RISK ASSESSMENT GUIDANCE FOR SUPERFUND: VOLUME 1 - … · Risk Assessment Guidance for Superfund: Volume I - Human Health Evaluation Manual (RAGS/HHEM) Part B is one ofa three-partseries.

Publication 9285.7-01 BDecember 1991

PB92-96333311111111111111111111111111 '" I1I11 III

Risk Assessment Guidancefor Superfund:

Volume 1-Human Health Evaluation Manual

(Part B, Development ofRisk-based Preliminary

Remediation Goals)

Interim

Office of Emergency and Remedial ResponseU.S. Environmental Protection Agency

Washington, DC 20460

REPRODUCED BYu.s. DEPARTMENT OF COMMERCE

NATIONAL TECHNICALINFORMATION SERVICESPRINGFIELD. VA 22161

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 reliedupon, to create any rights enforceable by any party in litigation with the United States. EPA officials maydecide to follow the guidance provided in this document, or to act at variance with the guidance, based on ananalysis of specific site circumstances. The Agency also reserves the right to change this guidance at any timewithout public notice.

This guidance is based on policies in the Final Rule of the National Oil and Hazardous SubstancesPollution Contingency Plan (NCP), which was published on March 8, 1990 (55 Federal Register 8666). TheNCP 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 31.3.2 National Contingency Plan 31.3.3 Guidance Documents , 3

1.4 INITIAL DEVELOPMENT OF PRELIMINARY REMEDIATION GOALS 4

1.5 MODIFICATION OF PRELIMINARY REMEDIATION GOALS 5

1.6 DOCUMENTATION AND COMMUNICATION OF PRELIMINARYREMEDIATION 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 102.4.2 Selection of the Most Likely ARAR-based

PRG for Each Chemical 10

2.5 EXPOSURE PATHWAYS, PARAMETERS, AND EQUATIONS 11

2.5.1 Ground Water/Surface Water 132.5.2 Soil 13

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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 152.8.2 Identification of Uncertainties 162.8.3 Other Considerations in Modifying PRGs 172.8.4 Post-remedy Assessment 18

3.0 CALCULATION OF RISK-BASED PRELIMINARYREMEDIATION GOALS 19

3.1 RESIDENTIAL LAND USE 20

3.1.1 Ground Water or Surface Water 203.1.2 Soil 23

3.2 COMMERCIAL/INDUSTRIAL LAND USE 24

3.2.1 Water 243.2.2 Soil 25

3.3 VOLATILIZATION AND PARTICULATE EMISSION FACfORS 26

3.3.1 Soil-to-air Volatilization Factor 263.3.2 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 344.1.2 Soil 35

4.2 COMMERCIAL/INDUSTRIAL LAND USE 36

4.2.1 Water 364.2.2 Soil 364.2.3 Soil-to-air Volatilization Factor 38

4.3 RADIATION CASE STUDY 38

4.3.1 Site History 404.3.2 At the Scoping Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404.3.3 After the Baseline Risk Assessment 43

REFERENCES 47

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APPENDIX A

APPENDIX B

CONTENTS (Continued)

Page

ILLUSTRATIONS OF CHEMICALS THAT "LIMIT" REMEDIATON 49

RISK EQUATIONS FOR INDIVIDUAL EXPOSURE PATHWAYS 51

B.1 GROUND WATER OR SURFACE WATER - RESIDENTIAL LAND USE 51

B.1.1 Ingestion 51B.1.2 Inhalation of Volatiles 52

B.2 SOIL - RESIDENTIAL LAND USE 52

B.2.1 Ingestion of Soil 52B.2.2 Inhalation of Volatiles 52B.2.3 Inhalation of Particulates 53

B.3 SOIL - COMMERCIAL/INDUSTRIAL LAND USE 53

B.3.1 Ingestion of Soil 53B.3.2 Inhalation of Volatiles 53B.3.3 Inhalation of Particulates 54

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EXHIBITS

Exhibit Page

1-1 RELATIONSHIP OF HUMAN HEALTH EVALUATION TOTHE CERCLA PROCESS 2

2-1 TYPICAL EXPOSURE PATHWAYS BY MEDIUM FORRESIDENTIAL AND COMMERCIAL/INDUSTRIALLAND USES 12

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Term

Applicable or Relevant andAppropriate Requirements(ARARs)

Cancer Risk

Conceptual Site Model

Exposure Parameters

Exposure Pathway

Exposure Point

Exposure Route

Final Remediation Levels

DEFINITIONS

Definition

"Applicable" requirements are those clean-up standards, standardsof control, and other substantive environmental protectionrequirements, criteria, or limitations promulgated under federal orstate law that specifically address a hazardous substance, pollutant,contaminant, remedial action, location, or other circumstance at aComprehensive Environmental Response, Compensation, andLiability Act (CERCLA) site. "Relevant and appropriate"requirements are those clean-up standards which, while not"applicable" at a CERCLA site, address problems or situationssufficiently similar to those encountered at the CERCLA ~ite thattheir use is well-suited to the particular site. ARARs can be action­specific, location-specific, or chemical-specific.

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

A "model" of a site developed at scoping using readily availableinformation. Used to identify all potential or suspected sources ofcontamination, types and concentrations of contaminants detectedat the site, potentially contaminated media, and potential exposurepathways, including receptors. This model is also known as"conceptual evaluation model".

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

The course a chemical or physical agent takes from a source to anexposed organism. An exposure pathway describes a uniquemechanism by which an individual or population is exposed tochemicals or physical agents at or originating from a site. Eachexposure pathway includes a source or release from a source, anexposure point, and an exposure route. If the exposure point differsfrom 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 organism and a chemicalor physical agent.

The way a chemical or physical agent comes in contact with anorganism (Le., by ingestion, inhalation, dermal contact).

Chemical-specific clean-up levels that are documented in theRecord of Decision (ROD). They may differ from preliminaryremediation goals (PRGs) because of modifications resulting fromconsideration of various uncertainties, technical and exposurefactors, as well as all nine selection-of-remedy criteria outlined inthe National Oil and Hazardous Substances Pollution ContingencyPlan (NCP).

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Term

Hazard Index (HI)

Hazard Quotient (HQ)

"Limiting" Chemical(s)

Preliminary Remediation Goals(PRGs)

Quantitation Limit (QL)

Reference Dose (RID)

Risk-based PRGs

Slope Factor (SF)

Target Risk

DEFINITIONS (Continued)

Definition

The sum of two or more hazard quotients for multiple substancesand/or multiple exposure pathways.

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

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

Initial clean-up goals that (1) are protective of human health andthe environment and (2) comply with ARARs. They are developedearly in the process based on readily available information and aremodified to reflect results of the baseline risk assessment. Theyalso are used during analysis of remedial alternatives in theremedial investigation/feasibility study (RIfFS).

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

The Agency's preferred toxicity value for evaluating potentialnoncarcinogenic effects in humans resulting from contaminantexposures at CERCLA sites. (See RAGS/HHEM Part A for adiscussion of different kinds of reference doses and referenceconcentrations.)

Concentration levels set at scoping for individual chemicals thatcorrespond to a specific cancer risk level of 10-6 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 responseper unit intake of a chemical over a lifetime. The slope factor isused to estimate an upper-bound probability of an individual'sdeveloping cancer as a result of a lifetime of exposure to aparticular 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 carcinogeniceffects, the target risk is a cancer risk of 10-6. For noncarcinogeniceffects, the target risk is a hazard quotient of 1.

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Acronym/Abbreviation

ARARs

CAA

CERCLA

CFR

CWA

EAG

ECAO

EF

EPA

FWQC

HEAST

HHEM

HI

HQ

HRS

IRIS

LLW

MCL

MCLG

NCP

NPL

OSWER

OERR

ACRONYMS/ABBREVIATIONS

Definition

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 OfficeSuperfund 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/Abbreviation

PNSI

PEF

PRG

RAGS

RCRA

RfC

RID

RIfFS

RME

ROD

RPM

SARA

SDWA

SF

TR

VF

WQS

ACRONYMS/ABBREVIATIONS (Continued)

Definition

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 InvestigationlFeasibility 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 Toxies Integration Branch (TIB) of EPA's Office of Emergency andRemedial Response, Hazardous Site Evaluation Division. A large number of EPA Regional and Headquartersmanagers and technical staff provided valuable input regarding the organization, content, and policyimplications of the manual throughout its development. We would especially like to acknowledge the effortsof the staff in the Regions, as well as the following offices:

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

ICF Incorporated (under EPA Contract Nos. 68-01-7389, 68-W8-0098, and 68-03-3452), S. Cohen andAssociates (under EPA Contract No. 68-09-0170), and Environmental Quality Management, Incorporated(under EPA Contract No. 68-03-3482), provided technical assistance to EPA in support of the developmentof 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 Caddresses 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-basedpreliminary remedial goals (PRGs) for a Comprehensive Environmental Response, Compensation, andLiability Act (CERCLA) site. Initially developed at the scoping phase using readily available information, risk­based PRGs generally are modified based on site-specific data gathered during the remedialinvestigation/feasibility study (RIfFS). This guidance does not discuss the risk management decisions that arenecessary at a CERCLA site (e.g., selection of final remediation goalS). The potential users of Part Barethos~involved in the remedy selection and implementation process, including risk assessors, risk assessmentreviewers, remedial project managers, and other decision-makers.

This manual is being distributed as an interim document to allow for a period of field testing andreview. RAGS/HHEM will be revised in the future, and Parts A, B, and C will be incorporated into a singlefinal guidance document. Additional information for specific subject areas is being developed for inclusionin 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 besent to:

u.S. Environmental Protection AgencyToxies Integration Branch (OS-230)Office of Emergency and Remedial Response401 M Street, SWWashington, DC 20460

Telephone:FAX:

202-260-9486202-260-6852

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CHAPTER 1

INTRODUCTION

The purpose of this guidance is to assist riskassessors, remedial project managers (RPMs), andothers involved with risk assessment and decision­making at Comprehensive EnvironmentalResponse, Compensation, and Liability Act(CERCLA) sites in developing preliminaryremediation goals (PRGs). This guidance is thesecond part (Part B) in the series Risk AssessmentGuidance for Superfund: Volume I - HumanHealth Evaluation Manual (RAGS/HHEM).

Part A of this series (EPA 1989d) assists indefining and completing a site-specific baseline riskassessment; much of the information in Part A isnecessary background for Part B. Part B providesguidance on using U.S. Environmental ProtectionAgency (EPA) toxicity values and exposureinformation to derive risk-based PRGs. Initiallydeveloped at the scoping phase using readilyavailable information, risk-based PRGs generallyare modified based on site-specific data gatheredduring the remedial investigation/feasibility study(RIIFS). Part C of this series (EPA 1991d) assistsRPMs, site engineers, risk assessors, and others inusing risk information both to evaluate remedialalternatives during the FS and to evaluate theselected remedial alternative during and after itsimplementation. Exhibit 1-1 illustrates how thethree parts of RAGS/HHEM are all used duringthe RIfFS and other stages of the site remediationprocess.

The remainder of this introduction addressesthe definition of PRGs, the scope of Part B, thestatutes, regulations, and guidance relevant toPRGs, steps in identifying and mOdifying PRGs,the communication and documentation of PRGs,and the organization of the remainder of thisdocument.

1.1 DEFINITION OFPRELIMINARYREMEDIATION GOALS

In general, PRGs provide remedial design staffwith long-term targets to· use during analysis and

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selection of remedial alternatives. Ideally, suchgoals, if achieved, should both comply withapplicable or relevant and appropriaterequirements (ARARs) and result in residual risksthat fully satisfy the National Oil and HazardousSubstances Pollution Contingency Plan (NCP)requirements for the protection of human healthand the environment. By developing PRGs earlyin the decision-making process (before the RIIFSand the baseline risk assessment are completed),design staff may be able to streamline theconsideration of remedial alternatives.

Chemical-specific PRGs are concentrationgoals for individual chemicals for specific mediumand land use combinations at CERCLA sites.There are two general sources of chemical-specificPRGs: (1) concentrations based on ARARs and(2) concentrations based on risk assessment.ARARs include concentration limits set by otherenvironmental regulations (e.g., non-zero maximumcontaminant level goals [M€LGs] set under theSafe Drinking Water Act [SDWA)). The secondsource for PRGs, and the focus of this document,is risk assessment or risk-based calculations thatset concentration limits using carcinogenic and/ornoncarcinogenic toxicity values under specificexposure conditions.

1.2 SCOPE OF PART B

The recommended approaCh for developingremediation goals is to identify PRGs at scoping,modify them as needed at the end of the RI orduring the FS based on site-specific informationfrom the baseline risk assessment, and ultimatelyselect remediation levels in the Record of Decision(ROD). In order to set chemical-specific PRGs ina site-specific context, however, assessors mustanswer fundamental questions about the site.Information on the chemicals that are presentonsite, the specific contaminated media, land-useassumptions, and the exposure assumptions behindpathways of individual exposure is necessary inorder to develop chemical-specific PRGs. Part Bprovides guidance for considering this informationin developing chemical-specific PRGs.

EXHIBIT 1-1

RELATIONSHIP OF THE HUMAN HEALTH EVALUATIONTO THE CERCLA PROCESS

CERCLA REMEDIAL PROCESS

RemedialInvestigation

Scoping

FeasibilityStudy

Remedy Selection R d"al De "erne I Slgn/ Delelion/r- and Record of - R d"al " -Dec

" " erne I Action Five-year ReviewISlon

HUMAN HEALTH EVALUATION MANUAL

PART ABaseline Risk Assessment

PARTBDevelopment of Risk-based

Preliminary Remediation Goals

PARTeRisk Evaluation of Remedial Alternatives

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Because Part B focuses on developingchemical-specific PROs based on protection ofhuman health, there are important types ofinformation that are not considered and that maysignificantly influence the concentration goalsneeded to satisfy the CERCLA criteria forselection of a remedy. For example, noconsideration is given to ecological effects in 'thisguidance. Other types of remedial action "goals"not addressed in detail include action-specificARARs (e.g., technology- or performance-basedstandards) and location-specific ARARs.

Throughout Part B, the term "chemical­specific" should be understood to refer to bothnonradioactive and radioactive chemical hazardoussubstances, pollutants, or contaminants. Therefore,the process described in this guidance of selectingand mOdifying PRGs at a site should be applied toeach radionuclide of potential concern.Chapter 10 of RAGS/HHEM Part A providesbackground information concerning radionuclides,and Chapter 4 of RAGS/HHEM Part B includesradionuclide risk-based equations and a case studyof a hypothetical radiation site.

This guidance only addresses in detail theinitial selection of risk-based PRGs. Detailedguidance regarding other factors that can be usedto further modify PRGs during the remedyselection process is presented in other documents(see Section 1.3).

1.3 RELEVANT STATUTES,REGULATIONS, ANDGUIDANCE

This section provides relevant background onthe CERCLA statute and the regulations createdto implement the statute (Le., the NCP). Inaddition, other CERCLA guidance documents arelisted and their relationship to the site remediationprocess is discussed.

1.3.1 CERCLA/SARA

CERCLA, as amended by the SuperfundAmendments and Reauthorization Act of 1986(SARA), is the authority for EPA to take responseactions. (Throughout this guidance, reference toCERCLA should be understood to mean"CERCLA as amended by SARA.")

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Several sections of CERCLA, especiallysection 121 (Clean-up Standards), set out therequirements and goals of CERCLA. Twofundamental requirements are that selectedremedies be protective of human health and theenvironment, and comply with ARARs. CERCLAindicates a strong preference for the selection ofremedial alternatives that permanently andsignificantly reduce the volume, toxicity, ormObility of wastes. To the maximum extentpracticable, the selected remedial alternativesshould effect permanent solutions by usingtreatment technologies. Both the law and theregulation (see below) call for cost-effectiveremedial alternatives.

1.3.2 NATIONAL CONTINGENCY PLAN

Regulations implementing CERCLAarefoundin Volume 40 of the Code of Federal Regulations(CPR), Part 300, and are referred to collectively asthe NCP. Section 300.430 of the NCP, and severalportions of the preambles in the Federal Register(55 Federal Register 8666, March 8, 1990 and 53Federal Register 51394, December 21, 1988),address how the Superfund and other CERCLAprograms are to implement the Act's requirementsand goals concerning clean-up levels.

Nine criteria have been developed in the NCPto use in selecting a remedy. These criteria arelisted in the next box. The first criterion - overallprotection of human health and the environment- is the focus of this document. This criterioncoupled with compliance with ARARs are referredto as "threshold criteria" and must be met by theselected remedial alternative. PRGs are developedto quantify the standards that remedial alternativesmust meet in order to achieve these thresholdcriteria. See the second box on the next page forhighlights from the NCP on remediation goals.

1.3.3 GUIDANCE DOCUMENTS

There are several existing documents thatprovide gudiance on related steps of the siteremediation process. These documents aredescribed in the box on page five. Whendocuments are referenced throughout thisguidance, the abbreviated titles, indicated inparentheses after the full titles and bibliographicinformation, are used.

NINE EVALUATION CRITERIA FORANALYSIS 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 OFPRELIMINARYREMEDIATION GOALS

The NCP preamble indicates that, typically,PRGs are developed at scoping or concurrent withinitial RIfFS activities (Le., prior to completion ofthe baseline risk assessment). This earlydetermination of PRGs facilitates development ofa range of appropriate remedial alternatives andcan focus selection on the most effective remedy.

Development of PRGs early in the RIfFSrequires 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 preliminaryassessment/site inspection (PNSI) reports or in theconceptual site model that is developed prior to orduring scoping. (When a site is listed on theNational Priorities List [NPL], much of thisinformation is compiled during the PNSI as partof the Hazard Ranking System [HRS]documentation record.) Once these factors areknown, all potential ARARs must be identified.When ARARs do not exist, risk-based PRGs arecalculated using EPA health criteria (i.e., referencedoses or cancer slope factors) and default or site­specific exposure assumptions.

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NCP RULE HIGHLIGHTSRISK AND REMEDIATION GOALS

(40 CFR 300.430(e)(2))

"In developing and, as appropriate, screening... alternatives, the lead agency shall: (i) Establishremedial action objectives speCifying contaminantsand media of concern, potential exposurepathways, and remediation goals. Initially,preliminary remediation goals are developed basedon readily available information, such as chemical­specific ARARs or other reliable information.Preliminary remediation goals should be modified,as necessary, as more information becomesavailable during the RI/FS. Final remediationgoals will be determined when the remedy isselected. Remediation goals shall establishacceptable exposure levels that are protective ofhuman health and the environment and shall bedeveloped by considering the following:

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

(1) For systemic toxicants, acceptableexposure levels shall representconcentration levels to which the humanpopulation, including sensitive subgroups,may be exposed without adverse effectduring a lifetime or part of a lifetime,incorporating an adequate margin ofsafety;

(2) For \mown or suspected carcinogens,acceptable exposure levels are generallyconcentration levels that represent anexcess upper-bound lifetime cancer riskto an individual of between 10-4 and 10-6

using information on the relationshipbetween dose and response. The 10-6

risk level shall be used as the point ofdeparture for determining remediationgoals for alternatives when ARARs arenot available or are not sufficientlyprotective because of multiplecontaminants at a site or multiplepathways of exposure ..."

It is important to remember that risk-basedPRGs (either at scoping or later on) are initialguidelines. They do not establish that cleanup tomeet these goals is warranted. A risk-basedconcentration, as calculated in this guidance, willbe considered a final remediation level only afterappropriate analysis in the RIfFS and ROD.

GUIDANCE DOCUMENTS

Risk Assessment Guidance for Supelfund: Volume I - Human Health Evaluation Manual Part A (EPA 1989a)(RAGSIHHEM Part A) contains background information and is particularly relevant for developing exposure andtoxicity assessments that are required when refining chemical-specific risk-based concentrations, and accountingfor site-specific factors such as mUltiple exposure pathways.

Guidance for Conducting Remedial Investigations lmd Feasibility Studies Under CERCLA (EPA 1988c) (RIfFSGuidance) presents detailed information about implementing the RIfFS and general information on the use ofrisk-based factors and ARARs in the context of the RIfFS.

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

CERCLA Compliance with Other Laws Manuals (Part I, EPA 1988a; and Part II, EPA 1989a) (CERCLACompliance Manuals) provide guidance for complying with ARARs. Part I addresses the Resource Conservationand 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 Waste) (EPA 198ge)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 remediationlevels, including appropriate sampling and statistical procedures to test whether the chemical concentrations aresignificantly below the remediation levels.

Interim Final Guidance on Preparing Superfund Decision Documents (EPA 1989b) (ROD Guidance) providesguidance that: (1) presents standard formats for documenting CERCLA remedial action decisions; (2) clarifiesthe roles and responsibilities of EPA, states, and other federal agencies in developing and issuing decisiondocuments; 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 thathave been issued by EPA, shown in order of date of issuance.

Role of the Baseline RiskAssessment in Superfund Remedy Selection Decisions (EPA 1991c) provides clarificationon the role of the baseline risk assessment in developing and selecting CERCLA remedial alternatives.

Guidance for Data Useability in Risk Assessment (EPA 1990b) (Data Useability Guidance) provides guidance onhow to Obtain a minimum level of quality for all environmental analytical data required for CERCLA riskassessments. It can assist with determining sample quantitation limits (SOLs) for chemical-specific analyses.

Guidance on Remedial Actions for Superfund Sites with PCB Contamination (EPA 199Oc) describes therecommended approaCh for evaluating and remediating CERCLA sites having PCB contamination.

Conducting Remedial Investigations/Feasibility Studies for CERCLA Municipal Landfill Sites (EPA 1991a)(Municipal Landfill Guidance) offers guidance on how to streamline both the RIfFS and the selection of a remedyfor municipal landfills.

1.S MODIFICATION OFPRELIMINARYREMEDIATION GOALS

The initial list of PRGs may need to be revisedas new data become available during the RIfFS.Therefore, upon completion of the baseline risk

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assessment, it is important to review the media andchemicals of potential concern, future land use,and exposure assumptions originally identified atscoping. Chemicals may be added or dropped fromthe list, and risk-based PRGs may need to berecalculated using site-specific exposure factors.PRGs that are modified based on the results of thebaseline risk assessment must stilI meet the

"threshold criteria" of: (1) protection of humanhealth and the environment and (2) compliancewith ARARs. However, the NCP also allows formodification of PRGs during final remedyselection based on the "balancing" and "modifying"criteria and factors relating to uncertainty,exposure, and technical feasibility.

Final remediation levels are not determineduntil the site remedy is ready to be selected; finalremediation levels are then set out in the ROD.PRGs are refined into final remediation goalsthroughout the process leading up to remedyselection. The ROD itself, however, shouldinclude a statement of final clean-up levels basedon these goals, as noted in NCP section300.430(e)(2)(i)(A). In the ROD, it is preferableto use the term "remediation level" rather than"remediation goal" in order to make clear that theselected remedy establishes binding requirements.

1.6 DOCUMENTATION ANDCOMMUNICATION OFPRELIMINARYREMEDIATION GOALS

Clear and concise communication o(risk-basedPRGs among the risk assessor, the RPM, theARARs coordinator, site engineers, analyticalchemists, hydrogeologists, and others is importantin the development of PRGs. The involvement ofthe RPM in the direction and development ofrisk-based PRGs is important to ensure thatcommunication is facilitated and that the PRGsare used effectively in streamlining the RIIFSprocess.

Because PRGs are most useful during theRIIFS (e.g., for streamlining the consideration ofremedial alternatives), it is important tocommunicate them to site engineers as soon aspossible. A memorandum from either the site riskassessor or the RPM to the site engineers andothers concerned with PRGs would be appropriatefor transmitting the initial PRGs. A brief coverpage could highlight key assumptions, as well asChanges, if any, to the standard equations (Le.,those presented in this guidance). Following thisbrief discussion, the PRGs could be presentedusing a table similar to that in Section 3.4 of thisguidance.

The RI/FS Guidance recommends that"chemical- and/or risk-based remedial objectives

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associated with the alternative should bedocumented in the final RI/FS report to the extentpossible." Therefore, the RI/FS report is a logicalplace to present PRGs that have been modifiedafter the baseline risk assessment. A summarytable such as the one developed in Section 3.4 ofPart B could be incorporated into the RI/FSfollowing the presentation of the baseline riskassessment. Along with the table, a discussion ofissues of particular interest, such as assumptionsused and the relationship between ARARs andrisk-based PRGs at the site, could be included.Also, it is always appropriate to discuss howfindings of the baseline risk assessment wereincorporated into the calculation of PRGs.

1.7 ORGANIZATION OFDOCUMENT

The remainder of this guidance is organizedinto three additional chapters and two appendices.Chapter 2 discusses the initial identification ofPRGs and provides guidance for modifyingappropriate values during the RIIFS. Chapter 3outlines equations that can be used to calculaterisk-based PRGs for residential and commercial!industrial land uses. These equations arepresented in both "reduced" format (i.e.,incorporating certain default assumptions discussedin Chapter 2) and expanded format (Le., with allvariables included so that the user of this guidancecan incorporate site-specific values). Particularconsiderations regarding radionuclides are providedin Chapter 4.

Appendix A supports several points made inChapter 2 by providing illustrations of remedialalternatives where one or more chemicals "limit"remediation and, thUS, represent a major portionof the residual risk. Appendix B lists equations formedia-specific exposure pathways, enabling the riskassessor to derive site-specific equations that differfrom those presented in Chapter 3.

Throughout Chapters 2, 3, and 4, case studiesare presented that illustrate the process ofdetermining PRGs. These case studies arecontained in boxes with a shadow box appearance.Other types of boxed information (e.g., NCPquotes) is contained in boxes such as those inChapter 1, which have thicker lines on the top andbottom than on the sides.

CHAPTER 2

IDENTIFICATION OF PRELIMINARYREMEDIATION GOALS

This chapter provides guidance on the initialidentification of PRGs during the scoping phase ofthe RIfFS. As discussed in Chapter 1,medium-specific PRGs (ARAR-based and/orrisk-based) should be identified during scoping forall chemicals of potential concern using readilyavailable information. Sections are provided inthis chapter on how to use this information toidentify media and chemicals of potential concern,the most appropriate future land use, potentialexposure pathways, toxicity information, potentialARARs, and risk-based PRGs. Finally, a sectionis provided on the modification of PRGs.

When using PRGs developed during scoping,the design engineers should understand that thesemay be modified significantly depending oninformation gathered about the site. Thesubsequent process of identifying ~ sitecontaminants, media, and other factors (Le., duringthe baseline risk assessment) may require that thefocus of the RIfFS be shifted (e.g., chemicalswithout ARARs may become more or lessimportant). Thus, the design of remedialalternatives should remain flexible until themodified (Le., more final) PRGs are available.

Prior to identifying PRGs during scoping, aconceptual site model should be developed (seethe next bOX). Originally developed to aid inplanning site activities (e.g., the RIfFS), theconceptual site model also contains informationthat is valuable for identifying PRGs. Forexample, it can be relied upon to identify whichmedia and chemicals need PRGs. Moreinformation on developing and using a conceptualsite model during the RIfFS process can be foundin Chapter 2 of the RI/FS Guidance and Chapter 4of RAGS/HHEM Part A.

To illustrate the process of calculatingrisk-based PRGs at the scoping stage ofremediation, hypothetical CERCLA sites will beexamined in boxes in appropriate sectionsthroughout Chapters 2, 3, and 4. See the box on

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CONCEPTUAL SITE MODEL

During project planning, the RPM gathers andanalyzes available information and develops theconceptual site model (also called the conceptualevaluation model). This model is used to assessthe nature and the extent of contamination. It alsoidentifies potential contaminant sources, potentialexposure pathways, and potential human and/orenvironmental receptors. Further, this model helpsto identify data gaps and assists staff in developingstrategies for data collection. Site history andPNSI data generally are extremely useful sourcesof information for developing this model. Theconceptual site model should include known andsuspected sources of contamination, types ofcontaminants and affected media, known andpotential routes of migration, and known orpotential human and environmental receptors.

the next page for an introduction to the first site.(The radiation case study is addressed inChapter 4.) The information (e.g., toxicity values)contained in these case studies is for illustrationonly, and should not be used for any otherpurpose. These case studies have been simplified(e.g., only ground water will be examined) so thatthe steps involved in developing risk-based PRGscan be readily discerned.

2.1 MEDIA OF CONCERN

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

• currently contaminated media to whichindividuals may be exposed or through whichchemicals may be transported to potentialreceptors; or

CASE STUDY: INTRODUCTION

The XYZ Co. site contains an abandonedindustrial facility that is adjacent to a high­density residential neighborhood. Remnants ofdrums, lagoons, and waste piles were found atthe site. Ground water in the area of the site isused by residents as a domestic water supply.There is also a small lake downgradient from thesite that is used by some of the local residentsfor fishing and swimming.

• currently uncontaminated media that maybecome contaminated in the future due tocontaminant transport.

Several important media often requiring directremediation are ground water, surface water, soil,and sediment. Currently, only the first three ofthese media are discussed in this chapter andaddressed by the equations provided in Chapters 3and 4. If other media that may require thedevelopment of risk-based concentrations (e.g.,sediments) are identified at scoping, appropriateequations for those media should be developed.Regional risk assessors should be consulted asearly as possible to assist with this process.

CASE STUDY: IDENTIFY MEDIAOF CONCERN

The PNSI for the example site indicates that'ground water beneath the site is contaminated.The source of this contamination appears tohave been approximately 100 leaking drums ofvarious chemicals that were buried in the soil buthave since been removed. Lagoons and wastepiles also may have contributed to thecontamination. Thus, ground water and soil aremedia of concern.

Although evidence of lake watercontamination was not found during the PNSI,there is a reasonable possibility that it maybecome contaminated in the future due tocontaminant transport either via ground-waterdischarge or surface water run-off. Thus,surface water (the lake) and sediments also maybe media of concern.

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2.2 CHEMICALS OF CONCERN

This step involves developing an initial list ofchemicals for which PRGs need to be developed.Chapters 4 and 5 of RAGS/HHEM Part A provideimportant additional information on identifyingchemicals of potential concern for a site andshould be consulted prior to development of theconceptual site model and PRGs at scoping.

Initially, the list of chemicals of potentialconcern should include any chemical reasonablyexpected to be of concern at the site based on whatis known during scoping. For example, importantchemicals previously detected at the site, based onthe PNSI, the conceptual site model, or otherprior investigations, generally should be included.In addition, the list may include chemicals that thesite history indicates are likely to be present insignificant quantities, even though they may not yetbe detected. Sources of this latter type ofinformation include records of chemicals used ordisposed at the facility, and interviews with currentor former employees. The list also may includechemicals that are probable degradation productsof site contaminants where these are determined tobe potential contributors of significant risk. Anenvironmental chemist should be consulted forassistance in determining the probable degradationproducts of potential site-related chemicals andtheir persistence under site conditions. Generally,the chemicals for which PRGs should be developedwill correspond to the list of suspected sitecontaminants included in the sampling and analysisplan.

2.3 FUTURE LAND USE

This step involves identifying the mostappropriate future land use for the site so that theappropriate exposure pathways, parameters, andequations (discussed in the next section) can beused to calculate risk-based PRGs. RAGS/HHEMPart A (Chapter 6) and an EPA Office of SolidWaste and Emergency Response (OSWER)directive on the role of the baseline riskassessment in remedy selection decisions (EPA1991b) provide additional guidance on identifyingfuture land use. The standard default equationsprovided in Chapter 3 of Part B only addressresidential and commercial/industrial land uses. Ifland uses other than these are to be assumed (e.g.,recreational), then exposure pathways, parameters,

CASE STUDY: IDENTIFY CHEMICALSOF CONCERN

The PNSI for the XYZ Co. site identified thefollowing seven chemicals in ground-watersamples: benzene, ethylbenzene, hexane,isophorone, triallate, 1,1,2-trichloroethane, andvinyl chloride. Therefore, these chemicals areobvious choices for chemicals of potentialconcern.

Although not detected in any of the PNSIsamples, site history indicates that one othersolvent - carbon tetrachloride - also was used insignificant quantities by the facility that operatedat the site. This chemical, therefore, is added tothe list of chemicals of potential concern.

and equations will need to be developed for theothers as well.

In general, residential areas should be assumedto remain residential. Sites that are surrounded byoperating industrial facilities can be assumed toremain industrial areas unless there is anindication that this is not appropriate. Lackingsite-specific information (e.g., at scoping), it maybe appropriate to assume residential land use.This assumption will generally lead to conservative(i.e., lower concentration) risk-based PRGs. If notenough site-specific information is readily availableat scoping to select one future land use overanother, it may be appropriate to develop aseparate set of risk-based PRGs for each possibleland use.

When waste will be managed onsite, land-useassumptions and risk-based PRG developmentbecome more complicated because the assumptionsfor the site itself may be different from the landuse in the surrounding area. For example, if wasteis managed onsite in a residential area, therisk-based PRGs for the ground water beneath thesite (or at the edge of the waste management unit)may be based on residential exposures, but therisk-based PRGs for the site soils may be based onan industrial land use with some management orinstitutional controls.

If a land-use assumption is used that is lessconservative (i.e., leads to higher risk-basedconcentrations) than another, it generally will benecessary to monitor the future uses of that site.

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For example, if residential land use is not deemedto be appropriate for a particular site because localzoning laws prohibit residential development, anychanges in local zoning would need to bemonitored. Such considerations should be clearlydocumented in the site's ROD.

CASE STUDY: IDENTIFY FUTURELAND USE

Based on established land-use trends, localrenovation projects, and population growthprojections in the area of the XYZ Co. site, themost reasonable future use of the land isdetermined to be residential use. Thus, site­specific information is sufficient to show that thegenerally more conservative assumption ofresidential land use should serve as the basis fordevelopment of risk-based PRGs.

2.4 APPLICABLE OR RELEVANTAND APPROPRIATEREQUIREMENTS

Chemical-specific ARARs are evaluated asPRGs because they are often readily available andprovide a preliminary indication about the goalsthat a remedial action may have to attain. Thisstep involves identifying all readily availablechemical-specific potential ARARs for thechemicals of potential concern (for each mediumand probable land use). Because at scoping itoften is uncertain which potential ARAR is themost likely one to become the ARAR-based PRG,all potential ARARs should be included in atabular summary (i.e., no potential ARAR shouldbe discarded). If there is doubt about whether avalue is a potential ARAR, and therefore whetherit could be used as a PRG, it should be included atthis stage.

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

• the NCP (see specifically 55 Federal Register8741-8766 for a description of ARARs, and

8712-8715 for using ARARs as PRGs; see also53 Federal Register 51394); and

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

2.4.1 CHEMICAL-, LOCATION-, ANDACTION-SPECIFIC ARARs

The Agency has identified three general typesof federal and state ARARs:

• chemical-specific, are usually health- or riskmanagement-based numbers or methodologiesthat, when applied to site-specific conditions,result in the establishment of numerical values(e.g., chemical-specific concentrations in agiven medium);

• location-specific, are restrictions placed uponthe concentration of hazardous substances orthe conduct of activities solely because theyare in special locations (e.g., wetlands); and

• action-specific, are usually technology- oractivity-based requirements or limitations onactions taken with respect to hazardous wastes.

This guidance primarily addresses only chemical­specific ARARs since it focuses on theidentification of chemical-specific concentrationsthat represent target goals (e.g., PRGs) for a givenmedium.

2.4.2 SELECTION OF THE MOST LIKELYARAR-BASED PRG FOR EACHCHEMICAL

This section briefly describes which, if any, ofseveral potential ARAR values for a givenchemical is generally selected as the most likelyARAR-based PRG (and therefore the most likelyPRG at this point). Although the process foridentifying the most likely ARAR-based PRG isspecific to the medium, in general the processdepends on two considerations: (1) theapplicability of the ARAR to the site; and (2) thecomparative stringency of the standards beingevaluated. The previously cited documents shouldbe carefully considered for specificrecommendations on identifying ARARs.

Ground Water. SDWA maximum contaminantlevels (MCLs), non-zero MCLGs, state drinkingwater standards, and federal water quality criteria

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(FWQC) are common ARARs (and, therefore,potential PRGs) for ground water. Other types oflaws, such as state anti-degradation laws, may bePRGs if they are accompanied by allowableconcentrations of a chemical. (Although stateanti-degradation laws that are expressed asqualitative standards may also be potentialARARs, they generally would not be consideredPRGs.)

As detailed in the NCP (see next box), the firststep in identifying ground-water PRGs is todetermine whether the ground water is a currentor potential source of drinking water. If theaquifer is a potential source of drinking water,then potential ARARs generally will include thefederal non-zero MCLG, MCL, or state drinkingwater standard, and the most stringent (i.e., thelowest concentration) is identified as the mostlikely ARAR-based PRG.

NCP ON GROUND-WATER GOALS(NCP Preamble;

55 Federal Register 8717, March 8, 1990)

"Ground water that is not currently a drinkingwater source but is potentially a drinking watersource in the future would be protected to levelsappropriate to its use as a drinking water source.Ground water that is not an actual or potentialsource of drinking water may not requireremediation to a 10'" to 1O~ level (except whennecessary to address environmental concerns orallow for other beneficial uses; ...)."

If the aquifer is not a potential source ofdrinking water, then MCLs, MCLGs, state drinkingwater requirements, or other health-based levelsgenerally are not appropriate as PRGs. Instead,environmental considerations (i.e., effects onbiological receptors) and prevention of plumeexpansion generally determine clean-up levels. Ifan aquifer that is not a potential source ofdrinking water is connected to an aquifer that is adrinking water source, it may be appropriate to usePROs to set clean-up goals for the point ofinterconnection.

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

Surface Water. FWQC and state water qualitystandards (WQS) are common ARARs for surfacewater. An important determination for identifyingARARs and other criteria as potential PRGs forsurface water is the current designated and futureexpected use of the water body; Because surfacewater potentially could serve many uses (e.g.,drinking and fishing), several ARARs may beidentified as potential PRGs for a chemical, witheach ARAR corresponding to an identified use. Astate WQS is generally the most likely ARAR forsurface water unless a federal standard is morestringent.

Ifsurface water is a current or potential sourceof drinking water, MCLs, state drinking waterstandards, non-zero MCLGs, and FWQC arepotential ARARs. The analysis to determinewhich of these drinking water standards is the mostlikely ARAR-based PRG is the same as thatconducted for ground water. An FWQC based oningestion of water and fish might be an ARAR forsurface water used for drinking.

If the designated or future expected use ofsurface water is fishing or shellfishing, and thestate has not promulgated a WQS, an FWQCshould be considered as a potential ARAR. Theparticular FWQC (i.e., for water and fish ingestionor fish ingestion alone) selected as the potentialARAR depends on whether exposure from one orboth of the routes is likely to occur and, therefore,on the designated use of the water body. If otheruses of the water are designated (e.g., swimming),a state WQS may be available.

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

2.5 EXPOSURE PATHWAYS,PARAMETERS, ANDEQUATIONS

This step is generally conducted for eachmedium and land-use combination and involvesidentifying the most appropriate (1) exposurepathways and routes (e.g., residential ingestion ofdrinking water), (2) exposure parameters (e.g.,

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2 liters/day of water ingested), and (3) equations(e.g., to incorporate intake). The equationsinclude calculations of total intake from a givenmedium and are based on the identified exposurepathways and associated parameters. Informationgathered in this step should be used to calculaterisk-based PRGs using the default equationsidentified in Chapters 3 and 4. Site-specificequations can be derived if a different set ofexposure pathways is identified for a particularmedium; this option also is discussed in Chapters3 and 4.

When risk-based concentrations are developedduring scoping, readily available site-specificinformation may be adequate to identify anddevelop the exposure pathways, parameters, andequations (e.g., readily available information mayindicate that the exposure duration should be 40years instead of the standard default of 30 years).In the absence of readily available site-specificinformation, the standard default information inChapters 3 and 4 generally should be used for thedevelopment of risk-based PRGs.

Exhibit 2-1 lists a number of the potentialexposure pathways that might be present at aCERCLA site. The exposure pathways included inthe 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 ofthe exposure pathways of possible importance at agiven CERCLA site. For example, theconsumption of ground water that continues to becontaminated by soil leachate is not addressed.Guidance on goal-setting to address this exposurepathway is currently under development by EPA.In addition, the standard default equations do notaddress pathways such as plant and animal uptakeof contaminants from soil with subsequent humaningestion. Under certain circumstances, these orother exposure pathways may present significantrisks to human health. The standard defaultinformation, however, does address the quantifiableexposure pathways that are often significantcontributors of risk for a particular medium andland use.

Chapters 3 and 4 show how exposures fromseveral pathways are addressed in a single equationfor a medium. For example, in the equation forground water and surface water under theresidential land-use assumption, the coefficientsincorporate default parameter values for ingestionof drinking water and inhalation of volatiles during

EXHIBIT 2-1

TYPICAL EXPOSURE PATHWAYS BY MEDIUMFOR RESIDENTIAL AND COMMERCIAL/INDUSTRIAL LAND USESa,b

Exposure Pathways, Assuming:

Medium

Ground Water

Surface Water

Soil

Residential Land Use

Ingestion from drinking

InhalaJion of volaJiles

Dermal absorption from bathing

Immersion - externaf

Ingestion from drinking

Inhalation of volaJiles

Dermal absorption from bathing

Ingestion during swimming

Ingestion of contaminated fish

Immersion - externaf

Ingestion

Inhalation of particulates

Inhalation of volatiles

Direct external exposurec

Exposure to ground water contaminatedby soil leachate

Ingestion via plant uptake

Dermal absorption from gardening

Commercial/Industrial Land Use

Ingestion from drinkingd

Inhalation of volatiles

Dermal absorption

Ingestion from drinkingd

Inhalation of volatiles

Dermal absorption

Ingestion

InhalaJion ofparticulates

InhalaJion of volaJiles

Direct external exposurec

Exposure to ground water contaminatedby soil leachate

Inhalation of particulates from trucksand heavy equipment

a Lists of land uses, media, and exposure pathways are not comprehensive.

b Exposure pathways included in RAGS/HHEM Part B standard default equations (Chapters 3 and 4) areitalicized.

C Applies to radionuclides only.

d Because the NCP encourages protection of ground water to maximize its beneficial use, risk-based PRGsgenerally 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 achievedthat define levels protective for the population at large, not simply worker populations. Residential exposurescenarios should guide risk-based PRG development for ingestion and other uses of potable water.

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household water use. Full details of parametersused to develop each equation and a summary ofthe "reduced" standard default equations areprovided in the text of these chapters.

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

The decision about whether the risk assessorshould collect site-specific human exposurepathway information (e.g., exposure frequency,duration, or intake rate data) is very important.There will frequently be methods available togather such information, some of which are moreexpensive and elaborate than others. Determiningwhether the ~esulting data are reasonablyrepresentative of populations in the surroundingarea, however, is often difficult. Collecting data bysurveying those individuals most convenient oraccessible to RPMs or risk assessors may notpresent a complete population exposure picture.In fact, poorly planned data gathering efforts maycomplicate the assessment process. For example,those surveyed may come to believe that theircontributions will playa more meaningful role inthe risk assessment than that planned by the riskassessors; this can result in significant demands onthe risk assessor's time.

Before such data collection has begun, the riskassessor should determine, with the aid ofscreening analyses, what benefits are likely toresult. Collection of the exposure data discussedin this section generally should not be attemptedunless significant differences are likely to result infinal reasonable maximum exposure (RME) riskestimates. If data collection is warranted,systematic and well-considered efforts· thatminimize biases in results should be undertaken.Estimates of future exposures are likely to relyheavily on conservative exposure assumptions. Bydefinition, these assumptions will be unaffected byeven the most extensive efforts to characterizecurrent population activity.

At this stage, the risk assessor, site engineer,and RPM should discuss information concerning

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the absence or presence of important exposurepathways, because remediation goals should bedesigned for specific areas of the site that aparticular remedy must address, and exposuresexpected for one area of the site may differsignificantly from those expected in another area.

2.5.1 GROUND WATER/SURFACE WATER

The residential land-use default equationspresented in Chapters 3 and 4 for ground water orsurface water are based on ingestion of drinkingwater and inhalation of volatile (vapor phase)chemicals originating from the household watersupply (e.g., during dish washing, clotheslaundering, and showering).

Ingestion of drinking water is an appropriatepathway for all chemicals with an oral cancer slopefactor or an oral chronic reference dose. For thepurposes of this guidance, however, inhalation ofvolatile chemicals from water is consideredroutinely only for chemicals with a Henry's Lawconstant of 1 x 10-5 atm-m3/mole or greater andwith a molecular weight of less than 200 g/mole.Before determining inhalation toxicity values for aspecific chemical (Section 2.6), it should beconfirmed that the Henry's Law constant andmolecular weight are in the appropriate range forinclusion in the inhalation pathway for water.

Default equations addressing industrial use ofground water are not presented. Because the NCPencourages protection of ground water to itsmaximum beneficial use, once ground water isdetermined to be suitable for drinking, risk-basedPRGs generally should be based on residentialexposures. Even if a site is located in an industrialarea, the ground water underlying a site in anindustrial area may be used as a drinking watersource for residents several miles away due tocomplex geological interconnections.

2.5.2 SOIL

The residential land-use standard defaultequations for the soil pathway are based onexposure pathways of ingestion of chemicals in soilor dust. The industrial land-use equations arebased on three exposure pathways: ingestion ofsoil and dust, inhalation of particulates, andinhalation of volatiles. Again, for the purposes ofthis guidance, inhalation of volatile chemicals isrelevant only for chemicals with a Henry's Lawconstant of 1 x 10-5 atm-m3/mole or greater and

with a molecular weight of less than 200 glmole.For the inhalation pathways, in addition to toxicityinformation, several chemical- and site-specificvalues are needed. These values include moleculardiffusivity, Henry's Law constant, organic carbonpartition coefficient, and soil moisture content (seeChapter 3 for details).

CASE STUDY: IDENTIFY EXPOSUREPATHWAYS, PARAMETERS,

AND EQUATIONS

For the potential residential land useidentified at the XYZ Co. site, the contaminatedground water (one of several media of potentialconcern) appears to be an important source offuture domestic water. Because site-specificinformation is not initially available to developspecific exposure pathways, parameters, andequations, the standard default assumptions andequations provided in Chapter 3 will be used tocalculate risk-based PRGs. Exposure pathwaysof concern for ground water, therefore, areassumed to be ingestion of ground water asdrinking water and inhalation of volatiles inground water during household use.

2.6 TOXICITY INFORMATION

This step involves identifying readily availabletoxicity values for all of the chemicals of potentialconcern for given exposure pathways so that theappropriate slope factors (SFs; for carcinogeniceffects) ·and reference doses (RIDs; fornoncarcinogenic effects) are identified or derivedfor use in the site-specific equations or thestandard default equations. Therefore, Chapter 7of RAGS/HHEM Part A should be reviewedcarefully before proceeding with this step.

The hierarchy for obtaining toxicity values forrisk-based PRGs is essentially the same as thatused in the baseline risk assessment. Briefly,Integrated Risk Information System (IRIS) is theprimary source for toxicity information; if noverified toxicity value is available through IRIS,then Health Effects Assessment Summary Tables(HEAST) is the next preferred source. When thedevelopment of a toxicity value is required (andappropriate data are available), consultation withthe Superfund Health Risk Assessment TechnicalSupport Center i~ warranted. EPA staff cancontact the Center by calling FTS-684-7300

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(513-569-7300) or by FAX at FTS-684-7159(513-569-7159). Others must fax to the abovenumber or write to:

Superfund Health Risk Technical SupportCenter

Environmental Criteria and Assessment OfficeU.S. Environmental Protection AgencyMail Stop 11426 West Martin Luther King DriveCincinnati, Ohio 45268

Other toxicity information that should beobtained includes EPA's weight-of-evidenceclassification for carcinogens (e.g., A, B1) and thesource of the information (e.g., IRIS, HEAST).

Note that throughout this document, the termhazard index (HI) is used to refer to the risk levelassociated with noncarcinogenic effects. An HI isthe sum of two or more hazard quotients (HQs).An HQ is the ratio of an exposure level of a singlesubstance to the RID for that substance. BecauseRIDs are generally exposure pathway-specific (e.g.,inhalation RID), the HQ is a single substance/single exposure pathway ratio. An HI, on theother hand, is usually either a single substance/multiple exposure pathway ratio, a multiplesubstance/single exposure pathway ratio, or amultiple substance/multiple exposure pathwayratio. In this document, however, only oneexposure pathway is included in the defaultequation for some land-use and mediumcombinations (e.g., residential soil). In order toremain consistent, the term HI has been usedthroughout RAGS/HHEM Part B, even though forsuch a pathway, the term HQ could apply.

2.7 TARGET RISK LEVELS

This step involves identifying target riskconcentrations for chemicals of potential concern.The standard default equations presented inChapters 3 and 4 are based on the following targetrisk levels for carcinogenic and noncarcinogeniceffects.

• For carcinogenic effects, a concentration iscalculated that corresponds to a 10-6incremental risk of an individual developingcancer over a lifetime as a result of exposureto the potential carcinogen from all significantexposure pathways for a given medium.

CASE STUDY: IDENTIFY TOXICITY INFORMATIONa

Reference toxicity values for cancer and noncancer effects (i.e., SFs and RtDs, respectively) are required forchemicals without ARAR-based PRGs (only the case study chemicals without ARARs are listed here). Consideringthe ground-water medium only, ingestion and inhalation are exposure pathways of concern. Toxicity informationis obtained from IRIS and HEAST, and is shown in the table below.

RtD SF Weight ofChemical (mglkg-day) Source (mglkg-dayyl Evidence Source

EXPOSURE ROUTE: INGESTION

Hexane 0.06 HEAST - - -Isophorone 0.2 IRIS 0.0039 C HEASTTriallate 0.013 IRIS - - -

EXPOSURE ROUTE: INHALATION

Hexane 0.04 HEAST - - -Isophorone - - - C HEASTTriallate - - - - -

a All information in this example is for illustration purposes only.

• For noncarcinogenic effects, a concentration iscalculated that corresponds to an HI of 1,which is the level of exposure to a chemicalfrom all significant exposure pathways in agiven medium below which it is unlikely foreven sensitive populations to experienceadverse health effects.

At scoping, it generally is appropriate to usethe standard default target risk levels describedabove and discussed in the NCP. That is, anappropriate pOint of departure for remediation ofcarcinogenic risk is a concentration thatcorresponds to a risk of 10-6 for one chemical in aparticular medium. For noncarcinogenic effects,the NCP does not specify a range, but it generallyis appropriate to assume an HI equal to 1.

2.8 MODIFICATION OFPRELIMINARYREMEDIATION GOALS

Upon completion of the baseline riskassessment (or as soon as data are available), it isimportant to review the future land use, exposureassumptions, and the media and chemicals ofpotential concern originally identified at scoping,and determine whether PRGs need to be modified.Modification may involve adding or subtracting

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chemicals of concern, media, and pathways orrevising individual chemical-specific goals.

2.8.1 REVIEW OF ASSUMPTIONS

Media of Concern. As a guide to determiningthe media and chemicals of potential concern, theOSWER directive Role of the Baseline RiskAssessment in Superfund Remedy Selection Decisions(EPA 1991c) indicates that action is generallywarranted at a site when the cumulativecarcinogenic risk is greater than 10-4 or thecumulative noncarcinogenic HI exceeds 1 based onRME assumptions. Thus, where the baseline riskassessment indicates that either the cumulativecurrent or future risk associated with a medium isgreater than 10-4 or that the HI is greater than 1,that medium presents a concern, and it generally isappropriate to maintain risk-based PRGs forcontaminants in that medium or develop risk-basedPRGs for additional media where PRGs are notclearly defined by ARARs.

When the cumulative current or futurebaseline cancer risk for a medium is within therange of 10-6 to 10-4, a decision about whether ornot to take action is a site-specific determination.Generally, risk-based PRGs are not needed for anychemicals in a medium with a cumulative cancerrisk of less than 10-6, where an HI is less than or

equal to 1, or where the PRGs are clearly definedby ARARs. However, there may be cases where amedium appears to meet the protectivenesscriterion but contributes to the contamination ofanother medium (e.g., soil contributing to ground­water contamination). In these cases, it may beappropriate to modify existing or develop new risk­based PRGs for chemicals of concern in the firstmedium, assuming that fate and transport modelscan adequately predict the impacts of concern onother media. EPA is presently developingguidance on quantifying the impact of soilcontamination on underlying aquifers.

Chemicals of Concern. As with the initialmedia of potential concern, the initial list ofspecific chemicals of potential concern in a givenmedium may need to be modified to reflectincreased information from the RIfFS concerningthe importance of the chemicals to the overall siterisk. Chemicals detected during the RIfFS thatwere not anticipated during scoping should beconsidered for addition to the list of chemicals ofpotential concern; chemicals anticipated duringscoping that were not detected during the RIfFSshould be deleted from the list. Ultimately, theidentity and number of contaminants that mayrequire risk-based PRGs depends both on theresults of the baseline risk assessment and theextent of action required, given site-specificcircumstances.

Following the baseline risk assessment, anychemical that has an associated cancer risk(current or future) within a medium of greaterthan 10-6 or an HI of greater than 1 should remainon the list of chemicals of potential concern forthat medium. Likewise, chemicals that presentcancer risks of less than 10-6 generally should notbe retained on the list unless there are significantconcerns about multiple contaminants andpathways.

Land Use. After the RIfFS, one future landuse can usually be selected based on the results ofthe baseline risk assessment and discussions withthe RPM. In many cases, this land use will be thesame as the land use identified at scoping. Inother cases, however, additional information fromthe baseline risk assessment that was not availableat scoping may suggest modifying the initial land­use and exposure assumptions. A qualitativeassessment should be made- and should beavailable from the baseline risk assessment - of

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the likelihood that the assumed future land usewill occur.

Exposure Pathways, Parameters, andEquations. For exposure pathways, this process ofmodifying PRGs consists of adding or deletingexposure pathways from the medium-specificequations in Chapters 3 and 4 to ensure that theequation accounts for all significant exposurepathways associated with that medium at the site.For example, the baseline risk assessment mayindicate that dermal exposure to contaminants insoil is a significant contributor to site risk. In thiscase, the risk-based PRGs may be modified byadding equations for dermal exposure. EPA policyon assessing this pathway is currently underdevelopment; the risk assessor should consult theSuperfund Health Risk Technical Support Center(FTS-684-7300 or 513-569-7300) to determine thecurrent status of guidance. Likewise, whenappropriate data (e.g., on exposure frequency andduration) have been collected during the RIfFS,site-specific values can be substituted for thedefault values in the medium-specific equations.

2.8.2 IDENTIFICATION OFUNCERTAINTIES

The uncertainty assessment for PRGs canserve as an important basis for recommendingfurther modifications to the PRGs prior to settingfinal remediation goals. It also can be used duringthe post-remedy assessment (see Section 2.8.4) toidentify areas needing particular attention.

Risk-based PRGs are associated with variedlevels of uncertainty, depending on many factors(e.g., confidence that anticipated future land use iscorrect). To place risk-based PRGs that have beendeveloped for a site in proper perspective, anassessment of the uncertainties associated with theconcentrations should be conducted. Thisassessment is similar to the uncertainty assessmentconducted during the baseline risk assessment (seeRAGS/HHEM Part A, especially Chapters 6, 7,and 8). In fact, much of the uncertaintyassessmen t conducted for a site's baseline riskassessment will be directly applicable to theuncertainty assessment of the risk-based PRGs.

In general, each component of risk-basedPRGs discussed in this chapter - from media ofpotential concern to target risk level - should beexamined, and the major areas of uncertaintyhighlighted. For example, the uncertainty

associated with the selected future land use shouldbe discussed. Furthermore, the accuracy of thetechnical models used (e.g., for volatilization ofcontaminants from soil) to reflect site-specificconditions (present and future) should bediscussed. If site-specific exposure assumptionshave been made, it is particularly important todocument the data supporting those assumptionsand to assess their relevance for potentiallyexposed populations.

As the chemical- and medium-specific PRGsare developed, many assumptions regarding theRME individual(s) are incorporated. AlthoughPRGs are believed to be fully protective for theRME individual(s), the proximity of other nearbysources of exposure (e.g., other CERCLA sites,RCRA facilities, naturally occurring backgroundcontamination) and/or the existence of the samecontaminants in multiple media or of multiplechemicals affecting the same population(s), maylead to a situation where, even after attainment ofall PRGs, protectiveness is not clearly achieved(e.g., cumulative risks may fall outside the riskrange). The more likely it is that multiplecontaminants, pathways, operable units, or othersources of toxicants will affect the RMEindividual(s), the more likely it will be thatprotectiveness is not achieved. This likelihoodshould be addressed when identifying uncertainties.

NCP PREAMBLE: EXPOSURE,TECHNICAL, AND

UNCERTMNTYFACTORS(55 Federal Register 8717, March 8, 1990)

"Preliminary remediation goals ... may berevised ... based on the consideration ofappropriate factors including, but not limited to:exposure factors, uncertainty factors, and technicalfactors. Included under exposure factors are:cumulative effect of multiple contaminants, thepotential for human exposure from other pathwaysat the site, population sensitivities, potentialimpacts on environmental receptors, and cross­media impacts of alternatives. Factors related touncertainty may include: the reliability ofalternatives, the weight of scientific evidenceconcerning exposures and individual andcumulative health effects, and the reliability ofexposure data. Technical factors may include:detection/quantification limits for contaminants,technical limitations to remediation, the ability tomonitor and control movement of contaminants,and background levels of contaminants. The finalselection of the appropriate risk level is made whenthe remedy is selected based on the balancing ofcriteria...."

The NCP preamble and rule state that factorsrelated to exposure, technical limitations, anduncertainty should be considered when mOdifyingPRGs (see next two boxes) and setting finalremediation levels.

2.8.3 OTHER CONSIDERATIONS INMODIFYING PRGs

NCP RULE: EXPOSURE, TECHNICAL,AND UNCERTMNTY FACTORS

(40 CFR 300.430(e)(2)(i»

"(i)...Remediation goals...shall be developed byconsidering the following:

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

While the final remedial action objectives mustsatisfy the original "threshold criteria" of protectionof human health and the environment andcompliance with ARARs, the factors in the"balancing and modifying criteria" (listed in Section1.3.2) also are considered in the detailed analysisfor choosing among remedial alternatives. In caseswhere the alternative that represents the bestbalance of factors is not able to attain cancer riskswithin the risk range or an HI of 1, institutionalcontrols may be used to supplement treatmentand/or containment-based remedial action toensure protection of human health and theenvironment.

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"(1) For systemic toxicants, acceptableexposure levels...;

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

"(3) Factors related to technical limitationssuch as detection/quantification limits forcontaminants;

"(4) Factors related to uncertainty; and

"(5) Other pertinent information."

Note that in the absence of ARARs, the 10-6cancer risk "point of departure" is used as astarting point for analysis of remedial alternatives,which reflects EPA's preference for managing risksat the more protective end of the risk range, otherthings being equal. Use of "point of departure"target risks in this guidance does not reflect apresumption that the final remedial action shouldattain such goals. (See NCP preamble, 55 FederalRegister 8718-9.)

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2.8.4 POST-REMEDY ASSESSMENT

To ensure that protective conditions exist afterthe remedy achieves all individual remediationlevels set out in the ROD, there generally will bea site-wide evaluation conducted followingcompletion of a site's final operable unit (e.g.,during the five-year review). This site-wideevaluation should adequately characterize theresidual contaminant levels and ensure that thepost-remedy cumulative site risk is protective.More detailed guidance on the post-remedyassessment of site "protectiveness" is currentlyunder development by EPA.

CHAP'fER3

CALCULATION OF RISK-BASEDPRELIMINARY REMEDIATION GOALS

This chapter presents standardized exposureparameters, the derivation of risk equations, andthe corresponding "reduced" equations, forcalculating risk-based PRGs at scoping for themedia and land-use assumptions discussed inChapter 2 (Le., ground water, surface water, andsoil for residential land use, and soil forcommercial/industrial land use). Both carcinogenicand noncarcinogenic effects are addressed.Standardized default exposure parametersconsistent with OSWER Directive 9285.6-03 (EPA1991b) are used in this chapter; where defaultparameters are not available in that guidance, thereferences used are cited. If other media requiringrisk-based PRGs are identified during the RI/FS,or other exposure parameters or land uses areassumed, then appropriate equations will need tobe modified or new ones developed.

Risk-based equations have been derived inorder to reflect the potential risk from exposure toa chemical, given a specific pathway, medium, andland-use combination. By setting the total risk forcarcinogenic effects at a target risk level of 10-6

(the NCP's point of departure for analysis ofremedial alternatives), it is possible to solve for theconcentration term (Le., the risk-based PRG). Thetotal risk for noncarcinogenic effects is set at anHI of 1 for each chemical in a particular medium.Full equations with pathway-specific defaultexposure factors are presented in boxes withuniformly thin borders. Reduced equations arepresented in the standard boxes (Le., thicker topand bottom borders). At the end of this chapter,the case study that began in Chapter 2 isconcluded (by showing how to calculate andpresent risk-based PRGs).

In general, the equations described in thischapter are sufficient for calculating the risk-basedPRGs at the scoping stage of the RI/FS. Note,however, that these equations are based onstandard default assumptions that may or may notreflect site-specific conditions. When risk-basedPRGs are to be calculated based on site-specific

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conditions, the risk assessor should modify the fullequations, and/or develop additional ones. Riskequations for individual exposure pathways for agiven medium are presented in Appendix B of thisdocument, and may be used to develop and/ormodify the full equations. (See the introduction toAppendix B for more detailed instructions.)

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

• Use of toxicity values in the equations aswritten currently assumes 100 percentabsorption effeciency. That is, for the sake ofsimplicity at scoping, it is assumed that thedose administered to test animals in toxicitystudies on which toxicity values are based wasfully absorbed. This assumption may need tobe revised in cases where toxicity values basedon route-to-route extrapolation are used, orthere are significant differences in absorptionlikely between contaminants in site media andthe contaminants in the vehicle used in thetoxicity study. Chapter 7 and Appendix A inRAGS/HHEM Part A (EPA 1989d) provideadditional details on this point.

• The risk-based PRGs should contain at mosttwo significant figures even though some ofthe parameters used in the reduced equationscarry additional significant figures.

• The equations presented in this chaptercalculate risk-based concentrations usinginhalation reference doses (RIDjs) andinhalation slope factors (SFjs). If only thereference concentration (RfC) and/orinhalation unit risk are available for aparticular compound in IRIS, conversion to anRID j and/or SFj will be necessary. Manyconverted toxicity values are available inHEAST.

• All standard equations presented hereincorporate pathway-specific default exposure

factors that generally reflect RME conditions.As detailed in Chapter 8 of RAGS/HHEMPart A (in the discussion on combiningpathway risks [Section 8.3]), RME risks fromone pathway should be combined with RMErisks from another pathway only where thereis good reason. Typically, RME from onepathway is not likely to occur with RME fromanother (unless there is a strong logicaldependent relationship between exposuresfrom the two pathways). If risk-basedconcentrations are developed for both thewater and the soil pathways, the risk assessorultimately may need to adjust exposureassumptions from one pathway (Le., the onewith the lower RME) to less conservative(more typical) values.

equation incorporates a water-air concentrationrelationship that is applicable only to chemicalswith a Henry's Law constant of greater than 1 x10-5 atm-m3/mole and a molecular weight of lessthan 200 g/mole. These criteria are not used toscreen out chemicals that are not of potentialconcern for this exposure pathway but only toidentify those that generally should be consideredfor the inhalation pathway when developing risk­based PRGs early in the process. Chemicals thatdo not meet these criteria may pose significant siterisks (and require risk-based goals) throughvolatiles inhalation. The ultimate decisionregarding which contaminants should beconsidered in the FS must be made on a site­specific basis following completion of the baselinerisk assessment.

3.1 RESIDENTIAL LAND USE

3.1.1 GROUND WATER OR SURFACEWATER

At scoping, risk from indoor inhalation ofvolatiles is assumed to be relevant only forchemicals that easily volatilize. Thus, the risk

In the case illustrated here, risks from twoexposure pathways from ground water or surfacewater are combined, and the risk-basedconcentration is derived to be protective forexposures from both pathways. Default risk fromground water or surface water would be calculatedas follows ("total" risk, as used below, refers to thecombined risk for a single chemical from allexposure pathways for a given medium):

Intake frominhalation ofvolatiles fromwater

Total = SFo x Intake from + SF; xrisk ingestion of

water

Concentrations Based on Carcinogenic Etl'ects.Total risk for carcinogenic effects of certainvolatile chemicals would be calculated bycombining the appropriate inhalation and oral SFswith the two intakes from water:

Based primarily on experimental data on thevolatilization of radon from household uses ofwater, Andelman (1990) derived an equation thatdefines the relationship between the concentrationof a contaminant in household water and theaverage concentration of the volatilizedcontaminant in air. In the derivation, all uses ofhousehold water were considered (e.g., Showering,laundering, dish washing). The equation uses adefault "volatilization" constant (K) upper-boundvalue of 0.0005 x 1000 Llm3. (The 1000 Llm3

conversion factor is incorporated into the equationso that the resulting air concentration is expressedin mg/m3.) Certain assumptions were made inderiving the default constant K (Andelman 1990).For example, it is assumed that the volume ofwater used in a residence for a family of four is720 Llday, the volume of the dwelling is 150,000 Land the air exchange rate is 0.25 m3/hr.Furthermore, it is assumed that the averagetransfer efficiency weighted by water use is 50percent (Le., half of the concentration of eachchemical in water will be transfered into air by allwater uses [the range extends from 30% for toiletsto 90% for dishwashers]). See the Andelmanpaper for further details.

Risk from inhala­tion of volatilesfrom householdwater (adult)

= Risk from +ingestion ofwater (adult)

Total riskfrom water

Under residential land use, risk from surfacewater or ground-water contaminants is assumed tobe due primarily to direct ingestion and toinhalation of volatiles from household water use.Therefore, only these exposure pathways areconsidered in this section. Additional exposurepathways (e.g., dermal absorption) are possible andmay be significant at some sites for somecontaminants, while perhaps only one exposurepathway (e.g., direct ingestion of water only) maybe relevant at others. In any case, the risk-basedPRG for each chemical should be calculated byconsidering all of the relevant exposure pathways.

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Adding appropriate parameters, and thenrearranging the equation to solve forconcentration, results in Equation (1).

Equation (1') on the next page is the reducedversion of Equation (1) using the standard defaultparameters, and is used to calculate the risk-basedPRG at a prespecified cancer risk level of 10-6. Itcombines the toxicity information of a chemicalwith standard default exposure parameters forresidential land use to generate the concentration

of that chemical that corresponds to a 10-0

carcinogenic risk level due to that chemical. Ifeither the SF0 or SFi in Equation (1') is notavailable for a particular chemical, the termcontaining that variable in the equation can beignored or equated to zero (e.g., for a chemicalthat does not have SFj , the term 7.5(SFi ) inEquation (1') is ignored). If any of the defaultparameter values are changed to reflect site­specific conditions, the reduced equation cannot beused.

RESIDENTIAL WATER - CARCINOGENIC EFFECTS

TR == SF" x C x IB.,. x EF x ED +BW x AT x 365 dayslyr

SF; x C x K x IRa X EF x EDBW x AT x 365 dayslyr

== EF x ED x ex r(SFo x IB.,.) + (SF; x K X IRa))BW X AT X 365 dayslyr

C (mgIL; risk­based)

where:

== TR x BW x AT x 365 dayslyrEF x ED x [(SF; x K x IRa) + (SFo x I~)l

(1)

Parameters

CTRSFj

SFoBWATEFEDIRaI~

K

Definition (units)

chemical concentration in water (mgIL)target excess individual lifetime cancer risk (unitless)inhalation cancer slope factor ((mglkg-dayr1

)

oral cancer slope factor ((mglkg-dayr1)

adult body weight (kg)averaging time (yr)exposure frequency (dayslyr)exposure duration (yr)daily indoor inhalation rate (m3/day)daily water ingestion rate (Uday)volatilization factor (unitless)

Default Value

10-6

chemical-specificchemical-specific70 kg70 yr350 dayslyr30 yr15 m3/day2 Uday0.0005 x 1000 L/m3 (Andelman 1990)

REDUCED EQUATION: RESIDENTIAL WATER - CARCINOGENIC EFFECTS

Risk-based PRG =(mgIL; TR == 10-6)

where:

1.7 X 10-4 (1 ')

== oral slope factor in (mglkg-dayr1

== inhalation slope factor in (mglkg-dayr1

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Concentrations Based on NoncarcinogenicEffects. Total HI would be calculated bycombining the appropriate oral and inhalationRIDs with the two intakes from water:

HI = Intake from oral ingestionRillo

+ Intake from inhalationRill;

Adding appropriate parameters, and thenrearranging the equation to solve forconcentration, results in Equation (2).

Equation (2') on the next page is the reducedversion of Equation (2) using the standard defaultparameters, and is used to calculate the risk-basedPRG at a prespecified HI of 1. It combines thetoxicity information of a chemical with standardexposure parameters for residential land use togenerate the concentration of that chemical thatcorresponds to an HI of 1. If either the RIDa orRID j in Equation (2') is not available for aparticular chemical, the term containing thatvariable in the equation can be ignored or equatedto zero (e.g., for a chemical that does not haveRID j , the term 7.5!RID j in Equations (2') isignored).

RESIDENTIAL WATER - NONCARCINOGENIC EFFECTS

TIll = C X I&, X EF X EDRillo X BW X AT X 365 days/yr

+ C x K x IRa X EF x EDRill; X BW X AT x 365 dayslyr

= EF X ED X ex [(l/Rillo X IRw ) + Cl/Rill; X K X IRa)]BW X AT X 365 dayslyr

C (mgIL; risk­based)

where:

Parameters Definition

TIll X BW X AT X 365 days/yrEF X ED X [(I/Rill j X K X IRa) + (l/Rillo X IRw)l

Default Value

(2)

C chemical concentration in water (mgIL)TIll target hazard index (unitless)Rillo oral chronic reference dose (mglkg-day) chemical-specificRill; inhalation chronic reference dose (mglkg-day) chemical-specificBW adult body weight (kg) 70 kgAT averaging time (yr) 30 yr (for noncarcinogens, equal to ED)EF exposure frequency (dayslyr) 350 dayslyrED exposure duration (yr) 30 yrIRa daily indoor inhalation rate (m3/day) 15 m3/dayIRw daily water ingestion rate (Llday) 2 LldayK volatilization factor (unitless) 0.0005 x 1000 Llm3 (Andelman 1990)

REDUCED EQUATION: RESIDENTIAL WATER - NONCARCINOGENIC EFFECTS

Risk-based PRG(mgIL; TIll = 1)

where:

= 73[7.5/Rill; + 2/Rillol

(2 ')

= oral chronic reference dose in mglkg-day= inhalation chronic reference dose in mglkg-day

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3.1.2 SOIL

Under residential land use, risk of thecontaminant from soil is assumed to be due todirect ingestion of soil only.

Additional exposure pathways (e.g., inhalationof particulates, inhalation of volatiles, ingestion offoodcrops contaminated through airborneparticulate deposits, consumption of ground watercontaminated by soil leachate) are possible at somesites. The risk assessor should evaluate whether

Because the soil ingestion rate is different forchildren and adults, the risk due to direct ingestionof soil is calculated using an age-adjusted ingestionfactor. The age-adjusted soil ingestion factor(IFsoil/adj) takes into account the difference in dailysoil ingestion rates, body weights, and exposuredurations for two exposure groups - children ofone to six years and others of seven to 31 years.Exposure frequency (EF) is assumed to beidentical for the two exposure groups. Forconvenience, this factor is calculated separately asa time-weighted soil intake, normalized to bodyweight, that can then be substituted in the totalintake equation. Calculated in this manner, thefactor leads to a more protective risk-basedconcentration compared to an adult-onlyassumption. Note that the ingestion factor is inunits of mg-yr/kg-day, and therefore is not directlycomparable to daily soil intake rate in units ofmglkg-day. See the box containing Equation (3)for the calculation of this factor.

Total risk = SFo x Intake from ingestion of soil

Concentrations Based on Carcinogenic Effects.Total risk for carcinogenic effects would becalculated by combining the appropriate oral SFwith the intake from soil:

inhalation or other exposure pathways aresignifi<;<mt at the site. Generally, for manyundisturbed sites with vegetative cover such asthose found in areas of residential land use, airpathways are relatively minor contributors of risk.Greater concern for baseline risk via air pathwaysexists under commercial/industrial land-useassumptions, given the increased activity levelslikely (see Section 3.2.2). Air pathway risks alsotend to be major concerns during remedial action(see RAGS/HHEM Part C). If these otherpathways are known to be significant at scoping,Appendix B and/or other information should beused to develop site-specific equations for the risk­based PRGs.

Adding appropriate parameters, and thenrearranging the equation to solve forconcentration, results in Equation (4).

Equation (4') below is the reduced version ofEquation (4) using the standard defaultparameters, and is used to calculate the risk-basedPRG at a prespecified cancer risk level of 10-6. Itcombines the toxicity information of a chemicalwith standard exposure parameters for residentialland use to generate the concentration of thatchemical that corresponds to a 10-6 carcinogenicrisk level due to that chemical.

= Risk from ingestion of soil(child to adult)

Total risk from soil

AGE-ADJUSTED SOIL INGESTION FACTOR

IFsoiVadj (mg-yr/kg-day) IRsoiVage7.31 X EDage7-31_BWage7_31

(3)

Parameter Definition Default Value

IFsoiVadjBWagel-6BWage7.31EDagel-6EDage7_31IRsoiVagel-6IRsoiVage7.31

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)

114 mg-yr/kg-day15 kg70 kg6 yr24 yr200 mg/day100 mg/day

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TR =

RESIDENTIAL SOIL - CARCINOGENIC EFFECTS

~ x ex 10-6 kglmg x EF X IFsoiVadi­AT x 365 dayslyr

C (mglkg; risk- =based)

where:

TR x AT x 365 dayslyearSF0 x 10-6 kglmg x EF x IFsoiVadj

(4)

Parameters

CTRSFoATEF

IFsoiVadj

Definition (units)

chemical concentration in soil (mglkg)target excess individual lifetime cancer risk (unitless)oral cancer slope factor «mglkg-dayr1

)

averaging time (yr)exposure frequency (dayslyr)age-adjusted ingestion factor (mg-yr/kg-day)

Default Value

10-6

chemical-specific70 yr350 dayslyr114 mg-yr/kg-day (see Equation (3))

REDUCED EQUATION: RESIDENTIAL SOIL - CARCINOGENIC EFFECTS

Risk-based PRG(mglkg; TR = 10-6)

where:

=(4 ')

3.2.1 WATER

= oral slope factor in (mglkg-dayyl

Concentrations Based on NoncarcinogenicEffects. Total HI would be calculated bycombining the appropriate oral RID with theintake from soil:

3.2 COMMERCIAL/INDUSTRIALLAND USE

HI = Intake from ingestionRfDo

Adding appropriate parameters, and thenrearranging the equation to solve forconcentration, results in Equation (5).

Equation (5') is the reduced version ofEquation (5) using the standard defaultparameters, and is for calculating the risk-basedPRG at a prespecified HI of 1. It combines thetoxicity information of a chemical with standardexposure parameters for residential land use togenerate the concentration of that chemical thatcorresponds to an HI of 1.

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Once ground water is determined to besuitable for drinking, risk-based concentrationsshould be based on residential exposures. This isbecause the NCP seeks to require protection ofground water to allow for its maximum beneficialuse (see Section 2.3). Thus, under the commercial!industrial land-use scenario, risk-based PRGs forground water are calculated according to

procedures detailed in Section 3.1.1. Similarly, forsurface water that is to be used for drinking, therisk-based PRGs should be calculated forresidential populations, and not simply workerpopulations.

RESIDENTIAL SOIL - NONCARCINOGENIC EFFECTS

THI = C x 10-6 kg/mg x EF X IF'oivadj-Rill0 x AT x 365 dayslyr

C (mglkg; risk­based)

where:

Parameters

CTHIRilloAT

EF

IFsoiVadj

THI x AT x 365 daystvrl/Rill0 x 10-6 kg/mg x EF x IFsoilladj

Definition (units)

chemical concentration in soil (mglkg)target hazard index (unitless)oral chronic reference dose (mglkg-day)averaging time (yr)

exposure frequency (daysiyr)age-adjusted ingestion factor (mg-yr/kg-day)

Default Value

1chemical-specific30 yr (for noncarcinogens, equal to ED [which

is incorporated in IFsoiVadj))350 daysiyr114 mg-yr/kg-day (see Equation (3))

(5)

REDUCED EQUATION: RESIDENTIAL SOIL - NONCARCINOGENIC EFFECTS

Risk-based PRG(mgikg; lHI = 1)

where:

= (5 ')

It is possible to consider only exposure pathways ofsite-specific importance by deriving a Site-specificrisk-based PRG (e.g., using the equations inAppendix B).

In the default case illustrated below, intakesfrom the three exposure pathways are combinedand the risk-based PRG is derived to be protectivefor exposures from all three pathways. In this case,the risk for a specific chemical from soil due to thethree exposure pathways would be calculated asfollows:

Rillo = oral chronic reference dose in mglkg-day

3.2.2 SOIL

Under commercial/industrial land use, risk ofthe contaminant from soil is assumed to be due todirect ingestion, inhalation of volatiles from thesoil, and inhalation of particulates from the soil,and is calculated for an adult worker only. Forthis type of land use, it is assumed for calculatingdefault risk-based PRGs that there is greaterpotential for use of heavy equipment and relatedtraffic in and around contaminated soils and thusgreater potential for soils to be disturbed andproduce particulate and volatile emissions than inmost residential land-use areas. Additionalexposure pathways (e.g., dermal exposure) arepossible at some sites, while perhaps only oneexposure pathway (e.g., direct ingestion of soilonly) may be relevant at others; Appendix B maybe used to identify relevant exposure pathways tobe combined. In such cases, the risk is calculatedby considering all the relevant exposure pathwaysidentified in the RI.

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Total riskfrom soil

= Risk from ingestion of soil (worker)

+ Risk from inhalation of volatiles fromsoil (worker)

+ Risk from inhalation of particulatesfrom soil (worker)

Concentrations Based on Carcinogenic Effects.Total risk for carcinogenic effects would becalculated by combining the appropriate inhalationand oral SFs with the three intakes from soil:

3.3 VOLATILIZATION ANDPARTICULATE EMISSIONFACTORS

Total risk = SFo x Intake from ingestion of soil(worker)

+ SFi x Intake from inhalation ofvolatiles from soil (worker)

+ SFj x Intake from inhalation ofparticulates (worker)

Adding appropriate parameters, and thenrearranging the equation to solve forconcentration, results in Equation (6). Asdiscussed 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 ofEquation (6) using the standard defaultparameters, and is used to calculate the risk-basedPRG at a prespecified cancer risk level of 10-6. Itcombines the toxicity information of a chemicalwith standard exposure parameters forcommercial/industrial land use to generate theconcentration of that chemical that corresponds toa 10-6 carcinogenic risk level due to that chemical.

Concentrations Based on NoncarcinogenicEffects. Total HI would be calculated bycombining the appropriate oral and inhalationRIDs with the three intakes from soil:

HI = Intake from ingestionRIDo

(Intake from inhalation of volatiles+ and particulates)

RID;

Adding appropriate parameters, and thenrearranging the equation to solve forconcentration, results in Equation (7).

Equation (7') is the reduced version ofEquation (7) using the standard defaultparameters, and is used to calculate the risk-basedPRG at a prespecified HI of 1. It combines thetoxicity information of a chemical with standardexposure parameters for commercial/industrial landuse to generate the concentration of that chemicalthat corresponds to an HI of 1.

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3.3.1 SOIL-TO-AIR VOLATILIZATIONFACTOR

The volatilization factor (VF) is used fordefining the relationship between theconcentration of contaminants in soil and thevolatilized contaminants in air. This relationshipwas established as a part of the Hwang and Falco(1986) model developed by EPA's ExposureAssessment Group (EAG). Hwang and Falcopresent a method intended primarily to estimatethe permissible residual levels associated with thecleanup of contaminated soils. This method hasbeen used by EPA in estimating exposures to PCBsand 2,3,7,8-TCDD from contaminated soil (EPA1986; EPA 1988a). One of the pathwaysconsidered in this method is the intake byinhalation of volatilized contaminants.

The basic principle of the Hwang and Falcomodel is applicable only if the soil contaminantconcentration is at or below saturation. Saturationis the soil contaminant concentration at which theadsorptive limits of the soil particles and thesolubility limits of the available soil moisture havebeen reached. Above saturation, pure liquid-phasecontaminant is present in the soil. Under suchconditions, the partial pressure of the purecontaminant and the partial pressure of air in theinterstitial soil pore spaces cannot be calculatedwithout first knowing the mole fraction of thecontaminant in the soil. Therefore, abovesaturation, the PRG cannot be accuratelycalculated based on volatilization. Because of thislimitation, the chemical concentration in soil (C)calculated using the VF must be compared withthe soil saturation concentration (Csat) calculatedusing Equation (6a) or (7a). If C is greater thanCsat' then the PRG is set equal to Csat'

The VF presented in this section assumes thatthe contaminant concentration in the soil ishomogeneous from the soil surface to the depth ofconcern and that the contaminated material is notcovered by contaminant-free soil material. For thepurpose of calculating VF, depth of concern isdefined as the depth at which a near impenetrablelayer or the permanent ground-water level isreached.

COMMERCIAl)INDUSTRIAL SOIL - CARCINOGENIC EFFECTS

TR = §fo x C X 10-6 kg/mg X EF X ED X IRsoiL + SF; X C X EF X ED X IRair X ClNF + 1/PEF)BW x AT x 365 dayslyr BW x AT x 365 dayslyr

C (mglkg; risk- =based)

where:

TR x BW x AT x 365 days!YrEF x ED X [(SFo X 10-6 kglmg x IRsoil) + (SFi x IRair X [1NF + 1/PEFJ)]

(6)

Parameters

CTRSF;SFoBWATEFEDIRsoilIRairVFPEF

Definition (units)

chemical concentration in soil (mglkg)target excess individual lifetime cancer risk (unitless)inhalation cancer slope factor «mglkg-dayr1

)

oral cancer slope factor «mglkg-dayr1)

adult body weight (kg)averaging time (yr)exposure frequency (dayslyr)exposure duration (yr)soil ingestion rate (mglday)workday inhalation rate (m3/day)soil-to-air volatilization factor (m3/kg)particulate emission factor(m3/kg)

Default Value

10-6

chemical-specificchemical-specific70 kg70 yr250dayslyr25yr50 mglday20 m3/daychemical-specific (see Section 3.3.1)4.63 x 109 m3/kg (see Section 3.3.2)

where:

(6a)

Parameters Definition (units)

soil saturation concentration (mglkg)soil-water partition coefficient (L/kg)organic carbon partition coefficient (L/kg)organic carbon content of soil (fraction)solubility (mgIL-water)soil moisture content, expressed as a weight fractionsoil moisture content, expressed as L-water/kg-soil

Default Value

chemical-specific, or K.x: x DCchemical-specificsite-specific, or 0.02chemical-specificsite-specificsite-specific

REDUCED EQUATION: COMMERCIAl)INDUSTRIAL SOIL - CARCINOGENIC EFFECTS

Risk-based PRG =(mglkg; TR = 10-6)

where:

2.9 X 10-4[«5 x 10-5

) x SFo) + (SF; x «20NF) + (4.3 x 10-~))]

(6 ')

SFa =SF; =VF =

oral slope factor in (mglkg-dayr1

inhalation slope factor in (mglkg-dayr1

chemical-specific soil-to-air volatilization factor in m3/kg (see Section 3.3.1)

If PRG > Coat, then set PRG = Coat (where Coat = soil saturation concentration (mg/kg); see Equation (6a)and Section 3.3.1).

-27-

COMMERCIAl)INDUSTRIAL SOIL - NONCARCINOGENIC EFFECTS

TIU = C X 10-6 kg/mg X EF X ED X IR'oil- +RtDo X BW X AT X 365 days/yr

C X EF X ED X IRa;r X (lNF + IIPEF)RtDi X BW X AT X 365 days/yr

C (mglkg; =risk-based)

where:

THI X BW X AT X 365 daystvrED X EF X [((I/RtDo) X 10-6 kglmg X IR,oil) + ((I/RtD;) X IRair X (INF + I/PEF))]

(7)

Parameters Definition (units) Default Value

C chemical concentration in soil (mglkg)THI target hazard index (unitless) 1

RtDo oral chronic reference dose (mglkg-day) chemical-specificRtD j inhalation chronic reference dose (mglkg-day) chemical-speciticBW adult body weight (kg) 70 kgAT averaging time (yr) 25 yr (always equal to ED)EF exposure frequency (days/yr) 250 days/yrED exposure duration (yr) 25 yr

IR,oi' soil ingestion rate (mglday) 50 mgldayIRair workday inhalation rate (m3/day) 20 m3/dayVF soil-to-air volatilization factor (m3/kg) chemical-specific (see Section 3.3_1)PEF particulate emission factor (m3/kg) 4.63 X 109 m3/kg (see Section 3.3.2)

Csat = (K.J X S X nm) + (s X 8 m) (7a)

where:

Parameters Definition (units) Default Value

C,at soil saturation concentration (mglkg)Kd soil-water partition coefficient (L/kg) chemical-specific, or K.x: X OC

K.x: organic carbon partition coefficient (L/kg) chemical-specificOC organic carbon content of soil (fraction) site-specific, or 0.02s solubility (mgIL-water) chemical-specificnm soil moisture content, expressed as a weight fraction site-specific8 m soil moisture content, expressed as L-water/kg-soil Site-specific

REDUCED EQUATION: COMMERCIAl)INDUSTRIAL SOIL - NONCARCINOGENIC EFFECTS

Risk-basedPRG (mglkg;THI = 1)

where:

RtDo

RtD j

VF

= 102[(5 x 1O-5/RtDo) + ((1/RtD;) x ((20NF) + (4.3 x 1O-~))]

= oral chronic reference dose in mglkg-day= inhalation chronic reference dose in mglkg-day

chemical-specific soil-to-air volatilization factor in m3/kg (see Section 3.3.1)

(7 ')

If PRG > Csa" then set PRG = Csal (where Csal = soil saturation concentration (mglkg); see Equation (7a) andSection 3.3.1).

-28-

A chemical-specific value for VF is used in thestandard default equations (Equations (6), (6'),(7), and (7') in Section 3.2.2) and is developed inEquation (8). The VF value calculated usingEquation (8) has been developed for specific use inthe other equations in this guidance; it may not beapplicable in other technical contexts. Equation(8) lists the standard default parameters forcalculating VE If site-specific information isavailable, Equation (8) may be modified tocalculate a VF that is more appropriate for theparticular site. Supporting references should beconsulted when substituting site-specific data toensure that the model and specific parameters canbe appropriately applied to the given site.

3.3.2 PARTICULATE EMISSION FACTOR

The particulate emission factor (PEF) relatesthe contaminant concentration in soil with theconcentration of respirable particles (PM lO) in theair due to fugitive dust emissions from surfacecontamination sites. This relationship is derivedby Cowherd (1985) for a rapid assessmentprocedure applicable to a typical hazardous wastesite where the surface contamination provides arelatively continuous and constant potential foremission over an extended period of time (e.g.,years). The particulate emissions fromcontaminated sites are due to wind erosion and,therefore, depend on the erodibility of the surface

SOIL-TO-AIR VOLATILIZATION FACTOR

VF (m3/kg)

where:

(LS x V x DH)A

x (3.14 x IX x T)1J2

(2 x Dei X Ex Kas X 10-3 kg/g)(8)

-----f!1.i X E)

E + (Ps)(l-E)/K"s

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 aside of the contaminated area (LS) is assumed to be 45 m; this is based on a contaminated area of 0.5 acre whichapproximates the size of an average residential lot. The "typical" values LS, DH, and V are from EPA 1986. "Typical"values for E, OC, and Ps are from EPA 1984, EPA 1988b, and EPA 1988f. Site-specific data should be substitutedfor the default values listed below wherever possible. Standard values for chemical-specific D i, H, and Koc can beobtained by calling the Superfund Health Risk Technical Support Center.

Parameter

VFLSVDHA

DeiE

Kas

Definition (units)

volatilization factor (m3/kg)length of side of contaminated area (m)wind speed in mixing zone (m/s)diffusion height (m)area of contamination (cm2

)

effective diffusivity (cm2/s)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 (cm2/s)Henry's law constant (atm-m3/mol)soil-water partition coefficient (cm3/g)organic carbon partition coefficient (cm3/g)organic carbon content of soil (fraction)

-29-

45 m2.25 m/s2m20,250,000 cm2

Dix EO.33

0.35(HIK.i) x 41, where 41 is a units

conversion factor2.65 g/cm3

7.9 x 108 schemical-specificchemical-specificchemical-specific, or Koc x OCchemical-specificsite-specific, or 0.02

material. The equation presented below, Equation(9), is representative of a surface with "unlimitederosion potential," which is characterized by baresurfaces of finely divided material such as sandyagricultural soil with a large number ("unlimitedreservoir") of erodible particles. Such surfaceserode at low wind speeds, and particulate emissionrates are relatively time-independent at a givenwind speed.

This model was selected for use inRAGS/HHEM Part B because it represents aconservative estimate for intake of particulates; itis used to derive Equations (6) and (7) in Section3.2.2.

Using the default parameter values given inthe box for Equation (9), the default PEF is equalto 4.63 x 109 m3/kg. The default values necessaryto calculate the flux rate for an "unlimitedreservoir" surface (i.e., G, Urn' UI' and F(x)) areprovided by Cowherd (1985), and the remainingdefault values (i.e., for LS, V, and DH) are"typical" values (EPA 1986). If site-specificinformation is available, Equation (9) may bemodified to calculate a PEF that is moreappropriate for the particular site. Again, theoriginal reference should be consulted whensubstituting site-specific data to ensureapplicability of the model to speCific siteconditions.

PARTICULATE EMISSION FACTOR

PEF (m3/kg)

where:

Parameter

LS x V x DH x 3600 s/hrA

Definition (units)

x 1000 glkg0.036 x (I-G) x (UmlU,)3 x F(x)

(9)

PEFLSVDHA0.036GUmU I

F(x)

particulate emission factor (m3/kg)width of contaminated area (m)wind speed in mixing zone (m/s)diffusion height (m)area of contamination (m2

)

respirable fraction (glm2-hr)fraction of vegetative cover (unitIess)mean annual wind speed (m/s)equivalent threshold value of wind speed

at 10 m (m/s)function dependent on UmfUt (unitIess)

4.63 X 109 m3/kg45 m2.25 m/s2m2025 m2

0.036 glm2-hro4.5 m/s12.8 m/s

0.0497 (determined using Cowherd 1985)

3.4 CALCULATION ANDPRESENTATION OF RISK­BASED PRGs

The equations presented in this chapter can beused to calculate risk-based PRGs for bothcarcinogenic and noncarcinogenic effects. If botha carcinogenic and a noncarcinogenic risk-basedPRG are calculated for a particular chemical, then

-30-

the lower' of the two values is considered theappropriate risk-based PRG for any givencontaminant. The case-study box below illustratesa calculation of a risk-based PRG. A summarytable - such as that in the final case-study box ­should be developed to present both the risk-basedPRGs and the ARAR-based PRGs. The tableshould be labeled as to whether it presents theconcentrations that were developed during scopingor after the baseline risk assessment.

CASE STUDY: CALCULATE RISK-BASED PRGs·

Risk-based PRGs for ground water for isophorone, one of the chemicals detected in ground-water monitoringwells at the site, are calculated below. Initial risk-based PRGs for isophorone (carcinogenic and noncarcinogeniceffects) are derived using Equations (l ') and (2') in Section 3.1.1. Equations (1 ') and (2') combine the toxicityinformation of the chemical (oral RID of 0.2 mglkg-day and oral SF of 0.0039 [mglkg-dayr\ inhalation values arenot available and, therefore, only the oral exposure route is considered) with standard exposure parameters. Thecalculated concentrations in mgIL correspond to a target risk of 10-6 and a target HQ of 1, as follows:

Carcinogenic 1.7 x 10-4 Noncarcinogenic 73risk-based PRG 2(SFo) risk-based PRG 2/RIDo

= 1.7 x 10-4 = --lL...2(0.0039) 2/0.2

= 0.022 mgIL = 7.3 mgIL

The lower of the two values (i.e., 0.022 mgIL) is selected as the appropriate risk-based PRG. Risk-based PRGs arecalculated similarly for the other chemicals of concern.

• All information in this example is for illustration purposes only_

CASE STUDY: PRESENT PRGs DEVELOPED DURING SCOPING·

Site: XYZ Co.Location: Anytown, AnystateMedium: Ground Water

Land Use: ResidentialExposure Routes: Water Ingestion, Inhalation of

Volatiles

Risk-based PRGs(mgIL)* ARAR-based PRG

Chemical10-6 HQ = 1 Type Concentration (mgIL)

Benzene - - MCL 0.005Carbon Tetrachloride - - MCL 0.005Ethylbenzene - - MCLG 0.7***

MCL 0.7Hexane - 0.33 - -Isophorone 0.022** 7.3 - -Triallate - 0.47 - -1,1,2-Trichloroethane - - MCLG 0.003***

MCL 0.005Vinyl chloride - - MCL 0.002

All information in this example is for illustration purposes only.These concentrations were calculated using the standard default equations in Chapter 3.Of the two potential risk-based PRGs for this chemical, this concentration is the selected risk-based PRG.Of the two potential ARAR-based PRGs for this chemical, this concentration is selected as the ARAR-

based PRG.

-31-

CHAPTER 4

RISK-BASED PRGs FORRADIOACTIVE CONTAMINANTS

This chapter presents standardized exposureparameters, derivations of risk equations, and"reduced" equations for calculating risk-basedPRGs for radioactive contaminants for thepathways and land-use scenarios discussed inChapter 2. In addition, a radiation site case studyis provided at the end of the chapter to illustrate(1) how exposure pathways and radionuclides ofpotential concern (including radioactive decayproducts) are identified, (2) how initial risk-basedPRGs for radionuclides are calculated usingreduced equations based on information availableat the scoping phase, and (3) how risk-based PRGscan be re-calculated using full risk equations andsite-specific data obtained during the baseline riskassessment. Chapters 1 through 3 and AppendicesA and B provide the basis for many of theassumptions, equations, and parameters used inthis chapter, and therefore should be reviewedbefore proceeding further into Chapter 4. Also,Chapter 10 in RAGS/HHEM Part A should beconsulted for additional guidance on conductingbaseline risk assessments at sites contaminatedwith radioactive substances.

In general, standardized default exposureequations and parameters used to calculate risk­based PRGs for radionuclides are similar instructure and function to those equations andparameters developed in Chapter 3 fornonradioactive chemical carcinogens. Both typesof risk equations:

• Calculate risk-based PRGs for each carcinogencorresponding to a pre-specified target cancerrisk level of 10-6. As mentioned in Section2.8, target risk levels may be modified after thebaseline risk assessment based on site-specificexposure conditions, technical limitations, orother uncertainties, as well as on the nineremedy selection criteria specified in the NCP.

• Use standardized default exposure parametersconsistent with OSWER Directive 9285.6-03(EPA 1991b). Where default parameters are

Preceding page blank -33-

not available in that guidance document, otherappropriate reference values are used andcited.

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

There are, however, several important areas inwhich risk-based PRG equations and assumptionsfor radioactive contaminants differ substantiallyfrom those used for chemical contaminants.Specifically, unlike chemical equations, riskequations for radionuclides:

• Accept input quantities in units of activity(e.g., picocuries (pCi» rather than in units ofmass (e.g., milligrams (mg». Activity units aremore appropriate for radioactive' substancesbecause concentrations of radionuclides insample media are determined by directphysical measurements of the activity of eachnuclide present, and because adverse humanhealth effects due to radionuclide intake orexposure are directly related to the amount,type, and energy of the radiation deposited inspecific body tissues and organs.

• Consider the carcinogenic effects ofradionuclides only. EPA designates allradionuclides as Class A carcinogens based ontheir property of emitting ionizing radiationand on the extensive weight of epidemiologicalevidence of radiation-induced cancer inhumans. At most CERCLA radiation sites,potential health risks are usually based on theradiotoxicity, rather than the chemical toxicity,of each radionuclide present.

• Use cancer slope factors that are bestestimates (Le., median or 50th percentilevalues) of the age-averaged, lifetime excesstotal cancer risk per unit intake of aradionuclide (e.g., per pCi inhaled or ingested)or per unit external radiation exposure (e.g.,per microRoentgen) to gamma-emitting

Total risk SFo x Intake from ingestion ofof radionuclides

+ SFj x Intake from inhalation ofvolatile radionuclides

In the case illustrated below, risks from thetwo default exposure routes are combined, asfollows:

Total carcinogenic risk is calculated for eachradionuclide separately by combining itsappropriate oral and inhalation SFs with the twoexposure pathways for water, as follows:

Risk from ingestion of radionuclidesin water (adult)

Risk from indoor inhalation of volatileradionuclides released from water(adult)

+

Total riskfrom water

At the scoping phase, risk from indoorinhalation of volatile radionuclides is assumed tobe relevant only for radionuclides with a Henry'sLaw constant of greater than 1 x 10-5 atm-m3/moleand a molecular weight of less than 200 glmole.However, radionuclides that do not meet thesecriteria also may, under certain site-specific water­use conditions, be volatilized into the air fromwater, and thus pose significant site risks (andrequire risk-based goals). Therefore, the ultimatedecision regarding which contaminants should beconsidered must be made by the risk assessor on asite-specific basis following completion of thebaseline risk assessment.

radionuclides. Slope factors given in IRIS andHEAST have been calculated for individualradionuclides based on their unique chemical,metabolic, and radiological properties andusing a non-threshold, linear dose-responsemodel. This model accounts for the amountof each radionuclide absorbed into the bodyfrom the gastrointestinal tract (by ingestion)or through the lungs (by inhalation), thedistribution and retention of each radionuclidein body tissues and organs, as well as the age,sex, and weight of an individual at the time ofexposure. The model then averages the riskover the lifetime of that exposed individual(Le., 70 years). Consequently, radionuclideslope factors are not expressed as a function ofbody weight or time, and do not requirecorrections for gastrointestinal absorption orlung transfer efficiencies.

Risk-based PRG equations for radionuclidespresented in the following sections of this chapterare derived initially by determining the total riskposed by each radioactive contaminant in a givenpathway, and then by rearranging the pathwayequation to solve for an activity concentration setequal to a target cancer risk level of 10-6. At thescoping phase, these equations are "reduced" - andrisk-based PRGs are calculated for eachradionuclide of concern - using standardizedexposure assumptions for each exposure routewithin each pathway and land-use combination.After the baseline risk assessment, PRGs can berecalculated using full risk equations and site­specific exposure information obtained during theRI.

4.1 RESIDENTIAL LAND USE

4.1.1 GROUND WATER OR SURFACEWATER

By including appropriate exposure parameters foreach type of intake, rearranging and combiningexposure terms in the total risk equation, andsetting the target cancer risk level equal to 10-6,the risk-based PRG equation is derived as shownin Equation (10).

Under the residential land-use scenario, riskfrom ground-water or surface water radioactivecontaminants is assumed to be due primarily todirect ingestion and inhalation of volatileradionuclides released from the water to indoorair. However, because additional exposure routes(e.g., external radiation exposure due toimmersion) are possible at some sites for someradionuclides, while only one exposure route maybe relevant at others, the risk assessor alwaysshould consider all relevant exposure routes andadd or modify exposure routes as appropriate.

Equation (10'), presented in the next box, isthe reduced version of Equation (10) based on thestandard default values listed below. It is used tocalculate risk-based PRGs for radionuclides inwater at a pre-specified cancer risk level of 10-6 bycombining each radionuclide's toxicity data withthe standard default values for residential land-useexposure parameters.

After the baseline risk assessment, the riskassessor may choose to modify one or more of theexposure parameter default values or assumptions

-34-

Total risk

RW (pCiIL;risk-based)

where:

RADIONUCLIDE PRGs: RESIDENTIAL WATER - CARCINOGENIC EFFECTS

= [SFo x RW x IRw x EF x ED] + [SF; x RW x K x IRa X EF x ED]

= TREF x ED x [(SFo x IRw) + (SF; x K x IRa)]

(10)

Parameters

RWTRSFj

SFoEFEDIRaIRwK

Definition (units)

radionuclide PRG in water (pCiIL)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 (m3jday)daily water ingestion rate (Llday)volatilization factor (unitless)

Default Value

10-6

radionuclide-specificradionuclide-specific350 days/yr30 yr15 m3jday2 Llday0.0005 x 1000 LIm' (Andelman 1990)

REDUCED EQUATION FOR RADIONUCLIDE PRGs:RESIDENTIAL WATER - CARCINOGENIC EFFECTS

Risk-based PRG =(pCiIL; TR = 1O~)

where:

9.5 X 10-11 (10')

= oral (ingestion) slope factor (risk/pCi)= inhalation slope factor (risk/pCi)

in the risk equations to reflect Site-specificconditions. In this event, radionuclide PRGsshould be calculated using Equation (10) instead ofEquation (10').

4.1.2 SOIL

Under residential land-use conditions, riskfrom radionuclides in soil is assumed to be due todirect ingestion and external exposure to gammaradiation. Soil ingestion rates differ for childrenand adults, therefore age-adjusted ingestion ratefactors are used in the soil pathway equation.Calculation of the risk from the external radiationexposure route assumes that any gamma-emittingradionuclide in soil is uniformly distributed in thatsoil within a finite soil depth and density, anddispersed in an infinite plane geometry.

-35-

The calculation of external radiation exposurerisk also includes two additional factors, thegamma shielding factor (Se) and the gammaexposure time factor (Te), which can be adjusted toaccount for both attenuation of radiation fields dueto shielding (e.g., by structures, terrain, orengineered barriers) and for exposure times of lessthan 24-hours per day, respectively. Se is expressedas a fractional value between 0 and 1, delineatingthe possible risk reduction range from 0% to100%, respectively, due to shielding. The defaultvalue of 0.2 for Se for both residential andcommercial/industrial land-use scenarios reflectsthe initial conservative assumption of a 20%reduction in external exposure due to shieldingfrom structures (see EPA 1981). Te is expressed asthe quotient of the daily number of hours anindividual is exposed directly to an externalradiation field divided by the total number ofexposure hours assumed each day for a given land-

use scenario (i.e., 24 hours for residential and 8hours for commercial/industrial). The defaultvalue of 1 for Te for both land-use scenariosreflects the conservative assumptions of a 24-hrexposure duration for residential populations (i.e.,24/24 = 1) and an 8-hr exposure duration forworkers (i.e., 8/8 = 1). Values for both factors can(and, if appropriate, should) be modified by therisk assessor based on site-specific conditions.

In addition to direct ingestion of soilcontaminated with iadionuclides and exposure toexternal radiation from gamma-emittingradionuclides in soil, other soil exposure routes arepossible, such as inhalation of resuspendedradioactive particles, inhalation of volatileradionuclides, or ingestion of foodcropscontaminated by root or leaf uptake. The riskassessor should therefore identify all relevantexposure routes within the soil pathway and, ifnecessary, develop equatiOns for risk-based PRGsthat combine these exposure routes.

in soil are calculated for a pre-specified cancer risklevel of 10-6.

The age-adjusted soil ingestion factor(IFsoil/adj) used in Equation (11) takes into accountthe difference in soil ingestion for two exposuregroups - children of one to six years and all otherindividuals from. seve.n to 31 y~ars. IFsoil/adj iscalculated for radioactive contammants as shown inEquation (12). Section 3.1.2 provides additionaldiscussion on the age-adjusted soil ingestion factor.

If any parameter values or exposureassumptions are adjusted after the baseline riskassessment to reflect site-specific conditions, soilPRGs should be calculated using Equation (11).

4.2 COMMERCIAL/INDUSTRIALLAND USE

4.2.1 WATER

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

Total riskfrom soil

+

Risk from direct ingestion of radio­nuclides in soil (child to adult)

Risk from external radiation fromgamma-emitting radionuclides in soil

Under the commercial/industrial land usescenario, risk-based PRGs for radionuclides inground water (and for radionuclides in surfacewater used for drinking water purposes) are basedon residential exposures and calculated accordingto the procedures detailed in Section 4.1.1 (seeSection 3.2.1 for the rationale for this approaCh).Risk-based PRGs should be calculated consideringthe possibility that both the worker and generalpopulation at large may be exposed to the samecontaminated water supply.

Equation (11 ') is the reduced version ofEquation (11) based on the standard default valueslisted below. Risk-based PRGs for radionuclides

Adding appropriate parameters, then combiningand rearranging the equation to solve forconcentration, results in Equation (11).

Total risk for carcinogenic effects from eachradionuclide of potential concern is calculated bycombining the appropriate oral slope factor, SF0'

with the total radionuclide intake from soil, plusthe appropriate external radiation slope factor,SFe, with the radioactivity concentration in soil:

Total risk = SF0 x Intake from direct ingestionof soil

+ SF. x Concentration of gamma­emitting radionuclides in soil

-36-

4.2.2 SOIL

Under the commercial/industrial land usescenario, four soil exposure routes - directingestion, inhalation of volatile radionttclides,inhalation of resuspended radioactive particulates,and external exposure due to gamma-emittingradionuclides - are combined to calculate risk­based radionuclide PRGs in soil for adult workerexposures. Additional exposure routes (e.g.,ingestion of foodcrops contaminated byradionuclide uptake) are possible at some sites,while only one exposure route (e.g., externalradiation exposure only) may be relevant at others.The risk assessor should therefore consider andcombine all relevant soil exposure routes, asnecessary and appropriate, based on site-specificconditions.

RADIONUCLIDE PRGs: RESIDENTIAL SOIL - CARCINOGENIC EFFECTS

TR(SFo X 10-

3 x EF x IFsoiVadj) + (SFe x 103 x ED x D x SD x (l-Se) x Te)

RS x [(SFo x 1O-3g1mg x EF X IFsoi,/adj) + (SFe x 103g!kg x ED x D x SD x (l-Se) x Te)]Total risk =

RS (pCi/g; =risk-based)

where:

Parameters

RSTRSFo

SFeEFED

IFsoiVadjDSD

SeTe

Definition (units)

radionuclide PRG 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 (dayslyr)exposure duration (yr)age-adjusted soil ingestion factor (mg-yr/day)depth of radionuclides in soil (m)soil density (kglm3

)

gamma shielding factor (unitless)gamma exposure time factor (unitless)

Default Value

10-6

radionuclide-specificradionuclide-specific350 dayslyr30 yr3600 mg-yr/day (see Equation (12))0.1 m1.43 x 10

3 kglm3

0.2 (see Section 4.1.2)1 (see Section 4.1.2)

(11)

REDUCED EQUATION FOR RADIONUCLIDE PRGs:RESIDENTIAL SOIL - CARCINOGENIC EFFECTS

Risk-based PRG(pCi/g; TR = 10-6)

where:

= 1 X 10-6

1.3 X 103 (SFo) + 3.4 x 106 (SFe)

(11 ')

= oral (ingestion) slope factor (risk/pCi)= external exposure slope factor (risk/yr per pCi/m2

)

AGE-ADJUSTED SOIL INGESTION FACTOR

IFsoiVadj (mg-yr/day) =

where:

(IRsoiVage 1-6 X EDage 1-6) + (IRsoiVage 7-31 X EDage 7-31) (12)

Parameters

IFsoiVadjIRsoivage 1-6

IRsoiVage 7-31

EDage 1-6

EDage 7-31

Definition (units)

age-adjusted soil ingestion factor (mg-yr/day)ingestion rate of soil ages 1-6 (mglday)ingestion rate of soil ages 7-31 (mglday)exposure duration during ages 1-6 (yr)exposure duration during ages 7-31 (yr)

-37-

Default Value

3600 mg-yr/day200 mglday100 mglday6 yr24 yr

In the case illustrated below, total risk fromradionuclides in soil is calculated as the summationof the individual risks from each of the fourexposure routes listed above:

Total riskfrom soil

= Risk from direct ingestion of radio­nuclides in soil (worker)

4.2.3 SOIL-TO-AIR VOLATILIZATIONFACTOR

The VF, defined in Section 3.3.1 for chemicals,also applies for radioactive contaminants with thefollowing exceptions.

+ Risk from inhalation of volatileradionuclides (worker)

+ Risk from inhalation of resuspendedradioactive particulates (worker)

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

Total risk for carcinogenic effects for eachradionuclide is calculated by combining theappropriate ingestion, inhalation, and externalexposure SF values with relevant exposureparameters for each of the four soil exposureroutes as follows:

Total = SFo x Intake from direct ingestion ofrisk radionuclides in soil (worker)

+ SFj x Intake from inhalation ofvolatile radionuclides (worker)

+ SFj x Intake from inhalation of resus­pended radioactive particulates(worker)

+ SFe x Concentration ofgamma-emittingradionuclides in soil (worker)

Adding appropriate parameters, and thencombining and rearranging the equation to solvefor concentration, results in Equation (13).

Equation (13') below is the reduced version ofEquation (13) based on the standard default valuesbelow and a pre-specified cancer risk level of 10-6.

It combines the toxicity information of aradionuclide with standard exposure parameters forcommercial/industrial land use to generate theconcentration of that radionuclide correspondingto a 10-6 carcinogenic risk level due to thatradionuclide.

If any parameter default values or assumptionsare changed after the baseline risk assessment to

reflect site-specific conditions, radionuclide soilPRGs should be derived using Equation (13).

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• Most radionuclides are heavy metal elementsand are non-volatile under normal, ambientconditions. For these radionuclides, VF valuesneed not be calculated and the risk due to theinhalation of volatile forms of these nuclidescan be ignored for the purposes ofdetermining 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 undercertain chemical or environmental conditions,such as when they are combined chemicallywith volatile organic compounds (i.e., the so­called radioactively-labeled or "tagged" organiccompounds), or when they can ,exist in theenvironment in a variety of physical forms,such as C-14 labeled carbon dioxide (C02) gasand tritiated water vapor. For theseradionuclides, VF values should be calculatedusing the Hwang and Falco (1986) equationprovided in Section 3.3.1 based on thechemical species of the compound with whichthey are associated.

• The naturally occurring, non-volatileradioisotopes of radium, namely Ra-226 andRa-224, undergo radioactive decay and forminert, gaseous isotopes of radon, i.e., Rn-222(radon) and Rn-220 (thoron), respectively.Radioactive radon and thoron gases emanatefrom their respective parent radium isotopesin soil, escape into the air, and can posecancer risks if inhaled. For Ra-226 and Ra­224 in soil, use the default values shown in thebox on page 40 for VF and for SFi inEquation (12) and Equation (12 ').

4.3 RADIATION CASE STUDY

This section presents a case study of ahypothetical CERCLA radiation site, the ACMERadiation Co. site, to illustrate the process ofcalculating pathway-specific risk-based PRGs forradionuclides using the risk equations andassumptions presented in the preceding sections ofthis chapter. The radiation site case study ismodeled after the XYZ Co. site study discussed ;n

RADIONUCLIDE PRGs: COMMERCIAUINDUSTRIAL SOIL - CARCINOGENIC EFFECTS

Total = RS x ED x [(SFo x 1O-3g1mg x EF x IRsoil) + (SF; x 103g1kg x EF x IRa;r x 1NF)risk

+ (SF; x 103g1kg x EF x IRa;r x l/PEF) + (SFe x 103g1kg x D x SD x (l-Se) x Te)]

RS =(pCi/g;risk-based)

where:

TR (13)

Parameters

RSTRSF;SFoSFeEFEDIRair

IRsoil

VFPEFDSDSeTe

Definition (units)

radionuclide PRG in soil (pei/g)target excess individual lifetime cancer risk (unitless)inhalation slope factor (risk/pei)oral (ingestion) slope factor (risk/pCi)external exposure slope factor (riskiyr per pCi/m2)

exposure frequency (dayslyr)exposure duration (yr)workday inhalation rate of air (m3/day)daily soil ingestion rate (mglday)soil-to-air volatilization factor (m3/kg)particulate emission factor (m3/kg)depth of radionuclides in soil (m)soil density (kglm3)

gamma shielding factor (unitless)gamma exposure factor (unitless)

Default Value

10-6radionuclide-specificradionuclide-speciticradionuclide-specific250 dayslyr25 yr20 m3/day50 mgldayradionuclide-specific (see Section 4.2.3)4.63 x 109 m3/kg (see Section 3.3.2)0.1 m1.43 x 103 kglm3

0.2 (see Section 4.1.2)1 (see Section 4.1.2)

REDUCED EQUATION FOR RADIONUCLIDE PRGs:COMMERCIAUINDUSTRIAL SOIL - CARCINOGENIC EFFECTS*

Risk-based PRG =(pCi/g; TR = 10-6)

where:

1 X 10-6 (13 ')

= oral (ingestion) slope factor (risk/pei)= inhalation slope factor (risk/pei)= external eA-pDSure slope factor (riskiyr per pCi/m2

)

= radionuclide-specific soil-to-air volatilization factor in m3/kg (see Section 3.3.1)

*NOTE: See Section 4.2.3 when calculating PRGs for Ra-226 and Ra-224.

Chapters 2 and 3. It generally follows a two-phaseformat which consists of a "at the scoping stage"phase wherein risk-based PRGs for radionuclidesof potential concern are calculated initially usingreduced equations based on PA/SI data, and thena second, "after the baseline risk assessment" phasewherein radionuclide PRGs are recalculated using

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full equations and modified site-specific parametervalues based on RIfFS data.

Following an overview of the history andcurrent status of the site presented in Section 4.3.1,Section 4.3.2 covers a number of important stepstaken early in the scoping phase to calculatepreliminary risk-based PRGs assuming a specific

SOIL DEFAULT VALUES FOR VF AND SF,FOR Ra-226 AND Ra-224

Default VF InhalationValue Slope

(~ ) Factor, SFj

Radium pCildRn* (risk/pCi)**

Ra-226 8 l.lE-ll

Ra-224 200 4.7E-ll

* Calculated using values taken from NCRP1976 and UNSCEAR 1982: Assumptions: (1) anaverage Ra-226 soil concentration of 1 pCi/gassociated with an average ambient Rn-222 airconcentration of 120 pCi/m3 and (2) an averageRa-224 soil concentration of 1 pCi/g associatedwith an average ambient Rn-220 air concentrationof 5 pCi/m3

.

** Slope factor values are for Rn-222 (plusprogeny) and for Rn-220 (plus progeny).

land-use scenario. Section 4.3.3 then discusses howinitial assumptions and calculations can bemodified when additional site-specific informationbecomes available.

4.3.1 SITE HISTORY

The ACME Radiation Co. site is anabandoned industrial facility consisting of a largefactory building situated on ten acres of landsurrounded by a high-density residentialneighborhood. Established in 1925, the ACMECo. manufactured luminous watch dials and gaugesusing radium-based paint and employedapproximately 100 workers, mostly women. Withthe declining radium market, ACME phased outdial production and expanded its operations in1960 to include brokering (collection and disposal)of low-level radioactive waste (LLW). After thecompany was issued a state license in 1961, ACMEbegan receiving LLW from various nearbyhospitals and research laboratories. In 1975, actingon an anonymous complaint of suspectedmishandling of radioactive waste, state officialsvisited the ACME Co. site and cited the companyfor numerous storage and disposal violations.After ACME failed to rectify plant conditionsidentified in initial and subsequent citations, thestate first suspended, and then later revoked itsoperating license in 1978. Around the same time,

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officials detected radium-226 (Ra-226)contamination at a few neighboring locations offsite. However, no action was taken against thecompany at that time. When ACME filed forbankruptcy in 1985, it closed its facility beforecompleting cleanup.

In 1987, the state and EPA conducted anaerial gamma survey over the ACME RadiationCo. site and surrounding properties to investigatethe potential extent of radioactive contaminationin these areas. The overflight survey revealedseveral areas of elevated exposure rate readings,although individual gamma-emitting radionuclidescould not be identified. When follow-up groundlevel surveys were performed in 1988, numerous"hot spots" of Ra-226 were pinpointed at variouslocations within and around the factory building.Three large soil piles showing enhancedconcentrations of Ra-226 were discovered alongthe southern border. Approximately 20 rustingdrums labelled with LLW placards also werediscovered outside under a covered storage area.Using ground-penetrating radar, EPA detectedsubsurface magnetic anomalies in a few locationswithin the property boundary which suggested thepossibility of buried waste drums. Based oninterviews with people living near the site and withformer plant workers, the state believes thatradium contaminated soil may have been removedfrom the ACME site in the past and used locallyas fill material for the construction of new homesand roadbeds. Site access is currently limited (butnot entirely restricted) by an existing securityfence.

In 1988, EPA's regional field investigationteam completed a PNSI. Based on the PNSIdata, the ACME Radiation Co. site scored above28.50 using the HRS and was listed on theNational Priorities List in 1989. Early in 1990, anRIfFS was initiated and a baseline risk assessmentis currently in progress.

4.3.2 AT THE SCOPING PHASE

In this subsection, several steps are outlined toshow by example how initial site data are used atthe scoping phase to calculate risk-based PRGs forradionuclides in specific media of concern.Appropriate sections of Chapters 2 and 3 shouldbe consulted for more detailed explanations foreach step considered below.

Identify Media of Concern. A large streamruns along the western border of the site and feedsinto a river used by some of the local residents forfishing and boating. Supplemental water intakeducts for the municipal water treatment plant arelocated approximately 300 yards downriver, and thesite is situated over an aquifer which serves as theprimary drinking water supply for a community ofapproximately 33,000 people.

Analyses of ground water, soil, and streamsediment samples taken during the PNSI revealedsignificant levels of radionuclide contamination.Potential sources of contamination include the soilpiles, process residues in soil, and radionuclidesleaking from buried drums. Air filter samples andsurface water samples from the stream and rivershowed only background levels of activity.(Background concentrations were determined fromanalyses conducted on a limited number of air,ground water, surface water, and soil samplescollected approximately one mile from the site.)

The data show that the media of potentialconcern at this site include ground water and soil.Although stream water and river water were notfound to be contaminated, both surface waterbodies may become contaminated in the future dueto the migration of radionuclides from sediment,from the exposed soil piles, or from leaking drums.Thus, surface water is another medium of potentialconcern.

For simplicity, only soil will be discussed asthe medium of concern during the remainder ofthis case study. Procedures discussed for thismedium can nevertheless be applied in a similarmanner to all other media of concern.

Identify Initial List of Radionuclides ofConcern. The PNSI for the ACME Radiation Co.site identified elevated concentrations of fiveradionuclides in soil (Ra-226, tritium (H-3),carbon-14 (C-14), cesium (Cs-137), and strontium(Sr-9O». These comprise the initial list ofradionuclides of potential concern.

Site records indicate that radioisotopes ofcobalt (Co-60), phosphorus (P-32), sulfur (S-35),and americium (Am-241 and Am-243) wereincluded on the manifests of several LLW drums inthe storage area and on the manifests of otherdrums suspected to be Imried onsite. Therefore,although not detected in any of the initial soilsamples analyzed, CO-60, P-32, S-35, Am-241, and

-41-

Am-243 are added to the list for this mediumbecause of their potential to migrate from leakingburied drums into the surrounding soil.

Identify Probable Land Uses. The ACMERadiation Co. site is located in the center of arapidly developing suburban community comprisedof single and multiple family dwellings. The areaimmediately encircling the site was recently re­zoned for residential use only; existing commercialand light industrial facilities are currently beingrelocated. Therefore, residential use is determinedto be the most reasonable future land use for thissite.

Identify Exposure Pathways, Parameters, andEquations. During the scoping phase, availablesite data were neither sufficient to identify allpossible exposure pathways nor adequate enoughto develop site-specific fate and transportequations and parameters. Therefore, in order tocalculate initial risk-based PRGs for radionuclidesof potential concern in soil, the standardizeddefault soil exposure equation and assumptionsprovided in this chapter for residential land use inSection 4.1.2 are selected. (Later in this case study,examples are provided to illustrate how the fullrisk equation (Equation (11» and assumptions aremodified when baseline risk assessment databecome available.)

For the soil pathway, the exposure routes ofconcern are assumed to be direct ingestion of soilcontaminated with radionuclides and exposure to

external radiation from gamma-emittingradionuclides. Again, although soil is the onlymedium discussed throughout this case study,exposure pathways, parameters, equations, andeventually risk-based concentrations would need tobe identified and developed for all other media andexposure pathways of potential concern at anactual site.

Identify Toxicity Information. To calculatemedia-specific risk-based PRGs, reference toxicityvalues for radiation-induced cancer effects arerequired (Le., SFs). As stated previously, soilingestion and external radiation are the exposureroutes of concern for the soil pathway. Toxicityinformation (i.e., oral, inhalation, and externalexposure SFs) for all radionuclides of potentialconcern at the ACME Radiation Co. site areobtained from IRIS or HEAST, and are shown inthe box on the following page.

~N,

RADIATION CASE STUDY:TOXICI1Y INFORMATION FOR RAmONUCLIIJES OF POTENTIAL CONCERN'"

Radioactive ICRI> Inhalation Ingestion External ExposureHalf-life Decay Lung Slope Factor Slope Factor Slope Factor

Radionuclides (yr) Mode Classification (risk/pCi) (risk/pCi) (risklyr per pCi/m~)

B-3 12 beta g 7.8E-14 5.5E-14 NA

C-14 5730 beta 0 6.4E-15 9.1E-13 NA"

P-32 0.04 helil D 3.0E-12 3.5E-12 NA

S-35 0.24 heta D 1.91'.-13 2.21'.-13 NA

Co-GO 5 hcta/gal11l11il Y 1.(,f~-1O 1.5E-ll 1.31:-10

Sr-90 29 beta D 5.GE-ll 3.3E-ll NA

Cs-137 30 beta D 1.9E-11 2.8E-ll NA

Ra-22(, I()()O alpha/gamma W 3.0E-0<) 1.2E-lO 4.2E-13

Am-24 I 432 alpha/gamma W 4.0E-08 3.1E-lO 1.6E-12

Am-243 7380 alpha/gamma W 4.0E-08 3.1E-lO 3.6E-12

... Sources: BEAST and Federal Guidance Report No. 11. All information in this example is for illustration only.

NA = Not applicable (i.e., these radionuclides arc not gamma-emitters and the direct radiation exposure pathway can be ignored).

Calculate Risk-based PRGs. At this step, risk­based PRGs are calculated for each radionuclide ofpotential concern using the reduced risk Equation(11 ') in Section 4.1.2, SF values obtained fromIRIS and HEAST, and standardized default valuesfor parameters for the residential land-usescenario. To calculate the risk-based PRG for Co­60 at a pre-specified target risk level of 10,6, forexample, its ingestion SF of 1.5 x 10,11 and itsexternal exposure SF of 1.3 x 10,10 are substitutedinto Equation (11 '), along with the standardizeddefault values, as follows:

RADIATION CASE STUDY:INITIAL RISK-BASED PRGs FOR

RADIONUCLIDES IN SOIL·

Risk-based PRG =for Co-60(pCi/g; TR = 1O~)

1 X 10.6

Radionuclides

H-3Sr-90 (only)P-32S-35C-14Co-60Cs-137 (only)Ra-226 (only)Am-241Am-243 (only)

Risk-based Soil PRG (pei/g)

14,00023

2203,500

8500.002

270.60.27.9 x 10.2

where:

SFo = oral (ingestion) slope factor for Co-60 = 1.5 x10.11 (risk/pei)

SF. = external exposure slope factor for Co-60 = 1.3x 10-10 (risklyr per pCi/m2)

Substituting the values for SF and SF for Co-60o einto Equation (11 ') results in:

Risk-based PRG for Co-60 (pCi/g; TR = 10~) ==

[(1.3 X 103 )(1.5 x 10.11) + (3.4 x 106)(1.3 x 1O.1~1

= 0.002 pCi of Co-60/g of soil

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

4.3.3 AFfER THE BASELINE RISKASSESSMENT

In this subsection, several steps are outlinedwhich demonstrate how Site-specific data obtainedduring the baseline risk assessment can be used torecalculate risk-based PRGs for radionuclides insoil. Appropriate sections of Chapters 2 and 3should be consulted for more detailed explanationsfor each step considered below.

Review Media of Concern. During the RIfFS,gamma radiation surveys were conducted in theyards of several homes located within a two-blockradius of the ACME Radiation Co. site. Elevatedexposure rates, ranging from approximately two tofour times the natural background rate, were

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* calculated for illustration only using Equation(11 ') in Section 4.1.2. Values have been roundedoff.

measured on properties immediately bordering thesite. Measurements onsite ranged from 10 to 50times background. In both cases, enhanced soilconcentrations of Ra-226 (and decay products) andseveral other gamma-emitting radionuclides werediscovered to be the sources of these elevatedexposure rates. Therefore, soil continues as amedium 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 elevatedconcentrations in soil samples collected at theACME Radiation Co. site. These made up theinitial list of radionuclides of potential concern.Although not detected during the first round ofsampling, five additional radionuclides (P-32, S-35,Co-60, Am-241, and Am-243) were added to thislist because of their potential to migrate fromburied leaking drums into the surrounding soil.

With additional RIIFS data, someradionuclides are now added to the list, whileothers are dropped. For example, soil analysesfailed to detect P-32 (14-day half-life) or S-35 (87­day half-life) contamination. Decay correctioncalculations strongly suggest that theseradionuclides should not be present onsite indetectable quantities after an estimated burial timeof 30 years. Therefore, based on these data, P-32and S-35 are dropped from the list. Soil data alscconfirm that decay products of Ra-226, Sr-90, Cs­137, and Am-243 (identified in the first box below)

are present in secular equilibrium (Le., equalactivity concentrations) with their respective parentisotopes.

Assuming secular equilibrium, slope factors forthe parent isotope and each of its decay seriesmembers are summed. Parent isotopes aredesignated with a "+0" to indicate the composite

slope factors of its decay chain (shown in bold facein the second box below). Thus, Ra-226+ 0, Sr­90+0, Cs-137+0, and Am-243+0 replace theirrespective single-isotope values in the list ofradionuclides of potential concern, and theircomposite SFs are used in the full soil pathwayequation to recalculate risk-based concentrations.

RADIATION CASE STUDY: DECAY PRODUCTS

Parent Radionuclide Decay Product(s) (Half-life)

Ra-226 Rn-222 (4 days), Po-218 (3 min), Pb-214 (27 min), Bi-214 (20min), Po-214 « 1 s), Pb-21O (22 yr), Bi-21O (5 days), Po-21O

(138 days)

Sr-9O Y-90 (14 hr)

Cs-137 Ba-137m (2 min)

Am-243 Np-239 (2 days)

RADIATION CASE STUDY: SLOPE FACTORS FOR DECAY SERIES·

Slope FactorsDecay Series Inhalation Ingestion External

Ra-226 3.0E-09 1.2E-1O 4.2E-13Rn-222 7.2E-13 2.2E-14Po-218 5.8E-13 2.8£-14 0.0£+00Pb-214 2.9£-12 1.8£-13 1.5£-11Bi-214 2.2£-12 1.4£-13 8.0£-11Po-214 2.8E-19 1.0£-20 4.7£-15Pb-21O 1.7£-09 6.5£-10 1.8£-13Bi-21O 8.1£-11 1.9£-12 0.0£+00Po-21O 2.7£-09 2.6£-10 4.8£-16Ra-226+D 7.5E-09 l.OE-09 9.6E-ll

Sr-9O 5.6£-11 3.3£-11 0.0£+00Y-9O 5.5£-12 3.2£-12 0.0£+00Sr-90+D 6.2E-ll 3.6E-11 O.OE+OO

Cs-137 1.9£-11 2.8E-11 0.0£+00Ba-137m 6.0£-16 2.4£-15 3.4£-11Cs-137+D 1.9E-ll 2.8E-ll 3.4E-ll

Am-243 4.0£-08 3.1£-10 3.6£-12Np-239 1.5£-12 9.3£-13 1.1£-11Am-243+D 4.0E-08 3.IE-IO 1.5E-ll

• All information in this example is for illustration purposes only.

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Review Land-use Assumptions. At this step,the future land-use assumption chosen duringscoping is reviewed. Since the original assumptionof future residential land use is supported by RIffSdata, it is not modified.

Modify Exposure Pathways, Parameters, andEquations. Based on site-specific information, theupper-bound residence time for many of theindividuals living near the ACME Radiation Co.site is determined to be 45 years rather than thedefault value of 30 years. Therefore, the exposureduration parameter used in Equation (11) inSection 4.1.2 is substituted accordingly. It is alsodetermined that individuals living near the site areonly exposed to the external gamma radiation fieldapproximately 18 hours each day, and that theirhomes provide a shielding factor of about 0.5 (Le.,50%). Therefore, values for Te and Se are changedto 0.75 (Le., 18 hr124 hr) and 0.5, respectively.

Modify Toxicity Information. As discussedabove in the section on modifying the list ofradionuclides of concern, oral, inhalation, andexternal 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 seriesmembers that are in secular equilibrium.

Recalculate Risk-based PRGs. At this step,risk-based PRGs are recalculated for all remainingradionuclides of potential concern using the fullrisk equation for the soil pathway (Le., Equation(11)) modified by revised site-specific assumptionsregarding exposures, as discussed above.

To recalculate the risk-based PRG for Co-60at a pre-specified target risk level of 10-6, forexample, its ingestion SF of 1.5 x 10-11 , and itsexternal exposure SF of 1.3 x lOc10 are substitutedinto Equation (11), along with other site-specificparameters, as shown in the next box.

In a similar manner, risk-based PRGs can berecalculated for all remaining radionuclides ofpotential concern in soil at the ACME RadiationCo. site. These revised PRGs are presented in thebox on the next page. In those cases wherecalculated risk-based PRGs for radionuclides arebelow current detection limits, risk assessorsshould contact the Superfund Health RiskTechnical Support center for additional guidance.

RADIATION CASE STUDY: REVISED RISK EQUATION FOR RESIDENTIAL SOIL

RS for Co-60 (pCi/g; =risk· based)

=where:

TR

0.003 pCi/g

Parameters

RSTRSFo

SF.EFED

IFsoiVadj

DSDS.T.

Definition (units)

radionuclide PRG in soil (pCi/g)target excess individual lifetime cancer risk (unitles.<;)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 (kglm3

)

gamma shielding factor (unitless)gamma exposure time factor (unitless)

Revised Value

10-6

1.5 X 10-11 (risk/pCi)1.3 x 10-10 (risk/yr per pCi/m2)

350 days/yr45 yr5100 mg-yr/day0.1 m1.43 x 1W kglm3

0.50.75

(Note: To account for the revised upper-bound residential residency time of 45 years, the age-adjusted soilingestion factor was recalculated using the equation in Section 4.1.2 and an adult exposure duration of 39 yearsfor individuals 7 to 46 years of age.)

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RADIATION CASE STUDY:REVISED RISK-BASED PRGs FOR RADIONUCLIDES IN SOIL*

Radionuclides

H-3Sr-90+DC-14Co-60Cs-137+DRa-226+DAm-241Am-243+D

Risk-based Soil PRG (pCi/g)

10,20020

6200.0030.010.0040.20.03

* Calculated for illustration only. Values have been rounded off.

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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 ParticulateEmissions from Surface Contamination. Prepared for EPA Office of Health and Environmental Assessment.EPN600/8-85/002.

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

EPA 1984. Evaluation and Selection ofModels for EstimatingAir Emissions from Hazardous Waste Treatment,Storage, and Disposal Facilities. Office of Air Quality Planning and Standards. EPN450/3-84/020.

EPA 1986. Development of Advisory Levels for PCBs Cleanup. Office of Health and EnvironmentalAssessment. EPN600/21.

EPA 1988a. CERCLA Compliance With Other Laws Manual, Part I (Interim Final). Office of Emergencyand Remedial Response. EPN540/G-89/006 (OSWER Directive #9234.1-01).

EPA 1988b. Estimating Exposures to 2,3,7,8-TCDD (External Review Draft). Office of Health andEnvironmental Assessment. EPN600/6-88/005A

EPA 1988c. Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA. InterimFinal. Office of Emergency and Remedial Response. EPN540/G-89/004 (OSWER Directive #9355.3-01).

EPA 1988d. Guidance on RemedialActions for Contaminated Ground Water at Superfund Sites. Interim Final.Office of Emergency and Remedial Response. EPN540/G-88/003 (OSWER Directive #9283.1-2).

EPA 1988f. Superfund Exposure Assessment Manual. Office of Emergency and Remedial Response.EPN540/l-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 AirAct and Other EnvironmentalStatutes and State Requirements. Office of Emergency and Remedial Response. EPN540/G-89/009 (OSWERDirective #9234.1-01).

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

EPA 1989c. Methods fbr Evaluating the Attainment ofCleanup 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. EPN540/l-89/002.

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

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EPA. 1990b. Guidance for Data Usability in Risk Assessment. Office of Solid Waste and EmergencyResponse. EPN540/G-90/008 (OSWER Directive #9285.7-05).

EPA. 1990c. Guidance on RemedialActions for Superfund Sites with PCB Contamination. Office of Emergencyand Remedial Response. EPN540/G-90/007 (OSWER Directive #9355.4-01).

EPA. 199Od. "National Oil and Hazardous Substances Pollution Contingency Plan (Final Rule)." 40 CFRPart 300; 55 Federal Register 8666.

EPA. 1991a. Conducting Remedial Investigations/Feasibility Studies for CERCLA Municipal Landfill Sites.Office of Emergency and Remedial Response. EPN540/P-91/001 (OSWER Directive #9355.3-11).

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

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

EPA. 1991d. Risk Assessment Guidance for Superfund: Volume I - Human Health Evaluation Manual (PanC, Risk Evaluation ofRemedialAlternatives). Interim. Office of Emergency and Remedial Response. OSWERDirective 9285.7-01C.

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

Hwang, S.T., and Falco, l.W. 1986.. Estimation ofMultimedia Exposures Related to Hazardous Waste Facilities.Cohen, Y. (ed). Plenum Publishing Corp.

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APPENDIX A

ILLUSTRATIONS OF CHEMICALSTHAT "LIMIT" REMEDIATION

In many cases, one or two chemicals will drivethe cleanup at a site, and the resulting cumulativemedium or site risk will be approximately equal tothe potential risk associated with the individualremediation goals for these chemicals. These"limiting chemicals" are generally either chemicalsthat are responsible for much of the baseline risk(because of either high toxicity or presence in highconcentrations), or chemicals that are leastamenable to the selected treatment method. Bycleaning up these chemicals to their goals, theother chemicals typically will be cleaned up tolevels much lower than their corresponding goals.The example given in the box below provides asimple illustration of this principle.

The actual circumstances for mostremediations will be much more complex thanthose described in the example (e.g., chemicals willbe present at different baseline concentrations and

will be treated/removed at differing rates);however, the same principle of one or perhaps twochemicals limiting the site cleanup usually applies,even in more complex cases.

Unless much is known about the performanceof a remedy with respect to all the chemicalspresent at the site, it may not be possible todetermine which of the site contaminants will drivethe final risk until well into remedyimplementation. Therefore, it generally is notpossible to predict the cumulative risk that will bepresent at the site during or after remediation. Insome situations, enough will be known about thesite conditions and the performance of the remedyto estimate post-remedy concentrations ofchemicals or to identify the chemical(s) that willdominate the residual risk. If this type ofinformation is available, it may be necessary tomodify the risk-based remediation goals forindividual 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 ugIL, which is associated with apotential risk of 100{). Chemical B's goal is 10 ugIL, which is also associated with a potential risk of 100{). Thecalculated cumulative risk at remediation goals is therefore 2 x 100{). Assuming for the purposes of this illustrationthat 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 theconcentration of A reaches 0.5 ugIL, then remediation is complete. A is at its goal and has a risk of 100{). B is at1/20 of its goal with a risk of 5 x 10-8. The total risk (1 x 100{) + 5 X 10-8) is approximately 100{) and is due to thepresence of A

This example illustrates that the final risk for a chemical may not be equal to the potential risk associated withits remediation goal, and, in fact, can be much less than this risk. Although the potential risk associated withChemical B's goal is 100{), the final residual risk associated with B is 5 X 10-8. Thus, if one were to calculate thecumulative risk at PRGs prior to remedy implementation, one would estimate total medium risk of 2 x 100{), however,the residual cumulative risk after remediation is 1 x 100{).

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APPENDIXB

RISK EQUATIONS FOR INDIVIDUALEXPOSURE PATHWAYS

This appendix presents individual riskequations for each exposure pathway presented inChapter 3. These individual risk equations can beused and rearranged to derive full risk equationsrequired for calculating risk-based PRGs.Depending on the exposure pathways that are ofconcern for a land-use and medium combination,different individual risk equations can be combinedto derive the full equation reflecting thecumulative risk for each chemical within themedium. See Chapter 3 for examples of howequations are combined and how they need to berearranged to solve for risk-based PRGs. Notethat in this appendix, the term HQ is used to referto the risk level associated with noncarcinogeniceffects since the equations are for a singlecontaminant in an individual exposure pathway.

The following sections list individual riskequations for the ground water, surface water, andsoil pathways. Risk equations for exposurepathways not listed below can be developed andcombined with those listed. In particUlar, dermalexposure and ingestion of ground watercontaminated by soil leachate, for which guidance

is currently being developed by EPA, could beincluded in the overall exposure pathwayevaluation.

B.I GROUND WATER ORSURFACE WATER­RESIDENTIAL LAND USE

Both the ingestion of water and the inhalationof volatiles are included in the standard defaultequations in Section 3.1.1. If only one of theseexposure pathways is of concern at a particularsite, or if one or both of these pathways needs tobe combined with additional pathways, a site­specific equation can be derived.

The parameters used in the equationspresented in the remainder of this section areexplained in the following text box.

B.l.l INGESTION

The cancer risk due to ingestion of acontaminant in water is calculated as follows:

PARAMETERS FOR SURFACE WATER/GROUND WATER - RESIDENTIAL LAND USE

Parameter

CSFj

SFoRfDoRfD j

BWAT

EFEDKIRaIRw

Definition

chemical concentration in water (mgIL)inhalation cancer slope factor «mglkg-day)"l)oral cancer slope factor «mglkg-day)"l)oral chronic reference dose (mglkg-day)inhalation chronic reference dose (mglkg-day)adult body weight (kg)averaging time (yr)

exposure frequency (days/yr)exposure duration (yr)volatilization factor (L/m3

)

daily indoor inhalation rate (m3/day)daily water ingestion rate (Llday)

Default Value

chemical-specificchemical-specificchemical-specificchemical-specific70 kg70 yr for cancer risk30 yr for noncancer HI (equal to ED)350 days/yr30 yr0.0005 x 1000 Llm3 (Andelman 1990)15 m3/day2 L/day

Preceding page blank -51-

The noncancer HQ due to ingestion of acontaminant in water is calculated as follows:

Risk from ingestion = §E, xof water (adult)

HQ due to ingestionof water (adult)

C x IRw x EFx EDBW x AT x 365 dayslyr

C x IRw x EFx EDRfDox BWxATx365 dayslyr

and/or inhalation of particulates, are of concern ata particular site, then a site-specific equation canbe derived.

The parameters used in the equationspresented in the remainder of this section areexplained in the text box below.

B.1.2 INHALATION OF VOLATILES

The cancer risk due to inhalation of a volatilecontaminant in water is calculated as follows:

B.2.l INGESTION OF SOIL

The cancer risk from ingestion ofcontaminated soil is calculated as follows:

The noncancer HQ from ingestion ofcontaminated soil is calculated as follows:

Risk frominhalationof volatilesin water(adult)

SF; x C x K x IRa X EF x EDBW x AT x 365 dayslyr

Risk fromingestionof soil

= SF.o x ex 10-6 kglmg x EF X IFsoiVadj

AT x 365 dayslyr

The noncancer HQ due to inhalation of a volatilecontaminant in water is calculated as follows:

The cancer risk caused by inhalation ofvolatiles released from contaminated soil is:

HQ fromingestionof soil

HQ due toinhalationof vOlatilesin water(adult)

= C x K x IR.xEFxEDRfD; x BW x AT x 365 dayslyr

B.2.2

= ex 10-6 kglmg x EF X IFsoiVadj

RfDo x AT x 365 dayslyr

INHALATION OF VOLATILES

B.2 SOIL - RESIDENTIAL LANDUSE

Only the first exposure pathway below ­ingestion of soil - is included in the standarddefault equations in Section 3.1.2. If additionalexposure pathways, including inhalation ofvolatiles

Risk from = SF; x C x ED x EF X lR.ir X (INF)inhalation AT x BW x 365 dayslyrof volatiles

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

PARAMETERS FOR SOIL - RESIDENTIAL LAND USE

Parameter

CSF;SFoRfDoRfD;BWAT

EFEDIRa

IFso;Vadj

VFPEF

Definition

chemical concentration in soil (mglkg)inhalation cancer slope factor «mglkg-dayr1

)

oral cancer slope factor «mglkg-dayr1)

oral chronic reference dose (mglkg-day)inhalation chronic reference dose (mglkg-day)adult body weight (kg)averaging time (yr)

exposure frequency (dayslyr)exposure duration (yr)daily indoor inhalation rate (m3/day)age-adjusted soil ingestion factor (mg-yr/kg-day)soil-to-air VOlatilization factor (m3/kg)particulate emission factor (m3/kg)

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Default Value

chemical-specificchemical-specificchemical-specificchemical-specific70 kg70 yr for cancer risk30 yr for noncancer HI (equal to ED)350 dayslyr30 yr15 m3/day114 mg-yr/kg-daychemical specific (see Section 3.3.1)4.63 x 109 m3/kg (see Section 3.3.2)

B.2.3 INHALATION OF PARTICULATES

HQ frominhalationof volatiles

= C x ED x EF x IRair x OIVF)RtDi x BW x AT x 365 dayslyr

B.3.l INGESTION OF SOIL

The cancer risk from ingestion ofcontaminated soil is calculated as follows:

Cancer risk due to inhalation ofcontaminated soil particulates is calculated as:

Risk fromingestionof soil

= SE, x C X W-6 kglmg x EF x ED x IRsojlBW x AT x 365 dayslyr

B.3.2 INHALATION OF VOLATILES

The noncancer HQ from ingestion of contaminatedsoil is calculated as follows:

Risk = SFj x C x ED x EF x IRai, x O/PEF)from AT x BW x 365 dayslyrinhala-tion ofparticulates

The noncancer HQ from particulate inhalation iscalculated using this equation:

HQfrom =ingestionof soil

C X 10-6 kglmg x EF x ED x IRsoilRtDo x BW x AT x 365 dayslyr

B.3 SOIL - COMMERCIAL/INDUSTRIAL LAND USE

The parameters used in the equationspresented in the remainder of this section areexplained in the text box below.

All three of the exposure pathwaysdetailed below are included in the standard defaultequation in Section 3.2.2. If only one or somecombination of these exposure pathways are ofconcern at a particular site, a Site-specifiC equationcan be derived.

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

C x ED x EF x IRa" X OM)RtDj x BW x AT x 365 dayslyr

SFj x C x ED x EF x IRair x OM)AT x BW x 365 dayslyr

=

The cancer risk caused by inhalation ofvolatiles released from contaminated soil is:

Risk from =inhalationof volatiles

HQ frominhalationof volatiles

Note that the VF value has been developedspecifically for these equations; it may not beapplicable in other technical contexts.

C x ED x EF x IRaj, x O/pEF)RtDj x BW x AT x 365 dayslyr

HQfrom =inhalationof parti­culates

PARAMETERS FOR SOIL - COMMERCIAl)INDUSTRIAL LAND USE

Parameter Definition Default Value

CSFj

SFoRtDoRtDjBWAT

EFEDIRai,IRsoil

VFPEF

chemical concentration in soil (mglkg)inhalation cancer slope factor «mglkg-day)"l)oral cancer slope factor «mglkg-day)"l)oral chronic reference dose (mglkg-day)inhalation chronic reference dose (mglkg-day)adult body weight (kg)averaging time (yr)

exposure frequency (days/yr)exposure duration (yr)workday inhalation rate (m3/day)soil ingestion rate (mglday)soil-to-air volatilization factor (m3/kg)particulate emission factor (m3/kg)

chemical-specificchemical-specificchemical-specificchemical-specific70 kg70 yr for cancer risk30 yr for noncancer HI (equal to ED)250 dayslyr25 yr20 m3/day50 mgldaychemical specific (see Section 3.3.1)4.63 x 109 m3/kg (see Section 3.3.2)

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The noncancer HQ from particulate inhalation iscalculated using this equation:

B.3.3 INHALATION OF PARTICULATES

Cancer risk due to inhalation ofcontaminated soil particulates is calculated as: HQ from

inhalationC x ED x EF X IR,;r x (l/PEF)Rill; x BW x AT x 365 dayslyr

Risk from =inhalationof particulates

SF; x C x ED x EF x IRa;r x (l/pEF)AT x BW x 365 dayslyr

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