Review Draft— Do Not Cite or Quote—December 1994
w-Ott. OSUjg-A^
United States
Environmental Protection
Agency
Office of
Solid Waste and
Emergency Response
9355.-4-14FS
EPA/540/R-94/101
PB95-963529
December 1994
Soil Screening Guidance
Office of Emergency and Remedial Response
Hazardous Site Control Division
Quick Reference Fact Sheet
NOTICE: This document is draft for review only and should not be used until the guidance is finalized following public comment and peer review.
BACKGROUND
On June 19,1991, the U.S. Environmental Protection Agency's
(EPA's) Administrator charged the Office of Solid Waste and
Emergency Response (OSWER) with conducting a 30-day
study to outline options for accelerating the rate of cleanups at
National Priorities List (NPL) sites. One of the specific
proposals of the study was for OSWER to "examine the means
to develop standards or guidelines for contaminated soils."
On June 23, 1993, EPA announced the development of "Soil.
Trigger Levels" as one of the Administrative Improvements to
ISuperfund program. On September 30, 1993, a draft fact
eet was released that presented generic Soil Screening Levels
(SSLs) for 30 chemicals. The fact sheet presented standard-
ized equations to model exposures to soil contaminants via
ingestion, inhalation, and migration to ground water. The fact
sheet provided generic defaults for each parameter in the equa-
tions and a sampling methodology to measure soil contaminant
levels. The SSL initiative underwent widespread review both
within and outside the Agency. Suggestions were made on
how to improve the methodology and increase the usefulness
of screening levels by finding simple ways to modify them
using site-specific data.
Based on that review, EPA modified the SSLs into a Soil
Screening framework that emphasizes the application of
standardized equations for the site-specific evaluation of soil
contaminants. This framework provides an overall approach
for developing SSLs for specific contaminants and exposure
pathways at a site under a residential land use scenario. Areas
with soil contaminant concentrations below SSLs generally
would not warrant further study or action under the
Comprehensive Environmental Response, Compensation, and
Liability Act (CERCLA).
^jne
The Soil Screening framework's point of departure is a simple
niethodology for calculating site-specific SSLs using easily
itained site data with standardized equations. An option for
'conducting a more detailed site-specific analysis is also
included in the framework. In addition, default parameters are
used in the standardized equations to produce a table of
generic Soil Screening Levels for 107 chemicals that update
those presented in the September 30, 1993, draft SSL fact
sheet. These generic SSLs are included in the framework as
a default option for use when site-specific values are not
available.
PURPOSE OF SOIL SCREENING
FRAMEWORK
The Soil Screening framework represents the first of several
tools EPA plans to develop to standardize the evaluation and
cleanup of contaminated soils. SSLs streamline the remedial
investigation/feasibility study (RI/FS) process by accelerating
and increasing consistency in decisions concerning soil
contamination. As a future companion to the Soil Screening
framework, EPA also intends to develop a methodology to
identify levels of contamination that clearly warrant a response
action or, possibly, concentrations for which treatment would
be required. The screening levels at the low end and the
higher concentration values that warrant response can be used
to identify the bounds of a risk management continuum (Figure
1). Generally, within this continuum lies a range of possible
cleanup levels that will continue to be determined on a site-
specific basis.
EPA anticipates the use of the Soil Screening framework as a
tool to facilitate prompt identification of the contaminants and
exposure areas of concern during both remedial actions and
some removal actions under CERCLA. SSLs do not trigger
No further study
warranted under
CERCLA
Site-specific
cleanup
goal/level
Response
action clearly
warranted
"Zero"
concentration
Screening
level
Response
level
Very high
concentration
Figure 1. Risk management spectrum for
contaminated soil.
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the need for response actions or define "unacceptable" levels
of contaminants in soil. SSLs may serve as Preliminary
^Remediation Goals (PRGs) under certain conditions (see
section on Use of SSLs as Preliminary Remediation
/Cleanup Levels). In the future, EPA will consider
the guidance to address the Resource Conservation
and Recovery Apt (RCRA) Corrective Action program.
The SSLs are, as noted above, intended for use as a tool; their
use is not mandatory at sites being addressed under CERCLA.
The framework leaves a broad range of discretion to the site
manager, both on whether the SSL approach is appropriate for
a site and, if it is used, on the appropriate method. This
guidance anticipates three optional approaches—simple site-
specific, detailed site-specific, and generic. In the first two,
some or all default values would be replaced as appropriate
with site-specific data. Furthermore, the models themselves
are not codified as rules and can be modified if appropriate,
although some explanation should be provided if such
modification is made.
SOIL SCREENING FRAMEWORK
A Soil Screening Level is a chemical concentration in soil that
represents a level of contamination below which there is no
concern under CERCLA, provided conditions associated with
the SSLs are met. Generally, if contaminant concentrations in
soil fall below the SSL, and there are no significant ecological
receptors of concern, then no further study or action is
nted for residential use of that area. (Some States have
Iveloped screening numbers that are more stringent than the
generic SSLs presented in this fact sheet; therefore further
study may be warranted under State programs.) Concentra-
tions in soil above either the generic or site-specific screening
level would not automatically designate a site as "dirty" or
trigger a response action. However, exceeding a screening
level suggests that a further evaluation of the potential risks
that may be posed by site contaminants is appropriate to
determine the need for a response action.
The Soil Screening framework presents three approaches for
establishing screening levels. The option emphasized in this
Fact Sheet is a simple method that incorporates readily obtain-
able, site-specific data into standardized equations to derive
site-specific screening levels for selected contaminants. When
questions still exist at a site regarding whether or not contam-
inant levels are of concern, as a second approach, more
tailored screening levels can be derived for most contaminants
by incorporating additional site data into more complex fate
and transport models. The third approach is to apply the
generic SSLs presented in Appendix A. Although the default
parameters used to derive the generic SSLs are not necessarily
"worst case," they are conservative.
The progression from generic to simple site-specific and
etailed (full-scale) site-specific SSLs usually will involve an
•crease in investigation costs and a decrease in conservatism
(Figure 2). Generally, the decision of which method to use
More
Conservatism
•>• Less
Generic
SSL
Simple
Site-Specific
Method
Detailed Srte-
>• Specific Method
Investigation Costs
Less ^ >• More
Figure 2. Components of the Soil Screening
framework.
involves balancing the increased investigation costs with the
potential savings associated with higher (but protective) SSLs.
Therefore, the framework promotes the option of using site-
specific data to derive screening levels. More guidance
regarding which option to use is presented later in this fact
sheet.
Site-Specific SSLs: Simple Method
The simple method for developing site-specific SSLs requires
the collection of a small number of easily obtained site
parameters (e.g., fraction organic carbon, percent soil moisture,
and dry bulk; density) for use in the standardized equations so
that the calculated screening levels can be appropriately con-
servative for the site but not as conservative as the generic
values. Once derived, the user then compares measured site or
area contaminant concentrations to the site-specific screening
levels. If concentrations do not exceed the SSLs for each
pathway of concern, it would generally be appropriate to
exclude the area from further investigation. If the levels are
exceeded, the site manager may decide that a more
comprehensive evaluation is needed to determine the risk
posed via a particular exposure pathway (see Technical
Background section).
Site-Specific SSLs: Detailed Approach
A more detailed method for developing site-specific SSLs is a
full-scale model evaluation requiring the collection of addi-
tional site data. Full-scale modeling allows the application of
complex transport and fate models and allows for consideration
of a finite contaminant source. Applying these models will
further define the risk associated with exposure via the
inhalation or migration to ground water pathway. The model
application may show that there is no concern over exposure
from the pathway, thereby eliminating it from further concern.
This potential outcome provides the incentive for incurring the
cost and time to conduct a comprehensive site evaluation.
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Generic SSLs
Generic SSLs can be used in place of site-specific screening
levels. The decision to use generic SSLs will likely be driven
by time and cost. The site manager must weigh the cost of
conducting a more site-specific investigation with the potential
for deriving a higher SSL that provides for an appropriate level
of protection. The Technical Background section of this
guidance presents a more detailed discussion of the level of
effort required to conduct further study of site conditions and
risks. Appendix A provides generic SSLs for 107 chemicals.
SCOPE OF SOIL SCREENING FRAMEWORK
The Soil Screening framework has been developed for 107
chemicals using assumptions for residential land use activities
for three pathways of exposure (see Figure 3):
• Ingestion of soil
• Inhalation of volatiles and fugitive dusts
• Ingestion of contaminated ground water caused by migra-
tion of chemicals through soil to an underlying potable
aquifer.
Reviews of risk assessments at hazardous waste sites indicate
that these pathways are the most common routes of human
exposure to contaminants in the residential setting. These are
also the pathways for which generally accepted methods,
models, and assumptions have been developed that lend
themselves to a standardized approach. Data on dermal
exposures have also been considered, and the generic SSL for
Direct Ingestion
of Ground
Water and Soil
Inhalation
Blowing
Dust and'
Volatilization
Highlight 1: Key Attributes of the SSL Framework
• Standardized equations are presented to address
three individual human exposure pathways.
• Parameters are identified for which site-specific
information is needed to develop site-specific SSLs.
• Default values are provided and used to calculate
generic SSLs that are consistent with Superfund's
concept of "Reasonable Maximum Exposure" (RME).
• SSLs are generally based on a 10"6 risk for
carcinogens, or a hazard quotient of 1 for noncar-
cinogens. SSLs for migration to ground water are
based on nonzero maximum contaminant level goals
(MCLGs), or, when not available, maximum contami-
nant levels (MCLs). Where neither of these are
available, the aforementioned risk-based targets are
used.
Figure 3. Exposure pathways addressed by the
Soil Screening framework.
pentachlorophenol has been modified accordingly. The scope
of the SSL framework is limited to human exposure via the
pathways listed above; therefore, sites with other significant
exposure pathways, nonresidential land uses, possible
ecological concerns, or unusual site conditions should
consider their associated risks on a site-specific basis apart
from the SSL framework. Key attributes of the Soil
Screening framework are given in Highlight 1.
Soil Ingestion Pathway
For the direct soil ingestion pathway, only generic SSLs were
developed. Simple and full-scale site-specific methods were
not developed because cost and complexity make developing
site-specific data for this pathway, such as soil ingestion rates
or chemical-specific bioavailability, generally impracticable.
However, EPA is evaluating the data available to support
adjustment of the exposure frequency term based on regional
climatic conditions.
Inhalation Pathway
For inhalation of volatiles and fugitive dust, both generic
values and a method for incorporating site-specific data into
the standardized equations have been developed. To estimate
the site-specific potential for volatilization of contaminants, soil
conditions such as fraction organic carbon, soil moisture
content, and dry bulk density must be evaluated. To estimate
the site-specific potential for generation of fugitive dusts, other
parameters must be evaluated, such as mean annual windspeed,
threshold friction velocity, and the mode soil aggregate size to
further tailor the SSLs to the site. For both the inhalation of
volatiles and fugitive dust pathways, a site-specific
determination of the area of contamination and meteorologic
inputs can be incorporated into dispersion calculations.
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Migration to Ground Water
*The simple site-specific method for addressing potential
:ninant migration to ground water uses the same soil
eters required to address volatilization, along with easily
able hydrogeologic parameters. The simple site-specific
method for this exposure pathway also requires a determination
of the area of contamination.
Other Pathways
Additional exposure pathways to contaminants in soil—dermal
absorption, plant uptake, and migration of volatiles into
basements—may contribute significantly to the risk to human
health in a residential setting. The Superfund program has
evaluated the data and methods available to address these
potential exposures and has incorporated as much information
as possible into the SSL framework.
Based on limited empirical data, the ingestion SSL for
pentachlorophenol has been adjusted to account for potential
dermal exposure. Additionally, empirical data indicate that
plant uptake may be important for some chemicals (Le., As,
Cd, Hg, Ni, Se, Zn). The fact that these chemicals' potential
for plant uptake and dermal absorption has been noted in
Appendix A should not be misinterpreted to mean that other
chemicals are not of potential concern for dermal exposure or
plant uptake. As additional information becomes available,
other chemicals may be addressed as well.
It this time, Superfund does not believe that the potential for
migration of contaminants into basements can be reasonably
incorporated into the SSL framework. The parameters required
for the models (e.g., the number and size of cracks in
basement walls) do not lend themselves to standardization or
to evaluation of potential future exposure, and the models have
not been adequately validated. The Technical Background
Document (U.S. EPA, 1994e) provides a detailed analysis of
available modeling of this pathway.
Other Land Uses
Longer-term efforts will be required to develop standardized
tools to address exposures relevant to other land uses such as
industrial land use. The results of these efforts may be
included in future revisions of this guidance.
Ecological Receptors
As part of the baseline risk assessment, an ecological assess-
ment should be conducted at every Superfund site. The SSL
framework does not attempt to define significant ecological
receptors or quantify ecological risks. However, a comparable
list of screening level benchmarks, called Ecotox Thresholds,
is being developed by Office of Emergency and Remedial
Response (OERR) for application during the ecological risk
assessment addressed in OSWER Directive No. 9285.7-17
(U.S. EPA, 1994d). These values are defined as media-
specific chemical concentrations above which there is sufficient
concern regarding adverse effects to ecological receptors to
warrant further site investigation. OERR is developing
guidance on designing and conducting ecological risk
assessments, that will describe the use of such screening values
in the Superfund Remedial Investigation process.
HOW TO USE THE SOIL SCREENING
FRAMEWORK
The decision to use the Soil Screening framework at a site will
be driven by the potential benefits of eliminating areas,
exposure pathways, or contaminants from further investigation.
By identifying areas where concentrations of contaminated soil
are below levels of concern under CERCLA, the framework
provides a means to focus resources on exposure areas,
contaminants, and exposure pathways of concern.
Highlight 2 outlines flie process of applying the Soil Screening
framework at a site. To enable early comparison with site
background concentrations and to provide information
necessiary for determining an adequate sample size, site-
specific SSLs should be developed as early in the process as
possible. They can be adjusted during the process to
accommodate additional site information and the resulting
changes to the conceptual site model.
Developing a Conceptual Site Model
The primary condition for use of SSLs is that exposure path-
ways of concern and conditions at the site match those taken
into account by the Soil Screening framework. Thus, at all
sites it will be necessary to develop a conceptual site model to
identify likely contaminant source areas, exposure pathways,
and potential receptors. This information can be used to
Highlight 2: Using the Soil Screening Framework
• Develop site conceptual model and compare with
SSL conceptual model to determine applicability of
framework.
• Determine if background contaminant concentrations
are above generic SSLs.
• Select approach (simple or detailed she-specific,
generic) and develop SSLs.
• Measure average soil contaminant concentrations in
exposure areas (EAs) of concern.
• Compare average soil concentrations with SSLs and
eliminate site or area of site where EA mean
concentration is less than SSL.
• Consider further study or use of SSLs as PRGs for
sites or site areas with contaminant concentrations
greater than SSLs.
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determine the applicability of the framework at the site and the
need for additional information.
A conceptual site model is developed from available site
sampling data, historical records, aerial photographs, and
hydrogeologic information. The model establishes a hypothesis
about possible contaminant sources, contaminant fate and
transport, exposure pathways, and potential receptors. The
DQO Guidance for Superfund (U.S. EPA, 1993a) provides an
excellent discussion on the development of a conceptual site
mode]. The rationale for including the contaminant migration
to ground water exposure pathway should be consistent with
EPA ground water policy (U.S. EPA, 1988, 1990b, 1992a,
1992b, 1993b).
The conceptual model upon which the generic SSLs are based
is a 30-acre property that has been divided up for residential
use. Thus, the generic SSLs have been developed to be
protective for source areas up to 30 acres. The contamination
is assumed to be evenly distributed across the area of concern
and extends from the ground surface to the top of the aquifer.
The soil type is assumed to be loam that has 50 percent
vegetative cover. Loam is soil with approximately equal
proportions of sand and silt Exposure to contaminants can
occtir via ingestion of soils, inhalation of volatiles and fugitive
dusts, or migration to ground water.
For the migration to ground water pathway, the point of
compliance is assumed to be at the edge of the site, which is
assumed to be homogeneously contaminated. No attenuation
is considered in the unsaturated zone; however, dilution is
assumed within the aquifer to the point of compliance. For the
generic conceptual site model, the source is assumed to extend
acrpss the entire site. See Figures 3 and 4 for a graphic
representation of aspects of the conceptual model applicable to
the Soil Screening framework.
Partitioning of contaminant mass between media is not
addressed in the SSL framework because the fate and transport
models used to derive the generic SSLs are based on the
assumption of an infinite source. Although the assumption is
highly conservative, a finite source model cannot be applied
unless there are accurate data regarding source size and
volume. Obviously, in the case of the generic SSLs, such data
are not available. It is also unlikely that such data will be
available from the limited subsurface sampling that is done to
apply the simple site-specific method. Thus, it is most likely
that a finite source model would be applied as part of a
detailed site-specific investigation. EPA will continue to seek
consensus on the appropriate methods to incorporate
contaminant partitioning and a finite source into the simple
site-specific method. The results of these efforts may be
included in future updates to this guidance.
The Technical Background Document (U.S. EPA, 1994e)
presents information on equations and models that can
accommodate finite sources and predict the subsequent impact
on either ambient air or ground water. However, when using
SECTION VIEW
Receptor
Well
Land Surface
Unsaturated
Zone Water Table
Ground Water
-\_
Flow
Saturated Zone
Default assumptions:
• Infinite source
• Source extends to water table
• Well at downgradient edge of source
• 30-acre source size
Figure 4. Migration to ground water pathway-
SSL conceptual model.
a finite source model, the site manager should recognize the
uncertainties inherent in site-specific estimates of subsurface
contaminant distributions and use conservative estimates of
source size and concentrations to allow for such uncertainties.
The following questions should always be considered in the
development of the conceptual site model before applying the
Soil Screening framework:
• Is the site adjacent to surface waterbodies where the
potential for contamination of surface water by overland
flow or release of contaminated ground water should be
considered?
• Are there potential terrestrial or aquatic ecological
concerns?
• Is there potential for land use other than residential?
• Are there other likely human exposure pathways that
were not considered in development of the SSLs (e.g., local
fish consumption; raising of beef, dairy, or other
livestock)?
• Are there unusual site conditions (e.g., area of contamina-
tion greater than 30 acres, unusually high fugitive dust
levels due to soil being tilled for agricultural use, or heavy
traffic on unpaved roads)?
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If ftie conceptual site model indicates that residential assump-
. tions are appropriate for your site and no pathways of concern
other than those covered by the Soil Screening framework are
ent, then the framework may be applied directly to (he site.
i the conceptual site model indicates that the site is more
. omplex than the scenario outlined in this guidance, the frame-
work above will not be sufficient. Additional pathways, recep-
tors, or chemicals must be evaluated on a site-specific basis.
Considering Background Contamination
A necessary step in determing the usefulness of the SSL
framework is the consideration of background contaminant
concentrations, since the framework will have little utility
where background concentrations exceed the SSLs.
EPA may be concerned with two types of background at sites:
naturally occurring and anthropogenic. Natural background is
usually limited to metals whereas anthropogenic (i.e., human-
made) background includes both organic and inorganic contam-
inants.
Generally, EPA does not clean up below natural background;
however, where anthropogenic background levels exceed SSLs
and EPA has determined that a response action is necessary
and feasible, EPA's goal will be to develop a comprehensive
response to the widespread contamination. This will often
require coordination with different authorities that have
jurisdiction over other sources of contamination in the area
:uch as a regional air board or RCRA program). This will
:lp avoid response actions that create "clean islands" amid
widespread contamination. The background information and
understanding of the site developed as part of the conceptual
model can help determine background concentration.
When considering background, one should also consider the
bioavailability and mobility of compounds. Some compounds
may form complexes that are immobile and unlikely to cause
significant risk. This situation is more likely to occur with
naturally occurring compounds. Therefore, background con-
centrations of compounds exceeding the SSLs do not neces-
sarily pose a threat. Alternately, activities at a site can
adversely affect the natural soil geochemistry, resulting in the
mobilization of compounds. Consequently, background con-
tamination should be considered carefully. Regardless, where
background concentrations are higher than the SSLs, the SSLs
generally will not be the best tool for site decisionmaking.
Sampling Exposure Area
After the conceptual site model has been developed, and the
applicability of the Soil Screening framework is determined,
the next step is to collect a representative sample set for each
exposure area. An exposure area is defined as that geographic
^area in which an individual may be exposed to contamination
Dver time. Because SSLs are developed for a residential
Scenario, EPA assumes the exposure area is a 0.5-acre
residential lot.
In those situations where little or no sampling has been done,
it will be beneficial to collect the site data required for the
simple site-specific methodology in tandem with the collection
of samples to identify contaminant concentrations. The site
manager should work to limit the total number of trips to the
site by maximizing the usefulness of the samples collected.
(See section on Measuring Contaminant Concentrations in Soil
for additional guidance.)
Comparing Exposure Area Concentration
to SSLs
The fourth step is to compare onsite soil contaminant concen-
trations with site-specific SSLs or the generic SSLs listed in
Appendix A. At this point, it is reasonable to review the
conceptual site model with the actual site data in hand to
reconfirm the accuracy of the conceptual site model and the
applicability of the Soil Screening framework. Once this is
confirmed, site contaminant levels may be compared with the
SSLs.
In Appendix A, the first column to the right of the chemical
name presents levels based on direct ingestion of soil. The
second column presents the levels based on inhalation of vola-
tiles or soil particulates. The third column presents SSL values
for the migration to ground water pathway multiplied by a
dilution and attenuation factor (DAF) of 10 to account for
natural processes that reduce contaminant concentrations in the
subsurface. The fourth column contains the SSL multiplied
by a DAF of 1, which may be appropriate to use in instances
where there are high water tables, karst topography, fractured
bedrock, or source size greater than 30 acres. The lowest SSL
of the three pathways (ingestion, inhalation, and ground water
with DAF of 10) is highlighted in bold for each contaminant.
Generally, the comparison of SSLs to site contaminant levels
will result in one of three outcomes:
1. Site-measured values indicate that an area falls below all of
the SSLs. Soils from these areas of the site generally can
be eliminated from further evaluation under CERCLA.
2. Site-measured data indicate that one or more SSLs have
clearly been exceeded. In this case, the SSLs have helped
to identify site areas, contaminants, and exposure pathways
of potential concern on which to focus further .analysis or
data-gathering efforts.
3. A site-measured value exceeds one pathway-specific value
but not others. In this case, it is reasonable to focus
additional site-specific data collection efforts only on data
that will help determine whether there is truly a risk posed
via that pathway or by a limited set of chemicals at the
site. When an exceedance is marginally significant, a
closer look at site-specific conditions and exposures may
result in the area being eliminated from further study.
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Use of SSLs as Preliminary Remediation
Goals/Cleanup Levels
SSLs are not nationwide cleanup levels or standards. Where
the basis for response action exists and all exposure pathways
of concern are addressed by the SSLs, the SSLs may serve as
PROs as defined in HHEM, Part B (U.S. EPA, 1991d). A
PRO is a strictly risk-based value that serves as the point of
departure for the establishment of site-specific cleanup levels.
PRGs are modified to become final cleanup levels based on
a consideration of the nine-criteria analysis described in the
National Contingency Plan (NCP; Section 300.430 (3)(2)
(i)(A)), including cost, long-term effectiveness, and imple-
mentability. See Role of the Baseline Risk Assessment in
SuperfundRemedy Selection Decisions (U.S. EPA, 1991e) for
guidance on how to modify PRGs to generate cleanup levels.
The SSLs should only be used as site-specific cleanup levels
when a nine-criteria evaluation using the SSLs as PRGs for
soils indicates that a selected remedy achieving the SSLs is
protective, ARAR-compliant, and appropriately balances the
other criteria, including cost. An example is a small site or
exposure area where the cost of additional study would exceed
the cost of remediating to the generic SSLs.
Addressing Exposure to Multiple Chemicals
The SSLs generally correspond to a 10"6 risk level for carcino-
gens and a hazard quotient (HQ) of 1 for noncarcinogens.
This "target" hazard quotient is used to calculate a soil
concentration below which it is unlikely for even sensitive
populations to experience adverse health effects. The potential
for additive effects has not been "built in" to the SSLs through
apportionment. For carcinogens, EPA believes that setting a
lfJ6risk level for individual chemicals and pathways generally
will lead to cumulative risks within the 10~4 to 10"6 risk range
fo^ the combinations of chemicals typically found at Superfund
sites.
For noncarcinogens, there is no widely accepted risk range.
Thus, for developing national screening levels, options are
either (1) to set the risk level for individual contaminants at the
Rfb or RfC (i.e., a hazard quotient of 1), or (2) to set
chemical-specific concentrations by apportioning risk based on
some arbitrarily chosen fraction of the acceptable risk level
(e.g,, one-fifth or one-tenth the RfD or RfC). The Agency
believes, and EPA's Science Advisory Board agrees (U.S.
EPA, 1993d), that noncancer risks should be added only for
those chemicals with the same toxic endpoint or mechanism of
action.
Highlight 3 lists the chemicals from Appendix A that have
SSLs based on noncarcinogenic toxicity and affect the same
target organ. If more than one chemical detected at a site
affects the same target organ (i.e., has the same critical effect
as defined by the RfD methodology), site-specific SSLs for
each chemical in the group should be divided by the number
of chemicals present The concentration of contaminants at the
Highlight 3: SSL Chemicals with Noncarcinogenic
Toxic Effects on Specific Target Organs
Kidney
Acetone
1,1-Dichloroethane
Dimethyl phthalate
2,6-Dinftrotoluene
Di-n-octyl phthalate
Nitrobenzene
2,4,5-Trichlorophenol
Vinyl acetate
Liver
Acetone
Chlorobenzene
Di-n-octyl phthalate
Nitrobenzene
2,4,5-Trichlorophenol
Central Nervous System
Butanol
2,4-Dichlorophenol
2,4-Din'rtrotoluene
2,6-Dinitrotoluene
2-Methylphenol
Circulatory System
Antimony
Barium
p-Chloroaniline
c/s-1,2-Dichloroethylene
Nitrobenzene
Zinc
Reproductive System
Carbon disulfide
2-Chlorophenol
1,2,4-Trichlorobenzene
Gross Pathology
Diethyl phthalate
2-Methylphenol
Naphthalene
Nickel
Vinyl acetate
site should then be compared to the SSLs that have been
modified to account for this potential additivity.
Because the combination of contaminants will vary from site |
to site, apportioning risk to account for potential additive
effects could not be considered in the development of generic
SSLs. Furthermore, for certain noncarcinogenic organics (e.g.,
ethylbenzene, toluene), the; generic SSLs are not based on
toxicity but are determined instead by a "ceiling limit"
concentration (C^ at which these chemicals may occur as
nonaqueous phase liquids (NAPLs) in soil (see Technical
Background section). For these reasons, the potential for
additive effects and the need to apportion risk must be a site-
specific determination.
TECHNICAL BACKGROUND
The models and assumptions supporting the Soil Screening
framework were developed to be consistent with Superfund's
concept of "reasonable maximum exposure" (RME) in the
residential setting. The Risk Assessment Guidance for
Superfund, Volume 1 (U.S. EPA, 1989b) and the Standard
Default Exposure Factors guidance (U.S. EPA, 1991b) outlined
the Superfund program's approach to calculating an RME.
Since that time, the Agency (U.S. EPA, 1991a) has coined a
new term that the Superfund program believes corresponds to
the definition of RME: "high-end individual exposure."
The Superfund program's method to estimate the RME for
chronic exposures on a site-specific basis is to combine an
average exposure point concentration with reasonably
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Review Draft—Do Not Cite or Quote—December 1994
conservative values for intake and duration in the exposure
^ calculations. The default intake and duration assumptions are
* presented in the Standard Default Exposure Factors guidance
(U.S. EPA, 1991b). The duration assumptions were chosen to
^kpresent individuals living in a small town or other
^Kmtransient community. (Exposure to members of a more
transient community is assumed to be shorter and thus
associated with lower risk.) Exposure point concentrations are
either measured at the site (e.g., ground water concentrations
at a receptor well) or estimated using exposure models with
site-specific model inputs. An average concentration term is
used in most assessments where the focus is on estimating
long-term, chronic exposures. Where the potential for acute
toxicity is of concern, exposure estimates based on maximum
concentrations may be more appropriate.
The resulting site-specific estimate of RME is then compared
with chemical-specific toxicity criteria such as RfDs or RfCs.
EPA recommends using criteria from the Integrated Risk
Information System (IRIS) (U.S. EPA, 1994c) and Health
Effects Assessment Summary Tables (HEAST) (U.S. EPA,
1993c), although values from other sources may be used in
appropriate cases.
The Soil Screening framework differs from a site-specific
estimate of risk in that the exposure equations and models are
run in reverse to backcalculate to an "acceptable level" of
contaminant in soil. Toxicity criteria are used to define the
acceptable level: a level corresponding to a 10~6 risk for
_carcinogens and a hazard quotient of 1 for noncarcinogens.
tie concept of backcalculating to an acceptable level in soil
Pas presented in RAGS Part B (U.S. EPA, 199Id), and the
Soil Screening framework serves to update Part B for
addressing residential soils. Site-specific SSLs are consistent
with the Superfund approach to estimating RME on a site-
specific basis. Standard default factors are used for the intake
and duration assumptions, site-specific inputs are used in the
exposure models, and chemical-specific concentrations
averaged over the exposure area are used for comparison to the
SSLs.
Consistent with the site-specific SSLs, the generic SSLs use
the same intake and duration assumptions and are compared to
area average concentrations. However, the generic SSLs are
based on a hypothetical site model. In developing the
parameters for the hypothetical site, the Superfund program
considered the conservatism inherent in the exposure models
(e.g., assumption of an infinite source) and then combined
high-end and central tendency parameters for size, location,
and soil characteristics. The resulting generic SSLs should be
protective for most site conditions across the Nation.
OERR performed a sensitivity analysis to determine which
parameters most influenced the output of the volatilization and
fugitive dust models used to calculate SSLs for the inhalation
ithway. For fugitive dusts, the particulate emission factor
was most sensitive to threshold friction velocity,, which
was set at a "high-end" value. For calculation of the
«thw
EF)
volatilization factor (VF), soil moisture content was set at a
conservative value because it drives the air-filled soil porosity
that in turn provides the pathway for chemicals to volatilize
from soils. Climatic conditions have a significant impact on
dispersion of both volatile and particulate emissions and were
set at high-end values to be protective for conditions at most
sites. Different high-end meteorological data sets were
selected to calculate 90th percentile dispersion coefficients for
the VI1 and for the PEF.
For the migration of contaminants from soils to ground water,
only average soil conditions are used to calculate generic SSLs
because of the conservatism inherent in the partition equation.
The generic DAF for this pathway was developed using a
weight of evidence approach to be protective under most
hydrogeologic conditions across the country as described in the
following section on the migration to ground water.
Characteristics of the generic, hypothetical site used to develop
generic SSLs were described previously in the section
discussing the conceptual site model. The Technical
Background Document (U.S. EPA, 1994e) accompanying this
guidance describes the pathway-specific equations,
assumptions, and methodology that form the basis for both the
simple site-specific approach and the generic SSLs. The
Technical Background Document also describes development
of the specific default input values used to calculate generic
SSLs for the inhalation and migration to ground water
pathways.
The generic SSLs are based on default assumptions. EPA
recognizes that site-specific conditions may differ significantly
from these default assumptions. The Soil Screening
framework emphasizes the substitution of some of the generic
fate and transport assumptions with site-specific data to derive
site-specific SSLs. However, one purpose of the SSLs is to
define a level in soil below which no further study or action
would be required. Therefore, alternative levels that are set
using site-specific data should generally be calculated assuming
the RME/"high-end" individual exposure.
The following sections present the standardized equations and
default assumptions that form the basis for the simple site-
specific methodology and the generic SSLs. The soil ingestion
discussion is limited to default assumptions because only
generic SSLs have been developed for this pathway.
Direct Ingestion
Agency toxicity criteria for noncarcinogens establish a level of
daily exposure that is not expected to cause deleterious effects
over a lifetime (i.e., 70 years). Depending on the contaminant,
however, exceeding the RfD (i.e., the "acceptable" daily level)
for a short period of time may be cause for concern. For
example, if there is reason to believe that exposure to soil may
be higher at a particular stage of an individual's lifetime, one
would need to protect for that shorter period of high exposure.
Because a number of studies have shown that inadvertent
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Review Draft—Do Not Cite or Quote—December 1994
ingestion of soil is common among children age 6 and younger
(Calabrese et al., 1989; Davis et al., 1990; Van Wijnen et al.,
1990), the SSLs in the default option are set at concentrations
that are protective of this increased exposure during childhood
by ensuring that the chronic reference dose (or RfD) is not
exceeded during this shorter (6-year) time period (Equation 1).
If there is reason to believe that exposures at a site may be
significant over a short period of time (e.g., extensive soil
excavation work in a dry region), depending on the contami-
nanj, the site manager should consider the potential for acute
health effects as well.
Equation 1 : Screening Level Equation for
Ingestion of Noncarcinogenic
Contaminants in Residential Soil
omnni , ,.,„, (m3^j . THQ x BW x AT x 365 d/yr
' " " 1/RfD0 x 10"6 kg/mg x EF x ED x IR
Parameter/Definition (units)
THQrtarget hazard quotient (unitless)
BW/body weight (kg)
AT/averaging time (yr)
Rf D0 /oral reference dose (mg/kg-d)
EF/exposure frequency (d/yr)
ED/exposure duration (yr)
IR/soiJ ingestkm rate (mg/d)
Default
1
15
6s
chemical-specific
350
6
200
* For noncardnogens, averaging time is equal to exposure duration.
In some cases, children may ingest large amounts of soil (i.e.,
3 to 5 grams) in a single event. This behavior, known as pica,
may result in relatively high short-term exposures to
contaminants in soils. Such exposures may be of concern for
contaminants that primarily exhibit acute health effects.
Review of clinical reports on contaminants addressed in this
guidance suggests that acute effects of cyanide and phenol may
be of concern in children exhibiting pica behavior. If soils
containing cyanide and phenol are of concern and pica
behavior is expected at a site, the protectiveness of the
ingestion SSLs for these chemicals should be reconsidered.
For carcinogens, both the magnitude and duration of exposure
are important Duration is critical because the toxicity criteria
arc based on "lifetime average daily dose." Therefore, the total
dose received, whether it be over 5 years or 50 years, is
averaged over a lifetime of 70 years. To be protective of
exposures to carcinogens in the residential setting, OERR
foojses on exposures to individuals who may live in the same
residence for a "high-end" period of time (i.e., 30 years). As
mentioned previously, exposure to soil is higher during
childhood and decreases with age. Thus, Equation 2 uses a
time-weighted average soil ingestion rate for children and
adults. The derivation of this time-weighted average is
presented in U.S. EPA (1991d).
Equation 2: Screening Level Equation for
Ingestion of Carcinogenic
Contaminants in Residential Soil
Screening Level _ TR x AT x 365 d/yr
(mg/kg) SF0 x 10-* kg/mg x EF x IFsoH/adj
Parameter/Definition (units:)
TR/target cancer risk (unrtlesss)
AT/averaging time (yr)
SF0 /oral slope factor (mg/kg-d)"1
EF/exposure frequency (d/yr)
I Fsoii/ajj /age-adjusted soil ingestion
factor (mg-yr/kg-d)
Default
10"6
70
chemical-specific
350
114
Inhalation of Volatiles and Fugitive Dusts
Agency toxicity data indicate that risks from exposure to some
chemicals via inhalation far outweigh the risks via ingestion.
The models and assumptions used to calculate SSLs for
inhalation of volatiles and fugitive dusts are updates of the
equations presented in U.S. EPA's HHEM Part B guidance
(U.S. EPA, 1991d). The volatilization factor (VF), soil
saturation limit (Csat), particulate emission factor (PEF),
and dispersion model have all been revised.
Another change from the Part B methodology is the separation
of the ingestion and inhalation pathways. Toxicity criteria for
oral exposures are presented as administered doses in units of
milligrams per kilograms per day (mg/kg-d); whereas, the
inhalation criteria are presented as concentrations in air (pg/m3
or mg/m3) that require conversion to an estimate of internal
dose to be comparable to the oral route. EPA's Office of
Research and Development (ORD) now believes that the
conversion from concentration in air to internal dose is not
always appropriate and suggests evaluating these exposure
routes separately.
As explained in HHEM Part B, the basic principle of the
volatilization model is applicable only if the soil concentration
is at or below soil saturation (C^. Above this level the
model cannot predict an accurate VF. C^ is the concentration
at which soil air, pore water, and sorption sites are saturated
and above which free-phase contaminants may be present For
compounds that are liquid at ambient soil temperatures, C^
indicates a concentration above which NAPLs may be
suspected in site soils and further investigation may be
necessary. Thus, for liquid compounds for which the SSL
exceeds C^, the SSL is set: at C^. For compounds that are
solid at soil temperatures for which the SSL exceeds C^
volatile emissions can be assumed to be of no concern and the
SSL is calculated considering particulate emissions only (i.e.,
the 1/VF term in Equation 3 or 4 is set to zero).
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Review Draft—Do Not Cite or Quote—December 1994
Equation 3: Screening Level Equation for
Inhalation of Carcinogenic
Contaminants in Residential Soil
lening Level
TR x AT x 365 d/yr
URF x 1000 ng/mg x EF x ED x 1 + 1
Parameter/Definition (units)
TR/target cancer risk (unitless)
AT/averaging time (yr)
URF/inhalation unit risk factor
(ug/m3)"1
EF/exposure frequency (d/yr)
ED/exposure duration (yr)
VF/soil-to-air volatilization factor
(m3/kg)
PEF/particulate emission factor
(m3/kg)
Default
1.0'6
70
chemical-specific
350
30
chemical-specific
6.79 x108
Equation 4: Screening Level Equation for
Inhalation of Noncarcinogenic
Contaminants in Residential Soil
Screening Level
(mg/kg)
THQ x AT x 365 d/yr
EF x ED x
f
Tl-l
[RTC x (w * PEF J
rameter/Definition (units)
THQ/target hazard quotient (unitless)
AT/averaging time (yr)
EF/exposure frequency (d/yr)
ED/exposure duration (yr)
RfC/inhalation reference concentration
(mg/m3)
VF/soil-to-air volatilization factor
(m3/kg)
PEF/particulate emission factor
(m3/kg)
Default
1
30
350
30
chemical-specific
chemical-specific
6.79x10s
Equations 3 through 7 form the basis for deriving both simple
site-specific and generic SSLs for the inhalation pathway. The
following parameters in the standardized equations can be
replaced with specific site data to develop a more site-specific
SSL:
• VF and C^
— Average soil moisture content
— Average fraction organic carbon content
— Dry soil bulk density
Equation 5: Derivation of the Volatilization Factor
VF (m3/kg) = Q/C x Q.14 x a. x T)1/g x 10-4m2/cm2
(2 x Dai x 6a x KJ
where
Pel X 6a
" ea + (Ps) (1
Parameter/Definition (units)
VF/volatilization factor (m3/kg)
Q/C/inverse of the mean cone, at the
center of a 30-acre-square source
(g/m2-s per kg/m3)
T/exposure interval (s)
Dei /effective diffusivity (cm2/s)
6a/air-filled soil porosit
Dj /d'rffusivity in air (cm /s)
ft/total soil porosity (Lp^/L^,,)
w/average soil moisture content
(9v,ate/9soil or cn^wate/gsoij)
pb/dry soil bulk density (g/cnT3)
ps/soil particle density (g/cm3)
Kas/soil-air partition coefficient
(g-soil/cm3-air)
H/Henry's law constant (atm-m3/mol)
Kd /soil-water partition coefficient
(cm3/g)
Koc/organic carbon partition coefficient
(crrfrg)
foc/organic carbon content of soil (g/g)
Default
35.10
9.5x108s
D,(eBa8S/h2)
0.28 or n-wpb
chemical-specific
0.43 (loam)
0.1 (10%)
1.5 or (1 - n) ps
2.65
(H/Kd) x 41 (41 is a
conversion factor)
chemical-specific
Koc x foe
chemical-specific
0.006 (0.6%)
Equation 6: Derivation of the Soil Saturation Limit
_£
Tb
Parameter/Definition (units)
saturation concentration
(mg/kg)
S/solubility in water (mg/L-water)
pb/dry soil bulk density (kg/L)
n/total soil porosity (L^Ls,,,,)
ps /soil particle density (kg/L)
Kj/soil-water partition coefficient (L/kg)
Koc/soil organic carbon/water partition
coefficient (L/kg)
foc/fraction organic carbon of soil (g/g)
6^/water-filled soil porosity (L^ef/Lgoj,)
6a /ait-filled soil porosity (Lai/Lsoi|)
w/average soil moisture content
(kUwate/kSsoil or Lwate/kSsoil)
H'/Henry's law constant (unitless)
H/Henry's law constant (atm-m3/mol)
Default
chemical-specific
1.5 or (1 - n) ps
0.43 (loam)
2.65
Koc x foc (organics)
che m ical-specif ic
0.006 (0.6%)
wpb or 0.15
n - wpb or 0.28
0.1 (10%)
H x41, where 41 is
a conversion factor
chemical-specific
10
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Review Draft—Do Not Cite or Quote—December 1994
Equation 7: Derivation of the Paniculate Emission
Factor
occ/~3n,~\ _ r>tf> s, 3600s/h
0.036 X (1-V) X (Um/Ut)3 X F(X)
Parameter/Definition (units)
PEF/particuIate emission factor
(m3/kg)
Q/C/inverse of the mean cone, at the
canter of a 30-acre-square source
(g/m2-s per kg/m3)
V/fractfon of vegetative cover
(unitless)
Um /mean annual windspeed (m/s)
U, /equivalent threshold value of wind-
speed at 7 m (m/s)
F(x)/functton dependent on Um/Ut
derived using Cowherd (1 985)
(unitless)
Default
6.79 x108
46.84
0.5 (50%)
4.69
11.32
0.194
• PEF
— Mean annual windspeed
— Threshold friction velocity (as determined by):
- mode of the surface soil aggregate size
- roughness height
- correction for nonerodible particles
- f(x)
— Equivalent threshold windspeed at a 7-m anemometer
height
Site location (to some extent) and site size (i.e., "area of
contamination") can be factored into the simple site-specific
methodology for the inhalation pathways. The dispersion
factor (Q/C) for both volatiles and fugitive dusts was
calculated using a 90th percentile meteorological data set
selected from 29 data sets across the United States (see
Technical Background Document [U.S. EPA, 1994e]). Los
Angeles was selected as the 90th percentile data set for
volatiles and Minneapolis was selected as the 90th percentile
data set for fugitive dusts. Replacing the default city and site
she of 30 acres will affect the Q/C values in both the VF and
PEF equations (Equations 5 and 7). The Technical
Background Document supporting this guidance (U.S. EPA,
1994e) provides a table of Q/C values for 29 cities across the
country over a range of contaminant source areas for use in the
simple site-specific method.
The particulate emission factor derived by using the default
values in Equation 7 results in an ambient air concentration of
approximately 1.5 pg/m3. This represents an annual average
emission rate that is based on wind erosion and is not
appropriate for evaluating the potential for more acute
exposures.
Migration to Ground Water
The methodology for addressing migration of contaminants
from soil to ground water reflects the complex nature of
contaminant fate and transport in the subsurface. In this
methodology, a concentration in soil is backcalculated from an
acceptable ground water concentration. The generic SSLs
presented in Appendix A for this pathway represent a
conservative estimation of the concentration of a contaminant
in soil that would not result in exceedances of the acceptable
concentration of a contaminant in ground water. Flexibility to
consider site-specific conditions is addressed in the simple and
detailed site-specific methodologies.
The first step in applying the SSL framework is a comparison
of the SSL conceptual model presented earlier in this document
with the conceptual model developed for the site. This forms
the basis for determining the appropriateness of conducting a
more detailed investigation and the applicability of the SSL
guidance for the migration to ground water pathway. Some of
the assumptions used to develop the SSL conceptual model
have implications for the ground water pathway. Highlight 4
lists assumptions implicit in the conceptual model that should
be understood before applying the SSL ground water frame-
work.
Both the simple site-specific and generic methods are based on
the commonly used equilibrium soil/water partition equation
(Equation 8) that describes the ability of contaminants to sorb
Equation 8: Soil Screening Level Partitioning
Equation for Migration to Ground
Water
Screening Level
in Soil (mg/kg)
= C IK + (9"*e*H>)
w[ " " Pb
Parameter/Definition (units)
C^/target soil leachate
concentration (mg/L)
Kysoil-water partition coefficient
Koc/soil organic carbon/water
partition coefficient (L/kg)
foc /fraction organic carbon in soil
(g/g)
e^/water-filled soil porosity
C-wate/'-soil)
w/average soil moisture content
(kgwate/kSsoil or l-wate/kgsoil)
pb/dry soil bulk density (kg/L)
n/soil porosity (Lp^/L^,)
Ps/soil particle density (kg/L)
6a/air-filled soil porosity (
H'/Henry's law constant (unitless)
H/Henry's law constant
(atm-m3/mol)
Default
nonzero MCLG, MCL,
or HBL x 10 DAF
chemical-specific, «„,,
xfoc(organics)
chemical-specific
0.002 (0.2%)
0.3 or wpb
0.2 (20%)
1.5 or (1 - n) ps
0.43 (loam)
2.65
0.13 or (n - 6W)
Hx41
chemical-specific
(assume to be zero
for inorganic con-
taminants except
mercury)
11
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Review Draft—Do Not Cite or Quote—December 1994
Highlight 4: Simplifying Assumptions of the Default
Conceptual Model for Ground Water
1. The source of contamination is defined as an evenly
contaminated 30-acre site. Source size has signifi-
cant implications for the development of the dilution/
attenuation factor. Large sources generally tend to
result in low DAFs, while smaller sources generally
justify higher DAFs. Where actual source size differs
significantly from the default 30-acre assumption, the
user should consider a site-specific evaluation to
develop a more site-specific DAF.
2. The soil contamination extends from the surface to
the top of the aquifer. This is a reasonable assump-
tion for sites where the water table is fairly shallow
(e.g., 5 to 10 feet below surface). However, in areas
where the water table is very deep, this assumption
may not be valid and should be considered in the
decision to apply a detailed site-specific evaluation.
3. No attenuation is considered in the unsaturated
zone. This assumption also has implications for the
DAF. As discussed above, a detailed site-specific
evaluation should be considered at sites that have a
very thick uncontaminated unsaturated zone because
a higher DAF may be justified.
4. The point of compliance is at the edge of the site,
which is assumed to be uniformly contaminated.
This conservative assumption also has implications
for the calculation of the DAF. The user should
consider whether this assumption is valid for the site
in question and whether further evaluation would be
appropriate.
5. The simple site-specific or generic DAF assumes;
that an unconfined, unconsolidated aquifer with
homogeneous and isotropic hydrologic properties
underlies the site. A DAF greater than 1 may not be
appropriate for soils underlain by karst or fractured
rock aquifers.
6. NAPLs are not present. If NAPLs are present in
soils, the SSLs do not apply (i.e., further investiga-
tion is necessary).
to organic carbon in soil (Dragun, 1988). An adjustment to
relate sorbed concentration in soil to the analytically measured
total soil concentration has been added to the equation.
The partition equation contains parameters for chemical-
specific (Henry's law constant; Kd or K^ and subsurface
characteristic variables (dry bulk density, porosity, air-filled
and water-filled pore space). In the default method, national
default values for the parameters in the partition equation were
used to calculate the generic SSLs in Appendix A. Nonzero
ground water maximum contaminant level goals (MCLGs)
•ere used as the acceptable ground water limits for each
ntaminant in the partitioning equation. If nonzero MCLGs
were not available, maximum contaminant levels (MCLs) were
used. If MCLs were not available, concentrations associated
with a target cancer risk of 10"6 and/or a noncancer HQ of 1
were derived using Agency toxicity criteria. The acceptable
ground water limit is multiplied by the DAF of 10 to obtain a
target soil leachate concentration for calculating generic SSLs.
In the simple site-specific method, site-measured data would
replace the default values for the subsurface characteristic and
soil variables (i.e., fraction organic carbon, dry bulk density,
average soil moisture content). These variables would then be
used to calculate a more site-specific screening value. Even
this screening number is fairly conservative because of the
underlying assumptions regarding the absence of attenuation
and placement of the well adjacent to the source.
As described above, the C^ ceiling limit defines (for organic
chemicals that are liquid at soil temperatures) a concentration
above which chemicals may occur as NAPLs in soil. For
liquid chemicals present at concentrations greater than C^,
NAPL presence may be suspected and the Soil Screening
framework would not be applicable (i.e., further investigation
is necessary). See U.S. EPA (1992b) for guidance on deter-
mining the likelihood of NAPL occurrence in the subsurface
and on conducting the additional investigations necessary if
NAPL, occurrence is suspected at a site.
Partitioning of inorganic constituents in the subsurface is more
complex than for organics. A variety of soil conditions affect
the derivation of the partitioning coefficient for inorganics,
while organic carbon is the parameter that most affects organic
partitioning. For this reason, the EPA MINTEQ2 equilibrium
geochemical speciation model was used to calculate Kd values
for the metals, which were then used in Equation 8. Kd values
for metals are most significantly affected by pH; therefore,
metal Kd values were calculated over a range of subsurface pH
conditions (4.9 to 8.0). Kd values corresponding to this pH
range are presented in the revised Technical Background
Document (U.S. EPA, 1994e) for use in the simple site-
specific method. Based on the pH at the site, the appropriate
Kd should be selected and used in the calculation. Also note
that all metals except mercury are essentially nonvolatile and
their Henry's law constant (HO in Equation 8 should be set at
zero.
Generic SSLs for inorganics corresponding to a pH of 6.8 are
presented in; Appendix A for the default method. Table 1 lists
inorganic SSLs corresponding to pH values of 4.9 and 8.0 and
a DAI7 of 10. If pH conditions at a site are not known, the
generic SSL corresponding to a pH of 6.8 should be used in
the default method. Table 1 also includes SSLs for ionizing
organics, whose partitioning behavior is also pH dependent.
Readers are referred to the Technical Background Document
(U.S. EPA, 1994e) for a more detailed discussion of the
derivation of Kd values for inorganics and K,,,. values for
ionizing and nonionizing organics.
The framework also includes the option of using a leach test
instead of the partitioning equation. In some instances a leach
12
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Review Draft—Do Not Cite or Quote—December 1994
Table 1. pH-Speclfic SSLs for Metals
and Ionizing Organlcs (mg/kg) (DAF = 10)
Chemical
Arsenic
Barium
Beryllium
Cadmium
Chromium (+6)
Mercury
Nickel
Selenium
Thallium
Zinc
Benzoic acid
2,4-Dichlorophenol
Pentachtorophenol
2,4,5-Trfehlorophenol
2,4,6-Trfchlorophenol
pH4.9
13
16
0.1
0.06
31
0.006
1
9
0.2
180
300
0.5
0.2
200
0.07
pH8
16
340
19,000
230
14
4
140
1
0.5
1.6E+6
280
0.3
0.01
26
0.01
test may be more useful than the partitioning method, depend-
ing on the constituents of concern and the possible presence of
RCRA wastes. This guidance suggests using the EPA
Synthetic Precipitation Leaching Procedure (SPLP, EPA SW-
846 Method 1312, see the Technical Background Dcoument
[U.S. EPA, 1994e]). The SPLP was developed to model an
acid rain leaching environment and is generally appropriate for
a contaminated soil scenario. Like most leach tests, the SPLP
may not be appropriate for all situations (e.g., soils
contaminated with oily constituents may not yield suitable
results). Therefore, discretion is advised when applying the
SPLP.
The Agency is aware that there are many leach tests available
for application at hazardous waste sites, some of which may be
appropriate in specific situations (e.g., the Toxicity Charac-
teristic Leaching Procedure, known as the TCLP, models
leaching in a municipal landfill environment). It is beyond the
scope of this document to discuss in detail other leaching
procedures and the appropriateness of their use. Stabilization/
Solidification of CERCLA and RCRA Wastes (U.S. EPA,
1989c) and the SAB's review of leaching tests (U.S. EPA,
199 lc) contain information on the application of various leach
tesls to various waste disposal scenarios. The user is
encouraged to consult these doucments for further information.
DETERMINING THE DILUTION/
ATTENUATION FACTOR
As contaminants move through soil and ground water, they are
subjected to a number of physical, chemical, and biological
processes that generally reduce the eventual contaminant
concentration level at receptor points. The reduction in
concentration can be expressed succinctly by the DAF, defined
as the ratio of the soil leachate concentration to the receptor
point concentration. The lowest possible value of DAF is 1,
corresponding to the situation where there is no dilution or
attenuation of a contaminant; i.e., the concentration at the
receptor point is the same as that in the soil leachate. High
DAF values, on the other hand, correspond to a high degree of
dilution and attenuation of tlie contaminant from the leachate
to the receptor point.
The soil/water partition equation relates concentrations of
contaminants adsorbed to soil organic carbon to soil leachate
concentrations in the unsaturated zone. Contaminant migration
through the unsaturated zone to the water table generally
reduces the soil leachate concentration by attenuation processes
such as adsorption and degradation. Ground water transport in
the saturated zone further reduces concentrations through
adsorption, degradation, and dilution. Generally, to account for
this reduction in concentration, acceptable ground water limits
are multiplied by a DAF to obtain a target soil leachate
concentration for the partition equation.
! ! I
A default DAF of 10 is applied to calculate the generic SSLs.
A weight of evidence method was used to determine this
default DAF. In the weight-of-evidence approach, OERR
evaluated a number of methods for calculating DAFs.
Included in this approach was an evaluation of DAFs
calculated by the EPACMTP model, using a range of
assumptions including those ;associated with the conceptual site
model for the generic SSLs. The comparison also included
DAFs calculated from a mores simplified mixing-zone equation,
as well as acceptable DAFs used in existing State programs.
The comparison indicated that, for the default scenario, a DAF
of 10 is conservatively protective of the majority of site
conditions, including the site scenario developed for the
generic SSLs. The Technical Background Document (U.S.
EPA, 1994e) supporting this guidance contains additional detail
on the development of the generic DAF.
The simple site-specific method relies on a fairly simple
mixing zone equation (Equation 9) to calculate a site-specific
dilution factor to be used instead of the default DAF. In this
method, site-measured values for hydraulic gradient, hydraulic
Equation 9: Derivation of Dilution Factor
dilution factor = 1 + _1_
Parameter/Definition (units)
dilution factor (unitless)
K/aquifer hydraulic conductivity (m/yr)
i/hydraulic gradient (m/m)
d/mixing zone depth (m)
I/infiltration rate (m/yr)
L/source length parallel to ground water flow (m)
13
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Review Draft—Do Not Cite or Quote—December 1994
conductivity, and estimates of infiltration, contaminant source
length, and mixing-zone depth are used to calculate the dilution
factor. The mixing-zone depth is estimated from an equation
relating it to aquifer thickness, infiltration rate, ground water
ilocity, and source length parallel to flow (Equation 10).
Equation 10: Estimation of Mixing Zone Depth
d = (0.0112 L2)0'5 + da {1 - exp[(-LI)/(Kid,)]}
Parameter/Definition (units)
d/mixing zone depth (m)
L/source length parallel to ground water flow (m)
1/infiftration rate (m/yr)
K/aquifer hydraulic conductivity (m/yr)
da/aquifer thickness (m)
Detailed Site-Specific Method
In this investigation, site-specific data are collected and used
in a fate and transport model to determine whether a threat to
ground water exists and, if so, to further determine site-specific
cleanup goals as would typically be done for the remedial
investigation/feasibility study (RI/FS). Consequently it
represents the highest level of site-specificity in evaluating the
migration to ground water pathway. A DAF is not used in this
:1iod because the model would account for fate and transport
nanisms in the subsurface. The advantage of this approach
mt it accounts for site hydrogeologic, climatologlc, and
contaminant source characteristics and may result in fully
protective but less stringent remediation goals. However, the
additional cost of collecting the data required to apply the
model should be factored into the decision to conduct a
detailed site-specific investigation.
Choosing a model for site-specific application is integral to an
accurate evaluation of potential concern. However, the data
used in the application and interpretion of the results are
equally important. In an effort to provide useful information
for a model application, EPA's ORD Laboratories in Ada,
Oklahoma, and Athens, Georgia, conducted an evaluation of
nine unsaturated zone fate and transport models. The infor-
mation in this report is summarized in the Technical
Background Document (U.S. EPA, 1994e) supporting this
guidance. These nine models are only a subset of the poten-
tially appropriate models available to the public and are not
meant to be construed as having received EPA approval. EPA
also has developed guidance for the selection and application
of ground water transport and fate models and for interpreta-
tion of model applications. The user is referred to Ground
Water Modeling Compendium (U.S. EPA, 1994b) and Frame-
work for Assessing Ground Water Model Applications (U.S.
'A, 1994a) for further information.
MEASURING CONTAMINANT
CONCENTRATIONS IN SOIL
In order to compare site soil concentrations with the SSLs, it
is important to develop a sampling strategy that will result in
an accurate representation of site contamination. This Soil
Screening Guidance recommends that site managers use the
Data Quality Objectives (DQO) process (Figure 5) to develop
a sampling strategy that will satisfy Superfund program
objectives. The site manager can use the DQO process to
conveniently organize and document many site-specific
features and assumptions underlying the sampling plan. In the
last step of the DQO process, "Optimize the Design for
Obtaining Data," the site manager can choose between two
alternative approaches to measuring surface soil contaminant
concentrations. The first is a site-specific strategy that uses
site-specific estimates of contaminant variability to determine
how many .samples are needed to support the screening
decision. The second is a fairly prescriptive approach that can
be used in lieu of the site-specific strategy. Recommendations
for subsurface sampling that can be modified to accommodate
site-specific conditions are also included in the guidance.
Exposure to site contaminants over a long (chronic) period of
time is best represented by an arithmetic average concentration
for an exposure area (U.S. EPA, 1992d). Therefore, measure-
ment of site concentrations for comparison to the SSLs should
State the Problem
Identify the Decision
Identify Inputs to the Decision
Define the Study Boundaries
Develop a Decision Rule
Specify Limits on Decision Errors
Optimize the Design for Obtaining Data
Figure 5. The Data Quality Objectives process.
14
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Review Draft—Do Not Cite or Quote—December 1994
be based on the arithmetic mean concentration as well. For the
purposes of this guidance, the Agency has assumed that the
size of a typical residential lot (0.5 acre) is an appropriate
averaging area for residential land use. For large sites that
could be divided into multiple residential lots, the site should
be sectioned into appropriate 0.5-acre parcels.
For measurement of surface soil samples for the inhalation and
ingcstkm pathways, samples should be collected over a depth
of 6 inches because it is the top 6 inches of soil that is most
likely to be ingested or inhaled as fugitive dusts. Additional
sanipling beyond 6 inches may be appropriate, depending on
the contaminant's mobility. If soils at the site are of concern
for the migration to ground water pathway as well as the
ingesdon and/or inhalation pathways, then surface soils should
be sampled first since the results of the composite samples
may indicate source areas to target for subsurface sampling.
As discussed previously, the initial steps for implementing the
Soil Screening framework are to (1) develop the conceptual
site model and determine the applicability of the framework;
(2) determine if background concentrations exceed the
(generic) SSLs; and (3) select the method (simple site-specific,
detailed site-specific, or generic) to determine the SSLs. Once
these steps have been completed, it will then be necessary to
choose either a site-specific or a generic, prescriptive sampling
strategy for surface soils.
Surface Soils—Site-Specific Strategy
The site-specific sampling strategy utilizes a sampling design
approach that allows statistically valid conclusions to be drawn
about contaminant concentrations at a site based on relatively
limited sampling. EPA recommends that site managers use
this strategy to determine the number of samples needed to
compare average contaminant concentrations within each
exposure area against the SSLs. The site-specific strategy
provides procedures for ensuring that screening decisions can
be made with acceptable levels of confidence despite
variability in soil contaminant concentrations that can
sometimes mask true conditions at the site. This approach
provides flexibility to incorporate site-specific information
about likely contamination patterns so that sampling can be
concentrated in areas where uncertainty about the risk posed by
soil contaminants is greatest.
The sampling design developed for the site should be based on
the conceptual site model and should reflect conditions at the
site. It is flexible in that the information used to develop the
conceptual site model (historical records, aerial photographs,
existing sampling data, etc.) can also be used to develop an
appropriate sampling strategy. Such a strategy may include
stratification of the site, if appropriate, into areas where soil
contaminant concentrations are expected to clearly exceed the
SSLs, areas where soil contaminant concentrations are expected
to fall well below the SSLs, and areas of the site where there
is greater uncertainty as to whether soil contaminant
concentrations exceed the SSLs.
This classification of areas of the site can help in designing an
efficient sampling plan, since the number of samples required
to support good decision making depends on the contaminant
variability likely to be encountered and how greatly
contaminant concentrations differ from the SSLs. By grouping
similar areas together, each area can be sampled in accordance
with the level of uncertainty or variability associated with that
area. For example, EPA expects that a relatively small number
of samples will be needed to make the screening decision
where average contaminant concentrations clearly exceed or
are well below the SSLs. More intensive sampling is expected
for those areas where relatively high contaminant variability or
concentrations close to the SSLs make it more difficult to
determine with confidence whether the average contaminant
concentration exceeds the screening level.
Inherent in the statistically based site-specific sampling strategy
is the specification of limits on decision errors, which is
performed in the sixth step of the DQO process. Limits on
decision errors are quantitative performance requirements for
the quality and quantity of data that will support the screening
decision. These performance requirements are specified in
terms of the probability of making a decision error, which can
occur in two ways:
• Type I: The data mislead the site manager into
deciding that the exposure area concentration is below
the SSLs when the true average contaminant
concentration exceeds the screening level; or
• Type IT: The data mislead the site manager into
deciding that the exposure area concentration is above
the SSL and further investigation is required when in
fact the true average contaminant concentration is less
than the SSL.
To ensure consistency in applying the framework, EPA has
specified tolerable limits on decision errors at the program
level. The Technical Background Document (U.S. EPA,
1994e) provides a full discussion of the Soil Screening
framework's limits on decision errors and of the site-specific
strategy in general. EPA encourages the project manager to
seek the assistance of a statistician or the Regional quality
assurance staff for the development of the sampling strategy.
For more detailed guidance on the DQO process the user
should refer to the Technical Background Document and Data
Quality Objectives for Superfund (Interim Final) (U.S. EPA,
1993a).
Surface Soils—Prescriptive Approach
The guidance provides a second sampling methodology—a
"prescriptive approach"—that can be used as an alternative to
the site-specific approach. A sampling design effort is
required for the site-specific strategy, whereas the prescriptive
approach provides a simple, standard sampling approach that,
will be most useful for small sites that do not warrant an'
extensive design effort. It emphasizes composite sampling for
15
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Review Draft—Do Not Cite or Quote—December 1994
nonvolatile contaminants and specifies the number of samples
to be collected for analysis of volatile contaminants. It differs
from the site-specific approach in that the same sampling
strategy must be applied to each 0.5-acre exposure area.
it does not explicitly control decision errors,
simulations suggest that it does not underestimate
mean concentrations for commonly occurring patterns of soil
contamination. Additional simulations comparing the
performance of the prescriptive approach to the site-specific
strategy will be a subject of peer review.
Studies by ORD indicate that at least 20 samples per exposure
area are needed to closely estimate the true mean. To balance
the need for statistical confidence in determining a meaningful
arithmetic mean contaminant concentration with the costs of
analyzing multiple samples for each exposure area, EPA
recognizes the benefits of composite samples and advocates
compositing, where appropriate. Compositing may mask
contaminant levels that are slightly higher than the SSL, but
areas of high contamination will still be detected. Compositing
is a reasonable approach and an efficient use of resources since
the Superfund program is interested in the average exposure
over time. (See the Technical Background Document [U.S.
EPA, 1994e] for a more detailed discussion of compositing and
its limitations.)
Using the prescriptive approach, 20 discrete samples can be
reduced to four composite samples. (The exposure area can be
divided into quadrants and five random samples can be
Collected and composited within each quadrant.) The contam-
tiant concentrations from the four composite samples should
"be compared directly with their respective SSLs. If any one of
the composites equals or exceeds the SSL, then that portion of
the exposure area should be studied further.
Compositing is not appropriate for volatile organic compounds
(VOCs) since much of the contaminant will be lost during
homogenization of the soil (U.S. EPA, 1989a, 1992c). For
VOCs, 10 discrete samples can be taken per exposure area and
any sample above the SSL would trigger the need for
additional study in that exposure area. Additionally, it is not
appropriate to average the contaminant levels in each exposure
area and evaluate the mean concentration against the SSLs
because 10 discrete samples may underestimate the tree mean.
Subsurface Sampling
For the migration to ground water pathway, subsurface soils
that have constituents that might contribute to ground water
contamination are of primary concern. Therefore, it is the
source areas that are of interest and not necessarily a 0.5-acre
exposure area as specified for the ingestion and inhalation
pathways. To determine whether contaminants in the subsur-
face soils (defined as below 6 inches for the purposes of
implementing SSLs) potentially pose a risk to ground water,
guidance suggests sampling at least two boreholes using
lit spoon or Shelby tube samples in each source area.
Samples should begin at 6 inches below ground surface and
continue at 2-foot intervals until no contamination is
encountered. If the average concentration in any borehole
exceeds the SSL, then further site-specific study is warranted.
Subsurface sampling depths and intervals can be adjusted at a
site to accommodate site-specific information on subsurface
contaminant distributions and geological conditions. In
addition, soil investigation for the migration to ground water
pathway should not be conducted independent of ground water
investigation. Ground water should be sampled to determine
whether there is concern for existing ground water contam-
ination, and the results should be considered in the holistic
application of the Soil Screening framework.
Geostatistics
If the SSLs are to be compared with the data resulting from
the initial sample collection efforts of the remedial
investigation, the site manager may want to consider using
geostatistics to estimate contaminant concentrations across the
site. Geostatistics is probably most appropriate to use in the
detailed site-specific approach. Geostatistics is a field of study
in which statistical analyses of geologic or environmental data
are conducted. It differs from single-sample classical statistics
in that it assumes that variability and independence between
samples is not random, but that there is some spatial continuity
between samples. Geostatistics can be used to estimate
contaminant concentrations at unsampled points and estimate
average contaminant concentrations across the site.
Software packages have been developed to facilitate
geostatistical analyses. One package is GEO-EAS, developed
by EPA's Environmental Monitoring Systems Laboratory in
Las Vegas, Nevada. Assistance and consultation with skilled
geostatisticians is recommended prior to initiating any
sampling plan to ensure that the sampling strategy will capture
the critical data necessary for the geostatistical analyses.
WHERE TO GO FOR FURTHER
INFORMATION
More detailed discussions of the technical background and
assumptions supporting the development of the Soil Screening
framework are presented in the Technical Background
Document, for Soil Screening Guidance (U.S. EPA, 1994e).
For additional copies of this Fact Sheet and/or the Technical
Background Document, call the National Technical Information
Service (NTIS) at (703) 487-4650.
16
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Review Draft—Do Not Cite or Quote—December 1994
NOTICE: This guidance is based on policies in the Final Rule of the National Oil and Hazardous Substances Pollution
Contingency Plan (NCP), which was published on March 8, 1990 (55 Federal Register 8666). The NCP should be considered
the authoritative source.
The policies set out in this document are intended solely as guidance to the U.S. Environmental Protection Agency (EPA)
personnel; they are not final EPA actions and do not constitute rulemaking. These policies are not intended, nor can they be
rel|ed upon, to create any rights enforceable by any party in litigation with the United States. EPA officials may decide to follow
the guidance provided in this document, or to act at variance with the guidance, based on an analysis of specific site
circumstances. EPA also reserves the right to change the guidance at any time without public notice.
REFERENCES
Calabrese, EJ., H. Pastides, R. Barnes, et al. 1989. How
Much Soil Do Young Children Ingest: An Epidemiologic
Study. In: Petroleum Contaminated Soils, Vol. 2. EJ.
Calabrese and P.T. Kostecki, eds. pp. 363-417. Chelsea,
MI, Lewis Publishers.
Cowherd, C., G. Muleski, P. Engelhart, and D. Gillette. 1985.
Rapid Assessment of Exposure to Paniculate Emissions
from Surf ace Contamination. EPA/600/8-85/002. Prepared
for Office of Health and Environmental Assessment, U.S.
Environmental Protection Agency, Washington, DC. NHS
PB85-192219 7AS.
Davis, S., P. Waller, R. Buscnom, J. Ballou, and P. White.
1990. Quantitative estimates of soil ingestion in normal
children between the ages of 2 and 7 years: population-
based estimates using Al, Si, and Ti as soil tracer elements.
Archives of Environmental Health, 45:112-122.
Dragun, J. 1988. The Soil Chemistry of Hazardous Materials.
Hazardous Materials Control Research Institute, Silver
Spring, MD.
U.S. EPA. 1988. Guidance on Remedial Actions for
Contaminated Ground Water at Superfund Sites. Directive
9283.1-2. EPA/540/G-88/003. Office of Emergency and
Remedial Response, Washington, DC. NTIS PB89-
184618/CCE.
U.S. EPA. 1989a. Methods for Evaluating the Attainment of
Soil Cleanup Standards. Volume 1: Soils and Solid
Media. EPA 230/02-89-042. Statistical Policy Branch,
Office of Policy, Planning, and Evaluation, Washington,
DC.
U.S. EPA. 1989b. Risk Assessment Guidance for Superfund:
Volume 1: Human Health Evaluation Manual, Part A,
Interim Final. EPA/540/1-89/002. Office of Emergency
and Remedial Response, Washington, DC. NTIS PB90-
155581/CCE.
U.S. EPA. 1989c. Stabilization/Solidification ofCERCLA and
RCRA Wastes. EPA/625/6-89/022.
U.S. EPA. 1990a. Guidance on Remedial Actions for
Superfund Sites with PCB Contamination. EPA 540G-
90/007. Office of Emergency and Remedial Response,
Washington, DC. NTIS PB91-921206/CCE.
U.S. EPA. 1990b. Suggested ROD Language for Various
Ground Water Remediation Options. Directive 9283.1-03.
Office of Emergency and Remedial Response,
Washington, DC. NTIS PB91-921325/CCE.
U.S. EPA. 199 la. Guidance for Risk Assessment. Risk
Assessment Council, Office of the Administrator,
Washington, DC.
U.S. EPA. 199 Ib. Hwnan Health Evaluation Manual,
Supplemental Guidance: Standard Default Exposure
Factors. Publication 9285.6-03. Office of Emergency and
Remedial Response, Washington, DC. NTIS PB91-921314.
U.S. EPA. 199 Ic. Leachability Phenomena. Recommenda-
tions and Rationale for Analysis of Contaminant Release by
the Environmental Engineering Committee. EPA-SAB-
EEC-92-003. Science Advisory Board, Washington, DC.
U.S. EPA. 1991d. Risk Assessment Guidance for Superfund,
Volume 1: Human Health Evaluation Manual (Part B,
Development of Risk-Based Preliminary Remediation
Goals). Publication 9285.7-01B. Office of Emergency and
. Remedial Response, Washington, DC. NTIS PB92-963333.
U.S. EPA. 1991e. Role of the Baseline Risk Assessment in
Superfund Remedy Selection Decisions. Publication
9355.0-30. Office of Emergency and Remedial Response,
Washington, DC. NTIS PB91-921359/CCE.
U.S. EPA. 1992a. Considerations in Ground-Water
Remediation at Superfund Sites and RCRA Facilities—
Update. Directive 9283.1-06. Office of Emergency and
Remedial Response, Washington, DC. NTIS PB91-
238584/CCE.
U.S. EPA. 1992b. Estimating Potential for Occurrence of
DNAPL at Superfund Sites. Publication 9355.4-07FS.
Office of Emergency and Remedial Response, Washington,|
DC. NTIS PB92-963338.
17
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Review Draft—Do Mot Cite or Quote—December 1994
U.S. EPA. 1992c. Guidance for Data Usability in Risk
Assessment (Part A). Office of Emergency and Remedial
1 Response, Washington, DC. NTIS PB92-963356.
_ EPA. 1992d. Supplemental Guidance to RAGS:
^Calculating the Concentration Term, Volume 1, Number 1.
Publication 9285.7-011. Office of Emergency and
Remedial Response, Washington, DC. NTISPB92-963373.
U.S. EPA. 1993a. Data Quality Objectives for Superfund:
Interim Final Guidance. EPA 540-R-93-071. Publication
9255.9-01. Office of Emergency and Remedial Response,
Washington, DC. NTIS PB94-963203.
U.S. EPA. 1993b. Guidance for Evaluating Technical
Impracticability of Ground-Water Restoration. Directive
9234.2-25. EPA/540-R-93-080. Office of Emergency and
Remedial Response, Washington, DC.
U.S. EPA. 1993c. Health Effects Assessment Summary
Tables (HEAST): Annual Update, FY1993. Environmen-
tal Criteria and Assessment Office, Office of Health and
Environmental Assessment, Office of Research and
Development, Cincinnati, OH.
U.S. EPA. 1993d. Science Advisory Board Review of the
Office of Solid Waste and Emergency Response draft Risk
Assessment Guidance for Superfund (RAGS), Human
Health Evaluation Manual (HHEM). EPA-SAB-EHC-93-
007. Science Advisory Board, Washington, DC.
U.S. EPA, 1994a. Framework for Assessing Ground Water
Modeling Applications. EPA-500-B-94-004. Resource
Management and Information Staff. Office of Solid Waste
and Emergency Response, Washington, DC.
U.S. EPA. 1994b. Ground Water Modeling Compendium,
Second Edition. EPA-500-B-94-003. Resource
Management and Information Staff. Office of Solid Waste
and Emergency Response, Washington, DC.
U.S. EPA. 1994c. Integrated Risk Information System (IRIS).
Dulutli, MN.
U.S. EPA. 1994d. Role of the Ecological Risk Assessment in
the Baseline Risk Assessment. OSWER Directive No.
9285.7-17. Office of Solid Waste and Emergency
Response, Washington, DC. August 12.
U.S. EPA. 1994e. Technical Background Document for Soil
Screening Guidance. EPA/540/R-94/102. Office of
Emergency and Remedial Response, Washington, DC.
PB95-963530.
Van Wijnen, JJEL, P. Clausing, and B. Bmnekreef. 1990.
Estimated Soil Ihgestion by Children. Environmental
Research, 51:147-162.
18
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Review Draft—Do Not Cite or Quote—December 1994
Appendix A. Generic Soil Screening Levels for Superfund*
NOTICE: These
specific exposure
CAS No.
83-32-9
67-64-1
309-00-2
120-12-7
71-43-2
56-55-3
205-99-2
207-08-9
50-32-8
111-44-4
117-81-7
75-27-4
75-25-2
71-36-3
85-68-7
86-74-8
75-15-0
56-23-5
57-74-9
108-90-7
124-48-1
67-66-3
218-01-9
72-54-8
72-55-9
50-29-3
53-70-3
84-74-2
95-50-1
106-46-7
91-94-1
75-34-3
107-06-2
75-35-4
156-59-2
156-60-5
78-87-5
542-75^6
60-57-1
84-66-2
131-11-3
121-14-2
606-20-2
values were developed for use in application of the Soil Screening Guidance
pathways constituting a residential scenarb and should only be used in that
, \
JB|0 K
Chemical
Acenaphthene
Acetone
Aldrin
Anthracene
Benzene
Benzo(a)anthracene
Benzo(6)fluoranthene
Benzo(/c)fluoranthene
Benzo(a)pyrene
Bis(2-chlorethyl)ether
Bis(2-ethy!hexy!)phthalate
Bromodichloromethane
Bromoform
Butanol
Butyl benzyl phthalate
Carbazole
Carbon disulfide
Carbon tetrachloride
Chlordane
Chtarobenzene
Chlorodibromomethane
Chtaroform
Chrysene
ODD
DDE
DDT
Dibenzo(a,/i)anthracene
Di-/7-butyl phthalate
1 ,2-Dichlorobenzene (o)
1 ,4-Dichbrobenzene (p)
3,3-Dichlorobenzidine
1,1-Dichbroethane
1 ,2-Dichtaroethane
1 , 1 -Dfchbroethylene
cfe-1 ,2-Dichloroethylene
frans-1 ,2-Dichloroethylene
1 ,2-Dichbropropane
1 ,3-Dichloropropene
Dieldrin
Diethyl phthalate
Dimethyl phthalate
2,4-Dinrtrotoluene
2,6-Dinitrotoluene
Pathway-specific values for
surface soils
(mg/kg)
Ingestion Inhalation
4,700 b —c
7,800 b 62,000 d
0.04 e 0.5 e
23,000 b — c
22 e 0.5°
0.9 8 — c
0.9 e - c
g e e
0.09 e-f -c
0.6 e 0.3 e'f
46° 210 d
5e 1,800 d
81 a 46 e
7,800 b : 9,700 d
1 6,000 b 530 d
32 e ~- c
7,800 b 11 b
5el 0.2 e
0.5 e 10 e
1,600b 94 b
8e 1,900 d
110 e 0.2°
88 e — c
38 C
2 e <=
2e 80 e
0.09 e-f . •— c
7,800 b 100d
7.IDOO b 300 d
27 e 7,700 b
-j a c
7,800 b 980 b
7 e 0.3 e
1 e 0.04 e
780 b 1,500d
1,600b 3,600 d
9e 11 b
4e 0.1 e
0.04 e 2 e
63,000 b 520 d
7.8E+5b 1,600d
160 b — c
78 b' — °
only. They were devebped for
context.
Migration to ground water
pathway levels (mg/kg)
With 10
DAF
200 b
8b
0.005°
4,300 b
0.02
0.7
4
4
4
3E-4 e-f
11
0.3
0.5
8b
68
0.2 e-f
14 b
0.03
2
0.6
0.2
0.3
1
0.7*
0.5 e
18
11
120 b
6
1
0.01 "•'
11 b
0.01 f
0.03
0.2
0.3
0.02
0.001 e-f
0.001 e'f
110 b
1,200 b
0.2 b'f
0.1 b-f
Wtthl
DAF
20 b
0.8 b
5E-4e'f
430 b
0.002 f
0.07 f
0.4
0.4
0.4
3E-5 "•'
1
0.03
0.05
0.8 b
7
0.02 "•'
1b
0.003 f
0.2
0.06
0.02
0.03
0.1 f
0.07 e
0.05 e
0.1 e
1
12 b
0.6
0.1'
0.001 °'f
1b
0.001 f
0.003 '
0.02
0.03
0.002 f
1E-4e'f
1E-4e'f
11 b
120 b
0.02 b>f
0.01 b'f
19
(continued)
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Review Draft—Do Not Cite or Quote—December 1994
Appendix A (continued)
»
CAS No.
117-84-0
115-29-7
72-20-8
100-41-4
206-44-0
86-73-7
76-44-8
1024-57-3
118-74-1
87-68-3
319-84-6
319-85-7
58-89-9
77-47-4
67-72-1
193-39-5
78-59-1
72-43-5
74-83-9
|75-09-2
*91-20-3
98-95-3
1336-36-3
129-00-0
100-42-5
79-34-5
127-18-4
108-88-3
8001-35-2
120-82-1
71-55-6
79-00-5
79-01-6
108-05-4
75-01-4
1330-20-7
65-85-0
106-47-8
95-57-8
120-83-2
^105-67-9
F51-28-5
95-48-7
/ \
010
Chemical
Di-n-octyl phthalate
Endosulfan
Endrin
Ethylbenzene
Fluoranthene
Fluorene
Heptachlor
Heptachlor epoxide
Hexachlorobenzene
Hexachloro-1 ,3-butadiene
a-HCH (a-BHC)
p-HCH (p-BHC)
Y-HCH (Lindane)
Hexachlorocyclopentadiene
Hexachloroethane
lndeno(1 ,2,3-c,d)pyrene
Isophorone
Methoxychlor
Methyl bromide
Methylene chloride
Naphthalene
Nitrobenzene
Polychlorinated biphenyls (PCBs)
Pyrene
Stryene
1 ,1 ,2,2-Tetrachloroethane
Tetrachloroethylene
Toluene
Toxaphene
1 ,2,4-Trichlorobenzene
1,1,1 -Trichloroethane
1 ,1 ,2-Trichloroethane
Trichloroethylene
Vinyl acetate
Vinyl chloride
Xylenes (total)
lonizable Organics
Benzoic acid
p-Chloroaniline
2-Chlorophenol
2,4-Dichiorophenol
2,4-Dimethylphenol
2,4-Dinitrophenol
2-Methylphenol
Pathway-specific values for
surface soils
(mg/kg)
Ingestion Inhalation
1,600b
470 b
23 b
7,800 b
3,100 b
3,100 b
0.1 •
0.07 e
0.4 •
8e
0.1 •
0.4 e
0.5 e
550 b
46 e
0.9 e
670 e
390 fcl
110b
85 e
3,100 b
39 b
1h
2,300 b
1 6,000 bl
3e
12 e
1 6,000 b
0.6 *
780 b
c
11 e
58*
78,000 b
0.3 e
1.6E+5b
3.1E+5b
310 b
390 b
240 b
1,600b
160 b
3,900 b
c
c
c
260 d
... c
c
0.3 e
1 e
1 e
1 e
0.9 e
16e
... c
2b
49 e
c
3,400 d
c
2b
7e
c
110b
c,h
c
1,400d
0.4 e
1 1 e
520 d
5d
240 b
980 d
0.8 e
36
370 b
0.002 e'f
320 d
c
c
53,000 d
-- . c
c
._ c
c
Migration to ground water
pathway levels (mg/kg)
With 10
DAF
g
4b
0.4
5
980 b
160 b
0.06
0.03
0.8
0.1 f
4E-4 e'f
0.002 e
0.006
10
0.2 e'f
35
0.2 e-f
62
0.1 b
0.01 f
30 b
0.09 b'f
h
1,400b
2
0.001 e'f
0.04
5
0.04 f
2
Q.9
0.01 f
0.02
84 b
0.01 f
74
280 b'!
0.3 b-f-i
2W
0.5 "•'
3 bli
0.1 b'f'i
6b.i
Withl
DAF
g
0.4 b
0.04
0.5
98 b
16b
0.006
0.003
0.08 f
0.01 f
4E-5e-f
2E-4 e'f
6E-4f
1
0.02 e'f
3
0.02 e>f
6
0.01 blf
0.001 '
3b
0.009 b'f
h
140 b
0.2
1E-4e'f
0.004 f
0.5
0.004 f
0.2 f
0.09
0.001 f
0.002 f
8b
0.001 f
7
28 w
0.03 Wi
0.2 b>fli
0.05 b-f'j
Oo b.f.i
.0
0.01 blf-i
0.6 bli
20
(continued)
-------
Review Draft—Do Not Cite or Quote—December 1994
Appendix A (continued)
Pathway-specific values for
surface soils
Migration to ground water
CAS No.
86-30-6
621-64-7
87-86-5
108-95-2
95-95-4
88-06-2
7440-36-0
7440-38-2
7440-39-3
7440-41-7
7440-43-9
7440-47-3
7439-92-1
74J39-97-6
7440-02-0
7782-49-2
74^0-22-4
7440-28-0
7440-62-2
7440-66-6
57-12-5
BHB
Chemical
W-N'rtrosodiphenylamine
W-Nitrosodi-n-propylamine
Pentachlorophenol
Phenol
2,4,5-Trichlorophenol
2,4,6-Trichlorophenol
Inorganics
Antimony
Arsenic &
Barium
Beryllium
Cadmium &
1
Chromium (6+)
Lead
Mercury &
Nickel 4?
1
Selenium &
Silver
Thallium
Vanadium
Zinc ^
Cyanide
(mg/kg)
Ingestion Inhalation
130 •
0.09 e-f
3e,j
47,000 b
7,800 b
58 e
31 b
0.4 e
5,500 b
0.1 e
39 b
390 b
400 '
23 b
1,600b
390 b
390 b
... c
550 b
23,000 b
1,600b
__ c
c
c
c
210 e
__°
380 e
3.5E+5 b
690 e
920 e
140 e
—
7b.i
6,900 e
c
c
c
... c
c
c
pathway leve
With 10
DAF
0.2 e'f>l
2E-5 ••«
0.01 w
49 w
120 w
0.06 «•*'
k
15s
32'
180 '
6!
19 '
—
3j
21 '
3'
k
0.4 '
k
42,000 b,i
k
is (mg/Kg)
Withl
DAF
0.02 e'f>l
2E-6 e-fli
0.001 fli
5b,i
12 w
0.006 e'f'i
k
1 '
3j
181
0.61
2!
—
0.3 '
21
0.31
-k
0.04 !
k
4,200 b,i
k
DAF m Dilution and attenuation factor.
Screening levels based on human health criteria only.
Calculated values correspond to a noncancer hazard quotient of 1.
No toxte'rty criteria available for that route of exposure.
Soil saturation concentration (C^).
Calculated values correspond to a cancer risk level of 1 in 1,000,000.
Level is at or below Contract Laboratory Program required quantitation limit for Regular Analytical Services (HAS).
Chemical-specific properties are such that this pathway is not of concern at any soil contaminant concentration.
A preliminary remediation goal of 1 ppm has been set for PCBs based on Guidance on Remedial Actions for Superfund Sites with
PCB Contamination, EPA/540G-90/007, Office of Emergency and Remedial Response, U.S. Environmental Protection Agency,
Washington, DC, 1990, and on Agency-wide efforts to manage PCB contamination.
1 SSL for pH of 6.8.
1 Ingestion SSL adjusted by a factor of 0.5 to account for dermal exposure.
k Soil/Water partition coefficients not available at this time. _ ^CD^, „ 0-»
1 A preliminary remediation goal of 400 mg/kg has been set for lead based on Revised Interim Soil Lead Guidance for CERCLA Sites
and RCRA Corrective Action Facilities, OSWER Directive #9355.4-12, Office of Solid Waste and Emergency Response, U.S.
Environmental Protection Agency, Washington, DC, July 14, 1994.
& Indicates potential for soil-plant-human exposure.
Levels developed for residential use only:
Residential
Industrial
Agricultural
21
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