human health evaluation manual - superfund risk … · evaluation. 1.1 overview of the human health...

,EPA

United StatesEnvironmental ProtectionAgency

Office of Emergency andRemedial ResponseWasnmgton DC 20460

EPA 540 1-89002December 1989

Risk AssessmentGuidance for SuperfundVolume IHuman HealthEvaluation Manual(Part A)

SDMS DocID 2072484

Interim Final

CHAPTER 1

INTRODUCTION

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The Comprehensive Environmental Response,Compensation, and Liability Act of 1980. asamended (CERCLA, or "Superfund"), establishesa national program for responding to releases ofhazardous substances into the environment7 TheNational Oil and Hazardous Substances PollutionContingency Plan (NCP) is the regulation thatimplements CERCLA.2 Among other things, theNCP establishes the. overall approach fordetermining appropriate remedial actions atSuperfund sites. The overarching mandate of trieSuperfund program is to protect human healthand the environment from current and' potentialthreats posed by uncontrolled hazardous substancereleases! and the NCP echoes this mandate.

To help meet this Superfund mandate, EPA'sOffice of Emergency and Remedial Response hasdeveloped a human health evaluation process aspart of its remedial response program, Theprocess of gathering and assessing human healthrisk information described in this manual isadapted from well-established chemical riskassessment principles and procedures (NAS 1983;CRS 1983; OSTP 1985). It is designed to be.consistent with EPA's published risk assessmentguidelines (EPA 1984; EPA 1986a-e; EPA 1988a;EPA 1989a) and other Agency-wide riskassessment policy. The Human Health EvaluationManual revises and replaces the Superfund PublicHealth Evaluation Manual (EPA 1986f).5 Itincorporates new information and builds onseveral years of Superfund program experienceconducting risk assessments at hazardous wastesites. In addition, the Human Health EvaluationManual together with the companionEnvironmental Evaluation Manual (EPA 1989b)replaces EPA's 1985 Endangerment AssessmentHandbook, which should no longer be used (seeSection 2.2.1).

The goal of the Superfund human healthevaluation process is to provide a framework fordeveloping the risk information necessary to assistdecision-making at remedial sites. Specificobjectives of the process are to:

• provide an analysis of baseline risks4

and help determine the need for actionat sites;

• provide a basis for determining levelsof chemicals that can remain onsite andstill be adequately protective of publichealth;

• provide a basis for comparing potentialhealth impacts: of various remedialalternatives; and

• provide a consistent process forevaluating and documenting public healththreats at sites.

The human health evaluation processdescribed in this manual is an integral pan of theremedial response process defined by "CERCLAand the NCP. The risk information generated bythe human health evaluation process is designedto be used in the remedial investigation/feasibilitystudy (RI/FS) at Superfund sites. Although riskinformation is fundamental to the RI/FS and tothe remedial response program in general,Superfund site experience has led EPA to balancethe need for information with the need to takeaction at sites quickly and to streamline theremedial process. Revisions proposed to the NCPin 1988 reflect EPA program managementprinciples intended to promote the efficiency andeffectiveness of the remedial response: process.Chief among these principles is a bias for action.EPA's Guidance for Conducting Remedial

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Investigations and Feasibility Studies UnderCERCLA (EPA 1988b) also was revised in 1988to incorporate management initiatives designed tostreamline the RI/FS process and to makeinformation collection activities during the RImore efficient. The Risk Assessment Guidance forSuperfund, of which this Human Health EvaluationManual is Volume I,5 has been developed toreflect the emphasis on streamlining the remedialprocess. The Human Health Evaluation Manualis a companion document to the RI/FS guidance.It provides a basic framework for developinghealth risk information at Superfund sites and alsogives specific guidance on appropriate methodsand data to use. Users of the Human HealthEvaluation Manual should be familiar with theRI/FS guidance, as well as with other guidancesreferenced throughout later chapters cf thismanual.

The Human Health Evaluation Manual isaddressed primarily to the individuals actuallyconducting human health evaluations for sites(frequently contractors to EPA, other federalagencies, states, or potentially responsible panics).It also is targeted to EPA staff responsible forreview and oversight of risk assessments (e.g.,technical staff in the regions) and thoseresponsible for ensuring an adequate evaluation ofhuman health risks (i.e., remedial projectmanagers, or RPMs). Although the term* riskassessor and risk assessment reviewer are used inthis manual, it is emphasized that they generallyrefer to teams of individuals in appropriatedisciplines (e.g., lexicologists, chemists,hydrologists, engineers). It is recommended thatan appropriate team of scientists and engineers beassembled for the human health evaluation ateach specific site. It is the responsibility ofRPMs, along with the leaders of human healthevaluation teams, to match the scientific supportthey-deem appropriate with the resources at theirdisposal.

Individuals having different levels of scientifictraining and experience are likely to use themanual in designing, conducting, and reviewinghuman health evaluations. Because assumptionsand judgments are required in many parts of theanalysis, the individuals conducting the evaluationare key elements in the process. The manual isnot intended to instruct non-technical personnelhow to perform technical evaluations, nor to allow

professionals trained in one discipline to performthe work of another.

KEY PLAYERS IN SUPERFUNDSITE RISK ASSESSMENT/

RISK MANAGEMENT

Risk Assessor. The individual or team of individualswho actually organizes and analyzes site data, developsexposure and risk calculations, and prepares humanbeattb evaluation (Le, risk assessment) reports. Riskaasesson for Superfund sites frequently are contractorsto EPA, other federal agencies, states, or potentiallyresponsible parties.

Risk Assessment Reviewer. The individual or team ofindividual* within an EPA region who provides technicaloversight and quality assurance review of human healthevaluation activities.

Remedial Project Manager fRPMY, The individual whomanages and oversees all RI/FS activities, including toehuman health' evaluation, for a site: The RPM isresponsible Cor ensuring adequate evaluation of humanhealth risks and for determining the level of resourcesto be committed to the human health evaluation.

r. The individual or group of individualswho serve* as primary decision-maker for a die,generally regional Superfund management inconauttolion with the RPM and members of thetechnical staff. The identity of the risk manager maydiffer from region to tegron and tor sites of varyingcomplexity. '

The Human Health Evaluation Manualadmittedly cannot address all site circumstances.Users of the manual must exercise technical andmanagement judgment, andshould consult withEPA regional risk' assessment contacts andappropriate headquarters staff when encounteringunusual or particularly complex technical issues.

The first three chapters of this manualprovide background information to help place thehuman health evaluation process in the context ofthe Superfund remedial process. This chapter(Chapter 1) summarizes the human healthevaluation process during the RI/FS. The threemain parts of this process - baseline riskassessment, refinement of preliminary remediationgoals, and remedial alternatives risk evaluationare described in detail in subsequent chapters.Chapter 2 discusses in a more general way therole of risk information in the overall Superfund

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remedial program by focusing on the statutes,regulations, and guidance relevant to the humanhealth evaluation. Chapter 2 also identifies andcontrasts Superfund studies related to the humanhealth, evaluation. Chapter 3 discusses issuesrelated to planning for the human healthevaluation.

1.1 OVERVIEW OF THE HUMANHEALTH EVALUATIONPROCESS IN THE RI/FS

Section 300.430 of the proposed revised NCPreiterates that the purpose of the remedial processis to implement remedies that reduce, control, oreliminate risks to human health and theenvironment. The remedial investigation andfeasibility study (RI/FS) is the methodology thatthe Superfund program has established forcharacterizing the nature and extent of risks posedby uncontrolled hazardous waste sites and fordeveloping and evaluating remedial options. The1986 amendments to CERCLA reemphasized theoriginal statutory mandate that remedies meet athreshold requirement to protect human healthand the environment and that they be cost-effective, while adding new emphasis to thepermanence of remedies. Because the RI/FS is ananalytical process designed to support riskmanagement decision-making for Superfund sites,the assessment of health and environmental riskplays an essential role in the RI/FS.

. This manual provides guidance on the humanhealth evaluation activities that are conductedduring the RI/FS. The three basic parts of theRI/FS human health evaluation are:

(1) baseline risk assessment (described inPan A of this manual);

(2) refinement of preliminary remediationgoals (Part B); and

(3) remedial alternatives risk evaluation(Pan C).

Because these risk information activities areintertwined with the RI/FS, this section describesthose activities in the context of the RI/FSprocess. It relates the three parts of the human

health evaluation to the stages of the RI/FS,which are:

• project scoping (before the RI);

• site characterization (RI);

• establishment of remedial actionobjectives (FS);

• development and screening ofalternatives (FS); and

• detailed analysis of alternatives (FS).

Although the RI/FS process and related riskinformation activities are presented in a fashionthat makes the steps appear sequential anddistinct, in practice the process is highlyinteractive. In fact, the RI and FS are conductedconcurrently. Data collected in the RI influencesthe development of remedial alternatives in theFS, which in turn affects the data needs and scopeof treatability studies and additional fieldinvestigations. The RI/FS should^ be viewed; as aflexible process that can and should be tailored tospecific circumstances and information needs ofindividual sites, not as a- rigid appixiach" that mustb*^ conductedidentically at: every sifcggljkewise,thehuman healths evaluation'^here should be viewed the same way.

,*,-< t.~ •- - -'•* •"•••-»->-'•v^'^V'.f'i S^w"£'S*' ' '

Two concepts are essential to the phasedRI/FS approach. First, initial data collectionefforts develop a general understanding of the site.Subsequent data collection effort focuses on fillingpreviously unidentified gaps in the understandingof site characteristics and gathering informationnecessary toDevaluate remedial alternatives.Second, key data needs should be identified ascarry in the process as possible to ensure thatdata collection is always directed toward providinginformation relevant to selection of a remedialaction. In this way, the overall sitecharacterization effort can be continually scopedto minimize the collection of unnecessary (fata andpiflxirpJTg data quality.

The RI/FS provides decision-makers with atechnical evaluation of the threats posed at a site,a characterization of the potential routes ofexposure, an assessment of remedial alternatives(including their relative advantages and

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disadvantages), and an analysis of the trade-offs inselecting one alternative over another. EPA'sinterim final Guidance for Conducting RemedialInvestigations and Feasibility Studies underCERCLA (EPA 1988b) provides a detailedstructure for the RI/FS. The RI/FS guidanceprovides further background that is helpful inunderstanding the place of the human healthevaluation in the RI/FS process. The role thatrisk information plays in these stages of the RI/FSis described below, additional background can befound in the RI/FS guidance and in a summary ofthe guidance found in Chapter 2. Exhibit 1-1illustrates the RI/FS process, showing where in theprocess risk information is gathered and analyzed.

1.1.1 PROJECT SCOPING

The purpose of project scoping is to definemore specifically the appropriate type and extentof investigation and analysis that should beundertaken for a given site. During scoping, toassist in evaluating the possible impacts of releasesfrom the site on human health and theenvironment, a conceptual model of the siteshould be established, considering in a qualitativemanner the sources of contamination, potentialpathways of exposure, and potential receptors.(Scoping is also the starting point for the riskassessment, during which exposure pathways areidentified in the conceptual model for furtherinvestigation and quantification.)

PROJECT SCOPING

Program experience has shown that scoping B a veryimportant step for the human health evaluation process,and both the health and environmental evaluation teamsneed to get involved in the RI/FS during the scopingstage. Planning tor site data collection activities isnecessary to focns Che human health evaluation (andeoviroflmentat evaluation) on the minimum amount ofsampling information in order to meet time aad budgetconstraints, white at the same time ensuring that enoughinformation is gathered to assess risks adequately. (SeeChapter3 for tnfonna tion on planning the human healthevaluation.)

The preliminary characterization duringproject scoping is initially developed with readilyavailable information and is refined as additionaldata are collected. The main objectives of scopingare to identify the types of decisions that need tobe made, to determine the types (includingquantity and quality) of data needed, and todesign efficient studies to collect these data.Potential site-specific modeling activities shouldbe discussed at initial scoping meetings to ensurethat modeling results will supplement the samplingdata and effectively support risk assessmentactivities.

1.1.2 SITE CHARACTERIZATION (RI)

During site characterization, the sampling and.analysis plan developed during project scoping isimplemented and field data are collected andanalyzed to determine the nature and extent ofthreats to human health and the environmentposed by a site. The major components of sitecharacterization are:

• collection and analysis of field data tocharacterize the site;

• development of a baseline riskassessment for both potential humanhealth effects and potentialenvironmental effects; and

• treatability studies, as appropriate.

Pan of the human health evaluation, thebaseline risk assessment (Part A of this manual)is an analysis of the potential adverse healtheffects (current or future) caused by hazardoussubstance releases from a site in the absence ofany actions to control or mitigate these releases(i.e., under an assumption of no action). Thebaseline risk assessment contributes to the sitecharacterization and subsequent development,evaluation, and selection of appropriate responsealternatives. The results of™ the baseline riskassessment are used to:,

• help -.determine;;, whether additionalresponse action is necessary at the site,

• modify, preliminary remediation goals;;

EXHIBIT 1-1

RISK INFORMATION ACTIVITIES IN THE RI/FS PROCESS

Page I-S

RI/FSSTAGES

RISKINFORMATIONACTIVITIES

ProjectScoping

Review datacollectedin siteinspection

Reviewsampling/datacollectionplans

Formulatepreliminaryremediationfoals (PRGs)

Determinelevel ofeffort forbaseline risk

RI/FS:Site Establishment of Development & Detailed

Characterization Remedial Action ' Screening of Analysis of(HI) Objectives (FS) Alternatives (FS) Alternatives (FS)

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• help support selection of the "no-action^remedial alternative, where appropriate*and/.j

• document, themagnitude of? risk • at a%

site,;and the;primary causes of thaMiska

Baseline risk assessments are site-specific andtherefore may vary in both detail and the extentto which qualitative and quantitative analyses areused, depending on the complexity and particularcircumstances of the site, as well as the availabilityof applicable or relevant and appropriaterequirements (ARARs) and other criteria,advisories, and guidance. After an initial planningstage (described more fully in Chapter 3), thereare four steps in the baseline risk assessmentprocess: data collection and analysis; exposureassessment; toxicity assessment; and riskcharacterization. Each step is described brieflybelow and presented in Exhibit 1-2.

Data collection and evaluation involvesgathering and analyzing the site data relevant tothe human health evaluation and identifying thesubstances present at the site that are the focusof the risk assessment process. (Chapters 4 and5 address data collection and-evaluation.)

An exposure assessment is conducted toestimate the magnitude of actual and/or potentialhuman exposures, the frequency and duration ofthese exposures, and the pathways by whichhumans are potentially exposed. In the exposureassessment, reasonable maximum estimates ofexposure are developed for both current andfuture land-use assumptions. Curremr exposureestimates are used to determine whether a threatexists based on existing exposure conditions at thesite.̂ Future exposure estimates axe:- used* toprovide decision-makers with an understanding ofpotential future exposures and threats and includea qualitative estimate of the likelihood of suchexposures occurring. Conducting an exposureassessment involves analyzing contaminantreleases; identifying exposed populations;identifying all potential pathways of exposure;estimating exposure point concentrations forspecific pathways, based both on environmentalmonitoring data and predictive chemical modelingresults; and estimating contaminant intakes forspecific pathways. The results of this assessmentare pathway-specific intakes for current and future

exposures to individual substances. (Chapter 6addresses-exposure assessment.)

The toxicitv assessment component of theSuperfund baseline risk assessment considers: (1)the types of adverse health effects associated withchemical exposures; (2) the relationship betweenmagnitude of exposure and adverse effects; and (3)related uncertainties such as the weight ofevidence of a particular chemical's carcinogenicityin humans. Typically, the Superfund site riskassessments rely heavily on existing toxicityinformation developed on specific chemicals.Toxicity assessment for contaminants found atSuperfund sites is generally accomplished in twosteps: hazard identification and dose-responseassessment The first step, hazard identification,is the process of determining whether exposure toan agent can cause an increase in the incidence ofan adverse health effect (e.g., cancer, birth defect).Hazard identification also involves characterizingthe nature and strength of the evidence ofcausation. The second step, dose-responseevaluation, is the process of quantitativelyevaluating the toxicity information andcharacterizing the relationship between she dose fof the contaminant administered or received and |the incidence of adverse health effects in theexposed population. From this quantitative dose-response relationship, toxicity values are derivedthat can be used to estimate the incidence ofadverse effects occurring in humans at differentexposure levels. (Chapter 7 addresses toxicityassessment)

The risk characterization summarizes andcombines outputs of the exposure and toxicityassessments to characterize baseline risk, both inquantitative expressions and qualitative statements.During risk characterization, chemical-specifictoxicity information is compared against bothmeasured contaminant exposure levels and thoselevels predicted through fate and transportmodeling to determine whether current or futurelevels at or near the site are of potential concern.(Chapter 8 addresses risk characterization.)

The level of effort required to conduct abaseline risk assessment depends largely on thecomplexity of the site. In situations where theresults of the baseline risk assessment indicatethat the site poses little or no threat to humanhealth or the environment and that no further (or

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EXHIBIT 1-2

PART A: BASELINE RISK ASSESSMENT

Data Collection andEvaluation

Gather and analyze relevantsite data

Identify potential chemicals ofconcern

Exposure Assessment

• Analyze contaminant releases

• Identify exposed populations -

• Identify potential exposurepathways

• Estimate exposureconcentrations for pathways

• Estimate contaminant intakes forpathways

Risk Characterization

• Characterize potential for adversehealth effects to occur

— Estimate cancer risks

— Estimate noocancer basard' quotients

• Evaluate uncertainty

• Summarlie risk information

Toxicity Assessment

• Collect qualitative andquantitative toxicity information

• Determine appropriate toxicityvalues

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limited) action will be necessary, the FS should bescaled-down as appropriate.

The " documents developed during sitecharacterization include a brief preliminary sitecharacterization summary and the draft RI report,which includes either the complete baseline riskassessment report or a summary of it. Thepreliminary site characterization summary may beused to assist in identification of ARARs and mayprovide the Agency for Toxic Substances andDisease Registry (ATSDR) with the data necessaryto prepare its health assessment (different frombaseline risk assessment or other EPA humanhealth evaluation activities; see Chapter 2). Thedraft RI report is prepared after the completionof the baseline risk assessment, often along withthe draft FS report.

1.1.3 FEASIBILITY STUDY

The purpose of the feasibility study is toprovide the decision-maker with an assessment ofremedial alternatives, including their relativestrengths and weaknesses, and the trade-offs inselecting one alternative over another. The FSprocess involves developing a reasonable range ofalternatives and analyzing these alternatives indetail using nine evaluation criteria. Because theRI and FS are conducted concurrently, thisdevelopment and analysis of alternatives is aninteractive process in which potential alternativesand remediation goals are continually refined asadditional information from the RI becomesavailable.

Establishing protective remedial actionobjectives.. .The first step in the FS process,involves developing remedial action objectives thataddress contaminants and media of concern,potential exposure pathways, and preliminaryremediation goals. Under the proposed revisedNCP and the interim RI/FS guidance, preliminaryremediation goals typically are formulated firstduring project scoping or concurrent with initialRI activities (i.e., prior to completion of thebaseline risk assessment). The preliminaryremediation goals are therefore based initially onreadily available chemical-specific ARARs (e.g.,maximum contaminant levels (MCLs) for drinkingwater). Preliminary remediation goals forindividual substances are refined or confirmed atthe conclusion of the baseline risk assessment

(Part B of this manual addresses the refinementof preliminary remediation goals). These refinedpreliminary remediation goals are based both onrisk assessment and on chemical-specific ARARs.Thus, they are intended to be protective and tocomply with ARARs. The analytical approachused to develop these refined goals involves:

• identifying chemical-specific ARARs;

• identifying levels based on riskassessment where chemical-specificARARs are not available or situationswhere multiple contaminants or multipleexposure pathways make ARARs notprotective;

• identifying non-substance-specific goalsfor exposure pathways (if necessary); and

• determining a refined preliminaryremediation goal that is protective ofhuman health for all substance/exposurepathway combinations being addressed.

Development and screening of alternatives.Once temedial action objectives have beendeveloped, general response actions, such astreatment, containment, excavation, pumping, orother actions that may be taken to satisfy thoseobjectives should be developed. In the process ofdeveloping alternatives for remedial action at asite, two important activities take place. First,volumes or areas of waste or environmental mediathat need to be addressed by the remedial actionare determined by information on the nature andextent of contamination, ARARs, chemical-specificenvironmental fate and toxicity information, andengineering analyses. Second, the remedial actionalternatives and associated technologies arescreened to identify those that would be effectivefor the contaminants and media of interest at thesite. The information developed in these twoactivities is used in assembling technologies intoalternatives for the site as a whole or for aspecific operable unit

The Superfund program has long permittedremedial actions to be staged through multipleoperable units. Operable units are discreteactions that comprise incremental steps toward thefinal remedy. Operable units may be actions thatcompletely address a geographical portion of a site

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or a specific site problem (e.g., drums and tanks,contaminated ground water) or the entire site.Operable units include interim actions (e.g.,pumping and treating of ground water to retardplume migration) that must be followed bysubsequent actions to fully address the scope ofthe problem (e.g., final ground-water operableunit that defines the remediation goals andrestoration timeframe). Such operable units maybe taken in response to a pressing problem thatwill worsen if unaddressed, or because there is anopportunity to undertake a limited action that willachieve significant risk reduction quickly. Theappropriateness of dividing remedial actions intooperable units is determined by considering theinterrelationship of site problems and the need ordesire to initiate actions quickly. To the degreethat site problems are interrelated, it may be mostappropriate tof address the problems together.However, where : problems are reasonablyseparable, phased responses implemented througha sequence of operable units may promote morerapid risk reduction.

In situations where numerous potentialremedial alternatives are initially developed, it maybe necessary to screen the alternatives to narrowthe list to be evaluated in detail. Such screeningaids in streamlining the feasibility study whileensuring that the most promising alternatives arebeing considered.

Detailed analysis of alternatives. During thedetailed analysis, each' alternative is assessedagainst specific evaluation,criteria and the resultsof this assessment arrayed such that comparisonsbetween alternatives can be made and key trade-offs identified. Nine evaluation criteria, some ofwhich are related to human health evaluation andrisk, have been developed to address statutoryrequirements as well as additional technical andpolicy considerations that have proven to beimportant for selecting among remedialalternatives. These evaluation criteria, which areidentified and discussed in the interim final RI/FSguidance, serve as the basis for conducting thedetailed analyses during the FS and forsubsequently selecting, an appropriate remedialaction. The nine evaluation criteria are asfollows:

(1) overall protection of human health andthe environment; .

(2) compliance with ARARs (unless waiverapplicable);

(3) long-term effectiveness and permanence;

(4) reduction of toxicity, mobility, or volumethrough the use of treatment;

(5) short-term effectiveness;

(6) implememability;

(7) cost;

(8) state acceptance; and

(9) community acceptance.

Risk information is required at the detailedanalysis stage of the RI/FS so that each alternativecan be evaluated in relation to the relevant NCPremedy selection criteria.

The detailed analysis must, according to theproposed NCP, include an evaluation of eachalternative against the nine criteria. The first twocriteria (i.e., overall protectiveness and compliancewith ARARs) are threshold determinations andmust be met before a remedy can be selected.Evaluation of the bverall protectiveness of analternative during the RI/FS should focus on howa specific alternative achieves protection over timeand how site risks are reduced.

The next five criteria (numbers 3 through 7)are primary balancing criteria. The last two(numbers 8 and 9) are considered modifyingcriteria, and risk information does not play adirect role in the analysis of them. Of the fiveprimary balancing criteria, risk information is ofparticular importance in the analysis ofeffectiveness and permanence. Analysis of long-term effectiveness and permanence involves anevaluation of the results of a remedial action interms of residual risk at the site after responseobjectives have been met. A primary focus of thisevaluation is the effectiveness of the controls thatwill be applied to manage risk posed by treatmentresiduals and/or any untreated wastes that may beleft on the site, as well as the volume and natureof that material. It should also consider thepotential impacts on human health and theenvironment should the remedy fail. An

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evaluation of short-term effectiveness addressesthe impacts of the alternative during theconstruction and implementation phase unti lremedial response objectives will be met. Underthis criterion, alternatives should be evaluated withrespect to the potential effects on human healthand the environment during implementation of theremedial action and the length of time untilprotection is achieved.

1.2 OVERALL ORGANIZATION OFTHE MANUAL

The next two chapters present additionalbackground material for the human healthevaluation process. Chapter 2 discusses statutes,regulations, guidance, and studies relevant to theSuperfund human health evaluation. Chapter 3discusses issues related to planning for the humanhealth evaluation. The remainder of the manualis organized by the three parts of the humanhealth evaluation process:

• the baseline risk assessment is coveredin Pan A of the manual (Chapters 4through 10);

• refinement of preliminary remediationgoals is covered in Part B of the manual

(not included as part of this interim finalversion); and

• the risk evaluation of remedialalternatives is covered in Part C of themanual (not included as pan of thisinterim final version).

Chapters 4 through 3 provide detailedtechnical guidance for conducting the steps of abaseline risk assessment, and Chapter 9 providesdocumentation and review guidelines. Chapter 10contains additional guidance specific to baselinerisk assessment for sites contaminated withradionuclides. Sample calculations, sample tableformats, and references to other guidance areprovided throughout the manual All material ispresented both in technical terms and in simplertext. It should be stressed that the manual isintended to be comprehensive and to provideguidance for more situations than usually arerelevant to any single site. Risk assessors neednot use those parts of the manual that do notapply to their site.

Each chapter in Pan A includes a glossary ofacronyms and definitions of commonly used terms.The manual also includes two appendices:Appendix A provides technical guidance formaking absorption adjustments and Appendix Bis an index

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are not The corresponding Type II error wouldbe to conclude that onsite contaminantconcentrations are not higher than backgroundconcentrations when in fact they are. A Type Ierror could result in unnecessary remediation,while a Type II error could result in a failure toclean up a site when such an action is necessary.

In customary notations, a (alpha) denotes theprobability that a Type I error will occur, and 0(beta) denotes the probability that a Type II errorwill occur. Most statistical comparisons refer toa, also known as the level of significance of thetest. If a = 0.05, there is a 5 percent (i.e.. 1 in20) chance that we will. conclude thatconcentrations of contaminants are higher thanbackground when they actually are not.

Equally critical considerations in determiningthe number of background samples are ft and aconcept called 'power/ The power of a statisticaltest has the value 1 - ft and is defined as thelikelihood that the test procedure detects a falsenull hypothesis. Power functions for commonlyused statistical tests can be found in most generalstatistical textbooks. Power curves are a functionof a (which normally is fixed at 0.05), sample size(Le., the number of background and/or onsitesamples), and the amount of variability in thedata. Thus, if a 15 percent likelihood of failingto detect a false null hypothesis is desired (i.e., ft= 0.15), enough background samples must becollected to ensure that the power of the test isat least 0.85.

A small number of background samplesincreases the likelihood of a Type II error. If aninsufficient number of background samples iscollected, fairly large differences between site andbackground concentrations may not be statisticallysignificant, even though concentrations in themany site samples are higher than the fewbackground samples. To guard against thissituation, the statistical power associated with thecomparison of background samples with sitesamples should be evaluated.

In general, when trying to detect smalldifferences as statistically significant, the numberof background samples should be similar to thenumber of onsite samples that will be used for thecomparison(s) (e.g., the number of samples takenfrom one well). (Note that this does not mean

that the background sample size must equal thetotal number of onsite samples.) Due to theinherent variability of air concentrations (seeSection 4.6), background sample size for air needsto be relatively large.

4.4.4 COMPARING BACKGROUNDSAMPLES TO SITE-RELATEDCONTAMINATION

The medium sampled influences the kind ofstatistical comparisons that can be made withbackground data. For example, air monitoringstations and ground-water wells are normallypositioned based on onsite factors and gradientconsiderations. Because of this purposiveplacement (see Section 4.6.1), several wells ormonitors cannot be assumed to be a randomsample from a single population and hence cannotbe evaluated collectively (i.e., the sampling resultscannot be combined).- Therefore, the informationfrom each well or air monitor should be comparedindividually with background.

Because there typically are many site-related,media-specific sampling location data to comparewith background, there usually is a 'multiplecomparison problem' that most be addressed. Ingeneral, the probability of experiencing a Type Ierror in the entire set of statistical tests increaseswith the number of comparisons being made. Ifa * 0.05, there is a 1 in 20 chance of a Type Ierror in any single test If 20 comparisons arebeing made, it therefore is likely that at least oneType I error will occur among all 20 tests.Statistical Analysis of Ground-water MonitoringData at RCRA Facilities (EPA 1989c) is usefulfor designing sampling plans for comparing,information from many fixed' locations withbackground.

It may be useful at times to look, atcomparisons other than onsite versus background.For example, upgradient wells can be comparedwith downgradient wells. Also, there may beseveral areas within the site that should becompared for differences in site-relatedcontaminant concentration. These areas ofconcern should be established before samplingtakes place. If a more complicated comparisonscheme is planned, a statistician should beconsulted frequently to help distribute thesampling effort and design the analysis.

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A statistically significant difference betweenbackground samples and site-related contaminationshould not, by itself, trigger a cleanup action. Theremainder of this manual still must be applied sothat the lexicological » rather than simply thestatistical - significance of the contamination canbe ascertained.

4.5 PRELIMINARY IDENTIFI-CATION OF POTENTIALHUMAN EXPOSURE

A preliminary identification of potentialhuman exposure provides much neededinformation for the SAP. This activity involvesthe identification of (1) media of concern. (2)areas of concern (i.e., general locations of themedia to be sampled)/ (3) types of chemicalsexpected at the site, and (4) potential routes ofcontaminant transport through the environment(e.g., inter-media transfer, food chain). Thissection provides general information on thepreliminary identification of potential humanexposure pathways, as well as specific informationon the various media. (Also, see Chapter 6 fora detailed discussion of exposure assessment)

4.5.1 GENERAL INFORMATION

Prior to discussing various specific exposuremedia, general information on the following isprovided: media, types of chemicals, areas ofconcern, and routes of contaminant transport isaddressed.

Media of concern (including biota). Forrisfoassessment purposes^ media of concern at a site;

• any;, currently^ media to;,which individuals may be exposed orthrough which chemicals may betransported to potential receptors: and

;

i • ' anv currently nncrtf|tnni'i|at*f< media that-may become contaminated in the futuredue to contaminant transport.

Several medium-specific actors in sampling mayinfluence the risk assessment For example,limitations in sampling the medium may limit the

detailed evaluation of exposure pathways describedin Chapter 6. To illustrate this, if soil samplesare not collected at the surface of a site, then itmay not be possible to accurately evaluatepotential exposures involving direct contact withsoils or exposures involving the release ofcontaminants from soils via wind erosion (withsubsequent inhalation of airborne contaminants byexposed individuals). Therefore, based on theconceptual model of the site discussed previously,the risk assessor should make sure thatappropriate samples are collected from eachmedium of concern.

Areas of concern. Areas of concern refer tothe general sampling locations at or near the site.For large sites, areas of concern may be treatedin the RI/FS as "operable units," and may includeseveral media; Areas of concern also can bethought of as the locations of potentially exposedpopulations (e.g., nearest residents) or biota (e.g.,wildlife feeding areas).

Areas of concern should be identified basedon site-specific characteristics. These areas arechosen purposrvely by the investigators during theinitial scoping meeting. Areas of concern shouldinclude areas of the site that:

(1) have different chemical types;

(2) have different anticipated concentrationsor hot spots;

(3) are a release source of concern;

(4) differ from each other in terms of theanticipated spatial or temporal variabilityof contamination;

(5) must be sampledequipment; and/or

using different

(6) are more or less costly to sample.

In some instances, the risk assessor may wantto estimate concentrations that are representativeof the site as a whole, in addition to each area ofconcern. In these cases, two conditions generallyshould be met in defining areas of concern: (1)the boundaries of the areas of concern should notoverlap and (2) all of the areas of concern

11

together should account for the entire area of thesite.

Depending on the exposure pathways thatare being evaluated in the risk assessment, it maynot be necessary to determine site-widerepresentative values. In this case, areas ofconcern do not have to account for the entirearea of the site.

Types of chemicals. The types of chemicalsexpected at a hazardous waste site may dictate thesite areas and media sampled. For example,certain chemicals (e.g., diorins) that >biocohcentrate in aquatic life also are likely to bepresent in the sediments. If such chemicals areexpected at a particular site and humans areexpected to ingest aquatic life, sampling ofsediments and aquatic life for the chemicals maybe particularly important

Due to differences in the relative toxidties ofdifferent species of the same chemical (e.g., Cr+3

versus Cr™), the species should be noted whenpossible.

Routes of contaminant transport In additionto medium-specific concerns, there may be severalpotential current and future routes of contaminanttransport within a medium and between media ata site. For instance, discharge of ground water orsurface runoff to surface water could occur.Therefore, when possible, samples should becollected based on routes of potential transportFor cases in which contamination has not yetreached points of human exposure but may betransported to those areas in the future, samplingbetween the contaminant source and the exposurelocations should be conducted to help evaluatepotential future concentrations to whichindividuals may be exposed (e.g, throughmodeling). (See Chapter 6 for additionaldiscussion on contaminant transport)

SOIL

Soil represents a medium of direct contactexposure and often is the main source ofcontaminants released into other media. As such,the number, location, and type of samplescollected from soils will have a significant effecton the risk assessment See the box on this page

for guidance that provides additional detailedinformation concerning soil sampling, includinginformation on sampling locations, general soiland vegetation conditions, and samplingequipment, strategies, and techniques. In additionto the general sampling considerations discussedpreviously, the following specific issues related tosoil sampling are discussed below: theheterogeneous nature of soils, designation of hotspots, depth of samples, and fate and transportproperties.

SOIL SAMPLING GUIDANCE

Test Methods for Evaluating Solid Waste (SW-846): Physical/Chemical Methods (EPAI986a)

Field Manual for Grid Scunplingof PCS SpillSites to Verify Cleanups (EPA 1986b)

A Compendium of Superfund Field Operation*Methods (EPA 1987c)

SoBSampBng Quality Assurance Guide (EPAReview Draft 1989b)

Heterogeneous nature of soils. One of thelargest problems in sampling soil (or other solidmaterials) is that its generally heterogeneousnature makes collection of representative samplesdifficult (and compositing of samples virtuallyimpossible — see Section 4.<S3). Therefore, alarge number of soil samples aiay be required toobtain sufficient data to calculate _ an exposureconcentration. Composite samples sometimes arecollected to obtain a more homogeneous, sampleof a particular area; however, as discussed in alater section, compositing samples also serves tomask contaminant hot spots (as well as areas oflow contaminant concentration).

Designation of hot spots. Hot spots (Le.,areas of very high contaminant concentrations)may have a significant impact on direct contactexposures. The sampling plan should considercharacterization of hot spots through extensivesampling, field screening, visual observations, ora combination of the above.

12

Depth of samples. Sample depth should beapplicable for the exposure pathways andcontaminant transport routes of concern andshould be chosen purposively within that depthinterval. If a depth interval is chosen purposively,a random procedure to select a sampling pointmay be established. Assessment of surfaceexposures will be more certain if samples arecollected from the shallowest depth that can bepractically obtained, rather than, for example, zeroto two feet Subsurface soil samples areimportant, however, if soil disturbance is likely orif leaching of chemicals to ground water is ofconcern, or if the site has current or potentialagricultural uses.

Fate and transport properties. The samplingplan should consider physical and chemicalcharacteristics of soil that are important forevaluating fate and transport. For example, soilsamples being collected to identify potentialsources of ground-water contamination must beable to support models that estimate bothquantities of chemicals leaching to ground waterand the time needed for chemicals .to leach to andwithin the ground water.

4.5.3 GROUND WATER

Considerable expense and effort normally arerequired for the installation and development ofmonitoring wells and the collection of ground-water samples. Wells must not introduce foreignmaterials and most provide a representativehydraulic connection to the geologic formations ofinterest In addition, ground-water samples needto be collected using an approach that adequatelydefines the contaminant plume with respect topotential exposure points. Existing potentialexposure points (e.g., existing drinking water wells)should be sampled.

More detailed information concerning ground-water sampling considerations (e.g., samplingequipment, types, and techniques) can be found inthe references in the box on this page. Inaddition to the general sampling considerationsdiscussed previously in Section 4.5.1, those specificfor ground water - hydrogeologic properties, welllocation and depth, and filtered vs. unfilteredsamples - are discussed below.

GROUND-WATER SAMPLINGGUIDANCE

Practical Guide to Ground-water Sampling(EPA 1985a)

A Compendium of Superfund Field OperationsMethods (EPA 1987c)

Handbook: 1987d)

Statistical Methods for Evaluating GroundWater from Hazardous Waste Facilities (EPA1988b)

Guidance on Remedial Actions forContaminated Ground Water at SuperfundSites (EPA I988e)

Ground-water SampSagfor Metals Analyses(EPA 19894) I

Hydrogeologic properties. The extent towhich the hydrogeologic properties (e.g., hydraulicconductivity, porosity," bulk density, fractionorganic carbon, productivity) of the aquifer(s) arecharacterized may have a significant effect on therisk assessment The ability to estimate futureexposure concentrations depends on the extent towhich hydrogeologic properties needed to evaluatecontaminant migration are quantified. Repetitivesampling of wells is necessary to obtain samplesthat are unaffected by drilling and welldevelopment and that accurately reflecthydrdgepiogic properties of the aquifer(s).

Wefl location and depth. The location ofwells should be such that both the horizontal andvertical extent of contamination can becharacterized. Separate water-bearing zones mayhave different aquifer classifications and uses andtherefore may need to be evaluated separately inthe risk assessment In addition, sinking orfloating layers of contamination may be presentat different depths of the wells.

Filtered vs. unfiltered samples. Data fromfiltered and unfiltered ground-water samples azeuseful for evaluating chemical migration in ground •water, because comparison of chemical

13

concentrations in unfiltered versus filtered samplescan provide important information on the form inwhich a chemical exists in ground water. Forinstance, if the concentration of a chemical ismuch greater in unfiltered samples compared tofiltered samples, it is likely that the majority of :the chemical is sorbed onto paniculate matter andnot dissolved in the ground water. Thisinformation on the form of chemical (i.e.,dissolved or suspended, on paniculate matter) isimportant to understanding chemical mobilitywithin the aquifer.

If chemical; analysis reveals: significantlydifferent concentrations in the filtered andunfiltered samples, try to determine whether there 'is a high concentration of suspended particles orif apparently: high concentrations are due tosampling or well construction artifacts.Supplementary samples can be collected in a -:

manner that will minimise the influence of theseartifacts. In addition, consider the effects of thefollowing.

• Filter size. A 0.45 urn filter may screenout some potentially mobile particulatesto which contaminants are absorbed andthus under-represent contaminantconcentrations. (Recent researchsuggests that a 1.0 um may be a moreappropriate filter size.)

• Pumping velocity. Pumping at too higha rate will entrain particulates (to whichcontaminants are absorbed) that wouldnot normally be mobile; this couldoverestimate contaminant concentrations.

• Sample oxidation. After contact with air,many metals oxidize and form insolublecompounds that may be filtered out; thismay underestimate inorganic chemicalconcentrations.

• Well construction material* Corrosionmay elevate some metal concentrationseven in stainless steel wells.

If unfiltered water is of potable quality, datafrom unfiltered water samples should be used toestimate exposure (see Chapter 6). The RPMshould ultimately decide the type of samples that

are collected. If only one type of sample iscollected (e.g., unfiltered), justification for notcollecting the other type of sample (e.g., filtered)should be provided in the sampling plan.

4.5.4 SURFACE WATER AND SEDIMENT

Samples need to be collected from any nearbysurface .water body potentially receiving dischargefrom the site. Samples are needed at a sufficientnumber of sampling points to characterizeexposure pathways, and at potential dischargepoints to the water body to determine if the site(or some other source) is contributing to surfacewater/sediment coritaminatiohr Some importantconsiderations for surface water/sediment samplingthat may affect the risk assessment for varioustypes and portions of water bodies (i.e., loticwaters; lentic waters, estuaries; sediments) arediscussed below: Mores detailed1;; informationconcerning surface water and sediment sampling,such as selecting sampling locations and samplingequipment, types, and techniques, is provided inthe references given in the box below.

SURFACE WATER AND SEDIMENTSAMPLING GUIDANCE

Procedures far Handling and Chemicalj4nafysis of Sediment and Water Samples(EPA and COE 1981)

Sediment SampSng Quality Assurance User'sGuide (EPA 1984)

Methods Manual for Bottom Sediment Sampleaffection (EPA 1985b)

A Compendium cfSuperfund Field OperationsMethods (EPA I987c)

An Overview of Sediment OjaEty in theUntied States (EPA 1987e)

Proposed. Guide far Sediment Collection,

(The American Society for Testing andMaterials, undated)

14

Lotic waters. Lotic waters are fast-movingwaters such as rivers and streams. Variations inmixing across the stream channel and downstreamin rivers and streams can make it difficult toobtain representative samples. Although theselection of sampling points will be highlydependent on the exposure pathways of concernfor a particular site, samples generally should betaken both toward the middle of the channelwhere the majority of the flow occurs and alongthe banks where flow is generally lower. Samplinglocations should be downgradient of any possiblecontaminant sources such as tributaries or effluentoutfalls. Any facilities (e.g., dams, wastewatertreatment plants) upstream that affect flow volumeor water quality should be considered during thetiming of sampling. "Background* releasesupstream could confound the interpretation ofsampling results by diluting contaminants or byincreasing,;contaminant .loads. . In general,sampling should begin downstream and proceedupstream.

Lentic waters. Lentic waters are slow-movingwaters such as lakes, ponds, and impoundments.In general, lentic waters require more samplesthan lotic waters because of the relatively lowdegree of mixing of lentic waters. Thermalstratification is a major factor to be consideredwhen sampling lakes. If the water body isstratified, samples from each layer should beobtained. Vertical composites of these layers thenmay be made, if appropriate. For small shallowponds, only one or two sample locations (e.g., theintake and the deepest points) may be adequatedepending on the exposure pathways of concernfor the site. Periodic release of water should beconsidered when sampling impoundments, as thismay affect chemical concentrations andstratification.

Estuaries. Contaminant concentrations inestuaries will depend on tidal flow and salinity-stratification, among other factors. To obtain arepresentative sample, sampling should beconducted through a tidal cycle by taking threesets of samples on a given day. (1) at low tide;(2) at high tide; and (3) at 'half tide.* Each layerof salinity should be sampled.

Sediments. Sediment samples should becollected in a manner that minimi7/»< disturbanceof the sediments and potential contamination of

subsequent samples. Sampling in flowing watersshould begin downstream and end upstream.Wading should be avoided. Sediments of differentcomposition (i.e., mud, sand, rock) should not becomposited. Again, it is important to obtain datathat will suppon the evaluation of the potentialexposure pathways of concern. For example, forpathways such as incidental ingestion, sampling ofnear-shore sediments may be important; however,for dermal absorption of sediment contaminantsduring recreational use such as swimming, samplesfrom different points throughout the water bodymay be important If ingestion of benthic(bottom-dwelling) species or surface water will beassessed during the-risk-: assessment; sedimentshould be sampled so that characteristics neededfor modeling (e.g., fraction of organic carbon,panicle size distribution) can be determined (seeSection^).: < <••••

4.5.5 AIR

Guidance for developing an air sampling planfor Superfund sites is provided in Procedures forDispersion Modeling and Air Monitoring forSuperfund Air Pathway Analysis (EPA 1989e). •That document is Volume IV of a series of four '•]technical guidance manuals called Procedures forConducting Air Pathway Analyses for SuperfundApplications (EPA 1989e-h). The other threevolumes of the series include discussions ofpotential air pathways, air emission sources, andprocedures for estimating potential sourceemission rates associated with both the baselinesite evaluation and remedial activities at the site.

Air monitoring information, along withrecommendations for proper selection andapplication of air dispersion models, is includedin Volume IV. The section on air monitoringcontained in this volume presents step-by-stepprocedures to develop, conduct, and evaluate theresults of air concentration monitoring tocharacterize downwind exposure conditions fromSuperfund air emission sources. The first stepaddressed is the process of collecting andreviewing existing air monitoring informationrelevant to the specific site, including source,receptor, and environmental data. The secondstep involves determining the level ofsophistication for the air monitoring program; thelevels range from simple screening procedures torefined techniques. Selection of a given level will .

CHAPTER 6

EXPOSURE ASSESSMENT

/FROM: \•Site discovery• Preliminary

assessment•Site inspection

V*NPL listing ^

ToxicityAssessment

Data * DataCollection | Evaluation

RiskCharacterization

ExposureAssessment

TO:•Selection of

remedy• Remedial

design• Remedial

. action

EXPOSURE ASSESSMENT

» Characterize physical setting

• Identify potentially exposedpopulations

1 Identify potential exposurepathways

Estimate exposureconcentrations

Estimate chemical intakes

CHAPTER 6

EXPOSURE ASSESSMENT

This chapter describes the procedures forconducting an exposure assessment as pan of thebaseline risk assessment process at Superfundsites. The objective of the exposure assessment is"to estimate the type and magnitude of exposuresto the chemical; of, potential concern that arepresent at or migrating from a>sitef The resultsof the exposure assessment are combined withchemical-specific toxicity information tocharacterize potential risks.

The procedures and information presentedin this chapter represent some new approaches toexposure assessment as well as a synthesis ofcurrently available exposure assessment guidanceand information published by EPA. Throughoutthis chapter, relevant exposure assessmentdocuments are referenced as sources of moredetailed information supporting the exposureassessment process.

6.1 BACKGROUND-• . . ,„,,:-., •".: .! • • • . . • • , , - . , , ..;.•-::• . -I .

Exposure is defined as the contact of anorganism (humans in the case of health riskassessment) with a chemical or physical agent(EPA 1988a). The magnitude of exposure isdetermined by measuring or estimating theamount of an agent available at the exchangeboundaries (L&, the lungs, gut, skin) during aspecified time period. Exposure assessment is thedetermination or estimation (qualitative orquantitative) of the magnitude, frequency,duration, and route of exposure. Exposureassessments may consider past, present, and futureexposures, using varying assessment techniques foreach phase. Estimates of current exposures canbe based on measurements or models of existingconditions, those of future exposures can be basedon models of future conditions, and those of pastexposures can be based on measured or modeledpast concentrations or measured chemical

concentrations in tissues. Generally, Superfund;.exposure assessments are concerned with, currentand; future, exposures; If human monitoring isplanned to assess current or past exposures, theAgency for Toxic Substances and Disease Registry(ATSDR) should be consulted to take the lead inconducting these studies and in assessing thecurrent health status of the people near the sitebased on the monitoring results.

6.1.1 COMPONENTS OF ANEXPOSURE ASSESSMENT

The general procedure for conducting anexposure assessment is illustrated in Exhibit 6-1.This procedure is based on EPA's publishedGuidelines far Exposure Assessment (EPA 1986a)and on other related guidance (EPA 198Sa,1968b). It is an adaptation of the generalizedexposure assessment process to the particularneeds of Superfund site risk assessments.Although some exposure assessment activities mayhave been started earlier (e.g., during RI/FSscoping or even before the RI/FS process began),the detailed exposure assessment process beginsafter the chemical data have been collected and

ACRONYMS FOR CHAPTER 6

ATSDR - Agency for Tone Subtunces and Disease

BCFGDI

CHAMNOAA<

NTGS •OAQPS <

RME-SDI«

SEAM>USGS •

> Bfeconcentration Factor1 Cbrate Dally Intake> Center tor Exposure Aaseisniem Modeling> National Oceanograpoic and AlmospjiericAdministration

< National Technical Guidance StudiesOffice of Ah- QuaHiy Planning andStandard* ..

• RrBircnaMc ••MffriiH>nft ExposureSubchraaie Daily IntakeSnperfond Ezpofure Awessmeni ManualUS. GeologictI Survey

2

DEFINITIONS FOR CHAPTER 6

Absorbed Dose. The amount of a substance penetrating the exchange boundaries of an organism after contact. Absorbeddose is calculated from the intake and the absorption efficiency. It usually is expressed ai mass of a substance absorbedinto the body per unit body weight per unit time (e.g., mg/kg-day).

Administered Dose. The mass of a substance given to an organism and in contact with an exchange boundary (e.g.,gastrointestinal tract) per unit body weight per unit time (e.&, mg/kg-day).

Applied Dose. The amount of a substance given to an organism, especially through dermal contact

Chronic Daily Intake fCDIX Exposure expressed as man of a substance contacted per unit body weight per unit time,averaged over a long period of time (as a Superfund program guideline, seven years to a lifetime).

Contact Rate. Amount of medium (=-g., ground water, toil) contacted per unit time or event (feg. filers of water ingestedper day).

Exposure. Contact of an organism svith a chemical or physical agent Exposure is quantified as the amount of the agentavailable at the exchange boundaries of the organism (e.g., skin, lungs, gut) and available for absorption.

Exposure Assessment. The determirfitfon or estimation (qualitative or quantitative) of the fTPp'ft"<f*. frequency, duration,"and route of exposure. ;.

Exposure Event. An incident of conttct with a chemical or physical agent. An exposure event can be defined by time (eg,day, boor) or by the incident (e.g., eating a tingle meal of contaminated Gsb). •;

Exposure Pathway. The course a chemical or physical agent takes from a source to an exposed organism. An exposaxl-stiway describes a unique mechanism by which an individual or population is exposed to rnrmicah or physical agentsat or. originafBig from a site, Cach exposure pathway includes a source or release from a source, an exposure point,t-.td an exposure route. If the vuposore point differs from the source, a uaospon/exposiire Btediuni (ej., air) or media(in cases of intermedia transfer) also is included.

Exposure Point A location of potential contact between an organism and a chemical or physical agent

Exposure Route. The way a cbemkal or physical agent comes m contact with an organism 0ut, by ingestion, inhalation,dermal contact).

Intake. A measure of exposure oqanased as the mass of a substance in contact with the exeaaage boundary per unit bodywtight per unit time .(&£, 04 cJjemicalAg-day). Abo termed the normafized exposure rate; equivalent to administered

. dose.

Lifetime Avenme Daflr Intake. Exposure expressed at mats of a substance contacted! per unit tedjrweight per uait time,averaged over a utetime.

Subchrccic D«fly_|ntatg fSPH. Encaure expressed as man of a substance contw ted per unit body weight per anft time,to

validated end the chemicals of potential concernhave been selected (see Chapter 5, Section 533).The exposure assessment proceeds with thefollowing Steps.

Step 1 - Characterization of exposure setting(Section 62). In this step, the assessorcharac v arizes the exposure setting with respectto the general physical characteristics of thesite and the characteristics of the populationson and near the site. Basic site

characteristics such as climate, vegetation,ground-water hydrology, and the presence andlocation of surface water are identified in thisstep. Populations also are identified and aredescribed with respect to those characteristicsthat influence exposure, such as locationrelative to the site, activity pattens, and thepresence of sensitive subpopulations. Thisstep considers the: characteristics of thecurrent population, as well as those of any:

Pa«e 6-3

EXHIBIT 6-1

THE EXPOSURE ASSESSMENT PROCESS

STEP1Characterize Exposure

Setting

• Physical Environment

• 'Potentially Exposed, Populations

STEP 2Identify Exposure

Pathways

• Chemical Source/Release

• Exposure Point

• Exposure Route

STEPS

Quantify Exposure

ConcentrationIntakeVariables

Pathway-SpecificExposure

4

potential future populations that may differunder an alternate land use; '

Step 2 - Identification of exposure pathways(Section 6.3). In this step, the exposureassessor identifies those pathways by whichthe previously identified populations may beexposed. Each exposure pathway describesa unique mechanism by which a populationmay be exposed to the chemicals at ororiginating from the site. Exposure pathwaysare identified based on consideration of thesources, releases, types, and locations ofchemicals at the site; the likely environmentalfate (including persistence, partitioning,transport, and intermedia transfer) of thesechemicals; and the location and activities ofthe potentially exposed populations.Exposure points (points of potential contactwith the chemical) and routes of exposure(e.g., ingestion, inhalation) are identified foreach exposure pathway.

Step 3 - Quantification of exposure (Section6.4). In this step, the assessor quantifies themagnitude, frequency and duration ofexposure for each pathway identified in Step2. This step is most often conducted in twostages: estimation of exposure concentrationsand calculation of intakes.

Estimation of exposure concentrations(Section 6.5). In? this pan of step 3, theexposure assessor determines theconcentration of chemicals that will becontacted over the exposure period.Exposure concentrations are estimated usingmonitoring data and/or chemical transportand environmental fate models. Modeling'may be used to estimate future chemicalconcentrations in media: that are currentlycontaminated or that may becomecontaminated, and current concentrations inmedia and/or at locations for which there areno monitoring data.

Calculation of intakes (Section 6.6). In thispart of step 3, the exposure assessorcalculates chemical-specific exposures for eachexposure pathway identified in Step 2.Exposure estimates are expressed in termsof the mass of substance in contact with thebody per unit body weight per unit time (e.g.,

mg chemical per kg body weight per day, alsoexpressed as mg/kg-day). These exposureestimates are termed "intakes" (for thepurposes of this manual) and represent thenormalized exposure rate. Several termscommon in other EPA documents and theliterature are equivalent or related to intake(see box on this page and definitions box onpage 6-2). Chemical intakes are calculatedusing equations that include variables forexposure concentration, contact rate, exposurefrequency, exposure duration, body weight,and exposure averaging time. The values ofsome of these variables depend on siteconditions and the characteristics of thepotentially exposed population.

TERMS EQUIVALENT ORRELATED TO INTAKE

Normalized Exposure Rate. Equivalent to intake

Administered Dose. Equivalent to intake

Applied Dose. Equivalent to intake

Absorbed Dose. Equivalent to intake multiplied byan absorption factor

After intakes have been estimated, they areorganized' by population, as appropriate (Section6.7). Then, the sources of uncertainty (e.g.,variability in analytical data, modeling results,parameter assumptions) and their effect on theexposure estimates are evaluated and summarized(Section 6.8). This information on uncertainty isimportant to site decision-makers who mustevaluate the results of the exposure and riskassessment and make decisions regarding thedegree of remediation required at a site. Theexposure assessment concludes with a summary ofthe estimated intakes for each pathway evaluated(Section 6.9).

6.1.2 REASONABLE MAXIMUM EXPOSURE

Actions at Superfund sites should be basedon an estimate of the reasonable maximumexposure (RMS') expected to occur under bothcurrent and, future land-use conditions. Thereasonable rnarimum exposure is defined here as

5

the highest exposure that is reasonably expectedto occur at a site. RMEs are estimated forindividual pathways. If a population is exposedvia more than one pathway, the combination ofexposures across pathways also must represent anRME.

Estimates, of the reasonable maximumexposure necessarily1 involve the use ofprofessional judgment.* This chapter providesguidance for determining the RME at a site andidentifies some exposure variable valuesappropriate for use in this determination. Thespecific values identified should be regarded asgeneral recommendations, and could change basedon site-specific information and the particularneeds of the EPA remedial project manager(RPM). Therefore, these recommendations shouldbe used in conjunction with input from the RPMresponsible for the site.

In the past, exposures generally wereestimated for an average and an upper-boundexposure case, instead of a single exposure case(for both current and future land use) asrecommended here. The advantage of the twocase approach is that the resulting range ofexposures provides some measure of theuncertainty surrounding these estimates. Thedisadvantage of this approach is that the upper-bound estimate of exposure may be above therange of possible exposures, whereas the averageestimate is lower than exposures potentiallyexperienced by much of the population.,. The'intent of the RME is to estimate a conservative-exposure case (i.e^ well above the average case)'that is. still within; the range of possible exposures. ^Uncertainty is still evaluated under this approach.However, instead of combining many sources ofuncertainty into average and upper-boundexposure estimates, the variation in individualexposure variables is used to evaluate uncertainty(See Section 6.8). In this way, the variablescontributing most to uncertainty in the exposureestimate are more easily identified.

6.2 STEP 1: CHARACTERI-ZATION OF EXPOSURESETTING

The first step in evaluating exposure atSuperfund sites is to characterize the site withrespect to its physical characteristics as well asthose of the human populations on and near thesite. The output of this step is a qualitativeevaluation of the site and surrounding populationswith respect to those characteristics that influenceexposure. All information gathered during thisstep will support ihe identification of exposurepathways in Step 2. In addition, the informationon the potentially exposed populations will beused in Step 3 to determine the values of someintake variables.

6.2.1 CHARACTERIZE PHYSICALSETTING

Characterize the exposure setting with respectto the general physical characteristics of the site.Important site characteristics include thefollowing:

• climate (e.g., temperature,precipitation);

• meteorology (e.g., wind speed anddirection);

• geologic setting (e.g., location andcharacterization of underlying strata);

• vegetation (e.g., unvegetated, forested,grassy);

• soil type (e.g., sandy, organic, acid,basic);

• ground-water hydrology (e.g., depth,direction and type of flow); and

• location and description of surface water(e.g., type, flow rates, salinity).

Sources of this information include sitedescriptions and data from the preliminaryassessment (PA), site inspection (SI), and remedialinvestigation (RI) reports. Other sources includecounty soil surveys, wetlands maps, aerial

6

photographs, and reports by the National.Oceanographic and Atmospheric Association(NOAA) and the U.S. Geological Survey (USGS).The assessor also should consult with appropriatetechnical experts (e.g., hydrogeologists, airmodelers) as needed to characterize the site.

6.2.2 CHARACTERIZE POTENTIALLYEXPOSED POPULATIONS

Characterize the populations on or near thesite with respect to location relative to the site,activity patterns, and the presence of sensitivesubgroups.

Determine location of current populationsrelative to the site. Determine the distance anddirection of potentially exposed populations fromthe site. Identify those populations that^ areclosest to or' actually* living on; the site and that,therefore, may have the greatest potential forexposure. Be sure to include potentially exposed1

distant populations, such as public water supplyconsumers- 'and^'ritetohtrcbhsumers'?- of* fish orshellfish" or agricultural products' from the sitearea. Also include populations that could beexposed in the "future to chemicals that havemigrated from: the site. Potential sources of thisinformation include:

• site visit;;

• other information, gathered as pan ofthe SI or during the initial stages of theRt

• population surveys conducted near thesite;

• topographic, land use, housing or othermaps; and

• recreational and commercial fisheriesdata.

Determine current land use. Characterizethe activities and activity patterns of thepotentially exposed population. The followingland use categories will be applicable most oftenat Superfund sites:

• residential;• commercial/industrial; and

• recreational.

Determine the current land use or uses ofthe site and surrounding area. The best sourceof this information is a site visit. Look forhomes, playgrounds, parks, businesses, industries,or other land uses on or in the vicinity of the site.Other sources on local land use include:?

• zoning maps;o

• state or local zoning or other land use-related laws and regulations;

• datay fronv the U.S. Bureau of theCensus;"

• topographic, land use, housing or othermaps;, and

• aerial photographs.

Some land uses at a site may not fit neatlyinto one of the three land use categories andother land use classifications may be moreappropriate (e.g., agricultural land use). At some*sites, it may be most appropriate to have morethan one land: use category] •'v

After defining the land use(s) for a site,identify human activities and activity patternsassociated with each land use. This is basicallya "common sense* evaluation and is not based onany specific data sources, but rather on a generalunderstanding of what activities occur inresidential, business, or recreational areas.

Characterize activity patterns by doing thefollowing.

• Determine the percent of time that thepotentially exposed population(s) spendin the potentially contaminated area.For example, if the potentially exposedpopulation is commercial or industrial,a reasonable maximum daily exposureperiod is likely to be 8 hours, (a typicalwork day). Conversely, if the populationis residential, a maximum daily exposureperiod of 24 hours is possible.

• Determine if activities occur primarilyindoors, outdoors, or both. For example,

7

office workers may spend all their timeindoors, whereas construction workersmay spend all their time outdoors.

• Determine how activities change withthe seasons. For exampje, someoutdoor, summertime recreationalactivities (e.g., swimming, fishing) willoccur less frequently or not at all duringthe winter months. Similarly, childrenare likely to play outdoors less frequentlyand with more clothing during the wintermonths.

• Determine if the site itself may be usedby local populations, particularly if accessto the site is not restricted OF otherwiselimited (e.g;, by distance). For sample,children living in the area could playonsite, and local residents could hunt orhike onsite.

• Identify any site-specific populationcharacteristics that might influenceexposure. For example, if the site islocated near major commercial orrecreational fisheries or sheliSsheries,the potentially exposed population islikely to eat more locally-caught fish andshellfish than populations located inland.

Determine future land use. Detenniae if anyactivities associated with a current land" use are1

likely to be different under an: alternate futuresland use. > For example; if ground water is notcurrently used in the area, of tne site as a source.

^fdrinkihg water but is of potable quality, future"use of ground water as drinking water srould be^

Igle. • Also determine, if land use of the siterepaid change in the future. For example^

a site is currently classified as industrial.determinenPlt could poisibly" be used forresidential or recreational purposes in the future.

Because residential land use is most oftenassociated with the greatest exposures, it isgenerally the most conservative choice to makewhen deciding what type of alternate fand usemay occur in the future. However, an assumptionof future residential land use may not bejustifiable if the probability that the site willsupport residential use in the future is exceedinglysmall.

Therefore, determine possible alternate futureland, uses based on available information andprofessional judgment Evaluate pertinentinformation sources, including (as available):

• master plans (city or county projectionsof future land use);

• Bureau of the Census projections; and

• established land use trends in the generalarea and the area immediatelysurrounding the site (use Census Bureauor state or local reports, or use generalhistorical accounts of the area).

Note that while these sources provide potentiallyuseful information, they should notbe interpretedas providing proof that a certain land irse will orwilTnotf occur; *

Assume future residential land use if it seemspossible based on the evaluation of the availableinformation. For example, if the site is currentlyindustrial but is located near residential areas inan urban area, future residential land use may bea reasonable possibility. If the site is industrialand is located in a very rural area with a lowpopulation density and projected low growth,future residential use would probably be unlikely,in this case, a. more likely alternate future landuse may be recreational. At some sites, it may bemost reasonable to assume that the land use willnot change in the future.

There are no hard-and-fast rules by which todetermine alternate future land use; The use.ofprofessional judgment; in this step: is critical- Be^sure to consult with the RPM about anv decisionregarding alternate future land use1. Support theselection of any alternate land use with a logical,reasonable argument in the exposure assessmentchapter of the risk assessment report Alsoinclude a qualitative statement of the likelihoodof the future land use occurring.

Identify subpopulations of potential concern.Review information on the site area to determineif any subpopulations may be at increased riskfrom chemical exposures due to increasedsensitivity, behavior patterns that may result inhigh exposure, and/or current or past exposuresfrom other sources. Subpopulations that may be

8

more sensitive to chemical exposures includeinfants and children, elderly people, pregnant andnursing women, and people with chronic illnesses.Those potentially at higher risk due to behaviorpatterns include children, who are more likely tocontact soil, and persons who may eat largeamounts of locally caught fish or locally grownprcuuce (e.g., home-grown vegetables).Subpopulations at higher risk due to exposuresfrom other sources include individuals exposed tochemicals during occupational activities andindividuals living in industrial areas.

To identify subpopulations of potentialconcern in the site area, determine locations ofschools, day care centers, hospitals, nursing homes,retirement communities, residential areas withchildren, important commercial or recreationalfisheries near the site, and major industriespotentially involving chemical exposures. Uselocal census data and information from localpublic health officials for this determination.

63 STEP 2: IDENTIFICATIONOF EXPOSURE PATHWAYS

This section describes an approach foridentifying potential human exposure pathways ata Superfund site. An exposure pathway describesthe course a chemical or physical agent takes fromthe source to the exposed individual An exposurepathway analysis links the sources, locations, andtypes of environmental releases with populationlocations and activity patterns to determine thesignificant pathways of human exposure.

An exposure pathway generally consists offour elements: (1) a source and mechanism ofchemical release, (2) a retention or transportmedium (or media in cases involving mediatransfer of chemicals), (3) a point of potentialhuman contact with the contaminated medium(referred to as the exposure point), and (4) anexposure route (e.g., ingestion) at the contactpoint A medium contaminated as a result of apast release can be a contaminant source for othermedia (e.g., soil contaminated from a previousspill could be a contaminant source for groundwater or surface water). In some cases, the sourceitself (Le., a tank, contaminated soil) is theexposure point, without a release to any other

medium. In these latter cases, an exposurepathway consists of (1) a source, (2) an exposurepoint, and (3) an exposure route. Exhibit 6-2illustrates the basic elements of each type ofexposure pathway.

The following sections describe the basicanalytical process for identifying exposurepathways at Superfund sites and for selectingpathways for quantitative analysis. The pathwayanalysis described below is meant to be aqualitative evaluation of pertinent site andchemical information, and not a rigorousquantitative evaluation of factors such as sourcestrength, release rates, and chemical fate andtransport. Such factors are considered later inthe exposure assessment during the quantitativedetermination of exposure concentrations (Section6.5).

6J.1 IDENTIFY SOURCES ANDRECEIVING MEDIA

To determine possible release sources for asite in the absence of remedial action, use allavailable site descriptions and data from the PA,SI, and RI reports. Identify potential releasemechanisms and receiving media for past, current,and future releases. Exhibit 6-3 lists some typicalrelease sources, release mechanisms, and receivingmedia at Superfund sites. Use monitoring data inconjunction with information on source locationsto; support the analysis of past, continuing, orthreatened releases. For example, soilcontamination near an old tank would suggest thetank (source) ruptured or leaked (releasemechanism) to the ground (receiving media). Besure toi note any source that couldbe an exposurepoint in addition to a release source (e.g., openbarrels or tanks, surface waste piles or lagoons,contaminated soil).

Map the suspected source areas and theextent of contamination using the availableinformation and monitoring data. As an aid inevaluating air sources and releases, Volumes I andII of the National Technical Guidance Studies(NTGS; EPA 1989a,b) should be consulted.

9

EXHIBIT 6-2

ILLUSTRATION OF EXPOSUREPATHWAYS

Prevailing Wind Direction

TransportMedium (Air)

Releaae Mechanism(Volatilization)

ExposurePoint

Waato Pll«(Source)

Releaae Mechanism(SKo Leaching)

Transport Medium(Ground Water)

10

EXHIBIT 6-3

COMMON CHEMICAL RELEASE SOURCES ATSITES IN THE ABSENCE OF REMEDIAL ACTION

ReceivingMedium

ReleaseMechanism Release Source

Air

Surface water

Ground water

Soil

Sediment

Biota

Volatilization

Fugitive dustgeneration

Surface runoff

Episodic overlandflow

Ground-waterseepage

Leaching

Leaching

Surface runoff

Episodic overlandflow

Fugitive dustgeneration/deposition

Tracking

Surface runoff,Episodic overlandflow

Ground-waterseepage

leaching

Uptake(direct contact,ingestion, inhalation)

Surface wastes — lagoons,ponds, pits, spills

Contaminated surface waterContaminated surface soilContaminated wetlandsLeaking drums

Contaminated surface soilWaste piles

Contaminated surface soil

Lagoon overflowSpills, leaking containers

Contaminated ground water

Surface or buried wastesContaminated soil

Surface or buried wastes


Lagoon overflowSpills, leaking containers

Contaminated surface soilWaste piles


Surface wastes — lagoons,ponds, pits, spills


Contaminated ground water

Surface or buried wastesContaminated soil

Contaminated soil, surfacewater, sediment, groundwater or air

Other biota

11

6.3.2 EVALUATE FATE AND TRANSPORTIN RELEASE MEDIA

Evaluate the fate and transport of thechemicals to predict future exposures and to helplink sources with currently contaminated media.The fate and transport analysis conducted at thisstage of the exposure assessment is not meant toresult, in a quantitative evaluation- of media-specific, chemical concentrations. Rather, theintent.is to identify media that are receiving,ormay receive site-related chemicals. At this stage,the assessor should answer the questions: Whatchemicals occur in the sources at tfie site and inthe- eiSvirOKsmenf?"; In what inetiM* (onsite ando£feite7 do?; they occur nbw?r In w&afinedia andat what location may they occur in the future?'Screening-level analyses using available data andsimplified calculations or analytical models mayassist in this qualitative evaluation.

.... After a chemical is released to theenvironment it may be:

;• • transported (e.g., convected downstream; in water or on suspended sediment or, through the atmosphere};

• physically transformed (e.g., volatilization,precipitation);

• chemically transformed («. g., photolysis,Liyurolysis, oxidation, redaction, etc.);

• biologically transformed (e.g,bicdegradation); and/or

• accumulated in one 01 atore media(including the receiving medium).

To de^nnine the fate of the chemicals ofpotential < v;.ncern at a particular site, obtaininformatics on their physical/;\semical andenvironmental fate properties. Use computer databases (e.g., SRCs Environmental FateCHEMFATS, and BIODEG data Mscs; BIOSIS;AQUIRE) r;d the open literature as necessaryas sources or up-to-date inform Mion on thephysical/chemical and fate properties of thechemicals ov potential concern. Exhibit 6-4 listssome impor-nat chemical-specific fee parametersand briefly describes how these caa be used toevaluate a chemical's environmental fate.

Also consider site-specific characteristics(identified in Section 6.2.1) that may influencefate and transport. For example, soilcharacteristics such as moisture content, organiccarbon content, and cation exchange capacity cangjeatly influence the movement of many chemicals.A high water table may increase the probability ofleaching of chemicals in soil to ground water.

Use all applicable chemical and site-specificinformation to evaluate transport within andbetween media and retention or accumulationwithin a single medium. Use monitoring data toidentify media that are contaminated now and thefate pathway analysis to identify media that maybe contaminated now (for media not sampled) orin the future. Exhibit 6-5 presents someimportant questions to consider when developingthese pathways. Exhibit 6-6 presents a series offlow charts useful when evaluating the fate andtransport of chemicals at a site.

6JU IDENTIFY EXPOSURE POINTS ANDEXPOSURE ROUTES

After contaminated or potentially,contaminated media have been identified, identifyexposure points by determining if and where anyof the potentially exposed populations (identifiedin Step 1) can contact these media. Considerpopulation locations and activity patterns in thearea, including those of subgroups that may be ofparticular concern. Any point of potential contactwan a contaminated medium is an exposure point.Tiy to identify those exposure points where, thejconcentration:, tbatc will''-'bevcontacted is" thegreateso Therefore, consider including anycontaminated media or sources onsite, as apotential exposure point if.the site is currentlyused, if access to the site* under current conditionsis not restricted or otherwise limited (e.g., by-distance), or if contact is possible under analternate future land use. For potential offsiteexposures, the highest exposure concentrationsoften will be at the points closest to anddowngradient or downwind of the site. La somecases, highest concentrations may be encounteredat points distant from the site. For example, site-related chemicals may be transported anddeposited in a distant water body where they maybe subsequently bioconcentrated by aquaticorganisms.

12

EXHIBIT 6-4

IMPORTANT PHYSICAL/CHEMICAL ANDENVIRONMENTAL FATE PARAMETERS

provides a measure of the extent of chemical partitioning between organic carbon and water atequilibrium. The higher the K^, the more likely a chemical is to bind to soil or sediment than toremain in water.

Kd provides a soil or sediment-specific measure of the extent of chemical partitioning between soilor sediment and water, unadjusted for dependence upon organic carbon. To adjust for thefraction of organic carbon present in soil or sediment (foj, use K,, = K^-x f^. The higher the K,,,the more likely a chemical is to bind to soil or sediment than to remain in water.

K^ provides a measure of the extent of chemical partitioning between water and octanol atequilibrium. The greater the K „. the more likely a chemical is to partition to octanol than toremain in water. Octanol is used as a surrogate for Upids (fat), and K^can be used to predictbioconccntration in aquatic organisms.

Solubility is an upper limit on a chemical's dissolved concentration in water at a specified temperature.Aqueous concentrations in excess of solubility may indicate sorption onto sediments, thepresence of solubilinng chemicals such as solvents, or the presence of a non-aqueous phaseliquid.

Henry's Law Constant provides a measure of the extent of chemical partitioning between air and water atequilibrium. The higher the Henry's Law constant, the more likely a chemical is to volatilizethan to remain in the water.

Vapor Pressure is the pressure exerted by a chemical vapor in equilibrium with its solid or liquid form atany given temperature. It is used to calculate the rate of volatilization of a pure substance from asurface or in estimating a Henry's Law constant for chemicals with tow water solubility. Thehigher the vapor pressure, the more likely a chemical is to exist in a gaseous state.

Diflusivity describes the movement of a molecule in a liquid or gas medium as a result of differences inconcentration. It is used to calculate the dispersive component of chemical transport Thehigher the diffusrvity, the more likely a chemical is to move in response to concentrationgradients. _ '

BioconceBftrattoo Factor (BCD provides a measure of the extent of chemical partitioning at equilibriumbetween a biological medium such as fish tissue or plant tissue and an external medium such aswater. The higher the BCF. the greater the accumulation in living tissue is likely to be.

Media-specific Half-life provides a relative measure of the persistence of a chemical in a given medium,^though actual values can vary greatly depending on site-specific conditions. The greater thehalf-life, the more persistent a chemical is likely to be.

Page fr-13

EXHIBIT 6-5

IMPORTANT CONSIDERATIONS FOR DETERMININGTHE ENVIRONMENTAL FATE AND TRANSPORTOF THE CHEMICALS OF POTENTIAL CONCERN

AT A SUPERFUND SITE

What are the principal mechanisms for change or removal in each of the environmentalmedia?

How does the chemical behave in air, water, soil, and biological media? Does kbioaccumulate or biodegrade? Is it absorbed or taken up by plants?

• Does the agent react with other compounds in the environment?

Is there intermedia transfer? What are the mechanisms for intermedia transfer? Whatare the rates of the intermedia transfer or reaction mechanism?

• How long might the chemical remain in each environmental medium? How does itsconcentration change with time in each medium?

» What are the products into which the agent might degrade or change in the environment?Are these products potentially of concern?

Is a steady-state concentration distribution in the environment or in specific segments ofthe environment achieved?

Pa«e 6-14

EXHIBIT 6-6

FLOW CHART FORFATE AND TRANSPORT ASSESSMENTS

Environmental fate and transport assessment: atmosphere

Contaminant Release

*PotentialVolatilization ofContaminants

from Site

*Consider Directionand Rale ofContaminant

Migration withinAir. Major

Mechanisms: WindCurrents,Dispersion

rPotential Release of

Fugitive Dust/Contaminated

Particles from Site

' iConsider Direction andDistance of ParticulateMovement with Wind

Currento; MajorMechanisms: Wind Speed,Particle Size, Gravitational

Settling, Precipitation

f i i

CouldContaminants

Potentially ReachAgricultural,Hunting or

Fishing Areas?

DetermineProbable

Boundaries ofElevated

Concentrations

Consider Transferof Contaminants toPlants or AnimalsConsumed by Hu-mans; Assess Fate

in these Media

IdentifyPopulations

Directly ExposedtoCo

Consider Transferof Contaminants

to Surface Water;Assess Fate inthis Medium

Source: Adapted from EPA 1988b.

(continued)

15

EXHIBIT 6-6 (continued)


Environmental fate and transport assessment: surface water and sediment

Contaminant Release

I :

Could Exchangeof Water

BetMcea SurfaceWater and

Grouad Waterbe Stgntflcaat?

Release to Surface Water

Consider iMrertioe and Rate of ContaminantftilaralkM Within Waterbody

Astest Distance Downstream, or Area* of Lakes and Estuaries

Major Mechanics: Currents In Affected Rjven or Streams;Dispenioa in Im r̂admetitt: Tidal Currents and flushinf in

Estoviries; Partitkminf to Sediment

EstimateConcentrations

in Sediment

Estimate Sur, .e Water Contaminant Concentrations

Major Factors: : urce Release Strength. Dilutioa Volume

Could Water)Used for IrriffiUoncrWaterti

Lhegtock.orDOM Waterbot

wSMWtFWi

TraBsferef

to GroundWater; AaatasFatebilbJi

Medium

ConsiderTraaaferof

CoajtaflsinantsPleats or

Consumed by iHumao; Assec-1

Fate la theseMedia fj

ConsiderSediment as a

Source ofSurface WaterContaminants

KC•• Volatfl*?'

Identify HemaaPopulatfaxM

DirectlyExposed io

SurfaceWater

Transferor

to AirAssess Fate

ta thto Medium

Identify HumanPopulations

DirectlyExposed toSediment

Sottrer: Adapt* from EPA 198U>.

(continued)

16

EXHIBIT 6-6 (continued)


Environmental Tale and transport assessment: soils and ground water

Contaminant Release

i.

Release to Soils at orSurrounding the Site

Consider Rale of Contaminant Percolation Through UnsaturaledSoils Based on Soil Permeabilities, Water or Liquid Recharge Rates

Release to GroundWater Beneath Site

CouldContaminants

PotentiallyReach Ground

Water?

DoesContaminatedSoil Support

Edible Species?

Are Contaminants Vola-tile? Are Contaminantsin Fine Particle Form orSorbed to Particulates?

Consider Direction and Rate ofGrc'ind Water Flow Using

Available Hydrogeologic Data,or by Assuming These Will Ap-proximate Surface Topography

Reach A SurfaceWaterbody?

Reach Any WellsLocated

DowngradiMit?

Is Plume Sufficiently NearGround Surface to Allow

Direct Uptake of Contami-nated Ground Water by

Plants or Animals?

It Well Water Used forirrigation or for Wateringlivestock, or Could it be? .

ConsiderTransferor

Contaminant*to Surface

Water; Asses*Fate in thisMedium

(identifyHuman

'opulationsOirectly

; xnosed to'ill Water

Consider Transfer of Contami-nants to Plants or AnimaU

Consumed by Humans;Assess Fate in these Media

Consider Transfer ofContaminants to

Atmosphere: AssessFate in this Medium

Identify HumanPopulations

Directly Exposed^ to Soils

Sourct-Adaputlfrom EPA 1988b;

17

After determining exposure points, identifyprobable exposure routes (i.e., ingestion,inhalation, dermal contact) based on the mediacontaminated and the anticipated activities at theexposure points. In some instances, an exposurepoint may exist but an exposure route may not(e.g., a person touches contaminated soil but iswearing gloves). Exhibit 6-7 presents apopulation/exposure route matrix that can be usedin determining potential exposure routes at a site.

6.3.4 INTEGRATE INFORMATION ONSOURCES, RELEASES, FATE ANDTRANSPORT, EXPOSURE POINTS,AND EXPOSURE ROUTES INTOEXPOSURE PATHWAYS

Assemble the information developed in theprevious three steps and determine the completeexposure pathways that exist for the site. Apathway^js, complete- if theras.is* (1) a" source- orchemical; release from a source, (2) an exposureppMjs-.wherec, contact, can, occurs .and (3) < an'exposure route:,, by; which" <;ontact, can: occur.Otherwise, the pathway is incomplete, such as thesituation where shere is a scr.rce releasing to airbut there are no aearby people. If available fromATSDR, human monitoring data indicatingchemical accumulation or chemical-related effectsin the site area can be used as evidence tosupport conclusions about which exposurepathways are complete; however, negative datafrom such studies should not he used to concludethat a pathway is incomplete.

From all complete exposure pathways at asite, select those pathways that will be evaluatedfurther in the exposure assessment If exposureto a sensitive subpopulation is possible, select thatpathway for quantitative evaluation. All pathwaysshould be selected for furthest evaluation- unlessthere is sound! justification :&g., based on theresults of a screening analysis) to eliminate apathway from detailed analysis; Such ajustification could be based on one of thefollowing:

• the exposure resulting from the pathwayis mucii less than -bat from anotherpathway involving ?.h« same medium atthe same exposure point;

• the potential magnitude of exposure^_ilom a pathuay-k- Inw; or --

the probability of the exposure occurringis very low and the risks associated withthe occurrence are not high (if apathway has catastrophic consequences,it should be selected for evaluation evenif its probability of occurrence is very

Use professional judgment and experience tomake these decisions. Before deciding to excludea pathway from quantitative analysis, consult withthe RPM. If a pathway is excluded from furtheranalysis, clearly document the reasons for thedecision in the exposure assessment section of therisk assessment report.

For some complete pathways it may not bepossible to quantify exposures in the subsequentsteps of the analysis because of a lack of data onwhich to base estimates of chemical release,environmental concentration, or human intake.Available modeling results should complement andsupplement the available monitoring data tominimize such problems. However, uncertaintiesassociated with the modeling results may be toolarge to justify quantitative exposure assessmentin the absence of monitoring data to validate themodeling results. These pathways shouldnevertheless be carried through the exposureassessment so that risks can be qualitativelyevaluated or so that this information can beconsidered during the uncertainty analysis of theresults of the exposure assessment (see Section6.8) and the risk assessment (see Chapter 8).

SUMMARIZE INFORMATION ONALL COMPLETE EXPOSUREPATHWAYS

Summarize pertinent information on allcomplete exposure pathways at the site byidentifying potentially exposed populations,exposure media, exposure points, and exposureroutes. Also note if the pathway has beenselected for quantitative evaluation; summarize thejustification if a pathway has been excluded.Summarize pathways for current land use and anyalternate future land use separately. Thissummary information is useful for defining thescope of the next step (quantification of exposure)

Pa* 6-11

EXHIBIT 6-7

MATRIX OF POTENTIAL EXPOSURE ROUTES

Exposure Medium/ Residential Commercial/IndustrialExposure Route Population Population

! Ground Water

IngestionDermal Contact

Surface Water

IngestionDermal Contact

Sediment

Incidental IngestionDermal Contact

AirInhalation of VaporPhase ChemicalsIndoorsOutdoors

Inhalation ofParticnlates

IndoorsOutdoors

Soil/Dust

Incidental IngestioaDermal Contact

Food

InajestionFish and ShellfishMeat and GameDairyEggsVegetables

•

LL

LL

CC

LL

LL

L.CL.C

LLL.CLL

' AA

AA

AA

AA

AA

AA

—— ~

——•̂

RecreationalPopulation

——

L,CL.C

CL,C

—L

—L

L.CL,C

LLLLL

LCA '

i txponav IM children may bt tiptififomify gr*at*r that foothills< exposure io adult* (highest apontn it Slufy to occur during occupational activities)

— * Expotun of this population via this rout* is not litety to occur.

19

and also is useful as documentation of theexposure pathway analysis. Exhibit 6-8 providesa sample format for presenting this information.

6.4 STEP 3: QUANTIFICATIONOF EXPOSURE! GENERALCONSIDERATIONS

The next step in the exposure assessmentprocess is to quantify the magnitude, frequencyand duration of exposure for the populations andexposure pathways selected for quantitativeevaluation. This step is most often conducted, intwo stages: first, exposure concentrations areestimated, then, pathway-specific intakes arequantified. The specific methodology forcalculating exposure concentrations and pathway-specific exposures are presented in Sections 6.5and 6.6, respectively. This section describes someof the basic concepts behind these process as.

6.4.1 QUANTIFYING THE REASONABLEMAXIMUM EXPOSURE

Exposure is defined as the contact of anorganism with a chemical or physical agent. Ifexposure occurs over time, the total exposure canbe divided by a time period of interest to obtainan average exposure rate per unit time. Thisaverage exposure rate also can be expressed as afunction of body weight For the purposes :f thismanual, exposure normalized for time and bodyweight is termed 'intake", and is expressed ia unitsof mg chemical/kg body weight-day.

Exhibit 6-9 presents a generic equation forcalculating chemical intakes and defines the intakevariables. There are three categories of variablesthat are used to estimate intake:

(1) chemical-related variable - exposureconcentration;

(2) variables that describe the exposedpopulation - contact rate, exposurefrequency and duration, and body weight;and

(3) assessment-determinedaveraging time.

variable -

Each intake variable in the equation has arange of values. For Superfund exposureassessments, intake variable values for a givenpathway should be selected so that thecombination of all intake variables results in anestimate of the reasonable maximum exposure forthat pathway. As defined previously, thereasonable maximum exposure (RME) is themaximum exposure that is reasonably expected tooccur at a site. Under this approach, some intakevariables may not be at their individual maximumvalues but when in combination with othervariables will result in estimates of the RME.Some recommendations for determining the valuesof the individual intake variables are discussedbelow. These recommendations are based onEPA's determination of what would result in anestimate of the RME. As discussed previously, adetermination of "reasonable" cannot be basedsolely on quantitative information, but alsorequires the use of professional judgment.Accordingly, the recommendations below are basedon a combination of quantitative information andprofessional judgment These are generalrecommendations, however, and could changebased on site-specific information or the particularneeds of the risk manager. Consult with the RPMbefore varying from these recommendations.

Exposure concentration. The concentrationterm in the intake equation is the arithmeticaverage of the concentration that is contacted overthe exposure period. Although this concentrationdoes not reflect the maximum concentration thatcould be contacted at any one time, it is regardedas a reasonable estimate of the concentrationlikely to be contacted over time. This is becausein most situations, assuming long-term contactwith the maximum concentration is notreasonable, (For exceptions to this generalization,see discussion of hot spots in Section 6.5.3.)

Because of the uncertainty associated withanv estimate of exposure concentration, the upperconfidence limit de.. the 95 percent upperconfident limit) on the arithmetic average will beused for *>"'* variable. There are standardstatistical methods which can be used to calculatethe upper confidence limit on the arithmeticmean. Gilbert (1987, particularly sections 11.6and 13.2) discusses methods that can be appliedto data that are distributed normally or lognormally. Kriging is another method that

20

EXHIBIT 6-8

EXAMPLE OF TABLE FORMAT FOR SUMMARIZINGCOMPLETE EXPOSURE PATHWAYS AT A SITE

Potentially Exposed Exposure Route, MediumPopulation and Exposure Point

Pathway Selectedfor Evaluation?

Reason for Selectionor Exclusion

Cii tT jnd UM

Residents

IndustrialWorkers

Residents

Residents

Ingestion of ground water^mj6^;wll^dowi^i

gradient of the site

Inhalation of chemicalsvolatilized from groundwater during home use

Direct contact withchemicals of potentialconcern in soil on thesite

pirect contact with chemi-cals

Yes

Yes

Yes

concernin soil bo the site

Ingestion of chemicalsthat have accumulated infish located in onsiteponds

Yes

No

Residents use groundwater from local wells .,as drinkinjs water. "7* ••

Some of the chemicalsof potential concern inground water are volatile,and ground water is usedby local residents.

Contaminated soil is inan area potentially usedby outside maintenanceworkers.

Area could be developed,'in the future as »^'""'>residential area.,,,,

The potential for signifi-cant exposure via thispathway is low becausenone of the chemicals ofpotential concern accumulateextensively in fish.

25

it may not be appropriate to group samples at all,but may be most appropriate to treat the sampledata separately when estimating intakes. Still, inother instances', the assessor may wish to use themaximum concentration from a medium as theexposure concentration for a given pathway as ascreening approach to place an upper bound onexposure. In these cases it is important toremember that if a screening level approachsuggests a potential health concern, the estimatesof exposure should be modified u reflect moreprobable exposure conditions.

In those instances where it is appropnate togroup .sampling data from a particular medium,calculate for each exposure medium and eachchemical the 95 percent upper confidence limit onthe arithmetic average chemical concentration.See Chapter 5 for guidance on how to treatsample concentrations below the quantitationlimit.

Modeling approaches. In some instances, itmay not be appropriate to use monitoring dataalone, and fate and transport models may berequired to estimate .exposure concentrations.Specific instances where monitoring data alonemay not be adequate are as follows.

• Where exposure points are spatiallyseparate from monitoring points.Models may be required when exposurepoints are remote from sources ofcontamination if mechanisms for releaseand transport to exposure points exist(e.g., ground-water transport, airdispersion).

• Where temporal distribution of data islacking. Typically, data from Superfundinvestigations are collected over arelatively short period of time. Thisgenerally will give a clear indication ofcurrent site conditions, but both long-term and short-term exposure estimatesusually are required in Superfundexposure assessments. Although theremay be situations where it is reasonableto assume that concentrations willremain constant over a long period oftime, in many cases the time span of themonitoring data is not adequate topredict future exposure concentrations.

Environmental models may be requiredto make these predictions.

• Where monitoring data are restricted bythe limit of quantitation. Environmentalmodels may be needed to predictconcentrations of contaminants that maybe present at concentrations that arebelow the quantitation limit but that maystill cause toxic effects (even at such lowconcentrations). For example, in thecase of a ground-water plume discharginginto a river, the dilution afforded by theriver may be sufficient to reduce theconcentration of the chemical to a levelthat could not be detected by directmonitoring. However, as discussed inSection 5.3.1, the chemical may besufficiently toxic or btoaccumulative thatu could present a health risk atconcentrations below the limit ofquantitation. Models may be requiredto make exposure estimates in thesetypes of situations.

A wide variety of models are available foruse in exposure assessments. SEAM (EPA 1988b)and the Erasure Assessment Methods Handbook(EPA 1989f) describe some of the modelsavailable and provide guidance in selectingappropriate modeling techniques. Also, theCenter for Exposure Assessment Modeling(CEAM -- Environmental Research Laboratory(ERL) Atiiens), the Source Receptor AnalysisBranch (Office of Air Quality Planning andStandards, or OAQPS); and modelers in EPAregional offices can provide assistance in selectingappropriate models. Finally, Volume IV of theNTCS (EPA 1989c) provides guidance for air andatmospheric dispersion modeling for Superfundsites. Be sure to discuss the fate and transportmodels to be used in the exposure assessment withthe RPM.

The level of effort to be expended inestimating exposure concentrations will depend onthe type and quantity of data available, the levelof detail required in the assessment, and theresources available for the assessment. In general,estimating exposure concentrations will involveanalysis of site monitoring data and application ofsimple, screening-level analytical models. Themost important factor in determining the level of

26

effort will be the quantity and quality of theavailable data. In general, larger data sets willsupport the use of more sophisticated models.

Other considerations. When evaluatingchemical contamination at a site, it is importantto review the spatial distribution of the data andevaluate it in ways that have the most relevanceto the pathway being assessed. In shon, considerwhere the contamination is with respect to knownor anticipated population activity patterns. Mapsof both concentration distribution and activitypatterns will be useful for the exposureassessment. It is the intersection of activitypatterns and contamination that defines anexposure area. Data from random sampling orfrom systematic grid pattern sampling may bemore representative of a given exposure pathwaythan data collected only from hot spots.

Generally, verified GC/MS laboratory datawith adequate quality control will be required tosupport quantitative exposure assessment Fieldscreening data generally cannot be incorporatedwhen estimating exposure concentrations becausethey are derived using less sensitive analyticalmethods and are subject to less stringent qualitycontrol.

Other areas to be considered in estimatingexposure concentrations are as follows.

• Steady-state vs. non-steadv-stateconditions. Frequently, it may benecessary to assume steady-stateconditions because the informationrequired to estimate non-steady-stateconditions (such as source depletionrate) is not readily available. This islikely to overestimate long-term exposureconcentrations for certain pathways.

• Number and type of exposure parametersthat must be assumed. In developingexposure models, values for site-specificparameters such as hydraulicconductivity, organic carbon content ofsoil, wind speed and direction, and soiltype may be required. These values maybe generated as pan of the RL In caseswhere these values are not available,literature values may be substituted. Inthe absence of applicable literature

values, the assessor must consider if areliable exposure concentration estimatecan be made.

Number and type of fate processes tobe considered. In some cases, exposuremodeling may be limited toconsiderations of mass balance, dilution,dispersion, and equilibrium partitioning.In other cases, models of more complexfete processes, such as chemical reaction,biodegradation, and photolysis may beneeded. However, prediction of suchfate processes requires significantly largerquantities of model calibration andvalidation data than required for lesscomplex fate processes. For those siteswhere these more complex fate processesneed to be modeled, be sure to consultwith the RPM regarding the added datarequirements.

ESTIMATE EXPOSURECONCENTRATIONS IN GROUNDWATER

Exposure concentrations in ground water can f:f-be based on monitoring data alone or on acombination of monitoring and modeling. Insome cases, the exposure assessor may favor theuse of monitoring data over the use of complexmodels to develop exposure concentrations. It ismost appropriate to use ground-water samplingdata as estimates of exposure concentrations whenthe sampling points correspond to exposurepoints, such as samples taken from a drinkingwater tap. However, samples taken directly froma domestic well or drinking water tap should beinterpreted cautiously. For example/where thewater is acidic, inorganic chemicals such as leador copper may leach from the distribution system.Organic chemicals such as phthalates may migrateinto water from plastic piping. Therefore,interpretations of these data should consider thetype and operation of the pumping," storage, anddistribution system involved.

.eMost of thejime, data from monitoring wells^

at the exrxKyje_poiafc—Several issues should beconsidered when using monitoring.well data toestimate.these concentrations. First, detenninejfthe aquifer has sufficient production capacity and;'

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T_uses. soTt generally should be"assumed that water could be" drawn from^nywhefe *in the aquifer, regardless of the> locatioiPo?existing wells relative to the contaminant plume.In a few situations, however, it may not bereasonable to assume that water will be drawnfrom directly beneath a specific source (e.g., awaste management unit such as a landfill) in thefuture. In_these_cases, it should be assumed thatwater couldbe^drawnjrom directly adjacent to the.source. Selection of the location(s) used toevaluate future~gfou1ad-water exposures should bemade in consultation with the~RPM: Second,compare me construction or wells (e.g., drinkingwater wells) in the area with the construction ofthe monitoring wells. For example, drinking waterwells may draw water fromjaorejhan one aqffifer,whereas individual monitoring welis~areTisaalIy"screened in a specific aquifer. In some cases itmay be appropriate to separate data from twoaquifers that have very limited hydraulicconnection if drinking water wells in the areadraw water from only one of them. Consult ahydrogeologist for assistance in the aboveconsiderations.

Another issue to consider is filtration ofwater samples. While filtration of ground-watersamples provides useful information forunderstanding chemical transport within an aquifer(see Section 4.53 for more details), the use offiltered samples for estimating exposure is verycontroversial because these data mayunderestimate chemical concentrations in waterfrom, an unfiltered tap. Therefore, data fromunfiltered samples should be used to estimateexposure concentrations. Consult with the RPMbefore using <iata fmtn filtered

Ground-water monitoring data are oftea oflimited use for evaluating long-term exposureconcentrations because they are generallyrepresentative of current site conditions and notlong-term trends. Therefore, ground-water modelsmay be needed to estimate exposureconcentrations. Monitoring data should be usedwhen possible to calibrate the models.

Estimating exposure concentrations in groundwater using models can be a complex task becauseof the many physical and chemical processes thatmay affect transport and transformation in ground

water. Among the important mechanisms thatshould be considered when estimating exposureconcentrations in ground water are leaching fromthe surface, udvection (including infiltration, flowthrough the • unsaturatcd zone, and flow withground wa&r), dispersion, sorption (includingadsorption, desorption, and ion exchange), andtransformation (including biological degradation,hydrolysis, oxidation, reduction, complexation,dissolution, and precipitation). Anotherconsideration is that not all chemicals may bedissolved m water, but may be present instead innonaqueous phases that float on top of groundwater or sink to the bottom of the aquifer.

} -The proper selection and application of soil

and ground-water models requires a thoroughunderstanding of the physical, chemical, andhydrogeologic characteristics of the site. SEAM(EPA I98£b) provides & discussion of the factorscontrolling soil and ground-water contaminantmigration as well as descriptions of various soiland ground ̂ vater models. For more in-depthguidance o.u the selection and; application ofappropriate ground-w£ter models, consultSelection Crixgria for Mathematical Models Used inExposure Assessments: Ground-water Models (EPA1988c). As %ith all modeling, the assessor shouldcarefully evaluate the applicability of the model tothe site beiat evaluated, and should consult witha hydrogeolcgist as necessary. '

If ground-water modeling is noFused;'current3'concentratioasv can be a£«d to represent; futureconcentrations in groun«i water assuming steady-state conditions; This assumption should be noted *~in the exposure assessment chapter and in theuncertainties and conclusions of the riskassessment

&5J ESTIMATE EXPOSURECONCENTRATIONS IN SOIL

Estimates of current exposure concentrationsin soil cac be based directly on summarizedmonitoring data if it is assumed thatconcentrations remain constant over time. Suchan assumption may not be appropriate for somechemicals and some sites where leaching,volatilization, photolysis, biodegradation, winderosion, and surface runoff will reduce chemicalconcentrations over time. Soil monitoring dataand site conditions should be carefully screened to

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identify situations where source depletion is likelyto be important. SEAM (EPA 1988b) givessteady-state equations for estimating many of theseprocesses. However, incorporating these processesinto the calculation of exposure concentrations forsoil involves considerable effort. If a modelingapproach is not adopted in these situations,assume a constant concentration over time andbase exposure concentrations on monitoring data.This assumption should be clearly documented.

In evaluating monitoring data for theassessment of soil contact exposures, the spatialdistribution of the data is a critical factor. Thespatial distribution of soil contamination can beused as a basis for estimating the averageconcentrations contacted over time if it is assumedthat contact with soil is spatially random (i.e., ifcontact with soil in all areas of the site is equallyprobable). Data from random sampling programsor samples from evenly spaced grid networksgenerally can be considered as representative ofconcentrations across the site. At many siteshowever, sampling programs are designed tocharacterize only obviously contaminated soils orhot spot areas. Care must be taken in evaluatingsuch data sets for estimating exposureconcentrations. Samples from areas where directcontact is not realistic (such as where a steepslope or thick vegetation prevents current access)should not be considered when estimating currentexposure concentrations for direct contactpathways. Similarly, the depth of the sampleshould be considered; surface soil samples shouldbe evaluated separately from subsurface samplesif.direct contact with surface soil or inhalation ofwind blown dust are potential exposure pathwaysat the site.

In some cases, contamination may beunevenly distributed across a site, resulting in hotspots (areas of high contamination relative toother areas of the site). If a hot spot is locatednear an area which, because of site or populationcharacteristics, is visited or used more frequently,exposure to the hot spot should be assessedseparately. The area over which the activity isexpected to occur should be considered whenaveraging the monitoring data for a hot spot Forexample, averaging soil data over an area the sizeof a residential backyard (e.g., an eighth of anacre) may be most appropriate for evaluatingresidential soil pathways.

6.5.4 ESTIMATE EXPOSURECONCENTRATIONS IN AIR

There are three general approaches toestimating exposure concentrations in air: (1)ambient air monitoring, (2) emissionmeasurements coupled with dispersion modeling,and (3) emission modeling coupled with dispersionmodeling. Whichever approach is used, theresulting exposure concentrations should be asrepresentative as possible of the specific exposure"pathways being evaluated. If long-term exposuresare being evaluated, the exposure concentrationsshould be representative of long-term averages.If short-term exposures are of interest, measuredor modeled peak concentrations may be mostrepresentative.

If monitoring data have been collected at asite, their adequacy for use in a risk assessmentshould be evaluated by considering howappropriate they are for the exposures beingaddressed. Volume II of the NTGS (EPA 1989b)provides guidance for measuring emissions andshould be consulted when evaluating theappropriateness of emission data. See Chapter 4(Section 4.53) for factors to consider whenevaluating the appropriateness of ambient airmonitoring data; As long as there are nosignificant analytical problems affecting airsampling data, background levels are notsignificantly higher than potential site-relatedlevels, and site-related levels are not below theinstrument detection limit, air monitoring data canbe used to derive exposure concentrations. Therestill will be uncertainties inherent in using thesedata because they usually are not representativeof actual long-term average air concentrations.This may be because there were only a few samplecollection periods, samples were collected duringonly one type of meteorological or climaticcondition, or because the source of the chemicalswill change over time. These uncertainties shouldbe mentioned in the risk assessment.

In the absence of monitoring data, exposureconcentrations often can be estimated usingmodels. Two kinds of models are used toestimate air concentrations: emission models thatpredict the rate at which chemicals may bereleased into the air from a source, and dispersionmodels that predict associated concentrations inair at potential receptor points.

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Outdoor air modeling. Emissions may occuras a result of the volatilization of chemicals fromcontaminated media or as a result of thesuspension of onsite soils. Models that predictemission rates for volatile chemicals or dustrequire numerous input parameters, many ofwhich are site-specific. For volatile chemicals,emission models for surface water and soil areavailable in SEAM (EPA I988b). Volume IV ofthe NTGS (EPA 1989c) also provides guidance forevaluating volatile emissions at Superfund sites.Emissions due to suspension of soils may resultfrom wind erosion of exposed soil particles andfrom vehicular disturbances of the soil. Topredict soil or dust emissions, EPA's fugitive dustmodels provided in AP42 (EPA 1985b) or modelsdescribed in SEAM (1988b) may be used.Volume IV of the NTGS (EPA 1989c) also willbe useful in evaluating fugitive dust emissions atSuperfund sites. Be sure to critically review allmodels before use to determine their applicabilityto the situation and site being evaluated. Ifnecessary, consult with air modelers in EPAregional offices, the Exposure Assessment Groupin EPA headquarters or the Source ReceptorAnalysis Branch in OAQPS.

After emissions have been estimated ormeasured, air dispersion models can be applied toestimate air concentrations at receptor points. Inchoosing a dispersion model, factors that must beconsidered include the type of source and thelocation of the receptor relative to the source.For area or point sources, EPA's Industrial SourceComplex model (EPA 1987a) or the simpleGaussian dispersion models di.snis.srd in SEAM(EPA 1988b) can provide air concentrationsaround the source. Other models can be foundin Volume IV of the NTGS (EPA 1989c). TheSource Receptor Analysis Branch of OAQPS alsocan be contacted for assistance. Again, criticallyreview all models for their applicability.

Indoor air modeling. Indoor emissions mayoccur as a result of transport of outdoor-generateddust or vapors indoors, or as a result ofvolatilization of chemicals indoors during use ofcontaminated water (e.g., during showering,cooking, washing). Few models are available forestimating indoor air concentrations from outsidesources. For dust transport indoors, it cangenerally be assumed that indoor concentrationsare less than those outdoors. For vapor transport

indoors, concentrations indoors and outdoors canbe assumed to be equivalent in most cases.However, at sites where subsurface soil gas orground-water seepage are entering indoors, vaporconcentrations inside could exceed those outdoors.Vapor concentrations resulting from indoor use ofwater may be greater than those outdoors,depending on the emission source characteristics,dispersion indoors, and indoor-outdoor airexchange rates. Use models discussed in theExposure Assessment Methods Handbook (EPA1989f) to evaluate volatilization of chemicals fromindoor use of water.

6.5.5 ESTIMATE EXPOSURECONCENTRATIONS IN SURFACEWATER

Data from surface water sampling andanalysis may be used alone or in conjunction withfate and transport models to estimate exposureconcentrations. Where the sampling pointscorrespond to exposure points, such as atlocations where fishing or recreational activitiestake place, or at the intake to a drinking watersupply, the monitoring data can be used alone toestimate exposure concentrations.- However, thedata must be carefully screened. The complexityof surface water processes may lead to certainlimitations in monitoring data. Among these arethe following.

• Temporal representativeness. Surfacewater bodies are subject to seasonalchanges in flow, temperature, and depththat may significantly affect the fiate andtransport of contaminants. Releases tosurface water bodies often depend onstorm conditions to produce surfacerunoff and soil erosion. Lakes aresubject to seasonal stratification andchanges in biological activity. Unless thesurface water monitoring program hasbeen designed to account for thesephenomena, the data may not representlong-term average concentrations orshort-term concentrations that may occurafter storm events.

• Spatial representsitrfene&s. Considerablevariation in concentration can occur withrespect to depth and lateral location insurface water bodies. Sample locations

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should be examined relative to surfacewater mixing zones. Concentrationswithin the mixing zone may besignificantly higher than at downstreampoints where complete mixing has takenplace.

Quantitation limit limitations. Wherelarge surface water bodies are involved,contaminants that enter as a result ofground-water discharge or runoff fromrelatively small areas may be significantlydiluted. Although standard analyticalmethods may not be able to detectchemicals at these levels, the toxic effectsof the chemicals and/or their potentialto bioaccumulate may neverthelessrequire that such concentrations be

• Contributions from other sources.Surface water bodies are normally subjectto contamination from many sources(e.g., pesticide runoff, stormwater,wastewater discharges, acid minedrainage). Many of the chemicalsassociated with these sources may bedifficult to distinguish from site-relatedchemicals. In many cases backgroundsamples wfll be useful in assessing site-related contaminants from othercontaminants (see Section 4.4).However, there may be other caseswhere a release and transport model maybe required to make the distinction.

Many analytical and numerical models areavailable to estimate the release of contaminantsto surface water and to predict the fate ofcontaminants once released. The models rangefrom simple mass balance relationships tonumerical codes that contain terms for chemicaland biological reactions and interactions withsediments. In general, the level of informationcollected during the RI will tend to limit the useof the more complex models.

There are several documents that can btconsulted when selecting models to estimatesurface water exposure concentrations, includingSEAM (EPA 1988b), the Exposure AssessmentMethods Handbook (EPA 1989Q, and Selection

Criteria for Mathematical Models Used in ExposureAssessments: Surface Water Models (EPA 1987b).SEAM lists equations for surface water runoff andsoil erosion and presents the basic mass balancerelationships for estimating the effects of dilution.A list of available numerical codes for morecomplex modeling also is provided. The selectioncriteria document (EPA 1987b) provides a morein-depth discussion of numerical codes and othermodels. In addition, it provides guidelines andprocedures for evaluating the appropriate level ofcomplexity required for various applications. Thedocument lists criteria to consider when selectinga surface water model, including: (1) type of waterbody, (2) presence of steady-state or transientconditions, (3) point versus non-point sources ofcontamination, (4) whether 1, 2, or 3 spatialdimensions should be considered, (5) the degreeof mixing. (6) sediment interactions, and (7)chemical processes. Each of the referenceddocuments should be consulted prior to anysurface water modeling.

6.5.6 ESTIMATE EXPOSURECONCENTRATIONS IN SEDIMENTS

In general, use sediment monitoring data toestimate exposure concentrations. Sedimentmonitoring data can be expected to provide bettertemporal representativeness than surface waterconcentrations. This will especially be true in thecase of contaminants such as PCBs, PAHs, andsome inorganic chemicals, which are likely toremain bound to the sediments. When usingmonitoring data to represent exposureconcentrations for direct contact exposures, datafrom surfidal, near-shore sediments should beused. . _ . . : . ! _ _ _ .

If modeling is needed to estimate sedimentexposure concentrations, consult SEAM (EPA1988b). SEAM treats surface water and sedimenttogether for the purpose of listing availablemodels for the release and. transport ofcontaminants. Models for soil erosion releasesare equally applicable for estimating exposureconcentrations for surface water and sedimentMany of the numerical models listed in SEAMand the surface water selection criteria document(EPA 1987b) contain sections devoted to sedimentfate and transport.

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