DRAFT - DO NOT CITE OR QUOTE - S« it«mb«r 29,1993
AEPA
United Static
Environmental Protection
Agency
Office of
Solid Waste and
Emergency Response
PB93-963508
9355.4-14
September 1993
Draft Soil Screening Level
Guidance
Office of Emergency and Remedial Response
Hazardous Site Control Division (5203G)
Quick Reference Fact Sheet
NOTICE: This document is draft and should only be used in the context of demonstration pilots being overseen by the U.S. EPA. The methods
used to support the approach dscussad herein wfl undergo rigorous technical review and public comment before this document is finalzad along
with SSLs for approximately 60 additional chemicals in the summer of 1994.
BACKGROUND
On June 19,1991, the U.S. Environmental Protection Agency's
(EPA's) Administrator chargeuTthe Office~oT So&TWaste and
Emergency Response (OSWER) with conducting a 30-day
study to outline options for accelerating the rate of cleanups at
National Priority List (NPL) sites. The study found that the
current investigation/remedy selection process takes over 3
years to complete because each site is treated as a unique
problem, requiring the preparation of site-specific risk
ssments. cleanup levels, and technical solutions. The study
that standardizing the remedial planning and remedy
selection process would significantly reduce the time it takes
to start cleanups and would improve consistency across the
Regions. One of the specific proposals 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
the Superfund-program. This fact sheet presents Soil
Screening Levels (SSLs) (formerly known as trigger levels) for
30 chemicals and represents OSWER's first step toward
standardizing the evaluation and cleanup of contaminated soils
under the Comprehensive Environmental Response
Compensation and Liability Act (CERCLA).
An SSL is a chemical concentration in soil that represents a
level of contamination above which there is sufficient concern
to warrant further site-specific study. Concentrations in soil
above this screening level would not automatically designate
a site as "dirty." nor trigger a response action. However, they
suggest that a further evaluation of the potential risks that may
be posed by site contaminants is appropriate. Generally, if
contaminant concentrations in soil fall below the screening
€and the site meets specific residential use conditions, no
er study or action is warranted for that area under
CLA (Superfund). However, some States have developed
screening numbers that are more stringent than those presented
in this fact sheet, and therefore further study may be warranted
under State programs.
PURPOSE OF SSLs
The primary purpose of the SSLs is to accelerate decision-
making concerning contaminated soils. Initic! applications will
focus remedial investigations by eliminating from further study
site areas that do. not. warrant further study, under CERCLA.
In fostering prompt identification of the contaminants and
exposure areas of concern, the SSLs may also help simplify or
accelerate the baseline risk assessment and may serve as
Preliminary Remediation Goals (PRGs) under specified
conditions. EPA will explore other potential applications as it
proceeds to refine and expand this guidance. Such applications
may include removal response actions, site assessment/NPL
listing, voluntary cleanups, and Resource Conservation and
Recovery Act (RCRA) Corrective Actions.
ATTRIBUTES OF SSLs
The 30 SSLs presented in this document have been developed
using residential land use human exposure assumptions and
considering three pathways of exposure to the contaminants
(see Figure 1):
• ingestion of soil
• inhalation of volatiles and fugitive dusts
• migration of contaminants through soil to an underlying
potable aquifer.
These pathways have proven to be'the most common routes of
human exposure to contaminants in the residential setting at
hazardous waste sites evaluated by EPA. Also, substantial
efforts have been made to model these particular pathways.
Other routes/pathways may contribute significantly to the risk
posed by exposure to specific contaminants (e.g., dermal
exposure or exposure via food chain contamination). OSWER
will continue to seek consensus on the appropriate methods
required to quantify additional routes/pathways generically.
The results of these efforts may be included in the final
guidance.
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DRAFT - DO NOT CITE OR QUOTE - S ,pt»mb»r 29, 1993
Direct Ingestion
of Groundwater
and Soil
Inhalation
Blowing
Dust and
Volatilization
Not Addressed:
• Ecological effects
• Dermal absorption
• Indoor exposure to volatiles from soil and water
• Consumption of fish, beef, or dairy products
• Land uses other than residential
Figure 1. Pathways addressed by soil screening.
An overview of key SSL attributes includes:
>SSLs calculated for the ingestion and inhalation pathways
are based on standard equations modified from the Human
Health Evaluation Manual (Part B) (U.S. EPA. 1991).
• SSLs for migration to groundwater pathways are based on
a partitioning equation coupled with a dilution and
attenuation factor (DAF).
• Conservative default values were used to calculate levels
protective of "high end" individual exposures.
• SSLs are generally based on a 10"* risk for carcinogens, or
a hazard quotient of 1 for noncarcinogens; SSLs fix-
protection of groundwater are based on nonzero maximum
contaminant level goals (MCLGs), or maximum contami-
nant levels (MCLs). if available, or these same risk-based
targets otherwise.
• SSLs are calculated for individual exposure pathways
The SSLs correspond to a 10~* risk level for carcinogens jnd
a hazard quotient of 1 for noncarcinogens and the potential in
additive effects has not been "built in" to the SSLs thrown*
apportionment. For carcinogens, EPA believes that setting A
1CT6 risk level for individual chemicals and pathways »«il
generally lead to cumulative risks within the risk range (10 *
to 10"6) for the combinations of chemicals typically found u
iuperfund sites.
For noncarcinogens, there is no widely accepted "risk range.*
Thus, for developing national numbers, options are either (I)
to set the risk level for individual contaminants at the reference
dose (RfD) or reference concentration (RfQ (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/RfC). The Agency believes, and the Science Advisory
Board agrees (U.S. EPA, 1993b), that noncancer risks should
be added only for those chemicals with the same toxic
endpoint or mechanism of action. Because the combination of
contaminants will vary from site to site, the potential for
additive effects and the need to apportion risk must be a site-
specific determination.
Practically speaking, however, the five SSLs listed in Table 1
that are based on noncarcinogenic effects (RfDs) all have
different endpoints of toxicity (i.e., the critical effects on which
the RfDs are based are different). Thus risks for cumulative
exposure would not be additive. Furthermore', for the
noncarcinogenic volatiles (e.g., ethylbenzene and toluene), the
SSLs based on the ingestion pathway are very high, higher
than what is physically possible. In these cases, it is necessary
to establish a reasonable "ceiling limit" for the amount of
chemical that may be in the soil matrix at sites likely to use
this guidance. For the purposes of this guidance. this_"ceiling
limit" is based on the soil saturation limit (C,^), not toxicity,
and serves as the SSL for that chemical. For these reasons,
straight apportionment of SSLs in this fact sheet would be
inappropriate.
For the groundwater pathway only, SSLs are part of a four-
tiered approach to evaluating soil contaminants that may leach
to groundwater. The tiers reflect increasing levels of site
specificity and cost but generally decreasing levels of
conservatism. The first tier SSLs rely heavily on concentration
levels derived from mathematical models and generic
assumptions. If contaminant levels at a site do not exceed the
first tier SSLs and other site exposure pathways are accounted
for in the assumptions used to derive the SSLs, then the area
or site is no longer of concern under CERCLA remedial
authority. If contaminant levels at a site equal or exceed the
first tier SSLs, or other pathways of concern are present, full
site investigation may be initiated or one may consider higher
tier screening analyses. The other three tiers are distinguished
by their approach to, evaluating the soil-to-groundwater
pathway. Tier 2 uses site-specific values in a partitioning
equation. Tier 3 uses a leach test, and Tier 4 involves full-scale
site-specific modeling.
LIMITATIONS OF SSLs
SSLs do not trigger the need for response actions or define
"unacceptable" levels of contaminants in soil. In addition, the
levels are not necessarily protective of all known human
exposure pathways, reasonable land uses, or ecological threats.
SSLs were not developed as nationwide cleanup levels or
standards. They are risk-based levels that have not yet been
modified based on the Superfund remedy selection criteria that
.ire designed to tailor final cleanup levels to site-specific
tt minions (NCP Section 300.430 (3)(2)(i)(A)).
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DRAFT • DO NOT CITE OR QUOTE • September 29,1993
1 Table 1.
Superfund Proposed Soil Screening Levels*
L Pathway-specific values for 'Voundwater pathway levels
m surface soils (mg/kg) Surface soil (mg/kg)
Chemical
a-BHC
Benzene
Benzo(a)pyrene
Carbon tetrachloride
Chlordane
Chlorobenzene
Chloroform
Chrysene
DDT
1 ,4-Oichlorobenzene
1,1-Dichbroethane
1,1-Dichbroethene
Dieldrin
Ethylbenzene
Methylene chloride
Naphthalene •
PCB- 1260
Pentachlorophenol'
Tetrachloroethene
Toluen*
. 1 ,2,4-Trichlorobenzene
1 1,1.1 -Trichloroethane -
[ Trichloroethene
Vinyl chloride
Xylenes (mixed)
Arsenic
Cadmium
Chromium (VI)
Mercury
Nickel
5SL»
Ingeatton Inhalation (m9^g)b Unadjusted
0.1 d
22d
0.11 d
4.9 d
0.49d
1.600*
100 d
110 d
1.9d
27 d
&(
7.800*
1.1 d
0.04 d
7.800*
85d
3,100*
...y...
5.3d
12d
16,000
780*
7.000*
58d
0.34 d
160,000
0.37 d
39*
390 '
23'
1.600*
1.0 d
2.5 d
13.38
1.5d
0.69
170°
1.1 d
0.38 9
3.98
80 9
450°
0.17 d
S.I9
58a
44d
528
h
h
41 d
' 1509
93°
420 9
13d
0.02 d
' 979
2,600 d
6,200 d
930 d
41*
47,000 d
0.1 d
2.5 d
'0.11 d
1.5d
0.49 d
170°
1.1 d
0.38 9
1.9d
27 d
450 9
0.17 d
0.04 d
589
44d
52 9
h
h
12 d
ISO9
93°
420°
13d
0.02 d
979
0.37 d
39*
390 '
23'
1,600*
0.0001 *
0.001 *
0.71 d
0.003*
0.2 d
0.05
0.02
0.04
0.23
0.08*
0.62
0.002"
0.0001 *
0.33
0.001 *
2.5
0,82 -
0.001 •••»• -T
0.003*
0.36
0.23*
0.07
0.001 *
0.0002 *
5.7
1.4 1
0.81 '
1.9'
0.3'
8.2'
With 10 With 100
DAF3 DAF°
0.001
0.01
7.1
0.03
2
0.5
0.2
0.4
2.3
0.8
6.2
0.02
0.001
3.3
0.007
25
- 8.2
0.009
0.03
3.6
2.3
0.7
0.01
0.002
57
14'
8.1
19'
3'
82'
d 0.01 d
d 0.1
71
0.3
20
5
2
4
23
8
62
0.2
* 0.01
33
" 0.07
250
. 82
"•' 0.09'
0.3
36
23
7
* 0.1
* 0.02
570
1401
81 '
1901
30'
U201
" Screening Levels based on human health criteria only.
b Surface soil SSLs represent the lower of
c DAF - Dilution and attenuation
factor.
ingestion and inhalation values.
d Calculated values correspond to a cancer risk level of 1 in
8 Level is at or below Contract Laboratory
Program required
1 ,000,000.
quantrtation limit fof Regular Analytical
Services (RAS).
' Calculated values correspond to a noncancer hazard quotient of 1 .
9 Soil saturation concentration (Cnt).
h No toxicrty criteria available for that route of exposure.
1 A preliminary remediation goal
with PCB Contamination (U.S.
' SSLs for pH of 6.8.
of 1 ppm
has been set lor PCBs oased on
EPA, 1990) and on Agency
•wide efforts to
Guidance on Remedial Actions
for Superfund Sites
manage PCB contamination.
However. SSLs can serve as PRGs in the following cases:
• Where site conditions mimic the model assumptions
underlying the SSLs (i.e.. all pathways of concern at a
given site match those accounted for in the SSLs), or
• Where the site manager or owner decides not to incur costs
of additional site-specific study to arrive at less
conservative but still protective levels.
The primary condition for use of the SSLs is that exposure
pathways of concern and site conditions must match those
taken into account by the levels. Thus, at all sites it will be
necessary to develop a simple conceptual site model to identify
likely source areas, exposure pathways, and potential receptors
to assist in determining the extent to which the SSLs can serve
as PRGs. In addition to developing a conceptual site model.
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DRAFT - DO NOT CITE OR QUOTE - September 29, 1993
the following questions should always be considered by the
decisionmaker before applying the SSLs:
• Are there potential ecological concerns?
Is there potential for land use other than residential?
• Are there other likely human exposure pathways that
were not considered in deve.*vment of the SSLs (e.g.. local
fish consumption: raising of beef, dairy, or other livestock)?
• Are there unusual site conditions (e.g.. unusually large
area of contamination, unusually high fugitive dust levels)?
If any of these four conditions exist, then SSLs cannot be used
to screen out sites or portions of sites from further evaluation.
In addition, SSLs should not be viewed independently of either
natural or anthropogenic background concentrations. Where
natural background levels are higher than SSLs, generally the
SSLs will be of little value since it is inappropriate to conduct
further study or action to address contaminants below
background. Similarly, when anthropogenic background levels
exceed the SSLs, EPA does not encourage additional study or
action without first attempting to coordinate such action with
the authority responsible for managing the more broadly
contaminated area. In either case, the collection of site-
specific data is highly recommended.
HOW TO USE SSLs
le 1 contains SSLs for 30 chemicals. The first column to
right of the chemical name presents values based on soil
ingestion. The second column presents the lower of two
values derived to protect for either inhalation of volatiles or
soil particulates. The third column simply presents the lowest
number of the first two columns and may be used as the SSL
for surface soils under most residential circumstances. For
sites, where groundwater is a pathway of concern, SSL values
for the migration to the groundwater pathway apply. Three
different SSLs address migration of contaminants to ground-
water, the selection of an appropriate SSL -for this pathway
depends on site-specific conditions as discussed below. The
first column of groundwater values reflects the levels
calculated by the partitioning equation with no correction factor
added for dilution and attenuation in the subsurface
(unadjusted). The next two columns reflect the levels adjusted
by factors of 10 and 100. respectively (10 and 100 DAF), to
account for such dilution and attenuation.
As mentioned above, the first step in applying the SSL
guidance is to develop a simple conceptual model of the site
based on available site sampling data, historical records, aerial
photographs, and site hydrogeologic information. This model
will establish a hypothesis about the possible contaminant
sources, their fate and transport, potential exposure pathways.
d human or environmental receptors. If the conceptual
odel indicates that potential exposure pathways and receptors
are fully accounted for in the SSL methodology, the SSLs may
be directly applied to the site. However, if the model indicates
that the site is either very large or complex or that there are
exposure pathways NOT accounted for in the SSL
methodology, SSLs will not be suitable to fully evaluate the
site. They can be used, however, in the site evaluation since
SSLs have been derived on a pathway-specific basis, and, thus,
it will only be necessary to evaluate those exposuc? •vuhways
that are not already considered in the SSL methodology.
The second step involves collecting a representative sample set
for each exposure area. (See Measuring Soil Levels for more
detailed guidance on sample numbers and locations.) An
exposure area is defined as that geographic area in which an
individual may be exposed to contamination regularly. It may
involve the entire site, portions of a site, or a simple residential
loL To maximize efficiency, data collection should be
coordinated with other early sampling efforts that may be
undertaken to gain a better understanding of basic site
hydrogeology, ecological threats, or the potential for
application of various treatment technologies. For example,
the decision may be made early on to collect data for site-
specific modeling purposes at a particular site; in this case, the
site manager should work to limit total trips to the site and
minimize the number of samples collected and their locations.
The third step is to compare site-specific-data-with the SSLs
in Table 1. .At this point, it is reasonable to revisit the original
conceptual site model with the actual site data in hand to
reconfirm their accuracy. Generally, this comparison will
result in one of three outcomes:
1. Site-measured values indicate that an area falls well below
any SSL in the table. These areas of the site can be
eliminated from further evaluation.
2. Site-measured data indicate that one or more SSLs have
clearly been exceeded by a wide margin. In this case, the
SSLs have helped to identify contaminants and exposure
pathways of concern on which to focus further analysis or
data gathering efforts.
3. A site-measured value exceeds one pathway-specific value
but not the 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 from
that pathway at the site. When an exceedence is marginally
significant, a closer look at site-specific conditions and
exposures may result in the area being eliminated from
further study. If this is the case for the groundwater
pathway, a manager may choose to collect data specified in
the next higher tier(s).
For an NPL site at which SSLs are exceeded, a quick analysis
can determine whether the cumulative risks posed by the site
exceed the 10"4 risk level for carcinogens (or hazard index [HT]
of 1 for noncarcinogens), which generally is the trigger for
remedial action under Superfund. Where the basis for
response action exists, and exposure pathways of concern are
addressed by the SSLs. the SSLs become PRGs as defined in
the Human Health Evaluation Manual. Part B (U.S. EPA.
1991).
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DRAFT - DO NOT CITE OR QUOTE - September 29,1993
In accordance with the National Contingency Plan (NCP), the
decisionmaker will need to consider a variety of factors in
determining wliether any modification of the SSLs (PRGs) is
appropriate in setting final cleanup levels (NCP Section
.430(e)(2Xi)(A)). Ultimately, final cleanup levels are set
gh the evaluation of the NCP's nine criteria, including
cost, long-term effectiveness, and implementability. If
groundwater is the driving path ..ay, even at this final stage,
the option exists to consider other SSL tiers in identifying final
cleanup levels.
TECHNICAL BACKGROUND
The models and assumptions used to develop the SSLs
construct scenarios representative of a "reasonable maximum
exposure" (RME) in the residential setting. U.S. EPA (1989b)
outlined the Superfund program's approach to calculating an
RME. Since that time, the EPA (U.S. EPA. 1991) has coined
a new term that corresponds to the definition of RME: "high-,
end individual exposure." The Superfund program's method
to estimate the high-end (outlined in U.S. EPA. 1989b) is to
combine an arithmetic average value for site concentration with
high-end values for intake and duration. The estimate of high-
end exposure is then compared to chemical-specific Agency
toxicity criteria found in the Integrated Risk Information
System (IRIS) and Health Effects Assessment Summary Tables
(HEAST). The method used to set SSLs combines high-end
default values for the intake and duration parameters with
Agency toxicity criteria to back-calculate to a screening level
soil. Therefore, attainment of SSLs should be measured
on an arithmetic average.
Although the generic assumptions are not considered overly
conservative. EPA recognizes that site-specific conditions may
differ significantly from the generic assumptions used in the
models. Therefore, for the groundwater pathway the
subsequent tiers of the SSLs allow for the substitution of some
of the generic fate and transport assumptions with site-specific
data to derive alternative "screening levels" that are more site-
specific. Bear in mind, however, that 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 using
site-specific data, although less conservative, must still be
protective of "high-end" individual exposures.
The following sections present the equations and generic
assumptions used to calculate the Screening Levels for each
pathway evaluated.
Direct Ingestion
Agency toxicity criteria for noncarcinogens establish a level of
"daily" exposure that is not expected to cause deleterious
effects over a lifetime of exposure (i.e., 70 years). Depending
the contaminant, however, exceeding the RID (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 want to protect for that shorter
period of high exposure. Because a number of studies have
shown that inadvertent ingestion of soil is common among.
children age 6 and younger (Calabrese et aJ., 1989; Davis et
al., 1990; Van Wijnen et al., 1990). OERR set SSLs at
concentrations that are protective of this increased exposure
during childhood by ensuring that the chronic Reference Dose
(or RfC) 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 contaminant, the site manager should
consider the potential for acute health effects as we'l.
Equation 1: Screening Level Equation for
Ingestion of Noncarclnogenic
Contaminants In Residential Sou
«~^ , _ ln,*flf_ THO x BW x AT x 366 *Vr
.. •". 1/R'08 x ID"6 kg/mg x EF « ED x IR
Parameter/Definition (units)
THQAarget hazard quotient (unitless)
Rf D0 /oral reference dose (mg/kg-d)
BW/body weight (kg) '"'..'.
AT/averaging time (yr)
EF/exposure frequency _(d/yr) .
ED/exposure duration (yr)
IR/soil ingestion rate (mg/d)8
•*^* i
Dttisuii
1
Chemical -specific
IS
6*
350
6
200
* For noncarcinogans, Averaging, Time » equal to Expocur*
Duration.
For carcinogens, both the magnitude and duration of exposure
are important. Duration is critical because the tnxicity criteria
are 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 pruective of
exposures to carcinogens in the residential setting. OERR
focuses on exposures to individuals who may live in the same
residence for a "high-end" period, o/ time (i.e.. 30 years). As
mentioned previously, exposure to soil is higher during
childhood and decreases with age. Thus, Fquahon 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 (1991).
Inhalation of Volatiles and Fugitive Dusts
Agency toxicity criteria indicate "".: risks from eiposure to
some chemicals via inhalation far outweigh the risks via
ingestion; therefore, the SSLs have been designed to *fcfresi
this pathway. The models and assumptions used to calculate
SSLs for inhalation of volatiles and fugitive duos are ufxlaics
of the equations presented in U.S. EPA's HHEM Pm B
guidance (U.S. EPA, 1991) and are presented in Eg«uix«u )
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DRAFT - DO NOT CITE OR QUOTE • September 29, 1993
Equation 2: Screening Level Equation for
Ingestion of Carcinogenic
^ Contaminants (ii Residential Soil
r Screening Level _ TR x AT x 365 dyr
iroyKfl) SF0 x 10a kfl/mg x EF x IF^^
Parameter/Definition (units)
TRAarget cancer risk (unitless)
SF0 /oral slope factor (mgAg-d)'1
AT/averaging time (yr)
EF/exposure frequency (d/yr)
I F.OJV^ j /age-adjusted soil ingestion
factor (mg-yr/Vg-d)
Default
10*
Chemical-specific
70
350
114
Equation 3: Screening Level Equation for
Inhalation of Carcinogenic
Contaminants In Residential Soil
Screening Laval
(mg/Vg)
TR x AT x 365
URF x 1000 uo/mg x EF x ED x
r i 1 I
\W *PETJ
Parameter/Definition (unlta)
cancer risk (unitless)
F/inhalation unit risk factor
^tfttarget
^B^F/inha
I (ug/m
AT/averaging time (yr)
EF/exposure frequency (d)
EO/exposure duration (yr)
VF/soii-to-air volatilization factor
(m3/kg)
PEF/particulate emission factor
(m3/kg)
Default
Chemical-specific
70
350
30
Chemical-specific
4.51 x 10*
through 7. The volatilization factor (VF), soil saturation
limit (CM), and dispersion model have all been revised.
Another change from the Part B methodology is the separation
of the ingestion and inhalation pathways. Agency toxicity
criteria for oral exposures are presented as internal doses in
units of mg/kg-d; whereas, the inhalation criteria are presented
as concentrations in air (ug/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.
explained in Part B. the basic principle of the volatilization
is applicable only if the soil concentration is at or below
soil saturation. Thus, for those compounds for which the SSL
exceeds the soil saturation limit (C,J, the SSL is set at €„,.
Equation 4: Screening Level Equation for
Inhalation of Noncarclnogenlc
Contaminants In Residential Soil
Screening Level
THQ x AT x 365 d/yr
EF x ED x
[wrx [w * "PET J
Parameter/Definition (unrtt,
THQ/target hazard quotient (unitless)
AT/averaging time (yr)
EF/exposure frequency (d)
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
4.7 x 108
Equation 5: Derivation of (he Volatilization Factor
VF (m'/kg) - (/soil-air partition coefficient
(g-soil/cm3-air)
T/exposure interval (s)
D, /diffusivrty in air (cm2/s)
H/Henry's law constant (atm-m3/mol)
^ /soil-water partition coefficient
(cm3/g)
^/organic carbon partition coefficient
(cnvVg)
OC/organic carbon content of soil
(fraction)
Default
101.8
p,-ep
1-(P/PJ
10% or 0.1
1.5
2.65
X 41 (41 is a
conversion factor)
7.9x10*8
Chemical-specific
Chemical-specific
K^xOC
Chemical-specific
2% or 0.02
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DRAFT • DO NOT CITE OR QUOTE - September 29,1993
Equation 6: Derivation of the Soil Saturation Limn
(Kd x C. x p) • (C. x PJ » (C, x H' x PJ
Parameter/Definition (unit*)
Cu/soil saturation concentration
(mg/kg)
K^soil-water partition coefficient (L/kg)
KOC /organic carbon partition coefficient
OC/organic carbon content of soil
(fraction)
Cw /upper-limit of free moisture in soil
(mg/L-water)
6m /soil moisture content
(kg-water/kg-soil)
S/solubilrty in water (mg/L-water)
ji/soil bulk density (kg/L}~
Pw /water-filled soil porosity (unitJess)
H'/Henry's law constant Junftless)
H/Henry's law constant (atm-m3/mol)
P. /air-filled soil porosity (unitless)
3/soil moisture content
(L-water/kg soil)
P, /total soil porosity (unitless)
/true soil density or pa/tide density
Default
K^xOC
Chemical-specific
2% or 0.02
10% or 0.1
Chemical-specific
1.5
P - P
Hx 41. where 41 is
a conversion factor
Chemical-specific
P,-6p
10% or 0.1
1 - (P/P.)
2.65 ,
«
Equation 7: Derivation of the Paniculate Emission
Factor
PPF^/kg) . (Q/r.) * 3600S/H
0.036 x (1-G) x (0,,/U,)3 x F(x)
Parameter/Definition (units)
PEF/particulate emission factor
(m3/kg)
(Q/C)/inverse of the mean cone, at the
center of a 0.5-acre, square source
(g/m2-s per kg/m3)
0.036/respirable fraction (g/m2-h)
G/fraction of vegetative cover
(unitless)
Um /mean annual wind speed (m/s)
U, /equivalent threshold value of wind
speed at 10 m (m/s)
|p(x)/function dependent on UmAJ,
r derived using Cowherd (1985)
I (unitless)
Default
4.7x10°
101.8
0.036
0
4.5
12.8
0.04.97
The paniculate emission factor (PEF) derived by using the
default values in Equation 7 is approximately 0.2 ug/m3. This
represents an annual average emission rate estimate that is not
appropriate for estimating acute effects. Gvci the next few
months, OSWER will be investigating the impact of acute
exposure estimates on the SSLs.
Migration to Ground water
The methodology for addressing potential contamination of
groundwater from contaminants in soil reflects the complex
nature of contaminant fate and transport in the subsurface.
SSLs for migration to groundwater are based on a tiered
approach (see Figure 2). Tier 1 SSLs (presented in Table 1)
are based on the commonly used linear form of the Freundlich
partitioning equation that describes the ability of contaminants
to sorb to organic carbon in soil (Dragun, 1988). Equation 8
incorporates the linear Freundlich equation, along with an
adjustment to relate sorbed concentration in soil to the
analytically measured total soil concentration.
1
Conservatism
^-JteM-SccMoing-tavals _
• Partitioning equation
• OAF of 10, 100
Tier 2 Screening Levels
• Site-specific partitioning equation
• OAF of 10. 100
Tier 3 Evaluation
• SPLP. OAF of 10. 100
Tier 4 Evaluation
• Use of fate and transport model
in site-specific application
-
Increasing
'
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DRAFT - DO NOT CITE OR QUOTE - September 29, 1993
avi
*
MCLGs were the same as the MCLs. If nonzero MCLGs were
not available, MCLs were used, and, if MCLs were not
available, risk-specific concentrations were derived using
gency toxiciiy criteria, a target cancer risk of 10"6, and/or a
ncancer Hazard Quotient of 1. Default values obtained from
.S. EPA's ORD Laboratory in Athens, Georgia, are used for
soil porosity, fraction water content, and bulk density (U.S.
EPA, 1985). The soil organic carbon content value of 0.002
used for calculating the SSLs was selected from information on
the distribution of this parameter in U.S. soils (Carsel et al.,
198o). The value used for the organic carbon partitioning
coefficient (K^) is the geometric mean of measured values
reported in the literature (from a comprehensive literature
search [Truesdale, 1992]). For inorganic constituents, the EPA
MINTEQ2 chemical speciation model was used to calculate Kj
values, which were then used in Equation 8 in place of the K^.
x fw parameters. Kd values for metals are significantly
affected by a variety of soil conditions, the most significant of
which is pH. For this reason, metal Kj values for three pH
conditions were used to develop the SSLs: 4.9. 6.8. and 8.0.
Table 1 contains SSLs for inorganics corresponding to a pH of
6.8. Table 2 contains inorganic SSLs corresponding to pH
values of 4.9 and 8.0. If pH conditions at a site are not
known, the SSL corresponding to a pH of 6.8 should be used.
Table 2 also includes SSLs for pentachlorophenol (PCP),
whose partitioning behavior is also highly pH dependent.
***
The partitioning equation relates contaminant concentrations in
il adsorbed to soil organic carbon to soil leachate
ant concentrations in the unsaturated zone.
ontaminant migration through the unsaturated zone to the
water table generally reduces the soil leachate concentration by
attenuation processes such as adsorption and degradation.
Groundwater transport in the saturated zone further reduces
concentrations through attenuation and dilution. Generally, to
account for those mechanisms in the subsurface environment.
a correction factor should be applied to the partitioning
equation value. Use of the EPA's Composite Model for
leachate migration with Transformation Products (EPACMTP)
'(U.S.' EPA. 1993a) has identified a DAF of 10 as an
appropriate correction factor to be applied to the partitioning
value inmost cases. However, there are specific circumstances
under which use of a DAF is not recommended, such as in
areas of wry- shallow groundwater or karst topography.
Likewise, there are other circumstances in which a higher DAF
may be appropriate. Further discussion of these situations as
well as details on the EPACMTP model are included on the
next page of this fact sheet.
The assumptions factored into the Tier 1 levels are
conservative, rendering the SSLs fairly stringent If site
concentrations do not exceed the SSLs multiplied by the
appropriate DAF, then the pathway is excluded from further
investigation. However, if site concentrations do exceed the
Tier 1 SSLs, they may be used as PRGs (when appropriate),
or a Tier 2,3, or 4 investigation may be conducted. Each tier
requires more site-specific information but may lead to a less
stringent "screening" concentration.
The Tier 2 levels represent a minimal increase in site-
specificity and perhaps less conservative Screening Levels.
The partitioning equation •used in the Tier 1 calculation
(Equation 8) remains as the base for the Tier 2 levels along -
with the same DAF (either 1, 10, or 100). However, site-
measured values of organic carbon, soil porosity, fraction water
content, and soil bulk density are substituted into the equation
to calculate Screening Levels more tailored to site
characteristics. If site concentrations do not exceed the Tier 2
SSLs, then the pathway is excluded from further investigation
or concern. The rationale behind this decision is that, because
Tier 2 incorporates site-specific information, the levels are
more representative of actual site conditions than Tier 1. If
site concentrations exceed the Tier 2 SSLs, the user has the
option of conducting a Tier 3 or 4 investigation, realizing the
increase in site-specificity and cost associated with collecting
additional site data.
The Tier 3 investigation involves conducting a specific leach
test, the Synthetic Precipitation Leaching Procedure (SPLP)
(U.S. EPA, 1992c). If the leach test results divided by the
Table 2. Proposed Groundwater Pathway SSLs for Inorganics and Pentachlorophenol,
as a Function of pH"
Proposed
Unadjusted
Chemical pH 4.9
Arsenic
Cadmium
Chromium (VI)
Mercury
Nickel
Pentachlorophenol
1.2
0.006
3.1
0.0002
0.32
0.017
8.0
1.6
10.0
1.4
0.42
15.7
0.000^
groundwater pathway SSLs (mg/kg)
With
4.9
12.5
0.08
31.4
0.002
3.2
0.17
"Screening Levels based on human health criteria only.
bDAF . Dilution :attenuation factor.
°Level at or below Contract Laboratory Program required quantnaton limit
10 OAF"
8.0
15.7
100
13.6
4.2
157
0.009C
for Regular Analytical
With 100
4.9
125
0.81
314
0.02
31.7
1.7
Services (RAS)
DAF*
80
157
1.001
136
422
1.573
0 09
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DRAFT - DO NOT CfTE OR QUOTE - Saptambw 29,1993
DAF of 10 exceed the acceptable groundwater limit (e.g.,
nonzero MCLG, MCL, 10"6 risk-based values), then further
investigation would be warranted. The SPLP may not be
applicable to all contaminated soils (e.g., oily types of waste
not yield suitable results). Therefore the user is advised to
discretion when applying the SPLP. Additional guidance
on the use and limitations of the SPLP will be provided in the
final guidance. _ •, " ••
Tier 4 represents the highest level of site-specificity in
evaluating the migration to groundwater pathway. In this
investigation, site-specific data are collected and used in a fate
and transport model to confirm the threat to groundwater and
further determine site-specific cleanup goals as would typically
be done for the remedial investigation/feasibility study (RI/FS).
A DAF is not used in tnisKtier. because.Jhe model would
account for fate and transport mechanisms in the subsurface.
The advantage of this approach is that it accounts for site
hydrogeoJogic.; climate-logic, 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 Tier .4 investigation.
An evaluation of 10 fate and transport models for potential use
in the Tier 4 evaluation will be included in the technical
background document for this fact sheet scheduled to be issued
by OERR by January of 1994.. .
The tiered framework for migration to groundwater represents
J^ sliding scale of increasing site-specificity and. decreasing
^ronservatism. The assumptions factored into the Tier 1 SSLs
are conservative and therefore result in fairly stringent levels
that may not be appropriate in all situations. However, the
framework allows the user the flexibility to move away from
this conservative level by incorporating increasing levels of site
empirical data. In this way, site managers or owners of small.
relatively uncomplicated sites may benefit from the Tier 1
levels by bypassing the additional costs associated with
collecting additional data to conduct further investigations.
However, it is likely to be in the interest of site, managers or
owners of large and complex sites to conduct* a" more sue-
specific investigation to develop remediation- goals that are
more tailored to site-specific conditions.
DETERMINING THE DILUTION/
ATTENUATION FACTOR
For wastes disposed of on land, the leaching of contaminants
into the subsurface and subsequent migration into and througti
groundwater typically constitute a very significant pathway for
human and environmental exposure. As contaminants move
through the soil and groundwater. they are subjected to a
number of physical, chemical, and biological processes thai
affect the eventual contaminant concentration level at receptor
lints. These processes include, but are not limited to.
ittenuation due to sorption of contaminants onto soil and
aquifer grains, chemical transformation (e.g., hydrolysis, redo*
reactions, precipitation), biological degradation, and dilution
due to mixing of the leachate from thr disposal unit with
ambient groundwater. The contaminant concentration arriving
at a receptor point is therefore generally lower than the original
contaminant concentration in the leachate leaving the site.
The reduction in concoitration can be expressed succinctly by
the DAF, defined as the ratio of original leachate concentration
to the receptor point concentration. The lowest possible value
of DAF is therefore 1, corresponding to the situation where
there is no dilution or attenuation of a contaminant at all; i.e.,
the concentration at the receptor point is the same as that in
the leachate as it leaves the waste site. High DAF values on
the other hand correspond to a high degree of dilution and
attenuation of the contaminant from the leachate to the receptor
point
The Agency has developed subsurface fate and transport
models to assess the impact on groundwater quality due to
migration of contaminants from wastes on land. Specifically.
these models predict the DAF for a potential site of a domestic
drinking water receptor well, which may withdraw water from
the saturated zone under, or downgradient of, a contaminated
area. The model used to develop DAFs for this guidance is
the-EPACMTS,-which: consists of4kree main'modules:
1. An unsaturated zone:.flow and contaminant fate and
transport module
2. A saturated zone groundwater flow and contaminant fate
and transport module
3. A Monte Carlo driver, module, which generates model
parameters from nationwide probability distributions.
The unsaturated and saturated zone modules simulate the
migration of contaminants from the base of a land disposal unit
to a downgradient receptor well. The Agency has extensively
verified both the unsaturated and saturated zone modules
against other available analytical and numerical models to
ensure accuracy and efficiency. Both the unsaturated zone and
the saturated zone modules of the EPACMTP. used for the
calculation of DAFs for the SSLs, have been reviewed by the
EPA Science Advisory Board and found to be suitable for
generic applications such as the derivation of nationwide
DAFs.
Modeling Procedure
For nationwide Monte Carlo model applications, the input to
the model is in the form of probability distributions of each of
the model input parameters. The output from the model
consists of the probability distribution of DAF values.
representing the likelihood that any specific DAF value is
exceeded.
For each model input parameter, a probability distribution is
provided, describing the nationwide likelihood that the
parameter has a certain value. The parameters are divided into
.our main groups:
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DRAFT • DO NOT CITE OR QUOTE • September 29, 1993
1. Source-specific parameters, e.g., area of the waste unit.
infiltration rate
2. Chemical-specific parameters, e.g., hydrolysis constants.
f organic carbon partition coefficient
Unsaturated zone-specific parameters, e.g.. depth to water
table.^eiL hydraulic conductivity
4. Saturated zone-specific parameters, e.g., saturated zone
thickness, ambient groundwater flow rate, location of
nearest receptor well.
During the Monte Carlo simulation, values for each model
parameter are randomly drawn from their respective probability
distributions. In the calculation of the DAFs for the SSLs. site
data from over 1,300 sites were used to define parameter
ranges and distributions. Each combination of randomly drawn
parameter values represents one out of a practically infinite
universe of possible waste sites. The fate and transport
modules are executed for the specific set of model parameters,
yielding a corresponding DAF value. This procedure is
repeated, typically on the order of several thousand times, to
ensure that the-entire universe of possible parameter
combinations (waste sites) is adequately sampled. At the
conclusion of the analysis, a cumulative frequency distribution
of DAF values is constructed and plotted.
The Agency performed a number of sensitivity analyses
consisting of fixing one parameter at a time to determine the
^krameter(s) that have the greatest impact on DAFs. The
^Rults of the sensitivity analyses indicate that the climate (net
precipitation), soil types, and size of the contaminated area
have the greatest effect on the DAFs. The Agency feels that
the size of the contaminated area lends itself most readily to
practical application of the SSLs.
To calculate the DAF for the SSLs. the drinking water well
was located 25 feet downgradient of the edge of the
contaminated area, and the location of the intake point
(receptor well screen) was assumed to vary within the
boundaries of 15 and 300 feet within the aquifer (these values
are based on empirical data reflecting a national sample
distribution of depth of residential drinking water wells). The
sensitivity analyses indicated that the placement of the well 25
feet downgradient of the contaminated area is more
conservative than allowing the well to be located directly
beneath the contaminated area. The location of the intake
point allows for mixing within the aquifer. OSWER believes
that this is a reasonable assumption because there will always
be some dilution attributed to the pumping of water for
residential use from an aquifer. The placement of the well was
assumed to vary uniformly within the boundary of the plume.
Figure 3 shows a schematic of the compliance point location.
From these analyses, the largest allowable areas corresponding
DAFs of 10 and 100 at the 90th percentile protection level
approximately 10 and 1 acre, respectively. Therefore, for
sites of up to 10 acres, a DAF of 10 should be applied to the
unadjusted SSLs, while for sites at or below 1 acre, a DAF of
100 should be applied to the unadjusted SSLs. If a 95th
percentile protecliveness level is used, a DAF of 10 is
PLAN VIEW
Parameters:
• X (distance from source to well) - 25 ft
• Y(ttansverseweUloc«tkCT) a MoRtsCa.-ie within -
width of plume
• Z (well intake point below water table) - Monte
Carlo, range 15 -» 300 ft
• Rainfall - Monte Carte
• Soil type • Monte Carte
• Depth to aquifer - Monte Carte
• Assumes infinite source term
Figure 3. Soil to groundwater pathway-
calculating tiie DAF.
protective for areas under 1/2 acre and a DAF of 100 is
protective for areas less than 1/10 acre. OSWER is
considering whether the 90th or 95th percentile protectiveness
level should be used in the final guidance. When sites are
located in areas of unusually shallow water table, within 5 feet
of surface, the unadjusted SSLs should be used In this
scenario, contamination is located in or directly, above the
saturated zone; therefore, any dilution and attenuation
processes within the unsaturated zone would be negligible.
MEASURING SOIL LEVELS
As described in U.S. EPA (1992b). exposure to site
contaminants over a long (chronic) period of time is best
represented by an arithmetic average concentration; therefore,
attainment of the SSLs should be based on the arithmetic mean
concentration as well. The issue then becomes the number of
samples required to adequately estimate the mean and the area
over which the sample concentrations should be averaged.
Studies by EPA's Exposure Assessment Group in ORD
indicate that 20 to 30 samples per exposure area are needed to
calculate an upper confidence limit (UCL,S) on the ariihmetic
mean that is very close to the true mean (U.S. EPA, 1992b).
i.e.. to adequately estimate the true mean without underestimat-
ing it. An appropriate exposure/averaging area can vary •"
10
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DRAFT • DO NOT CfTE OR QUOTE - September 29,1993
size, depending on site-specific conditions. At some sites, this
may be the entire site; at others, this may be only a portion .of
the site. For the purposes of this guidance, the Agency
^ueves that the size of a typical residential lot (1/4 acre) is an
: averaging area for the most conservative case (i.e..
sidential land use). For large sites that could be divided into
many areas equivalent to the size of a residential lot the
number of samples needed to characterize the site becomes
quite high. This, coupled with the costs of analytical services
for each sample, could make the sampling costs onerous.
Therefore, OERR recommends following guidance for
measuring soil contaminant levels at NPL sites.
Sample Pattern
A grid pattern such as a triangular or square/rectangular grid
is recommended to establish sample locations for each
exposure area (U.S. EPA, 1987). Biased sampling must also
be used in areas of suspected contamination or stained soils
and must be evaluated separately from the samples obtained by
systematic sampling.
Number of Samples
As mentioned, it is necessary to balance the need to achieve
statistical confidence in determining a meaningful arithmetic
mean concentration of contaminants in each exposure area with
the cost of obtaining the 20 to 30 samples recommended by
|RD. Compositing of discrete samples is an option since EPA
interested in determining the arithmetic mean of the
contaminant concentration(s). Twenty discrete samples can be
composited down to four or five composite samples, while
maintaining confidence that the area average is not grossly
underestimated. Compositing may mask contaminant levels
that are slightly higher than the SSL, but areas of high
contamination will still be detected. Compositing is both a
reasonable approach and an efficient use of resources, since
Superfund is interested in average exposure over time.
However, none of the composite samples should exceed the
prescribed SSL for any.contaminant ~ For volatile organic
compounds (VOCs). compositing is not appropriate (U.S. EPA.
1989a. 1992a). Therefore, OERR advocates that 10 discrete
samples should be taken per exposure area for VOCs. and no
sample can exceed the Screening Level(s). Both the discrete
VOC samples and the composites must be analyzed by
Contract Laboratory Program (CLP) (or equivalent) methods.
(NOTE: Seven of the 30 contaminant SSLs for the
groundwater migration pathway at a DAF of 10 are below CLP
RAS or CLP-equivalent detection limits. For these
contaminants, special analytical services should be requested
for recalibration of the instruments. For example, to measure
low levels of VOCs. the gas chromatograph/mass spectrometer
(GC/MS) can be recalibrated to detect at 1, 2. 5. 10, and 25
ppb.
Use of Field Methods
Where available and appropriate, field methods (soil gas
surveys, immunoassays. X-ray fluorescence) can be used.
Again, for compounds other than VOCs. compositing samples
is acceptable as long as it is consistent with the field
methodology. If any sample concentration exceeds an SSL,
fi-iher site study is required. In addition. 10% to 20% of field
samples must be sent to a CLP (or equivalent) laboratory for
confirmatory analysis (U.S. EPA. 1992a). Please note that
field methods must be capable of achieving appropriate
detection limits for most groundwater "SLs.
Depth
When measuring soil levels at the surface for the inhalation
and ingestion pathways, samples should be taken at a depth of
6 inches. Additional sampling beyond 6 inches may be
appropriate, depending on the contaminant's mobility, to
'account for geographic differences in construction practices
where soil disturbances are reasonably expected. For example,
in the Northeast, the ground may be excavated to IS feet
before laying the foundation and constructing the basement of
a home. Excavated overburden is commonly used as fill
material around the property so that contaminants that were at
depth are now near the surface. Thus, it is important to be
cognizant of construction practices in the area.
For the groundwater pathway, the entire soil column, from the
surface to the top of the aquifer, should be sampled For the
evaluation of vertical stratification, samples should not be
averaged over depth (i.e., the soil core should not be
composited over depth), but rather individual samples should
be evaluated at appropriate depth intervals. One soil core per
exposure area may be sufficient However, where dense
nonaqueous phase liquids (DNAPLs) are suspected, soil cores
may be taken more frequently.
Sampling for Background Contamination
For metals, background sampling is necessary to '•« certain that
OSWER is not defining levels below background as of
regulatory concern. If a statistical comparison of background
concentration and site samples indicates that background
metals concentrations are significantly above the SSLs, use of
the SSLs will be of limited value, as discussed earlier.
Additional Sampling Needed for
Groundwater Tier 2
To use groundwater Tier 2, site-specific soil characteristics
must be determined by sampling. Parameters to measure
include bulk density, porosity, organic carbon content and
water content
Geostatistics
For large areas where the data are not widely scattered,
geostatistical approaches, such as krigirig. can be used to
estimate sample concentration trends across the exposure area
(U.S. EPA, 1989a).
11
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DRAFT • DO NOT CITE OR QUOTE • September 29,1903
WHERE TO GO FOR FURTHER
INFORMATION
*:
additional copies of this Fact Sheet, call the National
hnical Information Service (NTIS) at (703) 487-4650.
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.
Carsel. R£., R.S. Parrish, R.L. Jones, JX. Hansen, and Ri.
Lamb. 1988. Characterizing the Uncertainty of Pesticide
Leaching in Agricultural Soils. /. ofContam. Hyd. 2:111-
124.
Cowherd, C., G. Muleski, P. Engelhart, and D. Gfllete. 1985.
Rapid Assessment of Exposure to Particulate Emissions
from'Surface Contamination. Prepared for EPA Office of
Health and Environmental Assessment EPA/600/8-85/002.
Davis, S., P. Waller, R. Buschom, 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.
HMCRI. Silver Spring, MD.
Truesdale. R.S. 1992. Preliminary Soil Action Levels for
Superfund Sites. Draft Interim Report Prepared for Office
of Emergency and Remedial Response. U.S. EPA.
Research Triangle Institute, Research 'triangle Park. NC.
U.S. EPA. 1985. Water Quality Assessment: A Screening
Procedure for Toxic and Conventional Pollutants
WPA/600/6-85/002b.
U.S. EPA. 1987. Data Quality Objectives for Remedial
Response Activities: Development Process. EPA/540/G-
87/003.
U.S. EPA. 1989a. Methods for Evaluating the Attainment of
Soil Cleanup Standards. Volume 1. EPA 230/02-89-042.
U.S. EPA. 1989b. Risk Assessment Guidance for Superfund
Human Health Evaluation Manual: Pan A.
U.S. EPA. 1990. Guidance on Remedial Actions for
Superfund Sites with PCB Contamination. EPA 540G-
90 007. Office of Emergency and Remedial Response,
Washington, DC. August.
U.S. EPA. 1991. Risk Assessment Guidance for Superfund,
Human Health Evaluation Manual: Part B.
U.S. EPA. 1992i Guidance for Data Usability in Risk
Assessment (Pan A).
U.S. EPA. 1992b. Supplemental Guidance to RAGS:
Calculating Ihe Concentration Term.
U.S. EPA. 1992c. Synthetic Precipitation Leaching Procedure
(SPLP), Method 1312. In: Test Methods for Evaluating
Solid Waste. Physical/Chemical Methods. EPA Publication
SW-846. Third Edition (September 1986). as amended by
Update I (July).
U.S. EPA. 1993a. Background Document for EPA's
Composite Model for Leachate Migration with
Transformation Products, EPACMTP. Office of Solid
Waste. July.
U.S. EPA. 1993b. 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.
Van Wijnen. J.H., P. Clausing, and B. Bmnekreef. 1990.
Estimated Soil Ingestion by Children. Environmental
Research, 51:147-162.
NOTICE: The policies sat out in this document are intono««) u>«iy as guidance; they are not final U.S. Environmental Protection
Agency (EPA) actions. These policies are not intended, no nn they be relied upon, to create any rights enforceable by any party
in litigation with the United States. EPA officials may dec** » tottow the guidance provided in this document, or to act at variance
with the guidance, based on an analysis of site-specific cvox*-nances. The Agency also reserves the right to change this
guidance at any time without public notice.
This guidance is based on policies in the Final Rule of tne s«ionai OH and Hazardous Substances Pollution Contingency Plan
(NCP), which was published on March 8, 1990 (55 FeoVa/ ««*?J'«K 8666). The NCP should be considered the authoritative
source.
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