&EFA
United States
Environmental
Protection Agency
Office of Solid Waste
and Emergency
Response
Office of
Research and
Development
EPA/540/S-94/500
December 1993
Engineering
Forum Issue
Considerations in Deciding to Treat
Contaminated Unsaturated Soils In Situ
Index
1.0 Introduction
2.0 Critical Factors in Technology Selection
2.1 Technology Characteristics
2.2 Generic Critical Factors for Feasibility
Screening of In Situ Treatment
3.0 Technology-Specific Factors
3.1 Delivery and Recovery Systems
3.2 In Situ Solidification/Stabilization
3.3 Soil Vapor Extraction
3.4 In Situ Bioremediation
3.5 Bioventing
3.6 In Situ Vitrification
3.7 In Situ Radiofrequency Heating
3.8 Soil Flushing
3.9 Steam/Hot Air Injection and Extraction
4.0 Acknowledgments
5.0 References
1.0 Introduction
This Issue Paper was developed for the EPA national
Engineering Forum. This group of EPA professionals,
representing EPA's Regional Offices^ is committed to identi-
fying and resolving the engineering issues related to the
remediation of Superfund and RCRA sites. The Forum
operates under the auspices of and advises EPA's Techni-
cal Support Project.
The purpose of this Issue Paper is to assist the user in
deciding if in situ treatment of contaminated soil is a poten-
tially feasible remedial alternative and to assist in the pro-
cess of reviewing and screening in situ technologies. The
definition of an in situ technology is a technology applied to
treat the hazardous constituents of a waste or contaminated
environmental medium where they are located. Central to
the definition of in situ technology is the concept that the
contaminated material is not excavated. The technology
must be capable of reducing the risk posed by these con-
taminants to an acceptable level (U.S. EPA, 1990, EPA/
540/2-90/002, p. 1).
Many biological, chemical, and physical mechanisms are
available to treat contaminants in soils. These mechanisms
can be either applied to excavated soil or used in situ. The
costs, logistical concerns, and regulatory requirements
associated with excavation, ex situ treatment, and disposal
can make in situ treatment an attractive alternative. In situ
treatment entails the iise of chemical or biological agents or
physical manipulations to degrade, remove, or immobilize
contaminants without requiring bulk soil removal. Contain-
ment technologies, such as capping, liners, and grout walls,
are not considered in this Issue Paper.
This Issue Paper is intended to assist in the identification
of applicable alternatives early in the technology screening
process. The Issue Paper discusses and lists important
tSS) Printed on R*ydtd Papw
Superfund Technical Support Center
for Engineering and Treatment
Risk Reduction Engineering
Laboratory
Engineering Forum
Technology Innovation Office
Office of Solid Waste and Emergency
Response, U.S. EPA, Washington, DC
Walter W. Kovalick, Jr., Ph.D.
Director
-------
considerations for in situ technologies. More detailed infor-
mation, is available on each technology from a variety of
reference sources. These references should be consulted
for all of the technologies that are likely to be useful at a
specific site. In addition to the in situ technologies dis-
cussed in this Issue Paper, technology screening also would
consider potentially useful ex situ technologies. Final tech-
nology selection typically will be based on site-specific
evaluation and treatability testing (U.S. EPA, 1992, EPA/
540/R-92/071a).
Applying the treatment agents to the largely undisturbed
in situ geology give,s in situ treatment unique advantages
and challenges. The obvious advantage is that no bulk
excavation is required for in situ treatment. Preventing
excavation eliminates the cost and environmental conse-
quences of moving the contaminated material. The condi-
tions of the subsurface will never be as controlled as in an
ex situ reactor, however. As a result, in situ treatment
requires more extensive site characterization both before
and after treatment, is harder to simulate in the laboratory,
and must be designed and operated to minimize the spread
of contamination.
The principal feature of in situ treatment is controlled
delivery and recovery of energy, fluids, or other treatment
agents to the subsurface. The treatment agent usually is
water, air, or steam but may be energy input by conduction
or radiation. For both physical- and energy-based in situ
treatment agents, controlled application is a key to success.
Systems must be available to apply treatment agents and to
control the spread of contaminants and treatment agents
beyond the treatment zone.
Several in situ technologies also rely on the ability to
recover the treatment agent and contained contaminants
from the subsurface. For example, recovery of flushing fluid
containing contaminants is an integral part of soil flushing,
and the collection and treatment of steam and condensate
are essential to steam/hot air injection and extraction treat-
ment.
Assessing the feasibility of in situ treatment and selecting
appropriate in situ technologies requires an understanding of
the characteristics of the contaminants, the site, and the
technologies, and of how these factors and conditions
interact to allow effective delivery, control, and recovery of
treatment agents and/or the contaminants.
This Issue Paper discusses established and innovative in
situ treatment technologies that are available or should be
available for full-scale application by 1996. Emerging tech-
nologies that are still being tested in the laboratory and are
not available for full-scale implementation are not discussed.
Examples of emerging technologies include: in situ oxida-
tion or reduction, electrokinetics, hot brine injection, polymer
injection, and soil freezing.
2.0 Critical Factors in Technology
Selection
This section describes critical factors to consider in the
selection of in situ treatment methods and during evaluation
of in situ technologies. Factors to be discussed include the
general technology capabilities and generic critical factors
that influence the general suitability of in situ treatment
when compared to ex situ treatment. Section 3.0 provides
more detailed technology descriptions and the technology-
specific critical factors.
The process for screening and selecting technologies is
described in Guidance for Conducting Remedial Investiga-
tions and Feasibility Studies under CERCLA - Interim Final
(U.S. EPA, 1988, EPA/540/G-89/004). The guidance docu-
ment describes preliminary screening of technologies based
on effectiveness, implementability, and cost. The effective-
ness evaluation considers the protection of human health
and the environment and reductions in mobility, toxicity, and
volume of contaminant achieved by an alternative. The
implementability evaluation considers the technical and
administrative feasibility of constructing, operating, and
maintaining a remedial action alternative. The cost evalua-
tion considers the relative cost of alternatives.
This Issue Paper will assist the user in prescreening in
situ technologies for contaminated soil by determining whe-
ther the technologies are technically feasible for a particular
site. This paper is not meant to replace Feasibility Study
Guidance. Consideration and selection of remedial technol-
ogies is based on criteria that are defined by the National
Contingency Plan. This Issue Paper describes the potential
effectiveness of in situ technologies for treating the various
types of chemical groups, and reviews both the general and
the technology-specific factors to consider during preliminary
evaluations of the effectiveness, implementability, and cost
of in situ approaches to treatment. Although this Issue
Paper describes only in situ treatment, the user should keep
in mind that selection of in situ technology candidates will
not necessarily eliminate consideration of the ex situ op-
tions. At many sites, both in situ and ex situ technologies
may be competing candidates late in the technology selec-
tion process.
Selecting a technology often requires several iterations
with increasingly well-defined data to refine the selection.
As the project progresses, technology-specific and site-
specific information becomes available. This information
must be used to better define which technologies are suit-
able for waste materials and conditions at the site. As the
decision maker obtains more information about site condi-
tions, waste characteristics, and treatability study results,
this Issue Paper can be used to help further refine selection
of candidate technologies. However, as the list of candi-
dates is narrowed, additional published sources and expert
opinion should be sought to obtain more detailed information
about the candidate technologies.
Treatment of Soils In Situ
-------
2.7 Technology Characteristics
The applicability of the technology to the contaminants
present, the technology maturity, and the ability of the
technology to operate in the unsaturated and/or saturated
zones should be considered in technology selection. The
applicability of the technology to general types of contami-
nants is summarized in Table 2-1. The characteristics of
the technologies are summarized in Table 2-2. Preliminary
selection of technology candidates can be based on the
capabilities of in situ technologies to treat chemical groups
present at the site.
The chemical contaminant groups considered are divided
into three general groups: organics, inorganics, and reac-
tives. The types of organics considered are halogenated
and nonhalogenated volatile organic compounds (VOCs),
halogenated and nonhalogenated semivolatile organic com-
pounds (SVOCs), polychlorinated biphenyls (PCBs),
pesticides, dioxins and furans, organic cyanides, and organ-
ic corrosives^ Inorganics are subdivided into volatile metals
(and metalloids), nonvolatile metals, asbestos, radioactive
materials, inorganic corrosives, and inorganic cyanides.
Reactive species may be either oxidizers or reducers. The
types of materials in these subgroups are outlined below.
More detailed lists of constituents within each contaminant
group are given in Technology Screening Guide for Treat-
ment of CERCLA Soils and Sludges (U.S. EPA, 1988,
EPA/540/2-88/004, pp. 10-12).
VOCs are carbon compounds with boiling points lower
than 200°C as analyzed by EPA SW-846 method 8240.
SVOCs are carbon compounds, other than those covered in
the more specific subdivisions, analyzed by EPA SW-846
method 8270. PCBs are any of several compounds pro-
duced by replacing hydrogen atoms in a biphenyl group with
chlorine. Pesticides are compounds other than PCBs ana-
lyzed by EPA SW-846 methods 8080 or 8150. Dioxins and
furans are environmentally persistent, toxic, heterocyclic
hydrocarbons. Organic cyanides are carbon compounds
with a CN group attached. Organic corrosives are carbon
compounds that in aqueous solution have a pH less than or
equal to 2 or greater than or equal to 12.5, or that exhibit a
strong tendency to dissolve materials.
Volatile metals are metals or metalloids where the stable
species in an oxidizing atmosphere (metal or oxide) has a
boiling point less than 630°C. Nonvolatile metals are metals
where the stable species in an oxidizing atmosphere (metal
or oxide) has a boiling point equal to or greater than 630°C.
Asbestos is any of several minerals that readily separate
into long, flexible fibers. Radioactive materials are isotopes
that decay by particle or energy release from the nucleus.
Inorganic cyanides are compounds with a CN group at-
tached. Inorganic corrosives are compounds that in aque-
ous solution have a pH less than or equal to 2 or greater
than or equal to 12.5, or that exhibit a strong tendency to
dissolve materials.
Substances with a strong affinity to acquire electrons are
called oxidizers, whereas substances with a strong tendency
to donate electrons are called reducers.
Treatment often requires a sequence of operations to
deal with a combination of wastes. When evaluating wastes
containing contaminants from more than one chemical
constituent group, each waste group initially should be
considered separately to develop a list of potentially appli-
cable treatment technologies for each chemical group pres-
ent in the soil. The technology lists can be compared to
determine if some candidate technologies are able to treat
all of the groups present.
If one technology is unable to treat all of the groups,
development of a treatment train may be required. For
example at a site with a combination of VOCs and metal
contaminants, soil vapor extraction (SVE) can be used to
remove the VOCs followed by in situ solidification/stabiliza-
tion to reduce the mobility of the metals. The selected
treatment train also must be reviewed for potential interfer-
ences or adverse effects. For example, SVE may increase
the proportion of hexavalent chromium, increasing the
mobility and toxicity of the chromium.
One of the following three characteristics is indicated for
each in situ technology in Table 2-1:
1. Demonstrated Effectiveness - The technology has been
shown to treat some contaminants in the chemical group
to acceptable levels when applied to contaminated soil.
Treatment may involve removal, destruction, immobili-
zation, or toxicity reduction. The demonstration may
have been at the laboratory, pilot, or production scale.
2. Potential Effectiveness - Literature reports indicate there
is or is not a mechanistic basis for the technology to re-
move, destroy, immobilize, or otherwise treat some of the
chemicals in the group when used to treat soil.
3. Possible Adverse Effects - The contaminant is likely to
interfere with the treatment technology or to adversely
affect safety, health, or the environment. Adverse effects
may occur only when the contaminant concentration is
above a threshold level. In many cases, the adverse
effect may be alleviated by pretreatment to reduce the
concentration of the adverse contaminant.
Table 2-2 indicates the maturity of the technology and its
applicability for saturated and unsaturated media. The
maturity is indicated by the ranking shown below (U.S. EPA,
1992, EPA/542/R-92/011, p. 1). Technology maturity is an
important factor in the cost and timeliness of technology
implementation.
1. Established Technology - The technology has been used
on a commercial scale and has been established for use
in full-scale remediations (e.g., incineration, capping,
solidification/stabilization).
2. Innovative Technology - The technology is an alternative
treatment technology (i.e., "alternative" to land disposal)
for which use at Superfund-type sites is inhibited by lack
of data on cost and performance.
To further assist in the review of technology candidates,
Table 2-2 indicates the media typically treated, typical treat-
ment agents or amendments, and delivery and recovery
methods. Figure 2-1 shows the approximate range of in situ
Treatment of Soils In Situ
-------
Table 2-1. Effectiveness of In Situ Treatment on General Contaminant Groups for Soil
Contaminant Groups
Organic
Inorganic
Reactive
Halogenated Volatiles
Halogenated Semivolatiles
Nonhalogenated Volatiles
Nonhalogenated Semivolatiles
PCBs
Pesticides
Dioxins/Furans
Organic Cyanides
Organic Corrosives
Volatile Metals
Nonvolatile Metals
Asbestos
Radioactive Materials
Inorganic Cyanides
Inorganic Corrosives
Oxidizers
Reducers
In Situ
Solidification/
Stabilization
(a) (b)
Xd>
Y(2)
X
T
Y
Y
T
Y
•(3)
•
•
•
•
•
T
T
Soil
Vapor
Extraction
(b) (c)
•
T
•
•
Q
Q
Q
Q
Q
Q
Q
Q
U
Q
Q
Q
T
In Situ
Bioremediation
(d)
Y
T
Y
Y
Y
Y
T
Y
X
X<5>
X(5)
Q
X
X
X
X
X
Bioventing
(e)
Q
Y<4)
•
•
Q
a
Q
Q
X
X<5>
X<5)
Q
X
X
X
X
X
In Situ
Vitrification
(d) (0
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
•
Y
Y
Y
Y
Radio-
Frequency
Heating
(f)
Y
Y
•
•
Y
Y
Q
Q
Q
Q
a
Q
a
a
Q
a
a
Soil
Flushing
(b) (9)
•
Y
Y
•
Y
Y
Y
Y
Y
Y
•
Q
Y
Y
Y
Y
Y
Steam Injection
Stationary
System
(b) (f) (h)
•
Y
•
Y
Y
Y
Y
Y
Y
Y<6>
Y<6>
Q
Y<6>
YW>
YW>
Y<6>
Y<6>
Mobile
System
(b) (0 (h)
•
Y
•
Y
Q
Q
Q
Q
Q
Q
Q
Q
Q
a
Q
Q
Q
5T
31
• Demonstrated Effectiveness: Successful treatability test at some scale completed,
T Potential Effectiveness: Mechanistic basis indicating that technology will work.
Q No Expected Effectiveness: No mechanistic basis indicating that technology will work.
X Potential Adverse Effects.
(1) Vaporization and emission of volatile organic compounds may pose a hazard during mixing.
(2) Semivolatile organics are difficult to treat, but low concentrations of some compounds can be treated.
(3) Arsenic and mercury are difficult to immobilize with cement-based binder formulations.
(4) Possible to treat by cometabolism techniques.
(5) Metals can interfere with bioremediation or bioventing of organics; however, bioremediation methods for low
concentrations of metals are being developed.
(6) Potential effectiveness only for water-soluble compounds.
Adapted from the following sources:
(a) U.S. EPA, 1993, EPA/530/R-93/012.
(b) Donehey et al., 1992, pp. 104-105.
(c) U.S. EPA, 1991, EPA/540/2-91/006, p. 2.
(d) U.S. EPA, 1988, EPA/540/2-88/004, p. 13.
(e) U. S. Air Force, 1992, pp. 5-10.
(f) Houthoofd et al., 1991, EPA/600/9-91/002, pp. 190-203.
(g) U.S. EPA, 1991, EPA/540/2-91/021, p. 2.
(h) U.S. EPA, 1991, EPA/540/2-91/005, p. 2.
-------
Table 2-2. Summary of In Situ Technology Characteristics
Technology/Maturity
Solidification/
stabilization (a)(b)
(See Section 3.2)
Established
Soil vapor extraction (b)(c)
(See Section 3.3)
Innovative
In situ bioremediation (d)
(See Section 3.4)
Innovative
Bioventing (e)
(See Section 3.5)
Innovative
In situ vitrification (d)(f)
(See Section 3.6)
Innovative
Radiofrequency heating (f)
(See Section 3.7)
Innovative
Soil flushing (b)(g)
(See Section 3.8)
Innovative
Steam/hot air injection
stationary system (b)(f)(h)
(See Section 3.9)
Innovative
Steam/hot air injection
mobile (auger) system
(b)(f)(h) (See Section 3.9)
Innovative
Media Typically Treated
Saturated or unsaturated soil,
sediment, or sludge
Approximate depth limits:
30 feet for auger system,
several feet for in-place mixing,
and not a major constraint for
grout injection
Unsaturated soil
Saturated or unsaturated soil,
sediment, or sludge
Unsaturated soil, sediment, or
sludge
Saturated or unsaturated soil,
sediment, or sludge
Approximate depth limit 20 feet with
possible extension to 30 feet
Unsaturated soil, sediment, or
sludge
Unsaturated or saturated soil
Saturated or unsaturated soil
Saturated or unsaturated soil
Approximate depth limit:
30 feet for auger system
Typical Agents or
Amendments
Cement, fly ash, blast furnace
slag, lime, or bitumen
Air
Aqueous solution containing an
electron acceptor (typically oxy-
gen), nutrients, pH modifiers, or
additives
Air
Electrical energy by conduction
Electrical energy by radiation
Water, acidic solutions, basic
solutions, chelating agents, or
surfactants
Steam and/or hot air
Steam and/or hot air
Delivery Methods
(see Section 3.1)
Auger mixing, in-place
mixing, or injection
Passive air inlet or
injection wells
Surface infiltration,
tilling, or water injec-
tion wells
Passive air inlet or
injection wells
Electrodes
Radiofrequency
antennae system
Extraction fluid
injection wells
Steam injection wells
Auger mixing
Recovery Methods
(see Section 3.1)
None required
Air extraction wells (off-
gas treatment may be
required)
None required
Air extraction wells may
be used (off-gas
treatment may be
required)
Off-gas collection and
treatment
Off-gas collection and
treatment
Extraction fluid recovery
wells
Condensate recovery
wells and off-gas
collection and treatment
Off-gas collection and
treatment
Adapted from the following sources:
(a) U.S. EPA, 1993, EPA/530/R-93/012.
(b) Donehey et al., 1992, pp. 104,105.
(c) U.S. EPA, 1991, EPA/540/2-91/006, p. 2.
(d) U.S. EPA, 1988, EPA/540/2-88/004, p. 13.
(e)U.S. Air Force, 1992, pp. 5-10.
(f) Houthoofd et al., 1991, EPA/600/9-91/002, pp. 190-203.
(g) U.S. EPA, 1991, EPA/540/2-91/021, p. 2.
(h) U.S. EPA, 1991, EPA/540/2-91/005, p. 2.
Treatment of Soils In Situ
-------
remediation costs. The costs shown are based on limited
data reported in the literature. The sources rarely give full
characterization of elements included in the cost estimates.
The ranges should be viewed as preliminary indications of
approximate comparative costs of the various technologies.
Factors Increasing Cost
In Situ S/S
SVE (Off-Gas Not Treated)
SVE (Off-Gas Treated)
Bloremedlatlon
Bioventing
In Situ Vitrification
Steam/Hot Air Injection and Extraction
Difficult mixing
Small volume treated
Low air conductivity
Low air conductivity
Low hydraulic conductivity
Low ambient temperature
Low air conductivity
Low ambient temperature
High moisture content
High moisture content
High treatment temperature
Low hydraulic conductivity
Expensive solubility
enhancement additives
Low air conductivity
200 400
Treatment Cost ($/ton)
600
800
Figure 2-1. Estimated Cost Ranges of
In Situ Remediation Technologies
2.2 Generic Critical Factors for Feasibility
Screening of In Situ Treatment
Several critical factors apply to the evaluation of in situ
treatment at most sites. These generic critical factors have
broad application regardless of the specific technology. Five
categories have been identified to assist in organizing
consideration of the potential feasibility of the in situ treat-
ment for a particular site. This evaluation relates to the
three screening criteria named in the National Contingency
Plan (NCP) instituted by the Comprehensive Environmental
Response, Compensation, and Liability Act (CERCLA) of
1980 and described in the Guidance for Conducting Reme-
dial Investigations and Feasibility Studies under CERCLA -
Interim Final (U.S. EPA, 1988, EPA/540/G-89/004): effec-
tiveness, implementability, and cost. The five categories are
described in Table 2-3.
These generic factors give an overall framework for
evaluating the potential for using in situ technologies. Site
conditions that give a poor ranking in one or even several
factors do not necessarily indicate that in situ approaches
are unlikely to succeed. All of the generic and technology-
specific factors (see Section 3.0) of in situ and competing ex
situ technologies should be considered to indicate the gen-
eral trend of applicability of in situ treatment and to help
identify possible candidate treatment technologies.
The generic critical factors are geologic and in situ waste
material characteristics that are significant in controlling or
affecting the effectiveness or implementability of in situ
technologies. Although these factors generally are of inter-
est at all sites, some have more effect on the performance
of specific technologies. The user must not draw a conclu-
sion that in situ treatment is inappropriate based on one or
two unfavorable factors. The design features of a particular
technology may be able to eliminate or avoid some of the
limitations inherent with most in situ treatment technologies.
For example, in situ solidification/stabilization (S/S) technolo-
gies using mechanical mixing are less affected by the initial
Treatment of Soils In Situ
-------
Table 2-3. Generic Factors Influencing Selection of In Situ Treatment
Factor Influencing Selection of
In Situ Treatment
Hydrogeologic flow regime
(See Section 2.2.1)
Regulatory standards
(See Section 2.2.2)
Time available for remediation
(See Section 2.2.3)
Removal logistics
(See Section 2.2.4)
Waste conditions
(See Section 2.2.5)
Conditions Favoring Selection of
In Situ Treatment
High or moderate conductivity uniformly distributed in
formation
or
Low-conductivity regions surrounded by regions of high or
moderate horizontal conductivity (a)
Deep water table and/or competent aquitard below
contaminated volume
Wastes that are difficult to treat in accordance with Land
Disposal Restriction (LDR) requirements
Completion time not critical
Large volume of waste
Waste not accessible due to existing structures
Excavation difficult due to matrix characteristics or depth
Poor transportation infrastructure
Large volume of waste
Low contaminant concentrations
Basis
Treatment reagents must reach contaminated
matrix by advective or diffusions! flow
Delivery and recovery of treatment agents must
be controlled
LDRs apply to excavated material, unless the
material is excavated and treated within a
Corrective Action Management Unit (CAMU)
In situ treatment requires more time to complete
than ex situ treatment
In situ treatment does not require excavation
It is not economical to excavate large volumes for
treatment of low concentrations
In situ treatment may reduce the need for capital-
intensive treatment equipment
(a) The low-conductivity regions must be "thin" with respect to diffusion path length, which can be feet or inches for gas-phase diffusion in dry soils and inches or less
for water-phase diffusion. (See Table 2-2 for information on type of treatment agent.)
soil conductivity than are technologies that require delivery
of fluid flow (see Table 2-2). Moreover, technologies such
as steam injection, in situ vitrification, and radiofrequency
heating, although generally slower than conventional ex situ
methods, can proceed more quickly than in situ bioremed-
iation or soil vapor extraction.
2.2.1 Hydrogeologic Flow Regime
The hydrogeologic flow regime characterizes the gas and
liquid flow in the subsurface. Examination of flow regime
characteristics is directed at answering questions such as
the following:
• Will contaminant removal be achieved at an accept-
able rate?
• Will contaminant removal be complete and uniform?
• Will contaminants or treatment agents escape from the
treatment area?
The flow regime factor is controlled mainly by the amount
of available primary and secondary fluid flow routes, the
magnitude and homogeneity of hydraulic conductivity, fluid
levels and pressures, and the proximity to a discharge loca-
tion. Information needed to define the hydrogeologic flow
regime includes a complete understanding of the geologic
strata and how they were deposited, full characterization of
the fluids and deposits for fluid transmission properties, and
monitoring of soil moisture and water levels through at least
three seasons of one year.
Geologic, hydraulic, and fluid-behavior data are needed
to evaluate the flow regime. Geologic data include, in part,
primary and secondary effective conductivity, history of geo-
logic strata formation, and the stratigraphic and structural
characteristics of the deposit. Hydrologic data include both
surface water and groundwater flow, level, and pressure
characteristics. Surface water data, such as stream/lake
hydrographs and precipitation, infiltration, and recharge
measurements, are needed to understand the general water
balance of the system, whereas groundwater data, including
pressure graphs, well hydrographs, and hydraulic conductivi-
ty and dispersion measurements, are needed to calculate
water and mass flux through the system.
Understanding the spatial variation of conductivity also is
essential to evaluate candidate in situ treatment technolo-
gies. Preferred flow pathways develop in the subsurface
Treatment of Soils In Situ
-------
due either to inhomogeneities in the conductivity or to geo-
logic facies. Most soils have preferential flowpaths that are
responsible for much of the conductivity. The preferential
paths can arise from a number of causes such as root
intrusions, shrink/swell or wet/dry cycling, or uneven settling
(U.S. EPA, 1990, EPA/600/2-90/011, p. 39). These pre-
ferred pathways result in high hydraulic conductivity con-
trasts that can diminish the reliability and efficiency of in situ
treatment methods. Geologic deposits with little or no
vertical fracturing or with no highly developed bedding
planes and those containing hydraulic conductivity contrasts
of less than an order of magnitude will be conducive to in
situ methods. Implementation time will be less and removal
will be more complete when the system tends toward homo-
geneity.
A geology with uniformly distributed high conductivity is
most conducive to application of in situ treatment. Hydraulic
conductivity of more than 10~3 cm/sec is most favorable to
technologies that require flow of water solutions (see Table
2-2). For technologies that require air or vapor flow (see
Table 2-2), an air conductivity of more than 10"4 cm/sec is
most favorable (U.S. EPA, 1990, EPA/600/2-90/011, pp. 40
and 54). In situ treatment still can be applied in geologies
with much lower conductivities. However, contaminant
transport in the lower conductivity regions will occur by
slower diffusion processes rather than by bulk material flow.
Feasibility depends on the type of treatment agent, the
contaminant transport mechanisms, and the details of the
distribution of the primary and secondary flowpaths.
Many in situ treatment technologies require injection of
treatment agents such as steam, chemicals, or nutrients.
Often the treatment agents must then be collected from the
subsurface for further processing. The subsurface geology
should be amenable to containment of the treatment agents
in the contaminated area. Containment will be maximized
when vertical and horizontal hydraulic gradients are low or if
the treatment zone is bounded geologically by deposits with
low hydraulic conductivity. Close proximity to groundwater
discharge areas such as streams, lakes, and seeps can
jeopardize containment of in situ treatment agents.
2.2.2 Regulatory Standards
The regulatory standards factor characterizes the overall
regulatory climate at the site based on federal, state, and
local regulations. Examination of regulatory standards is
directed at answering questions such as these:
• What contaminant cleanup levels are required?
• Are land-use restrictions consistent with the candidate
technologies?
• Will in situ treatment cause unacceptable alteration of
soil conditions?
• Is injection of treatment chemicals consistent with
Land Disposal Restrictions (LDRs) and other regula-
tions, as required?
If the site is a CERCLA site, 40 CFR 300.400(g) requires
that any remedial alternative must satisfy (or provide a
waiver of) all Applicable or Relevant and Appropriate Re-
quirements (ARARs). Applicable requirements include
federal and state environmental standards, cleanup stan-
dards, and control standards that specifically address a
hazardous substance, pollutant, contaminant, remedial
action, location, or other circumstance at a CERCLA site.
Relevant and appropriate requirements are standards that
are not "applicable" but that specifically address a problem
or situation sufficiently similar to those encountered at a
CERCLA site (i.e., their use is well suited to the particular
site).
If the site is not a CERCLA site, it will not need to satisfy
a formal list of ARARs; however, it is probable that certain
regulatory requirements must still be met in the cleanup. In
either case, these requirements will be specific to the site
where treatment will occur and may vary from site to site.
Cleanup levels are one of the most important of the
regulatory requirements that will determine whether in situ
treatment is potentially acceptable. Treatability studies will
help to determine if an in situ treatment method can meet
the required performance levels. For extraction technolo-
gies, the total residual contaminant levels must be deter-
mined to demonstrate remediation. For technologies that
reduce contaminant mobility, such as S/S or in situ vitrifica-
tion, the cleanup levels will be stated in terms of leaching
resistance. Leaching data such as results from the Toxicity
Characteristic Leaching Procedure (TCLP) or other leaching
tests will be needed to demonstrate that the method immo-
bilizes the contaminants. The ability to demonstrate that an
in situ treatment method meets the regulatory performance
requirements will determine the acceptability of that type of
treatment method. Thus, regulatory requirements should be
considered at the screening level to the extent that they are
known. Although the requirements may not have been
finalized at the time screening is conducted, the most cur-
rent list available should be used.
In situ treatment may require more extensive sampling
than ex situ treatment to demonstrate that required treat-
ment performance levels have been achieved. With in situ
treatment, the variation in natural conditions and the distri-
bution of the contaminant must be determined. This often
requires extensive sampling to build a statistical basis for
evaluating whether or not analytical results represent in situ
conditions. In contrast, in a typical ex situ treatment system,
waste material is excavated, prepared, and homogenized as
part of the treatment operation. These homogenized batch-
es can be represented with a smaller number of samples
than corresponding in situ materials.
In the past, regulatory requirements favored in situ
treatment in some cases because excavation of contami-
nated material would have caused it to be treated as a
RCRA waste subject to the treatment standards and Best
Demonstrated Available Technologies (BDATs) under the
LDRs. Recently, however, the EPA published a final rule
allowing the use of Corrective Action Management Units
(CAMUs) at RCRA sites (58 FR 8658, February 16, 1993),
which can eliminate this advantage for in situ treatment.
Although these regulations were developed for corrective
actions at RCRA facilities, the regulations also may be
Treatment of Soils In Situ
-------
applied as ARARs to CERCLA sites, particularly where
CERCLA remediation involves management of RCRA haz-
ardous wastes. A CAMU is defined as:
"an area within a facility that is designated by the Re-
gional Administrator under part 264 subpart S, for the
purpose of implementing corrective action requirements
under section 264.101 and RCRA section 3008(h). A
CAMU shall only be used for the management of reme-
diation wastes pursuant to implementing such corrective
action requirements at the facility" (40 CFR 260.10).
CAMUs were designed to provide more flexibility in treat-
ment of waste generated during corrective actions. An
important provision of the new regulations is the specifica-
tion in 40 CFR 264.552(a)(1) and (2) that:
"(1) Placement of remediation wastes into or within a
CAMU does not constitute land disposal of hazard-
ous wastes; and
(2) Consolidation or placement of remediation wastes
into or within a CAMU does not constitute creation
of a unit subject to MTRs (minimum technology
requirements)."
As a result, an area or several areas at a RCRA facility (or
CERCLA site) can be designated as a CAMU and the
wastes can be removed from the ground, treated, and
replaced within the boundaries of that CAMU without being
required to comply with the LDR treatment standards.
EPA's goal in issuing these regulations is to encourage the
use of more effective treatment technologies at a specific
site. In situ treatment could still be the favored option at
sites where the Regional Administrator does not establish a
CAMU and where the ex situ treatment is subject to treat-
ment standards and BOAT under the LDRs.
Technologies that accomplish the treatment in situ may
reduce or eliminate point source air emissions or other
discharges. Many in situ treatment technologies, however,
do have aboveground components. For example, materials
are injected; groundwater is extracted, treated, and reinjec-
, ted; or vapors are captured and treated. The aboveground
portion still may be subject to appropriate environmental
regulations. Technologies that require injection of fluids
may need to follow Underground Injection Control regula-
tions.
2.2.3 Time Available for Remediation
The available time factor characterizes the amount of
time allowed to set up, operate, and remove the treatment
technology. Determining the time available to complete
remediation is directed at answering questions such as:
• Can the cleanup be completed in a time frame con-
sistent with health, safety, and environmental protec-
tion?
• Can the cleanup be completed in a time frame con-
sistent with end-use requirements?
The time available for remediation is controlled first by
the need to protect human safety and health and the envi-
ronment. Remediation must proceed quickly if a toxic
contaminant is present, the contaminant concentration is
high, or the contaminant is mobile and near a critical eco-
system. Time available may be controlled also by the value
or intended end use for the site. It is undesirable to hold a
high-value site out of productive use for a long period.
In situ remediation typically requires more treatment time
than the analogous ex situ treatment technology. In situ
bioremediation, for example, typically requires about 4 to 6
years (U.S. EPA and U.S. Air Force, 1993, p. 60). Excava-
tion allows essentially immediate remediation of the site.
However, the excavated material often must be shipped and
stored before treatment. Rapid remediation is needed if the
contaminant presents an imminent danger due to hazard
level, mobility, or other factors. Rapid remediation of an
imminent hazard generally favors an ex situ remediation
approach.
The importance of the length of remediation time may be
lessened if the time constraint is driven by economic or end-
use requirements. Many in situ technologies can be applied
concurrently with other site operations. For example, well
and injection/extraction equipment for bioventing, soil vapor
extraction, or fixed-system steam injection do not occupy the
full surface area of a site. Depending on the technology
and the site use, it may be possible to continue routine site
operations during an in situ remediation. However, the need
for rapid remediation still generally increases the favorability
of ex situ treatment technologies.
2.2.4 Removal Logistics
The removal logistics factor characterizes the feasibility
of excavating, handling, and transporting the contaminated
soil. Examination of removal logistics is directed at answer-
ing questions such as:
• Is the material accessible for excavation?
• Can the contaminated soil or water be moved efficient-
ly by conventional bulk material-handling equipment
and techniques?
• Will on-site (and if needed off-site) infrastructure sup-
port transport of waste materials?
. Removal logistics are determined by access to the
contaminated site for excavation, the ability to handle
excavated materials, space for placement of ex situ treat-
ment equipment, and the road and rail system on and
around the site.
Data needed to evaluate the removal logistics include a
map of the site showing the general arrangement of struc-
tures and infrastructure and an approximate assessment of
the subsurface conditions such as the location of contami-
nation and the location of major geologic and hydrogeologic
features such as surface water and aquifers.
Treatment of Soils In Situ
-------
Poor removal logistics favor in situ treatment. In situ
treatment generally is favored by conditions such as con-
tamination located under a building that is to remain after
remediation; presence of buried piping or utility lines in the
area; contamination located at great depth or under a rock
formation; poor road or rail access; nearby businesses,
schools, or heavy traffic areas; or site location in a remote
area distant from treatment facilities or sources of backfill.
Contamination located deeper than 5 feet or occupying a
volume of more than 1,000 m3 increases both the cost and
the complexity of excavation (U.S. EPA, 1990, EPA/600/2-
90/01 1, p. 60). Specialized delivery and recovery systems
may be necessarylo overcome poor site logistics.
2.2.5 Waste Conditions
The waste conditions factor characterizes the chemical
and physical form of the waste with respect to the ability to
effectively treat or remove the contaminant. Examination of
waste conditions is directed at answering questions such as:
• Are the concentration and distribution of contaminants
consistent with effective in situ treatment?
* Does the waste distribution or condition allow effective
delivery of treatment agents to the contaminant?
The waste conditions factor is controlled by the in situ
conditions of the contaminant and matrix. The conditions
requiring characterization include the concentration and
distribution of the contaminant, the chemical form and spec-
iation of the contaminant and matrix, and physical properties
of the waste and matrix.
Data needed to characterize the waste conditions include
a survey of the location, concentration measurements, and a
description of the form of contaminant, matrix, and debris in
the remediation site. Some soil sampling data may be
available, but assessment of the waste condition at the
preliminary evaluation stage typically will be based largely
on historical records.
The understanding of waste conditions must be constant-
ly reevaluated as additional data are obtained. In addition
to estimating the areal extent and concentration of contami-
nation, the assessment must address the possibility of the
contaminant being contained in drums or tanks and the
potential presence of noncontaminant debris that could
make excavation difficult or obstruct the flow of in situ treat-
ment agents.
In general, contaminants that are either highly concen-
trated or spread over a relatively small area are best treated
by ex situ methods. In particular, contaminants contained in
drums or underground tanks are difficult to treat with in situ
methods. Dilute or widely distributed contaminants tend to
favor in situ treatment. When the contaminant is present at
low concentration, ex situ processing requires excavation,
handling, and, processing of a high proportion of matrix
materials relative to a small amount of contaminant.
3.0 Technology-Specific Factors
This section outlines the characteristics of in situ tech-
nologies and describes factors identified by current testing
programs as influencing the effectiveness, implementability,
and cost of specific in situ treatment technologies. Review-
ing these technology-specific critical factors will help guide
planning of site characterization activities and identification
of technology candidates. Where possible, specific values
are given to indicate what level of a factor is favorable for
application of in situ treatment.
The user must consider all of the generic factors {see
Table 2-3) and technology-specific factors during evaluation
of technology alternatives. The more important factors are
indicated in Tables 3-1 to 3-8 by an asterisk (*) to assist in
the evaluation. However, the evaluation must not focus on
only one factor or one technology. All of the factors should
be evaluated for all technologies that are potentially effective
for the contaminants present at the site. After full consid-
eration of all the factors, the decision maker can examine
the overall indications for favorable and unfavorable trends
to identify technologies with a high probability of being effec-
tive and implementable. The generic factors will help indi-
cate if in situ approaches are generally favored for the site
and contaminants in question. If an in situ technology
seems attractive, the technology-specific factors can help
guide selection of a group of candidates for more detailed
testing and evaluation.
The success or failure of an applied technology often
depends on site-specific conditions or design features.
Selection of technology candidates should be based on site-
specific knowledge and requirements, tempered by the
overall effect of all of the critical factors, Treatability testing
typically will be required to support final technology selection
prior to completion of the feasibility study (FS) or prepara-
tion of the Record of Decision (ROD) (U.S. EPA, 1992,
EPA/540/R-92/0713).
Action levels are provided where possible to give a
starting basis for considering technology alternatives. The
action levels give an approximate "yardstick" to use when
considering technology candidates. However, these single-
value indications cannot characterize or summarize all of the
complex situations that occur in practice. There is no sub-
stitute for experience, site-specific knowledge, and treatabili-
ty testing. The user must be aware of the limitations of
giving a single value to characterize complex interactions.
Site-specific conditions can cause the action levels to be
different at a particular site or with a particular combination
of contaminant and matrix. Design or operating features
may be applied to overcome technology limitations. For
example, at a site where in situ bioremediation is ideal
except for the condition of low soil temperature, a number of
methods are available to improve the soil energy balance.
Many of the technology-specific critical factors show thresh-
old effects. The factor may have an important effect at
some level but have no effect below the cutoff level. For
example, metals such as zinc are trace nutrients at low
levels but toxic to biological systems at higher levels.
10
Tr&atm&nt of Soils In Situ
-------
3.1 Delivery and Recovery Systems
Efficient delivery and recovery methods control the
effectiveness, implementability, and cost of in situ treatment.
An array of delivery techniques are available to apply or
inject treatment fluids into the subsurface. The types of
delivery systems for in situ treatment can be classed gener-
ally as gravity driven, pressure driven, auger mixing, and
energy coupling. Recovery systems typically fall in the
gravity-driven or pressure-driven classification (U.S. EPA,
1990, EPA/600/2-89/066, p. 2).
With the exception of radiofrequency heating and in situ
vitrification, the in situ treatment methods discussed below
require delivery and control of liquid, slurry, gas, vapor, or a
combination in the soil. For some technologies (see Table
2-2), the fluids also must be recovered after passing through
the contaminated in situ volume. Fluid delivery may be
accomplished by conventional gravity infiltration through
surface or trench application or by pressure injection
through wells. Conventional recovery methods include
trenches or wells. The conventional methods rely on flow
patterns determined by the design and placement of the
drains or wells and the subsurface stratigraphy. As de-
scribed below, innovative techniques are available to modify
the subsurface conditions to improve flow rates or flow
control.
In situ treatment agents, summarized in Table 2-2, in-
clude fluids delivered to the contaminated volume. Possible
treatment fluids include hot gasses or vapors; water; or
water-containing nutrients, surfactants, anions, cations,
bacteria, S/S binder, or other treatment agents. For a
technology to be effective, implementable, and economically
competitive; the treatment agents must be delivered in a
well-controlled manner. Conventional gravity- and pressure-
driven methods are available to deliver and recover fluids.
Gravity-driven methods rely on infiltration and collection due
to hydraulic gradients. Typically delivery is by surface
distribution and collection is by trench or similar drains.
Pressure-driven methods rely on pressure gradients sup-
plied by a source pump, a blower or steam generator, or an
extraction pump or blower. A system of wells typically is
used for delivery and recovery. The conventional delivery
and recovery systems are highly dependent on the physico-
chemical environment in the subsurface.
Innovative approaches are being developed and tested to
improve the performance of delivery and recovery
technologies in low-conductivity or ^heterogeneous geologic
settings. The innovative delivery and recovery technologies
may be devised to increase the conductivity in the treatment
zone, decrease the conductivity below the treatment zone,
or improve the efficiency of contact between the treatment
agents and the material to be treated. Conductivity .modifi-
cation technologies include hydraulic fracturing, pneumatic
fracturing, radial well drilling, jet slurrying, and kerfing.
Technologies to improve the distribution or application
efficiency of treatment agents include colloidal gas bubble
(aphron) generation, ultrasonic methods, and cyclic pumping
or steaming (U.S. EPA, 1990, EPA/540/2-90/002, p. 96).
Auger-mixing technologies have been developed to
deliver treatment agents with less reliance on a favorable
existing geology. Auger mixing is applicable to delivery but
not to recovery of treatment agents. The main examples of
auger delivery are steam injection and addition and mixing
of solidification/stabilization binders with augers. One ven-
dor is testing auger mixing for addition of bioremediation
nutrients.
Technologies to apply energy rather than fluids also are
available for in situ treatment. Energy delivery systems
reduce dependence on in situ conductivity but are sensitive
to other in situ parameters. The key to energy delivery is
good coupling of the electric or electromagnetic field to the
soil being heated. The electric properties change as the
moisture content changes. The energy input processes
vaporize water so the electrical coupling properties of the
soil must change as treatment proceeds. The changing soil
properties increase the challenge in designing an efficient
energy application system.
Systems for pneumatic fracturing and hydraulic fracturing
to improve subsurface conductivity and a system to inject
oxygen microbubbles to remediate groundwater have been
accepted in the SITE Program. The demonstration of a
pneumatic fracturing system was completed at a site located
in South Plainfield, New Jersey (Mack and Aspan, 1993, p.
321). The Applications Analysis Report is in preparation
(U.S. EPA, 1992, EPA/540/R-92/077, p. 5).
For further information on delivery and recovery technol-
ogies, contact:
Michael Roulier (513) 569-7796
or
Wendy Davis-Hoover (513) 569-7206
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
3.2 In Situ Solidification/Stabilization
In situ solidification/stabilization refers to treatment
processes that mix or inject treatment agents into the
contaminated material in place to accomplish one or more of
the following objectives:
• Improve the physical characteristics of the waste by
producing a solid from liquid or semiliquid wastes
• Reduce the contaminant solubility
• Decrease the exposed surface area across which
mass transfer of contaminants may occur.
In situ S/S relies on the delivery and effective mixing of
binders with the contaminated soil. The critical factors
applicable for in situ solidification/stabilization with inorganic
binders such as cementitious materials (cements and pozzo-
lans), silicates, or lime are shown in Table 3-1.
Treatment of Soils In Situ
11
-------
Table 3-1. Solidification/Stabilization Critical Factors and Conditions for Cement-Based Treatment Systems'8'
Factor Influencing
Technology Selection
Presence of VOCs (*)
Contaminant
depth 0
Specific gravity,
viscosity, and
general mixing
properties (*)
SVOC content of
waste (*)
Oil and grease content
of waste (*)
teachability data (*)
Phenol content
Fine particle
Soluble inorganic salts
(e.g., chlorides) not tar-
geted by binder
formulation
Cyanide content of the
waste
Sulfate content of the
waste
Binder heat of
hyd ration
Conditions Favoring Selection
of In Situ Treatment
<50ppb{1)(2)
Varies with technology (1)
No action levels
specified (1)(3)
SVOCs <10,000 ppm (4)
No action levels
specified (1)
No action levels
specified (2)
<5% (5)
Limited amount of fine insoluble
paniculate (4)
No action levels
specified (1)
<3,000 mg/kg (4)
<1 ,500 ppm for Type I Portland
cement (6)
Various cement types can toler-
ate higher sulfate levels but no
action level specified (6)(3)
No action levels
specified (5)
Basis
« VOCs can vaporize during processing or curing;
therefore, low levels of VOCs are favorable
• Organic materials can interfere with bonding
• In-place mixing with conventional construction type
equipment is limited to near surface
• Auger systems demonstrated to 30 feet
• Grout injection depth typically is not a major limitation
« Good mixing is needed to ensure contact of the waste
and binder so a good S/S product is obtained
• Organic materials can interfere with bonding
» SVOCs can vaporize during processing or curing;
therefore, low levels of volatile compounds are favorable
(due to heat evolution in some processes, the favorable
limit can be much lower for some contaminants and S/S
binder combinations)
* Oil and grease can coat the waste particles inhibiting
setting or reducing the strength of the final product
• Mobile and soluble materials are more difficult to treat
• Phenol concentration greater than 5% can reduce the
compressive strength of the final product
• Fine particulates can coat the waste particles and
weaken the bond between the waste solids and cement
• Low concentrations are more favorable
• Threshold effects commonly occur
• Above some concentration levels, soluble salts can
reduce the physical strength of the final product, cause
large variations in setting time, or reduce the
dimensional stability of the cured matrix
• Cyanides interfere with bonding of waste materials
• Presence of sulfates can retard setting
» High sulfate levels in waste can cause treated waste to
spall during curing due to formation of expansive
hydrates
« Large amount of heat generated-by binder hydration
reactions, particularly in large mass treatment, can
increase temperature and volatilize organic
contaminants
Data Needs
• Analysis for VOCs
« Treataoility tests measuring
volatile emissions
* Waste composition and spatial
distribution
* Waste-specific gravity
• Waste particle morphology and
size distribution
* Waste viscosity
• Analysis for SVOCs and PAHs
« Treatability tests measuring
volatile emissions
• Analyse for oil and grease
• teachability testing
» Phenol content in waste
• Particle-size analysis, particularly
size fraction under 200 mesh
• Treatability testing
• Analysis of inorganic content
• Analysis for cyanides
• Analysis for sulfate
• Total and time-dependent heat
output due to hydration of binder
• Treatability tests measuring
volatile emissions
(a) Also see Table 2-3 for generic factors,
(*) Indicates higher-priority factors,
(1) Conner, 1990, pp. 189,205, and 464-477.
(2) U.S. EPA, 1993, EPA/530/R-93/012, pp. 4-51 and A-8.
(3) U.S. EPA, 1990, EPA/540/2-90/002, pp. 14-16.
(4) U.S. EPA, 1988, EPA/540/2-88/004, p. 93.
(5) U.S. EPA, 1991, EPA 540/2-91/009, p. 3.
(6) Amiella and Blythe, 1990, p. 93.
12
Treatment of Soils In Situ
-------
, The most common binders are Portland cement, pozzo-
lans (siliceous or aluminous materials that can react with
calcium hydroxide to form compounds with cementitious
properties), and cement/pozzolan mixtures. Inorganic binder
systems using sodium silicate, cement/silicate, or proprietary
binder systems also are in use. Solidification/stabilization
encompasses a wide variety of physical and chemical mech-
anisms to reduce contaminant mobility and/or impart other
desirable properties to the waste. S/S treatment using
inorganic binders ties up free water by hydration reactions.
Mobility of inorganic compounds can be reduced by forma-
tion of insoluble hydroxides, carbonates, or silicates; sub-
stitution of the metal into a mineral structure; sorption;
physical encapsulation; and other mechanisms.
S/S treatment of organic contaminants with cementitious
formulations is more complex than treatment of inorganic
contaminants. Wastes where organics are the primary
contaminant of concern generally are not suited to S/S
treatment because of the potential for volatilization of organ-
ics and reduced S/S product quality when organics are
present. This is particularly true with VOCs where the
mixing process and heat generated by cement hydration
reactions can increase organic vapor losses. However, S/S
can be applied to wastes that contain lower levels of organ-
ics (particularly when inorganics are present at high
concentrations) and/or the organics have a low vapor pres-
sure, high water solubility, or both. Furthermore, recent
studies have indicated that addition of silicates or modified
clays to the binder system may improve S/S performance
with organics (U.S. EPA, 1993, EPA/530/R-93/012, pp. 4-12
and 4-13).
The most significant challenge in applying S/S in situ for
contaminated soils is achieving complete and uniform mixing
of the binder with the contaminated matrix (U.S. EPA, 1990,
EPA/540/2-90/002, p. 12). Three basic approaches are
used for mixing the binder with the matrix:
• Vertical auger mixing
• In-place mixing
• Injection grouting.
In vertical auger mixing, a system of augers is used to
inject and mix binder into the soil. Auger-type mixing sys-
tems developed by Novaterra (formerly Toxic Treatments
USA); International Waste Technologies (IWT)/Geo-Con,
Inc.; and S.M.W. Seiko, Inc. have been accepted in the
Superfund Innovative Technology Evaluation (SITE) Demon-
stration Program. SITE demonstrations have been complet-
ed for the Novaterra (U.S. EPA, 1991, EPA/540/A5-90/008)
and IWT systems (U.S. EPA, 1990, EPA/540/A5-89/004).
The treatment depth is limited by the length of available
auger equipment. Current testing indicates a limit of about
30 feet. Based on the SITE Program test of in situ S/S
using the IWT/Geo-Con auger system, estimated treatment
costs were $111/ton and $194/ton for 4-auger and 1-auger
systems, respectively. The costs included equipment,
startup and fixed costs, labor, supplies, utilities, analytical,
facility modification, and demobilization (U.S. EPA, 1990,
EPA/540/A5-89/004, p. 26). Note that some of the auger
systems, particularly the Novaterra system, may inject
steam (or steam and hot air) instead of binders to perform
steam stripping of organics. These operations are discus-
sed in Section 3.9.
In-place mixing involves spreading and mixing of binder
reagents with waste by conventional earth-moving equip-
ment such as draglines, backhoes, or clamshell buckets.
The technology is applicable only to surface or shallow
deposits of contamination.
The reported cost of in-place mixing is $38/yd3. The cost
includes labor, equipment, monitoring and testing, reagents,
and miscellaneous supplies. Not included are costs for
equipment mobilization and demobilization, engineering and
administration, and health and safety (Arniella and Blythe,
1990, p. 101).
For injection grouting, a binder containing dissolved or
suspended treatment agents is forced into the formation
under pressure and allowed to permeate the soil. Grout
injection can be applied to contaminated formations lying
well below the ground surface. The injected grout then
cures in place to give an in situ treated mass. Grout injec-
tion is widely used for soil stabilization. A grouting system
for very fluid wastes developed by Hazardous Waste Control
has been accepted for testing in the SITE Program (U.S.
EPA, 1992, EPA/540/R-92/077, p. 100).
For further information on in situ solidification/
stabilization technologies, contact:
Patricia Erickson (513) 569-7884
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
26 West Martin Luther King Drive
3.3 Soil Vapor Extraction
In situ soil vapor extraction (SVE) is the process of
removing VOCs from the unsaturated zone to the surface
for treatment. Blowers attached to extraction wells alone or
in combination with air injection wells induce airflow through
the soil matrix. The airflow strips the volatile compounds
from the soil and carries them to extraction wells. The
process is driven by partitioning of volatile materials from
condensed phases (sorbed on soil particles, dissolved in
pore water, or nonaqueous liquid phases) to the clean air
being introduced by the vacuum extraction process. Air
emissions from the systems typically are controlled ex situ
by adsorption of the volatiles onto activated carbon, thermal
destruction (i.e., incineration or catalytic oxidation), or con-
densation by refrigeration (U.S. EPA, 1991, EPA/540/2-
91/006, p. 3). Application of soil vapor extraction relies on
the ability to deliver, control the flow, and recover stripping
air. A decision logic for treatability testing based on contam-
inant vapor pressure and air permeability of the soil has
been described in the literature (U.S. EPA, 1992,
EPA/600/K-92/003, pp. 4-8 and 4-9).
The critical factors to consider during review of SVE
technology application are presented in Table 3-2. The SVE
Treatment of Soils In Situ
13
-------
Table 3-2. Soil Vapor Extraction Critical Factors and Conditions*"'
Factor Influencing
Technology Selection
Contaminant vapor pres-
sure, Pv (*)
Air conductivity of soil (*)
Soil moisture content^*)
Clay content of soil (*)
Humic content in soil (*)
Soil sorption capacity (*)
Contaminant water
solubility {*)
Henry's law constant (*}
Dominant contaminant
phase
Soil temperature
Depth to groundwater
Conditions Favoring Selection
of In Situ Treatment
P¥ >0,5 mmHg at 20°C
(Reference describes decision
logic) (1)
>10~* cm/sec (2)
(Decision logic described) (1)
<10 volume % (2)
No action levels specified (1)
No action levels specified (3)
Specific surface area
<0.1 m2/g (2)
<100 mg/L (2)
>0,001 dimensionless (4)
Contaminant present as a sep-
arate phase (vapor or liquid) and
not sorbed to the soil (2)
>20°C (2)
Contaminant in the unsaturated
zone (2)(5)
Basis
• Contaminants of higher volatility are more easily
removed by air stripping
• High conductivity results in a large radius of
influence for extraction weiis
• Soil moisture inhibits airflow and can reduce
vapor pressure of soluble organics
* Low clay content is desirable
• Presence of clay increases sorption and inhibits
volatilization
« Low humic content is desirable
* Presence of humic materials increases sorption
and inhibits volatilization
• Contaminants held by sorption mechanisms are
more difficult to remove
* Dissolved orpnfcs are more difficult to remove
by air stripping
• Compounds that partition to the vapor phase are
more easily removed by stripping
• Vapors are more easily removed by air stripping
* Higher soil temperatures are more favorable to
volatilization
• Technology only effective in the unsaturated
zone
• Need to avoid water intrusion into extraction
wells
Data Needs
* Contaminant vapor pressure at
expected soil temperature
• Hydrogeologic flow regime
• Soil moisture content
• Soil composition
* Soil color
• Soil texture
* Soil composition
• Soil color
• Soil texture
* Soil-specific surface area
• Soil absorption isotherms
• Contaminant solubility at expected
soil temperature
• Henry's law constant
• Contaminant composition and
physical form
• Soil temperature
• Depth to groundwater
* Seasonal variation of groundwater
conditions
(a) Also see Table 2-3 for generic factors.
(*) indicates higher-priority factors.
(1) U.S. EPA, 1912. EPA/600/K-92/003, pp. 4-8 and 4-9.
(2) U.S. EPA, 1990, EPA/600/2-90/011, p. 40.
(3) U.S. EPA, 1988. EPA/540/2-88/004, p. 89.
(4) U.S. EPA, 1992. EPA/540/R-92/077, p. 175.
(5) U.S. EPA, 1991. EPA/540/2-91/003, p. 52.
technology has been used in commercial operations for
several years. It has been chosen as a component of the
RODs at more than 80 Superfund sites (U.S. EPA, 1992,
EPA 542/R/92-011, pp. 31-46).
Vertical wells are the most widely used SVE design
method. Vertical wells are best used at sites where the
contamination extends far below the land surface. Horizon-
tal wells or trenches may be more practical than vertical
wells where the depth to groundwater is less than 12 feet.
Vertical wells generally are inappropriate for sites with a
shallow water table due to the potential upwelling of the
water table that may occur after application of a high vacu-
um (U.S. EPA, 1991, EPA/540/2-91/003, p. 52).
SVE systems have been accepted in the SITE Program
(U.S. EPA, 1992, EPA/540/R-92/077). SITE demonstrations
of soil vapor extraction systems were completed at a Super-
fund site in Burbank, California (U.S. EPA, 1991, EPA/540/-
A5-91/002) and a Superfund site in Groveland, Massachu-
setts (U.S. EPA, 1989, EPA/540/A5-89/003). A reference
handbook on soil vapor extraction (U.S. EPA, 1991, EPA/5-
40/2-91/003) and screening computer software for an ap-
proach to the design, operation, and monitoring of SVE
systems are available (U.S. EPA, 1993, EPA/600/R-93/028).
Based on available data, SVE treatment cost estimates
typically are $50/ton for treatment of soil. The reported
estimates of cost ranges are $15 to $60/yd3 (U.S. EPA,
1990, EPA/600/2-90/011, p. 40) and $27 to $66/ton (U.S.
EPA, 1989, EPA/540/A5-89/003, p. 11). The cost ranges
14
Treatment of Soils In Situ
-------
include consideration of site preparation; equipment pur-
chase, installation, and operation; residual well cuttings
disposal; analysis; and demobilization. The high end of the
range includes off-gas treatment, whereas the lower cost
does not. Off-gas treatment can amount to more than 50%
of the total cost of an SVE system (U.S. EPA, 1990, 937.5-
06/FS, p. 3-141).
For further information on soil vapor extraction technolo-
gies, contact:
Michael Gruenfeld (908) 321-6625
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
Building #10 (MS 104)
2890 Woodbridge Avenue
Edison, NJ 08837-3679
3.4 In Situ Bioremediation
In biological processes, microorganisms degrade organic
compounds either directly to obtain carbon and/or energy, or
fortuitously in a cometabolic process with no significant
benefit to the microorganism. The ultimate goal of in situ
bioremediation is to convert organic contaminants into
biomass and innocuous by-products of microbial metabolism
such as carbon dioxide, inorganic salts, and water. Suc-
cessful in situ bioremediation can occur only if microbial
populations are present that can be stimulated to degrade
the contaminants of concern. In situ bioremediation capital-
izes on natural biological processes to enhance in situ
degradation of organic contaminants. Although biodegrada-
tion of organic contaminants occurs naturally in situ, often a
critical factor, such as oxygen, is limiting, thus limiting the
amount of biodegradation that can occur.
To increase the amount of biodegradation that occurs, in
situ amendments often are necessary. These amendments
may include electron acceptors (such as oxygen), carbon
sources, moisture, nutrients, or heat. The critical factors to
consider during review of in situ bioremediation applications
are presented in Table 3-3.
Bacteria, actinomycetes, and fungi in the subsurface
make up the most significant group of organisms involved in
biodegradation. These communities are diverse and adap-
table, capable of taking advantage of xenobiotic compounds.
Microbial populations at older sites generally are acclimated
to the contaminants of concern. Consequently, lack of
biodegradation in situ rarely is due to lack of populations
able to degrade the compounds, but more likely is due to
environmental conditions that limit the extent and rate of
biodegradation. Typically the most important parameters
are electron acceptor availability, moisture levels, tempera-
ture, pH, and nutrients.
Another critical parameter affecting the extent of in situ
bioremediation is bioavailability of the contaminant(s) of
concern. Bioavailability is a general term to describe the
accessibility of contaminants to the degrading populations.
Bioavailability consists of (1) a physical aspect related to
phase distribution and mass transfer, and (2) a physiological
aspect related to the suitability of the contaminant as a sub-
strate (U.S. EPA, 1993, EPA/540/S-93/501, p. 4). Com-
pounds with greater aqueous solubilities and lower affinity to
sorb onto the soil generally are more bioavailable to soil
microorganisms and are more readily degraded. Bioavail-
ability also depends on the suitability of the compound as a
metabolic substrate or cosubstrate.
Aerobic (>0.2 mg/L oxygen) or anaerobic conditions may
predominate in the subsurface. Mineralization of many
organic compounds occurs aerobically; therefore, aerobic
bioremediation is the most developed and most feasible in
situ biotechnology. In situ bioremediation under aerobic
conditions involves delivering oxygen and nutrients to the
subsurface through an injection well or infiltration system.
The oxygen and nutrients enhance the activity of indigenous
aerobic microorganisms that degrade the contaminants of
concern. In general, aerobic processes can be suitable for
remediation of petroleum hydrocarbons, halogenated and
nonhalogenated aromatics, polyaromatic hydrocarbons,
halogenated and nonhalogenated phenols, biphenyls,
organophosphates, and some pesticides and herbicides.
Biodegradation rates are compound specific, so treatability
judgments should be based on literature data for the con-
taminants present or on treatability tests.
Although mineralization of many compounds occurs
aerobically, some halogenated hydrocarbons may be
transformed under anaerobic conditions. These halogenat-
ed hydrocarbons include unsaturated alkyl halides (e.g.,
PCE and TCE) and saturated alkyl halides (e.g., 1,1,1-
trichloroethane and trihalomethane). In addition, supplying
nitrate as an electron acceptor under anaerobic conditions
may allow biodegradation of some phenols, cresols, and
lower-molecular-weight polycyclic aromatic hydrocarbons
(PAHs).
Anaerobic bioremediation is at a much earlier stage of
development than aerobic bioremediation. Establishing and
maintaining anaerobic conditions in situ is more difficult than
establishing and maintaining aerobic conditions. Anaerobic
treatment systems can have undesirable secondary effects
such as formation of volatile forms of metals (such as meth-
ylated mercury or arsines), toxic "deadend" intermediates
such as vinyl chloride and hydrogen sulfide, or nuisance
odor compounds.
Addition of amendments to promote in situ biodegrada-
tion generally relies on the ability of aqueous solutions to
infiltrate into the contaminated area. Aqueous-supplied
amendments have met with limited success, as the electron
acceptor or nutrient often is metabolized before it reaches
the contaminated area. Consequently, there is a high level
of microbial activity near or in the infiltration wells, often
resulting in plugging and poor flow.
In extreme environments, moisture or heat addition may
significantly improve bioremediation processes. Surface
insulation, warm water infiltration, and buried heat tape have
been used to increase the soil temperature. Their use has
Treatment of Soils In Situ
15
-------
Table 3-3. Bioremediation Critical Factors and Conditions'"'
Factor Influencing
Technology Selection
Spatial variation of
waste composition or
concentration (*}
Contaminant
biodegradability (*)
Oxygen content (*)
Available soil water (*)
Presence of elevated
levels of metals, highly
chlorinated organics, pes-
ticides and herbicides, or
inorganic salts (*)
In situ temperature
Soil nutrient content
Water solubility
pH
Redox potential
Organic carbon content
Conditions Favoring Selection of
In Situ Treatment
No action levels specified (1)
Ratio of biological oxygen demand
(BOD) to chemical oxygen demand
(COD) >0.1 (3)
Aerobic metabolism; dissolved 02
>0.2 mg/L (4)
Air-filled pore space of >10% (4)
Anaerobic metabolism; gas-phase
02 concentration <1% (4)
>25% and <85% of water-holding
capacity (4)
No action levels specified (1)
>10°C (3)
Optimum temperature typically
20°C to 40°C (5)
Carbon/nitrogen/phosphorus ratios
about 100:10:1 (4)
Carbon/sulfur ratio noted as
important but no action level
specified (1)
>1, 000 mg/L (2)
Between 5-9 pH units (5)
Aerobes and facultative anaer-
obes: >50 millivolts (mV) (4)
Anaerobes: <50 mV (4)
Total organic carbon (TOC) of
groundwater between 10 and
1000 mg/L (3)
Basis
• Homogeneous conditions are desirable
• Large variation in the contaminant concentration
causes variation in biological activity giving
inconsistent biodegradation
• Resistance to biological action inhibits
decontamination
• Oxygen depletion slows aerobic biological activity
• Oxygen is toxic to anaerobic systems
• High moisture content reduces bacterial activity by
limiting the transport of oxygen
» Low moisture content inhibits bacterial activity
• Materials can be toxic to microorganisms
• Lower levels are desirable
* Threshold effects commonly occur
• Optimum temperature range increases growth rate
• More diverse microbial populations are present in
optimum range
« Lack of adequate nutrients slows biological activity
• Contaminants with low solubility generally are more
difficult to degrade
• Toxic contaminants with high solubility, however, may
be more effective in suppressing bioactivity
• When pH is outside of range, biological activity is
inhibited
* Reflects oxygen availability in the soil
• Indicates the oxidation/reduction potential of the
matrix
• Low concentrations may cause organisms to favor
other food; high concentrations may be toxic to the
organisms
Data Needs
• Waste composition and spatial
distribution
* Waste composition
• Waste BOD and COD
* Presence of metals or salts
* Treatability testing
« Oxygen monitoring
• Percent water saturation of
pores
• Identification of specific com-
pound, oxidation state (metals),
and concentration
• Temperature history and/or
monitoring covering at least
three seasons
« Carbon/nitrogen/
phosphorus ratio
• Form of nitrogen (e,g., nitrate,
ammonia, organic nitrogen)
• Carbon/sulfur ratio
* Contaminant solubility in water
at treatment temperature
• Soil pH
* Soil redox potential
•TOC
(a) Also see Table 2-3 for generic factors.
(*) Indicates higher-priority factors.
(1) U.S. EPA, 1988, EPA/540/2-88/004, p. 114.
(2) U.S. EPA, 1990, EPA/600/2-90/011, p. 48.
(3) U.S. EPA, 1990, EPA/600/2-90/027, p. 85.
(4) U.S. EPA, 1993, EPA/540/S-93/501, p. 3.
(5) U.S. EPA, 1990, EPA/540/2-90/002, pp. 40 and 47.
Treatment of Soils In Situ
-------
resulted in increased microbial activity and contaminant
degradation (Leeson et al., 1993).
The reported costs for application of in situ bioremedia-
tion range from $14 to $98/ton (U.S. EPA and U.S. Air
Force, 1993, p. 60). The EPA Vendor Information System
For Innovative Treatment Technologies (VISITT), Version 2,
contains information from 11 vendors on in situ soil biorem-
ediation technologies. The costs indicated by the vendors
typically range from $8 to $250/yd3 (U.S. EPA, 1993, EPA/
542/R-93-001).
A variety of in situ bioremediation systems have been
accepted in the SITE Program. Technologies include the
use of naturally occurring microorganisms, addition of cul-
tured bacteria, and addition of white-rot fungi. Water and
nutrients generally are applied by well injection or infiltration.
However, one technology assembles a containment tank in
situ to form a controlled area for the bioremediation, and
one technology uses vertical augers to distribute organisms
and nutrients. All of the technologies stimulate aerobic
biodegradation, except one, which combines anaerobic and
aerobic microbial activity (U.S. EPA, 1992, EPA/540/R-
92/077, p. 208).
For further information on bioremediation technologies,
contact:
Carl Potter (513) 569-7231
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
3.5 Bioventing
Bioventing is the process of aerating subsurface soils to
stimulate in situ biological activity and promote bioremedia-
tion. Although bioventing is related to SVE, their primary
objectives are different. SVE is designed and operated to
maximize the volatilization of low-molecular-weight com-
pounds, with some biodegradation occurring. In contrast,
bioventing is designed to maximize biodegradation of aerobi-
cally biodegradable compounds, regardless of their molecu-
lar weight, with some volatilization occurring. Although both
technologies involve venting of air through the subsurface,
the differences in objectives result in different design and
operation of the remedial systems. Bioventing uses lower
air flow.
Bioventing normally is applied to certain types of organ-
ics, particularly petroleum hydrocarbons. It generally is not
considered useful for treating compounds such as PCBs
and chlorinated hydrocarbons.
The critical factors to consider during review of biovent-
ing are presented in Table 3-4. The significant features of
this technology include optimizing airflow to reduce volatil-
ization while maintaining aerobic conditions for biodegra-
dation; monitoring local soil gas conditions to ensure aerobic
conditions, not just monitoring vent gas composition; adding
moisture and nutrients as required to increase biodegra-
dation rates at some sites; and manipulating the water table
(dewatering) as required to ensure air/contaminant contact.
The in situ respiration test is useful as a rapid screening test
of the applicability of bioventing (Hinchee and Ong, 1992, p.
1305).
Table 3-4. Bioventing Critical Factors and Conditions'"'
Factor Influencing
Technology Selection
Spatial variation of
waste composition or
concentration (*)
Initial soil gas
concentrations (*)
Soil permeability (*)
Presence of elevated
levels of metals, highly
chlorinated organics,
pesticides and herbi-
cides, or inorganic
salts (*)
PH
Conditions Favoring Selection of
In Situ Treatment
No action levels specified (1 )
Initial soil gas concentrations of 02
(<5%), C02 (>10%), and total petro-
leum hydrocarbons (-10,000 ppm) (2)
Soil air permeabilities >0.1 darcy (2)
No action levels specified (1)
Between 5-9 pH units (3)
Basis
• Homogeneous conditions are desirable
• Large variation in the contaminant concentration causes varia-
tion in biological activity giving inconsistent biodegradation
• These concentrations suggest high microbial activity due to
hydrocarbon degradation and generally indicate that bioventing
is feasible
• Low soil permeabilities restrict airflow through the soil,
decreasing the amount of air that can be provided for microbial
activity
• Lower levels are desirable
• Threshold effects commonly occur
• Materials can be toxic to microorganisms
• When pH is outside of range, biological activity is inhibited
Data Needs
• Waste composition
and spatial
distribution
• Soil gas monitoring
• Soil air permeability
testing
• Waste composition
• Soil pM
(a) Also see Table 2-3 for generic factors.
(*) Indicates higher-priority factors.
(1) U.S. EPA, 1988, EPA/540/2-88/004, p. 114.
(2) Hinchee et al., 1992.
(3) U.S. EPA, 1990, EPA/540/2-90/002, pp. 40 and 47.
Treatment of Soils In Situ
17
-------
Understanding the distribution of contaminants is impor-
tant to any in situ remediation process. Much of the hydro-
carbon residue at a fuel-contaminated site is found in the
unsaturated zone soils, in the capillary fringe, and immedi-
ately below the water table. Seasonal water table fluctua-
tions typically spread residues in the area immediately
above and below the water table. Any successful bioreme-
diation effort must treat these areas. Bioventing provides
oxygen to unsaturated zone soils and can be extended
below the water table when integrated with a dewatering
system.
Currently, conventional enhanced bioreclamation pro-
cesses use water to carry oxygen or an alternative electron
acceptor to the contaminated zone. This is common wheth-
er the contamination is present in the groundwater or in the
unsaturated zone. In most cases where water is used as
the oxygen carrier, the oxygen solubility is the limiting factor
for biodegradation. If pure oxygen is used and 40 mg/L of
dissolved oxygen is achieved, approximately 80,000 Ib of
water must be delivered to the formation to degrade 1 Ib of
hydrocarbon. If 500 mg/L of hydrogen peroxide is success-
fully delivered, then approximately 13,000 Ib of water must
be used to degrade the same amount of hydrocarbon. As a
result, even if hydrogen peroxide can be successfully used,
substantial volumes of water must be pumped through the
contaminated formation to deliver sufficient oxygen.
The use of an air-based oxygen supply for enhancing
biodegradation relies on airflow through contaminated soils
at rates and configurations that will both ensure adequate
oxygenation for aerobic biodegradation and minimize or
eliminate the production of a hydrocarbon-contaminated off-
gas. The addition of nutrients and moisture may be desir-
able to increase biodegradation rates; however, field re-
search to date does not indicate the need for these addi-
tions (Dupont et al., 1991; Miller et al., 1991). A key feature
of bioventing is the use of narrowly screened soil gas moni-
toring points to sample gas in short vertical sections of the
soil. These points are required to monitor local oxygen
concentrations, because oxygen levels in the vent well are
not representative of local conditions.
Bioventing systems can be configured in either injection
or extraction mode, or a combination of the two to push or
pull air through the vadose zone. A system using only air
injection has the advantage of not creating a point source
emission. This technology relies on the ability to move air
through the contaminated soil. Low-permeability soils are
more difficult to treat with bioventingr
Bioventing was accepted in the SITE Program in June
1991. Treatability tests were performed at the Reilly Tar
site in St. Louis Park, Minnesota, and the site was found to
be suitable for a test of the effectiveness of bioventing in
treating PAHs. A single-vent system was installed and will
be operated for a 3-year test period (Alleman, 1993). The
U.S. EPA has completed one field study of bioventing and is
conducting several others (Sayles, 1993).
The reported range of costs for applying bioventing is
$60 to $90/ton (U.S. EPA and U.S. Air Force, 1993, p. 61).
tact:
For further information on bioventing technologies, con-
Gregory Sayles (513) 569-7607
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
3.6 In Situ Vitrification
In situ vitrification is a thermal treatment process that
converts contaminated soils to stable glass and crystalline
solids. It originally was developed to stabilize transuranic
contaminated wastes and is being extended to treatment of
other hazardous wastes. For in situ vitrification processes,
high voltage is applied via electrodes placed in the soil to
induce current flow. The current heats the soil to melt-
formation temperature. Heating destroys or vaporizes
organic contaminants. After heating stops, the melt cools to
form a stable solid material. Application of in situ vitrification
requires conduction of electricity through the media to be
treated.
One application of the technology is based on electric
melter technology, and the principle of operation is joule
heating, which occurs when an electrical current is passed
through a molten mass. Field application requires insertion
of electrodes into contaminated soils to supply the current
flow. Because unmelted soil is not conductive, a starter
path of flaked graphite and frit is placed between the elec-
trodes to act as the initial flowpath for electricity. Resis-
tance heating in the starter path creates a melt to carry
more current. The melt grows outward and downward from
the starter path (U.S. EPA, 1990, EPA/540/2-90/002, p. 17).
The melt can grow to encompass a volume of 1000 tons.
The maximum treatment depth is about 20 feet with possible
extension to 30 feet as the technology develops. Large
areas are treated in overlapping blocks.
Critical factors to consider during review of in situ vitrifi-
cation technology application are presented in Table 3-5.
The electric current flow heats soil to temperatures as
high as 1370°C (U.S. EPA, 1991, EPA 540/2-91/009, p. 7).
If the silica content of the soil is high enough, contaminated
soil is converted into durable glass. The combustible
wastes are pyrolyzed and other contaminants are incorpo-
rated into the vitreous mass. Off-gases released during the
melting process are trapped in an off-gas hood.
The main requirement for the technology is the ability for
the soil melt to carry current during heating and then solidify
to a stable mass as it cools. Wet soils can be treated by in
situ vitrification, but highly permeable soils and the presence
of groundwater increase operating costs. If the soil moisture
is recharged by groundwater, the electrical input needed to
vaporize the water increases costs. Buried combustibles or
containers such as tanks and drums introduce the possibility
of explosion.
18
Treatment of Soils In Situ
-------
The reported typical treatment rate is 3 to 5 tons per
hour (U.S. EPA, 1991, EPA 540/2-91/009, p. 7). In situ
vitrification is reported to provide above average long-term
effectiveness and permanence, and reductions in toxicity,
mobility, and volume.
In situ vitrification has been tested on a large scale ten
times, including two demonstrations on transuranic-
contaminated (radioactive) sites: (1) at Geosafe's test site,
and (2) at the U.S. Department of Energy's (DOE's) Hanford
Nuclear Reservation. More than 130 tests at various scales
have been performed on a broad range of waste types in
soils and sludges. The technology has been selected as a
preferred remedy at several private, EPA Superfund, and
DOE sites but has not been implemented in full-scale appli-
cation. In situ vitrification has been selected for the SITE
Program (U.S. EPA, 1992, EPA/540/R-92/077, p. 97). Tests
are being performed at the Parsons/ETM site in Grand
Ledge, Michigan.
There have been no full-scale applications to serve as a
basis for cost estimation. A DOE life-cycle cost analysis
suggests the overall cost of in situ vitrification would be
approximately $790/ton (U.S. EPA and U.S. Air Force, 1993,
p. 63). A commercial vendor of the technology indicates an
estimated cost range of $300 to $400/ton (Hansen and
FitzPatrick, 1991).
For further information on in situ vitrification technologies,
contact:
Teri Richardson (513) 569-7949
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
Table 3-5. In Situ Vitrification Critical Factors and Conditions04
Factor Influencing
Technology Selection
Soil composition (*)
Contaminant
depth {•)
Organic liquid content of
contaminated material (*)
Presence of in situ
voids (*)
Conductive metal
content (*)
Presence of sealed
containers (*)
Presence of combustible
solids
Presence of
groundwater
Surface slope
Location of
structures
Conditions Favoring Selection of
In Situ Treatment
>30% Si02
>1.4%Na20+K20
on dry weight basis (1)
>6 ft and
<20ft(1)
<1 to 7% organic content depending on
the BTU content of the organic (1)
Individual void volume <150 ft3 (1)(2)
<5% to 15% of total melt weight and
continuous conductive path <90% of
distance between electrodes (1)(2)
None present (1)
<3,200 kg combustible solids per meter of
depth or average concentration <30% in
the soil to be treated (1)
Groundwater control required if contami-
nation is below the water table and soil
hydraulic conductivity is >10~4cm/sec (1)
<+/-5% (1)
Underground structures and utilities
located >20 ft from melt zone (1)
Basis
• Required to form melt and cool to stable
treated waste form
• Overburden assists in capture of volatile
metals
• Deep contamination requires surface excava-
tion to allow placement of electrodes
• Can generate excessive hot off-gas on
combustion
• Can generate excessive off-gas
• Can cause excessive subsidence
• Can create a conductive path resulting in
uneven current flow and uneven heating
• Containers can rupture during heating
resulting in a large pulse of off-gas generation
• Can generate excessive off-gas volumes on
combustion
• Water inflow increases energy required to
vaporize water
• Melt may flow under influence of gravity
• Items closer than 20 ft to the melt zone must
be protected from heat
Data Needs
• Weight loss on ignition
• Soil mineral composition as
oxides (x-ray fluorescence)
• Contaminant composition and
distribution
• Contaminant composition
• Heat of combustion of organic
materials
• Subsurface geology
• Subsurface matrix conditions
• Contaminant composition and
distribution
• Contaminant composition and
distribution
• Contaminant distribution
• Location of water table
• Seasonal variation of
groundwater conditions
• Site surface slope
• Contaminant composition and
distribution
• Subsurface conditions
(a) Also see Table 2-3 for generic factors.
(*) Indicates higher-priority factors.
(1) Pacific Northwest Laboratory, 1993.
(2) U.S. EPA, 1991, EPA 540/2-91/009, p. 3.
..^atment of Soils In Situ
19
-------
3.7 In Situ Radiofrequency Heating
Radiofrequency heating is a technique for rapid and
uniform heating of large volumes of soil in situ. This tech-
nique heats the soil to the point where volatile and semi-
volatile contaminants are vaporized into the soil pore space.
Vented electrodes are then used to recover the gases
formed in the pores during the heating process. The ex-
tracted gases can be incinerated or subjected to other
treatment methods. Application of radiofrequency heating
relies on efficient electromagnetic coupling of the radiofre-
quency source and the media being heated.
Radiofrequency heating is accomplished by use of
electromagnetic energy in the radiofrequency band. The
heating process does not rely on the thermal conductivity of
the soil. The energy is introduced into the soil matrix by
electrodes inserted into drilled holes. The mechanism of
heat generation is similar to that of a microwave oven. A
modified radio transmitter serves as the power source, and
the industrial, scientific, and medical band provides the
frequency at which the modified transmitter operates. The
exact operational frequency is obtained from an evaluation
of the areal extent of the contamination and the dielectric
properties of the soil matrix.
The critical factors to consider during review of radiofre-
quency heating technology application are presented in
Table 3-6. Full implementation of a radiofrequency heating
system at a contaminated hazardous waste site requires
four major subsystems.
• A radiofrequency energy depositions array
• Radiofrequency power-generating, transmitting, moni-
toring, and control systems
• A gas and liquid condensate handling and treatment
system
• A vapor containment and collection system.
Radiofrequency heating originally was developed and
tested for recovery of heavy oil. Three treatability tests of
radiofrequency heating on contaminated soils have been
performed. The first test was conducted at Volk Air National
Guard Base, Camp Douglas, Wisconsin. The treated vol-
ume was 500 ft3 heated to a depth of 7 feet. The contami-
nants were in a fire training area where waste oils, fuels,
and other hydrocarbons had been placed and ignited to
simulate aircraft fires (U.S. Air Force, 1989, p. 1). The
second test, performed at Rocky Mountain Arsenal, heated
a 1600-ft3 volume to a depth of 13 feet to treat organo-
chlorine pesticides and organophosphorus compounds (U.S.
Table 3-6. Radiofrequency Heating Critical Factors and Conditions13'
Factor Influencing Tech-
nology Selection
Conditions Favoring Selec-
tion of In Situ
Treatment
Basis
Data Needs
Moisture content (*)
No action level
specified (1)
A low moisture content Is desirable
High moisture content increases cost due to energy
needed to vaporize water
Radiofrequency (RF) energy absorption properties
(dielectric constant and loss tangent) change as soil
dries, complicating design and operation of the RF
energy supply system
Soil moisture content
Contaminant boiling point (*)
Boiling point below 300°C (2)
Approximate economic limit of radiofrequency heating
Contaminant boiling point or
vapor pressure as a function of
temperature
Conductive metal content I
No action level specified (3)
Metals strongly absorb RF energy, creating uneven
heating
Subsurface matrix composition
Soil dielectric
constant
No action level specified (1)
Dielectric material is needed to couple with
radiofrequency fields for energy transfer
Change of properties with changing moisture content
is more important than actual magnitude of the
dielectric constant
Dielectric constant as a
function of moisture content
Soil loss tangent
No action level specified (1)
Dielectric material is needed to couple with
radiofrequency fields for energy transfer
Change of properties with changing moisture content
is more important than actual magnitude of the loss
tangent
Loss tangent as a function of
moisture content
(a) Also see Table 2-3 for generic factors,
(*) Indicates higher-priority factors.
(l)Srestyetal., 1986, p. 88.
(2) U.S. EPA, 1990, EPA/540/2-9Q/QQ2, p. 83.
(3) Just and Stockwell, 1993, p. 248.
20
Treatment of Soils In Situ
-------
Army, 1992, p. 2-1). A demonstration of a phased-acray
radiofrequency antenna system to heat vadose zone clay
deposits contaminated with chlorinated hydrocarbons was
completed at the DOE Savannah River Laboratory (Kase-
vich et al., 1993, p. 23). Two radiofrequency heating tech-
nologies have been accepted in the SITE Program. The
demonstrations are being conducted at Kelly Air Force
Base, Texas and are scheduled for completion in 1994 (U.S.
EPA, 1992, EPA/540/R-92/077, p. 109).
The vendor indicates that the approximate cost range for
application of radiofrequency heating is $30 to $100/ton of
soil treated, depending on the moisture content (5% to 20%)
and the treatment temperature (100°C to 250°C) (U.S. EPA,
1989, EPA/600/S2-89/008, p. 2)(Sresty et al., 1992, p. 363).
For further information on radiofrequency heating tech-
nologies, contact:
Janet Houthoofd (513) 569-7524
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
3.8 Soil Flushing
Soil flushing is a process whereby the zone of contami-
nation is flooded with an appropriate washing solution to re-
move the contaminant from the soil. Water or an aqueous
solution is injected into or sprayed onto the area of contami-
nation. The contaminants are mobilized by solubilization,
formation of emulsions, or a chemical reaction with the
flushing solutions. After passing through the contamination
zone, the contaminant-bearing fluid is collected by strategi-
cally placed wells and brought to the surface for disposal,
recirculation, or on-site treatment and reinjection. Applica-
tion of soil washing relies on the ability to deliver, control the
flow, and recover the flushing fluid.
The critical factors to consider during review of soil
flushing technology application are shown in Table 3-7. Soil
flushing requires the identification of a flushing solution that
is available in sufficient quantity at a reasonable cost.
Flushing solutions may be water; acidic aqueous solu-
tions (such as sulfuric, hydrochloric, nitric, phosphoric, or
carbonic acids); basic solutions (such as sodium hydroxide);
chelating or complexing agents; reducing agents; or surfac-
tants. Water will extract water-soluble or water-mobile
constituents. Acidic solutions can be used to remove metals
or basic organic materials. Basic solutions may be used for
some metals such as zinc, tin, or lead and some phenols.
Chelating, complexing, and reducing agents may be needed
to recover some metals. Surfactants can assist in emulsifi-
cation of hydrophobic organics (U.S. EPA, 1991, EPA/540/2-
91/021, p. 2).
Soil flushing to remove organic materials has been
demonstrated at both bench and pilot scale. Several sys-
tems are in operation and many systems are being de-
signed for remediation of Superfund sites. Studies have
been conducted to determine the appropriate solvents for
mobilizing various classes and types of chemical constitu-
ents. Most of the applications involve remediation of VOCs
(U.S. EPA, 1992, EPA/542/R-92/011, pp. 26-29).
The soil flushing technology may be easy or difficult to
apply, depending on the ability to flood the soil with the
flushing solution and to install collection wells or subsurface
drains to recover all the applied liquids. Provisions also
must be made for ultimate disposal of the elutriate. The
achievable level of treatment varies and depends on the
contact of the flushing solution with the contaminants, the
appropriateness of the solutions for the contaminants, and
the hydraulic conductivity of the soil. The technology is
more applicable to permeable soils.
Water can be used to flush water-soluble or water-mobile
organics and inorganics. Hydrophilic organics are readily
solubilized in water. Organics amenable to water flushing
can be identified according to their soil/water partition coeffi-
cients or estimated from their octanol/water partition coeffi-
cients. Organics considered generally amenable to soil
flushing with water or water and surfactants are those with
an octanol/water partition coefficient (K^) of less than about
1000. High-solubility organics (e.g., lower-molecular-weight
alcohols, phenols, and carboxylic acids) and other organics
with a coefficient less than 10 may already have been
flushed from the site by natural processes. Medium solubili-
ty organics (Koc = 10 to 1000) that can be effectively re-
moved from soils by water flushing include low- to medium-
molecular-weight ketones, aldehydes, and aromatics and
lower-molecular-weight halogenated hydrocarbons, such as
TCE and tetrachloroethylene (PCE) (U.S. EPA, 1990, EPA/-
600/2-90/011, p. 50).
Soil flushing for inorganic treatment is less well devel-
oped than soil flushing for organics. Some applications at
Superfund sites have been reported, however. One system
is operational at a landfill with mixed organics and metals,
and another is operational at a chromium-contaminated site
(U.S. EPA, 1992, EPA/542/R-92/011, pp. 27 and 29).
Several other inorganic treatment systems are in the de-
sign or predesign phases at Superfund sites. Inorganics
that can be flushed from soil with water are soluble salts
such as the carbonates of nickel, zinc, and copper. Ad-
justing the pH with dilute solutions of acids or bases will
enhance inorganic solubilization and removal.
Removal of inorganic contaminants by soil flushing
typically requires injection and recovery of a chemical leach-
ing solution. The leaching solution must be selected to
remove the contaminant while not harming the in situ envi-
ronment. Selection of the leaching solution also may be
limited by Land Disposal Restrictions or Underground Injec-
tion Control regulations.
Estimated costs for application of soil flushing range from
$75 to $200/yd3, depending on the waste quantity. These
are rough estimates and are not based on field studies (U.S.
EPA and U.S. Air Force, 1993, p. 56).
Treatment of Soils In Situ
21
-------
Table 3-7, Soil Flushing Critical Factors and Conditions**'
Factor Influencing
Technology Selection
Equilibrium partitioning of
contaminant between soil
and extraction fluid (*)
Complex waste mixture (*)
Soil-specific surface area (*}
Contaminant solubility in
water (*)
Octanol/water partitioning
coefficient (*)
Spatial variation in waste
composition (*)
Hydraulic conductivity {*}
Clay content (*}
Cation exchange
capacity (*)
pHO
Buffering capacity (*)
Flushing fluid
characteristics (*}
Soil total organic carbon
content
Contaminant vapor pressure
Fluid viscosity
Organic contaminant density
Conditions Favoring
Selection of In Situ
Treatment
No action levels specified (1)
No action levels specified (1)
<0.1m2/g(2)
>1,OOOmg/L(2)
Between 10 and 1000 (2)
No action levels specified (1)
>10~3 cm/sec
No action levels specified (3)
No action levels specified (3)
No action levels specified (3)
No action levels specified (3)
Fluid should have low toxic-
ity, low cost, and allow for
treatment and reuse (1)
Fluid should not plug or have
other adverse effects on the
soil (1)
<1 wt% (2)
<10 mmHg (2)
<2 centipoise (cP) (2)
>2 g/cm3 (2)
Basis
* Contaminant preference to partition to the extractant is
desirable
* High partitioning of contaminant into the extraction fluid
decreases fluid volumes
• Complex mixtures increase difficulty in formulation of a
suitable extraction fluid
• High surface area increases sorption on soil
* Soluble compounds can be removed by water flushing
• Very soluble compounds tend to be removed by natu-
ral processes
• More hydrophilic compounds are amenable to removal
by water-based flushing fluids
• Changes in waste composition may require
reformulation of extraction fluid
• Good conductivity allows efficient delivery of flushing
fluid
• Low clay content is desirable
« Presence of clay increases sorption and inhibits
contaminant removal
« Low cation exchange capacity is desirable
* Cation exchange capacity increases sorption and
inhibits contaminant removal
• May affect treatment additives required, compatibility
with materials of construction, or flushing fluid
formulation
* Indicates matrix resistance to pH change
• Toxicity increases health risks and increases regulatory
compliance costs
• Expensive or nonreusable fluid increases costs
« If the fluid adheres to the soil or causes precipitate
formation, conductivity may drop, making continued
treatment difficult
• Soil flushing typically is more effective with lower soil
organic concentrations
• Volatile compounds tend to partition to the vapor phase
• Lower-viscosity fluids flow through the soil more easily
• Dense insoluble organic fluids can be displaced and
collected by soil flushing
Data Needs
* Equilibrium partitioning
coefficient
* Contaminant composition
• Specific surface area of soil
* Contaminant solubility
• Octanol/water partitioning
coefficient
* Statistical sampling of
contaminated volume
• Hydrogeologic flow regime
• Soil composition
* Soil color
» Soil texture
• Cation exchange capacity
* Soil pH
* Soil buffering capacity
* Fluid characterization
• Bench- and pilot-scale testing
• Total organic carbon content of
soil
* Contaminant vapor pressure at
operating temperature
* Fluid viscosity at operating
temperature
* Contaminant density at
operating temperature
(a) Also see Table 2-3 for generic factors.
(*) Indicates higher-priority factors.
(1) U.S. EPA, 1988, EPA/540/2-88/004, p. 79.
(2) U.S. EPA, 1990, EPA/600/2-90/011, p. 54.
(3) U.S. EPA, 1991, EPA/540/2-91/021, p. 3.
22
Treatment of Soils In Situ
-------
The Superfund site at Palmetto Wood, South Carolina,
cited costs of $3,710,000 (capital) and $300,000 (annual
operation and maintenance). These totals, on a unit basis,
equal $185/yd3 for capital costs and $15/yd3 per year for
operation and maintenance (U.S. EPA, 1990, EPA/600/2-
90/011, p. 53).
For further information on soil flushing technologies,
contact:
Michael Gruenfeld (908) 321-6625
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
Building #10 (MS 104)
2890 Woodbridge Avenue
Edison, NJ 08837-3679
3.9 Steam/Hot Air Injection
and Extraction
In situ steam injection/extraction removes volatile and
semivolatile hazardous contaminants from soil and ground-
water without requiring excavation. Steam injection may be
supplemented by hot air injection. In a few experimental
studies, hot air or hot combustion off-gas has been injected
to strip organics from in situ soil without steam (Smith and
Hinchee, 1993, p. 156). Waste constituents are removed
from the soil by this technology but are not actually treated.
Steam enhances the stripping of volatile contaminants from
soil and can be used to displace contaminated groundwater
under some conditions.
Steam extraction is effective for compounds with lower
vapor pressures than those remediated with ambient-tem-
perature SVE systems. By increasing the temperature from
initial conditions to the steam temperature, the vapor pres-
sure of the contaminants increases, causing them to be
more volatile. Steam is injected to form a displacement
front by steam condensation to displace groundwater. The
contaminated liquid and steam condensate are then col-
lected for further treatment and/or recycling to the steam
generator.
Mobilized nonaqueous-phase liquid and groundwater also
may be collected for treatment and disposal. Application of
steam/hot air injection and extraction relies on the ability to
deliver, control the flow, and recover the heating fluid.
The critical factors to consider during review of steam/hot
air injection and extraction technology application are
presented in Table 3-8.
A limited number of commercial-scale in situ steam
injection/extraction systems currently are in operation in the
United States, but in situ steam injection/extraction is a
rapidly developing technology. In situ steam injection/
extraction is being considered as a component of the reme-
dy for only one Superfund site, i.e., the San Fernando
Valley in California (Area 1) (U.S. EPA, 1991, EPA/540/2-
91/005, p. 6).
There are two main types of steam/hot air injection/-
extraction systems: a mobile system and a stationary
system. The mobile system consists of a unit that volatilizes
contaminants in small areas in a sequential manner by
injecting steam and hot air through rotating cutter blades
that pass through the contaminated medium. The stationary
system uses wells to inject steam into the soil to volatilize
and displace contaminants from the undisturbed subsurface.
Examples of both types of steam injection technologies have
been accepted in the SITE Program (U.S. EPA, 1992,
EPA/540/R-92/077).
For the mobile technology, the most significant factor
influencing cost is the treatment rate. Treatment rate is
determined primarily by the soil type (soils with higher clay
content require longer treatment times), the waste type, and
the on-line efficiency. An evaluation of a SITE demonstra-
tion indicated costs of $67 to $317/yd3 for treatment rates of
10 to 3 yd3/hr, respectively. These costs are based on a
70% on-line efficiency and include consideration of site
preparation; equipment purchase, installation, and operation;
and demobilization (U.S. EPA, 1991, EPA/540/A5-90/008, p.
21). Cost estimates for the general application of steam/hot
air injection fall in the range of $50 to $300/yd3 (U.S. EPA,
1991, EPA/540/2-91/005, p. 6).
Table 3-8. Steam/Hot Air Injection and Extraction Critical Factors and Conditions'8'
Factor Influencing
Technology Selection
Soil conductivity (*)
Humic content in soil (*)
Contaminant vapor
pressure (*)
Conditions Favoring
Selection of In Situ
Treatment
No action levels specified (1)
No action levels specified (1)
Boiling point below 250°C (2)
Basis
• Low soil conductivity inhibits vapor flow
• Low humic content is desirable
• . Presence of humic materials increases sorption
and inhibits volatilization
• More volatile contaminants are more easily
removed by air stripping
Data Needs
• Hydrogeologic flow regime
• Soil composition
• Soil color
• Soil texture
• Contaminant boiling point or
vapor pressure as a function
of temperature
(a) Also see Table 2-3 for generic factors.
(*) Indicates higher-priority factors.
(1) U.S. EPA, 1988, EPA/540/2-88/004, p. 89.
(2) U.S. EPA, 1990, EPA/600/2-89/066, p. 51.
Treatment of Soils In Situ
23
-------
For further information on steam/hot air injection tech-
nologies, contact:
Michael Gruenfeld (908) 321-6625
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
Building f 10 (MS 104)
2890 Woodbridge Avenue
Edison, NJ 08837-3679
4.0 Acknowledgments
This Engineering Issue Paper was developed for the U.S.
EPA Engineering Forum by the U.S. EPA Risk Reduction
Engineering Laboratory (RREL) through Contract No. 68-CQ-
0003 with the Battelle Memorial Institute. Battelle provided
primary authorship and layout of the document, while many
other people contributed in a significant way by providing
direction, guidance, assistance, information, or review.
The EPA Technical Project Manager was Janet
Houthoofd. The Engineering Forum lead contacts were
Robert Stamnes, Region 10, and Paul Leonard, Region 3.
The Battelle Work Assignment Manager was Susan
Brauning, and the principal author was Lawrence Smith.
Other contributors or reviewers were Thomasine Bayless,
Joan Colson, Patricia Erickson, Chi-Yuan (Evan) Fan,
Michael Gruenfeld, Carl Potter, Teri Richardson, Michael
Roulier, Gregory Sayles, Laurel Staley, and Robert Stenburg
- EPA RREL; Linda Fiedler - EPA Technology Innovation
Office; John Matthews - EPA Robert S. Kerr Environmental
Research Laboratory; and Bruce Alleman, Lynn Copley-
Graves, Robert Hinchee, Andrea Leeson, and Thomas
Naymik - Battelle.
Acknowledgments are due also to the primary Engineer-
ing Forum Superfund Contacts shown in the box below.
EPA Engineering
Region 1
Region 2
Region 3
Region 4
Region 5
Region 6
Region 7
Region 8
Region 9
Region 10
Headquarters
Forum Superfund
Lynne Jennings
Chet Janowski
Richard Ho
Paul Leonard
Jon Bornholm
Anthony Holoska
Deborah Griswold
Steve Kinser
Desiree Golub
Ken Erickson
Bob Stamnes
Richard Steimle
Contacts
(617) 573-9634
(617) 573-9623
(212) 264-9543
(215) 597-3163
(404) 347-7791
(312) 886-7503
(214) 655-6730
(913) 551-7728
(303) 293-1838
(415)744-2324
(206) 553-1512
(703) 308-8846
5.0 References
Alleman, Bruce, 1993. Personal Communication, (614)
424-5715. Battelle Memorial Institute. Columbus, Ohio.
Arniella, Elio F. and Leslie J. Blythe, 1990. "Solidifying
Traps Hazardous Wastes." Chemical Engineering.
97(2):92-102. February.
Conner, Jessie R., 1990. Chemical Fixation and Solidifica-
tion of Hazardous Wastes. Van Nostrand Reinhold.
New York, New York.
Donehey, Angela J., Reva A. Hyde, R.B. Piper, M.W. Roy,
and S.S. Walker, 1992, "In Situ Physical and Chemical
Treatments." In Proceedings of the 1992 U.S. EPA/
A&WMA International Symposium on In Situ Treatment
of Contaminated Soil and Water. Air & Waste Manage-
ment Association. Pittsburgh, Pennsylvania, pp. 98-106.
Dupont, R. Ryan, William J. Doucette, and Robert E. Hin-
chee, 1991. "Assessment of In Situ Bioremediation
Potential and the Application of Bioventing at a Fuel-
Contaminated Site." In Robert E. Hinchee and Robert F.
Olfenbuttel (Eds.), In Situ Bioreclamation: Applications
and Investigations for Hydrocarbon and Contaminated
Site Remediation, pp. 262-282. Butterworth-Heinemann.
Stoneham, Massachusetts.
Hansen, J.E. and V.F. FitzPatrick, 1991. In Situ Vitrification
Applications, Geosafe Corporation. Richland, Washing-
ton.
Hinchee, Robert E. and Say Kee Ong, 1992. "A Rapid In
Situ Respiration Test for Measuring Aerobic Biodegra-
dation Rates of Hydrocarbons in Soil." Journal of the Air
& Waste Management Association. 42(10):1305-1312.
October.
Houthoofd, Janet M., John H. McCready, and Michael H.
Roulier, 1991. "Soil Heating Technologies for In Situ
Treatment: A Review." In Proceedings of the 17th Annu-
al Hazardous Waste Research Symposium. EPA/600/9-
91/002. Office of Research and [Development, Risk Re-
duction Engineering Laboratory. Cincinnati, Ohio, pp.
190-203.
Just, Sharon R. and Kenneth J. Stockwell, 1993. "Com-
parison of the Effectiveness of Emerging In Situ Tech-
nologies and Traditional Ex Situ Treatment of Solvent-
Contaminated Soils." In ACS Symposium Series 518 -
Emerging Technologies in Hazardous Waste Manage-
ment III. American Chemical Society. Washington, DC.
pp. 238-277.
Kasevich, Raymond, Raymond Holmes, David Faust, and
Richard Beleski, 1993. "Radio Frequency Heat Enhanc-
es Contaminant Removal." Soils, pp. 18-23. March.
Leeson, Andrea, Robert E. Hinchee, Jeffrey A. Kittel, Grego-
ry Sayles, Catherine Vogel, and Ross Miller, 1993.
"Optimizing Bioventing in Shallow Vadose Zones in Cold
Climates," Hydrological Sciences Journal. 38(4): in
press.
Mack, James P. and Howard N. Aspan, 1993. "Using
Pneumatic Fracturing Extraction to Achieve Regulatory
Compliance and Enhance VOC Removal from Low-
Permeability Formations." Remediation. 3(3):309-326.
24
Treatment of Soils In Situ
-------
Miller, Ross N., Catherine C. Vogel and Robert E. Hinchee,
1991. "A Field-Scale Investigation of Petroleum Hydro-
carbon Biodegradation in the Vadose Zone Enhanced by
Soil Venting at Tyndall AFB, Florida." In Robert E. Hin-
chee and Robert F. Olfenbuttel (Eds.), In Situ Bioreclam-
ation: Applications and Investigations for Hydrocarbon
and Contaminated Site Remediation, pp. 283-302. But-
terworth-Heinemann. Stoneham, Massachusetts.
Pacific Northwest Laboratory, 1993. ReOpt Remediation
Technology Database. PNL. Richland, Washington.
Sayles, Gregory D. 1993. Personal Communication. (513)
569-7607., U.S. Environmental Protection Agency.
Cincinnati, OH.
Smith, Lawrence A. and Robert E. Hinchee, 1993. In Situ
Thermal Technologies for Site Remediation. Lewis
Publishers. Ann Arbor, Michigan.
Sresty, Guggilam C., Harsh Dev, Richard H. Snow, and
Jack E. Bridges, 1986. "Recovery of Bitumen From Tar
Sand Deposits With the Radio Frequency Process."
SPE Reservoir Engineering, pp. 85-94. Society of Petro-
leum Engineers. January.
Sresty, Guggilam C., Harsh Dev, and Janet Houthoofd,
1992. "In Situ Decontamination by Radio Frequency
Heating." In Proceedings of the 1992 U.S. EPA/A&WMA
International Symposium on In Situ Treatment of Con-
taminated Soil and Water. Air & Waste Management
Association. Pittsburgh, Pennsylvania, pp. 356-364.
U.S. Air Force, 1989. In Situ Soil Decontamination by Ra-
dio-Frequency Heating — Field Test. ESL-TR-88-62. Air
Force Engineering & Services Center. Tyndall Air Force
Base, Florida.
U.S. Air Force, 1992. Test Plan and Technical Protocol for
a Field Treatability Test for Bioventing, Rev. 2. U.S. Air
Force Center for Environmental Excellence. Brooks Air
Force Base, Texas.
U.S. Army, 1992. Final Rocky Mountain Arsenal In Situ
Radio Frequency Heating/Vapor Extraction Pilot Test
Report, Vol. I, 5300-01-12-AAFP. Rocky Mountain Arse-
nal. Commerce City, Colorado.
U.S. Environmental Protection Agency, 1988. Guidance for
Conducting Remedial Investigations and Feasibility Stud-
ies under CERCLA - Interim Final. EPA/540/G-89/004.
Office of Emergency and Remedial Response. Washing-
ton, DC.
U.S. Environmental Protection Agency, 1988. Technology
Screening Guide for Treatment of CERCLA Soils and
Sludges. EPA/540/2-88/004. Office of Emergency and
Remedial Response. Washington, DC.
U.S. Environmental Protection Agency, 1989. Project Sum-
mary - Radiofrequency Enhanced Decontamination of
Soils Contaminated with Halogenated Hydrocarbons.
EPA/600/S2-89/008. Office of Research and Develop-
ment, Risk Reduction Engineering Laboratory. Cincin-
nati, Ohio.
U.S. Environmental Protection Agency, 1989. Terra Vac In
Situ Vacuum Extraction System - Applications Analysis
Report. EPA/540/A5-89/003. Office of Research and
Development, Risk Reduction Engineering Laboratory.
Cincinnati, Ohio.
U.S. Environmental Protection Agency, 1990. Assessing
UST Corrective Action Technologies: Early Screening of
Clean-up Technologies for the Saturated Zone. EPA/-
600/2-90/027. Office of Research and Development,
Risk Reduction Engineering Laboratory. Cincinnati,
Ohio.
U.S. Environmental Protection Agency, 1990. Assessing
UST Corrective Action Technologies: Site Assessment
and Selection of Unsaturated Zone Treatment Technol-
ogies. EPA/600/2-90/011. Office of Research and De-
velopment, Risk Reduction Engineering Laboratory. Cin-
cinnati, Ohio.
U.S. Environmental Protection Agency, 1990. Cost of
Remedial Action (CORA) Model - Version 3.0. 937.5-
06/FS. Office of Solid Waste and Emergency Response.
Washington, DC.
U.S. Environmental Protection Agency, 1990. Handbook on
In Situ Treatment of Hazardous Waste-Contaminated
Soils. EPA/540/2-90/002. Office of Research and De-
velopment, Risk Reduction Engineering Laboratory.
Cincinnati, Ohio.
U.S. Environmental Protection Agency, 1990. International
Waste Technologies Geo-Con In Situ Stabilization/-
Solidification - Applications Analysis Report. EPA/5-
40/A5-89/004. Office of Research and Development,
Risk Reduction Engineering Laboratory. Cincinnati,
Ohio.
U.S. Environmental Protection Agency, 1990. Technologies
of Delivery or Recovery for the Remediation of Hazard-
ous Waste Sites. EPA/600/2-89/066. Office of Research
and Development, Risk Reduction Engineering Labora-
tory. Cincinnati, Ohio. (NTIS: PB90-156 225/AS)
U.S. Environmental Protection Agency, 1991. AWD Tech-
nologies Integrated AquaDetox®/SVE Technology -
Applications Analysis Report. EPA/540/A5-91/002.
Office of Research and Development, Risk Reduction
Engineering Laboratory. Cincinnati, Ohio.
U.S. Environmental Protection Agency, 1991. Engineering
Bulletin - In Situ Soil Flushing. EPA/540/2-91/021.
Office of Emergency and Remedial Response. Wash-
ington, DC. and Office of Research and Development,
Risk Reduction Engineering Laboratory. Cincinnati, Ohio.
U.S. Environmental Protection Agency, 1991. Engineering
Bulletin - In Situ Soil Vapor Extraction Treatment. EPA/-
540/2-91/006. Office of Emergency and Remedial Re-
sponse. Washington, DC. and Office of Research and
Development, Risk Reduction Engineering Laboratory.
Cincinnati, Ohio.
U.S. Environmental Protection Agency, 1991. Engineering
Bulletin - In Situ Steam Extraction Treatment. EPA/-
540/2-91/005. Office of Emergency and Remedial Re-
sponse. Washington, DC. and Office of Research and
Development, Risk Reduction Engineering Laboratory.
Cincinnati, Ohio.
U.S. Environmental Protection Agency, 1991. Soil Vapor
Extraction Technology: Reference Handbook. EPA/540/-
2-91/003. Office of Research and Development, Risk
Reduction Engineering Laboratory. Cincinnati, Ohio.
Treatment of Soils In Situ
-------
U.S. Environmental Protection Agency, 1991. Superfund
Engineering Issue - Treatment of Lead-Contaminated
Soils. EPA/540/2-91/009. Office of Solid Waste and
Emergency Response. Washington, DC. and Office of
Research and Development, Risk Reduction Engineering
Laboratory. Cincinnati, Ohio.
U.S. Environmental Protection Agency, 1991. Toxic Treat-
ments, In Situ Steam/Hot Air Stripping Technology -
Applications Analysis Report. EPA/540/A5-90/OQ8.
Office of Research and Development, Risk Reduction
Engineering Laboratory. Cincinnati, Ohio.
U.S. Environmental Protection Agency, 1992. Guide for
Conducting Treatability Studies under CERCLA, Final.
EPA/540/R-092/071a. Office of Research and Develop-
ment, Risk Reduction Engineering Laboratory, and Office
of Emergency and Remedial Response, Office of Solid
Waste and Emergency Response. Washington, DC.
U.S. Environmental Protection Agency, 1992. Innovative
Treatment Technologies: Semi-Annual Status Report, 4th
ed. EPA/542/R-92/011. Office of Solid Waste and
Emergency Response, Technology Innovation Office.
Washington, DC.
U.S. Environmental Protection Agency, 1992. Seminar on
the Use of Treatability Guidelines in Site Remediation.
EPA/600/K-92/003. Office of Research and Develop-
ment. Washington, DC.
U.S. Environmental Protection Agency, 1992. The Super-
fund Innovative Technology Evaluation Program - Tech-
nology Profiles, 5th ed. EPA/540/R-92/077. Office of
Research and Development, Risk Reduction Engineering
Laboratory. Cincinnati, Ohio.
U.S. Environmental Protection Agency, 1993. Decision-
Support Software for Soil Vapor Extraction Technology
Application: Hyperventilate. EPA/600/R-93/028. Office
of Research and Development. Risk Reduction Engi-
neering Laboratory. Cincinnati, Ohio.
U.S. Environmental Protection Agency, 1993. Engineering
Issue - In Situ Bioremediation of Contaminated Unsatu-
rated Subsurface Soils. EPA/540/S-93/501. Office of
Research and Development. Robert S. Kerr Environ-
mental Research Laboratory. Ada, Oklahoma, and
Office of Solid Waste and Emergency Response. Wash-
ington, DC.
U.S. Environmental Protection Agency, 1993. Technical
Resources Document on Solidification/Stabilization and
Its Application to Waste Materials. EPA/530/R-93/012.
Risk Reduction Engineering Laboratory. Cincinnati, Ohio.
U.S. Environmental Protection Agency, 1993. VISITT Ven-
dor Information System For Innovative Treatment Tech-
nologies. VISITT User Manual, Version 2. EPA/542/R-
93-001, Office of Solid Waste and Emergency Re-
sponse. Washington, DC.
U.S. Environmental Protection Agency and U.S. Air Force,
1993. Remediation Technologies Matrix Reference
Guide. Draft report. U.S. Environmental Protection
Agency, Technology Innovation Office, Washington, DC.
and U.S. Air Force, Armstrong Laboratory Environics
Directorate. Tyndall Air Force Base, Florida.
j. Treatment of Soils In Situ
-KV.S. GOVERNMENT HUNTING OFFICE: MM - S5O-OOI/8O3S3
------- |