United States
Environmental Protection
Agency
Office of Solid Waste and
Emergency Response
Washington, DC 20460
Publication 9355.4-23
July 1996
Superfund
xvEPA Soil Screening Guidance:
User's Guide
Second Edition
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Soil Screening Guidance
User's Guide
Second Edition
Office of Emergency and Remedial Response
U.S. Environmental Protection Agency
Washington, DC 20460
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ACKNOWLEDGMENTS
The development of this guidance was a team effort led by the staff of the Office of Emergency and Remedial Response.
David Cooper served as Team Leader for the overall effort. Marlene Berg coordinated the series of Outreach meetings with
interested parties outside the Agency. Sherri Clark, Janine Dinan and Loren Henning were the principal authors. Paul White
of EPA's Office of Research and Development provided tremendous support in the development of statistical approaches to
site sampling.
Exceptional technical assistance was provided by several contractors. Robert Truesdale of Research Triangle Institute (RTI)
led their team effort in the development of the Technical Background Document under EPA Contract 68-W1-0021. Craig
Mann of Environmental Quality Management, Inc. (EQ) provided expert support in modeling inhalation exposures under
EPA Contract 68-D3-0035. Dr. Smita Siddhanti of Booz-Allen & Hamilton, Inc. provided technical support for the final
production of the User's Guide and Technical Background Document under EPA Contract 68-W1-0005.
In addition, the authors would like to thank all EPA, State, public and peer reviewers whose careful review and thoughtful
comments contributed to the quality of this document.
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DISCLAIMER
Notice: The Soil Screening Guidance is based on policies set out in the Preamble to 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).
This guidance document sets forth recommended approaches based on EPA's best thinking to date with respect to soil
screening. This document does not establish binding rules. Alternative approaches for screening may be found to be more
appropriate at specific sites (e.g., where site circumstances do not match the underlying assumptions, conditions and models
of the guidance). The decision whether to use an alternative approach and a description of any such approach should be
placed in the Administrative Record for the site. Accordingly, if comments are received at individual sites questioning the
use of the approaches recommended in this guidance, the comments should be considered and an explanation provided for the
selected approach. The Soil Screening Guidance: Technical Background Document (TBD) may be helpful in responding to
such comments.
The policies set out in both the Soil Screening Guidance: User's Guide and the supporting TBD 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 relied upon, to create any rights enforceable by any
party in litigation with the United States government. 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.
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TABLE OF CONTENTS
1.0 INTRODUCTION 1
1.1 Purpose 1
1.2 Role of Soil Screening Levels 2
1.3 Scope of Soil Screening Guidance 3
2.0 SOIL SCREENING PROCESS 5
2.1 Step 1: Developing a Conceptual Site Model 5
2.1.1 Collect Existing Site Data 5
2.1.2 Organize and Analyze Existing Site Data 5
2.1.3 Construct a Preliminary Diagram of the CSM 5
2.1.4 Perform Site Reconnaissance 7
2.2 Step 2: Comparing CSM to SSL Scenario 7
2.2.1 Identify Pathways Present at the Site Addressed by Guidance 7
2.2.2 Identify Additional Pathways Present at the Site Not Addressed by Guidance 8
2.2.3 Compare Available Data to Background 8
2.3 Step 3: Defining Data Collection Needs for Soils 9
2.3.1 Stratify the Site Based on Existing Data 9
2.3.2 Develop Sampling and Analysis Plan for Surface Soil 12
2.3.3 Develop Sampling and Analysis Plan for Subsurface Soils 14
2.3.4 Develop Sampling and Analysis Plan to Determine Soil Characteristics 17
2.3.5 Determine Analytical Methods and Establish QA/QC Protocols 18
2.4 Step 4: Sampling and Analyzing Site Soils & DQA 18
2.4.1 Delineate Area and Depth of Source 20
2.4.2 Perform DQA Using Sample Results 20
2.4.3 Revise the CSM 20
2.5 Step 5: Calculating Sitespecific SSLs 20
2.5.1 SSL EquationsSurface Soils 21
2.5.2 SSL EquationsSubsurface Soils 23
2.5.3 Address Exposure to Multiple Chemicals 32
2.6 Step 6: Comparing Site Soil Contaminant Concentrations to Calculated SSLs 33
2.7 Step 7: Addressing Areas Identified for Further Study 36
REFERENCES 37
ATTACHMENTS
A. Conceptual Site Model Summary A-l
B. Soil Screening DQOs for Surface Soils and Subsurface Soils B-l
C. Chemical Properties for SSL Development C-l
D. Regulatory and Human Health Benchmarks Used for SSL Development D-l
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LIST OF EXHIBITS
Conceptual Risk Management Spectrum for Contaminated Soil
Exposure Pathways Addressed by SSLs
Key Attributes of the User's Guide
Soil Screening Process
Data Quality Objectives Process
Defining Study Boundaries
Designing Sampling and Analysis Plan for Surface Soils
Designing Sampling and Analysis Plan for Subsurface Soils
U.S. Department of Agriculture Soil Texture Classification
Site-Specific Parameters for Calculating Subsurface SSLs
Q/C Values by Source Area, City, and Climatic Zone
Simplifying Assumptions for SSL Migration to Ground Water Pathway
SSL Chemical with Non-carcinogen Toxic Effects on Specific Target Organ/Systems
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LIST OF ACRONYMS
ARAR
Applicable or Relevant and Appropriate Requirement
ASTM
American Society for Testing and Materials
CERCLA
Comprehensive Environmental Response, Compensation and Liability Act
CLP
Contract Laboratory Program
CSM
Conceptual Site Model
CV
Coefficient of Variation
DAF
Dilution Attenuation Factor
DNAPL
Dense Nonaqueous Phase Liquid
DQA
Data Quality Assessment
DQO
Data Quality Objective
EA
Exposure Area
EPA
Environmental Protection Agency
HBL
Health Based Limit
HEAST
Health Effects Assessment Summary Table
HELP
Hydrological Evaluation of Landfill Performance
HHEM
Human Health Evaluation Manual
HQ
Hazard Quotient
IRIS
Integrated Risk Information System
ISC2
Industrial Source Complex Model
MCL
Maximum Contaminant Level
MCLG
Maximum Contaminant Level Goal
NAPL
Nonaqueous Phase Liquid
NOAEL
No-Observed-Adverse-Effect Level
NPL
National Priorities List
NTIS
National Technical Information Service
OERR
Office of Emergency and Remedial Response
PA/SI
Preliminary Assessment/Site Inspection
PCB
Polychlorinated Biphenyl
PEF
Particulate Emission Factor
PRG
Preliminary Remediation Goal
Q/C
Site-Specific Dispersion Model
QA/QC
Quality Assurance/Quality Control
QL
Quantitation Limit
RAGS
Risk Assessment Guidance for Superfimd
RCRA
Resource Conservation and Recovery Act
RfC
Reference Concentration
RfD
Reference Dose
RI
Remedial Investigation
RI/FS
Remedial Investigation/Feasibility Study
RME
Reasonable Maximum Exposure
ROD
Record of Decision
SAB
Science Advisory Board
SAP
Sampling and Analysis Plan
SPLP
Synthetic Precipitation Leaching Procedure
SSL
Soil Screening Level
TBD
Technical Background Document
TCLP
Toxicity Characteristic Leaching Procedure
USDA
U.S. Department of Agriculture
VF
Volatilization Factor
VOC
Volatile Organic Compound
V
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1.0 INTRODUCTION
1.1 Purpose
The Soil Screening Guidance is a tool that the U.S.
Environmental Protection Agency (EPA) developed
to help standardize and accelerate the evaluation and
cleanup of contaminated soils at sites on the
National Priorities List (NPL) with future residential
land use.1 This guidance provides a methodology for
environmental science/engineering professionals to
calculate risk-based, site-specific, soil screening
levels (SSLs) for contaminants in soil that may be
used to identify areas needing further investigation
at NPL sites.
SSLs are not national cleanup standards. SSLs
alone do not trigger the need for response actions or
define "unacceptable" levels of contaminants in soil.
In this guidance, "screening" refers to the process of
identifying and defining areas, contaminants, and
conditions, at a particular site that do not require
further Federal attention. Generally, at sites where
contaminant concentrations fall below SSLs, no
further action or study is warranted under the
Comprehensive Environmental Response,
Compensation and Liability Act (CERCLA). (Some
States have developed screening numbers that are
more stringent than the generic SSLs presented here;
therefore, further study may be warranted under
State programs.) Generally, where contaminant
concentrations equal or exceed SSLs, further study
or investigation, but not necessarily cleanup, is
warranted.
SSLs are risk-based concentrations derived from
equations combining exposure information
assumptions with EPA toxicity data. This User's
Guide focuses on the application of a simple site-
specific approach by providing a step-by-step
methodology to calculate site-specific SSLs and is
part of a larger framework that includes both generic
and more detailed approaches to calculating
screening levels. The Technical Background
Document (TBD) (EPA, 1996), provides more
information about these other approaches. Generic
SSLs for the most common contaminants found at
NPL sites are included in the TBD. Generic SSLs are
calculated from the same equations presented in this
guidance, but are based on a number of default
assumptions chosen to be protective of human
health for most site conditions. Generic SSLs can be
used in place of site-specific screening levels;
however, in general, they are expected to be more
conservative than site-specific levels. The site
manager should weigh the cost of collecting the data
necessary to develop site-specific SSLs with the
potential for deriving a higher SSL that provides an
appropriate level of protection.
The framework presented in the TBD also includes
more detailed modeling approaches for developing
screening levels that take into account more
complex site conditions than the simple site-specific
methodology emphasized in this guidance. More
detailed approaches may be appropriate when site
conditions (e.g., a thick vadose zone) are different
from those assumed in the simple site-specific
methodology presented here. The technical details
supporting the methodology used in this guidance
are provided in the TBD.
SSLs developed in accordance with this guidance are
based on future residential land use assumptions and
related exposure scenarios. Using this guidance for
sites where residential land use assumptions do not
apply could result in overly conservative screening
levels; however, EPA recognizes that some parties
responsible for sites with non-residential land use
might still find benefit in using the SSLs as a tool to
conduct a conservative initial screening.
SSLs developed in accordance with this guidance
could also be used for Resource Conservation and
Recovery Act (RCRA) corrective action sites as
"action levels," since the RCRA corrective action
program currently views the role of action levels as
generally fulfilling the same purpose as soil
screening levels.2 In addition, States may use this
guidance in their voluntary cleanup programs, to the
extent they deem appropriate. When applying SSLs
to RCRA corrective action sites or for sites under
State voluntary cleanup programs, users of this
guidance should recognize, as stated above, that SSLs
are based on residential land use assumptions. Where
these assumptions do not apply, other approaches
1 Note that the Superfund program defines "soil" as having a particle
size under 2mm, while the RCRA program allows for particles under
9mm in size.
2 Further information on the role of action levels in the RCRA corrective
action program is available in an Advance Notice of Proposed
Rulemaking (signed April 1996).
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for determining the need for further study might be
more appropriate.
1.2 Role of Soil Screening Levels
In identifying and managing risks at sites, EPA
considers a spectrum of contaminant
concentrations. The level of concern associated
with those concentrations depends on the likelihood
of exposure to soil contamination at levels of
potential concern to human health or to ecological
receptors.
Exhibit 1 illustrates the spectrum of soil
contamination encountered at Superfund sites and
the conceptual range of risk management responses.
At one end are levels of contamination that clearly
warrant a response action; at the other end are
levels that are below regulatory concern. Screening
levels identify the lower bound of the
spectrumlevels below which EPA believes there is
no concern under CERCLA, provided conditions
associated with the SSLs are met. Appropriate
cleanup goals for a particular site may fall anywhere
within this range depending on site-specific
conditions.
No further study Site-specific Response
warranted under cleanup action clearly
CERCLA goal/level warranted
"Zero" Screening Response Very high
concentration level level concentration
Exhibit 1. Conceptual Risk Management
Spectrum for Contaminated Soil
EPA anticipates the use of SSLs as a tool to
facilitate prompt identification of contaminants and
exposure areas of concern during both remedial
actions and some removal actions under CERCLA.
However, the application of this or any screening
methodology is not mandatory at sites being
addressed under CERCLA or RCRA. The framework
leaves discretion to the site manager and technical
experts (e.g., risk assessors, hydrogeologists) to
determine whether a screening approach is
appropriate for the site and, if screening is to be
used, the proper method of implementation. If
comments are received at individual sites questioning
the use of the approaches recommended in this
guidance, the comments should be considered and an
explanation provided as part of the site's Record of
Decision (ROD). The decision to use a screening
approach should be made early in the process of
investigation at the site.
EPA developed the Soil Screening Guidance to be
consistent with and to enhance the current
Superfund investigation process and anticipates its
primary use during the early stages of a remedial
investigation (RI) at NPL sites. It does not replace
the Remedial Investigation/Feasibility Study (RI/FS)
or risk assessment, but use of screening levels can
focus the RI and risk assessment on aspects of the
site that are more likely to be a concern under
CERCLA. By screening out areas of sites, potential
chemicals of concern, or exposure pathways from
further investigation, site managers and technical
experts can limit the scope of the remedial
investigation or risk assessment. SSLs can save
resources by helping to determine which areas do
not require additional Federal attention early in the
process. Furthermore, data gathered during the soil
screening process can be used in later Superfund
phases, such as the baseline risk assessment,
feasibility study, treatability study, and remedial
design. This guidance may also be appropriate for
use by the removal program when demarcation of
soils above residential risk-based numbers coincides
with the purpose and scope of the removal action.
The process presented in this guidance to develop
and apply simple, site-specific soil screening levels is
likely to be most useful where it is difficult to
determine whether areas of soil are contaminated to
an extent that warrants further investigation or
response (e.g., whether areas of soil at an NPL site
require further investigation under CERCLA through
an RI/FS). As noted above, the screening levels
have been developed assuming residential land use.
Although some of the models and methods
presented in this guidance could be modified to
address exposures under other land uses, EPA has
not yet standardized assumptions for those other
uses.
Applying site-specific screening levels involves
developing a conceptual site model (CSM),
collecting a few easily obtained site-specific soil
parameters (such as the dry bulk density and percent
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moisture), and sampling to measure contaminant
levels in surface and subsurface soils. Often, much of
the information needed to develop the CSM can be
derived from previous site investigations [e.g., the
Preliminary Assessment/Site Inspection (PA/SI)]
and, if properly planned, SSL sampling can be
accomplished in one mobilization.
An important part of this guidance is a
recommended sampling approach that balances the
need for more data to reduce uncertainty with the
need to limit data collection costs. Where data are
limited such that use of the "maximum test" (Max
test) presented here is not appropriate, the guidance
provides direction on the use of other conservative
estimates of contaminant concentrations for
comparison with the SSLs.
This guidance provides the information needed to
calculate SSLs for 110 chemicals. Sufficient
information may not be available to develop soil
screening levels for additional chemicals. These
chemicals should not be screened out, but should be
addressed in the baseline risk assessment for the site.
The Risk Assessment Guidance for Superfund
(RAGS), Volume 1: Human Health Evaluation
Manual ( 111IEM), Part A, Interim Final. (U.S. EPA,
1989a) provides guidance on conducting baseline
risk assessments for NPL sites. In addition, the
baseline risk assessment should address the
chemicals, exposure pathways, and areas at the site
that are not screened out.
Although SSLs are "risk-based," they do not
eliminate the need to conduct a site-specific risk
assessment. SSLs are concentrations of
contaminants in soil that are designed to be
protective of exposures in a residential setting. A
site-specific risk assessment is an evaluation of the
risk posed by exposure to site contaminants in
various media. To calculate SSLs, the exposure
equations and pathway models are run in reverse to
backcalculate an "acceptable level" of a
contaminant in soil. For the ingestion, dermal, and
inhalation pathways, toxicity criteria are used to
define an acceptable level of contamination in soil,
based on a one-in-a-million (lO6) individual excess
cancer risk for carcinogens and a hazard quotient
(HQ) of 1 for non-carcinogens. SSLs are
backcalculated for migration to ground water
pathways using ground water concentration limits
[nonzero maximum contaminant level goals
(MCLGs), maximum contaminant levels (MCLs), or
health-based limits (HBLs) (lO6 cancer risk or a HQ
of 1) where MCLs are not available].
SSLs can be used as Preliminary Remediation Goals
(PRGs) provided appropriate conditions are met
(i.e., conditions found at a specific site are similar to
conditions assumed in developing the SSLs). The
concept of calculating risk-based contaminant levels
in soils for use as PRGs (or "draft" cleanup levels)
was introduced in the RAGS HHEM, Part B,
Development of Risk-Based Preliminary
Remediation Goals. (U.S. EPA, 1991c). The
models, equations, and assumptions presented
in the Soil Screening Guidance to address
inhalation exposures supersede those
described in RAGS HHEM, Part B, for
residential soils. In addition, this guidance
presents methodologies to address the
leaching of contaminants through soil to an
underlying potable aquifer. This pathway
should be addressed in the development of
PRGs.
PRGs may then be used as the basis for developing
final cleanup levels based on the nine-criteria
analysis described in the National Contingency Plan
[Section 300.430 (3)(2)(I)(A)]. The directive
entitled Role of the Baseline Risk Assessment in
Superfund Remedy Selection Decisions (U.S. EPA,
199Id) discusses the modification of PRGs to
generate cleanup levels. The SSLs should only be
used as cleanup levels when a site-specific nine-
criteria evaluation of the SSLs as PRGs for soils
indicates that a selected remedy achieving the SSLs
is protective, complies with Applicable or Relevant
and Appropriate Requirements (ARARs), and
appropriately balances the other criteria, including
cost.
1.3 Scope of Soil Screening
Guidance
In a residential setting, potential pathways of
exposure to contaminants in soil are as follows (see
Exhibit 2):
Direct ingestion
Inhalation of volatiles and fugitive dusts
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Ingestion of contaminated ground water caused by
migration of chemicals through soil to an
underlying potable aquifer
Dermal absorption
Ingestion of homegrown produce that has been
contaminated via plant uptake
Migration of volatiles into basements.
Direct Ingestion
of Ground Inhalation
Exhibit 2. Exposure Pathways Addressed
by SSLs.
The Soil Screening Guidance addresses each of these
pathways to the greatest extent practical. The first
three pathways -- direct ingestion, inhalation of
volatiles and fugitive dusts, and ingestion of potable
ground water are the most common routes of
human exposure to contaminants in the residential
setting. These pathways have generally accepted
methods, models, and assumptions that lend
themselves to a standardized approach. The
additional pathways of exposure to soil
contaminants, dermal absorption, plant uptake, and
migration of volatiles into basements, may also
contribute to the risk to human health from
exposure to specific contaminants in a residential
setting. This guidance addresses these pathways to a
limited extent based on available empirical data. (See
Step 5 and the TBD for further discussion).
The Soil Screening Guidance addresses the
human exposure pathways listed previously
and will be appropriate for most residential
settings. The presence of additional pathways
or unusual site conditions does not preclude
the use of SSLs in areas of the site that are
currently residential or likely to be
residential in the future. However, the risks
associated with additional pathways or
conditions (e.g., fish consumption, raising of
livestock, a heavy truck traffic on unpaved
roads) should be considered in the RI/FS to
determine whether SSLs are adequately
protective.
An ecological assessment should also be
performed as part of the RI/FS to evaluate
potential risks to ecological receptors.
The Soil Screening Guidance should not be
used for areas with radioactive contaminants.
Exhibit 3 provides key attributes of the Soil
Screening Guidance: User's Guide.
Exhibit 3: Key Attributes of the User's
Guide
Standardized equations are presented to
address human exposure pathways in a
residential setting consistent with
Superfund's concept of "Reasonable
Maximum Exposure" (RME).
Source size (area and depth) can be
considered on a site-specific basis using
mass-limit models.
Parameters are identified for which site-
specific information is needed to develop
SSLs.
Default values are provided to calculate
generic SSLs when site-specific information
is not available.
SSLs are based on a 10-6 risk for
carcinogens or a hazard quotient of 1 for
noncarcinogens. SSLs for migration to
ground water are based on (in order of
preference): nonzero maximum contaminant
level goals (MCLGs), maximum contaminant
levels (MCLs), or the aforementioned risk-
based targets.
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2.0 SOIL SCREENING PROCESS
CSM during RIs. Developing the CSM involves
several steps, discussed in the following subsections.
The soil screening process (Exhibit 4) is a step-by-
step approach that involves:
Developing a conceptual site model (CSM)
Comparing the CSM to the SSL scenario
Defining data collection needs
Sampling and analyzing soils at site
Calculating site-specific SSLs
Comparing site soil contaminant concentrations
to calculated SSLs
Determining which areas of the site require
further study.
It is important to follow this process to implement
the Soil Screening Guidance properly. The remainder
of this guidance discusses each activity in detail.
2.1 Step 1: Developing a
Conceptual Site
Model
The CSM is a three-dimensional "picture" of site
conditions that illustrates contaminant distributions,
release mechanisms, exposure pathways and
migration routes, and potential receptors. The CSM
documents current site conditions and is supported
by maps, cross sections, and site diagrams that
illustrate human and environmental exposure
through contaminant release and migration to
potential receptors. Developing an accurate CSM is
critical to proper implementation of the Soil
Screening Guidance.
As a key component of the RI/FS and EPA's Data
Quality Objectives (DQO) process, the CSM should
be updated and revised as investigations produce new
information about a site. Data Quality Objectives for
Superfund: Interim Final Guidance (U.S. EPA,
1993a) and Guidance for Conducting Remedial
Investigations and Feasibility Studies under
CERCLA (U.S. EPA, 1989c) provide a general
discussion about the development and use of the
2.1.1 Collect Existing Site Data. The initial
design of the CSM is based on existing site data
compiled during previous studies. These data may
include site sampling data, historical records, aerial
photographs, maps, and State soil surveys, as well as
information on local and regional conditions
relevant to contaminant migration and potential
receptors. Data sources include Superfund site
assessment documents (i.e., the PA/SI),
documentation of removal actions, and records of
other site characterizations or actions. Published
information on local and regional climate, soils,
hydrogeology, and ecology may be useful. In
addition, information on the population and land use
at and surrounding the site will be important to
identify potential exposure pathways and receptors.
The RI/FS guidance (U.S. EPA, 1989c) discusses
collection of existing data during RI scoping,
including an extensive list of potential data sources.
2.1.2 Organize and Analyze Existing Site
Data. One of the most important aspects of the
CSM development process is to identify and
characterize all potential exposure pathways and
receptors at the site by considering site conditions,
relevant exposure scenarios, and the properties of
contaminants present in site soils.
Attachment A, the Conceptual Site Model
Summary, provides four forms for organizing site
data for soil screening purposes. The CSM summary
organizes site data according to general site
information, soil contaminant source
characteristics, exposure pathways and receptors.
Note: If a CSM has already been developed for the
site in question, use the summary forms in
Attachment A to ensure that it is adequate.
2.1.3 Construct a Preliminary Diagram of the
CSM. Once the existing site data have been
organized and a basic understanding of the site has
been attained, draw a preliminary "sketch" of the
site conditions, highlighting source areas, potential
exposure pathways, and receptors.
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Exhibit 4
Soil Screenina Process
Step
One:
Develop Conceptual Site Model
Collect existing site data (historical records, aerial photographs, maps, PA/SI data, available background
information, State soil surveys, etc.)
Organize and analyze existing site data
Identify known sources of contamination
Identify affected media
Identify potential migration routes, exposure pathways, and receptors
Construct a preliminary diagram of the CSM
Perform site reconnaissance
Confirm and/or modify CSM
Identify remaining data gaps
Step
Two:
Compare Soil Component of CSM to Soil Screening Scenario
Confirm that future residential land use is a reasonable assumption for the site
Identify pathways present at the site that are addressed by the guidance
Identify additional pathways present at the site not addressed by the guidance
Compare pathway-specific generic SSLs with available concentration data
Estimate whether background levels exceed generic SSLs
Step
Three:
Define Data Collection Needs for Soils to Determine Which Site Areas Exceed SSLs
Develop hypothesis about distribution of soil contamination (i.e., which areas of the site have soil
contamination that exceed appropriate SSLs?)
Develop sampling and analysis plan for determining soil contaminant concentrations
Sampling strategy for surface soils (includes defining study boundaries, developing a decision rule,
specifying limits on decision errors, and optimizing the design)
Sampling strategy for subsurface soils (includes defining study boundaries, developing a decision rule,
specifying limits on decision errors, and optimizing the design)
Sampling to measure soil characteristics (bulk density, moisture content, organic carbon content,
porosity, pH)
Determine appropriate field methods and establish QA/QC protocols
Step
Four:
Sample and Analyze Soils at Site
Identify contaminants
Delineate area and depth of sources
Determine soil characteristics
Revise CSM, as appropriate
Step
Five:
Derive Site-specific SSLs, if needed
Identify SSL equations for relevant pathways
Identify chemical of concern for dermal exposure and plant uptake
Obtain site-specific input parameters from CSM summary
Replace variables in SSL equations with site-specific data gathered in Step 4
Calculate SSLs
Account for exposure to multiple contaminants
Step
Six:
Compare Site Soil Contaminant Concentrations to Calculated SSLs
For surface soils, screen out exposure areas where all composite samples do not exceed SSLs by a factor of 2
For subsurface soils, screen out source areas where the highest average soil core concentration does not
exceed the SSLs
Evaluate whether background levels exceed SSLs
Step
Seven:
Decide How to Address Areas Identified for Further Study
Consider likelihood that additional areas can be screened out with more data
Integrate soil data with other media in the baseline risk assessment to estimate cumulative risk at the site
Determine the need for action
Use SSLs as PRGs
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Ultimately, when site investigations are complete,
this sketch will be refined into a three-dimensional
diagram that summarizes the data. Also, a brief
summary of the contamination problem should
accompany the CSM. Attachment A provides an
example of a complete CSM summary.
2.1.4 Perform Site Reconnaissance. At this
point, a site visit would be useful because conditions
at the site may have changed since the PA/SI was
performed (e.g., removal actions may have been
taken). During site reconnaissance, update site
sketches/topographic maps with the locations of
buildings, source areas, wells, and sensitive
environments. Anecdotal information from nearby
residents or site workers may reveal undocumented
disposal practices and thus previously unknown areas
of contamination that may affect the current CSM
interpretation.
Based on the new information gained from site
reconnaissance, update the CSM as appropriate.
Identify any remaining data gaps in the CSM so that
these data needs can be incorporated into the
Sampling and Analysis Plan (SAP).
2.2 Step 2: Comparing CSM to
SSL Scenario
The Soil Screening Guidance is likely to be
appropriate for sites where residential land use is
reasonably anticipated. However, the CSM may
include other sources and exposure pathways that
are not covered by this guidance. Compare the CSM
with the assumptions and limitations inherent in the
SSLs to determine whether additional or more
detailed assessments are needed for any exposure
pathways or chemicals. Early identification of areas
or conditions where SSLs are not applicable is
important so that other characterization and
response efforts can be considered when planning
the sampling strategy.
2.2.1 Identify Pathways Present at the
Site Addressed by Guidance. The following are
potential pathways of exposure to soil contaminants
in a residential setting and are addressed by this
guidance document:
Direct ingestion
Inhalation of volatiles and fugitive dusts
Ingestion of contaminated ground water caused by
migration of chemicals through soil to an under-
lying potable aquifer
Dermal absorption
Ingestion of homegrown produce that has been
contaminated via plant uptake
Migration of volatiles into basements.
This guidance quantitatively addresses the ingestion,
inhalation, and migration to ground water pathways
and also addresses, more qualitatively, the potential
for dermal absorption and plant uptake based on
limited empirical data. Whether some or all of the
pathways are relevant at the site depends upon the
contaminants and conditions at the site.
For surface soils under the residential land use
assumption, routinely consider the direct ingestion
route in the soil screening decision. Inhalation of
fugitive dusts and dermal absorption can be of
concern for certain chemicals and site conditions.
For subsurface soils, risks from inhalation of
volatile contaminants and migration of soil
contaminants to an underlying aquifer are potential
concerns for this scenario. The inhalation pathway
may be eliminated from further analysis if the
presence of volatile contaminants are not suspected
in the subsurface soils. Likewise, consideration of
the ground water pathway may be eliminated if
ground water beneath or adjacent to the site is not a
potential source of drinking water. Coordinate this
decision on a site-specific basis with State or local
authorities responsible for ground water use and
classification. The rationale for excluding this
exposure pathway should be consistent with EPA
ground water policy (U.S. EPA, 1988a, 1990a,
1992a, 1992c, and 1993b).
The potential for plant uptake of contaminants
should be addressed for both surface and subsurface
soils.
In addition to the more common pathways of
exposure in a residential setting, concerns have been
raised regarding the potential for migration of
7
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volatile organic compounds (VOCs) from subsurface
soils into basements. The Johnson and Ettinger
model (1991) was developed to address this
pathway, and an analysis of the potential use of this
model for soil screening is provided in the TBD
(U.S. EPA, 1996). The analysis suggests that the use
of the model is limited due to its sensitivity to a
number of parameters such as distance from the
source to the building, building ventilation rate and
the number and size of cracks in the basement wall.
Such data are difficult to obtain for a current use
scenario, and extremely uncertain for any future use
scenario. Thus, instead of relying exclusively on the
model, data from a comprehensive soil-gas survey
are recommended to address the potential for
migration of VOCs in the subsurface. Soil-gas data
and site-specific information on soil permeability
can be used to replace default parameters in the
Johnson and Ettinger model to obtain a more
reliable estimate for the impact of this pathway on
site risk.
2.2.2 Identify Additional Pathways
Present at the Site Not Addressed bv
Guidance. The presence of additional pathways
does not preclude the use of SSLs in site areas that
are currently residential or likely to be residential in
the future. However, the risks associated with these
additional pathways should also be considered in the
RI/FS to determine whether SSLs are adequately pro-
tective. Where the following conditions exist, a
more detailed site-specific study should be
performed:
The site is adjacent to bodies of surface water
where the potential for contamination of surface
water by overland flow or release of
contaminated ground water into surface water
through seeps should be considered.
There are potential terrestrial or aquatic
ecological concerns.
There are 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).
There are unusual site conditions such as the
presence of nonaqueous phase liquids (NAPLs),
large areas of contamination, unusually high
fugitive dust levels due to soil being tilled for
agricultural use, or heavy traffic on unpaved
roads.
There are certain subsurface site conditions
such as karst, fractured rock aquifers, or
contamination extending below the water table,
that result in the screening models not being
sufficiently conservative.
2.2.3 Compare Available Data to
Background. 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.,
man-made) background can include both organic and
inorganic contaminants. A comparison of available
data (e.g., State soil surveys) on local background
concentrations with generic SSLs may indicate
whether background concentrations at the site are
elevated. Although background concentrations
exceeding generic SSLs do not necessarily indicate
that a health threat exists, further investigation may
be necessary.
Generally, EPA does not cleanup below natural
background levels; 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 address area soils. This
will often require coordination with different
authorities that have jurisdiction over other sources
of contamination in the area (such as a regional air
board or RCRA program). This will help avoid
response actions that create "clean islands" amid
widespread contamination.
To determine the need for a response action, the
site investigation should include gathering site-
specific background data for any potential chemicals
of concern and their speciation, because
contaminant solubility in water and bioavailability
(absorption into an organism) are important
considerations for the risk assessment. Speciation
of compounds such as metals and congener-specific
analysis of similar organic chemicals [e.g., dioxins,
polychlorinated biphenyls (PCBs)] can sometimes
provide improved estimates of exposure and
subsequent toxicity of chemically related
compounds. While water solubility is not often a
8
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good predictor of uptake of a toxicant into the
blood of an exposed receptor for physiological
reasons, relative bioavailability and toxicity can
sometimes be estimated through analytical
speciation of related compounds. For example,
various forms of metals are more or less toxic and
can behave as quite disparate compounds in terms of
exposure and risk. Inorganic forms of metals are
not likely to cross biological membranes as easily or
may not bioaccumulate as readily as
organometallics. Different valences of metals can
produce dramatically different toxicities (e.g.,
chromium). Different matrices can render metals
more or less bioaccessible (e.g., lead in auto
emissions from leaded gas vs. lead in mine wastes).
Similarly, the position and number of halogens on
complex organic molecules can affect uptake and
toxicity (e.g., dioxins). When applying these
concepts to a screening analysis, the risk assessor
should establish a credible rationale based on
relevant literature and site data that supports actual
differences in uptake and/or toxicity, since one
cannot predict bioavailability from simple solubility
studies. More likely, such an in-depth evaluation of
chemical speciation and bioavailability would be
conducted as part of a more detailed site-specific
risk assessment.
2.3 Step 3: Defining Data
Collection Needs for
Soils
Once the CSM has been developed and the site
manager has determined that the Soil Screening
Guidance is appropriate to use at a site, an SAP
should be developed. Attachment A, the Conceptual
Site Model Summary, lists the data needed to apply
the Soil Screening Guidance. The summary will help
identify data gaps in the CSM that require collection
of site-specific data. The soil SAP is likely to
contain different sampling strategies that address:
Surface soil
Subsurface soil
Soil characteristics
To develop sampling strategies that will properly
assess site contamination, EPA recommends that
site managers consult with the technical experts in
their Region, including risk assessors, toxicologists,
chemists and hydrogeologists. These experts can
assist the site manager to use the DQO process to
satisfy Superfund program objectives. The DQO
process is a systematic planning process developed
by EPA to ensure that sufficient data are collected
to support EPA decision making. A full discussion of
the DQO process is provided in Data Quality
Objectives for Superfund: Interim Final Guidance
(U.S. EPA, 1993a) and the Guidance for the Data
Quality Objectives Process (U.S. EPA, 1994a).
Most key elements of the DQO process have
already been incorporated as part of this Soil
Screening Guidance (see Exhibits 5 through 8 and
Attachment B). The remaining elements involve
identifying the site-specific information needed to
calculate SSLs. For example, the dry bulk density
and the fraction of organic carbon content will need
to be collected for the subsurface soil investigation.
The following sections present an overview of the
sampling strategies needed to use the Soil Screening
Guidance. For a more detailed discussion, see the
supporting TBD.
2.3.1 Stratify the Site Based on Existing
Data. At this point in the soil screening process,
existing data can be used to stratify the site into
three types of areas requiring different levels of
investigation:
Areas unlikely to be contaminated
Areas known to be highly contaminated
Areas that may be contaminated and cannot be
ruled out.
Areas that are unlikely to be contaminated generally
will not require further investigation if historical site
use information or other site data, which are
reasonably complete and accurate, confirm this
assumption. These may be areas of the site that
were completely undisturbed by hazardous-waste-
generating activities.
9
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Exhibit 5: Data Quality Objectives Process
1. State the Problem
Summarize the contamination problem that will require new environmental
data, and identify the resources available to resolve the problem.
~
2. Identify the Decision
Identify the decision that requires new environmental
data to address the contamination problem.
~
3. Identify Inputs to the Decision
Identify the information needed to support the decision, and
specify which inputs require new environmental measurements.
~
4. Define the Study Boundaries
Specify the spatial and temporal aspects of the environmental
media that the data must represent to support the decision.
T
5. Develop a Decision Rule
Develop a logical "if... then ..." statement that defines the conditions that
would cause the decision maker to choose among alternative actions.
J
6. Specify Limits on Decision Errors
Specify the decision maker's acceptable limits on decision errors, which are
used to establish performance goals for limiting uncertainty in the data.
Expanded in
Exhibit 6
-------
Exhibit 6: Defining the Study Boundaries
<
Back to Exhibit 5, Step 5, "Develop a Decision Rule"
11
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A crude estimate of the degree of soil contamination
can be made for other areas of the site by comparing
site concentrations to the generic SSLs in Appendix
A of the TBD. Generic SSLs have been calculated
for 110 chemicals using default values in the SSL
equations, resulting in conservative values that will
be protective for the majority of site conditions.
The pathway-specific generic SSLs can be compared
with available concentration data from previous site
investigations or removal actions to help divide the
site into areas with similar levels of soil
contamination and develop appropriate sampling
strategies.
The surface soil sampling strategy discussed in this
document is most appropriate for those areas that
may be contaminated and can not be designated as
uncontaminated. Areas which are known to be
contaminated (based on existing data) will be
investigated and characterized in the RI/FS.
2.3.2 Develop Sampling and Analysis Plan
for Surface Soil. The surface soil sampling
strategy is designed to collect the data needed to
evaluate exposures via direct ingestion, dermal
absorption, and inhalation of fugitive dusts.
As explained in the Supplemental Guidance to
RAGS: Calculating the Concentration Term (U.S.
EPA, 1992d), an individual is assumed to move
randomly across an exposure area (EA) over time,
spending equivalent amounts of time in each
location. Thus, the concentration contacted over
time is best represented by the spatially averaged
concentration over the EA. Ideally, the surface soil
sampling strategy would determine the true
population mean of contaminant concentrations in
an EA. Because determination of the "true" mean
would require extensive sampling at high costs, the
maximum contaminant concentration from
composite samples is used as a conservative estimate
of the mean.
This Max test strategy compares the results of
composite samples with the SSLs. Another, more
complex strategy called the Chen test is presented in
Part 4 of the TBD.
The User's Guide uses the Max test rather than the
Chen test because the Max test is based on a
statistical null hypothesis that is more appropriate
for NPL sites (i.e., the EA requires further
investigation). Although the Chen test is not well
suited for screening decisions at NPL sites, it may be
useful in a non-NPL, voluntary cleanup context.
The depth over which surface soils are sampled
should reflect the type of exposures expected at the
site. The Urban Soil Lead Abatement
Demonstration Project (U.S. EPA 1993d) defined
the top 2 centimeters as the depth of soil where
direct contact predominantly occurs. The decision
to sample soils below 2 centimeters depends on the
likelihood of deeper soils being disturbed and brought
to the surface (e.g., from gardening, landscaping or
construction activities).
Note that the size, shape, and orientation of
sampling volume (i.e., "support") for heterogenous
media have a significant effect on reported
measurement values. For instance, particle size has
a varying affect on the transport and fate of
contaminants in the environment and on the
potential receptors. Comparison of data from
methods that are based on different supports can be
difficult. Defining the sampling support is
important in the early stages of site
characterization. This may be accomplished
through the DQO process with existing knowledge
of the site, contamination, and identification of the
exposure pathways that need to be characterized.
Refer to Preparation of Soil Sampling Protocols:
Sampling Techniques and Strategies (U.S. EPA,
1992e) for more information about soil sampling
support.
The SAP developed for surface soils should specify
sampling and analytical procedures as well as the
development of QA/QC procedures. To identify the
appropriate analytical procedures, the screening
levels must be known. If data are not available to
calculate site-specific SSLs (Section 2.5.1), then the
generic SSLs in Appendix A of the TBD should be
used.
The following strategy can be used for surface
soils to estimate the mean concentration of
semivolatiles, inorganics, and pesticides in an
exposure area. Volatiles are not included in the
estimations because they are not expected to remain
at the surface for an extended period of time.
12
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Exhibit 7: Designing a Sampling and Analysis Plan for Surface Soils
1. Subdivide Site
Into EAs
2. Divide EA
Into a Grid
3. Organize
Surface
Sampling
Program for
EA
O1 oe
04 ฐ2
u O3
OS
O4 (~\2
Q3 O^
OS
ฐ6 O1
OS
01 ฐ2
u O6
Q4 O3
01 ฐ5 04
O3
Q2 Q6
For surface soils, the individual
unit for decision making is an
"EA," or exposure area. It
measures 0.5 acre in area or
less.
This step defines the number of
specimens (N) that will make up
one composite sample.
Placement of sample locations
on the grid was developed
using a default sample size of
6 (which is based on
acceptable error rates for a CV
of 2.5) and a stratified random
sampling pattern.
If the EA CV is suspected to be greater than 2.5, use the table
below to select an adequate sample size or refer to the TBD for
other sample design options.
Probability of Decision Error at 0.5 SSL and 2 SSL Using Max Test
II
>
o
2.5a
O
<
11
o
CO
O
<
=3.5
O
<
=4.0
Sample Size ^
o
LO
o
LU
E2.0d
m
o
cn
e2.0
LO
o
LU
e2.0
LO
o
LU
e2.0
C = 4 specimens per compositeฎ
6
0.21
0.08
0.28
0.11
0.31
0.11
0.35
0.16
7
0.25
0.05
0.31
0.08
0.36
0.09
0.41
0.15
8
0.25
0.04
0.36
0.05
0.42
0.07
0.41
0.09
9
0.28
0.03
0.36
0.04
0.44
0.07
0.48
0.08
The CV is the coefficient of variation for individual, uncomposited measurements across the entire EA,
including measurement error.
Sample size (N) = number of composite samples
En 5 = Probability of requiring further investigation when the EA mean is 0.5 SSL
d
^2.0 = Probability of not requiring further investigation when the EA mean is 2.0 SSL
eC = number of specimens per composite sample, when each composite consists of points from a stratified
random or systemic grid sample from across the entire EA.
NOTE: All decision error rates are based on 1,000 simulations that assume that each composite is
representative of the entire EA, half the EA has concentrations below the limit of detection, and half the EA
has concentrations that follow a gamma distribution (a conservative distributional assumption).
13
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Divide areas to be sampled in the screening
process into 0.5-acre exposure areas, the size of
a suburban residential lot. If the site is currently
residential, the exposure area should be the
actual residential lot size. The exposure areas
should not be laid out in such a way that they
unnecessarily combine areas of high and low
levels of contamination. The orientation and
exact location of the EA, relative to the
distribution of the contaminant in the soil, can
lead to instances where sampling the EA may
have contaminant concentration results above
the mean, and in other instances, results below
the mean. Try to avoid straddling contaminant
"distribution units" within the 0.5-acre EA.
Composite surface soil samples. Because the
objective of surface soil screening is to estimate
the mean contaminant concentration, the
physical "averaging" that occurs during
compositing is consistent with the intended use
of the data. Compositing allows sampling of a
larger number of locations while controlling
analytical costs, since several individual samples
are physically mixed (homogenized) and one or
more subsamples are drawn from the mixture
and submitted for analysis.
Strive to achieve a false negative error rate of 5
percent (i.e., in only 5 percent of the cases, soil
contamination is assumed to be below the
screening level when it is really above the
screening level). EPA also strives to achieve a
20 percent false positive error rate (i.e., in only
20 percent of the cases, soil contamination is
assumed to be above the screening level when it
is really below the screening level). These error
rate goals influence the number of samples to be
collected in each exposure area. For this
guidance, EPA has defined the "gray region" as
one-half to 2 times the SSL. Refer to Section
2.6 for further discussion.
The default sample size chosen for this guidance
(see Exhibit 7) provides adequate coverage for a
coefficient of variation (CV) based upon 250
percent variability in contaminant values
(CV=2.5). (If a CV larger than 2.5 is expected,
use an appropriate sample size from the table in
Exhibit 7 of the User's Guide, or tables in the
TBD.)
Take six composite samples, for each exposure
area, with each composite sample made up of
four individual samples. Exhibit 7 shows other
sample sizes needed to achieve the decision error
rates for other CVs. Collect the composites
randomly across the EA and through the top 2
centimeters of soil, which are of greatest
concern for incidental ingestion of soil, dermal
contact, and inhalation of fugitive dust.
Analyze the six samples per exposure area to
determine the contaminants present and their
concentrations.
For further information on compositing across or
within EA sectors, developing a random sampling
strategy, and determining sample sizes that control
decision error rates, refer to the TBD.
Note that the Max test requires a Data Quality
Assessment (DQA) test following sampling and
analysis (Section 2.4.2) to ensure that the DQOs
(i.e., decision error rate goals) are achieved. If DQOs
are not met, additional sampling may be required.
2.3.3 Develop Sampling and Analysis Plan
for Subsurface Soils. The subsurface and surface
soil sampling strategies differ because the exposure
mechanisms differ. Exposure to surface
contaminants occurs randomly as individuals move
around a residential lot. The surface soil sampling
strategy reflects this type of random exposure.
In general, exposure to subsurface contamination
occurs when chemicals migrate up to the surface or
down to an underlying aquifer. Thus, subsurface
sampling focuses on collecting the data required for
modeling the volatilization and migration to ground
water pathways. Measurements of soil
characteristics and estimates of the area and depth
of contamination and the average contaminant
concentration in each source area are needed to
supply the data necessary to calculate the inhalation
and migration to ground water SSLs.
14
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Exhibit 8: Designing a Sampling and Analysis Plan for Subsurface Soils
1. Delineate Source Area
Contaminant
Source
Soil Borings
2. Choose
Subsurface
Soil Sampling
Locations
3. Design Subsurface
Sampling and Analysis
Plan
Lab/Field
Analysis for soil
parameters'3
For screening purposes, EPA
recommends drilling 2 to 3
borings per source area in
areas of highest suspected
concentrations. Soil sampling
should not extend past water
table or saturated zone.
Soil Boring a
(depth below ground surface in feet)
Lab Analysis for
soil contaminants
Picture depicts a continuous boring with 2 foot segments. For information on other methods such as interval sampling and
depth weighted analysis, please refer to 2.3.3 of the User's Guide or 4.2 of the TBD.
Soil Texture, Dry Bulk Density, Soil Organic Carbon, pH. Retain samples for possible discrete contaminant sampling.
15
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Source areas are the decision units for subsurface
soils. A source area is defined by the horizontal
extent, and vertical extent or depth of
contamination. For this purpose, "contamination"
is defined by either the Superfund's Contract
Laboratory Program (CLP) practical quantitation
limits (QLs) for each contaminant, or the SSL.
Sites with multiple sources should develop
separate SSLs for each source.
The SAP developed for subsurface soils should
specify sampling and analytical procedures as well as
the development of QA/QC procedures. To identify
the appropriate procedures, the SSLs must be
known. If data are not available to calculate site-
specific SSLs (Section 2.5.2), then the generic SSLs
in Appendix A of the TBD should be used.
The primary goal of the subsurface sampling
strategy is to estimate the mean contaminant
concentration and average soil characteristics within
the source area. As with the surface soil sampling
strategy, the subsurface soil sampling strategy
follows the DQO process (see Exhibits 5, 6, and 8).
The decision rule is based on comparing the mean
contaminant concentration within each
contaminant source with source-specific SSLs.
Current investigative techniques and statistical
methods cannot accurately determine the mean
concentration of subsurface soils within a
contaminated source without a costly and intensive
sampling program that is well beyond the level of
effort generally appropriate for screening. Thus,
conservative assumptions should be used to develop
hypotheses on likely contaminant distributions.
This guidance bases the decision to investigate a
source area further on the highest mean soil boring
contaminant concentration within the source,
reflecting the conservative assumption that the
highest mean subsurface soil boring concentration
among a set of borings taken from the source area
represents the mean of the entire source area.
Similarly, estimates of contaminant depths should be
conservative. The investigation should include the
maximum depth of contamination encountered
within the source without going below the water
table.
For each source, the guidance recommends taking 2
or 3 soil borings located in the areas suspected of
having the highest contaminant concentrations
within the source. These subsurface soil sampling
locations are based primarily on knowledge of likely
surface soil contamination patterns (see Exhibit 6)
and subsurface conditions. Flowever, buried sources
may not be discernible at the surface. Information
on past practices at the site included in the CSM can
help identify subsurface source areas.
For sites contaminated with VOCs, the subsurface
sampling strategy should include soil gas surveys as
well as soil matrix sampling. VOCs are commonly
found in vapor phase in the unsaturated zone, and
soil matrix samples may yield results that are
deceptively low. Soil gas data are needed to help
locate sources, define source size, to place soil
boring locations within a source, and can also be used
in conjunction with modeling to address VOC
transport in the vadose zone for both the
volatilization and migration to ground water
pathways.
Take soil cores from the soil boring using either
split spoon sampling or other appropriate sampling
methods. Description and Sampling of
Contaminated Soils: A Field Pocket Guide (U.S.
EPA, 199If), and Subsurface Characterization and
Monitoring Techniques: A Desk Reference Guide,
Vol. I & II (U.S. EPA, 1993e), can be consulted for
information on appropriate subsurface sampling
methods.
Sampling should begin at the ground surface and
continue until either no contamination is
encountered or the water table is reached.
Subsurface sampling intervals can be adjusted
at a site to accommodate site-specific infor-
mation on subsurface contaminant
distributions and geological conditions (e.g.,
thick vadose zones in the West). The concept of
"sampling support" introduced in Section 2.3.2 also
applies to subsurface sampling. For example, sample
splits and subsampling should be performed
according to Preparation of Soil Sampling
Protocols: Sampling Techniques and Strategies
(U.S. EPA, 1992e).
16
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If each subsurface soil core segment represents the
same subsurface soil interval (e.g., 2 feet), then the
average concentration from the surface to the depth
of contamination is the simple arithmetic average
of contaminant concentrations measured for core
samples representative of each of the 2-foot
segments from the surface to the depth of
contamination. However, if the sample intervals
are not all of the same length (e.g., some are 2 feet
while others are 1 foot or 6 inches), then the
calculation of the average concentration in the total
core must account for the different lengths of the
segments.
If Ci is the concentration measure in a core sample,
representative of a core interval or segment of
length lj, and the n-th segment is considered to be
the last segment sampled in the core (i.e., the n-th
segment is at the depth of contamination), then the
average concentration in the core from the surface
to the depth of contamination should be calculated
as the following depth-weighted average (c).
_ i = 1
C " n
i = l
Alternatively, the average boring concentration can
be determined by adding the total contaminant
masses together (from the sample results) for all
sample segments to get the total contaminant mass
for the boring. The total contaminant mass is then
divided by the total dry weight of the core (as
determined by the dry bulk density measurements)
to estimate average soil boring concentration.
For the leach test option, collect discrete samples
along a soil boring from within the zone of
contamination and composite them to produce a
sample representative of the average soil boring
concentration. Take care to split each discrete
sample before analysis so that information on
contaminant distributions with depth will not be
lost. A leach test may be conducted on each soil
core.
Finally, the soil investigation for the migration to
ground water pathway should not be conducted
independently of ground water investigations.
Contaminated ground water may indicate the
presence of a nearby source area that would leach
contaminants from soil into aquifer systems.
2.3.4 Develop Sampling and Analysis Plan
to Determine Soil Characteristics. The soil
parameters necessary for SSL calculations are soil
texture, dry bulk density, soil organic carbon, and
pH. Some can be measured in the field, while others
require laboratory measurement. Although
laboratory measurements of these parameters
cannot be obtained under Superfund's CLP,
independent soil testing laboratories across the
country can perform these tests at a relatively low
cost.
To appropriately apply the volatilization and
migration-to-ground water models, average or
typical soil properties should be used for a source in
the SSL equations (see Step 5). Take samples for
measuring soil parameters with samples for
measuring contaminant concentrations. If possible,
consider splitting single samples for contaminant
and soil parameter measurements. Many soil testing
laboratories can handle and test contaminated
samples. However, if testing contaminated samples
for soil parameters is a problem, samples may be
obtained from clean areas of the site as long as they
represent the same soil texture and are taken from
approximately the same depth as the contaminant
concentration samples.
Soil Texture. Soil texture class (e.g., loam, sand,
silt loam) is necessary to estimate average soil
moisture conditions and to apply the Hydrological
Evaluation of Landfill Performance (HELP) model
to estimate infiltration rates (see Attachment A).
The appropriate texture classification is determined
by a particle size analysis and the U.S. Department
of Agriculture (USDA) soil textural triangle shown
in Exhibit 9. This classification system is based on
the USDA soil particle size classification.
The particle size analysis method in Gee and Bauder
(1986) can provide this particle size distribution.
Other methods are appropriate as long as they
provide the same particle size breakpoints for
sand/silt (0.05 mm) and silt/clay (0.002 mm). Field
methods are an alternative for determining soil
17
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textural class; Exhibit 9 presents an example from
Brady (1990).
Dry Bulk Density. Dry soil bulk density (pb) is
used to calculate total soil porosity and can be
determined for any soil horizon by weighing a thin-
walled tube soil sample (e.g., Shelby tube) of known
volume and subtracting the tube weight [American
Society for Testing and Materials (ASTM) D 2937].
Determine moisture content (ASTM 2216) on a
subsample of the tube sample to adjust field bulk
density to dry bulk density. The other methods (e.g.,
ASTM D 1556, D 2167, D 2922) are generally
applicable only to surface soil horizons and are not
appropriate for subsurface characterization. ASTM
soil testing methods are readily available in the
Annual Book of ASTM Standards, Volume 4.08, Soil
and Rock; Building Stones, available from ASTM,
100 Barr Harbor Drive, West Conshohocken, PA,
19428.
Organic Carbon and pH. Soil organic carbon is
measured by burning off soil carbon in a controlled-
temperature oven (Nelson and Sommers, 1982).
This parameter is used to determine soil-water
partition coefficients from the organic carbon soil-
water partition coefficient, Koc. Soil pH is used to
select site-specific partition coefficients for metals
(Table C-4, Attachment C) and ionizing organics
(Table C-2, Attachment C). This simple
measurement is made with a pH meter in a soil/water
slurry (McLean, 1982) and may be measured in the
field using a portable pH meter.
2.3.5 Determine Analytical Methods and
Establish QA/QC Protocols. Assemble a list of
feasible sampling and analytical methods during this
step. Verify that a CLP method and a field method
for analyzing the samples exist and that the
analytical method QL or field method QL is
appropriate for (i.e., is below) the site-specific or
generic SSL. Sampler's Guide to the Contract
Laboratory Program (U.S. EPA, 1990b) and User's
Guide to the Contract Laboratory Program (U.S.
EPA, 1991e) contain further information on CLP
methods.
Field methods, such as soil gas surveys,
immunoassay, or X-ray fluorescence, can be used if
the field method quantitation limit is below the SSL.
EPA recommends the use of field methods where
applicable and appropriate. However, at least 10
percent of both the discrete samples and the
composites should be split and sent to a CLP
laboratory for confirmatory analysis. (Quality
Assurance for Superfund Environmental Data
Collection Activities, U.S. EPA, 1993c).
Because a great amount of variability and bias can
exist in the collection, subsampling, and analysis of
soil samples, some effort should be made to
characterize this variability and bias. A Rationale
for the Assessment of Errors in the Sampling of Soils
(U.S. EPA, 1990c) outlines an approach that
advocates the use of a suite of QA/QC samples to
assess variability and bias. Field duplicates and splits
are some of the best indicators of overall variability
in the sampling and analytical processes.
Field methods will be useful in defining the study
boundaries (i.e., area and depth of contamination)
during both site reconnaissance and sampling. The
design and capabilities of field portable
instrumentation are rapidly evolving. Documents
describing the standard operating procedures for field
instruments are available though the National
Technical Information Service (NTIS).
Regardless of whether surface or subsurface soils are
sampled, the Superfund quality assurance program
guidance (U.S. EPA, 1993c) should be consulted.
Standard limits on the precision and bias of sampling
and analytical operations conducted during sampling
do apply and should be followed to give consistent
and defensible results.
2.4 Step 4: Sampling and
Analyzing Site Soils
& DQA
Once the sampling strategies have been developed
and implemented, the samples should be analyzed
according to the analytical laboratory and field
methods specified in the SAP. Results of the anal-
yses should identify the concentrations of potential
contaminants of concern for which site-specific
SSLs will be calculated.
18
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Exhibit 9: U.S. Department of Agriculture soil texture classification.
100.
700 3?
Criteria Used with the Field Method for Determining Soil Texture Classes (Source: Brady, 1990)
Criterion
Sand
Sandy loam
Loam
Silt loam
Clay loam
Clay
1. Individual grains Yes Yes
visible to eye
2. Stability of dry Do not form Do not form
clods
3. Stability of wet Unstable Slightly stable
clods
4. Stability of Does not Does not form
"ribbon" when form
wet soil rubbed
between thumb
and fingers
Some
Few
Easily Moderately
broken easily broken
Moderately Stable
stable
Does not form Broken appearance
No
Hard and
stable
Very stable
Thin, will break
No
Very hard
and stable
Very stable
Very long,
flexible
U.S.
Department
of Agriculture
0.002
Particle Size, mm
0.05 0.10 0.25 0.5
1.0
2.0
Clay
Silt
Very Fine
Fine
Med.
Coarse
Very Coarse
Gravel
Sand
Source: USDA.
19
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2.4.1 Delineate Area and Depth of Source.
Both spatial area and depth data, as well as soil
characteristic data, are needed to calculate site-
specific SSLs for the inhalation of volatiles and
migration to ground water pathways in the
subsurface. Site information from the CSM or soil
gas surveys can be used to estimate the areal extent
of the sources.
2.4.2 Perform DQA Using Sample Results.
After sampling has been completed, a DQA should
be conducted if all composite samples are less than 2
times the SSL. This is necessary to determine if the
original CV estimate (2.5), and hence the number of
samples collected (6), was adequate for screening
surface soils.
To conduct the DQA for a composite sample whose
mean is below 2 SSL, first calculate the sample CV
for the EA in question from the sample mean (x),
the number of specimens per composite sample (C),
and sample standard deviation (s) as follows:
CV = s
x
Use the sample size table in Exhibit 7 to check, for
this CV, whether the sample size is adequate to meet
the DQOs for the sampling effort. If sampling
DQOs are not met, supplementary sampling may be
needed to achieve DQOs.
However, for EAs with small sample means (e.g., all
composites are less than the SSL), the sample CV
calculated using the equation above may not be a
reliable estimate of the population CV (i.e., as x
approaches zero, the sample CV will approach
infinity). To protect against unnecessary additional
sampling in such cases, compare all composites
against the formula SSL /Jc . If the maximum
composite sample concentration is below the value
given by the equation, then the sample size may be
assumed to be adequate and no further DQA is
necessary. In other words, EPA believes that the
default sample size will adequately support walk-
away decisions when all composites are well below
the SSL. The TBD describes the development of this
formula and provides additional information on
implementing the DQA process.
2.4.3 Revise the CSM. Because these analyses
reveal new information about the site, update the
CSM accordingly. This revision could include
identification of site areas that exceed the generic
SSLs.
2.5 Step 5: Calculating Site-
specific SSLs
With the soil properties data collected in Step 4 of
the screening process, site-specific soil screening
levels can now be calculated using the equations
presented in this section. For a description of how
these equations were developed, as well as
background on their assumptions and limitations,
consult the TBD.
All SSL equations were developed to be consistent
with RME in the residential setting. The Superfund
program estimates the RME for chronic exposures
on a site-specific basis by combining an average
exposure-point concentration with reasonably con-
servative values for intake and duration (U.S. EPA,
1989a; RAGS HHEM, Supplemental Guidance:
Standard Default Exposure Factors, U.S. EPA,
1991a). Thus, all site-specific parameters (soil,
aquifer, and meteorologic parameters) used to
calculate SSLs should reflect average or typical site
conditions in order to calculate average exposure
concentrations at the site.
Equations for calculating SSLs are presented for
surface and subsurface soils in the following sections.
For each equation, site-specific input
parameters are highlighted in bold and
default values are provided for use when site-
specific data are not available. Although these
defaults are not worst case, they are conservative.
At most sites, higher, but still protective SSLs can be
calculated using site-specific data. The TBD
describes development of these default values and
presents generic SSLs calculated using the default
values.
Attachment D provides toxicity criteria for 110
chemicals commonly found at NPL sites. These
criteria were obtained from Integrated Risk
Information System (IRIS) (U.S. EPA, 1995b) or
Health Effects Assessment Summary Tables
(HEAST) (U.S. EPA, 1995a), which are regularly
20
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updated. Prior to calculating SSLs at a site,
check all relevant chemical-specific values in
Attachment D against values from IRIS or
HEAST. Only the most current values should
be used to calculate SSLs.
Where toxicity values have been updated, the
generic SSLs should also be recalculated with current
toxicity information.
2.5.1 SSL EquationsSurface Soils.
Exposure pathways addressed in the process for
screening surface soils include direct ingestion,
dermal contact, and inhalation of fugitive dusts.
Direct Ingestion. The Soil Screening Guidance
addresses chronic exposure to noncarcinogens and
carcinogens through direct ingestion of
contaminated soil in a residential setting. The
approach for calculating noncarcinogenic SSLs
presented in this guidance leads to screening levels
that are approximately 3 times more conservative
than PRGs calculated based on the approach
presented in RAGS HHEM, Part B (i.e., using a 30-
year, time-weighted average soil ingestion rate for
comparison to chronic toxicity criteria). Because a
number of studies have shown that inadvertent
ingestion of soil is common among children age 6
and younger (Calabrese et al., 1989; Davis et al.,
1990: Van Wijnen et al., 1990), several commenters
suggested that screening values should be based on
this increased exposure during childhood. However,
other commenters believe that comparing a six-year
exposure to a chronic reference dose (RfD) is
unnecessarily conservative. In their analysis of this
issue, the Science Advisory Board (SAB) stated that,
for most chemicals, the approach of combining the
higher six-year exposure for children with chronic
toxicity criteria is overly protective (U.S. EPA,
1993f). However, they noted that the approach
may be appropriate for chemicals with chronic RfDs
based on toxic endpoints that are specific to
children (e.g., fluoride and nitrates) or where the
dose-response curve is steep [i.e., the difference
between the no-observed-adverse-effect level
(NOAEL) and the adverse effect level is small].
Thus for the purposes of screening, Office of
Emergency Remedial Response (OERR) opted to
base the generic SSLs for noncarcinogenic
contaminants on the more conservative "childhood
only" exposure (Equation 1). The issue of whether
to maintain this more conservative approach
throughout the Baseline Risk Assessment and
establishing remediation goals will depend on how
the specific chemical's toxicology relates to the
issues raised by the SAB.
Equation 1
Screening Level Equation for
Ingestion of Noncarcinogenic
Contaminants in Residential
Soil
Screening
Level
(mg/kg)
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)
Default
THQ/target hazard quotient
1
(unitless)
BW/body weight (kg)
15
AT/averaging time (yr)
6a
RfD0/oral reference dose (mg/kg-d)
chemical-specific
(Attachment D)
EF/exposure frequency (d/yr)
350
ED/exposure duration (yr)
6
IR/soil ingestion rate (mg/d)
200
aFor noncarcinogens, averaging time equals to
exposure duration.
For carcinogens, both the magnitude and duration of
exposure are important. Duration is critical because
the toxicity 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 protective of
exposures to carcinogens in the residential setting,
Superfund focuses on exposures to individuals who
may live in the same residence for a high-end period
of time (e.g., 30 years) because exposure to soil is
higher during childhood and decreases with age.
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, 1991c.
Default values are used for all input parameters in
the direct ingestion equations. The amount of data
required to derive site-specific values for these
parameters (e.g., soil ingestion rates, chemical-
specific bioavailability) makes their collection and
use impracticable for screening. Therefore, site-
specific data are not generally available for this
21
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exposure route. The generic ingestion SSLs
presented in Appendix A of the TBD are
recommended for all NPL sites.
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 10-6 kg/mg x EF x IF soi|/adj
Parameter/Definition (units)
Default
TR/target cancer risk (unitless)
10-6
AT/averaging time (yr)
70
SF0/oral slope factor (mg/kg-d)"1
chemical-specific
(Attachment D)
EF/exposure frequency (d/yr)
350
IFSOii/adj /age-adjusted soil
114
ingestion factor (mg-yr/kg-d)
Dermal Contact. Contaminant absorption through
dermal contact may contribute risk to human health
in a residential setting. However, incorporation of
dermal exposures into the soil screening process is
limited by the amount of data available to quantify
dermal absorption from soil for specific chemicals.
Previous EPA studies suggest that absorption via the
dermal route must be greater than 10 percent to
equal or exceed the ingestion exposure (assuming
100 percent absorption of a chemical via ingestion;
Dermal Exposure Assessment: Principles and
Applications, U.S. EPA, 1992b).
Of the 110 compounds evaluated, available data
show greater than 10 percent dermal absorption for
pentachlorophenol (Wester et al., 1993).
Therefore, pentachlorophenol is the only chemical
for which the Soil Screening Guidance directly
considers dermal exposure. The ingestion SSL for
pentachlorophenol should be divided in half to
account for the assumption that exposure via the
dermal route is equivalent to the ingestion route.
Preliminary studies show that certain semivolatile
compounds (e.g., benzo(a)pyrene) may also be of
concern for this exposure route. As adequate dermal
absorption data are developed for such chemicals,
the ingestion SSLs may need to be adjusted. The
Agency will provide updates on this issue as
appropriate.
Inhalation of Fugitive Dusts. Inhalation of
fugitive dusts is a consideration for semivolatile
organics and metals in surface soils. However,
generic fugitive dust SSLs for semivolatile organics
are several orders of magnitude higher than the
corresponding generic ingestion SSLs. EPA believes
that since the ingestion route should always be
considered in screening decisions for surface soils,
and ingestion SSLs appear to be adequately
protective for inhalation exposures to fugitive dusts
for organic compounds, the fugitive dust exposure
route need not be routinely considered for organic
chemicals in surface soils.
Likewise, the ingestion SSLs are significantly more
conservative than most of the generic fugitive dust
SSLs. As a result, fugitive dust SSLs need not be
calculated for most metals. However, chromium is
an exception. For chromium, the generic fugitive
dust SSL is below the ingestion SSL. This is due to
the carcinogenicity of hexavalent chromium, Cr+6,
through the inhalation exposure route. For most
sites, fugitive dust SSLs calculated using the
conservative defaults will be adequately protective.
However, if site conditions that will result in higher
fugitive dust emissions than the defaults (e.g., dry,
dusty soils; high average annual windspeeds;
vegetative cover less than 50 percent) are likely,
consider calculating a site-specific fugitive dust SSL.
Equations 3 and 4 are used to calculate fugitive dust
SSLs for carcinogens and noncarcinogens. These
equations require calculation of a particulate
emission factor (PEF, Equation 5) that relates the
concentration of contaminant in soil to the
concentration of dust particles in air. This PEF
represents an annual average emission rate based on
wind erosion that should be compared with chronic
health criteria. It is not appropriate for evaluating
the potential for more acute exposures.
Both the emissions portion and the dispersion
portion of the PEF equation have been updated
since the first publication of RAGS HHEM, Part B,
in 1991. As in Part B, the emissions part of the PEF
equation is based on the "unlimited reservoir" model
developed to estimate particulate emissions due to
wind erosion (Cowherd et al., 1985). Additional
information on the update of the PEF equation is
provided in the TBD. Cowherd et al. (1985) present
methods for site-specific measurement of the
22
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parameters necessary to calculate a PEF. A site-
specific dispersion model (Q/C) is then selected as
described in the section on calculating SSLs for the
volatile inhalation pathway later in this document.
assume an infinite source, they can violate mass-
balance considerations, especially for small sources.
Equation 3: Screening Level Equation for
Inhalation of Carcinogenic
Fugitive Dusts from Residential
Soil
Screening
Level
(mg/kg)
TR x AT x 365 d/yr
URF x 1,000 |ig/mg x EF x ED x 1
PEF
Parameter/Definition (units) Default
TR/target cancer risk (unitless)
AT/averaging time (yr)
URF/inhalation unit risk factor
(|ig/m3)-1
EF/exposure frequency (d/yr)
ED/exposure duration (yr)
PEF/particulate emission
factor (m3/kg)
10-6
70
chemical-specific
(Attachment D)
350
30
1.32 x 109
(Equation 5)
Equation 5: Derivation of the Particulate
Emission Factor
PEF (rrP/kg) = Q/C x 3,600 s/h
0.036 x (1-V) x (Um/Utp x F(x)
Parameter/Definition (units)
Default
PEF/particulate emission factor (m3/kg)
1.32 x 109
Q/C/inverse of mean conc. at
center of a 0.5-acre-square
source (g/m2-s per kg/m3)
90.80
V/fraction of vegetative cover
(unitless)
0.5 (50%)
Um/rnean annual windspeed
4.69
(m/s)
Ut/equivalent threshold value of
11.32
windspeed at 7 m (m/s)
F(x)/function dependent on
Um/Ut derived using Cowherd
0.194
et al. (1985) (unitless)
Equation 4: Screening Level
Equation for
Inhalation of Noncarcinogenic
Fugitive Dusts from Residential
Soil
Screening Level = THQ x AT x 365 d/yr
(mg/kg) EF x ED x
[1x1]
RfC PEF
Parameter/Definition (units)
Default
THQ/target hazard quotient
1
(unitless)
AT/averaging time (yr)
30
EF/exposure frequency (d/yr)
350
ED/exposure duration (yr)
30
RfC/inhalation reference
chemical-specific
concentration (mg/m3)
(Attachment D)
PEF/particulate emission
1.32 x 109
factor (m3/kg)
(Equation 5)
2.5.2 SSL Equations-Subsurface Soils.
The Soil Screening Guidance addresses two exposure
pathways for subsurface soils: inhalation of volatiles
and ingestion of ground water contaminated by the
migration of contaminants through soil to an under-
lying potable aquifer. Because the equations
developed to calculate SSLs for these pathways
To address this concern, the guidance also includes
equations for calculating mass-limit SSLs for each of
these pathways when the size (i.e., area and
depth) of the contaminated soil source is
known or can be estimated with confidence.
Attachment D provides the toxicity criteria and
regulatory benchmarks for 110 chemicals
commonly found at NPL sites. These criteria were
obtained from IRIS (U.S. EPA, 1995b), HEAST
(U.S. EPA, 1995a), and Drinking Water Regulations
and Health Advisories (U.S. EPA, 1995c), which are
regularly updated. Prior to calculating SSLs at a
site, all relevant chemical-specific values in
Attachment D should be checked against the
most recent version of their sources to ensure
that they are up to date.
Toxicity data are not available for all chemicals for
the inhalation exposure route. At the request of
commenters, EPA has looked into methods for
extrapolating inhalation toxicity values from oral
toxicity data. The TBD presents the results of this
analysis along with information on current EPA
23
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practices for conducting such route-to-route
extrapolations.
Chemical properties necessary to calculate SSLs for
the inhalation and migration to ground water path-
ways include solubility, air and water diffusivities,
Henry's law constant, and soil/water partition coeffi-
cients. Attachment C provides values for 110
chemicals commonly found at NPL sites.
Site-specific parameters necessary to calculate SSLs
for subsurface soils are listed on Exhibit 10, along
with recommended sources and measurement
methods. In addition to the soil parameters described
in Step 3, other site-specific input parameters
include soil moisture, infiltration rate, aquifer
parameters, and meteorologic data. Guidance for
collecting or estimating these other parameters at a
site is provided on Exhibit 10 and in Attachment A.
Inhalation of Volatiles. Equations 6 and 7 are used
to calculate SSLs for the inhalation of carcinogenic
and noncarcinogenic volatile contaminants.To use
these equations to calculate inhalation SSLs, a
volatilization factor (VF) must be calculated.
The VF equation can be broken into two separate
models: a model to estimate the emissions and a
dispersion model (reduced to the term Q/C) that
simulates the dispersion of contaminants in ambient
air. In addition, a soil saturation limit (C sat) must be
calculated to ensure that the VF model is applicable
to soil contaminant conditions at a site.
Volatilization Factor (VF). The soil-to-air VF
(Equation 8) is used to define the relationship
between the concentration of the contaminant in
soil and the flux of the volatilized contaminant to
air. The Soil Screening Guidance replaces the
Hwang and Falco (1986) model used as the
basis for the RAGS HHEM, Part B, VF
equation with the simplified equation
developed by Jury et al. (1984).
The Jury model calculates the maximum flux of a
contaminant from contaminated soil and considers
soil moisture conditions in calculating a VF. The
models are similar in their assumptions of an infinite
contaminant source and vapor phase diffusion as the
only transport mechanism (i.e., no transport takes
place via nonvapor-phase diffusion and there is no
mass flow due to capillary action). In some
situations, information about the size of the source
is available and SSLs can be calculated using the
mass-limit approach.
Equation 6: Screening Level
Equation for
Inhalation of Carcinogenic Volatile
Contaminants in
Residential Soil
Screening
Level = TR x AT x 365 d/yr
(mq/kq) URF x 1,000 |iq/mq x EF x ED x 1
VF
Parameter/Definition (units)
Default
TR/target cancer risk (unitless)
10-6
AT/averaging time (yr)
70
URF/inhalation unit risk factor
chemical-specific
(|ig/m3)-1
(Attachment D)
EF/exposure frequency (d/yr)
350
ED/exposure duration (yr)
30
VF/soil-to-air volatilization
chemical-specific
factor (m3/kg)
(Equation 8)
Equation 7: Screening Level
Equation for
Inhalation of Noncarcinogenic
Volatile Contaminants in
Residential Soil
Screening Level = THQ x AT x 365 d/yr
(mg/kg) EF x ED
X [ 1 X 1 I
RfC VF
Parameter/Definition (units)
Default
THQ/target hazard quotient
1
(unitless)
AT/averaging time (yr)
30
EF/exposure frequency (d/yr)
350
ED/exposure duration (yr)
30
RfC/inhalation reference
chemical-specific
concentration (mg/m3)
(Attachment D)
VF/soil-to-air volatilization
chemical-specific
factor (m3/kg)
(Equation 8)
Other than initial soil concentration, air-filled soil
porosity is the most significant soil parameter
affecting the final steady-state flux of volatile
contaminants from soil (U.S. EPA, 1980). In other
words, the higher the air-filled soil porosity, the
greater the emission flux of volatile constituents.
24
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Exhibit 10. Site-specific Parameters for Calculating Subsurface SSLs
SSL Pathway
Parameter
Migration to
Inhalation ground water Data source
Method
Source Characteristics
Source area (A)
Source length (L)
Source depth
Sampling data Measure total area of contaminated soil
Sampling data Measure length of source parallel to ground water
flow
Sampling data Measure depth of contamination or use
conservative assumption
Soil Characteristics
Soil texture
O
o
Lab measurement
Particle size analysis (Gee & Bauder, 1986) and
USDA classification; used to estimate 8W& I
Dry soil bulk density (pb)
Field measurement
All soils: ASTM D 2937; shallow soils: ASTM D
1556, ASTM D 2167, ASTM D 2922
Soil moisture content (w)
O
o
Lab measurement
ASTM D 2216; used to estimate dry soil bulk
density
Soil organic carbon (foc)
Lab measurement
Nelson and Sommers (1982)
Soil pH
o
o
Field measurement
McLean (1982); used to select pH-specific
(ionizable organics) and Kj (metals)
Moisture retention exponent (b)
o
o
Look-up
Attachment A; used to calculate 0W
Saturated hydraulic conductivity
(Ks)
Avg. soil moisture content (0W)
o
o
Look-up
Attachment A; used to calculate 0W
Calculated
Attachment A
Meteorological Data
Air dispersion factor (Q/C)
Q/C table (Table 5)
Select value corresponding to source area,
climatic zone, and city with conditions similar to
site
Hydrogeologic Characteristics (DAF)
Hydrogeologic setting
Infiltration/recharge (I)
Hydraulic conductivity (K)
O
Hydraulic gradient (i)
Aquifer thickness (d)
Conceptual site
model
HELP model;
Regional estimates
Field measurement;
Regional estimates
Field measurement;
Regional estimates
Field measurement;
Regional estimates
Place site in hydrogeologic setting from Aller et
al. (1987) for estimation of parameters below
(see Attachment A)
HELP (Schroeder et al., 1984) may be used for
site-specific infiltration estimates; recharge
estimates also may be taken from Aller et al.
(1987) or may be estimated from knowledge of
local meteorologic and hydrogeologic conditions
Aquifer tests (i.e., pump tests, slug tests)
preferred; estimates also may be taken from
Aller et al. (1987) or Newell et al. (1990) or may
be estimated from knowledge of local
hydrogeologic conditions
Measured on map of site's water table
(preferred); estimates also may be taken from
Newell et al. (1990) or may be estimated from
knowledge of local hydrogeologic conditions
Site-specific measurement (i.e., from soil boring
logs) preferred; estimates also may be taken
from Newell et al. (1990) or may be estimated
from knowledge of local hydrogeologic conditions
9 Indicates parameters used in the SSL equations.
O Indicates parameters/assumptions needed to estimate SSL equation parameters.
25
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Equation 8: Derivation of the
Volatilization
Factor
VF (m3/kg) = Q/C x (3.14 x DA x T) 1'2
x 10"4 (m2/cm2)
(2 x pb x Da)
where
Da= [(9a10/3 D, H' + 6wiฐ/3 Dw)/n2]
H'
Parameter/Definition (units)
Default
VF/volatilization factor (m3/kg)
Da /apparent diffusivity (cm2/s)
-
Q/C/inverse of the mean
68.81
conc. at the center of a
0.5-acre-square source
(g/m2-s per kg/m3)
T/exposure interval (s)
9.5 x 108
pb/dry soil bulk density
1.5
(g/cm3)
6a /air-filled soil porosity (Lai/Lsoi|)
n"ew
n/total soil porosity (Lpore/Lsoi|)
1-fPb/Ps)
0w/water-filled soil porosity
0.15
C-water"-SOil)
ps /soil particle density (g/cm3)
2.65
Dj /diffusivity in air (cm2/s)
chemical-specific3
H'/dimensionless Henry's law
chemical-specific3
constant
Dw /diffusivity in water (cm2/s)
chemical-specific3
Kd /soil-water partition coefficient
chemical-specific3
(cm3/g) = Koc foc (organics)
Koc /soil organic carbon partition
chemical-specific3
coefficient (cm3/g)
foc/fraction organic carbon in
0.006 (0.6%)
soil (g/g)
aSee Attachment C.
Among the soil parameters used in Equation 8,
annual average water-filled soil porosity (0W) has the
most significant effect on air-filled soil porosity (0a)
and hence volatile contaminant emissions.
Sensitivity analyses have shown that soil bulk
density (pi-,) has too limited a range for surface soils
(generally between 1.3 and 1.7 g/cm3) to affect
results with nearly the significance of soil moisture
content (U.S. EPA, 1996).
Dispersion Model (Q/C). The box model in RAGS
HHEM, Part B has been replaced with a Q/C term
derived from the modeling exercise using the AREA-
ST model incorporated into EPA's Industrial Source
Complex Model (ISC2) platform. The AREA-ST
model was run with a full year of meteorological
data for 29 U.S. locations selected to be
representative of a range of meteorologic conditions
across the Nation (EQ, 1993). The results of these
modeling runs are presented in Exhibit 11 for square
area sources of 0.5 to 30 acres in size. When
developing a site-specific VF for the inhalation
pathway, place the site into a climatic zone (see
Attachment B). Then select a Q/C value from
Exhibit 11 that best represents a site's size and
meteorological conditions.
Soil Saturation Limit (Csat). The soil saturation limit
(Equation 9) is the contaminant concentration at
which soil pore air and pore water are saturated with
the chemical and the adsorptive limits of the soil
particles have been reached. Above this
concentration, the contaminant may be present in
free phase. Csat concentrations represent an upper
limit to the applicability of the SSL VF model
because a basic principle of the model (Flenry's law)
does not apply when contaminants are present in
free phase. VF-based inhalation SSLs are reliable
only if they are at or below Csat.
Equation 9 is used to calculate the soil saturation
limit for each organic chemical in site soils. As an
update to RAGS FIFIEM, Part B, this equation takes
into account the amount of contaminant that is in
the vapor phase in the pore spaces of the soil in
addition to the amount dissolved in the soil's pore
water and sorbed to soil particles. Csat values should
be calculated using the same site-specific soil
characteristics used to calculate SSLs (e.g., bulk
density, average water content, and organic carbon
content). Because VF-based SSLs are not accurate
for soil concentrations above Csat, these SSLs should
be compared to Csat concentrations before they are
used for soil screening.
26
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Exhibit 11. QIC Values by Source Area, City, and Climatic Zone
Zone I
Seattle
Salem
Zone II
Fresno
Los Angeles
San Francisco
Zone III
Las Vegas
Phoenix
Albuquerque
Zone IV
Boise
Winnemucca
Salt Lake City
Casper
Denver
Zone V
Bismark
Minneapolis
Lincoln
Zone VI
Little Rock
Houston
Atlanta
Charleston
Raleigh-Durham
Zone VII
Chicago
Cleveland
Huntington
Harrisburg
Zone VIII
Portland
Hartford
Philadelphia
Zone IX
Miami
QIC (g/m2-s per kg/m3)
0.5 Acre 1 Acre 2 Acre 5 Acre 10 Acre 30 Acre
82.72
73.44
62.00
68.81
89.51
95.55
64.04
84.18
69.41
69.23
78.09
100.13
75.59
83.39
90.80
81.64
73.63
79.25
77.08
74.89
77.26
97.78
83.22
53.89
81.90
74.23
71.35
90.24
85.61
72.62
64.42
54.37
60.24
78.51
83.87
56.07
73.82
60.88
60.67
68.47
87.87
66.27
73.07
79.68
71.47
64.51
69.47
67.56
65.65
67.75
85.81
73.06
47.24
71.87
65.01
62.55
79.14
74.97
64.38
57.09
48.16
53.30
69.55
74.38
49.59
65.40
53.94
53.72
60.66
77.91
58.68
64.71
70.64
63.22
57.10
61.53
59.83
58.13
60.01
76.08
64.78
41.83
63.72
57.52
55.40
70.14
66.33
55.66
49.33
41.57
45.93
60.03
64.32
42.72
56.47
46.57
46.35
52.37
67.34
50.64
55.82
61.03
54.47
49.23
53.11
51.62
50.17
51.78
65.75
55.99
36.10
55.07
49.57
47.83
60.59
57.17
50.09
44.37
37.36
41.24
53.95
57.90
38.35
50.77
41.87
41.65
47.08
60.59
45.52
50.16
54.90
48.89
44.19
47.74
46.37
45.08
46.51
59.16
50.38
32.43
49.56
44.49
43.00
54.50
51.33
42.86
37.94
31.90
35.15
46.03
49.56
32.68
43.37
35.75
35.55
40.20
51.80
38.87
42.79
46.92
41.65
37.64
40.76
39.54
38.48
39.64
50.60
43.08
27.67
42.40
37.88
36.73
46.59
43.74
27
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Equation 9: Derivation of the Soil Saturation
Limit
Csat = _i (KdPb + ew+H'6a)
Pb
Parameter/Definition (units) Default
Csa,/Sฐil saturation concentration
(mg/kg)
S/solubility in water (mg/L-water) chemical-specific3
pb/dry soil bulk density (kg/L) 1-5
Kd/soil-water partition coefficient
(L/kg)
Koc /soil organic carbon/water
partition coefficient (L/kg)
foc/fraction organic carbon in
soil (g/g)
0w/water-filled soil porosity
C-water"-SOil)
H'/dimensionless Henry's law
constant
0a/air-filled soil porosity (Lair/Lsoil)
n/total soil porosity (Lpore/Lsoi|)
ps /soil particle density (kg/L)
aSee Attachment C.
Csat values represent chemical-physical limits in soil
and are not risk based. However, since they
represent the concentration at which soil pore air is
saturated with a contaminant, volatile emissions
reach their maximum at Csat. In other words, at Csat
the emission flux from soil to air for a chemical
reaches a plateau. Volatile emissions will not
increase above this level no matter how much more
chemical is added to the soil. Chemicals with VF-
based SSLs above Csat are not likely to present a
significant volatile inhalation risk at any soil
concentration. To illustrate this point, the TDB
presents an analysis of the inhalation risk levels at
Csat for a number of chemicals commonly found at
Superfimd sites whose generic SSLs (calculated using
the default parameters shown in Equation 9) are
above Csat.
The analysis indicates that these Csat values are all
well below the screening risk targets of a 10-6 cancer
risk or an HQ of 1.
Although the inhalation risks appear to be
negligible, Csat does indicate a potential for
nonaqueous phase liquid (NAPL) to be present in
soil and a possible risk to ground water. Thus, EPA
believes that further investigation is warranted.
Table C-3 (Attachment C) provides the physical
state, liquid or solid, of various compounds at
ambient soil temperature. When an inhalation SSL
exceeds Csat for compounds that are liquid at
ambient soil temperature, the SSL is set at Csat.
Where soil concentrations exceed a Csat-based SSL,
site managers should refer to EPA's guidance,
Estimating the Potential for Occurrence of DNAPL
at Superfiind Sites (U.S. EPA, 1992c) for further
information on determining the likelihood of dense
nonaqueous phase liquid (DNAPL) in the subsurface.
Note that free-phase contaminants may be present
at concentrations below Csat if multiple organic
contaminants are present. The DNAPL guidance
(U.S. EPA, 1992c) also provides tools for evaluating
the potential for such multiple component mixtures
in soil.
For organic compounds that are solid at ambient soil
temperature, concentrations above Csat do not pose
a significant inhalation risk or a potential for NAPL
occurrence. Thus, soil screening decisions should be
based on the appropriate SSL for other site
pathways (e.g., migration to ground water, direct
ingestion).
Migration to Ground Water SSLs. The Soil
Screening Guidance uses a simple linear equilibrium
soil/water partition equation or a leach test to
estimate contaminant release in soil leachate. It also
uses a simple water-balance equation to calculate a
dilution factor to account for reduction of soil
leachate concentration from mixing in an aquifer.
The methodology for developing SSLs for the migra-
tion to ground water pathway was designed for use
during the early stages of a site evaluation when
information about subsurface conditions may be
limited. Hence, the methodology is based on rather
conservative, simplified assumptions about the
release and transport of contaminants in the
Koc x foc (chemical-
specific3)
chemical-specific3
0.006 (0.6%)
0.15
chemical-specific3
1-(Pb/Ps)
2.65
28
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subsurface (Exhibit 12). These assumptions are
inherent in the SSL equations and should be reviewed
for consistency with the conceptual site model (see
Step 2) to determine the applicability of SSLs to the
migration to ground water pathway.
Exhibit 12: Simplifying Assumptions for
the SSL Migration to Ground Water
Pathway
Infinite source (i.e., steady-state
concentrations are maintained over the
exposure period)
Uniformly distributed contamination from the
surface to the top of the aquifer
No contaminant attenuation (i.e., adsorption,
biodegradation, chemical degradation) in soil
Instantaneous and linear equilibrium soil/water
partitioning
Unconfined, unconsolidated aquifer with
homogeneous and isotropic hydrologic
properties
Receptor well at the downgradient edge of the
source and screened within the plume
No contaminant attenuation in the aquifer
No NAPLs present (if NAPLs are present, the
SSLs do not apply).
To calculate SSLs for the migration to ground water
pathway, multiply the acceptable ground water
concentration by the dilution factor to obtain a
target soil leachate concentration. For example, if
the dilution factor is 10 and the acceptable ground
water concentration is 0.05 mg/L, the target
soil/water leachate concentration would be 0.5 mg/L.
Next, the partition equation is used to calculate the
total soil concentration (i.e., SSL) corresponding to
this soil leachate concentration. Alternatively, if a
leach test is used, compare the target soil leachate
concentration to extract concentrations from the
leach tests.
Equation 10: Soil Screening Level
Partitioning Equation for
Migration to Ground Water
Screening Level
in Soil (mg/kg) = Cw [ Kj + (6W + 6a H')]
Pb
Parameter/Definition (units)
Default
Cw/target soil leachate concentration
nonzero MCLG,
(mg/L)
MCL, or HBLa x
dilution factor
Kd/soil-water partition coefficient
chemical-specificb
(L/kg)
Koc /soil organic carbon/water
Koc x foc (organics)
partition coefficient (L/kg)
chemical-specificb
foc /fraction organic carbon in
0.002 (0.2%)
soil (g/g)
0w/water-filled soil porosity
0.3
C-water"-soil)
6a/air-filled soil porosity (Lair/Lsoil)
n"ew
pb/dry soil bulk density (kg/L)
1.5
n/soil porosity (Lpore/Lsoil)
HPb/Ps)
ps/soil particle density (kg/L)
2.65
H'/dimensionless Henry's law
chemical-specificb
constant
(assume to be zero
for inorganic con-
taminants except
mercury)
aChemical-specific (see Attachment D).
bSee Attachment C.
Soil/Water Partition Equation. The soil/water
partition equation (Equation 10) relates
concentrations of contaminants adsorbed to soil
organic carbon to soil leachate concentrations in the
zone of contamination. It calculates SSLs
corresponding to target soil leachate contaminant
concentrations (Cw). An adjustment has been added
to the equation to relate sorbed concentration in
soil to the measured total soil concentration. This
adjustment assumes that soil-water, solids, and gas
are conserved during sampling. If soil gas is lost
during sampling, 9a should be assumed to be zero.
Likewise, for inorganic contaminants except
29
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mercury, there is no significant vapor pressure and
H' may be assumed to be zero.
The use of the soil/water partition equation to
calculate SSLs assumes an infinite source of
contaminants extending to the top of the aquifer.
More detailed models may be used to calculate
higher SSLs that are still protective in some
situations. For example, contaminants at sites with
shallow sources, thick unsaturated zones, degradable
contaminants, or unsaturated zone characteristics
(e.g., clay layers) may attenuate before they reach
ground water. The TBD provides information on
the use of unsaturated zone models for soil
screening. The decision to use such models should be
based on balancing the additional investigative and
modeling costs required to apply the more complex
models against the cost savings that will result from
higher SSLs.
Leach Test. A leach test may be used instead of the
soil/water partition equation. In some instances, a
leach test may be more useful than the partitioning
method, depending on the constituents of concern
and the possible presence of RCRA wastes. If this
option is chosen, soil parameters are not needed for
this pathway. However, a dilution factor must still
be calculated. This guidance suggests using the EPA
Synthetic Precipitation Leaching Procedure (SPLP,
EPA SW-846 Method 1312, U.S. EPA, 1994d). 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, apply the
SPLP with discretion.
EPA is aware that many leach tests are available for
application at hazardous waste sites, some of which
may be appropriate in specific situations (e.g., the
Toxicity Characteristic Leaching Procedure (TCLP)
models leaching in a municipal landfill
environment). It is beyond the scope of this
document to discuss in detail leaching procedures and
the appropriateness of their use.
Stabilization/Solidification of CERCLA and RCRA
Wastes (U.S. EPA, 1989b) and the EPA SAB's
review of leaching tests (U.S. EPA, 1991b) discuss
the application of various leach tests to various
waste disposal scenarios. Consult these documents
for further information.
See Step 3 for guidance on collecting subsurface soil
samples that can be used for leach tests. To ensure
adequate precision of leach test results, leach tests
should be conducted in triplicate.
Dilution Factor Model. As soil leachate moves
through soil and ground water, contaminant
concentrations are attenuated by adsorption and
degradation. In the aquifer, dilution by clean ground
water further reduces concentrations before
contaminants reach receptor points (i.e., drinking
water wells). This reduction in concentration can be
expressed by a dilution attenuation factor (DAF),
defined as the ratio of soil leachate concentration to
receptor point concentration. The lowest possible
DAF is 1, corresponding to the situation where there
is no dilution or attenuation of a contaminant (i.e.,
when the concentration in the receptor well is equal
to the soil leachate concentration). On the other
hand, high DAF values correspond to a large
reduction in contaminant concentration from the
contaminated soil to the receptor well.
The Soil Screening Guidance addresses only one of
these dilution-attenuation processes: contaminant
dilution in ground water. A simple mixing zone
equation derived from a water-balance relationship
(Equation 11) is used to calculate a site-specific
dilution factor. Mixing-zone depth is estimated from
Equation 12, which relates it to aquifer thickness
along with the other parameters from Equation 11.
Mixing zone depth should not exceed aquifer
thickness (i.e., use aquifer thickness as the upper
limit for mixing zone depth).
Because of the uncertainty resulting from the wide
variability in subsurface conditions that affect
contaminant migration in ground water, defaults are
not provided for the dilution model equations.
Instead, a default DAF of 20 has been selected as
protective for contaminated soil sources up to 0.5
acre in size. Analyses using the mass-limit models
described below suggest that a DAF of 20 may be
protective of larger sources as well; however, this
hypothesis should be evaluated on a site-specific
basis. A discussion of the basis for the default DAF
and a description of the mass-limit analysis is found
in the TBD. However, since migration to ground
30
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water SSLs are most sensitive to the DAF, site-
specific dilution factors should be calculated.
Equation 11: Derivation of Dilution Factor
dilution factor = 1 + Kid
1l
Parameter/Definition (units)
Default
dilution factor (unitless)
K/aquifer hydraulic
conductivity (m/yr)
i/hydraulic gradient (m/m)
l/infiltration rate (m/yr)
d/mixing zone depth (m)
L/source length parallel to
ground water flow (m)
20 (0.5-acre
source)
Equation 12: Estimation of Mixing Zone Depth
d = (0.0112 L2)0-5 + da {1 - exp[(-LI)/(Kida)]}
Parameter/Definition (units)
d/mixing zone depth (m)
L/source length parallel to ground water
flow (m)
l/infiltration rate (m/yr)
K/aquifer hydraulic conductivity (m/yr)
i/hydraulic gradient (m/m)
da/aquifer thickness (m)
Mass-Limit SSLs. Use of infinite source models to
estimate volatilization and migration to ground
water can violate mass balance considerations,
especially for small sources. To address this concern,
the Soil Screening Guidance includes models for
calculating mass-limit SSLs for each of these
pathways (Equations 13 and 14) that provide a
lower limit to SSLs when the area and depth
(i.e., volume) of the source are known or can
be estimated reliably.
A mass-limit SSL represents the level of
contaminant in the subsurface that is still protective
when the entire volume of contamination either
volatilizes or leaches over the 30-year exposure
duration and the level of contaminant at the
receptor does not exceed the health-based limit.
To use mass-limit SSLs, determine the area and
depth of the source, calculate both standard and
mass-limit SSLs, compare them for each chemical of
concern and select the higher of the two values.
Analyze the inhalation and migration to ground
water pathways separately.
Equation 13: Mass-Limit Volatilization Factor
VF = Q/C x [ T x (3.15 x 107 s/yr) ]
(pbxdsx 106 g/Mg)
Parameter/Definition (units)
Default
ds/average source depth (m)
site-specific
T/exposure interval(yr)
30
Q/C/inverse of mean conc. at
center of a square source
(g/m2-s per kg/m3)
68.81
pb/dry soil bulk density (kg/L
or Mg/m3)
1.5
Equation 14: Mass-Limit Soil Screening Level
for Migration to Ground Water
Screening Level
in Soil = (Cw x
I x ED)
(mg/kg) pb x ds
Parameter/Definition (units)
Default
Cw/target soil leachate concentration
(mg/L)
(nonzero MCLG,
MCL, or HBL)a x
dilution factor
ds/depth of source (m)
site-specific
l/infiltration rate (m/yr)
0.18
ED/exposure duration (yr)
70
pb/dry soil bulk density (kg/L)
1.5
aChemical-specific, see Attachment D.
Note that Equations 13 and 14 require a site-specific
determination of the average depth of
contamination in the source. Step 3 provides
guidance for conducting subsurface sampling to
determine source depth. Where the actual average
depth of contamination is uncertain, a conservative
estimate should be used (e.g., the maximum possible
depth in the unsaturated zone). At many sites, the
average water table depth may be used unless there is
reason to believe that contamination extends below
the water table. In this case SSLs do not apply and
31
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further investigation of the source in question is
needed.
Plant Uptake. Consumption of garden fruits and
vegetables grown in contaminated residential soils
can result in a risk to human health. This exposure
pathway applies to both surface and subsurface soils.
The TBD includes an evaluation of the soil-plant-
human pathway along with a discussion of the site-
specific factors that influence plant uptake and
plant contamination concentration. Generic
screening levels are calculated for arsenic, cadmium,
mercury, nickel, selenium, and zinc based on
empirical data on the uptake (i.e., bioconcentration)
of these inorganics into plants. In addition, levels of
inorganics that have been reported to cause
phytotoxicity (Will and Suter, 1994) are presented.
Organic compounds are not addressed due to lack of
empirical data.
The empirical data indicate that site-specific factors
such as soil type, pH, plant type, and chemical form
strongly influence the uptake of metals into plants.
Where site conditions allow for the mobility and
bioavailability of metals, the results of our generic
analysis suggest that the soil-plant-human pathway
may be of particular concern for sites with soils
contaminated with cadmium and arsenic. However,
the phytotoxicity of certain metals may limit the
amount that can be bioconcentrated in plant tissues.
The data on phytotoxicity suggest that, with the
exception of arsenic, metal concentrations in soil
that are considered toxic to plants are well below the
levels that may impact human health through the
soil-plant-human pathway. This implies that
phytotoxic effects may prevent completion of this
pathway for these metals. However, like plant
uptake, phytotoxicity is also greatly influenced by
the site-specific factors mentioned above. Thus, it is
necessary to evaluate on a site-specific basis, the
potential bioavailability of certain inorganics for the
soil-plant-human pathway and the potential for
phytotoxic effects in order to assess possible human
health and ecological impacts through plant uptake.
2.5.3 Address Exposure to Multiple
Chemicals. The SSLs generally correspond to a
lO6 risk level for carcinogens and a hazard quotient
of 1 for noncarcinogens. This "target" hazard
quotient is used to calculate a soil concentration
below which it is unlikely that sensitive populations
will 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 lO6 risk level for individual
chemicals and pathways generally will lead to
cumulative site risks within the lO4 to lO6 risk
range for the combinations of chemicals typically
found at NPL sites.
For noncarcinogens, there is no widely accepted risk
range, and EPA recognizes that cumulative risks
from noncarcinogenic contaminants at a site could
exceed the target hazard quotient. However, EPA
also recognizes that noncancer risks should be
added only for those chemicals with the same
toxic endpoint or mechanism of action.
Ideally, chemicals would be grouped according to
their exact mechanism of action, and effect-specific
toxicity criteria would be available for chemicals
exhibiting multiple effects. Instead, data are often
limited to gross toxicological effects in an organ
(e.g., increased liver weight) or an entire organ
system (e.g., neurotoxicity), and RfDs/reference
concentrations (RfCs) are available for just one of
the several possible endpoints of toxicity for a
chemical.
Given the currently available criteria,
noncarcinogenic contaminants should be grouped
according to the critical effect listed as the basis for
the RfD/RfC. If more than one chemical detected at
a site affects the same target organ/system, SSLs for
those chemicals should be divided by the number of
chemicals present in the group. Exhibit 13 lists
several chemicals with noncarcinogenic affects in
the same target organ/system. However, the list is
limited, and a toxicologist should be consulted prior
to using SSLs on a site-specific basis.
If additive risks are being considered in developing
site-specific SSLs for subsurface soils, recognize that,
for certain chemicals, SSLs may be based on a
"ceiling limit" concentration (Csat) instead of
toxicity. Because they are not risk-based, Csat-based
SSLs should not be modified to account for
additivity.
32
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2.6 Step 6: Comparing Site Soil
Contaminant
Concentrations to
Calculated SSLs
Now that the site-specific SSLs have been calculated
for the potential contaminants of concern, compare
them with the site contaminant concentrations. At
this point, it is reasonable to review the CSM with
the actual site data to confirm its accuracy and the
overall applicability of the Soil Screening Guidance.
In theory, an exposure area would be screened from
further investigation when the true mean of the
population of contaminant concentrations falls
below the established screening level. However,
EPA recognizes that data obtained from sampling
and analysis are never perfectly representative and
accurate, and that the cost of trying to achieve
perfect results would be quite high. Consequently,
EPA acknowledges that some uncertainty in data
must be tolerated, and focuses on controlling the
uncertainty which affects decisions based on those
data. Thus, in the Soil Screening Guidance, EPA has
developed an approach for surface soils to minimize
the chance of incorrectly deciding to:
Screen out areas when the correct decision
would be to investigate further (Type I error);
or
Decide to investigate further when the correct
decision would be to screen out the area (Type
II error).
The approach sets limits on the probabilities of
making such decision errors, and acknowledges that
there is a range (i.e., gray region) of contaminant
levels around the screening level where the
variability in the data will make it difficult to
determine whether the exposure area average
concentration is actually above or below the
screening level. The Type I and Type II decision
error rates have been set at 5 percent and 20
percent, respectively, and the gray region has been
set between one-half and two times the SSL. By
specifying the upper edge of the gray region as twice
the SSL, it is possible that exposure areas with mean
contaminant concentration values slightly above the
SSL may be screened from further study.
Commenters have expressed concern that this is not
adequately protective for SSLs based on
noncarcinogenic effects. However, EPA believes
that the approaches taken in this guidance to address
chronic exposure to noncarcinogens are
conservative enough for the majority of site
contaminants (i.e., comparison of the 6 year
"childhood only" exposure to the chronic RfD);
and, use of maximum composite concentrations
provide high coverage of the true population mean
(i.e., there is high probability that the value equals
or exceeds the true population mean).
Thus, for surface soils, the contaminant
concentrations in each composite sample from an
exposure area are compared to two times the SSL.
Under the Soil Screening Guidance DQOs, areas are
screened out from further study when contaminant
concentrations in all of the composite samples are
less than two times the SSLs. Use of this decision
rule (comparing contaminant concentrations to
twice the SSL) is appropriate only when the quantity
and quality of data are comparable to the levels
discussed in this guidance, and the toxicity of the
chemical has been evaluated against the criteria
presented in Section 2.5.1.
For existing data sets that may be more limited than
those discussed in this guidance, the 95 percent
upper-confidence limit on the arithmetic mean of
contaminant concentrations in surface soils (i.e., the
Land method as described in the Supplemental
Guidance to RAGS: Calculating the Concentration
Term (U.S. EPA, 1992d) should be used for
comparison to the SSLs. The TBD discusses the
strengths and weaknesses of using the Land method
for making screening decisions.
33
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Exhibit 13: SSL Chemicals with
Noncarcinogenic Toxic Effects on Specific Target
Organ/System
Target Organ/System
Effect
Kidney
Acetone
Increased weight; nephrotoxicity
1,1-Dichloroethane
Kidney damage
Cadmium
Significant proteinuria
Chlorobenzene
Kidney effects
Di-n-octyl phthalate
Kidney effects
Endosulfan
Glomerulonephrosis
Ethylbenzene
Kidney toxicity
Fluoranthene
Nephropathy
Nitrobenzene
Renal and adrenal lesions
Pyrene
Kidney effects
Toluene
Changes in kidney weights
2,4,5-Trichlorophenol
Pathology
Vinyl acetate
Altered kidney weight
Liver
Acenaphthene
Hepatotoxicity
Acetone
Increased weight
Butyl benzyl phthalate
Increased liver-to-body weight and liver-to-brain weight ratios
Chlorobenzene
Histopathology
Di-n-octyl phthalate
Increased weight; increased SGOT and SGPT activity
Endrin
Mild histological lesions in liver
Ethylbenzene
Liver toxicity
Flouranthene
Increased liver weight
Nitrobenzene
Lesions
Styrene
Liver effects
Toluene
Changes in liver weights
2,4,5-Trichlorophenol
Pathology
Central Nervous System
Butanol
Hypoactivity and ataxia
Cyanide (amenable)
Weight loss, myelin degeneration
2,4 Dimethylphenol
Prostatration and ataxia
Endrin
Occasional convulsions
2-Methylphenol
Neurotoxicity
Mercury
Hand tremor, memory disturbances
Styrene
Neurotoxicity
Xylenes
Hyperactivity
Adrenal Gland
Nitrobenzene
Adrenal lesions
1,2,4-Trichlorobenzene
Increased adrenal weights; vacuolization in cortex
34
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Exhibit 13: (continued)
Target Organ/System
Effect
Circulatory System
Antimony
Altered blood chemistry and myocardial effects
Barium
Increased blood pressure
trans-1,2-Dichloroethene
Increased alkaline phosphatase level
c/s-1,2-Dichloroethylene
Decreased hematocrit and hemoglobin
2,4-Dimethylphenol
Altered blood chemistry
Fluoranthene
Hematologic changes
Fluorene
Decreased RBC and hemoglobin
Nitrobenzene
Hematologic changes
Styrene
Red blood cell effects
Zinc
Decrease in erythrocyte superoxide dismutase (ESOD)
Reproductive System
Barium
Fetotoxicity
Carbon disulfide
Fetal toxicity and malformations
2-Chlorophenol
Reproductive effects
Methoxychlor
Excessive loss of litters
Phenol
Reduced fetal body weight in rats
Respiratory System
1,2-Dichloropropane
Hyperplasia of the nasal mucosa
Hexachlorocyclopentadiene
Squamous metaplasia
Methyl bromide
Lesions on the olfactory epithelium of the nasal cavity
Vinyl acetate
Nasal epithelial lesions
Gastrointestinal System
Hexachlorocyclopentadiene
Stomach lesions
Methyl bromide
Epithelial hyperplasia of the forestomach
Immune System
2,4-Dichlorophenol
Altered immune function
p-Chloroaniline
Nonneoplastic lesions of splenic capsule
Source: U.S. EPA, 1995b, U.S. EPA, 1995a
35
-------
In this guidance, fewer samples are collected for
subsurface soils than for surface soils; therefore,
different decision rules apply.
Since subsurface soils are not characterized as well,
there is less confidence that the concentrations
measured are representative of the entire source.
Thus, a more conservative approach to screening is
warranted. Because it may not be protective to allow
for comparison to values above the SSL, mean
contaminant concentrations from each soil boring
taken in a source area are compared with the
calculated SSLs. Source areas with any mean soil
boring contaminant concentration greater than the
SSLs generally warrant further consideration. On the
other hand, where the mean soil boring contaminant
concentrations within a source are all less than the
SSLs, that source area is generally screened out.
2.7 Step 7: Addressing Areas
Identified for Further
Study
The chemicals, exposure pathways, and areas that
have been identified for further study become a
subject of the RI/FS. The results of the baseline risk
assessment conducted as part of the RI/FS will
establish the basis for taking remedial action. The
threshold for taking action differs from the criteria
used for screening. As outlined in Role of the
Baseline Risk Assessment in Superfund Remedy
Selection Decisions (U.S. EPA, 1991 d), remedial
action at NPL sites is generally warranted where
cumulative risks for current or future land use exceed
lxlO"4 for carcinogens or a HQ of 1 for
noncarcinogens. The data collected for soil
screening are useful in the RI and baseline risk
assessment. However, additional data will probably
need to be collected during future site investigations.
Once the decision has been made to initiate remedial
action, the SSLs can then serve as preliminary
remediation goals. This process is referenced in
Section 1.2 of this document.
FOR FURTHER INFORMATION
More detailed discussions of the technical
background and assumptions supporting the
development of the Soil Screening Guidance are
presented in the Soil Screening Guidance: Technical
Background Document (U.S. EPA, 1996). For
additional copies of this guidance document, the
Technical Background Document, or other EPA
documents, call the National Technical Information
Service (NTIS) at (703) 487-4650 or 1-800-553-
NTIS (6847).
36
-------
REFERENCES
Aller, L., T. Bennett, J.H. Lehr, R.J. Petty, and G.
Hackett. 1987. DRASTIC: A Standardized
System for Evaluating Ground Water Pollution
Potential Using Hydrogeologic Settings.
Prepared for U.S. EPA, Office of Research and
Development, Ada, OK. National Water Well
Association, Dublin, OH. EPA-600/2-87-035.
American Society for Testing Materials. 1995.
Annual Book of ASTM Standards. Volume
4.08. Soil and Rock Building Stones.
Philadelphia, PA.
Brady, N.C. 1990. The Nature and Properties of
Soz/s.Macmillan Publishing Company, New
York, NY.
Calabrese, E.J., H. Pastides, R. Barnes, et al. 1989.
How much soil do young children ingest: an
epidemiologic study. Petroleum Contaminated
Soils, Vol. 2. E.J. Calabrese and P.T. Kostecki,
eds. pp. 363-417. Lewis Publishers, Chelsea,
MI.
Cowherd, C., G. Muleski, P. Engelhart, and D.
Gillette. 1985. Rapid Assessment of Exposure
to Particulate Emissions from Surface
Contamination. Prepared for U.S. EPA, Office
of Health and Environmental Assessment,
Washington, DC. EPA/600/8-85/002. NTIS
PB85-192219 7AS.
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.
Arch. Environ. Health 45:112-122.
Dragun, J. 1988. The Soil Chemistry of Hazardous
Materials. Hazardous Materials Control
Research Institute, Silver Spring, MD.
EQ (Environmental Quality Management). 1993.
Evaluation of the Dispersion Equations in the
Risk Assessment Guidance for Superfund
(RAGS): Volume IHuman Health Evaluation
Manual (Part B, Development of Preliminary
Remediation Goals). Contract No. 68-02-
D120. Prepared for Office of Emergency and
Remedial Response, Washington, DC.
Gee, G.W., and J.W. Bauder. 1986. Particle size
analysis. A. Klute (ed.), Methods of Soil
Analysis. Part 1. Physical and Mineralogical
Methods. 2nd Edition, 9(1):383-411, American
Society of Agronomy, Madison, WI.
Hwang, S. T., and J. W. Falco. 1986. Estimation of
Multimedia Exposure Related to Hazardous
Waste Facilities. Y. Cohen, Ed. Plenum
Publishing.
Johnson, P.C. and R.A. Ettinger. 1991. Heuristic
model for predicting the intrusion rate of
contaminant vapors into buildings.
Environmental Science and Technology 25(8):
1445-1452.
Jury, W.A., W.J. Farmer, and W.F. Spencer. 1984.
Behavior assessment model for trace organics
in soil: II. Chemical classification and
parameter sensitivity. J. Environ. Qual.
13(4):567-572.
McLean, E.O. 1982. Soil pH and lime
requirement. In: A.L. Page (ed.), Methods of
Soil Analysis. Part 2. Chemical and
Microbiological Properties. 2nd Edition,
9(2): 199-224, American Society of Agronomy,
Madison, WI.
Nelson, D.W., and L.E. Sommers. 1982. Total
carbon, organic carbon, and organic matter. In:
A.L. Page (ed.), Methods of Soil Analysis. Part
2. Chemical and Microbiological Properties.
2nd Edition, 9(2):539-579, American Society
of Agronomy, Madison, WI.
Newell, C.J., L.P. Hopkins, and P.B. Bedient.
1990. A hydrogeologic database for ground
water modeling. Ground Water 28(5):703-714.
Schroeder, P.R., A.C. Gibson, and M.D. Smolen.
1984. Hydrological Evaluation of Landfill
Performance (HELP) Model; Volume 2:
Documentation for Version 1. EPA/530-SW-
84-010. Office of Research and Development,
37
-------
U.S. EPA, Cincinnati, OH. NTIS PB85-
100832.
U.S. EPA. 1980. Land Disposal of Hexachloro-
benzene Wastes Controlling Vapor Movement in
Soil. EPA-600/2-80-119 Office of Research
and Development, Cincinnati, OH. NTIS
PB80-216575.
U.S. EPA. 1988a. Guidance on Remedial Actions
for Contaminated Ground Water at Superfund
Sites. Office of Emergency and Remedial
Response, Washington, DC. Directive 9283.1-
2. EPA/5 40/G-8 8/003. NTIS PB89-
184618/CCE.
U.S. EPA. 1988b. Superfund Exposure Assessment
Manual. OSWER Directive 9285.5-1.Office of
Emergency and Remedial Response,
Washington, DC. EPA/540/1-88/001. NTIS
PB89-135859.
U.S. EPA. 1989a. Risk Assessment Guidance for
Superfund (RAGS): Volume 1: Human Health
Evaluation Manual (IIIIEM), Part A, Interim
Final. Office of Emergency and Remedial
Response, Washington, DC. EPA/540/1-
89/002. NTIS PB90-155581/CCE.
U.S. EPA. 1989b. Stabilization/Solidification of
CERCLA and RCRA Wastes. EPA/625/6-
89/022.
U.S. EPA. 1989c. Guidance for Conducting
Remedial Investigations and Feasibility Studies
under CERCLA. Office of Emergency and
Remedial Response, Washington, DC.
EPA/540/G-89/004. OSWER Directive 9355.3-
01. NTIS PB89-184626.
U.S. EPA. 1990a. Suggested ROD Language for
Various Ground Water Remediation Options.
Office of Emergency and Remedial Response,
Washington, DC. Directive 9283.1-03. NTIS
PB91-921325/CCE.
U.S. EPA. 1990b. Sampler's Guide to the Contact
Laboratory Program. Office of Emergency and
Remedial Response, Washington, DC. NTIS
PB91-921330CDH.
U.S. EPA 1990c. A Rationale for the Assessment
of Errors in the Sampling of Soils.
Environmental Monitoring Systems
Laboratory, Office of Research and
Development, Las Vegas, NV. EPA/600/4-
90/013. NTIS PB90-242306.
U.S. EPA. 1991a. Human Health Evaluation
Manual (HHEM), Supplemental Guidance:
Standard Default Exposure Factors. Office of
Emergency and Remedial Response,
Washington, DC. Publication 9285.6-03. NTIS
PB91-921314.
U.S. EPA. 1991b. Leachability Phenomena.
Recommendations and Rationale for Analysis
of Contaminant Release by the Environmental
Engineering Committee. Science Advisory
Board, Washington, DC. EPA-SAB-EEC-92-
003.
U.S. EPA. 1991c. Risk Assessment Guidance for
Superfund (RAGS), Volume 1: Human Health
Evaluation Manual (HHEM), Part B,
Development of Risk-Based Preliminary
Remediation Goals. Office of Emergency and
Remedial Response, Washington, DC.
Publication 9285.7-01B. NTIS PB92-963333.
U.S. EPA. 1991 d. Role of the Baseline Risk
Assessment in Superfund Remedy Selection
Decisions. Office of Emergency and Remedial
Response, Washington, DC. Publication
9355.0-30. NTIS PB91-921359/CCE.
U.S. EPA. 1991e. User's Guide to the Contract
Laboratory Program. Office of Emergency and
Remedial Response, Washington, DC. NTIS
PB91-921278CDH.
U.S. EPA, 199If. Description and Sampling of
Contaminated Soils: A Field Pocket Guide.
Office of Environmental Research
Information, Cincinnati, OH. EPA/625/12-
91/002.
U.S. EPA. 1992a. Considerations in Ground-
Water Remediation at Superfund Sites and
RCRA FacilitiesUpdate. Office of Emergency
and Remedial Response, Washington, DC.
Directive 9283.1-06. NTIS PB91-
238584/CCE.
U.S. EPA. 1992b. Dermal Exposure Assessment:
Principles and Applications. Interim Report.
Office of Research and Development,
Cincinnati, OH. EPA/600/8-91/01 IB.
38
-------
U.S. EPA. 1992c. Estimating Potential for
Occurrence of DNAPL at Superfund Sites.
Office of Emergency and Remedial Response,
Washington, DC. Publication 9355.4-07FS.
NTIS PB92-963338.
U.S. EPA. 1992d. Supplemental Guidance to
RAGS; Calculating the Concentration Term.
Volume 1, Number 1, Office of Emergency and
Remedial Response, Washington, DC. NTIS
PE92-963373
U.S. EPA. 1992e. Preparation of Soil Sampling
Protocols: Sampling Techniques and
Strategies. Office of Research and
Development, Washington, DC. EPA/600/R-
92/128.
U.S. EPA. 1993a. Data Quality Objectives for
Superfund: Interim Final Guidance.
Publication 9255.9-01. Office of Emergency
and Remedial Response, Washington, DC. EPA
540-R-93-071. NTIS PB94-963203.
U.S. EPA. 1993b. Guidance for Evaluating
Technical Impracticability of Ground-Water
Restoration. EPA/540-R-93-080. Office of
Emergency and Remedial Response,
Washington, DC. Directive 9234.2-25.
U.S. EPA. 1993c. Quality Assurance for
Superfund Environmental Data Collection
Activities. Quick Reference Fact Sheet. Office
of Emergency and Remedial Response,
Washington, DC. NTIS PB93-963273.
U.S. EPA 1993d. The Urban Soil Lead
Abatement Demonstration Project. Vol I:
Integrated Report Review Draft. National
Center for Environmental Publications and
Information. EPA 600/AP93001/A. NTIS
PB93-222-651.
U.S. EPA, 1993e. Subsurface Characterization
and Monitoring Techniques: A Desk Reference
Guide. Vol. I & II . Environmental Monitoring
Systems Laboratory, Office of Research and
Development, Las Vegas, NV. EPA/625/R-
93/003a.
U.S. EPA, 1993f. Risk Assessment Guidance for
Superfund (RAGS), Human Health Evaluation
Manual (HHEM). Science Advisory Board
Review of the Office of Solid Waste and
Emergency Response draft. Washington, DC.
EPA-SAB-EHC-93-007.
U.S. EPA. 1994a. Guidance for the Data Quality
Objectives Process. Quality Assurance
Management Staff, Office of Research and
Development, Washington, DC. EPA QA/G-4.
U.S. EPA. 1994c. Methods for Evaluating the
Attainment of Cleanup StandardsVolume 3:
Reference-Based Standards for Soils and Solid
Media. Environmental Statistics and
Information Division, Office of Policy,
Planning, and Evaluation, Washington, DC.
EPA 230-R-94-004.
U.S. EPA. 1994d. Test Methods for Evaluating
Solid Waste, Physical/Chemical Methods (SW-
846), Third Edition, Revision 2. Washington,
DC.
U.S. EPA. 1995a. Health Effects Assessment
Summary Tables (HEAST): Annual Update,
FY 1993. Environmental Criteria and
Assessment Office, Office of Health and
Environmental Assessment, Office of Research
and Development, Cincinnati, OH.
U.S. EPA. 1995b. Integrated Risk Information
System (IRIS). Cincinnati, OH.
U.S. EPA. 1995c. Drinking Water Regulations and
Health Advisories. Office of Water,
Washington, DC.
U.S. EPA. 1996. Soil Screening Guidance:
Technical Background Document. Office of
Emergency and Remedial Response,
Washington, DC. EPA/540/R95/128.
Van Wijnen, J.H., P. Clausing, and B. Brunekreef.
1990. Estimated soil ingestion by children.
Environ Research 51:147-162.
Wester et al. 1993. Percutaneous absorption of
pentachlorophenol from soil. Fundamentals of
Applied Toxicology, 20.
Will, M.E. and G.W. Suter II. 1994. Toxicological
Benchmarks for Screening Potential
Contaminants of Concern for Effects on
Terrestrial Plants, 1994 Revision. ES/ER/TM-
8/R1. Prepared for the U.S. Department of
Energy by the Environmental Sciences
Division of Oak Ridge National Laboratory.
39
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Attachment A
Conceptual Site Model Summary
-------
-------
Attachment A
Conceptual Site Model Summary
Step 1 of the Soil Screening Guidance: User's Guide describes the development of a conceptual site
model (CSM) to support the application of soil screening levels (SSLs) at a site. The CSM summary
forms at the end of this attachment contain the information necessary to:
Determine the applicability of SSLs to the site
Calculate SSLs.
By identifying data gaps, these summary forms will help focus data collection and evaluation on the
site-specific development and application of SSLs. The site investigator should use the summary
forms during the SSL sampling effort to collect site-specific data and continually update the CSM
with new information as appropriate.
The CSM summary forms indicate the information required for determining the applicability of the
soil screening process to the site. Forms addressing source characteristics may be photocopied if more
than one source is present at a site.
A site map showing contaminated soil sources and exposure areas (EAs) should be attached to the
summary. If available, additional pages of other maps, summaries of analytical results, or more
detailed descriptions of the site may be attached to the summary.
Form 1. General Site Information
The information included in this form is identical to the first page of the Site Inspection (SI) Data
Summary form (page B-3 in Guidance for Performing Site Inspections Under CERCLA, U.S. EPA,
1992). However, the form should be updated to reflect any site activities conducted since the SI was
completed.
Form 2. Site Characteristics
Form 2 indicates the information necessary to address the migration to ground water pathway and
identify subsurface conditions that may limit the applicability of subsurface SSLs.
A hydrogeologic setting is defined as a unit with common hydrogeologic characteristics and therefore
common vulnerability to contamination. Each setting provides a composite description of the
hydrogeologic factors that control ground water movement and recharge. These factors can be used
to make generalizations in the CSM about ground water conditions.
After placing the site into one of Heath's ground water regions (Heath, 1984), consider geologic and
geomorphic features of the site and select a generic hydrogeologic setting from Aller et al. (1987)
that is most similar to the site. If existing site information is not sufficient to definitively place the
site in a setting, it should be possible to narrow the choice to two or three settings that will reduce the
range of values necessary to develop SSLs. A copy of the setting diagram from Aller et al. (1987)
should be attached to the CSM checklist to provide a general picture of subsurface site conditions.
Ground Water Flow Direction. The direction of ground water flow in the uppermost aquifer
underlying each source is needed to determine source length parallel to that flow. If ground water flow
direction is unknown or uncertain, assume it is parallel to the longest source dimension.
A-l
-------
Aquifer Parameters. Aquifer parameters needed to estimate a site-specific dilution factor include
hydraulic conductivity (K), hydraulic gradient (i), and aquifer thickness (da). Site-measured values for
these parameters are the preferred alternative. Existing site documentation should be reviewed for in
situ measurements of aquifer conductivity (i.e., from pump test data), water table maps that can be
used to estimate hydraulic gradient, and boring logs that indicate the thickness of the uppermost
aquifer. Detailed information on conducting and interpreting aquifer tests can be found in Nielsen
(1991).
If site-measured values are not available, hydrogeologic knowledge of regional geologic conditions or
measured values in the literature may be sources of reasonable estimates. Values from a similar site in
the same region and hydrogeologic setting also may be used, but must be carefully reviewed to ensure
that the subsurface conceptual models for the two sites show reasonable agreement. For all of these
options, it is critical that the estimates and sources be reviewed by an experienced hydrogeologist
knowledgeable of regional hydrogeologic conditions.
A third option is to obtain parameter estimates for the site's hydrogeologic setting from Aller et al.
(1987) or from the American Petroleum Institute's (API's) hydrogeologic database (HGDB) (Newell
et al., 1989, 1990). Aller et al. (1987) present ranges of values for K and i by hydrogeologic setting.
The HGDB contains measured values for these parameters and aquifer depth for a number of sites in
each hydrogeologic setting. If HGDB data are used, the median value presented for each setting
should be used unless site-specific conditions indicate otherwise. Aquifer parameter values from these
sources also can serve as a check of the validity of site-measured values or estimates obtained from
other sources.
If outside sources such as Aller et al. (1987) are used to characterize site hydrogeologic conditions,
the appropriate references and diagrams should be attached to the CSM checklist.
Infiltration Rate. Infiltration rate is used to calculate SSLs for subsurface soils (see Step 5). The
simplest way to estimate infiltration rate (I) is to assume that infiltration is equal to recharge and
obtain recharge estimates for the site's hydrogeologic setting from Aller et al. (1987). When using
the Aller et al. (1987) estimates the user should recognize that these are estimates of average
recharge conditions throughout the setting and site-specific values may differ to some extent. For
example, areas within the setting with steeper than average slopes will tend to have lower infiltration
rates and areas with flatter than average slopes will tend to have higher infiltration than average. An
alternative is to use infiltration rates determined for a better-characterized site in the same
hydrogeologic setting and with similar meteorological conditions as the site in question.
A third alternative is use the HELP model. Although HELP was originally written for hydrologic
evaluation of landfills (Schroeder et al., 1984), inputs to the HELP program can be modified to
estimate infiltration in undisturbed soils in natural settings. The most recent version of HELP and
the most recent user's guide and documentation can be obtained by sending an address and two double-
sided, high-density, DOS-formatted disks to:
attn. Eunice Burk
U.S. EPA
5995 Center Hill Ave.
Cincinnati, OH 45224
(513) 569-7871.
A-2
-------
Meteorologic Parameters. Select a site-specific Q/C value from in the guidance for the
volatilization factor (VF) equation or particulate emission factor (PEF) equation to place the site in a
climatic zone (Figure A-l).
Several site-specific parameters are required to calculate a PEF if fugitive dusts are of concern at the
site (see Step 5 for surface soils). The threshold windspeed at 7 meters above ground surface (Uu7) is
calculated from source area roughness height and the mode soil aggregate size as described in Cowherd
et al. (1985). Mode soil aggregate size refers to the mode diameter of aggregated soil particles
measured under field conditions.
Other site-specific variables necessary for calculating the PEF include fraction vegetative cover (V)
and the mean annual windspeed (Um). Fraction vegetative cover is estimated by visual observations of
the surface of known or suspected source areas at the site. Mean annual windspeed can be obtained
from the National Weather Service surface station nearest to the site.
Form 3. Exposure Pathways and Receptors
Form 3 includes information necessary to determine the applicability of the Soil Screening Guidance
to a site (see Step 2 of the User's Guide). This form summarizes the site information necessary to
identify and characterize potential exposure pathways and receptors at the site, such as site
conditions, relevant exposure scenarios, and the properties of soil contaminants listed on Form 4.
Table A-l provides an example of exposure pathways that are not addressed by the guidance, but
have relevance to CSM development.
Table A-1. Example Identification of Exposure Pathways Not Addressed by SSLs
Receptors/
Exposure Pathways
Contaminant
Characteristics
Site Conditions
Human /Direct Pathways
ingestion
(acute exposure)
acute health effects
(e.g., cyanide, phenol)
residential setting
inhalation - fugitive dusts (acute
exposure)
acute health effects
high fugitive dusts (e.g., from soil
tillage, heavy traffic on dirt roads;
construction)
Human /Indirect Pathways
consumption of meat or dairy
products
bioaccumulation,
biomagnification
nearby meat or dairy production
fish consumption
biomagnification
nearby surface waters with
recreational or subsistence fishing
Ecological Pathways
aquatic
aquatic toxicity
nearby surface waters or wetlands
terrestrial
toxicity to terrestrial
organisms (e.g., DDT, Hg)
sensitive species on or near site
A-3
-------
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3
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-------
Form 4. Soil Contaminant Source Characteristics
This form prompts the investigator to provide information on source characteristics, including soil
contaminant levels and the physical and chemical parameters of site soils needed to calculate SSLs.
One form should be completed for each contaminated soil source. Initially, the form should be filled
out to the greatest extent possible with existing site information collected during CSM development
(see Step 1 of the User's Guide). The forms should be updated after the SSL sampling effort is
complete.
Measurement of contaminant levels and the soil parameters listed on this form is described in Step 3
of this guidance.
Average soil moisture content (0W) defines the fraction of total soil porosity that is filled by
water and air. These parameters are necessary for determining the volatilization factor (VF) and the
soil saturation limit (Csat) and to apply the soil/water partition equation. It is important that the
moisture content used to calculate these parameters represent the annual average soil moisture
conditions. Moisture content measurements on discrete soil samples should not be used because they
are affected by preceding rainfall events and thus may not represent average conditions. Volumetric
average soil water content may be estimated by the following relationship developed by Clapp and
Hornberger (1978) and presented in the Superfund Exposure Assessment Manual (U.S. EPA, 1988):
0W = n (I/Ks) l/(2b+3)
where
n = total soil porosity (Lpore/Lsoji)
I = infiltration rate (m/yr)
Ks = saturated hydraulic conductivity (m/yr)
b = soil-specific exponential parameter (unitless).
Total soil porosity (n) is estimated from dry soil bulk density (pb) as follows:
n = 1 - (pb/ps)
where
ps = soil particle density = 2.65 kg/L.
Values for Ks and the exponential term l/(2b+3) are shown in Table A-2 by soil texture class (soil
class determination is discussed under Step 3).
Site-specific values for infiltration rate (I) may be estimated using the HELP model or may be
assumed to be equivalent to recharge (see Form 2).
A-5
-------
Table A-2. Parameter Estimates for Calculating Average Soil
Moisture Content (6W)
Soil texture
Ks(m/yr)
1/(2b+3)
Sand
Loamy sand
Sandy loam
Silt loam
Loam
Sandy clay loam
Silt clay loam
Clay loam
Sandy clay
Silt clay
Clay
540
230
120
60
40
13
20
10
8
5
1,830
0.090
0.085
0.080
0.074
0.073
0.058
0.054
0.050
0.042
0.042
0.039
Source: U.S. EPA, 1988.
Worksheets
The worksheets following Forms 1 through 4 provide a convenient means of assembling chemical-
specific parameters necessary to calculate SSLs for the contaminants of concern (Worksheet 1),
existing site data on contaminant concentrations collected during CSM development or the SSL
sampling effort (Worksheet 2), and SSLs calculated for EAs (Worksheet 3) or contaminant sources
(Worksheet 4) of concern at the site.
CSM Diagram
The CSM diagram is a product of CSM development that represents the linkages among contaminant
sources, release mechanisms, exposure pathways and routes, and receptors to summarize the current
understanding of the soil contamination problem (see Step 1 of the guidance). An example SSL CSM
diagram, Figure A-2 (U.S. EPA, 1989), and a site sketch, Figure A-3 (U.S. EPA, 1987) are provided
following the Worksheets.
A-6
-------
References
Aller, L., T. Bennett, J.H. Lehr, R.J. Petty, and G. Hackett. 1987. DRASTIC: A Standardized System
for Evaluating Ground Water Pollution Potential Using Hydrogeologic Settings. Prepared for
U.S. EPA Office of Research and Development, Ada, OK. National Water Well Association,
Dublin, OH. EPA-600/2-87-035.
Clapp, R.B., and G.M. Hornberger. 1978. Empirical equations for some soil hydraulic properties.
Water Resources Research, 14:601-604.
Cowherd, C., G. Muleski, P. Engelhart, and D. Gillette. 1985. Rapid Assessment of Exposure to
Particulate Emissions from Surface Contamination. Prepared for Office of Health and
Environmental Assessment, U.S. EPA, Washington, DC. NTIS PB85-192219 7AS.
EPA/600/8-85/002.
Heath, R.C. 1984. Ground-Water Regions of the United States. USGS Water Supply Paper 2242. U.S.
Geological Survey, Reston, VA.
Newell, C.J., L.P. Hopkins, and P.B. Bedient. 1989. Hydrogeologic Database for Ground Water
Modeling. API Publication No. 4476. American Petroleum Institute, Washington, DC.
Newell, C.J., L.P. Hopkins, and P.B. Bedient. 1990. A hydrogeologic database for ground water-
modeling. Groundwater, 28(5):703-714.
Nielsen, D.M. (ed.). 1991. Practical Handbook of Ground-Water Monitoring. Lewis Publishers,
Chelsea, MI.
Schroeder, P.R., A.C. Gibson, and M.D. Smolen. 1984. Hydrological Evaluation of Landfill
Performance (HELP) Model; Volume 2: Documentation for Version 1. NTIS PB85-100832.
Office of Research and Development, U.S. EPA, Cincinnati, OH. EPA/530-SW-84-010.
U.S. EPA. 1987. Data Quality Objectives for Remedial Response Activities. Example Scenario:
RI/FS Activities at a Site with Contaminated Soil and Groundwater. Office of Emergency
and Remedial Response, Washington, DC. NTIS PB88-13188.
U.S. EPA 1988. Superfund Exposure Assessment Manual. OSWER Directive 9285.5-1. Office of
Emergency and Remedial Response, Washington, DC. EPA/540/1-88/001. NTIS PB89-
135859.
U.S. EPA. 1989. Guidance for Conducting Remedial Investigations and Feasibility Studies under
CERCLA. EPA/540/G-89/004. OSWER Directive 9355.3-01. Office of Emergency and
Remedial Response, Washington, DC. NTIS PB89-184626.
U.S. EPA. 1992. Guidance for Performing Site Inspections Under CERCLA. EPA/540-R-92-0021.
Office of Emergency and Remedial Response, Washington, DC. NTIS PB92-963375.
A-7
-------
Soil Screening Guidance
Conceptual Site Model Summary Forms
Form 1: General Site Information Site Name
EPA Region Date
Contractor Name and Address:
State Contact:
1. CERCLIS ID No.
Address
County
_CitY
State
Zip Code
Congressional District_
2. Owner Name
Owner Address
City
State
_Operator Name
_Operator Address_
City
State
3. Type of ownership (check all that apply):
~ Private ~ Federal Agency
Other
~ State
~ County
Ref.
~ Municipal
4. Approximate size of property
acres
Ref.
5. Latitude
" Longitude o | . " Ref.
6. Site status ~ Active ~ Inactive ~ Unknown
Ref.
7. Years of operation From_
To
~ Unknown Ref.
Previous investigations
Type Agency/State/Contractor
Date
Ref.
Ref.
Ref.
Ref.
Ref.
Ref.
Ref. = reference(s) on information source
A-
-------
Soil Screening Guidance
Conceptual Site Model Summary Forms
Figure A-1. U.S. climatic zones Site Name
Hydroqeoloqic Characteristics (migration to ground water pathway)
Is ground water of concern at the site? Dyes ~ no (if no. move to Infiltration Rate below).
Heath region Hydrogeologic setting
(attach setting diagram)
Check setting characteristics that apply: ~ karst ~ fractured rock ~ solution limestone
Describe the stratigraphy and hydrogeologic characteristics of the site. (Attach available maps and cross-sections.)
Ref.
Identify and describe nearby sites in similar settings that have already been characterized.
Ref.
Aquifer Parameters Unit Typical Min. Max. Reference or Source
hydraulic conductivity (K)
m/y
hydraulic gradient (i)
m/m
thickness (dg)
m
General direction of ground water flow across the site (e.g., NNE, SW):
(attach map.) Ref.
Infiltration rate (I) m/yr Method
Meteorological Characteristics (inhalation pathway)
climatological zone: (zone#, city) Q/C (g/m2-s per kg/m3)
fract. vegetative cover (V) (unitless) Reference
mean annual windspeed (Um) m/s Reference
equivalent threshold value of windspeed at 7 m (Ut) m/s
fraction dependent on Um/Ut (unitless)
Comments:
A-9
-------
Soil Screening Guidance
Conceptual Site Model Summary Forms
Form 3: Exposure Pathways and Receptors
Land Use Conditions
Site Name
Current site use:
Surrounding land use:
residential
Future land use:
residential
residential
industrial
industrial
industrial
commercial
agricultural
recreational
commercial
agricultural
recreational
other
commercial
agricultural
recreational
other
other
Size of exposure areas (in acres)
Contaminant Release Mechanisms (check all that apply):
Source# ~ leaching ~ volatilization ~ fugitive dusts ~ erosion/runoff ~ uptake by plants
Source# ~ leaching ~ volatilization ~ fugitive dusts ~ erosion/runoff ~ uptake by plants
Source# ~ leaching ~ volatilization ~ fugitive dusts ~ erosion/runoff ~ uptake by plants
(describe rationale for not including any of the above release mechanisms)
Media affected (or potentially affected) by soil contamination.
Source# ~ air ~ ground water ~ surface water ~ sediments ~ wetlands
Source# ~ air ~ ground water ~ surface water ~ sediments ~ wetlands
Source# ~ air ~ ground water ~ surface water ~ sediments ~ wetlands
Check if present on-site or on surrounding land (attach map showing locations)
~ wetlands ~ surface water ~ subsistence fishing ~ recreational fishing ~ dairy/beef production
Check SSL exposure pathways applicable at site; describe basis for not including any
pathway
~ ingestion ~ inhalation ~ migration to ground water ~ dermal ~ soil-plant-human
Check Potential for:
~ Acute Effects (describe)
~ Other Human Exposure Pathways (describe)
~ Ecological concerns (describe)
A-10
-------
Soil Screening Guidance
Conceptual Site Model Summary Forms
Form 4: Soil Contaminant Source Characteristics
Source No.:
Name:
Type:
Location:
Waste type:
Description (describe history of contamination, other information)
Site Name
(e.g., drum storage area)
(e.g., spill, dump, wood treater)
(site map)
(e.g., solvents, waste oil)
Describe past/current remedial or removal actions
Source depth: m (~ measures ~ estimated) Ref.
Source area: acres m2 (~ measures ~ estimated) Ref.
Source length parallel to ground water flow: m (if uncertain, use longest source dimension)
Contaminant types (check all that apply): ~ volatile organics ~ other organics ~ metals ~ other inorganics
Soil Contaminants Present (list):
(attach Worksheet #1)
Describe previous soil analyses, (attach available results and map showing sample locations)
(attach Worksheet #2)
Are NAPLs suspected? DYes ~ No Reason_
Average Soil Characteristics
average water content (0J (L wate/L soi|) Ref.
fraction organic carbon (foc) g/g Ref.
dry bulk density (pb) (kg/L) Ref.
pH Ref.
A-ll
-------
Worksheet 1. Contaminant-specific properties Site Name
Regulatory and Human Health Benchmarks1
Contaminant
CAS#
MCLG,
MCL, or
HBL (mg/L)
Sources
(no.)
RfD
(mg/kg/-d)
SF0
(mg/kg/-d)"1
URF
(|ig/m3)"1
RfC
(mg/m3)
Chemical Properties2
Contaminant
CAS#
Sources
(no.)
K 3
OC
(L/kg)
K 4
d
(L/kg)
H5
D- 5
ia
(cm2/s)
D- 5
IW
(cm2/s)
S5
(mg/L)
1. Attachment D
2. Attachment C
3. For organic compounds
4. For metals and inorganic compounds
5. Not applicable to metals except mercury
A-12
-------
Worksheet 2. Contaminant concentrations by source Site Name
Source #:
Contaminant
CAS#
average
standard
deviation
number of
samples
minimum
maximum
variance
Source #:
Contaminant
CAS#
average
standard
deviation
number of
samples
minimum
maximum
variance
A-13
-------
Worksheet 3. Surface SSLs by Exposure Area (EA) Site Name
EA #: SSL type: ~ site-specific ~ generic (default)
Contaminant
CAS#
Soil Screening Level
ingestion
other (plant uptake; fugitive dust)
EA #: SSL type: ~ site-specific ~ generic (default)
Contaminant
CAS#
Soil Screening Level
ingestion
other (plant uptake; fugitive dust)
A-14
-------
Worksheet 4. Subsurface SSLs by source Site Name
Source #: SSL type: ~ site-specific ~ generic (default)
Contaminant
CAS#
Soil Screening Level
inhalation of volatiles
migration to ground water
Source #: SSL type: ~ site-specific ~ generic (default)
Contaminant
CAS#
Soil Screening Level
inhalation of volatiles
migration to ground water
A-15
-------
PRIMARY
SOURCES
PRIMARY
RELEASE
MECHANISM
SECONDARY
SOURCES
SECONDARY PATHWAY
RELEASE
MECHANISM
RECEPTOR
HUMAN BIOTA
Area
Site
EXPOSURE ROUTE
Residents
Trespassers
Terrestrial
Aquatic
Dust and/or
Volatile
Emissions
Ingestion
Inhalation
Dermal Contact
Ingestion
Dermal Contact
Plant Uptake
Garden
Vegetables
Ingestion
Infiltration/
Percolation
Ground Water
Storm Water
Runoff
Dust and/or
Volatile
Emissions
Ingestion
Inhalation
Dermal Contact
Ingestion
Inhalation
Dermal Contact
-------
WOODED AREA
FILL MATERIAL
DEPRESSION
(DIRECT CONTACT)
\
LACUSTRINE DEPOSITS
GLACIAL TILL
SHALE BEDROCK
POTENTIAL
CONTAMINANT
MIGRATION
PATHWAY
SITE CROSS SECTION
Figure A-3. Example Site Sketch (adapted from U.S. EPA, 1987)
A-17
-------
Attachment B
Soil Screening DQOs for Surface Soils and Subsurface Soils
-------
-------
Soil Screening DQOs for Surface Soils Using the Max Test
DQO Process Steps
Soil Screening Inputs/Outputs
State the Problem
Identify scoping team
Develop conceptual site model (CSM)
Define exposure scenarios
Specify available resources
Write brief summary of contamination
problem
Site manager and technical experts (e.g., toxicologists, risk assessors,
statisticians)
CSM development (described in Step 1)
Direct ingestion and inhalation of fugitive particulates in a residential setting;
dermal contact and plant uptake for certain contaminants
Sampling and analysis budget, scheduling constraints, and available personnel
Summary of the surface soil contamination problem to be investigated at the site
Identify the Decision
Identify decision
Identify alternative actions
Do mean soil concentrations for particular contaminants (e.g.
potential concern) exceed appropriate screening levels?
Eliminate area from further study under CERCLA
or
Plan and conduct further investigation
contaminants of
Identify Inputs to the Decision
Identify inputs
Define basis for screening
Identify analytical methods
Ingestion and particulate inhalation SSLs for specified contaminants
Measurements of surface soil contaminant concentration
Soil Screening Guidance
Feasible analytical methods (both field and laboratory) consistent with program-
level requirements
Define the Study Boundaries
Define geographic areas of field
investigation
Define population of interest
Divide site into strata
Define scale of decision making
Define temporal boundaries of study
Identify practical constraints
The entire NPL site, (which may include areas beyond facility boundaries),
except for any areas with clear evidence that no contamination has occurred
Surface soils (usually the top 2 centimeters, but may be deeper where activities
could redistribute subsurface soils to the surface)
Strata may be defined so that contaminant concentrations are likely to be
relatively homogeneous within each stratum based on the CSM and field
measurements
Exposure areas (EAs) no larger than 0.5 acre each (based on residential land
use)
Temporal constraints on scheduling field visits
Potential impediments to sample collection, such as access, health, and safety
issues
Develop a Decision Rule
Specify parameter of interest
Specify screening level
Specify "if..., then..." decision rule
"True mean" (|i) individual contaminant concentration in each EA. However,
since the determination of the "true mean" would require the collection and
analysis of many samples, another sample statistic, the maximum composite
concentration, or "Max Test" is used.
Screening levels calculated using available parameters and site data (or generic
SSLs if site data are unavailable)
Ideally, if the "true mean" EA concentration exceeds the screening level, then
investigate the EA further. If the "true mean" is less than the screening level,
then no further investigation of the EA is required under CERCLA.
B-l
-------
Soil Screening DQOs for Surface Soils Using the Max Test (continued)
DQO Process Steps
Soil Screening Inputs/Outputs
Specify Limits on Decision Errors*
Define baseline condition (null
The EA needs further investigation
hypothesis)
Define the gray region**
From 0.5 SSL to 2 SSL
Define Type 1 and Type II decision errors
Type 1 error: Do not investigate further ("walk away from") an EA whose "true
mean" exceeds the screening level of 2 SSL
Type II error: Investigate further when an EA's "true mean" falls below the
screening level of 0.5 SSL
Identify consequences
Type 1 error: potential public health consequences
Type II error: unnecessary expenditure of resources to investigate further
Assign acceptable probabilities of Type 1
Goals:
and Type II decision errors
Type 1: 0.05 (5%) probability of not investigating further when "true mean" of
the EA is 2 SSL
Type II: 0.20 (20%) probability of investigating further when "true mean" of
the EA is 0.5 SSL
Define QA/QC goals
CLP precision and bias requirements
10% CLP analyses for field methods
Optimize the Design
Determine how to best estimate "true
Samples composited across the EA as physical estimates of EA mean (x).
mean"
Use maximum composite concentration as a conservative estimate of the true
EA mean.
Determine expected variability of EA
A conservatively large expected coefficient of variation (CV) from prior data
surface soil contaminant concentrations
for the site, field measurements, or data from other comparable sites and
expert judgment. A minimum default CV of 2.5 should be used when
information is insufficient to estimate the CV.
Design sampling strategy by evaluating
Lowest cost sampling design option (i.e., compositing scheme and number of
costs and performance of alternatives
composites) that will achieve acceptable decision error rates
Develop planning documents for the field
Sampling and Analysis Plan (SAP)
investigation
Quality Assurance Project Plan (QAPjP)
* Since the DQO process controls the degree to which uncertainty in data affects the outcome of decisions that are
based on that data, specifying limits on decision errors will allow the decision maker to control the probability of making
an incorrect decision when using the DQOs.
** The gray region represents the area where the consequences of decision errors are minor, (and uncertainty in
sampling data makes decisions too close to call).
B-2
-------
Soil Screening DQOs for Subsurface Soils
DQO Process Steps
Soil Screening Inputs/Outputs
State the Problem
Identify scoping team
Site manager and technical experts (e.g., toxicologists, risk assessors,
hydrogeologists, statisticians).
Develop conceptual site model (CSM)
CSM development (described in Step 1).
Define exposure scenarios
Inhalation of volatiles and migration of contaminants from soil to potable
ground water (and plant uptake for certain contaminants).
Specify available resources
Sampling and analysis budget, scheduling constraints, and available
personnel.
Write brief summary of contamination
Summary of the subsurface soil contamination problem to be investigated at
problem
the site.
Identify the Decision
Identify decision
Do mean soil concentrations for particular contaminants (e.g., contaminants
of potential concern) exceed appropriate SSLs?
Identify alternative actions
Eliminate area from further action or study under CERCLA
or
Plan and conduct further investigation.
Identify Inputs to the Decision
Identify decision
Volatile inhalation and migration to ground water SSLs for specified
contaminants
Measurements of subsurface soil contaminant concentration
Define basis for screening
Soil Screening Guidance
Identify analytical methods
Feasible analytical methods (both field and laboratory) consistent with
program-level requirements.
Specify the Study Boundaries
Define geographic areas of field
The entire NPL site (which may include areas beyond facility boundaries),
investigation
except for any areas with clear evidence that no contamination has
occurred.
Define population of interest
Subsurface soils
Define scale of decision making
Sources (areas of contiguous soil contamination, defined by the area and
depth of contamination or to the water table, whichever is more shallow).
Subdivide site into decision units
Individual sources delineated (area and depth) using existing information or
field measurements (several nearby sources may be combined into a single
source).
Define temporal boundaries of study
Temporal constraints on scheduling field visits.
Identify (list) practical constraints
Potential impediments to sample collection, such as access, health, and
safety issues.
B-3
-------
Soil Screening DQOs for Subsurface Soils (continued)
Develop a Decision Rule
Specify parameter of interest
Specify screening level
Specify "if..., then..." decision rule
Mean soil contaminant concentration in a source (i.e., discrete contaminant
concentrations averaged within each boring).
SSLs calculated using available parameters and site data (or generic SSLs if
site data are unavailable).
If the mean soil concentration exceeds the SSL, then investigate the source
further. If mean soil concentration in a source is less than the SSL, then no
further investigation is required under CERCLA.
Specify Limits on Decision Errors
Define QA/QC goals
CLP precision and bias requirements
10% CLP analyses for field methods
Optimize the Design
Determine how to estimate mean
concentration in a source
Define subsurface sampling strategy by
evaluating costs and site-specific
conditions
Develop planning documents for the field
investigation
For each source, the highest mean soil boring concentration (i.e., depth-
weighted average of discrete contaminant concentrations within a boring).
Number of soil borings per source area; number of sampling intervals with
depth.
Sampling and Analysis Plan (SAP)
Quality Assurance Project Plan (QAPjP)
B-4
-------
Attachment C
Chemical Properties for SSL Development
-------
-------
Attachment C
Chemical Properties
This attachment provides the chemical properties necessary to calculate inhalation and migration to
ground water SSLs (see Section 2.5.2) for 110 chemicals commonly found at Superfund sites. The
Technical Background Document for Soil Screening Guidance describes the derivation and sources
for these property values.
Table C-l provides soil organic carbon - water partition coefficients (Koc), air and water
diffusivities (D, a and D, w), water solubilities (S), and dimensionless Henry's law constants
(H').
Table C-2 provides pH-specific Koc values for organic contaminants that ionize under natural
pH conditions. Site-specific soil pH measurements (see Section 2.3.5) can be used to select
appropriate Koc values for these chemicals. Where site-specific soil pH values are not
available, values corresponding to a pH or 6.8 should be used (note that the Koc values for
these chemicals in Table C-l are for a pH of 6.8).
Table C-3 provides the physical state (liquid or solid) for organic contaminants. A
contaminant's liquid or solid state is needed to apply and interpret soil saturation limit (Csat)
results (see Section 2.5.2, p.23).
Table C-4 provides pH-specific soil-water partition coefficients (K^) for metals. Site-specific
soil pH measurements (see Section 2.3.5) can be used to select appropriate Kd values for
these metals. Where site-specific soil pH values are not available, values corresponding to a
pH of 6.8 should be used.
Except for air and water diffusivities, the chemical properties necessary to calculate SSLs for
additional chemicals may be found in the Superfund Chemical Data Matrix (SCDM). Additional air
and water diffusivities may be obtained from the CHEMDAT8 and WATER8 models, both of which
can be downloaded off EPA's SCRAM electronic bulletin board system. Accessing information is
OAQPS SCRAM BBS
(919)541-5742 (24 hr/d, 7 d/wk except Monday AM)
Line Settings: 8 bits, no parity, 1 stop bit
Terminal emulation: VT100 or ANSI
System Operator: (919)541-5384 (normal business hours EST)
C-l
-------
Table C-1. Chemical-Specific Properties used in SSL Calculations
O
o
Di,a
Di.w
S
H'
CAS No.
Compound
(L/kg)
(cm2/s)
(cm2/s)
(mg/L)
(dimensionless)
83-32-9
Acenaphthene
7.08E+03
4.21 E-02
7.69E-06
4.24E+00
6.36E-03
67-64-1
Acetone
5.75E-01
1.24E-01
1.14E-05
1.00E+06
1.59E-03
309-00-2
Aldrin
2.45E+06
1.32E-02
4.86E-06
1.80E-01
6.97E-03
120-12-7
Anthracene
2.95E+04
3.24E-02
7.74E-06
4.34E-02
2.67E-03
56-55-3
Benz(a)anthracene
3.98E+05
5.10E-02
9.00E-06
9.40E-03
1.37E-04
71-43-2
Benzene
5.89E+01
8.80E-02
9.80E-06
1.75E+03
2.28E-01
205-99-2
Benzo(ฃ>)fluoranthene
1.23E+06
2.26E-02
5.56E-06
1.50E-03
4.55E-03
207-08-9
Benzo(/()fluoranthene
1.23E+06
2.26E-02
5.56E-06
8.00E-04
3.40E-05
65-85-0
Benzoic acid
6.00E-01
5.36E-02
7.97E-06
3.50E+03
6.31 E-05
50-32-8
Benzo(a)pyrene
1.02E+06
4.30E-02
9.00E-06
1.62E-03
4.63E-05
111-44-4
Bis(2-chloroethyl)ether
1.55E+01
6.92E-02
7.53E-06
1.72E+04
7.38E-04
117-81-7
Bis(2-ethylhexyl)phthalate
1.51E+07
3.51 E-02
3.66E-06
3.40E-01
4.18E-06
75-27-4
Bromodichloromethane
5.50E+01
2.98E-02
1.06E-05
6.74E+03
6.56E-02
75-25-2
Bromoform
8.71E+01
1.49E-02
1.03E-05
3.10E+03
2.19E-02
71-36-3
Butanol
6.92E+00
8.00E-02
9.30E-06
7.40E+04
3.61 E-04
85-68-7
Butyl benzyl phthalate
5.75E+04
1.74E-02
4.83E-06
2.69E+00
5.17E-05
86-74-8
Carbazole
3.39E+03
3.90E-02
7.03E-06
7.48E+00
6.26E-07
75-15-0
Carbon disulfide
4.57E+01
1.04E-01
1.00E-05
1.19E+03
1.24E+00
56-23-5
Carbon tetrachloride
1.74E+02
7.80E-02
8.80E-06
7.93E+02
1.25E+00
57-74-9
Chlordane
1.20E+05
1.18E-02
4.37E-06
5.60E-02
1.99E-03
106-47-8
p-Chloroaniline
6.61E+01
4.83E-02
1.01E-05
5.30E+03
1.36E-05
108-90-7
Chlorobenzene
2.19E+02
7.30E-02
8.70E-06
4.72E+02
1.52E-01
124-48-1
Chlorodibromomethane
6.31E+01
1.96E-02
1.05E-05
2.60E+03
3.21 E-02
67-66-3
Chloroform
3.98E+01
1.04E-01
1.00E-05
7.92E+03
1.50E-01
95-57-8
2-Chlorophenol
3.88E+02
5.01 E-02
9.46E-06
2.20E+04
1.60E-02
218-01-9
Chrysene
3.98E+05
2.48E-02
6.21 E-06
1.60E-03
3.88E-03
72-54-8
DDD
1.00E+06
1.69E-02
4.76E-06
9.00E-02
1.64E-04
72-55-9
DDE
4.47E+06
1.44E-02
5.87E-06
1.20E-01
8.61 E-04
50-29-3
DDT
2.63E+06
1.37E-02
4.95E-06
2.50E-02
3.32E-04
53-70-3
Dibenz(a,/7)anthracene
3.80E+06
2.02E-02
5.18E-06
2.49E-03
6.03E-07
84-74-2
Di-n-butyl phthalate
3.39E+04
4.38E-02
7.86E-06
1.12E+01
3.85E-08
95-50-1
1,2-Dichlorobenzene
6.17E+02
6.90E-02
7.90E-06
1.56E+02
7.79E-02
106-46-7
1,4-Dichlorobenzene
6.17E+02
6.90E-02
7.90E-06
7.38E+01
9.96E-02
91-94-1
3,3-Dichlorobenzidine
7.24E+02
1.94E-02
6.74E-06
3.11E+00
1.64E-07
75-34-3
1,1-Dichloroethane
3.16E+01
7.42E-02
1.05E-05
5.06E+03
2.30E-01
107-06-2
1,2-Dichloroethane
1.74E+01
1.04E-01
9.90E-06
8.52E+03
4.01 E-02
75-35-4
1,1-Dichloroethylene
5.89E+01
9.00E-02
1.04E-05
2.25E+03
1.07E+00
156-59-2
c/s-1,2-Dichloroethylene
3.55E+01
7.36E-02
1.13E-05
3.50E+03
1.67E-01
156-60-5
trans-1,2-Dichloroethylene
5.25E+01
7.07E-02
1.19E-05
6.30E+03
3.85E-01
120-83-2
2,4-Dichlorophenol
1.47E+02
3.46E-02
8.77E-06
4.50E+03
1.30E-04
78-87-5
1,2-Dichloropropane
4.37E+01
7.82E-02
8.73E-06
2.80E+03
1.15E-01
542-75-6
1,3-Dichloropropene
4.57E+01
6.26E-02
1.00E-05
2.80E+03
7.26E-01
60-57-1
Dieldrin
2.14E+04
1.25E-02
4.74E-06
1.95E-01
6.19E-04
84-66-2
Diethylphthalate
2.88E+02
2.56E-02
6.35E-06
1.08E+03
1.85E-05
105-67-9
2,4-Dimethylphenol
2.09E+02
5.84E-02
8.69E-06
7.87E+03
8.20E-05
C-2
-------
Table C-1 (continued)
O
o
Di,a
Di,w
S
H'
CAS No.
Compound
(L/kg)
(cm2/s)
(cm2/s)
(mg/L)
(dimensionless)
51-28-5
2,4-Dinitrophenol
1.00E-02
2.73E-02
9.06E-06
2.79E+03
1.82E-05
121-14-2
2,4-Dinitrotoluene
9.55E+01
2.03E-01
7.06E-06
2.70E+02
3.80E-06
606-20-2
2,6-Dinitrotoluene
6.92E+01
3.27E-02
7.26E-06
1.82E+02
3.06E-05
117-84-0
Di-n-octyl phthalate
8.32E+07
1.51E-02
3.58E-06
2.00E-02
2.74E-03
115-29-7
Endosulfan
2.14E+03
1.15E-02
4.55E-06
5.10E-01
4.59E-04
72-20-8
Endrin
1.23E+04
1.25E-02
4.74E-06
2.50E-01
3.08E-04
100-41-4
Ethylbenzene
3.63E+02
7.50E-02
7.80E-06
1.69E+02
3.23E-01
206-44-0
Fluoranthene
1.07E+05
3.02E-02
6.35E-06
2.06E-01
6.60E-04
86-73-7
Fluorene
1.38E+04
3.63E-02
7.88E-06
1.98E+00
2.61 E-03
76-44-8
Heptachlor
1.41E+06
1.12E-02
5.69E-06
1.80E-01
4.47E-02
1024-57-3
Heptachlor epoxide
8.32E+04
1.32E-02
4.23E-06
2.00E-01
3.90E-04
118-74-1
Hexachlorobenzene
5.50E+04
5.42E-02
5.91 E-06
6.20E+00
5.41 E-02
87-68-3
Hexachloro-1,3-butadiene
5.37E+04
5.61 E-02
6.16E-06
3.23E+00
3.34E-01
319-84-6
a-HCH (a-BHC)
1.23E+03
1.42E-02
7.34E-06
2.00E+00
4.35E-04
319-85-7
I3-HCH (I3-BHC)
1.26E+03
1.42E-02
7.34E-06
2.40E-01
3.05E-05
58-89-9
y-HCH (Lindane)
1.07E+03
1.42E-02
7.34E-06
6.80E+00
5.74E-04
77-47-4
Hexachlorocyclopentadiene
2.00E+05
1.61 E-02
7.21 E-06
1.80E+00
1.11E+00
67-72-1
Hexachloroethane
1.78E+03
2.50E-03
6.80E-06
5.00E+01
1.59E-01
193-39-5
lndeno(1,2,3-cd)pyrene
3.47E+06
1.90E-02
5.66E-06
2.20E-05
6.56E-05
78-59-1
Isophorone
4.68E+01
6.23E-02
6.76E-06
1.20E+04
2.72E-04
7439-97-6
Mercury
3.07E-02
6.30E-06
4.67E-01
72-43-5
Methoxychlor
9.77E+04
1.56E-02
4.46E-06
4.50E-02
6.48E-04
74-83-9
Methyl bromide
1.05E+01
7.28E-02
1.21E-05
1.52E+04
2.56E-01
75-09-2
Methylene chloride
1.17E+01
1.01E-01
1.17E-05
1.30E+04
8.98E-02
95-48-7
2-Methylphenol
9.12E+01
7.40E-02
8.30E-06
2.60E+04
4.92E-05
91-20-3
Naphthalene
2.00E+03
5.90E-02
7.50E-06
3.10E+01
1.98E-02
98-95-3
Nitrobenzene
6.46E+01
7.60E-02
8.60E-06
2.09E+03
9.84E-04
86-30-6
A/-Nitrosodiphenylamine
1.29E+03
3.12E-02
6.35E-06
3.51E+01
2.05E-04
621-64-7
A/-Nitrosodi-n-propylamine
2.40E+01
5.45E-02
8.17E-06
9.89E+03
9.23E-05
1336-36-3
PCBs
3.09E+05
7.00E-01
87-86-5
Pentachlorophenol
5.92E+02
5.60E-02
6.10E-06
1.95E+03
1.00E-06
108-95-2
Phenol
2.88E+01
8.20E-02
9.10E-06
8.28E+04
1.63E-05
129-00-0
Pyrene
1.05E+05
2.72E-02
7.24E-06
1.35E-01
4.51 E-04
100-42-5
Styrene
7.76E+02
7.10E-02
8.00E-06
3.10E+02
1.13E-01
79-34-5
1,1,2,2-Tetrachloroethane
9.33E+01
7.10E-02
7.90E-06
2.97E+03
1.41 E-02
127-18-4
Tetrachloroethylene
1.55E+02
7.20E-02
8.20E-06
2.00E+02
7.54E-01
108-88-3
Toluene
1.82E+02
8.70E-02
8.60E-06
5.26E+02
2.72E-01
8001-35-2
Toxaphene
2.57E+05
1.16E-02
4.34E-06
7.40E-01
2.46E-04
120-82-1
1,2,4-T richlorobenzene
1.78E+03
3.00E-02
8.23E-06
3.00E+02
5.82E-02
71-55-6
1,1,1-Trichloroethane
1.10E+02
7.80E-02
8.80E-06
1.33E+03
7.05E-01
79-00-5
1,1,2-Trichloroethane
5.01E+01
7.80E-02
8.80E-06
4.42E+03
3.74E-02
79-01-6
Trichloroethylene
1.66E+02
7.90E-02
9.10E-06
1.10E+03
4.22E-01
95-95-4
2,4,5-Trichlorophenol
1.60E+03
2.91 E-02
7.03E-06
1.20E+03
1.78E-04
88-06-2
2,4,6-T richlorophenol
3.81E+02
3.18E-02
6.25E-06
8.00E+02
3.19E-04
C-3
-------
Table C-1 (continued)
O
o
Di,a
Di,w
S
H'
CAS No.
Compound
(L/kg)
(cm2/s)
(cm2/s)
(mg/L)
(dimensionless)
108-05-4
Vinyl acetate
5.25E+00
8.50E-02
9.20E-06
2.00E+04
2.10E-02
75-01-4
Vinyl chloride
1.86E+01
1.06E-01
1.23E-06
2.76E+03
1.11E+00
108-38-3
m-Xylene
4.07E+02
7.00E-02
7.80E-06
1.61E+02
3.01 E-01
95-47-6
o-Xylene
3.63E+02
8.70E-02
1.00E-05
1.78E+02
2.13E-01
106-42-3
p-Xylene
3.89E+02
7.69E-02
8.44E-06
1.85E+02
3.14E-01
Koc = Soil organic carbon/water partition coefficient.
Di a = Diffusivity in air (25 -C).
Dj|w = Diffusivity in water (25 -C).
S = Solubility in water (20-25 -C).
H' = Dimensionless Henry's law constant (HLC [atm-m3/mol] * 41) (25-C).
Kd = Soil-water partition coefficient.
C-4
-------
Table C-2. Koc Values for Ionizing Organics as a Function of pH
PH
Benzoic
Acid
2-
Chloro-
phenol
2,4-Dichloro
phenol
2,4-
Dinitro-
phenol
Pentachloro-
phenol
2,3,4,5-
Tetrachloro-
phenol
2,3,4,6-
Tetrachloro-
phenol
2,4,5-Trichloro-
phenol
2,4,6-
Trichloro-
phenol
4.9
5.0
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
6.0
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
7.0
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9
8.0
5.54E+00
4.64E+00
3.88E+00
3.25E+00
2.72E+00
2.29E+00
1.94E+00
1.65E+00
1.42E+00
1.24E+00
1.09E+00
9.69E-01
8.75E-01
7.99E-01
7.36E-01
6.89E-01
6.51 E-01
6.20E-01
5.95E-01
5.76E-01
5.60E-01
5.47E-01
5.38E-01
5.32E-01
5.25E-01
5.19E-01
5.16E-01
5.13E-01
5.09E-01
5.06E-01
5.06E-01
5.06E-01
3.98E+02
3.98E+02
3.98E+02
3.98E+02
3.98E+02
3.98E+02
3.97E+02
3.97E+02
3.97E+02
3.97E+02
3.97E+02
3.96E+02
3.96E+02
3.96E+02
3.95E+02
3.94E+02
3.93E+02
3.92E+02
3.90E+02
3.88E+02
3.86E+02
3.83E+02
3.79E+02
3.75E+02
3.69E+02
3.62E+02
3.54E+02
3.44E+02
3.33E+02
3.19E+02
3.04E+02
2.86E+02
1.59E+02
1.59E+02
1.59E+02
1.59E+02
1.59E+02
1.58E+02
1.58E+02
1.58E+02
1.58E+02
1.58E+02
1.57E+02
1.57E+02
1.57E+02
1.56E+02
1.55E+02
1.54E+02
1.53E+02
1.52E+02
1.50E+02
1.47E+02
1.45E+02
1.41E+02
1.38E+02
1.33E+02
1.28E+02
1.21E+02
1.14E+02
1.07E+02
9.84E+01
8.97E+01
8.07E+01
7.17E+01
2.94E-02
2.55E-02
2.23E-02
1.98E-02
1.78E-02
1.62E-02
1.50E-02
1.40E-02
1.32E-02
1.25E-02
1.20E-02
1.16E-02
1.13E-02
1.10E-02
1.08E-02
1.06E-02
1.05E-02
1.04E-02
1.03E-02
1.02E-02
1.02E-02
1.02E-02
1.02E-02
1.01E-02
1.01E-02
1.01E-02
1.01E-02
1.01E-02
1.00E-02
1.00E-02
1.00E-02
1.00E-02
9.05E+03
1.73E+04
4.45E+03
2.37E+03
1.04E+03
7.96E+03
1.72E+04
4.15E+03
2.36E+03
1.03E+03
6.93E+03
1.70E+04
3.83E+03
2.36E+03
1.02E+03
5.97E+03
1.67E+04
3.49E+03
2.35E+03
1.01E+03
5.10E+03
1.65E+04
3.14E+03
2.34E+03
9.99E+02
4.32E+03
1.61E+04
2.79E+03
2.33E+03
9.82E+02
3.65E+03
1.57E+04
2.45E+03
2.32E+03
9.62E+02
3.07E+03
1.52E+04
2.13E+03
2.31 E+03
9.38E+02
2.58E+03
1.47E+04
1.83E+03
2.29E+03
9.10E+02
2.18E+03
1.40E+04
1.56E+03
2.27E+03
8.77E+02
1.84E+03
1.32E+04
1.32E+03
2.24E+03
8.39E+02
1.56E+03
1.24E+04
1.11 E+03
2.21 E+03
7.96E+02
1.33E+03
1.15E+04
9.27E+02
2.17E+03
7.48E+02
1.15E+03
1.05E+04
7.75E+02
2.12E+03
6.97E+02
9.98E+02
9.51 E+03
6.47E+02
2.06E+03
6.44E+02
8.77E+02
8.48E+03
5.42E+02
1.99E+03
5.89E+02
7.81 E+02
7.47E+03
4.55E+02
1.91 E+03
5.33E+02
7.03E+02
6.49E+03
3.84E+02
1.82E+03
4.80E+02
6.40E+02
5.58E+03
3.27E+02
1.71 E+03
4.29E+02
5.92E+02
4.74E+03
2.80E+02
1.60E+03
3.81 E+02
5.52E+02
3.99E+03
2.42E+02
1.47E+03
3.38E+02
5.21 E+02
3.33E+03
2.13E+02
1.34E+03
3.00E+02
4.96E+02
2.76E+03
1.88E+02
1.21 E+03
2.67E+02
4.76E+02
2.28E+03
1.69E+02
1.07E+03
2.39E+02
4.61 E+02
1.87E+03
1.53E+02
9.43E+02
2.15E+02
4.47E+02
1.53E+03
1.41 E+02
8.19E+02
1.95E+02
4.37E+02
1.25E+03
1.31 E+02
7.03E+02
1.78E+02
4.29E+02
1.02E+03
1.23E+02
5.99E+02
1.64E+02
4.23E+02
8.31 E+02
1.17E+02
5.07E+02
1.53E+02
4.18E+02
6.79E+02
1.13E+02
4.26E+02
1.44E+02
4.14E+02
5.56E+02
1.08E+02
3.57E+02
1.37E+02
4.10E+02
4.58E+02
1.05E+02
2.98E+02
1.31E+02
C-5
-------
Table C-3. Physical State of Organic SSL Chemicals
Compounds liquid at soil temperatures Compounds solid at soil temperatures
CAS No.
Chemical
Melting
Point (ฐC)
CAS No.
Chemical
Melting
Point (ฐC)
67-64-1
Acetone
-94.8
83-32-9
Acenaphthene
93.4
71-43-2
Benzene
5.5
309-00-2
Aldrin
104
117-81-7
Bis(2-ethylhexyl)phthalate
-55
120-12-7
Anthracene
215
111-44-4
Bis(2-chloroethyl)ether
-51.9
56-55-3
Benz(a)anthracene
84
75-27-4
Bromodichloromethane
-57
50-32-8
Benzo(a)pyrene
176.5
75-25-2
Bromoform
8
205-99-2
Benzo(ฃ>)fluoranthene
168
71-36-3
Butanol
-89.8
207-08-9
Benzo(/<)fluoranthene
217
85-68-7
Butyl benzyl phthalate
-35
65-85-0
Benzoic acid
122.4
75-15-0
Carbon disulfide
-115
86-74-8
Carbazole
246.2
56-23-5
Carbon tetrachloride
-23
57-74-9
Chlordane
106
108-90-7
Chlorobenzene
-45.2
106-47-8
p-Chloroaniline
72.5
124-48-1
Chlorodibromomethane
-20
218-01-9
Chrysene
258.2
67-66-3
Chloroform
-63.6
72-54-8
DDD
109.5
95-57-8
2-Chlorophenol
9.8
72-55-9
DDE
89
84-74-2
Di-n-butyl phthalate
-35
50-29-3
DDT
108.5
95-50-1
1,2-Dichlorobenzene
-16.7
53-70-3
Dibenzo(a,/?)anthracene
269.5
75-34-3
1,1-Dichloroethane
-96.9
106-46-7
1,4-Dichlorobenzene
52.7
107-06-2
1,2-Dichloroethane
-35.5
91-94-1
3,3-Dichlorobenzidine
132.5
75-35-4
1,1-Dichloroethylene
-122.5
120-83-2
2,4-Dichlorophenol
45
156-59-2
c/s-1,2-Dichloroethylene
-80
60-57-1
Dieldrin
175.5
156-60-5
trans-1,2-Dichloroethylene
-49.8
105-67-9
2,4-Dimethylphenol
24.5
78-87-5
1,2-Dichloropropane
-70
51-28-5
2,4-Dinitrophenol
115-116
542-75-6
1,3-Dichloropropene
NA
121-14-2
2,4-Dinitrotoluene
71
84-66-2
Diethylphthalate
-40.5
606-20-2
2,6-Dinitrotoluene
66
117-84-0
Di-n-octyl phthalate
-30
72-20-8
Endrin
200
100-41-4
Ethylbenzene
-94.9
206-44-0
Fluoranthene
107.8
87-68-3
Hexachloro-1,3-butadiene
-21
86-73-7
Fluorene
114.8
77-47-4
Hexachlorocyclopentadiene
-9
76-44-8
Heptachlor
95.5
78-59-1
Isophorone
-8.1
1024-57-3
Heptachlor epoxide
160
74-83-9
Methyl bromide
-93.7
118-74-1
Hexachlorobenzene
231.8
75-09-2
Methylene chloride
-95.1
319-84-6
a-HCH (a-BHC)
160
98-95-3
Nitrobenzene
5.7
319-85-7
I3-HCH (I3-BHC)
315
100-42-5
Styrene
-31
58-89-9
y-HCH (Lindane)
112.5
79-34-5
1,1,2,2-Tetrachloroethane
-43.8
67-72-1
Hexachloroethane
187
127-18-4
Tetrachloroethylene
-22.3
193-39-5
lndeno(1,2,3-cd)pyrene
161.5
108-88-3
Toluene
-94.9
72-43-5
Methoxychlor
87
120-82-1
1,2,4-T richlorobenzene
17
95-48-7
2-Methylphenol
29.8
71-55-6
1,1,1-Trichloroethane
-30.4
621-64-7
/V-Nitrosodi-n-propylamine
NA
79-00-5
1,1,2-Trichloroethane
-36.6
86-30-6
/V-Nitrosodiphenylamine
66.5
79-01-6
Trichloroethylene
-84.7
91-20-3
Naphthalene
80.2
108-05-4
Vinyl acetate
-93.2
87-86-5
Pentachlorophenol
174
75-01-4
Vinyl chloride
-153.7
108-95-2
Phenol
40.9
108-38-3
m-Xylene
-47.8
129-00-0
Pyrene
151.2
95-47-6
o-Xylene
-25.2
8001-35-2
Toxaphene
65-90
106-42-3
p-Xylene
13.2
95-95-4
2,4,5-T richlorophenol
69
88-06-2
2,4,6-T richlorophenol
69
115-29-7
Endosullfan
106
NA = Not available.
C-6
-------
Table D4. Metal K
-------
Attachment D
Regulatory and Human Health Benchmarks
Used for SSL Development
I
-------
Attachment D
Regulatory and Human Health Benchmarks for SSL Development
This attachment provides regulatory and human health benchmarks necessary to calculate SSLs for
110 chemicals commonly found at National Priority List (NPL) sites. The sources of these values
(shown in the following table) are regularly updated by EPA. Prior to calculating SSLs at a site,
check all relevant chemical-specific values in this attachment against the most
recent version of their sources to ensure that they are up-to-date.
-------
Attachment D. Regulatory and Human Health Benchmarks Used for SSL Development
Maximum
Contaminant Level
Goal
(mg/L)
Maximum
Contaminant Level
(mg/L)
Water Health Based
Limits
(mg/L)
Cancer Slope Factor
(mg/kg-d)"1
Unit Risk Factor
(Mg/m3)-1
Reference Dose
(mg/kg-d)
Reference
Concentration
(mg/m3)
CAS
Number
Chemical Name
MCLG Ref a
(PMCLG) KeTl
MCL (PMCL)
Ref. a
HBLb Basis
Care.
Classc
SF0
Ref. a
Care.
Classc
URF
Ref. a
RfD Ref.a
RfC Ref.a
83-32-9
67-64-1
309-00-2
Acenaphthene
Acetone (2-Propanone)
Aldrin
2E+00
4E+00
5E-06
RfD
RfD
SF0
D
B2
1.7E+01
1
D
B2
4.9E-03
1
6.0E-02 1
1.0E-01 1
3.0E-05 1
120-12-7
Anthracene
1E+01
RfD
D
D
3.0E-01 1
7440-36-0
Antimony
6.0E-03 3
6.0E-03
3
4.0E-04 1
7440-38-2
Arsenic
5.0E-02
3
A
1.5E+00
1
A
4.3E-03
1
3.0E-04 1
7440-39-3
Barium
2.0E+00 3
2.0E+00
3
7.0E-02 1
5.0E-04 2
56-55-3
Benz(a )anthracene
1E-04
SF0
B2
7.3E-01
4
B2
71-43-2
Benzene
5.0E-03
3
A
2.9E-02
1
A
8.3E-06
1
205-99-2
Benzo(ib )fluoranthene
1E-04
SF0
B2
7.3E-01
4
B2
207-08-9
Benzo(k )fluoranthene
1E-03
SF0
B2
7.3E-02
4
B2
65-85-0
Benzoic acid
1E+02
RfD
4.0E+00 1
50-32-8
Benzo(a )pyrene
2.0E-04
3
B2
7.3E+00
1
B2
7440-41 -7
Beryllium
4.0E-03 3
4.0E-03
3
B2
4.3E+00
1
B2
2.4E-03
1
5.0E-03 1
111-44-4
Bis(2-chloroethyl)ether
8E-05
SF0
B2
1.1E+00
1
B2
3.3E-04
1
117-81-7
Bis(2-ethylhexyl)phthalate
6.0E-03
3
B2
1.4E-02
1
B2
2.0E-02 1
75-27-4
Bromodichloromethane
1.0E-01 *
3
B2
6.2E-02
1
B2
2.0E-02 1
75-25-2
Bromoform (tribromomethane)
1.0E-01 *
3
B2
7.9E-03
1
B2
1.1E-06
1
2.0E-02 1
71-36-3
Butanol
4E+00
RfD
D
D
1.0E-01 1
85-68-7
Butyl benzyl phthalate
7E+00
RfD
C
C
2.0E-01 1
7440-43-9
Cadmium
5.0E-03 3
5.0E-03
3
B1
1.8E-03
1
1.0E-03** 1
86-74-8
Carbazole
4E-03
SF0
B2
2.0E-02
2
75-15-0
Carbon disulfide
4E+00
RfD
1.0E-01 1
7.0E-01 1
56-23-5
Carbon tetrachloride
5.0E-03
3
B2
1.3E-01
1
B2
1.5E-05
1
7.0E-04 1
57-74-9
Chlordane
2.0E-03
3
B2
1.3E+00
1
B2
3.7E-04
1
6.0E-05 1
106-47-8
p -Chloroaniline
1E-01
RfD
4.0E-03 1
108-90-7
Chlorobenzene
1.0E-01 3
1.0E-01
3
D
D
2.0E-02 1
2.0E-02 2
124-48-1
Chlorodibromo methane
6.0E-02 3
1.0E-01 *
3
C
8.4E-02
1
C
2.0E-02 1
67-66-3
Chloroform
1.0E-01 *
3
B2
6.1E-03
1
B2
2.3E-05
1
1.0E-02 1
95-57-8
2-Chlorophenol
2E-01
RfD
5.0E-03 1
* Proposed MCL = 0.08 mg/L, Drinking Water Regulations and Health Advisories , U.S. EPA (1995).
** Cadmium RfD is based on dietary exposure.
-------
Attachment D (continued)
Maximum
Contaminant Level
Maximum
Contaminant Level
Water Health Based
Limits
Cancer Slope Factor
Unit Risk Factor
Reference Dose
Reference
Concentration
Goal
(mg/L)
(mg/L)
(mg/L)
(mg/kg-d)
(|jg/m )
(mg/kg-d)
(mg/m3)
CAS
Number
Chemical Name
MCLG Ref a
(PMCLG) KeTl
MCL (PMCL)
Ref. a
HBLb Basis
Care.
Classc
SF0
Ref. a
Care.
Classc
URF
Ref. a
RfD
Ref. a
RfC Ref.a
7440-47-3
Chromium
1.0E-01 3
1.0E-01
3
A
A
1.2E-02
1
5.0E-03
1
16065-83-1
Chromium (III)
4E+01
RfD
1.0E+00
1
18540-29-9
Chromium (VI)
1.0E-01
3*
A
A
1.2E-02
1
5.0E-03
1
218-01-9
Chrysene
1E-02
SF0
B2
7.3E-03
4
57-12-5
Cyanide (amenable)
(2.0E-01) 3
(2.0E-01)
3
D
D
2.0E-02
1
72-54-8
DDD
4E-04
SF0
B2
2.4E-01
1
B2
72-55-9
DDE
3E-04
SF0
B2
3.4E-01
1
B2
50-29-3
DDT
3E-04
SF0
B2
3.4E-01
1
B2
9.7E-05
1
5.0E-04
1
53-70-3
Dibenz(a,h )anthracene
1E-05
SF0
B2
7.3E+00
4
B2
84-74-2
Di-n -butyl phthalate
4E+00
RfD
D
D
1.0E-01
1
95-50-1
1,2-Dichlorobenzene
6.0E-01 3
6.0E-01
3
D
D
9.0E-02
1
2.0E-01 2
106-46-7
1,4-Dichlorobenzene
7.5E-02 3
7.5E-02
3
B2
2.4E-02
2
B2
8.0E-01 1
91-94-1
3,3-Dichlorobenzidine
2E-04
SF0
B2
4.5E-01
1
B2
75-34-3
1,1-Dichloroethane
4E+00
RfD
C
C
1.0E-01
7
5.0E-01 2
107-06-2
1,2-Dichloroethane
5.0E-03
3
B2
9.1E-02
1
B2
2.6E-05
1
75-35-4
1,1-Dichloroethylene
7.0E-03 3
7.0E-03
3
C
6.0E-01
1
C
5.0E-05
1
9.0E-03
1
156-59-2
cis -1,2-Dichloroethylene
7.0E-02 3
7.0E-02
3
D
D
1.0E-02
2
156-60-5
trans -1,2-Dichloroethylene
1.0E-01 3
1.0E-01
3
2.0E-02
1
120-83-2
2,4-Dichlorophenol
1E-01
RfD
3.0E-03
1
78-87-5
1,2-Dichloropropane
5.0E-03
3
B2
6.8E-02
2
B2
4.0E-03 1
542-75-6
1,3-Dichloropropene
5E-04
SF0
B2
1.8E-01
2
B2
3.7E-05
2
3.0E-04
1
2.0E-02 1
60-57-1
Dieldrin
5E-06
SF0
B2
1.6E+01
1
B2
4.6E-03
1
5.0E-05
1
84-66-2
Diethylphthalate
3E+01
RfD
D
D
8.0E-01
1
105-67-9
2,4-Dimethylphenol
7E-01
RfD
2.0E-02
1
51-28-5
2,4-Dinitrophenol
4E-02
RfD
2.0E-03
1
121-14-2
2,4-Dinitrotoluene**
1E-04
SF0
B2
6.8E-01
1
2.0E-03
1
606-20-2
2,6-Dinitrotoluene**
1E-04
SF0
B2
6.8E-01
1
1.0E-03
2
117-84-0
Di-n -octyl phthalate
7E-01
RfD
2.0E-02
2
115-29-7
Endosulfan
2E-01
RfD
6.0E-03
2
72-20-8
Endrin
2.0E-03 3
2.0E-03
3
D
D
3.0E-04
1
* MCL for total chromium is based on Cr (VI) toxicity.
** Cancer Slope Factor is for 2,4-, 2,6-Dinitrotoluene mixture.
-------
Attachment D (continued)
Maximum
Contaminant Level
Maximum
Contaminant Level
Water Health Based
Limits
Cancer Slope Factor
Unit Risk Factor
Reference Dose
Reference
Concentration
Goal
(mg/L)
(mg/L)
(mg/L)
(mg/kg-d)
(|jg/m )
(mg/kg-d)
(mg/m3)
CAS
Number
Chemical Name
MCLG Ref a
(PMCLG) KeTl
MCL (PMCL)
Ref. a
HBLb Basis
Care.
Classc
SF0
Ref. a
Care.
Classc
URF
Ref. a
RfD
Ref. a
RfC Ref.a
100-41 -4
Ethylbenzene
7.0E-01 3
7.0E-01
3
D
D
1.0E-01
1
1.0E+00 1
206-44-0
Fluoranthene
1E+00
RfD
D
D
4.0E-02
1
86-73-7
Fluorene
1E+00
RfD
D
4.0E-02
1
76-44-8
Heptachlor
4.0E-04
3
B2
4.5E+00
1
B2
1.3E-03
1
5.0E-04
1
1024-57-3
Heptachlor epoxide
2.0E-04
3
B2
9.1E+00
1
B2
2.6E-03
1
1.3E-05
1
118-74-1
Hexachlorobenzene
1.0E-03
3
B2
1.6E+00
1
B2
4.6E-04
1
8.0E-04
1
87-68-3
Hexachloro-1,3-butadiene
1.0E-03 3
1E-03
SF0
C
7.8E-02
1
C
2.2E-05
1
2.0E-04
2
319-84-6
a-HCH (a-BHC)
1E-05
SF0
B2
6.3E+00
1
B2
1.8E-03
1
319-85-7
p-HCH (p-BHC)
5E-05
SF0
C
1.8E+00
1
C
5.3E-04
1
58-89-9
y-HCH (Lindane)
2.0E-04 3
2.0E-04
3
B2
1.3E+00
2
C
3.0E-04
1
77-47-4
Hexachlorocyclopentadiene
5.0E-02 3
5.0E-02
3
D
D
7.0E-03
1
7.0E-05 2
67-72-1
Hexachloroethane
6E-03
SF0
C
1.4E-02
1
C
4.0E-06
1
1.0E-03
1
193-39-5
lndeno(1,2,3-cc/ )pyrene
1E-04
SF0
B2
7.3E-01
4
B2
78-59-1
Isophorone
9E-02
SF0
C
9.5E-04
1
C
2.0E-01
1
7439-97-6
Mercury
2.0E-03 3
2.0E-03
3
D
D
3.0E-04
2
3.0E-04 2
72-43-5
Methoxychlor
4.0E-02 3
4.0E-02
3
D
D
5.0E-03
1
74-83-9
Methyl bromide
5E-02
RfD
D
D
1.4E-03
1
5.0E-03 1
75-09-2
Methylene chloride
5.0E-03
3
B2
7.5E-03
1
B2
4.7E-07
1
6.0E-02
1
3.0E+00 2
95-48-7
2-Methylphenol (o -cresol)
2E+00
RfD
C
C
5.0E-02
1
91-20-3
Naphthalene
1E+00
RfD
D
D
4.0E-02
6
7440-02-0
Nickel
1E-01
HA*
A
A
2.4E-04
1
2.0E-02
1
98-95-3
Nitrobenzene
2E-02
RfD
D
D
5.0E-04
1
2.0E-03 2
86-30-6
N -Nitrosodiphenylamine
2E-02
SF0
B2
4.9E-03
1
B2
621-64-7
N -Nitrosodi-n -propylamine
1E-05
SF0
B2
7.0E+00
1
B2
87-86-5
Pentachlorophenol
1.0E-03
3
B2
1.2E-01
1
B2
3.0E-02
1
108-95-2
Phenol
2E+01
RfD
D
D
6.0E-01
1
129-00-0
Pyrene
1E+00
RfD
D
D
3.0E-02
1
7782-49-2
Selenium
5.0E-02 3
5.0E-02
3
D
D
5.0E-03
1
7440-22-4
Silver
2E-01
RfD
D
D
5.0E-03
1
100-42-5
Styrene
1.0E-01 3
1.0E-01
3
2.0E-01
1
1.0E+00 1
79-34-5
1,1,2,2-Tetrachloroethane
4E-04
SF0
C
2.0E-01
1
C
5.8E-05
1
* Health advisory for nickel (MCL is currently remanded); EPA Office of Science and Technology, 7/10/95.
-------
Attachment D (continued)
Maximum
Contaminant Level
Maximum
Contaminant Level
Water Health Based
Limits
Cancer Slope Factor
Unit Risk Factor
Reference Dose
Reference
Concentration
uoai
(mg/L)
(mg/L)
(mg/L)
(mg/kg-d)
(|jg/m )
(mg/kg-d)
(mg/m3
)
CAS
Number
Chemical Name
MCLG
(PMCLG)
Ref. a
MCL (PMCL)
Ref. a
HBLb Basis
Care.
Classc
SF0
Ref. a
Care.
Classc
URF
Ref. a
RfD Ref.a
RfC
Ref. a
127-18-4
Tetrachloroethylene
5.0E-03
3
5.2E-02
5
5.8E-07
5
1.0E-02 1
7440-28-0
Thallium
5.0E-04
3
2.0E-03
3
108-88-3
Toluene
1.0E+00
3
1.0E+00
3
D
D
2.0E-01 1
4.0E-01
1
8001-35-2
Toxaphene
3.0E-03
3
B2
1.1E+00
1
B2
3.2E-04
1
120-82-1
1,2,4-Trichlorobenzene
7.0E-02
3
7.0E-02
3
D
D
1.0E-02 1
2.0E-01
2
71-55-6
1,1,1-Trichloroethane
2.0E-01
3
2.0E-01
3
D
D
1.0E+00
5
79-00-5
1,1,2-Trichloroethane
3.0E-03
3
5.0E-03
3
C
5.7E-02
1
C
1.6E-05
1
4.0E-03 1
79-01-6
Trichloroethylene
zero
3
5.0E-03
3
1.1E-02
5
1.7E-06
5
95-95-4
2,4,5-Trichlorophenol
4E+00
RfD
1.0E-01 1
88-06-2
2,4,6-Trichlorophenol
8E-03
SF0
B2
1.1E-02
1
B2
3.1E-06
1
7440-62-2
Vanadium
3E-01
RfD
7.0E-03 2
108-05-4
Vinyl acetate
4E+01
RfD
1.0E+00 1
2.0E-01
1
75-01-4
Vinyl chloride (chloroethene)
2.0E-03
3
A
1.9E+00
2
A
8.4E-05
2
108-38-3
m -Xylene
1.0E+01
3*
1.0E+01
3*
D
D
2.0E+00 2
95-47-6
o -Xylene
1.0E+01
3*
1.0E+01
3*
D
D
2.0E+00 2
106-42-3
p -Xylene
1.0E+01
3*
1.0E+01
3*
D
D
2.0E+00 1 **
7440-66-6
Zinc
1E+01
RfD
D
D
3.0E-01 1
* MCL for total xylenes [1330-20-7] is 10 mg/L.
** RfD for total xylenes is 2 mg/kg-day.
a References: 1 = IRIS, U.S. EPA (1995)
2 = HEAST, U.S. EPA (1995)
3 = U.S. EPA (1995)
4 = OHEA, U.S. EPA (1993)
5 = Interim toxicity criteria provided by Superfund
Health Risk Techincal Support Center,
Environmental Criteria Assessment Office
(ECAO), Cincinnati, OH (1994)
6 = ECAO, U.S. EPA (1994i)
7 = ECAO, U.S. EPA (1994h)
b Health Based Limits calculated for 30-year exposure duration, 10~6 risk or hazard quotient = 1.
c Categorization of overall weight of evidence for human carcinogenicity:
Group A: human carcinogen
Group B: probable human carcinogen
B1: limited evidence from epidemiologic studies
B2: "sufficient" evidence from animal studies and "inadequate" evidence or
"no data" from epidemiologic studies
Group C: possible human carcinogen
Group D: not classifiable as to health carcinogenicity
Group E: evidence of noncarcinogenicity for humans
------- |