vvEPA
United States
Environmental Protection
Agency
Office of Research and
Development
Washington, DC 20460
EPA/540/R-92/003
December 1991
Risk Assessment Guidance
for Super fund:
Volume I -
Human Health Evaluation
Manual (Part B,
Development of Risk-based
Preliminary Remediation
Goals)
Interim
-------
EPA/540/R-92/003
Publication 9285.7-01 B
December 1991
Risk Assessment Guidance
for Superfund:
Volume I -
Human Health Evaluation Manual
(Part B, Development of
Risk-based Preliminary
Remediation Goals)
Interim
Office of Emergency and Remedial Response
U.S. Environmental Protection Agency
Washington, DC 20460
Printed on Recycled Paper
-------
NOTICE
The policies set out in this document are intended solely as guidance; they are not final U.S.
Environmental Protection Agency (EPA) actions. These policies are not intended, nor can they be relied
upon, to create any rights enforceable by any party in litigation with the United States. EPA officials may
decide to follow the guidance provided in this document, or to act at variance with the guidance, based on an
analysis of specific site circumstances. The Agency also reserves the right to change this guidance at any time
without public notice.
This guidance is based on policies in the Final Rule of the National Oil and Hazardous Substances
Pollution Contingency Plan (NCP), which was published on March 8, 1990 (55 Federal Register 8666). The
NCP should be considered the authoritative source.
-------
CONTENTS
Page
NOTICE ii
EXHIBITS vi
DEFINITIONS vii
ACRONYMS/ABBREVIATIONS ix
ACKNOWLEDGEMENTS xi
PREFACE xii
1.0 INTRODUCTION 1
1.1 DEFINITION OF PRELIMINARY REMEDIATION GOALS 1
1.2 SCOPE OF PART B 1
1.3 RELEVANT STATUTES, REGULATIONS, AND GUIDANCE 3
1.3.1 CERCLA/SARA 3
1.3.2 National Contingency Plan 3
1.3.3 Guidance Documents 3
1.4 INITIAL DEVELOPMENT OF PRELIMINARY REMEDIATION GOALS 4
1.5 MODIFICATION OF PRELIMINARY REMEDIATION GOAN 5
1.6 DOCUMENTATION AND COMMUNICATION OF PRELIMINARY
REMEDIATION GOALS 6
1.7 ORGANIZATION OF DOCUMENT 6
2.0 IDENTIFICATION OF PRELIMINARY REMEDIATION GOALS 7
2.1 MEDIA OF CONCERN 7
2.2 CHEMICALS OF CONCERN 8
2.3 FUTURE LAND USE 8
2.4 APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS 9
2.4.1 Chemical-, Location-, and Action-specific ARARs 10
2.4.2 Selection of the Most Likely ARAR-based
PRG for Each Chemical 11
2.5 EXPOSURE PATHWAYS PARAMETERS, AND EQUATIONS 11
2.5.1 Ground Water/SurfaceWater 13
2.5.2 Soil 13
-in-
-------
CONTENTS (Continued)
Page
2.6 TOXICITY INFORMATION 14
2.7 TARGET RISK LEVELS 14
2.8 MODIFICATION OF PRELIMINARY REMEDIATION GOALS 15
2.8.1 Review of Assumptions 15
2.8.2 Identification of Uncertainties 16
2.8.3 Other Considerations in Modifying PRGs 17
2.8.4 Post-remedy Assessment 18
3.0 CALCULATION OF RISK-BASED PRELIMINARY
REMEDIATION GOALS 19
3.1 RESIDENTIAL LAND USE 20
3.1.1 Ground Water or Surface Water 20
3.1.2 Soil 23
3.2 COMMERCIAL/INDUSTRIAL LAND USE 24
3.2.1 Water 24
3.2.2 Soil 25
3.3 VOLATILIZATION AND PARTICIPATE EMISSION FACTORS 26
3.3.1 Soil-to-air Volatilization Factor 26
3.3.2 Particulate Emission Factor 29
3.4 CALCULATION AND PRESENTATION OF RISK-BASED PRGS 30
4.0 RISK-BASED PRGs FOR RADIOACTIVE CONTAMINANTS 33
4.1 RESIDENTIAL LAND USE 34
4.1.1 Ground Water or Surface Water 34
4.1.2 Soil 35
4.2 COMMERCIAL/INDUSTRIAL LAND USE 36
4.2.1 Water 36
4.2.2 Soil 36
4.2.3 Soil-to-air Volatilization Factor 38
4.3 RADIATION CASE STUDY 38
4.3.1 Site History 40
4.3.2 At the Scoping Phase 40
4.3.3 After the Baseline Risk Assessment 43
REFERENCES 47
-------
CONTENTS (Continued)
Page
APPENDIX A ILLUSTRATIONS OF CHEMICALS THAT "LIMIT" REMEDIATON 49
APPENDLX B RISK EQUATIONS FOR INDIVIDUAL EXPOSURE PATHWAYS 51
B.I GROUND WATER OR SURFACE WATER - RESIDENTIAL LAND USE ... .51
B.I.I Ingestion 51
B.1.2 Inhalation of Volatiles 52
B.2 SOIL- RESIDENTIAL LAND USE 52
B.2. 1 Ingestion of Soil 52
B.2.2 Inhalation of Volatiles 52
B.2.3 Inhalation of Participates 53
B.3 SOIL -COMMERCIAL/INDUSTRIAL LAND USE 53
B.3.1 Ingestion of Soil 53
B.3.2 Inhalation of Volatiles 53
B.3.3 Inhalation of Participates 54
-v-
-------
EXHIBITS
Exhibit Page
1-1 RELATIONSHIP OF HUMAN HEALTH EVALUATION TO
THE CERCLA PROCESS 2
2-1 TYPICAL EXPOSURE PATHWAYS BY MEDIUM FOR
RESIDENTIAL AND COMMERCIAL/INDUSTRIAL
LAND USES 12
-------
DEFINITIONS
Term
Definition
Applicable or Relevant and
Appropriate Requirements
(ARARs)
Cancer Risk
Conceptual Site Model
Exposure Parameters
Exposure Pathway
Exposure Point
Exposure Route
Final Remedialion Levels
"Applicable" requirements are those clean-up standards, standards
of control, and other substantive environmental protection
requirements, criteria, or limitations promulgated under federal or
state law that specifically address a hazardous substance, pollutant,
contaminant, remedial action, location, or other circumstance at a
Comprehensive Environmental Response, Compensation, and
Liability Act (CERCLA) site. "Relevant and appropriate"
requirements are those clean-up standards which, while not
"applicable" at a CERCLA site, address problems or situations
sufficiently similar to those encountered at the CERCLA site that
their use is well-suited to the particular site. ARARs can be action-
specific, location-specific, or chemical-specific.
Incremental probability of an individual's developing cancer over a
lifetime as a result of exposure to a potential carcinogen.
A "model" of a site developed at scoping using readily available
information. Used to identify all potential or suspected sources of
contamination, types and concentrations of contaminants detected
at the site, potentially contaminated media, and potential exposure
pathways, including receptors. This model is also known as
"conceptual evaluation model".
Variables used in the calculation of intake (e.g., exposure duration,
inhalation rate, average body weight).
The course a chemical or physical agent lakes from a source to an
exposed organism. An exposure pathway describes a unique
mechanism by which an individual or population is exposed to
chemicals or physical agents at or originating from a site. Each
exposure pathway includes a source or release from a source, an
exposure point, and an exposure route. If the exposure point differs
from the source, a transport/exposure medium (e.g., air) or media
(in cases of intermedia transfer) also would be indicated.
A location of potential contact between an orgnism and a chemical
or physical agent.
The way a chemical or physical agent comes in contact with an
organism (i.e., by ingestion, inhalation, dermal contact).
Chemical-specific clean-up levels that are documented in the
Record of Decision (ROD). They may differ from preliminary
remediation goals (PRGs) because of modifications resulting from
consideration of various uncertainties, technical and exposure
factors, as well as all nine selection-of-remedy criteria outlined in
the National Oil and Hazardous Substances Pollution Contingency
Plan (NCP).
-------
DEFINITIONS (Continued)
Term
Definition
Hazard Index (HI)
Hazard Quotient (HQ)
''Limiting" Chemical(s)
Preliminary Remediation Goals
(PRGs)
Quantitation Limit (QL)
Reference Dose (RfD)
Risk-based PRGs
Slope Factor (SF)
Target Risk
The sum of two or more hazard quotients for multiple substances
and/or multiple exposure pathways.
The ratio of a single substance exposure level over a specified time
period to a reference dose for that substance derived from a similar
exposure period.
Chemical(s) that are the last to be removed (or treated) from a
medium by a given technology. In theory, the cumulative residual
risk for a medium may approximately equal the risk associated with
the limiting chemical(s).
Initial clean-up goals that (1) are protective of human health and
the environment and (2) comply with ARARs. They are developed
early in the process based on readily available information and are
modified to reflect results of the baseline risk assessment. They
also are used during analysis of remedial alternatives in the
remedial investigation/feasibility study (RI/FS).
The lowest level at which a chemical can be accurately and
reproducibly quantitated. Usually equal to the method detection
limit multiplied by a factor of three to five, but varies for different
chemicals and different samples.
The Agency's preferred toxicity value for evaluating potential
noncarcinogenic effects in humans resulting from contaminant
exposures at CERCLA sites. (See RAGS/HHEM Part A for a
discussion of different kinds of reference doses and reference
concentrations.)
Concentration levels set at scoping for individual chemicals that
correspond to a specific cancer risk level of 10'or an HQ/HI of 1.
They are generally selected when ARARs are not available.
A plausible upper-bound estimate of the probability of a response
per unit intake of a chemical over a lifetime. The slope factor is
used to estimate an upper-bound probability of an individual's
developing cancer as a result of a lifetime of exposure to a
particular level of a potential carcinogen.
A value that is combined with exposure and toxicity information to
calculate a risk-based concentration (e.g., PRG). For carcinogenic
effects, the target risk is a cancer risk of 10'. For noncarcinogenic
effects, the target risk is a hazard quotient of 1.
-Vlll-
-------
ACRONYMS/ABBREVIATIONS
Acronym/
Abbreviation
Definition
ARARs
CAA
CERCLA
CFR
CWA
BAG
ECAO
EF
EPA
FWQC
HEAST
HHEM
HI
HQ
HRS
IRIS
LLW
MCL
MCLG
NCP
NPL
OSWER
OERR
Applicable or Relevant and Appropriate Requirements
Clean Air Act
Comprehensive Environmental Response, Compensation, and Liability Act
Code of Federal Regulations
Clean Water Act
Exposure Assessment Group
Environmental Criteria and Assessment Office
Superfund Health Risk Technical Support Center
Exposure Frequency
U.S. Environmental Protection Agency
Federal Water Quality Criteria
Health Effects Assessment Summary Tables
Human Health Evaluation Manual
Hazard Index
Hazard Quotient
Hazard Ranking System
Integrated Risk Information System
Low-level Radioactive Waste
Maximum Contaminant Level
Maximum Contaminant Level Goal
National Oil and Hazardous Substances Pollution Contingency Plan
National Priorities List
Office of Solid Waste and Emergency Response
Office of Emergency and Remedial Response
-------
ACRONYMS/ABBREVIATIONS (Continued)
Acronyms/
Abbreviation
Definition
PA/SI
PEF
PRO
RAGS
RCRA
RfC
RfD
RI/FS
RME
ROD
RPM
SARA
SDWA
SF
TR
VF
WQS
Preliminary Assessment/Site Inspection
Particulate Emission Factor
Preliminary Remediation Goal
Risk Assessment Guidance for Superfund
Resource Conservation and Recovery Act
Reference Concentration
Reference Dose
Remedial Investigation/Feasibility Study
Reasonable Maximum Exposure
Record of Decision
Remedial Project Manager
Superfund Amendments and Reauthorization Act
Safe Drinking Water Act
Slope Factor
Target Risk
Volatilization Factor
State Water Quality Standards
-------
ACKNOWLEDGEMENTS
This manual was developed by the Toxics Integration Branch (TIB) of EPA's Office of Emergency and
Remedial Response, Hazardous Site Evaluation Division. A large number of EPA Regional and Headquarters
managers and technical staff provided valuable input regarding the organization, content, and policy
implications of the manual throughout its development. We would especially like to acknowledge the efforts
of the staff in the Regions, as well as the following offices:
Guidance and Evaluation Branch, Office of Waste Programs Enforcement;
Remedial Operations and Guidance Branch, Office of Emergency and Remedial Response;
Policy and Analysis Staff, Office of Emergency and Remedial Response;
Environmental Response Branch, Office of Emergency and Remedial Reaponse;
Office of General Counsel; and
Exposure Assessment Group, Office of Research and Development.
ICF Incorporated (under EPA Contract Nos. 68-01-7389, 68-W8-0098, and 68-03-3452), S. Cohen and
Associates (under EPA Contract No. 68-D9-0170), and Environmental Quality Management, Incorporated
(under EPA Contract No. 68-03-3482), provided technical assistance to EPA in support of the development
of this manual.
-------
PREFACE
Risk Assessment Guidance for Superfund: Volume I - Human Health Evaluation Manual
(RAGS/HHEM) Part B is one of a three-part series. Part A addresses the baseline risk assessment; Part C
addresses human health risk evaluations of remedial alternatives. Part B provides guidance on using U.S.
Environmental Protection Agency (EPA) toxicity values and exposure information to derive risk-based
preliminary remedial goals (PRGs) for a Comprehensive Environmental Response, Compensation, and
Liability Act (CERCLA) site. Initially developed at the scoping phase using readily available information, risk-
based PRGs generally are modified based on site-specific data gathered during the remedial
investigation/feasibility study (RI/FS). This guidance does not discuss the risk management decisions that are
necessary at a CERCLA site (e.g., selection of final remediation goals). The potential users of Part B are
those involved in the remedy selection and implementation process, including risk assessors, risk assessment
reviewers, remedial project managers, and other decision-makers.
This manual is being distributed as an interim document to allow for a period of field testing and
review. RAGS/HHEM will be revised in the future, and Parts A, B, and C will be incorporated into a single
final guidance document. Additional information for specific subject areas is being developed for inclusion
in a later revision. These areas include:
development of goals for additional land uses and exposure pathways;
development of short-term goals;
additional worker health and safety issues; and
determination of final remediation goals (and attainment).
Comments addressing usefulness, changes, and additional areas where guidance is needed should be
sent to:
U.S. Environmental Protection Agency
Toxics Integration Branch (OS-230)
Office of Emergency and Remedial Response
401 M Street, SW
Washington, DC 20460
Telephone 202-260-9486
FAX: 202-260-6852
-------
CHAPTER 1
INTRODUCTION
The purpose of this guidance is to assist risk
assessors, remedial project managers (RPMs), and
others involved with risk assessment and decision-
making at Comprehensive Environmental
Response, Compensation, and Liability Act
(CERCLA) sites in developing preliminary
remediation goals (PRGs). This guidance is the
second part (Part B) in the series Risk Asseswnent
Guidance for Superfund: Volume I Human
Health Evaluation Manual (RAGS/HHEM).
Part A of this series (EPA 1989d) assists in
defining and completing a site-specific baseline risk
assessment; much of the information in Part A is
necessary background for Part B. Part B provides
guidance on using U.S. Environmental Protection
Agency (EPA) toxicity values and exposure
information to derive risk-based PRGs. Initially
developed at the scoping phase using readily
available information, risk-based PRGs generally
are modified based on site-specific data gathered
during the remedial investigation/feasibility study
(RI/FS). Part C of this series (EPA 1991d) assists
RPMs, site engineers, risk assessors, and others in
using risk information both to evaluate remedial
alternatives during the FS and to evaluate the
selected remedial alternative during and after its
implementation. Exhibit 1-1 illustrates how the
three parts of RAGS/HHEM are all used during
the RI/FS and other stages of the site remediation
process.
The remainder of this introduction addresses
the definition of PRGs, the scope of Part B, the
statutes, regulations, and guidance relevant to
PRGs, steps in identifying and modifying PRGs,
the communication and documentation of PRGs,
and the organization of the remainder of this
document.
1.1 DEFINITION OF
PRELIMINARY
REMEDIATION GOALS
In general, PRGs provide remedial design staff
with long-term targets to. use during analysis and
selection of remedial alternatives. Ideally, such
goals, if achieved, should both comply with
applicable or relevant and appropriate
requirements (ARARs) and result in residual risks
that fully satisfy the National Oil and Hazardous
Substances Pollution Contingency Plan (NCP)
requirements for the protection of human health
and the environment. By developing PRGs early
in the decision-making process (before the RI/FS
and the baseline risk assessment are completed),
design staff may be able to streamline the
consideration of remedial alternatives.
Chemical-specific PRGs are concentration
goals for individual chemicals for specific medium
and land use combinations at CERCLA sites.
There are two general sources of chemical-specific
PRGs: (1) concentrations based on ARARs and
(2) concentrations based on risk assessment.
ARARs include concentration limits set by other
environmental regulations (e.g., non-zero maximum
contaminant level goals [MCLGs] set under the
Safe Drinking Water Act [SDWA]). The second
source for PRGs, and the focus of this document,
is risk assessment or risk-based calculations that
set concentration limits using carcinogenic and/or
noncarcinogenic toxicity values under specific
exposure conditions.
1.2 SCOPE OF PART B
The recommended approach for developing
remediation goals is to identify PRGs at scoping,
modify them as needed at the end of the RI or
during the FS based on site-specific information
from the baseline risk assessment, and ultimately
select remediation levels in the Record of Decision
(ROD). In order to set chemical-specific PRGs in
a site-specific context, however, assessors must
answer fundamental questions about the site.
Information on the chemicals that are present
onsite, the specific contaminated media, land-use
assumptions, and the exposure assumptions behind
pathways of individual exposure is necessary in
order to develop chemical-specific PRGs. Part B
provides guidance for considering this information
in developing chemical-specific PRGs.
-1-
-------
EXHIBIT 1-1
RELATIONSHIP OF THE HUMAN HEALTH EVALUATION
TO THE CERCLA PROCESS
CERCLA REMEDIAL PROCESS
Remedial
Investigation
Feasibility
Study
Remedy Selection
and Record of
Decision
Remedial Design/
Remedial Action
Deletion/
Five-year Review
HUMAN HEALTH EVALUATION MANUAL
PART A
Baseline Risk Assessment
PARTB
Development of Risk-based
Preliminary Remediation Goals
PARTC
Risk Evaluation of Remedial Alternatives
-2-
-------
Because Part B focuses on developing
chemical-specific PRGs based on Protection of
human health, there are important types of
information that are not considered and that may
significantly influence the concentration goals
needed to satisfy the CERCLA criteria for
selection of a remedy. For example, no.
consideration is given to ecological effects in" this
guidance. Other types of remedial action "goals"
not addressed in detail include action-specific
ARARs (e.g., technology- or performance-based
standards) and location-specific ARARs.
Throughout Part B, the term "chemical-
specific" should be understood to refer to both
nonradioactive and radioactive chemical hazardous
substances, pollutants, or contaminants. Therefore,
the process described in this guidance of selecting
and modifying PRGs at a site should be applied to
each radionuclide of potential concern.
Chapter 10 of RAGS/HHEM Part A provides
background information concerning radionuclides,
and Chapter 4 of RAGS/HHEM Part B includes
radionuclide risk-based equations and a case study
of a hypothetical radiation site.
This guidance only addresses in detail the
initial selection of risk-based PRGs. Detailed
guidance regarding other factors that can be used
to further modify PRGs during the remedy
selection Process is presented in other documents
(see Section 1.3).
1.3 RELEVANT STATUTES,
REGULATIONS, AND
GUIDANCE
This section provides relevant background on
the CERCLA statute and the regulations created
to implement the statute (i.e., the NCP). In
addition, other CERCLA guidance documents are
listed and their relationship to the site remediation
process is discussed.
1.3.1
CERCLA/SARA
CERCLA, as amended by the Superfund
Amendments and Reauthorization Act of 1986
(SARA), is the authority for EPA to take response
actions. (Throughout this guidance, reference to
CERCLA should be understood to mean
"CERCLA as amended by SARA.")
Several sections of CERCLA especially
section 121 (Clean-up Standards), set. out the
requirements and goals of CERCLA. Two
fundamental requirements are that selected
remedies be protective of human health and the
environment, and comply with ARARs. CERCLA
indicates a strong preference for the selection of
remedial alternatives that permanently and
significantly reduce the volume, toxicity, or
mobility of wastes. To the maximum extent
practicable, the selected remedial alternatives
should effect permanent solutions by using
treatment technologies. Both the law and the
regulation (see below) call for cost-effective
remedial alternatives.
1.3.2 NATIONAL CONTINGENCY PLAN
Regulations implementing CERCLA are found
in Volume 40 of the Code of Federal Regulations
(CFR), Part 300, and are referred to collectively as
the NCP. Section 300.430 of the NCP, and several
portions of the preambles in the Federal Register
(55 Federal Register 8666, March 8, 1990 and 53
Federal Register 51394, December 21, 1988),
address how the Superfund and other CERCLA
programs are to implement the Act's requirements
and goals concerning clean-up levels.
Nine criteria have been developed in the NCP
to use in selecting a remedy. These criteria are
listed in the next box. The first criterion - overall
protection of human health and the environment
~~ is the focus of this document. This criterion
coupled with compliance with ARARs are referred
to as "threshold criteria" and must be met by the
selected remedial alternative. PRGs are developed
to quantify the standards that remedial alternatives
must meet in order to achieve these threshold
criteria. See the second box on the next page for
highlights from the NCP on remediation goals.
1.3.3 GUIDANCE DOCUMENTS
There are several existing documents that
provide gudiance on related steps of the site
remediation process. These documents are
described in the box on page five. When
documents are referenced throughout this
guidance, the abbreviated titles, indicated in
parentheses after the full titles and bibliographic
information, are used.
-3-
-------
NINE EVALUATION CRITERIA FOR
ANALYSIS OF REMEDIAL ALTERNATIVES
(40 CFR 300..430(e)(9)(iii))
Threshold Criteria:
Overall Protection of Human Health and the
Environment
Compliance with ARARs
Balancing Criteria:
Long-term Effectiveness and Permanence
Reduction of Toxicity, Mobility, or Volume
Through Treatment
Short-term Effectiveness
Implementability
Cost
Modifying Criteria:
State Acceptance
Community Acceptance
1.4 INITIAL DEVELOPMENT OF
PRELIMINARY
REMEDIATION GOALS
The NCP preamble indicates that, typically,
PRGs are developed at scoping or concurrent with
initial RI/FS activities (i.e., prior to completion of
the baseline risk assessment). This early
determination of PRGs facilitates development of
a range of appropriate remedial alternatives and
can focus selection on the most effective remedy.
Development of PRGs early in the RI/FS
requires the following site-specific data:
media of potential concern;
chemicals of potential concern; and
probable future land use.
This information may be found in the preliminary
assessment/site inspection (PA/SI) reports or in the
conceptual site model that is developed prior to or
during scoping. (When a site is listed on the
National Priorities List [NPL], much of this
information is compiled during the PA/SI as part
of the Hazard Ranking System [HRS]
documentation record.) Once these factors are
known, all potential ARARs must be identified.
When ARARs do not exist, risk-based PRGs are
calculated using EPA health criteria (i.e., reference
doses or cancer slope factors) and default or site-
specific exposure assumptions.
NCP RULE HIGHLIGHTS
RISK AND REMEDIATION GOALS
(40 CFR 300.430(e)(2)]
"In developing and, as appropriate, screening
... alternatives, the lead agency shall: (i) Establish
remedial action objectives specifying contaminants
and media of concern, potential exposure
pathways, and remediation goals. Initially,
preliminary remediation goals are developed based
on readily available information, such as chemical-
specific ARARs or other reliable information.
Preliminary remediation goals should be modified,
as necessary, as more information becomes
available during the RI/FS. Final remediation
goals will be determined when the remedy is
selected. Remediation goals shall establish
acceptable exposure levels that are protective of
human health and the environment and shall be
developed by considering the following
(A) Applicable or relevant and appropriate
requirements..., and the following factors:
(1) For systemic toxicants, acceptable
exposure levels shall represent
concentration levels to which the human
population, including sensitive subgroups,
may be exposed without adverse effect
during a lifetime or part of a lifetime,
incorporating an adequate margin of
safety;
(2) For known or suspected carcinogens,
acceptable exposure levels are generally
concentration levels that represent an
excess upper-bound lifetime cancer risk
to an individual of between 10^ and 10"'
using information on the relationship
between dose and response. The 10"6
risk level shall be used as the point of
departure for determining remediation
goals for alternatives when ARARs are
not available or are not sufficiently
protective because of multiple
contaminants at a site or multiple
pathways of exposure ..."
It is important to remember that risk-based
PRGs (either at scoping or later on) are initial
guidelines. They do not establish that cleanup to
meet these goals is warranted. A risk-based
concentration, as calculated in this guidance, will
be considered a final remediation level only after
appropriate analysis in the RI/FS and ROD.
-4-
-------
GUIDANCE DOCUMENTS
Risk Assessment Guidance for Superfund: Volume I - Human Health Evaluation Manual Part A (EPA 198%)
(RAGS/HHEM Part A) contains background information and is particularly relevant for developing exposure and
toxicity assessments that are required when refining chemical-specific risk-based concentrations, and accounting
for site-specific factors such as multiple exposure pathways.
Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA (EPA 1988c) (RI/FS
Guidance) presents detailed information about implementing the RI/FS and general information on the use of
risk-based factors and ARARs in the context of the RI/FS.
Guidance on Remedial Action for Contaminated Ground Water at Superfund Sites (EPA 1988d) (Ground-water
Guidance) details some of the key issues in development, evaluation, and selection of ground-water remedial
actions at CERCLA sites.
CERCLA Compliance with Other Laws Manuals (Part I, EPA 1988a and Part II, EPA 1989a) (CERCLA
Compliance Manuals) provide guidance for complying with ARARs. Part I addresses the Resource Conservation
and Recovery Act (RCRA), the Clean Water Act (CWA), and the SDWA; Part II addresses the Clean Air Act
(CAA), other federal statutes, and state requirements.
Methods for Evaluating the Attainment of Cleanup Standards (Volume 1: Soils and Solid Wrote) (EPA 1989e)
and Methods for Evaluating the Attainment of Cleanup Standards (Volume 2: Water) (Draft, 1988, EPA
Statistical Policy Branch) (Attainment Guidance) provide guidance on evaluating the attainment of remediation
levels, including appropriate sampling and statistical procedures to test whether the chemical concentrations are
significantly below the remediation levels.
Interim Final Guidance on Preparing Superfund Decision Documents (EPA 1989b) (ROD Guidance) provides
guidance that (1) preaentd standard formats for documenting CERCLA remedial action decisions; (2) clarifies
the roles and responsibilities of EPA, states, and other federal agencies in developing and issuing decision
documents; and (3) explains how to address changes made to proposed and selected remedies.
Catalog of Superfund Program Publications, Chapter 5 (EPA 1990a) lists all ARARs guidance documents that
have been issued by EPA, shown in order of date of issuance.
Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions (EPA 1991c) provides clarification
on the role of the baseline risk assessment in developing and selecting CERCLA remedial alternatives.
Guidance for Data Useability in Risk Assessment (EPA 1990b) (Data Usability Guidance) provides guidance on
how to obtain a minimum level of quality for all environmental analytical data required for CERCLA risk
assessments. It can assist with determining sample quantitation limits (SQL-S) for chemical-specific analyses.
Guidance on Remedial Actions for Superfund Sites with PCB Contamination (EPA 1990c) describes the
recommended approach for evaluating and remediating CERCLA sites having PCB contamination.
Conducting Remedial Investigatwns/Feasibility Studies for CERCLA Municipal Landfill Sites (EPA 199la)
(Municipal Landfill Guidance) offers guidance on how to streamline both the RI/FS and the selection of a remedy
for municipal landfills.
1.5 MODIFICATION OF assessment, it is important to review the media and
PRFT TMTNARY chemicals of potential concern, future land use,
and exposure assumptions originally identified at
REMEDIATION GOALS scoping. Chemicals may be added or dropped from
the list, and risk-based PRGs may need to be
The initial list of PRGs may need to be revised recalculated using site-specific exposure factors.
as new data become available during the RI/FS. PRGs that are modified based on the results of the
Therefore, upon completion of the baseline risk baseline risk assessment must still meet the
-5-
-------
"threshold criteria" of: (1) protection of human
health and the environment and (2) compliance
with ARARs. However, the NCP also allows for
modification of PRGs during final remedy
selection based on the "balancing" and "modifying"
criteria and factors relating to uncertainty,
exposure, and technical feasibility.
Final remediation levels are not determined
until the site remedy is ready to be selected; final
remediation levels are then set out in the ROD.
PRGs are refined into final remediation goals
throughout the process leading up to remedy
selection. The ROD itself, however, should
include a statement of final clean-up levels based
on these goals, as noted in NCP section
300.430(e)(2)(i)(A). In the ROD, it is preferable
to use the term "remediation level" rather than
"remediation goal" in order to make clear that the
selected remedy establishes binding requirements.
1.6 DOCUMENTATION AND
COMMUNICATION OF
PRELIMINARY
REMEDIATION GOALS
Clear and concise communication of risk-based
PRGs among the risk assessor, the RPM, the
ARARs coordinator, site engineers, analytical
chemists, hydrogeologists, and others is important
in the development of PRGs. The involvement of
the RPM in the direction and development of
risk-based PRGs is important to ensure that
communication is facilitated and that the PRGs
are used effectively in streamlining the RJ/FS
process.
Because PRGs are most useful during the
RJ/FS (e.g., for streamlining the consideration of
remedial alternatives), it is important to
communicate them to site engineers as soon as
possible. A memorandum from either the site risk
assessor or the RPM to the site engineers and
others concerned with PRGs would be appropriate
for transmitting the initial PRGs. A brief cover
page could highlight key assumptions, as well as
changes, if any, to the standard equations (i.e.,
those presented in this guidance). Following this
brief discussion, the PRGs could be presented
using a table similar to that in Section 3.4 of this
guidance.
The RI/FS Guidance recommends that
"chemical- and/or risk-based remedial objectives
associated with the alternative should be
documented in the final RI/FS report to the extent
possible." Therefore, the RI/FS report is a logical
place to present PROS that have been modified
after the baseline risk assessment. A summary
table such as the one developed in Section 3.4 of
Part B could be incorporated into the RI/FS
following the presentation of the baseline risk
assessment. Along with the table, a discussion of
issues of particular interest, such as assumptions
used and the relationship between ARARs and
risk-based PRGs at the site, could be included.
Also, it is always appropriate to discuss how
findings of the baseline risk assessment were
incorporated into the calculation of PRGs.
1.7 ORGANIZATION OF
DOCUMENT
The remainder of this guidance is organized
into three additional chapters and two appendices.
Chapter 2 discusses the initial identification of
PROS and provides guidance for modifying
appropriate values during the RI/FS. Chapter 3
outlines equations that can be used to calculate
risk-based PRGs for residential and commercial/
industrial land uses. These equations are
presented in both "reduced" format (i.e.,
incorporating certain default assumptions discussed
in Chapter 2) and expanded format (i.e., with all
variables included so that the user of this guidance
can incorporate site-specific values). Particular
considerations regarding radionuclides are provided
in Chapter 4.
Appendix A supports several points made in
Chapter 2 by providing illustrations of remedial
alternatives where one or more chemicals "limit"
remediation and, thus, represent a major portion
of the residual risk. Appendix B lists equations for
media-specific exposure pathways, enabling the risk
assessor to derive site-specific equations that differ
from those presented in Chapter 3.
Throughout Chapters 2, 3, and 4, case studies
are presented that illustrate the process of
determining PRGs. These case studies are
contained in boxes with a shadow box appearance.
Other types of boxed information (e.g., NCP
quotes) is contained in boxes such as those in
Chapter 1, which have thicker lines on the top and
bottom than on the sides.
-6-
-------
CHAPTER 2
IDENTIFICATION OF PRELIMINARY
REMEDIATION GOALS
This chapter provides guidance on the initial
identification of PRGs during the scoping phase of
the RI/FS. As discussed in Chapter 1,
medium-specific PRGs (ARAR-based and/or
risk-based) should be identified during scoping for
all chemicals of potential concern usine readily
available information. Sections are provided in
this chapter on how to use this information to
identify media and chemicals of potential concern,
the most appropriate future land use, potential
exposure pathways, toxicity information, potential
ARARs, and risk-based PRGs. Finally, a section
is provided on the modification of PRGs.
When using PRGs developed during scoping.
the design engineers should understand that these
mav be modified significantly depending on
information gathered about the site. The
subsequent process of identifying kgv. site
contaminants, media, and other factors (i.e., during
the baseline risk assessment) may require that the
focus of the RI/FS be shifted (e.g., chemicals
without ARARs may become more or less
important). Thus, the design of remedial
alternatives should remain flexible until the
modified (i.e., more final) PRGs are available.
Prior to identifying PRGs during scoping, a
conceptual site model should be developed (see
the next box). Originally developed to aid in
planning site activities (e.g., the RI/FS), the
conceptual site model also contains information
that is valuable for identifying PRGs. For
example, it can be relied upon to identify which
media and chemicals need PRGs. More
information on developing and using a conceptual
site model during the RI/FS process can be found
in Chapter 2 of the RI/FS Guidance and Chapter 4
of RAGS/HHEM Part A.
To illustrate the process of calculating
risk-based PRGs at the scoping stage of
remediation, hypothetical CERCLA sites will be
examined in boxes in appropriate sections
throughout Chapters 2, 3, and 4. See the box on
CONCEPTUAL SITE MODEL
During project planning, the RPM gathers and
analyzes available information and develops the
conceptual site model (also called the conceptual
evaluation model). This model is used to assess
the nature and the extent of contamination. It also
identifies potential contaminant sources, potential
exposure pathways, and potential human and/or
environmental receptors. Further, this model helps
to identify data gaps and assists staff in developing
strategies for data collection. Site history and
PA/SI data generally are extremely useful sources
of information for developing this model. The
conceptual site model should include known and
suspected sources of contamination, types of
contaminants and affected media, known and
potential routes of migration, and known or
potential human and environmental receptors.
the next page for an introduction to the first site.
(The radiation case study is addressed in
Chapter 4.) The information (e.g. toxicity values')
contained in these case studies is for illustration
only, and should not be used for any other
purpose. These case studies have been simplified
(e.g., only ground water will be examined) so that
the steps involved in developing risk-based PRGs
can be readily discerned.
2.1 MEDIA OF CONCERN
During scoping, the first step in developing
PRGs is to identify the media of potential concern.
The conceptual site model should be very useful
for this step. These media can be either:
currently contaminated media to which
individuals may be exposed or through which
chemicals may be transported to potential
receptors; or
-7-
-------
CASE STUDY INTRODUCTION
The XYZ Co. site contains an abandoned
industrial facility that is adjacent to a high-
density residential neighborhood. Remnants of
drums, lagoons, and waste piles were found at
the site. Ground water in the area of the site is
used by residents as a domestic water supply.
There is also a small lake downgradient from the
site that is used by some of the local residents
for fishing and swimming.
currently uncontaminated media that may
become contaminated in the future due to
contaminant transport.
Several important media often requiring direct
remediation are ground water, surface water, soil,
and sediment. Currently, only the first three of
these media are discussed in this chapter and
addressed by the equations provided in Chapters 3
and 4. If other media that may require the
development of risk-based concentrations (e.g.,
sediments) are identified at scoping, appropriate
equations for those media should be developed.
Regional risk assessors should be consulted as
early as possible to assist with this process.
CASE STUDY IDENTIFY MEDIA
OF CONCERN
The PA/SI for the example site indicates that
ground water beneath the site is contaminated.
The source of this contamination appears to
have been approximately 100 leaking drums of
various chemicals that were buried in the soil but
have since been removed. Lagoons and waste
piles also may have contributed to the
contamination. Thus, ground water and soil are
media of concern.
Although evidence of lake water
contamination was not found during the PA/SI,
there is a reasonable possibility that it may
become contaminated in the future due to
contaminant transport either via ground-water
discharge or surface water run-off. Thus,
surface water (the lake) and sediments also may
be media of concern.
2.2 CHEMICALS OF CONCERN
This step involves developing an initial list of
chemicals for which PRGs need to be developed.
Chapters 4 and 5 of RAGS/HHEM Part A provide
important additional information on identifying
chemicals of potential concern for a site and
should be consulted prior to development of the
conceptual site model and PRGs at scping.
Initially, the list of chemicals of potential
concern should include any chemical reasonably
expected to be of concern at the site based on what
is known during scoping. For example, important
chemicals previously detected at the site, based on
the PA/SI, the conceptual site model, or other
prior investigations, generally should be included.
In addition, the list may include chemicals that the
site history indicates are likely to be present in
significant quantities, even though they may not yet
be detected. Sources of this latter type of
information include records of chemicals used or
disposed at the facility, and interviews with current
or former employees. The list also may include
chemicals that are probable degradation products
of site contaminants where these are determined to
be potential contributor of significant risk. An
environmental chemist should be consulted for
assistance in determining the probable degradation
products of potential site-related chemicals and
their persistence under site conditions. Generally,
the chemicals for which PRGs should be developed
will correspond to the list of suspected site
contaminants included in the sampling and analysis
plan.
2.3 FUTURE LAND USE
This step involves identifying the most
appropriate future land use for the site so that the
appropriate exposure pathways, parameters, and
equations (discussed in the next section) can be
used to calculate risk-based PRGs. RAGS/HHEM
Part A (Chapter 6) and an EPA Office of Solid
Waste and Emergency Response (OSWER)
directive on the role of the baseline risk
assessment in remedy selection decisions (EPA
1991b) provide additional guidance on identifying
future land use. The standard default equations
provided in Chapter 3 of Part B only address
residential and Commercial/industrial land uses. If
land uses other than these are to be assumed (e.g.,
recreational), then exposure pathways, parameters,
-------
CASE STUDY: IDENTIFY CHEMICALS
OF CONCERN
The PA/SI for the XYZ Co. site identified the
following seven chemicals in ground-water
samples: benzene, ethylbenzene, hexane,
isophorone, triallate, 1,1,2-trichloroethane, and
vinyl chloride. Therefore, these chemicals are
obvious choices for chemicals of potential
concern.
Although not detected in any of the PA/SI
samples, site history indicates that one other
solvent carbon tetrachloride also was used in
significant quantities by the facility that operated
at the site. This chemical, therefore, is added to
the list of chemicals of potential concern.
and equations will need to be developed for the
others as well.
In general, residential areas should be assumed
to remain residential. Sites that are surrounded by
operating industrial facilities can be assumed to
remain industrial areas unless there is an
indication that this is not appropriate. Lacking
site-specific information (e.g., at scoping), it may
be appropriate to assume residential land use.
This assumption will generally lead to conservative
(i.e., lower concentration) risk-based PRGs. If not
enough site-specific information is readily available
at scoping to select one future land use over
another, it may be appropriate to develop a
separate set of risk-based PRGs for each possible
land use.
When waste will be managed onsite, land-use
assumptions and risk-based PRO development
become more complicated because the assumptions
for the site itself may be different from the land
use in the surrounding area. For example, if waste
is managed onsite in a residential area, the
risk-based PRGs for the ground water beneath the
site (or at the edge of the waste management unit)
may be based on residential exposures, but the
risk-based PRGs for the site soils may be based on
an industrial land use with some management or
institutional controls.
If a land-use assumption is used that is less
conservative (i.e., leads to higher risk-based
concentrations) than another, it generally will be
necessary to monitor the future uses of that site.
For example, if residential land use is not deemed
to be appropriate for a particular site because local
zoning laws prohibit residential development, any
changes in local zoning would need to be
monitored. Such considerations should be clearly
documented in the site's ROD.
CASE STUDY IDENTIFY FUTURE
LAND USE
Based on established land-use trends, local
renovation projects, and population growth
projections in the area of the XYZ Co. site, the
most reasonable future use of the land is
determined to be residential use. Thus, site-
specific information is sufficient to show that the
generally more conservative assumption of
residential land use should serve as the basis for
development of risk-based PROS.
2.4 APPLICABLE OR RELEVANT
AND APPROPRIATE
REQUIREMENTS
Chemical-specific ARARs are evaluated as
PRGs because they are often readily available and
provide a preliminary indication about the goals
that a remedial action may have to attain. This
step involves identitying all readily available
chemical-specific potential ARARs for the
chemicals of potential concern (for each medium
and probable land use). Because at scoping it
often is uncertain which potential ARAR is the
most likely one to become the ARAR-based PRG,
all potential ARARs should be included in a
tabular summary (i.e., no potential ARAR should
be discarded). If there is doubt about whether a
value is a potential ARAR, and therefore whether
it could be used as a PRG, it should be included at
this stage.
This section summarizes the concept of
ARARs and identifies the major types of ARARs,
but provides only limited guidance on identifying
the most appropriate (likely) ARAR of all possible
ARARs to use as the chemical-specific PRG.
More detailed information about the identification
and evaluation of ARARs is available from two
important sources:
the NCP (see specifically 55 Federal Register
8741-8766 for a description of ARARs, and
-9-
-------
8712-8715 for using ARARs as PRGs; see also
53 Federal Register 51394); and
CERCLA Compliance Manuals (EPA 1988a
and 1989a).
2.4.1 CHEMICAL-, LOCATION-, AND
ACTION-SPECIFIC ARARs
The Agency has identified three general types
of federal and state ARARs:
chemical-specific, are usually health- or risk
management-based numbers or methodologies
that, when applied to site-specific conditions,
result in the establishment of numerical values
(e.g., chemical-specific concentrations in a
given medium);
location-specific, are restrictions placed upon
the concentration of hazardous substances or
the conduct of activities solely because they
are in special locations (e.g., wetlands); and
action-specific, are usually technology- or
activity-based requirements or limitations on
actions taken with respect to hazardous wastes.
This guidance primarily addresses only chemical-
specific ARARs since it focuses on the
identification of chemical-specific concentrations
that represent target goals (e.g., PRGs) for a given
medium.
2.4.2 SELECTION OF THE MOST LIKELY
ARAR-BASED PRO FOR EACH
CHEMICAL
This section briefly describes which, if any, of
several potential ARAR values for a given
chemical is generally selected as the most likely
ARAR-based PRO (and therefore the most likely
PRG at this point). Although the process for
identifying the most likely ARAR-based PRG is
specific to the medium, in general the process
depends on two considerations: (1) the
applicability of the ARAR to the site; and (2) the
comparative stringency of the standards being
evaluated. The Previously cited documents should
be carefully considered for specific
recommendations on identifying ARARs.
Ground Water. SDWA maximum contaminant
levels (MCLs), non-zero MCLGs, state drinking
water standards, and federal water quality criteria
(FWQC) are common ARARs (and, therefore,
potential PRGs) for ground water. Other types of
laws, such as state anti-degradation laws, may be
PRGs if they are accompanied by allowable
concentrations of a chemical. (Although state
anti-degradation laws that are expressed as
qualitative standards may also be potential
ARARs, they generally would not be considered
PRGs.)
As detailed in the NCP (see next box), the first
step in identifying ground-water PRGs is to
determine whether the ground water is a current
or potential source of drinking water. If the
aquifer is a potential source of drinking water,
then potential ARARs generally will include the
federal non-zero MCLG, MCL, or state drinking
water standard, and the most stringent (i.e., the
lowest concentration) is identified as the most
likely ARAR-based PRG.
NCP ON GROUND-WATER GOALS
(NCP Preamble;
55 Federal Regirter 8717, March 8, 1990)
"Ground water that is not currently a drinking
water source but is potentially a drinking water
source in the future would be protected to levels
appropriate to its use as a drinking water source.
Ground water that is not an actual or potential
source of drinking water may not require
remediation to a 10"" to 10"" level (except when
necessary to address environmental concerns or
allow for other beneficial uses;. . .)."
If the aquifer is not a potential source of
drinking water, then MCLs, MCLGs, state drinking
water requirements, or other health-based levels
generally are not appropriate as PRGs. Instead,
environmental considerations (i.e., effects on
biological receptors) and prevention of plume
expansion generally determine clean-up levels. If
an aquifer that is not a potential source of
drinking water is connected to an aquifer that is a
drinking water source, it maybe appropriate to use
PRGs to set clean-up goals for the point of
interconnection.
For chemicals without MCLs, state standards,
or non-zero MCLGs, the FWQC may be
potentially relevant and appropriate for ground
water when that ground water discharges to surface
water that is used for fishing or shellfishing.
-10-
-------
Surface Water. FWQC and state water quality
standards (WQS) are common ARARs for surface
water. An important determination for identifying
ARARs and other criteria as potential PRGs for
surface water is the current designated and future
expected use of the water body. Because surface
water potentially could serve many uses (e.g.,
drinking and fishing), several ARARs may be
identified as potential PRGs for a chemical, with
each ARAR corresponding to an identified use. A
state WQS is generally the most likely ARAR for
surface water unless a federal standard is more
stringent.
If surface water is a current or potential source
of drinking water, MCLs, state drinking water
standards, non-zero MCLGs, and FWQC are
potential ARARs. The analysis to determine
which of these drinking water standards is the most
likely ARAR-based PRG is the same as that
conducted for ground water. An FWQC based on
ingestion of water and fish might be an ARAR for
surface water used for drinking.
If the designated or future expected use of
surface water is fishing or shellfishing. and the
state has not promulgated a WQS, an FWQC
should be considered as a potential ARAR. The
particular FWQC (i.e., for water and fish ingestion
or fish ingestion alone) selected as the potential
ARAR depends on whether exposure from one or
both of the routes is likely to occur and, therefore,
on the designated use of the water body. If other
uses of the water are designated (e.g., swimming),
a state WQS may be available.
Soil. In general, chemical-specific ARARs
may not be available for soil. Certain states,
however, have promulgated or are about to
promulgate soil standards that may be ARARs and
thus may be appropriate to use as PRGs. In
addition, several EPA policies may be appropriate
to use in developing PRGs (e.g., see EPA 1990c
for guidance on PCB clean-up levels).
2.5 EXPOSURE PATHWAYS,
PARAMETERS, AND
EQUATIONS
This step is generally conducted for each
medium and land-use combination and involves
identifying the most appropriate (1) exposure
pathways and routes (e.g., residential ingestion of
drinking water), (2) exposure parameters (e.g.,
2 liters/day of water ingested), and (3) equations
(e.g., to incorporate intake). The equations
include calculations of total intake from' a given
medium and are based on the identified exposure
pathways and associated parameters. Information
gathered in this step should be used to calculate
risk-based PRGs using the default equations
identified in Chapters 3 and 4. Site-specific
equations can be derived if a different set of
exposure pathways is identified for a particular
medium; this option also is discussed in Chapters
3 and 4.
When risk-based concentrations are developed
during scoping, readily available site-specific
information may be adequate to identify and
develop the exposure pathways, parameters, and
equations (e.g., readily available information may
indicate that the exposure duration should be 40
years instead of the standard default of 30 years).
In the absence of readily available site-specific
information, the standard default information in
Chapters 3 and 4 generally should be used for the
development of risk-based PRGs.
Exhibit 2-1 lists a number of the potential
exposure pathways that might be present at a
CERCLA site. The exposure pathways included in"
the medium-specific standard default equations
(see Chapters 3 and 4) are italicized in this exhibit.
Note that Chapters 3 and 4 may not address all of
the exposure pathways of possible importance at a
given CERCLA site. For example, the
consumption of ground water that continues to be
contaminated by soil leachate is not addressed.
Guidance on goal-setting to address this exposure
pathway is currently under development by EPA.
In addition, the standard default equations do not
address pathways such as plant and animal uptake
of contaminants from soil with subsequent human
ingestion. Under certain circumstances, these or
other exposure pathways may present significant
risks to human health. The standard default
information, however, does address the quantifiable
exposure pathways that are often significant
contributors of risk for a particular medium and
land use.
Chapters 3 and 4 show how exposures from
several pathways are addressed in a single equation
for a medium. For example, in the equation for
ground water and surface water under the
residential land-use assumption, the coefficients
incorporate default parameter values for ingestion
of drinking water and inhalation of volatile s during
-11-
-------
EXHIBIT 2-1
TYPICAL EXPOSURE PATHWAYS BY MEDIUM
FOR RESIDENTIAL AND COMMERCIAL/INDUSTRIAL LAND USES'"
Medium
Exposure Pathways, Assuming:
Residential Land Use
Commercial/Industrial Land Use
Ground Water
Surface Water
Soil
Ingestion from drinking
Inhalation of volatiles
Dermal absorption from bathing
Immersion - external"
Ingestion from drinking
Inhalation of volatiles
Dermal absorption from bathing
Ingestion during swimming
Ingestion of contaminated fish
Immersion - external"
Ingestion
Inhalation of particulate
Inhalation of volatiles
Direct external exposure'
Exposure to ground water contaminated
by soil leachate
Ingestion via plant uptake
Dermal absorption from gardening
Ingestion from drinkingd
Inhalation of volatiles
Dermal absorption
Ingestion from drinkingd
Inhalation of volatiles
Dermal absorption
Ingestion
Inhalation of particuhtes
Inhalation of volatiles
Direct external exposure
Exposure to ground water contaminated
by soil leachate
Inhalation of particulate from trucks
and heavy equipment
'Lists of land uses, media, and exposure pathways are not comprehensive.
'Exposure pathways included in RAGS/HHEM Part B standard default equations (Chapters 3 and 4) are
italicized.
"Applies to radionuclides only.
"Becausce the NCP encourages protection of ground water to maximize its beneficial use, risk-based PRGs
generally should be based on residential exposures once ground water is determined to be suitable for drinking.
Similarly, when surface water will be used for drinking, general standards (e.g., ARARs) are to be achieved
that define levels protective for the population at large, not simply worker populations. Residential exposure
scenarios should guide risk-based PRG development for ingestion and other uses of potable water.
-12-
-------
household water use. Full details of parameters
used to develop each equation and a summary of
the "reduced" standard default equations are
provided in the text of these chapters.
Certain modifications of the default equations
may be desirable or necessary. For example, if an
exposure pathway addressed by an equation in
Chapter 3 seems inappropriate for the site (e.g.,
because the water contains no volatiles and,
therefore, inhalation of volatiles is irrelevant), or
if information needed for a pathway (e.g., a
chemical-specific inhalation slope factor [see
Section 2.6]) is not readily available or derivable,
then that pathway can be disregarded at this stage.
The decision about whether the risk assessor
should collect site-specific human exposure
pathway information (e.g., exposure frequency,
duration, or intake rate data) is very important.
There will frequently be methods available to
gather such information, some of which are more
expensive and elaborate than others. Determining
whether the resulting data are reasonably
representative of populations in the surrounding
area, however, is often difficult. Collecting data by
surveying those individuals most convenient or
accessible to RPMs or risk assessors may not
present a complete population exposure picture.
In fact, poorly planned data gathering efforts may
complicate the assessment process. For example,
those surveyed may come to believe that their
contributions will play a more meaningful role in
the risk assessment than that planned by the risk
assessors; this can result in significant demands on
the risk assessor's time.
Before such data collection has begun, the risk
assessor should determine, with the aid of
screening analyses, what benefits are likely to
result. Collection of the exposure data discussed
in this section generally should not be attempted
unless significant differences are likely to result in
final reasonable maximum exposure (RIME) risk
estimates. If data collection is warranted,
systematic and well-considered efforts' that
minimize biases in results should be undertaken.
Estimates of future exposures are likely to rely
heavily on conservative exposure assumptions. By
definition, these assumptions will be unaffected by
even the most extensive efforts to characterize
current population activity.
At this stage, the risk assessor, site engineer,
and RPM should discuss information concerning
the absence or presence of important exposure
pathways, because remediation goals should be
designed for specific areas of the site that a
particular remedy must address, and exposures
expected for one area of the site may differ
significantly from those expected in another area.
2.5.1 GROUND WATER/SURFACE WATER
The residential land-use default equations
presented in Chapters 3 and 4 for ground water or
surface water are based on ingestion of drinking
water and inhalation of volatile (vapor phase)
chemicals originating from the household water
supply (e.g., during dish washing, clothes
laundering, and showering).
Ingestion of drinking water is an appropriate
pathway for all chemicals with an oral cancer slope
factor or an oral chronic reference dose. For the
purposes of this guidance, however, inhalation of
volatile chemicals from water is considered
routinely only for chemicals with a Henry's Law
constant of 1 x 10"5atm-m"Vmole or greater and
with a molecular weight of less than 200 g/mole.
Before determining inhalation toxicity values for a
specific chemical (Section 2.6), it should be
confirmed that the Henry's Law constant and
molecular weight are in the appropriate range for
inclusion in the inhalation pathway for water.
Default equations addressing industrial use of
ground water are not presented. Because the NCP
encourages protection of ground water to its
maximum beneficial use, once ground water is
determined to be suitable for drinking, risk-based
PROS generally should be based on residential
exposures. Even if a site is located in an industrial
area, the ground water underlying a site in an
industrial area may be used as a drinking water
source for residents several miles away due to
complex geological interconnections.
2.5.2 SOIL
The residential land-use standard default
equations for the soil pathway are based on
exposure pathways of ingestion of chemicals in soil
or dust. The industrial land-use equations are
based on three exposure pathways: ingestion of
soil and dust, inhalation of particulate, and
inhalation of volatiles. Again, for the purposes of
this guidance, inhalation of volatile chemicals is
relevant only for chemicals with a Henry's Law
constant of 1 x 10"5atm-mVmole or greater and
-13-
-------
with a molecular weight of less than 200 g/mole.
For the inhalation pathways, in addition to toxicity
information, several chemical- and site-specific
values are needed. These values include molecular
diffusivity, Henry's Law constant, organic carbon
partition coefficient, and soil moisture content (see
Chapter 3 for details).
CASE STUDY IDENTIFY EXPOSURE
PATHWAYS, PARAMETERS,
AND EQUATIONS
For the potential residential land use
identified at the XYZ Co. site, the contaminated
ground water (one of several media of potential
concern) appears to be an important source of
future domestic water. Because site-specific
information is not initially available to develop
specific exposure pathways, parameters, and
equations, the standard default assumptions and
equations provided in Chapter 3 will be used to
calculate risk-based PRGs. Exposure pathways
of concern for ground water, therefore, are
assumed to be ingestion of ground water as
drinking water and inhalation of volatiles in
ground water during household use.
2.6 TOXICITY INFORMATION
This step involves identifying readily available
toxicity values for all of the chemicals of potential
concern for given exposure pathways so that the
appropriate slope factors (SFs; for carcinogenic
effects) and reference doses (RfDs; for
noncarcinogenic effects) are identified or derived
for use in the site-specific equations or the
standard default equations. Therefore, Chafrter 7
of RAGS/HHEM Part A should be reviewed
carefully before proceeding with this step.
The hierarchy for obtaining toxicity values for
risk-based PRGs is essentially the same as that
used in the baseline risk assessment. Briefly,
Integrated Risk Information System (IRIS) is the
primary source for toxicity information; if no
verified toxicity value is available through IRIS,
then Health Effects Assessment Summary Tables
(HEAST) is the next preferred source. When the
development of a toxicity value is required (and
appropriate data are available), consultation with
the Superfund Health Risk Assessment Technical
Support Center is warranted. EPA staff can
contact the Center by calling FTS-684-7300
(513-569-7300) or by FAX at FTS-684-7159
(513-569-7159). Others must fax to the above
number or write to:
Superfund Health Risk Technical Support
Center
Environmental Criteria and Assessment Office
U.S. Environmental Protection Agency
Mail Stop 114
26 West Martin Luther King Drive
Cincinnati, Ohio 45268
Other toxicity information that should be
obtained includes EPA's weight-of-evidence
classification for carcinogens (e.g., A, B 1) and the
source of the information (e.g., IRIS, HEAST).
Note that throughout this document, the term
hazard index (HI) is used to refer to the risk level
associated with noncarcinogenic effects. An HI is
the sum of two or more hazard quotients (HQs).
An HQ is the ratio of an exposure level of a single
substance to the RfD for that substance. Because
RfDs are generally exposure pathway-specific (e.g.,
inhalation RfD), the HQ is a single substance/
single exposure pathway ratio. An HI, on the
other hand, is usually either a single substance/
multiple exposure pathway ratio, a multiple
substance/single exposure pathway ratio, or a
multiple substance/multiple exposure pathway
ratio. In this document, however, only one
exposure pathway is included in the default
equation for some land-use and medium
combinations (e.g., residential soil). In order to
remain consistent, the term HI has been used
throughout RAGS/HHEM Part B, even though for
such a pathway, the term HQ could apply.
2.7 TARGET RISK LEVELS
This step involves identifying target risk
concentrations for chemicals of potential concern.
The standard default equations presented in
Chapters 3 and 4 are based on the following target
risk levels for carcinogenic and noncarcinogenic
effects.
For carcinogenic effects, a concentration is
calculated that corresponds to a 10"'
incremental risk of an individual developing
cancer over a lifetime as a result of exposure
to the potential carcinogen from all significant
exposure pathways for a given medium.
-14-
-------
CASE
STUDY: IDENTIFY TOXICITY INFORMATION1
Reference toxicity values for cancer and
noncancer effects
(i.e., SFs and RfDs, respectively) are required for
chemicals without ARAR-based PRGs (only the case study chemicals without ARARs are listed here). Considering
the ground-water medium only, ingestion and inhalation are exposure pathways of concern. Toxicity information
is obtained from IRIS and HEAST, and is shown
Chemical
EXPOSURE ROUTE
Hexane
Isophorone
Triallate
EXPOSURE ROUTE:
Hexane
Isophorone
Triallate
RfD
(mg/kg-day)
in the table
Source
below.
SF Weight of
(mg/kg-day) Evidence Source
INGESTION
0.06
0.2
0.013
HEAST
IRIS
IRIS
0.0039 c HEAST
INHALATION
0.04
' All information in this example is
HEAST
c HEAST
for illustration purposes only. I
. For nonearcinogenic effects, a concentration is
calculated that corresponds to an HI of 1,
which is the level of exposure to a chemical
from all significant exposure pathways in a
given medium below which it is unlikely for
even sensitive populations to experience
adverse health effects.
At scoping, it generally is appropriate to use
the standard default target risk levels described
above and discussed in the NCP. That is, an
appropriate point of departure for remediation of
carcinogenic risk is a concentration that
corresponds to a risk of ICT'for one chemical in a
particular medium. For nonearcinogenic effects,
the NCP does not specify a range, but it generally
is appropriate to assume an HI equal to 1.
2.8 MODIFICATION OF
PRELIMINARY
REMEDIATION GOALS
Upon completion of the baseline risk
assessment (or as soon as data are available), it is
important to review the future land use, exposure
assumptions, and the media and chemicals of
potential concern originally identified at scoping,
and determine whether PRGs need to be modified.
Modification may involve adding or subtracting
chemicals of concern, media, and pathways or
revising individual chemical-specific goals.
2.8.1 REVIEW OF ASSUMPTIONS
Media of Concern. As a guide to determining
the media and chemicals of potential concern, the
OSWER directive Role of the Baseline Risk
Assessment in Superfund Remedy Selection Decisions
(EPA 1991c) indicates that action is generally
warranted at a site when the cumulative
carcinogenic risk is greater than 10"4or the
cumulative nonearcinogenic HI exceeds 1 based on
RME assumptions. Thus, where the baseline risk
assessment indicates that either the cumulative
current or future risk associated with a medium is
greater than 10" or that the HI is greater than 1,
that medium presents a concern, and it generally is
appropriate to maintain risk-based PRGs for
contaminants in that medium or develop risk-based
PRGs for additional media where PRGs are not
clearly defined by ARARs.
When the cumulative current or future
baseline cancer risk for a medium is within the
range of 10"6to 10"4, a decision about whether or
not to take action is a site-specific determination.
Generally, risk-based PRGs are not needed for any
chemicals in a medium with a cumulative cancer
risk of less than 10", where an HI is less than or
-15-
-------
equal to 1, or where the PRGs are clearly defined
by ARARs. However, there maybe cases where a
medium appears to meet the protectiveness
criterion but contributes to the contamination of
another medium (e.g., soil contributing to ground-
water contamination). In these cases, it may be
appropriate to modify existing or develop new risk-
based PRGs for chemicals of concern in the first
medium, assuming that fate and transport models
can adequately predict the impacts of concern on
other media. EPA is presently developing
guidance on quantifying the impact of soil
contamination on underlying aquifers.
Chemicals of Concern. As with the initial
media of potential concern, the initial list of
specific chemicals of potential concern in a given
medium may need to be modified to reflect
increased information from the RI/FS concerning
the importance of the chemicals to the overall site
risk. Chemicals detected during the RI/FS that
were not anticipated during scoping should be
considered for addition to the list of chemicals of
potential concern; chemicals anticipated during
scoping that were not detected during the RI/FS
should be deleted from the list. Ultimately, the
identity and number of contaminants that may
require risk-based PRGs depends both on the
results of the baseline risk assessment and the
extent of action required, given site-specific
circumstances.
Following the baseline risk assessment, any
chemical that has an associated cancer risk
(current or future) within a medium of greater
than 10 'or an HI of greater than 1 should remain
on the list of chemicals of potential concern for
that medium. Likewise, chemicals that present
cancer risks of less than 10"6generally should not
be retained on the list unless there are significant
concerns about multiple contaminants and
pathways.
Land Use. After the RI/FS, one future land
use can usually be selected based on the results of
the baseline risk assessment and discussions with
the RPM. In many cases, this land use will be the
same as the land use identified at scoping. In
other cases, however, additional information from
the baseline risk assessment that was not available
at scoping may suggest modifying the initial land-
use and exposure assumptions. A qualitative
assessment should be made and should be
available from the baseline risk assessment of
the likelihood that the assumed future land use
will occur.
Exposure Pathways, Parameters, and
Equations. For exposure pathways, this process of
modifying PRGs consists of adding or deleting
exposure pathways from the medium-specific
equations in Chapters 3 and 4 to ensure that the
equation accounts for all significant exposure
pathways associated with that medium at the site.
For example, the baseline risk assessment may
indicate that dermal exposure to contaminants in
soil is a significant contributor to site risk. In this
case, the risk-based PRGs may be modified by
adding equations for dermal exposure. EPA policy
on assessing this pathway is currently under
development; the risk assessor should consult the
Superfund Health Risk Technical Support Center
(FTS-684-7300 or 513-569-7300) to determine the
current status of guidance. Likewise, when
appropriate data (e.g., on exposure frequency and
duration) have been collected during the RI/FS,
site-specific values can be substituted for the
default values in the medium-specific equations.
2.8.2 IDENTIFICATION OF
UNCERTAINTIES
The uncertainty assessment for PROS can
serve as an important basis for recommending
further modifications to the PROS prior to setting
final remediation goals. It also can be used during
the post-remedy assessment (see Section 2.8.4) to
identify areas needing particular attention.
Risk-based PRGs are associated with varied
levels of uncertainty, depending on many factors
(e.g., confidence that anticipated future land use is
correct). To place risk-based PRGs that have been
developed for a site in proper perspective, an
assessment of the uncertainties associated with the
concentrations should be conducted. This
assessment is similar to the uncertainty assessment
conducted during the baseline risk assessment (see
RAGS/HHEM Part A, especially Chapters 6, 7,
and 8). In fact, much of the uncertainty
assessment conducted for a site's baseline risk
assessment will be directly applicable to the
uncertainty assessment of the risk-based PROS.
In general, each component of risk-based
PRGs discussed in this chapter from media of
potential concern to target risk level - should be
examined, and the major areas of uncertainty
highlighted. For example, the uncertainty
-16-
-------
associated with the selected future land use should
be discussed. Furthermore, the accuracy of the
technical models used (e.g., for volatilization of
contaminants from soil) to reflect site-specific
conditions (present and future) should be
discussed. If site-specific exposure assumptions
have been made, it is particularly important to
document the data supporting those assumptions
and to assess their relevance for potentially
exposed populations.
As the chemical- and medium-specific PRGs
are developed, many assumptions regarding the
RME individual(s) are incorporated. Although
PRGs are believed to be fully protective for the
RME individual(s), the proximity of other nearby
sources of exposure (e.g., other CERCLA sites,
RCRA facilities, naturally occurring background
contamination) and/or the existence of the same
contaminants in multiple media or of multiple
chemicals affecting the same population(s), may
lead to a situation where, even after attainment of
all PRGs, protectiveness is not clearly achieved
(e.g., cumulative risks may fall outside the risk
range). The more likely it is that multiple
contaminants, pathways, operable units, or other
sources of toxicants will affect the RME
individual(s), the more likely it will be that
protectiveness is not achieved. This likelihood
should be addressed when identifying uncertainties.
2.8.3 OTHER CONSIDERATIONS IN
MODIFYING PRGs
The NCP preamble and rule state that factors
related to exposure, technical limitations, and
uncertainty should be considered when modifying
PRGs (see next two boxes) and setting final
remediation levels.
While the final remedial action objectives must
satisfy the original "threshold criteria" of protection
of human health and the environment and
compliance with ARARs, the factors in the
"balancing and modifying criteria" (listed in Section
1.3.2) also are considered in the detailed analysis
for choosing among remedial alternatives. In cases
where the alternative that represents the best
balance of factors is not able to attain cancer risks
within the risk range or an HI of 1, institutional
controls may be used to supplement treatment
and/or containment-based remedial action to
ensure protection of human health and the
environment.
NCP PREAMBLE: EXPOSURE,
TECHNICAL, AND
UNCERTAINTY FACTORS
(55 Federal Register 8717, March 8, 1990)
"Preliminary remediation goals . . . may be
revised . . . based on the consideration of
appropriate factors including, but not limited to
exposure factors, uncertainty factors, and technical
factors. Included under exposure factors are
cumulative effect of multiple contaminants, the
potential for human exposure from other pathways
at the site, population sensitivities, potential
impacts on environmental receptors, and cross-
media impacts of alternatives. Factors related to
uncertainty may include the reliability of
alternatives, the weight of scientific evidence
concerning exposures and individual and
cumulative health effects, and the reliability of
exposure data. Technical factors may include
detection/quantification limits for contaminants,
technical limitations to remediation, the ability to
monitor and control movement of contaminants,
and background levels of contaminants. The final
selection of the appropriate risk level is made when
the remedy is selected based on the balancing of
criteria...."
NCP RULE: EXPOSURE, TECHNICAL,
AND UNCERTAINTY FACTORS
(40 CFR 300.430(e)(2)(i))
"(i)... Remediation goals...shall be developed by
considering the following
"(A) Applicable or relevant and appropriate
requirements...and the following factors:
"(1) For systemic toxicants, acceptable
exposure levels...;
"(2) For known or suspected carcinogens,
acceptable exposure levels...;
"(3) Factors related to technical limitations
such as detection/quantification limits for
contaminant
"(4) Factors related to uncertainty and
"(5) Other pertinent information."
-17-
-------
Note that in the absence of ARARs, the 10"6
cancer risk "point of departure" is used as a
starting point for analysis of remedial alternatives,
which reflects EPA's preference for managing risks
at the more protective end of the risk range, other
things being equal. Use of "point of departure"
target risks in this guidance does not reflect a
presumption that the final remedial action should
attain such goals. (See NCP preamble, 55 Federal
Register 8718-9.)
2.8.4 POST-REMEDY ASSESSMENT
To ensure that protective conditions exist after
the remedy achieves all individual remediation
levels set out in the ROD, there generally will be
a site-wide evaluation conducted following
completion of a site's final operable unit (e.g.,
during the five-year review). This site-wide
evaluation should adequately characterize the
residual contaminant levels and ensure that the
post-remedy cumulative site risk is protective.
More detailed guidance on the post-remedy
assessment of site "protectiveness" is currently
under development by EPA.
-18-
-------
CHAPTER 3
CALCULATION OF RISK-BASED
PRELIMINARY REMEDIATION GOALS
This chapter presents standardized exposure
parameters, the derivation of risk equations, and
the corresponding "reduced" equations, for
calculating risk-based PRGs at scoping for the
media and land-use assumptions discussed in
Chapter 2 (i.e., ground water, surface water, and
soil for residential land use, and soil for
commercial/industrial land use). Both carcinogenic
and noncarcinogenic effects are addressed.
Standardized default exposure parameters
consistent with OSWER Directive 9285.6-03 (EPA
1991b) are used in this chapter; where default
parameters are not available in that guidance, the
references used are cited. If other media requiring
risk-based PRGs are identified during the RI/FS,
or other exposure parameters or land uses are
assumed, then appropriate equations will need to
be modified or new ones developed.
Risk-based equations have been derived in
order to reflect the potential risk from exposure to
a chemical, given a specific pathway, medium, and
land-use combination. By setting the total risk for
carcinogenic effects at a target risk level of 10"6
(the NCP's point of departure for analysis of
remedial alternatives), it is possible to solve for the
concentration term (i.e., the risk-based PRO). The
total risk for noncarcinogenic effects is set at an
HI of 1 for each chemical in a particular medium.
Full equations with pat pathway-pecific default
exposure factors are presented in boxes with
uniformly thin borders. Reduced equations are
presented in the standard boxes (i.e., thicker top
and bottom borders). At the end of this chapter,
the case study that began in Chapter 2 is
concluded (by showing how to calculate and
present risk-based PRGs).
In general, the equations described in this
chapter are sufficient for calculating the risk-based
PRGs at the scoping stage of the RI/FS. Note,
however, that these actuations are based on
standard default assumptions that may or may not
reflect site-specific conditions. When risk-based
PRGs are to be calculated based on site-specific
conditions, the risk assessor should modify the full
equations, and/or develop additional ones. Risk
equations for individual exposure pathways for a
given medium are presented in Appendix B of this
document, and may be used to develop and/or
modify the full equations. (Seethe introduction to
Appendix B for more detailed instructions.)
Before examining the calculation of risk-based
PRGs, several important points should be noted:
Use of toxicity values in the equations as
written currently assumes 100 percent
absorption efficiency. That is, for the sake of
simplicity at scoping, it is assumed that the
dose administered to test animals in toxicity
studies on which toxicity values are based was
fully absorbed. This assumption may need to
be revised in cases where toxicity values based
on route-to-route extrapolation are used, or
there are significant differences in absorption
likely between contaminants in site media and
the contaminants in the vehicle used in the
toxicity study. Chapter 7 and Appendix A in
RAGS/HHEM Part A (EPA 1989d) provide
additional details on this point.
The risk-based PRGs should contain at most
two significant figures even though some of
the parameters used in the reduced equations
carry additional significant figures.
The equations presented in this chapter
calculate risk-based concentrations using
inhalation reference doses (RfCVs) and
inhalation slope factors (SF;s). If only the
reference concentration (RfC) and/or
inhalation unit risk are available for a
particular compound in IRIS, conversion to an
RfD; and/or SF;will be necessary. Many
converted toxicity values are available in
HEAST.
All standard equations presented here
incorporate pathway-specific default exposure
-19-
-------
factors that generally reflect RME conditions.
As detailed in Chapter 8 of RAGS/HHEM
Part A (in the discussion on combining
pathway risks [Section 8.3]), RME risks from
one pathway should be combined with RME
risks from another pathway only where there
is good reason. Typically, RME from one
pathway is not likely to occur with RME from
another (unless there is a strong logical
dependent relationship between exposures
from the two pathways). If risk-based
concentrations are developed for both the
water and the soil pathways, the risk assessor
ultimately may need to adjust exposure
assumptions from one pathway (i.e., the one
with the lower RME) to less conservative
(more typical) values.
3.1 RESIDENTIAL LAND USE
3.1.1 GROUND WATER OR SURFACE
WATER
Under residential land use, risk from surface
water or ground-water contaminants is assumed to
be due primarily to direct ingestion and to
inhalation of volatiles from household water use.
Therefore, only these exposure pathways are
considered in this section. Additional exposure
pathways (e.g., dermal absorption) are possible and
may be significant at some sites for some
contaminants, while perhaps only one exposure
pathway (e.g., direct ingestion of water only) may
be relevant at others. In any case, the risk-based
PRG for each chemical should be calculated by
considering all of the relevant exposure pathways.
In the case illustrated here, risks from two
exposure pathways from ground water or surface
water are combined, and the risk-based
concentration is derived to be protective for
exposures from both pat pathways. Default risk from
ground water or surface water would be calculated
as follows ("total" risk, as used below, refers to the
combined risk for a single chemical from all
exposure pathways for a given medium):
Total risk
from water
= Risk from
ingestion of
water (adult)
+ Risk from inhala-
tion of volatiles
from household
water (adult)
equation incorporates a water-air concentration
relationship that is applicable only to chemicals
with a Henry's Law constant of greater than 1 x
10"5atm-mVmole and a molecular weight of less
than 200 g/mole. These criteria are not used to
screen out chemicals that are not of potential
concern for this exposure pathway but only to
identify those that generally should be considered
for the inhalation pathway when developing risk-
based PRGs early in the process. Chemicals that
do not meet these criteria may pose significant site
risks (and require risk-based goals) through
volatiles inhalation. The ultimate decision
regarding which contaminants should be
considered in the FS must be made on a site-
specific basis following completion of the baseline
risk assessment.
Based primarily on experimental data on the
volatilization of radon from household uses of
water, Andelman (1990) derived an equation that
defines the relationship between the concentration
of a contaminant in household water and the
average concentration of the volatilized
contaminant in air. In the derivation, all uses of
household water were considered (e.g., showering,
laundering, dish washing). The equation uses a
default "volatilization" constant (K) upper-bound
value of 0.0005 x 1000 L/m3. (The 1000 L/m3
conversion factor is incorporated into the equation
so that the resulting air concentration is expressed
in mg/m3.) Certain assumptions were made in
deriving the default constant K (Andelman 1990).
For example, it is assumed that the volume of
water used in a residence for a family of four is
720 L/day, the volume of the dwelling is 150,000 L
and the air exchange rate is 0.25 mYhr.
Furthermore, it is assumed that the average
transfer efficiency weighted by water use is 50
percent (i.e., half of the concentration of each
chemical in water will be transfered into air by all
water uses [the range extends from 30$% for toilets
to 90% for dishwashers]). See the Andelman
paper for further details.
Concentrations Based on Carcinogenic Effects.
Total risk for carcinogenic effects of certain
volatile chemicals would be calculated by
combining the appropriate inhalation and oral SFs
with the two intakes from water:
At scoping, risk from indoor inhalation of
volatiles is assumed to be relevant only for
chemicals that easily volatilize. Thus, the risk
Total = SFox Intake from
risk ingestion of
water
SF;x Intake from
inhalation of
volatiles from
water
-20-
-------
Adding appropriate parameters, and then
rearranging the equation to solve for
concentration, results in Equation (1).
Equation (!') on the next page is the reduced
version of Equation (1) using the standard default
parameters, and is used to calculate the risk-based
PRO at a prespecified cancer risk level of 106. It
combines the toxicity information of a chemical
with standard default exposure parameters for
residential land use to generate the concentration
of that chemical that corresponds to a 10"'
carcinogenic risk level due to that chemical. If
either the SF0or SF;in Equation (!') is not
available for a particular chemical, the term
containing that variable in the equation can be
ignored or equated to zero (e.g., for a chemical
that does not have SF;, the term 7.5(SF;) in
Equation (!') is ignored). If any of the default
parameter values are changed to reflect site-
specific conditions, the reduced equation cannot be
used.
RESIDENTIAL WATER - CARCINOGENIC EFFECTS
TR
SF~ x C x IR^ x EF x ED + SR x C x K x IR,
x EF x ED
BW x AT x 365 days/yr BW x AT x 365 days/yr
C (mg/L; risk-
based)
where
Parameters
C
TR
SF
SF0
BW
AT
EF
ED
IR»
IR!
K
EF x ED x C x FfSF,, x IRJ) + fSE x K x IR.)1
BW x AT x 365 days/yr
TR x BW x AT x 365 davs/vr
EF x ED x [(SFj x K x IR.) + (SFoXlRJ
Definition (units)
chemical concentration in water (mg/L)
target excess individual lifetime cancer risk (unitless)
inhalation cancer slope factor ((mg/kg-day)4)
oral cancer slope factor ((mg/kg-day)4)
adult body weight (kg)
averaging time (yr)
exposure frequency (days/yr)
exposure duration (yr)
daily indoor inhalation rate (mVday)
daily water ingestion rate (L/day)
volatilization factor (unitless)
(1)
]
Default Value
1 (Y6
10
chemical-specific
chemical-specific
70kg
70 yr
350 days/yr
30 yr
15 mVday
2 L/day
0.0005 x 1000 L/m3(Andelman 1990)
Risk-based PRO
(mg/L; TR = 10"*)
REDUCED EQUATION RESIDENTIAL WATER - CARCINOGENIC EFFECTS
1.7 xlO"4
2(SF0) + 7.5(SFO
where
SF0
SF
= oral slope factor in (mg/kg-day)"1
= inhalation slope factor in (mg/kg-day)"1
-21-
-------
Concentrations Based on Noncarcinogenic
Effects. Total HI would be calculated by
combining the appropriate oral and inhalation
RfDs with the two intakes from water:
HI = Intake from oral ingestion
RfD0
+ Intake from inhalation
RfD,
Adding appropriate parameters, and then
rearranging the equation to solve for
concentration, results in Equation (2).
Equation (2') on the next page is the reduced
version of Equation (2) using the standard default
parameters, and is used to calculate the risk-based
PRG at a prespecified HI of 1. It combines the
toxicity information of a chemical with standard
exposure parameters for residential land use to
generate the concentration of that chemical that
corresponds to an HI of 1. If either the RfD0or
RfD; in Equation (2') is not available for a
particular chemical, the term containing that
variable in the equation can be ignored or equated
to zero (e.g., for a chemical that does not have
RfD,, the term 7.5/RfD,in Equations (2') is
ignored).
RESIDENTIAL WATER - NONCARCINOGENIC EFFECTS
THI
C (mg/L; risk-
based)
where:
C x IR... x EF x ED
RfD0 x BW x AT x 365 days/yr
EF x ED x C x [d/RfD., x IRJ + Cl/RfD, x K x IR.11
BW x AT x 365 days/yr
THI x BW x AT x 365 days/yr
EF x ED x [(1/RfD, x K x IRa) + (l/RfD0 x IRJ]
C x K x IR. x EF x ED
j x BW x AT x 365 days/yr
(2)
Parameters Definition
Default Value
C chemical concentration in water (mg/L) -
THI target hazard index (unitless) 1
RfD0 oral chronic reference dose (mg/kg-day)
RfD; inhalation chronic reference dose (mg/kg-day)
BW adult body weight (kg)
AT averaging time (yr)
EF exposure frequency (days/yr)
ED exposure duration (yr)
IR, daily indoor inhalation rate (mVday)
IR, daily water ingestion rate (L/day)
K volatilization factor (unitless)
chemical-specific
chemical-speeific
70kg
30 yr (for noncarcinogens, equal to ED)
350 days/yr
30yr3
15 mVday
2 L/day
0.0005 x 1000 L/m3(Andelman 1990)
Risk-based PRG =
(mg/L; THI = 1)
REDUCED EQUATION: RESIDENTIAL WATER - NONCARCINOGENIC EFFECTS
73 (2')
[7.5/RfDi + 2/RfD0]
where:
RfD0
RfD
= oral chronic reference dose in mg/kg-day
= inhalation chronic reference dose in mg/kg-day
-22-
-------
3.1.2 SOIL
Under residential land use, risk of the
contaminant from soil is assumed to be due to
direct ingestion of soil only.
Total risk from soil
= Risk from ingestion of soil
(child to adult)
Because the soil ingestion rate is different for
children and adults, the risk due to direct ingestion
of soil is calculated using an age-adjusted ingestion
factor. The age-adjusted soil ingestion factor
(IF,oii/Mi) takes into account the difference in daily
soil ingestion rates, body weights, and exposure
durations for two exposure groups children of
one to six years and others of seven to 31 years.
Exposure frequency (EF) is assumed to be
identical for the two exposure groups. For
convenience, this factor is calculated separately as
a time-weighted soil intake, normalized to body
weight, that can then be substituted in the total
intake equation. Calculated in this manner, the
factor leads to a more protective risk-based
concentration compared to an adult-only
assumption. Note that the ingestion factor is in
units of mg-yr/kg-dav. and therefore is not directly
comparable to daily soil intake rate in units of
mg/kg-day. See the box containing Equation (3)
for the calculation of this factor.
Additional exposure pathways (e.g., inhalation
of particulate, inhalation of volatiles, ingestion of
foodcrops contaminated through airborne
particulate deposits, consumption of ground water
contaminated by soil leachate) are possible at some
sites. The risk assessor should evaluate whether
inhalation or other exposure pathways are
significant at the site. Generally, for many
undisturbed sites with vegetative cover such as
those found in areas of residential land use, air
pathways are relatively minor contributors of risk.
Greater concern for baseline risk via air pathways
exists under commercial/industrial land-use
assumptions, given the increased activity levels
likely (see Section 3.2.2). Air pathway risks also
tend to be major concerns during remedial action
(see RAGS/HHEM Part C). If these other
pathways are known to be significant at scoping,
Appendix B and/or other information should be
used to develop site-specific equations for the risk-
based PRGs.
Concentrations Based on Carcinogenic Effects.
Total risk for carcinogenic effects would be
calculated by combining the appropriate oral SF
with the intake from soil:
Total risk = SF0x Intake from ingestion of soil
Adding appropriate parameters, and then
rearranging the equation to solve for
concentration, results in Equation (4).
Equation (4') below is the reduced version of
Equation (4) using the standard default
parameters, and is used to calculate the risk-based
PRG at a prespecified cancer risk level of 106. It
combines the toxicity information of a chemical
with standard exposure parameters for residential
land use to generate the concentration of that
chemical that corresponds to a 10"'carcinogenic
risk level due to that chemical.
AGE-ADJUSTED SOIL INGESTION FACTOR
IF
Wadj (mg-yr/kg-day) = IRsoWagel^JLlDage
BWagel.6
Parameter Definition
IR,
«l/age7-31.
xED,,
(3)
BW,
age-adjusted soil ingestion factor (mg-yr/kg-day)
average body weight from ages 1-6 (kg)
average body weight from ages 7-31 (kg)
exposure duration during ages 1-6 (yr)
exposure duration during ages 7-31 (yr)
ingestion rate of soil age 1 to 6 (mg/day)
ingestion rate of soil all other ages (mg/day)
age7-31
Default Value
114 mg-yr/kg-day
15kg
70kg
6 yr
24 yr
200 mg/day
100 mg/day
-23-
-------
RESIDENTIAL SOIL - CARCINOGENIC EFFECTS
TR
C (mg/kg; risk-
based)
where:
Parameters
C
TR
SF0
AT
EF
*-*- sniM^Ai
SF. x C x KT6 kg/me x EF x
AT x 365 days/yr
TR x AT x 365 days/year
SF0 x 10"* kg/mg x EF x
Definition (units)
chemical concentration in soil (mg/kg)
target excess individual lifetime cancer risk (unitless)
oral cancer slope factor ((mg/kg-day)4)
averaging time (yr)
exposure frequency (days/yr)
age-adjusted ingestion factor (mg-yr/kg-day)
Default Value
chemical-specific
70 yr
350 days/yr
114 mg-yr/kg-day (see Equation (3))
Risk-based PRO
(mg/kg; TR = lO'6)
REDUCED EQUATION RESIDENTIAL SOIL - CARCINOGENIC EFFECTS
0.64
SR,
(4')
where:
SF0
= oral slope factor in (mg/kg-day)"1
Concentrations Based on Noncarcinogenic
Effects. Total HI would be calculated by
combining the appropriate oral RfD with the
intake from soil:
HI = Intake from ingestion
RfD0
Adding appropriate parameters, and then
rearranging the equation to solve for
concentration, results in Equation (5).
Equation (5') is the reduced version of
Equation (5) using the standard default
parameters, and is for calculating the risk-based
PRO at a prespecified HI of 1. It combines the
toxicity information of a chemical with standard
exposure parameters for residential land use to
generate the concentration of that chemical that
corresponds to an HI of 1.
3.2 COMMERCIAL/INDUSTRIAL
LAND USE
3.2.1 WATER
Once ground water is determined to be
suitable for drinking, risk-based concentrations
should be based on residential exposures. This is
because the NCP seeks to require protection of
ground water to allow for its maximum beneficial
use (see Section 2.3). Thus, under the commercial/
industrial land-use scenario, risk-based PRGs for
ground water are calculated according to
procedures detailed in Section 3.1.1. Similarly, for
surface water that is to be used for drinking, the
risk-based PRGs should be calculated for
residential populations, and not simply worker
populations.
-24-
-------
RESIDENTIAL SOIL - NONCARCEVOGENIC EFFECTS.
THI = C x IP"* kg/mg x EF x IF.H,/
RfD0 x AT x 365 days/yr
C (mg/kg; risk- =
based)
where
Parameters
C
THI
RfD0
AT
EF
THI x AT x 365 davs/vr
l/RfD0 x lO'6 kg/mg x EF x
(5)
Definition (units)
Default Value
chemical concentration in soil (mg/kg)
target hazard index (unitless) 1
oral chronic reference dose (mg/kg-day) chemical-specific
averaging time (yr) 30 yr (for noncarcinogens, equal to ED [which
is incorporated in IFsoil,,J)
exposure frequency (days/yr) 350 days/yr
age-adjusted ingestion factor (mg-yr/kg-day) 114 mg-yr/kg-day (see Equation (3))
REDUCED EQUATION: RESIDENTIAL SOIL - NONCARCEVOGENIC EFFECTS
Risk-based PRO = 2.7 x 10s (RfD0)
(mg/kg; THI = 1)
where
RfD0 = oral chronic reference dose in mg/kg-day
(5')
3.2.2 SOIL
Under commercial/industrial land use, risk of
the contaminant from soil is assumed to be due to
direct ingestion, inhalation of volatiles from the
soil, and inhalation of particulate from the soil,
and is calculated for an adult worker only. For
this type of land use, it is assumed for calculating
default risk-based PRGs that there is greater
potential for use of heavy equipment and related
traffic in and around contaminated soils and thus
greater potential for soils to be disturbed and
produce particulate and volatile emissions than in
most residential land-use areas. Additional
exposure pathways (e.g., dermal exposure) are
possible at some sites, while perhaps only one
exposure pathway (e.g., direct ingestion of soil
only) may be relevant at others; Appendix B may
be used to identify relevant exposure pathways to
be combined. In such cases, the risk is calculated
by considering all the relevant exposure pathways
identified in the RI.
In the default case illustrated below, intakes
from the three exposure pathways are combined
and the risk-based PRO is derived to be protective
for exposures from all three pathways. In this case,
the risk for a specific chemical from soil due to the
three exposure pathways would be calculated as
follows:
Total risk
from soil
= Risk from ingestion of soil (worker)
+ Risk from inhalation of volatiles from
soil (worker)
+ Risk from inhalation of particulate
from soil (worker)
It is possible to consider only exposure pathways of
site-specific importance by deriving a site-specific
risk-based PRG (e.g., using the equations in
Appendix B).
-25-
-------
Concentrations Based on Carcinogenic Effects.
Total risk for carcinogenic effects would be
calculated by combining the appropriate inhalation
and oral SFs with the three intakes from soil:
Total risk = SFn
SF;
X Intake from ingestion of soil
(worker)
Intake from inhalation of
volatiles from soil (worker)
+ SF;X Intake from inhalation of
particulate (worker)
Adding appropriate parameters, and then
rearranging the equation to solve for
concentration, results in Equation (6). As
discussed in more detail in Section 3.3.1, Equation
(6a) is used to test the results of Equation (6).
Equation (6') is the reduced version of
Equation (6) using the standard default
parameters, and is used to calculate the risk-based
PRG at a prespecified cancer risk level of 10 6. It
combines the toxicity information of a chemical
with standard exposure parameters for
commercial/industrial land use to generate the
concentration of that chemical that corresponds to
a 10 'carcinogenic risk level due to that chemical.
Concentrations Based on Noncarcinogenic
Effects. Total HI would be calculated by
combining the appropriate oral and inhalation
RfDs with the three intakes from soil:
HI = Intake from ingestion
RfD0
(Intake from inhalation of volatiles
+ and rarticulates) _
RfD,
Adding appropriate parameters, and then
rearranging the equation to solve for
concentration, results in Equation (7).
Equation (7') is the reduced version of
Equation (7) using, the standard default
parameters, and is used to calculate the risk-based
PRG at a prespecified HI of 1. It combines the
toxicity information of a chemical with standard
exposure parameters for commercial/industrial land
use to generate the concentration of that chemical
that corresponds to an HI of 1.
3.3 VOLATILIZATION AND
PARTICULATE EMISSION
FACTORS
3.3.1 SOIL-TO-AIR VOLATILIZATION
FACTOR
The volatilization factor (VF) is used for
defining the relationship between the
concentration of contaminants in soil and the
volatilized contaminants in air. This relationship
was established as a part of the Hwang and Falco
(1986) model developed by EPA's Exposure
Assessment Group (BAG). Hwang and Falco
present a method intended primarily to estimate
the permissible residual levels associated with the
cleanup of contaminated soils. This method has
been used by EPA in estimating exposures to PCBs
and 2,3,7,8-TCDD from contaminated soil (EPA
1986; EPA 1988a). One of the pathways
considered in this method is the intake by
inhalation of volatilized contaminants.
The basic principle of the Hwang and Falco
model is applicable only if the soil contaminant
concentration is at or below saturation. Saturation
is the soil contaminant concentration at which the
adsorptive limits of the soil particles and the
volubility limits of the available soil moisture have
been reached. Above saturation, pure liquid-phase
contaminant is present in the soil. Under such
conditions, the partial pressure of the pure
contaminant and the partial pressure of air in the
interstitial soil pore spaces cannot be calculated
without first knowing the mole fraction of the
contaminant in the soil. Therefore, above
saturation, the PRG cannot be accurately
calculated based on volatilization. Because of this
limitation, the chemical concentration in soil (C)
calculated using the VF must be compared with
the soil saturation concentration (C!at calculated
using Equation (6a) or (7a). If C is greater than
Csa, then the PRG is set equal to Csat.
The VF presented in this section assumes that
the contaminant concentration in the soil is
homogeneous from the soil surface to the depth of
concern and that the contaminated material is not
covered by contaminant-free soil material. For the
purpose of calculating VF, depth of concern is
defined as the depth at which a near impenetrable
layer or the permanent ground-water level is
reached.
-26-
-------
COMMERCIAL/INDUSTRIAL SOIL - CARCINOGENIC EFFECTS
TR = SE, x C x IP"* kg/mg x EF x ED x IR,H, + SF, x C x EF x ED x IR,ir x (1/VF + 1/PEF)
BW x AT x 365 days/yr BW x AT x 365 days/yr
C (mg/kg; risk- =
based)
where:
Parameters
C
TR
SF
SF0
BW
AT
EF
ED
IR
W
PEF
CMt
where
Parameters
CMt
Kd
OC
s
nn,
em
TR x BW x AT x 365 days/yr
EF x ED x [(SF0 x 10'6 kg/mg x IR^,) + (SF, x IRair x [1/VF + 1/PEF])]
(6)
Definition (units)
chemical concentration in soil (mg/kg)
target excess individual lifetime cancer risk (unitless)
inhalation cancer slope factor ((mg/kg-day1"1)
oral cancer slope factor ((mg/kg-day)")
adult body weight (kg)
averaging time (yr)
exposure frequency (days/yr)
exposure duration (yr)
soil ingestion rate (mg/day)
workday inhalation rate (mYday)
soil-to-air volatilization factor (mYkg)
particulate emission factor(mYkg)
i x s x nm) + (s x em)
Definition (units)
soil saturation concentration (mg/kg)
soil-water partition coefficient (L/kg)
organic carbon partition coefficient (L/kg)
organic carbon content of soil (fraction)
solubility (mg/L-water)
soil moisture content, expressed as a weight fraction
soil moisture content, expressed as L-water/kg-soil
Default Value
10"
chemical-specific
chemical-specific
70kg
70 yr
250 days/yr
25 yr
50 mg/day
20 mYday
chemical-specific (see Section 3.3. 1)
4.63 x 10'mYkg (see Section 3.3.2)
(6a)
Default Value
chemical-specific, or Kocx OC
chemical-specific
site-specific, or 0.02
chemical-specific
site-specific
site-specific
REDUCED EQUATION: COMMERCIAL/INDUSTRIAL SOIL - CARCINOGENIC EFFECTS
= 2.9 x IP'4
Risk-based PRO =
(mg/kg; TR = 10"*) [((5 x 10'5) x SF0) + (SF, x ((20/VF) + (4.3 x 10'9)))]
where
SF0
SF,
W
- oral slope factor in (mg/kg-day)4
= inhalation slope factor in (mg/kg-day)4
= chemical-specific soil-to-air volatilization factor in mYkg (see Section 3.3.1)
If PRG > Csatthen set PRG = Csat (where Csat = soil saturation concentration (mg/kg); see Equation (6a)
and Section 3.3.1).
-27-
-------
COMMERCIAL/INDUSTRIAL SOIL - NONCARCEVOGENIC EFFECTS
THI
C x IP"* kg/me x EF x ED x IR.^,,
RfD0 x BW x AT x 365 days/yr
C x EF x ED x IR.;, x f 1/VF + l/PEF)
RfD, x BW x AT x 365 days/yr
C (mg/kg; =
risk-based) ED x EF x [((l/RfD0) x 10* kg/mg x
THI x BW x AT x 365 days/yr
(V)
+ ((1/RfD,) x IRair x (1/VF + 1/PEF))]
where:
Parameters
C
THI
RfD0
RfD
BW
AT
EF
ED
IR-u
VF
PEF
where
Parameters
Crat
Kd
K,,,.
OC
s
nra
Definition (units')
chemical concentration in soil (mg/kg)
target hazard index (unitless)
oral chronic reference dose (mg/kg-day)
inhalation chronic reference dose (mg/kg-day)
adult body weight (kg)
averaging time (yr)
exposure frequency (days/yr)
exposure duration (yr)
soil ingestion rate (mg/day)
workday inhalation rate (ins/day)
soil-to-air volatilization factor (mVleg)
particulate emission factor (mYkg)
CMt = (Kd x s x nm) + (s x em)
Definition (units)
soil saturation concentration (mg/kg)
soil-water partition coefficient (L/kg)
organic carbon partition coefficient (L/kg)
organic carbon content of soil (fraction)
volubility (mg/L-water)
soil moisture content, expressed as a weight fraction
soil moisture content, expressed as L- water/kg- soil
Default Value
1
chemical-specific
chemical-specific
70kg
25 yr (always equal to ED)
250 days/yr
25 yr
50 mg/day
20 mVday
chemical-specific (see Section 3.3. 1)
4.63 x 10'mVkg (see Section 3.3.2)
(7a)
Default Value
chemical-specific, or Kotx OC
chemical-specific
site-specific, or 0.02
chemical-specific
site-specific
site-specific
REDUCED EQUATION: COMMERCIAL/INDUSTRIAL SOIL - NONCARCINOGENIC EFFECTS
102 (V)
Risk-based
PRO (mg/kg;
THI = 1)
where:
RfD0
RfD
VF
[(5 x 10"VRfD0) + ((1/RfDi) x ((20/VF) + (4.3 x 10'9)))]
= oral chronic reference dose in mg/kg-day
= inhalation chronic reference dose in mg/kg-day
= chemical-specific soil-to-air volatilization factor in mVkg (see Section 3.3.1)
If PRG > Caat, then set PRO = Csat, (where CM = soil saturation concentration (mg/kg); see Equation (7a) and
Section 3.3.1 ).
-28-
-------
A chemical-specific value for VF is used in the
standard default equations (Equations (6), (6 '),
(7), and (7') in Section 3.2.2) and is developed in
Equation (8). The VF value calculated using
Equation (8) has been developed for specific use in
the other equations in this guidance it may not be
applicable in other technical contexts. Equation
(8) lists the standard default parameters for
calculating VI?. If site-specific information is
available, Equation (8) may be modified to
calculate a VF that is more appropriate for the
particular site. Supporting references should be
consulted when substituting site-specific data to
ensure that the model and specific parameters can
be appropriately applied to the given site.
3.3.2 PARTICULATE EMISSION FACTOR
The particulate emission factor (PEF) relates
the contaminant concentration in soil with the
concentration of respirable particles (PM10) in the
air due to fugitive dust emissions from surface
contamination sites. This relationship is derived
by Cowherd (1985) for a rapid assessment
procedure applicable to a typical hazardous waste
site where the surface contamination provides a
relatively continuous and constant potential for
emission over an extended period of time (e.g.,
years). The particulate emissions from
contaminated sites are due to wind erosion and,
therefore, depend on the credibility of the surface
SOIL-TO-AIR VOLATILIZATION FACTOR
VF (m3/kg)
where:
a (cm2/s)
(LS x V x PHI
A
(3.14 x « x
(2 x Dd x E x K,, x 10'3 kg/g)
(8)
(P.. x
E + (RJ
Standard default parameter values that can be used to reduce Equation (8) are listed below. These represent "typical"
values as identified in a number of sources. For example, when site-specific values are not available, the length of a
side of the contaminated area (LS) is assumed to be 45 m; this is based on a contaminated area of 0.5 acre which
approximates the size of an average residential lot. The "typical" values LS, DH, and V are from EPA 1986. "Typical"
values for E, OC, and p, are from EPA 1984, EPA 1988b, and EPA 1988f. Site-specific data should be substituted
for the default values listed below wherever possible. Standard values for chemical-specific D,, H, and Kotcan be
obtained by calling the Superfund Health Risk Technical Support Center.
Parameter
VF
LS
V
DH
A
D
E
P.
T
D
H
Kd
K
oc
Definition (units)
volatilization factor (mVkg)
length of side of contaminated area (m)
wind speed in mixing zone (m/s)
diffusion height (m)
area of contamination (cm2)
effective diffusivity (ctnYs)
true soil porosity (unitless)
soil/air partition coefficient (g soil/cm3 air)
true soil density or particulate density (g/cm3)
exposure interval (s)
molecular diffusivity (ctnYs)
Henry's law constant (atm-m3/mol)
soil-water partition coefficient (cmYg)
organic carbon partition coefficient (cmYg)
organic carbon content of soil (fraction)
Default
45 m
2.25 m/s
2m
20,250,000 cm2
Dx E033
0.35
(H/Kd) x 41, where 41 is a units
conversion factor
2.65 g/cm3
7.9xl08s
chemical-specific
chemical-specific
chemical-specific, or Kocx OC
chemical-specific
site-specific, or 0.02
-29-
-------
material. The equation presented below, Equation
(9), is representative of a surface with 'unlimited
erosion potential," which is characterized by bare
surfaces of finely divided material such as sandy
agricultural soil with a large number ("unlimited
reservoir") of erodible particles. Such surfaces
erode at low wind speeds, and particulate emission
rates are relatively time-independent at a given
wind speed.
This model was selected for use in
RAGS/HHEM Part B because it represents a
conservative estimate for intake of particulate; it
is used to derive Equations (6) and (7) in Section
3.2.2.
Using the default parameter values given in
the box for Equation (9), the default PEF is equal
to 4.63 x lO'mYkg. The default values necessary
to calculate the flux rate for an "unlimited
reservoir" surface (i.e., G, Um, Ut, and F(x)) are
provided by Cowherd (1985), and the remaining
default values (i.e., for IS, V, and DH) are
"typical" values (EPA 1986). If site-specific
information is available, Equation (9) may be
modified to calculate a PEF that is more
appropriate for the particular site. Again, the
original reference should be consulted when
substituting site-specific data to ensure
applicability of the model to specific site
conditions,
PARTICULATE EMISSION FACTOR
PEF (m3/kg)
where:
Parameter
PEF
LS
V
DH
A
0.036
G
u
U
F(x)
LS x V x DH x 3600 s/hr
A
Definition (unitsl
particulate emission factor (mVkg)
width of contaminated area (m)
wind speed in mixing zone (m/s)
diffusion height (m)
area of contamination (m2)
respirable fraction (g/m2-hr)
fraction of vegetative cover (unitless)
mean annual wind speed (m/s)
equivalent threshold value of wind speed
at 10 m (m/s)
function dependent on Um/U,(unitless)
x 1000 e/ka (9)
0.036 x (1-G) x (Um/U,)3 x F(x)
Default
4.63 x 10'mVkg
45m
2.25 m/s
2m
2025 m2
0.036 g/m2-hr
0
4.5 m/s
12.8 m/s
0.0497 (determined using Cowherd 1985)
3.4 CALCULATION AND
PRESENTATION OF RISK-
BASED PRGs
The equations presented in this chapter can be
used to calculate risk-based PRGs for both
carcinogenic and noncarcinogenic effects. If both
a carcinogenic and a noncarcinogenic risk-based
PRO are calculated for a Particular chemical, then
the lower" of the two values is considered the
appropriate risk-based PRG for any given
contaminant. The case-study box below illustrates
a calculation of a risk-based PRG. A summary
table such as that in the final case-study box
should be developed to present both the risk-based
PRGs and the ARAR-based PRGs. The table
should be labeled as to whether it presents the
concentrations that were developed during scoping
or after the baseline risk assessment.
-30-
-------
CASE STUDY CALCULATE RISK-BASED PRGs'
Risk-based PRGs for ground water for isophorone, one of the chemicals detected in ground-water monitoring
wells at the site, are calculated below. Initial risk-based PRGs for isophorone (carcinogenic and noncarcinogenic
effects) are derived using Equations (!' ) and (2') in Section 3.1.1. Equations (!') and (2') combine the toxicity
information of the chemical (oral RfD of 0.2 mg/kg-day and oral SF of 0.0039 [mg/kg-day]4; inhalation values are
not available and, therefore, only the oral exposure route is considered) with standard exposure parameters. The
calculated concentrations in mg/L correspond to a target risk of 10"'and a target HQ of 1, as follows:
Carcinogenic = 1.7 x IP'4
risk-based PRO 2(SF0)
= 1.7 x 10-"
2(0.0039)
Noncarcinogenic = 73
risk-based PRO 2/RfD0
= 73
2/0.2
The lower of the two values (i.e., 0.022 mg/L) is selected as the appropriate risk-based PRG. Risk-based PRGs are
calculated similarly for the other chemicals of concern.
"All information in this example is for illustration purposes only
1
CASE STUDY: PRESENT PRGs DEVELOPED DURING SCOPING*
Site: XYZ Co. Land Use: Residential
Location: Anytown, Anystate Exposure Routes Water Ingestion, Inhalation of
Medium Ground Water Volatiles
Chemical
Benzene
Carbon Tetrachloride
Ethylbenzene
Hexane
Isophorone
Triallate
1,1,2-Trichloroethane
Vinyl chloride
Risk-based PRGs
(mg/L)*
\ O /
10"'
0.022'"
HQ = 1
0.33
7.3
0.47
ARAR-based PRG
Type
MCL
MCL
MCLG
MCL
MCLG
MCL
MCL
Concentration (mg/L)
0.005
0.005
Q 7***
0.7
0.003***
0.005
0.002
All information in this example is for illustration purposes only.
^^
These concentrations were calculated using the standard default equations in Chapter 3.
"Of the two potential risk-based PRGs for this chemical, this concentration is the selected risk-based PRG.
Of the two potential ARAR-based PRGs for this chemical, this concentration is selected as the ARAR-
based PRG. I
-31-
-------
CHAPTER 4
RISK-BASED PRGs FOR
RADIOACTIVE CONTAMINANTS
This chapter presents standardized exposure
parameters, derivations of risk equations, and
"reduced" equations for calculating risk-based
PRGs for radioactive contaminants for the
pathways and land-use scenarios discussed in
Chapter 2. In addition, a radiation site case study
is provided at the end of the chapter to illustrate
(1) how exposure pathways and radionuclides of
potential concern (including radioactive decay
products) are identified, (2) how initial risk-based
PRGs for radionuclides are calculated using
reduced equations based on information available
at the scoping phase, and (3) how risk-based PRGs
can be re-calculated using full risk equations and
site-specific data obtained during the baseline risk
assessment. Chapters 1 through 3 and Appendices
A and B provide the basis for many of the
assumptions, equations, and parameters used in
this chapter, and therefore should be reviewed
before proceeding further into Chapter 4. Also,
Chapter 10 in RAGS/HHEM Part A should be
consulted for additional guidance on conducting
baseline risk assessments at sites contaminated
with radioactive substances.
In general, standardized default exposure
equations and parameters used to calculate risk-
based PRGs for radionuclides are similar in
structure and function to those equations and
parameters developed in Chapter 3 for
nonradioactive chemical carcinogens. Both types
of risk equations:
Calculate risk-based PRGs for each carcinogen
corresponding to a pre-specified target cancer
risk level of 10"'. As mentioned in Section
2.8, target risk levels may be modified after the
baseline risk assessment based on site-specific
exposure conditions, technical limitations, or
other uncertainties, as well as on the nine
remedy selection criteria specified in the NCP.
Use standardized default exposure parameters
consistent with OSWER Directive 9285.6-03
(EPA 1991 b). Where default parameters are
not available in that guidance document, other
appropriate reference values are used and
cited.
Incorporate pathway-specific default exposure
factors that generally reflect RME conditions.
There are, however, several important areas in
which risk-based PRG equations and assumptions
for radioactive contaminants differ substantially
from those used for chemical contaminants.
Specifically, unlike chemical equations, risk
equations for radionuclides:
Accept input quantities in units of activity
(e.g., picocuries (pCi)) rather than in units of
mass (e.g., milligrams (mg)). Activity units are
more appropriate for radioactive substances
because concentrations of radionuclides in
sample media are determined by direct
physical measurements of the activity of each
nuclide present, and because adverse human
health effects due to radionuclide intake or
exposure are directly related to the amount,
type, and energy of the radiation deposited in
specific body tissues and organs.
Consider the carcinogenic effects of
radionuclides only. EPA designates all
radionuclides as Class A carcinogens based on
their property of emitting ionizing radiation
and on the extensive weight of epidemiological
evidence of radiation-induced cancer in
humans. At most CERCLA radiation sites,
potential health risks are usually based on the
radiotoxicity, rather than the chemical toxicity,
of each radionuclide present.
Use cancer slope factors that are best
estimates (i.e., median or 50th percentile
values) of the age-averaged, lifetime excess
total cancer risk per unit intake of a
radionuclide (e.g., per pCi inhaled or ingested)
or per unit external radiation exposure (e.g.,
per microRoentgen) to gamma-emitting
-33-
-------
radionuclides. Slope factors given in IRIS and
HEAST have been calculated for individual
radionuclides based on their unique chemical,
metabolic, and radiological properties and
using a non-threshold, linear dose-response
model. This model accounts for the amount
of each radionuclide absorbed into the body
from the gastrointestinal tract (by ingestion)
or through the lungs (by inhalation), the
distribution and retention of each radionuclide
in body tissues and organs, as well as the age,
sex, and weight of an individual at the time of
exposure. The model then averages the risk
over the lifetime of that exposed individual
(i.e., 70 years). Consequently, radionuclide
slope factors are not expressed as a function of
body weight or time, and do not require
corrections for gastrointestinal absorption or
lung transfer efficiencies.
Risk-based PRO equations for radionuclides
presented in the following sections of this chapter
are derived initially by determining the total risk
posed by each radioactive contaminant in a given
pathway, and then by rearranging the pathway
equation to solve for an activity concentration set
equal to a target cancer risk level of 10"'. At the
scoping phase, these equations are "reduced" and
risk-based PRGs are calculated for each
radionuclide of concern using standardized
exposure assumptions for each exposure route
within each pathway and land-use combination.
After the baseline risk assessment, PRGs can be
recalculated using full risk equations and site-
specific exposure information obtained during the
RI.
4.1 RESIDENTIAL LAND USE
4.1.1 GROUND WATER OR SURFACE
WATER
Under the residential land-use scenario, risk
from ground-water or surface water radioactive
contaminants is assumed to be due primarily to
direct ingestion and inhalation of volatile
radionuclides released from the water to indoor
air. However, because additional exposure routes
(e.g., external radiation exposure due to
immersion) are possible at some sites for some
radionuclides, while only one exposure route may
be relevant at others, the risk assessor always
should consider all relevant exposure routes and
add or modify exposure routes as appropriate.
In the case illustrated below, risks from the
two default exposure routes are combined, as
follows:
Total risk = Risk from ingestion of radionuclides
from water in water (adult)
+ Risk from indoor inhalation of volatile
radionuctides released from water
(adult)
At the scoping phase, risk from indoor
inhalation of volatile radionuclides is assumed to
be relevant only for radionuclides with a Henry's
Law constant of greater than 1 x 105atm-mVmole
and a molecular weight of less than 200 g/mole.
However, radionuclides that do not meet these
criteria also may, under certain site-specific water-
use conditions, be volatilized into the air from
water, and thus pose significant site risks (and
require risk-based goals). Therefore, the ultimate
decision regarding which contaminants should be
considered must be made by the risk assessor on a
site-specific basis following completion of the
baseline risk assessment.
Total carcinogenic risk is calculated for each
radionuclide separately by combining its
appropriate oral and inhalation SFs with the two
exposure pathways for water, as follows:
Total risk = SF0x Intake from ingestion of
of radionuclides
+ SF; x Intake from inhalation of
volatile radionuclides
By including appropriate exposure parameters for
each type of intake, rearranging and combining
exposure terms in the total risk equation, and
setting the target cancer risk level equal to 10"6,
the risk-based PRG equation is derived as shown
in Equation (10).
Equation (10 '), presented in the next box, is
the reduced version of Equation (10) based on the
standard default values listed below. It is used to
calculate risk-based PRGs for radionuclides in
water at a pre-specified cancer risk level of 10'by
combining each radionuclide's toxicity data with
the standard default values for residential land-use
exposure parameters.
After the baseline risk assessment, the risk
assessor may choose to modify one or more of the
exposure parameter default values or assumptions
-34-
-------
RW (pCi/L;
risk-based)
where:
Parameters
RW
TR
SF,
SF0
EF
ED
K
RADIONUCLIDE PRGs: RESIDENTIAL WATER - CARCINOGENIC EFFECTS
TR
EF x ED x [(SF0 x IRJ + (SFj x K x IR,)]
Definition (units')
radionuclide PRO in water (pCi/L)
target excess individual lifetime cancer risk (unitless)
inhalation slope factor (risk/pCi)
oral (ingestion) slope factor (risk/pCi)
exposure frequency (days/yr)
exposure duration (yr)
daily indoor inhalation rate (mVday)
daily water ingestion rate (L/day)
volatilization factor (unitless)
(10)
Default Value
10"
radionuclide-specific
radionuclide-specific
350 days/yr
30yr3
15 mVday
2 L/day
0.0005 x 1000 L/m3(Andelman 1990)
Risk-based PRO
(pCi/L; TR = ICT6)
REDUCED EQUATION FOR RADIONUCLIDE PRGs:
RESIDENTIAL WATER - CARCINOGENIC EFFECTS
9.5 x IP'"
2(SF0) + 7.5(8^)
(10')
where
SF0
SF,
= oral (ingestion) slope factor (risk/pCi)
= inhalation slope factor (risk/pCi)
in the risk equations to reflect site-specific
conditions. In this event, radionuclide PRGs
should be calculated using Equation (10) instead of
Equation (10').
4.1.2 SOIL
Under residential land-use conditions, risk
from radionuclides in soil is assumed to be due to
direct ingestion and external exposure to gamma
radiation. Soil ingestion rates differ for children
and adults, therefore age-adjusted ingestion rate
factors are used in the soil pathway equation.
Calculation of the risk from the external radiation
exposure route assumes that any gamma-emitting
radionuclide in soil is uniformly distributed in that
soil within a finite soil depth and density, and
dispersed in an infinite plane geometry.
The calculation of external radiation exposure
risk also includes two additional factors, the
gamma shielding factor (Se) and the gamma
exposure time factor (Te), which can be adjusted to
account for both attenuation of radiation fields due
to shielding (e.g., by structures, terrain, or
engineered barriers) and for exposure times of less
than 24-hours per day, respectively. Seis expressed
as a fractional value between O and 1, delineating
the possible risk reduction range from 0% to
100%, respectively, due to shielding. The default
value of 0.2 for Sefor both residential and
commercial/industrial land-use scenarios reflects
the initial conservative assumption of a 20%
reduction in external exposure due to shielding
from structures (see EPA 1981). Teis expressed as
the quotient of the daily number of hours an
individual is exposed directly to an external
radiation field divided by the total number of
exposure hours assumed each day for a given land-
-35.
-------
use scenario (i.e., 24 hours for residential and 8
hours for commercial/industrial). The default
value of 1 for Tefor both land-use scenarios
reflects the conservative assumptions of a 24-hr
exposure duration for residential populations (i.e.,
24/24 = 1) and an 8-hr exposure duration for
workers (i.e., 8/8 = 1). Values for both factors can
(and, if appropriate, should) be modified by the
risk assessor based on site-specific conditions.
In addition to direct ingestion of soil
contaminated with radionuclides and exposure to
external radiation from gamma-emitting
radionuclides in soil, other soil exposure routes are
possible, such as inhalation of resuspended
radioactive particles, inhalation of volatile
radionuclides, or ingestion of foodcrops
contaminated by root or leaf uptake. The risk
assessor should therefore identify all relevant
exposure routes within the soil pathway and, if
necessary, develop equations for risk-based PRGs
that combine these exposure routes.
In the case illustrated below, the risk-based
PRO is derived to be protective for exposure from
the direct ingestion and external radiation routes.
Total risk from soil due to ingestion and external
radiation is calculated as follows:
Total risk = Risk from direct ingestion of radio-
from soil nuclides in soil (child to adult)
+ Risk from external radiation from
gamma-emitting radionuclides in soil
Total risk for carcinogenic effects from each
radionuclide of potential concern is calculated by
combining the appropriate oral slope factor, SF0,
with the total radionuclide intake from soil, plus
the appropriate external radiation slope factor,
SFe, with the radioactivity concentration in soil:
Total risk = SFn
+ SF
x Intake from direct ingestion
of soil
x Concentration of gamma-
emitting radionuclides in soil
Adding appropriate parameters, then combining
and rearranging the equation to solve for
concentration, results in Equation (11).
Equation (1 1') is the reduced version of
Equation (11) based on the standard default values
listed below. Risk-based PRGs for radionuclides
in soil are calculated for a pre-specified cancer risk
level of 10-6.
The age-adjusted soil ingestion factor
(IFS .) used in Equation (11) takes into account
the difference in soil ingestion for two exposure
groups children of one to six years and all other
individuals from seven to 31 years. IF!0il/adj is
calculated for radioactive contaminants as shown in
Equation (12). Section 3.1.2 provides additional
discussion on the age-adjusted soil ingestion factor.
If any parameter values or exposure
assumptions are adjusted after the baseline risk
assessment to reflect site-specific conditions, soil
PRGs should be calculated using Equation (11).
4.2 COMMERCIAL/INDUSTRIAL
LAND USE
4.2.1 WATER
Under the commercial/industrial land use
scenario, risk-based PRGs for radionuclides in
ground water (and for radionuclides in surface
water used for drinking water purposes) are based
on residential exposures and calculated according
to the procedures detailed in Section 4.1.1 (see
Section 3.2.1 for the rationale for this approach).
Risk-based PRGs should be calculated considering
the possibility that both the worker and general
population at large may be exposed to the same
contaminated water supply.
4.2.2 SOIL
Under the commercial/industrial land use
scenario, four soil exposure routes direct
ingestion, inhalation of volatile radionuclides,
inhalation of resuspended radioactive particulate,
and external exposure due to gamma-emitting
radionuclides are combined to calculate risk-
based radionuclide PRGs in soil for adult worker
exposures. Additional exposure routes (e.g.,
ingestion of foodcrops contaminated by
radionuclide uptake) are possible at some sites,
while only one exposure route (e.g., external
radiation exposure only) may be relevant at others.
The risk assessor should therefore consider and
combine all relevant soil exposure routes, as
necessary and appropriate, based on site-specific
conditions.
-36-
-------
RADIONUCLIDE PRGs: RESIDENTIAL SOIL - CARCINOGENIC EFFECTS
Total risk = RS x [(SF0 x IQ-'g/mg x EF x IF^,^) + (SFe x 103g/kg x ED x D x SD x (l-Se) x Te)]
TR (11)
RS(pCi/g;
risk-based)
where
Parameters
RS
TR
SF0
SFe
EF
ED
D
SD
(SF0 x 10'3 x EF x IF^dj) + (SFe x 103 x ED x D x SD x (l-Se) x TJ
Definition (units)
radionuclide PRO in soil (pCi/g)
target excess individual lifetime cancer risk (unitless)
oral (ingestion) slope factor (risk/pCi)
external exposure slope factor (risk/yr per pCi/m2)
exposure frequency (days/yr)
exposure duration (yr)
age-adjusted soil ingestion factor (mg-yr/day)
depth of radionuclides in soil (m)
soil density (kg/m3)
gamma shielding factor (unitless)
gamma exposure time factor (unitless)
Default Value
10-'
radionuclide-specific
radionuclide-specific
350 days/yr
30 yr
3600 mg-yr/day (see Equation 12))
O.lm
1.43xl03kg/m3
0.2 (see Section 4.1.2)
1 (see Section 4.1.2)
Risk-based PRO
(pCi/g; TR = 10-*)
REDUCED EQUATION FOR RADIONUCLIDE PRGs:
RESIDENTIAL SOIL - CARCINOGENIC EFFECTS
= 1x10-'
1.3 x 103 (SF0) + 3.4 x 10* (SFe)
where:
SF0
SFe
= oral (ingestion) slope factor (risk/pCi)
= external exposure slope factor (risk/yr per pCi/m2)
(11')
AGE-ADJUSTED SOIL INGESTION FACTOR
IF,^ (mg-yr/day)
where:
Parameters
IF,oil/adj
IR«oil/age 1-6
IRwil/age 7-31
ED»w
EDage 7-31
(M*soil/age 1-6 x EDage M) + (IRjoji/agg 7.J1 X
Definition (units)
age-adjusted soil ingestion factor (mg-yr/day)
ingestion rate of soil ages 1-6 (mg/day)
ingestion rate of soil ages 7-31 (mg/day)
exposure duration during ages 1-6 (yr)
exposure duration during ages 7-3 1 (yr)
EDage7.31) (12)
Default Value
3600 mg-yr/day
200 mg/day
100 mg/day
6yr
24 yr
-37-
-------
In the case illustrated below, total risk from
radionuclides in soil is calculated as the summation
of the individual risks from each of the four
exposure routes listed above:
Total risk = Risk from direct ingestion of radio-
from soil nuclides in soil (worker)
+ Risk from inhalation of volatile
radionuclides (worker)
+ Risk from inhalation of resuspended
radioactive particulate (worker)
+ Risk from external radiation from
gamma-emitting radionuclides (worker)
Total risk for carcinogenic effects for each
radionuclide is calculated by combining the
appropriate ingestion, inhalation, and external
exposure SF values with relevant exposure
parameters for each of the four soil exposure
routes as follows:
Total = SF0x Intake from direct ingestion of
risk radionuclides in soil (worker)
+ SF; X Intake from inhalation of
volatile radionuclides (worker)
+ SF; X Intake from inhalation of resus-
pended radioactive particulate
(worker)
+ SFex Concentration of gamma-emitting
radionuclides in soil (worker)
Adding appropriate parameters, and then
combining and rearranging the equation to solve
for concentration, results in Equation (13).
Equation (13') below is the reduced version of
Equation (13) based on the standard default values
below and a pre-specified cancer risk level of 106.
It combines the toxicity information of a
radionuclide with standard exposure parameters for
commercial/industrial land use to generate the
concentration of that radionuclide corresponding
to a 10"' carcinogenic risk level due to that
radionuclide.
If any parameter default values or assumptions
are changed after the baseline risk assessment to
reflect site-specific conditions, radionuclide soil
PRGs should be derived using Equation (13).
4.2.3 SOIL-TO-AIR
FACTOR
VOLATILIZATION
The VF, defined in Section 3.3.1 for chemicals,
also applies for radioactive contaminants with the
following exceptions.
Most radionuclides are heavy metal elements
and are non-volatile under normal, ambient
conditions. For these radionuclides, VF values
need not be calculated and the risk due to the
inhalation of volatile forms of these nuclides
can be ignored for the purposes of
determining PRGs.
A few radionuclides, such as carbon-14 (C-14),
tritium (H-3), phosphorus-32 (P-32), sulfur-35
(S-35), and other isotopes, are volatile under
certain chemical or environmental conditions,
such as when they are combined chemically
with volatile organic compounds (i.e., the so-
called radioactively-labeled or "tagged" organic
compounds), or when they can exist in the
environment in a variety of physical forms,
such as C-14 labeled carbon dioxide (C02) gas
and tritiated water vapor. For these
radionuclides, VF values should be calculated
using the Hwang and Falco (1986) equation
provided in Section 3.3.1 based on the
chemical species of the compound with which
they are associated.
The naturally occurring, non-volatile
radioisotopes of radium, namely Ra-226 and
Ra-224, undergo radioactive decay and form
inert, gaseous isotopes of radon, i.e., Rn-222
(radon) and Rn-220 (thoron), respectively.
Radioactive radon and thoron gases emanate
from their respective parent radium isotopes
in soil, escape into the air, and can pose
cancer risks if inhaled. For Ra-226 and Ra-
224 in soil, use the default values shown in the
box on page 40 for VF and for SF;in
Equation (12) and Equation (12 ').
4.3 RADIATION CASE STUDY
This section presents a case study of a
hypothetical CERCLA radiation site, the ACME
Radiation Co. site, to illustrate the process of
calculating pathway-specific risk-based PRGs for
radionuclides using the risk equations and
assumptions presented in the preceding sections of
this chapter._ The radiation site case study is
modeled after the XYZ Co. site study discussed in
-38-
-------
RADIONUCLIDE PRGs: COMMERCIAL/EVDUSTRIAL SOIL - CARCINOGENIC EFFECTS
Total = RS x ED x [(SF0 x 10Jg/tag x EF x IRwi,) + (SF, x itfgfcg x EF x IR8ir x 1/VF)
risk
i x lOfykg x EF x IR^ x 1/PEF) + (SFe x lOfykg x D x SD x (l-Se) x Te)]
TR _
x (1/VF + 1/PEF) +
RS =
(pCi/g; ED x [(SF^lO-'xEFxIR,,,,,) +
risk-based)
where.
Parameters
RS
TR
EF
ED
VF
PEF
D
SD
S,
Te
Definition (units)
radionuclide PRO in soil (pCi/g)
target excess individual lifetime cancer risk (unitless)
inhalation slope factor (risk/pCi)
oral (ingestion) slope factor (risk/pCi)
external exposure slope factor (risk/yr per pCi/m2)
exposure frequency (days/yr)
exposure duration (yr)
workday inhalation rate of air (mVday)
daily soil ingestion rate (mg/day)
soil-to-air volatilization factor (mVkg)
particulate emission factor (mYkg)
depth of radionuclides in soil (m)
soil density (kg/m3)
gamma shielding factor (unitless)
gamma exposure factor (unitless)
(13)
Default Value
10"
radionuctide-specific
radionuclide-specific
radionuclide-specific
250 days/yr
25 yr
20 mVday
50 mg/day
radionuclide-specific (see Section 4.2.3)
4.63 x 10'mVkg (see Section 3.3.2)
O.lm
1.43xl03kg/m3
0.2 (see Section 4.1.2)
1 (see Section 4.1.2)
Risk-based PRO =
REDUCED EQUATION FOR RADIONUCLIDE PRGs:
COMMERCIAL/INDUSTRIAL SOIL - CARCINOGENIC EFFECTS*
Ix 10*
(pCi/g; TR = KT6) [(3.1 x 102(SF0)) + ((1.3 x 108/VF + 2.7 x 10'2) (SFj)) + (2.9 x 10* (SFe))]
(13')
where:
SF0
SF,
SFe
VF
= oral (ingestion) slope factor (risk/pCi)
= inhalation slope factor (risk/pCi)
= external exposure slope factor (risk/yr per pCi/m2)
= radionuclide-specific soil-to-air volatilization factor in mVkg (see Section 3.3. 1)
*NOTE See Section 4.2.3 when calculating PROS for Ra-226 and Ra-224.
Chapters 2 and 3. It generally follows a two-phase
format which consists of a "at the scoping stage"
phase wherein risk-based PRGs for radionuclides
of potential concern are calculated initially using
reduced equations based on PA/SI data, and then
a second, "after the baseline risk assessment" phase
wherein radionuclide PRGs are recalculated using
full equations and modified site-specific parameter
values based on RI/FS data.
Following an overview of the history and
current status of the site presented in Section 4.3.1,
Section 4.3.2 covers a number of important steps
taken early in the scoping phase to calculate
preliminary risk-based PRGs assuming a specific
-39-
-------
SOIL DEFAULT VALUES FOR VF AND SF,
FOR Ra-226 AND Ra-224
Radium
Default VF
Value
/ pCi/ltgRa \
\ pCi/nr* Rn*/
Inhalation
slope
Factor SF:
(risk/pCi)**
Ra-226
Ra-224
200
LIE-11
4.7E-11
* Calculated using values taken from NCRP
1976 and UNSCEAR 1982 Assumptions: (1) an
average Ra-226 soil concentration of 1 pCi/g
associated with an average ambient Rn-222 air
concentration of 120 pCi/m3and (2) an average
Ra-224 soil concentration of 1 pCi/g associated
with an average ambient Rn-220 air concentration
of 5 pCi/m3.
** Slope factor values are for Rn-222 (plus
progeny) and for Rn-220 (plus progeny).
land-use scenario. Section 4.3.3 then discusses how
initial assumptions and calculations can be
modified when additional site-specific information
becomes available.
4.3.1 SITE HISTORY
The ACME Radiation Co. site is an
abandoned industrial facility consisting of a large
factory building situated on ten acres of land
surrounded by a high-density residential
neighborhood. Established in 1925, the ACME
Co. manufactured luminous watch dials and gauges
using radium-based paint and employed
approximately 100 workers, mostly women. With
the declining radium market, ACME phased out
dial production and expanded its operations in
1960 to include brokering (collection and disposal)
of low-level radioactive waste (LLW). After the
company was issued a state license in 1961, ACME
began receiving LLW from various nearby
hospitals and research laboratories. In 1975, acting
on an anonymous complaint of suspected
mishandling of radioactive waste, state officials
visited the ACME Co. site and cited the company
for numerous storage and disposal violations.
After ACME failed to rectify plant conditions
identified in initial and subsequent citations, the
state first suspended, and then later revoked its
operating license in 1978. Around the same time,
officials detected radium-226 (Ra-226)
contamination at a few neighboring locations off
site. However, no action was taken against the
company at that time. When ACME filed for
bankruptcy in 1985, it closed its facility before
completing cleanup.
In 1987, the state and EPA conducted an
aerial gamma survey over the ACME Radiation
Co. site and surrounding properties to investigate
the potential extent of radioactive contamination
in these areas. The overflight survey revealed
several areas of elevated exposure rate readings,
although individual gamma-emitting radionuclides
could not be identified. When follow-up ground
level surveys were performed in 1988, numerous
"hot spots" of Ra-226 were pinpointed at various
locations within and around the factory building.
Three large soil piles showing enhanced
concentrations of Ra-226 were discovered along
the southern border. Approximately 20 rusting
drums labelled with LLW placards also were
discovered outside under a covered storage area.
Using ground-penetrating radar, EPA detected
subsurface magnetic anomalies in a few locations
within the property boundary which suggested the
possibility of buried waste drums. Based on
interviews with people living near the site" and with
former plant workers, the state believes that
radium contaminated soil may have been removed
from the ACME site in the past and used locally
as fill material for the construction of new homes
and roadbeds. Site access is currently limited (but
not entirely restricted) by an existing security
fence.
In 1988, EPA's regional field investigation
team completed a PA/SI. Based on the PA/SI
data, the ACME Radiation Co. site scored above
28.50 using the HRS and was listed on the
National Priorities List in 1989. Early in 1990, an
RI/FS was initiated and a baseline risk assessment
is currently in progress.
4.3.2 AT THE SCOPING PHASE
In this subsection, several steps are outlined to
show by example how initial site data are used at
the scoping phase to calculate risk-based PRGs for
radionuclides in specific media of concern.
Appropriate sections of Chapters 2 and 3 should
be consulted for more detailed explanations for
each step considered below.
-40-
-------
Identify Media of Concern. A large stream
"runs along the western border of the site and feeds
into a river used by some of the local residents for
fishing and boating. Supplemental water intake
ducts for the municipal water treatment plant are
located approximately 300 yards downriver, and the
site is situated over an aquifer which serves as the
primary drinking water supply for a community of
approximately 33,000 people.
Analyses of ground water, soil, and stream
sediment samples taken during the PA/SI revealed
significant levels of radionuclide contamination.
Potential sources of contamination include the soil
piles, process residues in soil, and radionuclides
leaking from buried drums. Air filter samples and
surface water samples from the stream and river
showed only background levels of activity.
(Background concentrations were determined from
analyses conducted on a limited number of air,
ground water, surface water, and soil samples
collected approximately one mile from the site.)
The data show that the media of potential
concern at this site include ground water and soil.
Although stream water and river water were not
found to be contaminated, both surface water
bodies may become contaminated in the future due
to the migration of radionuclides from sediment,
from the exposed soil piles, or from leaking drums.
Thus, surface water is another medium of potential
concern.
For simplicity, only soil will be discussed as
the medium of concern during the remainder of
this case study. Procedures discussed for this
medium can nevertheless be applied in a similar
manner to all other media of concern.
Identify Initial List of Radionuclides of
Concern. The PA/SI for the ACME Radiation Co.
site identified elevated concentrations of five
radionuclides in soil (Ra-226, tritium (H-3),
carbon-14 (C- 14), cesium (CS-137), and strontium
(Sr-90)). These comprise the initial list of
radionuclides of potential concern.
Site records indicate that radioisotopes of
cobalt (Co-60), phosphorus (P-32), sulfur (S-35),
and americium (Am-241 and Am-243) were
included on the manifests of several LLW drums in
the storage area and on the manifests of other
drums suspected to be buried onsite. Therefore,
although not detected in any of the initial soil
samples analyzed, Co-60, P-32, S-35, Am-241, and
Am-243 are added to the list for this medium
because of their potential to migrate from leaking
buried drums into the surrounding soil.
Identify Probable Land Uses. The ACME
Radiation Co. site is located in the center of a
rapidly developing suburban community comprised
of single and multiple family dwellings. The area
immediately encircling the site was recently re-
zoned for residential use only; existing commercial
and light industrial facilities are currently being
relocated. Therefore, residential use is determined
to be the most reasonable future land use for this
site.
Identify Exposure Pathways, Parameters, and
Equations. During the scoping phase, available
site data were neither sufficient to identify all
possible exposure pathways nor adequate enough
to develop site-specific fate and transport
equations and parameters. Therefore, in order to
calculate initial risk-based PRGs for radionuclides
of potential concern in soil, the standardized
default soil exposure equation and assumptions
provided in this chapter for residential land use in
Section 4.1.2 are selected. (Later in this case study,
examples are provided to illustrate how the full
risk equation (Equation (11)) and assumptions are
modified when baseline risk assessment data
become available.)
For the soil pathway, the exposure routes of
concern are assumed to be direct ingestion of soil
contaminated with radionuclides and exposure to
external radiation from gamma-emitting
radionuclides. Again, although soil is the only
medium discussed throughout this case study,
exposure pathways, parameters, equations, and
eventually risk-based concentrations would need to
be identified and developed for all other media and
exposure pathways of potential concern at an
actual site.
Identify Toxicity Information. To calculate
media-specific risk-based PRGs, reference toxicity
values for radiation-induced cancer effects are
required (i.e., SFs). As stated previously, soil
ingestion and external radiation are the exposure
routes of concern for the soil pathway. Toxicity
information (i.e., oral, inhalation, and external
exposure SFs) for all radionuclides of potential
concern at the ACME Radiation Co. site are
obtained from IRIS or HEAST, and are shown in
the box on the following page.
-41-
-------
RADIATION CASE STUDY: 1
TOXICITY INFORMATION FOR RADIONUCLIDES OF POTENTIAL CONCERN*
Radioactive
Hal- life
Radionuclides (yr)
H-3
C-14
P-32
S-35
Co-60
Sr-90
Cs-137
Ra-226
Am-241
Am-243
* Sources:
NA = Not
12
5730
0.04
0.24
5
29
30
1600
432
7380
HEAST and Federal Guidance
ICRP Inhalation Ingestion
Decay Lung Slope Factor Slope Factor
Mode Classification (risk/pCi) risk/pCi
beta «
O
beta o
&
beta D
beta D
beta/gamma Y
beta D
beta D
alpha/gamma w
alpha/gamma w
alpha/gamma w
Report No. 11. All information in
7.8E-14
6.4E-15
3.013-12
1.9E-13
I.6E-10
5.6E-11
1.9E-11
3.0E-09
4.0E-08
4.0E-08
this example is for illustration only.
applicable (i.e., these radionuclides are not garnma-emitters and the direct radiation exposure pathway
5.5E-14
9.1E-13
3.5E-12
2.2E-13
1.5E-11
3.3E-11
2.8E-11
1 .2E-10
3.1E-10
3.1E-10
can be ignored).
External Exposure 1
Slope Factor 1
(risk/yr per pCi/m2) 1
NA I
NA 1
NA 1
NA 1
1.3E-10 1
NA 1
NA 1
4.2E-13 1
1.6E-12 1
3.6E-12 1
1
1
-------
Calculate Risk-based PRGs. At this Step, risk-
based PRGs are calculated for each radionuclide of
potential concern using the reduced risk Equation
(11') in Section 4.1.2, SF values obtained from
IRIS and HEAST, and standardized default values
for parameters for the residential land-use
scenario. To calculate the risk-based PRO for Co-
60 at a pre-specified target risk level of 10"', for
example, its ingestion SF of 1.5 x 10"" and its
external exposure SF of 1.3 x 10"10are substituted
into Equation (11 '), along with the standardized
default values, as follows:
Risk-based PRO = Ix 1Q-*
for Co-60 1.3 x 103 (SF0) + 3.4 x 10* (SFe)
(pCi/g; TR = 10-*)
where:
SF0= oral (ingestion) slope factor for Co-60 = 1.5 x
10-"(risk/pCi)
SF = external exposure slope factor for Co-60 = 1.3
xlOIO(nsk/yrperpCi/m2)
Substituting the values for SF0and SFefor Co-60
into Equation (1 1') results in:
Risk-based PRO for Co-60 (pCi/g; TR = l(r*) =
1x10"*
[(1.3 x 103)(1.5 x lO'11) + (3.4 x 10*)(1.3 x 10'10)]
= 0.002 pCi of Co-60/g of soil
In a similar manner, risk-based PRGs can be
calculated for all other radionuclides of concern in
soil at the ACME Radiation Co. site. These PRGs
are presented in the next box.
4.3.3 AFTER THE BASELINE RISK
ASSESSMENT
In this subsection, several steps are outlined
which demonstrate how site-specific data obtained
during the baseline risk assessment can be used to
recalculate risk-based PRGs for radionuclides in
soil. Appropriate sections of Chapters 2 and 3
should be consulted for more detailed explanations
for each step considered below.
Review Media of Concern. During the RI/FS,
gamma radiation surveys were conducted in the
yards of several homes located within a two-block
radius of the ACME Radiation Co. site. Elevated
exposure rates, ranging from approximately two to
four times the natural background rate, were
RADIATION CASE STUDY:
INITIAL RISK-BASED PRGs FOR
RADIONUCLIDES IN SOIL*
Risk-based Soil PRO (pCi/g)
H-3
Sr-90 (only)
P-32
S-35
C-14
Co-60
Cs-137 (only)
Ra-226 (only)
Am-241
Am-243 (only)
* Calculated for illustration only using Equation
(11') in Section 4.1.2. Values have been rounded
off.
measured on properties immediately bordering the
site. Measurements onsite ranged from 10 to 50
times background. In both eases, enhanced soil
concentrations of Ra-226 (and decay products) and
several other gamma-emitting radionuclides were
discovered to be the sources of these elevated
exposure rates. Therefore, soil continues as a
medium of potential concern.
Modify List of Radionuclides of Concern.
During scoping, five radionuclides (Ra-226, H-3,
C-14, (Cs-137, and Sr-90) were detected in elevated
concentrations in soil samples collected at the
ACME Radiation Co. site. These made up the
initial list of radionuclides of potential concern.
Although not detected during the first round of
sampling, five additional radionuclides (P-32, S-35,
Co-60, Am-241, and Am-243) were added to this
list because of their potential to migrate from
buried leaking drums into the surrounding soil.
With additional RI/FS data, some
radionuclides are now added to the list, while
others are dropped. For example, soil analyses
failed to detect P-32 (14-day half-life) or S-35 (87-
day half-life) contamination. Decay correction
calculations strongly suggest that these
radionuclides should not be present onsite in
detectable quantities after an estimated burial time
of 30 years. Therefore, based on these data, P-32
and S-35 are dropped from the list. Soil data also
confirm that decay products of Ra-226, Sr-90, Cs-
137, and Am-243 (identified in the first box below)
-43-
-------
are present in secular equilibrium (i.e., equal
activity concentrations) with their respective parent
isotopes.
Assuming secular equilibrium, slope factors for
the parent isotope and each of its decay series
members are summed. Parent isotopes are
designated with a " +D" to indicate the composite
slope factors of its decay chain (shown in bold face
in the second box below). Thus, Ra-226+D, Sr-
90+D, Cs-137+D, and Am-243+D replace their
respective single-isotope values in the list of
radionuclides of potential concern, and their
composite SFs are used in the full soil pathway
equation to recalculate risk-based concentrations.
RADIATION CASE STUDY DECAY PRODUCTS
Parent Radionuclide
Ra-226
Sr-90
Cs-137
Am-243
Decay Product(s) (Half-life)
Rn-222 (4 days), Po-218 (3 mm), Pb-214 (27 mm), Bi-214 (20
rein), Po-214 (<1 s), Pb-210 (22 yr), Bi-210 (5 days), Po-210
(138 days)
Y-90(14hr)
Ba-137m (2 min)
Np-239 (2 days)
RADIATION CASE STUDY SLOPE
FACTORS FOR
1
DECAY SERIES'
Slope Factors
Decay Series
Ra-226
Rn-222
Po-218
Pb-214
Bi-214
Po-214
Pb-210
Bi-210
Po-210
Ra-226+D
Sr-90
Y-90
Sr-90+D
Cs-137
Ba-137m
Cs-137+D
Am-243
Np-239
Am-243+D
"All information in this exanm
Inhalation
3.0E-09
7.2E-13
5.8E-13
2.9E-12
2.2E-12
2.8E-19
1.7E-09
8.1E-11
2.7E-09
7.5E-09
5.6E-11
5.5E-12
6.2E-11
1.9E-11
6.0E-16
1.9E-11
4.0E-08
1.5E-12
4.0E-08
)le is for illustration
Ingestion
1.2E-10
2.8E-14
1.8E-13
1.4E-13
l.OE-20
6.5E-10
1.9E-12
2.6E-10
l.OE-09
3.3E-11
3.2E-12
3.6E-11
2.8E-11
2.4E-15
2.8E-11
3.1E-10
9.3E-13
3.1E-10
Purposes only.
External
4.2E-13
2.2E-14
O.OE+00
1.5E-11
8.0E-11
4.7E-15
1.8E-13
O.OE+00
4.8E-16
9.6E-11
O.OE+00
O.OE+00
O.OE+00
O.OE+00
3.4E-11
3.4E-11
3.6E-12
1.1E-11
1.5E-11
-44-
-------
Review Land-use Assumptions. At this step,
'the future land-use assumption chosen during
scoping is reviewed. Since the original assumption
of future residential land use is supported by RI/FS
data, it is not modified.
Modify Exposure Pathways, Parameters, and
Equations. Based on site-specific information, the
upper-bound residence time for many of the
individuals living near the ACME Radiation Co.
site is determined to be 45 years rather than the
default value of 30 years. Therefore, the exposure
duration parameter used in Equation (11) in
Section 4.1.2 is substituted accordingly. It is also
determined that individuals living near the site are
only exposed to the external gamma radiation field
approximately 18 hours each day, and that their
homes provide a shielding factor of about 0.5 (i.e.,
50%). Therefore, values for Teand Seare changed
to 0.75 (i.e., 18 hr/24 hr) and 0.5, respectively.
Modify Toxicity Information. As discussed
above in the section on modifying the list of
radionuclides of concern, oral, inhalation, and
external exposure slope factors for Ra-226, Sr-90,
Cs-137, and Am-243 were adjusted to account for
the added risks (per unit intake and/or exposure)
contributed by their respective decay series
members that are in secular equilibrium.
Recalculate Risk-based PRGs. At this step,
risk-based PRGs are recalculated for all remaining
radionuclides of potential concern using the full
risk equation for the soil pathway (i.e., Equation
(11)) modified by revised site-specific assumptions
regarding exposures, as discussed above.
To recalculate the risk-based PRO for Co-60
at a pre-specified target risk level of 10"', for
example, its ingestion SF of 1.5 x 10"", and its
external exposure SF of 1.3 x 10"10are substituted
into Equation (11), along with other site-specific
parameters, as shown in the next box.
In a similar manner, risk-based PRGs can be
recalculated for all remaining radionuclides of
potential concern in soil at the ACME Radiation
Co. site. These revised PRGs are presented in the
box on the next page. In those cases where
calculated risk-based PRGs for radionuclides are
below current detection limits, risk asseasors
should contact the Superfund Health Risk
Technical Support Center for additional guidance.
RADIATION CASE STUDY: REVISED RISK EQUATION FOR RESIDENTIAL SOIL
RS for Co-60 (pCi/g; =
risk-based) (SF0 x 10'3 x EF x
TR
where:
Parameters
RS
TR
SF!
EF
ED
IF
lr
D
SD
S,
soil/adj
+ (SFe x 103 x ED x D x SD x (l-Se) x Te)
= 0.003 pCi/g
Definition (units)
radionuclide PRO in soil (pCi/g)
target excess individual lifetime cancer risk (unitless)
oral (ingestion) slope factor (risk/pCi)
external exposure slope factor (risk/yr per pCi/m2)
exposure frequency (days/yr)
exposure duration (yr)
age-adjusted soil ingestion factor (mg-yr/day)
depth of radionuclides in soil (m)
soil density (kg/m3)
gamma shielding factor (unitless)
gamma exposure time factor (unitless)
Revised Value
104
1.5xlO-"(risk/pCi)
1.3xlO'10(nsk/yrperpCi/m2)
350 days/yr
45 yr
5100 mg-yr/day
0.1 m
1.43xl03kg/m3
0.5
0.75
(Note: To account for the revised upper-bound residential residency lime of 45 years, the age-adjusted soil
ingestion factor was recalculated using the equation in Section 4.1.2 and an adult exposure duration of 39 years
for individuals 7 to 46 years of age.)
-45-
-------
RADIATION CASE STUDY:
REVISED RISK-BASED PRGs FOR RADIONUCLIDES IN SOIL*
Radionuclides
Risk-based Soil PRO (pCi/g)
10,200
20
620
0.003
0.01
0.004
0.2
0.03
Calculated for illustration only. Values have been rounded off.
H-3
Sr-90+D
C-14
Co-60
Cs-137+D
Ra-226+ D
Am-241
Am-243+D
-46-
-------
REFERENCES
Andelman, J.B. 1990. Total Exposure to Volatile Organic Chemicals in Potable Water. N.M. Ram, R.F.
Christman, K.P. Cantor (eds.). Lewis Publishers.
Cowherd, C., Muleski, G., Engelhart, P., and Gillete, D. 1985. Rapid Assessment of Exposure to Paniculate
Emissions from Surface Contamination. Prepared for EPA Office of Health and Environmental Assessment.
EPA/600/8-85/002.
Environmental Protection Agency (EPA). 1981. Population Exposures to External Natural Radiation
Background in the U.S. Office of Radiation Programs. ORP/SEPD-80-12.
EPA. 1984. Evaluation and Selection of Models for Estimating Air Emissions from Hazardous Waste Treatment,
Storage, and Disposal Facilities. Office of Air Quality Planning and Standards. EPA/450/3-84/020.
EPA. 1986. Development of Advisoy Levels for PCBs Cleanup. Office of Health and Environmental
Assessment. EPA/600/21.
EPA. 1988a. CERCLA Compliance With Other Laws Manual, Part I (Interim Final). Office of Emergency
and Remedial Response. EPA/540/G-89/006 (OSWER Directive #9234.1-01).
EPA. 1988b. Estimating Exposures to 2,3,7,8-TCDD (External Review Draft). Office of Health and
Environmental Assessment. EPA/600/6-88/005A.
EPA. 1988c. Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA. Interim
Final Office of Emergency and Remedial Response. EPA/540/G-89/004 (OSWER Directive #9355.3-01).
EPA. 1988d. Guidance on Remedial Actions for Contaminated Ground Water at Superfund Sites. Interim Final.
Office of Emergency and Remedial Response. EPA/540/G-88/003 (OSWER Directive #9283. 1-2).
EPA. 1988f. Superfund Exposure Assessment Manual. Office of Emergency and Remedial Response.
EPA/540/1-88/001 (OSWER Directive 9285.5-1).
EPA. 1988. Availability of the Integrated Risk Information System (IRIS). 53 Federal Register 20162.
EPA. 1989a. CERCLA Compliance With Other Laws Manual, Part II: Clean Air Act and Other Environmental
statutes and State Requirements. Office of Emergency and Remedial Response. EPA/540/G-89/009 (OSWER
Directive #9234.1-01).
EPA. 1989b. Interim Final Guidance on preparing Superfund Decision Documents. Office of Emergency and
Remedial Response. OSWER Directive 9355.3-02.
EPA. 1989c. Methods for Evaluating the Attainment of Cleanup Standards (Volume 1: Soils and Solid Waste).
Statistical Policy Branch. NTIS #PB89-234-959/AS.
EPA. 1989d. Risk Assessment Guidance for Superfund: Volume I-Human Health Evaluation Manual (Part A,
Baseline Risk Assessment). Interim Final. Office of Emergency and Remedial Response. EPA/540/1-89/002.
EPA. 1990a. Catalog of Superfund Program Publications. Office of Emergency and Remedial Response.
OSWER Directive 9200.7-02A.
-47-
-------
EPA. 1990b. Guidance for Data Usabiliy in Risk Assessment. Office of Solid Waste and Emergency
Response. EPA/540/G-90/008 (OSWER Directive #9285.7-05).
EPA. 1990c. Guidance on Remedial Actions for Superfund Sites with PCB Contamination. Office of Emergency
and Remedial Response. EPA/540/G-90/007 (OSWER Directive #9355.4-01).
EPA. 1990d. "National Oil and Hazardous Substances Pollution Contingency Plan (Final Rule)." 40 CFR
Part 300; 55 Federal Register 8666.
EPA. 1991a. Conducting Remedial Investigations/Feasibility Studies for CERCLA Municipal Landfill Sites.
office of Emergency and Remedial Response. EPA/540P-91/001 (OSWER Directive #9355.3-11).
EPA. 1991b. Risk Assessment Guidance for Superfund Vol. 1, Human Health Evaluation Manual Supplemental
Guidance: "Standard Default Exposure Factors. " (Interim Final). Office of Emergency and Remedial
Response. OSWER Directive 9285.6-03.
EPA. 1991c. Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions. Office of Solid
Waste and Emergency Response. OSWER Directive 9355.0-30.
EPA. 199 Id. Risk Assessment Guidance for Superfund: Volume I -Human Health Evaluation Manual (Part
C, Risk Evaluation of Remedial Alternatives). Interim. Office of Emergency and Remedial Response. OSWER
Directive 9285.7-01 C.
EPA. Health Effects Assessment Summary Tables (HEAST). Published quarterly by the Office of Research
and Development and Office of Solid Waste and Emergency Response. NTIS #PB 91-921100.
Hwang, S.T., and Falco, J.W. 1986., Estimation of Multimedia Exposures Related to Hazardous Waste Facilities.
Cohen, Y. (cd). Plenum Publishing Corp.
-48-
-------
APPENDIX A
ILLUSTRATIONS OF CHEMICALS
THAT "LIMIT" REMEDIATION
In many cases, one or two chemicals will drive
the cleanup at a site, and the resulting cumulative
medium or site risk will be approximately equal to
the potential risk associated with the individual
remediation goals for these chemicals. These
"limiting chemicals" are generally either chemicals
that are responsible for much of the baseline risk
(because of either high toxicity or presence in high
concentrations), or chemicals that are least
amenable to the selected treatment method. By
cleaning up these chemicals to their goals, the
other chemicals typically will be cleaned up to
levels much lower than their corresponding goals.
The example given in the box below provides a
simple illustration of this principle.
The actual circumstances for most
remediations will be much more complex than
those described in the example (e.g., chemicals will
be present at different baseline concentrations and
will be treated/removed at differing rates);
however, the same principle of one or perhaps two
chemicals limiting the site cleanup usually applies,
even in more complex cases.
Unless much is known about the performance
of a remedy with respect to all the chemicals
present at the site, it may not be possible to
determine which of the site contaminants will drive
the final risk until well into remedy
implementation. Therefore, it generally is not
possible to predict the cumulative risk that will be
present at the site during or after remediation. In
some situations, enough will be known about the
site conditions and the performance of the remedy
to estimate post-remedy concentrations of
chemicals or to identify the chemical(s) that will
dominate the residual risk. If this type of
information is available, it may be necessary to
modify the risk-based remediation goals for
individual chemicals.
SIMPLE ILLUSTRATION OF A CHEMICAL THAT LIMITS REMEDIATION
Two chemicals (A and B) are present in ground water at a site at the same baseline concentrations.
Remediation goals were identified for both A and B. Chemical A's goal is 0.5 ug/L, which is associated with a
potential risk of 10"6. Chemical B's goal is 10 ug/L., which is also associated with a potential risk of 10"6. The
calculated cumulative risk at remediation goals is therefore 2 x 10"*. Assuming for the purposes of this illustration
that A and B are treated or removed at the same rate, then the first chemical to meet its goal will be B.
Remediation must continue at this site, however, until the goal for chemical A has been met. When the
concentration of A reaches 0.5 ug/L, then remediation is complete. A is at its goal and has a risk of 10"'. B is at
1/20 of its goal with a risk of 5 x 10"8. The total risk (1 x 10"6+ 5 x 10"6) is approximately 10* and is due to the
presence of A.
This example illustrates that the final risk for a chemical may not be equal to the potential risk associated with
its remediation goal, and, in fact, can be much less than this risk. Although the potential risk associated with
Chemical B's goal is 10"6, the final residual risk associated with B is 5 x 10"8. Thus, if one were to calculate the
cumulative risk at PRGs prior to remedy implementation, one would estimate total medium risk of 2 x 10"', however,
the residual cumulative risk after remediation is 1 x 10"'.
I
-49-
-------
APPENDIX B
RISK EQUATIONS FOR INDIVIDUAL
EXPOSURE PATHWAYS
This appendix presents individual risk
equations for each exposure pathway presented in
Chapter 3. These individual risk equations can be
used and rearranged to derive full risk equations
required for calculating risk-based PRGs.
Depending on the exposure pathways that are of
concern for a land-use and medium combination,
different individual risk equations can be combined
to derive the full equation reflecting the
cumulative risk for each chemical within the
medium. See Chapter 3 for examples of how
equations are combined and how they need to be
rearranged to solve for risk-based PRGs. Note
that in this appendix, the term HQ is used to refer
to the risk level associated with noncarcinogenic
effects since the equations are for a single
contaminant in an individual exposure pathway.
The following sections list individual risk
equations for the ground water, surface water, and
soil pathways. Risk equations for exposure
pathways not listed below can be developed and
combined with those listed. In particular, dermal
exposure and ingestion of wound water
contaminated by soil leachate, for which guidance
is currently being developed by EPA could be
included in the overall exposure pathway
evaluation.
B.I GROUND WATER OR
SURFACE WATER -
RESIDENTIAL LAND USE
Both the ingestion of water and the inhalation
of volatiles are included in the standard default
equations in Section 3.1.1. If only one of these
exposure pathways is of concern at a particular
site, or if one or both of these pathways needs to
be combined with additional pathways, a site-
specific equation can be derived.
The parameters used in the equations
presented in the remainder of this section are
explained in the following text box.
B.I.I INGESTION
The cancer risk due to ingestion of a
contaminant in water is calculated as follows:
PARAMETERS FOR SURFACE WATER/GROUND WATER - RESIDENTIAL LAND USE
Parameter Definition
C chemical concentration in water (mg/L)
SFj inhalation cancer slope factor ((mg/kg-day)4)
SF0 oral cancer slope factor ((mg/kg-day)"1)
RfD0 oral chronic reference dose (mg/kg-day)
RfD; inhalation chronic reference dose (mg/kg-day)
BW adult body weight (kg)
AT averaging time (yr)
EF exposure frequency (days/yr)
ED exposure duration (yr)
K volatilization factor (L/m3)
IRa daily indoor inhalation rate (mVday)
IR,, daily water ingestion rate (L/day)
Default Value
chemical-specific
chemical-specific
chemical-specific
chemical-specific
70kg
70 yr for cancer risk
30 yr for noncancer HI (equal to ED)
350 days/yr
30 yr
0.0005 x 1000 L/rn(Andelman 1990)
15 mVday
2 L/day
-51-
-------
Risk from ingestion = SF,, x
of water (adult)
C x IR,Tx EFx ED
BW x AT x 365 daystyr
The noncancer HQ due to ingestion of a
contaminant in water is calculated as follows:
HQ due to ingestion =
of water (adult)
C x IR.., x EFx ED
RfD0 x BW x AT x 365 days/yr
B.I.2 INHALATION OF VOLATILES
The cancer risk due to inhalation of a volatile
contaminant in water is calculated as follows:
Risk from
inhalation
of volatiles
in water
(adult)
= SE x C x K x IR. x EFx ED
BW x AT x 365 days/yr
The noncancer HQ due to inhalation of a volatile
contaminant in water is calculated as follows:
HQ due to
inhalation
of volatiles
in water
(adult)
C x K x IR.xEFxED
x BW x AT x 365 daysyyr
B.2
SOIL
USE
- RESIDENTIAL LAND
Only the first exposure pathway below
ingestion of soil is included in the standard
default equations in Section 3.1.2. If additional
exposure pathways, including inhalation of volatiles
and/or inhalation of particulate, are of concern at
a particular site, then a site-specific equation can
be derived.
The parameters used in the equations
presented in the remainder of this section are
explained in the text box below.
B.2.1 INGESTION OF SOIL
The cancer risk from ingestion of
contaminated soil is calculated as follows:
Risk from = SF, x C x IP'6 kg/mg x EF x IF.,?il/adj
ingestion
of soil
AT x 365 days/yr
The noncancer HQ from ingestion of
contaminated soil is calculated as follows:
HQfrom = C x IP"6 kg/mg x EF x IF.,.,,^
ingestion RfD0 x AT x 365 days/yr
of soil
B.2.2 INHALATION OF VOLATILES
The cancer risk caused by inhalation of
volatiles released from contaminated soil is:
Risk from = SF, x C x ED x EF x IR,ir x (1/VF)
inhalation AT x BW x 365 days/yr
of volatiles
The equation for calculating the noncancer HQ
from inhalation of volatiles released from soil is:
Parameter
C
SFi
SF0
RfD
BW
AT
EF
ED
IF,
soil/adj
VF
PEF
PARAMETERS FOR SOIL - RESIDENTIAL LAND USE
Definition Default Value
chemical concentration in soil (mg/kg)
inhalation cancer slope factor ((mg/kg-day)"1)
oral cancer slope factor ((mg/kg-day)""
oral chronic reference dose (mg/kg-day)
inhalation chronic reference dose (mg/kg-day)
adult body weight (kg)
averaging time (yr)
exposure frequency (days/yr)
exposure duration (yr)
daily indoor inhalation rate (mVday)
age-adjusted soil ingestion factor (mg-yr/kg-day)
soil-to-air volatilization factor (mVkg]
particulate emission factor (m/kg)
chemical-specific
chemical-specific
chemical-specific
chemical-specific
70kg
70 yr for cancer risk
30 yr for noncancer HI (equal to ED)
350 days/yr
30 yr
15 mYday
114 mg-yr/kg-day
chemical specific (see Section 3.3.1)
4.63 x 10'mVkg (see Section 3.3.2)
-52-
-------
HQ from = C x ED x EF x IR,,r x (l/VF)
inhalation RfDj x BW x AT x 365 days/yr
of volatiles
B.2.3 INHALATION OF PARTICULATE
Cancer risk due to inhalation of
contaminated soil particulate is calculated as:
Risk SF x C x ED x EF x IR,ir x (\/PEF)
from AT x BW x 365 days/yr
inhala-
tion of
particulate
The noncancer HQ from particulate inhalation is
calculated using this equation:
HQ from =
inhalation
of parti-
culate
B.3 SOIL - COMMERCIAL/
INDUSTRIAL LAND USE
All three of the exposure pathways
detailed below are included in the standard default
equation in Section 3.2.2. If only one or some
combination of these exposure pathways are of
concern at a particular site, a site-specific equation
can be derived.
The parameters used in the equations
presented in the remainder of this section are
explained in the text box below.
B.3.1 INGESTION OF SOIL
The cancer risk from ingestion of
contaminated soil is calculated as follows:
Risk from = SFff x C x 10"* kg/ma x EF x ED x IR.ri,
ingestion BW x AT x 365 days/yr
of soil
The noncancer HQ from ingestion of contaminated
soil is calculated as follows:
HQ from =
ingestion
of soil
B.3.2 INHALATION OF VOLATILES
The cancer risk caused by inhalation of
volatiles released from contaminated soil is:
Risk from
inhalation
of volatiles
SF, x C x ED x EF x IR,ir x (l/VF)
AT x BW x 365 days/yr
The equation for calculating the noncancer HQ
from inhalation of volatiles released from soil is:
C x ED x EF x IR.,ir x (l/VF)
i x BW x AT x 365 days/yr
HQfrom
inhalation
of volatiles
Note that the VF value has been developed
specifically for these equations; it may not be
applicable in other technical contexts.
PARAMETERS FOR SOIL - COMMERCIAL/INDUSTRIAL LAND USE
Parameter
C
SP'o
RfD0
BW
AT
EF
ED
VF
PEF
Definition
chemical concentration in soil (mg/kg)
inhalation cancer slope factor ((mg/kg-day)"1)
oral cancer slope factor ((mg/kg-day4)
oral chronic reference dose (mg/kg-day)
inhalation chronic reference dose (mg/kg-day)
adult body weight (kg)
averaging time (yr)
exposure frequency (days/yr)
exposure duration (yr)
workday inhalation rate (mVday)
soil ingestion rate (mg/day)
soil-to-air volatilization factor (mVkg)
particulate emission factor (mVkg)
Default Value
chemical-specific
chemical-specific
chemical-specific
chemical-specific
70kg
70 yr for cancer risk
30 yr for noncancer HI (equal to ED)
250 days/yr
25 yr
20 mVday
50 mg/day
chemical specific (see Section 3.3. 1)
4.63 x 10'mVkg (see Section 3.3.2)
-53-
-------
B.3.3 INHALATION OF PARTICULATE The noncancer HQ from participate inhalation is
calculated using this equation:
Cancer risk due to inhalation of
contaminated soil particulate is calculated as: HQ from = C x ED x EF x IR1ir x M/PEF)
inhalation RfD; x BW x AT x 365 days/yr
Risk from ; SFj x C x ED x EF x IR,ir x (1/PEFl
inhalation AT x BW x 365 days/yr
of particulate
-54-
-------
United States Center for Environmental Research BULK RATE
Environmental Protection Information POSTAGE &FEES PAID
Agency Cincinnati OH 45268-1072 EPA
PERMIT No. G-35
Official Business
Penalty for Private Use, $300
EPA/540/R-92/003
------- |