UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON. D.C. 20480
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IOUO WASTI ANO iM6*eiNC¥ RtS'ONSC
OSWIR Directive 9285,7-011
HiUQRWTOI
SUBJECTi
rmoxt
TO I
Human Health Evaluation Manual, Part if
"Development of Risk-based Preliminary Remediation
Goals"
Henry Longest II, Diractor
Office of Emergency and
Bruca Diamond, Diractor
Offica of Waste Programs
ponse
forcement
Rational Waata Management Division Directors
Pirpwe
Tha purpoaa of thia directive ia to transmit the Risk
Assessment Guidance for Superfund (1AGSJ, Human Health Evaluation
Manual, Part Is "Development of Risk-based Preliminary
Remediation Goals" to be used in the remedial investigation and
feasibility study (RX/PS) process. This guidance supplements tha
Human Health Evaluation Manual, Part A—Baseline Risk Assessment,
and Part C—Risk Evaluation of Remedial Alternatives.
Bigfrnreund
As a first step in the FS, section 300.430(e) of the
National Oil and Hazardoua Substances Pollution Contingency Plan
(NCP) calls for the development of remedial action objectives and
preliminary remadietion goals (PRGs). As part of the revision to
the 1986 Superfund Public Health Evaluation Manual, a workgroup
was formed to define the role of risk aesessment in setting PRGs.
The interim guidance dietributed today incorporates numerous
comments received over the last two years from Regional and
Headquarters management on the role of risk and ARARs in the goal
setting process.
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The process outlined in this guidance will aid mmm, site
engineers and risk assessors in davaloping PRCs that satisfy the
Hthrashold criteria" of tha HCP: protaction of human health and
the environaent, and compliance with ARAXi. These goals ara
typically foraulated during tha initial atagas of tha RI/FS to
focus tha development of reaedial altamativas on technologiea
that may achiava appropriata targat lavala, tharaby limiting tha
nuabar of altarnativas analysed and streaalining tha procass. As
this guidance advocatas tha uaa of health-based MULRs as PRGs, it
should ba usad in conjunction with tha "CXRCLA Compliance with
Other Laws Manual" and tha "ARARs Q's and A's" fact ahaat series,
Tha Ragional Risk Manageaent Workgroup is addrassing savaral
isauas ragarding tha rola of ARARs and cuaulative aita risk in
tha goal-setting procass that ara conaidarad outsida tha scope of
this risk assaasaant guidanca. Supplaaantal guidanca will ba
davslopad as thasa riak aanagaaant isauas ara succaaafully
raaolvad.
This docuaent is being distributad as Inter1» guidanca
panding raviaw of tha RAGS aariaa by tha science Adviaory Board
(SAB). It is our intantion to begin updating and consolidating
tha series in FY 92. At that tiae, we will incorporate SAB's
consents and the results of ongoing, KPA-sponsored reeearch
projects. We alao strongly urge RPKa and Regional risk assessors
to contact tha Toxics Integration Branch of tha Office of
Eaergency and Reaedial Response (FTS 260-9416) with any
suggestions for further iaproveaent.
Attachment
cc: Regional Branch Chiefs
Regional Section Chiefs
Regional Toxics Integration Coordinators
Workgroup Members
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t OtO*# Nvi(T>c«r
9285.7-01B
X 0H
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Publication 9285,7-010
December 1 991
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
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NOTICE
The policies set out in this document are intended solely as guidance; they arc 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 Stales, 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.
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CONTENTS
Page
NOTICE ii
EXHIBITS vj
DEFINITIONS , vii
ACRONYMS/ABBREVIATIONS . . ix
ACKNOWLEDGEMENTS 3d
PREFACE ................... xii
1.0 INTRODUCTION 1
1.1 DEFINITION OF PRELIMINARY REMEDIATION GOALS 1
1.2 SCOPE OF PART B !
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 GOALS 5
1.6 DOCUMENTATION AND COMMUNICATION OF PRELIMINARY
REMEDIATION GOALS ft
1.7 ORGANIZATION OF DOCUMENT 6
2.# IDENTIFICATION OF PRELIMINARY REMEDIATION GOALS .................
2.1 MEDIA OF CONCERN
2.2 CHEMICALS OF CONCERN *
2.3 FUTURE LAND USE .n
2.4 APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS . .
2.4.1 Chemical-, Location-, and Action-specific ARARs
2.4.2 Selection of the Most Likely ARAR-based
PRG for Each Chemical ....
2.5 EXPOSURE PATHWAYS, PARAMETERS, AND EQUATIONS
2.5.1 Ground Water/Surface Water
2.5.2 Soil
-iii-
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CONTENTS (Continued!
Page
2.6 TOXICITY INFORMATION 14
2.7 TARGET RISK LEVELS 14
2 8 MODIFICATION OF PRELIMINARY REMEDIATION GOALS ............... 15
2.84 Review of Assumptions 15
2.8.2 Identification of Uncertainties .............. ........................ 16
2,83 Other Considerations in Modifying PRCs .............................. 17
2.8.4 Post-remedy Assessment .................. .............. ........... 18
3.® CA.LC11 aTION OF RISK-BASED FMUMINAlY
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 PARTICULATE 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 PRCs 30
4.# RISK-BASED PRCs FOR RADIOACTIVE CONTAMINANTS 33
4.1 RESIDENTIAL LAND USE 34
4.1.1 Ground Water or Surface Water 34
4X2 Soil 35
4.2 COMMERCIAL/INDUSTRIAL LAUD USE 36
4.2.1 Water 36
4.2.2 Soil 36
4,23 Soil-to-aif Volatilization Factor . 38
43 RADIATION CASE STUDY 38
4.3.1 Site History 40
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CONTENTS (Continued)
Page
APPENDIX A ILLUSTRATIONS OF CHEMICALS THAT "LIMIT REMEDIATON ..... 49
APPENDIX B RISK EQUATIONS FOR INDIVIDUAL EXPOSURE PATHWAYS 51
B.l GROUND WATER OR SURFACE WATER - RESIDENTIAL LAND USE ...... 51
B. 1.1 Ingestion 51
B.l.2 Inhalation of Volaiiles 52
B.2 SOIL - RESIDENTIAL. LAND USE 52.
B.2.1 Ingestion of Soil 52
B.2.2 Inhalation of Volaiiles 52
B.2,3 Inhalation of Particulates 53
B.3 SOIL - COMMERCIAL/INDUSTRIAL LAND USE 53
B.3.1 Ingestion of Soil 53
8.3.2 Inhalation of Volatile* 53
B.3.3 Inhalation of Particulates . 54
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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
*
-VI-
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DEFINITIONS
Term
Definition
Applicable or Relevant awl
Appropriate Requirements
(ARARs)
Cancer Risk
Conceptual Site Model
Exposure Parameters
Exposure Pathway
Exposure Point
Exposure Route
Final Remediation 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 takes from a source to an
exposed organism. An exposure pathway describes 3 unique
mechanism by which an individual or population is exposed to
chemicals or physical agents at or originating from a sue r j^h
exposure pathway includes a source or release from a source, jn
exposure point, and an exposure route. If the exposure point differs
from the source, a transport/exposure medium (e.g.. an, or media
(in cases of intermedia transfer) also would be indicated
A location of potential contact between an organism and a chemical
or physical agent.
The way a chemical or physical agent comes in contact *uh 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 goats (PRGs) because of modifications lesultnc lu'm
consideration of various uncertainties, technical and exposure
factors, as well as all nine selection-of-remedy cruen.i nullified in
the National Oil and Hazardous Substances Pollution
Plan (NCP).
-vi i-
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DEFINITIONS (Continued)
Term
Definition
Hazard Index (HI)
Hazard Quotient (HQ)
'Untiling* Chemical(s)
Preliminary Remediation Goals
(PRGs)
He sum of wo or more hazard quoitenu 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 chemicai(s).
Initial dean-Hp 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).
Quantitation Limit (QL) The lowest level at which a chemical can be accurately and
reproducibly quantittted. Usually equal to the method detection
limit multiplied by a factor of three to five, but varies for different
chemicals and different samples.
Reference Dose (RfD) 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.)
Risk-based PRGs Concentration levels set at scoping for individual chemicals that
correspond to a specific cancer risk level of 10"6 or an HQ H! of ].
They are generally selected when ARARs are not available
Slope Factor (SF) 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 10 a
particular level of a potential carcinogen.
Target Risk A value that is combined with exposure and toxicity information 10
calculate a risk-based concentration (e,g,, PRG). For caronogcnic
effects, the target risk is a cancer risk of 10"*. For noncarcmoecnic
effects, the target risk is a hazard quotient of 1.
-vni-
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ACRONYMS/ABBREVIATIONS
%
Acronym/
Abbreviation Definition
ARARs Applicable or Relevant and Appropriate Requirements
CAA Clean Air Act
CERCLA Comprehensive Environmental Response, Compensation, and Liability Act
CFR Code of Federal Regulations
CWA Clean Water Act
EAG Exposure Assessment Group
ECAO Environmental Criteria and Assessment Office
Superfund Health Risk Technical Support Center
EF Exposure Frequency
EPA U.S. Environmental Protection Agency
FWQC Federal Water Quality Criteria
HEAST Health Effects Assessment Summary Tables
HHEM Human Health Evaluation Manual
Hi Hazard Index
HQ Hazard Quotient
HRS Hazard Ranking System
IRIS Integrated Risk Information System
LLW Low-level Radioactive Waste
MCL Maximum Contaminant Level
MCLG Maximum Contaminant Level Goal
NCP National Oil and Hazardous Substances Pollution Contingency Plan
NPL National Priorities List
OSWER Office of Solid Waste and Emergency Response
OERR Office of Emergency and Remedial Response
•LX-
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ACRONYMS/ABBREVIATIONS (Continue*
Acronyms/
Abbreviation Definition
PA/SI
Preliminary Assessment/Site Inspection
PEF
Particulate Emission Factor
PRG
Preliminary Remediation Goal
RAGS
Risk Assessment Guidance for Superfund
RCRA
Resource Conservation and Recovery Act
RfC
Reference Concentration
RfD
Reference Dose
RI/FS
Remedial Investigation/Feasibility Study
RME
Reasonable Maximum Exposure
ROD
Record of Decision
RPM
Remedial Project Manager
SARA
Superfund Amendments and Reauthorization Act
SDWA
Safe Drinking Water Act
SF
Slope Factor
TR
Target Risk
VF
Volatilization Factor
WQS
State Water Quality Standards
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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 specially 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 Response;
• 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.
¦XI
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PREFACE
Risk Assessment Guidance /or Superfund: Volume / *— Human Health Evaluation Manual
(RAGS/HHEM) Part B is one of a three-part series. Pari. A addresses the baseline risk assessment; Pari 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 he
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
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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 as 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 Assessment
Guidance for Superfund: Volume / — 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
(Rl/FS). Part C of this series (EPA I991d) 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
ihree parts of RAGS/HHEM are all used during
the Rl/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 fulty 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 Rl/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 oi ihtr R1 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 PRGv m
a site-specific context, however, assessors most
answer fundamental questions about the sue
Information on the chemicals that ate present
onsite. the specific contaminated media. land «%<.•
assumptions, and the exposure assumption* Nnmd
pathways of individual exposure is nei«>vm m
order to develop chemical-specific PRC.* Pjm H
provides guidance for considering thr* infermjiu-n
in developing chemical-specific PRC*.
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EXHIBIT 14
RELATIONSHIP OF THE HUMAN HEALTH EVALUATION
TO THE CERCLA PROCESS
CERCLA REMEDIAL PROCESS
Scoping
Remedial
InvesDtinor
1—
Feaability
Study
Remedy Selection
»t»d Record of
Decision
Retried!*] Design/
Remedial Action
Deletion/
Rve-ycar Review
HUMAN HEALTH EVALUATION MANUAL
PASTA
Baseline Ride Assesment
PARTS
Development of RM-based
Prelaiunuy Rem«iMon Goals
PAKTC
Risk Evaluation of Remedial Alternatives
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Because Pari B focuses on developing
chemical-specific PRGs based on protection of
human health, there are important types of
information that are not considered awl that may
significantly influence the concentration goals
needed to satisfy the CERCLA criteria for
selection of a remedy. For example, j»
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 oniv 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 1.31.
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 document* are
listed and their relationship to the site remediation
process is discussed.
13,1 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 tiiai 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
IJJ GUIDANCE DOCUMENTS
There are several existing documents thai
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.
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NINE EVALUATION CRITERIA FOR
analysis of remedial alternatives
(40 era 3Q0.43Q(eXW)5
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
• Impiementabiliiy
• Cost
Modifying Criteria:
« State Acceptance
• community Acceptance
NCP RULE HIGHLIGHTS
RISK AND REMEDIATION GOALS
(40 CFR 300.430(e)f2))
"In developing and, as appropriate, screening
... alternatives, the lead agency shall: ft) Establish
remedial action objectives specifying contaminants
and media of concern, potential exposure
pathways, and remediation goals. Initially,
prelmioajf remediation goals are developed based
on readily available infarmatioo, such as chemical -
spectfic ARARs or other reliable information,
freliminary remediation goal* should be modified,
as necessary, m more information becomes
available during the RI/FS. Final remediation
goals wffi be determioed when the remedy is
selected. Remediation goals shall establish
acceptable exposure levels that are protective of
human health and tbe environment and shall be
developed by considering the following;
(A) Applicable or relevant and appropriate
requirements and the following factors:
(1) For systemic tcaricaots, 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 general k
concentration levels that represent an
excess upper-bound lifetime cancer risk
to an individual of between 10'" and lo-
using information on the relationship
between dose and response The m*
risk level shall be used as tbe pomi of
departure for determining remedial ion
goals far alternatives when AJRARs are
not available or are not suffoeoiiv
protective because of routfipie
contaminants at a site or multiple
pathways of exposure
1.4 INITIAL DEVELOPMENT OF
PRELIMINARY
REMEDIATION GOALS
The NCP preamble indicates that, typically,
PRGs arc developed at scoping or concurrent with
initial RI/FS activities (i.e., prior to completion of
the baseline risk assessment). His 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.
It is important to remember that risk based
PROs (either at scoping or liter on) arc imtui
guidelines. They do not establish that Ucjnup i...
meet thee goals is warranted, A risk
concentration, as calculated in this guidance «.,u
be considered a final remediation level i>niv jitcr
appropriate analysis in the RI/FS and ROD
-------
GUIDANCE DOCUMENTS
• Risk Assessment Guidance for Superfund: Volume I — Human Health Evaluation Manual Pan A (EPA 1989a)
(RAGS/HHEM Pari A) contains background information and is particularly relevant for developing exposu re and
toxicity assessments thai are required when refining chemical-specific risk-based concentrations, and accounting
for site-specie teas such as multiple exposure pathways.
• Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA (EPA 1988c) (R1/F5
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 l
(Municipal Landfill Guidance) offers guidance m how to streamline both the RI/FS and the selection of a re met*
for municipal landfills.
1.5 MODIFICATION OF
PRELIMINARY
REMEDIATION GOALS
The initial list of PRGs may need to be revised
as new data become available during the RI/FS.
Therefore, upon completion of the baseline risk
assessment, it is important to review the media and
chemicals of potential concern, future land use,
and exposure assumptions originally identified at
scoping. Chemicals may be added or dropped from
the list, and risk-based PRGs may need to he
recalculated using site-specific exposure ( < >t • fu-
baseline risk assessment must still men :?u-
-------
"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 thai the PRGs
are used effectively in streamlining the RI/FS
process
Because PRGs are most useful during the
Rl/FS (e.g., for streamlining the consideration of
remedial alternatives), it is important to
communicate them to site engineer* 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 PRGs 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
PRGs 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 chemical* "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 thai differ
from those presented in Chapter 3
Throughout Chapters 2, 3, and 4, caw studies
are presented that illustrate the process of
determining PRGs. These case Mudio. are
contained in boxes with a shadow box appearance.
Other types of boxed information
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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 I,
medium-specific PRGs (ARAR-based and/or
risk-based) should be identified during scoping for
all chemicals of potential concern using readily
available information. Sections arc provided in
this chapter on low 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
may be modified significantly depending on
information gathered about the site. The
subsequent process of identifying tev 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 bo* on
CONCEPTUAL SITE MODEL
During project planning, the RPM. gathers and
analyzes available information and develop* the
conceptual sue model (also called the conceptual
evaluation model). This model is used to assess
the nature and ibe 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/51 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 tirsi sue.
(The radiation case study is addressed in
Chapter 4.) The information (e.g.. toxicity values)
contained in these case studies is for illustration
oalv. and should not be used for anv other
purpose. These case studies have been simplified
(e.g., only ground water will be examined) so thai
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 umuern.
The conceptual site model should be verv useful
for this step. These media can be either
• currently contaminated media to which
individuals may be exposed or through wfuth
chemicals may be transported to potcmul
receptors; or
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CASE STUDY; INTRODUCTION
The XYZ Co. site contains an abandoned
industrial facility that is adjacent to a high*
density residential neighborhood. Rem rants of
drums, lagoons, and waste piles were found ai
the site. Ground water in the are® 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.
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 scopins.
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 delected 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 contributors 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 jnjivsis
plan.
23 FUTURE LAND USE
This step involves identifying the must
appropriate future land use for the sue tfut the
appropriate exposure pathways, parameters, jnd
equations (discussed in the next section} van he
used to calculate risk-based PRGs. RAGS HHFM
Part A (Chapter 6) and an EPA Office of s..i,d
Waste and Emergency Response (OSWf-Rj
directive on the role of the baseline r<%k
assessment in remedy selection decisions < I PA
1991b) provide additional guidance on tUentiftinc
future land use. The standard default ^yjtn.ns
provided in Chapter 3 of Part B onh jOOkss
residential and commercial/industrial Un.i um-s I!
land uses other than these are to be awurmd «<¦ * .
recreational), then exposure pathways. p,lf jmru-fy
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 thai were buried in the soil but
have since been removed. Lagoons and waste
pita 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.
-------
CASE STUDY: IDENTIFY CHEMICALS
OF CONCERN
The PA/SI for {he XYZ Co. mm identified the
Mewing seven chemicals to ground-water
samples: benzene, eUiytbenzene, hexane,
isophorone, imitate, 1,1.2-trichloroethaoc, and
vinyl chloride. Therefore, these chemicals we
obvious choices for chemicals of potential
concern.
Although not detected in my of tlx. PA/SI
samples, site history indicates that ate other
solvent — carte tetrachloride —also was used its
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 thai 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 PROs 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 tbe land a
determined to be residential use. Thus, site-
spedflc information is sufficient to show that the
generally nxxe conservative assumption of
residential tod use should serve »the basis for
development of risk-based PRGs.
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 identifying 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 m a
tabular summary (Le., no potential ARAR
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 idemthing
the most appropriate (likely) ARAR of all pouible
ARARs to use as the chemical-specific PRG
More detailed information about the ideniilicauon
and evaluation of ARARs is available ir.>m mo
important sources:
• the NCP (see specifically 55 Fcc< '.. ••-•xrurr
8741-8766 for a description of aK Vr jnj
-------
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 eheniical-
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 PRG 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 docannenis should
be carefully considered for specific
recommendations on identifying ARARs.
Groundwater. 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 Regiuer 8717, March 8, 1990}
"Ground water that is not currently a dnnfcjng
water taunt but 6 potentially a dunking 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 Iff* level (except when
necessary to addrca environmental concerns or
allow for other beneficial met;. .
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 bo| appropriate as PRCs Insipid,
environmental cons Mentions (ie.» effect,-. on
biological receptors) and prevention of plume
expansion generally determine clean up ieveh If
an aquifer that is not a potential sounc of
drinking water is connected to an aquifer thai is a
drinking water source, it may be appropriate to use
PRGs to set clean-up goals for the point of
interconnection.
For chemicals without MCLs. state MjnOjftK
or non-zero MCLGs. the FWQC mjv n;
potentially relevant and appropriate f.
-------
Surface Water. FWQC and state water quality
standards (WQS) are common aRAjRs 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 io 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 noi
address pathways such as plant and animal uptake
of contaminants from soil with subsequent human
ingestion. Under certain circumstances, these or
other exposure pathway* 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 equaiion
for a medium. For example, in the equji»>n inr
ground water and surface water under the
residential land-use assumption, the cmlfk writs
incorporate default parameter values for intonon
of drinking water and inhalation of voijnk- ,j» n n g
-------
EXHIBIT 24
TYPICAL EXPOSURE PATHWAYS BY MEDIUM
FOE RESIDENTIAL AND COMMERCIAL/INDUSTRIAL LAND USES°'b
Exposure Pathways, Assuming:
Medium
Residential Land Use
Commercial/Industrial Land Use
Ground Water
Ingestion from drinking
Ingestion from drinking*1
Inhalation of volatiles
Inhalation of volatiles
Dermal absorption from bathing
Dermal absorption
Immersion - external'
Surface Water
Ingestion from drinking
Ingestion from drinking*
Inhalation of voiatilts
Inhalation of volatiles
Dermal absorption from bathing
Dermal absorption
Ingestion during swimming
Ingestion of contaminated fish
Immersion - external*
Soil
Ingestion
Inhalation of particulates
InfuUnXW/t of
Inhalation of voia tiles
Inhalation of volatiles
Direct exUrnai exposure0
Direct mtrmt fxpmun?
Exposure to ground water contaminated
by soil leachate
Exposure to ground water contaminated
by soil leachate
Ingestion vis plant uptake
Dermal absorption from gardening
Inhalation of particulates from trucks
and heavy equipment
* Lists of land uses, media, and exposure pathways are not comprehensive.
b Exposure pathways included In RAGS/HHEM Part B standard default equations (Chapters 3 and 4) are
italicized.
c Applies to radionuclides only.
4 Because 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.
-------
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 ten of these chapters.
Certain modifications of the default equations
may be desirable or necessary. For example, if an
exposure pathway addressed by an equation Jo
Chapter 3 seems inappropriate for the site (e.g.f
because the water contains no voiaiiles 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 I hat 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 ire 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 (RMEl 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.
2J.I 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*5 atm-m3/mole or greater ng
with a molecular weight of less than 200 g/raole.
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
PRGs 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 particulates, 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 1CTS atm-m3/mole or greater and
-I.V
-------
with a molecutai weight of less than 200 g,rr.ole-
For the inhalation pathways, in addition to toxicity
information, several chemical- and stte-speafic
values are needed These values include molecular
diffusivuv. Henry's Law constant, organic carbon
partition coefficient, and soil moisture content (see
Chapter 3 for details).
2 J 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
effete) and reference doses (RfDs. for
noncarcinogenic effects) are identified or derived
for use in the site-specific equations or she
standard default equations. Therefore. Charier 7
of RAGS/HHEM Part A shomM be reviewed
carefully before woceediM with this step.
He hierarchy for obtaining toxicity values for
risfe-basai PRGs is essentially the same as that
used in ihc 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 Supcrfund 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 he
obtained includes EPA's weight-of-evidence
classification for carcinogens (e.g., A 81) and !he-
sou rce of the information (e g . IRIS, HEAST)
Note that throughout this document, the term
hazard index (HI) is used lo refer to the risk level
associated with noncarcinogenic effects. An HI is
the sum of two or more hazard quotients (HQsV
An HO 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/ungje exposure pathway ratio, or a
multiple substance/multiple exposure pathway
ratio. In this document, however. onl\ une
exposure pathway is included in the default
equation for some land-use and medium
combinations (e.g., residential soil) In order to
remain consistent, lie term H! has been used
throughout RAGS/HHEM Pan B, even though I'-t
such a pathway, the term HQ could apply.
2.7 TARGET RISK LEVELS
This step involves identifying target nsk
coftceatfiifoiKS for chemicals of potential emu em.
The standard default equations presented in
Chapters 3 and 4 are based on the following urea
risk levels tor carcinogenic and noncarunm^nK
effects.
• For airtaeteiifeeffectt, a concern ran..* -
calculated that corresponds u> a io*
incremental risk of as individual develop^
cancer over « lifetime as a result '"1
to the potential carcinogen from alt McmiHam
exposure pathways for a given medium
CASE STUDY: IDENTIFY EXPOSURE
PATHWAYS, PARAMETERS,
AND KQUATIONS
For the potential residential fond use
identified at the XYZ Co. site, the contaminated
ground water (one of several media of potential
concern) appears to &e an important source of
future domestic water. Because sue specific
information is not mitialfy amilaWe to develop
specific exposure pathways, parameters, and
equations, the standard default assumpiKim and
equahop-s provided in Chapter 3 will &e used to
caleu,ate nsk-based PRGs. Exposure pathways
of concern for ground water, therefore. are
assumed to be ingestion of ground waier m
dnokiBg water and iatotoltei of vototiies m
ground water during household use.
•14-
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-—
CASE STUDY: IDENTIFY TOXICITY INFORMATION1
Reference toocity 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-waier medium only, ingestion and inhalation are exposure pathways of concern. Toxicity information
is obtained from IRIS and HEAST, and ts shown in the tabic below.
Chemical
Rffi j
(mg/kg-day) j
Source
SF
(mg/kg-day)1
Weight of
Evidence
Source
EXPOSURE ROUTE:
INGESTION
Hexane
0,06
HEAST
—
bophorooe
0.2
IRIS
0.0039
c
HEAST
Tnailate
0.0B
IRIS
—
—
—
EXPOSURE ROUTE:
INHALATION
Hexane
0.04
HEAST
...
Isophorone
—
—
—
c
HEAST
Tnaltete
—
_
—
* All information in ihis example is for iltasrattM purpose* ooly.
• For noncarcinogenic effects, a concentration is
calculated that corresponds to an HI of I,
which is the level of exposure to a chemical
from all sifnificant 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 NCR "Hat is, an
appropriate point of departure for remediation of
carcinogenic risk is a concentration that
corresponds to a risk of ID"6 for one chemical in a
particular medium. For noncarcinogenic 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.
241.1 REVIEW OF ASSUMPTIONS
Media of Concern. As a guide to determining
the media and chemicals of potential concern, the
OSWER directive R@k of the Baseline Risk
Assessment in Superfund Remedy Selection Decisions
(EPA 1991c) indicates that action is generally
warranted at a site when the cumulative
cardiogenic risk is greater than nv4 or the
cumulative noncarcinogenic 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 iO*4 or that the HI is greater than I.
that medium presents a concern, and it gcncu^ />
appropriate to maintain risk-based PRG> lor
contaminants in that medium or develop risk-tu^-d
PRGs for additional media where PRG> are noi
clearly defined by ARARs.
When the cumulative current or luiurc
baseline cancer risk for a medium in wiihm the
range of IO4 to Iff4, a decision about whether or
not to take action is a site-specific determination.
Generally, risk-based PRGs are not needed lot jr>
chemicals in a medium with a cumulative ijruer
risk of less than 10"*, where an HI is t
-1 v
-------
equal to I, or where the PRGs are clearly defined
by ARARs. However, there may be cases where a
medium appears to meet the protectiveness
criterion bat 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 ihe baseline risk assessment, any
chemical that has an associated cancer risk
(current or future) within a medium of greater
than IQ"4 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"6 generally 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
Sttperhind 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 PRGs can
serve as an important basis for recommending
further modifications to the PRGs 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 baseioe 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 PRGs.
In general, each component of risk-based
PRGs discussed in this chapter — from media of
potential concern to target risk level — should he
examined, and the major areas of uncertainly
highlighted. For example, the uiK-enamiy
-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 individuals) 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, proteciiveness 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
proteciiveness 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 l» institutional
controls may be used to supplement treatment
and/or containment-based remedial action to
ensure protection of human health and the
environment.
• • -SI; - r
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 expc&ures 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 tlx balancing of
criteria...."
NCP RULE: EXPOSURE, TECHNICAL,
AND UNCERTAINTY FACTORS
(40 CFR 300.43O(eX2Xi))
*(i) Remediation goals.-shall be developed by
considering the following:
"(A) Applicable or relevant and appropriate
requirements...and the following factors:
"(/) For systemic tcocicants, acceptable
exposure levels..,;
"(2) For known or suspected carcinogens,
acceptable exposure levels..;
"(J) Factors related to technical limitations
such as detectlon/quantificaiion limits, for
contaminants;
"(4) Factors related to uncertawiv ami
"(5) Other pertinent information "
-------
Note thai in the absence of ARARs. the 10"6
cancer risk "point of departure" is used as a
starting point for analysts 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 docs not reflect a
presumption that the final remedial action should
attain such eoals, (See N'CP preamble, 55 Federal
Register 8718-9.)
2.8.4 POST-REMEDY ASSESSMENT
To ensure that protective conditions exist aftet
the remedy achieves all individual remediation
levels set out tit 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
-------
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 seeping 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 ^e 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 I0"6
(the NCP's point of departure for analysts of
remedial alternatives), it is possible to solve for the
concentration term (i.e., the risk-based PRG). The
total risk for noncarcinogenic effects is set at an
HI of 1 for each chemical in a particular medium.
Full equations with pathway-specific 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 equations are based on
standard default assumptions that mav 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. (See the 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 effeciency. That is, for the sake of
simplicity at scoping, it is assumed thai 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 tn
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 <>/
the parameters used in the reduced equations
carry additional significant figures.
• The equations presented in this chapter
calculate risk-based concentrations uMrte
inhalation reference doses (RfD,<> jnd
inhalation slope factors (SF,s). If ontv the
reference concentration (RfC) and <>r
inhalation unit risk are available for j
particular compound in IRIS, conversion to *n
RU>i and/or SF, will be necessary Mjtn
converted toxicity values arc available m
HEAST,
• All standard equations present cC si-
incorporate pathway-specific default
•19-
-------
factors that generally reflect RME conditions.
As detailed in Chapter 8 of RAGS/HHEM
Fart A (in the discission on combining
pathway risks {Section 8.3J). 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.
34 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 volatile® 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 pathways. Default risk from
ground water or surface water would be calculated
as follows f total* risk, as used below, refers to the
combined risk for a single chemical from all
exposure pathways for a given medium):
Total risk = Risk from + Risk from inflate-
from water ingestion of tion of volatile*
water (adult) from household
water (adult)
At scoping, risk from indoor inhalation of
volatiles is assumed to be relevant only for
chemicals that easily volatilize. Thus, the risk
equation incorporates a water-air concentration
relationship that is applicable only to chemicals
with a Henry's Law constant of greater than 1 x
10'5 atm-mJ/n»ole afld 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
identity 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-
sped flc 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-hound
value of 0.0005 x 1000 Um3. (The 1000 Lm'
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 IW).
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 1L
and the air exchange rate is 0.25 m' hr
Furthermore, it is assumed that the average
transfer efficiency weighted by water use is 50
percent (ie,, half of the concentration ot each
chemical in water will be transferee into air m all
water uses [the range extends from 3t» for unlets
to 90% for dishwashers)). See the Andelman
paper for further details.
Concentrations Based on Carcinogenic K fleet s,
Total risk for carcinogenic effects of a-nain
volatile chemicals would be calculated n
combining the appropriate inhalation and
with the two intakes from water:
Total = SF„ x Intake from + SF( *. ** »m
risk ingestion of .nrw.r
water •* - n
-20-
-------
.*
Adding appropriate parameters. and then
rearranging the equation to solve for
concentration. resDits m Equation 11).
Equation {1') on the next page is ihe reduced
version of Equation (I) using she standard default
parameters, and is used to calculate the risk-based
PRG at a prespeafied cancer risk level of 10^. It
combines the toxicity information of a chemical
with standard default exposure parameters for
residential land we to generate tie concentration
of that chemical that corresponds to a 10"
carcinogenic risk level due to that chemical. If
either the SF0 or SF( in Equation (1 ) is not
available for a particular chemical, the term
combining that variable in the equation can be
ignored or equated to zero (e.g.. for a chemical
that does not tuve SF|f the term 7.5(SF,) in
Equation (!') it ignored.. If any of the default
ef anetsL,iiifg * m, cftMggt «t Mm, m-
used
RESIDENTIAL WATER - CAftClfWMWC EFFECTS
TR
SFft»Ct
-------
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
RfD„
+ Intake from inhalation
RfD,
Adding appropriate parameters, and then
rearranging the equation to solve for
concentration, results in Equation (2).
Equation (2') on the neit page is the reduce
version of Equation (2) using the standard defau
parameters, and is used to calculate the risk-base
PRO at a prespecified HI of 1, It combines th
toxicity information of a chemical with standar
exposure parameters for residential land use t
generate the concentration of that chemical thi
corresponds to an HI of 1, If either the RfD0 o
RfDj in Equation (2') is not available for
particular chemical, the terra containing tha
variable in the equation can be ignored or equates
to zero (e.g., for a chemical that does not hav
RfDj, the term 7.5/RfD( in Equations (2") i
ignored).
RESIDENTIAL WATER - NONCARCINOGENIC EFFECTS
THI
C x IR_. x EF x ED
RfDc x BW x AT x 365 days^r
CxKxIR-xEFxED
RfD, x BW x AT x 365 dayvyr
C (tng/L; risk-
based)
where:
EF x ED x C x tn/RfD. x IR.J » fl/RlD, xKx IR.>1
BW X AT X 365 day%ftr
THI x BW x AT x 365 dawVr
EF x ID x ((1/RfD, iKx IR4) + (l/RfD„ x IR»>]
C2)
Eaaamsa .Bslaajos
Default Value
C chemical concentration in water (mg/L) —
THI target hazard index {unities*} 1
RfDa oral chronic reference dose (mg/kg-day) chemical-specific
RfD, inhalation chronic reference dose (mg/kg-day) chemical-specific
BW adult body weight (kg) 70 leg
AT averaging time (yr) 30 yr (for noncarcinogens, equal to ED)
EF exposure frequency (days/yr) 350 day*yr
ED exposure duration (yr) 30 yr
fR, daily indoor inhalation rate (m'/day) 15 mVday
IR» daily water ingestion rate (LAJay) 2 Uday
K volatilization factor (uniiless) 0.0005 x 1000 LAd* (Andelman 1990)
REDUCED EQUATIONS RESIDENTIAL WATER - NONCARCINOGENIC EFFECTS
Risk-based PRO
(mg/L; THI = 1}
where:
RfDe =
RfD, =
73
[7.5/RfD, + 2/RrD„
(2')
oral chronic reference dose in rngflcg-day
inhalation chronic reference dose in mg/kg-day _
-------
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. Iran 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
(IFjoi^p 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-vr/kg-dav. and therefore is not directly
comparable to daily soil intake rate in units of
ffgAg-fe- See the box containing Equation (3)
for the calculation of this factor.
Additional exposure pathways (e.g.. inhalation
of particulates, inhalation of volatiles, ingestion of
foodcrops contaminated through airborne
particulate deposits, consumption of ground water
contaminated by soil kachaic) arc 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 3.12). Air pathway risks also
lend 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 » SF„ x 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 10"*. 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"6 carcinogenic
risk level due 10 that chemical.
AGE-ADJUSTED SOIL INGESTION FACTOR
(mg-yr/kg-day) « tR.n*.yi* * EPn^H-t- + X-EP^nu
BWv„,
(3)
Parameter
Definition
Vglye
BW,.,,
BWipH1
ED^r,,
IRnafcifel*
age-adjusted sotl ingestion fector (mg-yr^-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 10 6 (mg/day)
ingestion rate of soil all other ages (mg/day)
114 mg-yr/kg-day
15 kg
70 kg
6yr
24 yr
200 rag/day
100 mg/day
-23-
-------
RESIDENTIAL SOIL - CARCINOGENIC
EFFECTS
TR =
SF. x C x 10- kaftnt x EF x IF
AT x 365 days^yr
€ (mg/kg; rtsk-
based)
TR x AT x 365 davs/vear
SFa x I04 kf/mg i EF x IF_^
(4)
where;
Parameters
Definition (units >
Default Value
C
TR
SF0
AT
EF
chemical concentration in soil (mg/kg)
target excess individual lifetime C8Qoer risk (unitless)
oral cancer slope factor ((mg/kg-day)1)
averaging time (yr)
exposure frequency (dayslyt)
age-adjusted ingestion factor (mg-yiAg-diy)
JO"6
chemtcaf-speeifk;
70 yr
350dayvyr
114 mg-yr/kg-day (see Equation (3))
REDUCED EQUATION: RESIDENTIAL SOIL - CARCINOGENIC EFFECTS
Risk-based PRG » 0.64
became the NCP seeks to require protection ut
ground water to allow tor its maximum beneficial
use (see Section 2.3). Thus, under the commercial
industrial land-use scenario, risk-based PRCs for
ground water are calculated according jo
procedures detailed in Section 3.1.1 SimilarU, for
surface water that is to be used for dnnkmc. the
risk-based PRGs should be calculjird (or
residential populations, and not simpl\ worker
populations.
-------
RESIDENTIAL SOIL - NON'CARCINOGENIC EFFECTS
TH1 = C i 10~* ke/mg x F.F x IF...,.,,,
RfD„ x AT x 365 tfayvyr
C (mg/kg; risk-
THI i AT x 365 davsA-r
m
based)
i /RfD0 x tO* kg/mg x EF s IF^,^
where:
Parameters
Definition (units*
C
chemical concentration in sal {m§%g)
—
THI
target hazard index {oniiless)
!
RfD0
oral chronic reference dose (mgAj-day)
cbemicaUpeafic
AT
averaging time (yr)
30 yr (for noocarcinogeos, equal to ED (which
Ef
is incorporated in rFl l)ri
from soil
+ Risk from inhalation of volantej from
soil (worker)
+ Rift Bran inhalation of particulates
from soil (worker)
It is possible to consider only exposure pathways of
site-specific Importance by deriving a siic-spcufu
risk-based PRG (e.g., using the equations in
Appendix B).
-------
Concentrations Based on Carcinogenic Effects.
Total risk for carcinogenic effects would., be
calculated bv combining tie appropriate inhalation
and oral SFs with the three intakes from soil:
Total risk = SF0 * Intake from ingestion of soil
(worker)
+ SP, * Intake from inhalation' of
vetattles from soil (worker)
+ SF, x Intake from inhalation of
particulates (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 JO4, 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 1CT6 carcinogenic risk level due to thai 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
R®0
(Intake from inhalation of volatile*.
~ and particulates)
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.[ '~- 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 (EAG). 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-TCDP from contaminated soil (EPA
2986, 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 (he soil contaminant
concentration is at or below saturation. Saturation
is the soil contaminant concentration at which the
adsorptive limits of the soil panicles and the
solubility 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 (CMl) calculated
using Equation (6a) or (7a). If C is greater than
Cm, then the PRG is set equal to CU1
The VF presented in this section assume- that
the contaminant concentration in the soil is
homogeneous from the soil surface to the depth of
concern and that the contaminated material is nor
covered by contaminant-free soil material For the
purpose of calculating VF, depth of utniem is
defined as the depth at which a near impcnetuMe
layer or the permanent ground-water level is
reached.
-------
COMMERCIAL/INDUSTRIAL SOIL - CARCINOGENIC EFFECTS
TR = SF„
x C x 10"* kifms. x EF x ED x IR._, + SF. x C x EF x ED x IR._ x H/VF + 1/FEF1
BW x AT x MS days/yr
BW x AT * 365 days/yr
C (mg,1cg: risk-
based)
TR x BW x AT x 365 dawvr m
EF x ED x f(SF0 x 10* kg/mg x IR^) 4- (SF, sIR.itl/VFr. l.PEFj))
where:
Parameters
Definition (units)
Detail Value
C
TR
SF,
SPe
BW
AT
EF
ED
^•OlJ
mm
VF
PEF
chemical concentration in sod (oig/kg)
target excess individual lifetime cancer risk (unities
inhalation cancer slope factor ((mg/kg-day)"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 (mVoay)
soil-to-air voiatiloatioo factor (m5/kg)
particulate emission factor(mVkg)
a) 10*
cbemical-spectfic
cbeoacal-specific
70 kg
10 ft
25D days/yr
25 yr
50 tag/day
20 mVctay
ebemical-speaSc (see Section 3.3.1)
4.63* l(f m'/kg (see Section 3.3.2)
Cm * (K„ ISiy + (SJ 8b)
(6a)
where:
Parameter
Definition ("units!
PefauH Value
K-
K«
OC
$
n.
sal saturation coocentration (mgftg) —
soil-water partition coefficient (LAg) cbemical-spedQc, or x OC
organic carton partition coefficient (L/fcg) cteOKal-specific
organic carbon content of soil (fraction) she-specific, or 0.02
solubility (mg/L^water) cteneaUpedfic
soil moisture content, expressed as a weight fraction site-specific
soil moot are comem, expressed as L-wmcr/kg-sod site-specific
REDUCED EQUATION: COMMERCIAL/INDUSTRIAL SOIL - CARCINOGENIC EFFECTS
Risk-teed PEG - 2.9 x W4 (6 ')
(mg/kg; TR m Iff4) {({5 i 10-5) i SFC) + (SF, * {(20/VF) + (4J i Iff*)))]
where:
SF„ « oral slope fiictor in (mg/kg-day)'1
SF, » mhalatioa stope factor in (mg/kg-d*y)''
VF ¦ chemiai-ipeciic soil-to-air volatilization factor in mJfcg (see Section 3.3.1)
If PRG > C., then set PRO - C^, (where C„, = soil saturation concentration (nag/kg); see Equation (fta.
and Section 33,1).
•27-
-------
commercial/industrial SOIL - NONCaRCINOCKNK effects
THI
C (mgfi&Si *
risk-based)
where:
Parameters
C
THI
RfD0
RfD,
BW
AT
EF
ED
1R,C
VF
PEF
Ck + C « EF x ED x SR„ x (1/VF + 1/PEF)
RID, x BW i AT x liS cteyWyt
RfD, x BW x AT x 36^ Oayvyr
THI« BW i AT x 365 daWvr
ED i EF * {((1/RfD,) s 10"* kg/tog * !R—) + ((1/RfD;) * IR^ x (1/VF 4 I /P fc Fj~; j
(?)
fiSt&«wo Wtt
chemical concentrator, m soil (Tig/kg)
target hazard mdc* (untfiew;
orai chronic reference dose {m^g-day|
inhalation chronic reference dose (mg/kg-day)
adult body weight
sal infection we (mg/tiay)
wrtatej inhalation rate (mJ/tf*y)
sou-to-wr wtoiiaaiioii faoor (m'/kg)
purtieolate emission factor (mMcg)
C» - CK„ * s s n») + |s x •„)
i
chemtcal-speafk
chemical-specific
70 kg
25 yr (afways equal to £ D)
2® daysftr
25 yr
50 mg/day
20 m '/day
chemical-specific {see Sea wo 3.3 1)
4,63 x 10* mVkg {sec Section 33.2)
i7a)
wtocre:
c„
K,
K«
OC
s
soil Saturation concentration (trig/kg)
soil-water partition coefficient (IJkg)
organic carbon partition coefficient (Ukg)
organic carbon content c>! sen) (fraction)
solubility (rng/I--waiefl
soil moisture corners;, expressed as a weight fraction
soil moisture content, expressed as i.-water Ag-«ofl
.PSftilVjgg
eieinicat-spittaffc, or s GC
y tftr
or 0.02
s»ie«specifc
si:ie.specific
REDUCED EQUATION: COMMERCIAL/INDUSTRIAL SOIL - NONCARC1NOCENIC EFrKCTN
Risk.-toed = 102
PRO (mjtjkg; |(5 * KT'/RfD.) + (fl.RtD.j * {(2ftVF) ~ (4J x lO"*))))
THI « I)
where;
RfD, « oral chro»c reference toe in mj/k|4ay
RfD, * inhalation chronic reference dose in mg*g«lay
VF ¦ ctewail-spectSt sort-to-air wtutttenioB factor in mVkg (see Section 33.1)
If PRO > C^,, then set PRG = Cm {where Cw = soil saturation concentration (mg/kg); see Equal**-., ' ¦
Section 3.3.1).
-------
A chemical-specific value for VP is used in the
standard default equations (Equations (6), (6*),
(7), and (?*) 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 VF. 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 panicles {PMW) 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 10 wind erosion and.
therefore, depend on the erodibility of the surface
SOIL-TO-AIR VOLATILIZATION FACTOR
VF{or7kg) » (LSk V»Dffi x f3J4x a iTt" (8 s
A (2 x D„ x E x K„ x tOJ kg/g)
where:
# (crrr/s) = (D_ x El
E * (p.X 1-E)/K»
Standard default parameter values thai can be used to reduce Equation (8) are listed below. These represent "typical"
values as identified m a number of sources. For example, when site-specific values are not available, the length of a
side of ihe contaminated area (LS) s assumed to be 45 m; this is based on a contaminated area of 0.5 acre whictr
approximates the size of an average residential tot. He "typical" values 15, DH, and ¥ are from EPA 1986 'Typical'
values for E, OC. and p, are from EPA 1984, EPA 1988b, and EPA 1988f. Site-spectfie data should be subsisted
for the default values listed below wherever possible. Standard values for chemical-specific D„ H, and k^. can he
obtained by calling the Superfund Health Risk Technical Support Center.
Parameter
DeHuH
VF
volatilization factor (mJ/kg)
—
LS
length of side of contaminated area (m)
45 m
V
w»od speed in mixing zone (m/s)
2.25 m/s
DH
diffusion height (m)
2 m
A
area of contamination (enr)
20,250,000 cm1
effective diffusmty (cm:/s)
D.xEV
E
true soil porosity (unities)
0.35
K
sott/air partition coefficient (g so»lfcmJ air)
(H/K^) x 41, where 41 ts a unrn
conversion factor
P.
true soil density or particulate density {g/cm1)
2.65 g/cm1
T
exposure interval (s)
7.9 x Vf s
D,
molecular diffusely (cm:/s)
chemical-specific
H
Henry's law constant (aimm'/mot)
ctsemieat-specific
K,
soil-water partition coefficient (em'/g)
chemical-specific, or Kw x OC
K.<
organic carbon partition coefficient (cmJ/g)
chemical-specific
OC
organic carbon content of soil (fraction)
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 toy bare
surfaces of finely divided material such as sandy
agricultural soil with a large number ('unlimited
reservoir") of erodible particles. Such surfaces
erode it 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 particulates; it
is used to derive Equations (6) and (7) in Section
3.2.2.
3.4 CALCULATION AND
PRESENTATION OF RISK-
BASED PRCs
The equations presented in this chapter can be
used to calculate risk-based PRGs for both
carcinogenic and noncarcinogenic effects. Ifboth
a carcinogenic and a poncarcinoeenic risk-based
PRG are calculated for a particular chemical, then
Using the default parameter values given in
the box for Equation (9). the default PEF is equal
to 4.63 x 109 m3/kg. The default values necessary
to calculate the flux rate for an "unlimited
reservoir* surface (i.e., G, UB, U,, and F(x)) are
provided by Cowherd (1985). and the remaining
default values (ie., for LS, 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.
the lower-of the two Values ts considered ihc
appropriate risk-based PRG for am given
contaminant. The case-study box below. iIIummio
a calculation of a risk-based PRG. A -umrrur.
table — such as that in the final case stuJv n-\ -
should be developed to present both the n>k ru^-d
PRGs and the ARAR-hased PRGs The uhIt-
should be labeled as to whether it pressnt> the
concentrations that were developed during
or after the baseline risk assessment
particulate emission factor
PEF {orVkgj
- LS x V x DH * 3600 s/hr
it 1000 e/ka
A
0 036 x (1-G) i (U„U,)' x F(x)
where
Parameier
Definition
0.036 g/ml-hr
G
fraction of vegetative cover (umtiess)
0
u.
mean annual wind speed (tn/s)
4,5 mA
u,
equivalent threshold value of wind speed
12.8 mJi
at 10 m (m/i)
F(x)
function dependent on tJ„/U, (uniiiess)
0.0497 (determined using Cowherd 1985.
-30-
-------
CASE STUDY: CALCULATE RISK-BASED PRCs'
Risk-based PRGs for ground water for isoptoorooe, one of the chemicals detected in ground-water monitoring
welts ai the site, are calculated beto*. Initial risk-based PRGs for isophorooe (carcinogenic and noocaronogcnic
effects) are derived using Equations (1') and (2 *) in Section 3.1.1, Equations (I') and (2*) combine the toxicity
information of the chemical {oral RfD of 0.2 mg^g-day and oral SF of 0,0039 [mg/kg-day]"'; inhalation values are
not available and, therefore, only the oral exposure route ts considered) with standard exposure parameters. The
calculated concentrations in mg/L correspond to a target risk of Iff* and a target HO of 1, as follows.
Carcinogenic
risk-based PEG
2CSFJ
Noncarcinogcmc
risk-based PRG
73
2/RfD.
17 x KT1
2(0.0039)
0.022 rng/l.
JL
mi
7.3 mg/L
The lower of tlie wo values (i.e., 0.022 mg/L) is selected as the appropriate rislNwsed PRG. Rsk-based PRGs are
calculated similarly for the other chemicals of concern.
1 All information in this example is for illustration purposes only.
CASE STUDY; PRESENT PRGs DEVELOPED DURING SCOPING'
Site XYZ Co.
Location; Anytown, Anystate
Medium: Ground Water
Land Use: Residential
Exposure Routes. Water Ingestion, Inhalation of
Voiatiies
Chemical
Risk-based PRGs
(mg/L)*
ARAR-based PRG
Iff*
HO = 1
Type
Concentration (mg/L)
Benzene
—
—
MCL
0.005
Carbon Tetrachloride
_
_
MCL
0.005
Ett^ltoenzene
—
_
MCLG
0,7* •*
MCL
0.7
Hexane
_
0.33
_
_
Isophorone
0.022* *
73
—
_
Tnaflate
—
0.47
—
—
1,1,2-Tnchloroethane
_
_
MCLG
0.003* **
MCL
0.005
| Vinyl chloride
—
—
MCL
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 PRt«
Of the two potential ARAR-tescd PRGs for this chemical, this concentration a selected as the ARAK
based PRG.
-31-
-------
CHAPTER 4
RISK-BASED PRGs FOR
RADIOACTIVE CONTAMINANTS
*
This chapter presents standardized exposure
parameters, derivations of risk equations, and
"reduced* equations (or calculating risk-based
PRGs for radioactive contaminants for the
pathways and land-use scenarios discussed in
Chapter 2. in addition, a radiation sue case study
is provided ai the end of the chapter to illustrate
(I) low 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 wed in
this chapter, and therefore should be. reviewed
More 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, standardisied default exposure
equations and parameters used to calculate risk,
based PRGs for radionuclides are similar in
structure a ad function to those equations and
parameters developed in Chapter 3 for
nonradioactive chemical carcinogens, toll types
of risk equations:
• Calculate risk-based PRGs for each carcinogen
corresponding to a pre-specified target cancer
risk level of 10"6. As meaitooed 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 i# the NCP.
• Use standardized default exposure parameters
consistent with OSWER Directive 9285.6-01
(EPA 1991b). Where default parameters are
not available in chat 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.» pfcocurics (pCi)) rather than in units of
mass (e.g., milligrams (mg)) Activity units are
more appropriate for radioactive substances
because concentrations of radionuclides m
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 m
humans. At mat CERCLA radiation sues,
potential health risks are usually based on the
radio toxicity, father than the chemical toxica-,,
of each nrtkmudkle proem.
• Use cancer slope feaon that ire best
estimates (ie.» median or 50th percentile
valves) of the age-averaged, lifetime excess
total cancer risk per unit intake oi a
radionuclide (e.g.. per pC> inhaled or mgeMcd)
or per unit external radiation exposure ;c i-.
per microRoentgen) to gamma vMuuru1
-------
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 son-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, is well as the age,
sex, arid 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 rjot expressed as a function of
body weight or time, and do not require
corrections for gastrointestinal absorption or
lung transfer efficiencies.
Risk-based PRG 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"6. 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
Rl.
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 rak = Risk firora ingestion of radionuclides
from water in water (aduk)
+ Risk from indoor inhalation of volatile
radionuclides 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 I x 10'5 atnt-tn3/mole
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 « SF„ * Intake from ingestion of
of radionuclides
+ SFj * 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 K)"6.
the risk-based PRG equation is derived as shown
in Equation (10).
Equation (10 ), presented in the next ho*, 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-spetified 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 «>i the
exposure parameter default values or jNvumpt,.n>
-34-
-------
RADIONUCLIDE PRCs: RESIDENTIAL WATER - CARCINOGENIC EFFECTS
Total risk
= (SF, i RW i JR. x EF x ED] + [SF, xRWxKxIR.sEF* EDJ
RW (pCi/L;
= TR
(10)
risk-based)
EF x ED x ((SFa x IE.) + (SF, i K x IR,)]
where:
Parameters
Definition (units)
Default Value
RW
radionuclide PRG in water (pCi/L)
_
TR
target excess individual lifetime cancer risk, (unities:)
104
SF,
inhalation slope factor (risk/pCi)
radionuclide-specific
SF,
oral (ingestion) slope factor (risk/pG)
radionuclide-specific
EF
exposure frequency (days/yr)
350 days^r
ED
exposure duration (yr)
30 yr
1R,
daily indoor inhalation rate (m'/day)
IS m3/day
ID
* -s.
daily water ingestion rate (Way)
2 IMay
k
vtfatifization factor (urwleat)
0.0005 x 1000 L/ttr (Andelman 1990)
REDUCED EQUATION TOR RADIONUCLIDE PRGs:
RESIDENTIAL WATER - CARCINOGENIC EFFECTS
Risk-based PRG « 9.5 x Iff" (10')
(pCi/L; TR ¦ 10*) 2(SF0) + WfSF)
where;
SF, = oral (ingestion) slope factor (nsk/pCi)
SF, = inhalation slope factor (nslc/pG)
in the risk equations to reflect site-specific
conditions. In this event, radionuclide PRCs
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 arc 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. Se is expressed
as a fractional value between 0 and t, delineating
the possible risk reduction range from 0't to
100%, respectively, due to shielding. The default
value of 0.2 for Se for both reside nmi and
commercial/industrial land-use scenarios reflects
the initial conservative assumption of u 2OS-
reduction in external exposure due to shielding
from structures (see EPA 1981). Te is cxprc-ssfd as
the quotient of the daily number of hour*, an
individual is exposed directly to an cxtcrrui
radiation field divided by the total number <>f
exposure hours assumed each day for a gncn un«j
-35-
-------
use scenario vie., 24 hours for residential and 8
hours for commercial-industrial). The default
value of 1 for Te for 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 sue specific conditions.
In addition to direct ingestion of soil
contaminated wuh 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-emuting radionuclides in soil
Total risk for carcinogenic effects from each
radionuclide of potential concern is calculated by
combining the appropriate oral slope factor, SFV
with the total radionuclide intake from soil, plus
the appropriate externa! radiation slope factor,
SFe, wuh the radioactivity concentration in soil.
T«jI risk = 8F# * Intake from direct ingestion
of soil
+ SF, i Coacemnoiofl of gamma-
eraittinf radkxjuciidet m soil
Aiding appropriate parameters, then combining
and rearranging the equation to solve for
concentration, results in Equation (II).
Equation (II*) is the reduced version of
Equation (II) based on the standard default vuiues
listed below. Risk-based PRGs for radionuclides-
in soil are calculated for a pre-specified cancer risk
level of 10*.
The age-adjusted soil ingestion factor
(IFsoii/auj) used it Equation (11) takes into account
the difference in soil ingestion for two exposure
groups — children of one to six yean and all other
individuals from seven to 31 years. IF^^, is
calculated for radioactive contaminants as shown in
Equation (12). Section 3.1.2 provides additional
discussion on theage«adjttsied 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 PRCs for radionuclides in
ground water (and for radionuclides in surface
water used for drinking water purpose.*,) arc based
on residential exposures and calculated according
to the procedures detailed in Section 4 ] ! >see
Section 3.2.1 for the rationale for this approach t
Risk-based PRGs should be calculated considering
tft€ possibility that both the worker ami general
population ai large may 0e exposed to ihe virne
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 particulates,
and external exposure due to gamma < nun me
radionuclide — are combined to calculate mk-
based radionuclide PRGs to soil for adult murker
exposures. Additional exposure routes tea,
ingestion Of foodcrops contamin.iuj K
radionuclide uptake) are possible at -.one v.tc.v
while only one exposure route tee ctitrmji
radiation cxpoture only) may be relevant .it others
The risk assessor should therefore jnd
combine all relevant soil exposure n»«to, as
necessary and appropriate, based on mu- ^(x-ufsc
conditions.
. Vv
-------
RADIONUCLIDE PRGs: RESIDENTIAL SOIL - CARCINOGENIC EFFECTS
Total risk =
RS * l(SF0 x lO^g/img * EF % JF^^) + (SF, x lOtykg x ED x D x SD x {1-S.) x TJJ
R5 (pCi/jj; =
TR
nil
risk-based)
(SFa x 105 x EF x IF^) t {SF, x 10' x ED x D x SD x (1-S,) x T.)
where:
ElSIXlSfi
Bsaajgiisnia
Default Value
RS
radionuclide PRG in soil (pCi/g)
TR
target excess individual lifetime cancer rat (unities*)
104
SF„
oral (ingestion) slope factor (risk/pCi)
radiooucMe-specific
SF.
external exposure slope factor (rok/yr per pCi/m2)
radionuclide-spedflc
EF
exposure frequency (days#-)
350 days^rr
ED
exposure duration (yr>
30 yr
1P
age-adjusted sal ingestion factor (mg-yr/day)
3600 mg-yrAtoy (see Equation (12))
D
depth of radionuclides in soil (m)
0,1 m
SD
soil density (kg/tn})
1.43 x 101 kfta1
s.
gamma shielding fisctw (unuless)
0,2 (see Section 4.1.2)
T,
gamma exposure time factor (unitless)
1 (see Section 4.1.2)
REDUCED EQUATION FOR RADIONUCLIDE PRGs:
RESIDENTIAL SOIL - CARCINOGENIC EFFECTS
Risk-based PRG
(pCi/g; TR » 10*)
= 1 x 10"
i'i x lO^SF,) + 3.4 X 10* (SFt)
(ill
where:
SF0
SF,
oral (ingestion) slope factor (risk/pCi)
external exposure slope factor (nsk^rr per pCi/nr)
AGE-ADJUSTED SOIL INGESTION FACTOR
IF.**, (mg-yr/day)
= 14 x EDW ,4) + f.ji x
Ml)
(12)
where;
Parameters
Definition funtts>
Default Value
14
ED„,U
^®»§* HI
age-adjusted sort ingest toe factor (mg-yr/day)
ingestion rate of soil ages 1-4 (mg/day)
ingestion rate of soil ages 7-3t (mg/day)
exposure duration during ages 1-6 (yr)
exposure duration during ages 7-31 (yr)
3600 mg-yrMay
200 mg/day
100 mg«ay
6yr
24 yr
-------
In the case illustrated below, total risk from
radionuclides in soil ts 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 sal (worker)
+ Risk from inhalation of volatile
radionuclides (worker)
+ Risk from inhalation of resuspended
radioactive particulates (worker)
+ Risk from external radiation from
ganuna-eoMtiag wtoonuciKte (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 » 8F„ x Intake from direct ingestion of
risk radiceaeldes in sot J (worker)
+ SF, x Intake from inhalation of
volatile radionuclides (worker)
+ SF, x Intake from inhalation of resus-
pended radioactive particulates
(worker)
+ SF, x 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-specifted cancer risk level of It)"6,
it combine 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 iO"6 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
PRCs should be derived using Equation (13)
4.2J 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 radionuclide 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
(SOS), 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 "lagged" organic
compounds), or when they can exist in the
environment in a variety of physical forms,
such as C-14 labeled carbon dioxide (CO;) gas
and tritiated water vapor. For these
radionuclides, VF values should be calculated
using the Hwang and Fate© (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 and
Ra-224, undergo radioactive decay and lorm
inert, gaseous isotopes of radon, i«. . Rn :::
(radon) and Rn-220 (thoron). ropccmdv.
Radioactive radon and thoron ease, cnuojtc
from their respective parent radium ivnnpcs
in soil, escape into the air. and un pmc
cancer risks if inhaled. For Ra-226 jnd K.i
224 in soil, use the default values shown m the
box on page 40 for VF and for Nf in
Equation (12) and Equation (12 i
43 RADIATION CASE STUDY
This section presents a case wuJv ,.i j
hypothetical CERCLA radiation sue. the \< ME
Radiation Co. site, to illustrate the pr.so* of
calculating pathway-specific risk-bascJ t.»r
radionuclides using the risk i- md
assumptions presented in the precedin-.- •>., > n- .if
this chapter. The radiation site ,.u
modeled after the XYZ Co. site stuih >Jiv ,«¦* m
-------
Total
risk
RADIONUCLIDE PRCs: COMMERCIAL/INDUSTRIAL SOIL - CARCINOGENIC EFFECTS
= RS x EDx |(SFa x 10 3g^rng * EF x IR.J + (SF, x ia'g/*S * Ef x IR„r x l/VF)
+ (SF, x * EF x lE^ x 1/PEF) + (SF, x lOfykg x D x SD x (i«S«) x T,)i
RS =
(pCi/g:
ruktuscd)
where:
ficamgigg
RS
TR
SF,
SF0
SF,
EF
ED
1R„
'^«od
VF
PEF
D
SD
S,
T,
TR
ED * [(SFaxlO'JxEFxIRB-) t- (SFjxlO'xEFxtR^.) x (1/VF + UPEF) + {SF/lADx^t-S^TJJ
Definition (units>
radionuclide PRG in soil (pCi/g)
urgu excess ifxHwdoal lifetime cancer risk (unites)
inhalation slope factor (ru*/pCi)
oral (mgcsuoo) slope factor (nsUpCi)
external exposure slope factor (rstjyr per pCi/tn:)
exposure frequency (daysftr)
exposure duration (yr)
workday inhalation rate of air {mJ/day)
daily soil ingestion rate (mgrtlay)
soil-to-air volatilization factor (m3fkg)
particulate emission factor (mJ/kg)
depth of radionuclides in sal (m)
soil density (kg/mJ)
gamma shielding factor (unit Jess)
gamma exposure factor (unities*)
(13}
Default Value
104
radionwlxle-speciftc
racMofwettJe-spedfic
radiomidtde-specific
250 daysfyr
25 «
20 mJttay
50 mg/day
radtofluctide-spedfic (see Section 4.2.3)
4,631 10* m'/kg (see Section 13,2)
0,1 m
1.43 x 10l kg/m3
0.2 {see Section 4.1.2)
1 (see Section 4.1.2)
Risk-tvsed PRG =
IpCi.g; TR = 10*)
where:
REDUCED EQUATION FOR RADIONUCLIDE PRCs:
COMMERCIAL/INDUSTRIAL SOIL — CARCINOGENIC EFFECTS*
1 x 10*
P-I x !(H(SF0)) + ((1.3 * lOVVF + 2.7 x 10 *) (SF,)) + (2.9 x 10° (SF,)}]
i l;
SF0
SF,
SF,
VF
oral (ingestion) slope factor (risk/pCi)
mtaiaiioe slope factor (risk/pG)
external exposure slope factor (nsk/yr per pCiAn1)
radtaauctide-ipecifc soiHo-a»r volatilization factor in mJ/Vg (see Section 3.3.1)
•NOTE: See Section 4,23 when calculating PRGs 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 arc calculated initially using
reduced equations based on PA/SI data, and then
a second, "after the baseline risk assessment" pha>e
wherein radionuclide PRGs are recalculated using
full equations and modified site-specific pjfimcu r
values based on Rl/FS data.
Following an overview of the tnM» n 4 * I.
Section 4.3.2 covers a number of imptmns
taken early in the scoping phase u>
preliminary risk-based PRGs assuming .» ;x. v
.vi.
-------
SOIL DEFAULT VALUES FOR VF AND SF,
FOR Ra-226 AND Ra-224
Default VF Inhalation
Value Slope
I rj \ Factor, SF,
Radium ' pan* an- ;mk,'pCi)**
Ra-226 8 MF.-U
Ra 224 200 4.TE-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/nr and (2) an average
Ra-224 soil concentration of ! pCVg associated
with an average ambient Rn-220 air concentration
of 5 pCi/m1
** Slope factor values are lor 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 waich 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 cued the company
for numerous storage and disposal violations.
After ACME failed to rectify- plant conditions
identified in iniiial 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
interview® 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 tbui
not entirely restricted) by an existing security
fence.
In 1988, EPA's regional field investigation
team completed a PA/Sl. Based on the PA. SI
data, the ACME Radiation Co. site scored jb<>\e
28.50 using the HRS and was listed on t he-
National Priorities List in 1989. Early in an
RI/FS was initiated and a baseline risk a^soxnent
is currently in progress.
43.2 AT THE SCOPING PHASE
In this subsection, several steps are outlined : »
show by example how initial site data are u>cd at
the scoping phase to calculate risk-based PR« !> >r
radionuclides in specific media of mnn-rn
Appropriate sections of Chapters 2 and < <-bt «IJ
be consulted for more detailed expijnjn> * r
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 ihe 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 ($-35),
and americium (Am-241 and Axn-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-24l 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.
Identity 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 studv.
examples are provided to illustrate how the full
risk equation (Equation (II)) and assumptions arc
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-emunng
radionuclides. Again, although soil is the unh
medium discussed throughout this ease studv.
exposure pathways, parameters, equations and
eventually risk-based concentrations would ncco io
be identified and developed for all other media jnd
exposure pathways of potential concern ji an
actual site.
Identify Toxicity Information. To t^kuKite
media-specific risk-based PRGs, reference toxicity
values for radiation-induced cancer effects arc
required (i.e., SFs). As stated previously *>il
ingestion and external radiation are the exposure
routes of concern for the soil pathway T
-------
RAIMA HON CASK STUDY:
TOXICITY INFORMATION FOR KADlONUCl.im S oh I'OTKNTIAI. CONCKRN*
UiiflioriuLfKlcs
111
CM4
l»-32
s-.vs
("i t-MJ
Sr-90
Am-24I
Am-243
Radioiiciivc
Half-life
(yr)
12
5730
0(M
0,24
5
29
3D
HrtXi
432
viWf
Decay
Mixlc
bcia
hci.i
hti.i
Kiii
hciii
hcia
ulphM/giiinma
atpha/gamma
I cuv
I yp.g
OiisMfitauon
g
S
P
1)
Y
D
I)
W
W
w
fnhHlatnm
Slope l-.itiiir
(rtsk/pO)
7.81'-H
6.41> IS
3.01 ¦> 12
1.91:-13
i.<»!•:-io
5,61;-11
1.91:-11
3.0I-4W
401-08
4.0E-06
Ingestion
SitijK l acit*
(nsk/pCi)
5 s i .. 14
9.1 If-13
3.51--12
2,21:-13
LSI;-II
¦ 3.3IMI
2 81: 11
1 21- HI
3 U -10
3 H-M0
External lupusurc
5l»pc Factor
(rakyyr per pCi/nr)
• Source* 1IEAST ani! Federal Guidance Report No II. AJI tnf.unwsion in this eewipie is for ilusiraifen only,
NA m Not applica^® {i*., these radionuclides are mil gamma-emitters stud (tic direct radiation exposure pMttwuy can be Ignored).
NA
NA
NA
NA
i.31-;-io
NA
NA
4,211-13
L6E-12
V6F.-I2
-------
Calculate Risk-based PRGs, At this step, nsk-
based PRGs arc calculated for each radionuclide of
potential concern using the reduced risk Equation
HI') in Section 4.1.2. SF values obtained from
IRIS and HEAST. and standardised 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"6, for
example, us ingestion SF of 1,5 x 10'11 and its
external exposure SF of 1.3 x 10'10 are substituted
into Equation (11*), along with the standardized
default values, as follows:
Risk based PRG * 1 i 10*
for Co-60 1.3 * lO'fSFj + 3.4 % 10* (SF.)
(pCi/g; TR . 10*)
where:
SF0 » oral (infcsioa) slope factor for Co-60 » 1.5 x
Iff" (risk/SpO)
SF, = aaeniai exposure slope factor for Co-60 * 1 »3
* 10* (raio-VT per pCi/rtr)
Substituting the values for SFe and SFe for Co-60
into Equation (ir ) results in:
Risk-based PEG for CO-60 (pCifc TR » 10"*) «
i « iff*
= 0,002 pCi of Co4»0/g of sal
In a similar manner, risk-based PRC* can be
calculated for all other radionuclides of concern in
soi! at the ACME Radiation Co. site, These PRGs
•ire presented in the next box.
4.3.3 AFTER THE BASELINE RISE
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
sot!. 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
-i—— ——
RADIATION Cask STL'DY:
INITIAL RISK BVSKl) PRGs FOR
RADIONUCLIDES IN SOIL*
Radionuclides Rtsk-bascd Soil PRG (pCi/g)
H-3
Sr-90 (only)
P-32
S-35
C-14
Co-60
Cs-137 (only)
Ra-226 (only}
Am-2*1
Aia-243 (only)
• Calculated for iKustranon ocly utttig Equation
(11') in Section 4.J .2. Values law teen founded
off.
measured on properties immediately bordering the
site. Measurements ortsitc ranged from 10 to SO
times background. In both cases, enhanced soil
concentrations of Ra-226 (and decay products) and
several other gamma-emitting radionuclides «.<• re-
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 (he
ACME Radiation Co. sue. 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 io 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
Oilers are dropped. For example, soil analyses
failed to detect P-32 (14-day half-life) or S- *5 (8">
day half-life) contamination. Decay correct ion
calculations strongly suggest that ihese
radionuclides should not be preseni onsite in
detectable quantities after an estimated burial time
of 30 years Therefore, based on these data, P %2
and S-35 are dropped from the list. Soil dais ato
confirm that decay products of Ra-226. Sr <*,* Cs
137, and Am 243 (identified in the first box be Mm
14.000 '
23
2®
3,500
850
§.002
27
06
0.2
7,9 * W:
-43-
-------
art present m ^ecuUf equilibrium {. c. equai
acuviiv concentrations, %vnh their respective parent
isotopes.
Assuming secular equilibrium, slope factors for
the parent isotope and each of Hi decay series
members arc summed. Parent isotopes are
designated with a " + D" 10 indicate the composite
slope factor of iu decay chain ishown in bold lace
in ihe second box below) "ttius, Ra026->-D, Sr-
90+D, C-s-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 tn the tull soil pathwa*.
equation to recalculate risk-based concentrations
RADIATION CASE STUDY: DECAY MtODUCIS
Parent Radionuclide
Deay Produces) (Half-life)
Ra-226
Rn-222 ;J cays), P days)
_____
RADIATION CASE STUDY: SLOPE f ACTORS FOR DECAY SERIES*
Slope Factors
PwvStng
Inhatotion
Ingestion
External
Ra-226
3.0E-O9
1 2E-10
4.2E-13
Rn-222
?2E-n
—
2.2E-14
Po-218
5 KB-13
28E14
aoe+oo
Pb-214
2vj- ;2
1.8E-13
1J1-11
Bi-214
2 21--:?,
1.4E-13
&.0E-11
P0-214
2SE-19
I.0E-20
4.7E-15
Pb-210
1
6
-------
Review Land-use Assumptions. Al this step,
the future land-use assumption chosen during
scoping is reviewed. Since the original assumption
of future residential laud use is supported by Rl/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 Te and Sc are changed
to 0.75 (i.e., IS hr/24 hr) and 0.5, respectively.
Modify Toxicity Information. As discussed
above in the section on modifying the list of
radionuclides of concent, 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 PRCs. At this step,
risk-based PRGs are recalculated for ail remaining
radionuclides of potential concern using the full
risk equation for the soil pathway (i.e.. Equation
(11)) modified by revised '-ne-specific assumptions
regarding exposures, as discussed above.
To recalculate the risk-based PRO for Co-60
at a pre-spectfied target risk level of 10"6. for
example, its ingestion $F of 1.5 x 10"U, and its
external exposure SF of 1.3 x 10'10 are 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 assessors
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/f;
risk-based)
TR
where:
Parameters
RS
TR
SFa
SF,
EF
ED
IF,
D
SD
8*
T,
mMj
(SF„ i 10J x EF x IF^) + (SF, i I# x ED x D x SD * (I -Se) * T,)
0.003 pCi/g
Definition funilsl
radionuclide PRG in soil (pCi/g)
target exceu todMduai lifetime cancer nsk (uouless)
oral (ingestion) slope factor (risk/pCi)
external exposure slope factor (rtsfuyr per pCi/br)
exposure frequency (days/yr)
exposure duration (yr)
age-adjusted soil ingest ion factor (mg-yrAlay)
depth of radionuclides in soil (m)
soil density (kg/m1)
gamma shielding factor (unities*)
gamma exposure time factor (umtless)
Revised Value
to-*
IS I 10 " (rttk/pCi)
t J * JO-* (roktyr per pG/tir)
35© days,*yr
45 yr
5100 mg-yr/day
0.1 m
1 43* 105 kg/m5
§.5
0.75
(Note: To account for the revised upper-bound residential residency time of 45 years, the age-adjusted soti
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 PRCs FOR RADIONUCLIDES IN SOIL*
Radionuclides
Risk-Cosed Sal PRO (pCi/g)
H-3
Sr-90+D
C-U
co-m
Cs-l.V7+D
Ra-226+D
Am-241
Am-243+D
10,200
20
620
0,003
0.01
0.004
0.2,
0.03
Calculated for illustration only. Values have been rounded off.
-46-
-------
REFERENCES
Andelman, J.B. 1990. Tola! Expo-sure to Volatile Organic Chemicals in Potable Water. N.M. Ram, R.F.
Christman, K.P. Cantor (eds.). Lewis Publishers.
Cowherd, C. Mulesfci, G„ Engelhart, P., and Gillete, D. 1985. Rapid Assessment of Exposure to Particulate
Emissions from Surface Contamination. Prepared for EPA Office of Health and Environmental Assessment.
EPA/600/8-85AJ02.
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 Advisory 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 13,7,8-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. EP A/540/G-89/004 (OSWER Directive #9355,3-0! >.
EPA. I988d. Guidance on Remedial Actions for Contaminated Ground Water at Superfund Sites, interim Final.
Office of Emergency and Remedial Response. EPA/S40/G-88/003 (OSWER Directive #9283 1-2)
EPA 19881 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 20to:
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 Emergent and
Remedial Response. OSWER Directive 9355,3-02.
EPA 1989c. Methods fbr Evaluating the Attainment of Cleanup Standards (Volume 1: Soils and Solid
Statistical Policy Branch. NTIS #PB89-234-959/AS.
EPA. I989d. Risk Assessment Guidance for Superfund: Volume I — Human Health Evaluation Manual
-------
EPA. 1990b. Guidance for Data Usability in Risk Assessment. Office of Solid Waste and Emergency
Response. EPA/540/G-90-008 (OSWER Directive #92S5.7-05).
EPA. 1990c. Guidance m Remedial Actions for Superfund Sires with PCB Contamination. Office of Emergency
and Remedial Response. EPA/540/G-9Q/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 Remedied Investigations/Feasibility Studies for CERCLA Municipal Landfill Sites.
Office of Emergency and Remedial Response. EPA540/P-91AXH (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 Superfttnd Remedy Selection Decisions. Office of Solid
Waste and Emergency Response. OSWER Directive 9355.0-30.
EPA 199 Id. Risk Assessment Guidance for Superfund: Volume / — Human Health Evaluation Manual (Part
C, Risk Evaluation of Remedial Alternatives). Interim. Office of Emergency and Remedial Response. OSWER
Directive 9285.7-01C.
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. (ed). Plenum Publishing Corp.
•4S-
-------
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
thai 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
Remedmtoo goals were identified for both A and B. Chemical A's goal is 0.5 ug/L, which a associated with I
potential risk of 10*. Chemical B's goal ts 10 ug/L, which o also associated with a potential risk of 10* I he
calculated cumulative risk at remediation goals ts therefore 2 x 10"*. Assuming for the purposes of the illustration
that A and i are treated Of removed at the same rate, then the 8m chemical to meet its goal wtii he it
Remediation must continue at this site, however, until the goaf for chemical A has been met. When the
concentration of A reaches 05 ug/L, then remediation is complete. A is at its goaf and has a risk of 10"* B is *t
1/20 of its goal with a risk of 5 x 10"*. The total rtsk {I x 10"* + 5 * 10"*) is approximately Iff4 and ts due u> ir*
presence of A.
This example illustrates that the final risk tor a chemical may not be equal to the potential risk associate
its remediation goal, and, in feet, can be much less than this risk. Although the potential risk associated »un
Chemical B's goal a 10* the final residual risk associated with B is 5 x 104. Thus, if one were to calcuUir i v
cumulative risk at PRCs prior to remedy implementation, one would estimate total medium risk of 2 x 10* cr
the residua! cumulative risk after remediation a i x 10"*
-4M.
-------
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 Ml 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 ground water
contaminated by soil leachate. for which guidance
is currently being developed by EPA, could be
included in the overall exposure pathway
evaluation.
B.1 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 io
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.l.L 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
Bs&i! Yah?e
c
chemical concentration m water (mg/L)
SF;
inhalation cancer slope factor {{mg/kg-day)'J)
cfteowal-specife
SFa
oral cancer slope factor ((mg/kg-day)1)
chemical-specific
RfD0
oral chronic reference dose {mg/kg-day)
ctoetnical-specific
RID,
inhalation chronic reference dose (mg/kg-day)
chemicaupeafie
BW
adult body weight (kg)
70 kg
AT
averaging time (yr)
70 yr far cancer risk
30 yr fit* noocaacer HI (equal to 1 t)
EF
exposure frequency (days/yr)
350days/yr
ED
exposure duration (yr)
30 yr
K
volatilization factor (Urn3)
0.0005 x 1000 Urn1 (Andebnan
IR.
daily indoor inhalation rate (mJAtey)
IS mVday
IR»
daily water ingestion rate (L/day)
2 Way
-51-
-------
Rtsk from ingestion = SF. % C % 1R,. x EF x ED
of water (adult) BW x AT x 365 daystyr
The noncancer HQ due to ingestion of a
contaminant in water is calculated as follows:
HO due to ingestion = C x JR.. x EF x ED
of water (adult} RfD0x BWi AT* 365 day*tyr
B.1.2 INHALATION OF VOLAT1LES
The cancer risk clue to inhalation of a volatile
contaminant in water is calculated as follows:
Risk from - SF. x C x K x 11L x EF i ED
inhalation BW x AT 1365 day^r
of volatile*
in water
(adult)
The noncancer HQ due to inhalation of a volatile
contaminant in water is calculated as follows:
HQ due to = C x K x IR-xEPxED
inhalation RfD; x BW x AT x 365 day&tyr
Of voiaules
in water
(adult)
B.2 SOIL - RESIDENTIAL LAND
USE
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 volatile
and,'or inhalation of particulates, 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 Iff* kHmt x EF x IF...,.,^
ingestion AT x 365 days^r
ofsoil
The noncancer HQ from ingestion of
contaminated soil is calculated » follows:
ingestion C RfD.xATx 365 dayvyr-"
of soil
1..2.2 INHALATION OF VOLATILES
The cancer risk awed by inhalation of
volatiles released from contaminated soil is:
Risk tan - SF x C x ED x EF x IR.„_ x f l/VPt
itshatattoci AT x BW x 365 days^r
of volatile*
The equation for calculating the noncancer HQ
from inhalation of volatiles released from soil is:
PARAMETERS FOR SOIL - RESIDENTIAL LAND USE
ElCi«*er
Definition
DefaultValue
C
chemical concentration in soil (mg/kg)
SF,
inhalation cancer slope factor ((mg/kg-day)'1)
chemical-specific
SF.
oral cancer slope factor ((mg/kg-day)'1)
chemical-specific
RfD0
oral chronic reference doae (mg/kg-day)
cbemtcaUpecific
RfD,
inhalation chronic reference dose (mg/kg-day)
chemical-specific
BW
adult body weight (kg)
70 kg
AT
averaging time (yr)
70 yr for cancer risk
30 yr far noncancer HI (equal to ED)
EF
exposure frequency (days^r)
350 dajntyr
ED
exposure duration (yr)
30 yr
IR,
daily indoor inhalation rate (n^/day)
15 tnVday
age-adjusted soil ingestion facta (mg-yr/kg-day)
114 mg-yr/kg-day
VF
sotl-to-air volatilization factor (m'/kg)
chemical specific (see Seaion 3.3.1)
PEF
pariiculaie emission factor (m3/kg)
4.63 x 10* mJ/kg (see Section 3.3,2)
-52-
I
-------
HQ from = C. » ED x EF x IR.. x (l/VFl
inhalation Rffl, x BW x AT x 365 days/yr
of voiatiles
B.2.3 INHALATION OF PARTICULATES
Cancer risk due to inhalation of
contaminated soil particulates is calculated as;
Risk - SF x C x ED x EF x IR. . x H/PEFl
from AT x BW x 365 days/yr
inhala-
tion of
particulates
The noncancer HQ from particulate inhalation is
calculated using this equation:
HQ from - C x ED x EF x IR._ x tUFEF\
inhalation RfD, x BW x AT x 365 days^r
of parti-
culates
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.
BJ.l INGESTION OF SOIL
The cancer risk from ingestion of
contaminated soil is calculated as follows.
Risk from = SF. x C x 10* kg/mg x EF x ED x IR..,
ingestion BW x AT x 365 days^r
of soil
The noncancer HQ'from ingestion of contaminated
soil is calculated as follows:
HO from = Cx 10* total x EF x ED x IR..,
ingestion RfDa x BW x AT x 365 days^r
of soil
BJ.2 INHALATION OF VOLATILES
The cancer risk caused by inhalation of
volatile® released from contaminated soil is:
Risk from « SF. x C x ED x EF x IR... x fl/VFI
inhalation AT x BW x 365 days,yr
of voiaiiles
The equation for calculating the noncancer HQ
from inhalation of voiatiles released from soil is:
HQ from - C x ED x EF x 1R.,. x n/VPi
inhalation RfD, x BW x AT x 365 days/yr
of voiatiles
Note that the VF value has been developed
specifically for thee equations; it may not be
applicable in other technical contexts.
PARAMETERS rot SOIL - COMMERCIAL/INDUSTRIAL land use
Parameter
fjfiftult Value
C
chemical concentration to soil (mg/tg)
_
SF,
inhalation cancer slope factor ((mg/fcg-day)"1)
chemical-specific
SF0
oral cancer slope bet or ((mg/kg-day)')
chemical-specific
RfD„
oral chronic reference dose (mg/kg-day)
chemical-specific
RfD,
inhalation chronic reference dote (mg/kg-day)
cftemtaii-spectfic
BW
adult body weight (kg)
70 kg
AT
averaging time (yr)
70 yr for cancer risk
30 yr for noncancer HI (equal to ED)
EF
expowre frequency (days/yr)
2S0 days/yr
ED
exposure duration (yr)
25 yr
IRj*
workday inhalation rate (mJ/day)
20 mVday
IR^i,
soil ingestion rate (mg/day)
50 mg/day
VF
soif-to-atr volatilization factor (nvVkg)
chemical specific (sec Section 3 J.! |
PEF
particulate emission factor (m'/kg)
4,63 x 10* m5/kg (see Section 3,3.2)
-53-
-------
B.J.3 INHALATION OF PARTICULATES
Cancer risk due to inhalation of
contaminated soil particulates is calculated as;
Risk from « SF xCxEDxEFx 1R.. i H/PF.R
inhalation AT x BW x 365 days^r
of particulates
The noncancer HQ from particulate inhalation is
calculated using this equation:
HO from = C i ED x £F x tR . x 1t/PEF>
inhalation RfD, x BW x AT x 365 days/yr
------- |