vvEPA
           United States
           Environmental Protection
           Agency
               Office of Research and
               Development
               Washington, DC 20460
EPA/540/R-92/003
December 1991
Risk Assessment Guidance
for Super fund:

Volume I -
Human Health Evaluation
Manual (Part B,
Development of Risk-based
Preliminary Remediation
Goals)

Interim

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                                EPA/540/R-92/003
                             Publication 9285.7-01 B
                                 December 1991
   Risk Assessment Guidance
          for Superfund:
            Volume I -
Human Health Evaluation Manual
     (Part B, Development of
     Risk-based Preliminary
       Remediation Goals)
               Interim
    Office of Emergency and Remedial Response
       U.S. Environmental Protection Agency
           Washington, DC 20460
                             Printed on Recycled Paper

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                                            NOTICE
        The policies  set out in this document are intended solely as guidance; they are not final U.S.
Environmental Protection Agency (EPA) actions.  These policies are not intended, nor can they be relied
upon, to create any rights enforceable by any party in litigation with the United States. EPA officials may
decide to follow the guidance provided in this document, or to act at variance with the guidance, based on an
analysis of specific site circumstances. The Agency also reserves the right to change this guidance at any time
without  public notice.

        This guidance is based on policies in the Final Rule  of the National Oil and Hazardous Substances
Pollution Contingency Plan (NCP), which was published on March 8, 1990 (55 Federal Register 8666). The
NCP should be considered  the authoritative source.

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                                CONTENTS

                                                                        Page

NOTICE    	ii

EXHIBITS	vi

DEFINITIONS 	vii

ACRONYMS/ABBREVIATIONS                                          ix

ACKNOWLEDGEMENTS  	xi

PREFACE	xii

1.0    INTRODUCTION  	 1

      1.1  DEFINITION OF PRELIMINARY REMEDIATION GOALS	1

      1.2  SCOPE OF PART B	1

      1.3  RELEVANT STATUTES, REGULATIONS, AND GUIDANCE	3

          1.3.1 CERCLA/SARA	3
          1.3.2 National Contingency Plan	3
          1.3.3 Guidance Documents	3

      1.4  INITIAL DEVELOPMENT OF PRELIMINARY REMEDIATION GOALS	4

      1.5  MODIFICATION OF PRELIMINARY REMEDIATION GOAN	5

      1.6  DOCUMENTATION AND COMMUNICATION OF PRELIMINARY
          REMEDIATION GOALS	6

      1.7  ORGANIZATION OF DOCUMENT	6

2.0    IDENTIFICATION OF PRELIMINARY REMEDIATION GOALS                7

      2.1  MEDIA OF  CONCERN	7

      2.2 CHEMICALS OF CONCERN	8

      2.3 FUTURE LAND USE	8

      2.4 APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS	9

          2.4.1 Chemical-, Location-, and Action-specific ARARs	10
          2.4.2 Selection of the Most Likely ARAR-based
                PRG for Each Chemical	11

      2.5 EXPOSURE PATHWAYS  PARAMETERS, AND EQUATIONS	11

          2.5.1 Ground Water/SurfaceWater	13
          2.5.2 Soil	13
                                     -in-

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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

          2.8.1 Review of Assumptions	15
          2.8.2 Identification of Uncertainties	16
          2.8.3 Other Considerations in Modifying PRGs	17
          2.8.4 Post-remedy Assessment	18

3.0    CALCULATION OF RISK-BASED PRELIMINARY
      REMEDIATION         GOALS                                 19

      3.1   RESIDENTIAL LAND USE	20

          3.1.1 Ground Water or Surface Water	20
          3.1.2  Soil	23

      3.2   COMMERCIAL/INDUSTRIAL LAND USE	24

          3.2.1 Water	24
          3.2.2 Soil	25

      3.3   VOLATILIZATION AND PARTICIPATE EMISSION FACTORS	26

          3.3.1 Soil-to-air Volatilization Factor	26
          3.3.2 Particulate Emission Factor	29

      3.4   CALCULATION AND PRESENTATION OF RISK-BASED PRGS	30

4.0    RISK-BASED PRGs FOR RADIOACTIVE CONTAMINANTS                33

      4.1 RESIDENTIAL  LAND  USE	34

          4.1.1 Ground Water or Surface Water	34
          4.1.2  Soil	35

      4.2 COMMERCIAL/INDUSTRIAL LAND USE	36

          4.2.1  Water	36
          4.2.2  Soil	36
          4.2.3 Soil-to-air Volatilization Factor	38

      4.3 RADIATION  CASE STUDY 	38

          4.3.1 Site History	 40
          4.3.2 At the Scoping  Phase	40
          4.3.3 After the Baseline Risk Assessment	43

REFERENCES  	47

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                              CONTENTS (Continued)

                                                                              Page

APPENDIX A    ILLUSTRATIONS OF CHEMICALS THAT "LIMIT" REMEDIATON          49

APPENDLX B    RISK EQUATIONS FOR INDIVIDUAL EXPOSURE PATHWAYS  	51

       B.I  GROUND WATER OR SURFACE WATER - RESIDENTIAL LAND USE  ... .51

           B.I.I Ingestion	51
           B.1.2 Inhalation of Volatiles	52

       B.2  SOIL- RESIDENTIAL LAND USE	52

           B.2. 1  Ingestion of Soil	52
           B.2.2  Inhalation of Volatiles	52
           B.2.3  Inhalation of Participates	53

       B.3  SOIL -COMMERCIAL/INDUSTRIAL LAND USE	53

           B.3.1  Ingestion of Soil	53
           B.3.2  Inhalation of Volatiles	53
           B.3.3 Inhalation of Participates	54
                                         -v-

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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

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                                        DEFINITIONS
             Term
                          Definition
Applicable or Relevant and
Appropriate Requirements
(ARARs)
Cancer Risk
Conceptual Site Model
Exposure  Parameters


Exposure Pathway
Exposure Point
Exposure  Route
Final  Remedialion Levels
"Applicable"  requirements are those clean-up standards, standards
of   control,   and  other  substantive  environmental  protection
requirements, criteria, or limitations promulgated under federal or
state law that specifically address a hazardous substance, pollutant,
contaminant, remedial action,  location, or other circumstance at a
Comprehensive  Environmental Response,  Compensation,  and
Liability  Act (CERCLA) site.    "Relevant  and appropriate"
requirements  are  those clean-up standards which, while  not
"applicable"  at a CERCLA site, address problems or situations
sufficiently similar to those encountered at the CERCLA site that
their use is well-suited to the particular site. ARARs can be action-
specific,  location-specific, or chemical-specific.

Incremental probability of an individual's developing cancer over a
lifetime as a result of exposure to a potential carcinogen.

A "model" of a site developed at scoping using readily available
information. Used to identify all potential or suspected sources of
contamination, types  and concentrations of contaminants detected
at the site, potentially contaminated media, and  potential exposure
pathways, including  receptors.   This  model is also known as
"conceptual evaluation model".

Variables used in the calculation of intake (e.g., exposure duration,
inhalation rate, average body weight).

The course a  chemical or physical agent lakes from a source to an
exposed  organism.   An exposure pathway  describes a unique
mechanism by which an individual or population is exposed to
chemicals or physical agents at or originating  from a site. Each
exposure pathway includes a source or release  from a source, an
exposure point, and an exposure route. If the exposure point differs
from the source, a transport/exposure medium (e.g., air) or media
(in cases of intermedia transfer) also would be indicated.

A location of potential contact between an orgnism and a chemical
or physical agent.

The way a chemical or physical agent comes in contact with an
organism (i.e., by ingestion, inhalation,  dermal contact).

Chemical-specific clean-up levels that  are  documented in  the
Record of Decision  (ROD).  They may  differ  from preliminary
remediation goals (PRGs) because of modifications resulting from
consideration of various  uncertainties,  technical  and exposure
factors, as well as  all nine selection-of-remedy criteria outlined in
the National Oil and  Hazardous Substances Pollution Contingency
Plan (NCP).

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                                  DEFINITIONS  (Continued)
             Term
                          Definition
Hazard Index (HI)
Hazard Quotient (HQ)
''Limiting"  Chemical(s)
Preliminary  Remediation Goals
(PRGs)
Quantitation Limit (QL)
Reference Dose (RfD)
Risk-based PRGs
Slope Factor (SF)
Target Risk
The sum of two or more hazard quotients for multiple substances
and/or multiple exposure pathways.

The ratio of a single substance exposure level over a specified time
period to a reference dose for that substance derived from a similar
exposure period.

Chemical(s) that are the last to be removed (or treated) from a
medium by a given technology. In theory, the cumulative residual
risk for a medium may approximately equal the risk associated with
the limiting chemical(s).

Initial clean-up goals that (1) are protective of human health and
the environment and (2) comply with ARARs. They are developed
early in the process based on readily available information and are
modified to reflect results of the baseline risk assessment.  They
also  are used during  analysis  of  remedial  alternatives in the
remedial investigation/feasibility study  (RI/FS).

The  lowest level at which a chemical can be accurately and
reproducibly quantitated. Usually equal to the method detection
limit multiplied by a factor of three to  five, but varies for different
chemicals and different samples.

The Agency's preferred toxicity value for evaluating potential
noncarcinogenic  effects in  humans resulting from contaminant
exposures  at CERCLA sites.  (See RAGS/HHEM Part A  for a
discussion of different kinds  of reference doses  and reference
concentrations.)

Concentration levels set at scoping for individual chemicals that
correspond to a specific cancer risk level of 10'or an HQ/HI of 1.
They are generally selected when ARARs are not available.

A plausible upper-bound estimate of the probability of a response
per unit intake of a chemical over a lifetime. The slope factor is
used to estimate  an  upper-bound probability of an  individual's
developing cancer as  a  result  of  a  lifetime of exposure  to a
particular level of a potential carcinogen.

A value that is combined with exposure and toxicity information to
calculate a risk-based concentration  (e.g., PRG). For  carcinogenic
effects, the target  risk is a cancer risk of 10'. For noncarcinogenic
effects, the target risk is a hazard quotient of 1.
                                               -Vlll-

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                            ACRONYMS/ABBREVIATIONS
     Acronym/
    Abbreviation
                             Definition
ARARs

CAA

CERCLA

CFR

CWA

BAG

ECAO


EF

EPA

FWQC

HEAST

HHEM

HI

HQ

HRS

IRIS

LLW

MCL

MCLG

NCP

NPL

OSWER

OERR
Applicable or Relevant and Appropriate Requirements

Clean Air Act

Comprehensive Environmental Response, Compensation, and Liability Act

Code of Federal Regulations

Clean Water Act

Exposure  Assessment Group

Environmental Criteria and Assessment Office
Superfund Health Risk Technical Support Center

Exposure  Frequency

U.S. Environmental Protection Agency

Federal Water Quality Criteria

Health Effects Assessment Summary Tables

Human Health Evaluation Manual

Hazard Index

Hazard Quotient

Hazard Ranking System

Integrated Risk Information System

Low-level Radioactive Waste

Maximum Contaminant Level

Maximum Contaminant Level Goal

National Oil and Hazardous Substances Pollution Contingency Plan

National Priorities List

Office of Solid Waste and Emergency Response

Office of Emergency  and Remedial Response

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                       ACRONYMS/ABBREVIATIONS (Continued)
     Acronyms/
    Abbreviation
                              Definition
PA/SI

PEF

PRO

RAGS

RCRA

RfC

RfD

RI/FS

RME

ROD

RPM

SARA

SDWA

SF

TR

VF

WQS
Preliminary Assessment/Site Inspection

Particulate Emission Factor

Preliminary Remediation Goal

Risk Assessment Guidance for Superfund

Resource Conservation and Recovery Act

Reference Concentration

Reference Dose

Remedial Investigation/Feasibility Study

Reasonable Maximum Exposure

Record of Decision

Remedial Project Manager

Superfund Amendments and Reauthorization  Act

Safe Drinking Water Act

Slope Factor

Target Risk

Volatilization  Factor

State Water Quality Standards

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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 especially like to acknowledge the efforts
of the staff in the Regions, as well as the following offices:

               Guidance and Evaluation Branch, Office of Waste Programs Enforcement;
               Remedial Operations and Guidance Branch, Office of Emergency and Remedial Response;
               Policy and Analysis Staff, Office of Emergency and Remedial Response;
               Environmental Response  Branch, Office of Emergency and Remedial Reaponse;
               Office of General Counsel; and
               Exposure Assessment Group, Office of Research and Development.

        ICF Incorporated (under EPA Contract Nos. 68-01-7389, 68-W8-0098, and 68-03-3452), S. Cohen and
Associates (under EPA Contract No. 68-D9-0170), and Environmental Quality Management, Incorporated
(under EPA Contract No. 68-03-3482),  provided technical assistance to EPA in support of the development
of this manual.

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                                           PREFACE
       Risk Assessment Guidance for Superfund:    Volume  I - Human Health  Evaluation Manual
(RAGS/HHEM) Part B is one of a three-part series. Part A addresses the baseline risk assessment; Part C
addresses human health risk evaluations of remedial alternatives. Part B provides guidance on using U.S.
Environmental Protection Agency (EPA) toxicity values and exposure information to derive risk-based
preliminary remedial  goals  (PRGs) for a  Comprehensive Environmental Response, Compensation, and
Liability Act (CERCLA) site.  Initially developed at the scoping phase using readily available information, risk-
based  PRGs  generally  are modified based  on site-specific data gathered  during  the remedial
investigation/feasibility study (RI/FS).  This guidance does not discuss the risk management decisions that are
necessary at a CERCLA  site (e.g., selection of final remediation goals). The potential users of Part B are
those involved in the remedy selection and implementation process, including risk assessors, risk assessment
reviewers, remedial project managers,  and other decision-makers.

       This manual is being distributed as an interim document to allow for a period of field testing and
review. RAGS/HHEM will be revised  in the future, and Parts A,  B, and C will be incorporated  into a single
final guidance  document.  Additional information for specific subject areas is being developed for  inclusion
in a later revision. These  areas include:

       •      development of goals for additional land uses and exposure pathways;
       •      development of short-term  goals;
       •      additional worker health and safety  issues; and
       •      determination of final remediation goals (and attainment).

       Comments addressing usefulness, changes, and  additional areas where guidance is needed should be
sent to:

               U.S. Environmental Protection Agency
               Toxics Integration  Branch  (OS-230)
               Office of Emergency  and Remedial Response
               401 M Street, SW
               Washington, DC 20460

               Telephone     202-260-9486
               FAX:           202-260-6852

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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  at  Comprehensive  Environmental
Response,  Compensation, and  Liability Act
(CERCLA) sites  in  developing preliminary
remediation goals (PRGs). This guidance is the
second part (Part B) in the series Risk Asseswnent
Guidance for Superfund:   Volume I — Human
Health Evaluation Manual (RAGS/HHEM).

    Part A  of this series (EPA  1989d) assists in
defining and completing a site-specific baseline risk
assessment; much of the information in Part A is
necessary background for Part B. Part B provides
guidance on using U.S.  Environmental Protection
Agency  (EPA)  toxicity  values  and  exposure
information to derive risk-based PRGs. Initially
developed  at the scoping phase  using readily
available information, risk-based PRGs  generally
are modified based on site-specific data gathered
during  the remedial investigation/feasibility  study
(RI/FS). Part C of this series (EPA  1991d) assists
RPMs, site  engineers, risk assessors, and others in
using risk information both to evaluate remedial
alternatives during the FS and to evaluate the
selected remedial alternative during and after its
implementation.  Exhibit 1-1 illustrates how the
three parts  of RAGS/HHEM are all used during
the RI/FS and other stages of the site remediation
process.

    The remainder of this introduction addresses
the definition of PRGs, the scope  of Part B, the
statutes,  regulations, and  guidance relevant to
PRGs, steps in identifying and modifying PRGs,
the communication and documentation of PRGs,
and the  organization of  the remainder of this
document.

1.1     DEFINITION OF
        PRELIMINARY
        REMEDIATION GOALS

    In general, PRGs provide remedial design staff
with long-term targets to. use during analysis and
selection of remedial alternatives.  Ideally, such
goals, if achieved,  should both comply with
applicable  or   relevant   and   appropriate
requirements (ARARs) and result in residual risks
that fully satisfy the National Oil and Hazardous
Substances Pollution Contingency Plan  (NCP)
requirements for the protection of human health
and the environment. By developing PRGs early
in the decision-making process (before the RI/FS
and the baseline risk assessment are completed),
design staff may be able to  streamline the
consideration of remedial alternatives.

    Chemical-specific PRGs are concentration
goals for individual chemicals for specific medium
and land use combinations at CERCLA sites.
There are two general sources of chemical-specific
PRGs: (1) concentrations based on ARARs and
(2)  concentrations   based on  risk assessment.
ARARs include concentration limits set by other
environmental regulations (e.g., non-zero maximum
contaminant level goals [MCLGs] set under the
Safe Drinking Water Act [SDWA]). The second
source for PRGs, and the focus of this document,
is risk assessment or risk-based calculations that
set concentration limits using carcinogenic and/or
noncarcinogenic toxicity values under specific
exposure conditions.

1.2    SCOPE  OF PART B

    The recommended approach for developing
remediation goals  is to identify PRGs at scoping,
modify them as needed at the end of the RI  or
during the FS based on site-specific information
from the baseline risk assessment, and ultimately
select remediation levels in the Record of Decision
(ROD). In order to set chemical-specific PRGs  in
a site-specific context, however, assessors must
answer fundamental questions  about  the  site.
Information on the chemicals that are present
onsite, the specific contaminated media, land-use
assumptions, and the exposure assumptions behind
pathways of individual exposure is necessary  in
order to develop chemical-specific PRGs. Part B
provides guidance for considering this information
in developing chemical-specific PRGs.
                                              -1-

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                                   EXHIBIT 1-1

          RELATIONSHIP OF THE HUMAN HEALTH EVALUATION
                          TO THE CERCLA  PROCESS
CERCLA REMEDIAL PROCESS












Remedial
Investigation
Feasibility
Study


Remedy Selection
and Record of
Decision


Remedial Design/
Remedial Action


Deletion/
Five-year Review
HUMAN  HEALTH EVALUATION MANUAL
                 PART A
            Baseline Risk Assessment
              PARTB
        Development of Risk-based
       Preliminary Remediation Goals
                                               PARTC
                                     Risk Evaluation of Remedial Alternatives
                                        -2-

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    Because  Part B  focuses on developing
chemical-specific  PRGs  based on Protection of
human  health, there  are important types  of
information that are not considered and that may
significantly influence the concentration  goals
needed  to satisfy the  CERCLA  criteria  for
selection  of a remedy.    For example,  no.
consideration is given to ecological effects in" this
guidance. Other types of remedial action "goals"
not addressed in  detail  include  action-specific
ARARs (e.g., technology- or  performance-based
standards)  and location-specific  ARARs.

    Throughout Part B, the  term  "chemical-
specific" should be understood to refer  to both
nonradioactive and radioactive chemical hazardous
substances, pollutants, or contaminants. Therefore,
the process described in this guidance  of selecting
and modifying PRGs at a  site should be applied to
each   radionuclide  of potential  concern.
Chapter 10  of RAGS/HHEM  Part A provides
background information concerning radionuclides,
and Chapter 4 of RAGS/HHEM Part B includes
radionuclide risk-based equations and a case study
of a hypothetical radiation site.

    This guidance only  addresses in detail the
initial selection of risk-based PRGs.   Detailed
guidance regarding other factors that can be used
to further  modify PRGs during  the  remedy
selection Process is presented in other documents
(see Section 1.3).

1.3     RELEVANT STATUTES,
        REGULATIONS, AND
        GUIDANCE

    This section provides relevant  background on
the CERCLA statute and the  regulations created
to implement the statute (i.e.,  the  NCP).  In
addition, other CERCLA  guidance documents are
listed and their relationship to  the site  remediation
process is discussed.
1.3.1
CERCLA/SARA
    CERCLA, as amended  by the Superfund
Amendments and Reauthorization Act of 1986
(SARA), is the authority for EPA to take response
actions. (Throughout this guidance, reference to
CERCLA  should  be understood to  mean
"CERCLA as amended by SARA.")
    Several sections  of CERCLA especially
section  121 (Clean-up Standards), set.  out the
requirements  and goals  of CERCLA.  Two
fundamental requirements  are  that  selected
remedies be protective of human health and the
environment, and comply with ARARs. CERCLA
indicates a strong preference for the selection of
remedial  alternatives that permanently  and
significantly  reduce  the  volume,  toxicity,  or
mobility of wastes.    To the maximum extent
practicable,  the  selected remedial alternatives
should  effect permanent solutions  by using
treatment technologies.  Both the  law  and the
regulation  (see  below)  call  for cost-effective
remedial alternatives.

1.3.2    NATIONAL CONTINGENCY PLAN

    Regulations implementing CERCLA are found
in Volume 40 of the Code of Federal Regulations
(CFR), Part 300, and are referred to collectively as
the NCP.  Section 300.430 of the NCP, and several
portions of the preambles in the  Federal Register
(55 Federal Register 8666, March 8,  1990 and 53
Federal  Register  51394, December 21, 1988),
address how the Superfund and  other CERCLA
programs are to implement the Act's requirements
and goals concerning clean-up levels.

    Nine criteria  have been developed in the NCP
to use in selecting a remedy. These criteria are
listed in the next box.  The first criterion - overall
protection of human health and the  environment
~~ is the focus of this document. This criterion
coupled with compliance with ARARs are referred
to as "threshold criteria" and must be met by the
selected remedial alternative. PRGs are developed
to quantify the standards that remedial alternatives
must  meet in order to achieve  these threshold
criteria. See the second box on the next page for
highlights from the NCP on remediation goals.

1.3.3    GUIDANCE DOCUMENTS

    There are several existing  documents that
provide gudiance on  related steps of  the site
remediation process.     These  documents  are
described in the box on  page five.   When
documents  are referenced throughout  this
guidance,  the abbreviated titles, indicated  in
parentheses after the full titles and bibliographic
information, are used.
                                              -3-

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       NINE EVALUATION CRITERIA FOR
    ANALYSIS  OF REMEDIAL ALTERNATIVES
            (40 CFR 300..430(e)(9)(iii))

   Threshold Criteria:
      Overall Protection of Human Health and the
      Environment
      Compliance with ARARs
   Balancing Criteria:
    • Long-term Effectiveness and Permanence
    • Reduction of Toxicity, Mobility, or Volume
      Through Treatment
    • Short-term Effectiveness
    • Implementability
    • Cost
   Modifying Criteria:
      State Acceptance
      Community Acceptance
1.4     INITIAL DEVELOPMENT OF
        PRELIMINARY
        REMEDIATION GOALS

    The NCP preamble indicates that, typically,
PRGs are developed at scoping or concurrent with
initial RI/FS activities (i.e., prior to completion of
the  baseline risk  assessment).    This early
determination of PRGs  facilitates development of
a range of appropriate  remedial alternatives  and
can focus selection on the most effective remedy.

    Development of PRGs  early in the RI/FS
requires the following site-specific data:

•   media of potential concern;
•   chemicals of potential concern; and
•     probable future land use.

This information may be found in the preliminary
assessment/site inspection (PA/SI) reports or in the
conceptual site model that is developed prior to or
during  scoping.  (When a site  is listed  on the
National  Priorities List [NPL], much  of  this
information is compiled during the PA/SI as part
of   the   Hazard Ranking  System  [HRS]
documentation record.) Once these factors are
known, all potential ARARs must be identified.
When ARARs do not exist, risk-based PRGs are
calculated using  EPA health criteria (i.e., reference
doses or cancer slope factors) and default or site-
specific exposure assumptions.
            NCP RULE HIGHLIGHTS
        RISK AND REMEDIATION GOALS
              (40 CFR 300.430(e)(2)]

       "In developing and, as appropriate, screening
   ... alternatives, the lead agency shall: (i) Establish
   remedial action objectives specifying contaminants
   and  media of concern, potential  exposure
   pathways, and remediation  goals.     Initially,
   preliminary remediation goals are developed based
   on readily available information, such as chemical-
   specific ARARs or other reliable information.
   Preliminary remediation goals should be modified,
   as necessary,  as more information becomes
   available during the  RI/FS. Final remediation
   goals will be determined when the remedy is
   selected.    Remediation goals shall establish
   acceptable exposure levels that are protective of
   human health and the environment and  shall be
   developed by considering the following

   (A)  Applicable or relevant  and appropriate
       requirements..., and the following factors:

       (1) For systemic toxicants, acceptable
           exposure  levels  shall represent
           concentration levels to which the human
           population, including sensitive  subgroups,
           may be exposed without adverse effect
           during a lifetime or part of a lifetime,
           incorporating  an adequate margin of
           safety;

       (2) For known or suspected carcinogens,
           acceptable exposure levels are generally
           concentration levels that represent an
           excess upper-bound lifetime cancer risk
           to an individual of between 10^ and 10"'
           using information on the relationship
           between dose and response. The 10"6
           risk level shall be used as the point of
           departure for determining remediation
           goals for alternatives when ARARs are
           not available  or are not sufficiently
           protective because  of   multiple
           contaminants  at a  site or multiple
           pathways of exposure  ..."
    It is important to remember that risk-based
PRGs (either at scoping or later on) are initial
guidelines. They do not establish that cleanup to
meet these  goals is warranted.   A risk-based
concentration, as calculated in this  guidance, will
be considered a final remediation level only after
appropriate analysis in the RI/FS and ROD.
                                                  -4-

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                                        GUIDANCE DOCUMENTS

   •   Risk Assessment Guidance for Superfund: Volume I - Human Health Evaluation Manual Part A  (EPA 198%)
       (RAGS/HHEM Part A) contains background information and is particularly relevant for developing exposure and
       toxicity assessments that are required when refining chemical-specific risk-based concentrations, and accounting
       for site-specific  factors such as multiple exposure pathways.

   •  Guidance for Conducting Remedial Investigations and Feasibility Studies  Under CERCLA (EPA 1988c) (RI/FS
       Guidance) presents detailed information about implementing the RI/FS and general information  on the use of
       risk-based factors and ARARs in the context of the RI/FS.

   •  Guidance on Remedial Action for Contaminated Ground Water at Superfund Sites (EPA 1988d) (Ground-water
       Guidance) details some of the key issues in development, evaluation, and selection of ground-water remedial
       actions at CERCLA sites.

   •  CERCLA Compliance with Other Laws Manuals (Part I, EPA 1988a  and Part II, EPA 1989a) (CERCLA
       Compliance Manuals) provide guidance for complying with ARARs. Part  I addresses the Resource Conservation
       and Recovery Act (RCRA), the Clean Water Act (CWA), and the SDWA; Part II addresses the Clean Air Act
       (CAA), other federal statutes, and state requirements.

   •  Methods for Evaluating the Attainment of Cleanup Standards (Volume 1: Soils and Solid Wrote)  (EPA 1989e)
       and Methods for Evaluating the Attainment of Cleanup Standards (Volume 2: Water) (Draft, 1988, EPA
       Statistical Policy Branch) (Attainment Guidance) provide guidance on evaluating the attainment of remediation
       levels, including appropriate sampling and  statistical procedures to test whether the chemical concentrations are
       significantly below the remediation levels.

   •  Interim Final Guidance on Preparing Superfund Decision Documents (EPA 1989b) (ROD Guidance) provides
       guidance that (1) preaentd standard formats for documenting CERCLA remedial action decisions; (2) clarifies
       the roles and responsibilities of EPA, states, and other federal agencies in developing and  issuing decision
       documents; and (3) explains how to address changes made to proposed and selected remedies.

   •  Catalog of Superfund Program Publications, Chapter 5 (EPA 1990a) lists all ARARs guidance documents that
       have been issued by EPA, shown in order of date of issuance.

   •  Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions (EPA  1991c) provides clarification
       on the role of the baseline risk assessment  in developing and selecting CERCLA remedial alternatives.

   •  Guidance for Data Useability in Risk Assessment (EPA 1990b) (Data Usability Guidance) provides guidance on
       how to obtain a minimum level of quality for all environmental analytical data required for CERCLA risk
       assessments. It can assist  with determining  sample quantitation  limits (SQL-S) for chemical-specific analyses.

   •Guidance on Remedial Actions for Superfund Sites with PCB Contamination (EPA 1990c) describes the
       recommended approach for evaluating and remediating CERCLA sites having  PCB contamination.

   •  Conducting Remedial Investigatwns/Feasibility Studies for CERCLA Municipal Landfill Sites (EPA 199la)
       (Municipal Landfill Guidance) offers guidance on how to streamline both the RI/FS and the selection of a remedy
       for municipal landfills.
1.5  MODIFICATION   OF                     assessment, it is important to review the media and
        PRFT  TMTNARY                            chemicals of potential concern, future land use,
                                                        and  exposure assumptions originally  identified  at
        REMEDIATION  GOALS                 scoping. Chemicals may be added or dropped  from
                                                        the  list, and risk-based PRGs may need to be
    The initial list of PRGs may need to be revised        recalculated using site-specific exposure factors.
as new data become available during the RI/FS.        PRGs that are modified based on the results of the
Therefore, upon completion of the baseline risk        baseline  risk  assessment must  still  meet the
                                                   -5-

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"threshold criteria" of: (1) protection of human
health and the environment and (2) compliance
with ARARs. However, the NCP also allows for
modification  of PRGs  during  final  remedy
selection based on the "balancing" and "modifying"
criteria and factors relating  to uncertainty,
exposure, and technical feasibility.

    Final remediation levels are not determined
until the site remedy is ready to be selected; final
remediation levels are then set  out in the ROD.
PRGs  are  refined into final remediation  goals
throughout the process leading up  to  remedy
selection.    The  ROD itself,  however, should
include a statement of final clean-up levels based
on  these  goals,  as noted in NCP  section
300.430(e)(2)(i)(A). In the ROD, it is preferable
to use the  term "remediation level" rather than
"remediation  goal" in order to make clear that the
selected remedy establishes binding requirements.

1.6 DOCUMENTATION  AND
       COMMUNICATION  OF
       PRELIMINARY
       REMEDIATION GOALS

    Clear and concise communication of risk-based
PRGs  among the risk assessor, the RPM,  the
ARARs coordinator,  site  engineers,  analytical
chemists, hydrogeologists, and others is important
in the development of PRGs. The involvement of
the RPM  in the  direction and development of
risk-based  PRGs is  important to ensure that
communication is facilitated and that the PRGs
are used effectively in streamlining the RJ/FS
process.

    Because  PRGs  are most useful  during  the
RJ/FS (e.g., for streamlining the consideration of
remedial  alternatives),  it  is important  to
communicate them  to site engineers  as  soon as
possible. A memorandum from either the  site risk
assessor or the RPM to the site  engineers and
others concerned with PRGs would be  appropriate
for transmitting the initial PRGs. A brief  cover
page could highlight key assumptions, as well as
changes,  if any, to  the standard equations (i.e.,
those presented in this guidance). Following this
brief discussion,  the PRGs  could be  presented
using a table similar to that in Section 3.4 of this
guidance.

    The  RI/FS   Guidance  recommends that
"chemical- and/or risk-based remedial objectives
associated  with  the  alternative  should  be
documented  in the final RI/FS report to the extent
possible." Therefore, the RI/FS  report  is a logical
place to  present PROS that have been modified
after the baseline  risk assessment. A summary
table such as the one developed in Section 3.4 of
Part B  could be  incorporated into  the RI/FS
following the  presentation of  the baseline risk
assessment.  Along with the table, a discussion of
issues of particular interest, such as assumptions
used and the relationship between ARARs and
risk-based PRGs at the site, could be included.
Also, it  is  always appropriate to  discuss how
findings  of  the  baseline risk  assessment were
incorporated into the calculation of PRGs.

1.7 ORGANIZATION  OF
       DOCUMENT

    The remainder of this guidance is organized
into three additional chapters  and two appendices.
Chapter  2 discusses the  initial identification of
PROS  and  provides guidance  for  modifying
appropriate  values during the  RI/FS. Chapter 3
outlines equations  that can be  used to calculate
risk-based PRGs for residential and commercial/
industrial land  uses.    These  equations  are
presented  in both "reduced" format  (i.e.,
incorporating certain default assumptions discussed
in Chapter 2) and expanded format (i.e., with all
variables  included so that the user of this guidance
can incorporate  site-specific values).  Particular
considerations regarding  radionuclides are provided
in Chapter 4.

    Appendix A supports several points made in
Chapter 2 by providing illustrations of remedial
alternatives where one or more  chemicals "limit"
remediation  and, thus, represent a major portion
of the residual risk.  Appendix B lists equations for
media-specific exposure pathways, enabling the risk
assessor to derive site-specific equations that differ
from those presented in Chapter 3.

    Throughout Chapters 2, 3, and 4, case studies
are presented  that  illustrate the  process  of
determining  PRGs.    These  case studies  are
contained in  boxes with a shadow box appearance.
Other types of  boxed information  (e.g.,  NCP
quotes) is contained in boxes  such as those  in
Chapter 1, which have thicker lines on the top and
bottom than  on the sides.
                                               -6-

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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  1,
medium-specific   PRGs (ARAR-based  and/or
risk-based) should be identified during scoping for
all chemicals of potential  concern usine readily
available  information.  Sections are provided in
this chapter  on how to use this information to
identify media and chemicals of potential concern,
the most appropriate future land use, potential
exposure pathways, toxicity information, potential
ARARs, and risk-based PRGs. Finally, a section
is provided on the  modification of PRGs.

    When using PRGs developed during scoping.
the design engineers should understand that these
mav be  modified significantly depending on
information   gathered  about  the site.  The
subsequent  process  of  identifying kgv. site
contaminants, media, and other factors (i.e., during
the baseline risk assessment) may require that the
focus of the RI/FS  be  shifted  (e.g., chemicals
without ARARs  may  become more  or less
important).     Thus, the  design  of remedial
alternatives  should  remain flexible until  the
modified (i.e., more final) PRGs are available.

    Prior to identifying PRGs during scoping, a
conceptual site model should be developed (see
the next box).  Originally developed to aid in
planning site  activities (e.g., the RI/FS),  the
conceptual site model also contains information
that is valuable   for identifying PRGs.   For
example, it can be relied upon to identify which
media and  chemicals need PRGs.    More
information on developing and using a conceptual
site model during the RI/FS process can be found
in Chapter 2  of the RI/FS Guidance and Chapter 4
of RAGS/HHEM Part A.

    To illustrate  the process  of calculating
risk-based  PRGs at the  scoping stage  of
remediation, hypothetical CERCLA sites will be
examined in  boxes in  appropriate sections
throughout Chapters 2, 3,  and 4. See the box on
          CONCEPTUAL SITE MODEL

     During project planning, the RPM gathers and
   analyzes available information and develops the
   conceptual site model (also called the conceptual
   evaluation model). This model is used to assess
   the nature and the extent of contamination. It also
   identifies potential contaminant sources, potential
   exposure pathways, and potential human and/or
   environmental receptors. Further, this model helps
   to identify data gaps and assists staff in developing
   strategies for data collection.   Site history and
   PA/SI data generally are extremely useful sources
   of information for developing this model. The
   conceptual site model should include known and
   suspected sources of contamination, types of
   contaminants and affected media, known and
   potential routes of migration, and known or
   potential human and environmental receptors.
the next page for an introduction to the first site.
(The  radiation  case  study is addressed  in
Chapter 4.) The information (e.g. toxicity values')
contained in these case studies is for illustration
only,  and  should not be used for  any other
purpose. These case  studies have been simplified
(e.g., only  ground water will be examined) so that
the steps involved in developing  risk-based PRGs
can be readily discerned.

2.1     MEDIA OF CONCERN

    During scoping, the first step in developing
PRGs is to identify the media of potential concern.
The conceptual site model should be very useful
for this step. These media can be either:

•  currently  contaminated media  to which
    individuals may be exposed or through which
   chemicals  may be transported to potential
   receptors; or
                                             -7-

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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. Remnants of
   drums, lagoons, and waste piles were found at
   the site. Ground water in the area of  the site is
   used by residents as  a domestic water  supply.
   There is also a small lake downgradient from the
   site that is used by some of the local residents
   for fishing and swimming.
•   currently  uncontaminated  media  that  may
    become contaminated in  the  future due to
    contaminant transport.

    Several important media often requiring direct
remediation are ground water,  surface water, soil,
and sediment. Currently, only the first three of
these  media  are  discussed in this  chapter  and
addressed by the equations provided in Chapters 3
and 4.   If other media that  may require the
development of risk-based concentrations (e.g.,
sediments) are identified at scoping, appropriate
equations for those media should  be developed.
Regional risk assessors  should be consulted as
early as possible to assist with this  process.
       CASE STUDY IDENTIFY MEDIA
                OF CONCERN

     The PA/SI for the example site indicates that
   ground water beneath the site is contaminated.
   The source of this contamination appears to
   have been approximately 100 leaking drums of
   various chemicals that were buried in the soil but
   have since been removed. Lagoons and waste
   piles also may   have contributed to the
   contamination. Thus, ground water and soil are
   media  of concern.

     Although  evidence  of  lake  water
   contamination was not found during the PA/SI,
   there is a reasonable possibility that it may
   become contaminated in the  future due to
   contaminant transport  either via ground-water
   discharge or surface water run-off.   Thus,
   surface water (the lake) and sediments also may
   be media of concern.
2.2  CHEMICALS  OF  CONCERN

    This step involves developing an initial list of
chemicals for which PRGs need to be developed.
Chapters 4 and 5 of RAGS/HHEM Part A provide
important additional information on identifying
chemicals of potential concern  for a site and
should be consulted prior to development of the
conceptual site model  and PRGs at scping.

    Initially, the list of chemicals  of potential
concern should include any  chemical reasonably
expected to be of concern at the site based on what
is known during scoping. For example, important
chemicals previously detected at the site, based on
the PA/SI, the conceptual  site model, or other
prior investigations, generally should be included.
In addition, the list may include  chemicals that the
site history indicates are likely to be present in
significant quantities, even though they may  not yet
be  detected.    Sources  of this latter type  of
information include records of chemicals used or
disposed at the facility,  and interviews with  current
or former employees.   The  list also may include
chemicals that are probable  degradation products
of site contaminants where these are determined to
be potential  contributor  of significant risk.  An
environmental chemist should be consulted for
assistance in determining the probable degradation
products of potential site-related chemicals and
their persistence under site  conditions.  Generally,
the chemicals for which PRGs should be developed
will correspond  to  the  list of suspected site
contaminants included in the  sampling and analysis
plan.

2.3     FUTURE LAND USE

    This  step  involves identifying  the most
appropriate future land use for the site so that the
appropriate exposure pathways, parameters, and
equations (discussed in the  next section)  can be
used to  calculate risk-based  PRGs. RAGS/HHEM
Part A  (Chapter 6) and an  EPA  Office of Solid
Waste  and  Emergency  Response  (OSWER)
directive on the  role  of the  baseline  risk
assessment in remedy selection  decisions (EPA
1991b)  provide additional guidance on identifying
future land use. The standard  default equations
provided in  Chapter  3 of  Part B only address
residential and Commercial/industrial land  uses. If
land uses other than these are to be assumed (e.g.,
recreational), then exposure pathways, parameters,

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     CASE STUDY: IDENTIFY CHEMICALS
                OF CONCERN

     The PA/SI for the XYZ  Co. site identified the
   following seven chemicals in ground-water
   samples:    benzene,   ethylbenzene, hexane,
   isophorone, triallate, 1,1,2-trichloroethane, and
   vinyl chloride.  Therefore, these chemicals are
   obvious choices for  chemicals of potential
   concern.

     Although not detected in any of the PA/SI
   samples, site history indicates that one other
   solvent — carbon tetrachloride — also was used in
   significant  quantities by the facility that operated
   at the site. This chemical, therefore, is added to
   the list of chemicals of potential concern.
and equations will need to be developed for the
others as well.

    In general, residential areas should be assumed
to remain residential. Sites that are surrounded by
operating industrial facilities can be assumed to
remain  industrial areas  unless  there is an
indication that this is not appropriate. Lacking
site-specific  information (e.g., at scoping), it may
be appropriate to assume residential  land use.
This  assumption will generally lead to conservative
(i.e., lower concentration) risk-based PRGs.  If not
enough site-specific information is readily available
at scoping  to select  one future land use  over
another,  it  may  be  appropriate  to  develop  a
separate  set  of risk-based PRGs for each possible
land use.

    When waste will be managed onsite, land-use
assumptions and risk-based PRO development
become more complicated because the assumptions
for the site itself may be different from the land
use in the surrounding area. For example,  if waste
is managed onsite  in a  residential  area,  the
risk-based PRGs for the ground water beneath the
site (or at the edge of the waste management unit)
may be based on residential exposures, but the
risk-based PRGs for the site soils may be based on
an industrial land use with some management or
institutional  controls.

    If a land-use assumption is used that is less
conservative (i.e.,  leads to higher  risk-based
concentrations) than another, it generally will be
necessary to monitor the future uses of that site.
For example, if residential land use is not deemed
to be appropriate for a particular site because local
zoning laws prohibit residential development,  any
changes in  local  zoning  would need to be
monitored.  Such considerations should be clearly
documented in the site's ROD.
       CASE STUDY IDENTIFY FUTURE
                  LAND USE

     Based on established land-use trends, local
   renovation projects, and population growth
   projections in the area of the XYZ Co. site, the
   most reasonable future use of the land is
   determined to be residential use. Thus,  site-
   specific information is sufficient to show that the
   generally  more  conservative assumption of
   residential land use should serve as the basis for
   development of risk-based PROS.
2.4     APPLICABLE OR RELEVANT
        AND APPROPRIATE
        REQUIREMENTS

    Chemical-specific ARARs are evaluated as
PRGs because they are often readily available  and
provide a preliminary indication about the goals
that  a remedial  action may have to attain. This
step  involves identitying all  readily available
chemical-specific  potential  ARARs  for  the
chemicals of potential concern (for each medium
and  probable land use).  Because at scoping it
often is uncertain which potential ARAR is  the
most likely one to become the ARAR-based PRG,
all potential ARARs  should  be included in a
tabular summary  (i.e., no potential ARAR should
be discarded). If there is  doubt about whether a
value is a potential ARAR, and therefore whether
it could be used as a PRG, it should be included at
this  stage.

    This  section summarizes the  concept of
ARARs and identifies the major types of ARARs,
but provides only limited guidance on identifying
the most appropriate (likely) ARAR of all possible
ARARs  to  use  as the chemical-specific PRG.
More detailed information about the identification
and evaluation of ARARs is available from two
important sources:

•   the NCP (see specifically 55 Federal Register
    8741-8766 for a description of ARARs,  and
                                                -9-

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    8712-8715 for using ARARs as PRGs; see also
    53 Federal Register 51394); and

•  CERCLA Compliance Manuals  (EPA  1988a
    and 1989a).

2.4.1    CHEMICAL-, LOCATION-, AND
        ACTION-SPECIFIC ARARs

    The Agency has identified three  general types
of federal and state ARARs:

•   chemical-specific, are usually health- or risk
    management-based numbers or methodologies
    that, when applied to site-specific conditions,
    result in the establishment of numerical  values
    (e.g., chemical-specific concentrations in a
    given medium);

•    location-specific, are restrictions placed upon
    the concentration of hazardous substances or
    the conduct of activities solely because they
    are in special locations (e.g., wetlands); and

•   action-specific,  are usually technology- or
    activity-based requirements or limitations on
    actions taken with respect to hazardous wastes.

This guidance primarily addresses only chemical-
specific  ARARs  since it  focuses  on  the
identification of chemical-specific concentrations
that represent target goals (e.g., PRGs) for a given
medium.

2.4.2    SELECTION OF THE MOST LIKELY
       ARAR-BASED PRO FOR EACH
        CHEMICAL

    This  section briefly describes which, if any, of
several potential ARAR  values  for a  given
chemical is generally selected as the most likely
ARAR-based PRO (and therefore the most likely
PRG  at this point).   Although the process for
identifying the most likely ARAR-based PRG is
specific to the  medium,  in  general the process
depends   on two  considerations:      (1)  the
applicability of the ARAR to the site; and (2) the
comparative  stringency of the standards  being
evaluated. The Previously cited documents should
be  carefully   considered  for  specific
recommendations on identifying ARARs.

    Ground Water. SDWA maximum contaminant
levels  (MCLs), non-zero  MCLGs, state drinking
water standards, and federal water quality criteria
(FWQC)  are common ARARs  (and, therefore,
potential PRGs) for ground water. Other types of
laws, such as state anti-degradation laws, may be
PRGs if  they  are accompanied by allowable
concentrations  of a chemical.   (Although state
anti-degradation  laws  that  are expressed  as
qualitative  standards may  also  be potential
ARARs, they generally would not be considered
PRGs.)

    As detailed in the NCP (see next box), the first
step  in identifying  ground-water PRGs  is  to
determine whether the ground water  is a current
or potential source of drinking water.    If the
aquifer is a potential source  of drinking water,
then potential ARARs generally will include the
federal non-zero MCLG, MCL, or state drinking
water standard, and the most stringent (i.e., the
lowest concentration) is identified as the most
 likely ARAR-based PRG.
       NCP ON GROUND-WATER GOALS
                (NCP Preamble;
      55 Federal Regirter 8717, March 8, 1990)

     "Ground water that is not currently a drinking
   water source but is potentially a drinking water
   source in the future would be protected to levels
   appropriate to its use as a drinking water source.
   Ground water that is not an actual or potential
   source  of drinking water may not require
   remediation to a  10"" to 10"" level  (except when
   necessary to address environmental concerns or
   allow for other beneficial uses;. . .)."
    If the  aquifer is not a potential source of
drinking water, then MCLs, MCLGs, state drinking
water requirements, or other health-based levels
generally are not appropriate as PRGs. Instead,
environmental  considerations (i.e.,  effects on
biological  receptors) and prevention of plume
expansion generally determine clean-up levels. If
an  aquifer that is not  a  potential  source of
drinking water is connected to an aquifer that is a
drinking water source, it maybe appropriate to use
PRGs  to  set  clean-up goals for the point of
interconnection.

    For chemicals without MCLs, state standards,
or  non-zero   MCLGs,  the  FWQC  may be
potentially relevant and  appropriate  for ground
water when that ground water discharges to surface
water that is used for fishing or shellfishing.
                                               -10-

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    Surface Water. FWQC and state water quality
standards (WQS) are common ARARs for surface
water. An important determination for identifying
ARARs and other criteria as potential PRGs for
surface water is the current designated and future
expected use of the water body. Because surface
water potentially could serve many uses (e.g.,
drinking and fishing), several ARARs  may  be
identified as potential PRGs for a chemical, with
each ARAR corresponding to an identified use. A
state WQS is generally the most likely ARAR for
surface  water unless a federal standard is more
stringent.

    If surface water is a current or potential source
of drinking  water, MCLs, state  drinking water
standards, non-zero  MCLGs, and  FWQC  are
potential ARARs.   The  analysis to determine
which of these drinking water standards is  the most
likely ARAR-based  PRG  is the same as that
conducted for ground water.  An FWQC based on
ingestion of water and fish might be an ARAR for
surface water used for drinking.

    If the designated or future expected use  of
surface  water is fishing or shellfishing. and the
state has  not promulgated a WQS, an FWQC
should be considered  as a potential  ARAR. The
particular FWQC (i.e., for water and fish ingestion
or fish ingestion alone)  selected  as the potential
ARAR depends on whether exposure from one  or
both of the routes is likely to occur and, therefore,
on the designated use of the water body. If other
uses of the water are designated (e.g., swimming),
a state WQS may be available.

    Soil. In general, chemical-specific  ARARs
may not be available for soil.   Certain states,
however, have  promulgated or are about  to
promulgate soil standards that may be ARARs and
thus may be appropriate to use as PRGs.  In
addition, several EPA policies may be appropriate
to use in developing PRGs (e.g.,  see EPA 1990c
for guidance on PCB clean-up levels).

2.5     EXPOSURE  PATHWAYS,
        PARAMETERS, AND
        EQUATIONS

    This step  is  generally conducted for each
medium and land-use combination and involves
identifying the most appropriate (1) exposure
pathways and routes (e.g., residential ingestion of
drinking water), (2)  exposure parameters (e.g.,
2 liters/day of water ingested), and (3) equations
(e.g., to  incorporate  intake).  The  equations
include calculations of total intake from' a given
medium and are based on the identified exposure
pathways and associated parameters. Information
gathered in this step should be used to calculate
risk-based  PRGs  using  the  default  equations
identified in Chapters 3  and 4.   Site-specific
equations can  be  derived if a  different  set of
exposure pathways is identified for a particular
medium;  this option also is discussed in Chapters
3 and 4.

    When risk-based concentrations are developed
during scoping, readily   available site-specific
information may be  adequate  to  identify and
develop the exposure pathways, parameters, and
equations (e.g.,  readily available information may
indicate that the exposure duration should be 40
years instead of the standard default of 30 years).
In the absence  of  readily available site-specific
information, the standard default information in
Chapters  3 and  4 generally should be used for the
development of risk-based PRGs.

    Exhibit 2-1 lists a number of the potential
exposure pathways that might be present at  a
CERCLA site. The  exposure pathways included in"
the medium-specific standard default equations
(see Chapters 3  and 4) are italicized in this exhibit.
Note that Chapters 3 and 4 may not address all of
the exposure pathways of possible importance at a
given CERCLA  site.     For example, the
consumption of ground water that continues to be
contaminated by soil leachate is not addressed.
Guidance on goal-setting to address this exposure
pathway is currently under development by EPA.
In addition, the  standard default equations do not
address pathways such as plant and animal uptake
of contaminants from soil with subsequent human
ingestion. Under certain circumstances, these or
other exposure  pathways may present significant
risks  to  human health.   The  standard default
information, however, does address the  quantifiable
exposure  pathways  that  are  often  significant
contributors of  risk for a particular medium and
land use.

    Chapters 3  and 4 show how exposures from
several pathways are addressed in a single equation
for a  medium.  For example, in the equation for
ground  water  and  surface  water  under the
residential land-use assumption, the coefficients
incorporate default  parameter values for ingestion
of drinking water and inhalation of volatile s during
                                               -11-

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                                          EXHIBIT 2-1

                   TYPICAL  EXPOSURE  PATHWAYS  BY  MEDIUM
     FOR  RESIDENTIAL  AND  COMMERCIAL/INDUSTRIAL  LAND  USES'"
     Medium
                                             Exposure Pathways, Assuming:
          Residential  Land Use
    Commercial/Industrial Land Use
 Ground Water
 Surface Water
 Soil
Ingestion from drinking
Inhalation of volatiles
Dermal absorption from bathing
Immersion - external"
Ingestion from drinking
Inhalation of volatiles
Dermal absorption from bathing
Ingestion during swimming
Ingestion of contaminated fish
Immersion - external"
Ingestion
Inhalation of particulate
Inhalation of volatiles
Direct external exposure'
Exposure to ground water contaminated
by soil leachate
Ingestion via plant uptake
Dermal absorption from gardening
Ingestion  from drinkingd
Inhalation of volatiles
Dermal absorption

Ingestion  from drinkingd
Inhalation of volatiles
Dermal absorption
Ingestion
Inhalation of particuhtes
Inhalation of volatiles
Direct external exposure
Exposure to  ground water contaminated
by soil leachate
Inhalation of particulate from trucks
and heavy equipment
'Lists of land uses, media, and exposure pathways are not comprehensive.
'Exposure pathways included in RAGS/HHEM Part B standard default equations (Chapters 3 and 4) are
italicized.
"Applies to radionuclides only.
"Becausce the NCP encourages protection of ground water to maximize its beneficial use, risk-based PRGs
generally should be based on residential exposures once ground water is determined to be suitable for drinking.
Similarly, when surface water will be used for drinking, general standards (e.g., ARARs) are to be achieved
that define levels  protective for the population at large, not simply worker populations.  Residential exposure
scenarios should guide risk-based PRG development for ingestion and other  uses of potable water.
                                                 -12-

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household water use. Full details of parameters
used to develop each equation and a summary of
the "reduced"  standard  default equations  are
provided in the text of  these chapters.

    Certain modifications of the default equations
may be desirable or necessary. For example, if an
exposure  pathway addressed by an equation in
Chapter 3 seems inappropriate for the site (e.g.,
because  the  water  contains  no volatiles and,
therefore, inhalation  of volatiles is irrelevant), or
if information needed for a pathway (e.g., a
chemical-specific  inhalation  slope  factor  [see
Section 2.6])  is not readily available or derivable,
then that pathway can be disregarded at this stage.

    The decision about whether the risk assessor
should collect site-specific  human  exposure
pathway information (e.g.,  exposure frequency,
duration,  or intake rate data)  is very important.
There  will frequently be methods  available to
gather such information, some of which are more
expensive and elaborate than others.  Determining
whether  the resulting  data are   reasonably
representative of populations in the surrounding
area, however, is often difficult. Collecting data by
surveying those individuals most convenient or
accessible to  RPMs or risk assessors may  not
present a complete population exposure picture.
In fact, poorly planned data gathering efforts may
complicate the assessment process. For example,
those surveyed may come to believe that their
contributions  will play  a more meaningful  role in
the risk assessment than that planned by the risk
assessors; this can result in significant demands on
the risk assessor's time.

    Before such data  collection has begun, the risk
assessor  should determine,  with  the  aid of
screening analyses,  what benefits are likely to
result.  Collection of  the exposure data discussed
in this section generally should not be attempted
unless  significant differences are likely to result in
final reasonable maximum exposure (RIME) risk
estimates.    If data collection is warranted,
systematic and well-considered  efforts' that
minimize biases in results should be undertaken.
Estimates of future exposures are likely to rely
heavily on conservative exposure assumptions. By
definition, these assumptions will be unaffected by
even the most extensive  efforts to characterize
current population  activity.

    At this stage, the risk  assessor, site engineer,
and RPM should discuss information concerning
the absence or presence of important exposure
pathways, because remediation goals should be
designed for  specific areas  of the site  that  a
particular remedy must address, and exposures
expected for  one area of the  site may differ
significantly from those expected in another area.

2.5.1    GROUND WATER/SURFACE WATER

    The  residential  land-use  default equations
presented in Chapters 3 and 4 for ground water or
surface water  are based on ingestion of drinking
water  and  inhalation of volatile (vapor phase)
chemicals originating from the household water
supply (e.g.,  during  dish  washing,  clothes
laundering, and showering).

    Ingestion  of drinking water is an appropriate
pathway for all chemicals with an oral cancer slope
factor  or an oral chronic reference dose.  For the
purposes of this guidance, however, inhalation of
volatile chemicals  from water is considered
routinely only for chemicals with a Henry's Law
constant of 1  x 10"5atm-m"Vmole or greater and
with a  molecular weight of less than 200 g/mole.
Before determining inhalation toxicity values for  a
specific chemical (Section 2.6),  it should be
confirmed  that the  Henry's  Law constant and
molecular weight are in the appropriate range for
inclusion in the inhalation pathway for water.

    Default equations addressing industrial use of
ground water are not presented.  Because the NCP
encourages  protection of ground  water to its
maximum beneficial use, once ground water is
determined to  be suitable for drinking, risk-based
PROS  generally should be based  on residential
exposures. Even if a site is located in an industrial
area, the ground water underlying a site in an
industrial  area may be used as a drinking water
source for residents several miles  away due to
complex geological interconnections.

2.5.2    SOIL

    The  residential   land-use  standard  default
equations for the soil pathway are based on
exposure pathways of ingestion of chemicals in soil
or dust.  The  industrial land-use  equations are
based  on three exposure pathways: ingestion of
soil  and dust, inhalation of  particulate,  and
inhalation of volatiles. Again, for the purposes of
this guidance, inhalation of volatile chemicals is
relevant only  for chemicals with a Henry's Law
constant of 1  x 10"5atm-mVmole or greater and
                                                -13-

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with a molecular weight of less than 200 g/mole.
For the inhalation pathways, in addition to toxicity
information, several chemical- and site-specific
values are needed.  These values include molecular
diffusivity, Henry's Law constant, organic carbon
partition coefficient, and soil moisture content (see
Chapter 3 for details).
     CASE STUDY IDENTIFY EXPOSURE
          PATHWAYS, PARAMETERS,
              AND EQUATIONS

     For the potential residential land use
   identified at the XYZ Co. site, the contaminated
   ground water (one of several media of potential
   concern) appears to be an important source of
   future domestic water.  Because site-specific
   information is not initially available to develop
   specific exposure pathways, parameters, and
   equations, the standard default assumptions and
   equations provided in Chapter 3 will be used to
   calculate risk-based PRGs.  Exposure pathways
   of concern for ground water, therefore, are
   assumed to be ingestion of ground water as
   drinking water and inhalation of volatiles in
   ground water during household use.
2.6  TOXICITY  INFORMATION

    This step involves identifying readily available
toxicity values for all of the chemicals of potential
concern for given exposure pathways so that the
appropriate slope factors  (SFs; for carcinogenic
effects)    and   reference doses    (RfDs;  for
noncarcinogenic effects) are identified or derived
for use in the site-specific  equations  or  the
standard default equations. Therefore, Chafrter 7
of RAGS/HHEM  Part A should  be  reviewed
carefully before proceeding with this step.

    The hierarchy for obtaining toxicity values for
risk-based PRGs is essentially the  same  as that
used in the baseline  risk assessment.    Briefly,
Integrated Risk Information System (IRIS) is the
primary source  for toxicity information; if no
verified toxicity value is available through IRIS,
then Health Effects Assessment Summary Tables
(HEAST) is the next preferred source.  When the
development of a toxicity value is required (and
appropriate data are available), consultation with
the Superfund Health  Risk Assessment Technical
Support Center is warranted.  EPA  staff can
contact the  Center by calling  FTS-684-7300
(513-569-7300) or by FAX  at FTS-684-7159
(513-569-7159). Others must fax to the above
number or write to:

    Superfund Health Risk Technical  Support
     Center
    Environmental  Criteria and Assessment Office
    U.S. Environmental Protection Agency
    Mail Stop 114
    26 West Martin Luther King Drive
    Cincinnati, Ohio 45268

    Other toxicity information that  should be
obtained  includes   EPA's weight-of-evidence
classification for carcinogens (e.g., A, B 1) and the
source of the information (e.g., IRIS, HEAST).

    Note that throughout this document, the term
hazard index (HI) is used to refer to the risk level
associated with noncarcinogenic effects. An HI is
the sum of two or  more hazard quotients (HQs).
An HQ is the  ratio  of an exposure level of a single
substance to the RfD for that substance. Because
RfDs are generally  exposure pathway-specific (e.g.,
inhalation RfD), the  HQ is a single  substance/
single  exposure pathway ratio. An HI, on the
other hand, is usually either a single  substance/
multiple exposure pathway ratio,  a  multiple
substance/single exposure pathway ratio, or a
multiple substance/multiple  exposure  pathway
ratio.    In this  document, however,  only  one
exposure  pathway is included in the  default
equation  for  some  land-use and  medium
combinations (e.g., residential soil). In order to
remain consistent, the  term HI has been used
throughout RAGS/HHEM Part B, even though for
such a  pathway, the term HQ could apply.

2.7 TARGET  RISK  LEVELS

    This step involves identifying target  risk
concentrations for chemicals of potential concern.
The standard  default  equations  presented in
Chapters 3 and 4 are based on the following target
risk levels for carcinogenic and noncarcinogenic
effects.

•   For carcinogenic  effects, a  concentration is
    calculated  that  corresponds to a  10"'
    incremental risk of an individual developing
    cancer over a lifetime as a result of exposure
    to the potential carcinogen from all significant
    exposure pathways for a given medium.
                                                -14-

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CASE
STUDY: IDENTIFY TOXICITY INFORMATION1
Reference toxicity values for cancer and
noncancer effects
(i.e., SFs and RfDs, respectively) are required for
chemicals without ARAR-based PRGs (only the case study chemicals without ARARs are listed here). Considering
the ground-water medium only, ingestion and inhalation are exposure pathways of concern. Toxicity information
is obtained from IRIS and HEAST, and is shown











Chemical
EXPOSURE ROUTE
Hexane
Isophorone
Triallate
EXPOSURE ROUTE:
Hexane
Isophorone
Triallate
RfD

(mg/kg-day)
in the table

Source
below.
SF Weight of
(mg/kg-day) Evidence Source
INGESTION
0.06
0.2


0.013
HEAST
IRIS
IRIS
— —
0.0039 c HEAST
—
INHALATION
0.04
—
—
' All information in this example is



HEAST
—
—
	
c HEAST











for illustration purposes only. I
. For nonearcinogenic effects, a concentration is
    calculated that  corresponds to an  HI of 1,
    which is the level of exposure to a chemical
    from all significant exposure  pathways in a
    given medium below which it is unlikely for
    even sensitive  populations  to experience
    adverse health effects.

    At scoping, it generally is appropriate to use
the standard default target risk levels described
above  and discussed  in the NCP.  That is,  an
appropriate point of departure for  remediation of
carcinogenic   risk  is  a  concentration  that
corresponds to a risk of ICT'for one chemical in a
particular medium.  For  nonearcinogenic  effects,
the NCP does not specify a range, but it generally
is appropriate to assume an HI equal to 1.

2.8 MODIFICATION  OF
       PRELIMINARY
       REMEDIATION   GOALS

    Upon completion   of  the baseline  risk
assessment (or as soon as data are  available), it is
important to review  the future land use, exposure
assumptions,  and the  media and chemicals of
potential concern originally identified at scoping,
and determine whether PRGs need to be modified.
Modification  may involve adding or subtracting
chemicals  of concern, media, and pathways or
revising individual  chemical-specific goals.

2.8.1    REVIEW OF ASSUMPTIONS

    Media  of Concern. As a guide to  determining
the media and chemicals of potential concern, the
OSWER  directive Role  of the  Baseline  Risk
Assessment in Superfund Remedy Selection Decisions
(EPA  1991c) indicates that action is  generally
warranted  at  a  site when the  cumulative
carcinogenic risk is  greater  than  10"4or the
cumulative  nonearcinogenic HI exceeds 1 based on
RME assumptions. Thus, where the baseline risk
assessment indicates  that either the  cumulative
current or future risk associated with a medium is
greater than 10" or that the HI is greater than 1,
that medium presents a concern, and it generally is
appropriate to  maintain  risk-based PRGs for
contaminants in that medium or develop risk-based
PRGs  for additional media where PRGs are not
clearly defined by ARARs.

    When   the  cumulative  current  or future
baseline  cancer risk for a medium is within the
range of 10"6to 10"4, a decision about whether or
not to  take action is a  site-specific determination.
Generally, risk-based PRGs are not needed for any
chemicals in a medium with a cumulative cancer
risk of less than 10", where an HI is less than or
                                               -15-

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equal to 1, or where the PRGs are clearly defined
by ARARs. However, there maybe cases where a
medium  appears  to meet the protectiveness
criterion but contributes to the contamination of
another medium (e.g., soil contributing to ground-
water contamination). In these  cases, it may be
appropriate to modify existing or develop new risk-
based PRGs for chemicals of concern in the first
medium, assuming that fate and transport models
can adequately predict the impacts of concern on
other media.    EPA is  presently  developing
guidance  on  quantifying the  impact of soil
contamination  on underlying aquifers.

    Chemicals of  Concern. As with the initial
media of potential  concern, the initial list of
specific chemicals of potential concern in a given
medium may need  to  be modified to  reflect
increased  information from the RI/FS concerning
the importance of the chemicals to the overall site
risk. Chemicals  detected during the RI/FS that
were not  anticipated during scoping should  be
considered for addition to the list of chemicals of
potential concern;  chemicals anticipated during
scoping that were not detected during the RI/FS
should be deleted  from the list. Ultimately, the
identity and number of contaminants that may
require  risk-based PRGs  depends both on the
results of the  baseline risk assessment and the
extent of action  required, given  site-specific
circumstances.

    Following the  baseline risk assessment, any
chemical  that has  an  associated  cancer risk
(current or future) within a medium of greater
than 10 'or an HI of greater than 1 should remain
on the list of chemicals of potential concern for
that medium.  Likewise, chemicals that present
cancer risks of less than 10"6generally should not
be retained on the list unless there are significant
concerns  about  multiple contaminants and
pathways.

    Land  Use. After the RI/FS, one  future land
use can usually be selected based on the results of
the baseline risk assessment and discussions with
the RPM.  In many cases, this land use will be the
same  as the land  use identified  at scoping.  In
other cases, however, additional  information from
the baseline risk assessment that was not available
at scoping  may suggest modifying the  initial land-
use and exposure  assumptions.   A qualitative
assessment should be made — and should  be
available from the baseline risk assessment — of
the likelihood that the assumed future land use
will occur.

    Exposure  Pathways,  Parameters,  and
Equations. For exposure pathways, this process of
modifying PRGs consists of adding or deleting
exposure pathways  from the  medium-specific
equations in Chapters 3 and 4 to ensure that the
equation accounts for all significant  exposure
pathways associated with  that medium at the site.
For example, the baseline risk assessment may
indicate that dermal exposure to contaminants in
soil is a significant contributor to site risk. In this
case, the risk-based  PRGs may be  modified by
adding equations for dermal exposure. EPA policy
on  assessing this pathway is currently under
development;  the risk assessor  should consult the
Superfund Health Risk Technical Support Center
(FTS-684-7300 or 513-569-7300) to determine the
current status  of guidance.    Likewise, when
appropriate data (e.g., on  exposure frequency and
duration) have been  collected  during the  RI/FS,
site-specific values  can  be  substituted for the
default values in the medium-specific equations.

2.8.2    IDENTIFICATION OF
        UNCERTAINTIES

    The uncertainty  assessment for PROS can
serve  as an important basis for recommending
further modifications  to the PROS prior to setting
final remediation goals. It also can be used during
the post-remedy assessment (see Section 2.8.4) to
identify areas needing particular attention.

    Risk-based  PRGs are  associated with varied
levels of uncertainty, depending on many factors
(e.g., confidence that  anticipated future land use is
correct). To place risk-based PRGs that have been
developed for a site in  proper perspective, an
assessment of the uncertainties associated with the
concentrations  should be  conducted.    This
assessment is similar to the uncertainty assessment
conducted during the baseline risk assessment (see
RAGS/HHEM Part A, especially Chapters 6, 7,
and 8).    In fact,  much  of the  uncertainty
assessment conducted  for a site's  baseline risk
assessment will be  directly  applicable  to  the
uncertainty assessment of the risk-based PROS.

    In  general,  each component of risk-based
PRGs discussed in this chapter — from media of
potential concern to target risk level - should be
examined, and  the major areas of uncertainty
highlighted.      For  example,   the  uncertainty
                                               -16-

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associated with the selected future land use should
be discussed.   Furthermore, the accuracy of the
technical models used (e.g., for volatilization of
contaminants from  soil) to reflect site-specific
conditions  (present  and  future)  should  be
discussed.    If site-specific exposure assumptions
have been made, it is particularly important to
document the data supporting those assumptions
and  to assess  their relevance for potentially
exposed populations.

    As the chemical- and medium-specific PRGs
are developed, many assumptions regarding  the
RME  individual(s)  are  incorporated.  Although
PRGs  are believed to be fully protective for the
RME individual(s),  the proximity of other nearby
sources of exposure (e.g., other CERCLA sites,
RCRA facilities, naturally occurring background
contamination) and/or the existence of the same
contaminants in multiple media  or  of multiple
chemicals affecting the same population(s), may
lead to a situation where, even  after attainment of
all PRGs, protectiveness is not clearly achieved
(e.g., cumulative risks may fall outside the risk
range).    The  more likely  it  is  that  multiple
contaminants, pathways, operable units, or other
sources  of toxicants  will affect the RME
individual(s), the more likely it will be that
protectiveness is not achieved. This likelihood
should be  addressed when identifying uncertainties.

2.8.3    OTHER CONSIDERATIONS IN
        MODIFYING PRGs

    The NCP preamble and rule state that factors
related to  exposure, technical limitations, and
uncertainty should be considered when modifying
PRGs  (see next two boxes)  and setting final
remediation levels.

    While the final remedial  action objectives must
satisfy  the original "threshold  criteria" of protection
of  human  health   and  the environment and
compliance  with ARARs, the factors in  the
"balancing and modifying criteria" (listed in Section
1.3.2)  also are considered in the detailed analysis
for choosing among remedial alternatives. In cases
where the  alternative that  represents  the best
balance of factors is  not able to attain cancer risks
within the  risk range or an  HI of 1, institutional
controls may be used to supplement  treatment
and/or containment-based   remedial  action  to
ensure protection  of  human health  and  the
environment.
      NCP PREAMBLE: EXPOSURE,
            TECHNICAL, AND
         UNCERTAINTY FACTORS
   (55 Federal Register 8717, March 8, 1990)

   "Preliminary remediation goals . . .  may be
revised . .  .  based on the consideration of
appropriate factors including, but not limited to
exposure factors, uncertainty factors, and technical
factors.   Included under exposure factors are
cumulative effect of multiple contaminants, the
potential for human exposure from other pathways
at the site,  population sensitivities, potential
impacts on environmental receptors, and cross-
media impacts of alternatives. Factors related to
uncertainty may  include   the reliability of
alternatives, the weight of scientific evidence
concerning  exposures   and    individual   and
cumulative health effects, and the reliability of
exposure data. Technical factors may  include
detection/quantification limits for  contaminants,
technical limitations to remediation, the ability to
monitor and control movement of contaminants,
and background levels of contaminants. The final
selection of the appropriate risk level is made when
the remedy is selected based on the balancing of
criteria...."
   NCP RULE: EXPOSURE, TECHNICAL,
      AND UNCERTAINTY FACTORS
          (40 CFR 300.430(e)(2)(i))

"(i)... Remediation goals...shall be developed by
considering the following

   "(A) Applicable or relevant and appropriate
   requirements...and the following factors:

     "(1)  For systemic toxicants, acceptable
     exposure levels...;

     "(2)  For known or suspected carcinogens,
     acceptable exposure levels...;

     "(3)  Factors related to technical limitations
     such as detection/quantification limits for
     contaminant

     "(4)  Factors related to uncertainty and

     "(5)  Other pertinent information."
                                                 -17-

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    Note that in the absence of ARARs, the 10"6
cancer risk "point of departure" is  used as a
starting point for analysis of remedial alternatives,
which reflects EPA's preference for managing risks
at the more protective end of the risk range, other
things  being equal.   Use of "point of departure"
target  risks in  this guidance does not  reflect a
presumption that the final remedial action should
attain such goals. (See NCP preamble, 55 Federal
Register 8718-9.)
2.8.4    POST-REMEDY ASSESSMENT

    To ensure that protective conditions exist after
the remedy  achieves all  individual remediation
levels set out in the ROD, there generally will be
a  site-wide evaluation  conducted following
completion of a site's  final operable unit (e.g.,
during the five-year review).   This  site-wide
evaluation should adequately characterize  the
residual contaminant levels and ensure that the
post-remedy cumulative  site risk is protective.
More detailed guidance on  the  post-remedy
assessment of site "protectiveness" is  currently
under development by EPA.
                                               -18-

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                                   CHAPTER 3
               CALCULATION  OF RISK-BASED
        PRELIMINARY REMEDIATION GOALS
    This chapter presents standardized exposure
parameters, the derivation of risk equations, and
the corresponding "reduced"  equations,  for
calculating risk-based PRGs at  scoping for the
media  and land-use assumptions  discussed in
Chapter 2 (i.e., ground water, surface water, and
soil  for  residential land  use, and  soil  for
commercial/industrial land  use). Both carcinogenic
and  noncarcinogenic  effects   are  addressed.
Standardized  default  exposure parameters
consistent with OSWER Directive 9285.6-03 (EPA
1991b) are used  in this chapter; where default
parameters are not available  in that guidance, the
references used are cited. If other media requiring
risk-based PRGs are identified during the RI/FS,
or other exposure parameters or land uses  are
assumed, then appropriate equations will need to
be modified or new ones developed.

    Risk-based equations have been derived in
order to reflect the potential risk from exposure to
a chemical, given a specific pathway, medium, and
land-use combination. By setting the total risk for
carcinogenic effects at a target risk level of 10"6
(the NCP's point of departure  for analysis of
remedial alternatives), it is  possible to solve for the
concentration term (i.e., the risk-based PRO). The
total risk for noncarcinogenic effects is set at an
HI of 1 for each chemical  in a particular medium.
Full  equations   with pat pathway-pecific default
exposure factors  are presented  in boxes with
uniformly  thin borders.  Reduced equations are
presented in the standard  boxes (i.e., thicker top
and bottom borders). At the end of this chapter,
the case study  that began in Chapter 2 is
concluded (by showing  how to calculate and
present risk-based PRGs).

    In general, the equations described in this
chapter are sufficient for calculating the risk-based
PRGs at the scoping stage  of the  RI/FS. Note,
however, that  these actuations are  based  on
standard default assumptions that  may or may not
reflect site-specific conditions. When risk-based
PRGs are to be calculated based on site-specific
conditions, the risk assessor should modify the full
equations, and/or develop additional ones. Risk
equations for individual exposure pathways for a
given medium are presented in Appendix B of this
document, and may be used to develop and/or
modify the full equations. (Seethe introduction to
Appendix B for more detailed instructions.)

    Before examining the calculation of risk-based
PRGs, several important points should be noted:

•  Use of toxicity values in  the equations  as
   written   currently  assumes   100  percent
    absorption efficiency. That is, for the sake of
    simplicity at scoping, it  is  assumed that the
   dose administered to test animals in toxicity
   studies on which toxicity values are based was
    fully absorbed. This assumption may need to
   be revised in cases where toxicity values based
   on  route-to-route extrapolation are used,  or
   there are significant differences in  absorption
   likely between contaminants in site  media and
   the contaminants in the  vehicle used in the
   toxicity study. Chapter 7 and Appendix A in
   RAGS/HHEM Part A (EPA 1989d) provide
   additional details on this  point.

•   The risk-based PRGs should contain at most
   two significant  figures even though some of
    the parameters used in the reduced equations
   carry additional  significant figures.

•  The  equations  presented  in  this  chapter
   calculate  risk-based   concentrations using
    inhalation reference doses  (RfCVs)  and
   inhalation slope factors (SF;s). If only the
   reference   concentration   (RfC)  and/or
   inhalation unit risk  are  available for a
   particular compound in IRIS, conversion to  an
   RfD; and/or  SF;will be necessary. Many
   converted toxicity  values  are  available  in
   HEAST.

• All   standard   equations  presented  here
   incorporate pathway-specific default exposure
                                            -19-

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     factors that generally reflect RME conditions.
     As detailed in Chapter 8  of RAGS/HHEM
     Part  A  (in the  discussion on combining
     pathway risks  [Section 8.3]), RME  risks from
     one pathway should be combined with RME
     risks from another pathway only where there
     is good reason.  Typically, RME  from  one
     pathway is not likely to occur with RME from
     another  (unless  there  is  a  strong logical
     dependent relationship between  exposures
     from the  two pathways).    If risk-based
     concentrations are developed for  both the
     water and the soil pathways, the risk assessor
     ultimately may  need  to  adjust  exposure
     assumptions from one pathway (i.e., the  one
     with  the lower  RME) to  less conservative
     (more typical)  values.

3.1    RESIDENTIAL  LAND USE

3.1.1   GROUND WATER OR SURFACE
        WATER

     Under residential land use, risk from surface
water or ground-water contaminants is assumed to
be  due primarily  to direct  ingestion and  to
inhalation of volatiles from household water use.
Therefore, only these  exposure  pathways  are
considered in this  section.   Additional  exposure
pathways  (e.g., dermal absorption) are possible and
may be  significant  at some  sites for  some
contaminants, while perhaps only one exposure
pathway (e.g., direct ingestion of water only) may
be relevant at others.  In any case, the risk-based
PRG for  each chemical should be calculated by
considering all of the relevant exposure  pathways.

     In the case illustrated here, risks  from two
exposure  pathways from ground water or surface
water   are   combined,   and   the risk-based
concentration is  derived to be protective  for
exposures  from both pat pathways. Default risk from
ground water or surface water would be  calculated
as follows ("total" risk, as used below, refers to the
combined risk for a single  chemical  from all
exposure pathways  for a given medium):
Total risk
from water
= Risk from
   ingestion of
   water (adult)
+ Risk from  inhala-
    tion of volatiles
    from household
    water (adult)
 equation incorporates a water-air concentration
 relationship that is applicable only to chemicals
 with a Henry's Law constant of greater than 1 x
 10"5atm-mVmole and a molecular weight of less
 than 200 g/mole. These criteria are not used to
 screen  out chemicals that  are not  of potential
 concern for this exposure pathway but only to
 identify those that generally  should be considered
 for the  inhalation pathway when developing risk-
 based PRGs early in the process. Chemicals that
 do not meet these criteria may pose significant site
 risks (and require risk-based goals)  through
 volatiles  inhalation.     The ultimate decision
 regarding   which   contaminants    should be
 considered in the FS  must be made on a site-
 specific basis following completion of the baseline
 risk  assessment.

    Based primarily on experimental data on the
 volatilization  of radon from household  uses of
 water, Andelman (1990) derived an equation that
 defines the relationship between the concentration
 of a  contaminant in household  water  and the
 average   concentration  of the  volatilized
 contaminant in air. In the derivation, all uses of
 household water were considered (e.g., showering,
 laundering, dish washing). The equation uses a
 default "volatilization"  constant (K) upper-bound
 value of 0.0005  x 1000 L/m3.  (The 1000 L/m3
 conversion factor is incorporated into  the  equation
 so that the resulting air concentration  is expressed
 in mg/m3.) Certain assumptions  were made in
 deriving the default constant  K (Andelman 1990).
 For example,  it is assumed  that the volume of
 water used in  a residence for a family of four is
 720 L/day, the  volume of the dwelling  is 150,000 L
 and  the  air  exchange rate  is  0.25   mYhr.
 Furthermore,  it  is  assumed that  the  average
 transfer efficiency weighted  by water use  is 50
 percent (i.e., half of the concentration  of each
 chemical in water will be transfered into air by all
water uses [the range extends from 30$% for toilets
 to 90%  for dishwashers]).  See the  Andelman
paper for further details.

    Concentrations Based on  Carcinogenic  Effects.
 Total risk for carcinogenic effects  of  certain
volatile  chemicals  would   be calculated  by
combining the  appropriate inhalation and oral SFs
with  the two intakes from water:
    At scoping,  risk from indoor inhalation of
volatiles is assumed to  be relevant only for
chemicals that easily volatilize.   Thus, the risk
                                         Total = SFox Intake from
                                         risk           ingestion of
                                                       water
                                                      SF;x Intake  from
                                                              inhalation of
                                                              volatiles from
                                                              water
                                               -20-

-------
Adding  appropriate  parameters,  and  then
rearranging   the   equation   to   solve   for
concentration, results in Equation (1).

    Equation (!') on the next page is the reduced
version of Equation (1) using the standard default
parameters, and is used to calculate the risk-based
PRO at a prespecified cancer risk level of 106. It
combines the toxicity information of a chemical
with standard default  exposure parameters  for
residential land use to generate the concentration
                                                  of that chemical  that  corresponds  to  a 10"'
                                                  carcinogenic risk level due to that chemical. If
                                                  either  the  SF0or  SF;in Equation  (!')  is not
                                                  available for  a  particular chemical, the term
                                                  containing that variable in the  equation  can be
                                                  ignored or equated to zero (e.g., for  a chemical
                                                  that  does not have  SF;,  the  term  7.5(SF;) in
                                                  Equation (!')  is ignored). If any of  the default
                                                  parameter values are changed to reflect site-
                                                  specific conditions, the reduced equation cannot be
                                                  used.
RESIDENTIAL WATER - CARCINOGENIC EFFECTS
TR
SF~ x C x IR^ x EF x ED + SR x C x K x IR,
x EF x ED
BW x AT x 365 days/yr BW x AT x 365 days/yr
	

C (mg/L; risk-
based)
where
Parameters
C
TR
SF
SF0
BW
AT
EF
ED
IR»
IR!
K
EF x ED x C x FfSF,, x IRJ) + fSE x K x IR.)1
BW x AT x 365 days/yr
TR x BW x AT x 365 davs/vr
EF x ED x [(SFj x K x IR.) + (SFoXlRJ

Definition (units)
chemical concentration in water (mg/L)
target excess individual lifetime cancer risk (unitless)
inhalation cancer slope factor ((mg/kg-day)4)
oral cancer slope factor ((mg/kg-day)4)
adult body weight (kg)
averaging time (yr)
exposure frequency (days/yr)
exposure duration (yr)
daily indoor inhalation rate (mVday)
daily water ingestion rate (L/day)
volatilization factor (unitless)


(1)
]

Default Value
1 (Y6
10
chemical-specific
chemical-specific
70kg
70 yr
350 days/yr
30 yr
15 mVday
2 L/day
0.0005 x 1000 L/m3(Andelman 1990)
Risk-based PRO
(mg/L; TR = 10"*)
               REDUCED EQUATION RESIDENTIAL WATER - CARCINOGENIC EFFECTS

                             1.7 xlO"4
                         2(SF0) + 7.5(SFO
   where
   SF0
   SF
               = oral slope factor in (mg/kg-day)"1
               = inhalation slope factor in (mg/kg-day)"1
                                               -21-

-------
    Concentrations Based on Noncarcinogenic
Effects.    Total  HI  would  be  calculated by
combining the appropriate oral  and inhalation
RfDs with the two intakes from water:

HI  =   Intake from oral ingestion
                  RfD0

        + Intake from inhalation
                  RfD,

Adding  appropriate  parameters,  and then
rearranging    the  equation to    solve  for
concentration, results in Equation (2).
                                            Equation (2') on the next page is the reduced
                                        version of Equation (2) using the standard default
                                        parameters, and is used to calculate the risk-based
                                        PRG at a prespecified HI of 1. It combines the
                                        toxicity information of a chemical with standard
                                        exposure  parameters for residential land use to
                                        generate the concentration of that chemical that
                                        corresponds  to an HI of 1. If either the RfD0or
                                        RfD; in Equation  (2') is not  available  for  a
                                        particular chemical,  the  term  containing that
                                        variable in the equation can be ignored or equated
                                        to zero (e.g., for a chemical that does not have
                                        RfD,,  the term  7.5/RfD,in Equations (2')  is
                                        ignored).
                        RESIDENTIAL WATER - NONCARCINOGENIC  EFFECTS
   THI
   C (mg/L; risk-
   based)

   where:
        C x IR... x EF x ED
     RfD0 x BW x AT x 365 days/yr
     EF x ED x C x [d/RfD., x IRJ + Cl/RfD, x K x IR.11
                    BW x AT x 365 days/yr

             	THI x BW x AT x 365 days/yr	
             EF x ED x [(1/RfD, x K x IRa)  + (l/RfD0 x IRJ]
C x K x IR. x EF x ED
  j x BW x AT x 365 days/yr
                                    (2)
   Parameters    Definition
                                        Default Value
   C            chemical concentration in water (mg/L) -
   THI          target hazard index (unitless)               1
   RfD0         oral chronic reference dose (mg/kg-day)
   RfD;          inhalation chronic reference dose (mg/kg-day)
   BW          adult body weight (kg)
   AT           averaging time (yr)
   EF           exposure frequency (days/yr)
   ED           exposure duration (yr)
   IR,           daily indoor inhalation rate (mVday)
   IR,           daily water ingestion rate (L/day)
   K            volatilization  factor (unitless)
                                         chemical-specific
                                         chemical-speeific
                                         70kg
                                         30 yr (for noncarcinogens, equal to ED)
                                         350 days/yr
                                         30yr3
                                         15 mVday
                                         2 L/day
                                         0.0005 x 1000 L/m3(Andelman 1990)
    Risk-based PRG =
    (mg/L; THI = 1)
REDUCED EQUATION: RESIDENTIAL WATER - NONCARCINOGENIC EFFECTS

                      73                                                      (2')
             [7.5/RfDi  + 2/RfD0]
    where:

    RfD0
    RfD
     = oral chronic reference dose in mg/kg-day
     = inhalation chronic reference dose in mg/kg-day
                                                -22-

-------
3.1.2    SOIL

    Under  residential  land use,  risk  of  the
contaminant from soil is assumed to be due to
direct ingestion of soil only.
Total risk from soil
= Risk from ingestion of soil
    (child to adult)
    Because the soil ingestion rate is different for
children and adults, the risk due to direct ingestion
of soil is calculated using an age-adjusted ingestion
factor.   The  age-adjusted  soil ingestion factor
(IF,oii/Mi) takes into account the difference in daily
soil ingestion rates, body weights, and exposure
durations for two exposure groups — children of
one to six years and others of seven to 31 years.
Exposure  frequency (EF)  is  assumed  to be
identical  for  the two  exposure  groups.   For
convenience, this factor is calculated separately as
a time-weighted soil intake, normalized to body
weight, that can then be substituted in the  total
intake equation.   Calculated in this manner, the
factor leads  to  a  more  protective  risk-based
concentration   compared   to    an   adult-only
assumption.  Note that the ingestion factor  is in
units of mg-yr/kg-dav. and therefore is not directly
comparable to daily soil intake rate in units of
mg/kg-day. See the box containing Equation (3)
for the calculation of this factor.

    Additional exposure pathways  (e.g., inhalation
of particulate, inhalation of volatiles, ingestion of
foodcrops  contaminated   through    airborne
particulate deposits, consumption of ground water
contaminated by soil leachate) are possible at some
sites. The risk assessor should evaluate whether
inhalation  or other  exposure pathways  are
significant  at the  site.    Generally, for many
undisturbed sites with vegetative cover such as
those found in areas of residential land use, air
pathways are relatively minor contributors of risk.
Greater concern for baseline risk via air pathways
exists   under   commercial/industrial land-use
assumptions, given the increased activity levels
likely (see Section 3.2.2). Air pathway risks also
tend to be  major concerns during remedial action
(see  RAGS/HHEM Part  C). If  these other
pathways are known to be significant at scoping,
Appendix B and/or  other information should be
used to develop site-specific equations for the risk-
based PRGs.

    Concentrations Based on Carcinogenic Effects.
Total  risk  for carcinogenic  effects would be
calculated by combining the appropriate  oral SF
with the intake from soil:

Total risk = SF0x Intake from ingestion of soil

Adding appropriate  parameters,  and then
rearranging   the   equation  to   solve  for
concentration, results in  Equation  (4).

    Equation (4') below  is the reduced version of
Equation  (4) using   the  standard  default
parameters, and is used to calculate the risk-based
PRG at a prespecified cancer risk level of 106. It
combines the toxicity information of a chemical
with standard exposure parameters  for residential
land use  to generate the concentration  of  that
chemical that corresponds to  a 10"'carcinogenic
risk level due to that chemical.
                               AGE-ADJUSTED SOIL INGESTION FACTOR
    IF
  Wadj (mg-yr/kg-day)  =  IRsoWagel^JLlDage
                                BWagel.6

Parameter        Definition
                               IR,
                                                      «l/age7-31.
     xED,,
(3)
                                                           BW,
                   age-adjusted soil ingestion factor (mg-yr/kg-day)
                   average body weight from ages 1-6 (kg)
                   average body weight from ages 7-31 (kg)
                   exposure duration during ages 1-6 (yr)
                   exposure duration during ages 7-31 (yr)
                   ingestion rate of soil age 1 to 6 (mg/day)
                   ingestion rate of soil all other ages (mg/day)
                                                              age7-31
                                             Default Value

                                              114 mg-yr/kg-day
                                              15kg
                                             70kg
                                             6 yr
                                             24 yr
                                             200 mg/day
                                              100 mg/day
                                                 -23-

-------
                           RESIDENTIAL SOIL - CARCINOGENIC EFFECTS
   TR
C (mg/kg; risk-
based)

where:

Parameters

C
TR
SF0
AT
EF
*-*- sniM^Ai
  SF. x C x KT6 kg/me x EF x
         AT x 365 days/yr
                            TR x AT x 365 days/year
                         SF0 x 10"* kg/mg x EF x
                  Definition  (units)

                  chemical concentration in soil (mg/kg)
                  target excess individual lifetime cancer risk (unitless)
                  oral cancer slope factor ((mg/kg-day)4)
                  averaging time (yr)
                  exposure frequency (days/yr)
                  age-adjusted ingestion factor (mg-yr/kg-day)
                                               Default Value
                                              chemical-specific
                                              70 yr
                                              350 days/yr
                                               114 mg-yr/kg-day (see Equation (3))
   Risk-based PRO
   (mg/kg; TR = lO'6)
REDUCED EQUATION RESIDENTIAL SOIL - CARCINOGENIC EFFECTS

              0.64
              SR,
                                                                                        (4')
   where:

   SF0
  = oral slope factor in (mg/kg-day)"1
    Concentrations Based  on Noncarcinogenic
Effects.    Total  HI would  be calculated by
combining the appropriate  oral RfD  with the
intake from soil:

HI      = Intake from ingestion
                  RfD0

Adding  appropriate  parameters,  and  then
rearranging    the  equation  to    solve  for
concentration, results in Equation (5).

    Equation  (5')  is  the  reduced  version of
Equation (5)  using   the  standard  default
parameters, and is for calculating the risk-based
PRO at a prespecified  HI of 1. It combines the
toxicity information of a chemical with standard
exposure parameters for residential land use to
generate the concentration of that chemical that
corresponds to an HI of 1.
                                    3.2  COMMERCIAL/INDUSTRIAL
                                            LAND USE

                                    3.2.1    WATER

                                        Once ground water  is  determined  to  be
                                    suitable for drinking, risk-based concentrations
                                    should be based on residential exposures. This is
                                    because the NCP  seeks to require protection of
                                    ground water to allow for its maximum beneficial
                                    use (see Section 2.3). Thus, under the commercial/
                                    industrial land-use scenario, risk-based PRGs for
                                    ground water   are calculated  according  to
                                    procedures detailed in Section 3.1.1. Similarly, for
                                    surface water that is to be used for drinking, the
                                    risk-based  PRGs should  be  calculated for
                                    residential populations, and  not simply worker
                                    populations.
                                               -24-

-------
                         RESIDENTIAL SOIL - NONCARCEVOGENIC EFFECTS.
   THI     =  C x IP"* kg/mg x EF x IF.H,/
                RfD0 x AT x 365 days/yr
   C (mg/kg; risk-    =
   based)
where

Parameters

C
THI
RfD0
AT

EF
     THI x AT x 365 davs/vr
l/RfD0 x lO'6 kg/mg x EF x
                                                                                             (5)
                  Definition  (units)
                                  Default Value
                  chemical concentration in soil (mg/kg) —
                  target hazard index (unitless)               1
                  oral chronic reference dose (mg/kg-day)      chemical-specific
                  averaging time (yr)                       30 yr (for noncarcinogens, equal to ED [which
                                                          is incorporated in IFsoil,,J)
                  exposure frequency (days/yr)                350 days/yr
                  age-adjusted ingestion factor (mg-yr/kg-day)   114 mg-yr/kg-day (see Equation (3))
              REDUCED EQUATION: RESIDENTIAL SOIL - NONCARCEVOGENIC EFFECTS

   Risk-based PRO      =    2.7 x 10s (RfD0)
   (mg/kg; THI =  1)

   where

   RfD0    = oral chronic reference dose in mg/kg-day
                                                                       (5')
3.2.2    SOIL

    Under  commercial/industrial land use, risk of
the contaminant from soil is assumed to be due to
direct ingestion, inhalation of volatiles from the
soil, and inhalation of particulate from the  soil,
and is calculated for an adult worker only. For
this type of land use, it is assumed for calculating
default  risk-based  PRGs  that  there  is  greater
potential for  use of heavy equipment and related
traffic in and around contaminated soils and thus
greater  potential for soils  to be disturbed and
produce particulate  and volatile emissions than in
most  residential land-use  areas.    Additional
exposure pathways (e.g., dermal exposure) are
possible at some sites, while perhaps  only one
exposure pathway  (e.g., direct ingestion of soil
only) may be relevant at  others; Appendix B may
be used to  identify  relevant  exposure pathways to
be combined. In such cases, the risk is calculated
by considering  all the relevant exposure pathways
identified in the RI.
                                   In the default case illustrated below, intakes
                               from the three exposure pathways are combined
                               and the risk-based PRO is derived to be protective
                               for exposures from all three pathways.  In this case,
                               the risk for a specific chemical from soil due to the
                               three exposure pathways would be calculated as
                               follows:
                               Total risk
                               from soil
                                                               = Risk from ingestion of soil (worker)

                                                               + Risk from inhalation of volatiles from
                                                                   soil  (worker)

                                                               + Risk from inhalation of particulate
                                                                   from soil (worker)
                               It is possible to consider only exposure pathways of
                               site-specific importance by deriving a site-specific
                               risk-based PRG (e.g., using  the equations  in
                               Appendix B).
                                                 -25-

-------
    Concentrations Based on Carcinogenic Effects.
Total risk for carcinogenic effects  would  be
calculated by combining the appropriate inhalation
and oral SFs with the three intakes from soil:
Total risk    =  SFn
                SF;
X Intake from ingestion of soil
   (worker)

   Intake from inhalation of
   volatiles from soil (worker)
            +  SF;X   Intake from inhalation of
                       particulate (worker)

Adding  appropriate   parameters,  and then
rearranging    the  equation  to   solve  for
concentration, results  in  Equation  (6).  As
discussed in  more  detail in Section 3.3.1, Equation
(6a) is used  to test the results of Equation (6).

    Equation  (6')  is the  reduced  version of
Equation (6)  using   the  standard  default
parameters, and is used to calculate the risk-based
PRG at a prespecified cancer risk level of 10 6. It
combines the toxicity information of a chemical
with   standard   exposure  parameters  for
commercial/industrial land use to generate  the
concentration of that chemical that corresponds to
a 10 'carcinogenic  risk level due to that chemical.

    Concentrations Based  on Noncarcinogenic
Effects.    Total  HI would  be calculated by
combining  the appropriate oral and inhalation
RfDs with the three intakes from soil:

HI  =  Intake from ingestion
              RfD0

       (Intake from inhalation of volatiles
    +        and  rarticulates) _
                RfD,

Adding  appropriate  parameters,  and then
rearranging    the  equation  to   solve  for
concentration, results in Equation (7).

    Equation  (7')  is  the  reduced  version of
Equation (7)  using,   the  standard  default
parameters, and is used to calculate the risk-based
PRG at a prespecified HI of 1. It combines the
toxicity information of a chemical with standard
exposure  parameters  for commercial/industrial land
use to generate the concentration of that chemical
that corresponds to an HI of 1.
3.3    VOLATILIZATION  AND
       PARTICULATE  EMISSION
       FACTORS

3.3.1   SOIL-TO-AIR VOLATILIZATION
       FACTOR

    The volatilization  factor (VF)  is  used  for
defining    the  relationship   between  the
concentration  of contaminants  in  soil and  the
volatilized contaminants in air. This relationship
was established as a part of the Hwang and Falco
(1986) model  developed by EPA's Exposure
Assessment Group  (BAG).  Hwang and Falco
present a method intended primarily to estimate
the permissible residual levels associated with the
cleanup of contaminated soils. This method has
been used by EPA in estimating exposures to PCBs
and 2,3,7,8-TCDD from contaminated soil (EPA
1986;  EPA 1988a).    One of the pathways
considered  in  this method is  the intake  by
inhalation of volatilized contaminants.

    The basic principle of the Hwang and Falco
model is applicable only if the soil contaminant
concentration is at or below saturation. Saturation
is  the soil contaminant concentration  at which the
adsorptive  limits of the soil particles and  the
volubility limits of the available soil moisture have
been reached. Above saturation, pure liquid-phase
contaminant is present in the soil.  Under such
conditions, the partial  pressure  of the  pure
contaminant and the partial pressure of  air in the
interstitial soil pore spaces cannot be calculated
without first knowing the mole  fraction of  the
contaminant in the soil.    Therefore,  above
saturation,    the  PRG cannot   be   accurately
calculated based on volatilization. Because of this
limitation, the chemical concentration in soil (C)
calculated using the VF must be compared with
the soil saturation concentration (C!at calculated
using Equation (6a) or (7a).  If C is  greater than
Csa, then the PRG is set  equal to Csat.

    The VF presented in this  section assumes that
the contaminant concentration  in  the soil  is
homogeneous from the soil surface to the depth of
concern and that the contaminated material is  not
covered by  contaminant-free soil  material. For the
purpose of calculating VF, depth of concern is
defined as  the depth at which a near  impenetrable
layer or  the permanent ground-water level is
reached.
                                               -26-

-------
                    COMMERCIAL/INDUSTRIAL SOIL - CARCINOGENIC EFFECTS
TR    =   SE, x C x IP"* kg/mg x EF x ED x IR,H,  + SF, x C x EF x ED x IR,ir x (1/VF +  1/PEF)
                 BW x AT x 365 days/yr                        BW x AT x 365 days/yr
C (mg/kg; risk-    =
based)
where:

Parameters

C
TR
SF
SF0
BW
AT
EF
ED
IR
W
PEF

       CMt

where

Parameters

CMt
Kd

OC
s
nn,
em
                                           TR x BW x AT x 365 days/yr
                        EF x ED x [(SF0 x  10'6 kg/mg x IR^,) + (SF, x IRair x [1/VF + 1/PEF])]
                                                                                                    (6)
 Definition (units)

 chemical  concentration in soil (mg/kg)
 target excess individual lifetime cancer risk (unitless)
 inhalation cancer slope factor ((mg/kg-day1"1)
 oral cancer slope factor ((mg/kg-day)")
 adult body weight (kg)
 averaging time (yr)
 exposure  frequency (days/yr)
 exposure duration (yr)
 soil ingestion  rate  (mg/day)
 workday inhalation rate  (mYday)
 soil-to-air volatilization factor (mYkg)
 particulate emission factor(mYkg)

i x s x nm)  + (s x em)
                 Definition  (units)

                 soil saturation concentration  (mg/kg)
                 soil-water partition coefficient (L/kg)
                 organic carbon partition coefficient (L/kg)
                 organic carbon content of soil (fraction)
                 solubility (mg/L-water)
                 soil moisture content, expressed as a weight fraction
                 soil moisture content, expressed  as L-water/kg-soil
                                                                  Default Value
                                                                  10"
                                                                  chemical-specific
                                                                  chemical-specific
                                                                  70kg
                                                                  70 yr
                                                                  250  days/yr
                                                                  25 yr
                                                                  50 mg/day
                                                                  20 mYday
                                                                  chemical-specific (see Section 3.3. 1)
                                                                  4.63 x 10'mYkg (see Section 3.3.2)
                                                                                                   (6a)
                                                                 Default Value
                                                                 chemical-specific, or Kocx OC
                                                                 chemical-specific
                                                                 site-specific, or 0.02
                                                                 chemical-specific
                                                                 site-specific
                                                                 site-specific
        REDUCED EQUATION: COMMERCIAL/INDUSTRIAL SOIL - CARCINOGENIC EFFECTS

                     =   	2.9 x IP'4	
Risk-based PRO     =  	
(mg/kg; TR = 10"*)     [((5 x 10'5) x SF0)  +  (SF, x ((20/VF) + (4.3 x 10'9)))]

where
  SF0
  SF,
  W
               -  oral slope factor in (mg/kg-day)4
               =  inhalation slope factor in (mg/kg-day)4
               =  chemical-specific soil-to-air volatilization factor in mYkg (see Section 3.3.1)
 If PRG > Csatthen set PRG = Csat (where Csat = soil saturation concentration (mg/kg); see Equation (6a)
 and Section  3.3.1).
                                                 -27-

-------
                 COMMERCIAL/INDUSTRIAL SOIL - NONCARCEVOGENIC EFFECTS
THI
                 C x IP"* kg/me x EF x ED x IR.^,,
                 RfD0 x BW x AT x 365 days/yr
                                                      C x EF x ED x IR.;, x f 1/VF + l/PEF)
                                                             RfD, x BW x AT x 365 days/yr
C (mg/kg; =	
risk-based)   ED x EF x [((l/RfD0) x 10* kg/mg x
                                THI x BW x AT x 365 days/yr
                                                                                                   (V)
                                                     + ((1/RfD,) x IRair x (1/VF + 1/PEF))]
where:

Parameters

C
THI
RfD0
RfD
BW
AT
EF
ED
IR-u
VF
PEF
where

Parameters

Crat
Kd
K,,,.
OC
s
nra
     Definition (units')

     chemical  concentration in soil (mg/kg)
     target hazard index (unitless)
     oral chronic reference dose (mg/kg-day)
     inhalation chronic  reference  dose (mg/kg-day)
     adult body weight  (kg)
     averaging time (yr)
     exposure  frequency (days/yr)
     exposure duration (yr)
     soil ingestion rate  (mg/day)
     workday inhalation rate (ins/day)
     soil-to-air volatilization factor (mVleg)
     particulate emission factor (mYkg)

CMt = (Kd x s x nm) + (s x em)
                 Definition (units)

                 soil  saturation concentration (mg/kg)
                 soil-water partition coefficient  (L/kg)
                 organic carbon partition coefficient (L/kg)
                 organic carbon content of soil (fraction)
                 volubility (mg/L-water)
                 soil moisture content, expressed as a weight fraction
                 soil  moisture content, expressed as L- water/kg- soil
                                                                  Default Value
                                                                   1
                                                                  chemical-specific
                                                                  chemical-specific
                                                                  70kg
                                                                  25 yr (always equal to ED)
                                                                  250 days/yr
                                                                  25 yr
                                                                  50 mg/day
                                                                  20 mVday
                                                                  chemical-specific (see Section 3.3. 1)
                                                                  4.63 x  10'mVkg (see Section 3.3.2)
                                                                                                   (7a)
                                                                  Default Value
                                                                  chemical-specific, or Kotx OC
                                                                  chemical-specific
                                                                  site-specific, or 0.02
                                                                  chemical-specific
                                                                  site-specific
                                                                  site-specific
     REDUCED EQUATION: COMMERCIAL/INDUSTRIAL SOIL - NONCARCINOGENIC EFFECTS

                                          102	                          (V)
Risk-based
PRO (mg/kg;
THI = 1)

where:

RfD0
RfD
VF
                     [(5 x 10"VRfD0) + ((1/RfDi) x ((20/VF) + (4.3 x 10'9)))]
                 = oral chronic reference dose in mg/kg-day
                 = inhalation chronic reference dose in mg/kg-day
                 = chemical-specific soil-to-air volatilization factor in mVkg (see Section 3.3.1)
If PRG > Caat, then set PRO = Csat, (where CM = soil saturation concentration (mg/kg); see Equation (7a) and
Section 3.3.1 ).
                                                 -28-

-------
    A chemical-specific value for VF is used in the
standard default equations (Equations (6), (6  '),
(7), and (7') in Section 3.2.2) and is developed in
Equation (8).  The  VF value  calculated using
Equation (8) has been developed for specific use in
the other equations in this guidance  it may not  be
applicable in other technical contexts.  Equation
(8) lists  the  standard  default parameters  for
calculating VI?.  If site-specific information is
available, Equation (8) may  be  modified  to
calculate  a VF that is  more appropriate for the
particular site. Supporting references should  be
consulted when substituting site-specific data to
ensure that the model and specific parameters can
be appropriately applied to the given site.
                                  3.3.2    PARTICULATE EMISSION FACTOR

                                      The particulate emission factor (PEF) relates
                                  the contaminant  concentration in  soil with the
                                  concentration of respirable particles (PM10) in the
                                  air due to fugitive dust emissions from surface
                                  contamination sites. This relationship is derived
                                  by  Cowherd  (1985)  for  a rapid assessment
                                  procedure applicable to  a typical hazardous waste
                                  site where the surface contamination provides a
                                  relatively continuous and  constant potential for
                                  emission  over an extended period of time  (e.g.,
                                  years).       The  particulate  emissions   from
                                  contaminated sites  are due  to wind erosion and,
                                  therefore,  depend on the credibility of the surface
                                 SOIL-TO-AIR VOLATILIZATION FACTOR
VF (m3/kg)

where:

a (cm2/s)
(LS x V x PHI
     A
                                                         (3.14 x « x
                                                   (2 x Dd x E x K,, x 10'3 kg/g)
                                                                             (8)
                               (P.. x
                            E + (RJ
   Standard default parameter values that can be used to reduce Equation (8) are listed below. These represent "typical"
   values as identified in a number of sources. For example, when site-specific values are not available, the length of a
   side of the contaminated area (LS) is assumed to be 45 m; this is based on a contaminated area of 0.5 acre which
   approximates the size of an average residential lot. The "typical" values LS, DH, and V are from EPA 1986. "Typical"
   values for E, OC, and p, are from EPA 1984, EPA 1988b, and EPA 1988f. Site-specific data should be substituted
   for the default values listed below wherever possible. Standard values for chemical-specific D,, H, and Kotcan be
   obtained by calling the Superfund Health Risk Technical Support Center.
   Parameter

   VF
   LS
   V
   DH
   A
   D
   E
   P.
   T
   D
   H
   Kd
   K
   oc
Definition  (units)

volatilization factor (mVkg)
length of side of contaminated area (m)
wind speed in mixing zone (m/s)
diffusion height  (m)
area of contamination (cm2)
effective diffusivity (ctnYs)
true soil porosity (unitless)
soil/air partition  coefficient (g  soil/cm3 air)

true soil density or particulate  density (g/cm3)
exposure interval (s)
molecular diffusivity (ctnYs)
Henry's law  constant (atm-m3/mol)
soil-water partition  coefficient  (cmYg)
organic carbon partition coefficient (cmYg)
organic carbon content of soil  (fraction)
                                                               Default
                                                               45 m
                                                               2.25 m/s
                                                               2m
                                                               20,250,000 cm2
                                                               Dx E033
                                                               0.35
                                                               (H/Kd) x 41, where 41 is a units
                                                                 conversion factor
                                                               2.65 g/cm3
                                                               7.9xl08s
                                                               chemical-specific
                                                               chemical-specific
                                                               chemical-specific, or Kocx OC
                                                               chemical-specific
                                                               site-specific, or 0.02
                                                   -29-

-------
material.  The equation presented below, Equation
(9), is representative of a surface with 'unlimited
erosion potential,"  which is characterized by bare
surfaces of finely divided material such as sandy
agricultural soil with a large number ("unlimited
reservoir") of erodible particles.  Such surfaces
erode at low wind speeds, and particulate emission
rates are relatively  time-independent at a given
wind speed.

    This   model  was  selected   for   use   in
RAGS/HHEM Part B because it represents  a
conservative estimate for intake of particulate; it
is used to derive  Equations (6) and (7) in Section
3.2.2.
    Using the default parameter values given in
the box for Equation (9), the default PEF is equal
to 4.63 x lO'mYkg. The default values necessary
to calculate  the flux rate for an "unlimited
reservoir" surface (i.e., G,  Um, Ut, and F(x)) are
provided by Cowherd (1985), and the  remaining
default values (i.e.,  for  IS,  V, and DH)  are
"typical"  values (EPA  1986).  If  site-specific
information is available, Equation  (9)  may be
modified to calculate  a  PEF that is  more
appropriate for  the particular  site. Again,  the
original  reference  should  be  consulted  when
substituting  site-specific   data   to  ensure
applicability of the model  to specific site
conditions,
PARTICULATE EMISSION FACTOR
PEF (m3/kg)

where:
Parameter
PEF
LS
V
DH
A
0.036
G
u
U

F(x)
LS x V x DH x 3600 s/hr
A

Definition (unitsl
particulate emission factor (mVkg)
width of contaminated area (m)
wind speed in mixing zone (m/s)
diffusion height (m)
area of contamination (m2)
respirable fraction (g/m2-hr)
fraction of vegetative cover (unitless)
mean annual wind speed (m/s)
equivalent threshold value of wind speed
at 10 m (m/s)
function dependent on Um/U,(unitless)
x 1000 e/ka (9)
0.036 x (1-G) x (Um/U,)3 x F(x)

Default
4.63 x 10'mVkg
45m
2.25 m/s
2m
2025 m2
0.036 g/m2-hr
0
4.5 m/s
12.8 m/s

0.0497 (determined using Cowherd 1985)
3.4     CALCULATION  AND
        PRESENTATION OF  RISK-
        BASED PRGs

    The equations presented in this chapter can be
used  to calculate  risk-based  PRGs for both
carcinogenic and noncarcinogenic effects. If both
a carcinogenic and a noncarcinogenic risk-based
PRO are calculated for a Particular chemical, then
the lower" of the two values  is considered the
appropriate  risk-based PRG for any  given
contaminant. The case-study box below illustrates
a calculation of a risk-based PRG. A summary
table — such as that in the final case-study box —
should be developed to present both the risk-based
PRGs  and the ARAR-based  PRGs. The  table
should be labeled as to whether it presents the
concentrations that were developed during scoping
or after the baseline risk assessment.
                                               -30-

-------
                           CASE STUDY CALCULATE RISK-BASED PRGs'

     Risk-based PRGs for ground water for isophorone, one of the chemicals detected in ground-water monitoring
wells at the site, are calculated below.  Initial risk-based PRGs for isophorone (carcinogenic and noncarcinogenic
effects) are derived using Equations (!' ) and (2') in Section 3.1.1. Equations (!') and (2') combine the toxicity
information of the chemical (oral RfD of 0.2 mg/kg-day and oral SF of 0.0039 [mg/kg-day]4; inhalation values are
not available and, therefore, only the oral exposure route is considered) with standard exposure parameters. The
calculated concentrations in mg/L correspond to a target risk of 10"'and a target HQ of 1, as follows:
Carcinogenic     =  1.7 x IP'4
risk-based PRO       2(SF0)

                 =   1.7 x 10-"
                     2(0.0039)
Noncarcinogenic  =     73
risk-based PRO        2/RfD0

                 =     73
                      2/0.2
The lower of the two values (i.e., 0.022 mg/L) is selected as the appropriate risk-based PRG. Risk-based PRGs are
calculated similarly for the other chemicals  of concern.
"All information in this example is for illustration purposes only
1
CASE STUDY: PRESENT PRGs DEVELOPED DURING SCOPING*
Site: XYZ Co. Land Use: Residential
Location: Anytown, Anystate Exposure Routes Water Ingestion, Inhalation of
Medium Ground Water Volatiles














•


Chemical

Benzene
Carbon Tetrachloride
Ethylbenzene

Hexane
Isophorone
Triallate
1,1,2-Trichloroethane

Vinyl chloride
Risk-based PRGs
(mg/L)*
\ O /

10"'
—
—
—

—
0.022'"
—
—

—

HQ = 1
—
—
—

0.33
7.3
0.47
—

—

ARAR-based PRG


Type
MCL
MCL
MCLG
MCL
—

—
MCLG
MCL
MCL

Concentration (mg/L)
0.005
0.005
Q 7***
0.7
—
—
—
0.003***
0.005
0.002
All information in this example is for illustration purposes only.






^^









These concentrations were calculated using the standard default equations in Chapter 3.
"Of the two potential risk-based PRGs for this chemical, this concentration is the selected risk-based PRG.
Of the two potential ARAR-based PRGs for this chemical, this concentration is selected as the ARAR- •
based PRG. I
                                                   -31-

-------
                                   CHAPTER  4
                       RISK-BASED  PRGs  FOR
               RADIOACTIVE  CONTAMINANTS
    This chapter presents standardized exposure
parameters, derivations  of risk equations, and
"reduced" equations  for  calculating risk-based
PRGs  for  radioactive  contaminants  for the
pathways and land-use  scenarios discussed in
Chapter 2. In addition, a radiation site case study
is provided at the end of the chapter to illustrate
(1) how exposure pathways and radionuclides of
potential  concern (including radioactive decay
products)  are identified, (2) how initial risk-based
PRGs  for  radionuclides are  calculated  using
reduced equations based on information available
at the scoping phase, and (3) how risk-based PRGs
can be re-calculated using full risk equations and
site-specific data obtained during the baseline risk
assessment.  Chapters 1 through 3 and Appendices
A  and B provide  the basis  for  many  of the
assumptions, equations, and parameters used in
this chapter, and therefore should be reviewed
before  proceeding further into Chapter 4. Also,
Chapter 10 in RAGS/HHEM  Part A should be
consulted for  additional guidance on conducting
baseline risk  assessments at sites contaminated
with radioactive substances.

    In  general, standardized  default exposure
equations and parameters used to calculate risk-
based  PRGs  for radionuclides  are  similar in
structure  and function to those  equations and
parameters  developed in  Chapter   3 for
nonradioactive chemical carcinogens. Both types
of risk  equations:

•   Calculate risk-based PRGs for each carcinogen
    corresponding to a pre-specified target cancer
    risk level of 10"'. As mentioned in  Section
    2.8, target risk levels may be modified after the
    baseline risk assessment based on site-specific
    exposure conditions, technical limitations, or
    other uncertainties, as well as on the nine
    remedy selection criteria specified in the NCP.

•   Use standardized default exposure parameters
    consistent with OSWER Directive 9285.6-03
    (EPA 1991 b). Where default parameters are
    not available in that guidance document, other
    appropriate reference values  are  used and
    cited.

•   Incorporate pathway-specific default exposure
    factors that generally  reflect RME conditions.

    There are, however, several important areas in
which risk-based PRG equations and assumptions
for radioactive contaminants differ substantially
from  those  used for chemical  contaminants.
Specifically,  unlike  chemical equations,  risk
equations for radionuclides:

•  Accept input  quantities in units of activity
    (e.g., picocuries (pCi)) rather than in units of
    mass (e.g., milligrams (mg)). Activity units are
    more appropriate for radioactive substances
    because  concentrations of radionuclides in
    sample media are  determined by  direct
    physical measurements of the activity of each
    nuclide present, and because adverse human
    health effects due to radionuclide intake or
    exposure  are directly related to the amount,
    type, and  energy of the radiation deposited in
    specific body tissues and organs.

•   Consider the  carcinogenic  effects of
    radionuclides only.   EPA designates  all
    radionuclides as Class A carcinogens based on
    their property of emitting ionizing radiation
    and  on the extensive weight of epidemiological
    evidence of  radiation-induced  cancer in
    humans. At most  CERCLA radiation sites,
    potential health risks  are usually based on the
    radiotoxicity, rather than the chemical toxicity,
    of each radionuclide present.

•  Use  cancer  slope factors that  are best
    estimates (i.e., median  or 50th percentile
    values) of the age-averaged, lifetime  excess
    total cancer risk per unit intake  of a
    radionuclide (e.g., per pCi inhaled or ingested)
    or per unit external radiation exposure (e.g.,
    per  microRoentgen) to  gamma-emitting
                                             -33-

-------
    radionuclides. Slope factors given in IRIS and
    HEAST have been calculated for individual
    radionuclides based on their unique chemical,
    metabolic, and  radiological properties  and
    using a non-threshold, linear dose-response
    model. This model accounts for the amount
    of each radionuclide absorbed into the body
    from the gastrointestinal tract (by ingestion)
    or through the  lungs  (by inhalation),  the
    distribution and retention of each radionuclide
    in body tissues and organs,  as well as the age,
    sex, and weight of an individual at the time of
    exposure. The model then averages the risk
    over the lifetime of that exposed individual
    (i.e., 70 years).   Consequently,  radionuclide
    slope factors are not expressed as a function of
    body  weight or time,  and do  not require
    corrections for gastrointestinal absorption or
    lung transfer efficiencies.

    Risk-based PRO equations for radionuclides
presented in the following sections of this chapter
are derived initially by determining the total risk
posed by each radioactive contaminant in a given
pathway,  and then by rearranging the pathway
equation to solve for an activity concentration set
equal to a target cancer risk level of 10"'. At the
scoping phase, these equations are "reduced" — and
risk-based PRGs  are calculated  for each
radionuclide  of concern — using standardized
exposure  assumptions for each exposure route
within each pathway and land-use combination.
After the baseline risk assessment, PRGs can be
recalculated using full  risk  equations and  site-
specific exposure information obtained during the
RI.

4.1    RESIDENTIAL LAND  USE

4.1.1    GROUND WATER OR SURFACE
       WATER

    Under the residential  land-use scenario, risk
from  ground-water or surface  water radioactive
contaminants is assumed to be due  primarily to
direct ingestion   and  inhalation  of volatile
radionuclides released from the water to indoor
air. However, because additional exposure routes
(e.g.,   external radiation   exposure  due  to
immersion) are possible at some sites for some
radionuclides, while only one exposure route may
be relevant at others, the risk assessor always
should consider all relevant exposure routes and
add or modify exposure routes as appropriate.
    In the case illustrated below, risks from the
two default  exposure routes are combined,  as
follows:

Total risk    = Risk from ingestion of radionuclides
from water      in water (adult)

            + Risk from indoor inhalation of volatile
               radionuctides  released from water
               (adult)

    At the scoping  phase,  risk from  indoor
inhalation of volatile radionuclides is  assumed to
be relevant only for radionuclides with a Henry's
Law constant of greater than 1 x 105atm-mVmole
and a molecular weight of less than 200 g/mole.
However, radionuclides that  do  not  meet these
criteria also may, under certain site-specific water-
use conditions, be volatilized into the air from
water, and thus pose  significant site risks (and
require risk-based goals). Therefore, the ultimate
decision regarding which contaminants should  be
considered must be made by  the risk assessor on a
site-specific  basis following  completion  of the
baseline risk assessment.

    Total carcinogenic risk is calculated for each
radionuclide   separately  by combining  its
appropriate oral and inhalation SFs with the two
exposure pathways for water, as follows:

Total risk    = SF0x Intake from ingestion of
                       of radionuclides

            +  SF; x    Intake from inhalation of
                       volatile radionuclides

By  including appropriate exposure parameters for
each type of intake, rearranging  and  combining
exposure  terms  in the total risk equation, and
setting the target cancer risk level equal to 10"6,
the risk-based PRG equation is derived as  shown
in Equation (10).

    Equation (10 '), presented in the next box, is
the reduced version of Equation (10) based on the
standard default values listed below. It is used to
calculate  risk-based PRGs  for radionuclides  in
water at a pre-specified cancer risk level of 10'by
combining each radionuclide's toxicity data with
the standard default values for  residential land-use
exposure parameters.

    After the baseline risk  assessment, the risk
assessor may choose to modify one or more of the
exposure parameter default values or assumptions
                                                -34-

-------
   RW (pCi/L;
   risk-based)

   where:

   Parameters

   RW
   TR
   SF,
   SF0
   EF
   ED
   K
               RADIONUCLIDE PRGs: RESIDENTIAL WATER - CARCINOGENIC EFFECTS
                    TR
    EF x ED x [(SF0 x IRJ + (SFj x K x IR,)]
Definition (units')

radionuclide PRO in water (pCi/L)
target excess individual lifetime cancer risk (unitless)
inhalation slope factor (risk/pCi)
oral (ingestion) slope factor (risk/pCi)
exposure frequency  (days/yr)
exposure duration (yr)
daily indoor inhalation rate (mVday)
daily water ingestion rate (L/day)
volatilization factor  (unitless)
                              (10)
Default Value
10"
radionuclide-specific
radionuclide-specific
350 days/yr
30yr3
15 mVday
2 L/day
0.0005 x 1000 L/m3(Andelman 1990)
    Risk-based PRO
    (pCi/L; TR = ICT6)
        REDUCED EQUATION FOR RADIONUCLIDE PRGs:
        RESIDENTIAL WATER - CARCINOGENIC EFFECTS

           9.5 x IP'"
        2(SF0) + 7.5(8^)
                             (10')
    where

    SF0
    SF,
= oral (ingestion) slope factor (risk/pCi)
= inhalation slope factor (risk/pCi)
in the  risk  equations  to  reflect site-specific
conditions.   In this event, radionuclide PRGs
should be calculated using Equation (10) instead of
Equation (10').

4.1.2 SOIL

    Under residential land-use conditions, risk
from radionuclides in soil is assumed to be due to
direct ingestion and  external exposure to gamma
radiation. Soil ingestion rates differ for children
and adults, therefore age-adjusted ingestion rate
factors  are used in  the soil pathway  equation.
Calculation of the risk from the external radiation
exposure route  assumes that any  gamma-emitting
radionuclide in soil is uniformly distributed in that
soil within a finite  soil depth and density, and
dispersed in an infinite plane geometry.
                                        The calculation of external radiation exposure
                                    risk also  includes two additional factors,  the
                                    gamma shielding factor (Se) and the gamma
                                    exposure time factor (Te), which can be adjusted to
                                    account for both attenuation of radiation fields due
                                    to  shielding  (e.g., by structures,  terrain,  or
                                    engineered barriers) and for exposure times of less
                                    than 24-hours per day, respectively. Seis expressed
                                    as a fractional value between O and 1, delineating
                                    the  possible risk reduction range from 0%  to
                                    100%, respectively, due to shielding. The default
                                    value of  0.2  for Sefor both residential  and
                                    commercial/industrial land-use scenarios reflects
                                    the  initial conservative assumption of  a 20%
                                    reduction  in external exposure due to  shielding
                                    from structures (see EPA 1981). Teis expressed as
                                    the  quotient of the daily  number of  hours an
                                    individual is  exposed  directly  to an  external
                                    radiation  field divided by  the total number of
                                    exposure hours assumed each day for a given land-
                                                 -35.

-------
use scenario (i.e.,  24 hours for residential and 8
hours  for commercial/industrial).  The  default
value of  1 for Tefor both land-use  scenarios
reflects the conservative assumptions  of a 24-hr
exposure duration for residential populations (i.e.,
24/24 =  1) and an 8-hr exposure  duration for
workers (i.e., 8/8 = 1). Values for both factors can
(and, if appropriate, should) be modified by the
risk assessor based on site-specific conditions.

    In  addition to  direct ingestion  of soil
contaminated with radionuclides and exposure to
external   radiation from gamma-emitting
radionuclides in soil, other soil exposure routes are
possible,  such  as inhalation  of resuspended
radioactive particles,  inhalation  of  volatile
radionuclides,  or   ingestion    of foodcrops
contaminated by root or leaf uptake. The risk
assessor should therefore  identify  all  relevant
exposure  routes within the soil pathway and, if
necessary, develop equations for risk-based PRGs
that combine these exposure routes.

    In the case illustrated below, the risk-based
PRO is  derived to be protective for exposure from
the direct ingestion and external radiation routes.
Total risk from soil due to ingestion and external
radiation is calculated as follows:

Total risk    = Risk from direct ingestion of radio-
from soil         nuclides  in soil (child to adult)

            + Risk from external radiation from
                gamma-emitting radionuclides in soil

    Total  risk for carcinogenic effects from each
radionuclide of potential concern is calculated by
combining the appropriate oral slope factor, SF0,
with the total radionuclide intake from soil, plus
the appropriate  external  radiation slope factor,
SFe, with the radioactivity concentration in soil:
Total risk    =   SFn
            +   SF
x   Intake from direct ingestion
    of soil

x   Concentration of gamma-
    emitting radionuclides in soil
Adding appropriate parameters, then combining
and rearranging the  equation  to solve  for
concentration, results  in Equation (11).

    Equation (1  1')  is the  reduced version of
Equation (11) based on the standard default values
listed below. Risk-based PRGs for radionuclides
                                   in soil are calculated for a pre-specified cancer risk
                                   level of 10-6.

                                      The  age-adjusted  soil  ingestion  factor
                                   (IFS   .) used in Equation (11) takes into account
                                   the difference  in soil ingestion for two exposure
                                   groups — children of one to six years and all other
                                   individuals from seven to  31 years.  IF!0il/adj is
                                   calculated for radioactive contaminants as  shown in
                                   Equation (12). Section 3.1.2 provides additional
                                   discussion on the age-adjusted soil ingestion factor.

                                      If any  parameter values or  exposure
                                   assumptions are adjusted after the  baseline risk
                                   assessment to reflect site-specific conditions, soil
                                   PRGs should be calculated using Equation (11).

                                   4.2     COMMERCIAL/INDUSTRIAL
                                          LAND  USE
4.2.1    WATER

    Under the commercial/industrial  land use
scenario,  risk-based PRGs for radionuclides in
ground water (and for radionuclides in  surface
water used for drinking water purposes) are based
on residential exposures and calculated according
to the procedures detailed in Section 4.1.1  (see
Section 3.2.1 for the rationale for this approach).
Risk-based PRGs should be calculated considering
the possibility that both the worker and  general
population at large may be exposed to the  same
contaminated water supply.

4.2.2    SOIL

    Under the commercial/industrial  land use
scenario,  four soil exposure  routes — direct
ingestion,  inhalation  of  volatile radionuclides,
inhalation of resuspended radioactive  particulate,
and  external exposure due to gamma-emitting
radionuclides —  are combined to calculate risk-
based radionuclide PRGs in soil for adult worker
exposures.    Additional  exposure routes  (e.g.,
ingestion    of foodcrops   contaminated  by
radionuclide uptake) are  possible at some  sites,
while  only one  exposure  route  (e.g.,  external
radiation exposure only) may be relevant at others.
The risk assessor should therefore consider and
combine  all relevant soil  exposure  routes, as
necessary and appropriate, based on site-specific
conditions.
                                                -36-

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              RADIONUCLIDE PRGs: RESIDENTIAL SOIL - CARCINOGENIC EFFECTS

Total risk  =    RS x  [(SF0 x IQ-'g/mg x EF x IF^,^) + (SFe x 103g/kg x ED x D x SD x (l-Se) x Te)]

                                        TR	                  (11)
 RS(pCi/g;
 risk-based)

 where

Parameters

 RS
 TR
 SF0
 SFe
 EF
 ED
 D
 SD
                (SF0 x 10'3 x EF x IF^dj) +  (SFe x 103 x ED x D x SD x (l-Se) x TJ
                Definition  (units)

                radionuclide PRO in soil (pCi/g)
                target excess individual lifetime cancer risk  (unitless)
                oral (ingestion) slope factor (risk/pCi)
                external exposure slope factor (risk/yr per pCi/m2)
                exposure frequency (days/yr)
                exposure duration (yr)
                age-adjusted soil ingestion factor (mg-yr/day)
                depth of radionuclides in soil  (m)
                soil density (kg/m3)
                gamma shielding factor  (unitless)
                gamma exposure time factor (unitless)
                                                               Default Value
                                                               10-'
                                                               radionuclide-specific
                                                               radionuclide-specific
                                                               350 days/yr
                                                               30 yr
                                                               3600 mg-yr/day (see Equation  12))
                                                               O.lm
                                                               1.43xl03kg/m3
                                                               0.2 (see Section 4.1.2)
                                                               1  (see  Section 4.1.2)
Risk-based PRO
(pCi/g; TR = 10-*)
                          REDUCED EQUATION FOR RADIONUCLIDE PRGs:
                          RESIDENTIAL SOIL - CARCINOGENIC EFFECTS

                         =              1x10-'
                             1.3 x 103 (SF0) + 3.4 x 10* (SFe)
  where:

  SF0
  SFe
                = oral (ingestion) slope factor (risk/pCi)
                = external exposure slope factor (risk/yr per pCi/m2)
                                                                                              (11')
AGE-ADJUSTED SOIL INGESTION FACTOR
IF,^ (mg-yr/day)
where:
Parameters
IF,oil/adj
IR«oil/age 1-6
IRwil/age 7-31
ED»w
EDage 7-31
— (M*soil/age 1-6 x EDage M) + (IRjoji/agg 7.J1 X

Definition (units)
age-adjusted soil ingestion factor (mg-yr/day)
ingestion rate of soil ages 1-6 (mg/day)
ingestion rate of soil ages 7-31 (mg/day)
exposure duration during ages 1-6 (yr)
exposure duration during ages 7-3 1 (yr)
EDage7.31) (12)

Default Value
3600 mg-yr/day
200 mg/day
100 mg/day
6yr
24 yr
                                                -37-

-------
    In the case illustrated below, total risk from
radionuclides in soil is calculated as the  summation
of the individual  risks from each  of the  four
exposure routes listed above:

Total  risk =  Risk from direct ingestion of radio-
from soil        nuclides in soil (worker)

           +  Risk from inhalation of volatile
               radionuclides (worker)

           +  Risk from inhalation of resuspended
               radioactive particulate  (worker)

           +  Risk from external radiation from
               gamma-emitting  radionuclides (worker)

    Total risk for carcinogenic effects for each
radionuclide  is calculated by  combining  the
appropriate ingestion, inhalation, and external
exposure SF values with  relevant  exposure
parameters for each of the  four soil exposure
routes as follows:

Total    = SF0x Intake from direct ingestion of
risk                radionuclides in soil (worker)

        +  SF; X   Intake from inhalation of
                   volatile radionuclides (worker)

        +  SF; X   Intake from inhalation of resus-
                   pended radioactive  particulate
                   (worker)

        + SFex Concentration  of gamma-emitting
                   radionuclides in soil (worker)

Adding   appropriate parameters,   and   then
combining and rearranging the equation to solve
for concentration, results in Equation (13).

    Equation (13') below is the reduced version of
Equation (13) based on the standard default values
below and a pre-specified cancer risk  level of 106.
It combines the  toxicity  information of a
radionuclide with standard exposure parameters for
commercial/industrial land use  to generate the
concentration of that radionuclide corresponding
to a  10"' carcinogenic  risk  level due  to  that
radionuclide.

    If any parameter default values or assumptions
are changed after the baseline risk assessment to
reflect site-specific conditions, radionuclide  soil
PRGs should be derived using Equation (13).
4.2.3    SOIL-TO-AIR
        FACTOR
VOLATILIZATION
    The VF, defined in Section 3.3.1 for chemicals,
also applies for radioactive contaminants with the
following  exceptions.

•    Most radionuclides are heavy metal elements
    and are non-volatile under normal, ambient
    conditions. For these radionuclides, VF values
    need not be calculated and the risk due to the
    inhalation of volatile forms of these nuclides
    can  be ignored  for  the purposes  of
    determining  PRGs.

•   A few radionuclides, such as carbon-14 (C-14),
    tritium (H-3), phosphorus-32 (P-32),  sulfur-35
    (S-35), and other isotopes, are volatile under
    certain chemical or environmental conditions,
    such as when they are combined chemically
    with volatile organic compounds (i.e., the so-
    called radioactively-labeled or "tagged"  organic
    compounds), or when they can exist  in the
    environment in a variety of physical forms,
    such as C-14 labeled carbon dioxide  (C02) gas
    and  tritiated  water   vapor.     For  these
    radionuclides, VF values  should be calculated
    using the Hwang and Falco (1986)  equation
    provided  in Section 3.3.1  based on  the
    chemical species of the compound with which
    they are associated.

• The  naturally  occurring,  non-volatile
    radioisotopes of radium, namely Ra-226 and
    Ra-224, undergo radioactive decay and form
    inert, gaseous isotopes of radon, i.e., Rn-222
    (radon) and Rn-220  (thoron),  respectively.
    Radioactive radon and thoron gases emanate
    from their respective  parent radium isotopes
    in soil, escape  into  the air, and can pose
    cancer risks if inhaled. For Ra-226 and Ra-
    224 in soil, use the default values shown in the
    box  on page  40 for VF  and for   SF;in
    Equation (12) and Equation (12 ').

4.3    RADIATION   CASE STUDY

    This  section presents a case  study of a
hypothetical CERCLA radiation site, the ACME
Radiation  Co.  site, to  illustrate the process of
calculating pathway-specific risk-based PRGs for
radionuclides  using the risk  equations and
assumptions presented in the preceding sections of
this chapter._   The  radiation site case study is
modeled after the XYZ Co. site study discussed in
                                                -38-

-------
       RADIONUCLIDE PRGs: COMMERCIAL/EVDUSTRIAL SOIL - CARCINOGENIC EFFECTS

Total     =  RS x  ED x  [(SF0 x 10Jg/tag x EF x IRwi,) + (SF, x itfgfcg x EF x IR8ir x 1/VF)
risk
                  i x lOfykg x EF x IR^ x 1/PEF) + (SFe x lOfykg x D x SD x (l-Se) x Te)]

                                                 TR _
                                                  x (1/VF + 1/PEF)  +
   RS      =
   (pCi/g;       ED x [(SF^lO-'xEFxIR,,,,,) +
   risk-based)
   where.

   Parameters

   RS
   TR
   EF
   ED
   VF
   PEF
   D
   SD
   S,
   Te
                Definition  (units)

                radionuclide PRO in soil (pCi/g)
                target excess individual lifetime cancer risk (unitless)
                inhalation slope factor (risk/pCi)
                oral (ingestion) slope factor (risk/pCi)
                external exposure slope  factor (risk/yr per pCi/m2)
                exposure frequency (days/yr)
                exposure duration (yr)
                workday inhalation rate  of air (mVday)
                daily soil ingestion rate (mg/day)
                soil-to-air volatilization factor (mVkg)
                particulate emission factor (mYkg)
                depth of radionuclides in soil (m)
                soil density (kg/m3)
                gamma shielding factor  (unitless)
                gamma exposure factor  (unitless)
                               (13)
Default Value
10"
radionuctide-specific
radionuclide-specific
radionuclide-specific
250 days/yr
25 yr
20 mVday
50 mg/day
radionuclide-specific (see Section 4.2.3)
4.63 x 10'mVkg (see Section 3.3.2)
O.lm
  1.43xl03kg/m3
0.2 (see Section 4.1.2)
1 (see Section 4.1.2)
   Risk-based PRO  =
                         REDUCED EQUATION FOR RADIONUCLIDE PRGs:
                  COMMERCIAL/INDUSTRIAL SOIL - CARCINOGENIC EFFECTS*

                                 	Ix 10*	
   (pCi/g; TR = KT6)    [(3.1 x 102(SF0)) + ((1.3 x 108/VF + 2.7 x 10'2) (SFj)) + (2.9 x 10* (SFe))]
                              (13')
   where:

   SF0
   SF,
   SFe
   VF
                = oral (ingestion) slope factor (risk/pCi)
                = inhalation slope factor (risk/pCi)
                = external exposure slope factor (risk/yr per pCi/m2)
                = radionuclide-specific soil-to-air volatilization factor in mVkg (see Section 3.3. 1)
   *NOTE See Section 4.2.3 when calculating PROS for Ra-226 and Ra-224.
Chapters 2 and 3. It generally follows a two-phase
format which consists of a "at the scoping stage"
phase wherein risk-based PRGs for radionuclides
of potential concern are calculated initially using
reduced equations based on PA/SI data,  and then
a second, "after the baseline risk assessment" phase
wherein radionuclide PRGs are recalculated using
                                                     full equations and modified site-specific parameter
                                                     values based on RI/FS data.

                                                         Following an overview of the history and
                                                     current status of the site presented in Section 4.3.1,
                                                     Section 4.3.2 covers a number of important steps
                                                     taken  early  in the scoping phase  to calculate
                                                     preliminary risk-based PRGs assuming a specific
                                                  -39-

-------
    SOIL DEFAULT VALUES FOR VF AND SF,
            FOR Ra-226 AND Ra-224
     Radium
Default VF
  Value
/ pCi/ltgRa \
\ pCi/nr* Rn*/
Inhalation
  slope
Factor SF:
(risk/pCi)**
     Ra-226

     Ra-224
   200
  LIE-11

 4.7E-11
      * Calculated using values taken from NCRP
   1976 and UNSCEAR 1982 Assumptions: (1) an
   average  Ra-226 soil concentration of 1 pCi/g
   associated with an average ambient Rn-222 air
   concentration of 120 pCi/m3and (2) an average
   Ra-224 soil concentration of  1 pCi/g associated
   with an average ambient Rn-220 air concentration
   of 5 pCi/m3.

      ** Slope factor values are for Rn-222 (plus
   progeny) and for Rn-220 (plus progeny).
land-use scenario. Section 4.3.3 then discusses how
initial assumptions and calculations can  be
modified when additional  site-specific information
becomes available.

4.3.1    SITE HISTORY

    The  ACME  Radiation  Co.  site is  an
abandoned industrial facility consisting of a large
factory  building situated  on ten acres of land
surrounded  by  a   high-density  residential
neighborhood.  Established in 1925, the ACME
Co. manufactured luminous watch  dials and gauges
using   radium-based paint  and  employed
approximately 100  workers, mostly women. With
the declining radium market, ACME phased out
dial production and expanded its operations in
1960 to include brokering  (collection and disposal)
of low-level radioactive waste (LLW).  After the
company was issued a state license in 1961, ACME
began receiving  LLW  from  various nearby
hospitals and research laboratories. In 1975, acting
on  an anonymous  complaint  of  suspected
mishandling of radioactive waste, state officials
visited the ACME Co. site and cited the company
for numerous storage  and disposal violations.
After ACME  failed  to rectify plant conditions
identified in initial and subsequent citations, the
state first suspended, and then later revoked its
operating license in 1978. Around the same time,
officials  detected  radium-226  (Ra-226)
contamination at a few neighboring locations off
site. However, no action was taken  against the
company at that time.  When ACME  filed for
bankruptcy in 1985, it closed its facility before
completing cleanup.

    In 1987, the state  and EPA conducted an
aerial gamma  survey over the ACME Radiation
Co. site and surrounding properties to investigate
the potential extent of radioactive contamination
in these  areas.  The overflight survey revealed
several areas of elevated exposure rate readings,
although  individual gamma-emitting radionuclides
could not be identified.  When follow-up ground
level surveys were performed in 1988, numerous
"hot spots" of Ra-226 were pinpointed at various
locations within and around the factory building.
Three large  soil piles   showing  enhanced
concentrations of Ra-226 were discovered along
the southern border. Approximately 20 rusting
drums labelled with LLW placards also were
discovered outside under a  covered storage area.
Using ground-penetrating  radar,  EPA detected
subsurface magnetic anomalies in a few locations
within the property boundary which suggested the
possibility of buried waste  drums. Based on
interviews with people living  near the site" and with
former plant workers,  the state believes that
radium contaminated soil may have been removed
from the ACME site in the  past and used locally
as fill material for the construction of new homes
and roadbeds. Site access is currently  limited (but
not entirely restricted)  by  an existing security
fence.

    In 1988, EPA's regional field investigation
team  completed a PA/SI.  Based on the PA/SI
data, the  ACME Radiation  Co. site scored  above
28.50  using the  HRS  and was listed on  the
National  Priorities List in 1989. Early  in 1990, an
RI/FS was initiated and a baseline risk assessment
is currently in progress.

4.3.2   AT THE SCOPING PHASE

    In this subsection, several steps are outlined to
show by  example how initial site data are used at
the scoping phase to calculate risk-based PRGs for
radionuclides  in  specific  media of concern.
Appropriate sections of Chapters 2 and 3 should
be consulted for more  detailed explanations for
each step considered below.
                                               -40-

-------
     Identify Media of Concern.  A large stream
"runs along the western border of the site and feeds
 into a river used by some of the local residents for
 fishing and boating.   Supplemental water intake
 ducts for the municipal water treatment plant are
 located approximately  300 yards downriver, and the
 site is situated over an aquifer which serves as the
 primary drinking water supply for  a community of
 approximately 33,000 people.

     Analyses of ground water, soil, and stream
 sediment samples taken during  the PA/SI revealed
 significant levels of radionuclide  contamination.
 Potential sources of contamination  include the soil
 piles, process residues in soil, and radionuclides
 leaking from buried drums. Air filter samples and
 surface water samples from the stream and river
 showed  only background  levels  of activity.
 (Background concentrations were determined from
 analyses conducted on a limited  number of air,
 ground  water, surface water,  and soil samples
 collected approximately one mile from the site.)

     The data show that the media of potential
 concern at this site include ground water and soil.
 Although stream water and river  water were not
 found to be  contaminated,  both surface water
 bodies may become contaminated in the future due
 to the migration of radionuclides  from  sediment,
 from the exposed soil piles, or from leaking drums.
 Thus, surface water is another medium of potential
 concern.

     For simplicity, only soil will be discussed as
 the medium  of concern during the remainder of
 this case study.   Procedures  discussed for this
 medium can nevertheless be applied in a similar
 manner to all other media of concern.

     Identify  Initial List of  Radionuclides  of
 Concern. The PA/SI for the ACME Radiation Co.
 site identified elevated concentrations of five
 radionuclides  in  soil  (Ra-226,  tritium (H-3),
 carbon-14 (C- 14), cesium (CS-137), and strontium
 (Sr-90)).   These  comprise  the  initial  list  of
 radionuclides  of potential concern.

     Site  records indicate  that radioisotopes  of
 cobalt (Co-60), phosphorus (P-32), sulfur (S-35),
 and americium  (Am-241  and Am-243)  were
 included on the manifests of several LLW drums in
 the  storage area and on the manifests of  other
 drums suspected to be buried  onsite. Therefore,
 although not detected in any  of  the initial soil
 samples analyzed, Co-60, P-32,  S-35, Am-241, and
Am-243 are added to the list for this medium
because of their potential to migrate from leaking
buried drums into the surrounding  soil.

    Identify Probable Land Uses.  The ACME
Radiation Co.  site is located in the center of a
rapidly developing suburban community comprised
of single and multiple family  dwellings. The area
immediately encircling the site was recently re-
zoned for residential use only; existing commercial
and light industrial facilities  are currently  being
relocated. Therefore,  residential use is determined
to be the most reasonable future land use for this
site.

    Identify Exposure Pathways,  Parameters, and
Equations. During the  scoping phase, available
site data were neither sufficient to identify all
possible exposure pathways nor adequate enough
to  develop  site-specific fate  and  transport
equations and parameters. Therefore, in order to
calculate initial risk-based PRGs for radionuclides
of potential  concern in  soil, the standardized
default soil exposure equation and assumptions
provided in this chapter for residential land use in
Section 4.1.2 are selected. (Later in this case  study,
examples are provided to illustrate how the full
risk equation (Equation (11)) and assumptions are
modified when baseline risk assessment data
become available.)

    For the soil pathway, the exposure routes of
concern are assumed to be direct ingestion of soil
contaminated with radionuclides and exposure to
external   radiation   from  gamma-emitting
radionuclides.  Again, although soil is the  only
medium discussed  throughout this case study,
exposure pathways,  parameters, equations, and
eventually risk-based  concentrations  would need to
be identified and developed for all other media and
exposure pathways  of  potential  concern  at an
actual site.

    Identify Toxicity Information.  To  calculate
media-specific risk-based PRGs, reference toxicity
values for  radiation-induced cancer effects are
required (i.e., SFs).   As stated previously, soil
ingestion and external radiation are the exposure
routes of concern for the soil pathway. Toxicity
information (i.e., oral,  inhalation, and external
exposure SFs)  for all radionuclides of potential
concern  at  the ACME  Radiation Co. site are
obtained from IRIS or HEAST, and are shown in
the box on the following page.
                                                 -41-

-------
RADIATION CASE STUDY: 1
TOXICITY INFORMATION FOR RADIONUCLIDES OF POTENTIAL CONCERN* •
Radioactive
Hal- life
Radionuclides (yr)
H-3
C-14
P-32
S-35
Co-60
Sr-90
Cs-137
Ra-226
Am-241
Am-243
* Sources:
NA = Not
12
5730
0.04
0.24
5
29
30
1600
432
7380
HEAST and Federal Guidance
ICRP Inhalation Ingestion
Decay Lung Slope Factor Slope Factor
Mode Classification (risk/pCi) risk/pCi
beta «
O
beta o
&
beta D
beta D
beta/gamma Y
beta D
beta D
alpha/gamma w
alpha/gamma w
alpha/gamma w
Report No. 11. All information in
7.8E-14
6.4E-15
3.013-12
1.9E-13
I.6E-10
5.6E-11
1.9E-11
3.0E-09
4.0E-08
4.0E-08
this example is for illustration only.
applicable (i.e., these radionuclides are not garnma-emitters and the direct radiation exposure pathway
5.5E-14
9.1E-13
3.5E-12
2.2E-13
1.5E-11
3.3E-11
2.8E-11
1 .2E-10
3.1E-10
3.1E-10

can be ignored).
External Exposure 1
Slope Factor 1
(risk/yr per pCi/m2) 1
NA I
NA 1
NA 1
NA 1
1.3E-10 1
NA 1
NA 1
4.2E-13 1
1.6E-12 1
3.6E-12 1
1
	 1

-------
     Calculate Risk-based PRGs.  At this Step, risk-
 based PRGs are calculated for each radionuclide of
 potential  concern using the  reduced risk Equation
 (11')  in Section 4.1.2, SF  values obtained from
 IRIS and HEAST, and standardized default  values
 for parameters for  the  residential  land-use
 scenario.  To calculate the risk-based PRO for Co-
 60 at  a pre-specified target risk level of 10"', for
 example, its ingestion SF  of 1.5 x 10"" and its
 external exposure SF of 1.3 x 10"10are substituted
 into Equation (11 '), along with the standardized
 default values, as follows:

 Risk-based PRO  =   	Ix 1Q-*	
 for Co-60            1.3 x 103 (SF0) + 3.4 x 10* (SFe)
 (pCi/g; TR = 10-*)

 where:

 SF0=   oral (ingestion) slope  factor for Co-60 = 1.5 x
        10-"(risk/pCi)

 SF = external exposure slope factor for Co-60 = 1.3
        xlOIO(nsk/yrperpCi/m2)

 Substituting the values for  SF0and SFefor Co-60
 into Equation (1 1') results  in:

 Risk-based PRO for Co-60 (pCi/g; TR = l(r*) =

    	1x10"*	
    [(1.3 x 103)(1.5 x lO'11)  +  (3.4 x 10*)(1.3 x 10'10)]

    =   0.002 pCi of Co-60/g of soil

    In a similar manner, risk-based PRGs can be
 calculated for all other radionuclides of concern in
 soil at the ACME Radiation Co. site. These  PRGs
 are presented in the next box.

 4.3.3    AFTER THE BASELINE RISK
        ASSESSMENT

    In this subsection, several steps are outlined
 which  demonstrate how  site-specific data obtained
 during the baseline risk assessment can be used to
 recalculate risk-based PRGs for radionuclides in
 soil. Appropriate sections  of Chapters  2  and 3
 should be consulted for more detailed explanations
 for each step considered below.

    Review Media of Concern. During the RI/FS,
 gamma radiation surveys were conducted in the
yards of several homes located within a two-block
 radius  of the ACME Radiation Co. site. Elevated
 exposure rates, ranging from approximately two to
 four times  the  natural  background rate,  were
           RADIATION CASE STUDY:
        INITIAL RISK-BASED PRGs FOR
          RADIONUCLIDES IN SOIL*
                   Risk-based Soil PRO (pCi/g)
  H-3
  Sr-90 (only)
  P-32
  S-35
  C-14
  Co-60
  Cs-137 (only)
  Ra-226 (only)
  Am-241
  Am-243 (only)
   * Calculated for illustration only using Equation
   (11') in Section 4.1.2. Values have been rounded
   off.
measured on properties immediately bordering the
site. Measurements onsite ranged from 10 to 50
times background.  In both eases, enhanced soil
concentrations of Ra-226 (and decay products) and
several  other gamma-emitting radionuclides were
discovered to be the sources of these elevated
exposure rates. Therefore, soil  continues  as a
medium of potential concern.

    Modify List of Radionuclides of Concern.
During  scoping, five radionuclides (Ra-226, H-3,
C-14, (Cs-137, and Sr-90) were detected in elevated
concentrations in soil samples  collected at the
ACME Radiation Co. site. These made  up the
initial list of radionuclides of potential concern.
Although not detected during the first round of
sampling, five additional radionuclides  (P-32,  S-35,
Co-60, Am-241, and Am-243) were added to this
list because  of their potential to migrate from
buried leaking drums into the surrounding soil.

    With additional  RI/FS  data,  some
radionuclides are  now  added to the list, while
others are dropped.   For example, soil analyses
failed to detect P-32 (14-day half-life) or S-35 (87-
day  half-life) contamination. Decay correction
calculations   strongly    suggest   that   these
radionuclides should not  be present onsite in
detectable quantities after an estimated burial time
of 30 years. Therefore, based on these data, P-32
and S-35 are dropped from the list. Soil data also
confirm that decay products of Ra-226, Sr-90, Cs-
137, and Am-243 (identified in the first box below)
                                                 -43-

-------
are present in secular equilibrium (i.e.,  equal
activity concentrations) with their respective parent
isotopes.

    Assuming secular equilibrium, slope factors for
the parent isotope and each of its decay  series
members  are  summed.    Parent  isotopes  are
designated with a " +D" to indicate the composite
slope factors of its decay chain (shown in bold face
in the second box below).  Thus, Ra-226+D, Sr-
90+D, Cs-137+D, and Am-243+D replace their
respective  single-isotope values  in the  list of
radionuclides of  potential concern,  and their
composite  SFs are used in the full soil pathway
equation to recalculate risk-based concentrations.

RADIATION CASE STUDY DECAY PRODUCTS
Parent Radionuclide
Ra-226
Sr-90
Cs-137
Am-243
Decay Product(s) (Half-life)
Rn-222 (4 days), Po-218 (3 mm), Pb-214 (27 mm), Bi-214 (20
rein), Po-214 (<1 s), Pb-210 (22 yr), Bi-210 (5 days), Po-210
(138 days)
Y-90(14hr)
Ba-137m (2 min)
Np-239 (2 days)




RADIATION CASE STUDY SLOPE

FACTORS FOR
1
DECAY SERIES'
Slope Factors
Decay Series
Ra-226
Rn-222
Po-218
Pb-214
Bi-214
Po-214
Pb-210
Bi-210
Po-210
Ra-226+D
Sr-90
Y-90
Sr-90+D
Cs-137
Ba-137m
Cs-137+D
Am-243
Np-239
Am-243+D
"All information in this exanm
Inhalation
3.0E-09
7.2E-13
5.8E-13
2.9E-12
2.2E-12
2.8E-19
1.7E-09
8.1E-11
2.7E-09
7.5E-09
5.6E-11
5.5E-12
6.2E-11
1.9E-11
6.0E-16
1.9E-11
4.0E-08
1.5E-12
4.0E-08
)le is for illustration
Ingestion
1.2E-10
—
2.8E-14
1.8E-13
1.4E-13
l.OE-20
6.5E-10
1.9E-12
2.6E-10
l.OE-09
3.3E-11
3.2E-12
3.6E-11
2.8E-11
2.4E-15
2.8E-11
3.1E-10
9.3E-13
3.1E-10
Purposes only.
External
4.2E-13
2.2E-14
O.OE+00
1.5E-11
8.0E-11
4.7E-15
1.8E-13
O.OE+00
4.8E-16
9.6E-11
O.OE+00
O.OE+00
O.OE+00
O.OE+00
3.4E-11
3.4E-11
3.6E-12
1.1E-11
1.5E-11

                                                -44-

-------
    Review Land-use Assumptions. At this step,
'the  future  land-use assumption chosen during
 scoping is reviewed. Since the original assumption
 of future residential land use is supported by RI/FS
 data, it is not modified.

    Modify Exposure Pathways, Parameters, and
 Equations. Based on site-specific information, the
 upper-bound  residence  time  for many of  the
 individuals living near the ACME Radiation Co.
 site  is determined to be  45 years rather than the
 default value  of 30 years. Therefore, the exposure
 duration  parameter  used in  Equation  (11)  in
 Section 4.1.2 is substituted accordingly. It is also
 determined that individuals living near the site are
 only exposed  to the external gamma radiation field
 approximately 18 hours  each day, and that their
 homes provide a shielding factor of about 0.5 (i.e.,
 50%). Therefore, values for Teand Seare changed
 to 0.75 (i.e., 18 hr/24 hr)  and 0.5, respectively.

    Modify Toxicity Information. As discussed
 above in the section  on modifying the list of
 radionuclides of  concern, oral, inhalation,  and
 external exposure  slope factors for Ra-226, Sr-90,
 Cs-137, and Am-243 were adjusted to account for
                                                    the added risks (per unit intake and/or exposure)
                                                    contributed  by  their  respective decay series
                                                    members that are in secular equilibrium.

                                                        Recalculate Risk-based PRGs. At this step,
                                                    risk-based PRGs are recalculated for all remaining
                                                    radionuclides of potential concern using the full
                                                    risk equation for the soil pathway (i.e., Equation
                                                    (11))  modified by revised  site-specific assumptions
                                                    regarding exposures, as  discussed above.

                                                        To recalculate the risk-based  PRO for Co-60
                                                    at a pre-specified  target  risk level of  10"', for
                                                    example, its ingestion  SF of 1.5 x 10"", and its
                                                    external exposure SF of 1.3 x 10"10are substituted
                                                    into Equation (11), along with other site-specific
                                                    parameters, as shown in the next box.

                                                        In a similar manner, risk-based PRGs can be
                                                    recalculated  for all remaining radionuclides of
                                                    potential concern in soil at the ACME Radiation
                                                    Co. site.  These revised  PRGs are presented in the
                                                    box on  the  next page.  In those  cases where
                                                    calculated risk-based PRGs for radionuclides are
                                                    below current detection  limits,  risk  asseasors
                                                    should contact the  Superfund Health  Risk
                                                    Technical Support Center  for additional guidance.
             RADIATION CASE STUDY: REVISED RISK EQUATION FOR RESIDENTIAL SOIL
RS for Co-60 (pCi/g;  =  	
risk-based)              (SF0 x 10'3 x EF x
                                                  TR
where:

Parameters

RS
TR

SF!
EF
ED
   IF
   lr
   D
   SD
   S,
     soil/adj
                                                  +  (SFe x 103 x ED x D x SD x (l-Se) x Te)
    =   0.003 pCi/g


Definition (units)

radionuclide PRO in soil (pCi/g)
target excess individual lifetime cancer risk (unitless)
oral (ingestion) slope factor (risk/pCi)
external exposure slope factor (risk/yr per pCi/m2)
exposure frequency (days/yr)
exposure duration (yr)
age-adjusted soil ingestion  factor (mg-yr/day)
depth of radionuclides in soil (m)
soil density (kg/m3)
gamma shielding factor (unitless)
gamma exposure time factor (unitless)
                                                                  Revised Value
104
1.5xlO-"(risk/pCi)
1.3xlO'10(nsk/yrperpCi/m2)
350 days/yr
45 yr
5100 mg-yr/day
0.1 m
1.43xl03kg/m3
0.5
0.75
   (Note: To account for the revised upper-bound residential residency lime of 45 years, the age-adjusted soil
   ingestion factor was recalculated using the equation in Section 4.1.2 and an adult exposure duration of 39 years
   for individuals 7 to 46 years of age.)
                                                  -45-

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                  RADIATION CASE STUDY:
  REVISED RISK-BASED PRGs FOR RADIONUCLIDES IN SOIL*
Radionuclides
                                 Risk-based Soil PRO (pCi/g)
                                          10,200
                                             20
                                            620
                                              0.003
                                              0.01
                                              0.004
                                              0.2
                                              0.03
  Calculated for illustration only. Values have been rounded off.
H-3
Sr-90+D
C-14
Co-60
Cs-137+D
Ra-226+ D
Am-241
Am-243+D
                             -46-

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                                 REFERENCES
Andelman, J.B. 1990. Total Exposure to Volatile Organic Chemicals in Potable Water. N.M. Ram, R.F.
Christman, K.P. Cantor (eds.). Lewis Publishers.

Cowherd, C., Muleski, G., Engelhart, P., and Gillete, D. 1985. Rapid Assessment of Exposure to Paniculate
Emissions from Surface Contamination.  Prepared for EPA Office of Health and Environmental Assessment.
EPA/600/8-85/002.

Environmental Protection Agency (EPA).    1981. Population Exposures to External Natural Radiation
Background in the U.S. Office of Radiation Programs. ORP/SEPD-80-12.

EPA. 1984. Evaluation and Selection of Models for Estimating Air Emissions from Hazardous Waste Treatment,
Storage, and Disposal Facilities. Office of Air Quality Planning and Standards. EPA/450/3-84/020.

EPA. 1986. Development of Advisoy Levels for  PCBs Cleanup.   Office of Health and  Environmental
Assessment.  EPA/600/21.

EPA. 1988a. CERCLA Compliance With Other Laws Manual, Part I (Interim Final). Office of Emergency
and Remedial Response.  EPA/540/G-89/006 (OSWER Directive #9234.1-01).

EPA. 1988b.  Estimating Exposures to 2,3,7,8-TCDD (External  Review  Draft). Office  of Health and
Environmental  Assessment. EPA/600/6-88/005A.

EPA. 1988c. Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA. Interim
Final  Office of Emergency and Remedial  Response. EPA/540/G-89/004 (OSWER Directive #9355.3-01).

EPA. 1988d. Guidance on Remedial Actions for Contaminated Ground Water at Superfund Sites. Interim Final.
Office of Emergency and Remedial Response. EPA/540/G-88/003 (OSWER Directive #9283. 1-2).

EPA. 1988f. Superfund Exposure Assessment Manual.    Office of Emergency and Remedial Response.
EPA/540/1-88/001 (OSWER Directive 9285.5-1).

EPA. 1988. Availability of the Integrated Risk Information System (IRIS). 53 Federal Register 20162.

EPA. 1989a. CERCLA Compliance With Other Laws Manual, Part II: Clean Air Act and Other Environmental
statutes and State Requirements.  Office of Emergency and Remedial Response. EPA/540/G-89/009 (OSWER
Directive #9234.1-01).

EPA. 1989b. Interim Final Guidance on preparing Superfund Decision Documents. Office of Emergency and
Remedial Response.  OSWER Directive 9355.3-02.

EPA. 1989c. Methods for Evaluating the Attainment of Cleanup Standards (Volume 1: Soils and Solid Waste).
Statistical Policy  Branch. NTIS #PB89-234-959/AS.

EPA. 1989d. Risk Assessment Guidance for Superfund: Volume I-Human Health Evaluation Manual (Part A,
Baseline Risk Assessment).  Interim Final. Office of Emergency and Remedial Response. EPA/540/1-89/002.

EPA. 1990a. Catalog of Superfund Program Publications.   Office of Emergency and Remedial Response.
OSWER Directive 9200.7-02A.
                                             -47-

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EPA. 1990b. Guidance for Data Usabiliy in Risk Assessment.   Office of Solid Waste and Emergency
Response. EPA/540/G-90/008 (OSWER Directive #9285.7-05).

EPA. 1990c. Guidance on Remedial Actions for Superfund Sites with PCB Contamination. Office of Emergency
and Remedial Response. EPA/540/G-90/007 (OSWER Directive #9355.4-01).

EPA. 1990d. "National Oil and Hazardous Substances Pollution Contingency Plan (Final Rule)." 40 CFR
Part 300; 55 Federal Register 8666.

EPA. 1991a. Conducting Remedial Investigations/Feasibility  Studies for CERCLA Municipal Landfill Sites.
office of Emergency and Remedial Response. EPA/540P-91/001 (OSWER Directive #9355.3-11).

EPA. 1991b.  Risk Assessment Guidance for Superfund Vol. 1, Human Health Evaluation Manual Supplemental
Guidance:    "Standard Default Exposure Factors. " (Interim Final). Office of Emergency and Remedial
Response.  OSWER Directive 9285.6-03.

EPA. 1991c.  Role of the Baseline Risk Assessment  in Superfund Remedy Selection Decisions. Office of Solid
Waste and Emergency  Response. OSWER Directive 9355.0-30.

EPA. 199 Id. Risk Assessment Guidance for Superfund: Volume I -Human Health Evaluation Manual (Part
C, Risk Evaluation of Remedial Alternatives). Interim. Office of Emergency and Remedial Response. OSWER
Directive  9285.7-01 C.

EPA. Health Effects Assessment Summary Tables (HEAST).  Published quarterly by the Office of Research
and Development and Office of Solid Waste and Emergency Response. NTIS #PB 91-921100.

Hwang, S.T.,  and Falco,  J.W. 1986., Estimation of Multimedia Exposures Related to Hazardous Waste Facilities.
Cohen, Y. (cd). Plenum Publishing Corp.
                                              -48-

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                                  APPENDIX  A

             ILLUSTRATIONS  OF CHEMICALS
                 THAT  "LIMIT" REMEDIATION
    In many cases, one or two chemicals will drive
the cleanup at a site, and the resulting cumulative
medium or site risk will be approximately equal to
the potential risk associated with the individual
remediation goals for these chemicals.    These
"limiting chemicals" are generally either chemicals
that are responsible for much of the baseline risk
(because of either high toxicity or presence in high
concentrations),  or  chemicals that  are least
amenable to the selected treatment method. By
cleaning up these chemicals to their  goals, the
other chemicals typically will be cleaned up to
levels much lower than their corresponding goals.
The example given in the box below provides a
simple  illustration of this principle.

    The  actual  circumstances for  most
remediations will be much more complex than
those described in the example (e.g., chemicals will
be present at different baseline concentrations and
will  be  treated/removed at differing  rates);
however, the same principle of one or perhaps two
chemicals limiting the site cleanup usually applies,
even in more complex cases.

    Unless much is known about the performance
of a remedy  with respect to all the  chemicals
present  at the site, it may not be possible  to
determine which of the site contaminants will drive
the  final   risk  until   well   into   remedy
implementation.   Therefore, it generally  is not
possible to predict the cumulative risk that will  be
present at the site during or after remediation.  In
some situations, enough will be known about the
site conditions and the performance of the remedy
to estimate  post-remedy concentrations  of
chemicals or to identify the chemical(s) that will
dominate the  residual risk.   If this type  of
information is available, it may be necessary  to
modify  the  risk-based  remediation  goals for
individual chemicals.
               SIMPLE ILLUSTRATION OF A CHEMICAL THAT LIMITS REMEDIATION

       Two chemicals (A and B) are present in ground water at a site at the same baseline concentrations.
   Remediation goals were identified for both A and B. Chemical A's goal is 0.5 ug/L, which is associated with a
   potential risk of 10"6. Chemical B's goal is 10 ug/L., which is also associated with a potential risk of 10"6. The
   calculated cumulative risk at remediation goals is therefore 2 x 10"*. Assuming for the purposes of this illustration
   that A and B are treated or removed at the same rate, then the first chemical to meet its goal will be B.
   Remediation must continue at this site, however, until the goal for chemical A has been met. When the
   concentration of A reaches 0.5 ug/L, then remediation is complete. A is at its goal and has a risk of 10"'. B is at
   1/20 of its goal with a risk of 5 x 10"8. The total risk (1 x 10"6+ 5 x 10"6) is approximately 10* and is due to the
   presence of A.

       This example illustrates that the final risk for a chemical may not be equal to the potential risk associated with
   its remediation goal, and, in fact, can be much less than this risk. Although the potential risk associated with
   Chemical B's goal is 10"6, the final residual risk associated with B is 5 x 10"8. Thus, if one were to calculate the
   cumulative risk at PRGs prior to remedy implementation, one would  estimate total medium risk of 2 x 10"', however,
   the residual cumulative risk after remediation is 1 x  10"'.
                                          I
                                              -49-

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                                 APPENDIX B
          RISK EQUATIONS FOR INDIVIDUAL
                       EXPOSURE PATHWAYS
    This appendix  presents  individual risk
equations for each exposure pathway presented in
Chapter 3. These individual risk equations can be
used and rearranged to derive full risk equations
required for calculating  risk-based  PRGs.
Depending on the exposure pathways that are of
concern for a land-use and medium combination,
different individual risk equations can be combined
to derive the full equation  reflecting the
cumulative risk for  each chemical within the
medium.   See  Chapter 3 for examples  of how
equations are combined and how they need to be
rearranged to solve for risk-based  PRGs. Note
that in this appendix, the term HQ is used to refer
to the risk level associated with noncarcinogenic
effects  since the  equations are  for a  single
contaminant in an individual exposure pathway.

    The following sections  list individual risk
equations for the ground water, surface water, and
soil pathways.   Risk  equations for exposure
pathways not listed below can be developed and
combined with those listed. In particular, dermal
exposure  and ingestion   of  wound  water
contaminated  by soil leachate, for which guidance
is currently being developed by EPA could be
included in  the  overall exposure pathway
evaluation.

B.I   GROUND WATER  OR
       SURFACE  WATER  -
       RESIDENTIAL  LAND  USE

   Both the ingestion of water and the inhalation
of volatiles are included in the standard default
equations in Section 3.1.1. If only one of these
exposure pathways is of concern at a particular
site, or if one or both of these pathways needs to
be combined  with additional pathways, a site-
specific equation can be derived.

   The parameters used in the  equations
presented in the  remainder of this section are
explained in the following text box.

B.I.I  INGESTION

   The cancer  risk due to  ingestion of  a
contaminant in water is calculated as follows:
          PARAMETERS FOR SURFACE WATER/GROUND WATER - RESIDENTIAL LAND USE
  Parameter      Definition

  C            chemical concentration in water (mg/L)
  SFj           inhalation cancer slope factor ((mg/kg-day)4)
  SF0           oral cancer slope factor ((mg/kg-day)"1)
  RfD0          oral chronic reference dose (mg/kg-day)
  RfD;          inhalation chronic reference dose (mg/kg-day)
  BW           adult body weight (kg)
  AT           averaging time (yr)

  EF           exposure frequency (days/yr)
  ED           exposure duration (yr)
  K            volatilization factor (L/m3)
  IRa           daily indoor inhalation rate (mVday)
  IR,,           daily water ingestion  rate (L/day)
         Default Value
         chemical-specific
         chemical-specific
         chemical-specific
         chemical-specific
         70kg
         70 yr for cancer risk
         30 yr for noncancer HI (equal to ED)
         350 days/yr
         30 yr
         0.0005 x 1000 L/rn(Andelman 1990)
          15 mVday
         2 L/day
                                            -51-

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Risk from ingestion =  SF,,  x
of water (adult)
                     C  x IR,Tx EFx  ED
                     BW x AT x 365 daystyr
The noncancer HQ due  to ingestion  of a
contaminant in water is calculated as follows:
HQ due to ingestion =
of water (adult)
                  C x IR.., x EFx ED
               RfD0 x BW x AT x 365 days/yr
B.I.2 INHALATION OF  VOLATILES

    The cancer risk due to inhalation of a volatile
contaminant in water is calculated as follows:
Risk from
inhalation
of volatiles
in water
(adult)
     =  SE x C x K x IR. x EFx ED
                 BW x AT x 365 days/yr
The noncancer HQ due to inhalation of a volatile
contaminant in water is calculated as follows:
HQ due to
inhalation
of volatiles
in water
(adult)
            C x  K x  IR.xEFxED
              x  BW x AT x 365 daysyyr
B.2
SOIL
 USE
                 - RESIDENTIAL LAND
    Only the first  exposure pathway below —
ingestion of soil —  is included in the standard
default equations in Section 3.1.2. If additional
exposure pathways, including inhalation  of volatiles
                                                        and/or inhalation of particulate, are of concern at
                                                        a particular site, then a site-specific equation can
                                                        be derived.

                                                            The  parameters used  in   the equations
                                                        presented in the  remainder  of this  section  are
                                                        explained in the text box below.

                                                        B.2.1  INGESTION OF  SOIL

                                                            The cancer risk from ingestion of
                                                        contaminated soil is calculated as follows:
                                                        Risk from  =  SF, x C x IP'6 kg/mg x EF x IF.,?il/adj
                                                        ingestion
                                                        of soil
AT x 365 days/yr
                                                        The noncancer HQ from ingestion  of
                                                        contaminated  soil is  calculated  as follows:

                                                        HQfrom =  C x IP"6 kg/mg x EF x IF.,.,,^
                                                        ingestion        RfD0 x AT x 365 days/yr
                                                        of soil

                                                        B.2.2 INHALATION OF  VOLATILES

                                                           The cancer risk  caused  by  inhalation of
                                                        volatiles released from contaminated  soil is:
                                                 Risk from  =  SF, x C x ED x EF x IR,ir x (1/VF)
                                                 inhalation          AT x BW x 365 days/yr
                                                 of volatiles

                                                 The equation for calculating the  noncancer HQ
                                                 from inhalation of volatiles released from soil is:
   Parameter

   C
   SFi
   SF0
   RfD
   BW
   AT

   EF
   ED
   IF,
     soil/adj
   VF
   PEF
                   PARAMETERS FOR SOIL - RESIDENTIAL LAND USE

            Definition                                       Default Value
            chemical concentration in soil (mg/kg)
            inhalation cancer slope factor ((mg/kg-day)"1)
            oral cancer slope factor ((mg/kg-day)""
            oral chronic reference dose (mg/kg-day)
            inhalation chronic  reference dose (mg/kg-day)
            adult body weight  (kg)
            averaging time (yr)

            exposure frequency (days/yr)
            exposure duration (yr)
            daily indoor inhalation rate (mVday)
            age-adjusted soil ingestion factor (mg-yr/kg-day)
            soil-to-air volatilization factor (mVkg]
            particulate emission factor (m/kg)
                                                                  chemical-specific
                                                                  chemical-specific
                                                                  chemical-specific
                                                                  chemical-specific
                                                                  70kg
                                                                  70 yr for cancer risk
                                                                  30 yr for noncancer HI (equal to ED)
                                                                  350 days/yr
                                                                  30 yr
                                                                   15 mYday
                                                                   114  mg-yr/kg-day
                                                                  chemical specific (see Section 3.3.1)
                                                                  4.63 x  10'mVkg (see Section 3.3.2)
                                                  -52-

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HQ from    =   C x ED x EF x IR,,r x (l/VF)
inhalation        RfDj x BW x AT x 365 days/yr
of volatiles

B.2.3  INHALATION OF  PARTICULATE

        Cancer risk due to  inhalation of
contaminated soil particulate is calculated as:

Risk    SF x C x ED x EF x IR,ir x (\/PEF)
from         AT x BW x 365 days/yr
inhala-
tion of
particulate

The  noncancer  HQ from  particulate inhalation is
calculated using this equation:

HQ from =
inhalation
of parti-
culate

B.3    SOIL - COMMERCIAL/
        INDUSTRIAL  LAND USE

        All  three of the  exposure  pathways
detailed below  are included  in the standard default
equation in Section 3.2.2.  If only one or some
combination of these  exposure  pathways are of
concern at a particular site, a site-specific equation
can be derived.

        The parameters  used in the equations
presented in the  remainder  of  this section are
explained in the text box below.
                                                    B.3.1  INGESTION OF  SOIL

                                                            The cancer risk  from ingestion of
                                                    contaminated soil is calculated as follows:
                                                    Risk from =  SFff x C x 10"* kg/ma x EF x ED x IR.ri,
                                                    ingestion            BW x AT x 365 days/yr
                                                    of soil
                                                    The noncancer HQ from ingestion of contaminated
                                                    soil is calculated as follows:
                                                    HQ from =
                                                    ingestion
                                                    of soil

                                                    B.3.2 INHALATION OF VOLATILES

                                                            The cancer risk caused by inhalation of
                                                    volatiles released from contaminated soil is:
                                                    Risk from
                                                    inhalation
                                                    of volatiles
                                                     SF, x C x ED x EF x IR,ir x (l/VF)
                                                          AT x BW x 365 days/yr
                                                    The equation for calculating the noncancer HQ
                                                    from inhalation of volatiles released from soil is:
                                                       C x ED x EF x IR.,ir x (l/VF)
                                                           i x BW x AT x 365 days/yr
                                                    HQfrom
                                                    inhalation
                                                    of volatiles
                                                    Note that the  VF value  has been developed
                                                    specifically for these equations; it may not be
                                                    applicable in other technical contexts.
                 PARAMETERS FOR SOIL - COMMERCIAL/INDUSTRIAL LAND USE
Parameter

C


SP'o
RfD0
BW
AT

EF
ED
VF
PEF
Definition

chemical concentration in soil (mg/kg)
inhalation cancer slope factor ((mg/kg-day)"1)
oral cancer slope  factor ((mg/kg-day4)
oral chronic reference dose (mg/kg-day)
inhalation chronic  reference dose (mg/kg-day)
adult body weight (kg)
averaging  time (yr)

exposure frequency (days/yr)
exposure duration (yr)
workday inhalation rate (mVday)
soil ingestion rate (mg/day)
soil-to-air  volatilization factor (mVkg)
particulate emission factor (mVkg)
                                                               Default Value
                                                                  chemical-specific
                                                                  chemical-specific
                                                                  chemical-specific
                                                                  chemical-specific
                                                                  70kg
                                                                  70 yr for cancer risk
                                                                  30 yr for noncancer HI (equal to ED)
                                                                  250 days/yr
                                                                  25 yr
                                                                  20 mVday
                                                                  50 mg/day
                                                                  chemical specific (see Section 3.3. 1)
                                                                  4.63 x 10'mVkg (see Section 3.3.2)
                                               -53-

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B.3.3 INHALATION OF PARTICULATE            The noncancer HQ from participate inhalation is
                                                    calculated using this equation:
        Cancer risk  due  to  inhalation  of
contaminated soil particulate is calculated as:           HQ from =    C x ED x EF x IR1ir x M/PEF)
                                                    inhalation      RfD; x BW x AT x 365 days/yr
Risk  from    ;  SFj x C x ED x EF x IR,ir x (1/PEFl
inhalation           AT x BW x 365 days/yr
of particulate
                                               -54-

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Environmental Protection              Information                                                                                                     POSTAGE &FEES PAID
Agency                             Cincinnati OH 45268-1072                                                                                                 EPA
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