl, 50
Bis(2-ethylhexyl)phthalate, 87t
Bis(chloromethyl)ether, 411, 72t
Bromacil, 37t
Calcium hydroxide, as a soil
    amendment, 45-46
Calcium nitrate, 67
Carbamate pesticides, 21
Carbaryl, 21,37t
Carbofuran, 37t
Carbon (organic), 48
Carbon dioxide flooding, 100-101
Carbon dioxide injection, 100-101
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Carbon tetrachloride, 51, 711, 72t
Carbonic acid, 7
Carboxylic acids, 33
Carotene, 20t
Catalysts, 20-22
    in polymerization reactions, 35-36
Cellulomonas, 53t
CERCLA, 3-5
    remediation criteria, 5-6
    National Contingency Plan, 4-6
Chemical and physical separation
    techniques, 86-95
Chemical bonds, dissociation
    energies, 69t
Chlordane, 26
Chloride compounds, 14
    acids and anhydrides, 24t
Chlorinated aromatic hydrocarbons, 54t
Chlorine, 22t
Chlorobenzene, 26, 52, 711, 72t
3-chlorobenzoate,  52
Chloroform,  51, 71t, 72t
Chloromethyl methyl ether, 711
Chlorophenol, 60
Chloroprene, 711,  72t
Chromic acid, 24
Chromium,
    leaching of, 91
    reduction of, 28-30
    soils contaminated with, 87
Clay,
    application of, 12
    content in soils, 31
    for organic binding, 12-13
Cleanup standards (see SARA), 3
Cooxidation, 51
Coal, use in permeable  barriers, 87-88
Colloidal gas aphrons,
    creation of, 38-39
    for biodergadation,  38-40
Cometabolism, 50-52
    analogue enrichment, 51
    definition of, 50-52
    mechanisms of, 50-52
Complexing and chelating agents, 8
Condensation of species, 26
Contaminants,
    partitioning in media, 69, 77-78
    solubility of, 11-12
Control of volatile materials, 78-86
Cooling agents, 85
Copper (II) smectite, 35
Creosote, 8, 10, 13t
Cresols, 60,  711, 72t
Crystallization, 17
Cyanide,
    oxidation of, 23
Cyanides, 24t
Cyclic pumping, 102
Cyclohexylamine, 20t
Cytochrome P-450 monooxygenase, 56
Dalapon, 37t
Darcy'slaw,91
2,4-D, 37t
ODD, 44
DDE, 24t
DDT, 37t, 44, 70
Dechlorination reactions, 31-35
Delivery/recovery,
    definitions, 1, 96
    systems, 96-102
Detergents,  54t, 64
Di-n-butyl phthalate, 87t
Dialkyl sulfides,
    oxidation of, 23
Diazinon, 37t
    degradation of, 56-57
Dicamba, 37t
Dichlorobromobenzene, 711
Dichlorobenzene, 71t
1,1-dichloroethane,  51
1,1-dichloroethylene, 51
1,2-dichloroethane,  51
1,2-dichloroethylene, 51
Dichloromethane, 51
2,4-dichlorophenol,  87t
Dieldrin, 24t, 37t
    formation from Aldrin, 75
Diesel fuel, 64-65
Diethyl ether, 711
Dimethoate, 21
Dimethyl sulfoxide, 33,  33t
Dioxins (TCDD), 24, 31-34, 72t, 75-77
    effects of composting on,
Dissolved organic carbon (DOC), 22
Dithiocarbamates, 24t
Dithionate,
    oxidation of, 22
Drainage,
    effects on soils, 47-49
Dry ice,
    use as a cooling agent, 85
Eglin AFB, Florida, 65
Electrodes, 17-18, 83, 90-92
Electrokinetics, 90-92
Electromagnetic energy,
    use  in radio frequency heating, 83
Electroosmosis (see Electrokinetics)
Electroplating wastes, 6
Elutriate, 7-8
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   collection of, 8
Emergency response actions, 3
Emulsifiers, 54t
Emulsions,
   formation of, 7
Encapsulation, 12,17
Endrin, 37t
Enzymatic degradation, 56-57
Enzymes, 56
Epichlorohydrin, 711, 73t
1,2-epoxybutane,  711
Epoxypropane, 711
Esters, 21. 54t
Ethanol, 711
Ethene, 19
Ethers, 7
Ethyl acetate, 711
Ethyl benzene, 79
Ethyl ether,
    use as a cooling agent, 85
Ethyl oleate,
    use as a photoenhancement
     agent, 75
Ethyl parathion, 21
Ethyl propionate, 7lt
Ethylene dibromide, 71t, 73t
Ethylene dichloride, 71t, 73t
Ethlyene glycol, 61-62
Ethylene oxide, 71t, 73t
Evapotransiration, 40
Excavation and removal of soils,.3
Exposure assessment, 4
Exposure pathways, 5
Feasibility studies, 4
Fenvalerate, 57
Ferrous sulfate, 29, 49
Fertilizers,
    additions of to decompose crop
     residues, 46
    advantages for biodegradation, 47
    disadvantages for
     biodegradation, 47
Fluoranthene, 87t
Fluoride, 17
Fluorine, 22t
Flushing solutions, 7-11
    contact with waste constituents, 7
    types, 9
Fly ash, 18
    use in permeable barriers, 87-88
Formaldehyde, 59-60
Fungi,  36
Gasoline,
    aerobic degradation of, 41, 62
    ground water contaminated with, 62
    soil contaminated with, 62
Gelling, 17
Glyphosate, 37t
Granite, 17
Graphite, 17, 19
Ground freezing, 93-95
Ground water, 22-24
    contamination, 62-67
    effect of hydraulic fracturing on
      recovery of, 97
    extraction of, 60-62
    phenol contamination, 65
    recovery of, 7-11, 60-67
Groveland Wells site, 79-80
Guidance  documents, 2
Half-cell potential (E1/2), 19
Hazardous waste site remediation, 4
Health assessments, 3
Heavy metals, 11-15
Helmholtz-Smpluchowski model,
    use in electrokinetics, 91
Henry's law constant, 79, 95
Heptachlor, 37t
    epoxide, 24t
Hexahydro-1,3,5-trinitro-
    1,3,5-triazine, 49
Hill AFB, Utah, 42
Hot brine  injection, 101-102
HSWA, 3
Humus,
    microbial decomposition of, 49
Hydraulic fracturing, 80, 96-97
Hydrobac, 59
Hydrogen peroxide, 22-25, 41-43, 62
Hydrogenolysis,  20
Hydrolysis,
    influences on, 20-22
    rates of, 20
Hydroxyl radical,  22t
Hydroxylation, 26
Hypochlorite, 27
Hypochlorus acid, 22t,
Immobilization,
    techniques for, 13-19
In situ treatment,
    definition of, 1
    mechanisms for, 2
Inorganics,
    waste components of, 16t
    vegetative uptake of, 57-59
Iron, 20, 26, 34
    powders used as reducing
      agent, 26
    reduction reactions for, 26
Isophorone, 87t
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Isoprene, 35
Jet-induced slurry method, 99-100
Karlsruhe, Germany, 22
Kelly AFB, Texas, 62-63
Kepone, 26
Kerfing, 99
Kiln dust, 14t
KPEG dechlorination, 32-35
Landfills, 3
Leachability rates, 12-14
Leachate,
    simulation of, 87-88
Lime,
    forpH control, 45-46
Lime-fly ash pozzolan systems, 12-14
Limestone,
    use in permeable barriers, 86-90
Lindane, 37t
Linuron, 37t
Low-level radioactive wastes, 17
Macroencapsulation, 11
Malaoxon, 24t
Malathion, 21,37t
Maleic anhydride, 711, 75t
Marconi reagent, 34
Metals
    effect of ground freezing on, 94
    recovery using flushing
      solutions, 7-8
Methane,
    as an enrichment for
      biodegration, 51
Methoxychlor, 37t
Methyl acetate, 711
Methyl chloroform, 711, 73t
Methyl ethyl ketone, 7lt
    spills of, 65
Methyl iodide,73t
Methyl parathion, 37t
Methyl prionate, 711
Methylene chloride,  59, 71t, 73t
Methyloccus capsulatus, 51
Microbes,
    genetically altered,  52-55
Microencapsulation, 11-12
Mirex, 37t
Moisture,
    control of for biodegradation, 40-41
    effect on chemical partitioning, 68
Mulches,
    effects on soils,  47
Naphthalene, 87t
National Contingency Plan (NPC), 4-6
NATO/CCMS Program, 3
Natural gas, 51
Naval Air Engineering Center, New
    Jersey, 61-62
Naval Civil Engineering Lab, 42
Nitrates, 18, 41,43
Nitric acid, 7
Nitrobacter, 53t
Nitrobenzene, 711, 73t
Nitrogen,
    in fertilizers, 46-47
    oxidation of,  23
    used as a cooling agent, 85, 95
Nitromethane, 71t
Nitrophenols, 24t, 26
2-nitropropane, 711, 73t
4-nitrophenol, 46
Nitrosomonas,
Nitrosomorpholine,
Nonanalogue enrichment,
    with methane, 51
    with other hydrocarbon
      substrates, 51-52
Norcardia, 51,62
Nucleophilic substitution,  reaction
    mechanisms, 31
Nutrients,
    addition of for
      biodegradation,  45-46
On-scene Coordinators, 1
Organic compounds, pyrolysis of, 17-19
Organic contaminants (basic), flushing
    solutions for, 7-11
Organics,
    bacterial degradation  of, 59-67
    chemical destruction of, 19-36
    effects of soil freezing on,94
    factors influencing
      volatilization, 77-86
    oxidation characteristics of, 20
    photolysis rates of, 77
    polymerization of,  35-36
    solubility of, 20
    use as soil amendments, 48
    waste components of, I6t
      xenobiotic  compounds, 41
Organophosphate  pesticides, 20-21
Oxidation potentials, 22t
Oxidation reactions, 19-25
    soil-catalyzed, 20-22
Oxidize rs,
Oxidizing agents, 22-25
    corrosive properties of, 25
    loading rates for, 24
    reactions with,  23
Oxygen sources, alternative, 62
Oxygen, 20, 32,  41, 42t, 50, 51
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    atomic, 22t
    control of for biodegradation, 41
Oxygenase, 51
Ozone, 22, 22t, 43
    hazardous products of
       reactions, 24t
    rate of decomposition of, 22
Paint sludge, 63
Paraooxon, 24t
    formation from parathion, 75
Parathion, 20-21,  37t
    hydroloysis  of, 20-21
PCS (see polychorinated biphenyls)
Pentachlorophenol (PCP), 37t
Perchloroethlyene,7H,  73t
Permeable barriers, 86-90
Pesticides, 21
    enzymatic treatment of, 20-22
    photoreactions of, 69
Petroleum and mining industries, 2
pH, 29, 37, 64
    control for biodegradation, 59
    effects on enzymes, 56
    effects on microbes, 45
    levels in soils, 45
Phenanthrene,  51, 87t
Phenol, 8, 23, 34t, 54t,  60, 711, 73t, 87t
    degradation of, 42
    oxidation of, 23
    spills of, 65
Phenoxyacetic acids, chlorinated, 26
Phorate, 37t
Phosgene, 711, 74t
    formation from chlorpicrin, 75
Phosphate,  62
    as a soil amendment, 46
Phosphoric acid, 21
    esters, 21
Phosphorus, in  fertilizers, 47
Photoenhancement agents, 75-77
Photolysis, 68-75
Photoreaction,  68
Physical entrapment, 12
Picloram, 37t
Pilot-scale treatability studies, 2
Plastics, 16t
Plating wastes,  18
Polychorinated  biphenyls, 13t, 18, 26,
    32-34, 70, 711, 74t
    bacterial degradation of, 52
    dechtorination by ultraviolet light, 68
    detoxification, 31-32
    formation from DDT, 70
    photolysis of, 75
Polycyclic aromatic hydrkocarbons, 43
   fungal metabolism of, 45
Polyethlyene glycols, 32
Polymerization, 15, 35-36,
   reactions, 19
Polymers use as flushing agents, 10
Portland cement systems, 12
Pozzolanic reactions, 14
PPM dechlorination process, 32
Preliminary screening, 5
Propanol,  711
Propylene oxide, 711, 74t
Pseudomonas,  53t, 62
   alcaligenes, 52
   cepacia, 52
   putida, 39, 42
Pyrene, 87t
Radial wells, 97-98
Radio frequency heating, 83-86
Radioactive wastes, 16t
RDX, 49-50
Redox  potential, 20, 40, 43
   of soils, 28
Reducing  agents, 25-31
Reduction reactions,  26-27
Reductive dehalogenation, 26
Remedial actions, 4
   alternatives, 5
   objectives, 5
   plan, 6
   public comment and review, 6
   process and costs, 5
Remedial Project Managers, 1
Remedial response capability, 3
Remediation goals and objectives, 4-5
Resins, 16t
Rhodopseudomonas, 53t
Runoff controls, 29, 44, 50
Ruthenium tetroxide, 24
Sampling strategy, 2
SARA, 3-5
Selenium, 30
   elemental, 30
   hexavalent, 30
Silicates, 20
Silver nitrate, 23
Simazine, 37t
Site characterization, 2
SITE Program, 3,  79, 81
Skrydstrup Chemical Waste Disposal,
    Denmark, 63
Sodium, acetate,  64
   bichromate, 29
   borohydrate,  28
   borohydride,  27
   as a reducing agent, 34
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    effects on soil permeability, 28
    hydroxide, 28
Soil cooling, 85-86
Soil flushing systems, 7-11
Soil permeability, effect of flushing
    solutions on, 8, 11
Soils,
    aeration of, 43
    biological activity in, 20
    clay fraction of, 20
    conditions for
       biodegradation,  36-38
    degree of saturation of, 20
    effects of flushing agents on, 8
    moisture of,  40
    permeability  of, 8
    pH, 10
    photolysis zones of, 68
    pore spaces of, 78
    porosity of, 14
    redox potential of, 44
    surface characteristics of, 48
    temperatures effecting microbial
       activity, 47
    tilling for aeration of, 42
    types of amenable to carbon dioxide
       injection, 100
    types of amenable to vapor
       extraction, 79
    use in permeable barriers, 87
    vapor extraction from,  78
Solidification/stabilization, 11-19
Solvents, 8
    chlorinated,  62
    hydrophobic, 32
    polar, 32
Sorption, 12, 20
Steam stripping, 81-83
Sulfates, 16t, 35
Sulfides, inorganic, 24t
Sulfur compounds, oxidation of, 24
Sulfur, as an acidification agent, 28
Surfactants, 7-8
    environmental characteristics of, 9t
    use as flushing agents, 8
    use in photolysis, 76
2,4,5-T, 37t, 52
Tars, 16t
Temperature,
    effects on dechlorination, 32
    effects on soils, 47-48
    effects on volatilization, 78
Terbacil,  37t
Tetrachloroethylene, 51
Tetrachlorobenzene, 37t
Tetrahydrofuran, 711
Thermoplastic microencapsulation, 12
Titanium oxides, use in photolysis, 76
TNT, 49
Toluene, spills of, 23, 33, 62, 65, 711,
    74t, 79,
Total organic carbon (TOC), 10, 65
Total petroleum hydrocarbons (TPH), 65
Toxaphene, 28
Toxicity assessment, 4
Treatment alternatives, advantages and
    disadvantages, 6
Treatment trains, 7
Triazines, 21
Trichlorobenzenes, biodegradation
    of, 43
1,1,1-Trichloroethane, 37t, 51
    spills Of, 65-67
1,1,2-trichloroethane, 51
Trichloroethylene,  26, 51, 63-64, 711,
    74t, 79
Trifluralin, 371
2,4,6-trinitrotoluene, 49
Ultrasonic methods,
    laboratory studies of, 98-99
    use in soils,  98-99
Ultraviolet light, 23
Ultraviolet radiation, 68-70, 76
Underground storage tank, leaking, 64-
    65, 79
United Chrome site, 91
Urea, as a soil amendment, 46
Vapor  extraction, 78-80
Vegetation, in contaminant uptake, 57-
    59
Verona Wells, 79
Vitrification, 17-19
Volatilization, control of at waste
    sites, 77-86
Volk Air National Guard Base,
    Wisconsin, 8, 10,  83
Washing solutions, 7-11, 9t
Waste-silicate matrix, 19
Water, effects of biodegradation on, 40-
    41
Water extraction, 7
White rot fungus, 52
Xylene,
    spills of, 65
    use as  photoenhancement agent,
    75-77
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                                        .S.GOVERNMENT PRINTING  OF F 1 CE t ! 99 0-7 4 8 - ! 5 9 / 00 3 8 4

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