United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
OSWER 9355.4-24
December 2002
Superfund
vvEPAi SUPPLEMENTAL GUIDANCE FOR
DEVELOPING SOIL SCREENING
LEVELS FOR SUPERFUND SITES
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OSWER 9355.4-24
December 2002
SUPPLEMENTAL GUIDANCE FOR DEVELOPING SOIL
SCREENING LEVELS FOR SUPERFUND SITES
Office of Emergency and Remedial Response
U.S. Environmental Protection Agency
Washington, DC 20460
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ACKNOWLEDGMENTS
This document was prepared by Industrial Economics, Incorporated (ffic) under EPA Contracts 68-
W6-0044 and 68-W-01-058 for the Office of Emergency and Remedial Response (OERR), U.S.
Environmental Protection Agency. Janine Dinan of EPA, the EPA Work Assignment Manager for
this effort, guided the development of the document and served as principal EPA author, along with
David Cooper of OERR. Eric Ruder, Henry Roman, Emily Levin, and Adena Greenbaum of lEc
provided expert technical assistance in preparing this document. Mr. Ruder directed the effort for
lEc, and he and Mr. Roman were primary authors of this document. Tom Robertson of
Environmental Quality Management (EQ) also provided key technical support for the modeling of
inhalation pathways. The authors would like to thank all EPA and external peer reviewers whose
careful review and thoughtful comments greatly contributed to the quality of this document.
The project team especially wishes to note the contributions of the late Craig Mann of EQ, whose
expert assistance in modeling inhalation exposures was critical to the development of both this
document and the original Soil Screening Guidance. Craig was a prominent researcher in the air
modeling field and programmer of the widely-used spreadsheet version of the Johnson and Ettinger
(1991) model. We dedicate this document to him.
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Disclaimer
This document provides guidance to EPA Regions concerning how the Agency intends
to exercise its discretion in implementing one aspect of the CERCLA remedy selection
process. The guidance is designed to implement national policy on these issues.
The statutory provisions and EPA regulations described in this document contain legally
binding requirements. However, this document does not substitute for those provisions
or regulations, nor is it a regulation itself. Thus, it cannot impose legally-binding
requirements on EPA, States, or the regulated community, and may not apply to a
particular situation based upon the circumstances. Any decisions regarding a particular
remedy selection decision will be made based on the statute and regulations, and EPA
decisionmakers retain the discretion to adopt approaches on a case-by-case basis that
differ from this guidance where appropriate. EPA may change this guidance in the
future.
11
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TABLE OF CONTENTS
1.0 INTRODUCTION 1-1
1.1 Purpose and Scope 1-2
1.2 Organization of Document 1-7
2.0 OVERVIEW OF SOIL SCREENING 2-1
2.1 The Screening Concept 2-1
2.2 The Tiered Screening Framework/Selecting a Screening Approach 2-3
2.3 The Seven-Step Soil Screening Process 2-5
Step 1: Develop Conceptual Site Model 2-5
Step 2: Compare CSM to SSL Scenario 2-7
Step 3: Define Data Collection Needs for Soils 2-7
Step 4: Sample and Analyze Site Soils 2-9
Step 5: Calculate Site- and Pathway-Specific SSLs 2-10
Step 6: Compare Site Soil Contaminant Concentrations to
Calculated SSLs 2-10
Step 7: Address Areas Identified for Further Study 2-13
3.0 EXPOSURE PATHWAYS 3-1
3.1 Exposure Pathways by Exposure Scenario 3-1
3.2 Exposure Pathway Updates 3-3
3.2.1 Direct Ingestion and Dermal Absorption of Soil Contaminants 3-4
3.2.2 Migration of Volatiles Into Indoor Air 3-10
in
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TABLE OF CONTENTS
(continued)
4.0 DEVELOPING SSLS FOR NON-RESIDENTIAL EXPOSURE SCENARIOS 4-1
4.1 Identification of Non-Residential Land Use 4-1
4.1.1 Factors to Consider in Identifying Future Land Use 4-1
4.1.2 Categories of Non-Residential Land Use and
Exposure Activities 4-2
4.1.3 Framework for Developing SSLs for
Non-Residential Land Uses 4-2
4.1.4 Land Use and the Selection of a Screening Approach 4-5
4.2 Modifications to the Soil Screening Process for
Sites With Non-Residential Exposure Scenarios 4-6
4.2.1 Step 1: Develop Conceptual Site Model 4-7
4.2.2 Step 2: Compare Conceptual Site Model to SSL Scenario 4-8
4.2.3 Step 5: Calculate Site- and Pathway-Specific SSLs 4-10
4.3 Additional Considerations for the Evaluation of
Non-Residential Exposure Scenarios 4-30
4.3.1 Involving the Public in Identifying Future Land Use at Sites 4-30
4.3.2 Institutional Controls 4-31
4.3.3 Applicability of OSHA Standards atNPL Sites 4-33
5.0 CALCULATION OF SSLS FOR A CONSTRUCTION SCENARIO 5-1
5.1 Applicability of the Construction Scenario 5-1
5.2 Soil Screening Exposure Framework for Construction Scenario 5-2
5.3 Calculating SSLs for the Construction Scenario 5-5
5.3.1 Calculation of Construction SSLs - Key Differences 5-5
5.3.2 SSL Equations for the Construction Scenario 5-7
IV
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TABLE OF CONTENTS
(continued)
REFERENCES R-l
APPENDICES
Appendix A:
Appendix B:
Appendix C:
Appendix D:
Appendix E:
Generic SSLs
SSL Equations for Residential Scenario
Chemical Properties and Regulatory/Human Health Benchmarks for SSL
Calculations
Dispersion Factor Calculations
Detailed Site-Specific Approaches for Developing Inhalation SSLs
v
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LIST OF EXHIBITS
Exhibit 1-1: Summary of Exposure Scenario Characteristics and Pathways
of Concern for Simple Site-Specific Soil Screening Evaluations 1-4
Exhibit 1-2: Summary of Default Exposure Factors For Simple Site-Specific
Soil Screening Evaluations 1-5
Exhibit 1-3: Soil Screening Overview 1-6
Exhibit 2-1: A General Guide to the Screening and SSL Concepts 2-2
Exhibit 2-2: Soil Screening Process 2-6
Exhibit 3-1: Recommended Exposure Pathways for Soil Screening Exposure Scenarios . . 3-2
Exhibit 3-2: Soil Contaminants Evaluated for Dermal Exposures 3-7
Exhibit 3-3: Recommended Dermal Absorption Fractions 3-10
Exhibit 4-1: Summary of the Commercial/Industrial Exposure Framework for Soil
Screening Evaluations 4-4
Exhibit 4-2: Site-Specific Parameters for Calculating Subsurface SSLs 4-20
Exhibit 4-3: Simplifying Assumptions for the SSL Migration to
Ground Water Pathway 4-27
Exhibit 5-1: Summary of the Construction Scenario Exposure Framework for
Soil Screening 5-3
Exhibit 5-2: Mean Number of Days with 0.01 Inch or More of Annual Precipitation .... 5-13
VI
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LIST OF EQUATIONS
Equation 3-1: Screening Level Equation for Combined Ingestion and Dermal
Absorption Exposure to Carcinogenic Contaminants in
Soil-Residential Scenario 3-5
Equation 3-2: Screening Level Equation for Combined Ingestion and Dermal
Absorption Exposure to Non-Carcinogenic Contaminants in
Soil-Residential Scenario 3-6
Equation 3-3: Calculation of Carcinogenic Dermal Toxicity Values 3-8
Equation 3-4: Calculation of Non-Carcinogenic Dermal Toxicity Values 3-8
Equation 3-5: Derivation of the Age-Adjusted Dermal Factor 3-9
Equation 4-1: Screening Level Equation for Combined Ingestion and
Dermal Absorption Exposure to Carcinogenic Contaminants
in Soil - Commercial/Industrial Scenario 4-14
Equation 4-2: Screening Level Equation for Combined Ingestion and
Dermal Absorption Exposure to Non-Carcinogenic Contaminants
in Soil - Commercial/Industrial Scenario 4-15
Equation 4-3: Screening Level Equation for Inhalation of Carcinogenic Fugitive Dusts -
Commercial/Industrial Scenario 4-17
Equation 4-4: Screening Level Equation for Inhalation of Non-Carcinogenic Fugitive
Dusts - Commercial/Industrial Scenario 4-17
Equation 4-5: Derivation of the Particulate Emission Factor - Commercial/Industrial
Scenario 4-18
Equation 4-6: Screening Level Equation for Inhalation of Carcinogenic Volatile
Contaminants in Soil - Commercial/Industrial Scenario 4-22
Equation 4-7: Screening Level Equation for Inhalation of Non-Carcinogenic Volatile
Contaminants in Soil - Commercial/Industrial Scenario 4-23
Equation 4-8: Derivation of the Volatilization Factor - Commercial/Industrial
Scenario 4-24
Equation 4-9: Derivation of the Soil Saturation Limit 4-25
Equation 4-10: Soil Screening Level Partitioning Equation for
Migration to Ground Water 4-28
Equation 4-11: Derivation of Dilution Attenuation Factor 4-28
Equation 4-12: Estimation of Mixing Zone Depth 4-29
Equation 4-13: Mass-Limit Volatilization Factor - Commercial/Industrial Scenario 4-29
Equation 4-14: Mass-Limit Soil Screening Level for Migration to Ground Water 4-29
vn
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LIST OF EQUATIONS
(continued)
Equation 5-1: Screening Level Equation for Combined Subchronic Ingestion and Dermal
Absorption Exposure to Carcinogenic Contaminants in Soil,
Construction Scenario - Construction Worker 5-8
Equation 5-2: Screening Level Equation for Combined Subchronic Ingestion and Dermal
Absorption Exposure to Non-Carcinogenic Contaminants in Soil,
Construction Scenario - Construction Worker 5-9
Equation 5-3: Screening Level Equation for Subchronic Inhalation of
Carcinogenic Fugitive Dusts, Construction Scenario
- Construction Worker 5-11
Equation 5-4: Screening Level Equation for Subchronic Inhalation of
Non-Carcinogenic Fugitive Dusts, Construction Scenario
- Construction Worker 5-11
Equation 5-5: Derivation of the Particulate Emission Factor, Construction Scenario
- Construction Worker 5-12
Equation 5-6: Derivation of the Dispersion Factor for Particulate Emissions from
Unpaved Roads - Construction Scenario 5-14
Equation 5-7: Screening Level Equation for Chronic Inhalation of Carcinogenic
Fugitive Dust, Construction Scenario - Off-Site Resident 5-15
Equation 5-8: Screening Level Equation for Chronic Inhalation of Non-Carcinogenic
Fugitive Dust, Construction Scenario - Off-Site Resident 5-15
Equation 5-9: Derivation of the Particulate Emission Factor, Construction Scenario
- Off-Site Resident 5-16
Equation 5-10: Mass of Dust Emitted by Road Traffic, Construction Scenario
- Off-Site Resident 5-17
Equation 5-11: Mass of Dust Emitted by Wind Erosion, Construction Scenario
- Off-Site Resident 5-17
Equation 5-12: Screening Level Equation for Subchronic Inhalation of Carcinogenic
Volatile Contaminants in Soil, Construction Scenario
- Construction Worker 5-18
Equation 5-13: Screening Level Equation for Subchronic Inhalation of
Non-Carcinogenic Volatile Contaminants in Soil, Construction Scenario
- Construction Worker 5-19
Equation 5-14: Derivation of the Subchronic Volatilization Factor, Construction Scenario
- Construction Worker 5-20
Equation 5-15: Derivation of the Dispersion Factor for Subchronic Volatile
Contaminant Emissions, Construction Scenario - Construction Worker . . . 5-21
Vlll
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LIST OF EQUATIONS
(continued)
Equation 5-16: Derivation of the Soil Saturation Limit 5-21
Equation 5-17: Mass-Limit Volatilization Factor, Construction Scenario
- Construction Worker 5-22
IX
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LIST OF ACRONYMS
ABS Absorption fraction
AF Skin-soil Adherence Factor
ARAR Applicable or Relevant and Appropriate Requirement
ASTM American Society for Testing and Materials
AT Averaging Time
ATSDR Agency for Toxic Substances and Disease Registry
BW Body Weight
CERCLA Comprehensive Environmental Response, Compensation, and Liability Act
C/I Commercial/Industrial
Csat Soil Saturation Limit
CSF Cancer Slope Factor
CSGWPP Comprehensive State Ground Water Protection Plan
CSM Conceptual Site Model
DAF Dilution Attenuation Factor
DDT p,p'-Dichlorodiphenyltrichloroethane
DOD Department of Defense
DOE Department of Energy
DQO Data Quality Objectives
Eco-SSLs Ecological Soil Screening Levels
ED Exposure Duration
EF Exposure Frequency
EPA Environmental Protection Agency
EV Event Frequency
HBL Health Based Level
HEAST Health Effects Assessment Summary Tables
HELP Hydrologic Evaluation of Landfill Performance
HI Hazard Index
HQ Hazard Quotient
1C Institutional Control
IF Age-adjusted Soil Ingestion Factor
IR Soil Ingestion Rate
IRIS Integrated Risk Information System
ISC3 Industrial Source Complex Dispersion Model
MCL Maximum Contaminant Level (in water)
MCLG Maximum Contaminant Level Goal (in water)
MRL Minimal Risk Level
NAPL Nonaqueous Phase Liquid
NPDWR National Primary Drinking Water Regulations
NPL National Priorities List
OSHA Occupational Safety and Health Administration
OSWER Office of Solid Waste and Emergency Response
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LIST OF ACRONYMS
(Continued)
PAH Polycyclic Aromatic Hydrocarbon
PA/SI Preliminary Assessment/Site Inspection
PCB Polychlorinated biphenyl
PEF Particulate Emission Factor
PRG Preliminary Remediation Goal
QA/QC Quality Assurance/Quality Control
Q/C Site-Specific Dispersion Factor
RAGS Risk Assessment Guidance for Superfund
RAS Regulatory Analytical Services
RBCA Risk-based Corrective Action
RCRA Resource Conservation and Recovery Act
RfC Reference Concentration
RfD Reference Dose
RI/FS Remedial Investigation/Feasibility Study
RME Reasonable Maximum Exposure
SA Surface Area
SAP Sampling and Analysis Plan
SCDM Superfund Chemical Data Matrix
SCS Soil Classification System
SPLP Synthetic Precipitation Leachate Procedure
SSG Soil Screening Guidance
SSL Soil Screening Level
TBD Technical Background Document
TC Soil-to-dust Transfer Coefficient
THQ Target Hazard Quotient
TR Target Cancer Risk
TRW Technical Review Workgroup for Lead
UCL Upper Confidence Limit
URF Unit Risk Factor
VF Volatilization Factor
VOC Volatile Organic Compound
XI
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1.0 INTRODUCTION
In 1996, EPA issued the Soil Screening Guidance (SSG), a tool developed by the Agency
to help standardize and accelerate the evaluation and cleanup of contaminated soils at sites on the
National Priorities List (NPL). The SSG provides site managers with a tiered framework for
developing risk-based, site-specific soil screening levels (SSLs).1 SSLs are not national cleanup
standards; instead, they are used to identify areas, chemicals, and pathways of concern at NPL sites
that need further investigation (i.e., through the Remedial Investigation/Feasibility Study) and those
that require no further attention under the Comprehensive Environmental Response, Compensation,
and Liability Act (CERCLA).2 The three-tiered framework includes a set of conservative, generic
SSLs; a simple site-specific approach for calculating SSLs; and a detailed site-specific modeling
approach for more comprehensive consideration of site conditions in establishing SSLs. The SSG
emphasizes the simple site-specific approach as the most useful method for calculating SSLs.
In developing the 1996 SSG, EPA chose to focus exclusively on future residential use of
NPL sites. At the time the guidance was developed, defining levels that would be safe for residential
use was very important because of the significant number of NPL sites with people living on-site
or in close proximity. In addition, the assumptions needed to calculate SSLs for residential use were
better established and more widely accepted than those for other land uses.
One of the most prevalent suggestions made during the public comment period on the 1996
SSG was that EPA should develop additional screening approaches for non-residential land uses.
This concern reflected the large number of NPL sites with anticipated non-residential future land
uses and the desire on the part of site managers to develop SSLs that are not overly conservative for
these sites.
Another concern raised during public comment addressed the risk to workers and others from
exposures to soil contaminants during construction activity. In the 1996 SSG, EPA presented
equations for developing SSLs for the inhalation of volatiles and fugitive dusts assuming that a site
was undisturbed by anthropogenic processes. This is likely to be a reasonable assumption for many
potential future activities at these sites, but not for construction that may be required to redevelop
a site. Activities such as excavation and traffic on unpaved roads can result in extensive soil
1 EPA uses the term "site manager" in this guidance to refer to the primary user of this document. However,
EPA encourages site managers to obtain technical support from risk assessors, site engineers, and others during all steps
of the soil screening process.
SSLs also can be incorporated into the framework for risk assessment planning, reporting, and review that
EPA has described in the Risk Assessment Guidance for Superfund Volume 1: Human Health Evaluation Manual Part
D (RAGS, PartD) (U.S. EPA, 1998). Specifically, SSLs can be incorporated into Standard Table 2 within this guidance,
which is designed to compile data to support the identification of chemicals of concern at sites.
1-1
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disturbance and dust generation that may lead to increased emissions of volatiles and particulates
for the duration of the construction project. Such increased short-term exposures are not addressed
by the 1996 SSG.
With this guidance document, EPA addresses the development of SSLs for residential land
use, non-residential land use, and construction activities.
1.1 Purpose and Scope
This document is intended as
companion guidance to the 1996 SSG
for residential use scenarios at NPL
sites. It builds upon the soil screening
framework established in the original
guidance, adding new scenarios for
soil screening evaluations. It also
updates the residential scenario in the
1996 SSG, adding exposure pathways
and incorporating new modeling data.
The following specific changes
included in this document supersede
the 1996 SSG:
New methods for developing SSLs
based on non-residential land use3
and construction activities;
New residential SSL equations for
combined exposures via ingestion
and dermal absorption4;
Updated dispersion modeling data
for the soil screening guidance air
exposure model; and
New methods to develop
residential and non-residential
SSLs for the migration of volatiles
from subsurface sources into indoor
RELATIONSHIP OF NON-RESIDENTIAL
SSL FRAMEWORK TO RAGS
EPA has previously provided guidance on evaluating exposure
and risk for non-residential use scenarios at NPL sites in the
following documents:
Risk Assessment Guidance for Superfund (RAGS),
Volume 1: Human Health Evaluation Manual
(HHEM), Supplemental Guidance, Standard Default
Exposure Factors, Interim Guidance (U.S. EPA,
1991a).
Risk Assessment Guidance for Superfund (RAGS),
Volume 1: Human Health Evaluation Manual
(HHEM), Part B, Development of Risk-based
Preliminary Remediation Goals (U.S. EPA, 1991b).
These two documents include default values and exposure
equations for a generic commercial/industrial exposure scenario
that have been widely used and that form the basis of many state
site cleanup programs, as well as RCRA's Risk Based Corrective
Action (RBCA) Provisional Standard for Chemical Releases.
However, the approaches detailed in these documents may not
always account for the full range of activities and exposures
within commercial and industrial land uses. The models,
equations, and default assumptions presented in this guidance
supersede those presented in the RAGS Supplemental Guidance
and RAGS Part B documents for evaluating exposures under non-
residential land use assumptions.
air.
A detailed discussion of EPA's recommended practices for identifying reasonably anticipated future land use
can be found in the EPA directive Land Use in the CERCLA Remedy Selection Process (1995a).
4 This document may be used in conjunction with the draft Risk Assessment Guidance for Superfund Volume
1: Human Health Evaluation Manual (Part E, Supplemental Guidance for Dermal Risk Assessment) -Interim Guidance
(U.S. EPA, 2001)
1-2
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Except for these new equations and updated modeling data, the soil screening process
remains the same as the one presented in the 1996 SSG. Therefore, this document presents the
process in less detail than the original guidance and focuses instead on the specific elements of soil
screening evaluation that differ for residential, non-residential, and construction scenarios. Users
of this guidance should refer to the SSG User's Guide and Technical Background Document (U.S.
EPA, 1996c and 1996b) for additional information on modeling approaches, data sources, and other
important details of conducting soil screening evaluations atNPL sites.
Although certain exposure pathways can be addressed using generic assumptions, this
document emphasizes the simple site-specific approach for developing SSLs. EPA believes that this
approach provides the best combination of site-specificity and ease of use. Exhibits 1-1 and 1-2
summarize the simple site-specific screening approaches discussed in this document. They address
three soil exposure scenarios: residential, non-residential (commercial/industrial), and construction.
Exhibit 1-1 describes the exposure characteristics and pathways of concern for each of the receptors
under these scenarios, and Exhibit 1-2 presents the relevant exposure factors. Pathways and
exposure factors listed in bold typeface under the residential scenario indicate changes from the
residential soil screening scenario originally presented in the 1996 SSG. These changes reflect
updates to EPA's method for evaluating exposures via the dermal contact and inhalation of indoor
vapors pathways. (See Chapter 3 for a detailed explanation of these methods.)
This document also discusses the detailed site-specific modeling approach to developing
SSLs. This approach can be used to conduct a more in-depth evaluation of any residential or
commercial/industrial scenario, but also is needed to develop SSLs for exposure scenarios associated
with additional non-residential land uses, such as recreational or agricultural use. These land uses
may involve exposure pathways that are not included in the generic and simple site-specific
approaches (e.g., ingestion of contaminated foods) and, therefore, require detailed site-specific
modeling.
The flowchart in Exhibit 1-3 provides an overview of the residential, commercial/industrial,
and construction exposure scenarios, illustrating the relationships among them and indicating the
sections of this document relevant to developing SSLs under each of the scenarios. As shown in the
flowchart, a soil screening evaluation involves identifying the likely anticipated future land use of
a site; selecting an approach to SSL development; developing SSLs according to EPA's seven-step
process; calculating supplemental construction SSLs (if necessary); and comparing site soil
concentrations to all applicable SSLs. In addition, because SSLs are based on conceptual site
models comprised of a complex set of assumptions about future land use and exposure scenarios,
care should be taken to ensure that future site activities are consistent with these assumptions (e.g.,
through the use of institutional controls).
This guidance document focuses solely on risks to humans from exposure to soil
contamination; it does not address ecological risks. For any soil screening evaluation (residential
or non-residential), an ecological assessment should be performed, independently of the soil
screening process for human health, to evaluate potential risks to ecological receptors. Assumptions
about human exposure pathways under specific land use scenarios are not relevant to assessing
ecological risks. Therefore, site managers should conduct a separate evaluation of risks to
ecological receptors.
1-3
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Exhibit 1-1
SUMMARY OF EXPOSURE SCENARIO CHARACTERISTICS AND PATHWAYS OF CONCERN
FOR SIMPLE SITE-SPECIFIC SOIL SCREENING EVALUATIONS
Scenario1
Receptor
Exposure
Characteristics
Pathways of
Concern
Residential2
On-site Resident
Substantial soil
exposures (esp.
children)
Significant time
spent indoors
Long-term
exposure
Ingestion (surface
and shallow sub-
surface soils)
Dermal
absorption
(surface and
shallow sub-
surface soils)2
Inhalation
(fugitive dust,
outdoor vapors)
Inhalation
(indoor vapors)
Migration to
ground water
Non-Residential
(Commercial/Industrial)
Outdoor Worker
Substantial soil
exposures
Long-term
exposure
Ingestion
(surface and
shallow sub-
surface soils)
Dermal
absorption
(surface and
shallow sub-
surface soils)
Inhalation
(fugitive dust,
outdoor
vapors)
Migration to
ground water
Indoor Worker
Minimal soil
exposures (no
direct contact
with outdoor
soils, potential
for contact
through
ingestion of soil
tracked in from
outside)
Long-term
exposure
Inhalation
(indoor vapors)
Ingestion (indoor
dust)
Migration to
ground water
Construction
Construction Worker
Exposed during
construction
activities only
Potentially high
ingestion and
inhalation exposures
to surface and
subsurface soil
contaminants
Short-term exposure
Ingestion (surface
and subsurface soil)
Dermal absorption
(surface and
subsurface soil)
Inhalation
(fugitive dust,
outdoor vapors)
Off-site Resident
Located at the site
boundary
Exposed during and
post-construction
Potentially high
inhalation exposures to
soil contaminants
Short- and long-term
exposure
Inhalation
(fugitive dust)
1 This exhibit presents information on simple site-specific soil screening evaluations for three exposure scenarios ~ residential, commercial/industrial,
and construction. Additional exposure scenarios (e.g., agricultural and recreational) may be appropriate for certain sites. Given the lack of generic
information available for these scenarios, site managers typically will need to use detailed site-specific modeling to develop SSLs for them.
2 Bold typeface indicates residential pathways that have changed since the 1996 SSG.
1-4
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Exhibit 1-2
SUMMARY OF DEFAULT EXPOSURE FACTORS FOR SIMPLE SITE-SPECIFIC SOIL SCREENING EVALUATIONS
Scenario1
Receptor
Exposure Frequency
(d/yr)
Exposure
Duration (yr)
Event Frequency
(events/d)
Soil Ingestion
Rate (mg/d)
Ground Water
Ingestion Rate3 (L/d)
Inhalation
Rate (m3/d)
Surface Area
Exposed (cm2)
Adherence
Factor (mg/cm2)
Body
Weight (kg)
Lifetime (yr)
Residential
On-site Resident2
350
30
[6 (child)4 for non-
cancer effects]
1
200 (child)
100 (adult)
2
205
2,800 (child)
5,700 (adult)
0.2 (child)
0.07 (adult)
15 (child)
70 (adult)
70
Non-Residential
(Commercial/Industrial)
Outdoor Worker
225
25
1
100
2
20
3,300
0.2
70
70
Indoor Worker
250
25
NA
50
2
20
NA
NA
70
70
Construction
Construction Worker
site-specific
site-specific
1
330
NA
20
3,300
0.3
70
70
Off -site Resident
site-specific
site-specific
NA
NA
NA
20
NA
NA
70
70
1 This exhibit presents information on simple site-specific soil screening evaluations for three exposure scenarios ~ residential, commercial/industrial, and
construction. Additional exposure scenarios (e.g., agricultural and recreational) may be appropriate for certain sites. Given the lack of generic information
available for these scenarios, site managers will typically need to use detailed site-specific modeling to develop SSLs for them.
2 Items in bold represent changes to the residential soil screening exposure scenario presented in the 1996 SSG.
3 SSLs for the migration to ground water pathway are based on acceptable ground water concentrations, which are, in order of preference: a non-zero
Maximum Contaminant Level Goal (MCLG), a Maximum Contaminant Level (MCL), or a health-based level (HBL) based on a 1 x 106 incremental lifetime
cancer risk or a hazard quotient of one due to ingestion of contaminated ground water. When an HBL is used, it is based on these ground water ingestion
rate values.
4 A child is defined as an individual between one and six years of age.
5 We evaluate residential inhalation exposure to children and adults using the RfC toxicity criterion, which is based on an inhalation rate of 20 iri /day. No
comparable toxicity criterion specific to childhood exposures is currently available. EPA has convened a workgroup to identify suitable default values for
modeling childhood inhalation exposures, as well as possible approaches for adjusting toxicity values for application to such exposures.
1-5
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Exhibit 1-3
SOIL SCREENING OVERVIEW
Residential
Identify Future
Land Use
(Section 4.1)
Other Non-Residential
Commercial/
Industrial (C/l)
Select Approach for Developing
Residential SSLs
(Generic, Simple Site-Specific, or
Detailed Site-Specific)
(Section 2.2)
Select Approach for Developing
C/l SSLs
(Generic, Simple Site-Specific, or
Detailed Site-Specific)
(Sections 2.2 and 4.1.4)
Conduct Detailed Site-Specific
Soil Screening
Develop Residential SSLs
(Sections 2.3, 3.1, and 3.2 and
Appendix B)
Select Approach for Calculating
Construction SSLs (Simple or
Detailed Site-Specific only)
(Sections 2.2 and 5.2)
Calculate Construction SSLs
(Sections 5.2 and 5.3)
Develop C/l SSLs
(Sections 2.3 and 4.2)
Does
Construction
Scenario Apply''
(Section 5.1)
Do Site
Soil Concentrations
Meet Minimum
Applicable SSLs?
Do Viable
Institutional
Control Options
Exist? (Sectio
4.3.2
Do Site
Soil
Concentrations
Meet Residential
SSLs?
1-6
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EPA is currently working with a multi-stakeholder workgroup to develop scientifically
sound, ecologically-based soil screening levels. The workgroup includes representatives from EPA,
Environment Canada, Department of Energy (DOE), Department of Defense (DOD), academia,
states, industry, and private consulting. This collaborative project will result in a Superfund
guidance document that includes a look-up table of generic ecological soil screening levels (Eco-
SSLs) for up to 24 chemicals that frequently are of ecological concern at Superfund sites. These
Eco-SSLs will be soil concentrations that are expected to be protective of the mammalian, avian,
plant, and invertebrate populations or communities that could be exposed to these chemicals.
1.2 Organization of Document
The remainder of this document is organized into four major chapters. Chapter 2 presents
a brief overview of soil screening evaluations. It discusses the soil screening concept, the three-
tiered screening framework, and the seven-step soil screening process. Chapter 3 focuses on the
exposure pathways considered in soil screening evaluation. It lists the key exposure pathways for
the three soil screening scenarios (residential, commercial/industrial, and construction) and presents
new methods for calculating SSLs for two exposure pathways dermal absorption (which
addresses the potential for concurrent exposure via the direct ingestion and dermal pathways) and
the migration of volatiles into indoor air. Chapter 4 addresses the development of non-residential
SSLs. It discusses approaches to identifying future land use, presents a non-residential exposure
framework, and provides equations for calculating site-specific non-residential SSLs. In addition,
Chapter 4 also discusses issues related to the derivation and application of non-residential SSLs,
including the importance of involving community representatives in identifying future land uses;
the selection and implementation of institutional controls to ensure that future site activities are
consistent with non-residential land use assumptions; and the relative roles of SSLs and OSHA
standards in protecting future workers from exposure to residual contamination at non-residential
sites. Finally, Chapter 5 describes methods for the development of construction SSLs that address
exposures due to construction activities occurring during site redevelopment.
Five appendices to this document provide supporting information for the development of
SSLs. Appendix A presents generic SSLs for residential and non-residential exposure scenarios.
The generic residential SSLs in Appendix A have been updated to reflect the changes discussed in
this document and supersede all previously published generic SSLs. Appendix B presents the
complete set of simple site-specific SSL equations for the residential exposure scenario that
incorporates changes to the 1996 SSG. Appendix C consists of chemical-specific information on
chemical and physical properties, as well as human health toxicity values for use in developing
SSLs. Appendix D provides tables of coefficients for calculating site-specific dispersion factors
for inclusion in the air dispersion equations used to calculate simple site-specific SSLs for the
inhalation pathway. Finally, Appendix E describes suggested modeling approaches that can be used
to develop detailed site-specific inhalation SSLs for the non-residential and construction scenarios.
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2.0 OVERVIEW OF SOIL SCREENING
This chapter of the guidance document provides a brief overview of soil screening
evaluations for sites on the NPL. It begins with a definition of the soil screening concept and a
discussion of its applicability and limitations, then describes three approaches to conducting soil
screening evaluations, and concludes with a review of EPA's seven-step soil screening process. For
a more in-depth and comprehensive discussion of these topics, please refer to Chapter 1.0 of EPA's
1996 SSG.
2.1 The Screening Concept
As used in this guidance, screening refers to the process of identifying and defining areas,
contaminants, and conditions at a site that do not warrant further federal attention under CERCLA.
Site managers make these determinations by comparing measured soil contaminant concentrations
to soil screening levels (SSLs). SSLs are soil contaminant concentrations below which no further
action or study regarding the soil at a site is warranted under CERCLA, provided that conditions
associated with the SSLs are met. In general, areas with measured concentrations of contaminants
below SSLs may be screened from further federal attention; if actual concentrations in the soil are
at or above SSLs, further study, though not necessarily cleanup action, is warranted.4 Exhibit 2-1
summarizes the definition and the applicability of the soil screening process and the associated
SSLs.
SSLs are risk-based soil concentrations derived for individual chemicals of concern from
standardized sets of equations. These equations combine EPA chemical toxicity data with
parameters defined by assumed future land uses and exposure scenarios, including receptor
characteristics and potential exposure pathways. Residential SSLs, initially described in the 1996
SSG and updated in this document, are based on exposure scenarios associated with residential
activities, while non-residential SSLs are based on scenarios associated with non-residential
activities.
For each chemical, SSLs are back-calculated from target risk levels. For the inhalation
pathway and for the combined direct ingestion/dermal absorption pathway (see Section 3.2), target
risk levels for soil exposures are a one-in-a-million (IxlO"6) excess lifetime cancer risk for
carcinogens and a hazard quotient (HQ) of one for non-carcinogens. SSLs for the migration to
ground water pathway are back-calculated from the following ground water concentration limits (in
order of preference): non-zero maximum contaminant level goals (MCLGs); maximum contaminant
levels (MCLs); or health-based limits (based on a cancer risk of IxlO"6 or an HQ of one).
4 Areas meeting federal SSLs may still warrant further study. Some EPA Regional Offices and states have
developed separate soil screening levels and/or preliminary remediation goals (PRGs) that may be more stringent than
those presented in this guidance (though these alternative levels are based on the same general methodology described
in this guidance). It is important that site managers confer with regional and state risk assessors when conducting soil
screening evaluations to ensure that any SSLs developed will be consistent with their accepted soil levels.
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Exhibit 2-1
A GENERAL GUIDE TO THE SCREENING AND SSL CONCEPTS
Screening Is:
A method for identifying and defining areas,
contaminants, and conditions at a site that generally
do not warrant further federal attention;
A means of focusing the Remedial Investigation/
Feasibility Study (RI/FS) and site risk assessment;
A means for gathering data for later phases of the
Superfund site remediation process.
SSLs Are:
Human health risk-based concentrations;
Levels below which no further action or study is
warranted under CERCLA, provided conditions
concerning potential exposures and receptors (e.g.,
future land use) are met;
Specific to assumed exposures and site conditions;
Potentially suitable for use as PRGs.
Screening Is Not:
Mandatory;
A substitute for an RI/FS or risk assessment;
Valid unless conditions associated with SSLs (e.g.,
assumed future land use and site activities) are met.
SSLs Are Not:
National cleanup standards;
Uniform across all sites;
Applicable to radioactive contaminants.
Although SSLs are "risk-based," the soil screening process does not eliminate the need to
conduct site-specific risk assessments as part of the Superfund cleanup process. However, the
screening process can help focus the risk assessment for a site on specific areas, contaminants, and
pathways, and data collected during the screening process can be used in the risk assessment.
Similarly, SSLs are not national cleanup standards, and exceedances of SSLs do not trigger the need
for response actions at NPL sites.
In addition, because SSLs are based on a set of assumptions about likely future land use and
site activities, they are only pertinent to the extent that future activities are consistent with these
assumptions. Institutional controls may serve to limit future land uses and associated exposures to
those assumed in a non-residential screening analysis, helping to ensure that the non-residential
SSLs (which may be based on less conservative exposure assumptions than residential SSLs) are
adequately protective. Institutional controls are not generally necessary for sites screened using
residential SSLs because the conservative assumptions incorporated in the residential exposure
scenario yield SSLs that are protective of non-residential uses as well. Further discussion of these
issues can be found in Land Use in the CERCLA Remedy Selection Process (U.S. EPA 1995a).
The use of SSLs for screening purposes during site investigation at CERCLA sites is not
mandatory. However, it is recommended by EPA as a tool to focus the RI/FS and site risk
assessment by identifying the contaminants and areas of concern, and to gather necessary
information for later phases of the RI/FS process.5
SSLs developed in accordance with this guidance can also be applied to Resource Conservation and Recovery
Act (RCRA) corrective action sites as "action levels," where appropriate, since the RCRA corrective action program
currently views the role of action levels as generally serving the same purpose as soil screening levels. For more
information, see 61 Federal Register 19432, 19439, and 19446 (May 1, 1996).
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SSLs also can be used as Preliminary Remediation Goals (PRGs) provided conditions found
during subsequent investigations at a specific site are the same as the conditions assumed in
developing the SSLs. EPA recognizes, however, that certain conservative assumptions built into
the generic and simple site-specific approaches to SSL development, while appropriate for a
screening analysis, may be overly conservative for setting PRGs and, ultimately, site cleanup levels.
For example, as described in the 1996 SSG, EPA chose to base generic and simple site-specific SSLs
for non-carcinogenic contaminants via soil ingestion on a conservative, childhood-only, six-year
exposure duration because several studies suggest that inadvertent soil ingestion is common among
children age 6 and younger (Calabrese et al., 1989; Davis et al., 1990; and VanWinjen et al., 1990).
The SAB noted that the combination of the six-year childhood exposure with a chronic RfD may
be appropriate for chemicals with toxic endpoints specific to children or with steep dose-repsonse
curves, but is likely to be overly protective for most contaminants (U.S. EPA, 1993). EPA believes
this protectiveness is appropriate for soil screening evaluations, but such conservatism may not be
necessary for developing PRGs and cleanup levels for many contaminants. Therefore, site managers
wishing to use SSLs as a basis for developing PRGs should carefully consider the assumptions built
into the SSLs and whether it may be appropriate to relax any of these assumptions for calculating
PRGs.
2.2 The Tiered Screening Framework/Selecting a Screening Approach
EPA's framework for soil screening assessment provides site managers with three approaches
to establish SSLs for comparison to soil contaminant concentrations:
Apply generic SSLs developed by EPA;
Develop SSLs using a simple site-specific methodology; or
Develop SSLs using a more detailed site-specific modeling approach.
These approaches involve using increasingly detailed site-specific information to replace
generic assumptions, thereby tailoring the screening model to more accurately reflect site conditions,
potential exposure pathways, and receptor characteristics. Additionally, progression from generic
to detailed site-specific methods generally results in less stringent screening levels because
conservative assumptions are often replaced with site-specific information while maintaining a
constant target risk level.
The first approach for developing screening levels is the simplest and least site-specific.
This approach assumes a generic exposure scenario, intended to be broadly protective under a wide
array of site conditions. The site manager simply compares measured soil concentrations to
chemical-specific SSLs derived by EPA based on the conservative generic scenario and provided
in a look-up table. (These tables, together with additional guidance on applying the generic SSLs
to individual sites, are presented in Appendix A of this document.) While this approach offers the
benefits of simplicity and ease of use, the generic SSLs are calculated using conservative
assumptions about site conditions and are thus likely to be more stringent than SSLs developed using
more site-specific approaches. Where site conditions differ substantially from the scenario used to
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derive the generic SSLs, generic levels may not be appropriate for identifying areas that can be
"screened out." The specific assumptions underlying the generic SSLs are identified in the equations
presented in Section 4.2.3 (non-residential exposure scenario) and in Appendix B (residential
exposure scenario).
The second approach, the simple site-specific methodology, allows site managers to calculate
SSLs using the same equations used to derive the generic SSLs. Unlike the generic approach, the
simple site-specific methodology offers some flexibility in the use of site-specific data for
developing SSLs. Though the target risk for SSLs remains the same, some of the generic default
input values may be replaced by site-specific information such as data on hydrological, soil, and
meteorological conditions. Thus, the simple site-specific approach retains much of the ease and
simplicity of the generic approach, while providing site managers increased freedom to replace the
conservative assumptions of the generic approach with data that more accurately reflect site
conditions. The result will be more tailored SSLs that are likely to be less stringent than the generic
values. As site managers change the assumptions used in developing the SSLs to reflect site-specific
information, they should have the changes reviewed by the regional risk assessor associated with
the site. Site managers should also document any changes they make to the exposure parameters
from the default values in order to develop simple site-specific SSLs.
As the name suggests, the detailed site-specific modeling approach is the most rigorous of
the three approaches and incorporates site-specific data to the greatest extent. This approach is
useful for developing SSLs that take into account more complex site conditions than those assumed
in the simple site-specific approach. The detailed approach may be appropriate, for example, to
demonstrate that the migration of soil contaminants to ground water does not apply at a particular
site, or to model distinct or unusual site conditions. Technical details supporting the use of this
approach can be found in Appendices D and E of this document and in the Technical Background
Document (TBD) for the 1996 SSG.
The decision regarding which of the three approaches is most appropriate for a given site
must balance the need for accuracy with considerations of cost and timeliness. While progression
from generic SSLs to a detailed site-specific modeling approach increases the accuracy of the
screening process, it also generally involves an increase in the resources, time, and costs required.
Deciding which option to use typically requires balancing the increased investigation effort with the
potential savings associated with higher (but still protective) SSLs. In general, EPA believes the
most useful approach to apply is the simple site-specific methodology, which provides a reasonable
compromise in terms of effort and site-specificity.
Although the simple site-specific approach is generally expected to be the most useful, there
are times when the generic or the detailed site-specific modeling approaches may be more
appropriate. The former can be used as an initial screening tool or as a "crude yardstick" to quickly
identify those areas which clearly do not pose threats to human health or the environment. In such
cases where exclusion appears clearly warranted, there is little need for more site-specific
information to justify this decision. The generic approach can also be used to quickly screen out
chemicals and focus the subsequent investigation on the key chemicals of concern. Generally,
detailed site-specific modeling is most useful in cases where: 1) the ability to conduct sophisticated
analyses, incorporating mostly site-specific data, could result in substantial savings in site
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investigation and cleanup costs due to an increase in the site area "screened out" of the remedial
process under CERCLA; or 2) site conditions are unique. For example, the detailed approach could
be used to assess unusual exposure pathways or conditions or to conduct fate and transport analyses
that describe the leaching of contaminants to ground water in a specific hydrogeologic setting.
2.3 The Seven-Step Soil Screening Process
Regardless of the screening approach chosen, the soil screening analysis consists of the seven
steps discussed in this section. EPA emphasizes that the overall seven-step site screening process
is not changing, and the same process is applied to residential and non-residential scenarios.
However, the evaluation of the non-residential and construction exposure scenarios described in this
guidance requires modifications to the steps of the screening process, especially to Steps 1, 2, and
5. These modifications are described in Section 4.2 and Section 5.3 of this document for the non-
residential and construction scenarios, respectively.
The seven-step soil screening process established in the 1996 SSG was designed to evaluate
the significance of soil contaminant concentrations at residential sites. Although some of the default
values and assumptions of the residential approach do not apply to commercial/industrial or
construction exposure scenarios, the same overall screening framework can be used to evaluate sites
under these scenarios. The basic elements of the seven steps are described below. Exhibit 2-2
presents a useful one-page summary of the full soil screening process. Please refer to the 1996 SSG
for additional information on the soil screening steps.
Step 1: Develop Conceptual Site Model
Developing a conceptual site model (CSM) is a critical step in properly implementing the
soil screening process at a site. The CSM is a comprehensive representation of the site that
documents current site conditions. It characterizes the distribution of contaminant concentrations
across the site in three dimensions and identifies all potential exposure pathways, migration routes,
and potential receptors. The CSM is initially developed from existing site data. This site data
should include input from community members about their site knowledge, concerns, and interests.
The CSM is a key component of the RI/FS and EPA's Data Quality Objectives (DQO) process, and
should be continually revised as new site investigations produce updated or more accurate
information. CSM summary forms and detailed information on the development of CSMs are
presented in Attachment A of the 1996 SSG User's Guide.
In addition, RAGS Part D, which is intended to assist site managers in standardizing risk
assessment planning, reporting, and review at CERCLA sites, provides a template that site mangers
can use to summarize and update data on the CSM. This template is the first in a series of standard
tables that EPA has developed to document important parameters, data, calculations, and
conclusions from all stages of Superfund human health risk assessments.
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Exhibit 2-2
SOIL SCREENING PROCESS
Step 1: Develop Conceptual Site Model
Collect existing site data (historical records, aerial photographs, maps, PA/SI data, available background
information, state soil surveys, etc.)
Collect community input
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 2: Compare CSM to SSL Scenario
Identify sources, pathways, and receptors likely to be present at the site and addressed by the soil screening
scenario
Identify additional sources, pathways, and receptors likely to be present at the site but not addressed by the soil
screening scenario
Step 3: Define Data Collection Needs for Soils
Develop hypothesis about distribution of soil contamination
Develop sampling and analysis plan for determining soil contaminant concentrations
Sampling strategy for surface soils following Data Quality Objectives (DQOs)
Sampling strategy for subsurface soils following Data Quality Objectives (DQOs)
Sampling strategy to measure soil characteristics (bulk density, moisture and organic carbon content,
porosity, pH)
Determine appropriate field methods and establish QA/QC protocols
Step 4: Sample and Analyze Soils
Identify contaminants
Delineate area and depth of sources
Determine soil characteristics
Revise CSM, as appropriate
Step 5: Calculate Site- and Pathway-Specific SSLs
Identify SSL equations for relevant pathways
Identify chemicals of concern for dermal exposure
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 6: Compare Site Soil Contaminant Concentrations to Calculated SSLs
For surface soils characterized using composite samples, screen out exposure areas where all composite
samples do not exceed SSLs by a factor of two
For surface soils characterized using discrete samples, screen out areas where the 95 percent upper confidence
limit (UCL,,) on the mean concentration for each contaminant does not exceed the corresponding SSL
For subsurface soils with indirect exposures, screen out source areas where the mean concentration of each
contaminant in each soil boring does not exceed the applicable SSL
For subsurface soils with direct exposures, screen out source areas where the highest soil boring concentration for
each contaminant does not exceed the applicable SSL
Evaluate whether background levels exceed SSLs
Step 7: 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, if appropriate
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Step 2: Compare CSM to SSL Scenario
In this step, the CSM for a site is compared to the SSL scenario and assumptions for
calculating generic and simple site-specific SSLs. This comparison should determine whether the
CSM is sufficiently similar to the SSL scenario so that use of the generic or simple site-specific SSL
scenario is appropriate. If the CSM contains sources, pathways, or receptors not covered by the
general SSL scenario, comparison to generic or simple site-specific SSLs alone may not be
sufficient to fully evaluate the site, suggesting the need to conduct detailed site-specific modeling.
However, it may be sufficient to eliminate some pathways or chemicals from further consideration.
It is crucial to engage in these efforts at this early stage in order to identify areas or conditions where
generic or simple site-specific SSLs are not sufficiently informative, so that other characterization
and response efforts can be considered when planning the sampling strategy (Step 3).
Step 3: Define Data Collection Needs for Soils
Upon initiating a soil screening evaluation, a site manager develops a Sampling and Analysis
Plan (SAP). The SAP should identify sampling strategies for filling any data gaps in the CSM
requiring collection of site-specific information. These strategies typically address contaminant
concentrations in surface and subsurface soil, as well as soil characteristics.
Before developing the SAP, the site manager should define the specific areas(s) to which the
soil screening process will be applied. Existing data can be used to determine what level and type
of investigation may be appropriate. Areas with known contamination will be thoroughly
investigated and characterized in the RI/FS. Areas that are unlikely to be contaminated based on
good historical documentation of the location of current and past storage, handling, or disposal of
hazardous materials at the site may generally be screened out at this stage; however, samples should
be taken to confirm this hypothesis. The remaining areas, those with uncertain contamination levels
and historical activities, are most appropriate for the soil screening sampling strategy outlined in the
1996 SSG.
For purposes of soil screening analyses, EPA distinguishes between surface and subsurface
soils as follows: surface soils are located within two centimeters of the ground surface, and
subsurface soils are located more than two centimeters below the surface. Because exposure to
contaminants in these two soil regions may occur via different mechanisms, sampling plans for these
two categories of soil should be designed to collect reliable data appropriate to the exposure models
involved. For example, the surface soil strategy should collect data appropriate for evaluating
exposure via direct ingestion, dermal contact, and inhalation of fugitive dusts as individuals move
randomly around a site. Typically, this requires a reliable estimate of the arithmetic mean of
contaminant concentrations in surface soils in exposure areas of concern. In general, the subsurface
soil sampling strategy should provide data to model the types of indirect exposure to subsurface
contamination that occurs when chemicals migrate up to the soil surface or down to an underlying
aquifer. Modeling these pathways usually requires an estimate of the average contaminant
concentration through each source, estimates of the dimensions of the source, and average soil
properties within the source. However, as discussed below, at some sites a sampling plan designed
to evaluate direct contact exposures may be appropriate for some subsurface soils.
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Site managers have two options for developing an SAP for surface soils: composite sampling
or discrete sampling. Either approach should allow you to calculate a reliable estimate of the
arithmetic mean of contaminant concentrations in surface soils. Composite sampling involves the
physical mixing of soils from multiple locations and then collecting one or more sub-samples from
the mixture. Details of a composite-based SAP are presented in the 1996 SSG. The maximum
contaminant concentration from composite sampling is a conservative estimate of the mean
concentration and can be used for soil screening evaluations. This approach can be an effective way
to estimate the mean contaminant concentration with lower sampling costs, because fewer samples
are needed. However, the mixing of soils in composite samples may disperse volatile contaminants
and also may dilute concentrations of other contaminants, resulting in less sensitivity to hot spots
and to other variations in contaminant concentrations. Alternatively, site managers can collect
discrete un-composited samples using a simple random sampling scheme (SRS), a stratified SRS6,
or systematic grid sampling with a random starting point. Details of alternative SAPs for discrete
sampling can be found in Guidance for Choosing a Sampling Design for Environmental Data
Collection (EPA 2000a). Because there is no spatial averaging of soil concentrations with this
method, a much larger number of soil samples is required to produce a reliable estimate of the mean
contaminant concentration. As a result, EPA recommends estimating the 95th percentile upper
confidence limit (UCL95) on the mean contaminant concentration as a conservative estimate of the
mean when performing a soil screening evaluation with data sets of un-composited samples.7
The 1996 SSG subsurface soil sampling strategy addresses exposure to subsurface
contamination that occurs when chemicals migrate up to the soil surface or down to an underlying
aquifer. It focuses on collecting the data required for modeling volatilization and migration to
ground water. As a result, the goals of this strategy are to measure the area and depth of
contamination, the average contaminant concentration in each source area, and the characteristics
of the soil. Accurately determining the mean concentration of subsurface soils using current
investigative techniques and statistical methods would require a costly and intensive sampling
program that is beyond the level of effort required for a screening analysis. Therefore, EPA
recommends that conservative assumptions be used to develop hypotheses on likely contaminant
distributions. EPA recommends taking 2 or 3 soil borings located in the areas suspected of having
the highest contaminant concentrations within each source. Because the subsurface sampling
approach is likely to be less comprehensive than the surface soil SAP, the soil screening analysis
focuses on the highest mean soil boring contaminant concentration within the source as a
conservative estimate of the mean contaminant concentration for the entire source area. The
subsurface SAP also should include the collection of site characteristics needed to determine site-
specific SSLs, including the following soil parameters: Soil Classification System (SCS) soil type,
dry bulk density (pb), soil organic carbon content (foc), and pH. Additional detail on this approach
can be found in the 1996 SSG User's Guide and Technical Background Document.
6Stratified SRS allows for random sample collection within sampling blocks designed to reflect anticipated site
activity patterns; thus, it more effectively targets areas where exposures are expected to occur.
EPA's Calculating Upper Confidence Limits For Exposure Point Concentrations at Hazardous Waste Sites,
provides a survey of statistical methods that may be used by site managers to estimate UCL95 values (U.S. EPA,2002a).
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For some CSMs, these three sampling approaches will suffice to characterize exposures to
contaminants in soil. However, other CSMs may feature residential activities (e.g., gardening) or
commercial/industrial (e.g., outdoor maintenance or landscaping) or construction activities that may
disturb soils to a depth of up to two feet, potentially exposing receptors to contaminants in
subsurface soil via direct contact pathways such as ingestion and dermal absorption. In such cases,
EPA anticipates that site managers will need to characterize contaminant levels by taking shallow
subsurface borings where appropriate. The specific locations of such borings should be determined
by the likelihood of direct contact with these subsurface soils and by the likelihood that soil
contamination is present at that depth. Given that contamination in these deeper soils is unlikely to
be characterized to the same extent as contamination in surface soils, the maximum measured
concentration of each contaminant in these borings should used as a conservative estimate of the
mean contaminant concentration for purposes of the soil screening evaluation.
Alternatively, if available evidence strongly indicates that contaminated subsurface soils will
be disturbed and brought to the surface (e.g., as the result of redevelopment activities), site managers
will need to characterize subsurface contamination more thoroughly and should collect a sufficient
number of samples to develop a UCL95 value for use in the soil screening evaluation.
For both surface and subsurface soils, site managers should use the Data Quality Objectives
(DQO) process in developing SAPs to ensure that sufficient data are collected to properly assess site
contamination and support decision-making concerning future Superfund site activities. The DQO
process is a systematic planning process designed to ensure that sufficient data are collected to
support EPA decision-making. Section 2.3 of the 1996 SSG describes this process in detail.
Step 4: Sample and Analyze Site Soils
Once sampling strategies have been developed and implemented, the samples are analyzed
according to the methods specified in the SAP. The analytic results provide the concentration data
for contaminants of concern that are used in the comparison to SSLs (Step 6). Soil analysis also
helps to define the areal extent and depth of contamination, as well as soil characteristics data. This
information is needed to calculate site-specific SSLs for the inhalation of volatiles and migration to
ground water pathways.
The analyses of soil contaminants and characteristics may reveal new information about site
conditions. It is critical that the CSM be updated to reflect this information.
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Step 5: Calculate Site- and Pathway-Specific SSLs
Using the data collected in Step 4 above, site-specific soil screening levels can be calculated
according to the methods presented under this step of the SSG. (If generic SSLs are used for
comparison with site contaminant concentrations, this step may be omitted.) Both the 1996 SSG and
this guidance document provide equations necessary to develop simple site-specific SSLs. Also,
an interactive SSL calculator for simple site-specific equations is available online at
http://risk.lsd.ornl.gov/calc_start.htm.8 Descriptions of how these equations were developed and
background information on underlying assumptions and limitations are available in the TBD for the
1996 SSG as well as in Chapters 3, 4, and 5 of this document. The default exposure assumptions
and equations for calculating residential SSLs can be found in Chapter 3 and in Appendix B of this
document. Additional information on default residential assumptions can be found in the 1996 SSG
User's Guide and TBD. The default assumptions and equations for calculating non-residential SSLs
are presented in Chapter 4. (Alternatively, tables of generic SSLs for these two scenarios are
presented in Appendix A.) The equations used to calculate SSLs based on construction activities
are presented in Chapter 5.
All SSL equations in the 1996 SSG were designed to be consistent with the concept of
Reasonable Maximum Exposure (RME) in the residential setting. In following the Superfund
program's approach for estimating RME, EPA uses reasonably conservative defaults for intake and
exposure duration, combined with values for site-specific parameters (e.g., for soil or hydrologic
conditions) that reflect average or typical site conditions, to develop risk-based SSLs. EPA bases
SSLs on RME assumptions rather than central tendency conditions because this approach results in
a conservative (though not a worst case) estimate of long-term exposure that is protective of the
majority of the population.
The 1996 SSG quantitatively addresses four exposure pathways direct ingestion,
inhalation of fugitive dusts, inhalation of volatiles in outdoor air, and ingestion of ground water
contaminated by the migration of contaminants through soil to an underlying potable aquifer. This
guidance includes these four pathways plus dermal contact exposures and inhalation of volatiles in
indoor air from vapor intrusion.
Step 6: Compare Site Soil Contaminant Concentrations
to Calculated SSLs
Once site-specific SSLs have been calculated (or the appropriate generic SSLs from
Appendix A have been identified), they are compared to the measured concentrations of
contaminants of concern. At this point, it is important to review the CSM to confirm its accuracy
in light of the actual site data that have been collected in previous steps of the soil screening process.
This also will help to ensure that the SSL scenarios are applicable to the site.
The SSL calculator currently includes default values for residential exposures; however, users can adjust these
defaults to reflect non-residential exposure scenarios.
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The following are four methods for deciding whether an exposure area can be screened from
further investigation two for surface soil contamination and two for subsurface soil
contamination. Each method specifies a particular estimator of the true mean concentration to be
used in a screening evaluation, as well as the screening level to which the estimate is compared.
Compare Maximum Composite Concentration to 2 x SSL (Surface
Soils). For surface soils that have been sampled using composite samples in
accordance with the DQOs discussed in the 1996 SSG, the maximum
composite sample concentration is compared to two times the SSL; areas
where the maximum composite sample concentration is less than two times
the SSL can be screened out. Further study is needed for areas where any
composite sample concentration equals or exceeds twice the applicable SSL
for one or more contaminants.9 The 1996 SSG notes that the surface soil max
test strategy that employs composites is applicable for semivolatiles,
inorganics, and pesticides only.
Compare 95 Percent Upper Confidence Limit on the Mean to SSL
(Surface Soils). For data sets consisting of discrete samples or data sets of
limited sample size, EPA uses statistical methods to calculate a conservative
estimate of the arithmetic mean concentration for each contaminant in an
exposure area. This estimate, the 95 percent upper confidence limit (UCL95)
on the mean is used to avoid underestimating the true mean (and thereby
ensure that the screening process is protective of human health). The UCL95
may be estimated by a variety of statistical methods depending on the
characteristics of the data set (e.g., the Chebyshev inequality, the bootstrap
method, and the jackknife method); these methods are described in
Calculating Upper Confidence Limits for Exposure Point Concentrations at
Hazardous Waste Sites (U.S. EPA, 2002a).
Compare Mean Concentration in Soil Borings to SSL (Subsurface
Soils/Indirect Exposure). Where direct contact exposure to subsurface soil
is not an issue, subsurface soil sampling under the SSL DQOs is generally
limited to two or three borings per source area. As discussed in Step 3,
subsurface soil sampling strategies focus on the collection of data for
modeling the volatilization and migration to ground water pathways (i.e., the
area and depth of contamination, soil characteristics, and the average
contaminant concentration in each source area. Because the expense and
level of effort involved in a precise determination of these values for a
subsurface contamination source is well beyond the level of effort generally
9 Given the sampling approach described in the 1996 SSG, which focused on a strategy of collecting composite
samples, two times the SSL was determined to be a reasonable upper limit for comparison that would still be protective
of human health. See the 1996 SSG TBD for a complete discussion of the protectiveness of this level (U.S. EPA,
1996b).
2-11
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appropriate for a screening evaluation, these soils tend not to be characterized
to the same extent as surface soils. Therefore, for these soils, the ^G adopts
a conservative approach for soil screening decisions of comparing mean
concentrations from each boring directly to the SSL. In areas where the
mean concentrations of all borings fall below the SSL, the area may be
screened out. In all other areas, further study is required.10
Compare Maximum Concentration in Soil Borings to SSL (Subsurface
Soils/Direct Exposure). At sites where activities may disturb subsurface
soils and result in direct contact exposures to contaminants in those soils,
EPA anticipates that site managers will characterize contaminant levels by
taking samples from additional subsurface borings in areas of soil likely to
be disturbed. Given that contamination in these deeper soils is unlikely to
be characterized to the same extent as contamination in surface soils, the
maximum measured concentration of each contaminant in these borings
should used as a conservative estimate of the mean contaminant
concentration and compared directly with the appropriate SSL. If the
maximum concentration of each contaminant in a given area falls below its
SSL, the area may be screened out. For all other areas, additional study is
required.11
Exposures to Multiple Chemicals
Exposures to multiple chemicals are treated similarly for non-residential and
residential soil screening evaluations. The project manager should coordinate with the risk
assessor to determine the health end points caused by each chemical and combinations of
several chemicals. EPA believes that the IxlO"6 target cancer risk level for individual
chemicals and pathways generally will lead to cumulative site risks within the IxlO"4 to
Ix 10"6 risk range for the combinations of chemicals typically found at NPL sites. For non-
carcinogens, EPA recommends that non-carcinogenic contaminants 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 or organ system, SSLs for those chemicals should be
divided by the number of chemicals present in the group
10 The SSL DQO sampling approach will not yield sufficient data for calculating a 95 percent UCL for the
arithmetic mean contaminant concentration in subsurface soil. However, should there be sufficient data for this
calculation, site managers have the option of comparing either the 95 UCL value for the site or the contaminant
concentrations in each boring to the SSL.
11 Alternatively, if available evidence indicates that contaminated subsurface soils will be disturbed and brought
to the surface (e.g., as the result of redevelopment activities), site managers will need to characterize subsurface
contamination more thoroughly and should collect a sufficient number of samples to develop a UCL95 value for
comparison to the SSL.
2-12
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Step 7: Address Areas Identified for Further Study
Areas that have been identified for further study become the subject of the RI/FS.
The results of the baseline risk assessment, which is part of the RI/FS, will establish the
basis for taking any remedial action; however, the threshold for initiating this action differs
from the screening criteria. As outlined in Role of the Baseline Risk Assessment in
SuperfimdRemedy Selection Decisions (U.S. EPA, 1991c), remedial action at NPL sites is
generally warranted where cumulative risks (i.e., total risk from exposure to multiple
contaminants at a site) for a current or future land use exceed IxlO"4 for carcinogens or a
hazard index (HI) of one for non-carcinogens. The data collected for soil screening
evaluations will be useful in developing the baseline risk assessment. However, site
managers will probably need to collect additional data during future site investigations
conducted as part of the RI/FS. These additional data will allow site managers to better
define the risks at a site and could ultimately indicate that no action is required. If a
decision is made to initiate remedial action, the SSLs may then serve as PRGs. For further
guidance on this issue, please consult Sections 1.2 and 2.7 of the 1996 SSG.
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3.0 EXPOSURE PATHWAYS
The 1996 SSG provides quantitative methods to derive SSLs for the following exposure
pathways under a residential soil exposure scenario:
Direct ingestion,
Inhalation of volatiles outdoors,
Inhalation of fugitive dust outdoors, and
Ingestion of ground water contaminated by the migration of soil leachate to
an underlying aquifer.
In addition, that document qualitatively addressed dermal absorption of contaminants from soil
exposure. Together, these five pathways formed the basis for EPA's generic and simple site-specific
approaches to residential soil screening evaluations.
This chapter updates the 1996 SSG in three ways. First, it presents a list of key exposure
pathways for three soil screening exposure scenarios: residential, commercial/industrial, and
construction. Second, it presents equations for a combined soil ingestion/dermal absorption SSL
that includes a new quantitative approach for evaluating dermal absorption. Third, it presents a new
quantitative approach for evaluating the inhalation of volatile contaminants present in indoor air as
the result of vapor intrusion.
3.1 Exposure Pathways by Exposure Scenario
Exhibit 3-1 lists default soil exposure pathways for each of three soil screening exposure
scenarios: residential, commercial/industrial, and construction. The list of pathways for each
scenario is not intended to be exhaustive; instead, each list represents a set of typical exposure
pathways likely to account for the majority of exposure to soil contaminants at a site. The actual
exposure pathways evaluated in a soil screening evaluation depend on the contaminants present, the
site conditions, and the expected receptors and site activities described in the CSM. A CSM may
include additional receptors or exposure pathways not addressed by this document or by the 1996
SSG (e.g., ingestion of contaminated fish by subsistence anglers). Conversely, not all the pathways
listed in Exhibit 3-1 for a particular scenario may apply to a given site. As a result, it is important
to compare the CSM with the assumptions and limitations associated with each applicable exposure
scenario to identify whether additional or more detailed assessments are needed for particular
exposure pathways. Early identification of the need for additional analysis is important because it
facilitates development of a comprehensive sampling strategy.
5-1
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Exhibit 3-1
RECOMMENDED EXPOSURE PATHWAYS FOR SOIL SCREENING EXPOSURE SCENARIOS
Potential Exposure
Pathways
Direct ingestion
Dermal absorption
Inhalation of volatiles
outdoors
Inhalation of fugitive
dust outdoors
Migration of volatiles
into indoor air
Ingestion of ground
water contaminated by
the migration of
leachate to an
underlying aquifer
Residential
Surface
Soil1
/
/
/
Subsurface
Soil
/
/
/
/
/
Commercial/Industrial
Outdoor Worker
Surface
Soil
/
/
/
Subsurface
Soil
/
/
/
/
Indoor Worker
Surface
Soil
/
Subsurface
Soil
/
/
Construction
Construction Worker
Surface
Soil
/
/
/
Subsurface
Soil
/
/
/
Off-Site Resident
Surface
Soil
/
Subsurface
Soil
1 For the purposes of soil screening evaluations, EPA defines surface soil as consisting of the top two centimeters of soil, and subsurface soil as soils located beneath the top two
centimeters. However, at sites where the CSM suggests that receptors will frequently come into direct contact with soils at depths greater than two centimeters, contaminant
concentrations in these soils should be compared to SSLs developed for surface soils.
3-2
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The methods for evaluating exposures via the inhalation of volatiles outdoors, the inhalation
of fugitive dust outdoors, and the ingestion of leachate-contaminated ground water under the
residential scenario have not changed since the publication of the 1996 SSG; detailed information
about the modeling approaches for these exposure pathways can be found in the 1996 SSG User's
Guide and Technical Background Document. Section 3.2 of this document discusses new methods
for developing SSLs for combined exposures via soil ingestion and dermal absorption and for the
migration of volatiles into indoor air. It also presents residential SSL equations for the soil
ingestion/dermal absorption pathway and directs readers to the spreadsheet models that can be used
to evaluate the indoor air pathway. For convenience, the complete set of residential SSL equations
and default assumptions has been reproduced in Appendix B. (SSL equations for the
commercial/industrial and construction scenarios are presented in Chapters 4 and 5, respectively.)
In addition, an interactive SSL calculator is available online at http://risk.lsd.ornl.gov/calc_start.
htm.
In general, each exposure scenario uses a similar modeling approach for a given exposure
pathway. Differences in exposure scenarios are reflected primarily in the specific default model
input values associated with the different types of exposures. However, in the case of the migration
to ground water pathway, both the modeling approach and model inputs for the residential and
commercial/industrial scenarios are identical, and hence so are the associated SSLs.10 This approach
is consistent with EPA's policy to protect potentially potable ground water resources. The treatment
of migration to ground water SSLs for commercial/industrial scenarios is discussed further in
Section 4.2.3.
3.2 Exposure Pathway Updates
Since publishing the 1996 SSG, EPA has developed new technical approaches for two
exposure pathways relevant to soil screening evaluations: dermal absorption and inhalation of
volatiles present in indoor air as the result of vapor intrusion. In addition, although EPA has not
changed the way it models soil ingestion exposures, this guidance provides site managers with new
SSL equations that combine soil ingestion and dermal absorption. This section presents an overview
of these new approaches to SSL development and includes the associated SSL equations for
residential exposure scenarios. (The residential SSL equations presented in this guidance supersede
the equations described in the 1996 SSG.) Chapter 4 of this document includes a discussion of the
application of these methods to non-residential exposure scenarios, and Chapter 5 addresses the
application of the ingestion/dermal approach for construction scenarios.
10 This pathway is not evaluated under the construction exposure scenario. Since the construction scenario
supplements either the residential or commercial/industrial scenario, migration to ground water SSLs from either of
those chronic exposure scenarios are expected to be protective of subchronic exposures via this pathway during
construction.
3-3
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3.2.1 Direct Ingestion and Dermal Absorption of Soil Contaminants
EPA has developed an approach that site managers can use to calculate SSLs for concurrent
exposures to contaminants via the direct ingestion and dermal absorption pathways. This approach
consists of a set of equations that allows a site manager to estimate the soil contaminant
concentration for which the combined potential exposure via these two pathways is equivalent to
an incremental lifetime cancer risk of 1x10"6 or an HQ of one the same target risks used for other
pathways. This yields SSLs that are protective of exposures that occur via these pathways
simultaneously. EPA developed this approach because concurrent exposures via these two pathways
are very likely during activities such as gardening, outdoor work, children's outdoor play, and
excavation.11
Equations 3-1 and 3-2 present EPA's approach to developing combined SSLs for the
ingestion and dermal pathways. Equation 3-1 is appropriate for addressing exposure to carcinogenic
compounds, and Equation 3-2 covers exposure to non-carcinogenic compounds. Site data may be
used to derive site-specific input values for the model parameters that appear in bold typeface. EPA
provides default values for these parameters that can be used when site-specific data are not
available. Appendix A presents generic ingestion/dermal SSLs for the residential exposure scenario
that were calculated using these equations and the specified default values.
11 Although these activities also may lead to exposure via inhalation, EPA will continue to evaluate these
exposures separately because of the potential for different health effects via the inhalation route. Differences in health
effects can be associated with differences in metabolic processes for contaminants entering the body via the
ingestion/dermal and inhalation exposure routes. As a result, EPA recommends developing separate SSLs for exposures
via inhalation.
3-4
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Equation 3-1
Screening Level Equation for Combined Ingestion and Dermal Absorption
Exposure to Carcinogenic Contaminants in Soil
- Residential Scenario
Screening
Level =
(mg/kg)
TRxATx365d/yr
6
kg/mg)[(SF0x|Fsoil/adj) + (SFABSxSFSxABSdxEV)]
Parameter/Definition (units)
TR/target cancer risk (unitless)
AT/averaging time (years)
EF/exposure frequency (days/year)
SFABS/dermally adjusted cancer slope factor (mg/kg-d)"1
SFS/age-adjusted dermal factor (mg-yr/kg-event)
ABSd/dermal absorption fraction (unitless)
EV/event frequency (events/day)
l cancer slope factor (mg/kg-d)"1
IFsoN/adj/age-adjusted soil ingestion factor (mg-yr/kg-d)
Default
1Q-6
70
350
chemical-specific
(Equation 3-3)
360
(Equation 3-5)
chemical-specific
(Exhibit 3-3 and Appendix C)
1
chemical-specific
(Appendix C)
114a
Calculated per RAGS, PARTB Equation 3. (U.S. EPA, 1991b)
Direct Ingestion
The components of Equations 3-1 and 3-2 that reflect modeling of exposures via soil
ingestion remain unchanged from the approach used in the 1996 SSG. For carcinogens, Equation
3-1 assumes a high end exposure duration (30 years) and incorporates a time-weighted average soil
ingestion rate for children and adults (incorporated in the soil ingestion factor, IFsoil/adj), because
exposure is higher during childhood and decreases with age. For non-carcinogens, Equation 3-2
focuses on childhood ingestion exposures only, a conservative approach that EPA believes is
appropriate for a screening analysis and is consistent with RME exposure.
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Equation 3-2
Screening Level Equation for Combined Ingestion and Dermal Absorption
Exposure to Non-Carcinogenic Contaminants in Soil
- Residential Scenario
Screening THQxBWxATx365d/yr
{ \ ( M
(mg/kg) (FFxEDxin 6ka/man 1 x|R + 1 xAFxABS xFVxSA
a/ ^ RfD0 ) ( RfDABS d ) \
Parameter/Definition (units)
THQ/target hazard quotient (unitless)
BW/body weight (kg)
AT/averaging time (years)
EF/exposure frequency (days/year)
ED/exposure duration (years)
RfDo/oral reference dose (mg/kg-d)
IR/soil ingestion rate (mg/d)
RfDABS/dermally-adjusted reference dose (mg/kg-d)
AF/skin-soil adherence factor (mg/cm2-event)
ABSd/dermal absorption factor (unitless)
EV/event frequency (events/day)
SA/skin surface area exposed-child (cm2)
Default
1
15
6a
350
6
chemical-specific
(Appendix C)
200
chemical-specific
(Equation 3-4)
0.2
chemical-specific
(Exhibit 3-3 and Appendix C)
1
2,800
3 For non-carcinogens, averaging time equals exposure duration.
Dermal Absorption
Although the 1996 SSG acknowledged that contaminant exposure through dermal absorption
could be a significant source of human health risks at contaminated sites, data limitations precluded
the development of broadly applicable simple site-specific equations for this pathway. EPA's
original approach recommended that dermal screening levels be calculated by dividing ingestion
SSLs in half for those compounds exhibiting significant (i.e., greater that ten percent) dermal
absorption. EPA based this approach on the assumption that exposures via the dermal route would
3-6
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be roughly equivalent to the ingestion route when dermal absorption from soil exceeds ten percent.12
At the time, only pentachlorophenol had been shown to exceed the ten percent absorption threshold;
for all other compounds, the dermal route did not need to be considered.
Since 1996, EPA has expanded its dermal absorption database to include more contaminants.
This information can be found in EPA's Risk Assessment Guidance for Superfund Volume I: Human
Health Evaluation Manual, Part E, Supplemental Guidance for Dermal Risk Assessment (RAGS
Part E - Interim Guidance, U.S. EPA, 2001). The modeling approach presented in this soil
screening guidance is derived from the risk assessment
methodology presented in RAGS Part E. This revised
approach provides a consistent and more broadly
applicable methodology for assessing the dermal
pathway for Superfund human health risk assessments.
The dermal pathway should be evaluated for
both residential and non-residential soil exposure
scenarios depending on the types of activities occurring
at a site (e.g., landscaping) and on the contaminants of
concern present. The approach to modeling dermal
absorption in this guidance supersedes EPA's original
approach and should therefore be used instead of the
dermal absorption method presented in the 1996 SSG.
Exhibit 3-2 presents a list of contaminants for which
data are available to develop dermal SSLs.13 This
exhibit includes seven individual compounds and two
classes of compounds polycyclic aromatic
hydrocarbons (PAHs) and semi-volatile organic
compounds demonstrating significant dermal absorption potential in EPA's dermal absorption
database. EPA will provide updates to this list as adequate absorption data are developed for
additional chemicals.
Exhibit 3-2
SOIL CONTAMINANTS EVALUATED
FOR DERMAL EXPOSURES
Arsenic
Benzo(a)pyrene
Cadmium
Chlordane
DDT
Lindane
PAHs
Pentachlorophenol
Semi-volatile organic compounds
12Dermal absorption efficiency is a function of the length of time that contaminated soils (or other media)
contact the skin of a receptor. Consistent with EPA's RAGS Part E interim guidance document for evaluating dermal
exposures to contaminants (U.S. EPA, 2001), all dermal absorption efficiency values reported in this document assume
24-hour exposure events.
13 Dermal absorption data are also available for PCBs and for 2,3,7,8-tetrachlorodibenzodioxin (TCDD);
however, EPA is developing separate guidance to address risks from release of these compounds. For PCBs, EPA is
in the process of updating its 1990 Guidance on Remedial Actions for Superfund Sites with PCB Contamination. For
TCDD and other chlorinated dioxins and furans, please consult the Draft Exposure and Human Health Reassessment
of2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds (U.S. EPA, 2000c).
3-7
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Equation 3-3
Calculation of Carcinogenic
Dermal Toxicity Values
SF - SFฐ
SF*BS ABS0
Parameter/Definition (units)
SFABS/dermally adjusted slope
factor (mg/kg-d)"1
SFo/oral slope factor (mg/kg-d )~1
ABSG/gastro-intestinal absorption
factor (unitless)
Default
chemical-specific
chemical-specific
(Appendix C)
chemical-specific
(Appendix C)
Because no toxicity data are
presently available for directly evaluating
dermal exposures to contaminants, EPA
has developed a method to extrapolate oral
toxicity values for use in dermal risk
assessments. This extrapolation method,
shown in Equations 3-3 and 3-4, is
necessary because most oral RfDs and
cancer slope factors are based on an
administered dose (e.g., in food or water)
while dermal exposure equations estimate
an absorbed dose. Specifically, dermal
exposure equations account for the relative
ability of a given contaminant to pass
through the skin and into the bloodstream.
The extrapolation method applies a gastro-
intestinal absorption factor (ABSGI) to the
available oral toxicity values to account for
the absorption efficiency of an
administered dose across the gastro-
intestinal tract and into the bloodstream.
Oral toxicity values should be adjusted
when the gastro-intestinal absorption of the
chemical in question is significantly less
than 50 percent; this cutoff reflects the
intrinsic variability in the analysis of
absorption studies. A list of chemical-
specific ABSGI factors for specific
compounds is presented as Exhibit C-7 in
Appendix C.
To be protective of exposures to
carcinogens in a residential setting,
Superfund focuses on individuals who may
live in an area for an extended period of
time (e.g., 30 years) from childhood
through adulthood. Equation 3-1 uses an
age-adjusted dermal factor (SFS) to account for changes in skin surface area, body weight, and
adherence factor. The SFS, presented in Equation 3-5, is a time-weighted average of these
parameters for receptors exposed from age one to 31. EPA recommends that a default SFS of 360
mg-yr/kg-event be used. For more information regarding the derivation of this time-weighted
average value, please consult RAGS, PartE Section 3.2.2.5, Equation 3.20.
Equation 3-4
Calculation of Non-Carcinogenic
Dermal Toxicity Values
RfDABS=RfD0xABSGI
Parameter/Definition (units)
RfDABS/dermally adjusted reference
dose (mg/kg-d)
RfD0/oral reference dose
(mg/kg-d)
ABSG/gastro-intestinal absorption
factor (unitless)
Default
chemical-specific
chemical-specific
(Appendix C)
chemical-specific
(Appendix C)
3-8
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Equation 3-5
Derivation of the Age-Adjusted Dermal Factor
SFS
S^ 6XAF1 6XED1 -e j , [SA7_31 xAF7 31 xED7 31 1
[ BW, 6 J [ BW731 J
Parameter/Definition (units)
SFS/age-adjusted dermal factor (mg-yr/kg-event)
SA^/skin surface area exposed-child (cm2)
SA7.31/skin surface area exposed-adult (cm2)
AF^e/skin-soil adherence factor-child (mg/cm2 - event)
AF7.31/skin-soil adherence factor-adult (mg/cm2 -event)
ED-i.g/exposure duration-child (years)
ED7_31/exposure duration-adult (years)
BW^/body weight-child (kg)
BW7_31/body weight-adult (kg)
Default
360
2,800
5,700
0.2
0.07
6
24
15
70
Although children will have a smaller total skin surface area (SA) exposed than adult
receptors, they are assumed to have a much higher soil to skin adherence factor (AF). Recent data
provide evidence to demonstrate that: 1) soil properties influence adherence, 2) soil adherence varies
considerably across different parts of the body, and 3) soil adherence varies with activity (Kissel et
al, 1996, Kissel et al, 1998, Holmes et al, 1999). Because children are assumed to have additional,
more sensitive body parts exposed (e.g., feet) and to engage in higher soil contact activities (e.g.,
playing in wet soil), this guidance recommends the use of a body part-weighted AF of 0.2 for
children and 0.07 for adults in residential exposure scenarios. In order to remain adequately
protective, EPA bases SSLs for residential exposures to non-carcinogenic contaminants via the
ingestion/dermal absorption pathways on a conservative "childhood only" scenario in which the
receptor is assumed to be between ages one through six. This is the approach reflected in Equation
3-2. For more information regarding the calculation of body part-weighted adherence factors, please
refer to Section 3.2.2 in RAGS, PartE.
Suggested default RME values in RAGS, PartE are appropriate for the dermal absorption-
related inputs to Equations 3-1, 3-2, and 3-5. The default values for these inputs are also consistent
with the residential scenario presented in the 1996 SSG. In addition to those inputs described above,
default values have been developed for event frequency (EV) and skin surface area exposed (SA).
Event frequency (EV, the number of events per day) is assumed to be equal to one. Children are
assumed to have 2,800 cm2 of exposed skin surface area (face, forearms, hands, lower legs, and
feet), while adults are assumed to have 5,700 cm2 exposed (face, forearms, hands, and lower legs).
These SA values represent the median (50th percentile) values for all children and adults (U.S. EPA,
1997a).
3-9
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The last input needed to calculate the dermal portion of the ingestion/dermal SSLs is the
chemical-specific dermal absorption fraction (ABSd). Values for seven individual compounds and
two classes of compounds are presented in Exhibit 3-3.14 For those compounds that are classified
as both semi-volatile and as a PAH, the ABSd default for PAHs should be applied.
Exhibit 3-3
RECOMMENDED DERMAL ABSORPTION FRACTIONS
Compound
Arsenic
Benzo(a)pyrene
Cadmium
Chlordane
DDT
Lindane
PAHs
Pentachlorophenol
Semi-volatile organic compounds
Dermal Absorption Fraction
(ABSd)
0.03
0.13
0.001
0.04
0.03
0.04
0.13
0.25
0.1
Source: U.S. EPA, RAGS, Part E, Supplemental Guidance for Dermal Risk Assessment,
Interim Guidance, 2001.
3.2.2 Migration of Volatiles Into Indoor Air
Subsurface contamination in either soil or ground water may adversely affect indoor air
quality through the infiltration of contaminant vapors into the basement or ground floor of an on-site
building. The potential for inhalation exposure via this pathway elicited substantial comment during
the development of the 1996 SSG.
In this update, EPA is incorporating vapor intrusion and the subsequent inhalation of
volatiles in indoor air into the soil screening process. This pathway may apply to both residential
and non-residential scenarios. A site manager's decision to evaluate this pathway should be based
14
The U.S. Environmental Protection Agency is developing separate guidance documents which address the
dermal risk from exposure to PCBs (Guidance on Remedial Actions for Super fund Sites with PCB Contamination, U.S.
EPA 1990, currently being updated) and dioxins (Draft Exposure and Human Health Reassessment of 2,3,7,8-
Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds, U.S. EPA, 2000c).
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on current and expected future site conditions (i.e., the current and/or potential future existence of
a building on or near a source area) and on the contaminants of concern at the site. Compounds
most likely to pose a significant risk via this pathway include volatile organic compounds (VOCs),
such as benzene, trichloroethylene, and vinyl chloride. This pathway may also apply to mercury,
the only metal that has an appreciable vapor pressure.
EPA recommends that this pathway be evaluated at sites where volatile contaminants have
been detected in subsurface soil or soil gas, or in groundwater above MCLs, and where buildings
either currently exist or are expected to be developed above or near the contamination. OSWER has
developed a draft guidance document that includes a tiered approach to help site managers identify
whether the vapor intrusion exposure pathway is complete at a given site, and if so, whether it
results in exposures above levels of concern (U.S. EPA, 2002b). We recommend site managers
consult this document if uncertain about the applicability of this exposure pathway at a given site.
The Johnson and Ettinger (1991) vapor intrusion model can by used by site managers if the
inhalation of volatile contaminants in indoor air is an exposure pathway of concern. This model
simulates both convective and diffusive transport of contaminant vapors from a contaminated source
area into a building directly above the source. The model may be used for buildings with basements
or with slab-on-grade foundations. The model treats the entire building as a single chamber, and
therefore does not consider room to room variation in ventilation. It uses chemical-specific data,
soil characteristics, and the structural properties of the building to generate an attenuation coefficient
that relates the indoor air contaminant concentration to the contaminant vapor concentration at the
source area. The output is a risk-based soil-screening concentration derived from a steady-state
concentration indoors that represents either a IxlO"6 individual lifetime cancer risk or a hazard
quotient of one for non-cancer effects, whichever yields the more stringent SSL.
EPA has developed a series of computer spreadsheets that allow for site-specific application
of the Johnson and Ettinger model (1991). Because there is substantial variation in the values for
the parameters used in the Johnson and Ettinger model, it is very difficult to identify suitable default
values for inputs such as building dimensions and the distance between contamination and a
building's foundation. As a result, EPA has not developed generic values for soil or other media for
this pathway. Instead, site managers are encouraged to calculate site-specific values for this
pathway using the spreadsheets provided and site-specific values for key input parameters (e.g.
building size and ventilation rate).
The vapor intrusion spreadsheets are available for calculating risk or risk-based
concentrations for contaminants in soil, soil gas, or ground water. Each medium-specific
spreadsheet is available in two versions: one designed for a simple site-specific screening approach
(e.g., SL-SCREEN) and one designed for a detailed site-specific modeling approach (e.g., SL-ADV).
The simple site-specific version employs conservative default values for many model input
parameters but allows the user to define values for several key variables (e.g., soil porosity, depth
of contamination). The detailed modeling version allows the user to select values for all model
variables and define multiple soil strata between the area of contamination and the building.
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Although EPA provides Johnson and Ettinger model spreadsheets for the calculation of risk-
based soil concentrations, these values are likely to be characterized by significant uncertainty. As
noted in EPA's draft vapor intrusion guidance document (2002b), this uncertainty arises from both
measurement error associated with the analysis of volatile compounds in soil samples and from
uncertainties in modeling the partitioning of volatile compounds in soil. If the CSM for a site
indicates that vapor intrusion may be an exposure pathway of concern, EPA recommends that the
pathway be evaluated using measured soil gas data and, if applicable, ground water data. These
data may be used in conjunction with the advanced versions of the Johnson and Ettinger model as
part of a site-specific analysis of the vapor intrusion pathway.
The model includes default input values based on a review of data for existing hazardous
waste sites. Although the default values used are conservative, because of the natural variation in
key parameters across sites, EPA recommends taking a range of outcomes into consideration, as
opposed to a single value, when conducting a soil screening evaluation. The site manager can assess
a range of values after focusing on the most sensitive input variables. In general, the default inputs
will yield conservative values. The vapor intrusion SSL spreadsheets and a user's guide that
describes the Johnson and Ettinger model in greater detail can be downloaded from the EPA web
site at http://www.epa.gOv/superfund/programs/risk/airmodel/johnson_ettinger.htm.15
15Revised spreadsheets consistent with the draft vapor intrusion guidance are currently being developed, and
are expected to be posted to the EPA website in January 2003.
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4.0 DEVELOPING SSLS FOR NON-RESIDENTIAL EXPOSURE
SCENARIOS
This chapter of the guidance document presents soil screening procedures for developing
SSLs for sites with non-residential future land use. It first discusses approaches to identifying and
categorizing future non-residential land use and presents EPA's framework for developing non-
residential SSLs. Next, it presents the specific modifications to the soil screening process required
to calculate non-residential SSLs. Finally, it highlights key issues to be considered when conducting
a non-residential soil screening assessment.
4.1 Identification of Non-Residential Land Use
The appropriate characterization of future land use at a site during the development of the
conceptual site model (CSM) enables a site manager to identify or calculate proper soil screening
levels for the site. It also enables future site investigations, such as the baseline risk assessment and
feasibility study, to focus on the development of practical and cost-effective remedial alternatives
that are consistent with the anticipated future land use. This section discusses the process for
identifying anticipated future site land uses and describes the implications of the results for the soil
screening process. It begins with a brief discussion of factors to consider when identifying future
land use, then provides an overview of the types of land uses included in the "non-residential"
universe, and concludes with a description of EPA's approach to integrating non-residential land use
into the soil screening framework.
4.1.1 Factors to Consider in Identifying Future Land Use
A detailed discussion of EPA's recommended practices for identifying reasonably anticipated
future land use can be found in the EPA directive Land Use in the CERCLA Remedy Selection
Process (\995a)1 In brief, that document stresses the importance of developing realistic
assumptions about the likely future uses of NPL sites through community involvement, including
early discussions with local land use planning authorities, local officials, and the public. The
Community Contact Coordinator could facilitate these discussions with the community. The
directive also provides examples of information sources that can be useful in identifying likely
future land uses such as: current land use, zoning laws and maps, population growth patterns,
existing institutional controls and land use designations, presence of endangered or threatened
species, and adjacent and nearby land uses.
Identification of future land use in the context of soil screening evaluations goes beyond
simply making assumptions about categories of use. It involves identifying the kinds of human
receptors that may be present (e.g., workers) and the types of activities they are likely to engage in
at the site. Risk from contamination at a site is a function of the specific activities that receptors
1 This document may be obtained from the EPA web site at: http://www.epa.gov/superfund/resources/
landuse.htm.
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undertake and the exposures to contaminants that are associated with those activities. The activities
can vary considerably, even across sites that fall within the same land use category; thus, when
developing the CSM, the assumptions about receptor activities at a site are as critical to the
screening process as assumptions about land use.
4.1.2 Categories of Non-Residential Land Use and Exposure Activities
The term "non-residential land use" encompasses a broad range of possible site uses,
including commercial, industrial, agricultural, and recreational. The commercial and industrial
categories are each individually quite broad as well; commercial uses range from churches and day
care centers to automobile repair shops and large-scale warehouse operations, and industrial uses
can include public utilities, transportation services, and a wide range of manufacturing activities.
The range of human activities at sites with non-residential uses may also vary considerably
in terms of location (e.g., indoors versus outdoors), physical exertion, frequency, and the potential
for contact with site contamination. These differences determine the types and intensity of
exposures likely to be experienced by receptors. For example, an indoor office worker is generally
not engaged in physically strenuous labor during the work day and experiences minimal exposures
to potentially contaminated site soil compared to a construction worker performing excavation work.
The office worker, however, may inhale volatilized compounds that migrate from contaminated soil
or ground water into the office space. Activities may vary even between sites within the same land
use category. For example, activities (and receptors) at a day care center are quite different from
activities at a store, though both would be considered commercial establishments. Thus, as
mentioned earlier, careful identification of activities associated with the likely future use of a site
is critical to proper assessment of potential exposure.
4.1.3 Framework for Developing SSLs for Non-Residential Land Uses
The non-residential screening framework focuses on a single non-residential land use
category that encompasses both commercial and industrial land uses. EPA selected this approach
for two reasons. First, as discussed in Section 3.2, it can be difficult to distinguish between
commercial and industrial sites on the basis of exposure potential. A wide range of potential
exposure levels (as determined by the range of potential site activities) characterizes both the
commercial and industrial categories, and because these ranges overlap, one category can not be
considered to have a consistently higher exposure potential than the other. Second, the screening
process focuses on future land use, and for many NPL sites, considerable uncertainty exists about
the specific activities likely to occur in the future. Therefore, the non-residential soil screening
framework includes one set of generic SSLs and SSL equations that apply to both commercial and
industrial land uses. In addition, the simple site-specific approach allows site managers to
differentiate between commercial and industrial sites when calculating SSLs by focusing on the
receptors and activities specific to the assumed future use.
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Normally, under the generic and simple site-specific screening methodologies, the receptors
for the commercial/industrial scenario are limited to workers. EPA does not warrant evaluation of
exposures to members of the public under a non-residential land use scenario for two reasons. First,
because public access is generally restricted at industrial sites, workers are the sole on-site receptor.
Second, even though the public usually has access to commercial sites (e.g., as customers), SSLs
that are protective of workers, who have a much higher exposure potential because they spend
substantially more time at a site, will also be protective of customers. However, if a future
commercial or industrial land use is likely to involve substantial exposure to the public (e.g.,
nursing homes, day care centers), the site should be evaluated using the residential soil
screening framework or a detailed site-specific screening methodology.
As shown in Exhibit 4-1, two potential worker receptors are addressed under the
commercial/industrial scenario. They are characterized by the intensity and location of their
activities, and by the frequency and duration of their exposures.
Outdoor Worker. This is a long-term receptor exposed during the work day
who is a full time employee of the company operating on-site and who
spends most of the workday conducting maintenance activities outdoors. The
activities for this receptor (e.g., moderate digging, landscaping) typically
involve on-site exposures to surface and shallow subsurface soils (at depths
of zero to two feet). The outdoor worker is expected to have an elevated soil
ingestion rate (100 mg per day) and is assumed to be exposed to
contaminants via the following pathways: incidental ingestion of soil, dermal
absorption of contaminants from soil, inhalation of fugitive dust, inhalation
of volatiles outdoors, and ingestion of ground water contaminated by
leachate.2'3 The outdoor worker is expected to be the most highly exposed
receptor in the outdoor environment under commercial/industrial conditions.
Thus, SSLs for this receptor are protective of other reasonably anticipated
outdoor activities at commercial/industrial facilities.
The soil ingestion rate of 100 mg per day for the outdoor worker is equal to the default residential adult
ingestion rate recommended in RAGS Volume I: Human Health Evaluation Manual, Supplemental Guidance: Standard
Default Exposure Factors, OSWER Directive 9285.6-03 (U.S. EPA, 1991a). The document recommends an ingestion
rate of 50 mg per day for a commercial/industrial worker and 100 mg per day for an adult resident. EPA selected the
latter value to reflect the increased ingestion exposures experienced by outdoor workers during landscaping or other
soil disturbing activities. Research is ongoing to gain better information on soil ingestion rates. The recommended
default values are subject to change as better data become available.
3 The ingestion of contaminated ground water exposure pathway for non-residential receptors is addressed by
SSLs for the migration of contaminants from soil into an underlying potable aquifer. The SSL equations and default
values used to model this pathway are identical to those used for residential exposure scenarios (See Section 3.1). In
addition, the rationale for a consistent set of migration to ground water SSLs across residential and
commercial/industrial uses is described in detail on page 4-24.
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Exhibit 4-1
SUMMARY OF THE COMMERCIAL/INDUSTRIAL EXPOSURE FRAMEWORK FOR
SOIL SCREENING EVALUATIONS
Exposure
Characteristics
Pathways of Concern
Receptors
Outdoor Worker
Substantial soil exposures
Long-term exposure
Ingestion (surface and shallow
subsurface soils)
Dermal absorption (surface and
shallow subsurface soils)
Inhalation (fugitive dust, outdoor
vapors)
Ingestion of contaminated
ground water1
Indoor Worker
Minimal soil exposures (little or no
direct contact with outdoor soils,
potential for contact through
ingestion of soil tracked in from
outside)
Long-term exposure
Ingestion (indoor dust)
Inhalation (indoor vapors)
Ingestion of contaminated ground
water1
Default Exposure Factors
Exposure Frequency (d/yr)
Exposure Duration (yr)
Soil Ingestion Rate (mg/d)
Inhalation Rate (mVd)
Body Weight (kg)
Lifetime (yr)
225
25
100
20
70
70
250
25
50
20
70
70
1 The same equations and default inputs (e.g., ground water ingestion rates) are used to calculate both residential
and commercial/industrial SSLs for this pathway because of concern for off-site residents who may be exposed
to contaminated ground water that migrates off-site.
Indoor Worker. This receptor spends most, if not all, of the workday
indoors. Thus, an indoor worker has no direct contact with outdoor soils.
This worker may, however, be exposed to contaminants through ingestion of
contaminated soils that have been incorporated into indoor dust, ingestion of
contaminated ground water, and the inhalation of contaminants present in
indoor air as the result of vapor intrusion.4 SSLs calculated for this receptor
The soil ingestion rate for the indoor worker, 50 mg per day, reflects decreased soil exposures relative to the
outdoor worker and is consistent with the default commercial/industrial soil ingestion rate recommended in RAGS
Volume I: Human Health Evaluation Manual, Supplemental Guidance: Standard Default Exposure Factors, OSWER
directive 9285.6-03 (U.S. EPA, 1991a). Research is ongoing to gain better information on soil ingestion rates. The
recommended default values are subject to change as better data become available.
4-4
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are expected to be protective of both workers engaged in low intensity
activities such as office work and those engaged in more strenuous activity
(e.g., factory or warehouse workers).
The commercial/industrial scenario does not include exposures during construction activities.
However, EPA recognizes that construction is likely to occur at many NPL sites and that it may lead
to significant short-term exposures. A separate soil screening scenario and SSL methodology for
construction activities designed to supplement either the residential or commercial/industrial SSL
is presented in Chapter 5.
4.1.4 Land Use and the Selection of a Screening Approach
The assumptions about future land use and future site activities may influence the selection
of a soil screening approach. In general, sites where the reasonably anticipated future use is either
commercial or industrial may be evaluated using any of the three screening approaches: the generic
approach, the simple site-specific approach, or the detailed site-specific modeling approach.
However, commercial sites with exposures akin to residential scenarios (i.e., where the future use
involves the housing, education, and/or care of children, the elderly, the infirm, or other sensitive
subpopulations) should be evaluated using the residential soil screening framework, if appropriate,
or using a detailed site-specific screening approach. Examples of such uses include, but are not
limited to: schools or other educational facilities, day care centers, nursing homes, elder care
facilities, hospitals, and churches.
Sites where the anticipated future land use is agricultural or recreational typically require
site managers to apply the detailed site-specific modeling approach for developing SSLs. For
example, agricultural sites may require site-specific modeling to address exposure pathways that
are not included in the generic and simple site-specific approaches (e.g., ingestion of contaminated
foods). In other situations, such as an evaluation of future recreational use, exposure scenarios may
be analogous to residential exposures, and application of residential SSLs to the site may be a
reasonable alternative to the detailed site-specific modeling approach.
Lastly, a soil screening evaluation of a construction scenario, which is described separately
in Chapter 5, should be conducted using either the simple site-specific or detailed site-specific
modeling approaches. Because of the difficulty of establishing default input values for a "standard"
construction project, these screenings can not be conducted using the generic approach.
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4.2 Modifications to the Soil Screening Process for Sites With Non-
Residential Exposure Scenarios
To conduct a soil screening evaluation for a non-residential exposure scenario, a site
manager should employ the same basic seven-step soil screening process outlined in Section 2.3.
However, there are some fundamental differences in the potential for exposure under non-
residential scenarios that necessitate modifications to certain steps of the framework. This section
describes in detail the key differences in these steps for the non-residential soil screening process.
Of the seven steps in the screening process, three must be adjusted for a non-residential soil
screening evaluation Step 1: Develop Conceptual Site Model (CSM); Step 2: Compare CSM to
SSL Scenario; and Step 5: Calculate Site- and Pathway-specific SSLs. The remaining steps,
consisting of Step 3: Define Data Collection Needs for Soils; Step 4: Sample and Analyze Site
Soils; Step 6: Compare Site Soil Contaminant Concentrations to Calculated SSLs; and Step 7:
Address Areas Identified for Further Study, are essentially unchanged. For detailed guidance on
performing these latter steps, please consult the 1996 SSG.
Regarding Step 3, EPA recommends that site managers develop a sampling plan for surface
soil that will provide a reliable estimate of the arithmetic mean of contaminant concentrations.
Section 2.3.2 of the 1996 SSG describes such a sampling plan utilizing composite samples.
Guidance on developing other sampling plans using discrete samples can be found in Guidance for
Choosing a Sampling Design for Environmental Data Collection (U.S. EPA 2000a). Although
there may be differences in the activities and exposures likely to occur under non-residential and
residential use scenarios, EPA is not recommending specific changes to the surface soil sampling
approach when performing non-residential soil screening evaluations. Unless there is site-specific
evidence to the contrary, an individual receptor is assumed to have random exposure to surface
soils at both residential and non-residential sites.
However, as in the 1996 SSG, EPA emphasizes that the depth over which soils are sampled
should reflect the type of exposures expected. Activities typical for non-residential site uses (e.g.,
landscaping and other outdoor maintenance activities) may result in direct contact exposure for
certain receptors to contaminants in shallow subsurface soils at depths of up to two feet. EPA
expects that site managers will characterize contaminant levels in the top two feet of the soil
column by taking shallow subsurface borings where appropriate. The specific locations of such
borings should be determined by the likelihood of direct contact with these subsurface soils and by
the likelihood that soil contamination is present at that depth. Given that these deeper soils are not
characterized to the same extent as the top two centimeters of soil, the maximum measured
contaminant concentration in the borings in a given exposure area should be compared directly with
the SSLs, as described in Section 2.3, Step 6. Alternatively, if available evidence indicates that
contaminated subsurface soils will be disturbed and brought to the surface (e.g., as the result of
redevelopment activities), site managers will need to characterize subsurface contamination more
thoroughly and should collect a sufficient number of samples to develop a UCL^ value for use in
the soil screening evaluation.
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4.2.1 Step 1: Develop Conceptual Site Model
The process of developing a CSM a comprehensive representation of a site that
illustrates contaminant distributions in three dimensions, along with release mechanisms, exposure
pathways, migration routes, and potential receptors is similar for non-residential and residential
soil screening evaluations. The key differences in developing a CSM for a site with anticipated
non-residential future land use are:
Identification of Land Use. Identifying the reasonably anticipated future
land use for an NPL site is critical to the development of the CSM. It is the
first step toward identifying the future site receptors and activities that
determine the key exposure pathways of concern. Future land use may also
influence the selection of a screening approach by a site manager. Future
industrial or commercial sites may be evaluated using any of the three
screening approaches (generic, simple site-specific, or detailed site-specific
modeling); sites with other non-residential future land uses (e.g., agriculture,
recreation) are appropriately addressed using a detailed site-specific
modeling approach.
Receptors for Non-Residential Uses. When developing CSMs for
commercial or industrial sites, the focus should be on worker receptors,
unless anticipated future site activities are expected to result in substantial
exposures to members of the public and/or children visiting the site (see
Section 4.1.3). CSMs for commercial or industrial sites should include
long-term receptors (e.g., indoor workers and outdoor workers) and, if
appropriate, short-term, high intensity receptors (e.g., construction workers).
For sites with future agricultural or recreational uses, CSMs should address
a wider range of potential receptors (e.g., farm workers and children/adults
exposed to contamination through consumption of agricultural products or
children/adults engaged in recreational activities).
Activities for Non-Residential Uses. In order to identify the exposure
pathways pertinent to future exposures, site managers should consider the
potential future site activities that may contribute to exposure. Examples of
activities likely to occur at commercial/industrial sites include: outdoor
maintenance work and landscaping, indoor commercial activities (e.g.
wholesale or retail sales) and office work.
A key part of CSM development for all soil screening evaluations is the identification of
ground water use. Site managers should consult EPA's policy on ground water classification
(presented in Section 4.2.3) and should coordinate with state or local authorities responsible for
ground water use and classification to determine whether the aquifer beneath or adjacent to the site
is a potential source of drinking water. The migration to ground water pathway is applicable to all
potentially potable aquifers, regardless of current or future land use.
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4.2.2 Step 2: Compare Conceptual Site Model to SSL Scenario
The non-residential soil screening scenario used in the generic and simple site-specific
screening approaches is likely to be appropriate for a wide range of commercial and industrial sites.
However, the CSM for agricultural or recreational sites, as well as for some commercial or
industrial sites, may include sources, exposure pathways, and receptors not covered by the
commercial/industrial scenario described in this document. Comparison of the CSM with this
scenario enables site managers to determine whether additional or more detailed assessments are
needed to address specific site contaminants or characteristics.
Six exposure pathways are included in the commercial/industrial soil screening scenario.
These pathways, as well as the relevant receptors for each pathway, are listed below:
Surface soil pathways:
Incidental direct ingestion indoor worker and outdoor worker.
Dermal absorption outdoor worker.
Inhalation of fugitive dusts outdoor worker.
Subsurface soil pathways:
Inhalation of volatiles resulting from vapor intrusion into indoor air
indoor worker.
Inhalation of volatiles migrating from soil to outdoor air outdoor worker.
Ingestion of contaminated ground water caused by migration of chemicals
through soil to an underlying potable aquifer indoor worker and outdoor
worker.
Site managers should consider these pathways and make thoughtful determinations about whether
receptors are likely to be exposed via each pathway.
It is important to carefully consider each of the possible pathways as part of the screening
process, even though a site manager may quickly decide that one or more specific pathways are not
relevant for a site. If, based on an analysis of reasonably anticipated future site activities, the site
manager identifies pertinent exposure pathways other than those listed above, these additional
pathways should be addressed using a detailed site-specific modeling approach.
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The commercial/industrial soil screening scenario does not evaluate exposures to off-site
receptors, except via the ingestion of ground water contaminated by soil leachate. In general, off-
site receptors are assumed to have very limited or no access to the site, which precludes direct
exposures. Indirect exposure to off-site residents (e.g., outdoor exposure to soil vapors and to
particulates due to wind erosion) is possible. Modeling results indicate that the on-site outdoor
worker is exposed to higher particulate and vapor concentrations than an off-site receptor located
at the site property line. As a result, outdoor worker SSLs for the inhalation of volatiles and
particulates outdoors should be protective of an off-site worker with similar exposure frequency
and duration. Off-site residents, however, have a higher exposure frequency and duration than
workers, and therefore SSLs based on modeling for these off-site receptors could be slightly lower
than SSLs based on outdoor worker exposures.
An analysis of these pathways that used very conservative (i.e., health protective)
assumptions to model emissions and transport of vapors and particulates to an off-site receptor
indicates that for most contaminants, SSLs calculated for on-site receptors would be protective of
indirect exposures to off-site residents.5 For some compounds, the modeled SSL for indirect off-
site exposure is less than the most protective SSL for commercial/industrial on-site receptors;
however, for most of these, the off-site SSL is within 30 percent of the on-site value.6 The
significance of this difference depends on several factors that need to be evaluated on a site-specific
basis, such as the nature and toxicity of the chemicals of concern, source characteristics, and the
actual distance to off-site receptors. Also, if the migration to ground water pathway is being
evaluated at a site (assuming a DAF of 20), on-site SSLs will likely be protective of indirect
inhalation exposures to off-site residents for nearly all contaminants in Appendix A, even using
conservative modeling assumptions.7 Given the results of this analysis, the Agency does not
recommend evaluating volatile or particulate exposures to off-site residents under the simple site-
specific commercial/industrial scenario.8 If a CSM suggests that off-site receptors may experience
significant exposures to site contaminants via pathways other than ingestion of ground water, these
exposures should be evaluated using a detailed site-specific modeling approach.
5The conservative assumptions include the presence of an infinite source, the presence of volatiles in surface
soils, and the location of the off-site receptor just beyond the site boundary.
Exceptions for the inhalation of volatiles pathway include 1,1,2-trichloroethane (36 percent lower for off-site
receptor), hexachlorobenzene (37 percent lower for off-site receptor), mercury (94 percent lower for off-site receptor),
and tetrachloroethylene (32 percent lower for off-site receptor). Chromium (VI) was the lone exception for the
inhalation of particulates pathway (50 percent lower for off-site receptor). If the migration to ground water pathway
is being evaluated, on-site SSLs would be sufficiently protective (using the conservative default assumptions) for all
but hexachlorobenzene, mercury, and chromium (VI).
7The only four contaminants for which on-site SSLs would not be protective under this scenario are chloroform
(27 percent lower for off-site receptor), hexachlorobenzene (37percent lower for off-site receptor),
hexachloropentadiene (6 percent lower for off-site receptor), and mercury (94 percent lower for off-site receptor).
8 As discussed in Chapter 5, exposures to an off-site resident receptor may need to be evaluated if a future
construction event is reasonably likely.
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4.2.3 Step 5: Calculate Site- and Pathway-Specific SSLs
This section presents equations appropriate for calculating SSLs for the generic and simple
site-specific soil screening approaches for each pathway in the commercial/industrial soil screening
scenario (with the exception of the indoor vapor intrusion pathway, which requires a spreadsheet
model to calculate SSLs). These equations and the default input values are designed to reflect
reasonable maximum exposure (RME) for chronic exposures in a commercial or industrial setting.
They incorporate reasonably conservative values for intake and duration and average or typical
values for all site-specific inputs describing soil, aquifer, and meteorologic characteristics.
For each equation, site-specific input parameters are indicated in bold.9 Where possible,
default values are provided for these parameters for use when site-specific data are not available.
These defaults were not selected to represent worst case conditions; however, they are conservative.
The generic SSLs for the commercial/industrial scenario were calculated using these equations and
the specified default values. Generic commercial/industrial SSLs are presented in Appendix A.
In addition, an interactive SSL calculator for the simple site-specific equations is available on-line
at http://risk.lsd.ornl.gov/calc_start.htm.10 The SSL calculator is updated periodically to reflect
changes in Agency guidance (e.g., additional pathways, updated toxicity values); users should
confirm that the calculator's chemical-specific inputs are consistent with the latest values available.
Chemical-specific data, including toxicity values, for use in developing simple site-specific
SSLs are provided in Appendix C. Prior to calculating SSLs at a site, each relevant chemical-
specific value in Appendix C should be checked against the most recent version of its source
and updated, if necessary. Toxicity values for the inhalation exposure route are not available for
all chemicals. The TBD to the 1996 SSG presents the results of EPA's review of methods for
extrapolating inhalation toxicity values from oral values. EPA found that route-to-route
extrapolations are not necessary if migration to ground water is considered, because the SSLs for
that pathway are sufficiently protective to address any underestimation of risk resulting from the
lack of inhalation toxicity data. If the migration to ground water pathway is not applicable to the
site, oral-to-inhalation extrapolations should be considered on a case-by-case basis. For
information on extrapolation methods, please consult EP A's Methods for Derivation of Inhalation
Reference Concentrations and Application of Inhalation Dosimetry (U.S. EPA, 1994).
In general, the basic forms of the SSL equations presented here are the same as those used
for the residential scenario; however, EPA has developed the following default input values that
reflect a commercial/industrial RME scenario:
9 The use of distributions for exposure factors (in a probabilistic risk assessment) is reserved for a detailed site-
specific modeling approach. Refer to EPA's Guiding Principles for Monte Carlo Analysis (U.S. EPA, 1997b) andPoftcy
for Use of Probabilistic Analysis in Risk Assessment (U.S. EPA, 1997d) for further information.
10 The SSL calculator currently includes default values for residential exposure scenarios; however, users can
adjust these defaults to reflect the non-residential exposure scenarios.
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Exposure frequency. For outdoor workers, EPA has established a default
exposure frequency of 225 days/year. This value is based on data from the
U.S. Census Bureau's 1990 Earnings by Occupation and Education Survey
and represents the average number of days worked per year by male and
female workers engaged in activities likely to be similar to those of the
outdoor worker receptor.11 Because we assume exposure frequency is equal
to the number of days worked per year, we recognize that this value may
overestimate exposures for receptors in regions of the U.S. where extreme
winters preclude exposure to site soils for extended periods during the year.
Similarly, the default may potentially underestimate exposures in more
temperate climates. Therefore, site managers conducting simple or detailed
site-specific soil screening evaluations may propose alternative, site-specific
values for this parameter that are supported by specific information on
climatic influences. For indoor workers, EPA has established a default
exposure frequency of 250 days/year. This value is based on a work
scenario of five days per week for 50 weeks per year (assuming two weeks
of vacation).
Exposure duration. Exposure duration is assumed to be equivalent to job
tenure for receptors in the non-residential soil screening scenario. EPA has
selected a value of 25 years as the default for this exposure factor. This is
the same value used m RAGS Part B (U.S. EPA, 1991b). It is supported by
an analysis of Bureau of Labor Statistics data which shows that the 95th
percentile value for job tenure for men and women in the manufacturing
sector are 25 years and 19 years, respectively (Burmaster, 1999). Job tenure
for non-industrial workers varies widely. The 95th percentile job tenure
values for workers in the transportation/utility and wholesale sectors are
only somewhat less than manufacturing workers 22 years and 18 years
for men and women, respectively. Values are lower for other non-industrial
sectors approximately 13 years for workers in the finance and service
sectors, and seven years for retail workers. Thus, the 25-year default value
is protective of workers across a wide spectrum of industrial and
commercial sectors. Site managers conducting simple or detailed site-
specific screening evaluations may propose alternative exposure durations
supported by job tenure data and the anticipated site use.
Other changes to default exposure factors that apply to individual pathways are discussed below,
along with their respective SSL equations.
11 The exposure frequency value of 225 days/year for outdoor workers assumes an eight-hour workday and
is based on data from the following occupational categories in the U.S. Census Bureau's 1990 Earnings by Occupation
and Education Survey: groundskeepers and gardeners, except farm; specified mechanics and repairers, not elsewhere
classified; not specified mechanics and repairers; painters, construction and maintenance; and construction laborers.
4-11
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SSL Equations for Surface Soils
The relevant pathways for exposure to surface soils for the commercial/industrial use
scenarios include direct ingestion, dermal absorption, and inhalation of fugitive dusts. As in the
residential soil screening process, the SSL equations for direct ingestion and dermal absorption
have been combined to reflect the concurrent nature of these exposures. The combined direct
ingestion/dermal absorption exposure pathway should be routinely considered in screening
evaluations that use the commercial/industrial scenario, though dermal absorption can not be
evaluated currently for all contaminants. (Where dermal absorption data are not available, the
ingestion/dermal SSL equations can be used to calculate an SSL based on the ingestion pathway
only.)
Typical activities for commercial/industrial site use, such as landscaping and outdoor
maintenance, may result in direct exposure to soils at depths of up to two feet. Thus, site managers
may need to extend the analysis of exposure through the direct ingestion, dermal absorption, and
inhalation of fugitive dusts pathways to include contaminants found in these subsurface soils. The
likelihood of these receptor activities occurring at a site should be addressed in the CSM and
reflected in the development of site-specific SSLs.
Direct Ingestion and Dermal Absorption. Equations 4-1 and 4-2 are
appropriate for addressing chronic ingestion and dermal absorption exposure of
commercial/industrial receptors to carcinogens and non-carcinogens, respectively. The equations
produce SSLs protective of concurrent exposures to these receptors via these two pathways.
As mentioned in Section 4.1.3, the commercial/industrial scenario does not evaluate
exposures to children. Thus, unlike the residential SSLs, the commercial/industrial direct
ingestion/dermal absorption SSLs for non-carcinogens are based on exposures to adults only.
The default recommended soil ingestion rate for workers depends on the type of activity
being performed. EPA recommends a 50 mg/day dust ingestion rate for indoor workers, as
suggested in RAGS Volume I: Human Health Evaluation Manual, Supplemental Guidance:
Standard Default Exposure Factors, OSWER directive 9285.6-03 (U.S. EPA, 1991a). The soil
ingestion SSLs for indoor employees protect against the ingestion of contaminants in indoor dust
that are derived from contaminated outdoor soil. In setting a default ingestion rate for outdoor
workers, we follow the same rationale as EPA's Technical Review Workgroup for Lead (TRW);
we assume that a higher ingestion rate is reasonable for a commercial/industrial worker engaged
in contact-intensive activities. Because outdoor workers are likely to experience more significant
exposures to surface soils than their indoor counterparts, EPA has adopted a default soil ingestion
rate of 100 mg/day for this receptor.
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SSLs for chronic exposures to contaminants via dermal absorption under the
commercial/industrial scenario are calculated based on the same methodology discussed in Section
3.2.1. The suggested default input values for the dermal exposure portion of the direct
ingestion/dermal absorption equations are consistent with those recommended in EPA's RAGS, Part
E with the exception of exposure frequency (U.S. EPA, 2001). This soil screening guidance
recommends that a default of 225 days per year be used for workers at commercial or industrial
sites as opposed to the 250 days per year suggested in RAGS, Part E. As described above, this
recommendation is based on occupational data from the U.S. Census Bureau. Event frequency
(EV, the number of events per day) is assumed to be equal to one. Adults are assumed to have
their face, forearms, and hands exposed. Therefore, this guidance recommends that a value of
3,300 cm2 be used as an estimate of the skin surface area exposed (SA). We also assume a default
adherence factor (AF) of 0.2 mg soil per square centimeter of exposed skin. Both the SA and AF
default values represent the median (50th percentile) values for all adult workers at commercial and
industrial sites based on EPA studies (U.S. EPA, 1997a). The chemical-specific dermal absorption
fractions (ABSd) are presented in Appendix C. For those compounds classified as both semi-
volatile and as a PAH, the ABSd default for PAHs should be applied.
4-13
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Equation 4-1
Screening Level Equation for Combined Ingestion and Dermal Absorption
Exposure to Carcinogenic Contaminants in Soil
- Commercial/Industrial Scenario
Screening TRxBWxATx365d/yr
1 0W0 J
(mg/kg) (EFxEDxIO 6kg/mg)((SF0x|R)+(SFABSxAFxABSdxSAxEV))
Parameter/Definition (units)
TR/target cancer risk (unitless)
BW/body weight (kg)
AT/averaging time (years)
EF/exposure frequency (days/year)
outdoor worker
indoor worker
ED/exposure duration (years)
outdoor worker
indoor worker
SFo/oral cancer slope factor (mg/kg-d)"1
IR/soil ingestion rate (mg/d)
outdoor worker
indoor worker
SFABS/dermally-adjusted cancer slope factor (mg/kg-d)"1
AF/skin-soil adherence factor (mg/cm2 -event)
ABSd/dermal absorption fraction (unitless)
SA/skin surface exposed (cm2)
EV/event frequency (events/day)
outdoor worker
indoor worker
Default
10"6
70
70
225
250
25
25
chemical-specific
(Appendix C)
100
50
chemical-specific
(Equation 3-3)
0.2
chemical-specific
(Exhibit 3-3 and Appendix C)
3,300
1
0
4-14
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Equation 4-2
Screening Level Equation for Combined Ingestion and Dermal Absorption
Exposure to Non-Carcinogenic Contaminants in Soil
- Commercial/Industrial Scenario
Screening THQxBWxATx365d/yr
(mg/kg) (FFxEDxin 6ka/man 1 x|R| +( 1 xAFxABS xSAxEVl
Parameter/Definition (units)
THQ/target hazard quotient (unitless)
BW/body weight (kg)
AT/averaging time (years)
EF/exposure frequency (days/year)
outdoor worker
indoor worker
ED/exposure duration (years)
outdoor worker
indoor worker
RfDo/oral reference dose (mg/kg-d)
IR/soil ingestion rate (mg/d)
outdoor worker
indoor worker
RfDABS/dermally-adjusted reference dose (mg/kg-d)
AF/skin-soil adherence factor (mg/cm2 -event)
ABSd/dermal absorption fraction (unitless)
S A/skin surface exposed (cm2)
EV/event frequency (events/day)
outdoor worker
indoor worker
Default
1
70
25a
225
250
25
25
chemical-specific
(Appendix C)
100
50
chemical-specific
(Equation 3-4)
0.2
chemical-specific
(Exhibit 3-3 and Appendix C)
3,300
1
0
a For non-carcinogens, averaging time equals exposure duration.
4-15
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Inhalation Of Fugitive DustS. Inhalation of fugitive dusts generated by wind
erosion may be of concern under the commercial/industrial scenario for semi-volatile organic
compounds and metals in surface soils. However, as in the residential scenario, the fugitive dust
exposure route need not be routinely considered for semi-volatile organics under the
commercial/industrial scenario for two reasons: (1) the default ingestion/dermal absorption SSLs
for these compounds are often several orders of magnitude lower (i.e., more stringent) than the
corresponding default fugitive dust SSLs; and (2) EPA believes the ingestion/dermal absorption
route always should be evaluated when screening surface soils. Thus, EPA considers
ingestion/dermal absorption SSLs to be adequately protective of fugitive dust exposures to semi-
volatile organic chemicals in surface soils under typical commercial/industrial conditions.
Similarly, generic ingestion/dermal absorption SSLs for most metals are more conservative
than the fugitive dust SSLs. Thus, fugitive dust SSLs do not need to be calculated for most metals
with the exception of chromium. The carcinogenicity of the hexavalent form of chromium (Cr+6)
via the inhalation route results in a generic fugitive dust SSL that is more stringent than the
ingestion/dermal absorption SSL. As a result the fugitive dust pathway should be evaluated
routinely for chromium.
The fugitive dust pathway should be considered carefully when developing the CSM at sites
with future commercial/industrial land use. The above rules of thumb for fugitive dust SSLs may
not be valid for site conditions or activities at sites that are expected to result in particularly high
fugitive dust emissions. Examples of conditions that contribute to potentially high fugitive dust
emissions include dry soils (moisture content less than approximately eight percent), finely divided
or dusty soils (high silt or clay content); high average annual wind speeds (greater than
approximately 5.3 m/s); and less than 50 percent vegetative cover. Examples of activities likely
to generate high dust levels include heavy truck traffic on unpaved roads and other construction-
related activities. Chapter 5 presents a method for addressing increased particulate exposures
during construction. For other scenarios characterized by high fugitive dust calculations, EPA
recommends using a detailed site-specific modeling approach to develop fugitive dust SSLs (see
Appendix E).
Equations 4-3 and 4-4 are appropriate for calculating fugitive dust SSLs for carcinogens
and non-carcinogens. These equations are unchanged from the 1996 SSG. However, different
default values are provided that reflect appropriate exposure frequency, exposure duration, and
averaging time (for exposures to non-carcinogens) for workers.
Equation 4-5 is used to calculate the particulate emission factor (PEF). This factor
represents an estimate of the relationship between soil contaminant concentrations and the
concentration of these contaminants in air as a consequence of particle suspension. Equation 4-5
is unchanged and includes the same defaults as those provided in the 1996 SSG, with the exception
of the dispersion factor for wind erosion, Q/Cwind, which has been modified slightly to reflect
updated dispersion modeling.
4-16
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Equation 4-3
Screening Level Equation for Inhalation of Carcinogenic Fugitive Dusts
- Commercial/Industrial Scenario
Screening TRxATx365d/yr
(mg/kg) URFxl,000|jg/mgxE
Parameter/Definition (units)
TR/target cancer risk (unitless)
AT/averaging time (yr)
URF/inhalation unit risk factor (ug/m3)"1
EF/exposure frequency (d/yr)
Outdoor Worker
ED/exposure duration (yr)
Outdoor Worker
PEF/particulate emission factor (m3/kg)
' y l~ r*\ y
PEF
Default
1Q-6
70
chemical-specific
(Appendix C)
225
25
1.36 x109
(Equation 4-5)
Equation 4-4
Screening Level Equation for Inhalation of Non-carcinogenic Fugitive Dusts
- Commercial/Industrial Scenario
(mg/kg) EFxEDx[-Lx_L]
V * *' RfC PEF
Parameter/Definition (units)
THQ/target hazard quotient (unitless)
AT/averaging time (yr)
Outdoor Worker
EF/exposure frequency (d/yr)
Outdoor Worker
ED/exposure duration (yr)
Outdoor Worker
RfC/inhalation reference concentration (mg/m3)
PEF/particulate emission factor (m3/kg)
Default
1
25a
225
25
chemical-specific
(Appendix C)
1.36x109
(Equation 4-5)
For non-carcinogens, averaging time equals exposure duration.
4-17
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Equation 4-5
Derivation of the Participate Emission Factor
- Commercial/Industrial Scenario
PEF-Q/C - 3'6ฐฐS/h
rtr vrf/o j d ซ
0.036x(1 -V)x(Um/Ut)3xF(x)
Parameter/Definition (units)
PEF/particulate emission factor (m3/kg)
Q/Cwind/inverse of the ratio of the geometric mean air concentration to the
emission flux at the center of a square source (g/rtf-s per kg/m3)
V/fraction of vegetative cover (unitless)
Um/mean annual windspeed (mis)
Ut/equivalent threshold value of windspeed at 7m (mis)
F(x)/function dependent on Um/U, derived using Cowherd et al. (1985)
(unitless)
Default
1.36x 109
93.77a
0.5 (50%)
4.69
11.32
0.194
3 Assumes a 0.5 acre emission source; for site-specific values, consult Appendix D.
As a result of the updated modeling, Q/Cwind can now be derived for any source size between
0.5 and 500 acres using the equation and look-up table in Appendix D, Exhibit D-2. (The default
Q/Cwind factor assumes a 0.5 acre source size, the size of a typical exposure unit.) The look-up table
in Exhibit D-2 provides the three constants for the Q/Cwind equation (A, B, and C) for each of 29
cities selected to be representative of the range of meteorologic conditions across the country. The
Q/Cwind constants for each city were derived from the results of EPA's Industrial Source Complex
(ISC3) dispersion model run in short-term mode using five years of hourly meteorological data.
To calculate a site-specific Q/Cwind factor, the site manager must first identify the climatic
zone and city most representative of meteorological conditions at the site. Appendix D includes
a map of climatic zones to help site managers select the appropriate Q/Cwind equation constants for
the site. Once the equation constants have been identified, Q/Cwind can be calculated for any source
size between 0.5 and 500 acres and input into Equation 4-5 to derive a site-specific PEF.
SSL Equations for Subsurface Soils
This guidance addresses three exposure pathways that are pertinent to contamination in
subsurface soils. These pathways include:
Inhalation of volatiles migrating from soil to indoor air;
Inhalation of volatiles migrating from soil to outdoor air; and
4-18
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Ingestion of contaminated ground water resulting from the leaching of
chemicals from soil and their migration to an underlying potable aquifer.
Because the equations developed to calculate SSLs for the last two of these three pathways
assume an infinite source, they can violate mass-balance considerations, especially for small
sources. To address this concern, the guidance also includes SSL equations for these pathways that
allow for mass-limits. These equations can be used only when the volume (i.e., area and depth) of
the contaminated soil source is known or can be estimated with confidence.
Exhibit 4-2 lists site-specific parameters necessary to calculate SSLs for the outdoor
inhalation of volatiles and the ingestion of ground water pathways, along with recommended
sources and measurement methods. The exhibit includes both key parameters used directly in the
SSL equations (solid dots) and supporting data or assumptions (hollow dots) used to estimate key
parameter values. Site-specific parameters for the migration of volatiles into indoor air pathway
are described in spreadsheets developed by EPA (described below).
Inhalation Of Volatiles Indoors. As discussed in Section 322, vapors
resulting from the volatilization of contaminants in soil may be transported into indoor spaces
through cracks or gaps in a building's foundation. The inhalation of these vapors by indoor workers
may be an important exposure pathway at sites with current or future commercial/industrial land
use. To facilitate the development of SSLs for this pathway, EPA has constructed a series of
spreadsheets that allow for the site-specific application of a screening-level model for indoor vapor
intrusion developed by Johnson and Ettinger (1991). These spreadsheets are available from the
EPA web site at http://www.epa.gov/superfund/programs/risk/airmodel/johnson_ettinger.htm.
The vapor intrusion spreadsheets are available for calculating risk or risk-based
concentrations for contaminants in soil, soil gas, or ground water. Each medium-specific
spreadsheet is available in two versions: one designed for a simple site-specific screening approach
(e.g., SL-SCREEN) and one designed for a detailed site-specific modeling approach (e.g., SL-
ADV). The simple site-specific version employs conservative default values for many model input
parameters but allows the user to define values for several key variables (e.g., soil porosity, depth
of contamination). The detailed modeling version allows the user to select values for all model
input parameters and define multiple soil strata between the area of contamination and the building.
Thus, site managers wanting to develop vapor intrusion SSLs using site-specific building
parameters should use the SL-ADV spreadsheets.
These spreadsheets employ toxicity values (inhalation unit risk values for cancer and
reference concentrations for non-cancer effects) based on an adult inhalation rate of 20 m3/day to
calculate SSLs for indoor vapor intrusion. This is the same rate used to develop residential SSLs
for this pathway. Because workers are typically exposed via this pathway for shorter periods than
residents, (eight to 10 hours each day versus up to 24 hours) the 20 m3/day inhalation rate is likely
to be a conservative estimate for some workers. However, data on worker activity levels and
4-19
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Exhibit 4-2
SITE-SPECIFIC PARAMETERS FOR CALCULATING SUBSURFACE SSLs
Parameter
Source Characteristics
Source area (A)
Source length (L)
Source depth
Soil Characteristics
Soil texture
Dry soil bulk density (pb)
Soil moisture content (w)
Soil organic carbon (foc)
Soil pH
Moisture retention exponent (b)
Saturated Hydraulic conductivity
(Ks)
Avg. soil moisture content (8W)
Meteorological Data
Air dispersion factor (Q/C)
Hydrogeologic Characteristics (DAF)
Hydrogeologic setting
Infiltration/recharge (1)
Hydraulic conductivity (K)
Hydraulic gradient (i)
Aquifer thickness (d)
SSL Pathway
Inhalation
of
Volatiles -
Outdoors
Ingestion
of
Ground
Water
Data Source
Sampling data
Sampling data
Sampling data
Lab
measurement
Field
measurement
Lab
measurement
Lab
measurement
Field
measurement
Look-up
Look-up
Calculated
Q/C tables
(Appendix D)
Conceptual site
model
HELP model;
Regional
estimates
Field
measurement;
Regional
estimates
Field
measurement;
Regional
estimates
Field
measurement;
Regional
estimates
Method for Estimating Parameter
Measure total area of contaminated soil.
Measure length of source parallel to ground water flow.
Measure depth of contamination or use conservative
assumption.
Particle size analysis (Gee & Bauder, 1986) and USDA
classification; used to estimate 8W& 1
All soils: ASTM D 2937; shallow soils: ASTMD1556,
ASTM D 2167, ASTM D 2922
ASTM D 2216; used to estimate dry soil bulk density
Nelson and Sommers (1982)
McLean (1982); used to select pH-specific Koc (ionizable
organics) and Kd (metals)
Attachment A to 1996 SSG; used to calculate 8W
Attachment A to 1996 SSG; used to calculate Ow
Attachment A to 1996 SSG
Select value corresponding to source area, climatic zone, and
city with conditions similar to site.
Place site in hydrogeologic setting from Aller et al. (1987) for
estimation of parameters below (see Attachment A to 1996
TBD).
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 based on 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 based on 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 based
on 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 based on knowledge of local hydrogeologic
conditions.
Indicates key parameters used in the SSL equation for each pathway.
Indicates supporting data/assumptions used to develop estimates of the values of the key parameters.
4-20
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inhalation rates reveal two distinct sets of indoor workers: those working primarily in an office
setting (daily inhalation rates ranging from 5.4 m3/day to 12.6 m3/day, with an average of 9.3
m3/day), and those engaged in physically demanding tasks for roughly half of their work day (daily
inhalation rates ranging from 13.6 m3/day to 18.5 m3/day, with an average of 16.2 nrVday) (U.S.
Department of Commerce, 1985; US EPA, 1989a; US EPA, 1997a). Thus, EPA believes that the
20 m3/day rate is a reasonable estimate of RME that is protective of indoor workers engaged in
strenuous workday activities associated with elevated breathing rates.
As noted in Section 3.2.2, risk-based concentrations for contaminants in soil calculated
using the Johnson and Ettinger spreadsheets may be highly uncertain. If the CSM for a site
indicates that vapor intrusion may be an exposure pathway of concern, EPA recommends that the
pathway be evaluated using measured soil gas data and, if applicable, ground water data. These
data may be used in conjunction with the advanced versions of the Johnson and Ettinger model as
part of a site-specific analysis of the vapor intrusion pathway.
Inhalation Of VolatlleS Outdoors. Equations 4-6 through 4-9 are appropriate
for calculating SSLs for the outdoor inhalation of volatiles pathway using the simple site-specific
approach. (A detailed site-specific modeling approach to this pathway is discussed in Appendix
E).
EPA recommends evaluating this pathway at sites where volatile contaminants have been
detected in subsurface source areas and where the surface soils covering those sources are
undisturbed (e.g. a covered lagoon). Equations 4-6 and 4-7 calculate the SSLs for the inhalation
of carcinogenic and non-carcinogenic volatile compounds, respectively. Each of these equations
incorporates a soil-to-air volatilization factor (VF) that relates the concentration of a contaminant
in soil to the concentration of the contaminant in air resulting from volatilization. Equation 4-8 is
appropriate for calculating the VF. Finally, to ensure that the VF model is applicable to soil
contaminant conditions at a site, a soil saturation limit (Csat) must be calculated for each volatile
compound. Equation 4-9 is appropriate for calculating this value.
4-21
-------
Relative to the inhalation modeling for the residential exposure scenario, the only differences for
commercial/industrial soil screening evaluations are the default values for exposure frequency,
exposure duration, and averaging time (for non-carcinogenic exposures) in Equations 4-6 and 4-7.
The toxicity values used in these equations (inhalation unit risk factors for cancer and reference
concentrations for non-cancer effects) are based on an adult inhalation rate of 20 m3/day, the same
rate used to evaluate the migration of volatiles into indoor air. As discussed in the previous section,
use of this value for outdoor workers is supported by data on the activity levels and associated
inhalation rates for different classes of workers (U.S. Department of Commerce, 1985; US EPA,
1989a; US EPA, 1997a) and is protective of workers engaged in strenuous activities.
Equation 4-6
Screening Level Equation for Inhalation of Carcinogenic Volatile Contaminants in Soil
- Commercial/Industrial Scenario
TRxATx365d/yr
Screening
Level =
(mg/kg) URFx1,000|jg/mgxEFxEDxJ-
Parameter/Definition (units)
TR/target cancer risk (unitless)
AT/averaging time (yr)
URF/inhalation unit risk factor (pg/m3)"1
EF/exposure frequency (d/yr)
Outdoor Worker
ED/exposure duration (yr)
Outdoor Worker
VF/soil-to-air volatilization factor (m3/kg)
Default
10-6
70
chemical-specific
(Appendix C)
225
25
chemical-specific
(Equation 4-8)
4-22
-------
Equation 4-7
Screening Level Equation for Inhalation of Non-carcinogenic Volatile Contaminants in Soil
- Commercial/Industrial Scenario
(mg/kg) EFxEDx[^x^]
V a a' RfC VF
Parameter/Definition (units)
THQ/target hazard quotient (unitless)
AT/averaging time (yr)
Outdoor Worker
EF/exposure frequency (d/yr)
Outdoor Worker
ED/exposure duration (yr)
Outdoor Worker
RfC/inhalation reference concentration (mg/m3)
VF/soil-to-air volatilization factor (m3/kg)
Default
1
25a
225
25
chemical-specific
(Appendix C)
chemical-specific
(Equation 4-8)
For non-carcinogens, averaging time equals exposure duration.
The VF equation for the commercial/industrial scenario (Equation 4-8) is identical to the
one included in the 1996 SSG for screening sites with future residential land use and is based on
the model developed by Jury et al. (1984). However, the dispersion factor (Q/Cvol) can now be
derived for any source size between 0.5 and 500 acres using the equation and look-up table in
Appendix D, Exhibit D-3. (The default Q/Cvol factor assumes a 0.5 acre source size. As reported
in Appendix A to the 1996 SSG, SSLs for a 0.5 acre source calculated under the infinite source
assumption are protective of uniformly contaminated 30-acre source areas of significant depth
up to 21 meters depending on contaminant and pathway, approximately 10 meters on average.) The
look-up table in Exhibit D-3 provides the three constants for the Q/Cvol equation (A, B, and C) for
each of 29 cities selected to be representative of a range of meteorologic conditions across the
country. The Q/Cvol constants for each city were derived from the results of modeling runs of EPA's
ISC3 dispersion model run in short-term mode using five years of hourly meteorological data.
4-23
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Equation 4-8
Derivation of the Volatilization Factor
- Commercial/Industrial Scenario
VF =
Q/Cvo|x(3.14xDAxT)1/2x1(T4(m2/cm2)
(2xPbxDA)
where:
Parameter/Definition (units)
VF/volatilization factor (m3/kg)
DA/apparent diffusivity (cm2/s)
Q/CVO,/inverse of the ratio of the geometric mean air concentration to
the volatilization flux at center of a square source (g/m2-s per kg/m3)
T/exposure interval (s)
pb/dry soil bulk density (g/cm3)
9a/air-filled soil porosity (Lair/Ls0ii)
n/total soil porosity (Lpore/LsoN)
ejwater-filled soil porosity (L^^/L^,)
ps/soil particle density (g/cm3)
D/diffusivity in air (cm2/s)
H'/dimensionless Henry's law constant
Dw/diffusivity in water (cm2/s)
Kd/soil-water partition coefficient (cm3/g)
Koc/soil organic carbon partition coefficient (cm3/g)
foc/fraction organic carbon in soil (gig)
Default
chemical-specific
chemical-specific
68.18a
9.5 x 108
1.5
n-ew
1-(Pb/Ps)
0.15
2.65
chemical-specificb
chemical-specific"
chemical-specific"
for organics: Kd = K^ xfoc
for inorganics: see Appendix Cc
chemical-specificb
0.006 (0.6%)
a Assumes a 0.5 acre emission source; for site-specific values, consult Appendix D.
b See Appendix C.
c Assume a pH of 6.8 when selecting default Kj values for metals.
4-24
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To calculate a site-specific Q/Cvol factor, site managers must first identify the climatic zone
and city most representative of meteorological conditions at the site. Appendix D includes a map
of climatic zones to help site managers select the appropriate Q/Cvol equation constants for the site.
The site manager should also consult with the site hydrogeologist to determine P/C^ inputs. Once
the Q/Cvol equation constants have been identified, a dispersion factor can be calculated for any
source size between 0.5 and 500 acres and input into Equation 4-8 to derive a site-specific VF.
The Csat equation (Equation 4-9) is also unchanged from the residential guidance; it
measures the contaminant concentration at which all soil pore space (both air- and water-filled) is
saturated with the compound and the adsorptive limits of the soil particles have been reached.
Equation 4-9
Derivation of the Soil Saturation Limit
s 7
sat ^ d b w
Parameter/Definition (units)
Csa/soil saturation concentration
(mg/kg)
S/solubility in water (mg/L-water)
pb/dry soil bulk density (kg/L)
Kd/soil-water partition coefficient
(L/kg)
Koc/organic carbon partition
coefficient (L/kg)
foc/fraction organic carbon
in soil (gig)
S^water-filled soil porosity
('-water''- soil)
H'/dimensionless Henry's
law constant
9a/air-filled soil porosity
n/total soil porosity
C-pore'LSoil)
Ps/soil particle density (kg/L)
Default
chemical-specific3
chemical-specific3
1.5
organics = Koc xfoc
inorganics = see
Appendix Cb
chemical-specific3
0.006 (0.6%)
0.15
chemical-specific3
n-ew
1 - (Pb/Ps)
2.65
3 See Appendix C.
b Assume a pH of 6.8 when selecting default Kj values
for metals.
Csat represents an upper bound on
the applicability of the VF model, because
compounds exceeding Csat may be present
in free phase, which would violate a key
principle of the model (i.e., that Henry's
Law applies). Csat values should be
calculated using the same site-specific soil
characteristics used to calculate SSLs.
Because VF-based inhalation SSLs are
reliable only if they are less than or equal
to Csat, these SSLs should be compared to
Csat concentrations before they are used in
a soil screening evaluation. If the
calculated SSL exceeds Csat and the
contaminant is liquid at typical soil
temperatures (see Appendix C, Exhibit C-
3), the SSL is set at Csat. If an organic
compound is liquid at soil temperature,
concentrations exceeding Csat indicate the
potential for nonaqueous phase liquid
(NAPL) to be present in soil. This poses
a possible risk to ground water, and more
investigation may be warranted. For
organic compounds that are solid at soil
temperatures, concentrations above Csat do
not pose a significant inhalation risk nor
are they indicative of NAPL
contamination. Soil screening decisions
for these compounds should be based on
SSLs for other exposure pathways. For
more information on Csat and the proper
selection of SSLs, please refer to the 1996
SSG.
4-25
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Migration to Ground Water.
This guidance calculates commercial/industrial
SSLs for the ingestion of leachate-
contaminated ground water using the same set
of equations and default input values presented
in the 1996 SSG. Thus, the generic SSLs for
this pathway are the same under
commercial/industrial and residential land use
scenarios.
EPA has adopted this approach for two
reasons. First, it protects off-site receptors,
including residents, who may ingest
contaminated ground water that migrates from
the site. Second, it protects potentially potable
ground water aquifers that may exist beneath
commercial/ industrial properties. (See text box
for EPA's policy on ground water
classification). Thus, this approach is
appropriate for protecting ground water
resources and human health; however, it may
necessitate that sites meet stringent SSLs if the
migration to ground water pathway applies,
regardless of future land use.
The simple site-specific ground water
approach consists of two steps. First, it
employs a simple linear equilibrium soil/water
partition equation to estimate the contaminant
concentration in soil leachate. Alternatively,
the synthetic precipitation leachate procedure
(SPLP) can be used to estimate this
concentration. Next, a simple water balance
equation is used to calculate a dilution factor to account for reduction of soil leachate concentration
from mixing in an aquifer. This calculation is based on conservative, simplified assumptions about
the release and transport of contaminants in the subsurface (see Exhibit 4-3). These assumptions
should be reviewed for consistency with the CSM to determine the applicability of SSLs to the
migration to ground water pathway.
Equation 4-10 is the soil/water partition equation; it is appropriate for calculating SSLs
corresponding to target leachate contaminant concentrations in the zone of contamination.
Equations 4-11 and 4-12 are appropriate for determining the dilution attenuation factor (DAF) by
which concentrations are reduced when leachate mixes with a clean aquifer. Because of the wide
variability in subsurface conditions that affect contaminant migration in ground water, default
values are not provided for input parameters for these dilution equations. Instead, EPA has
Ground Water Classification
In order to demonstrate that the ingestion of
ground water exposure pathway is not applicable for a
site, site managers may either perform a detailed fate and
transport analysis (as discussed in the TBD to the 1996
SSG), or may show that the underlying ground water has
been classified as non-potable. EPA's current policy
regarding ground water classification for Superfund sites
is outlined in an OSWER directive (U.S. EPA, 1997e).
EPA evaluates ground water at a site according to the
federal ground water classification system, which
includes four classes:
1 - sole source aquifers;
2A - currently used for drinking water;
2B - potentially usable for drinking water; and
3 - not usable for drinking water.
Generally, this pathway applies to all
potentially potable water (i.e., classes 1, 2A, and 2B),
unless the state has made a different determination
through a process analogous to the Comprehensive State
Ground Water Protection Plan (CSGWPP). Through
this process, ground water classification is based on an
aquifer or watershed analysis of relevant
hydrogeological information, with public participation,
in consultation with water suppliers, and using a
methodology that is consistently applied throughout the
state. If a state has no CSGWPP or similar plan, EPA
will defer to the state's ground water classification only
if it is more protective than EPA's. As of February
2001, 11 states (AL, CT, DE, GA, IL, MA, NH, NV,
OK, VT, and WI) have approved CSGWPP plans.
4-26
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developed two possible default DAFs (DAF=20
and DAF=1) that are appropriate for deriving
generic SSLs for this pathway. The selection of a
default DAF is discussed in Appendix A, and the
derivation of these defaults is described in the
TBD to the 1996 SSG. The default DAFs also can
be used for calculating simple site-specific SSLs,
or the site manager can develop a site-specific
DAF using equations 4-11 and 4-12.
To calculate SSLs for the migration to
ground water pathway, the acceptable ground
water concentration is multiplied by the DAF to
obtain a target soil leachate concentration (Cw).12
For example, if the DAF is 20 and the acceptable
ground water concentration is 0.05 mg/L, the
target soil leachate concentration would be 1.0
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, the target soil
leachate concentration is compared directly to
extract concentrations from the leach tests.
Exhibit 4-3
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)
For more information on the development of SSLs for this pathway, please consult the 1996
SSG.
MaSS-LilTlit SSLS. Equations 4-13 and 4-14 present models for calculating mass-limit
SSLs for the outdoor inhalation of volatiles and migration to ground water pathways, respectively.
These models can be used only if the depth and area of contamination are known or can be
estimated with confidence. These equations are identical to those in the 1996 SSG. Please consult
that guidance for information on using mass-limit SSL models.
12
The acceptable ground water concentration is, in order of preference: a non-zero Maximum Contaminant
Level Goal (MCLG), a Maximum Contaminant Level (MCL), or a health-based level (HBL) calculated based on an
ingestion rate of 2L/day and a target cancer risk of IxlO"6 or an HQ of 1. These values are presented in Appendix C.
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Equation 4-10
Soil Screening Level Partitioning Equation for Migration to Ground Water
Screening
Level = C
in Soil (mg/kg)
w
Pb
Parameter/Definition (units)
Cw/target soil leachate concentration (mg/L)
Kd/soil-water partition coefficient (L/kg)
Koc/soil organic carbon/water partition coefficient (L/kg)
foc/fraction organic carbon in soil (gig)
ejwater-filled soil porosity (Ua,er/UoM)
9a/air-filled soil porosity (^/L,.^)
pb/dry soil bulk density (kg/L)
n/soil porosity (Lpore/Lsoil)
Ps/soil particle density (kg/L)
H'/dimensionless Henry's law constant
Default
(nonzero MCLG, MCL, or HBLf x
dilution factor
for organics: Kd = K^ * foc
for inorganics: see Appendix Cb
chemical-specific0
0.002 (0.2%)
0.3
n-ew
1.5
1 - (Pb/Ps)
2.65
chemical-specific0
(assume to be zero for inorganic
contaminants except mercury)
a Chemical-specific (see Appendix C).
b Assume a pH of 6.8 when selecting default
0 See Appendix C.
values for metals.
Equation 4-11
Derivation of Dilution Attenuation Factor
Dilution
Attenuation - 1 H
Factor (DAF)
Parameter/Definition (units)
DAF/dilution attenuation
factor (unitless)
K/aquifer hydraulic
conductivity (m/yr)
i/hydraulic gradient (m/m)
I/infiltration rate (m/yr)
d/mixing zone depth (m)
L/source length parallel to
ground water flow (m)
Kxixd
|x|_
Default
20or1
(0.5-acre source)
Site-specific
Site-specific
Site-specific
Site-specific
Site-specific
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Equation 4-12
Estimation of Mixing Zone Depth
d = (0.0112L2)05 + da(1-exp[(-l_x|)/(Kxjxda)])
Parameter/Definition (units)
d/mixing zone depth (m)
L/source length parallel to ground water flow (m)
I/infiltration rate (m/yr)
K/aquifer hydraulic conductivity (m/yr)
i/hydraulic gradient (m/m)
da/aquifer thickness (m)
Default
Site-specific
Site-specific
Site-specific
Site-specific
Site-specific
Site-specific
Equation 4-13
Mass-Limit Volatilization Factor
- Commercial/Industrial Scenario
VF - Q/C v tTx (3-15x1ฐ s/Vr)]
(Pbxdsx106g/Mg)
Parameter/Definition (units)
ds/average source depth (m)
T/exposure interval (yr)
Q/CVO, /in verse of the ratio of the
geometric mean air concentration
to the volatilization flux at the
center of a square source
(g/m2-s per kg/m3)
pb/dry soil bulk density
(kg/L or Mg/m3)
Default
site-specific
30
68.18a
1.5
a Assumes a 0.5 acre emission source
Equation 4-14
Mass-Limit Soil Screening Level for Migration to
Ground Water
Screening (Cwx|xED)
in Soil (mg/kg) Pbxds
Parameter/Definition (units)
Cw/target soil leachate
concentration (mg/L)
dg/depth of source (m)
I/infiltration rate (m/yr)
ED/exposure duration (yr)
pb/dry soil bulk density (kg/L)
Default
(nonzero MCLG, MCL,
or HBLfx dilution
factor
site-specific
0.18
70
1.5
a Chemical-specific, see Appendix C.
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4.3 Additional Considerations for the Evaluation of Non-Residential
Exposure Scenarios
As described in this guidance document, conducting soil screening evaluations for non-
residential land use scenarios involves making well-reasoned assumptions about site use, potential
exposure pathways, and potential receptors. These decisions raise the following issues about the
derivation and application of non-residential SSLs:
The importance of involving community representatives in identifying the
likely future land use (and associated activities) at sites;
The selection and implementation of institutional controls to ensure that
future site uses and activities will be consistent with the non-residential land
use assumptions used to derive SSLs; and
The relative roles of SSLs and OSHA standards in protecting future
workers from exposure to residual contamination at non-residential sites.
This section provides guidance on these issues, outlining EPA policy and highlighting useful
resources.
4.3.1 Involving the Public in Identifying Future Land Use at Sites
The potential for site managers to apply non-residential land use assumptions in developing
SSLs is most useful when the likely future land use for a site can be identified early in the
Superfund process. As discussed in Section 3.1, community representatives (including local land
use planners, local officials and members of the general public) can provide a great deal of insight
about the reasonably anticipated future land use of sites. This can be one of the most important
aspects of overall community involvement, especially for sites that have been abandoned by
previous owners or sites where land use is likely to change. Site managers should look to the
community as a source of information about both current and reasonably anticipated future site
activities, which can help identify relevant exposure pathways that should be reflected in the CSM.
Early interaction with community representatives and local government officials can help
to ensure that the assumptions used in the soil screening evaluation will be supported by the
community. This also may lead to greater community support of subsequent Superfund activities
at a site, such as the baseline risk assessment and selection of remedies, which may be based, in
part, on these assumptions. EPA has developed guidance, Community Involvement in Superfund
Risk Assessments, A Supplement to RAGS Part A, to assist site managers in working with
communities and soliciting their input (U.S. EPA, 1999b). Site managers also can consult the
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OSWER directive, Land Use in the CERCLA Remedy Selection Process (U.S. EPA, 1995a) for
information on community involvement in the identification of future land use.13
4.3.2 Institutional Controls
Non-residential SSLs are based on specific assumptions about land use and access. These
assumptions are typically less conservative than those used to develop residential SSLs; thus, non-
residential SSLs may be less stringent than the corresponding residential values. These non-
residential SSLs can be protective of the key receptors associated with reasonably anticipated future
non-residential land uses, but they may not be universally protective of all receptors and activities.
Therefore, ensuring that contaminant levels are protective of exposures at sites or areas of sites that
are screened out under these less stringent SSLs depends on site use, activities, and accessibility
remaining consistent with the conceptual site model upon which screening decisions are based.
Effective, enforceable institutional controls (ICs) may be a very important tool for preventing
inappropriate land uses and activities that may result in unacceptable exposures. EPA defines ICs
as "non-engineered instruments such as administrative and/or legal controls that minimize the
potential for human exposure to contamination by limiting land or resource use" (U.S. EPA,
2000b).14
A non-residential screening assessment should include an evaluation of the
implementability and potential effectiveness of ICs for areas that are screened out. This evaluation,
which may consider multiple 1C options, allows the site manager to identify the best available
means (if any) to ensure long-term protectiveness at areas of sites screened out under less stringent,
non-residential SSLs. It should provide sufficient evidence to conclude that effective
implementation of ICs is feasible and can serve to "prevent an unanticipated change in land use that
could result in unacceptable exposures to residual contamination or, at a minimum, alert future
users to residual risks and monitor for any changes in use" (U.S. EPA, 1995a). If it does not appear
likely that such ICs can be established in the future, then it is inappropriate to screen out a site or
area of a site under non-residential SSLs. Instead, site managers may compare soil contaminant
concentrations to residential SSLs that would be protective given unrestricted land use.
A variety of ICs exist that can be used to prevent or limit exposure at a site. In general,
these fall into the four major categories summarized below (U.S. EPA, 2000b).
13 See http://www.epa.gov/oerrpage/superfund/resources/landuse.htm.
14 EPA also stresses that ICs are generally to be used in conjunction with engineering measures; that they can
be used during all stages of the cleanup process; and that they should ideally be "layered" (i.e. the simultaneous
application of multiple ICs) or implemented in series to provide overlapping assurances of protection from
contamination (U.S. EPA, 2000b).
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State and Local Government Controls Government controls are usually
implemented and enforced by a state or local government and can include
zoning restrictions, ordinances, statutes, building permits, or other
provisions that restrict land or resource use at a site. Since this category of
ICs is put in place under local jurisdiction, they may be changed or
terminated with little notice to EPA, and EPA generally has no authority to
enforce such controls.
Proprietary Controls. These controls have their basis in property law and
are unique in that they generally create legal property interests. In other
words, proprietary controls involve legal instruments placed in the chain of
title of the site or property. Common examples include covenants or
easements restricting future land use or prohibiting activities that may
compromise specific engineering remedies. The benefit of proprietary
controls is that they can be binding on subsequent purchasers of the property
(successors in title) and transferable, which may make them more reliable
in the long term than other types of ICs. However, property law is complex,
and variations in property laws across states can make it difficult to establish
and enforce appropriate proprietary controls.
Enforcement Tools with 1C Components. Under section 106(a) of
CERCLA, EPA has the authority to issue administrative orders to compel
land owners to limit certain site activities at both Federal and private sites.
Although this tool is frequently used by site managers, it may have
significant shortcomings that should be thoroughly evaluated. For example,
property restrictions that are part of an enforcement action are binding only
on the signatories and are not transferred through a property transaction,
which limits their long-term protectiveness.
Informational Devices. Informational tools provide information or
notification that residual or capped contamination may remain on site.
Common examples include state registries of contaminated properties, deed
notices, and advisories. Because such devices are not legally enforceable,
it is important to carefully consider the objective of this category of 1C.
Informational devices are most likely to be used as a secondary "layer" to
help ensure the overall reliability of other ICs.
Early and careful consideration of ICs can be valuable for soil screening evaluations
because it focuses attention on land use assumptions that can be maintained over time. In the
context of soil screening analyses, the 1C evaluation should identify the types of ICs available, the
existence of the authority necessary to implement an 1C, the willingness and ability of the
appropriate entity to effectively implement and enforce the 1C in both the short and long term, and
the relative cost associated with the implementation and maintenance of any 1C. Incorporating such
considerations as a part of the screening assessment allows site managers to anticipate and consider
potential barriers to the implementation of ICs.
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In addition, early consideration of 1C options assists site managers in identifying those
parties (e.g., local government agencies) who would be instrumental in ensuring the effective
implementation and management of any 1C selected. For example, a local government's ability to
effectively maintain or enforce an 1C may affect not only the type of 1C selected, but also the
decision of whether it is appropriate to utilize ICs to help achieve protection of human health.
Consideration of 1C options is thus a valuable tool for increasing the overall reliability of screening
decisions and should not be viewed as an afterthought to the soil screening process.
For more detailed information on how to evaluate and implement ICs, please consult the
following publications:
Institutional Controls: A Site Manager's Guide to Identifying, Evaluating and
Selecting Institutional Controls at Super fund and RCRA Corrective Action
Cleanups. Office of Solid Waste and Emergency Response. EPA 540-F-OO.
OSWER 9355-0-24-FS-P. September 2000.
Land Use in the Remedy Selection Process. OSWER Directive No. 9355.7-04.
May 1995.
4.3.3 Applicability of OSHA Standards at NPL Sites
Conducting soil screening evaluations at sites where workers are the primary receptors of
concern raises questions about the roles of commercial/industrial SSLs and OSHA standards in
protecting these receptors. Although both OSHA standards and SSLs protect the health of workers
exposed to toxic substances, the conditions of exposure implicit in each set of values differ. As a
result, OSHA standards are not suitable substitutes for SSLs.
The key distinctions between OSHA standards and commercial/industrial SSLs include the
underlying assumptions about the context of workplace exposures, the characteristics of the
workers being protected, and the level of protection afforded to workers (U.S. EPA, 1995b).
Context of Workplace Exposure. OSHA standards assume that workers
are exposed to hazardous chemicals used in or generated as a result of
routine work activities. These workers are assumed to be aware of the
chemicals to which they are exposed and can obtain information on them
through Right-to-Know laws. Further, they tacitly accept certain risks
associated with exposure because they receive a benefit (i.e., higher wages)
to compensate them for additional hazard. On the other hand,
commercial/industrial SSLs address worker exposures to general
environmental pollution contaminants whose presence at a site may be
independent of any current or future work activity (though work activities,
such as excavation, may lead to exposure).
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Characteristics of Worker Receptors. OSHA standards protect workers
who are likely, through self-selection, to be less sensitive to the chemicals
to which they are exposed; a worker who finds that he or she is highly
sensitive to a compound that is used during daily work activities would be
able to proactively seek other jobs or alternative job responsibilities that do
not involve exposure to that compound. Thus, unlike SSLs, which are based
on an RME scenario, OSHA standards are not designed to protect against
exposures to sensitive sub-populations.
Level of Protection Afforded to Workers. OSHA standards assume not
only that workers are knowingly exposed to specific chemicals in the
workplace, but also that they receive additional protection and training to
mitigate exposures. OSHA requires workers to be trained to control or
prevent exceedances of its exposure standards (including the use of personal
protective clothing and gear to help prevent excessive exposures). OSHA
also requires periodic worker health monitoring to ensure that excessive
exposures are not occurring. In contrast, RAGS Part A (U.S. EPA, 1989b)
indicates that a Superfund risk assessment is an analysis of potential adverse
health effects (current or future) caused by hazardous substances released
from a site in the absence of any actions or controls to mitigate exposures.
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5.0 CALCULATION OF SSLS FOR A CONSTRUCTION SCENARIO
Construction is likely to occur as part of the redevelopment process at many NPL sites,
regardless of the anticipated future land use. Although construction is typically of relatively short
duration (a year or less), it may lead to significant exposures to construction workers and off-site
residents as a result of soil-disturbing activities that include excavation and vehicle traffic on
unpaved roads. To help address this potential concern, EPA has developed a construction soil
screening scenario that site managers can use to develop construction SSLs.
EPA designed the construction scenario to supplement the residential and non-residential
screening scenarios. When appropriate, site managers should calculate construction SSLs in
addition to the SSLs for the appropriate land use scenario. This chapter of the guidance explains
when construction SSLs should be calculated, presents the exposure framework for the construction
scenario, and provides equations for calculating simple site-specific SSLs that reflect potential
exposure during construction activities. Information on using more detailed site-specific modeling
to develop construction SSLs is presented in Appendix E.
5.1 Applicability of the Construction Scenario
The construction scenario assumes that one or more residential or commercial buildings will
be erected on a site and that construction will occur within areas of residual soil contamination.
Because the activities associated with such a project are likely to result in significant direct contact
soil exposures (i.e., ingestion and dermal absorption) to construction workers and are likely to
increase emissions of both volatiles and paniculate matter from contaminated soils during the
construction period, EPA recommends that site managers evaluate the construction exposure
scenario whenever major construction is anticipated at a site. However, EPA realizes that
developing SSLs based on a construction scenario may be difficult, especially if there is
considerable uncertainly surrounding the details of future construction. In such cases, site managers
can evaluate several plausible construction scenarios representing a range of activities, areal extents,
and durations. The results of these evaluations can provide valuable information to help guide and
focus future construction activities.
EPA anticipates that the potential for increased exposure during construction will be a
concern at many sites. While we recognize that the construction scenario may produce SSLs that
are more stringent than those for the other scenarios, we emphasize that SSLs are not cleanup levels;
rather they are used to assist site managers in scoping the analyses that comprise the Superfund
process. In addition, construction SSLs can be used to inform future construction plans, highlighting
areas and construction activities that may pose significant risks to construction workers or other
receptors in the absence of mitigating measures.
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There are conditions under which site managers may choose not to evaluate the construction
scenario. These include:
No Redevelopment Currently Anticipated. If there are no existing plans for
redeveloping a site, the site manager may opt not to evaluate the construction
scenario at the time of the initial soil screening evaluation. However, in this
case, the soil screening evaluation should be accompanied by an analysis that
demonstrates the feasibility of implementing institutional controls in the
future to restrict activities that would disturb residual site contamination, such
as excavation or digging a well, unless screened out site areas are re-
evaluated.
Construction Will Not Disturb Contamination. If a site manager can
demonstrate that the proposed excavation does not include any areas of soil
contamination and that any unpaved roads created on-site for construction
vehicle traffic will not cross areas of surficial soil contamination, the
construction scenario need not be evaluated. Again, the soil screening
evaluation should identify effective institutional controls that can be
implemented in the future to restrict activities in the event that subsequent
construction would disturb residual soil contamination.
5.2 Soil Screening Exposure Framework for Construction Scenario
The construction soil screening scenario evaluates exposures to construction workers present
throughout a construction project, as well as exposures to nearby off-site residents. These receptors
are potentially subject to higher contaminant exposures via increased volatile and fugitive dust
emissions during construction activities.
Exhibit 5-1 summarizes the exposure framework for construction workers and off-site
residents.
Construction Worker. This is a short-term adult receptor who is exposed to
soil contaminants during the work day for the duration of a single construction
project (typically a year or less). If multiple non-concurrent construction
projects are anticipated, it is assumed that different workers will be employed
for each project. The activities for this receptor typically involve substantial
on-site exposures to surface and subsurface soils. The construction worker is
expected to have a very high soil ingestion rate and is assumed to be exposed
to contaminants via the following direct and indirect pathways: incidental soil
ingestion, dermal absorption, inhalation of volatiles outdoors, and inhalation
of fugitive dust.
5-2
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Exhibit 5-1
SUMMARY OF THE CONSTRUCTION SCENARIO EXPOSURE
FRAMEWORK FOR SOIL SCREENING
Exposure
Characteristics
Pathways of
Concern1
Receptors
Construction Worker
Exposed during construction
activities only
Potentially high ingestion and
inhalation exposures to surface
and subsurface soil contaminants
Short-term (subchronic) exposure
Ingestion (surface and subsurface
soil)
Dermal contact (surface and
subsurface soil)
Inhalation of volatiles outdoors
(subsurface soil)
Inhalation of fugitive dust due to
traffic on unpaved roads (surface
soil)2
Off-site Resident
Resides at the site boundary
Exposed both during and
post-construction
Potentially high inhalation
exposures to contaminants
in fugitive dust
Long-term (chronic)
exposure
Inhalation of fugitive dust
due to traffic on unpaved
roads and wind erosion
(surface soil)
Default Exposure Factors
Exposure Frequency (d/yr)
Exposure Duration (yr)
Soil Ingestion Rate3 (mg/d)
Inhalation Rate (m3/d)
Body Weight (kg)
Lifetime (yr)
250
1
330
20
70
70
350
30
NA
204
70
70
1 The inhalation of volatiles is not included as a pathway of concern for off-site residents because SSLs developed
for this pathway for the construction worker (short-term) and for the on-site worker receptor under the
commercial/industrial scenario (long-term) were shown to be protective for this receptor.
2 Analyses of the inhalation of fugitive dust pathway suggest that the most significant contribution to exposure
comes from disturbance of surface soil by traffic on unpaved roads. Therefore, the framework for simple site-
specific soil screening evaluation for this pathway focuses on surface soil. If a site manager determines that
excavation of subsurface soil or other earth-moving activities may lead to significant exposure to fugitive dust,
it may be appropriate to use a more detailed site-specific modeling approach to develop a construction SSL for
this pathway. Appendix E provides guidance on conducting such modeling.
3 The soil ingestion rate is revised from the previous default ingestion rate of 480 mg/d. See the discussion of
ingestion rate in section 5.3.2.
4 Residential inhalation exposure to children and adults is evaluated using the RfC toxicity criterion, which is based
on an inhalation rate of 20 nf/day. No comparable toxicity criterion specific to childhood exposures is currently
available. EPA has convened a workgroup to identify suitable default values for modeling childhood inhalation
exposures, as well as possible approaches for adjusting toxicity values for application to such exposures.
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Off-site Resident. This receptor is similar to the one evaluated in the
residential soil screening scenario but is located at the site boundary.21 The
off-site resident is exposed to contaminants both during and after construction,
for a total of 30 years. This receptor has no direct contact with on-site soils.
Under this framework, the only exposure pathway evaluated for this receptor
is the inhalation of fugitive dust, which is likely to be exacerbated during
construction as a result of dust generated by truck traffic on unpaved roads.
EPA's recommendations for focusing on specific exposure pathways and receptors are based
on analyses of the potential exposure levels resulting from different activities. EPA's analysis of the
impacts of different construction activities on fugitive dust emissions demonstrated that vehicle
traffic on contaminated unpaved roads typically accounts for the majority of emissions, with wind
erosion, excavation soil dumping, dozing, grading, and filling operations contributing lesser
emissions. Based on this analysis, EPA has focused the simple site-specific construction scenario
on fugitive dust emissions from traffic on contaminated unpaved roads. Information on evaluating
fugitive dust emissions resulting from other construction activities as part of a detailed site-specific
approach can be found in Appendix E.
In the case of volatile contaminants, excavation during construction can increase volatile
emissions by unearthing soil contamination and bringing it into direct contact with the air; this
increases the flux of volatile contaminants from the soil into the air. The equations for developing
simple site-specific SSLs for both the commercial/industrial and construction scenarios are based
on the assumption that contaminants are present at the soil surface. The complexity of modeling the
volatilization of contaminants from buried waste precludes the development of SSLs for this
situation under the simple site-specific approach. SSLs that reflect buried contamination can be
calculated for any scenario using the detailed site-specific approach (see Appendix E). Under the
conservative assumptions of the simple site-specific approach, SSLs for volatiles developed for the
outdoor worker receptor under the commercial/industrial scenario (or for a resident) should be
protective of the off-site resident under the construction scenario. (See discussion of the relative
exposures for on- and off-site receptors in Section 4.2.2).
EPA also conducted an analysis comparing the subchronic exposure levels to volatile
contaminants for on-site construction workers with those for off-site residents and found little
difference between the resulting SSLs for the two receptors. The difference in SSLs for these
receptors is less than 20 percent, well within the uncertainty associated with emissions modeling22
21 This is a conservative assumption, since the highest exposure concentrations for off-site residents occur at
the site boundary.
22 Modeling results indicate that a construction worker, who is located on-site, is exposed to higher
concentrations of volatiles than an off-site resident. However, an off-site resident is assumed to have a higher exposure
frequency than a construction worker during the construction period (i.e., seven days per week versus five days per
week). The net result is a slightly lower SSL for an off-site resident, approximately 18 percent lower than the SSL for
a construction worker. This difference is small relative to the uncertainty in the emission, dispersion, and exposure
modeling; thus, EPA believes that the construction worker SSL is sufficiently protective of subchronic exposures to off-
site residents.
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Therefore, EPA recommends that only construction workers be evaluated for subchronic exposure
to volatiles during construction activities.
In some cases, site managers also may wish to evaluate direct ingestion and dermal contact
exposures of off-site residents to contaminated dust that is deposited on an off-site property during
construction activities. For sites where contaminant concentrations meet residential SSLs, this
pathway is unlikely to result in significant risks, due to the reduction of contaminant concentrations
expected to occur as deposited dust mixes with uncontaminated soils. For sites meeting
commercial/industrial SSLs, this may be a pathway of concern for some contaminants, especially
metals, for which the commercial/industrial SSL for ingestion/dermal contact exposure is
significantly higher than the corresponding residential SSL that would apply to the off-site exposure.
For these contaminants, off-site deposition could potentially lead to concentrations that exceed
residential direct contact SSLs. However, the complexity of modeling off-site deposition of
contaminated dusts precludes EPA from developing an average default factor for estimating the off-
site concentration resulting from deposition, relative to on-site contamination levels. Therefore, this
pathway should be addressed on a site-specific basis.
5.3 Calculating SSLs for the Construction Scenario
This section presents EPA's recommended approach to calculating SSLs for construction-
related exposures. First, it describes key differences between the calculation of construction SSLs
and the calculation of residential or commercial/industrial SSLs. Then, it presents the equations
used to calculate construction SSLs using the simple site-specific soil screening approach.
5.3.1 Calculation of Construction SSLs - Key Differences
Besides differences in receptors and exposure factors, there are three key differences between
construction SSLs and residential or commercial/industrial SSLs:
Absence of Generic SSLs. EPA does not present generic SSLs for the
construction scenario. This decision reflects the difficulty of developing
standardized default exposure assumptions and other model input parameters
for a construction scenario. Construction-related exposures depend on many
parameters including, but not limited to: the size of the site; the size of the
contaminated source area; the dimensions of the building(s) being
constructed and its location relative to the source area and to the site
boundary; the type of building being constructed (e.g., a slab-on-grade
structure versus a building with a basement); and the overall duration of the
construction project. These parameters can vary considerably from project
to project, and current data do not allow EPA to identify a reasonable set of
generic default values (either central tendency or high end) for all of them.
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Therefore, EPA has not established generic SSLs for construction activities,
and the equations presented below do not include suggested default values
for all model input parameters. Site managers having difficulty determining
a site-specific value may wish to calculate SSLs using a range of plausible
values.
Subchronic Exposures. Under the guidelines established by the Superfund
program, exposures to construction workers of one year or less are classified
as subchronic exposures.23 This short exposure duration affects how site
managers use toxicity values in calculating SSLs for non-carcinogenic
effects. Specifically, calculations of SSLs based on non-carcinogenic effects
associated with subchronic exposures should incorporate toxicity values for
subchronic, not chronic, effects.24 Subchronic toxicity values are not as
widely available as chronic values, and unlike chronic RfDs and RfCs, no
EPA work group exists to review and verify subchronic RfDs or RfCs.
Subchronic toxicity values for a limited number of compounds are available
from EPA's Health Effects Assessment Summary Tables (HEAST).25 We
recommend that site managers seek assistance from EPA's regional risk
assessors and from EPA's Superfund Technical Support Center when
researching appropriate subchronic toxicity values. In addition, the Agency
for Toxic Substances and Disease Registry (ATSDR) publishes Minimal Risk
Levels (MRLs) that may be suitable for use as subchronic toxicity values.26
The SSL equations for the construction worker use the generic term "Health
Based Level" (HBL) to refer to these subchronic toxicity values. When
calculating SSLs for this receptor, site managers can use a subchronic RfD
or RfC from HEAST, a value recommended by the Superfund Technical
Support Center, an MRL, or another suitable subchronic value (accompanied
by appropriate documentation) as the HBL, as opposed to chronic or acute
toxicity values.
23 EPA defines subchronic exposures for Superfund purposes as exposures lasting between two weeks and
seven years. See U.S. EPA., 1989b, Chapters 6, 7, and 8.
24 There is no change with respect to SSLs based on carcinogenic effects, because the methodology averages
exposures over a lifetime.
25 HEAST presents tables of chemical-specific toxicity information and values based on data from Health
Effects Assessments, Health and Environmental Effects Documents, Health and Environmental Effects Profiles, Health
Assessment Documents, or Ambient Air Quality Criteria Documents. HEAST summarizes interim (and some verified)
RfDs and RfCs, as well as other toxicity information for specific chemicals. Although the HEAST data do not have the
agency-wide consensus of the IRIS data, the information contained in HEAST represents current toxicity data generated
by EPA. The most recent printed version of HEAST was printed in 1997.
26 ATSDR MRLs were developed in response to a CERCLA mandate and represent the highest exposure levels
that would not lead to the development of non-cancer health effects in humans based on acute (1-14 days), subchronic
(15-364 days), and chronic (365 days and longer) exposures via oral and inhalation pathways. MRLs are based on non-
cancer health effects only. MRLs are available from ATSDR'S website, http://atsdrl.atsdr.cdc.gov:8080/mrls.html.
5-6
-------
Focus on Subsurface Soil. Construction SSLs for the combined direct
ingestion/dermal absorption exposure pathway should be used to evaluate
contaminant concentrations in both surface and subsurface soils. The focus
on subsurface soils is appropriate because excavation and other earth-moving
activities could result in substantial exposures to soils at depths greater than
two centimeters (the 1996 SSG definition of surface soils).
5.3.2 SSL Equations for the Construction Scenario
This section presents the equations used to calculate construction SSLs for surface and
subsurface soils using the simple site-specific soil screening approach. As noted above, a generic
approach is not appropriate for evaluating the construction scenario. As an alternative to the simple
site-specific approach, site managers can perform detailed site-specific modeling to evaluate this
scenario; Appendix E presents suggestions for modeling inhalation pathways under construction
conditions using the detailed site-specific approach.
For each equation, site-specific input parameters are indicated in bold. Where possible,
default values for these parameters are provided for use when site-specific data are not available.
As in the other exposure scenarios, all site-specific inputs describing soil, aquifer, and meteorologic
characteristics should represent average or typical site conditions in order to produce risk-based
SSLs that reflect reasonable maximum exposure (RME).
Chemical-specific data, including chronic toxicity criteria, for use in developing simple site-
specific SSLs are provided in Appendix C. Prior to calculating SSLs, each relevant chemical-
specific value in Appendix C should be checked against the most recent version of its source and
updated, if necessary.
In general, the basic forms of the SSL equations for the construction scenario are similar to
those used for the other scenarios. Changes to default exposure parameters that apply to individual
pathways are discussed below, along with their respective SSL equations.
5-7
-------
SSL Equations for Surface Soils
The relevant pathways for exposure to surface soils under the construction scenario include
direct ingestion and dermal absorption for construction workers, and inhalation of fugitive dusts by
both construction workers and off-site residents.
Direct Ingestion and Dermal Absorption. Equations 5-1 and 5-2 are
appropriate for addressing subchronic ingestion and dermal absorption exposure of construction
workers to carcinogens and non-carcinogens, respectively. These equations produce SSLs for
combined exposure of construction workers via these pathways.
Equation 5-1
Screening Level Equation for Combined Subchronic Ingestion and Dermal Absorption
Exposure to Carcinogenic Contaminants in Soil
Construction Scenario - Construction Worker
SCL^|n9_ TRxBWxATx365d/yr
(mg/kg) (EFxEDxIO 6kg/mg)[(SF0x|R)+(SFABSxAFxABSdxSAxEV)]
Parameter/Definition (units)
TR/target cancer risk (unitless)
BW/body weight (kg)
AT/averaging time (years)
EF/exposure frequency (days/year)
ED/exposure duration (years)
SFo/oral cancer slope factor (mg/kg-d)"1
IR/soil ingestion rate (mg/d)
SFABS/dermally adjusted cancer slope factor (mg/kg-d)"1
AF/skin-soil adherence factor (mg/cm2 -event)
ABSd/dermal absorption fraction (unitless)
SA/skin surface area exposed (cm2)
EV/event frequency (events/day)
Default
io-6
70
70
site-specific
site-specific
chemical-specific
(Appendix C)
330
chemical-specific
(Equation 3-3)
0.3
chemical-specific
(Exhibit 3-3 and Appendix C)
3,300
1
5-S
-------
Equation 5-2
Screening Level Equation for Combined Subchronic Ingestion and Dermal Absorption
Exposure to Non-Carcinogenic Contaminants in Soil
Construction Scenario - Construction Worker
SCLeve'r9- THQxBWxATx365d/yr
(mg/kg) (FFxEDxin 6ka/ma1 1 1 x|R| +[ 1 xAFxABS xSAxFVl
a'^HBLsc ) ^HBLABS d )\
Parameter/Definition (units)
THQ/target hazard quotient (unitless)
BW/body weight (kg)
AT/averaging time (years)
EF/exposure frequency (days/year)
ED/exposure duration (years)
HBLsc/subchronic health-based limit (mg/kg-d)
IR/soil ingestion rate (mg/d)
HBLABS/dermally-adjusted subchronic health-based limit (mg/kg-d)
AF/skin-soil adherence factor (mg/cm2-event)
ABSd/dermal absorption fraction (unitless)
SA/skin surface exposed (cm2)
EV/event frequency (events/day)
Default
1
70
site specific3
site specific
site specific
chemical-specific
330
chemical-specific
(Equation 3-4)
0.3
chemical-specific
(Exhibit 3-3 and Appendix C)
3,300
1
a For non-carcinogens, averaging time equals to exposure duration.
Data on soil ingestion rates for adults engaged in outdoor work are not currently available.
However, EPA believes construction workers are likely to experience substantial exposures to soils
during excavation and other work activities; therefore, a high-end soil ingestion rate has been
selected to estimate exposures under this scenario. The default value of 330 mg/day (Stanek et al.,
1997) listed in Equations 5-1 and 5-2 replaces the previous default ingestion rate of 480 mg/day
(Hawley, 1985). While the Hawley value was based on a theoretical calculation for adults engaged
in outdoor physical activity, the revised default ingestion rate is based on the 95th percentile value
for adult soil intake rates reported in a soil ingestion mass-balance study.27
27T
Research is on-going to refine our knowledge about adult soil ingestion and to produce better ingestion rate
estimates for individuals engaged in strenuous activities. This default is therefore subject to change as better data
become available.
5-9
-------
The dermal absorption components of Equations 5-1 and 5-2 are based on the same
methodology discussed in Section 3.2.1, and they can be used to calculate SSLs for the same seven
compounds and two compound classes discussed in that section. The suggested default input values
for the dermal exposure equations are consistent with those recommended in EPA's interim dermal
guidance (U.S. EPA, 2001). Event frequency (EV, the number of events per day) is assumed to be
one. Construction workers are assumed to have their face, forearms, and hands exposed. Therefore,
this guidance recommends that a value of 3,300 cm2 be used as an estimate of the skin surface area
exposed (SA). We also assume a default adherence factor (AF) of 0.3 mg soil per square centimeter
of exposed skin. The SA default value is the same as that used for commercial/industrial outdoor
worker receptors; the AF value represents the 95th percentile value for construction workers. The
chemical-specific dermal absorption fractions (ABSd) are presented in Appendix C. For those
compounds that are classified as both semi-volatiles and as PAHs, the ABS ddefault for PAHs should
be applied. Subchronic oral toxicity values used to calculate this SSL should be adjusted in the same
manner as chronic oral RfDs (see Equation 3-4).
Inhalation Of FugltlVG DustS. Under a construction scenario, fugitive dusts may
be generated from surface soils by wind erosion, construction vehicle traffic on temporary unpaved
roads and other construction activities. Inhalation of these dusts containing semi-volatile organic
compounds and metals may be of concern to construction workers and off-site residents. As
described in Section 4.2.3, site managers need only evaluate the fugitive dust pathway for a single
contaminant, hexavalent chromium (Cr+6) under the residential and commercial/industrial scenarios;
however, due to the potential for increased dust exposure from truck traffic on unpaved roads during
construction, EPA recommends that SSLs for the construction scenario be calculated for semi-
volatile compounds and for all metals.28
Equations 5-3 and 5-4 are appropriate for calculating fugitive dust SSLs for carcinogens and
non-carcinogens for subchronic construction worker exposure. These equations are similar to the
fugitive dust SSL equations for other scenarios, with the exception of the health based limit
subchronic toxicity value term (HBLSC). In addition, the equation to calculate the subchronic
particulate emission factor (PEFSC, Equation 5-5) is significantly different from the residential and
non-residential PEF equations. The PEFSC in Equation 5-5 focuses exclusively on emissions from
truck traffic on unpaved roads, which typically contribute the majority of dust emissions during
construction. This equation requires estimates of parameters such as the number of days with at
least 0.01 inches of rainfall, the mean vehicle weight, and the sum of fleet vehicle distance traveled
during construction.
28 For purposes of this guidance, semi-volatile compounds are defined as those listed on EPA's Contract
Laboratory Program list of target semi-volatile compounds (see http://www.epa.gov/superfund/programs/clp/target.
htm). These compounds are identified on the exhibits in Appendix A. In addition, metals are listed at the bottom of
each exhibit in Appendix A.
5-10
-------
Equation 5-3
Screening Level Equation for Subchronic Inhalation of Carcinogenic Fugitive Dusts
Construction Scenario - Construction Worker
Screening TR x AT x 365d/yr
(mg/kg) URFxl,000|jg/mgxEFxE
Parameter/Definition (units)
TR/target cancer risk (unitless)
AT/averaging time (years)
URF/inhalation unit risk factor (ug/m3)"1
EF/exposure frequency (days/year)
ED/exposure duration (years)
PEFsc/subchronic road particulate emission factor (m3/kg)
:Dv 1
PEFSC
Default
io-6
70
chemical -specific
(Appendix C)
site-specific
site-specific
site-specific
(Equation 5-5)
Equation 5-4
Screening Level Equation for Subchronic Inhalation of Non-carcinogenic Fugitive Dusts
Construction Scenario - Construction Worker
Screening
Level
(mg/kg)
THQxATx365d/yr
EFxEDx
HBU
Parameter/Definition (units)
THQ/target hazard quotient (unitless)
AT/averaging time (years)
EF/exposure frequency (days/year)
ED/exposure duration (years)
HBLsc/subchronic health-based limit (mg/m3)
PEFsc/subchronic road particulate emission factor (m3/kg)
Default
1
site-specific3
site-specific
site-specific
chemical-specific
site-specific
(Equation 5-5)
For non-carcinogens, averaging time equals exposure duration.
5-11
-------
Equation 5-5
Derivation of the Particulate Emission Factor
Construction Scenario - Construction Worker
1 [ TxAR I
PEF -QIC v v
rcr \J./\j "
FD ^fi x (\/\ll^,\ฐ-4 x (365d/yr~P) v y\/KT
[ 365d/yr J
Parameter/Definition (units)
PEFsc/subchronic road particulate emission factor (m3/kg)
QICJ inverse of the ratio of the 1-h geometric mean air
concentration to the emission flux along a straight road
segment bisecting a square site (g/rtf-s per kg/m3)
Fo/dispersion correction factor (unitless)
T/total time over which construction occurs (s)
AR/surface area of contaminated road segment (m2)
LR/length of road segment (ft)
WR/width of road segment (ft)
W/mean vehicle weight (tons)
p/number of days with at least 0.01 inches of precipitation
(days/year)
EVKT/sum of fleet vehicle kilometers traveled during the exposure
duration (km)
Default
site-specific
23.02a
(Equation 5-6)
0.185
(Appendix E)
site-specific
274.213
(AR = LR x WR x 0.092903m2/ft2)
site-specific
site-specific
(Exhibit 5-2)
site-specific
a Assumes a 0.5 acre site
The number of days with at least 0.01 inches of rainfall can be estimated using Exhibit 5-2.
Mean vehicle weight (W) can be estimated by assuming the numbers and weights of different types
of vehicles. For example, assuming that the daily unpaved road traffic consists of 20 two-ton cars
and 10 twenty-ton trucks, the mean vehicle weight would be:
W = [(20 cars x 2 tons/car) + (10 trucks x 20 tons/truck)]/30 vehicles = 8 tons
The sum of the fleet vehicle kilometers traveled during construction (EVKT) can be estimated based
on the size of the area of surface soil contamination, assuming the configuration of the unpaved
road, and the amount of vehicle traffic on the road. For example, if the area of surface soil
contamination is 0.5 acres (or 2,024 m2), and one assumes that this area is configured as a square
with the unpaved road segment dividing the square evenly, the road length would be equal to the
square root of 2,024 m2, 45 m (or 0.045 km). Assuming that each vehicle travels the length of the
road once per day, 5 days per week for a total of 6 months, the total fleet vehicle kilometers traveled
would be:
ZVKT = 30 vehicles x 0.045 km/day x (52 wks/yr + 2) x 5 days/wk = 175.5 km
5-12
-------
Exhibit 5-2
MEAN NUMBER OF DAYS WITH 0.01 INCH OR MORE OF ANNUAL PRECIPITATION
120
5-13
-------
The equation for the sub chronic
dispersion factor for dust generated by
unpaved road traffic, Q/Csr, is presented in
Equation 5-6. Q/Csr was derived using
EPA's ISC3 dispersion model for a
hypothetical site under a wide range of
meteorological conditions. Unlike the Q/C
values for the other scenarios, the Q/Csr for
the construction scenario's simple site-
specific approach can be modified only to
reflect different site sizes between 0.5 and
500 acres; it cannot be modified for
climatic zone. Users conducting a detailed
site-specific analysis for the construction
scenario can develop a site-specific Q/Csr
value by running the ISC3 model. Further
details on the derivation of Q/Csr can be
found in Appendix E.
Equations 5-7 and 5-8 are
appropriate for calculating fugitive dust
SSLs for carcinogens and non-carcinogens
based on chronic exposure to off-site
residents. The fugitive dust SSL is
calculated for off-site residents who are
exposed both during construction and after construction is complete. During site construction, off-
site residents are assumed to be exposed to fugitive dust emissions from site traffic on temporary
unpaved roads. After construction, receptors are assumed to be exposed to emissions from wind
erosion. Although the construction exposure duration is considerably shorter than the
post-construction exposure duration, the magnitude of emissions due to unpaved road traffic may be
substantially higher than that due to wind erosion. For this reason, we evaluate chronic exposure to
off-site residents by combining the total mass emitted from both unpaved road traffic during
construction and wind erosion post-construction, normalizing this value over the total exposure
duration.
Equation 5-6
Derivation of the Dispersion Factor for
Particulate Emissions from Unpaved Roads
- Construction Scenario
[(In A -B)21
QIC -A * exo
u
Parameter/Definition (units)
Q/Csr /in verse of the ratio of the
1-h geometric mean air
concentration to the
emission flux along a
straight road segment
bisecting a square site
(g/m2-s per kg/m3)
A/constant (unitless)
A../areal extent of site surface
soil contamination (acres)
B/constant (unitless)
C/constant (unitless)
Default
23.02a
12.9351
0.5
5.7383
71.7711
aAssumes a 0.5 acre site
5-14
-------
Equation 5-7
Screening Level Equation for Chronic Inhalation of Carcinogenic Fugitive Dust
Construction Scenario - Off-Site Resident
Screening
Level =
(mg/kg) URFxl,000|jg/mgxEFxEDx
TRxATx365d/yr
PER,
Parameter/Definition (units)
TR/target cancer risk (unitless)
AT/averaging time (years)
URF/inhalation unit risk factor (ug/m3)~1
EF/exposure frequency (days/year)
ED/exposure duration (years)
PEFoff/off-site particulate emission factor (m3/kg)
Default
10-6
70
chemical-specific
(Appendix C)
350
30
4.40 x 108
(Equation 5-9)
Equation 5-8
Screening Level Equation for Chronic Inhalation of Non-carcinogenic Fugitive Dust
Construction Scenario - Off-Site Resident
Screening THQxATx365d/yr
(mg/kg) FFVEDV 1 v 1 I
[RfC PEFoffJ
Parameter/Definition (units)
THQ/target hazard quotient (unitless)
AT/averaging time (years)
EF/exposure frequency (days/year)
ED/exposure duration (years)
RfC/inhalation reference concentration (mg/m3)
PEFoff /off -site particulate emission factor (m3/kg)
Default
1
30a
350
30
chemical-specific
(Appendix C)
4.40 x 108
(Equation 5-9)
a For non-carcinogens, averaging time equals exposure duration.
5-15
-------
Equation 5-9 calculates the particulate emission factor for off-site residents (PEFoff). Because
it normalizes the mass of fugitive dust emitted over 30 years, this equation requires separate estimates
of the mass of dust emitted by traffic on unpaved roads during construction and the mass of dust
emitted by wind erosion. These are calculated using Equation 5-10 (based on U.S. EPA, 1985) and
Equation 5-11 (based on Cowherd et al., 1985), respectively.
Q/Coff can be derived for any source size between 0.5 and 500 acres using the equation and
look-up table in Appendix D, Exhibit D-4. (The default Q/Coff factor assumes a 0.5 acre source size.)
The look-up table in Exhibit D-4 provides the three coefficients for the Q/Coff equation (A, B, and C)
for each of 29 cities selected to be representative of the range of meteorologic conditions across the
country. The Q/Coff equation for each city was derived from the results of modeling runs of EPA's
ISC3 dispersion model using five years of meteorological data. To calculate a site-specific Q/Coff
factor, the site manager must first identify the climatic zone and city most representative of
meteorological conditions at the site. Appendix D includes a map of climatic zones to help site
managers select the appropriate Q/Coff coefficients. Once the coefficients have been identified,
Q/Coff can be calculated for any source size between 0.5 and 500 acres and input into Equation 5-9
to derive a site-specific PEFoff.
Equation 5-9
Derivation of the Particulate Emission Factor
Construction Scenario - Off-Site Resident
off"
off
where'.
M road+M wind
T -
AsitexEDx(3.1536x107s/yr)
Parameter/Definition (units)
PEFoff/off-site particulate emission factor (m3/kg)
Q/Coff/inverse of ratio of the geometric mean air concentration to the
emission flux at the boundary of a square source (g/rtf-s per kg/m3)
Jj/total time-averaged emission flux (g/m2-s)
Mroad/unit mass emitted from unpaved road traffic (g)
Mwind/unit mass emitted from wind erosion (g)
Asite/areal extent of site (m2)
ED/exposure duration (year)
Default
4.40 x 1Q8
89.03a
(Appendix D, Appendix E)
site-specific
site-specific
(Equation 5-10)
site-specific
(Equation 5-11)
2,024
30
aAssumes a 0.5 acre emission source
5-16
-------
Equation 5-10
Mass of Dust Emitted by Road Traffic
Construction Scenario - Off-Site Resident
M -556fw/3)04- (365d/y-p) WVKT
IVIroad 5bb(W/J) | 365d/^ J -VKJ
Parameter/Definition (units)
Mroad/unit mass emitted from unpaved road traffic (g)
W/mean vehicle weight (tons)
p/number of days per year with at least 0.01 inches of precipitation (days/year)
EVKT/sum of fleet vehicle kilometers traveled during construction (km)
Default
site-specific
site-specific
site-specific
(Exhibit 5-2)
site-specific
Equation 5-11
Mass of Dust Emitted by Wind Erosion
Construction Scenario - Off-Site Resident
Mwind = 0.036 x(1-V)x
U,
F(x) x Asurf x ED x 8,760hr/yr
Parameter/Definition (units)
Mwind/unit mass emitted from wind erosion (g)
V/fraction of vegetative cover (unitless)
Um/mean annual windspeed (mis)
U/equivalent threshold value of windspeed at 7m (mis)
F(x)/function dependent on Um/U, derived from Cowherd, et al., 1985 (unitless)
Asulf/areal extent of site with undisturbed surface soil contamination (m2)
ED/exposure duration (years)
Default
1.32E+05
0.5
4.69
11.32
0.194
2,024
30
5-17
-------
SSL Equations for Subsurface Soils
The relevant pathways for exposure to subsurface soils for the construction scenario include
direct ingestion, dermal absorption, and inhalation of volatiles outdoors. As noted above, these
pathways are evaluated for construction workers only. SSLs for ingestion and dermal absorption
exposure to subsurface soils are calculated in the same way as those for surface soils and as described
in the previous section.
Inhalation Of Volatiles. Equations 5-12 through 5-15 are appropriate for calculating
SSLs for subchronic outdoor inhalation of volatiles by construction workers. These equations are
appropriate for the simple site-specific approach; the detailed site-specific modeling approach to this
pathway is discussed in Appendix E. Equations 5-12 and 5-13 calculate the SSLs for the subchronic
inhalation of carcinogenic and non-carcinogenic volatile compounds, respectively. Equation 5-14
is appropriate for calculating the soil-to-air volatilization factor (VFSC) that relates the concentration
of a contaminant in soil to the concentration in air resulting from volatilization. The equation for the
subchronic dispersion factor for volatiles, Q/Csa, is presented in Equation 5-15. Q/Csa was derived
using EPA's SCREENS dispersion model for a hypothetical site under a wide range of meteorological
conditions. Unlike the Q/C values for the other scenarios, the Q/Csa for the construction scenario's
simple site-specific approach can be modified only to reflect different site sizes between 0.5 and 500
acres; it cannot be modified for climatic zone. Site managers conducting a detailed site-specific
analysis for the construction scenario can develop a site-specific Q/C value by running the
SCREENS model. Further details on the derivation of Q/Csa can be found in Appendix E.
Equation 5-12
Screening Level Equation for Subchronic Inhalation of Carcinogenic Volatile
Contaminants in Soil
Construction Scenario - Construction Worker
Sc^;ng = TRxATx365d/yr
(mg/kg) URFxl,000|jg/mgxEFxED:
Parameter/Definition (units)
TR/target cancer risk (unitless)
AT/averaging time (years)
URF/inhalation unit risk factor (pg/m
3"1
EF/exposure frequency (days/year)
ED/exposure duration (years)
VFsc/subchronic soil-to-air volatilization factor (m3/kg)
Default
-6
1Q-
70
chemical-specific
(Appendix C)
site-specific
site-specific
chemical-specific
(Equation 5-14)
5-18
-------
Equation 5-13
Screening Level Equation for Subchronic Inhalation of Non-Carcinogenic Volatile
Contaminants in Soil Construction Scenario - Construction Worker
Screening THQxATx365d/yr
LCVCI
(mg/kg) FF*FD* 1 * 1
I HBLSC VFSJ
Parameter/Definition (units)
THQ/target hazard quotient (unitless)
AT/averaging time (years)
EF/exposure frequency (days/year)
ED/exposure duration (years)
HBLsc/subchronic health-based limit (mg/m3)
VFsc/subchronic soil-to-air volatilization factor (m3/kg)
Default
1
site-specific3
site-specific
site-specific
chemical-specific
chemical-specific
(Equation 5-14)
a For non-carcinogens, averaging time equals exposure duration.
Equation 5-16 is appropriate for calculating the soil saturation limit (Csat) for each volatile
compound. As discussed in Section 4.2.3, Csat represents an upper bound on SSLs calculated using
the VF model. If the calculated SSL exceeds Csat and the contaminant is liquid at soil temperatures
(see Appendix C, Exhibit C-3), the SSL should be set at Csat. Soil screening decisions for organic
compounds that are solid at soil temperatures should be based on SSLs for other exposure pathways.
Because the equations developed to calculate SSLs for the inhalation of volatiles outdoors
assume an infinite source, they can violate mass-balance considerations, especially for small sources.
To address this concern, a mass-limit SSL equation for this pathway may be used (Equation 5-17).
This equation can be used only when the volume (i.e., area and depth) of the contaminated soil source
is known or can be estimated with confidence.
As discussed above, the simple site-specific approach for calculating construction scenario
SSLs uses the same emission model for volatiles as that used in the residential and non-residential
scenarios. However, the conservative nature of this model (i.e., it assumes all contamination is at the
surface) makes it sufficiently protective of construction worker exposures to volatiles. The toxicity
values used in these equations (inhalation unit risk factors for cancer and subchronic reference
concentrations for non-cancer effects) are based on an adult inhalation rate of 20 m3/day. This is
consistent with the rate used for residential and commercial/industrial SSLs. Although construction
worker receptors are exposed for shorter periods each day than residents (generally eight to 10 hours
versus 24 hours), data on worker-related activity levels and associated inhalation rates suggest that
the 20 nrVday rate is a reasonable estimate of RME for these workers (see Section 4.2.3 for a more
complete discussion of these data).
5-19
-------
Equation 5-14
Derivation of the Subchronic Volatilization Factor
Construction Scenario - Construction Worker
(3.14xDAxT)
1/2
2xpbxDA
where'.
x10 4m2/cm2xQ/Csax^
Fr,
Parameter/Definition (units)
VFsc/subchronic volatilization factor (rrrVkg)
DA/apparent diffusivity (cm2/s)
T/total time over which construction occurs (s)
pb/dry soil bulk density (g/cm3)
Q/Csa/inverse of the ratio of the 1-h geometric mean air concentration to
the volatilization flux at the center of a square site (g/rtf-s per kg/m3)
Fo/dispersion correction factor (unitless)
9a/air-filled soil porosity (^1^}
n/total soil porosity (Lpore/LsoN)
S^water-filled soil porosity
C-wate/'-soil)
Ps/soil particle density (g/cm3)
D/diffusivity in air (cm2/s)
H'/dimensionless Henry's law constant
D/diffusivity in water (cm2/s)
Kd/soil-water partition coefficient (cm3/g)
Koc/soil organic carbon partition coefficient (cm3/g)
foc/fraction organic carbon in soil (gig)
Default
chemical-specific3
chemical-specific3
site-specific
1.5
14.31b
(Equation 5-15)
0.185
n-ew
1-(Pb/Ps)
0.15
2.65
chemical-specific3
chemical-specific3
chemical-specific3
fororganics: Kd = Kocxfot
for inorganics: see
Appendix Cc
chemical-specific3
0.006 (0.6%)
3 See Appendix C
b Assumes a 0.5 acre site
c Assume a pH of 6.8 when selecting default
values
5-20
-------
Equation 5-15
Derivation of the Dispersion Factor for
Subchronic Volatile Contaminant Emissions
Construction Scenario - Construction Worker
Q/C =Axexp
(In A-B)2
Parameter/Definition (units)
Q/Csa/inverse of the ratio of the 1-h
geometric mean air concentration to
the volatilization flux at the center of
the square source (g/m2-s per kg/m3)
A/constant (unitless)
Ac/areal extent of site soil contamination
(acres)
B/constant (unitless)
C/constant (unitless)
Default
14.31a
2.4538
0.5
17.5660
189.0426
aAssumes a 0.5 acre emission source
Equation 5-16
Derivation of the Soil Saturation Limit
S t
Pb
Parameter/Definition (units)
Csat/soil saturation concentration (mg/kg)
S/solubility in water (mg/L-water)
pb/dry soil bulk density (kg/L)
Kj/soil-water partition coefficient (L/kg)
K,,c/organic carbon partition coefficient (L/kg)
foc/fraction organic carbon in soil (g/g)
6w/water-filled soil porosity (L^er/Uson)
H'/dimensionless Henry's law constant
6a/air-filled soil porosity (Lair/Lsoil)
n/total soil porosity (Lpore/Lsoil)
ps/soil particle density (kg/L)
Default
chemical-specific
chemical-specific
(Appendix C)
1.5
organic = K,,c x foc
inorganic = see
Appendix Ca
chemical-specific
(Appendix C)
0.006 (0.6%)
0.15
chemical-specific
(Appendix C)
n-ew
1 - (Pb/P.)
2.65
a Assume a pH of 6.8 when selecting default Kd values
5-21
-------
Equation 5-17
Mass-Limit Volatilization Factor
Construction Scenario - Construction Worker
"D Pb>
3g/Mg
Parameter/Definition (units)
VFsc/volatilization factor (m3/kg)
Q/Csa/inverse of the ratio of the 1-h geometric mean air concentration to the
volatilization flux at the center of a square source (g/m2-s per kg/m3)
Fo/dispersion correction factor (unitless)
T/exposure interval (year)
pb/dry soil bulk density (kg/L or Mg/m3)
ds/average source depth (m)
Default
14.31a
(Equation 5-15)
0.185
(Appendix E)
site-specific
(=ED)
1.5
site-specific
1 Assumes a 0.5 acre emission source
5-22
-------
REFERENCES
Aller, L., T. Bennett, J.H. Lehr, RJ. 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.
Agency for Toxic Substances and Disease Registry. 1999. Minimal Risk Levels for Hazardous
Substances, http://www.atsdr.cdc.gov/mrls.html.
Burmaster, David E. 1999. Distributions of Projected Job Tenure for Men and Women in Selected
Industries and Occupations in the United States, February 1996. Human and Ecological Risk
Assessment.
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. EJ. Calabrese and P.T.
Kostecki, eds. pp. 363-417. Lewis Publishers, Chelsea, MI.
Cowherd, C.G., G. Muleski, P. Engelhart, and D. Gillette. 1985. Rapid Assessment of Exposure
to Particulate Emissions from Surface Contamination Sites. U.S. EPA, Office of Health and
Environmental Assessment, Washington, D.C. EPA/600/8-85/002.
Davis, S., P. Waller, R. Buschom, J. Ballou, and P. White. 1990. Quantitative estimates of soil
ingestion in normal children between the ages of 2 and 7 years: population-based estimates
using Al, Si, and Ti as soil tracer elements. Arch. Env. Health 45:112-122.
Gee, G.W., and J.W. Bauder. 1986. Particle size analysis. A. Klute (ed.), Methods of Soil Analysis.
Part 1. Physical andMineralogicalMethods. 2ndEdition. 9(1):383-411. American Society
of Agronomy, Madison, WI.
Hawley, J.K. 1985. Assessment of health risk from exposure to contaminated soil. Risk Anal. 5:
289-302.
Holmes, K.K. Jr., and J.H. Shirai, and K.Y. Richter, and J.C. Kissel. 1999. Field Measurement of
Dermal Soil Loadings in Occupational and Recreational Activities. Environmental
Research. Section A 80:148-157.
Johnson, P.C. and R.A. Ettinger. 1991. Heuristic model for predicting the intrusion rate of
contaminant vapors into buildings. Environment 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.
R-l
-------
REFERENCES
(continued)
Kissel, J., K. Richter, and R. Fenske. 1996. Field Measurements of Dermal Soil Loading
Attributable to Various Activities: Implications for Exposure Assessment. Risk Analysis.
Kissel, J., J.H. Shirai, K.Y. Richter, and R.A. Fenske. 1998. Investigation of Dermal Contact with
Soil Using a Fluorescent Marker. J. Soil Contamination. 7:737-753.
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, Las Vegas, NV.
EPA/600/4-90/013. NTIS PB90-242306.
Stanek, E.J., EJ. Calabrese, R. Barnes, and P. Pekow. 1997. Soil Ingestion in Adults - Results of
a Second Pilot Study. Ecotoxicology and Environmental Safety . 36: 249-257.
U.S. Bureau of the Census. 1994. 1990 Census of Population and Housing, Earnings by Occupation
and Education (SSTF22). Washington, D.C. http://govinfo.kerr.orst.edu/earn-stateis.html.
U.S. Department of Commerce, National Technical Information Service, 1985. Development of
Statistical Distributions or Ranges of Standard Factors Used in Exposure Assessments.
EPA/600/8-85/010.
U.S. EPA. 1985. Compilation of Air Pollutant Emission Factors, Volume I: Stationary Point and
Area Sources, and Supplements. Office of Air Quality Planning and Standards, Research
Triangle Park, NC.
U.S. EPA. 1989a. Exposure Factors Handbook. Office of Research and Development,
Washington, D.C. EPA/600/8-89/043.
R-2
-------
REFERENCES
(continued)
U.S. EPA. 1989b. Risk Assessment Guidance for Super/and (RAGS): Volume I: Human Health
Evaluation Manual (HHEM) Part A. Office of Emergency and Remedial Response,
Washington, D.C. EPA/540/1-89/002. NTIS PB90-155581/CCE.
U.S. EPA. 1990. Guidance on Remedial Actions for Super fund Sites with PCB Contamination.
Office of Solid Waste and Emergency Response, Washington, D.C. NTIS PB91-
921206CDH. (Currently being updated by the EPA PCB work group.)
U.S. EPA. 199la. Risk Assessment Guidance for Superfund (RAGS), Volume I: Human Health
Evaluation Manual (HHEM), Supplemental Guidance, Standard Default Exposure Factors,
Interim Guidance. Office of Emergency and Remedial Response, Washington, D.C. OSWER
Directive 9285.6-03.1
U.S. EPA. 1991b. Risk Assessment Guidance for Superfund (RAGS), Volume I: Human Health
Evaluation Manual (HHEM), PartB, Development of Risk-Based Preliminary Remediation
Goals. Office of Emergency and Remedial Response, Washington, D.C. Publication
9285.7-01B. NTISPB92-963333.
U. S. EPA. 1991 c. Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions.
Office of Emergency and Remedial Response, Washington, D.C. Publication 9355.0-30
NTIS PB91-921359/CCE..
U.S. EPA. 1993. 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, D.C. EPA-SAB-EHC-93-007.
U.S. EPA. 1994. Methods for Derivation of Inhalation Reference Concentrations and Application
of Inhalation Dosimetry. EPA/600/8-90/066F. Office of Research and Development,
Washington, DC.
U.S. EPA. 1995a. Land Use in the CERCLA Remedy Selection Process. Office of Solid Waste and
Emergency Response, Washington, D.C. OSWER Directive 9355.7-04
U.S. EPA. 1995b. Regional Technical Position Paper on the Proper Use of Occupational Health
Standards for Superfund Baseline Risk Assessments. Memorandum from Drs. Gerry
Henningsen, Chris Weis, Susan Griffin, and Mark Wickstrom to Region VIII Remedial
Project Managers. February 13.
U. S. EPA. 1996a. Recommendation of the Technical Workgroup for Lead for an Interim Approach
to Assessing Risks Associated with Adult Exposures to Lead in Soil. Technical Review
Workgroup for Lead, Washington, D.C.
R-3
-------
REFERENCES
(continued)
U.S. EPA. 1996b. Soil Screening Guidance: Technical Background Document. Office of
Emergency and Remedial Response, Washington, DC. EPA/540/R95/128.
U.S. EPA. 1996c. Soil Screening Guidance: User's Guide. Second Edition. Office of Emergency
and Remedial Response, Washington, DC. Publication 9355.4-23.
U.S. EPA. 1997a. Exposure Factors Handbook. Office of Research and Development, Washington,
D.C. EPA/600/P-95/002Fa.
U.S. EPA. 1997b. Guiding Principles for Monte Carlo Analysis. Office of Research and
Development, Washington, D.C. EPA/630/R-97/001.
U.S. EPA. 1997c. Health Effects Assessment Summary Tables FY1997 Update. Document No.
EPA/540/r-97-036. Office of Solid Waste and Emergency Response, Washington, D.C.
U.S. EPA. 1997d. Policy for Use of Probabilistic Analysis in Risk Assessment. Office of Research
and Development, Washington, D.C. http://www.epa.gov/ncea/mcpolicy.htm.
U.S. EPA. 1997e. The Role ofCSGWPPs in EPA Remediation Programs. Office of Solid Waste
and Emergency Response, Washington, D.C. Directive 9283.1-09.
U.S. EPA. 1998. Risk Assessment Guidance for Superfund: Volume 1: Human Health Evaluation
Manual (Part D, Standardized Planning, Reporting, and Review of Superfund Risk
Assessment). Office of Emergency and Remedial Response, Washington, D.C. EPA
Publication 9285.7-0ID.
U.S. EPA. 1999a. Frequently Asked Questions on the Adult Lead Model: Guidance Document.
Technical Review Workgroup for Lead (TRW), Washington, D.C.
http://www.epa.gov/oerrpage/superfund/programs/lead/adfaqs.htm.
U.S. EPA. 1999b. Risk Assessment Guidance for Superfund (RAGS): Volume 1: Human Health
Evaluation Manual Supplement to Part A: Community Involvement in Superfund Risk
Assessments. Office of Emergency and Remedial Response, Washington, D.C. EPA/540/R-
98/042. NTISPB99-963303.
U. S. EPA. 2000a. Guidance for Choosing a Sampling Design for Environmental Data Collection,
Peer Review Draft. Office of Environmental Information, Washington, D.C. EPA QA/G-
5S.
U.S. EPA. 2000b. Institutional Controls: A Site Manager's Guide to Identifying, Evaluation and
Selecting Institutional Controls at Superfund andRCRA Corrective Action Cleanups. Office
of Solid Waste and Emergency Response, Washington, D.C. EPA 540-F-OO.
R-4
-------
REFERENCES
(continued)
U.S. EPA. 2000c. Exposure and Human Health Reassessment of 2,3,7,8-Tetrachlorodibenzo-p-
Dioxin (TCDD) and Related Compounds Draft. Office of Research and Development,
Washington, D.C. EPA/600/P-00/001Bg.
U.S. EPA. 2001. Risk Assessment Guidance for Superfund Volume I: Human Health Evaluation
Manual (Part E, Supplemental Guidance for Dermal Risk Assessment) -Interim Guidance.
Office of Emergency and Remedial Response, Washington, D.C. EPA/540/R/99/005.
U.S. EPA. 2002a. Calculating Upper Confidence Limits for Exposure Point Concentrations at
Hazardous Waste Sites. Office of Emergency and Remedial Response, Washington, D.C.
OSWER 9285.6-10.
U. S. EPA. 2002b. Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from
Groundwater and Soils (Subsurface Vapor Intrusion Guidance). Office of Solid Waste and
Emergency Response, Washington, D.C.
U.S. EPA. 2002c. Integrated Risk Information System (IRIS). Office of Research and Development,
National Center for Environmental Assessment http://www.epa.gov/iris.
U.S. EPA. 2002d. National Primary Drinking Water Standards.
http://www.epa.gov/safewater/mcl.html. Reviewed December, 2002.
Van Wijnen, J.H., P. Clausing, and B. Brunekreef. 1990. Estimated soil ingestion by children.
Environ Research 51:147-162.
R-5
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APPENDIX A
GENERIC SSLs FOR THE RESIDENTIAL AND
COMMERCIAL/INDUSTRIAL SCENARIOS
This appendix provides generic SSLs for 109 chemicals under residential and non-residential
(i.e., commercial/industrial) exposure scenarios. Exhibit A-l presents updated generic SSLs for the
residential exposure scenario. The generic SSLs for three of the pathways in this exhibit
inhalation of volatiles in outdoor air, inhalation of fugitive dust, and migration to ground water
were calculated using the same equations and default values for exposure assumptions found in the
1996 SSG (and reproduced in Appendix B of this document). However, they incorporate updated
values for dispersion factors, for toxicity, and for other chemical-specific parameters presented in
Appendix C. The exhibit also presents new SSLs for concurrent exposures via soil ingestion and
dermal absorption that are based, in part, on a new quantitative approach for evaluating dermal
absorption. SSLs for combined direct ingestion and dermal absorption exposures to contaminants
were calculated according to the method described in Section 3.2.1 of this document. The generic
residential SSLs in Exhibit A-l supersede those published in the 1996 SSG.
Exhibits A-2 and A-3 present commercial/industrial SSLs for the outdoor worker and indoor
worker receptors, respectively. These SSLs have been calculated using the equations and the default
values for exposure assumptions and other input parameters presented in Section 4.2.3 of this
guidance document. All generic SSLs presented in this appendix, both residential and
commercial/industrial, are rounded to two significant figures, with the exception of values less than
10 mg/kg, which are rounded to one significant figure.
As noted above, the values in this Appendix are based on chemical-specific physical and
toxicological parameters presented in Appendix C. The values in Appendix C represent the most
recent values available and are current as of the date of publication of this guidance. However,
physical/chemical and toxicological data are subject to revision and should therefore be confirmed
before referencing screening levels in the following tables. Trichloroethylene, in particular, is based
on a draft risk assessment, and because the document is still undergoing review, the health
benchmark values should be considered provisional.
EPA does not present generic SSLs for the construction exposure scenario because the
complexity and variability of exposure conditions for construction activities precludes the
development of such values. For information on developing SSLs for exposures during construction
activities, users should refer to Chapter 5 or Appendix E of the guidance document.
The generic residential and non-residential SSLs are not necessarily protective of all known
human exposure pathways or ecological threats. Before applying SSLs, it is therefore necessary to
compare the conceptual site model (developed in Step 1 of the soil screening process) with the
assumptions underlying the generic SSLs to ensure that site conditions and exposure pathways are
consistent with these assumptions (See Exhibit A-4.) If this comparison indicates that the site is
more complex than the generic SSL scenario, or that there are significant exposure pathways not
accounted for by the SSL scenario, then generic SSLs alone are not sufficient to evaluate the site,
and additional, more detailed site-specific investigation is necessary.
A-l
-------
In each exhibit, the first column presents SSLs based on the combined soil ingestion and
dermal absorption exposure pathway. When data on dermal absorption from soil are unavailable,
these SSLs are based on ingestion exposures only. SSLs for this pathway may be updated in the
future as dermal absorption data become available for other contaminants.
The second column in Exhibits A-l and A-2 presents SSLs for the outdoor inhalation of
volatiles pathway. Although residential receptors and indoor workers are potentially exposed to
volatiles in indoor air as well, EPA has not calculated generic SSLs for migration of volatiles into
indoor air because it is very difficult to identify suitable standardized default values for inputs such
as dimensions of commercial buildings and the distance between contamination and a building's
foundation. EPA provides spreadsheet models that can be used to calculate SSLs for this pathway
using the simple site-specific or detailed site-specific approaches.1 The third column in Exhibit A-l
and A-2 lists SSLs for the inhalation of fugitive dusts pathway. Because inhalation of fugitive dust
is typically not a concern for organic compounds, SSLs for this pathway are presented only for
inorganic compounds, which are listed at the end of each exhibit. Conversely, with the exception
of mercury, no SSLs for the inhalation of volatiles pathway are provided for inorganic compounds
because these chemicals exhibit extremely low volatility.
The user should note that several of the generic SSLs for the inhalation of volatiles pathway
are determined by the chemical-specific soil saturation limit (Csat) which is used to screen for the
presence of non-aqueous phase liquids (NAPLs). As indicated in Section 4.2.3, in situations where
the residual concentration of a compound that is a liquid at ambient soil temperature exceeds Csat,
the compound may exist as free-phase liquid (see Exhibit C-3 in Appendix C for a list of those
compounds present in liquid phase at typical ambient soil temperatures). In these cases, further
investigation will be required.
The final two columns in Exhibits A-l through A-3 present generic SSLs for the migration
to ground water pathway. The generic commercial/industrial SSLs for this pathway are the same
as those for residential use and are unchanged from the 1996 SSG. As discussed in Section 4.2.3,
this approach protects potential potable ground water resources that may be present beneath sites
with commercial/industrial uses and protects off-site residents who may ingest ground water
contaminated by the site. The migration to ground water SSLs are back-calculated from an
acceptable target soil leachate concentration using a dilution-attenuation factor (DAF). The first of
the two columns of SSLs for this pathway presents levels calculated using a DAF of 20 to account
for reductions in contaminant concentration due to natural processes occurring in the subsurface.
The second column presents SSL values for the migration to ground water pathway calculated
assuming a DAF of one (i.e., no dilution or attenuation between the source and the receptor well).
These levels should be used at sites where little or no dilution or attenuation of soil leachate
concentrations is expected; this will be the case at sites with characteristics such as shallow water
tables, fractured media, karst topography, or source size greater than 30 acres.
1 The vapor intrusion spreadsheets can be found on EPA's web site at http://www.epa.gov/superfund/
programs/risk/airmodel/johnson_ettinger.htm.
A-2
-------
After all possible SSLs for all potential receptors at a site have been identified from the
tables in Exhibits A-l through A-3, the site manager should select the lowest applicable SSL for
each exposure pathway to be used for comparison to site contaminant concentrations in soil.
Generally, where the relevant SSL for a given pathway of concern is not exceeded, the user may
eliminate the pathway from further investigation. If all pathways of concern are eliminated for an
area of the site based on comparison with residential SSLs, that area can be eliminated from further
investigation. However, if commercial/industrial SSLs are used in soil screening evaluations,
elimination of an area from further consideration is contingent on an analysis of institutional control
options. Users should consult Section 4.3.2 of the guidance document for more information.
The final exhibit in this appendix (Exhibit A-4) presents the default values for physical site
characteristics that are used in calculating SSLs (both residential and commercial/industrial) for the
inhalation and migration to ground water pathways. These values describe the nature of the
contaminant source area, the characteristics of site soil, meteorologic conditions, and hydrogeologic
characteristics, and serve either as direct input parameters for SSL equations or as assumptions for
developing input parameters for the equations.
This appendix does not include SSLs for lead, dioxin, or PCBs, because EPA has issued
separate documents that specify risk-based concentrations for these contaminants in soil. For
guidance on addressing soil contaminated with lead, dioxin, or PCBs, please refer to the following
sources:
Lead:
U.S. EPA, 1994. Revised Interim Soil Lead Guidance for CERCLA Sites andRCRA
Corrective Action Facilities, EPA/540/F-94/043, Office of Solid Waste and
Emergency Response, Washington, D.C. Directive 9355.4-12.
U.S. EPA, 1996. Recommendations of the Technical Review Workgroup for Lead for
an Interim Approach to Assessing Risks Associated with Adult Exposures to Lead in
Soil, Technical Review Workgroup for Lead (TRW), Washington, D.C.
US EPA, 1999. Frequently Asked Questions on the Adult Lead Model: Guidance
Document. Technical Review Workgroup for Lead (TRW), Washington, D.C.
http://www.epa.gov/oerrpage/superfund/programs/lead/
adfaqs.htm
A-3
-------
PCBs:
US EPA, 1990. Guidance on Remedial Actions for Super/and Sites with PCB
Contamination. Office of Solid Waste and Emergency Response, Washington, D.C.
NTIS PB91-921206CDH. (Currently being updated by the EPA PCB work group.)
Dioxin:
U.S. EPA. 1998. Approach for Addressing Dioxin in Soil at CERCLA andRCRA Sites.
OSWER Directive 9200.4-26.
U.S. EPA. 2000. Draft Exposure and Human Health Reassessment of 2,3,7,8-
Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds. Office of Research and
Development, Washington, D.C. EPA/600/P-00/001Bg. September.
Analysis of Effects of Source Size on Generic SSLs
The generic SSLs presented have been developed assuming an infinite source and a 0.5 acre
source size. For an analysis of the sensitivity of generic SSLs to changes in source size and the
depths to which infinite source SSLs are protective at larger sites, please refer to Attachment A and
Table A-3 in the Technical Background Document of the 1996 SSG. Additional detail is also
provided in the guidance documents specifically addressing screening levels for soils contaminated
with lead, dioxin, or PCBs (listed above).
A-4
-------
Exhibit A-1
GENERIC SSLs FOR RESIDENTIAL SCENARIO3
Compound
Organics
Acenaphthene
Acetone (2-Propanone)
Aldrin
Anthracene
Benz(a)anthracene
Benzene
Benzo(b)fluoranthene
Benzo(k)fluoranthene
Benzole acid
Benzo(a)pyrene
Bis(2-chloroethyl)ether
Bis(2-ethylhexyl)phthalate
Bromodichloromethane
Bromoform (tribromomethane)
Butanol
Butyl benzyl phthalate
Carbazole
Carbon disulfide
Carbon tetrachloride
Chlordane
p-Chloroaniline
Chlorobenzene
Chlorodibromomethane
Chloroform
2-Chlorophenol
Chrysene
ODD
DDE
DDT
Dibenz(a,h)anthracene
Di-n-butyl phthalate
1,2-Dichlorobenzene
1 ,4-Dichlorobenzene
3,3-Dichlorobenzidine
1,1-Dichloroethane
1,2-Dichloroethane
1,1-Dichloroethylene
cis-1 ,2-Dichloroethylene
trans-1 ,2-Dichloroethylene
2,4-Dichlorophenol
2,4-Dichlorophenoxy-
acetic acid
1,2-Dichloropropane
1 .3-DichloroDrooene
CAS No.
83-32-9
67-64-1
309-00-2
120-12-7
56-55-3
71-43-2
205-99-2
207-08-9
65-85-0
50-32-8
1 1 1 -44-4
1 1 7-81 -7
75-27-4
75-25-2
71 -36-3
85-68-7
86-74-8
75-1 5-0
56-23-5
57-74-9
1 06-47-8
1 08-90-7
124-48-1
67-66-3
95-57-8
218-01-9
72-54-8
72-55-9
50-29-3
53-70-3
84-74-2
95-50-1
1 06-46-7
91-94-1
75-34-3
1 07-06-2
75-35-4
1 56-59-2
1 56-60-5
120-83-2
94-75-7
78-87-5
542-75-6
Ingestion-
Dermal
(mg/kg)
3,400 b
7,800 b'c
0.04
17,000 b
0.6
12
0.6
6
310,000 b'ฐ
0.06
0.4
35
10
81
7,800 b'c
12,000 b
24
7,800 b'c
5
2
240 b
1,600 b'c
8
780 b'c
310
62
3
2
2
0.06
6,100 b
5,500 b
20
1
7,800 b'c
7
3900 b'c
780
1,600 b'c
180 b
690 b
9
6
Inhalation
of
Volatiles
(mg/kg)
C
c
3
C
C
0.8
C
c
c
c
0.2 e'f
C
c
52
C
C
c
720 "
0.3
72
C
380
C
C
c
c
c
c
g
c
c
600 d
g
c
1 ,200 b
0.4
290 b
C
C
c
c
15
1
Inhalation
of
Fugitive
Particulates
(mg/kg)
Migration to Ground Water
DAF-20
(mg/kg)
570
16
0.5
12,000 b
2
0.03
5
49
400 b'k
8
0.0004 e'f
3,600
0.6
0.8
17 b
930 d
0.6
32
0.07
10
0.7
1
0.4
0.6
4
160 e
16
54
32
2
2,300 d
17
2
0.007 e'f
23 b
0.02
0.06
0.4
0.7
1 b'k
0.4 b,k
0.03
0.004 e
DAF-1
(mg/kg)
29
0.8
0.02 e
590 b
0.08
0.002 '
0.2 e'f
2
20
0.4
0.00002 e'f
180
0.03
0.04
0.9 b
810 b
0.03
2
0.003 f
0.5
0.03
0.07
0.02
0.03
0.2
8
0.8
3
2
0.08
270 b
0.9
0.1 '
0.0003 e'f
1 b
0.001 f
0.003 '
0.02
0.03
0.05 b'f'k
0.02 b,k
0.001 '
0.0002 e
A-5
-------
Exhibit A-1 (continued)
GENERIC SSLs FOR RESIDENTIAL SCENARIO3
Compound
Organics (continued)
Dieldrin
Diethylphthalate
2,4-Dimethylphenol
2,4-Dinitrophenol
2,4-Dinitrotoluene
2,6-Dinitrotoluene
Di-n-octyl phthalate
Endosulfan
Endrin
Ethylbenzene
Fluoranthene
Fluorene
Heptachlor
Heptachlor Epoxide
Hexachlorobenzene
Hexachloro-1 ,3-butadiene
a-HCH (a-BHC)
P-HCH(P-BHC)
Y-HCH(Lindane)
Hexachlorocyclopentadiene
Hexachloroethane
lndeno(1 ,2,3-cd)pyrene
Isophorone
Methoxychlor
Methyl bromide
Methylene chloride
2-Methylphenol (o-cresol)
Naphthalene
Nitrobenzene
N-Nitrosodiphenylamine
N-Nitrosodi-n-propylamine
Pentachlorophenol
Phenol
Pyrene
Styrene
1 ,1 ,2,2-Tetrachloroethane
Tetrachloroethylene
Toluene
Toxaphene
1 ,2,4-Trichlorobenzene
1 ,1 ,1 -Trichloroethane
1,1,2-Trichloroethane
Trichloroethylene*
2,4,5-Trichlorophenol
2,4,6-Trichlorophenol
CAS No.
60-57-1
84-66-2
105-67-9
51-28-5
121-14-2
606-20-2
117-84-0
1 1 5-29-7
72-20-8
100-41-4
206-44-0
86-73-7
76-44-8
1024-57-3
118-74-1
87-68-3
319-84-6
319-85-7
58-89-9
77-47-4
67-72-1
1 93-39-5
78-59-1
72-43-5
74-83-9
75-09-2
95-48-7
91-20-3
98-95-3
86-30-6
621 -64-7
87-86-5
108-95-2
129-00-0
100-42-5
79-34-5
127-18-4
108-88-3
8001 -35-2
1 20-82-1
71-55-6
79-00-5
79-01-6
95-95-4
88-06-2
Ingestion-
Dermal
(mg/kg)
0.04
49,000 b
1 ,200 b
120 b
0.7
0.7
1 ,200 b
470 b'c
23
7,800 b'c
2,300 b
2,300 b
0.1
0.07
0.3
6
0.1
0.4
0.4
370 b
35
0.6
510 e
390 b'c
110
85
3,100 b
1,100 b
31
99
0.07 e'f
3
18,000 b
1 ,700 b
16,000 b'c
3
1
16,000 b'c
0.6
610 b
C
11
2
6,100 b
44
Inhalation
of Volatiles
(mg/kg)
1
C
C
C
C
C
C
C
C
400 a
C
C
4
5
1
8
0.7
6
C
29 b
54
C
C
C
9
13
C
170
90
C
C
C
C
C
1 ,500 d
0.6
1
650 d
87
3,200 d
1 ,200 d
1
0.07
C
200
Inhalation
of
Fugitive
Particulates
(mg/kg)
Migration to Ground Water
DAF-20
(mg/kg)
0.004 e
470 b
9 b
0.2 b'f'k
0.0008 e'f
0.0007 e'f
10,000 d
18 b
1
13
4,300 b
560 b
23
0.7
2
2
0.0005 e'f
0.003 e
0.009
400
0.5
14
0.5
160
0.2
0.02 e
15
84
0.1
1
0.0000
0.03
100 b
4,200 b
4
0.003 e'f
0.06
12
31
5
2
0.02
0.06
270 b'k
0.2
DAF-1
(mg/kg)
0.0002 e'f
23
0.4 b
0.008 b'f'k
0.00004 e'f
0.00003 e'f
10,000 d
0.9 b
0.05
0.7
210 b
28 b
1
0.03
0.1 f
0.1 f
0.00003 e'f
0.0001 e'f
0.0005 f
20
0.02
0.7
0.03 e'f
8
0.01
0.001 e'f
0.8
4
0.007 b'f
0.06
0.000002
0.001 f'k
5
210 b
0.2
0.0002 e'f
0.003 f
0.6
2
0.3
0.1
0.0009 f
0.003 f
14
0.008 e'f'k
A-6
-------
Exhibit A-1 (continued)
GENERIC SSLs FOR RESIDENTIAL SCENARIO3
Compound
Organics (continued)
Vinyl acetate
Vinyl chloride (chloroethene)
m-Xylene
o-Xylene
p-Xylene
CAS No.
108-05-4
75-01-4
108-38-3
95-47-6
106-42-3
Ingestion-
Dermal
(mg/kg)
78,000 b'c
0.4 c'e'h
160,000 b'c
160,000 b'c
160,000 b'c
Inhalation
of Volatiles
(mg/kg)
980 b
0.6
C
c
C
Inhalation
of
Fugitive
Particulates
(mg/kg)
...
...
...
...
...
Migration to Ground Water
DAF-20
(mg/kg)
170 b
0.01 *
210
190
200
DAF-1
(mg/kg)
8
0.0007 f''
10
9
10
Inorganics
Antimony
Arsenic
Barium
Beryllium
Cadmium
Chromium (total)
Chromium (III)
Chromium (VI)
Cyanide (amenable)
Mercury
Nickel
Selenium
Silver
Thallium
Vanadium
Zinc
7440-36-0
7440-38-2
7440-39-3
7440-41 -7
7440-43-9
7440-47-3
16065-83-1
18540-29-9
57-1 2-5
7439-97-6
7440-02-0
7782-49-2
7440-22-4
7440-28-0
7440-62-2
7440-66-6
31 b'c
0.4
5,500
160
70 bj
230 b'c
120,000 b'ฐ
230
1,600 b'c
23 b'CJ
1,600
390
390 b'c
6 b'c'm
550
23.000 b'ฐ
...
...
...
...
...
...
...
...
10 b'k
...
...
...
...
c
770
710,000 b
1 ,400 e
1 ,800 e
280 e
C
280 e
c
...
14,000 e
c
c
c
c
c
5
29 k
1 ,600 k
63
8 k
38
g
38
40
2 k
130 k
5
34 b'k
0.7
6,000 b
12.000 b'k
0.3
1 k
82
3
0.4 k
2
g
2
2
0.1 k
7
0.3
2 b'k
0.04 k
300 b
620
DAF = Dilution Attenuation Factor
a Screening level based on human health criteria only
b Calculated values correspond to a noncancer hazard quotient of 1. For exposure to multiple non-carcinogens, EPA evaluates
contaminants according to their critical effect. See section 2.3 for further discussion.
0 Ingestion-Dermal pathway: no dermal absorption data available; calculated based on ingestion data only. Inhalation of volatiles
pathway: no toxicity criteria available
d Soil Saturation Limit (Csat)
e Calculated values correspond to a cancer risk of 1 in 1,000,000. For multiple carcinogens, EPA believes values will accumulate
to be within acceptable risk levels. See section 2.3 for further discussion.
f Level is at or below Contract Laboratory Program required quantification limit for Regular Analytical Services (RAS)
9 Chemical-specific properties are such that this pathway is not of concern at any soil contaminant concentration
h SSL is based on continuous exposure to vinyl chloride over a lifetime.
' SSL is based on continuous exposure to vinyl chloride during adulthood.
' SSL is based on dietary RfD for Cadmium
k SSL for pH of 6.8
' SSL is based on RfD for mercuric chloride (CAS No. 007847-94-7)
SSL is based on RfD for thallium chloride (CAS No. 7791 -12-0)
f Health benchmark values are based on NCEA's Trichloroethylene Health Risk Assessment: Synthesis and Characterization -
External Review Draft (ORD, August, 2001). The trichloroethylene draft risk assessment is still under review. As a result, the
health benchmark values are subject to change.
A-7
-------
Exhibit A-2
GENERIC SSLs FOR COMMERCIAL/INDUSTRIAL SCENARIO: OUTDOOR WORKER RECEPTOR3
Compound
Organ/as
Acenaphthene
Acetone (2-Propanone)
Aldrin
Anthracene
Benz(a)anthracene
Benzene
Benzo(b)fluoranthene
Benzo(k)fluoranthene
Benzole acid
Benzo(a)pyrene
Bis(2-chloroethyl)ether
Bis(2-ethylhexyl)phthalate
Bromodichloromethane
Bromoform
(tribromomethane)
Butanol
Butyl benzyl phthalate
Carbazole
Carbon disulfide
Carbon tetrachloride
Chlordane
p-Chloroaniline
Chlorobenzene
Chlorodibromomethane
Chloroform
2-Chlorophenol
Chrysene
ODD
DDE
DDT
Dibenz(a,h)anthracene
Di-n-butyl phthalate
1 ,2-Dichlorobenzene
1,4-Dichlorobenzene
3,3-Dichlorobenzidine
1,1-Dichloroethane
1,2-Dichloroethane
1,1-Dichloroethylene
cis-1 ,2-Dichloroethylene
trans-1 ,2-Dichloroethylene
2,4-Dichlorophenol
2,4-Dichlorophenoxy-
acetic acid
1,2-Dichloropropane
1 ,3-Dichloropropene
CAS No.
83-32-9
67-64-1
309-00-2
120-12-7
56-55-3
71 -43-2
205-99-2
207-08-9
65-85-0
50-32-8
1 1 1 -44-4
117-81-7
75-27-4
75-25-2
71 -36-3
85-68-7
86-74-8
75-15-0
56-23-5
57-74-9
106-47-8
1 08-90-7
124-48-1
67-66-3
95-57-8
218-01-9
72-54-8
72-55-9
50-29-3
53-70-3
84-74-2
95-50-1
106-46-7
91 -94-1
75-34-3
1 07-06-2
75-35-4
1 56-59-2
156-60-5
120-83-2
94-75-7
78-87-5
542-75-6
Ingestion-
Dermal
(mg/kg)
37,000 b
110,000 b'c
0.2
180,000 b
2
58
2
23
1 ,000,000 b'ฐ
0.2
2
140 e
51
400 c,e
110,000 b'ฐ
140,000 b
96
110,000 b'c
24
7
2,700 b
23,000 b'c
38
11,000
3,400 b
230 e
13
9
8
0.2
68,000 b
62,000 b
80
4
110,000 b'ฐ
35
57,000 b'c
11,000 b'c
23,000 b'ฐ
2,100 b
8,500 b
47
32
Inhalation
of Volatiles
(mg/kg)
C
C
6
C
C
1
C
C
C
C
0.4
C
C
88 e
c
C
c
720 d
0.6
120 e
c
540 b
C
C
c
c
c
c
g
c
c
600
g
c
1 ,700
0.6
410 b
C
C
c
c
21
2
Inhalation
of
Fugitive
Particulates
(mg/kg)
...
...
...
...
...
...
...
...
...
...
...
...
...
...
...
Migration to Ground Water
DAF-20
(mg/kg)
570 b
16 b
0.5
12,000 b
2
0.03
5
49
400 bj
8
0.0004 e'f
3,600
0.6
0.8
17
930
0.6
32 b
0.07
10
0.7 b
1
0.4
0.6
4 bj
160 e
16
54
32
2
2,300 d
17
2
0.007 e'f
23
0.02
0.06
0.4
0.7
1 bj
0.4 bj
0.03
0.004 e
DAF-1
(mg/kg)
29
0.8 b
0.02 e
590 b
0.08 e'f
0.002 f
0.2 e'f
2
20 bj
0.4
0.00002 e'f
180
0.03
0.04
0.9
810
0.03 e'f
2 b
0.003 '
0.5
0.03 b'f
0.07
0.02
0.03
0.2 b'fj
8
0.8
3
2
0.08 e'f
270 b
0.9
0.1 f
0.0003 e'f
1
0.001 '
0.003 f
0.02
0.03
0.05 WJ
0.02 bj
0.001 '
0.0002 e
A-8
-------
Exhibit A-2 (continued)
GENERIC SSLs FOR COMMERCIAL/INDUSTRIAL SCENARIO: OUTDOOR WORKER RECEPTOR3
Compound
Organ/as (continued)
Dieldrin
Diethylphthalate
2,4-Dimethylphenol
2,4-Dinitrophenol
2,4-Dinitrotoluene
2,6-Dinitrotoluene
Di-n-octyl phthalate
Endosulfan
Endrin
Ethylbenzene
Fluoranthene
Fluorene
Heptachlor
Heptachlor Epoxide
Hexachlorobenzene
Hexachloro-1 ,3-butadiene
a-HCH (a-BHC)
P-HCH(P-BHC)
Y-HCH(Lindane)
Hexachlorocyclopentadiene
Hexachloroethane
lndeno(1 ,2,3-cd)pyrene
Isophorone
Methoxychlor
Methyl bromide
Methylene chloride
2-Methylphenol (o-cresol)
Naphthalene
Nitrobenzene
N-Nitrosodiphenylamine
N-Nitrosodi-n-propylamine
Pentachlorophenol
Phenol
Pyrene
Styrene
1 ,1 ,2,2-Tetrachloroethane
Tetrachloroethylene
Toluene
Toxaphene
1 ,2,4-Trichlorobenzene
1,1,1-Trichloroethane
1 ,1 ,2-Trichloroethane
Trichloroethylene*
2,4,5-Trichlorophenol
2,4,6-Trichlorophenol
CAS No.
60-57-1
84-66-2
105-67-9
51 -28-5
121-14-2
606-20-2
117-84-0
1 1 5-29-7
72-20-8
100-41-4
206-44-0
86-73-7
76-44-8
1 024-57-3
118-74-1
87-68-3
319-84-6
319-85-7
58-89-9
77-47-4
67-72-1
193-39-5
78-59-1
72-43-5
74-83-9
75-09-2
95-48-7
91 -20-3
98-95-3
86-30-6
621 -64-7
87-86-5
108-95-2
129-00-0
100-42-5
79-34-5
127-18-4
108-88-3
8001-35-2
1 20-82-1
71 -55-6
79-00-5
79-01 -6
95-95-4
88-06-2
Ingestion-
Dermal
(mg/kg)
0.2
550,000 b
14,000 b
1 ,400 b
3
3
14,000 b
6,800 b'c
340 b'c
110,000 b'c
24,000 b
24,000 b
0.7
0.3
1
25
0.5
2
2
4,100 b
140
2
2,000
5,700 b'c
1 ,600 b'c
420
34,000 b
12,000 b
340 b
390
0.3
10
210,000 b
18,000 b
230,000 b'c
16
6
230,000 b'c
3
6,800 b
C
56
8
68,000 b
170
Inhalation
of Volatiles
(mg/kg)
2
C
C
C
C
C
C
C
C
400 d
C
C
7
8
2
13
1
g
C
41
92
C
C
C
13
22
C
240 b
130 b
C
C
C
C
C
1 ,500 d
1
2
650 d
150
3,200 d
1 ,200 d
2
0.1
C
340
Inhalation
of
Fugitive
Particulates
(mg/kg)
...
...
...
...
...
...
...
...
...
...
...
...
...
...
...
...
Migration to Ground Water
DAF-20
(mg/kg)
0.004
470 b
9
0.2 b'fj
0.0008 e'f
0.0007 e'f
10,000 d
18
1
13
4,300 b
560 b
23
0.7
2
2
0.0005 e'f
0.003
0.009
400
0.5
14
0.5
160
0.2
0.02
15
84
0.1
1
0.00005 e'f
0.03 fj
100 b
4,200 b
4
0.003 e'f
0.06
12
31
5
2
0.02
0.06
270 bj
0.2 e'fj
DAF-1
(mg/kg)
0.0002 e'f
23 b
0.4
0.008 b'fj
0.00004 e'f
0.00003 e'f
10,000 d
0.9
0.05
0.7
210 b
28
1
0.03
0.1
0.1
0.00003 e'f
0.0001 e'f
0.0005 f
20
0.02 e'f
0.7
0.03 e'f
8
0.01
0.001 e'f
0.8
4
0.007 b'f
0.06 e'f
0.000002 e'f
0.001 fj
5
210 b
0.2
0.0002 e'f
0.003 f
0.6
2
0.3
0.1
0.0009 f
0.003 f
14 bj
0.008 e'fj
A-9
-------
Exhibit A-2 (continued)
GENERIC SSLs FOR COMMERCIAL/INDUSTRIAL SCENARIO: OUTDOOR WORKER RECEPTOR3
Compound
Organics (continued)
Vinyl acetate
Vinyl chloride (chloroethene)
m-Xylene
o-Xylene
p-Xylene
CAS No.
108-05-4
75-01 -4
108-38-3
95-47-6
106-42-3
Ingestion-
Dermal
(mg/kg)
1 ,000,000 b'c
4 c'e'h
1 ,000,000 b'c
1 ,000,000 b'c
1 ,000,000 b'c
Inhalation
of Volatiles
(mg/kg)
1 ,400 b
1
C
c
c
Inhalation
of
Fugitive
Particulates
(mg/kg)
...
...
...
Migration to Ground Water
DAF-20
(mg/kg)
170 b
0.01 f'hj
210
190
200
DAF-1
(mg/kg)
8
0.0007 f'h
10
9
10
Inorganics
Antimony
Arsenic
Barium
Beryllium
Cadmium
Chromium (total)
Chromium (III)
Chromium (VI)
Cyanide (amenable)
Mercury
Nickel
Selenium
Silver
Thallium
Vanadium
Zinc
7440-36-0
7440-38-2
7440-39-3
7440-41 -7
7440-43-9
7440-47-3
1 6065-83-1
18540-29-9
57-12-5
7439-97-6
7440-02-0
7782-49-2
7440-22-4
7440-28-0
7440-62-2
7440-66-6
450 b'c
2
79,000 b'c
2,300
900
3,400 b'c
1 ,000,000 b c
3,400 b'c
23,000 b'c
340
23,000 b'c
5,700 b'c
5,700 b'c
91
7,900 b'c
340.000 b'c
...
...
...
...
...
...
...
...
14
...
...
...
...
c
1 ,400
1 ,000,000 b
2,600
3,400
510
C
510
C
26,000
C
c
c
c
c
5
29 J
1 ,600 J
63 '
8 '
38 '
g
38 '
40
2 '
130 J
5 '
34 bj
0.7 '
6,000 b
12.000 bj
0.3
1 '
82 J
3 '
0.4 '
2 '
g
2 *
2
0.1 '
7 '
0.3 '
2 bj
0.04 J
300 b
620 bj
DAF = Dilution Attenuation Factor
a Screening level based on human health criteria only
b Calculated values correspond to a noncancer hazard quotient of 1. For exposure to multiple non-carcinogens, EPA evaluates
contaminants according to their critical effect. See section 2.3 for further discussion.
0 Ingestion-Dermal pathway: no dermal absorption data available; calculated based on ingestion data only. Inhalation of volatiles
pathway: no toxicity criteria available
d Soil Saturation Limit (Csat)
e Calculated values correspond to a cancer risk of 1 in 1,000,000. For multiple carcinogens, EPA believes values will accumulate
to be within acceptable risk levels. See section 2.3 for further discussion.
f Level is at or below Contract Laboratory Program required quantification limit for Regular Analytical Services (RAS)
9 Chemical-specific properties are such that this pathway is not of concern at any soil contaminant concentration
h SSL is based on continuous exposure to vinyl chloride during adulthood.
' SSL is based on dietary RfD for Cadmium
' SSL for pH of 6.8
k SSL is based on RfD for mercuric chloride (CAS No. 007847-94-7)
' SSL is based on RfD for thallium chloride (CAS No. 7791 -12-0)
f Health benchmark values are based on NCEA's Trichloroethylene Health Risk Assessment: Synthesis and Characterization -
External Review Draft (ORD, August, 2001). The trichloroethylene draft risk assessment is still under review. As a result, the
health benchmark values are subject to change.
A-10
-------
Exhibit A-3
GENERIC SSLs FOR COMMERCIAL/INDUSTRIAL SCENARIO: INDOOR WORKER RECEPTOR3
Compound
Organics
Acenaphthene
Acetone (2-Propanone)
Aldrin
Anthracene
Benz(a)anthracene
Benzene
Benzo(b)fluoranthene
Benzo(k)fluoranthene
Benzole acid
Benzo(a)pyrene
Bis(2-chloroethyl)ether
Bis(2-ethylhexyl)phthalate
Bromodichloromethane
Bromoform
(tribromomethane)
Butanol
Butyl benzyl phthalate
Carbazole
Carbon disulfide
Carbon tetrachloride
Chlordane
p-Chloroaniline
Chlorobenzene
Chlorodibromomethane
Chloroform
2-Chlorophenol
Chrysene
ODD
DDE
DDT
Dibenz(a,h)anthracene
Di-n-butyl phthalate
1 ,2-Dichlorobenzene
1 ,4-Dichlorobenzene
3,3-Dichlorobenzidine
1 ,1-Dichloroethane
1 ,2-Dichloroethane
1 ,1-Dichloroethylene
cis-1 ,2-Dichloroethylene
trans-1 ,2-Dichloroethylene
2,4-Dichlorophenol
2,4-Dichlorophenoxy-
acetic acid
CAS No.
83-32-9
67-64-1
309-00-2
120-12-7
56-55-3
71 -43-2
205-99-2
207-08-9
65-85-0
50-32-8
1 1 1 -44-4
117-81-7
75-27-4
75-25-2
71 -36-3
85-68-7
86-74-8
75-15-0
56-23-5
57-74-9
1 06-47-8
1 08-90-7
1 24-48-1
67-66-3
95-57-8
218-01-9
72-54-8
72-55-9
50-29-3
53-70-3
84-74-2
95-50-1
1 06-46-7
91-94-1
75-34-3
1 07-06-2
75-35-4
1 56-59-2
1 56-60-5
1 20-83-2
94-75-7
Ingestion-Dermal*
(mg/kg)
120,000 b
200,000 b
0.3
610,000 b
8
100 e
8
78
1 ,000,000 b
0.8
5
410 e
92
720 e
200,000 b
410,000 b
290 e
200,000 b
44
16
8,200 b
41 ,000 b
68
20,000 b
10,000 b
780 e
24
17
17
0.8
200,000 b
180,000 b
240 e
13
200,000 b
63
100,000 b
20,000 b
41 ,000 b
6,100 b
20,000 b
Migration to Ground Water
DAF=20
(mg/kg)
570 b
16 b
0.5
12,000 b
2
0.03
5
49
400 bj
8
0.0004 e'f
3,600
0.6
0.8
17 b
930 d
0.6
32
0.07
10
0.7
1
0.4
0.6
4 bj
160 e
16
54
32
2
2,300 d
17
2
0.007 e'f
23 b
0.02
0.06
0.4
0.7
1 bj
0.4 b
DAF=1
(mg/kg)
29
0.8 b
0.02 e
590 b
0.08
0.002 f
0.2 e'f
2
20 bj
0.4
0.00002 e'f
180
0.03
0.04
0.9 b
810 b
0.03
2
0.003 f
0.5
0.03
0.07
0.02
0.03
0.2 WJ
8
0.8
3
2
0.08
270 b
0.9
0.1
0.0003 e'f
1 b
0.001 f
0.003 '
0.02
0.03
0.05 b'fj
0.02 bj
A-ll
-------
Exhibit A-3 (continued)
GENERIC SSLs FOR COMMERCIAL/INDUSTRIAL SCENARIO: INDOOR WORKER RECEPTOR3
Compound
Organics(continued)
1 ,2-Dichloropropane
1 ,3-Dichloropropene
Dieldrin
Diethylphthalate
2,4-Dimethylphenol
2,4-Dinitrophenol
2,4-Dinitrotoluene
2,6-Dinitrotoluene
Di-n-octyl phthalate
Endosulfan
Endrin
Ethylbenzene
Fluoranthene
Fluorene
Heptachlor
Heptachlor Epoxide
Hexachlorobenzene
Hexachloro-1 ,3-butadiene
-HCH(--BHC)
-HCH(--BHC)
-HCH(Lindane)
Hexachlorocyclopentadiene
Hexachloroethane
lndeno(1 ,2,3-cd)pyrene
Isophorone
Methoxychlor
Methyl bromide
Methylene chloride
2-Methylphenol (o-cresol)
Naphthalene
Nitrobenzene
N-Nitrosodiphenylamine
N-Nitrosodi-n-propylamine
Pentachlorophenol
Phenol
Pyrene
Styrene
1 ,1 ,2,2-Tetrachloroethane
Tetrachloroethylene
Toluene
Toxaphene
1 ,2,4-Trichlorobenzene
1 ,1 ,1-Trichloroethane
1,1,2-Trichloroethane
Trichloroethylene*
2,4,5-Trichlorophenol
CAS No.
78-87-5
542-75-6
60-57-1
84-66-2
1 05-67-9
51-28-5
121-14-2
606-20-2
117-84-0
115-29-7
72-20-8
100-41-4
206-44-0
86-73-7
76-44-8
1 024-57-3
118-74-1
87-68-3
319-84-6
319-85-7
58-89-9
77-47-4
67-72-1
1 93-39-5
78-59-1
72-43-5
74-83-9
75-09-2
95-48-7
91 -20-3
98-95-3
86-30-6
621 -64-7
87-86-5
108-95-2
1 29-00-0
100-42-5
79-34-5
127-18-4
108-88-3
8001-35-2
1 20-82-1
71 -55-6
79-00-5
79-01-6
95-95-4
Ingestion-Dermal*
(mg/kg)
84
57
0.4
1 ,000,000 b
41 ,000 b
4,100 b
8
8
41 ,000 b
12,000 b
610 b
200,000 b
82,000 b
82,000 b
1
0.6
4
73
0.9
3
4
12,000 b
410
8
6,000
10,000 b
2,900 b
760
100,000 b
41 ,000 b
1 ,000 b
1 ,200
0.8
48
610,000 b
61 ,000 b
410,000 b
29
11
410,000 b
5
20,000 b
c
100
14
200,000 b
Migration to Ground Water
DAF=20
(mg/kg)
0.03
0.004
0.004
470 b
9
0.2 b'fj
0.0008 e'f
0.0007 e'f
10,000 d
18
1
13
4,300 b
560 b
23
0.7
2
2
0.0005 e'f
0.003
0.009
400
0.5
14
0.5
160
0.2
0.02
15
84
0.1
1
0.00005 e'f
0.03 fj
100 b
4,200 b
4
0.003 e'f
0.06
12
31
5
2
0.02
0.06
270 bj
DAF=1
(mg/kg)
0.001 f
0.0002
0.0002 e'f
23
0.4
0.008 b'fj
0.00004 e'f
0.00003 e'f
10,000 d
0.9
0.05
0.7
210 b
28
1
0.03
0.1
0.1
0.00003 e'f
0.0001 e'f
0.0005 f
20
0.02
0.7
0.03 e'f
8
0.01
0.001 e'f
0.8 b
4
0.007 b'f
0.06 e'f
0.000002
0.001 fj
5
210 b
0.2
0.0002 e'f
0.003 f
0.6
2
0.3
0.1
0.0009 f
0.003 f
14 bj
A-12
-------
Exhibit A-3 (continued)
GENERIC SSLs FOR COMMERCIAL/INDUSTRIAL SCENARIO: INDOOR WORKER RECEPTOR3
Compound
Organics(continued)
2,4,6-Trichlorophenol
Vinyl acetate
Vinyl chloride (chloroethene)
m-Xylene
o-Xylene
p-Xylene
CAS No.
88-06-2
108-05-4
75-01-4
108-38-3
95-47-6
106-42-3
Ingestion-Dermal*
(mg/kg)
520
1 ,000,000 b'c
8
1 ,000,000 b
1 ,000,000 b
1 ,000,000 b
Migration to Ground Water
DAF=20
(mg/kg)
0.2 e'fj
170 b
0.01 f'hj
210
190
200
DAF=1
(mg/kg)
0.008 e'fj
8
0.0007 f'h
10
9
10
Inorganics
Antimony
Arsenic
Barium
Beryllium
Cadmium
Chromium (total)
Chromium (III)
Chromium (VI)
Cyanide (amenable)
Mercury
Nickel
Selenium
Silver
Thallium
Vanadium
Zinc
7440-36-0
7440-38-2
7440-39-3
7440-41-7
7440-43-9
7440-47-3
1 6065-83-1
18540-29-9
57-12-5
7439-97-6
7440-02-0
7782-49-2
7440-22-4
7440-28-0
7440-62-2
7440-66-6
820 b
4
140,000 b
4,100 b
2,000 b''
6,100 b
1 ,000,000 b
6,100 b
41 ,000 b
610 b'k
41 ,000 b
10,000 b
10,000 b
160
14,000 b
610,000 b
5
29 J
1 ,600 J
63 '
8 '
38 J
g
38 J
40
2 '
130 J
5 '
34 bj
0.7 j
6,000 b
12,000 bj
0.3
1 '
82 J
3 '
0.4 J
2 j
g
2 '
2
0.1 '
7 '
0.3 '
2 bj
0.04 J
300 b
620 bj
DAF = Dilution Attenuation Factor
* No dermal absorption data available for indoor worker receptor; calculated based on ingestion data only
a Screening level based on human health criteria only
b Calculated values correspond to a noncancer hazard quotient of 1
0 Ingestion-Dermal pathway: no dermal absorption data available; calculated based on ingestion data only. Inhalation of
volatiles pathway: no toxicity criteria available
d Soil Saturation Limit (Csat)
e Calculated values correspond to a cancer risk of 1 in 1,000,000
f Level is at or below Contract Laboratory Program required quantification limit for Regular Analytical Services (RAS)
9 Chemical-specific properties are such that this pathway is not of concern at any soil contaminant concentration
h SSL is based on continuous exposure to vinyl chloride during adulthood.
' SSL is based on dietary RfD for Cadmium
' SSL for pH of 6.8
k SSL is based on RfD for mercuric chloride (CAS No. 007847-94-7)
' SSL is based on RfD for thallium chloride (CAS No. 7791 -12-0)
f Health benchmark values are based on NCEA's Trichloroethylene Health Risk Assessment: Synthesis and
Characterization - External Review Draft (ORD, August, 2001). The trichloroethylene draft risk assessment is still under
review. As a result, the health benchmark values are subject to change.
A-13
-------
Exhibit A-4
GENERIC SSLs: DEFAULT VALUES FOR PARAMETERS DESCRIBING SITE CONDITIONS -
INHALATION AND MIGRATION TO GROUND WATER PATHWAYS
Parameter
SSL Pathway
Inhalation
Migration
to
Ground
Water
Method
Source Characteristics
Continuous vegetative cover
Roughness height
Source area (A)
Source length (L)
Source depth
50 percent
0.5 cm for open terrain; used to derive Ut7
0.5 acres (2,024m2); used to derive L for GW
45 m (assumes square source)
Extends to water table (i.e., no attenuation in unsaturated zone)
Soil Characteristics
Soil texture
Dry soil bulk density ( j)
Soil porosity (n)
Vol. soil water content (Ow)
Vol. soil air content (Oa)
Soil organic carbon (foc)
Soil pH
Mode soil aggregate size
Threshold windspeed @ 7 m (Ut 7)
Loarrr, defines soil characteristics/parameters
1.5kg/L
0.43
0.15 (-INH); 0.30 (GW- Indoor INH)*
0.28 (-INH); 0.13 (GW- Indoor INH)*
0.006-(0.6%, INH); 0.602 (0.2%, GW)
6.8; used to determine'pH-specific Kd (metals) and KOC (ionizable
organic s)
0.5 mm; used to derive Ut7
11.32m/s
Meteorological Data
Mean annual windspeed (Um)
Air dispersion factor (Q/C)
Volatilization Q/C
Fugitive particulate Q/C
4.69 m/s (Minneapolis, MN)
90th percentile conterminous U.S.
68.18; Los Angeles, CA; 0.5-acre source
93.77; Minneapolis, MN; 0.5-acre source
Hydrogeologic Characteristics
(DAF)
Hydrogeologic setting
Dilution/attenuation factor (DAF)
Generic (national); surficial aquifer
20orl
Indicates parameters used directly in the SSL equations.
Indicates parameters/assumptions used to develop input parameters for SSL equations.
INH = Inhalation pathway.
GW = Migration to ground water pathway.
Indoor INH = Inhalation of volatiles in indoor air pathway.
* The inhalation of volatiles in indoor air pathway is evaluated using subsurface soil defaults for Ow and Oa. The model's default parameters assume
contamination located directly beneath a basement floor that is two meters below the ground surface.
A-14
-------
APPENDIX B
SSL EQUATIONS FOR RESIDENTIAL SCENARIO
This appendix provides equations for the simple site-specific approach to developing SSLs
for the residential exposure scenario. These equations, along with the default values for exposure
assumptions and other model parameters listed below them, were used to develop the generic
residential SSLs presented in Appendix A, Exhibit A-l. Site-specific parameters are indicated in
bold. Site managers can use site-specific values for these parameters when developing SSLs; the
default values for these parameters should be used when site-specific data are not available.
These equations allow site managers to calculate simple site-specific SSLs for chronic
exposures to contaminants via the combined routes of direct ingestion and dermal absorption,
outdoor inhalation of volatiles, outdoor inhalation of fugitive dust, and ingestion of leachate
contaminated ground water. With the exception of the combined equations for direct ingestion and
dermal absorption (Equations B-l and B-2), the equations in this appendix are identical to those
presented in the 1996 Soil Screening Guidance, though users should note that the default values for
the fugitive dust and volatiles dispersion factors have been updated since the original guidance was
published. For information on the applicability and use of these equations, users should refer to
Section 2.5 of the 1996 SSG for ingestion, inhalation, and ground water exposures, and Section 3.2
of RAGS, Part E for dermal exposures. The specific equations provided in this appendix are:
Equations B-l through B-5. Screening level equations for combined ingestion and dermal
absorption exposures to carcinogenic and non-carcinogenic soil contaminants, including
calculation of dermal toxicity values and the age-adjusted dermal factor.
Equations B-6 through B-8. Screening level equations for inhalation of carcinogenic and
non-carcinogenic contaminants in fugitive dust, including calculation of the Particulate
Emission Factor (PEF).
Equations B-9 through B-12. Screening level equations for inhalation of carcinogenic and
non-carcinogenic volatile contaminants, including calculation of the Volatilization Factor
(VF) and the chemical-specific soil saturation limits (Csat).
Equations B-13 through B-17. Screening level equations for ingestion of contaminants in
ground water, including calculation of chemical-specific dilution attenuation factors, site-
specific mixing-zone depth, and mass limit volatilization factors.
B-l
-------
Equation B-1
Screening Level Equation for Combined Ingestion and Dermal Absorption
Exposure to Carcinogenic Contaminants in Soil
- Residential Scenario
Screening
Level
(mg/kg)
TRxATx365d/yr
6
kg/mg)[(SF0x|Fsoil/adj) + (SFABSxSFSxABSdxEV)]
Parameter/Definition (units)
TR/target cancer risk (unitless)
AT/averaging time (years)
EF/exposure frequency (days/year)
SFABS/dermally adjusted cancer slope factor (mg/kg-d)"1
SFS/age-adjusted dermal factor (mg-yr/kg-event)
ABSd/dermal absorption fraction (unitless)
EV/event frequency (events/day)
l cancer slope factor (mg/kg-d)"1
IFsoN/adj/age-adjusted soil ingestion factor (mg-yr/kg-d)
Default
10-6
70
350
chemical-specific
(Equation B-3)
360
(Equation B-5)
chemical-specific
(Appendix C)
1
chemical-specific
(Appendix C)
114a
Calculated per RAGS, Part B, Equation 3.
B-2
-------
Equation B-2
Screening Level Equation for Combined Ingestion and Dermal Absorption
Exposure to Non-Carcinogenic Contaminants in Soil
- Residential Scenario
Screening THQxBWxATx365d/yr
( \ ( M
(mg/kg) (FFxEDxin 6ka/mcm 1 x|R + 1 xAFxABS xFVxSA
1 Rfฐo ) ( RfฐABS d ) \
Parameter/Definition (units)
THQ/target hazard quotient (unitless)
BW/body weight (kg)
AT/averaging time (years)
EF/exposure frequency (days/year)
ED/exposure duration (years)
RfDo/oral reference dose (mg/kg-d)
IR/soil ingestion rate (mg/d)
RfDABS/dermally-adjusted reference dose (mg/kg-d)
AF/skin-soil adherence factor (mg/cm2 -event)
ABSd/dermal absorption factor (unitless)
EV/event frequency (events/day)
S A/skin surface area exposed-child (cm2)
Default
1
15
6a
350
6
chemical-specific
(Appendix C)
200
chemical-specific
(Equation B-4)
0.2
chemical-specific
(Appendix C)
1
2,800
a For non-carcinogens, averaging time equals to exposure duration.
B-3
-------
Equation B-3
Calculation of Dermal Carcinogenic
Toxic ity Values
SF - SFฐ
ABS ABSG
Parameter/Definition (units)
SFABS/dermally adjusted slope
factor (mg/kg-d)"1
SFo/oral slope factor (mg/kg-d )~1
ABSG/gastro-intestinal absorption
factor (unitless)
Default
chemical-specific
chemical-specific
(Appendix C)
chemical-specific
(Appendix C)
Equation B-4
Calculation of Dermal Non-Carcinogenic
Toxicity Values
RfDABS = RfD0xABSGI
Parameter/Definition (units)
RfDABS/dermally adjusted reference
dose (mg/kg-d)
RfDo/oral reference dose
(mg/kg-d)
ABSG/gastro-intestinal absorption
factor (unitless)
Default
chemical-specific
chemical-specific
(Appendix C)
chemical-specific
(Appendix C)
Equation B-5
Derivation of the Age-Adjusted Dermal Factor
SFS
SA^xAF^xED^l [SA7_31xAF7_31xED7_31l
BVV6 J [ BW7_31 J
Parameter/Definition (units)
SFS/age-adjusted dermal factor (mg-yr/kg-event)
SA^/skin surface area exposed-child (cm2)
SA7.31/skin surface area exposed-adult (cm2)
AF^/skin-soil adherence factor-child (mg/cm2 - event)
AF^/skin-soil adherence factor-adult (mg/cm2 - event)
ED^g/exposure duration-child (years)
ED7_31/exposure duration-adult (years)
BW^/body weight-child (kg)
BW7_31/body weight-adult (kg)
Default
360
2,800
5,700
0.2
0.07
6
24
15
70
B-4
-------
Equation B-6
Screening Level Equation for Inhalation of Carcinogenic Fugitive Dusts
- Residential Scenario
Screening
Level =
(mg/kg) URFx1,000|jg/mgxEFxEDx!_
TRxATx365d/yr
PEF
Parameter/Definition (units)
TR/target cancer risk (unitless)
AT/averaging time (yr)
URF/inhalation unit risk factor (ug/m3)~1
EF/exposure frequency (d/yr)
ED/exposure duration (yr)
PEF/particulate emission factor (m3/kg)
Default
1Q-6
70
chemical-specific
(Appendix C)
350
30
1.36x109
(Equation B-8)
Equation B-7
Screening Level Equation for Inhalation of Non-carcinogenic Fugitive Dusts
- Residential Scenario
Screening
Level
THQxATx365d/yr
(mg/kg) EFxEDx[J_x_l_]
Parameter/Definition (units)
THQ/target hazard quotient (unitless)
AT/averaging time (yr)
EF/exposure frequency (d/yr)
ED/exposure duration (yr)
RfC/inhalation reference concentration (mg/m3)
PEF/particulate emission factor (m3/kg)
Default
1
30a
350
30
chemical-specific
(Appendix C)
1.36x109
(Equation B-8)
' For non-carcinogens, averaging time equals exposure duration.
B-5
-------
Equation B-8
Derivation of the Particulate Emission Factor
- Residential Scenario
PEF=Q/Cwindx
3,600s/h
0.036x(1 -V)x(Um/Ut)3xF(x)
Parameter/Definition (units)
PEF/particulate emission factor (m3/kg)
Q/Cwind/inverse of the ratio of the geometric mean air concentration to the
emission flux at center of a square source (g/rrf-s per kg/m3)
V/fraction of vegetative cover (unitless)
Um/mean annual windspeed (mis)
U,/equivalent threshold value of windspeed at 7m (mis)
F(x)/function dependent on Um/U, derived using Cowherd et al. (1985)
(unitless)
Default
1.36x 109
93.77a
0.5 (50%)
4.69
11.32
0.194
' Assumes as 0.5 acre source; for site-specific values, consult Appendix D.
Equation B-9
Screening Level Equation for Inhalation of Carcinogenic Volatile Contaminants in Soil
- Residential Scenario
Screening
Level
TRxATx365d/yr
(mg/kg) URFx1,000|jg/mgxEFxEDx^L
VF
Parameter/Definition (units)
TR/target cancer risk (unitless)
AT/averaging time (yr)
URF/inhalation unit risk factor (ug/m3)"1
EF/exposure frequency (d/yr)
ED/exposure duration (yr)
VF/soil-to-air volatilization factor (m3/kg)
Default
10-6
70
chemical-specific
(Appendix C)
350
30
chemical-specific
(Equation B-11)
B-6
-------
Equation B-10
Screening Level Equation for Inhalation of Non-carcinogenic Volatile Contaminants in Soil
- Residential Scenario
THQxATx365d/yr
(mg/kg) EFxEDx[-l-xJ_]
Parameter/Definition (units)
THQ/target hazard quotient (unitless)
AT/averaging time (yr)
Outdoor Worker
EF/exposure frequency (d/yr)
ED/exposure duration (yr)
RfC/inhalation reference concentration (mg/m3)
VF/soil-to-air volatilization factor (m3/kg)
Default
1
30a
350
30
chemical-specific
(Appendix C)
chemical-specific
(Equation B-11)
' For non-carcinogens, averaging time equals exposure duration.
B-7
-------
Equation B-11
Derivation of the Volatilization Factor
- Residential Scenario
VF
Q/Cvo|x(3.14xDAxT)1/2x10-4(m2/cm2)
(2*Pb*DA)
where:
Parameter/Definition (units)
VF/volatilization factor (m3/kg)
DA/apparent diffusivity (cm2/s)
Q/CVO,/inverse of the geometric mean air concentration to the
volatilization flux at the center of a square source
(g/m2-s per kg/m3)
T/exposure interval (s)
pb/dry soil bulk density (g/cm3)
9a/air-filled soil porosity (l^if/l^t)
n/total soil porosity (Lpore/L^oN)
e^water-filled soil porosity (^ter^on)
Ps/soil particle density (g/cm3)
D/diffusivity in air(cm2/s)
H'/dimensionless Henry's law constant
Dw/diffusivity in water (cm2/s)
Kd/soil-water partition coefficient (cm3/g)
Koc/soil organic carbon partition coefficient (cm3/g)
foc/fraction organic carbon in soil (gig)
Default
68.18a
9.5 x 108
1.5
n-ew
1-(Pb/Ps)
0.15
2.65
chemical-specific"
chemical-specificb
chemical-specific"
organics = Koc xfoc
inorganics = see Appendix Cc
chemical-specific"
0.006 (0.6%)
3 Assumes a 0.5 acre source; for site-specific values, consult Appendix D.
b See Appendix C.
c Assume a pH of 6.8 when selecting default Kj values for metals.
B-8
-------
Equation B-12
Derivation of the Soil Saturation Limit
Parameter/Definition (units)
Csa/soil saturation concentration
(mg/kg)
S/solubility in water (mg/L-water)
pb/dry soil bulk density (kg/L)
Kd/soil-water partition coefficient
(L/kg)
Koc/organic carbon partition
coefficient (L/kg)
foc/fraction organic carbon
in soil (gig)
ejwater-filled soil porosity
H'/dimensionless Henry's
law constant
9a/air-filled soil porosity
(Uir/Lsoi,)
n/total soil porosity
C-pore/Lsoil)
Ps/soil particle density (kg/L)
Default
chemical-specific3
1.5
organics = K^ xfoc
inorganics = see
Appendix Cb
chemical-specific3
0.006 (0.6%)
0.15
chemical-specific3
n-ew
1 - (Pb/Ps)
2.65
3 See Appendix C.
b Assume a pH of 6.8 when selecting default Kj values
for metals.
B-9
-------
Equation B-13
Soil Screening Level Partitioning Equation for Migration to Ground Water
Screening
Level = Cw
in Soil (mg/kg)
(V9.H')
r\n+
Parameter/Definition (units)
0,/target soil leachate concentration (mg/L)
Kd/soil-water partition coefficient (L/kg)
Koc/soil organic carbon/water partition coefficient (L/kg)
foc/fraction organic carbon in soil (gig)
ejwater-filled soil porosity (L^/L^,)
9a/air-filled soil porosity (^/L,.^)
pb/dry soil bulk density (kg/L)
n/soil porosity (Lpore/Lsoil)
Ps/soil particle density (kg/L)
H'/dimensionless Henry's law constant
Default
(nonzero MCLG, MCL, or HBLf x
dilution factor
organics = Koc xfoc
inorganics = see Appendix Cb
chemical-specific0
0.002 (0.2%)
0.3
n-ew
1.5
1 - (Pb/Ps)
2.65
chemical-specific0
(assume to be zero for inorganic
contaminants except mercury)
a Chemical-specific (see Appendix C).
b Assume a pH of 6.8 when selecting default
0 See Appendix C.
values for metals.
B-10
-------
Equation B-14
Derivation of Dilution Attenuation Factor
Dilution
Attenuation - 1 +
Factor (DAF)
Parameter/Definition (units)
DAF/dilution attenuation factor
(unitless)
K/aquifer hydraulic
conductivity (m/yr)
i/hydraulic gradient (m/m)
I/infiltration rate (m/yr)
d/mixing zone depth (m)
L/source length parallel to
ground water flow (m)
Kxjxd
|x|_
Default
20or1
(0.5-acre source)
Site-specific
Site-specific
Site-specific
Site-specific
Site-specific
Equation B-15
Estimation of Mixing Zone Depth
d = (0.0112L2)05 + da(1-exp[(-Lx|)/(Kxjxd )])
Parameter/Definition (units)
d/mixing zone depth (m)
L/source length parallel to ground water flow (m)
I/infiltration rate (m/yr)
K/aquifer hydraulic conductivity (m/yr)
i/hydraulic gradient (m/m)
da/aquifer thickness (m)
Default
Site-specific
Site-specific
Site-specific
Site-specific
Site-specific
Site-specific
B-ll
-------
Equation B-16
Mass-Limit Volatilization Factor
- Residential Scenario
VF _ c F* (3.15x107s/yr)]
vr w^voi
(PbXds
Parameter/Definition (units)
ds/average source depth (m)
T/exposure interval (yr)
Q/CVO| /inverse of the geometric
mean air concentration to the
volatilization flux at the center of
a square source
(g/m2-s per kg/m3)
pb/dry soil bulk density
(kg/L or Mg/m3)
x106g/Mg)
Default
site-specific
30
68.18a
1.5
a Assumes a 0.5 acre source; for site-specific values, consult
Appendix D.
Equation B-17
Mass-Limit Soil Screening Level for Migration to
Ground Water
Screening /c x|xED)
I pv/Pl - W
in Soil (mg/kg)
Parameter/Definition (units)
Cw/target soil leachate
concentration (mg/L)
ds/depth of source (m)
I/infiltration rate (m/yr)
ED/exposure duration (yr)
Pt/dry soil bulk density (kg/L)
a Chemical-specific, see Appendix C
PbXds
Default
nonzero MCLG, MCL,
or HBLf x dilution
factor
site-specific
0.18
70
1.5
B-12
-------
APPENDIX C
Chemical Properties and Regulatory/Human Health
Benchmarks for SSL Calculations
This appendix provides the chemical properties and regulatory and human health benchmarks
necessary to calculate SSLs for 109 chemicals commonly found at NPL sites. It consists of the
following exhibits:
Exhibit C-l provides chemical-specific organic carbon-water partition coefficients
(Koc), air and water diffusivities (Da and Dw), water solubilities (S), and
dimensionless Henry's law constants (H1).
Exhibit C-2 provides pH-specific Koc values for 10 organic contaminants that ionize
under natural pH conditions. Site-specific soil pH measurements (see EPA's 1996
SSG, Section 2.3.5) can be used to select appropriate Koc values for these
contaminants. Where site-specific soil pH values are not available, values
corresponding to a pH of 6.8 should be used. Note that Koc values presented in
Exhibit C-l for these contaminants are based on a default pH of 6.8).
Exhibit C-3 provides the physical state (liquid or solid) for organic contaminants.
This information is needed to apply and interpret soil saturation limit (Csat) results
when calculating SSLs for the inhalation of volatiles in outdoor air pathway.
Exhibit C-4 provides pH-specific soil-water partition coefficients (Kj) for metals.
Site-specific soil pH measurements (see 1996 SSG, 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.
Exhibit C-5 provides chemical-specific regulatory and human health benchmarks for
organic and inorganic contaminants. The chemical-specific Maximum Contaminant
Level Goal (MCLG), Maximum Contaminant Level (MCL), Water Health Based
Limit (HBL), Cancer Slope Factor (CSF), Unit Risk Factor (URF), Reference Dose
(RfD), and Reference Concentration (RfC) values presented in this exhibit are used
as inputs in the SSL equations in Sections 3, 4, and 5 of this document.
Exhibit C-6 presents chemical-specific absorption percentages for dermal contact
(ABSd) for all contaminants for which this pathway is relevant. The values presented
represent the average dermal absorption values across a range of soil types, loading
rates, and chemical concentrations for these contaminants.
Exhibit C-7 provides gastrointestinal absorption factors (ABSGI) for contaminants of
concern for the dermal pathway. These values are used for route-to-route
extrapolation of toxicity values. Specifically, these factors are used to adjust the oral
reference dose (RfD) and cancer slope factor (SF) for a contaminant, which is based
C-l
-------
on administered dose, to more accurately reflect the dermal dose, which is an
absorbed dose. Where there is greater than 50 percent gastrointestinal absorption
(e.g., ABSGI>.5), no adjustment is made.
With the exception of values for air diffusivity (Da), water diffusivity (Dw), and certain K^
values, all of the chemical properties used to calculate SSLs are also reported in the Superfund
Chemical Data Matrix (SCDM). Water and air diffusivities were obtained from EPA's CHEMDAT8
and WATERS models. For more information on the derivation of Koc values, or for a more detailed
discussion of the chemical properties presented in Exhibits C-l through C-4, please refer to the
Technical Background Document for the 1996 Soil Screening Guidance (SSG)1
The sources for the regulatory and human health benchmarks include the list of National
Primary Drinking Water Regulations (NPDWRs), maintained by EPA's Office of Ground Water and
Drinking Water, and EPA's Integrated Risk Information System (IRIS).2 The full list of sources for
the regulatory and chronic human health benchmarks is presented at the end of Exhibit C-5.
Chemical-specific dermal and gastro-intestinal absorption fractions for the dermal contact pathway
were obtained from EPA's RAGS, Part E, Supplemental Guidance for Dermal Risk Assessment (U. S.
EPA, 2001).
All of the sources of the values listed in Exhibits C-l through C-5 are regularly updated by
EPA. In addition, the information in Exhibits C-6 and C-7 was obtained from RAGS, Part E.
Therefore, prior to calculating SSLs for a site, regulatory/health benchmarks and chemical properties
should be checked against the most recent versions of the appropriate sources to ensure that they are
up to date. These sources may also be useful for identifying properties and benchmarks for
additional contaminants of concern not included in this appendix. Several of these sources are
available on-line at the following EPA web sites:
IRIS: http://www.epa.gov/iriswebp/iris/index.html
NPDWRs: http ://www.epa.gov/safewater/mcl .html
SCDM: http://www.epa.gov/superfund/resources/scdm/index.htm
CHEMDAT8: http://www.epa.gov/ttn/chief/index.html
WATERS: http://www.epa.gov/ttn/chief/index.html
The Koc value for 2,4-Dichlorophenoxyacetic acid was estimated using information from the 1996 Technical
Background Document and the Chemical Database for HWIR99 (U.S. EPA, 1999) along with the Office of Solid
Waste's Multimedia, Multipathway, and Multireceptor (3MRA) Assessment Model (U.S. EPA, 2001, Version 1.01).
The National Primary Drinking Water Regulations can be found at www.epa.gov/safewater/mcl.html. Human
health benchmarks are available through EPA's IRIS system which can be found at www.epa.gov/iris.
C-2
-------
Exhibit C-1
CHEMICAL-SPECIFIC PROPERTIES USED IN SSL CALCULATIONS
CAS No.
83-32-9
67-64-1
309-00-2
120-12-7
56-55-3
71 -43-2
205-99-2
207-08-9
65-85-0
50-32-8
111-44-4
1 1 7-81 -7
75-27-4
75-25-2
71 -36-3
85-68-7
86-74-8
75-15-0
56-23-5
57-74-9
106-47-8
108-90-7
124-48-1
67-66-3
95-57-8
21 8-01 -9
72-54-8
72-55-9
50-29-3
53-70-3
84-74-2
95-50-1
106-46-7
91 -94-1
75-34-3
107-06-2
75-35-4
156-59-2
156-60-5
120-83-2
94-75-7
78-87-5
542-75-6
60-57-1
84-66-2
105-67-9
51 -28-5
121-14-2
1 1 7-84-0
Compound
Acenaphthene
Acetone
Aldrin
Anthracene
Benz(a)anthracene
Benzene
Benzo(ฃ>)fluoranthene
Benzo(/()fluoranthene
Benzole acid
Benzo(a)pyrene
Bis(2-chloroethyl)ether
Bis(2-ethylhexyl)phthalate
Bromodichloromethane
Bromoform
Butanol
Butyl benzyl phthalate
Carbazole
Carbon disulfide
Carbon tetrachloride
Chlordane
p-Chloroaniline
Chlorobenzene
Chlorodibromomethane
Chloroform
2-Chlorophenol
Chrysene
ODD
DDE
DDT
Dibenz(a,/?)anthracene
Di-n-butyl phthalate
1 ,2-Dichlorobenzene
1 ,4-Dichlorobenzene
3,3-Dichlorobenzidine
1 ,1-Dichloroethane
1 ,2-Dichloroethane
1,1-Dichloroethylene
c/s-1 ,2-Dichloroethylene
frans-1 ,2-Dichloroethylene
2,4-Dichlorophenol
2,4-Dichlorophenoxyacetic acid
1 ,2-Dichloropropane
1 ,3-Dichloropropene
Dieldrin
Diethylphthalate
2,4-Dimethylphenol
2,4-Dinitrophenol
2,4-Dinitrotoluene
Di-n-octvl ohthalate
KOC
(L/kg)
7.08E+03
5.75E-01
2.45E+06
2.95E+04
3.98E+05
5.89E+01
1.23E+06
1.23E+06
5.76E-01
1.02E+06
1.55E+01
1.51E+07
5.50E+01
8.71 E+01
6.92E+00
5.75E+04
3.39E+03
4.57E+01
1 .74E+02
1.20E+05
6.61 E+01
2.19E+02
6.31 E+01
3.98E+01
3.88E+02
3.98E+05
1.00E+06
4.47E+06
2.63E+06
3.80E+06
3.39E+04
6.17E+02
6.17E+02
7.24E+02
3.16E+01
1.74E+01
5.89E+01
3.55E+01
5.25E+01
1 .47E+02
2.62E+01
4.37E+01
4.57E+01
2.14E+04
2.88E+02
2.09E+02
1 .02E-02
9.55E+01
8.32E+07
D,
(cm2/s)
4.21 E-02
1 .24E-01
1 .32E-02
3.24E-02
5.10E-02
8.80E-02
2.26E-02
2.26E-02
5.36E-02
4.30E-02
6.92E-02
3.51 E-02
2.98E-02
1 .49E-02
8.00E-02
1 .74E-02
3.90E-02
1 .04E-01
7.80E-02
1.18E-02
4.83E-02
7.30E-02
1 .96E-02
1 .04E-01
5.01 E-02
2.48E-02
1 .69E-02
1 .44E-02
1 .37E-02
2.02E-02
4.38E-02
6.90E-02
6.90E-02
1 .94E-02
7.42E-02
1 .04E-01
9.00E-02
7.36E-02
7.07E-02
3.46E-02
2.31 E-02
7.82E-02
6.26E-02
1 .25E-02
2.56E-02
5.84E-02
2.73E-02
2.03E-01
1 .51 E-02
Dw
(cm2/s)
7.69E-06
1.14E-05
4.86E-06
7.74E-06
9.00E-06
9.80E-06
5.56E-06
5.56E-06
7.97E-06
9.00E-06
7.53E-06
3.66E-06
1 .06E-05
1 .03E-05
9.30E-06
4.83E-06
7.03E-06
1 .OOE-05
8.80E-06
4.37E-06
1 .01 E-05
8.70E-06
1 .05E-05
1 .OOE-05
9.46E-06
6.21 E-06
4.76E-06
5.87E-06
4.95E-06
5.18E-06
7.86E-06
7.90E-06
7.90E-06
6.74E-06
1 .05E-05
9.90E-06
1 .04E-05
1.13E-05
1.19E-05
8.77E-06
7.31 E-06
8.73E-06
1 .OOE-05
4.74E-06
6.35E-06
8.69E-06
9.06E-06
7.06E-06
3.58E-06
S
(mg/L)
4.24E+00
1.00E+06
1 .80E-01
4.34E-02
9.40E-03
1.75E+03
1 .50E-03
8.00E-04
3.50E+03
1 .62E-03
1 .72E+04
3.40E-01
6.74E+03
3.10E+03
7.40E+04
2.69E+00
7.48E+00
1.19E+03
7.93E+02
5.60E-02
5.30E+03
4.72E+02
2.60E+03
7.92E+03
2.20E+04
1 .60E-03
9.00E-02
1 .20E-01
2.50E-02
2.49E-03
1.12E+01
1.56E+02
7.38E+01
3.11E+00
5.06E+03
8.52E+03
2.25E+03
3.50E+03
6.30E+03
4.50E+03
6.80E+02
2.80E+03
2.80E+03
1 .95E-01
1 .08E+03
7.87E+03
2.79E+03
2.70E+02
2.00E-02
H1
(dimensionless)
6.36E-03
1 .59E-03
6.97E-03
2.67E-03
1 .37E-04
2.28E-01
4.55E-03
3.40E-05
6.31 E-05
4. 63 E-05
7.38E-04
4. 18 E-06
6.56E-02
2.19E-02
3.61 E-04
5.17E-05
6.26E-07
1 .24E+00
1.25E+00
1 .99E-03
1 .36 E-05
1.52E-01
3.21 E-02
1.50E-01
1 .60E-02
3.88E-03
1 .64E-04
8.61 E-04
3.32E-04
6.03E-07
3.85E-08
7.79E-02
9.96E-02
1 .64E-07
2.30E-01
4.01 E-02
1.07E+00
1 .67E-01
3.85E-01
1 .30E-04
4.10E-07
1.15E-01
7.26E-01
6.19E-04
1 .85E-05
8.20E-05
1 .82E-05
3.80E-06
2.74E-03
C-3
-------
Exhibit-C-1 (continued)
CHEMICAL-SPECIFIC PROPERTIES USED IN SSL CALCULATIONS
CAS No.
1 1 5-29-7
72-20-8
100-41-4
206-44-0
86-73-7
76-44-8
1024-57-3
1 1 8-74-1
87-68-3
31 9-84-6
31 9-85-7
58-89-9
77-47-4
67-72-1
193-39-5
78-59-1
7439-97-6
72-43-5
74-83-9
75-09-2
95-48-7
91 -20-3
98-95-3
86-30-6
621-64-7
87-86-5
108-95-2
129-00-0
100-42-5
79-34-5
127-18-4
108-88-3
8001-35-2
120-82-1
71 -55-6
79-00-5
79-01-6
95-95-4
88-06-2
108-05-4
75-01-4
108-38-3
95-47-6
106-42-3
Compound
Endosulfan
Endrin
Ethylbenzene
Fluoranthene
Fluorene
Heptachlor
Heptachlor epoxide
Hexachlorobenzene
Hexachloro-1 ,3-butadiene
-HCH (--BHC)
-HCH (--BHC)
-HCH(Lindane)
Hexachlorocyclopentadiene
Hexachloroethane
lndeno(1 ,2,3-cd)pyrene
Isophorone
Mercury
Methoxychlor
Methyl bromide
Methylene chloride
2-Methylphenol
Naphthalene
Nitrobenzene
A/-Nitrosodiphenylamine
A/-Nitrosodi-n-propylamine
Pentachlorophenol
Phenol
Pyrene
Styrene
1 ,1 ,2,2-Tetrachloroethane
Tetrachloroethylene
Toluene
Toxaphene
1 ,2,4-Trichlorobenzene
1 ,1 ,1 -Trichloroethane
1,1,2-Trichloroethane
Trichloroethylene
2,4,5-Trichlorophenol
2,4,6-Trichlorophenol
Vinyl acetate
Vinyl chloride
m-Xylene
o-Xylene
p-Xylene
KOC
(L/kg)
2.14E+03
1.23E+04
3.63E+02
1.07E+05
1.38E+04
1.41E+06
8.32E+04
5.50E+04
5.37E+04
1.23E+03
1.26E+03
1.07E+03
2.00E+05
1.78E+03
3.47E+06
4.68E+01
9.77E+04
1.05E+01
1.17E+01
9.12E+01
2.00E+03
6.46E+01
1.29E+03
2.40E+01
5.92E+02
2.88E+01
1.05E+05
7.76E+02
9.33E+01
1.55E+02
1.82E+02
2.57E+05
1.78E+03
1.10E+02
5.01 E+01
1.66E+02
1.60E+03
3.81 E+02
5.25E+00
1.86E+01
4.07E+02
3.63E+02
3.89E+02
D:
(cm2/s)
1.15E-02
1 .25E-02
7.50E-02
3.02E-02
3.63E-02
1.12E-02
1 .32E-02
5.42E-02
5.61 E-02
1 .42E-02
1 .42E-02
1 .42 E-02
1 .61 E-02
2.50E-03
1 .90E-02
6.23E-02
3.07E-02
1 .56E-02
7.28E-02
1 .01 E-01
7.40E-02
5.90E-02
7.60E-02
3.12E-02
5.45E-02
5.60E-02
8.20E-02
2.72E-02
7.10E-02
7.10E-02
7.20E-02
8.70E-02
1.16E-02
3.00E-02
7.80E-02
7.80E-02
7.90E-02
2.91 E-02
3.18E-02
8.50E-02
1.06E-01
7.00E-02
8.70E-02
7.69E-02
Dw
(cm2/s)
4.55E-06
4.74E-06
7.80E-06
6.35E-06
7.88E-06
5.69E-06
4.23E-06
5.91 E-06
6.16E-06
7.34E-06
7.34E-06
7.34E-06
7.21 E-06
6.80E-06
5.66E-06
6.76E-06
6.30E-06
4.46E-06
1 .21 E-05
1.17E-05
8.30E-06
7.50E-06
8.60E-06
6.35E-06
8.17E-06
6.10E-06
9.10E-06
7.24E-06
8.00E-06
7.90E-06
8.20E-06
8.60E-06
4.34E-06
8.23E-06
8.80E-06
8.80E-06
9.10E-06
7.03E-06
6.25E-06
9.20E-06
1 .23E-05
7.80E-06
1 .OOE-05
8.44E-06
S
(mg/L)
5.10E-01
2.50E-01
1.69E+02
2.06E-01
1.98E+00
1 .80E-01
2.00E-01
6.20E+00
3.23E+00
2.00E+00
2.40E-01
6.80E+00
1 .80E+00
5.00E+01
2.20E-05
1.20E+04
4.50E-02
1.52E+04
1 .30E+04
2.60E+04
3.10E+01
2.09E+03
3.51 E+01
9.89E+03
1 .95E+03
8.28E+04
1 .35E-01
3.10E+02
2.97E+03
2.00E+02
5.26E+02
7.40E-01
3.00E+02
1 .33E+03
4.42E+03
1.10E+03
1.20E+03
8.00E+02
2.00E+04
2.76E+03
1 .61 E+02
1 .78E+02
1 .85E+02
H1
(dimensionless)
4.59E-04
3.08E-04
3.23E-01
6.60E-04
2.61 E-03
4. 47 E-02
3.90E-04
5.41 E-02
3.34E-01
4.35E-04
3.05E-05
5.74E-04
1.11E+00
1 .59E-01
6.56E-05
2.72E-04
4.67E-01
6.48E-04
2.56E-01
8.98E-02
4. 92 E-05
1 .98E-02
9.84E-04
2.05E-04
9.23E-05
1 .00 E-06
1 .63E-05
4.51 E-04
1.13E-01
1 .41 E-02
7.54E-01
2.72E-01
2.46E-04
5.82E-02
7.05E-01
3.74E-02
4.22E-01
1 .78E-04
3.19E-04
2.10E-02
1.11E+00
3.01 E-01
2.13E-01
3.14E-01
KOC = Organic carbon partition coefficient.
Dj = Diffusivity in air (25ฐC).
Dw = Diffusivity in water (25ฐC).
S = Solubility in water (20-25ฐC).
H' = Dimensionless Henry's Law Constant (HLC [atm-rrf/mol] * 41) (25 C).
C-4
-------
Exhibit C-2
Koc VALUES FOR IONIZING ORGANICS AS A FUNCTION OF pH
pH
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
Benzoic
Acid
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
2-Chloro-
phenol
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
2,4-
Dichloro-
phenoxy-
acetic
acid
6.53E+01
5.72E+01
5.08E+01
4.57E+01
4.16E+01
3.83E+01
3.57E+01
3.37E+01
3.20E+01
3.07E+01
2.97E+01
2.89E+01
2.82E+01
2.77E+01
2.73E+01
2.69E+01
2.67E+01
2.65E+01
2.63E+01
2.62E+01
2.61 E+01
2.60E+01
2.59E+01
2.59E+01
2.58E+01
2.58E+01
2.58E+01
2.57E+01
2.57E+01
2.57E+01
2.57E+01
2.57E+01
2,4-
Dichloro-
phenol
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 .41 E+02
1 .38E+02
1 .33E+02
1 .28E+02
1 .21 E+02
1.14E+02
1 .07E+02
9.84E+01
8.97E+01
8.07E+01
7.17E+01
2,4-
Dinitro-
phenol
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 .01 E-02
1 .01 E-02
1 .01 E-02
1 .01 E-02
1 .01 E-02
1 .OOE-02
1 .OOE-02
1 .OOE-02
1 .OOE-02
Penta-
chloro-
phenol
9.05E+03
7.96E+03
6.93E+03
5.97E+03
5.10E+03
4.32E+03
3.65E+03
3.07E+03
2.58E+03
2.18E+03
1 .84E+03
1.56E+03
1.33E+03
1.15E+03
9.98E+02
8.77E+02
7.81 E+02
7.03E+02
6.40E+02
5.92E+02
5.52E+02
5.21 E+02
4.96E+02
4.76E+02
4.61 E+02
4.47E+02
4.37E+02
4.29E+02
4.23E+02
4.18E+02
4.14E+02
4.10E+02
2,3,4,5-
Tetrachloro-
phenol
1.73E+04
1.72E+04
1.70E+04
1.67E+04
1.65E+04
1.61E+04
1.57E+04
1.52E+04
1 .47E+04
1 .40E+04
1.32E+04
1 .24E+04
1.15E+04
1.05E+04
9.51 E+03
8.48E+03
7.47E+03
6.49E+03
5.58E+03
4.74E+03
3.99E+03
3.33E+03
2.76E+03
2.28E+03
1.87E+03
1.53E+03
1.25E+03
1.02E+03
8.31 E+02
6.79E+02
5.56E+02
4.58E+02
2,4,6-
Tetrachloro-
phenol
4.45E+03
4.15E+03
3.83E+03
3.49E+03
3.14E+03
2.79E+03
2.45E+03
2.13E+03
1.83E+03
1.56E+03
1.32E+03
1.11 E+03
9.27E+02
7.75E+02
6.47E+02
5.42E+02
4.55E+02
3.84E+02
3.27E+02
2.80E+02
2.42E+02
2.13E+02
1.88E+02
1.69E+02
1.53E+02
1.41 E+02
1.31 E+02
1.23E+02
1.17E+02
1.13E+02
1.08E+02
1.05E+02
2,4,5-
Trichloro-
phenol
2.37E+03
2.36E+03
2.36E+03
2.35E+03
2.34E+03
2.33E+03
2.32E+03
2.31 E+03
2.29E+03
2.27E+03
2.24E+03
2.21 E+03
2.17E+03
2.12E+03
2.06E+03
1.99E+03
1.91 E+03
1.82E+03
1.71 E+03
1.60E+03
1 .47E+03
1 .34E+03
1.21 E+03
1.07E+03
9.43E+02
8.19E+02
7.03E+02
5.99E+02
5.07E+02
4.26E+02
3.57E+02
2.98E+02
2,4,6-
Trichloro-
phenol
1 .04E+03
1.03E+03
1.02E+03
1.01 E+03
9.99E+02
9.82E+02
9.62E+02
9.38E+02
9.10E+02
8.77E+02
8.39E+02
7.96E+02
7.48E+02
6.97E+02
6.44E+02
5.89E+02
5.33E+02
4.80E+02
4.29E+02
3.81 E+02
3.38E+02
3.00E+02
2.67E+02
2.39E+02
2.15E+02
1.95E+02
1.78E+02
1 .64E+02
1.53E+02
1 .44E+02
1.37E+02
1.31 E+02
C-5
-------
Exhibit C-3
PHYSICAL STATE OF ORGANIC CHEMICALS AT TYPICAL SOIL TEMPERATURES
Compounds Present in Liquid Phase
CAS No.
67-64-1
71-43-2
117-81-7
1 1 1 -44-4
75-27-4
75-25-2
71-36-3
85-68-7
75-1 5-0
56-23-5
1 08-90-7
1 24-48-1
67-66-3
95-57-8
84-74-2
95-50-1
75-34-3
1 07-06-2
75-35-4
1 56-59-2
1 56-60-5
78-87-5
542-75-6
84-66-2
117-84-0
1 00-41 -4
87-68-3
77-47-4
78-59-1
74-83-9
75-09-2
98-95-3
1 00-42-5
79-34-5
127-18-4
1 08-88-3
1 20-82-1
71-55-6
79-00-5
79-01-6
1 08-05-4
75-01-4
1 08-38-3
95-47-6
1 06-42-3
Chemical
Acetone
Benzene
Bis(2-ethylhexyl)phthalate
Bis(2-chloroethyl)ether
Bromodichloromethane
Bromoform
Butanol
Butyl benzyl phthalate
Carbon disulfide
Carbon tetrachloride
Chlorobenzene
Chlorodibromomethane
Chloroform
2-Chlorophenol
Di-n-butyl phthalate
1,2-Dichlorobenzene
1,1-Dichloroethane
1,2-Dichloroethane
1,1Dichloroethylene
c/s-1 ,2-Dichloroethylene
frans-1 ,2-Dichloroethylene
1 ,2-Dichloropropane
1,3-Dichloropropene
Diethylphthalate
Di-n-octyl phthalate
Ethylbenzene
Hexachloro-1 ,3-butadiene
Hexachlorocyclopentadiene
Isophorone
Methyl bromide
Methylene chloride
Nitrobenzene
Styrene
1 ,1 ,2,2-Tetrachloroethane
Tetrachloroethylene
Toluene
1 ,2,4-Trichlorobenzene
1 ,1 ,1 -Trichloroethane
1,1,2-Trichloroethane
Trichloroethylene
Vinyl acetate
Vinyl chloride
m-Xylene
o-Xylene
p-Xylene
Melting
Point (ฐC)
-94.8
5.5
-55
-51.9
-57
8
-89.8
-35
-115
-23
-45.2
-20
-63.6
9.8
-35
-16.7
-96.9
-35.5
-122.5
-80
-49.8
-70
N/A
-40.5
-30
-94.9
-21
-9
-8.1
-93.7
-95.1
5.7
-31
-43.8
-22.3
-94.9
17
-30.4
-36.6
-84.7
-93.2
-153.7
-47.8
-25.2
13.2
Compounds Present in Solid Phase
CAS No.
83-32-9
309-00-2
120-12-7
56-55-3
50-32-8
205-99-2
207-08-9
65-85-0
86-74-8
57-74-9
1 06-47-8
218-01-9
72-54-8
72-55-9
50-29-3
53-70-3
1 06-46-7
91-94-1
1 20-83-2
94-75-7
60-57-1
105-67-9
51-28-5
121-14-2
606-20-2
72-20-8
115-29-7
206-44-0
86-73-7
76-44-8
1 024-57-3
118-74-1
319-84-6
319-85-7
58-89-9
67-72-1
1 93-39-5
72-43-5
95-48-7
621 -64-7
86-30-6
91-20-3
87-86-5
1 08-95-2
1 29-00-0
8001-35-2
95-95-4
88-06-2
Chemical
Acenaphthene
Aldrin
Anthracene
Benz(a)anthracene
Benzo(/j)pyrene
Benzo(/j)fluoranthene
Benzo(/()fluoranthene
Benzole acid
Carbazole
Chlordane
p-Chloroaniline
Chrysene
ODD
DDE
DDT
Dibenzo(a,/?)anthracene
1,4-Dichlorobenzene
3,3-Dichlorobenzidine
2,4-Dichlorophenol
2,4-Dichlorophenoxyacetic acid
Dieldrin
2,4-Dimethylphenol
2,4-Dinitrophenol
2,4-Dinitrotoluene
2,6-Dinitrotoluene
Endrin
Endosulfan
Fluoranthene
Fluorene
Heptachlor
Heptachlor epoxide
Hexachlorobenzene
a-HCH (a-BHC)
P-HCH (P-BHC)
Y-HCH (Lindane)
Hexachloroethane
lndeno(1 ,2,3-ccf)pyrene
Methoxychlor
2-Methylphenol
A/-Nitrosodi-n-propylamine
A/-Nitrosodiphenylamine
Naphthalene
Pentachlorophenol
Phenol
Pyrene
Toxaphene
2,4,5-Trichlorophenol
2,4,6-Trichlorophenol
Melting
Point (ฐC)
93.4
104
215
84
176.5
168
217
122.4
246.2
106
72.5
258.2
109.5
89
108.5
269.5
52.7
132.5
45
140.5
175.5
24.5
115-116
71
66
200
106
107.8
114.8
95.5
160
231.8
160
315
112.5
187
161.5
87
29.8
N/A
66.5
80.2
174
40.9
151.2
65-90
69
69
C-6
-------
Exhibit C-4
METAL Kd VALUES (L/kg) AS A FUNCTION OF pHa
PH
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
Arsenic
2.5E+01
2.5E+01
2.5E+01
2.6E+01
2.6E+01
2.6E+01
2.6E+01
2.6E+01
2.7E+01
2.7E+01
2.7E+01
2.7E+01
2.7E+01
2.8E+01
2.8E+01
2.8E+01
2.8E+01
2.8E+01
2.9E+01
2.9E+01
2.9E+01
2.9E+01
2.9E+01
3.0E+01
3.0E+01
3.0E+01
3.0E+01
3.1E+01
3.1E+01
3.1E+01
3.1E+01
3.1E+01
Barium
1.1E+01
1.2E+01
1.4E+01
1.5E+01
1.7E+01
1.9E+01
2.1E+01
2.2E+01
2.4E+01
2.6E+01
2.8E+01
3.0E+01
3.1E+01
3.3E+01
3.5E+01
3.6E+01
3.7E+01
3.9E+01
4.0E+01
4.1E+01
4.2E+01
4.2E+01
4.3E+01
4.4E+01
4.4E+01
4.5E+01
4.6E+01
4.6E+01
4.7E+01
4.9E+01
5.0E+01
5.2E+01
Beryllium
2.3E+01
2.6E+01
2.8E+01
3.1E+01
3.5E+01
3.8E+01
4.2E+01
4.7E+01
5.3E+01
6.0E+01
6.9E+01
8.2E+01
9.9E+01
1.2E+02
1.6E+02
2.1E+02
2.8E+02
3.9E+02
5.5E+02
7.9E+02
1.1E+03
1.7E+03
2.5E+03
3.8E+03
5.7E+03
8.6E+03
1.3E+04
2.0E+04
3.0E+04
4.6E+04
6.9E+04
1.0E+05
Cadmium
1.5E+01
1.7E+01
1.9E+01
2.1E+01
2.3E+01
2.5E+01
2.7E+01
2.9E+01
3.1E+01
3.3E+01
3.5E+01
3.7E+01
4.0E+01
4.2E+01
4.4E+01
4.8E+01
5.2E+01
5.7E+01
6.4E+01
7.5E+01
9.1E+01
1.1E+02
1.5E+02
2.0E+02
2.8E+02
4.0E+02
5.9E+02
8.7E+02
1.3E+03
1.9E+03
2.9E+03
4.3E+03
Chromium
(+111)
1.2E+03
1.9E+03
3.0E+03
4.9E+03
8.1E+03
1.3E+04
2.1E+04
3.5E+04
5.5E+04
8.7E+04
1.3E+05
2.0E+05
3.0E+05
4.2E+05
5.8E+05
7.7E+05
9.9E+05
1.2E+06
1.5E+06
1.8E+06
2.1E+06
2.5E+06
2.8E+06
3.1E+06
3.4E+06
3.7E+06
3.9E+06
4.1E+06
4.2E+06
4.3E+06
4.3E+06
4.3E+06
Chromium
(+VI)
3.1E+01
3.1E+01
3.0E+01
2.9E+01
2.8E+01
2.7E+01
2.7E+01
2.6E+01
2.5E+01
2.5E+01
2.4E+01
2.3E+01
2.3E+01
2.2E+01
2.2E+01
2.1E+01
2.0E+01
2.0E+01
1.9E+01
1.9E+01
1.8E+01
1.8E+01
1.7E+01
1.7E+01
1.6E+01
1.6E+01
1.6E+01
1.5E+01
1.5E+01
1.4E+01
1.4E+01
1.4E+01
Mercury
4.0E-02
6.0E-02
9.0E-02
1.4E-01
2.0E-01
3.0E-01
4.6E-01
6.9E-01
1 .OE+00
1 .6E+00
2.3E+00
3.5E+00
5.1E+00
7.5E+00
1.1E+01
1.6E+01
2.2E+01
3.0E+01
4.0E+01
5.2E+01
6.6E+01
8.2E+01
9.9E+01
1 .2E+02
1 .3E+02
1 .5E+02
1 .6E+02
1 .7E+02
1 .8E+02
1 .9E+02
1 .9E+02
2.0E+02
Nickel
1.6E+01
1.8E+01
2.0E+01
2.2E+01
2.4E+01
2.6E+01
2.8E+01
3.0E+01
3.2E+01
3.4E+01
3.6E+01
3.8E+01
4.0E+01
4.2E+01
4.5E+01
4.7E+01
5.0E+01
5.4E+01
5.8E+01
6.5E+01
7.4E+01
8.8E+01
1.1E+02
1.4E+02
1.8E+02
2.5E+02
3.5E+02
4.9E+02
7.0E+02
9.9E+02
1.4E+03
1.9E+03
Silver
1 .OE-01
1 .3E-01
1 .6E-01
2.1E-01
2.6E-01
3.3E-01
4.2E-01
5.3E-01
6.7E-01
8.4E-01
1.1E+00
1.3E+00
1.7E+00
2.1E+00
2.7E+00
3.4E+00
4.2E+00
5.3E+00
6.6E+00
8.3E+00
1.0E+01
1.3E+01
1.6E+01
2.0E+01
2.5E+01
3.1E+01
3.9E+01
4.8E+01
5.9E+01
7.3E+01
8.9E+01
1.1E+02
Selenium
1.8E+01
1.7E+01
1.6E+01
1.5E+01
1.4E+01
1.3E+01
1.2E+01
1.1E+01
1.1E+01
9.8E+00
9.2E+00
8.6E+00
8.0E+00
7.5E+00
7.0E+00
6.5E+00
6.1E+00
5.7E+00
5.3E+00
5.0E+00
4.7E+00
4.3E+00
4.1E+00
3.8E+00
3.5E+00
3.3E+00
3.1E+00
2.9E+00
2.7E+00
2.5E+00
2.4E+00
2.2E+00
Thallium
4.4E+01
4.5E+01
4.6E+01
4.7E+01
4.8E+01
5.0E+01
5.1E+01
5.2E+01
5.4E+01
5.5E+01
5.6E+01
5.8E+01
5.9E+01
6.1E+01
6.2E+01
6.4E+01
6.6E+01
6.7E+01
6.9E+01
7.1E+01
7.3E+01
7.4E+01
7.6E+01
7.8E+01
8.0E+01
8.2E+01
8.5E+01
8.7E+01
8.9E+01
9.1E+01
9.4E+01
9.6E+01
Zinc
1.6E+01
1.8E+01
1.9E+01
2.1E+01
2.3E+01
2.5E+01
2.6E+01
2.8E+01
3.0E+01
3.2E+01
3.4E+01
3.6E+01
3.9E+01
4.2E+01
4.4E+01
4.7E+01
5.1E+01
5.4E+01
5.8E+01
6.2E+01
6.8E+01
7.5E+01
8.3E+01
9.5E+01
1.1E+02
1 .3E+02
1 .6E+02
1 .9E+02
2.4E+02
3.1E+02
4.0E+02
5.3E+02
a Non pH-dependent inorganic Kd values for antimony, cyanide, and vanadium are 45, 9.9, and 1 ,000 (L/kg), respectively.
C-7
-------
Exhibit C-5
REGULATORY AND HUMAN HEALTH BENCHMARKS
CAS
No.
83-32-9
67-64-1
309-00-2
120-12-7
7440-36-0
7440-38-2
7440-39-3
56-55-3
71-43-2
205-99-2
207-08-9
65-85-0
50-32-8
7440-41-7
1 1 1 -44-4
117-81-7
75-27-4
75-25-2
71-36-3
85-68-7
7440-43-9
86-74-8
75-1 5-0
56-23-5
57-74-9
1 06-47-8
1 08-90-7
1 24-48-1
67-66-3
Compound
Acenaphthene
Acetone (2-Propanone)
Aldrin
Anthracene
Antimony
Arsenic
Barium
Benz(a)anthracene
Benzene
Benzo(i>)fluoranthene
Benzo(/()fluoranthene
Benzoic acid
Benzo(a)pyrene
Beryllium
Bis(2-chloroethyl)ether
Bis(2-ethylhexyl)phthalate
Bromodichloromethane
Bromoform
(tribromomethane)
Butanol
Butyl benzyl phthalate
Cadmium
Carbazole
Carbon disulfide
Carbon tetrachloride
Chlordane
p-Chloroaniline
Chlorobenzene
Chlorodibromomethane
Chloroform
Maximum
Contaminant
Level Goal
(mg/L)
MCLG
(PCMLG) ReP
6E-03 3
2E+00 3
4E-03 3
5E-03 3
1 E-01 3
6E-02 3
Maximum
Contaminant
Level
(mg/L)
MCL
(PMCL)
ReF
6E-03
5E-02
2E+00
3
3
3
5E-03
3
2E-04
4E-03
3
3
6E-03
1 E-01 *
1 E-01 *
3
3
3
5E-03
3
5E-03
2E-03
3
3
1E-01
1 E-01 *
1 E-01 *
3
3
3
Water Health
Based Limit
(mg/L)
HBLb
2E+00
4E+00
5E-06
1E+01
Basis9
RfD
RfD
SF0
RfD
1E-04
SF0
1E-04
1E-03
1E+02
SF0
SF0
RfD
8E-05
SF0
4E+00
7E+00
RfD
RfD
4E-03
4E+00
SF0
RfD
1E-01
RfD
USED TO
DEVELOP SSLs
Cancer Slope Factor
(mg/kg-d)-1
Care.
Class0
SF0
ReP
D
B2
1.7E+01
1
D
A
1.5E+00
1
B2
A
B2
B2
7.3E-01
5.5E-02
7.3E-01
7.3E-02
4
1
4
4
B2
7.3E+00
1
B2
B2
B2
B2
1.1E+00
1 .4E-02
6.2E-02
7.9E-03
1
1
1
1
D
C
B2
2.0E-02
2a
B2
B2
1 .3E-01
3.5E-01
1
1
D
C
8.4E-02
1
B2
Unit Risk Factor
(ug/m3)-1
Care.
Class0
URF ReF
D
B2
4.9E-03 1
D
A
4.3E-03 1
B2
A
7.8E-06 1
B2
B2
B2
B1
B2
2.4E-03 1
3.3E-04 1
B2
B2
B2
1.1E-06 1
D
C
B1
1 .8E-03 1
B2
B2
1 .5E-05 1
1 .OE-04 1
D
C
B2
Reference
Dose
(mg/kg-d)
RfD
6.0E-02
1.0E-01
3.0E-05
3.0E-01
4.0E-04
3.0E-04
7.0E-02
ReP
1
1
1
1
1
1
1
4.0E+00
1
2.0E-03
1
2.0E-02
2.0E-02
2.0E-02
1.0E-01
2.0E-01
1 .OE-03f
1
1
1
1
1
1
1.0E-01
7.0E-04
5.0E-04
4.0E-03
2.0E-02
2.0E-02
1.0E-02
1
1
1
1
1
1
1
Reference
Concentration
(mg/m3)
RfC ReP
5.0E-04 2b
2.0E-05 1
7.0E-01 1
7.0E-04 1
6.0E-02 5
* Proposed MCL = 0.08 mg/L, Drinking Water Regulations and Health Advisories, U.S. EPA (1 995).
f Cadmium RfD is based on dietary exposure.
-------
Exhibit C-5 (Continued)
REGULATORY AND HUMAN HEALTH BENCHMARKS
CAS
No.
95-57-8
7440-47-3
1 6065-83-1
1 8540-29-9
218-01-9
57-1 2-5
72-54-8
72-55-9
50-29-3
53-70-3
84-74-2
95-50-1
1 06-46-7
91-94-1
75-34-3
1 07-06-2
75-35-4
1 56-59-2
1 56-60-5
1 20-83-2
94-75-7
78-87-5
542-75-6
60-57-1
84-66-2
1 05-67-9
51-28-5
121-14-2
606-20-2
117-84-0
Compound
2-Chlorophenol
Chromium
Chromium (III)
Chromium (VI)
Chrysene
Cyanide (amenable)
ODD
DDE
DDT
Dibenz(a,/?)anthracene
Di-n-butyl phthalate
1 ,2-Dichlorobenzene
1,4-Dichlorobenzene
3,3-Dichlorobenzidine
1,1-Dichloroethane
1,2-Dichloroethane
1,1-Dichloroethylene
c/s-1 ,2-Dichloroethylene
frans-1 ,2-Dichloroethylene
2,4-Dichlorophenol
2,4-Dichlorophenoxyacetic
acid
1,2-Dichloropropane
1,3-Dichloropropene
Dieldrin
Diethylphthalate
2,4-Dimethylphenol
2,4-Dinitrophenol
2,4-Dinitrotoluenet
2,6-Dinitrotoluenet
Di-n-octyl phthalate
Maximum
Contaminant
Level Goal
(mg/L)
MCLG
(PCMLG) ReP
1 E-01 3
2E-01 3
6E-01 3
7E-02 3
7E-03 3
7E-02 3
1 E-01 3
7E-02 3
Maximum
Contaminant
Level
(mg/L)
MCL
(PMCL) ReF
1 E-01 3
1 E-01 * 3
2E-01 3
6E-01 3
7E-02 3
5E-03 3
7E-03 3
7E-02 3
1 E-01 3
7E-02 3
5E-03 3
Water Health
Based Limit
(mg/L)
HBLb
2E-01
Basis9
RfD
4E+01
RfD
1E-02
SF0
4E-04
3E-04
3E-04
1E-05
4E+00
SF0
SF0
SF0
SF0
RfD
2E-04
4E+00
SF0
RfD
1E-01
RfD
5E-04
5E-06
3E+01
7E-01
4E-02
1E-04
1E-04
7E-01
SF0
SF0
RfD
RfD
RfD
SF0
SF0
RfD
USED TO DEVELOP SSLs
Cancer Slope Factor
(mg/kg-d)-1
Care.
Class0
SF0 ReP
A
A
B2
7.3E-03 4
D
B2
B2
B2
B2
2.4E-01 1
3.4E-01 1
3.4E-01 1
7.3E+00 4
D
D
C
B2
2.4E-02 2a
4.5E-01 1
C
B2
9.1E-02 1
C
D
B2
B2
B2
6.8E-02 2a
1.0E-01 1
1.6E+01 1
D
B2
B2
6.8E-01 1
6.8E-01 1
Unit Risk Factor
(ug/m3)-1
Care.
Class0
A
URF
1 .2E-02
ReF
1
A
1 .2E-02
1
D
B2
B2
B2
9.7E-05
1
B2
D
D
C
B2
C
B2
2.6E-05
1
C
D
B2
B2
B2
4.0E-06
4.6E-03
1
1
D
Reference
Dose
(mg/kg-d)
RfD
5.0E-03
3.0E-03
1.5E+00
3.0E-03
ReP
1
1
1
1
2.0E-02
1
5.0E-04
1
1.0E-01
9.0E-02
1
1
1.0E-01
2a
5.0E-02
1 .OE-02
2.0E-02
3.0E-03
1 .OE-02
1
5
1
1
1
3.0E-02
5.0E-05
8.0E-01
2.0E-02
2.0E-03
2.0E-03
1.0E-03
2.0E-02
1
1
1
1
1
1
2a
2a
Reference
Concentration
(mg/m3)
RfC ReP
1 .OE-04* 1
2.0E-01 2b
8.0E-01 1
5.0E-01 2b
2.0E-01 1
4.0E-03 1
2.0E-02 1
* MCL for total chromium is based on Cr (VI) toxicity.
f Cancer Slope Factor is for 2,4-, 2,6-Dinitrotoluene mixture.
* RfC for Chromium (VII is based on exoosure to Cr CVI1 oarticulates.
C-9
-------
Exhibit C-5 (Continued)
REGULATORY AND HUMAN HEALTH BENCHMARKS
CAS
No.
115-29-7
72-20-8
1 00-41 -4
206-44-0
86-73-7
76-44-8
1 024-57-3
118-74-1
87-68-3
319-84-6
319-85-7
58-89-9
77-47-4
67-72-1
1 93-39-5
78-59-1
7439-97-6
72-43-5
74-83-9
75-09-2
95-48-7
91-20-3
7440-02-0
98-95-3
86-30-6
621 -64-7
87-86-5
1 08-95-2
1 29-00-0
7782-49-2
7440-22-4
Compound
Endosulfan
Endrin
Ethylbenzene
Fluoranthene
Fluorene
Heptachlor
Heptachlor Epoxide
Hexachlorobenzene
Hexachloro-1 ,3-butadiene
-HCH (--BHC)
-HCH (--BHC)
-HCH (Lindane)
Hexachlorocyclopentadiene
Hexachloroethane
lndeno(1 ,2,3-cd)pyrene
Isophorone
Mercury
Methoxychlor
Methyl bromide
Methylene chloride
2-Methylphenol (o-cresol)
Naphthalene
Nickel
Nitrobenzene
A/-Nitrosodiphenylamine
A/-Nitrosodi-n-propylamine
Pentachlorophenol
Phenol
Pyrene
Selenium
Silver
Maximum
Contaminant
Level Goal
(mg/L)
MCLG
(PCMLG) ReP
2E-03 3
7E-01 3
1 E-03 3
2E-04 3
5E-02 3
2 E-03 3
4E-02 3
5E-02 3
Maximum
Contaminant
Level
(mg/L)
MCL
(PMCL)
2E-03
7E-01
ReF
3
3
4E-04
2E-04
1E-03
3
3
3
2E-04
5E-02
3
3
2E-03
4E-02
3
3
5 E-03
3
1E-03
3
5E-02
3
Water Health
Based Limit
(mg/L)
HBLb
2E-01
Basis9
RfD
1E+00
1E+00
RfD
RfD
1E-03
1E-05
5E-05
SF0
SF0
SF0
6E-03
1E-04
9E-02
SF0
SF0
SF0
5E-02
RfD
2E+00
1E+00
1E-01
2E-02
2E-02
1E-05
RfD
RfD
HA"
RfD
SF0
SF0
2E+01
1E+00
RfD
RfD
RfD
USED TO
DEVELOP SSLs
Cancer Slope Factor
(mg/kg-d)-1
Care.
Class0
SF0
ReP
D
D
D
D
B2
B2
B2
C
B2
C
B2
4.5E+00
9.1E+00
1.6E+00
7.8E-02
6.3E+00
1 .8E+00
1.3E+00
1
1
1
1
1
1
2a
D
C
B2
C
1 .4E-02
7.3E-01
9.5E-04
1
4
1
D
D
D
B2
7.5E-03
1
C
C
A
D
B2
B2
B2
4.9E-03
7.0E+00
1 .2E-01
1
1
1
D
D
D
D
Unit Risk Factor
(ug/m3)-1
Care.
Class0
URF ReF
D
D
D
B2
B2
B2
C
B2
C
1 .3E-03 1
2.6E-03 1
4.6E-04 1
2.2E-05 1
1 .8E-03 1
5.3E-04 1
C
D
C
4.0E-06 1
B2
C
D
D
D
B2
4.7E-07 1
C
C
A
2.4E-04 1
D
B2
B2
B2
D
D
D
D
Reference
Dose
(mg/kg-d)
RfD
6.0E-03
3.0E-04
1.0E-01
4.0E-02
4.0E-02
5.0E-04
1 .3E-05
8.0E-04
2.0E-04
ReP
1
1
1
1
1
1
1
1
2a
3.0E-04
6.0E-03
1 .OE-03
1
1
1
2.0E-01
3.0E-04*
5.0E-03
1 .4E-03
6.0E-02
5.0E-02
2.0E-02
2.0E-02
5.0E-04
1
2a
1
1
1
1
1
1
1
3.0E-02
3.0E-01
3.0E-02
5.0E-03
5.0E-03
1
1
1
1
1
Reference
Concentration
(mg/m3)
RfC ReP
1.0E+00 1
2.0E-04 1
3.0E-04 1
5.0E-03 1
3.0E+00 2a
3.0E-03 1
2.0E-03 2b
* RfD is for mercuric chloride (CAS No. 007847-94-7).
** Health advisory for nickel (MCL is currently remanded): EPA Office of Science and Technoloav. 7/10/95.
C-10
-------
Exhibit C-5 (Continued)
REGULATORY AND HUMAN HEALTH BENCHMARKS
CAS
No.
1 00-42-5
79-34-5
127-18-4
7440-28-0
1 08-88-3
8001-35-2
1 20-82-1
71-55-6
79-00-5
79-01-6
95-95-4
88-06-2
7440-62-2
1 08-05-4
75-01-4
1 08-38-3
95-47-6
1 06-42-3
7440-66-6
Compound
Styrene
1 ,1 ,2,2-Tetrachloroethane
Tetrachloroethylene
Thallium
Toluene
Toxaphene
1 ,2,4-Trichlorobenzene
1 ,1 ,1 -Trichloroethane
1,1,2-Trichloroethane
Trichloroethylene*
2,4,5-Trichlorophenol
2,4,6-Trichlorophenol
Vanadium
Vinyl acetate
Vinyl chlorided
(chloroethene)
m-Xylene6
o-Xylenee
p-Xylenee
Zinc
Maximum
Contaminant
Level Goal
(mg/L)
MCLG
(PCMLG)
1E-01
ReP
3
5E-04
1E+00
3
3
7E-02
2E-01
3E-03
zero
3
3
3
3
1E+01
1E+01
1E+01
3
3
3
Maximum
Contaminant
Level
(mg/L)
MCL
(PMCL)
1E-01
ReF
3
5E-03
2E-03
1E+00
3E-03
7E-02
2E-01
5E-03
5E-03
3
3
3
3
3
3
3
3
2E-03
1E+01
1E+01
1E+01
3
3
3
3
Water Health
Based Limit
(mg/L)
HBLb
4E-04
Basis9
SF0
4E+00
8E-03
3E-01
4E+01
RfD
SF0
RfD
RfD
1E+01
RfD
USED TO
DEVELOP SSLs
Cancer Slope Factor
(mg/kg-d)-1
Care.
Class0
C
SF0
2.0E-01
5.4E-01
ReP
1
6
D
B2
1.1E+00
1
D
D
C
5.7E-02
4.0E-01*
1
5
B2
1.1E-02
1
A
7.2E-01
(Adult)
1 .5E+00
(Lifetime)
1
1
D
D
D
D
Unit Risk Factor
(ug/m3)-1
Care.
Class0
C
URF ReF
5.8E-05 1
5.9E-06 6
D
B2
3.2E-04 1
D
D
C
1 .6E-05 1
1.1E-04" 5
B2
3.1E-06 1
A
4.4E-06 1
(Adult)
8.8E-06 -
(Lifetime)
D
D
D
D
Reference
Dose
(mg/kg-d)
RfD
2.0E-01
ReP
1
1 .OE-02
8.0E-05
2.0E-01
1
1
1
1 .OE-02
1
4.0E-03
3.0E-04
1.0E-01
1
5
1
7.0E-03
1.0E+00
3.0E-03
2.0E+00
2.0E+00
2.0E+00
3.0E-01
2a
2a
1
2a
2a
1
1
Reference
Concentration
(mg/m3)
RfC
1 .OE+00
ReP
1
4.0E-01
1
2.0E-01
2.2E+00
2a
5
4.0E-02
5
2.0E-01
1.0E-01
1
1
Health benchmark values are based on NCEA's Trichloroethylene Health Risk Assessment: Synthesis and Characterization - External Review Draft (ORD, August, 2001). Thetrichloroethylene draft risk assessment is still under review. As a result, the
lealth benchmark values are subject to change.
* The cancer slope factor is the upper end of the range given in the risk assessment. This conservative value s appropriate given that the SSL is used for screening purposes.
** The unit risk factor is extrapolated from an upper bound cancer slope factor of 4x1 0"1 per mg/kg-d. This extrapolation is supported by evidence of s milar carcinogenic effects via both inhalation and ingestion pathways.
a References:
1 = IRIS, U.S. EPA (2002c)
2a = HEAST, U.S. EPA (1997c)
2b = HEAST values from alternative tables, U.S. EPA (1997c)
3 = National Primary Drinking Water Standards, U.S. EPA (2002d)
4 = Provisional Guidance for Quantitative R sk Assessment of Polycyclic
Aromatic Hydrocarbons, Office of Health and Environmental Assessment,
U.S. EPA (1993)
5 = National Center for Environmental Assessment (NCEA), persona
communication (2002)
6 = California EPA, Toxicity Criteria Database,
www.oehha.ca.gov/risk/chemicaldb (2002)
Note:OHEA is now part of the National Center for Environmental
Assessment (NCEA).
b Health Based Limits calculated for 30-year exposure duration, 106 cancer risk or hazard
auotient=1 Assumes an inaestion rate of 2 L / dav RfD = 2 ma/ka-dav
c Carcinogen Class based on overall weight of evidence for human carcinogenicity:
Group A: human carcinogen
Group B: probable human carcinogen
B1 : limited evidence from epidemiologic stud es
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 human carcinogenicity
Group E: evidence of non-carcinogenicity for humans
d Both adult and lifet me cancer slope factors and unit risk factors are listed for vinyl chloride. The lifetime exposure pathway is used to
calculate the SSL in the direct contact exposure pathway ( ngestion-dermal) for the residential scenario. The adult va ue is appropriate for
the other residential pathways & the commercial/industrial pathways.
e Values isted are those for total xylenes: [CAS No. 1 330-20-7] MCLG/MCL = 1 0 mg/L
C-ll
-------
Exhibit C-6
DERMAL ABSORPTION FRACTION FROM SOIL
Compound
Arsenic
Cadmium
Chlordane
DDT
2,4-Dichlorophenoxyacetic acid
Lindane
PAHs
Pentachlorophenol
Dermal Absorption
Fraction (ABSd)a
0.03
0.001
0.04
0.03
0.05
0.04
0.13
0.25
Reference
Wester, et al. (1993a)
Wester, et al. (1992a)
U.S. EPA(1992a)
Wester, et al. (1992b)
Wester, et al. (1990)
Wester, et al. (1996)
Duff & Kissel (1996)
Wester, etal. (1990)
Wester, etal. (1993c)
Generic default for screening
Semivolatile organic compounds
0.1
a The values presented are mean values from empirical data.
Source: RAGS Part E, U.S. EPA, 2001.
C-12
-------
Exhibit C-7
GASTROINTESTINAL ABSORPTION EFFICIENCIES AND ADJUSTMENT OF DERMAL TOXICITY FACTORS
CAS Number
Compound
Percent
Absorbed*
ABSGI
Organics
57-74-9
50-29-3
94-75-7
87-86-5
N/A
N/A
Chlordane
DDT
2,4-Dichlorophenoxyacetic acid
Pentachlorophenol
Polycyclic aromatic hydrocarbons (PAHs)
All other organic compounds
80%
70-90%
>90%
76-1 00%
58-89%
generally >50%
1
1
1
1
1
1
Inorganics
7440-38-2
7440-43-9
Arsenic
Cadmium
95%
2.5-5%
1
0.025
* RAGS Part E, U.S. EPA, 2001 .
C-13
-------
APPENDIX D
DISPERSION FACTOR CALCULATIONS
When developing SSLs for the outdoor inhalation of fugitive dusts and volatiles using the
simple site-specific approach, site managers may want to calculate air dispersion factors (Q/C) that
reflect the site location/climate and site size. This appendix provides information regarding the
calculation of such "site-specific" dispersion factors (Q/C), which can be used in lieu of default
values provided in this document.
These Q/C values should be used in conjunction with the Particulate Emission Factor (PEF)
and Volatization Factor (VF) equations provided for outdoor workers under the
commercial/industrial scenario (Section 4.2.3) and for off-site residents under the construction
scenario in (Section 5.3.2).
The soil screening process presented in this guidance includes three receptor- and pathway-
specific Q/C values for which site managers can calculate site-specific values using the information
presented in this appendix. These include:
Q/Cwind: The dispersion factor for fugitive dusts emitted from soils; used to
derive commercial/industrial SSLs for the outdoor worker/landscaper
receptor.
Q/CVO]: The dispersion factor for volatiles emitted from soils; used to derive
commercial/industrial SSLs for the outdoor worker/landscaper receptor.
Q/Coff: The dispersion factor for fugitive dusts emitted from soils; used to
derive construction SSLs for the off-site resident receptor.
The equations for calculating these dispersion factors all take the general form of Equation
D-l. The specific instructions for calculating each of these receptor-specific dispersion factors are
presented below. Site managers should use the map shown in Exhibit D-l to identify their climate
zone and refer to the relevant lookup table (Exhibits D-2 through D-4) to identify the appropriate
values for the constants A, B, and C. To evaluate the dispersion factor, the ISC3 dispersion model
was used to estimate the maximum annual average on-site air concentration for the 29 national sites
previously modeled for the 1996 SSG. Maximum annual average air concentrations for the 29 sites
were estimated for a series of square site sizes ranging from 0.5 to 500 acres; the emission flux was
set equal to 1 g/m2-s. These data were used to generate the best-fit curve equation for predicting air
concentration as a function of site size. CURVEFIT was used to determine the best fit equation and
D-l
-------
the resulting default values for constants A, B, and C.1 This program performs a least squares curve
fit on X (site size), Y (concentration data). Curves are fitted and Equation coefficients, Correlation
Coefficient, and Best Fit parameters are computed. It was determined that a log normal distribution
had the highest correlation coefficient when comparing site size to the concentration data. For
additional information regarding the derivation of the dispersion modeling conducted, please refer
to Appendix E of this document or to Section 2.4.3 in the Technical Background Document of the
1996 Soil Screening Guidance.
Equation D-1
GENERAL FORM FOR CALCULATING RECEPTOR-AND
PATHWAY-SPECIFIC DISPERSION FACTORS (Q/C)
QIC = A x exp
C
Parameter/Definition (Units)
Q/C: Inverse of the ratio of the geometric mean air concentration to the
emission flux at the center of the source or at the boundary of the source*
(g/m2-s per kg/m2)
A, B, C: Constants based on air dispersion modeling for specific climate zones
Aslte: Area! extent of the site or contamination (acres)**
* Q/Cmnd and Q/Cvol are calculated for concentrations at the center of the
source. Only Q/Coff is calculated for the concentration at the site boundary in
the direction of the prevailing wind.
** Site size can range from 0.5 to 500 acres.
'CURVEFIT Version 2.11 A July 29, 1988 by Thomas S. Cox.
D-2
-------
ind (Outdoor Worker - Fugitive Dusts)
Dispersion modeling yielded the following default values for use in Equation D-l, above:
A = 16.2302
B = 18.7762
C = 216.1080
These represent the 90th percentile values for these constants based on the 29 meteorological
stations modeled. Using these values and a site area (Asite) of 0.5 acres, produces a default Q/Q^
of 93.77.
Exhibit D-2 presents values for the constants for use in the calculation of site-specific values
of Q/Cwind. Values are presented for each of the 29 meteorological stations used in the dispersion
model analysis. To calculate site-specific Q/Cwind, site managers first select the values of these
constants from the most appropriate monitoring station. The value of Q/Cwindcan then be used with
Equation 4-5 in Chapter 4 of this guidance to calculate an appropriate PEF value. This is used in
calculating SSLs for the inhalation of fugitive dusts pathway using Equations 4-3 and 4-4.
Q/Cvol(Outdoor Worker - Volatiles)
Dispersion modeling yielded the following default values for use in Equation D-l, above:
A = 11.9110
B = 18.4385
C = 209.7845
These represent the 90th percentile values for these constants based on the 29 meteorological
stations modeled. Using these values and a site area (Asite) of 0.5 acres, produces a default Q/Cvol
of 68.18.
Exhibit D-3 presents values for the constants for use in the calculation of site-specific values
of Q/Cvol. Values are presented for each of the 29 meteorological stations used in the dispersion
model analysis. To calculate site-specific Q/Cvol, site managers first select the values of these
constants from the most appropriate monitoring station. The value of Q/Qo! can then be used with
Equation 4-8 from Chapter 4 of this guidance to calculate an appropriate VF value. This is used in
calculating SSLs for the inhalation of volatiles pathway using Equations 4-6 and 4-7.
D-3
-------
Q/Cofr (Offsite Residents - Fugitive Dusts)
Dispersion modeling yielded the following default values for use in Equation D-l, above:
A = 11.6831
B = 23.4910
C = 287.9969
These represent the 90th percentile values for these constants based on the 29 meteorological
stations modeled. Using these values and a site area (Asite) of 0.5 acres, produces a default Q/Coff
of 89.03.
Exhibit D-4 presents values for the constants for use in the calculation of site-specific values
of Q/Coff. Values are presented for each of the 29 meteorological stations used in the dispersion
model analysis. To calculate site-specific Q/Coffi site managers first select the values of these
constants from the most appropriate monitoring station. The value of Q/Coff can then be used with
Equation 5-9 in Chapter 5 of the guidance to calculate an appropriate PEF value. This is used in
calculating SSLs for the inhalation of fugitive dusts pathway using Equations 5-7 and 5-8.
D-4
-------
Exhibit D-l
D-5
-------
Exhibit D-2
VALUES FOR THE CONSTANTS (A, B, AND C) FOR CALCULATING Q/Cwind
Q
Meteorological
Station
Zonel
Salem, OR
Seattle, WA
Zone 2
Fresno, CA
Los Angeles, CA
San Francisco, CA
Zone 3
Albuquerque, NM
Las Vegas, NV
Phoenix, AZ
Zone 4
Boise, ID
Casper, WY
Denver, CO
Salt Lake City, UT
Winnemucca, NV
ZoneS
Bismarck, ND
Lincoln, NE
Minneapolis, MN
Zone 6
Atlanta, GA
Charleston, SC
Houston, TX
Little Rock, AR
Raleigh, NC
Zone?
Chicago, IL
Cleveland, OH
Harrisburg, PA
Huntington, WV
ZoneS
Hartford, CT
Philadelphia, PA
Portland, ME
Zone 9
Miami, FL
' ' ^ wind ^'N^yvp
A
Constant
12.3783
14.2253
10.2152
11.9110
13.8139
14.9421
13.3093
10.2871
11.3161
7.1414
11.3612
13.2559
12.8784
15.0235
14.1901
16.2302
14.8349
13.7674
13.6482
12.4964
12.3675
16.8653
12.8612
15.5169
9.9253
12.5907
14.0111
10.4660
12.1960
B
Constant
18.9683
18.8366
19.2654
18.4385
20.1624
17.9869
19.8387
18.7124
19.6437
31.1794
19.3324
19.2978
17.9804
18.2526
18.5634
18.7762
17.9259
18.0441
18.1754
18.4476
18.6337
18.7848
20.5164
18.4248
18.6636
18.8368
19.6154
20.9077
19.0645
C
Constant
218.2086
218.1845
220.0604
209.7845
234.2869
205.1782
230.1652
212.2704
224.8172
382.6078
221.2167
221.3379
204.1028
207.3387
210.5281
216.1080
204.1516
204.8689
206.7273
210.2128
212.7284
215.0624
237.2798
211.7679
211.8862
215.4377
225.3397
238.0318
215.3923
D-6
-------
Exhibit D-3
VALUES FOR THE CONSTANTS (A, B, AND C) FOR
CALCULATING Q/CVO|
Meteorological
Station
Zonel
Salem, OR
Seattle, WA
Zone 2
Fresno, CA
Los Angeles, CA
San Francisco, CA
Zone 3
Albuquerque, NM
Las Vegas, NV
Phoenix, AZ
Zone 4
Boise, ID
Casper, WY
Denver, CO
Salt Lake City, UT
Winnemucca, NV
ZoneS
Bismarck, ND
Lincoln, NE
Minneapolis, MN
Zone 6
Atlanta, GA
Charleston, SC
Houston, TX
Little Rock, AR
Raleigh, NC
Zone?
Chicago, IL
Cleveland, OH
Harrisburg, PA
Huntington, WV
ZoneS
Hartford, CT
Philadelphia, PA
Portland, ME
Zone 9
Miami, FL
D / ("* A Y P'vr
X! ' C vol A X eXi
A
Constant
12.3783
14.2253
10.2152
11.9110
13.8139
14.9421
13.3093
10.2871
11.3161
17.6482
11.3612
13.2559
12.8784
15.0235
14.1901
16.2302
14.8349
13.7674
13.6482
12.4964
12.3675
16.8653
12.8612
15.5169
9.9253
12.5907
14.0111
10.4660
12.1960
/(ln^-5)2
C
B
Constant
18.9683
18.8366
19.2654
18.4385
20.1624
17.9869
19.8387
18.7124
19.6437
18.8138
19.3324
19.2978
17.9804
18.2526
18.5634
18.7762
17.9259
18.0441
18.1754
18.4476
18.6337
18.7848
20.5164
18.4248
18.6636
18.8368
19.6154
20.9077
19.0645
-
C
Constant
218.2086
218.1845
220.0604
209.7845
234.2869
205.1782
230.1652
212.2704
224.8172
217.0390
221.2167
221.3379
204.1028
207.3387
210.5281
216.1080
204.1516
204.8689
206.7273
210.2128
212.7284
215.0624
237.2798
211.7679
211.8862
215.4377
225.3397
238.0318
215.3923
D-7
-------
Exhibit D-4
VALUES FOR THE CONSTANTS (A, B, AND C) FOR CALCULATING Q/Coff
,,l> Asite-B)2]
Meteorological
Station
Zonel
Salem, OR
Seattle, WA
Zone 2
Fresno, CA
Los Angeles, CA
San Francisco, CA
Zone 3
Albuquerque, NM
Las Vegas, NV
Phoenix, AZ
Zone 4
Boise, ID
Casper, WY
Denver, CO
Salt Lake City, UT
Winnemucca, NV
Zone 5
Bismarck, ND
Lincoln, NE
Minneapolis, MN
Zone 6
Atlanta, GA
Charleston, SC
Houston, TX
Little Rock, AR
Raleigh, NC
Zone?
Chicago, IL
Cleveland, OH
Harrisburg, PA
Huntington, WV
ZoneS
Hartford, CT
Philadelphia, PA
Portland, ME
Zone 9
Miami, FL
!^ ' ^ off ^ ^ ^AF ^
A
Constant
14.5609
18.5578
11.5554
15.7133
13.1994
17.8252
12.1784
11.6831
12.2294
18.4275
12.0770
11.3006
16.5157
18.8928
17.6897
20.2352
15.8125
19.2904
18.9273
15.4094
15.4081
20.1837
13.4283
17.2968
12.1521
15.3353
16.4927
13.2438
17.7682
B
Constant
21.9974
21.5469
22.2571
21.8997
23.6414
22.8701
24.5606
23.5910
23.8156
22.9015
22.5621
25.8655
21.2894
22.2274
22.7826
22.3129
23.7527
21.9679
20.1609
21.7198
21.8656
21.6367
24.5328
22.2917
21.1970
21.6690
22.2187
23.2754
21.3218
C
Constant
265.3198
269.0431
268.0331
269.8244
283.5307
274.1261
296.4571
287.9969
286.4807
280.6949
272.5685
321.3924
252.8634
268.2849
273.2907
271.1316
288.6108
265.0506
242.9736
261.8926
261.3267
264.0685
302.1738
272.9800
252.6964
261.7432
268.3139
277.8473
253.6436
D-8
-------
APPENDIX E
DETAILED SITE-SPECIFIC APPROACHES FOR
DEVELOPING INHALATION SSLs
This appendix presents suggested methods of calculating SSLs for inhalation pathways using
a detailed site-specific approach. The detailed site-specific approach is the most rigorous of the
three approaches to SSL development and requires the largest amount of site-specific data. EPA
generally recommends that site managers use the simple site-specific approach, which represents
a reasonable balance between cost and site-specificity. This method is the focus of the soil screening
guidance documents. However, the detailed site-specific approach allows a site manager to model
more complex site conditions and employ less conservative assumptions than those used in the
simple site-specific approach. For example, a detailed approach could be used to model
volatilization of contaminants from either surface and subsurface (i.e., buried) soils, while the simple
site-specific modeling conservatively assumes all contamination is located at the soil surface. If
such modeling would produce SSLs more appropriate for site conditions and thus result in a
substantial savings in cleanup costs, the detailed site-specific approach would be a reasonable choice
for developing SSLs, despite the added cost and effort.
This appendix focuses on development of SSLs for the inhalation pathways (i.e., inhalation
of outdoor volatiles and fugitive dust) because exposure modeling for these pathways can be
complex and more detailed approaches that incorporate additional site-specific information may be
useful in soil screening evaluations. Detailed modeling of the migration to ground water pathway
can also be complex and useful in the soil screening process. Information on detailed site-specific
approaches to this pathway are discussed in the Technical Background Document io EPA's 1996 Soil
Screening Guidance.
The remainder of this appendix consists of two parts. The first presents a detailed site-
specific approach for developing inhalation SSLs under the commercial/industrial or non-residential
exposure scenario. The second section discusses a detailed site-specific approach for developing
inhalation SSLs under the construction exposure scenario.
INHALATION SSLs FOR THE NON-RESIDENTIAL EXPOSURE SCENARIO
This section presents methods appropriate for the detailed site-specific approach to
developing SSLs for the inhalation of volatiles and fugitive dust in outdoor air pathways. In
describing these methods, it focuses on their application to the commercial/industrial exposure
scenario; however, these methods could be applied to residential or other non-residential scenarios
as well.
E-l
-------
Detailed Site-Specific Approach to Developing Outdoor
Inhalation of Volatiles SSLs for the Outdoor Worker/Landscaper
The key difference between a detailed and a simple site-specific approach to developing
SSLs for the inhalation of volatiles in the outdoor air pathway is the use of a more rigorous model.
The Exposure Model for Soil Organic Fate and Transport (EMSOFT), can be used to estimate the
average emissions of volatiles from soil. This model, which is largely based on the work of Jury et
al. (1983, 1990), estimates volatile emissions from both surface and subsurface soil contamination.
It provides a one-dimensional analytical solution to mass transfer from soil to outdoor air. The
major advantages of using EMSOFT rather than the infinite source model and mass balance
approaches used in the simple site-specific SSL approach described in Section 4.3.2 of this guidance
are that EMSOFT:
Handles both surface and subsurface sources of emissions.
Accounts for a finite source of emissions.
Accounts for subsurface water convection (e.g., leaching).
Accounts for a soil-to-air boundary layer which impedes emissions of
contaminants with relatively low Henry's law constants.
Provides time-averaged emissions over the exposure duration.
The EMSOFT model is available at no charge from the U.S. EPA National Center for
Environmental Assessment (NCEA) web site at: http://www.epa.gov/ncea/emsoft.htm.
If the site is comprised of areas with both surface and subsurface soil contamination, the
EMSOFT model can be used to calculate the unit emission flux for each area independently. The
unit emission flux is calculated based on an initial soil concentration of 1 mg/kg or 1 x 10 "6g/g. This
is subsequently used to reverse-calculate the SSL for inhalation of volatiles.
When using the EMSOFT model for calculating SSLs, set the model options as follows:
A. Calculation Options
Check the box for "Time-Averaged Flux."
E-2
-------
B. Calculation Control
Set "Time Period for Averaging and Printing Flux and Soil Concentration
Results" equal to the exposure duration in units of days.
Set "Depth (Dl)..." equal to any value > 0 but < the depth to the bottom of
soil contamination.
Set "Depth (D2)..." equal to the same value as "Depth (Dl)."
C. Chemical Data
Set the value of the "Half Life" equal to 1,000,000 days; this will eliminate
calculation of transformation processes such as biodegradation.
Set the value of the "Number of Layers" equal to 1.
D. Soil Properties
Set the value of each soil property equal to an appropriate long-term average
value. EMSOFT assumes homogeneous soil properties from the soil surface
to an infinite depth; therefore, the selection of the soil properties values will
have a significant effect on calculated emissions.
E. Physical Constants
Set the value of the "Porewater Flux" to the appropriate long-term average
value for the site. For worst-case conditions, set the value equal to zero.
Set the value of the "Boundary Layer Thickness" to the appropriate value or
to the default value of 0.5 cm.
F. Layer Properties
Set the value of the "Cover Thickness" to the appropriate site-specific value.
For surface contamination, set this value equal to zero. The "cover" should
consist only of clean uncontaminated soil.
Set the value of the "Layer Thickness" equal to the appropriate site-specific
value. If the depth to the bottom of soil contamination is unknown, estimate
the thickness of the contaminated layer as the depth from the soil surface to
the top of the water table minus the depth from the soil surface to the top of
soil contamination. If an infinitely thick layer of soil contamination is
preferred, set the value of the "Layer Thickness" equal to a very large value
(e.g., 1,000,000 cm).
Set the value of the "Contaminant Concentration" equal to 1.0 mg/kg.
E-3
-------
Equation E-l along with the appropriate EMSOFT model results for areas of surface and subsurface
soil contamination, are used to calculate the SSLs for outdoor inhalation of volatiles.
Equation E-l
" x86,400 s/day x 10"6 g/g
m
< JTS >
where: VF = Volatilization factor (m3/kg)
Q/Cvol = Inverse of the ratio of the geometric mean air concentration to the
volatilization flux at the center of a square source (g/m2-s per
kg/m3)
< JTS > = Total EMSOFT time-averaged unit emission flux; sum of results
for both surface and subsurface soils (g/m2-s).
The dispersion factor (Q/Cvol) used in Equation E-l was evaluated using the Industrial Source
Complex (ISC3) dispersion model to estimate the maximum annual average on-site air concentration
for the 29 national sites previously modeled for the 1996 SSG. Maximum annual average air
concentrations for the 29 national sites were estimated for a series of square site sizes ranging from
0.5 to 500 acres; the emission flux was set equal to 1 g/m2-s. The ISC3 model run was set up using
the regulatory default options. Other selected options are identified in Exhibit E-1. These data were
then used to generate a best-fit curve equation for predicting air concentration as a function of site
size. Equation E-2 represents the best-fit curve equation for calculating the dispersion factor for
emissions of volatiles. The default A, B, and C constants in Equation E-2 represent the 90th
percentile of the 29 national sites with regard to dispersion. This equation is used to calculate the
long-term dispersion factor for on-site exposure to volatile emissions from soils.
Equation E-2
(\nAc-B)2
Q/Cvol=Axexp
C
where: Q/Cvol = Inverse of the ratio of the geometric mean air concentration
to the volatilization flux at the center of a square source
(g/m2-s per kg/m3)
A = Constant; default =11.9110
B = Constant; default = 18.4385
C = Constant: default = 209.7845
Ac = Areal extent of site soil contamination (acres).
E-4
-------
Exhibit E-l
OPTIONS SELECTED IN THE ISCST3 MODELING
Option description
Regulatory default option.
Emission Flux was set to 1 g/m2-sec.
Discrete receptor locations were established for site boundaries and out to at least 1000
meters.
Terrain elevations were not considered.
Rural Mode.
Default wind profile exponent values.
Default vertical potential temperature gradient values.
The downwind distance plume rise option was used.
Buoyancy-induced dispersion was used.
The wind system measurement height was set to ten meters.
No down wash considerations for area/line sources.
Program control parameters, receptors, and source input data were output with the results.
Concentrations during calm wind speed hours set to zero.
Averaging times were set to annual.
Exhibit E-2 shows the values of the A, B, and C constants for Equation E-2 for each of the
29 national sites. The appropriate constants for the most representative meteorological station may
be used instead of the default constants, or a more refined dispersion modeling analysis may be
performed for the actual site using EPA's ISC3 model.
E-5
-------
Exhibit E-2
VALUES FOR THE A, B, AND C CONSTANTS FOR CALCULATING Q/Cvol
Meteorological
Station
Albuquerque, NM
Atlanta, GA
Bismarck, ND
Boise, ID
Casper, WY
Charleston, SC
Chicago, IL
Cleveland, OH
Denver, CO
Fresno, CA
Harrisburg, PA
Hartford, CT
Houston, TX
Huntington, WV
Las Vegas, NV
Lincoln, NE
Little Rock, AR
Los Angeles, CA
Miami, FL
Minneapolis, MN
Philadelphia, PA
Phoenix, AZ
Portland, ME
Raleigh, NC
Salem, OR
Salt Lake City, UT
San Francisco, CA
Seattle, WA
Winnemucca, NV
A
Constant
14.9421
14.8349
15.0235
11.3161
17.6482
13.7674
16.8653
12.8612
11.3612
10.2152
15.5169
12.5907
13.6482
9.9253
13.3093
14.1901
12.4964
11.9110
12.1960
16.2302
14.0111
10.2871
10.4660
12.3675
12.3783
13.2559
13.8139
14.2253
12.8784
B
Constant
17.9869
17.9259
18.2526
19.6437
18.8138
18.0441
18.7848
20.5164
19.3324
19.2654
18.4248
18.8368
18.1754
18.6636
19.8387
18.5634
18.4476
18.4385
19.0645
18.7762
19.6154
18.7124
20.9077
18.6337
18.9683
19.2978
20.1624
18.8366
17.9804
C
Constant
205.1782
204.1516
207.3387
224.8172
217.0390
204.8689
215.0624
237.2798
221.2167
220.0604
211.7679
215.4377
206.7273
211.8862
230.1652
210.5281
210.2128
209.7845
215.3923
216.1080
225.3397
212.2704
238.0318
212.7284
218.2086
221.3379
234.2869
218.1845
204.1028
Once the Q/C and VF factors have been calculated, SSLs for inhalation exposure to volatile
contaminants in outdoor air by the outdoor worker can be calculated using Equations 4-6, 4-7, and
4-9 in Chapter 4 of this guidance document. Equations 4-6 and 4-7 are used to calculate SSLs for
carcinogenic and non-carcinogenic effects, respectively. Equation 4-9 calculates Csat which serves
as a ceiling for SSLs calculated using a VF model. If the SSL calculated using Equation 4-6 or 4-7
exceeds Csat and the contaminant is liquid at soil temperatures (see Appendix C, Exhibit C-3), the
SSL is set at Csat. The SSL calculated using these equations represents the screening level for both
surface and subsurface soils.
E-6
-------
Detailed Site-Specific Approach to Developing Fugitive
Dust Inhalation SSLs for Outdoor Workers
The simple site-specific fugitive dust equations (Equations 4-3 and 4-4 in this guidance
document) are also used to calculate fugitive dust SSLs for the outdoor worker for carcinogenic and
non-carcinogenic contaminants, respectively, under the detailed site-specific approach. The
particulate emission factor (PEF) represents an estimate of the relationship between the
concentration of contaminant in soil to the concentration of contaminant in air (as a consequence
of particle suspension). The PEF is calculated using either the "unlimited reservoir" model from
Cowherd et al. (1985) or the "emission factor" model from EPA's Compilation of Air Pollution
Factors (1985), as appropriate for site-specific conditions. The "unlimited reservoir" model is the
same model used in the simple site-specific approach and calculates emissions based on an unlimited
reservoir of erodible particles. This assumes that the surface material consists of dry finely divided
soils. The "emission factor" model assumes a "limited reservoir" of erodible particles that are
completely suspended in air after a single soil disturbance; subsequent emissions are a function of
the number of disturbances per year. The user is advised to review the appropriate sections of
Cowherd et al. (1985) for a discussion of when to use these different models. Both models can be
used to calculate the PM10 emission flux due to wind erosion. When using the "unlimited reservoir"
model as given in Cowherd et al. (1985), the wind erosion emission flux of PM10 (given as E10) is
calculated in units of mg/m2-h and must be converted to units of g/m2-s. When using the EPA
model, the "emission factor" or flux is calculated in units of g/m 2-yr and must be converted to units
of g/m2-s. The PEF is then calculated using Equation E-3.
Equation E-3
where: PEF = Particulate emission factor (m3/kg)
Q/Cwnd = Inverse of the ratio of the geometric mean air concentration
to the emission flux at the center of a square source (g/m2-s
per kg/m3)
Jw = PM10 emission flux (g/m2-s).
For a detailed site-specific analysis, the air dispersion factor Q/Cwind is not based on an
assumed exposure area of 0.5 acres. The exposure area for commercial/industrial land use may
range in size from less than one acre to hundreds of acres. For this reason, the value of Q/Cwindis
calculated as a function of site size.
To evaluate the dispersion factor for wind erosion, the ISC3 dispersion model was used to
estimate the maximum annual average on-site air concentration for the 29 national sites previously
E-7
-------
modeled for the 1996 SSG. Maximum annual average air concentrations for the 29 sites were
estimated for a series of square site sizes ranging from 0.5 to 500 acres; the emission flux was set
equal to 1 g/m2-s. These data were used to generate a best-fit curve equation for predicting air
concentration as a function of site size. Equation E-4 represents the best-fit curve equation for
calculating the dispersion factor for wind erosion. The default^, B, and C constants in Equation E-4
represent the 90th percentile of the 29 national sites with regard to emissions and dispersion in that
both are a function of meteorology. Equation E-4 is used to calculate the long-term dispersion
factor for on-site exposure to emissions from wind erosion.
Equation E-4
(In A,, - B)2
QICmnd = A x exp
C
where: Q/Cwind = Inverse of the geometric mean air concentration to the
emission flux at the center of a square source
(g/m2-s per kg/m3)
A = Constant; default = 16.2302
B = Constant; default = 18.7762
C = Constant; default = 216.1080
As = Areal extent of site surface contamination (acres).
Exhibit E-3 shows the values of the A, B, and C constants for Equation E-4 for each of the
29 national sites. The appropriate constants for the most representative meteorological station may
be used instead of the default constants, or a more refined dispersion modeling analysis may be
performed for the actual site using EPA's ISC3 model.
E-S
-------
Exhibit E-3
VALUES FOR THE A, B, AND C CONSTANTS FOR CALCULATING
Meteorological
Station
Albuquerque, NM
Atlanta, GA
Bismarck, ND
Boise, ID
Casper, WY
Charleston, SC
Chicago, IL
Cleveland, OH
Denver, CO
Fresno, CA
Harrisburg, PA
Hartford, CT
Houston, TX
Huntington, WV
Las Vegas, NV
Lincoln, NE
Little Rock, AR
Los Angeles, CA
Miami, FL
Minneapolis, MN
Philadelphia, PA
Phoenix, AZ
Portland, ME
Raleigh, NC
Salem, OR
Salt Lake City, UT
San Francisco, CA
Seattle, WA
Winnemucca, NV
A
Constant
14.9421
14.8349
15.0235
11.3161
7.1414
13.7674
16.8653
12.8612
11.3612
10.2152
15.5169
12.5907
13.6482
9.9253
13.3093
14.1901
12.4964
11.9110
12.1960
16.2302
14.0111
10.2871
10.4660
12.3675
12.3783
13.2559
13.8139
14.2253
12.8784
B
Constant
17.9869
17.9259
18.2526
19.6437
31.1794
18.0441
18.7848
20.5164
19.3324
19.2654
18.4248
18.8368
18.1754
18.6636
19.8387
18.5634
18.4476
18.4385
19.0645
18.7762
19.6154
18.7124
20.9077
18.6337
18.9683
19.2978
20.1624
18.8366
17.9804
C
Constant
205.1782
204.1516
207.3387
224.8172
382.6078
204.8689
215.0624
237.2798
221.2167
220.0604
211.7679
215.4377
206.7273
211.8862
230.1652
210.5281
210.2128
209.7845
215.3923
216.1080
225.3397
212.2704
238.0318
212.7284
218.2086
221.3379
234.2869
218.1845
204.1028
INHALATION SSLs FOR THE CONSTRUCTION EXPOSURE SCENARIO
This section presents methods appropriate for the detailed site-specific approach to
developing construction-specific SSLs for the inhalation of volatiles and fugitive dust in outdoor air
pathways. These SSLs reflect the increased inhalation exposures likely to result due to construction
activities such as excavation and vehicle traffic on temporary, unpaved roads. This section first
describes methods for evaluating the short-term inhalation exposures experienced by a construction
worker and then presents methods for evaluating increased inhalation exposures to off-site residents
living at the site boundary.
E-9
-------
Detailed Site-Specific Approach to Developing
Subchronic Inhalation SSLs for Construction Workers
For the construction worker exposure scenario, the primary assumption is that a
commercial/industrial building or group of buildings will be constructed at the site. Additional
assumptions are that the building or group of buildings will be constructed within the area of
residual soil contamination and that the total time of construction is less than one year. As discussed
in the guidance document, the short exposure duration of the construction worker constitutes a
subchronic exposure that should be evaluated using subchronic toxicity values (denoted here and
in the guidance document as HBLSC). See Section 5.3.1 of the guidance document for suggestions
on how to determine appropriate HBLSC values.
The dynamic processes inherent in construction activities are likely to increase emissions of
both volatiles and particulate matter from affected soils. Modeling studies have shown that high
emissions of volatiles can occur from both excavation of contaminated soils and from undisturbed
surface soil contamination. In the case of particulate matter, traffic on contaminated unpaved roads
typically accounts for the majority of emissions, with wind erosion, excavation soil dumping,
dozing, grading, and tilling operations contributing lesser emissions. The following approach can
be used to estimate SSLs for construction activities based on subchronic inhalation exposures of the
construction worker.
Volatile Emissions from Subsurface Soil Contamination
Because of the relatively short exposure duration of the construction worker, the emission
model used to estimate volatile emissions from undisturbed subsurface soils should take into
consideration the time that has elapsed since the time of initial soil contamination. If an estimate
of the elapsed time can be made with significant certainty, this value may be used as the starting
point for estimating time-averaged emissions during construction. Typically, however, this time
period cannot be estimated with a high degree of certainty. In such cases, it is assumed that
sufficient time has elapsed such that the volatile emissions at the soil surface have reached near
steady-state conditions. The time required for the volatile emissions from subsurface soil
contamination to reach near steady-state conditions is estimated by Equations E-5 and E-6 (API,
1998).
E-10
-------
Equation E-5
where:
d
Time required to reach near steady-state (s)
Vapor-phase retardation factor (unitless)
Soil air-filled porosity (cm3/cm3)
Depth to top of soil contamination (cm)
Apparent diffusivity (cm2/s), Eq. 4-8 in Chapter 4 of this
guidance document.
Equation E-6
where:
H'
Pb
Vapor-phase retardation factor (unitless)
Soil water-filled porosity (cm3/cm3)
Soil air-filled porosity (cm3/cm3)
Henry's law constant (unitless)
Soil dry bulk density (g/cm3)
Soil-water partition coefficient (cm3/g).
Equation E-7 (from Jury et al., 1990) is used to calculate the unit emission flux at the soil
surface. The "unit" emission flux assumes an initial soil contaminant concentration of 1 mg/kg or
10"6 g/g-soil. This equation should be run for a minimum of 100 time-steps, starting at time = TSS (or,
if available, the actual elapsed time since initial soil contamination) and extending to the end of the
duration of construction (T) in units of seconds.
E-ll
-------
Equation E-7
Jsub = Pb
d^
4DAt
- exp -
(d
4DAt
xl04cm2/m2
where:
'sub
Pb
DA
t
d
W
Unit emission flux from subsurface soils at each
time-step (g/m2-s)
Soil dry bulk density (g/cm3)
Apparent diffusivity (cm2/s), Eq. 4-8 in Chapter 4 of this
guidance document
Elapsed time at the end of each time-step (s)
Depth to top of soil contamination (cm)
Thickness of subsurface contaminated soil (cm).
If the depth to the bottom of soil contamination is unknown, the value of the thickness of
contaminated soil (W) is calculated as the depth to the top of the water table minus the depth to the
top of soil contamination (d). In addition, the 100 time-steps using Equation E-7 are of equal
intervals. These calculations can be performed easily using a PC-based spreadsheet program.
Please note that the EMSOFT model cannot presently be used for these calculations because the
averaging time period always begins at time = 0 and cannot be changed to time = TSS or any other
value. For a relatively short exposure duration such as for construction, beginning the time period
at t = 0 will underpredict the time-averaged unit emission flux in some cases.
From these data, Equation E-8 is used to estimate the cumulative unit mass emitted from
undisturbed subsurface soil contamination using a trapezoidal approximation of the integral.1 To
ensure that the total unit mass of each subsurface contaminant emitted does not exceed the total unit
initial mass in soil, a mass-balance is performed using Equations E-8 and E-9.
If the cumulative unit mass emitted from subsurface soils (Msub) exceeds the total unit initial
mass of subsurface contamination (MTsub), Equation E-7 may be rerun with a smaller time-step
interval and a greater number of time-steps until the unit mass emitted is less than the total unit
initial mass. As a more conservative alternative, the value of Msub may be set equal to the value of
MTsub.
a more complete description of the tapezoidal approximation and example calculations, see
Calculus and Analytic Geometry, pages 178-180 (Thomas, 1968).
E-12
-------
Equation E-8
r/j,
Msub
where: Msub = Cumulative unit mass emitted from
[h
-(j0 + 2Jl+2J2+... + 2Jn_l + Jn)
undisturbed subsurface soils (g)
h = Constant time-step interval (s),
A = T/100
T = Total time of construction (s)
J0 = Unit emission flux at time = 0 (g/m2-s),
set time zero = TSS or = the actual elapsed time
since initial soil contamination
J1:2...n = Unit emission flux at time-step J, and each
succeeding time-step where n = 100 (g/m2-s)
Asub = Areal extent of site with undisturbed
subsurface soil contamination (m2).
NOTE: In Microsoftฎ Excel, the formula forMsub can be written as:
= (((77100)/2)*C/0+ 2*SUMC/;.^_;) + Jn))*Asub
Equation E-9
MTSub = Pb x^sub x^xlO 2 m/cmxlO6 cm3/m3
where: MTsub = Total unit initial mass of subsurface contamination, (g)
pb = Soil dry bulk density (g/cm3)
Asub = Areal extent of site with undisturbed subsurface soil
contamination (m2)
W = Thickness of subsurface contaminated soil (cm).
E-13
-------
Volatile Emissions from Surface Soil Contamination and from Excavation
Volatile emissions from both surface soil contamination and from excavation of areas with
subsurface contamination are calculated assuming that contamination begins at the soil surface. The
cumulative unit mass emitted from areas of the site where surface contamination is found and from
site areas where subsurface contamination is expected to be excavated are added to the cumulative
unit mass emitted from subsurface soil contamination. The unit mass emitted from all three of these
areas of the site are then totaled and divided by the product of the total area of contamination and
the total duration of construction. In this manner, the emissions from all three site areas are
averaged over the total areal extent of contamination and over the duration of construction which
is also the exposure duration.
Equation E-10 (from Jury et al., 1990) is used to calculate the unit emission flux from surface
soil contamination. As with Equation E-7, the unit emission flux assumes an initial soil contaminant
concentration of 1 mg/kg or 10"6 g/g-soil. This equation should be run for a minimum of 100 time-
steps, starting at time = TSS (or, if available, the actual elapsed time since initial soil contamination)
and extending to the end of the duration of construction (7) in units of seconds. If the time to reach
near steady-state is used, the value of TSS for surface soil contamination should be set equal to that
of subsurface soil contamination as calculated by Equations E-5 and E-6. If subsurface soil
contamination is not present at the site, a best estimate should be made of the time since surface soil
contamination last occurred and this value substituted for the value of TSS.
Equation E-10
where:
J surf
Pb
t
L
^
nt
,1/2
1-exp -
L1
4DAt
cm2/m
Unit emission flux from surface soils at each
time-step (g/m2-s)
Soil dry bulk density (g/cm3)
Apparent diffusivity (cm2/s), Eq. 4-8 in Chapter 4 of this
guidance document
Elapsed time at the end of each time-step (s)
Depth to the bottom of soil contamination (cm).
From these data, Equation E-l 1 is used to estimate the cumulative unit mass emitted from
undisturbed surface soil contamination using a trapezoidal approximation of the integral. To ensure
that the total unit mass of each surface contaminant emitted does not exceed the total unit initial
mass in soil, a mass-balance is performed using Equations E-l 1 and E-12.
E-14
-------
Equation E-ll
Msurf= -<
+2J
xA
surf
where:
Lsurf
h
T
Jn
Cumulative unit mass emitted from
undisturbed surface soils (g)
Constant time-step interval (s),
h = T/100
Total time of construction (s)
Unit emission flux at time = 0 (g/m2-s),
set time zero = TSS or = the actual elapsed time
since initial soil contamination
Unit emission flux at time-step J, and each
succeeding time-step where n = 100 (g/m2-s)
Areal extent of site with undisturbed
surface soil contamination (m2).
M
Equation E-12
xLx\0~2 m/cmxlO6 cm3/m3
where:
Tsurf =
M
Pb
A
^surf
L
Total unit initial mass of surface contamination (g)
Soil dry bulk density (g/cm3)
Areal extent of site with undisturbed
surface soil contamination (m2)
Depth to the bottom of soil contamination (cm).
If the cumulative unit mass emitted from surface soils (Msut^ exceeds the total unit initial
mass of surface contamination (MTSUI^, Equation E-10 may be rerun with a smaller time-step interval
and a greater number of time-steps until the unit mass emitted is less than the total unit initial mass.
As a more conservative alternative, the value of Msurfmay be set equal to the value of MTsurf.
Equation E-13 (from Jury et al., 1984) is used to calculate the cumulative unit mass emitted
from the areal extent of excavation.
E-15
-------
Equation E-13
where: Mexcav = Cumulative unit mass emitted from
excavation (g)
pb = Soil dry bulk density (g/cm3)
DA = Apparent diffusivity (cm2/s), Eq. 4-8 in Chapter 4 of this
guidance document
TE = Duration of excavation (s); TE ends when the excavation is
covered by an impermeable material
Aexcav = Areal extent of excavation (m2).
Equation E-13 operates under the assumption of an infinitely deep emission source. This
should not be problematic, however, for the relatively short duration of excavation. Equation E-13
differs from Equations E-7 and E-10 in that excavation is assumed to expose subsurface soil
contamination to the atmosphere at time = 0. That is to say that excavation is assumed to
instantaneously uncover the subsurface contamination. The duration of the excavation event ends
when the areal extent of excavation is covered by an impermeable material (e.g., a concrete slab).
The total time-averaged unit emission flux from undisturbed subsurface soils, undisturbed
surface soils, and from excavation is calculated using Equation E-14.
Equation E-14
=
(Msub+Msurf+Mexcav)
where: < JT > = Total time-averaged unit emission flux (g/m2-s)
Msub = Cumulative unit mass emitted from
undisturbed subsurface soils (g)
Msurf = Cumulative unit mass emitted from
undisturbed surface soils (g)
Mexcav = Cumulative unit mass emitted from
excavation (g)
Ac = Areal extent of site soil contamination (m2)
T = Duration of construction (s).
E-16
-------
Calculation of the Soil-to-Air Volatilization Factor for the Construction Scenario
Because the exposure duration during construction is typically less than one year (i.e.,
subchronic), the dispersion factor must also reflect the same time period. The on-site subchronic
dispersion factor for a ground-level area emission source, Q/Csa, was derived by employing the EPA
SCREENS dispersion model to predict the maximum 1-h. average on-site unit
concentration for a ground-level area source of emissions. Identical dispersion modeling was
performed for square site sizes ranging 0.5 to 500 acres. A best curve was then fit to the paired data
of maximum concentration and site size to predict the value of Q/Csa This resulted in Equation E-15
for calculating the subchronic on-site dispersion factor for area sources.
Equation E-15
(\nAc-B)2
Q/Csa =
C
where: Q/Csa = Inverse of the ratio of the 1-h. geometric mean air
concentration and the volatilization flux at the center of a
square emission source (g/m2-s per kg/m3)
A = Constant; default = 2.4538
B = Constant; default = 17.5660
C = Constant; default = 189.0426
Ac = Areal extent of site soil contamination (acres).
The value of Q/Csa must be corrected for the averaging time represented by the duration of
construction. To accomplish this, a best curve was fit to the EPA correction factors for converting
1-h. average concentrations to 3-h., 8-h., and 24-h. averages (U.S. EPA, 1992). In addition, a fourth
data point was included representing the correction factor for converting the SCREENS 1-h. average
concentration to an annual average concentration. The median concentration was computed as the
geometric mean of all 29 national sites as determined using the ISC3 dispersion model. This
resulted in Equation E-16 for estimating the dispersion correction factor for averaging times less
than one year.
E-17
-------
Equation E-16
5.3537 -9.6318
FD =0.1852 + - + -
'c2
where: FD = Dispersion correction factor (unitless)
tc = Duration of construction (hr),
t = Tin units of hours.
The subchronic soil-to-air volatilization factor for the exposure of the construction worker
is calculated by Equation E-17.
Equation E-17
FD
where: VFSC = Subchronic soil-to-air volatilization factor (m3/kg)
Q/Csa = Inverse of the ratio of the 1-h. geometric mean air
concentration and the volatilization flux at the center of a
square emission source (g/m2-s per kg/m3), Eq. E-15
FD = Dispersion correct!on factor (unitless), Eq. E-16
= Total time-averaged unit emission flux, Eq. E-14.
Once these values have been calculated, the SSL for subchronic on-site inhalation exposure
to volatile emissions during construction can be calculated using Equations 5-12, 5-13, and 5-16 in
Chapter 5 of this guidance document. Equations 5-12 and 5-13 are used to calculate SSLs for
carcinogenic and non-carcinogenic effects, respectively, and Equation 5-16 calculates Csat, which
is an upper bound on SSLs calculated using the VF model. If the SSL calculated using Equation 5-
12 and 5-13 exceed Csat and the contaminant is liquid at soil temperatures (see Appendix C, Exhibit
C-3), the SSL is set at Csat. The value of the SSL calculated by these equations represents the soil
screening level for all three areas of soil contamination, i.e., surface soils, subsurface soils, and areas
of excavation.
E-18
-------
Fugitive Dust Emissions During Construction
The construction worker is assumed to be exposed to contaminants in the form of particulate
matter with an aerodynamic particle diameter of less than 10 microns (PM10). Fugitive dust
emissions are generated by construction vehicle traffic on temporary unpaved roads. In addition,
fugitive dust emissions are generated by other construction activities such as excavation, soil
dumping, dozing, grading, and tilling operations as well as from wind erosion of soil surfaces.
Reasonable maximum exposure (RME) of the construction worker to unpaved road emissions occurs
in proximity to the road(s). RME for wind erosion emissions and emissions from other construction
activities are assumed to occur at the center of the emission source. The ambient air dispersion of
emissions, therefore, is different for these two classes of emission sources. For this reason, the
subchronic exposure SSL for unpaved road traffic and the subchronic exposure SSL for other
construction activities (including wind erosion) are calculated separately.
The following fugitive dust emission equations represent approximations of actual emissions
at a specific site. Sensitive emission model parameters include the soil silt content and moisture
content. Silt is defined as soil particles smaller than 75 micrometers (//m) in diameter and can be
measured as that proportion of soil passing a 200-mesh screen, using the American Society for
Testing and Materials (ASTM) Method C-136. Soil moisture content is defined on a percent
gravimetric basis [(g-water/g-soil) x 100] and should be approximated as the mean value for the
duration of the construction project. In general, soil silt and moisture content are the most sensitive
model parameters for which default values have been assigned, however, site-specific values will
produce more accurate modeling results. Other emission model parameters have not been assigned
default values and are typically defined on a site-specific basis. These parameters include the total
distance traveled by construction site vehicles, mean vehicle weight, average vehicle speed, and the
area of soil disturbance.
Fugitive Dust Emissions from Unpaved Road Traffic
The subchronic particulate emission factor for unpaved road traffic (PEFJ is calculated
using Equation E-18 (EPA, 19895). Equation E-18 differs from Equation 5-5 in Chapter 5 of this
document in that it contains the unabridged equation for PM10 emissions from traffic on unpaved
roads. Equation E-18 therefore allows the user to enter a site-specific value for each variable.
E-19
-------
Equation E-18
D
365
(365 p) x28i.9x2J/KT
where: PEFSC = Subchronic particulate emission factor for
unpaved road traffic (m3/kg)
Q/Csr = Inverse of the ratio of the 1-h. geometric mean air
concentration to the emission flux along a straight
road segment bisecting a square site (g/m2-s per
kg/m3),Eq. E-19
FD = Dispersion correction factor (unitless), Eq. E-16
T = Total time over which construction occurs (s)
AR = Surface area of contaminated road segment (m2),
AR = LR x WR x 0.092903 m2/ft2
s = Road surface silt content (%), default = 8.5 %
W = Mean vehicle weight (tons)
Mdry = Road surface material moisture content under
dry, uncontrolled conditions (%), default = 0.2 %
p = Number of days per year with at least 0.01 inches
of precipitation (Exhibit E-l)
ZVKT = Sum of fleet vehicle kilometers traveled during
the exposure duration (km)
LR = Length of road segment (ft)
LR = square root of site surface contamination
configured as a square
WR = Width of road segment (ft), default = 20 ft.
Equation E-18 operates under the assumption of a road surface silt content of 8.5 percent as
the mean value for "construction sites - scraper routes" (see Table 13.2.2-1 of EPA, 1985). In
addition, the surface material moisture content under dry conditions is assumed to be 0.2 percent as
the default value (see Section 13.2.2 of EPA, 1985).
The number of days with at least 0.01 inches of rainfall can be estimated using Exhibit E-4.
Mean vehicle weight (W) can be estimated by assuming the numbers and weights of different types
of vehicles. For example, assume that the daily unpaved road traffic consists of 20 two-ton cars and
10 twenty-ton trucks. The mean vehicle weight would then be:
W = [(20 cars x 2 tons/car) + (10 trucks x 20 tons/truck)]/30 vehicles = 8 tons
E-20
-------
The sum of the fleet vehicle kilometers traveled during construction (SVKT) can be estimated
based on the size of the area of surface soil contamination, the configuration of the unpaved road,
and the amount of vehicle traffic on the road. For example, if the area of surface soil contamination
is 0.5 acres (or 2,024 m2), and one assumes that this area is configured as a square with the unpaved
road segment dividing the square evenly, the road length would be equal to the square root of 2,024
m2 (45 m or 0.045 km). Assuming that each vehicle travels the length of the road once per day, 5
days per week for a total of 6 months, the total fleet vehicle kilometers traveled would be:
ZVKT = 30 vehicles x 0.045 km/day x (52 wks/yr + 2) x 5 days/wk = 175.5 km.
Exhibit E-4
MEAN NUMBER OF DAYS WITH 0.01 INCH OR MORE OF ANNUAL PRECIPITATION
E-21
-------
The subchronic dispersion factor for on-site exposure to unpaved road traffic, Q/Csn was
derived by using the ISC3 dispersion model with a meteorological data set that mimics that of the
SCREENS dispersion model. A straight road segment was situated such that the road bisected the
site configured as a square. A series of square sites ranging in size from 0.5 to 500 acres with their
associated road segments were modeled. A series of receptors were placed along each road segment
and the road emissions were set equal to 1 g/m2-s. The final on-site 1-h. average unit concentration
was calculated as the mean of these receptors.
The subchronic dispersion factor for on-site exposure to unpaved road traffic is calculated
using Equation E-19.
Equation E-19
(\nAs-B)2
Q/Csr =Ax exp
C
where: Q/Csr = Inverse of the ratio of the 1-h. geometric mean air
concentration and the emission flux along a straight road
segment bisecting a square site
(g/m2-s per kg/m3)
A = Constant; default = 12.9351
B = Constant; default =5.7383
C = Constant; default = 71.7711
As = Areal extent of site surface contamination (acres).
Once these values have been calculated, the SSL for subchronic on-site inhalation exposure
to paniculate matter emissions from unpaved road traffic during construction can be calculated using
Equations 5-7 and 5-8 in Chapter 5 of this guidance document. Equations 5-7 and 5-8 are used to
calculate SSLs for carcinogenic and non-carcinogenic effects, respectively.
Fugitive Dust Emissions from Other Construction Activities
Other than emissions from unpaved road traffic, the construction worker may also be
exposed to particulate matter emissions from wind erosion, excavation soil dumping, dozing,
grading, and tilling or similar operations. These operations may occur separately or concurrently
and the duration of each operation may be different. For these reasons, the total unit mass emitted
from each operation is calculated separately and the sum is normalized over the entire area of
contamination and over the entire time during which construction activities take place.
E-22
-------
Equation E-20 is used to calculate the unit mass emitted from wind erosion of contaminated
soil surfaces (from Cowherd et al., 1985).
Equation E-20
Mmnd = 0.036x(l-F)x _L
where: Mwind = Unit mass emitted from wind erosion (g)
V = Fraction of vegetative cover (unitless),
default = 0
Um = Mean windspeed during construction (m/s),
default = 4.69 m/s (EPA, 1996)
Ut = Equivalent threshold value of windspeed at
7 m (m/s), default = 11.32 m/s (EPA, 1996)
F(x) = Function dependent on Um/Ut derived from
Cowherd et al. (1985) (unitless), default = 0.194
(EPA, 1996)
Asurf = Areal extent of site with surface soil contamination
(m2)
ED = Exposure duration (yr).
The unit mass emitted from the dumping of excavated soils can be calculated using Equation
E-21 (from EPA, 1985).
Equation E-21
1.3
=0.35x0.0016
2.2
PSO,l X Ae
*excav "-'-'v.vv-L"" , . 14 "ysoil
where: Mexcav = Unit mass emitted from excavation
soil dumping (g)
0.35 = PM10 particle size multiplier (unitless) (EPA, 1985)
Um = Mean windspeed during construction (m/s),
default = 4.69 m/s (EPA, 1996)
M = Gravimetric soil moisture content (%), default = 12
%, EPA (1985) Table 13.2.4-1, mean value for
municipal landfill cover
E-23
-------
psoil = In situ soil density (includes water) (Mg/m3),
default =1.68 Mg/m3
Aexcav = Areal extent of excavation (m2)
dexcav = Average depth of excavation (m)
NA = Number of times soil is dumped (unitless),
default = 2.
Equation E-22 (from EPA, 1985) is used to calculate the unit mass emitted from dozing
operations.
Equation E-22
where: Mdoz = Unit mass emitted from dozing operations (g)
0.75 = PM10 scaling factor (unitless)
s = Soil silt content (%), default = 6.9 %, EPA
(1985) Table 11.9-3, mean value for overburden
M = Gravimetric soil moisture content (%), default = 7.9
%, EPA (1985) Table 11.9-3, mean value for
overburden
ฃVKT = Sum of dozing kilometers traveled (km)
S = Average dozing speed (kph),
default = 11.4 kph, EPA (1985) Table 11.9-3,
mean value for graders.
The unit mass emitted from grading operations is calculated by Equation E-23 (from EPA,
1985).
Equation E-23
Mgrade'
where: Mgrade = Unit mass emitted from grading operations (g)
0.60 = PM10 scaling factor (unitless)
S = Average grading speed (kph),
default = 11.4 kph, EPA (1985) Table 11.9-3
mean value for graders
= Sum of grading kilometers traveled (km).
E-24
-------
Finally, Equation E-24 (from EPA, 1992a) is used to calculate the unit mass emitted from
tilling or similar operations.
Equation E-24
Mm= I.l(5)a6x^fi//x4,047m2/acrex l(T4/za/w2x \tfglkg*NA
where: Mm = Unit mass emitted from tilling or similar operations
(g)
s = Soil silt content (%), default = 18 %
EPA(1992a) Section 2.6.1.1
Atill = Areal extent of tilling (acres)
NA = Number of times soil is tilled (unitless),
default = 2.
The total time-averaged unit emission flux from wind erosion, excavation soil dumping,
dozing, grading, and tilling operations is calculated by Equation E-25.
Equation E-25
+Mdoz +Mgrade
where: = Total time-averaged PM10 unit emission flux for
construction activities other than traffic on unpaved
roads (g/m2-s)
Mwind = Unit mass emitted from wind erosion (g)
Mexcav = Unit mass emitted from excavation soil
dumping (g)
Mdoz = Unit mass emitted from dozing operations (g)
Mgrade = Unit mass emitted from grading operations (g)
Mm = Unit mass emitted from tilling operations (g)
Ac = Areal extent of site soil contamination (m2)
T = Duration of construction (s).
The subchronic particulate emission factor for the construction worker due to construction
activities other than unpaved road traffic is calculated by Equation E-26.
E-25
-------
Equation E-26
FD
where: PEF'SC = Subchronic particulate emission factor for
construction activities other than traffic on unpaved
roads (m3/kg)
Q/Csa = Inverse of the ratio of the 1-h. geometric mean air
concentration and the emission flux at the center of
the square emission source
(g/m2-s per kg/m3), Eq. E-15
FD = Dispersion correction factor (unitless), Eq. E-16
= Total time-averaged PM10 unit emission flux for
construction activities other than traffic on unpaved
roads (g/m2-s), Eq. E-25.
Once these values have been calculated, the construction worker subchronic exposure SSLs
for particulate matter emissions due to traffic on unpaved roads and due to other construction
activities are calculated separately using Equations 5-3 and 5-4 in Chapter 5 this guidance document.
Equations 5-3 and 5-4 are used to calculate SSLs for carcinogenic and non-carcinogenic effects,
respectively. With values of the SSL for unpaved road traffic and the SSL for other construction
activities, the lowest of the two SSLs should be used.
Particulate Matter Case Example
The following represents a theoretical case example illustrating the use of the previously
cited equations for determining the SSL for unpaved road traffic and the SSL for other construction
activities. The case example site consists of a 5-acre square area contaminated with hexavalent
chromium (chromium VI). Contamination occurs in both surface and subsurface soils. Construction
activities are anticipated to include unpaved road traffic, excavation soil dumping, dozing, grading,
and tilling. In addition, wind erosion of the construction site is expected. Actual soil excavation
will encompass one acre of soil to a depth of one meter. Likewise, one acre will be tilled twice for
landscaping purposes. Dozing and grading operations are expected to cover the entire 5 acres.
E-26
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SSL for Unpaved Road Traffic
From Equation E-18, the width of the road segment (Wp) is assumed to be 20 ft. The length
of the road segment (Lp) is calculated as the square root of the area of the 5-acre site configured as
a square:
LR = (5 acres x 43,560 ft2/acre)as = 467 ft.
Therefore, the area of the road segment (Ap) is the product of the width and length of the road
segment and a conversion factor of 0.092903 m2/ft2:
AR = 20 ft x 467 ft x 0.092903 m2/ft2 = 867 m2.
The total time period over which traffic will occur is estimated to be 6 months. Therefore,
the value of T is calculated by:
T= (52 wks/yr + 2) x 5 days/wk x 8 hrs/day x 3,600 s/hr = 3,744,000 s.
From Exhibit E-l, the value of the number of days with at least 0.01 inches of precipitation
(p) is determined to be 70 days. Assuming that 30 vehicles per day travel the entire length of the
road segment, the sum of the fleet vehicle kilometers traveled during the exposure duration (ZfrKT)
is calculated by:
ฃVKT= 30 vehicles x 467 ft/day x (52 wks/yr - 2) x 5 days/wk - 3,281 ft/km = 555 km.
For a square 5-acre site, the value ofQ/Csr is calculated to be 16.40 g/m2-s per kg/m3 from
Equation E-19. Assuming that the overall duration of construction is 6 months or 4,380 hours (7J,
the value of the dispersion correction factor (F^ is calculated to be 0.186 from Equation E-l6.
Finally, the values of the road surface silt content (s) and the dry road surface moisture content (M^
in Equation E-18 are set equal to the default values of 8.5 % and 0.2 %, respectively. The value of
the mean vehicle weight (W) in Equation E-18 is assumed to be 8 tons.
From these data, the value of the subchronic particulate emission factor for unpaved road
traffic (PEFJ is calculated by Equation E-18:
PEF =1640: 1 3.744.000x867
0.186
(0.2/0.2)03
PEF =7.74xl05 n
With a value of the PEFSC for chromium VI (a carcinogenic contaminant), the construction worker
subchronic exposure soil screening level for unpaved road traffic is calculated by Equation 5-3:
E-27
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L/KFx 1,000 ng/mgxEFxED x (l/PEFJ
SSL = 10~6x 70x365
"c (1.2 x i(T2) x 1,000 x 130 x 1 x (1/7.74 x 105)
= 13 mg/kg.
SSL for Wind Erosion and Other Construction Activities
The particulate emission factor for wind erosion and for construction activities other than
unpaved road traffic (PEF'J is calculated using Equations E-20 through E-26. In each of these
equations, the default values are used for each variable assigned a default value. In Equation E-20,
the value of the areal extent of the site with surface soil contamination (Asurf) is assigned a value of
5 acres or 20,235 m2. In Equation E-21, the value of the areal extent of excavation (AexcJ is set
equal to 1 acre or 4,047 m2, and the value of the average depth of excavation (dexcav) is set equal to
1 meter. In Equation E-24, the value of the areal extent of tilling (Atill) is also set equal to 1 acre or
4,047 m2. The values of the sum of dozing and grading kilometers traveled in Equations E-22 and
E-23 (ZVKT) are each calculated assuming that the entire 5 acres are dozed and graded three times
over the duration of construction. Assuming that the dozing and grading blades each have a length
of 8 ft (2.44 m) and that one dozing or grading pass across the length of the site is equal to the square
root of the site area (142 m), the value of ZVKTis calculated by:
I,VKT= ((\42m/2.44m) x \42rn x 3)/1,000m/km
ZVKT=24.79km.
From Equation E-15, the value of the dispersion factor (Q/CJ for a square 5-acre site is
calculated to be 9.44 g/m2-s per kg/m3. The value of the dispersion correction factor (Fj) is
calculated from Equation E-l 6 as 0.186 based on a value for the duration of construction (tj equal
to 6 months or 4,380 hours.
The total time-averaged PM10unit emission flux for construction activities other than traffic
on unpaved roads () is calculated by Equation E-25:
_ (8-80 x 104g) +Q.66 x 103g) +(7.37 x 102g) +(1.08 x 104g) +(5.04 x 103g)
20235w2x 3744000s
E-28
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From these data, the value of the subchronic particulate emission factor for construction
activities other than unpaved road traffic (PEF'J is calculated by Equation E-26:
0.186 1.40xlO~6
With a value of the PEF'SC for chromium VI, the construction worker subchronic exposure
SSL for construction activities other than unpaved road traffic is calculated by Equation 5-3:
TRxATx365days/yr
1,000 \iglmgxEFxED x (1/PEF^)
10~6x 70x365
(1.2 x i(T2) x 1,000 x 130 x 1 x (1/3.61 x 107)
SSL sc = 590 mg/kg.
Because the SSL for unpaved road traffic (13 mg/kg) is less than the SSL for construction
activities other than unpaved road traffic (590 mg/kg), the final value of the SSLscis set equal to the
value for unpaved road traffic.
Inhalation SSLs for the Off-site Resident2
The off-site resident receptor refers to a receptor who does not live on the site. The major
assumption is that the relevant exposure point is located at the site boundary. Dispersion modeling
has shown that an exposure point at the site boundary will always experience the highest off-site air
concentration from the ground-level nonbuoyant type of site emission sources considered for this
analysis. This receptor will experience volatile and particulate matter emissions from the site both
during construction and after construction is completed. In some cases, the magnitude of the
emissions during construction may exceed that of post-construction even though the post-
construction exposure duration is considerably longer.
2 The approach described in this section can also be applied to other off-site receptors, such as an off-
site commercial/industrial worker.
E-29
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Volatile Emissions
Simple site-specific inhalation SSLs due to volatile emissions that are calculated for the on-
site outdoor worker are considered to be protective of the off-site resident for two primary reasons.
First, the volatile emission model used in the simple site-specific analyses for off-site receptors
operates under the assumption that soil contamination begins at the soil surface. This assumption
equates to worst-case conditions in terms of the magnitude of emissions. Second, dispersion
modeling has shown that for a square area emission source the on-site air concentration will always
be higher than the off-site air concentration. Preliminary emission and dispersion modeling has
shown that considering the greater exposure frequency and longer exposure duration of the off-site
residential receptor, the resulting SSLs are typically lower than those of the on-site outdoor worker
by less than 30 percent. However, one must consider the relative uncertainty in these analyses. The
uncertainty is a function of several variables. First, the actual geometry of a site may not closely
resemble a square. Second, the emission model assumes that volatiles are emitted uniformly across
the entire areal extent of the site, whereas emissions from actual sites may be heterogeneous with
respect to both strength and location. Finally, the dispersion factor for the off-site receptor assumes
that it is located at the emission source boundary as an upper bound estimate; in reality, this may or
may not be the case. For these reasons, the difference in the on-site outdoor worker and off-site
residential SSLs is considered to be negligible.
Particulate Matter Emissions
The off-site resident is exposed to particulate matter emissions both during site construction
and after construction is complete. During site construction, this receptor is assumed to be exposed
to particulate matter emissions from unpaved road traffic, excavation soil dumping, dozing, grading,
and tilling operations as well as emissions from wind erosion. After construction, the receptor is
assumed to be exposed only to fugitive dust emissions from wind erosion. Although the
construction exposure duration is considerably shorter than the post-construction exposure duration,
the magnitude of emissions during construction may be higher than that due to wind erosion alone.
For this reason, the total unit mass emitted from all construction activities and the total unit mass
emitted from wind erosion are summed and normalized over the entire site area and over the total
exposure duration of the off-site resident receptor.
The unit masses of each contaminant emitted during construction from wind erosion,
excavation soil dumping, dozing, grading, and tilling operations are calculated using Equations E-20
through E-24. The post-construction unit mass emitted due to wind erosion (Mpcwind) is calculated
using Equation E-20. In this case, the value of the exposure duration (ED) in Equation E-20 must
be changed to reflect a long-term exposure (i.e., 30 years for residential or 25 years for
commercial/industrial exposure). In addition, the default value of the fraction of vegetative cover
(V) in Equation E-20 is changed from 0 to 0.5 for post-construction exposure. The unit mass emitted
from traffic on unpaved roads (Mmad) is calculated by Equation E-27.
E-30
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Equation E-27
2 6 x l"n ^>Nปฐ-8''T/r/7'J\0.4
[(365-/?)/365]x281.9x2FKT
where each variable has been defined previously in Equation E-18.
The total time-averaged unit emission flux for the off-site receptor is calculated by Equation E-28.
Equation E-28
+Mwmd +Mexcav +Mdoz +Mgrade
where: = Total time-averaged PM10 unit emission flux for the
off-site receptor (g/m2-s)
Mroad = Unit mass emitted from unpaved roads (g)
Mwind = Unit mass emitted from wind erosion (g)
Mexcav = Unit mass emitted from excavation soil
dumping (g)
Mdoz = Unit mass emitted from dozing operations (g)
Mgrade = Unit mass emitted from grading operations (g)
Mm = Unit mass emitted from tilling operations (g)
Mpcwind = Post-construction unit mass emitted from
wind erosion (g)
Asite = Areal extent of site (m2)
ED = Exposure duration (yr).
Equation E-28 combines the unit mass emitted from construction activities and from wind
erosion and normalizes these emissions across the entire site area and the exposure duration of the
off-site receptor. Because the emission source geometry at an actual site is unknown, spreading the
total emissions across the entire site facilitates calculation of the dispersion factor such that the
receptor is located at the point of maximum annual average concentration at the site boundary. This
concentration represents the maximum concentration at the point of public access.
The particulate emission factor for the exposure of the off-site receptor is calculated by
Equation E-29.
E-31
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Equation E-29
where: PEFoff = Particulate emission factor for
the off-site receptor (m3/kg)
Q/Coff = Inverse of the ratio of the geometric mean air
concentration at the emission flux at the site boundary
(g/m2-s per kg/m3), Eq. E-30
= Total time-averaged PM10 unit emission flux
for the off-site receptor (g/m2-s), Eq. E-28.
The dispersion factor for the off-site resident, Q/Coffi was derived by using EPA's ISC3
dispersion model to predict the maximum annual average unit concentration at the boundary of a
series of square ground-level area emissions sources. Site sizes ranged from 0.5 to 500 acres. A
best curve was fit to the paired data of maximum concentration and site size to predict the value of
(Q/C)off. This resulted in Equation E-30 for calculating the dispersion factor.
The dispersion factor for the off-site resident, Q/Coff, is therefore calculated using Equation
E-30.
Equation E-30
e/C^Mxexp
C
where: Q^o/f = Inverse of the ratio of the geometric mean air concentration
at the emission flux at the site boundary (g/m2-s per kg/m3)
A = Constant; default = 11.6831
B = Constant; default = 23.4910
C = Constant; default = 287.9969
Asite = Areal extent of the site (acres).
Exhibit E-5 shows the values of the A, B, and C constants used in Equation E-30 for each of
the 29 meteorological stations used in the dispersion modeling analysis. The appropriate constants
for the most representative meteorological station may be used instead of the default constants, or
a more refined dispersion modeling analysis may be performed for the actual site using EPA's ISC3
model.
E-32
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With a calculated value of the off-site receptor particulate emission factor (PEF^, the
inhalation soil screening level is calculated using Equations 5-3 and 5-4 in Chapter 5 of the
supplemental soil screening guidance document, as appropriate.
Exhibit E-5
VALUES FOR THE A, B, AND C CONSTANTS FOR CALCULATING Q/Coff
Meteorological
Station
Albuquerque, NM
Atlanta, GA
Bismarck, ND
Boise, ID
Casper, WY
Charleston, SC
Chicago, IL
Cleveland, OH
Denver, CO
Fresno, CA
Harrisburg, PA
Hartford, CT
Houston, TX
Huntington, WV
Las Vegas, NV
Lincoln, NE
Little Rock, AR
Los Angeles, CA
Miami, FL
Minneapolis, MN
Philadelphia, PA
Phoenix, AZ
Portland, ME
Raleigh, NC
Salem, OR
Salt Lake City, UT
San Francisco, CA
Seattle, WA
Winnemucca, NV
A
Constant
17.8252
15.8125
18.8928
12.2294
18.4275
19.2904
20.1837
13.4283
12.0770
11.5554
17.2968
15.3353
18.9273
12.1521
12.1784
17.6897
15.4094
15.7133
17.7682
20.2352
16.4927
11.6831
13.2438
15.4081
14.5609
11.3006
13.1994
18.5578
16.5157
B
Constant
22.8701
23.7527
22.2274
23.8156
22.9015
21.9679
21.6367
24.5328
22.5621
22.2571
22.2917
21.6690
20.1609
21.1970
24.5606
22.7826
21.7198
21.8997
21.3218
22.3129
22.2187
23.4910
23.2754
21.8656
21.9974
25.8655
23.6414
21.5469
21.2894
C
Constant
274.1261
288.6108
268.2849
286.4807
280.6949
265.0506
264.0685
302.1738
272.5685
268.0331
272.9800
261.7432
242.9736
252.6964
296.4751
273.2907
261.8926
269.8244
253.6436
271.1316
268.3139
287.9969
277.8473
261.3267
265.3198
321.3924
283.5307
269.0431
252.8634
E-33
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REFERENCES
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Vapor Migration to Enclosed Spaces, Site-Specific Alternatives to Generic Estimates.
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Cowherd, C.G., G. Muleski, P. Engelhart, and D. Gillette. 1985. Rapid Assessment of Exposure to
Paniculate Emissions from Surface Contamination Sites. EPA/600/8-85/002. Office of
Health and Environmental Assessment, U.S. Environmental Protection Agency, Washington,
D.C.
EPA (U.S. Environmental Protection Agency). 1996. Soil Screening Guidance: User's Guide.
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Protection Agency, Washington, D.C. Publication 9355.4-23.
EPA (U.S. Environmental Protection Agency). 1992a. Fugitive Dust Background Document and
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Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency,
Research Triangle Park, NC.
EPA (U.S. Environmental Protection Agency). 1992. Workbook of Screening Techniques for
Assessing Impacts of Toxic Air Pollutants (Revised). EPA-454/R-92-024. Office of Air
Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle
Park, NC.
EPA (U.S. Environmental Protection Agency). 1985. Compilation of Air Pollutant Emission
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Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle
Park, NC.
Jury, W.A., WJ. 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.
Jury, W.A., D. Russo, G. Streile, and H.E. Abd. 1990. Evaluation of volatilization by organic
chemicals residing below the soil surface. Water Resources Research 26 (1): 13-20.
Jury, W.A., W.F. Spencer, and W.J. Farmer. 1983. Behavior assessment model for trace organics
in soil: I. Model description. J. Environ. Qual. 12(4): 558-564.
Thomas, G. B. 1968. Calculus and Analytic Geometry, 4th edition. Addison-Wesley, New York.
Pages 178-180.
E-34
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