United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA-540/S2-84-003 Jan. 1985
Project Summary
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RECEIVED
MAR 5 1985
ENVIRONMENTAL PROTECTION AGENCY
LIBRARY, REGION V
Review of In-Place Treatment
Techniques for Contaminated
Surface Soils
Volumes 1 and 2
R. C. Sims, J. L Sims, D. L. Sorensen, J. McLean, R. Mahmood,
and R. R. Dupont
This two-volume report presents
information on in-place treatment tech-
nologies applicable to contaminated
soils at shallow depths. Volume 1
discusses the selection of the appro-
priate in-place treatment technology
for a particular site and provides
specific information on each technol-
ogy. Volume 2 provides background
information and relevant chemical data.
Selection of in-place treatment
technologies follows the process
outlined in the National Contingency
Plan. The type of in-place treatment
(extraction, immobilization, degrada-
tion, attenuation, or reduction of
volatiles) is determined on the basis of
information available from the remedial
investigation. Selection of a specific
technology involves assessment of
waste, soil, and site-specific variables.
The technology is implemented if it is
considered more cost-effective in
comparison with the alternatives.
Volume 1 provides a guide for selection
of in-place treatment technologies, a
discussion of each in-place treatment
technology, data for estimating the
costs of implementing in-place
treatment, and an appendix on cost
information.
The second volume supports the
treatment methodology described in
Volume 1. The information presented
on monitoring to determine treatment
effectiveness, characterization and
evaluation of the behavior and fate of
hazardous constituents in soil/waste
systems, and properties (including
adsorption, degradation, and
volatilization parameters) for various
compounds is intended to help the
manual user in making more complex
decisions and in selecting analyses
concerning site, soil, and waste interac-
tions.
This Project Summary was developed
by EPA's Hazardous Waste Engineering
Research Laboratory, Cincinnati, OH,
to announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Uncontrolled disposal of hazardous
wastes frequently produces large
quantities of contaminated soils. The cost
to excavate, haul, and dispose of these
soils in an approved landfill is often
prohibitive or impractical. In these
situations, an in situ treatment approach
may be effective in eliminating or
reducing the hazard to acceptable levels
In situ treatment of contaminated soils
must be based on an understanding of
factors and processes that determine the
behavior of chemicals in soil systems.
Specifically, an evaluation of chemical
properties, biochemical processes, and
environmental factors influencing the
behavior and fate of chemicals is re-
quired. The goals of in situ management
include treating contaminated soils until
acceptable levels of hazardous materials
are achieved and so that groundwater
and surface water resources are
protected without physically removing or
isolating the contaminated soil from the
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contiguous environment. Volume 1
presents a number of physical/chemical
and biological techniques, both tried and
conceptual, that may be useful in treating
hazardous waste contaminated soil in
place. Volume 2 provides more
fundamental information that will help
the site manager select and correctly
apply treatments in complex situations.
Scope of the Report
This report has been divided into two
volumes. Section 2 of Volume 1 provides
a guide for selection of in-place treatment
technologies. Section 3 provides a
discussion of each in-place treatment
technology, including process
description, information requirements for
application of the technology, wastes
amenable to treatment, current status of
the technology, ease of application,
potentially achievable levels of treat-
ment, reliability of the technology over
the long term, secondary impacts, and
equipment materials required to
implement the technology. Section 4
discusses engineering methods for
modifying the oxygen content, moisture
content, nutrient content, pH, and temp-
erature of the soil to optimize the
effectiveness of m-place treatment. In
addition, data for estimating the costs of
implementing in-place treatment are
provided in Section 4 and in an appendix
on cost information.
Fundamental soil/waste system
processes characterized and evaluated in
Volume 2 may serve as a base for
selecting and evaluating specific in situ
treatment, soil immobilization processes
for control of leaching and volatilization,
biodegradationprocesses, and transfor-
mation processes. Modeling of waste
constituents with respect to transport,
adsorption, and transport in soil systems
are also discussed.
So/7 and Site Factors
Before beginning in situ remedial
actions to treat hazardous-waste-con-
taminated soils, the site's characteristics
must be identified. When the contami-
nants migrate off site, what are the char-
acteristics of the route? What are the
characteristics of the off-site receiver?
Route characteristics determine the
potential for contamination, and receiver
characteristics and the corresponding
degree of public health hazard indicate
the time frame in which the remedial
action must be performed. Site character-
ization also may serve to explain how site
modification or management could help
protect human health. Those soil
characteristics that affect water
movement (i.e., infiltration and permea-
bility) and those factors that affect con-
taminant mobility are the most important.
The specific site and soil characteristics
that need to be identified when assessing
a site for in situ treatment as well as the
site and soil conditions that may be
managed to enhance soil treatment are
identified in Table 1.
The properties of waste that affect the
behavior and fate of chemicals in soil
systems must be characterized because
these properties directly affect how the
waste will be treated (or assimilated): (1)
degradation, (2) transformation ordetoxi-
cation, or (3) immobilization of
constituents. Factors important in
determining the behavior and fate--
and therefore the treatment pathways--
of waste constituents in soil are listed in
Table 2. For each chemical, or chemical
class, the information needed can be
summarized as characteristics related to:
(1) potential leaching (e.g., water solu-
bility, octanol/water partition
coefficients, solid sorption coeffi-
cient)
(2) potential volatilization (e.g., vapor
pressure, relative volatilization
index)
(3) potential decomposition (e.g., half-
life, degradation rate, biodegrada-
bility index)
(4) chemical reactivity (e.g., oxidation,
reduction, hydrolysis potential).
Comparing the properties of the soil at
a specific site with the characteristics
given above permits the potential for (1)
Table 1. Site and Soil Characteristics Identified as Important in In Situ Treatment
Site location/topography and slope
Soil type and extent
Soil profile properties
boundary characteristics
depth
texture"
amount and type of coarse fragments
structure*
color
degree of mottling
bulk density*
clay content
type of clay
cation exchange capacity*
organic matter content*
pH*
Eh*
aeration status*
Hydraulic properties and conditions
soil water characteristic curve
field capacity/permanent wilting point
water ho/ding capacity*
permeability* (under saturated and a range of unsaturated conditions)
infiltration rates*
depth to impermeable layer or bedrock
depth to groundwater, * including seasonal variations
flooding frequency
runoff potential*
Geological and hydrogeo/ogical factors
subsurface geological features
groundwater flow patterns and characteristics
Meteorological and c/imatological data
wind velocity and direction
temperature
precipitation
water budget
"Factors that may be managed to enhance soil treatment.
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Table 2. Soil-Based Waste Characteriza-
tion
Chemical class
Acid
Base
Polar neutral
Nonpolar nuetral
Inorganic
Soil Sorption Parameters
Freundlich sorption constants (K. N)
Sorption based on organic carbon
content (Koci
Octanol water partition coefficient (Kow)
Soil degradation parameters
Half-life (fy,)
Rate constant (first order)
Relative biodegradability
Chemical properties
Molecular weight
Melting point
Specific gravity
Structure
Water solubility
Volatilization parameters
Air: water partition coefficient (Kw)
Vapor pressure
Henry's law constant (J/KW)
Sorption based on organic carbon
content (Koc.)
Water solubility
Chemical reactivity
Oxidation
Reduction
Hydrolysis
Precipitation
Polymerization
Soil contamination parameters
Concentration in soil
Depth of contamination
The chemistry of heavy metals in soil
was divided into two interdependent but
separate categories: (1) solution
chemistry and (2) interfacial chemistry.
Discussions addressing the general
principles affecting the dissolution/
precipitation of the solid phase are
included because solid-phase formation
to scavenge metals from soil solution is a
primary objective of in situ treatment.
Soil sorption is perhaps the most im-
portant soil-waste process affecting the
toxic and recalcitrant fractions of the
hazardous waste. To effectively use the
sorption reaction as a treatment process,
the influence of soil sorption on the
extent and rate of leaching, and also on
biological decomposition of these
fractions, must be understood and
described. Understanding the effect of
different solid surfaces on hazardous
waste-constituents provides a
mechanism for rationally selecting
additional sorbents for use in augmenting
the natural ability of a soil system to
immobilize hazardous chemicals. Also,
understanding the relationship between
soil water content and extent of sorption
of hazardous chemicals provides the
hazardous waste manager with a process
for controlling the potential release and
migration of constituents through
leaching. Volume 2 contains a discussion
of the factors involved in soil sorption of
chemical constituents and the basic
factors influencing the sorption process
that may be used in treatment processes
to immobilize specific hazardous waste
fractions.
Immobilization
The relationship between immobiliza-
tion of chemical constituents in soil
systems (based on soil chemical
properties) and chemical class (based on
chemical structure) is summarized in
Table 3. Generally, nonionic constituents
of low water solubility and cationic
constituents have low mobilities and
leaching potential. Acid constituents at
neutral and high pH values are most
easily leached from soil systems.
Understanding the relationship
between soil water content and extent of
sorption of hazardous chemicals provides
the hazardous waste manager with a tool
for controlling potential release and
migration of constituents through the
control of the leaching process. One
commonly used isotherm that is useful in
describing the immobilization of organic
constituents in soil is the Freundlich
isotherm:
S = KC1/n
where
K and n are constants,
S = amount of chemical associated
with solid phase, or the solid
phase concentration,
C = amount of chemical associated
with the solution phase, or the
solution phase concentration.
The Freundlich isotherm related the
solid phase concentration to the solution
phase concentration at equilibrium
conditions.
An important linear isotherm can be
obtained from the Freundlich isotherm
when n=1, i.e.,
S = KdC
where Kd = the distribution coefficient.
The relationship between Kd1, soil
moisture content 0, and percent adsorp-
tion of an organic chemical can be used to
manage a soil system:
percent adsorbed = Kd/(Kd + 0)
soil treatment and (2) off-site
contamination to be determined.
By determining howtoxic, how concen-
trated, and how extensively inorganic
contaminants occurred at a disposal site,
a list of hazardous metals was developed:
As, Be, Cd, Cr, Cu, Pb, Hg, Ni, Se, Ag, and
Zn. As, Se, and Cr are the only metals that
can exist as anions in nature, and
because of their anionic nature, their
behavior in soil will differ from other
heavy metals. The behavior and fate of all
these metals are discussed in detail in the
full report.
Table 3. Leaching Potential of Chemicals in Soil Systems
Chemical Class
Nonionic
Ionic
Water
Solubility
Basic
Cationic
Acidic
Leaching
Potential high med low Low pH neutral pH
low pH neutral pH
Low
Medium
High
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The extent of sorption as a function of soil
moisture content for different values of
the distribution coefficient is illustrated in
Figure 1. Thus careful control of soil
moisture content will determine, to a
large extent, the relative immobilization
of a given set of chemical constituents
identified at a remedial site. Optimization
of cost effective and efficient treatment
may require a compromise between
optimum soil moisture content for bio-
degradation versus sorption.
The full report includes discussions of
soil microbiological factors related to in
situ treatment' the soil microbial environ-
ment , soil microorganisms, biogeochem-
istry of toxic metals, microbial decompo-
sition of xenobiotic compounds, genetic
engineering, co-metabolism, and
degradation of specific classes of organic
compounds
Biodegradation
The quantitative aspects of microbial
decomposition of organic constituents
are also discussed. Mathematically, the
rate of decomposition represents a sink
term in organic transport models--
models needed to predict potential
groundwater contamination with respect
to magnitude and type of contamination
and the time factor for contamination
(rate of transport). The power rate model,
the hyperbolic rate model, and the effect
of sorption on the rate of degradation are
considered. Results for degradation are
tabulated from the literature. Degrada-
tion rate as a function of soil concentra-
tion and chemical structure for the poly-
nuclear aromatic class of priority pollutants
is discussed.
To describe the behavior of waste
constituents in soil systems, Volume 2
considers one-dimensional transport
models, including a water flow model and
a solute transport model. The models
represent a first-cut approach to ranking
chemicals and chemical classes with
respect to potential mobility and,
therefore, an approach to ranking
chemicals with highest priority for
immobilization treatment.
Volatilization and
Photodegradation
The factors affecting volatilization of
organics in soil systems include: (1)
contaminant vapor pressure, (2)
contaminant concentration, (3) soil/
chemical adsorption reactions, (4)
contaminant .solubility in soil water, (5)
contaminant solubility in soil organic
o
to
90-
80.
70
60
50
Soil Moisture
» 0 = 20%
* 0 = 40%
• 0 = 60%
• 0 = 50%
20
0 10
Distribution Coefficient, Ka
Figure 1. Extent of sorption as a function of soil moisture 0 and K&
30
matter, and (6) soil temperature, water
content, organic content, porosity, and
bulk density.
The major contaminant property
affecting volatilization is its vapor
pressure, and the major environmental
factors affecting the contaminant's vapor
pressure are the soil/water and
air/water .partition coefficients that exist
for the soil/water/air environments
within a soil system. Additional
complexity results if the contaminant is
added along with an additional adsorbing
fluid such as oil in refinery waste, where
partitioning of the contaminant between
the oil/soil, oil/water, and oil/air phases
would also be expected to affect the vola-
tilization of vapor pressure of the volatile
compounds.
Photodegradation of organic com-
pounds may occur by two processes (1)
direct photodegradation and (2)
sensitized photooxidation. The relative
importance of photodegradation of
chemicals on or within a soil will depend
to a large extent upon its partitioning
between the air/water/soil media within
the soil system. Using photochemical
reactions to enhance compound biode-
gradation is an area of interest for hazard
mitigation from hazardous waste sites.
Monitoring
To ensure that the objectives of in situ
treatment are attained, a monitoring
program must be established to: (1)
ensure that the hazardous or toxic con-
stituents of the waste are being
degraded, detoxicated, or inactivated as
planned, (2) monitor degradation rates of
degradable constituents, (3) ensure that
waste constituents are not entering
runoff or leachate water and leaving the
area in unacceptable concentrations, and
(4) determine whether adjustments in
treatment management are needed to
maintain the treatment process.
A complete program would monitor soil
core and soil-pore liquid in the treatment
zone and outside the treatment zone,
groundwater, runoff water, and
atmosphere. Constituents that should be
monitored include those determined to be
hazardous in the initial site/waste char-
acterization study as well as expected,
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important degradation or transformation
products. The monitoring program may
also include substances needed for
treatment, whether these substance are
native to the soil or added as a treatment
agent. Volume 2 includes specific
monitoring information for each medium
(soil, water, and atmosphere) and cost
estimates for various monitoring
techniques.
An appendix to Volume 2 of the full
report contains a data base for assessing
the soil/waste interactions of individual
chemicals. Specific quantitative
information for each chemical includes:
(1) compound/chemical properties, (2)
adsorption parameters, (3) degradation
parameters, and (4) volatilization
parameters. Thus qualitative and
quantitative analyses can be conducted
for the site/soil/waste information
presented in the main section of the
report with the use of this data base.
Conclusions
In situ treatment of hazardous waste
contaminated soils requires considerable
information and understanding about
site/soil/waste interactions. Available
treatment techniques need to be carefully
evaluated and selected based on this
information and understanding. In
addition, evaluating the success of any
treatment or combination of treatments
requires an effective monitoring
program. This two-volume report
provides a basis for meeting these needs.
The full report was submitted in fulfill-
ment of Contract No. 68-03-3113, Task
41-1 by JRB Associates under
subcontract to Utah State University
under sponsorship of the U.S.
Environmental Protection Agency.
/?. C. Sims, J. L Sims, D. L Sorensen. J. McLean. R. Mahmood, andR. R. Dupont
are with Utah State University, Logan. UT 84322.
Naomi P. Barkley is the EPA Project Officer (see below).
The complete report consists of two volumes, entitled "Review of In-Place
Treatment Techniques for Contaminated Surface Soils:"
"Volume 1. Technical Evaluation," (Order No. PB85-124881; Cost: $17.501
"Volume 2. Background Information for In Situ Treatment," (Order No. PB
85-124 899; Cost: $29.50)
The above reports will be available only from: (cost subject to change)
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
* USOOVERNMENTPfllNTINaOFFICE-IMS - 559-111/10776
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