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ALABAMARISK‐BASEDCORRECTIVEACTIONGUIDANCEMANUALRevision3.
0February2017NOTICEThisdocumenthasbeenpreparedtoassistindividualsinunderstandingtheminimumnecessaryelementsofconductinganenvironmentalriskassessment.
Itisnotintendedasasubstitutefortheregulationsandshouldnotbeusedassuch.
Mentionoftradenamesorcommercialproductsdoesnotconstituteendorsementorrecommendationforuse.
Thehyperlinksandcitationsprovidedinthisdocumentareforhelpfulreferenceandmaybeusedinthedevelopmentofafacility'sriskassessmentplans,reports,etc.
ItshouldbenotedthatuseoftheprovidedhyperlinksandcitationsalonedoesnotensureDepartmentalapproval/acceptanceofsuchriskevaluations,plans,reports,etc.
September2005RevisedApril2008RevisedFebruary2017TheAlabamaDepartmentofEnvironmentalManagementdoesnotdiscriminateonthebasisofrace,color,nationalorigin,sex,religion,age,ordisability.
ARBCA(Revision3)2017iTABLEOFCONTENTSPageSECTION1.
0BACKGROUNDANDINTRODUCTION1-11.
1Introduction1-11.
2Applicability1-31.
3CoordinationwithOtherStates1-3SECTION2.
0TARGETCONCENTRATIONS2-1SECTION3.
0OVERVIEWOFTHEUSTARBCAPROCESS3-13.
1Introduction3-13.
2TieredApproachandRisk-BasedTargetLevels3-13.
3TheOverallInvestigationProcesswithARBCA3-33.
4TheARBCAProcessStepbyStep3-43.
5AnticipatedImpactsonSiteCosts3-43.
6ARBCA-EvaluatorQualifications3-5SECTION4.
0INITIAL-RESPONSEACTIONS4-14.
1SelectingtheTypeofInitialResponse4-14.
2Free-ProductRemoval4-14.
3ThreatstoUtilities4-1SECTION5.
0SITEASSESSMENTANDINVESTIGATION5-15.
1ChemicalsofPotentialConcern(COPCs)5-15.
2SiteAssessmentandPreliminaryInvestigation5-25.
2.
1SiteAssessment(SA)5-25.
2.
2PreliminaryInvestigation(PI)5-25.
3ComprehensiveInvestigation(CI)5-25.
4ReviewofSiteConditions5-35.
5PerformanceofaReceptorSurvey5-45.
6EvaluationofThreatstoUtilities5-55.
7Subsurface-DataCollectionActivities5-65.
8SurficialSoilSampling5-85.
9RepresentativeSoilandGroundwaterConcentrations5-85.
10RecommendedLaboratoryAnalyticalMethods5-8ARBCA(Revision3)2017iiSECTION6.
0RISK-BASEDEVALUATION:GENERALCONSIDERATIONS6-16.
1LandUse6-16.
1.
1DetermineCurrentLandUse6-26.
1.
2DetermineMostLikelyFutureLandUse6-26.
2On-siteandOff-site6-36.
3Receptors6-36.
4Human-ExposurePathways6-56.
4.
1PathwaysforInhalation6-56.
4.
2PathwaysforSurficialSoils6-66.
4.
3PathwaysforSubsurfaceSoils6-76.
4.
4PathwaysforGroundwater6-76.
4.
5OtherPathways6-86.
5ConceptualSiteModel(CSM)6-86.
6PointofExposure(POE)6-96.
7CalculationofRisksandRisk-BasedTargetLevels(RBTLs)6-106.
7.
1OverviewoftheSequence:RSLEvaluation,RM-1Evaluation,RM-2Evaluation6-106.
7.
2CalculationofRisk-BasedTargetLevels(RBTLs)6-116.
7.
2.
1Target-RiskLevel6-136.
7.
2.
2QuantitativeToxicityFactors6-146.
7.
2.
3PhysicalPropertiesoftheCOPCs6-156.
7.
2.
4ExposureFactors6-156.
7.
2.
5Fate-and-TransportParameters6-166.
7.
2.
5.
1SoilParameters6-166.
7.
2.
5.
2GroundwaterParameters6-196.
7.
2.
5.
3OtherFate-and-TransportParameters6-226.
7.
2.
6EquationsandModels6-246.
8ProtectionofDeeperGroundwater6-246.
9Groundwater-ResourceProtection6-246.
10Surface-WaterProtection6-266.
11EstimatingSentry-Well(SW)TargetConcentrationsforGroundwater-ResourceProtectionandSurface-WaterProtection6-276.
12ManagementandControlofNuisanceConditionsorConditionsRequiringInitial-AbatementMeasures6-286.
13EcologicalExposure6-296.
13.
1SurfaceWater6-296.
13.
2Sediments6-296.
13.
3Soils6-306.
14Lead6-30ARBCA(Revision3)2017iiiSECTION7.
0REGIONALSCREENINGLEVELEVALUATION7-17.
1WhentoPerformaRegionalScreeningLevelEvaluation7-17.
2ComparisonofDatawithPreliminaryScreeningValues7-1SECTION8.
0RISKMANAGEMENT-1EVALUATION8-18.
1CharacterizationandClassificationoftheSite8-18.
2DevelopmentoftheSiteConceptual-ExposureModel8-18.
3CalculationofRisksandDevelopmentofRM-1TargetLevels8-18.
4ComparisonofRM-1TargetLevelswithRepresentativeConcentrations8-28.
4.
1Soils8-28.
4.
1.
1SurficialSoil8-38.
4.
1.
2SubsurfaceSoil8-38.
4.
2Groundwater8-38.
4.
3SurfaceWater8-48.
5SelectionoftheNextCourseofAction8-5SECTION9.
0RISKMANAGEMENT-2EVALUATION9-19.
1ContentsofanRM-2WorkPlan9-19.
2ImplementationoftheWorkPlan9-19.
3PerformanceofanRM-2Evaluation9-29.
3.
1ConceptualSiteModel9-29.
3.
2TargetRisk9-29.
3.
3ExposureFactors9-29.
3.
4PhysicalProperties9-29.
3.
5ToxicologicalProperties9-29.
3.
6Fate-and-TransportParametersandBuildingParameters9-29.
3.
7Fate-and-TransportModels9-39.
3.
8CalculationofRepresentativeConcentrations9-39.
3.
9RM-2GroundwaterResourceProtectionEvaluation9-39.
3.
10VaporInhalationPathwayEvaluation9-49.
3.
11SourceWaterAssessmentAreas9-49.
3.
12RM-2SurfaceWaterProtectionEvaluation9-49.
3.
13EcologicalEvaluation9-59.
3.
14EvaluationofOtherPathways9-59.
4Risk-ManagementRecommendations9-5SECTION10.
0RISK-MANAGEMENTISSUES10-110.
1GroundwaterMonitoring10-110.
2CorrectiveActionPlans10-110.
3Land-UseControls10-210.
4No-Further-Action/CorrectiveActionProcessTerminatedProcedure10-2ARBCA(Revision3)2017ivSECTION11.
0REFERENCES11-1APPENDICESAppendixAListofAcronymsUsedinthisGuidanceManualAppendixBEstimationofRepresentativeSoilandGroundwaterConcentrationsAppendixCConcentrationsProtectiveofaStreamAppendixDBackCalculationofRisk-BasedTargetLevelsandForwardCalculationofRisksandHazardQuotientsAppendixEModels/EquationsforEstimatingRM-1andRM-2TargetLevelsAppendixFModels/EquationsforEstimatingRisksAppendixGDevelopmentofaSite-SpecificBiodecayRateFIGURESFigure3-1FlowDiagramoftheARBCAProcess(locatedattheendofSection3)Figure6-1GraphicalDisplayofaConceptualSiteModel(locatedattheendofSection6)FigureB-1CalculationofGroundwaterResourceProtectionTargetLevels(locatedatendofAppendixB)FigureC-1SchematicofLeachateMigrationfromtheSoilSourcetotheStream(locatedattheendofAppendixC)ARBCA(Revision3)20171-11.
0BACKGROUNDANDINTRODUCTION1.
1INTRODUCTIONTheAlabamaDepartmentofEnvironmentalManagement(ADEM),hereafterreferredtoas"theDepartment",hastheresponsibilityforoverseeingsoilandgroundwatercleanupswhicharemanagedunderavarietyofdifferentregulatoryprograms.
TheseincludesitesregulatedundertheComprehensiveEnvironmentalResponse,Compensation,andLiabilityAct(CERCLAorSuperfund)Program,theBrownfieldRedevelopmentandVoluntaryCleanupProgram,theUndergroundStorageTank(UST)Program,theResourceConservationandRecoveryAct(RCRA)Program,theDryCleanersTrustFund,theSolidWasteProgram,andothersitesbeingaddressedthroughstatestatutoryauthority.
TheDepartment'sobjectiveistoestablishaconsistentrisk-baseddecisionmakingprocessforallsites,throughwhichsoil,sediment,surfacewaterandgroundwatercorrectiveactiondecisionsaremade.
TheevaluationofthecumulativeriskpresentatasiteaccompaniedbythedevelopmentofRisk-BasedTargetLevels(RBTLs)isaconsistentlyprotectiveapproachforthemanagementofawidevarietyofimpactedsites.
Therisk-basedcorrectiveactionprocesshasbeenacceptedandwelldocumentedbytheUnitedStatesEnvironmentalProtectionAgency(USEPA).
Certaincleanupprograms(e.
g.
,UST,RCRA,CERCLA)mayhaveadditionalspecificrequirementsorregulationsforriskassessmentandcleanupcriteria.
Thisguidancemaynotbeusedasasubstituteforsuchrequirementsandregulations,althoughitmaybeusedinconjunctionwithsuchrequirementsandregulations.
TheAlabamaRisk-BasedCorrectiveAction(ARBCA)GuidanceManualhasbeendevelopedtoprovidetherisk-basedapproachfortheassessmentofthecumulativeriskatasite,thedevelopmentofRBTLsandselectionofappropriateRegionalScreeningLevels(RSLs)forcontaminatedsites.
SiteconcentrationsarefirstcomparedtoRSLs.
IfthesiteconcentrationsexceedRSLsoriftheindoorairvaporinhalationpathwayiscompleteandthereisanexceedanceoftheVaporIntrusionScreeningLevels(VISLs),RiskManagement-1(RM-1)Levels,orRiskManagement-2(RM-2)Levelsarethencalculated.
Theprocedurefordevelopmentandcomparisonofsitechemicalsofconcern(COC)concentrationswithappropriateRBTLsisalsoprovided.
ThemostcurrentversionoftheAlabamaEnvironmentalInvestigationandRemediationGuidance(AEIRG)shouldbeutilizedforsiteinvestigationrequirements.
Programspecificguidanceisalsoavailableforcertainprograms(i.
e.
,USTprogram).
Evaluatorsshouldbeawareofadditionalguidanceinperformingassessmentandremediationactivities.
EmergencyResponseactionsshallbeconductedinaccordancewiththerequirementsoftheADEMEmergencyResponseProgram(contactADEMFieldOperationsDivisionforapplicableinformation).
ARBCA(Revision3)20171-2ThisARBCAprocessrecognizesandbalancesthefollowing:(i)theneedtoprotectpublichealth,waterresources,andtheenvironmentoftheState,(ii)differencesinsite-specificcharacteristics,(iii)theexistinglawsandregulationsoftheState,and(iv)resourcelimitations.
Appropriaterisk-andexposure-assessmentpracticessuggestedbytheU.
S.
EPAandtheASTME1739-95StandardhavebeenintegratedintotheprocessforUSTs.
State-specificdefaultvalueshavebeenselectedwhichareappropriateforsiteslocatedinAlabama.
TheDepartmentrecognizesthat,asoftheeffectivedateofthisguidancedocument,therewillbeanumberofongoingriskassessmentsbasedontheApril2008ARBCAortheNovember2001,ARBCA:AlabamaRisk-BasedCorrectiveActionforUndergroundStorageTanksGuidanceManual,Revision1.
0.
ThoseriskassessmentswhichhavebeenrequestedandapprovedbytheDepartmentorsubmittedtotheDepartmentbytheeffectivedateofthisguidancewillcontinuetobeprocessedusingthepreviousguidance.
However,riskassessmentsrequestedaftertheeffectivedateofthisguidanceshallfollowtheguidancecontainedhereinandanyapplicable,revised,program-specificguidance.
ThosesiteswhichhavecorrectiveactionlimitsacceptedbytheDepartmentpriortothedateofthisguidancemaycontinuetoutilizethosecorrectiveactionlimitsastheircleanupgoals.
However,ifnewinformationarisesatsuchasiteandiscauseforrevisedsiteorareaevaluation,asdeterminedbytheDepartment,themost-currentguidanceshouldbeutilized.
Thisguidancewasdevelopedforusebyindividualswithexistingtechnicalexpertiseandskillintheareaofhydrogeologicalinvestigations,riskassessments,andriskmanagementissues.
CertainsubmissionsrequiredbytheDepartmentinvolvethepracticeofengineeringasthosetermsaredefinedinCodeofAlabama1975,asamended§34-11-1to34-11-37;and/orthepracticeofgeology,asthattermisdefinedinCodeofAlabama1975,asamended§34-41-1to34-41-24.
Anypersonpreparingorsubmittingsuchsubmissionshastheresponsibilitytoensurecompliancewiththeselawsandanyregulationspromulgatedthereunder,asmayberequiredbytheStateBoardofRegistrationforProfessionalEngineersandLandSurveyorsand/ortheAlabamaBoardofLicensureforProfessionalGeologists.
Allsubmissions,orpartsthereof,whicharerequiredbyStatelawtobepreparedbyalicensedengineer,landsurveyor,orgeologist,mustincludetheengineer's,landsurveyor's,and/orgeologist'ssignatureand/orseal(s),asrequiredbytheapplicablelicensurelaws.
ARBCA(Revision3)20171-31.
2APPLICABILITYTheintentofthisdocumentistoestablishaconsistentprocedureforinitiallyevaluatingasiteusingascreeningprocessandforthoseexceedances,determiningthecumulativeriskatasite.
Inthecasethattheriskatasiteexceedsappropriateriskvalues,thisdocumentwillguidetheuserthoughthedevelopmentofRBTLsthatareprotectiveofthecurrentandfuture(i)humanhealth,(ii)environment,(iii)emergencysituations,and,(iv)nuisanceconditions.
TheRBTLsaredevelopedtobeappliedbytheuserasaguideorgoalduringtheremediationprocesstoaidthesiteintheachievementofappropriatecumulativerisklevelsprotectiveofhumanhealthandtheenvironment.
Thisdocumentprovidesatechnicallydefensibleprocedureforestimatingcumulativeriskandestablishingriskmanagementlevelsatimpactedsites.
Thisdocumentisnotintendedasadetailedguidetoeveryaspectoftheriskassessmentpractice.
Itisintendedforusebycompetentprofessionalswithadequateknowledgeofenvironmentalriskassessmentprinciples.
Priorexperienceand/ortrainingwillbenecessaryforanindividualtocorrectlyconductandimplementtheriskassessmentaspartoftheoverallsitemanagementprocess.
Thisguidanceisnotintendedtoaddressriskatasiteduetoradionuclides.
Radionuclides,whethercoveredundertheAtomicEnergyActorTechnicallyEnhancedNaturallyOccurringRadioactiveMaterial(TENORM),arenotcoveredundertheARBCAGuidanceManual.
Ifradionuclidesarebelievedtobepresentatasite,theDepartmentshouldbecontactedforguidance.
Additionally,thisguidanceisnotintendedtoaddressworkersafetyissueswhichareadministeredundertheOccupationSafetyandHealthAdministration(OSHA).
Acronymsusedinthisdocumentmayhaveadifferentmeaningthanthesameacronymsusedinotherdocumentsorregulatoryprograms.
1.
3COORDINATIONWITHOTHERSTATESFacilitieshavetheresponsibilitytocoordinatewithotherstateenvironmentalagenciestoaddressanyrequirementsaboveandbeyondAlabamarequirementsifthereisthepotentialfortransboundarygroundwaterorsurfacewaterimpactstooccur.
Thisisofparticularconcernwhensurfacewaterformstheboundarybetweentwostates.
ARBCA(Revision3)20172-12.
0TARGETCONCENTRATIONSADEMAdmin.
Codech.
335-7-2providesMaximumContaminantLevels(MCLs)fordrinkingwaterforselectlistsofcontaminants.
TheMCLsarealsoreflectedintheRSLsandshouldbeusedasestablishedcorrectiveactionlimits.
Pleasenotethatthesepromulgatedvaluesaresubjecttochangeandanowner/operatororconsultantshouldverifythatthevaluesarecurrent.
TheRSLsareupdatedsemi-annuallyandgenerallyshouldcontainthemostcurrentvalues.
PleaserefertotheADEMAdministrativeCodeforthecurrentMCLvaluesorthesevaluesmayalsobefoundonUSEPA'sGroundwaterandDrinkingWaterwebsite.
TheARBCAprocessestablishesasite-specificevaluationprocessthatincludetheRSLs,VISLs(iftheindoorinhalationpathwayexists)Risk-Management-1(RM-1)levels,andRisk-Management-2(RM-2)levels.
Refertothesubsequentchaptersfordetails.
Whencorrectlyapplied,evaluation/remediationactivitiesutilizingtargetlevelsgeneratedfromRSLs,VISLs,RM-1levels,orRM-2levelsshouldsatisfythetargetcumulativerisklevelrequirementsestablishedbytheDepartment.
Chemical-specific,risk-based,targetlevelswillbedevelopedforsoil,groundwater,andsoilvapor.
TheRSLsandVISLsselectedortheRM-1levelsorRM-2levelsdevelopedwilldependonsite-specificconditionssuchascompleteexposurepathways,landuse,andfate-and-transportparameters.
Thespecificprocessusedtodetermineandapplythetargetconcentrationsandtoevaluatethesite-specificcumulativeriskatasiteisdescribedinsubsequentsectionsofthisdocument.
ARBCA(Revision3)20173-13.
0OVERVIEWOFTHEARBCAPROCESS3.
1INTRODUCTIONTheARBCAprocess(Figure3-1)includesarangeofsite-specificactivitiesthatbeginwiththefirstnoticeofasuspectedrelease.
ThisprocesscontinuesuntiltheDepartmentdeterminesthatthesite-specificconcentrationsareprotectiveofhumanhealthandtheenvironment.
Uponcompletionofthisprocess,theDepartmentwillindicatethatthecorrectiveactionperformancestandardshavebeenattainedandmayterminatethecorrectiveactionprocessprovidedthat(i)theARBCAprocesshasbeencorrectlyimplemented,(ii)thefutureuseofthesiteisconsistentwiththeassumptionsusedintheARBCAEvaluation,and(iii)therequirementsrelatedtoenvironmentalcovenant(s)perADEMAdmin.
Codediv.
335-5aremet,ifapplicable.
TheARBCAprocessintegratestheelementsofsitecharacterization,exposureassessment,riskcalculations,andrisk-managementactivities(includingcorrectiveactionandriskcommunication)todeterminesite-specificcumulativeriskprotectiveofhumanhealthandtheenvironment.
Eachelementoftheprocessisimportantandmustbecorrectlyappliedfortheadequateprotectionofhumanhealthandtheenvironment.
TheARBCAprocessisapplicableatallsitesirrespectiveofthecurrentphaseofactivitiesbeingconducted.
SincetheARBCAprocesscanbeginatanypointsubsequenttotheconfirmationoftherelease,sitescurrentlyunderassessmentshouldbecarefullyevaluatedtoensurethatasufficientqualityandquantityofdataisavailableorhasbeencollected.
Althoughcertainsectionsortablescontainedwithinthisguidancemaybeusedfollowingtheconfirmationofarelease,inordertoaccuratelydeterminethecumulativeriskatthesite,thesiteshouldbefullycharacterized,andaConceptualSiteModel(CSM)shouldbedevelopedpriortoacumulative-riskevaluation.
TheCSMshouldbeconsideredadynamicdocumentandupdatedasnewinformationarises.
RiskmanagementisanimportantpartoftheARBCAprocess.
Risk-managementactivitiesmayincludeactiveorpassiveengineeredcorrective-actionsystemsaswellasowner-imposedinstitutionalcontrols.
Institutionalcontrolsinclude,butarenotlimitedto,land-userestrictionssuchasanenvironmentalcovenant,receptorremovalorrelocation,andcommunicationwithpotentiallyaffectedparties.
Risk-managementissuesarediscussedindetailinSection10.
0.
3.
2TIEREDAPPROACHANDRISK-BASEDTARGETLEVELSTheARBCAprocessutilizesatieredapproach,witheachsubsequenttierbeingmoresite-specific.
Theprocessincludesthreetiersofevaluation:RegionalScreeningLevel(RSL)Evaluation,RiskManagement-1(RM-1)Level,andRiskManagement-2(RM-2)Levelasdiscussedbelow.
Figure3-1containsacomparisonofthedifferenttiersusedintheARBCAprocess.
IntheRM-1andRM-2Levels,site-specific,cumulativerisksarecalculatedand,ifexceeded,thensite-specificRisk-BasedTargetLevels(RBTLs)(concentrations)arecalculated.
AbriefdiscussionofthetypesofRBTLsutilizedinthisprocessispresentedinthefollowingparagraphs.
ARBCA(Revision3)20173-2TheMaximumContaminantLevel(MCL)isthemaximumpermissiblelevelofacontaminantindrinkingwaterwhichisdeliveredtoanyuserofapublic-watersystem.
Withrespecttogroundwater,certainchemicalshaveestablishedMCLs,therefore,RegionalScreeningLevel(RSL)EvaluationsusetheMCLs.
IntheabsenceofanMCL,thefollowingprocessshouldbeusedtodeterminethevaluesappropriatetoevaluategroundwater:IntheabsenceofanMCL,thetapwatervaluesfromtheRSLtableshouldbefirstconsulted.
Fornon-carcinogens,theRSLvalueinthetableusingatargethazardquotientof0.
1shouldbeused.
ForcompoundswithneitheranMCLnoranRSLtap-watervalue,arisk-basedconcentrationshouldbecalculatedbasedontheingestionofwaterandtheinhalationofvaporsduringdomesticuseofwaterinaccordancewiththeequationspresentedinAppendixEorfromanothersource(anyothersourcesshouldbeapprovedbytheDepartmentpriortouse).
ThecalculatedconcentrationisreferredtoastheDirectIngestionofGroundwaterConcentration(DIGC).
IfnoMCL,RSL,orthenecessaryinformationneededtocalculateaDIGCforaCOPCisavailable,anapprovedLifetimeHealthAdvisoryorSecondaryDrinkingWaterstandardmaybeutilized.
TheDepartmentshouldbecontactedforotherCOPCsforwhichinformationisnotreadilyavailable.
RSLsarerisk-basedconcentrationsdevelopedwiththeDepartmentofEnergy(DOE)OakRidgeNationalLaboratory(ORNL)underanInteragencyAgreementasanupdateoftheU.
S.
EPA,Region-3,Risk-BasedConcentrationstable;theU.
S.
EPA,Region-6,Human-Health,Medium-SpecificScreeningLevelstable;andtheU.
S.
EPA,Region-9,PreliminaryRemediationGoalstable.
TheRSLsaregeneric,risk-basedconcentrationsderivedwithouttheuseofsite-specificdata.
Theseconcentrationsmaybeappliedduringtheearlyphaseofsiteassessmentandinenvironmentalsiteassessmentswheretherepresentativesiteconcentrations(seeAppendixB)andthesourcearea(s)havebeenadequatelyidentifiedandcharacterized.
SitecharacterizationshouldbeconductedinaccordancewiththecurrentAlabamaEnvironmentalInvestigationandRemediationGuidance(AEIRG).
RM-1concentrationsaremedia-,receptor-andpathway-specificconcentrationscalculatedusingdefaultassumptionsandparameterspresentedinthemostcurrentRegionalScreeningLevels–User'sGuide.
TheRiskManagement-1(RM-1)targetconcentrationsarecalculatedusingthemodelspresentedinAppendixE.
RM-1concentrationswillvaryfromsitetosite.
AnRM-1Evaluationmaybeperformedifthesitehasbeen(i)satisfactorilycharacterized,and(ii)thesitedataindicatesthattheinput-parametervaluesusedtodeveloptheRM-1levelsarereasonablyapplicable.
TheRM-1EvaluationisfurtherdiscussedinSection8.
0.
RiskManagement-2(RM-2)targetconcentrationsaresite-specificconcentrationsbasedonsite-specificdata.
TheseconcentrationsarebasedoncumulativeriskandarebackcalculatedtoassistARBCA(Revision3)20173-3withcleanupobjectives.
AnRM-2EvaluationrequiresthecollectionofsitedataasdiscussedinSection5.
0ofthisdocument.
AdequatesoilandgroundwaterdataisnecessaryasdiscussedinthemostcurrentversionoftheAEIRG.
TheRM-2concentrationsarecalculatedusingthemodelsinAppendixEunlessalternatemodelshavebeenapprovedbytheDepartmentthroughsubmittalofanRM-2workplan.
ItisnecessarytocalculateRM-2concentrationsonlyifthecumulative-risklevelsexceedtheDepartment-approvedtarget-risklevelsforoneormorereceptors.
AnRM-2workplanshouldbedevelopedandapprovedbytheDepartmentasdiscussedinSection9.
0.
3.
3THEOVERALLINVESTIGATIONPROCESSWITHARBCAFigure3-1presentsasimplifiedflowchartthatillustratestheARBCAprocess.
AsshowninFigure6-1,theARBCAprocessisacombinationofdatacollectionanddataevaluationbasedonthereceptors,completeexposurepathways,andsite-specificconcentrationsappropriateforthesite.
TheARBCAprocessbeginswiththeacquisitionofinitialsitedatabyperformingaPreliminaryInvestigation(PI),aClosureSiteAssessment(CSA),oranEnvironmentalAssessment(EA).
Asaninitialscreen,maximumsoilandgroundwaterconcentrationsarecomparedtoexistingRSLs.
IftheconcentrationsexceedtheRSLs,oriftherearesensitivereceptorsatornearthesite,additionalsitedatashouldbecollectedthroughaSecondaryInvestigation(SI).
Siteassessmentsshouldbeperformedtoobtainsufficienttechnicallydefensibleandreliabledataforasite-specific,risk-basedevaluation.
AdescriptionofthetypeofdatawhichshouldbeobtainedislistedinSections5.
0and6.
0Afteranadequatesitecharacterizationhasbeenperformed(seeSections5.
0and6.
0),acomparisonofsiteconcentrationstoRSLsisconducted.
ShouldtherepresentativeconcentrationsexceedtheRSLsforanycompletepathway,orifsitecharacteristicssignificantlydifferfromtheassumptionsusedtodevelopRSLs,thenadditionaldatamayhavetobecollectedtoperformanRM-1Evaluation.
Note,atmostsites,RSLsmaybeacceptedastheremedialtargetlevelswithoutdeterminingthecumulativeriskatthesite.
TheDepartmentmayprovidethesitewithanindicationthatcorrectiveactionperformancestandardshavebeenattainedaftertheRSLshavebeenachieved.
ForsitesthatproceedtoanRM-1Evaluation,theCSMmustbedevelopedandincludeallcurrentandreasonablefuturereceptorsandallcompleteroutesofexposure.
RM-1cumulativerisksshouldthenbecalculatedandcomparedtotheallowableriskstandards.
Iftheallowableriskisexceeded,targetconcentrationsshouldbecalculatedandcomparedtorepresentativeconcentrations.
AfterperforminganRM-1Evaluation,oneoffouroptionsareusuallyavailable:(i)correctiveactionperformancestandardsattainedwithconditions(anenvironmentalcovenantperADEMAdmin.
div.
335-5maybeappropriate),(ii)remediationtomeetRM-1concentrationsandare-evaluationofthecumulativeriskpresentatthesite,(iii)monitoring,or(iv)anRM-2Evaluation.
RM-2concentrationscanbecalculatedatanystageoftheARBCAprocessafteradequatesitecharacterizationhasbeendoneandsufficientmonitoringdatahasbeenobtained.
PriortoARBCA(Revision3)20173-4performingtheRM-2riskcalculations,theCSMmustbeupdatedandincludeallcurrentandreasonable-futurereceptorsandallcompleteroutesofexposure.
RM-2cumulativerisksarethencalculatedandcomparedtotheallowableriskstandards.
Iftheallowableriskisexceeded,thetargetconcentrationsshouldbecalculatedandcomparedtorepresentativeconcentrationsforeachreceptor,foreachdecisionunit/exposuredomainforeachchemicalofconcern.
ThecomparisonofrepresentativeconcentrationstothecalculatedRM-2concentrationsshouldonlybeperformedaftersufficientmonitoringdatahasbeencollected.
Ifthesite'srepresentativeconcentrationsdonotexceedthecalculatedRM-2calculations,thefinalprocessnecessarywouldbetocalculatethesite-specificcumulativerisktoensurethatthecumulativeriskthresholdshavebeenmet.
AfterthecompletionofanRM-2Evaluation,theDepartmentmayindicatethatcorrectiveactionperformancestandardshavebeenattainediftheRM-2cumulativerisksdonotexceedthetarget-risklevels,ortheDepartmentwillrequireremediationand/orrisk-managementactivitiestoachieveRM-2targetrisks.
Site-specificrisk-managementactivitiesmayincludeanenvironmentalcovenantdevelopedandrecordedintheJudgeofProbate'sOfficeinaccordancewithADEMAdmin.
Codediv.
335-5.
Whereriskmanagementtakestheformofremediationtotargetconcentrations,cumulativerisksandhazardindicesmayneedtoberecomputedusingcurrentrepresentativesiteconcentrationstoensurethatrisklevelsarenotexceededbeforeanindicationthatcorrectiveactionperformancestandardshavebeenattainedisprovided.
TheARBCAprocessisaprogressiveapproachwhichallowsforadditionalsite-datacollectiontosupportasite-specific,risk-basedevaluationwithoutcompromisingtheprotectionofhumanhealthandtheenvironment.
3.
4THEARBCAPROCESSSTEPBYSTEPFigure3-1showsadetailedviewoftheARBCAprocess.
Pleasenotethatthisflowchartprovidesgeneralguidelines.
Insummary,theARBCAprocessbeginswiththediscoveryofareleasefollowedbytheperformanceofanadequatesiteassessment,theperformanceofinitial-abatementmeasuresasneeded,RSL,RM-1,and/orRM-2Evaluations,siteremediationwhenwarranted,confirmationofsiteremediationthroughmonitoring,andtheissuanceofaletterindicatingthatcorrectiveactionperformancestandardshavebeenmet.
Suchalettermayrequirethatland-usecontrolsremaininplacesuchasanenvironmentalcovenantdevelopedinaccordancewithADEMAdmin.
Codediv.
335-5.
3.
5ANTICIPATEDIMPACTSONSITECOSTSAstheprocessmovesfromtheRSLEvaluationtotheRM-1andpossiblyRM-2Evaluations,thecostofdatacollectionandriskevaluationwillmostlikelyincrease.
However,thecostofremediationislikelytodecreaseduetotheprobabilitythatthesite-specificRBTLsgenerallyincrease.
Despitethedifferenceamongthethreetiers(refertoFigure3-1),thereisoneverysignificantsimilarity.
Eachtierwillresultinanequallyacceptablelevelofprotectionforthesite-specific,humanandenvironmentalreceptors,wheretheacceptablelevelofprotectionisdefinedbytheDepartment.
ARBCA(Revision3)20173-53.
6ARBCA-EVALUATORQUALIFICATIONSImplementationofRM-1andRM-2Evaluationsrequirestheevaluatortobeexperiencedintheconceptsandproceduresofriskassessmentandriskmanagement.
TheDepartmentwillrequirethattheARBCAreportsaresignedbyeitheranAlabamaLicensedProfessionalGeologistoranAlabamaRegisteredProfessionalEngineer.
Inaddition,allreportsorplansshouldbesignedbyaresponsiblecorporateofficer,thegeneralpartnerortheproprietor,aprincipalexecutiveofficerorrankingelectedofficial,oradulyauthorizedrepresentativeofoneofthepreviouspersons.
Anypersonsigningsuchadocumentshouldmakethefollowingcertification:"Icertifyunderpenaltyoflawthatthisdocumentandallattachmentswerepreparedundermydirectionorsupervisionaccordingtoasystemdesignedtoassurethatqualifiedpersonnelproperlygatherandevaluatetheinformationsubmitted.
Basedonmyinquiryofthepersonorpersonswhomanagethesystem,orthosepersonsdirectlyresponsibleforgatheringtheinformation,theinformationsubmittedis,tothebestofmyknowledgeandbelief,true,accurate,andcomplete.
Iamawarethattherearesignificantpenaltiesforsubmittingfalseinformation,includingthepossibilityoffineandimprisonmentforknowingviolations.
"PerformRSLEvaluationBasedonanyexposurepathway(i.
e.
,soil,groundwater,soilvapor),isanEnvironmentalCovenant(EC)neededImplementECNofurtheractionwithconditionsYESFigure3-1.
(a)FlowDiagramoftheARBCAProcessforRSLEvaluationDosoilorgroundwaterconcentrationsexceedRSLsorVISLsNOPerformcorrectiveactionYESNofurtheractionProceedtoRM-1orRM-2EvaluationYESAlternativeNOARBCA(Revision3)—2017PerformRM-1EvaluationDoesthecumulativeriskfromsoil,groundwater,andsoilvaporconcentrationsexceed1*10-5ORdoestheHazardIndexexceed1.
0PerformcorrectiveactionBasedonanyexposurepathway(i.
e.
,soil,groundwater,soilvapor),isanEnvironmentalCovenant(EC)neededImplementECNofurtheractionwithconditionsYESNOProceedtoRM-2EvaluationYESAlternativeNOYESFigure3-1.
(b)FlowDiagramoftheARBCAProcessforRM-1EvaluationDogroundwaterconcentrationsexceedMCLsNOPerformadditionalcorrectiveactionand/ormonitoringYESNofurtheractionARBCA(Revision3)—2017PerformRM-2EvaluationDoesthecumulativeriskfromsoil,groundwater,andsoilvaporconcentrationsexceed1*10-5ORdoestheHazardIndexexceed1.
0PerformcorrectiveactionBasedonanyexposurepathway(i.
e.
,soil,groundwater,soilvapor),isanEnvironmentalCovenant(EC)neededImplementECNofurtheractionwithconditionsYESNONOYESFigure3-1.
(c)FlowDiagramoftheARBCAProcessforRM-2EvaluationDogroundwaterconcentrationsexceedMCLsNOPerformadditionalcorrectiveactionand/ormonitoringYESNofurtheractionARBCA(Revision3)—2017ARBCA(Revision3)20174-14.
0INITIAL-RESPONSEACTIONS4.
1SELECTINGTHETYPEOFINITIALRESPONSEDeterminationoftheappropriateinitial-responseactionatasiteinvolvesthecollectionofappropriatesitedataandremedialactiontoreduce/eliminateanyvaporproblemsorthreattopublicordomesticwatersupplies.
Notificationofappropriatepersonneliscriticalinordertoprovideforaneffectiveresponsetoapublic-safetythreat.
Public-safetyofficessuchastheFireDepartmentandEmergencyManagementofficesshouldbenotifiedintheeventofapublic-safetythreat.
TodeterminewhetherornotasiteislocatedwithinadesignatedSourceWaterAssessmentAreaIorII,contactthelocalwater-systemoperatorfortheareaofinterest.
TheUSGeologicalSurveyWater-ResourcesInvestigationsReportsentitledGeohydrologyandSusceptibilityofMajorAquiferstoSurfaceContaminationinAlabama;Areas1-13(U.
S.
GeologicalSurvey,1989)shouldbereferencedtodetermineifasiteisclassifiedasaG.
1site.
Thesereportsindicateareassusceptibleandhighlysusceptibletosurfacecontamination.
ThesedocumentsareavailablefromtheDepartmentortheGeologicalSurveyofAlabama.
Initial-responseactionsshouldbeusedtoreduceoreliminatethethreatofexposure.
Theseactionsarenotsubstitutesforregulatoryrequirementsorotheractionsnecessaryatalaterdatetoprotecthumanhealthortheenvironment.
Appropriatesite-specificactionsshouldbeperformedtoprotecthumanhealthandtheenvironment.
AdditionalinformationoninitialresponseactionsislocatedinthecurrentAEIRG.
4.
2FREE-PRODUCTREMOVALTherequirementtoremovefreeproductremainsacomponentofthesitecorrectiveaction.
Riskevaluation(RM-1orRM-2)maybeconductedatsiteswithfreeproduct.
However,thesitemustcontinuetoundergofree-productremoval.
Furthermore,groundwatermonitoringwillbenecessaryduringandafterthefree-productremovaltoverifythatsiteconditionsdonotposeanunacceptablelevelofrisk,andthatfreeproducthasbeenremoved,anditsabsenceisnotduetoatemporarychangeinwatertable.
AppendixBincludesinformationregardinghowtoaccountforfreeproductinthedevelopmentofrepresentativeconcentrationsforsoilandgroundwater.
4.
3THREATSTOUTILITIESThepotentialfordegradationofwater-supplylines,themovementofvaporsintostormandsanitarysewers,anddamagestoundergroundgas,phone,andelectricalutilitiesmustbeevaluatedaspartoftheARBCAprocess.
Whilethethreatstotheseutilitiescannotbeeasilyquantified,anevaluationmustbemadewhichdelineatesthepresenceandlocation(anddepth)ofvariousutilitiesonandadjacenttothesitewherethereleaseoccurred.
ARBCA(Revision3)20175-15.
0SITEASSESSMENTANDINVESTIGATIONThissectionhighlightskeyaspectsofthesite-assessmentprocessandthedatarequiredtoperformanARBCAevaluation.
ThemostcurrentversionoftheAEIRGincludesguidanceforperformingasiteinvestigation.
ThissectiondiscussesseveralinvestigationcomponentsnecessarytoperformatechnicallydefensibleARBCAEvaluation.
5.
1CHEMICALSOFPOTENTIALCONCERN(COPCs)Whileevaluatingasiteimpactedbyarelease,theDepartmentfocusesonChemicalsofPotentialConcern(COPCs)(Note:ThemeaningofthetermCOPCsusedinthismanualmaydifferfromitsuseinotherprogramsanddocuments).
Eachfacilitywillhaveauniquesetofchemicalsofpotentialconcern(COPCs)basedonpastactivitiesthathaveoccurredovertheyearsatthesite.
AthoroughhistoricalinvestigationshouldcommenceattheinitiationoftheCOPCsdeterminationprocess.
Ifthepastactivitiesareunknownatasite,thecompletelistofconstituentslocatedinADEMAdmin.
Coder.
335-14-2-AppendixVIII–HazardousConstituentsshouldbeconsideredinthesiteanalysis.
EachoftheCOPCshasuniquephysicalandchemicalpropertiesandbehavedifferentlywithintheenvironment(mobility,persistence,andinter-mediatransport)andpresentdifferentadverseenvironmentalandhuman-healtheffects.
AffectedenvironmentalmediashouldbesampledandanalyzedfortheappropriatelydeterminedCOPCsandcomparedtotheRSLs.
TheRSLsareconservative,chemical-specificscreeninglevelsforsoil,vapors,andgroundwaterforindustrialandunrestrictedlanduses.
ThesevaluesarepresentedintheRSLTableavailableonlinewiththelinkprovidedbelow.
TheappropriateRSLsshouldbeselectedbasedonthecurrentlanduseandthemostlikelyfuturelanduse(seeSection6.
1).
Inaddition,theDepartmentmaygrantacorrectiveactionperformancestandardsattainedletterifthemaximumsiteconcentrationsforeachmediumdonotexceedanymedium-specificRSLsandtheVISLs.
TherecommendedlaboratoryanalyticalmethodsfordeterminingtheconcentrationsoftheCOPCsarefoundinSW-846.
PleasenotethatalthoughSW-846containsamethodforTotalPetroleumHydrocarbons(TPH)-GasolineRangeOrganics(GRO)and-DieselRangeOrganics(DRO)(Method8015),andtheRSLsdocontainseveralTPHscreeninglevelsforthedifferentnumberofcarbons,neitherMethod8015northeTPHRSLsareacceptableforsiteand/orriskassessmentpurposes.
However,TPH,GRO,andDROcanbeveryusefulduringtheinitialassessmentofasitetoprovideinformationregardingwherethecontaminationmaybelocated.
ThesemethodsshouldbeutilizedunlessspecificauthorizationhasbeengrantedbytheDepartmenttoutilizeanalternateanalyticalmethod.
DuringtheRSLEvaluation,themaximumsiteconcentrationofeachCOPCshouldbecomparedwiththerespectiveRSLand/orVISL.
TheCOPCswhosemaximumconcentrationdoesnotexceedtheRSLareeliminated.
TheremainingchemicalsformthelistofChemicalsofConcern(COCs),whicharefurtherevaluatedundertheRM-1andRM-2process.
Note,thelistsofCOCsconsideredinbothRM-1andtheRM-2evaluationsareidentical.
FollowingthedeterminationofCOCs,thecumulativeriskshouldbedeterminedandRBTLsdevelopedforeachCOCasnecessarytoassistinguidingremediationactivities.
ARBCA(Revision3)20175-25.
2SITEASSESSMENTANDPRELIMINARYINVESTIGATIONDetailsregardingthesetypesofassessmentsareinthemostcurrentAEIRG.
Theseassessmentsaregenerallygearedtowardsdetectingareleaseordeterminingifsoiland/orgroundwaterhasbeenaffectedbyarelease.
Theassessmentactivitiesareperformedtodetermineifsoiland/orgroundwaterhavebeenaffectedinthelikelysourceareasandtodeterminetheextenttowhichsoiland/orgroundwaterhavebeenaffected.
Atthisstageofthesite-evaluationprocess,littleinformationisknownaboutthesite.
SinceverylittlesitedataarecollectedasapartoftheSiteAssessment(SA)orPreliminaryInvestigation(PI),itisappropriatetousetheseconservativelimitsasscreeninglevelssuchastheRSLs.
5.
2.
1SiteAssessment(SA)WiththeARBCAprocess,asiteowner/operatormaychoosetoutilizeRSLstoevaluatetheresultsofaSA.
ThiswillrequirethecollectionofsamplesandanalysisofthesamplesfortheCOPCsfromthemostlikelysourceareas.
Thefrequencyandnumberofsamplesarebasedonsite-specificfactors–additionalguidanceislocatedinthemostcurrentAEIRG.
5.
2.
2PreliminaryInvestigation(PI)ThePIshouldbeperformedtoobtainthenecessarysoilandgroundwaterCOPCdata,toobtainland-useinformation,andtodeveloptheConceptualSiteModel(CSM)fortheARBCAprocessasdiscussedinmoredetailwithinSection6.
0.
WhenperformingaPIwheresoilandgroundwatersamplesarecollected,concentrationscanbecomparedtotheRSLs.
5.
3COMPREHENSIVEINVESTIGATION(CI)TheCIshouldbeperformedto(i)obtainadequatedatatoclassifyeachsitetodetermineinitial-responseactions,(ii)obtainadequateinformationtoperformanRM-1andanRM-2Evaluationatthereleasesite,and(iii)determinethefulllateralandverticalextentofsoilandgroundwatercontamination.
TheprimaryguidancerecommendedforusetoperforminvestigationssuchastheCIisthemostcurrentversionoftheAEIRG–Section3.
0.
TheCIisgearedtowardsdefiningthelateralandverticalextentofcontaminationanddeterminingthesite-specificsoilproperties,hydraulicconductivity,stratigraphy,andlanduseofthesitenecessarytoperformanRM-1andanRM-2Evaluation.
ThekeycomponentsoftheCIare:IdentificationofthesoilandgroundwaterareasimpactedbyCOPCsappropriatetothetypeofwastereleasedsothataccuraterepresentativesoilandgroundwaterconcentrationscanbedetermined.
Identificationofthelateralandverticalextentofimpactstosoilandgroundwater.
UnlessARBCA(Revision3)20175-3otherwisedirectedbytheDepartment,theextentofimpactshouldbedelineatedbycomparingthesampledconcentrationstotheRSLs.
AnARBCAEvaluationrequiresthatathoroughassessmentofsourceareasbeperformedtoensurethatrepresentativeconcentrationsofchemicalsaredetectedatthesite.
Theextentofsoilcontaminationinthesourceareamustbeadequatelydelineated.
AnadequateassessmentoftheextentofthegroundwaterplumemustbeperformedpriortoperformingtheARBCAEvaluation.
Whenappropriate,futuredowngradientgroundwaterconcentrationsmaybeestimatedusingappropriatemodels.
Installationofgroundwater-monitoringwellsforassessment,monitoring,andtodeterminebackgroundlevelsofCOPCs.
Determinationofthehydraulicpropertiesofthesiteincludingdepthtogroundwater,groundwaterflowdirectionandrate,andhydraulicconductivityofthesite.
Identificationofthecurrentandfuturereceptors,allappropriateexposurepathways,andanyimmediateandlong-termhazardstohumanhealthandtheenvironment.
TheARBCAprocessinvolvesperformingasiteassessmenttocollectadequatedatatocalculatecumulativerisksasrequiredforanRM-1oranRM-2Evaluation.
TheassessmentshouldbeperformedsuchthatthelateralandverticalextentofimpactisdeterminedbycomparinginvestigationdatatotheRSLsuntildesirableconcentrationsarereached.
IfitbecomesapparentduringtheCIthattheRSLsandVISLswillbemet,thennoadditionalinformationmaybeneededatthesite.
However,ifthecumulativeriskscalculatedpertheRM-1EvaluationarelikelytoexceedtheacceptablerisklevelsorsiteconditionsaresignificantlydifferentthantheRM-1defaultvalues,theCIshouldincludecollectionofalldatanecessarytoperformanRM-2Evaluationasexpeditiouslyaspossible.
5.
4REVIEWOFSITECONDITIONSAnevaluationofthefollowingsiteconditionsisanintegralpartoftheARBCAprocess.
Thelevelofeffortshouldbesufficienttoaccuratelyprovideatechnicalbasisforalldeterminations.
GroundSurfaceCondition:Determinepercentageofthesitethatispaved.
Alsonotethegeneralconditionofthepavement.
LandUse:Detailedsurveyandassessmentofthecurrentandlikelyfutureuseofthelandwithin1,000feetofthesiteshouldbeperformed.
Thesurveyshouldidentifythecurrentuseofthepropertiesaseitherunrestrictedorother(e.
g.
,commercial,industrial,etc.
).
Themostlikelyfutureuseoftheimpactedorpotentiallyimpactedpropertiesshouldalsobedetermined(seeSection6.
1).
Receptors:Determinethehumanandecologicalreceptorspresentonandproximatetothesite.
Receptorsincludeadults,children,constructionworkers,water-usewells,surfacewaters,etc.
(seeSection5.
5).
ARBCA(Revision3)20175-4SourceHistory:Determinethehistoryofthesite.
Evaluatethelocation(s)ofpreviouslyinstalledUSTs,AbovegroundStorageTanks(ASTs),dispensers,wastetreatment,storageordisposalareas,abovegroundandbelowgroundpiping,etc.
Determineifsitestructuresinfluenceanymigrationpathwaysatthesite.
Prepareadetailedmapofthefacility,madetoscale,withabarscaleandnortharrow,indicatingthelayoutofpastandcurrentwastemanagementareas,productstorageorloading/unloadingactivities,piping,subsurfaceutilities,etc.
Theutilitiesshouldincludeburiedphonelines,stormwatersewers,sanitary-sewersystems,watersupplylines,electricallines,naturalgaslines,andanyotherstructureswhichmightbepresent.
RegionalHydrogeology:Reviewtheregionalhydrogeologytodeterminesoiltypesandaquifercharacteristics.
Publishedliteratureandinvestigationspreviouslyconductedonproximatesitesmayyieldimportantinformationforthehydrogeologicalcharacterization.
GroundwaterUse:Determinewhetherthereisgroundwateruseforpublicwatersupplywithinaone-mileradiusandforprivatedomesticwatersupplywithina1,000-footradiusofthesite.
DetermineifthesiteisinaSourceWaterAssessmentArea.
SurfaceWater:Locatesurface-waterbodieswithin1,000feetofthesitewhichcouldpotentiallybeaffectedbythereleaseatthesite.
Reviewthefacilityfilesforanyotherpertinentenvironmentaldata.
5.
5PERFORMANCEOFARECEPTORSURVEYThereceptorinventoryisacriticalelementoftheARBCAevaluation.
Actualandpotentialreceptorsmustbeidentified.
LandUse:Withina500-footradiusofthesite,identifythefollowing:schools,hospitals,residences,basements,day-carecenters,nursinghomes,andbusinesses.
Alsoidentifysurface-waterbodies,parks,recreationalareas,wildlifesanctuaries,wetlands,andagriculturalareas.
UtilitySurvey:Identifythelocationanddepthofallsubsurfaceutilitiesandothersubsurfacepathways,whichmayserveaspreferentialconduitsformigrationofthecontaminants.
Identifytheflowdirectionofthematerial(water,sewage,etc.
)withintheutilityline.
Water-WellInventory:Locateallpublicwater-supplywellswithina1-mileradiusofthesiteandallprivatewellsandwellwaterusewithina1,000-footradius.
InformationsourcesincludetheADEMWaterSupplyBranch,theUSGS,theAlabamaGeologicalSurvey,water-systemoperators,andinterviewsoflocalresidents.
Arepresentativesurveymustbemadeandmayrequiredoor-to-doorinterviewsofbusinessesandresidents.
Identifyexistingpotableandnon-potablewells.
Thecurrentuseandstatusofalllocatedwellsshouldbenoted.
ARBCA(Revision3)20175-5SurfaceWater:Locatesurface-waterbodieswithin1,000feetofthesitewhichcouldpotentiallybeaffectedbythereleaseatthesite.
EcologicalReceptors:Thedeterminationofecologicalreceptorswithina1,000-footradiusofthesiteisnecessary.
Thisincludes,butisnotlimitedto,theidentificationofwetlands,surface-waterbodies,sensitivehabitats,orthepresenceofendangeredspecies.
AnysitewhereecologicalreceptorsmaybeaffectedwillundergoanRM-2EvaluationutilizingUSEPA'sEcologicalScreeningValues.
Properidentificationofpotentialreceptorsinthepre-assessmentplanningwillfacilitateappropriateinitialresponseswhichmightincluderelocationofresidents,supplyofalternatedrinkingwater,orperformanceofinitial-abatementmeasures.
5.
6EVALUATIONOFTHREATSTOUTILITIESDuetothepotentialforpreferentialflowofcontaminatedgroundwaterandvaporsintoundergroundutilitylines/conduits,athoroughevaluationofpotentialandrealimpactstoundergroundutilitiesmustbeperformed.
Acombinationofsiteobservations,generalknowledgeaboutburiedutilities,anddiscussionswithutilityrepresentativesandsiteowner(s)shouldrevealthelocationsofsiteutilities.
Theevaluationshouldincludeataminimum:Locateallundergroundutilitylinesandconduitswithintheareaofknownorlikelysoilandgroundwaterimpacts,forbothon-siteandanyoff-siteproperties,towhichareleasemayhavemigratedortowhichareleasemaymigrateinthefuture(includesphonelines,waterlines,sanitarysewers,stormsewers,andnatural-gaslines).
Determinethedirectionofflowintheutilities(water,stormwater,andsewage).
Identifytheutilitylines/conduitsonabasemapwhichalsocontainsadiagramshowingtheextentandthicknessofanyfreeproductthatmaybepresentandtheimpactstosoilandgroundwater.
Determinedepthoftheutilitylines/conduitsrelativetothedepthofgroundwater.
Seasonalfluctuationsofthegroundwaterlevelsshouldbecarefullyevaluated.
Asappropriate,across-sectionaldiagramshouldbeprovidedillustratingthedepthtogroundwaterandthelocationsanddepthsofthelines/conduits.
Determinethetypesofmaterialsusedforlines/conduits(i.
e.
,PVC,terra-cotta,ductileiron,etc.
).
DetermineanypastimpactstoutilitiesandanycomplaintsthatmayhavebeenpreviouslyfiledwithanylocalorStateagency.
Asappropriate,sampletheutilitiesandvaultsusingeitherexplosimetersorbytakingairsamples.
Ifexplosiveconditionsareencountered,immediateemergencyresponseisnecessary.
ARBCA(Revision3)20175-6Iffreeproductispresent,itshouldberemediated.
Wheredissolvedcontaminationispresent,anevaluationofthepotentialeffectsofdissolvedcontaminationshouldbemade.
Whereautilityisthreatened,orwhereanexplosivesituationexists,appropriatemeasurestoeliminatefire,explosive,andvaporhazardsmustbeundertaken.
Additionalassessmentmaybenecessarytofullyevaluatethreatstoutilities.
5.
7SUBSURFACE-DATACOLLECTIONACTIVITIESThesubsurfacesiteinvestigationshouldbeguidedbythescopeofworkpreparedduringthePIplanningstage;however,appropriateadjustmentstothescopeofworkandmodificationstotheCSMshouldbemadeasdataarecollected,analyzed,andevaluatedduringsiteactivities.
TheGeologistorEngineerperformingthesiteassessmentmustremainflexibleduringtheassessmentprocedureandevaluatethesiteinformationinthefieldtodeterminethemostappropriateactivity.
GeologicDescription:Acontinuoussoilprofilefromatleastoneboringshouldbedevelopedwithdetailedlithologicdescriptions.
Particularemphasisshouldbeplacedoncharacteristicsthatcontrolchemicalmigrationanddistributionsuchaszonesofhigherorlesserpermeability,changesinlithology,correlationbetweensoil-vaporconcentrationsanddifferentlithologiczones,obviousareasofsoildiscoloration,organiccontent,fractures,andotherlithologiccharacteristics.
Soil-boringlogsshouldbesubmittedforeachholedrilledatthesite.
Thelogsshouldindicatedepthcorrelatingwithchangesinlithology(withlithologicdescriptions),soil-vaporanalyses,occurrenceofgroundwater,totaldepth,visualandolfactoryobservations,andanyotherpertinentdata.
Whenamonitoringwellisinstalled,as-builtdiagramswithdepthtogroundwatermustbesubmittedforeachwell.
SamplingforCOPCsinSoil:Theverticalandlateralextentofsubsurfaceimpactsshouldbedefinedduringthesiteassessment.
Ataminimum,discretesamplesshouldbecollectedwithinthesurfacesoils(lessthan12inchesindepth)andeveryfivefeetbelowgroundsurface(bgs)thereafterandshouldincludesamplesfromimmediatelyabovethesaturatedzone.
Thesesamplesshouldbefieldscreenedusingaproperlycalibratedfieldorganicvaporanalyzersuchasaflame-ionizationdetector(FID)oraphoto-ionizationdetector(PID).
Thesampleobtainedfromimmediatelyabovethesaturatedzoneandthesamplereflectingthehighestorganic-vaporlevelshouldbesubmittedtothelaboratoryforanalysisofappropriateCOPCs.
AdditionalsamplesmaybenecessarytofullycharacterizethesoilchemicaldistributionandtoquantifyexposuresforanRM-1orRM-2Evaluationorforthedevelopmentofacorrectiveactionplan.
Pleasenotethatanincrementalsamplingmethodologymaybeusedratherthancollectingdiscretesamples–pleaseseeAppendixC.
2.
1ofthemostcurrentAEIRGforadditionalguidanceconcerningacceptablesamplingmethods.
ARBCA(Revision3)20175-7SamplingforPhysicalSoilProperties:ForthosesiteswhichneedtomovetoanRM-1orRM-2Evaluation,site-specificsoilphysicalpropertiesshouldbeobtained.
Theseincludeporosity,watercontent,fractionalorganiccarboncontent,anddrysoilbulkdensity.
Thesamplingplanshouldbeadequatetodeterminesoilpropertiesrepresentativeof(i)thesourcearea,(ii)thesoilsthroughwhichtheCOPCsmigratetoreachgroundwater,(iii)thesoilsthroughwhichCOPCvaporsmigratetoreachthesurface,and(iv)thesaturatedsoilsforgroundwater-contaminantmigrationevaluations.
ForfurtherinformationrefertoASTMStandardD1587-08.
oFractionalorganiccarbon(foc)samplesmustbedeterminedusingsoilsamplesnotaffectedbytherelease(i.
e.
,outsideofthecontaminatedarea).
Thesampledoesnothavetobeanundisturbedsample.
ConsiderationmustbegiventocollectingmultiplesamplesifmultiplelithologiesarepresentwhichmightaffecttransportoftheCOPCs,oriftheCOPCsarecontainedwithinmultiplelithologies.
Bothavadosezonefractionalorganic-carbon(foc)sampleandasaturatedzone,fractionalorganic-carbon(focs)sampleshouldbecollectedwhenitappearsthesetwozonesmaydifferatasite.
SeeSection5.
10foradiscussionoflaboratorymethods.
oSamplescollectedforporositymeasurementsshouldbeundisturbed.
SuchasamplecanbecollectedusingaShelbytube.
ConsiderationmustbegiventocollectingmultiplesamplesifmultiplelithologiesarepresentwhichmightaffecttransportoftheCOPCs,oriftheCOPCsarecontainedwithinmultiplelithologies.
Bothavadose-zonetotalporosity(θT)andasaturated-zonetotalporosity(θTS)shouldbecollectedwhenitappearsthesetwozonesmaydifferatasite.
Generally,however,porositywillnotbemeasureddirectly.
Instead,porositywillbecomputedfromthedrybulkdensityandthespecificgravityusingEquation5-1locatedinSection5.
10.
oSamplescollectedfordrybulkdensitymeasurementsshouldbeundisturbedandcanbecollectedusingaShelbytube.
ConsiderationmustbegiventocollectingmultiplesamplesifmultiplelithologiesarepresentwhichmightaffecttransportoftheCOPCs,oriftheCOPCsarecontainedwithinmultiplelithologies.
Bothavadose-zonedrybulkdensityandasaturated-zonedrybulkdensityshouldbecollectedwhenitappearsthetwozonesmaydiffer.
SamplingforCOPCsinSurfaceWater:AppropriatesamplesshouldbecollectedwhenCOPCmigrationisknownorsuspectedtoaffectasurface-waterbody.
Watersamplesshouldbecollectedfrombothupstreamanddownstreamofagroundwater-dischargepoint.
Anadditionalstreamsampleshouldbecollectedatthegroundwater-dischargepoint.
SamplingforCOPCsinGroundwater:Ifthegroundwaterhasbeenaffected,temporarysamplingpointsmaybeusedtoscreenthelevelsofgroundwaterimpactsandtoassistindeterminingtheoptimallocation(horizontally)ofpermanentmonitoringwellsandtheARBCA(Revision3)20175-8depthofscreen.
Asufficientnumberofmonitoringwellsshouldbeinstalled(aminimumoffourforaPreliminaryInvestigation)todocumentCOPCmigrationandgroundwaterflow.
Wellplacementanddesignshouldconsider:oConcentrationofCOPCsinthesourceareaoProximityofpotentialorimpactedreceptor(s)oOccurrenceoffreeproductatthesiteoHydrogeologicconditions(water-tablefluctuations,hydraulicconductivity,andflowdirections)oGroundwateruse5.
8SURFICIALSOILSAMPLINGThecollectionofsurficial-soildata(0-1ftbgs)isnecessarywherethereisevidenceofasurfacespilloroverfillanditislikelythatsurficialsoilshavebeenaffected.
Thesedataareusedtoevaluatetheexposurepathwaysassociatedwiththesurficialsoil.
Thesepathwaysincludedirectcontact,ingestionofsoil,orvaporandparticulateinhalation.
However,forasitewhereanassessmenthasalreadybeenperformed,soildataat0to1-footbgsmaynotbeavailable.
Insuchcases,itisnecessarytoassessthesitetodetermineifsurficialsamplesshouldbecollected.
Careshouldbetakentocollectarepresentativesample,especiallyforthosevolatileCOPCsthathaveaHenry'sLawConstantof1x10-5atm-m3/moleorgreaterandwithamolecularweightoflessthan200g/mole.
5.
9REPRESENTATIVESOILANDGROUNDWATERCONCENTRATIONSTheperformanceofanRM-1and/oranRM-2Evaluationatasiterequiresthecalculationofsoiland/orgroundwaterrepresentativeconcentrationsandthecalculationofcumulativerisks.
IfthecalculatedcumulativerisksexceedtheDepartment-specifiedtarget-risklevels,therisk-basedtargetconcentrationscanbedeveloped.
Forsite-specificrisk-managementdecisions,itisnecessarytocomparethesetargetlevelswiththerepresentativesoil,groundwater,and/orsoil-vaporconcentrations.
Thedefinitionoftherepresentativeconcentrationiscriticaltodetermineifanunacceptableriskispresentatthesiteand/orifremediationatasiteisnecessary.
TherepresentativeconcentrationshouldbedeterminedasperAppendixB.
5.
10RECOMMENDEDLABORATORYANALYTICALMETHODSThesiteinvestigationshouldbeconductedtoobtainanalyticaldataforCOPCsandphysicalpropertiesofsoil.
TheacceptableanalyticalmethodsfordeterminingconcentrationsofCOPCsinsoil,groundwater,andsurfacewaterareprovidedinthemostcurrentAEIRG.
AnRSLEvaluationassumesgenericsoilpropertiesanddoesnotusesite-specificmeasurements.
IfanRM-1oranRM-2Evaluationistobeperformed,site-specificsoildatashouldbeobtained.
Acceptablelaboratorymethodsfordeterminingthefollowingsoilpropertiesarelistedasfollows:DryBulkDensity(g/cc)isthedryweightofsoilperunitvolumeofsoilandconsidersboththesolidsandtheporespace.
TheASTMMethodD2937-10,StandardTestMethodforDensityofARBCA(Revision3)20175-9SoilinPlacebytheDrive-CylinderMethod,definesdrybulkdensityasthedryweightofasoilsampledividedbythefieldvolumeofthesoilsample.
Anaccuratemeasurementofbulkdensityrequiresdeterminingthedryweightanddryvolumeofanundisturbedsample.
Thismethodinvolvescollectingacoreofaknownvolume,usingathin-walledsamplertominimizedisturbanceofthesoilsample,andtransportingthecoretothelaboratoryfor(i)drying,(ii)estimationofthedryweight,and(iii)estimationofdryvolumeorvolumeofdrysolids.
Porosity(cc/cc-soil)istheratioofthevolumeofvoidstothetotalvolumeofthesoilsample.
Manylaboratoriesusedrybulkdensityandspecificgravitydatatodetermineporosityusingthefollowing:SGnsρ=1(5-1)where,n=Porosity(cm3/cm3)sρ=Drybulkdensityofsoil(g/cm3)SG=Specificgravityorparticledensity(g/cm3)TheASTMMethodD854-10,StandardTestMethodsforSpecificGravityofSoilSolidsbyWaterPycnometer,maybeusedtodeterminespecificgravity.
Ifspecificgravityisnotavailable,then2.
65g/cm3canbeassumedformostmineralsoils.
Ifeffectiveporosityisrequiredforaparticularfate-and-transportmodel,itshouldbeestimatedfromaliteraturesource.
VolumetricWaterContent/MoistureContent(cc/cc)istheratioofthevolumeofwatertothevolumeofsoilinasample.
TheASTMMethodD2216-10,StandardTestMethodsforLaboratoryDeterminationofWater(Moisture)ContentofSoilandRockbyMass,isagravimetricovendryingmethod.
Thewatercontentvalueusedinmostmodelsisthevolumetricwatercontent.
Henceaconversionmaybenecessaryusingthefollowing:lswgwvρρθθ*=(5-2)where,θwv=Volumetricwatercontent(cm3-water/cm3-soil)θwg=Gravimetricwatercontent(g-water/g-soil)sρ=Drybulkdensityofsoil(g-drysoil/cm3-soil)lρ=Densityofwater(g/cm3)RefertoSection1.
4ofthemethodforspecialinstructionsondryingtemperatureandtimeformaterialcontainingsignificantamountsofhydrated(structural)water,suchasclays.
Ifthegravimetricwatercontentisoverestimated,drybulkdensitymeasuredwithMethodD2937-10willbetoosmall.
RefertoSection8ofMethodD2937-10.
ARBCA(Revision3)20175-10Further,ifporosityiscalculatedusingtheequationinTodd(1980),Porosity=1–(drybulkdensity/specificgravity*densityofwater),thenporositywillbeoverestimated.
Inotherwords,ifthegravimetricwatercontentiswrong,drybulkdensityandporositywillalsobewrong.
FractionalOrganicCarbonContentinSoil(g-C/g-soil)istheweightoforganiccarboninthesoilinthesampledividedbytheweightofthesoilandisoftenexpressedasaratio.
FractionalorganiccarboncontentcanbeestimatedusingtheASTMMethodD2974-07a,StandardTestMethodsforMoisture,Ash,andOrganicMatterofPeatandOtherOrganicSoils.
Thismethodmeasurestheorganicmattercontentofasample.
WhenusingtheASTMMethodD2974-07a,theresultmustbedividedby1.
724togetfractionalorganiccarboncontent(Pageandothers,1982).
Ifthelaboratoryresultsarereportedasapercent,fractionalorganiccarboncontentisobtainedbydividingtheresultsby100andthendividingby1.
724.
TheWalkleyBlack,rapid,dichromate-oxidationmethodforthedeterminationoforganic-carboncontent(Pageetal.
,1982)shouldnotbeused.
HydraulicConductivity(cm/sec)isthedischargeofwaterperunitarea,perunithydraulicgradientinasubsurfaceformation.
Forsomesites,itmaybeappropriatetouseacceptableliteraturevalues.
ThereferenceusedmustbeacceptabletotheDepartment.
Site-specificvaluesforhydraulicconductivity,ifnecessary,shouldbedeterminedusingacceptedfieldtestprocedures.
Theseincludeslugtestsand/orpumpingtests.
Undercertaincircumstances,theDepartmentmaydirectthesiteowner/operatortouseanalternativemethod.
Oneofthesealternativeswouldbetoperformasievetestandestimatethehydraulicconductivitybasedongrainsizedistribution.
Notethatmultipletestsforhydraulicconductivityshouldbeobtainedfromvariouswellsatthesitetoaddresstheheterogeneityofthesite.
ARBCA(Revision3)20176-16.
0RISK-BASEDEVALUATION:GENERALCONSIDERATIONSSeveralfactorsarecommontoARBCARM-1andRM-2Evaluations.
RM-1andRM-2targetlevelsarecalculatedwhenthecumulativerisksexceedtheacceptablerisklevels(i.
e.
,IELCR=1E-05forcarcinogenicriskandaHI=1.
0fornon-carcinogenicrisk).
Thereisnotarequirementtocalculatesite-specificRM-1orRM-2targetlevels.
RSLsandVISLsmaybeusedaswell.
TheadvantagetoRM-1andRM-2levelsisthattheyallowforsite-specificinputparameterstobeutilizedforthedevelopmentofthevaluesandtypicallygeneratelessconservativeandmoreaccuratetargetlevelsforaparticularsite.
Theseissuesarediscussedinthissection.
6.
1LANDUSECharacterizationofthepopulationandtheactivitiesnearareleasesiteisacriticalcomponentoftheARBCAprocess.
Thecumulativerisksandtargetlevelsvarydependingonwhetherthelanduseisunrestrictedversusindustrial,commercial,etc.
Somesitesmayhavemultiplelanduses.
Forsuchsites,thelandusethatyieldsthemostconservativeriskevaluationshouldbeconsidered.
Wheremultiplelandusesexistforasite,suchasasecond-floorresidenceoverafirst-floor-commercial-usebuilding,thesitewillbecarefullyevaluatedandanappropriateriskevaluationwillbeappliedbasedonsite-specificdataandavailablerisk-managementpractices(i.
e.
,landusecontrolssuchasenvironmentalcovenant).
ThecharacterizationofthepopulationshouldinitiallybedeterminedduringtheSiteAssessment(SA)orthePreliminaryInvestigation(PI)andismodifiedasnecessaryduringthedevelopmentoftheConceptualSiteModel(CSM)whichisoutlinedinmoredetailinSection6.
5.
Iftheinformationhasnotbeenobtained,thedatamustbeobtainedduringthenextphaseofonsiteworkactivitiesorpriortotheinitiationofthetiered,ARBCAEvaluationprocess.
WiththeARBCAprocess,landuseiscategorizedgenerallyaseitherunrestrictedorcommercial.
Ofthese,unrestrictedlandusegenerallyresultsinlowertargetlevels;thus,cleanuptounrestrictedstandardswillusuallyallowunrestricteduse.
ExamplesofunrestrictedandcommerciallanduseasutilizedintheARBCAEvaluationsarepresentedbelow.
Unrestricted:Typicallythisreferstoresidentialandincludes,butisnotlimitedto,schools,dwellings,homes,hospitals,child-carecenters,nursinghomes,playgrounds,recreationcenters,andanyotherareas/structureswithsensitivehumanactivity.
Groundwatermaybeusedasawatersupplyatunrestrictedsites.
Commercial:Includesgasstations,industrialoperations,stores,businesses,fleetoperations,etc.
,whereemployeeswork,butdonotreside,onacontinuingbasis.
Hotels,motels,andothertransientactivitiesareincludedinthecommercialdefinition.
ThecurrentlandusestatusshouldbeclearlyillustratedonmapssubmittedtotheDepartment.
Alandusemapwitharadiusof1,000feetshouldbepreparedformostsites.
Ifasiteutilizesanylanduseotherthananunrestricteduse,anenvironmentalcovenantdevelopedinaccordancewithADEMAdmin.
Codediv.
335-5shouldbesubmittedforreviewandrecordedintheJudgeofProbate'sOffice.
EPA's2011editionoftheExposureFactorsHandbookcanalsobeahelpfulARBCA(Revision3)20176-2resourcewhendetermininglanduseconsiderationsandpotentialimpacts.
6.
1.
1DetermineCurrentLandUseCurrentlandusesandactivitiesmustbeidentifiedandevaluatedtobeprotectiveoftheexistingreceptors.
Currentlandusereferstolanduseasitexiststoday.
Thiscanbereadilydeterminedbyasitevisit,andthereshouldbenoambiguityaboutcurrentlanduse.
Asitereconnaissanceshouldidentifyhomes,playgrounds,parks,businesses,industries,orotherlandusesatthesiteofthereleaseandincloseproximity.
Appropriatemaps(zoning,insurance,topographic,landuse,housing,etc.
),stateorlocalzoningboards,countypropertytaxrecords,theU.
S.
BureauoftheCensus,andaerialphotographscanprovideinformationfordetermininglanduse.
Undevelopedlandshouldbecharacterizedbythemostlikelyfutureuseofthatproperty.
Iftheundevelopedparcelislocatedinanareawhichispredominantlycommercial,thecommercialuseclassificationmaybeappropriatewhichmayrequiretheappropriatelandusecontrols(LUCs).
However,ifthesettingismoreruralandthelanduseismixed,theundevelopedlandshouldbeconsideredunrestrictedunlesstheowneriswillingtoimposetheappropriateLUCssuchasanenvironmentalcovenantdevelopedinaccordancewithADEMAdmin.
Codediv.
335-5toalterthelanduseclassificationtocommercial.
6.
1.
2DetermineMostLikelyFutureLandUseForallproperties,bothdevelopedandundeveloped,themostlikelyfuturelanduseshouldbedetermined.
Theobjectiveistodetermineifanyactivitiesassociatedwiththecurrentlandusearelikelytobedifferentinthefuturebasedonavailableinformationandtheuseofgoodprofessionaljudgment.
Knowledgeaboutthemostlikelyfutureuseofthesiteandadjacentpropertiesisnecessarytoidentifyreceptors,exposurepoints,exposurepathways,andexposurefactors.
ConsiderationofthesepathwaysintheARBCAprocessensuresthatthesite-specificdecisionsareasprotectiveoffuturesiteconditions/usesasreasonablypossible.
Theexposurestobeevaluatedinahumanhealthorenvironmentalriskassessmentdependupontheactivitiesthatcouldoccurunderreasonablefutureusesofthelandandgroundwateratthesite.
Mostlikelyfutureuseandactivitiescanbeidentifiedbasedonlocalzoningorotherordinances,knowledgeofcurrentlanduseandchanginglandusepatterns,zoningdecisions,communitymasterplans,interviewswithcurrentpropertyowners,commercialappraisalreports,proximitytowetlands,criticalhabitat,andotherenvironmentallysensitiveareas.
Carefulconsiderationoffuturelandandgroundwaterusagewillreducethepossibilitythattheselectedremedywillhavetobere-evaluatedduetochangesinlanduseassumptions.
Itshouldbenotedthat,ifcleanupisnotbasedonunrestricteduse,thefutureuseofthepropertyorgroundwaterwillbelimitedtotheusagescenarioutilizedforthecalculationoftherisksandcleanupgoalsandprotectedwithLUCssuchasanenvironmentalcovenantdevelopedinaccordancewithADEMAdmin.
Codediv.
335-5TheusershouldconsiderallgroundwaterapotentialdrinkingwatersourceintheARBCAprocessARBCA(Revision3)20176-3toensureprotectivenessoftheremedyandtopromoteresourceconservation.
Finalcleanuplevelsarebasedon-site-specificconditions,receptors,andcurrentandmostlikelyfuturelanduse.
FuturelandandgroundwaterusageisuncertainandmaybeinfluencedbyimposedLUCssuchasanenvironmentalcovenant.
6.
2ON-SITEANDOFF-SITEAllARBCAEvaluationsmustconsidertheimpactofthechemicalstoboththeon-sitereceptorsandoff-sitereceptors.
Thus,theCSMmustclearlyidentifyallcompletepathways,routesofexposure,andreceptorsthatmaybeimpactedbyContaminantsofPotentialConcern(COPCs)locatedon-siteandoff-site.
Withineacharea(on-site/off-site)theremaybemultiplelandusesandmultiplereceptors.
Forexample,acontaminatedgroundwaterplumecouldmigratebelowanoff-site,unrestrictedlanduseareaandacommercialarea.
Inthiscase,bothoff-siteunrestrictedandcommercialreceptorshavetobeconsideredwhiledevelopingtheCSM.
Forsimplification,thefollowingdefinitionsshouldbeused:On-site:Thepropertylocatedwithinthelegalpropertyboundarieswithinwhichthesourceofthereleaseislocated.
Thisincludesthesoil,groundwater,surfacewater,andairwithinthoseboundaries.
Off-site:Thepropertyorpropertieslocatedoutsidethepropertyboundariesoftheon-sitepropertywherethesourceofthereleaseislocated.
Thisincludesthesoil,groundwater,surfacewater,andairlocatedoff-site.
Thecharacterizationofthereleasewillincludeadeterminationoftheon-siteandoff-siteareasofimpact.
Theseareasareconsideredindeterminingthepathway-specificdecisionunitsorexposuredomains(DUs/EDs)ofthereceptor(s).
TheDU/EDistheareaoverwhichthereceptormaybeexposedtothecontaminatedmedium(s).
DeterminationoftheDU/EDiscriticalindevelopingrepresentativeconcentrationsseparatelyforgroundwaterandsoilforon-siteandoff-siteproperties.
AppendixBprovidesdetailsregardingthedevelopmentofrepresentativeconcentrationsforon-siteandoff-siteproperties.
6.
3RECEPTORSTheobjectiveofariskassessmentistoquantifytheadversehealtheffectstothecurrentreceptorsaswellasthemost-likelyfuturereceptors.
ForanARBCAEvaluation,thehumanreceptorstobeconsideredshouldincludepersonswholiveorworkwithinatleasta1,000-footradiusofthesiteboundary(and,attimes,moredependingonthesourceandhydrogeologicalconditions).
Forunrestricted-usereceptors,thecumulativeriskstobothadultsandchildrenshouldbeevaluated.
Adultsworkingatacommerciallocationoratconstruction-siteswillbeconsideredintheARBCAEvaluation.
Atrespasserwillgenerallyhavelessexposurethanresidentsandcommercialworkers;therefore,nospecificquantitativeanalysisneedbeperformedsolongastheproperjustificationisprovidedwithintheARBCAReport(e.
g.
,fencingandsecurityexiststoensurethattrespassersareunabletoenteraproperty).
ThemostlikelyexposedhumanreceptorsthatshouldbeincludedintheARBCAevaluationforaARBCA(Revision3)20176-4sitearelistedbelow;however,thisshouldnotbeconsideredacompletelist.
The2011USEPAExposureFactorsHandbookshouldbeconsultedtoprovidemoresite-specificactivity-basedinformationforpotentialreceptors:Residential–ChildResidential–AdultCommercialWorker–AdultConstructionWorker–AdultSurfacewaterbodiessuchascreeks,rivers,springs,ponds,lakes,bays,etc.
,shouldbeidentifiedwithinaminimum1,000-footradiusofthesite.
Surfacewaterbodiesshouldbeevaluatedtodeterminetheimpactsofdischarginggroundwaterorsurfacerunofffromthereleasesite.
Ataminimum,informationtobeevaluatedshouldincludethelocation,flowrates,depth,flowdirection,anduseclassificationfromADEMAdmin.
Codech.
335-6-11.
IfthewaterbodyinquestionisnotlistedinChapter11,theARBCAEvaluatorshouldassumetheFishandWildlifeuseclassification.
Typically,smallerstreamswillnotbelistedinChapter11.
On-siteaswellasoff-siteundergroundutilitiesand,specifically,theirabilitytoserveasconduitsshouldbefullyevaluated.
Adverseimpactsmayincludedegradationofwaterlines,degradationofsewerlines,vaporsinstormandsanitarysewers,propertydamagetooutercoatingsofgaslines,andpropertydamagestoburiedphoneandelectricallines.
WhereChemicalofConcern(COC)plumesextend,orlikelytoextend,beyondthesitepropertyboundary,anyadditionalreceptorsshouldalsobeidentifiedandtheirriskevaluated.
Intheabsenceofadditionalreceptors,theARBCAprocessrequirestheevaluationofthepotentialimpactofCOCplumesongroundwaterresourcesbeyondthelegalsiteboundary.
SeeSection6.
6fortheuseofthesecriteriainselectingthelocationofthepointofexposure.
Therearecertainsitessuchasconservationareas,sensitiveresourceareas,agriculturalareas,etc.
,wherelivestockorwildlifemaybethepotentialreceptors.
Intheseareas,ecologicalexposureofwetlands,sensitiveenvironments,wildlifeand/orthreatenedand/orendangeredspeciesshouldbethoroughlyevaluated.
Section6.
13addressesconcernsregardingecologicalriskevaluations.
ThepotentialrisktothesetypesofreceptorsshouldbeevaluatedunderanRM-2Evaluation.
TheDepartmentshouldbecontactedtoobtainadditionalguidanceontheseissues.
Moreinformationisavailableinthedocument,EcologicalRiskAssessmentGuidanceforSuperfund(U.
S.
EPA,1997).
Non-humanreceptorssuchasendangeredspeciesorotherecologicalreceptorsliveinmanytypesofareasthatmaybeimpactedbycontaminationandshouldbeevaluatedforpotentialecologicalimpacts.
SourceWaterAssessmentAreas(SWAAs)IorIIshouldbeidentifiedandevaluatedasnecessary.
AdefinitionandatabledescribingSWAAsIandIIarefoundinADEMAdmin.
Codech.
335-7-15.
ThesetypesofareasshouldbeevaluatedunderanRM-2Evaluation.
ARBCA(Revision3)20176-56.
4HUMANEXPOSUREPATHWAYSAreceptorcomesincontactwithCOPCsthroughacompleteexposurepathway.
Forapathwaytobecomplete,theremustbe(i)asourceofchemical,(ii)amechanismbywhichthechemicalisreleasedfromthesource,(iii)amediumthroughwhichachemicaltravelsfromthepointofreleasetothereceptor'slocation,and(iv)arouteofexposurebywhichthechemicalentersthereceptor'sbodyandpotentiallycausesadversehealtheffects.
Thesourceofachemicaldependsonthenatureofthesiteactivities,therelease,andthereleasearea.
Releasemechanismsmaycausechemicalstobereleasedeitherintheair,onthegroundsurface,orinthesubsurface.
Potentiallyimpactedmediaincludeair,surficialandsubsurfacesoil,surfacewater,andgroundwater.
Routesofentryincludeingestionofgroundwaterandsoilparticulates,indoorandpossiblyoutdoorinhalationofvaporsintheair,indoorandpossiblyoutdoorinhalationofvaporsfromsoilandgroundwater,inhalationofsoilparticulates,dermalcontactwithsoil,andleachingtogroundwaterfromsurficialandsubsurfacesoils.
Figure6-1isanexamplesiteconceptualexposuremodelthatillustratestherelationshipsbetweentheimpactedmedia,transportmechanisms,exposurepathways,andpotentialreceptorsthatcomprisecompletepathways.
Items(i),(ii),and(iii)arecriticalindeterminingtheexposuredomainofthereceptor(s).
TheDepartmenthasidentifiedthemostcommonlyencounteredexposurepathwaysforwhichanevaluationmustbeconductedtodeterminewhetheracompleteexposurepathwayexistsatthereleasesite.
Thesepathwaysarediscussedbelow.
6.
4.
1PathwaysforInhalationFortheinhalationpathway,thechemicalintakeoccursbytheindoorinhalationofvaporsortheoutdoorinhalationofvaporsand/orsoilparticulatesatasite.
Inmostcases,theoutdoorinhalationofvaporspathwayisnotthecriticalpathwayduetotheextremedilutionofoutsideairandthefactthatthesunlightdegradesmanyCOPCs.
TheDepartmentconsidersachemicaltobeapotentialsourceforvaporintrusionifithassufficientvolatilityandtoxicityinthesubsurfacewithsufficientmassorconcentrationtoposeapossibleinhalationriskwithinoverlyingbuildings.
FurtherguidanceonvaporintrusionrelatedtopetroleumandchlorinatedcompoundsisavailablefromtheU.
S.
EPAintwoguidancedocuments,AssessingandMitigatingtheVaporIntrusionPathwayfromSubsurfaceVaporSourcestoIndoorAirandAddressingPetroleumVaporIntrusionatLeakingUndergroundStorageTankSites.
Dependingonthetoxicityofthechemical,unacceptableexposuresmayoccuratconcentrationsbelowtheodor-thresholdlevels.
Inmostcases,thesourceforthesevaporsisvolatilechemicalsinsoiland/orgroundwater.
Chemicalsthathavemigratedthroughsubsurfacesoiltogroundwatermayvolatilizefromthesoiland/orgroundwater.
ThevolatileCOPCsmaydiffuseupwardthroughtheoverlyingcapillaryfringe,unsaturatedzone,andcracksinthefloor/foundationtoindoororoutdoorairwheretheexposuremayoccur.
Toquantitativelyevaluatethevaporinhalationpathway,mathematicalmodelsareusedtorelatetheallowableairand/orsoil-vaporconcentrationswiththesoilorgroundwaterconcentrations.
Risksfrominhalationofvaporsfromsoilorgroundwaterarecalculatedusingactualconcentrationsinsoilandgroundwaterandfateandtransportmodels.
Iftargetrisks(i.
e.
,IELCR=1E-05&HI=1.
0)areexceeded,targetconcentrationsprotectiveofindoor(andoutdoorasARBCA(Revision3)20176-6necessary)inhalationaredevelopedforRM-1andRM-2Evaluations.
Iftheallowableriskisexceeded,thenitmaybeappropriatetocollectsoil-vapormeasurements,oritmaybeappropriatetoproceeddirectlyintoremediationand/ormitigation.
Anevaluationshouldbeperformedtodeterminethenecessityofcollectingairand/orsoil-vaporsamplesforcomparisontotheindoor/outdoorairand/orsoil-vaportargetlevelswhicharelocatedintheVISLs.
Indoor-airmeasurementsshouldnotbeperformedatmanysitesduetotechnicaldifficultiesassociatedwithaccuratelymeasuringtheindoor-airconcentrationcontributedbysoiland/orgroundwaterimpacts.
Rather,eithermodelsusedtoestimateindoor-airconcentrationsortheuseofanempiricalrelation/attenuationfactortoestimateindoor-airconcentrationsbasedonsoil,groundwater,andsoilvaporshouldbeused.
Inthemajorityofcases,itismostappropriatetomeasuresoil-vaporconcentrationsandcomparethesemeasuredvalueswiththeVISLs.
Ifeitherthesubsurfacesoilorgroundwaterindoorinhalationpathwaysarecomplete,thesoilvaporpathwaysshouldbeconsideredcomplete/potentiallycompleteevenifactualsoilvapormeasurementswerenotcollected.
Thesiteconceptualexposuremodelshouldstatethatactualsoilvapormeasurementswerenotobtainedanddiscusswhynorepresentativeconcentrationsforsoilvaporareprovided.
Ifsoilvapordataisavailable,theriskwillbecomputedfromactualsoilvapormeasurements,notfromthesoilandwaterconcentrations.
FortheRM-1andRM-2Evaluations,theguidanceprovidedintheTechnicalGuideforAssessingandMitigatingtheVaporIntrusionPathwayfromSubsurfaceVaporSourcestoIndoorAir,theTechnicalGuideforAddressingPetroleumVaporIntrusionatLeakingUndergroundStorageTankSites,andtheRiskAssessmentGuidanceforSuperfund(RAGS)PartF(EPA2009)shouldbeusedtoquantitativelydetermineeithertheriskortheRisk-BasedTargetLevels(RBTLs)associatedwiththeoutdoorinhalationofsoilparticulates.
RefertoAppendixBandtheTechnicalGuideforAssessingandMitigatingtheVaporIntrusionPathwayfromSubsurfaceVaporSourcestoIndoorAirandtheTechnicalGuideforAddressingPetroleumVaporIntrusionatLeakingUndergroundStorageTankSitesforguidanceonthemethodsforestimationofrepresentativeconcentrations.
6.
4.
2PathwaysforSurficialSoilsSurficialsoilsaredefinedassoilsextendingfromthesurfacetoonefootbelowgroundsurface(bgs).
Theexposurepathwaysassociatedwithaffectedsurficialsoilincludethefollowing:IngestionofsoilparticulatesInhalationofsoilparticulatesOutdoorinhalationofvaporemissionsfromsoilDermalcontactwithsoilLeachingtogroundwater,potentialingestionofgroundwater,andmigrationtosurfacewaterToevaluatethesepathways,arepresentativenumberofsurficialsoilsamplesshouldbeobtainedfromtheaffectedarea/exposureunitordomain.
Thesemeasuredconcentrationsareusedtoestimatetherepresentativeconcentration(s)thatareusedtodetermineifthecumulativerisksareARBCA(Revision3)20176-7acceptable.
RefertoAppendixBforguidanceonthemethodsforestimationofrepresentativesurficialsoilconcentrations.
Althoughsurficialsoilisdefinedassoilsextendingfromthegroundsurfacetoonefootbgs,careshouldbetakennottodiluteanalyticalresultsbysamplingtheentire1-footinterval.
Incaseswherecleanfillhasbeenplacedontopofcontaminatedmedia,thesurfacesoilsamplesshouldbecollectedwithinthezoneofcontaminatedsoilswhileavoidingcollectingsamplesofthecleanfill.
Inothercaseswherecleanfillmaynotexist,butonlyaportionoftheone-footsoilcolumniscontaminated,thesamplingofsurficialsoilsshouldoccurattheshallowestportionofthetopone-footwherecontaminationisexpectedathigherconcentrations.
Note:Forconstructionworkers,"surficial"soilisdefinedastheexcavationdepth.
Thus,fortheconstruction-workerreceptor,theARBCAEvaluatorshoulddefinethedepthtoconstructionandusethesoilconcentrationdataoverthatdepthrangeastherepresentativeconcentrationsfortheconstructionworkerexposuredomainordecisionunit.
6.
4.
3PathwaysforSubsurfaceSoilsSubsurfacesoilsaredefinedassoilslocatedbelowonefootandextendingtothewatertable.
Ifanevaluatorwishestodefinesubsurfacesoilsdifferently,landusecontrolsinaccordancewithADEMAdmin.
Codediv.
335-5willbenecessary.
Whenevaluatingpotential,future,directcontactexposurepathwaysforaconstructionand/orcommercialworker,subsurfacesoilsmaybedefinedtoextendonefootbelowgroundsurfaceto15feetbelowgroundsurface.
Fifteenfeetbelowgroundsurfaceisacommonnominalmaximumdepth,plusasafetyfactor,forconstructionactivities.
However,ifitisanticipatedthatfutureexcavationdepthscouldexceed15feetbelowgroundsurface,theanticipateddepthofexcavationshouldbeusedtoevaluatetherisktoconstructionand/orcommercialworkers.
Theexposurepathwaysassociatedwithsubsurfacesoilsincludethefollowing:IndoorinhalationofvaporemissionsOutdoorinhalationofvaporemissionsLeachingtogroundwater,potentialingestionofgroundwater,andmigrationtosurfacewaterFuturepotentialingestionof,inhalationofvaporsandparticulatesfrom,anddermalcontactwithsoilduringexcavationactivities,asin6.
4.
2,above.
Toevaluatethesepathways,arepresentativenumberofsubsurfacesoilsamplesshouldbecollectedintheaffectedarea.
Representativesubsurfacesoilconcentrationsareusedtodetermineifthecumulativerisksareacceptable.
RefertoAppendixBforguidanceonthemethodsforestimationofrepresentativesubsurfacesoilconcentrations.
6.
4.
4PathwaysforGroundwaterExposurepathwaysfortheimpactedgroundwaterincludethefollowing:IndoorinhalationofvaporemissionsARBCA(Revision3)20176-8OutdoorinhalationofvaporemissionsIngestionofwateron-siteoroff-siteFutureingestionofwater(groundwaterresourceprotection)Impactstosurfacewaters(surfacewaterprotection)Toevaluatethesepathways,representativegroundwatersamplesshouldbeobtainedon-siteandoff-site.
Representativegroundwaterconcentrationsareusedtodetermineifthecumulativerisksareacceptable.
RefertoAppendixBforguidanceonthemethodsforestimationofrepresentativegroundwaterconcentrations.
6.
4.
5OtherPathwaysEachoftheaboveexposurepathwayslistedinSections6.
4.
1to6.
4.
4mustbeevaluatedaspartoftheexposureassessment;however,insomecasesitmaybedeterminedthatoneormoreoftheseexposurepathwaysareincompleteandwillnotbeevaluatedfurther.
Othersignificantexposurepathways,suchashumanconsumptionoffoodcropsorfishandshellfishgrowninimpactedmediaoruseofgroundwaterforirrigationoffoodcropsforhumanconsumption,shouldbeevaluatedifthesepathwaysarecomplete.
RefertotheRiskAssessmentGuidanceforSuperfundVolumeIHumanHealthEvaluationManualPartA(U.
S.
EPA,1989)forfurtherguidanceonevaluationofriskduetofoodintake.
AdditionalreferencesareavailableontheEPARSLwebsite.
6.
5CONCEPTUALSITEMODEL(CSM)TheinformationobtainedduringthesiteassessmentphaseasdescribedinSection5.
2andtheAEIRGisusedtodevelopaCSM.
TheCSMisageneralunderstandingorworkinghypothesisthatdepictstherelationshipbetweenthechemicalsourceareas(contaminatedsoilsandgroundwater,non-aqueousphaseliquids,etc.
),transportmechanisms(leaching,groundwatertransport,volatilization,etc.
),receptors(residents,commercialworkers,ecological,surfacewaters,etc.
),andexposureroutes(inhalation,ingestion,dermalcontact,etc.
).
AdetaileddiscussionregardingtheCSMmaybelocatedinSection2.
4.
3oftheITRC'sTechnicalandRegulatoryGuidancefortheTriadApproach–December2003.
TheCSMrequiresabasicunderstandingofthefollowingcharacteristics:ThephysicalconcentrationsanddistributionoftheCOPCsThefactorsaffectingchemicaltransportThepotentialforaCOPCtoreachareceptorWhenconductingtheARBCAEvaluation,aqualitativeevaluationmustbeperformedtoidentifythemechanismsbywhichCOPCswillmovefromaffectedsourcemediatothepointofexposure(POE)wherecontactwiththereceptoroccurs.
Ifmigrationorcontactisnotpossible(e.
g.
,duetoengineeringcontrolssuchasapavedsitethatwillpreventhumancontactwithcontaminatedsoil)undercurrentandmostlikelyfuturelanduseconditions,thesite-specificCOPCconcentrationsmaynotposeanyrisk,andthepathway(s)maybeconsideredincompletewhenconstructingthesiteconceptualexposuremodelafterallobligationstoensuretheassumptionsaremetthroughanARBCA(Revision3)20176-9environmentalcovenantenteredintheJudgeofProbate'sOfficeinaccordancewithADEMAdmin.
Codediv.
335-5.
Theexposuredomains(EDs)ordecisionunits(DUs)ofallreceptorsmustbeconsidered.
TheEDorDUistheareaoverwhichthereceptormaybeexposedtothecontaminatedmedium(surficialsoil,subsurfacesoil,groundwater,andsoilvapor).
Thisareamustbeestablishedfortheon-sitescenarioaswellasanyoff-siteimpactedorpotentiallyimpactedproperties.
AppendixBprovidesadetaileddiscussionondevelopingrepresentativesoilandgroundwaterconcentrations,whichrequiresidentificationoftheEDorDU.
ACSMisrequiredforRSL,RM-1,andRM-2Evaluations.
Atsomesiteswithmultipleoff-siteproperties,multipleCSMsmayhavetobedeveloped.
ThroughouttheARBCAEvaluationprocess,theCSMshouldbeevaluatedandrevisedtoreflectaccuratesiteconditions.
Figure6-1isagraphicalrepresentationthatmaybeusedasaworksheettodevelopaCSM.
Figure6-1isatemplateforthetabularrepresentationofaCSMandshouldbedevelopedforeachreceptorforcurrentandmostlikelyfuturelanduses.
TheARBCAEvaluatorshouldclearlydocumentallthesource-pathwayreceptor-routecombinationsandpresentclearjustificationfordecidingifthepathwayiscompleteornotcomplete.
TheremaybemultipleCSMsiftherearemultipleoff-site,impactedproperties.
6.
6POINTOFEXPOSURE(POE)ThePOEisthelocationwhereareceptorcomesincontactwithCOPCsundercurrentandmostlikelyfutureuseconditions.
AseparatePOEisassociatedwitheachcompleteexposurepathwayidentifiedintheCSM(refertoSection6.
5).
Fordirect-exposurepathways,thePOEislocatedatthesourceoftheCOPCs.
Forexample,fortheingestionofsurfacesoil,thePOEisatthesamelocationasthesource.
Forindirect-exposurepathways,thePOEandthesourceofCOPCsarephysicallyseparate.
Forexample,forthecaseofindoorinhalationofvaporsfromsubsurfacesoil,thePOEisinsidethebuilding(thebreathingspace)whereasthesourceisthesoilbelowthebuilding.
Thus,foreachcompleteexposurepathway,theARBCAEvaluatormustidentifythesourceandthePOE.
FortheGroundwaterResourceProtectionEvaluation,thegroundwateringestionPOEisassumedtobelocateddirectlybelowthesourceforaRSLEvaluation.
ForRM-1andRM-2Evaluations,thegroundwateringestionPOEwillbeestablishedatthenearestpointwhereawaterwellcurrentlyexists,orismostlikelytoexist,inthefuture.
Ifnosuchwellsexistorareunlikelytobeinstalled,thenthePOEwillbeatthedown-gradientpropertyboundary.
WithpriorDepartmentapproval,thePOEmaybelocatedatanalternatedistancefromthepropertyboundaryifjustifiedbasedon-site-specificconditionsandtheappropriateland-usecontrolsareinplace.
TheselectedPOEshouldnotbeahypotheticalormodeledwell,butshouldbeanactualwell.
Groundwatersamplesshouldbecollectedtoverifythewellconcentrationsasneededthroughoutthelifeofmonitoringrequirements.
Incertaincase-by-casescenarios,ahypotheticalwellmaybeallowed,butDepartmentalapprovalwouldbenecessary.
ASentryWell(SW)isamonitoringwellormultiplewellsthatmustbelocatedbetweentheCOPCsourceareaandthePOEalongtheflowdirection.
TheSW(s)shouldalsobeanactualwellandARBCA(Revision3)20176-10notahypotheticalormodeledwell.
TheSW(s)servestoprotectthePOE.
ForRM-1andRM-2Evaluations,SWtargetlevelswillbedevelopedandcomparedtothegroundwaterrepresentativeconcentrationsforthatlocation.
Formostsites,multipleSWsshouldbeselectedfortheGroundwaterResourceProtectionEvaluation.
Forsiteswithvariableorradialflow,multiplePOEsandSWslocatedalongdifferentflowdirectionsmayhavetobeevaluated.
Therefore,atmostsites,nearlyallwellsthatarenotnamedassource-areawellsshouldbenamedasSWs.
Thedistancefromthesoilsource,thatisaninputtotheequationsprovidedinAppendixEtoback-calculateallowablesoilandgroundwaterconcentrationsatthesourceandatSWs,isthedistancefromthesoilsourcetothelocationwheretheactualgroundwatermonitoringPOEwell(s)exists.
Inmostcases,thePOEwell(s)islocatednearthepropertyboundary.
6.
7CALCULATIONOFRISKSANDRISK-BASEDTARGETLEVELS(RBTLs)6.
7.
1OverviewoftheSequence:RSLEvaluation,RM-1Evaluation,RM-2EvaluationRisk-basedtargetlevels(RBTLs)shouldbecalculatedifsitemaximaexceedtheRegionalScreeningLevels(RSLs)ortheVaporIntrusionScreeningLevels(VISLs)andtheRM-1ortheRM-2cumulativerisksareexceeded.
BeforediscussinghowtheRBTLsarecalculated,abriefsummaryoftherisk-assessmentprocessisprovidedbelow:Thefirststepshouldbetocomparesiteconcentrationsofallthechemicalsofpotentialconcern(COPCs)forthetypeofproductreleasedtotheRSLsandVISLs.
AnyCOPCsthatexceedRSLsorVISLsgoforwardintoanRM-1Evaluationas"chemicalsofconcern"(COCs).
IfthesiteexceedstheRM-1risks,alltheRM-1COCsshouldmoveforwardintotheRM-2Evaluation.
Asapointofclarification,oncethescreeningstephasbeencompletedandtheCOCsdetermined,thatlistofcontaminantsshouldremainwithouthavingadditionalcontaminantsdroppedfromthelist.
ThefirststepinbothanRM-1EvaluationandanRM-2Evaluationistocomputethecumulativeriskandthehazardindexforeachreceptor.
Evaluatingonereceptoratatime,oneaddsuptherisksfromallthecarcinogenicCOCsforeveryoneofthatreceptor'scompletepathways.
Thisyieldsonecumulativeriskforthatreceptor.
Similarly,forallthenon-carcinogenicCOCs,oneaddsupthehazardquotientsforeachofthatreceptor'scompletepathways.
Whenaddedup,hazardquotients(HQs)becomethehazardindex(HI),whichisthesumoftheHQs.
FollowingthecompletionofthisexercisethereshouldbeacumulativeriskandanHIforeachreceptor.
Thecumulativeriskshouldnotexceed1*10-5,andthehazardindexshouldnotexceed1.
0.
InanRM-1Evaluation,ifanyreceptor'scumulativeriskexceeds1*10-5,ortheirhazardindexexceeds1.
0,onecaneitherdevelopRBTLsandcleanupthesitetothoselevels,orproceedtoanRM-2Evaluation.
InanRM-2Evaluation,thecumulativerisksandHIsneedtoberecomputedusingsite-specific,fateandtransportproperties.
ThisyieldsadifferentcalculationfromthoseobtainedintheRM-1Evaluation.
IntheRM-2Evaluation,ifanyreceptor'scumulativeriskorHIexceedsthelimitsof1*10-5forthecumulativeriskand1.
0fortheHI,thenonemustdevelopRBTLsusingsite-specificfate-and-transportproperties.
TheseRBTLswillbedifferentfromtheRBTLsobtainedARBCA(Revision3)20176-11intheRM-1Evaluation.
6.
7.
2CalculationofRisk-BasedTargetLevels(RBTLs)RBTLsaretheallowableconcentrationscalculatedusingtheback-calculationmode.
Cumulativerisksarecalculatedutilizingtheforward-calculationmode.
AppendixEpresentstheequationsandmodelsusedintheARBCAevaluationsinbackwardmodewhichisusedtocalculaterisk-basedtargetconcentrations.
ThesamemodelsandequationsareshowninforwardmodeinAppendixFwhichisusedtocalculaterisks.
Theseproceduresrequirequantitativevaluesof(i)target-risklevels,(ii)chemical-specifictoxicityvalues,(iii)physicalpropertiesoftheCOCs,(iv)receptor-specificexposurefactors,(v)fateandtransportparameters,(vi)buildingparameters,and(vii)uptakeequations/fate-and-transportmodels.
Eachofthesefactorsisdiscussedbelow.
ForanRSLEvaluation,RSLsandVISLshavebeencompiledbytheUSEPAforeachoftheCOPCsforthecommonlyencountered,complete,exposurepathways.
TheRSLsaretypicallyupdatedonasemi-annualbasis.
TheARBCAEvaluatorwillcalculatethetargetlevelsusingsite-specificdataandpathway-specificmodels.
RM-1targetlevelsshouldbedevelopedutilizingtheequations/modelsprovidedinAppendixE,theRSLtoxicityparameters,theRSLchemical-specificparameters,theRSLUser'sGuideTable1defaultexposurefactorsandfateandtransportparameters,andappropriatesite-specificdata.
ForanRM-2Evaluation,theequations/modelsprovidedinAppendixE,theRSLchemical-specificandtoxicityparameters,thestandarddefaultexposurefactorsandthefateandtransportparametersfactorslistedinTable1oftheRSLUser'sGuide,andappropriatesite-specificdatashouldbeusedunlessalternatemodelsareapprovedbytheDepartment.
Ifthecalculated,cumulativerisksexceedthetargetrisksforareceptor,theARBCAEvaluatormustcalculatecleanuplevelsorrisk-basedtargetlevels(RBTLs).
Therearemanydifferentcombinationsofcleanuplevelsthatcanensurethatthecumulativeriskforareceptordoesnotexceed1x10-5forcarcinogenichealtheffectsand1.
0fornon-carcinogenichealtheffects.
Threemethodsarediscussedforcarcinogenichealtheffectsnext.
Method1-ReduceeachriskfromeachCOCbythesameamountOnewaytocalculateRBTLsistosimplytaketherepresentativeconcentration(foreachCOC,foreachcompletepathway,foreachreceptor)anddivideitbyanacross-the-boardfactorthatwillresultinacumulativeriskforthereceptorbeingreduceddownto1x10-5.
Onemayeasilyseethefactorthatwillmakethecumulativeriskforthereceptorbe1x10-5bylookingatthecumulativeriskforthereceptor.
Forexample,ifthecumulativeriskforthereceptoris3.
36x10-5,thefactorbywhichtodivideeachrepresentativeconcentrationis3.
36.
Thisisbecause,ifthecumulativeriskexceedsthetargetriskof1x10-5byafactorof3.
36,dividingeachrepresentativeconcentrationby3.
36willreducethecumulativeriskdownto1x10-5.
Tip:Writethecumulativeriskasamultipleof10-5inordertoseethedivider.
ARBCA(Revision3)20176-12Method2-DividethetargetriskforeachCOCintoasmanyCOC-pathwaycombinationsasthereareforthereceptorAnotherwayofcomputingRBTLsistotakethe1x10-5totalallowableriskperreceptoranddivideitupequallyintothenumberCOCandcompletepathwaycombinationsforthereceptor.
WhencountingthenumberofCOCandcompletepathwaycombinations,onlycounttheCOCsthathavetherelevanttoxicologicalparametersavailabletocomputetheirrisk.
Forexample,iftheCOCsareBTEX,MtBE,andnaphthalene,andthefourcompletepathwaysareindoorandoutdoorinhalationfromsoilandfromgroundwater,then,forcarcinogenicrisk,thenumberofCOCandcompletepathwaycombinationsis16,becauseonlybenzene,ethylbenzene,MtBE,andnaphthalenehaveaninhalationunitrisk.
Therefore,thetargetriskforeachCOCandcompletepathwaycombinationis0.
0625x10-5.
TheARBCAEvaluatorshouldusethistargetriskintheappropriateequationstocomputeRBTLs.
Method3-RatiomethodAnotherwayofcomputingRBTLsistolookatsomeproportionsandsetupanequationthatcanbesolvedfortheRBTL(AlaskaDEC,2008).
ForcomputingtheriskandRBTLsfromtherepresentativeconcentrationforoneCOCandcompletepathwaycombination,therearetwoequivalentratiosthatcanbesolvedfortheRBTLfortheCOC:RBTLcocRepresentativeconcentrationcocTargetriskCalculatedriskcocRBTLcoc=RepresentativeconcentrationcocxTargetriskCalculatedriskcocSincethecumulativeriskofallCOCandcompletepathwaycombinationsneedstobekepttolessthan1x10-5,eachindividualtargetriskisgoingtobe1x10-5dividedbythenumberofCOCandcompletepathwaycombinations.
Callthelatterthe"numberofrisks"andadjustthepreviousequationtoshowthereducedtargetrisk.
RBTLcoc=RepresentativeconcentrationcocxTargetriskCalculatedriskcocxNumberofrisksThisequationcanbeusedtocomputeRBTLsthatwillsatisfythecriterionthatthecumulativeriskwillequal1x10-5.
Theabovemethodscanalsobeappliedfornon-carcinogenichealtheffects.
ARBCA(Revision3)20176-136.
7.
2.
1TargetRiskLevelArisk-baseddecisionmakingprocessrequiresthespecificationofatargetoracceptablerisklevelforbothcarcinogenicandnon-carcinogenic,adverse,healtheffects.
Forcarcinogeniceffects,riskisquantifiedusingtheIndividualExcessLifetimeCancerRisk(IELCR,RAGS,vol.
1,PartB,page21)thatrepresentsanincreaseintheprobabilityofanindividualdevelopingcancerduetoexposuretoaCOCthroughacompleteexposurepathway.
SinceareceptormaybeexposedtomultipleCOCsandexposurepathways,theacceptablerisklevelshouldaccountfortheeffectofsimultaneousexposuretomultipleCOCsandexposurepathways.
TheIELCRlevelusedtocalculateRSLsis1*10-6,whiletheIELCRlevelusedinthecalculationoftheRM-1andRM-2targetlevelsis1*10-5.
Fornon-carcinogeniceffects,riskisquantifiedusingaHazardQuotient(HQ)thatrepresentstheratiooftheestimateddoseforachemicalandanexposurepathwaytothereferencedose.
WhenareceptorisexposedtomultipleCOCsandmultipleexposurepathways,individualHQsmaybeaddedtogethertoestimatetheHazardIndex(HI).
TheHIisthesumofindividualHQs.
AnHQof0.
1shouldbeselectedwhenviewingtheRSLtablewhileanHIof1.
0shouldbeusedinthecalculationofRM-1andRM-2targetlevels.
Thetargetrisklevels(IELCRandHQand/orHI)maybeusedinoneoftwoways.
First,therepresentativeconcentrationsmaybeusedtocalculatethesite-specificcumulativerisksthatarethencomparedwiththetargetrisklevels.
Ifthecumulativerisks(sumofrisksforeachCOCandeachcompleteexposurepathwayforanindividualreceptor)exceedthetargetrisklevels,riskmanagementmaybenecessary.
Riskmanagementmayincludeactiveremediation,remediationbymonitorednaturalattenuation(MNA),institutionalcontrols,oracombination.
GroundwaterCOCsmustbeincludedwithinthecumulativeriskcalculationeveniftheestablishedMCLisnotexceeded.
Ingestionofgroundwatermustbeconsidered,and,whengroundwateringestionisacompletepathway,allCOCsmustbeincludedinthecumulativeriskevaluation.
(Note:NotallMCLsarebasedonthesametargetrisklevel.
SiteswillnothavetoberemediatedbelowtheMCLs,butthetarget,cumulative-risklevelsmustbemetwhentherearecontaminantsthatdonothaveanestablishedMCL).
Followingacumulativeriskevaluationwhereitisdeterminedthattheacceptableriskshavebeenexceeded,targetrisklevelsmaybeusedtobackcalculatethetargetcleanupconcentrations(RBTLs)foreachchemical,eachcompleteexposurepathway,eachmedium,andeachreceptor.
Thetargetconcentrationsarethenusedasaguideduringriskmanagementand/orremediationactivitiesandcomparedwiththerepresentativeconcentration(s)(seeAppendixB).
Onceitappearsthatthetargetconcentrationshavebeenmet,thecumulativerisksatthesiteshouldbere-evaluatedtoensurethatthetargetrisklevelshavebeenmet.
Fornon-carcinogeniceffectsfortheRSLs,aHQof0.
1shouldbeused(Note:ThereisanoptiontoselectanHQ=1.
0.
ThisoptionisnotallowedforuseintheStateofAlabama).
SincetheadditiveeffectsofmultiplechemicalsandmultipleexposurepathwaysmustbeconsideredforRM-1andRM-2Evaluations,anHIoflessthanorequalto1.
0mustbeusedinRM-1andRM-2.
Whendeterminingtheadditiveeffectsofmultiplechemicalsandmultipleexposurepathways,ingestionofgroundwatermustbeconsidered,andallCOCsmustbeincludedwithinthecumulativeriskARBCA(Revision3)20176-14evaluation.
FortheRM-1andtheRM-2Evaluations,thecumulativeIELCRatasite(thesumoftheIELCRforeachCOCandeachcompleteexposurepathway,forareceptor)lessthanorequalto1*10-5,andthecumulativeHIatasite(thesumofHQsforeachCOCandeachexposurepathway,forareceptor)lessthanorequalto1.
0arerequired.
AcumulativeriskevaluationshouldbecalculatedusingrepresentativeconcentrationsforeachCOCasdescribedinAppendixB.
Tocalculatethecumulativeriskforanareaofcontamination,theforwardcalculationmethodmustbeused.
Theforwardcalculationmethodcalculatesriskfromrepresentativeconcentrationsandreceptorspecificinputparameters.
Forevaluatingwhetherornotawatersupplywellorspringposesanunacceptablerisk,theforegoingtargetriskandhazardquotientvaluesarenotrequired.
Instead,thechemicalspecificconcentrationsatthewatersupplywellorspringshouldnotexceedtheMCLs,healthadvisoriesorthecalculatedtargetlevelsfordirectingestionofgroundwaterinaccordancewiththeequationslocatedinAppendixEorotherappropriatemodels.
TheCOCconcentrationsinthewatersupplywellorspringcanbedeterminedeitherbysite-specificsamplingorbyusingafateandtransportmodel.
AppendixEcontainsequationsneededfortheDomenicoModel,whichisbasedonlaminarflowinahomogeneousgeologicenvironment.
ForsitesinuniquegeologicalenvironmentsnotsuitedfortheDomenicoModel(suchaskarstorfracturedflowregimes),anothermoreappropriatemodelormodelingpackshouldbeapplied.
Itmaybenecessarytovalidateamodelthroughtheuseofhistoricalconcentrationsandpotentiometricdatatodemonstratethatthemodelcanapproximatedowngradientconcentrationsatasite.
ModeledconcentrationsatthePOE,SentryWell(SW),andsourcearealocationsmayneedtobeverifiedusingactualdata.
Additionalmonitoringorcorrectiveactionmayberequirediftheconcentrationsexceedthegroundwater-ingestiontargetlevelsatthePOEorvaluesprotectiveofthePOEattheSW.
Similarly,forimpactstosurfacewaterbodiestheabovetargetrisksdonotapply.
Thetargetsurfacewaterconcentrationsshouldutilizethetarget-risklevelsdeterminedanddevelopedbytheADEMWaterDivisioninaccordancewiththeWaterQualityCriteriaestablishedinADEMAdmin.
Codech.
335-6-10.
Theappropriateuseclassificationshouldbeused(i.
e.
,PublicWaterSupplystreams(consumptionofwaterandfish)orFishandWildlifestreams(consumptionoffishonly)).
6.
7.
2.
2QuantitativeToxicityFactorsThetoxicityofchemicalsisquantifiedusinganoralslopefactor(SFo),aninhalationunitrisk(IUR),andadermalslopefactor(SFABS)forchemicalswithcarcinogenicadversehealtheffects.
Forchemicalsthatcausenon-carcinogenicadversehealtheffects,toxicityistypicallyquantifiedbyoralreferencedose(RfDo),referenceconcentration(RfC),andadermalreferencedose(RfDABS).
ThemostcurrenttoxicityvaluesrecommendedbyEPAmustbeusedforARBCAEvaluations.
ForCOCsthatmaynothaveavalueinthesourceslistedbelow,pleasecontacttheDepartment.
AlternativevaluesmustbeapprovedbytheDepartment.
TheRSLGenericTableslisttoxicityvalues.
InabsenceofatoxicityvalueintheRSLs,thefollowinghierarchyofsourcesshouldbeused.
ARBCA(Revision3)20176-15IntegratedRiskInformationSystem(IRIS)NationalCenterforEnvironmentalAssessment(NCEA)EPARegion4RecommendationsandvariousMemorandumsHealthEffectsAssessmentSummaryTables(HEAST)AgencyforToxicSubstanceandDiseaseRegistry(ATSDR)CaliforniaEPACenterforEnvironmentalandHumanToxicology(CEHT),UniversityofFloridaReviewofliteraturebyqualifiedprofessionalstodeveloptoxicityfactorsDermalslopefactorandreferencedose(SFABSandRfDABS)maybeconvertedfromoralslopefactorandoralreferencedoseusingthefollowingformula:SFABS=SFo/ABSGIRfDABS=RfDo*ABSGIwhereABSGIisthegastrointestinalabsorptionfactorandrepresentsthebioavailabilityofthechemicalfollowingexposurethroughtheoralroute(U.
S.
EPA,2004,RAGSE,equations4.
2and4.
3).
6.
7.
2.
3PhysicalPropertiesoftheCOPCsTocalculatetherisksanddevelopthetargetlevels,theARBCAEvaluationrequiresselectedphysicalpropertiesoftheCOCs.
ThevaluesoftheseparametersarelistedintheChemicalSpecificParametersTablelocatedintheRSLGenericTables.
Sinceseveralofthesevaluesareexperimentallydetermined,theirvaluesmaydifferfromsomereferences.
TheDepartmentrequirestheuseofphysicalvaluestabulatedintheRSLGenericTablesandUser'sGuideforallARBCAEvaluations.
Iftheuseofalternatevaluesisnecessary,thesiteowner/operatormustprovidesufficientjustificationtotheDepartmenttoutilizeadifferentvalue.
TheuseofdifferentvalueswouldbeallowedonlyunderanRM-2Evaluation.
TheproposaltousethedifferentvaluesshouldbesubmittedintheRM-2workplanpriortotheuseofthevaluesintheevaluation.
6.
7.
2.
4ExposureFactorsExposurefactorsdescribethephysiologicalandbehavioralcharacteristicsofthereceptor.
Thesefactorsincludethefollowing:WateringestionrateBodyweightExposuredurationExposurefrequencySoilingestionrateExposuretimesforindoor/outdoorinhalationSkin-surfaceareafordermalcontactwithsoilARBCA(Revision3)20176-16Soil-skinadherencefactorAlistoftheexposurefactorsthatshouldbeusedtocalculatetheRM-1andRM-2levelsispresentedinTable1oftheRSLUser'sGuideandtheUSEPAExposureFactorsHandbook:2011Edition.
Theexposurefactorsaretypicallyestimatedbasedonliterature,andsite-specificmeasurementsarenotobtained.
WithpriorapprovaloftheDepartment,foranRM-2Evaluation,site-specificvaluesoftheexposurefactorsmaybeusedprovidedtheycanbeadequatelyjustified.
6.
7.
2.
5FateandTransportParametersFateandtransportparametersarenecessarytoestimatetherisksandtargetconcentrationsfortheindirect-exposurepathways.
Thesefactorscharacterizethephysicalsitepropertiessuchasdepthtogroundwater,soilporosity,andinfiltrationrateatasite.
ForanRM-1Evaluation,theDepartmenthasselectedtypicalandconservativevaluesforalloftheparametersthatarepresentedinTable1oftheRSLUser'sGuide.
ForanRM-2Evaluation,acombinationofsite-specificandRM-1valuesfortheseparametersmaybeused.
However,thevalueofeachparameterused,whethersite-pecificornot,mustbejustifiedbasedon-site-specificconditions.
Wheresite-specificconditionsaresignificantlydifferentfromtheRM-1assumptions,anRM-2Evaluationshouldbeperformed.
6.
7.
2.
5.
1SoilParametersAbriefdiscussionofthesoilparametersispresentedbelow:Wa-LengthofSoilSourceAreaParalleltoWind(cm)RM-1assumesalengthof1500cm,4498cm,or6362cm(small,medium,orlargesource,respectively)(thedefaultvalueofWa).
ThetypicalUSTsitewillutilizethe1500-cmlengthinanRM-1Evaluation.
RM-2allowsfordirectmeasurementoftheWa.
Thisisrarelydirectlymeasuredbecausewinddirectionisvariableandtheexactdimensionsofthesoilsourcemaynotbeknown.
Therefore,Waisusuallysetequaltolengthofgroundwatersourceparalleltogroundwaterflowdirection(W),seesection6.
7.
2.
5.
2.
Ls-DepthtoSubsurfaceSoilSources(cm)RM-1assumes30.
48cm,whichbydefinitionistheshallowestpossibleLs.
RM-2allowsfortheactualmeasureddepthofcontaminatedsoils.
Thismaybetheshallowest-detectedcontaminationoranaveragedepthoftheshallowest-detectedcontaminationfromseveralborings.
d-LowerDepthofSurficialSoilZone(cm)RM-1assumes30.
48cm,whichisthelowerboundofthesurficialsoilzone.
ARBCA(Revision3)20176-17RM-2mustalsouse30.
48cmduetothedefinitionofthesurficialsoilzone.
dsv–DepthtoSoil-VaporMeasurement(cm)RM-1assumes30.
48cm,whichisthedepthtothesoil-vaporsample.
RM-2allowsfortheactualdepthofthesoil-vaporsamplemeasured.
hcap-ThicknessofCapillaryFringe(cm)RM-1assumesathicknessof100cm.
RM-2hcapshouldbeathicknessrepresentativeofthesitesoils/sedimentsandisbasedonsoilgrainsize.
Typically,hcapshouldbebasedonliteraturevaluessincedirectmeasurementisnotpractical.
Notethathcapandthicknessofthevadosezone(hv),whenaddedtogether,shouldequaldepthtogroundwater,hcap+hv=Lgw.
hv-ThicknessofVadoseZone(cm)RM-1assumesthehvis200cm.
RM-2hviscalculatedbysubtractingthehcapfromtheLgw.
hcap+hv=Lgw.
ρs–VadoseZoneDrySoilBulkDensity(g/cm3)RM-1assumes1.
5g/cm3drysoilbulkdensityforthevadosezone.
RM-2allowsforadirectmeasurementofρs.
SeeSection5.
10foradiscussionrelatedtothedeterminationofsoilbulkdensity.
Ifmultiplemeasurementsfromthevadosezoneareavailable,usetheaveragevalue.
focv-FractionalOrganicCarbonContentintheVadoseZone(g-c/g-soil)RM-1assumesfocvis0.
002g-C/g-soil.
RM-2allowsfordirectmeasurementoffocv.
SeeSection5.
10foradiscussionofproperdeterminativemethods.
Ifmeasurementsoffractionalorganicmatter(notthesameasfractionalorganiccarbon)areavailable,thevalueshouldbecorrectedasdiscussedinSection5.
10.
Ifmultiplevaluesareavailable,theaveragevaluesmaybeused.
θT-TotalPorosityintheVadoseZone(cm3/cm3–soil)RM-1assumesaθTof0.
43cm3/cm3.
ARBCA(Revision3)20176-18RM-2allowsfordeterminationofθT.
InRM-1,theassumptionismadethatthetotalporosityisthesameinthevadosezone,capillaryfringe,andthesoilthatfillsthefoundationorwallcracks.
InRM-2,thereisnowaprovisiontovarytheporosityinthecapillaryfringeandinthesoilthatfillsfoundationorwallcracks.
SeeθTCAPandθTCRACKbelow.
SeeSection5.
10foradiscussionofproperdeterminativemethods.
θws-VolumetricWaterContentinVadoseZone(cm3/cm3)RM-1assumesθwsis0.
143cm3/cm3.
RM-2θwsvaluesaretypicallymeasuredasnotedinSection5.
10.
Whenusingasite-specificvalue,thevalueismeasuredonaweightbasis(gravimetric,gramsofwater/gramsofdrysoil)andmustbeconvertedtoavolumetricvalue(cm3ofwater/cm3ofsoil)asdiscussedinSection5.
10.
Notethatθas+θws=θT.
θas-VolumetricAirContentinVadoseZone(cm3/cm3)RM-1assumesθasvalueis0.
287cm3/cm3.
RM-2allowsforacalculatedθastobeutilized.
TheEvaluatormustdeterminewhatthetotalsoilporosityinthevadosezoneis,subtractthevolumetricwatercontent,andtheremainderisthevolumetricaircontent.
Therefore,θas=θT-θwsθTcap-TotalPorosityintheCapillaryFringe(cm3/cm3soil)RM-1assumesaθTcapof0.
43cm3/cm3.
RM-2allowsfordeterminationofθTcap.
InRM-1,theassumptionismadethattheθTcapisthesameinthevadosezone,capillaryfringe,andthesoilthatfillsthefoundationorwallcracks.
InRM-2,theporosityinthecapillaryfringecanbesite-specific.
Totalsoilporosityinthecapillaryfringeistypicallyassumedtobeequaltothetotalvadosezoneporosityunlesssite-specificdataisavailable.
θwcap-VolumetricWaterContentinCapillaryFringe(cm3/cm3)RM-1assumesθwcapis90%oftotalporosityinthecapillaryfringe,i.
e.
,0.
387cm3/cm3frommultiplying0.
43times0.
9.
Thesumoftheaircontentandthewatercontentinthecapillaryfringewouldequalthetotalporosityinthecapillaryfringe,θwcap+θacap=θTcap.
RM-2allowsforasite-specificθwcapvalue.
Thevalueistypicallyderivedbytaking90%ofthetotalsite-specificsoilporosityinthecapillaryfringe.
Totalsoilporosityinthecapillaryfringeistypicallyassumedtobeequaltothetotalvadosezoneporosityunlesssite-specificdataisavailable.
ARBCA(Revision3)20176-19θacap-VolumetricAirContentinCapillaryFringe(cm3/cm3)RM-1assumesthattheθacapis10%ofthetotalporosityinthevadosezone.
SincetheassumedθTis0.
43cm3/cm3,thevolumetricaircontentis0.
043cm3/cm3.
RM-2assumesthattheθacapis10%ofthetotalporosityinthevadosezone.
Therefore,θacap+θwcap=θT.
θTcrack–TotalPorosityinTheSoilinTheFoundationorWallCracks(cm3/cm3soil)θTcrackisthetotalporosityinthesoilinthefoundationorwallcracks.
Typically,itwouldbesetequaltothevadosezonesoilporosityinbothRM-1andRM-2Evaluations;however,ifsite-specificdataisavailable,itcanbeusedinRM-2.
θwcrack-VolumetricWaterContentintheFoundationorWallCracks(cm3/cm3)RM-1assumesθwcrackisequaltothevolumetricwatercontentinthesoilinthevadosezone.
TheRM-1valueis0.
143cm3/cm3.
Thesumoftheaircontentinthefoundationorwallcracks(θacrack)andtheθwcrackshouldequaltotalcrack-soilporosity(θTcrack),θwcrack+θacrack=θTcrack.
RM-2alsotypicallyassumesthattheθwcrackisthesameasthevolumetricwatercontentinthesoilinthevadosezone.
Asite-specificvaluecan,however,beused.
θacrack-Volumetricaircontentinfoundationwall/cracks(cm3/cm3)RM-1assumesthatthevolumetricaircontentinthesoilthatfillsthefoundationwallorcracksisthesameasinthesoilinthevadosezone.
Thevalueis0.
287cm3/cm3.
RM-2allowsforasite-specificθacracktobederived.
However,thevalueistypicallythesameasthevolumetricaircontentinthesoilinthevadosezone.
θacrack+θwcrack=θTcrack.
6.
7.
2.
5.
2GroundwaterParametersAbriefdiscussionofthegroundwaterparametersispresentedbelow:Lgw-DepthtoGroundwater(cm)RM-1assumesLgwis300cm,orapproximately10feet.
WhentheLgwissignificantlylessthan10feet,anRM-2Evaluationshouldbeperformedusingsite-specificLgwandotherfate-and-transportparametersevenifRM-1risksandtargetARBCA(Revision3)20176-20concentrationsarenotexceeded.
WheretheLgwasmeasuredinmonitoringwellsfluctuates,therecent-averagedepthtogroundwatershouldbeusedintheARBCAEvaluations.
Thisrecentaveragedepthshouldbecalculatedfromthelast1–2yearsofdata.
Forconsistency,staticwaterlevelsshouldbeutilizedunlessappropriatesupportforuseofthe"firstwaterencounteredwhiledrilling"canbeprovided.
Thesite-specificaveragedepthtogroundwatershouldbecalculatedbydeterminingtheaveragedepthtogroundwaterineachwellandthenaveragingthesinglewellaverages.
Wheresignificantdifferencesinstaticwaterlevelsoccuracrossthesite,theshallowestaveragedepthtogroundwatershouldbeutilized.
Theshallowestaveragedepthtogroundwatershouldbecalculatedbydeterminingtheaveragedepthtogroundwaterinafewwellswiththeshalloweststaticwaterlevelsandthenaveragingthesinglewellaverages.
Y-WidthofGroundwaterSourceAreaPerpendiculartoGroundwaterFlowDirection(cm)RM-1assumesthatYis1500cm,4498cm,or6362cm(small,medium,andlargesources,respectively).
ThetypicalUSTsitewillutilizethe1500-cmwidthinanRM-1Evaluation.
Othersitesinotherprogramsmaymeetorexceedthatvalue–thevalueusedshouldhaveabasis.
RM-2allowsforthesite-specificYtobemeasured.
InbothRM-1andRM-2,itisassumedthatYisidenticaltothesoilsourceareaandislocateddirectlybelowthesoilsourcearea.
Thesoilsourceareaisdeterminedbyevaluatingtheavailablesoildatalocatedinthesourceareawhichislocatedincloseproximitytotheoriginoftherelease(tanks,dispensers,piping).
ThisrequirestheARBCAEvaluatortoreconcilethesoilboringdatawiththepointoforiginoftherelease.
Besuretoincludeasitemap,whichshowsY,W,andWa.
Forexample,theARBCAEvaluatormaydrawaboundarythatenclosestheareaaroundthetanks,piping,and/ordispensersfromwherethereleaseoriginated.
Then,theARBCAEvaluatorshouldvalidatethisselectedsourceareabycomparingtheavailablesoil-boringdatatotheselectedsourcearea.
TheEvaluatorshouldthenadjustthesizeofthesourceareaifappropriate.
TheARBCAReportshouldincludethelocationofthetanks,piping,dispensers,wells,andboringstojustifytheselectionofthesourcearea.
W-LengthofGroundwaterSourceAreaParalleltoGroundwaterFlowDirection(cm)RM-1assumesthatWis1500cmor6362cm(smallorlargesources,respectively).
ThetypicalUSTsitewillutilizethe1500-cmlengthinanRM-1Evaluation.
RM-2allowsforthesite-specificWtobemeasured.
InbothRM-1andRM-2,itisassumedthatthegroundwatersourceareaisidenticaltothesoil-sourceareaandislocateddirectlybelowthesoilsourcearea.
Thesoilsourceareaisdeterminedinthesamemannerasdiscussedforparameter"Y".
TheARBCAReportshouldincludeamapwiththesourceareadelineated,aswellastheARBCA(Revision3)20176-21locationofthetanks,piping,dispensers,wells,andboringstojustifytheselectionofthesourcearea.
ThelengthsW,Y,andWashouldbedrawnonthemapinthereport.
θTS-TotalPorosityintheSaturatedZoneRM-1assumesthatθTSis0.
43cm3/cm3.
ThisisthesamevalueassumedforθT.
RM-2allowsforasite-specificθTSvaluetobeutilized.
Inmostcases,thisvaluewillbethesameastheθT.
BothaθTandaθTSshouldbecollectedwhenitappearsthatthepropertiesofthetwozonesmaysubstantiallydifferatasite.
AnestimateoftheθTSisneededwhenbiodecayisusedintheGroundwaterResourceProtectionEvaluationortheSurfaceWaterProtectionEvaluation.
ρss–SaturatedZoneDrySoilBulkDensity(g/cm3)RM-1assumes1.
5g/cm3.
RM-2allowsforadirectmeasurementofρss.
Inmostcases,thisvaluewillbethesameasthevadose-zonedrysoilbulkdensity.
Bothaρsandaρssshouldbecollectedwhenitappearsthatthesetwozonesmaydifferatasite.
focs-FractionalOrganicCarbonContentintheSaturatedZone(g-C/g-soil)RM-1assumesfocsis0.
002g-C/g-soilRM-2allowsfordirectmeasurementoffocsinthesaturatedzone.
Intheabsenceofameasuredvalue,usethevalueintheunsaturatedzone.
Bothafocvandafocsshouldbecollectedwhenitappearsthatthesetwozonesmaydifferatasite.
SeeSection5.
10foradiscussionofproperdeterminativemethods.
Iffractionalorganicmatterismeasured,itshouldbecorrectedtoestimatefocsasdiscussedinSection5.
10.
δgw-GroundwaterMixing-ZoneThickness(cm)RM-1assumesathicknessof200cm,whichisderivedfromthesaturatedlengthofa10-footwellscreen.
RM-2allowsforasite-specificvaluetobeutilized.
The200-cmvalueshouldbeconsideredaminimum.
AnequationtocalculateδgwislocatedintheEPASoilScreeningGuidance(1996,page45,equation45).
OtherproceduresfordeterminingδgwmaybeutilizedifapprovedbytheDepartment.
ARBCA(Revision3)20176-22K-HydraulicConductivityintheSaturatedZone(cm/year)RM-2allowsforasite-specificvaluetobeused.
LiteraturevaluesmaybeusedifthereferenceisacceptabletotheDepartment.
Site-specificmeasurementsmayalsobeusedasdiscussedinSection5.
10.
Typically,anaverageofthemeasuredvaluesmaybeused.
i-HydraulicGradientintheSaturatedZoneRM-2allowsforasite-specificvaluetobeused.
Site-specificmeasurementsmustbeobtained.
Anaveragegradientoverthelast1–2yearsshouldbedeterminedforuseintheARBCAEvaluation.
Tablesandcalculationsdocumentingthesite-representativegradientshouldbeincludedintheARBCAreport.
ThiscanbeincludedwithAttachment9.
Atsiteswherethegroundwaterflowdirectionshowsmarkedvariations,thehydraulicgradientandhenceUgw(seebelow)mayhavetobeestimatedinmorethanonedirection.
Ugw-GroundwaterDarcyVelocity(cm/yr)RM-1assumesaUgwof157.
68cm/yrInRM-1,Ugwisusedtoestimatethemean-fieldmixingdilutionattenuationfactorusingtheSummer'smodel.
TheRM-1defaultvalueis157.
68cm/yr.
InRM-2,asite-specificvalueofUgwhastobeused.
Thisvalueiscalculatedastheproductofsaturated-zonehydraulicconductivityandhydraulicgradient.
I-InfiltrationRate(cm/year)RM-1assumes14.
46cm/yrRM-2allowsasite-specificorregional-specificvalue.
Thevalueisobtainedfromregionaldata.
Iisobtainedbytaking10%oftheannualrainfall.
Averageannualrainfallvaluesarebasedona30-yearaverage.
Thesenormalvaluesareupdatedevery10years.
Sourcesofrainfall/climaticdataincludetheAlabamaStateClimatologyOffice,theSoutheastRegionalClimateCenter,andtheNationalClimaticDataCenter.
AnARBCAEvaluatormayalsouseanotherrainfallreferenceprovideditisapprovedbytheDepartment.
6.
7.
2.
5.
3OtherFateandTransportParametersAdditionalparametersareneededtoestimatetherisksandtargetlevelsfortheindirectexposurepathways.
Oftheseparameters,distancetothePOEanddistancetoaSentryWell(SW)havebeendiscussedinothersectionsofthisguidancedocument.
Abriefdiscussionofotherfateandtransportparametersispresentedbelow:ARBCA(Revision3)20176-23δa–Breathing-ZoneHeight(cm)RM-1assumes200cm.
RM-2mustalsouse200cm.
Ua–WindSpeedwithintheBreathingZone(m/s)RM-1assumes4.
69m/s.
RM-2allowsasite-specificorregional-specificvalue.
Kf–AndelmanVolatilizationFactorforDomesticWaterUse(L/m3)RM-1assumes0.
5L/m3.
RM-2mustalsouse0.
5L/m3.
Q/C–InverseofMeanConcentrationatCenterofSquareSource(g/m2-s)/(kg/m3)RM-1assumes81.
05(g/m2-s)/(kg/m3).
ThebasisforthisvaluecomesfromusingtheAtlanta,GAMeteorologicalStationwhereAConstant=14.
8349,BConstant=17.
9259,CConstant=204.
1516andAsite=0.
5acres.
RM-2allowsasite-specificvalue.
ThisvaluecanbecalculatedbasedonsiteareausingtheequationandinputsshowninEquationD-1oftheSupplementalGuidanceforDevelopingSoilScreeningLevelsforSuperfundSitesU.
S.
EPA(2002).
V–FractionofVegetativeCover(m2/m2)RM-1assumes0.
5(m2/m2).
RM-2allowsasite-specificvalue.
Ut–EquivalentThresholdValueofWindSpeedat7meters(m/s)RM-1assumes11.
32m/s.
RM-2mustalsouse11.
32m/s.
F(x)–Wind-SpeedDistributionFunctionfromCowherdandOthers,(1985)RM-1assumes0.
194.
RM-2mustalsouse0.
194.
ARBCA(Revision3)20176-246.
7.
2.
6EquationsandModelsTwotypesofequationsormodels,namely(i)theuptakeequationsand(ii)thefateandtransportmodels,arerequiredtocalculatetherisksandthetargetlevels.
ForRM-1andRM-2Evaluations,theDepartmenthasselectedtheequationsandmodelspresentedinAppendixEinbackwardmodeandinAppendixFinforwardmode.
TheseequationsandmodelscanbeusedtocalculatetherisksanddeveloptheRM-1andRM-2targetlevels.
PleasecontacttheDepartmentforknownvendorsofprivatelyavailablecomputationalsoftwarethatutilizestheARBCAmodelsandproducestheoutputneededtocompleteanARBCAriskassessment.
Othersoftwaremaybeused,butmustbeacceptedbytheDepartmentbeforetheARBCAEvaluationisconducted.
Ultimately,itisthefacility'sresponsibilitytoensurethatanaccurateassessmentisconductedandthatthereshouldnotbefullrelianceonanysoftwareused.
AlternatemodelsmaybeusedforanRM-2EvaluationwiththepriorapprovaloftheDepartmentthroughthesubmittalofanRM-2workplan.
TheARBCAEvaluatorshouldcontacttheDepartmenttoestablishifaworkplanisrequired.
Insomecases,themodels(e.
g.
,DomenicoModel)presentedinAppendixEmaynotbesuitableforuseatasite.
TheARBCAEvaluatorshouldexercisecautiontoensurethatthemodelsbeingappliedareappropriateforexistingsiteconditions.
6.
8PROTECTIONOFDEEPERGROUNDWATERWhileperformingARBCAEvaluationsthepotentialimpactstodeeperaquifersmustbeevaluated.
Insomecases,aqualitativeevaluationbasedontheverticalflowgradientsmaybesufficient.
However,inothercasesaquantitativeevaluationofpotentialverticalmigrationofCOCsmaybenecessary.
Monitoringwellsnestedandsetatdifferentdepthsmayneedtobeinstalledintothedeeperaquifer.
Severaldeeperwellsmayneedtobeinstalled,andmayneedtobeinstalledasTypeIIIdoubleormultiplecasedmonitoringwellsconstructedinaccordancewithSectionB.
3.
3oftheAEIRG.
Duetothesite-specificnatureofthehydrogeologyitmaybenecessarytosubmitaworkplanindicatinghowtheevaluationofthedeeperaquiferwillbeconducted.
6.
9GROUNDWATERRESOURCEPROTECTIONTheuseofgroundwaterasacurrentandapotentialfuturedrinkingwatersupplyisthebasisofthegroundwaterresourceprotectioncomponentoftheARBCAEvaluation.
Atsiteswheretherearecurrentlywatersupplywellslocatedoff-site,adeterminationofallowablesoilandgroundwaterCOClevelsmustbemadetoprotectthewatersupplywell.
Atsiteswheretherearenowatersupplywellspresent,theremedialmeasuresforsoilandgroundwaterarerequiredtobeprotectiveofthegroundwaterresourceforlikelyfutureuse.
TheDepartmentisrequiresthatreleasesbeevaluatedtoprotectthegroundwaterresourceforfutureuse.
Thesetwoscenariosaredescribedbelow:ARBCA(Revision3)20176-25Forsituationswherethereisawatersupplywell(s)(activeorinactive)within500feetofthesite,theGroundwaterResourceProtectionEvaluationallowsforthedeterminationofallowablesoilconcentrationsthatwillprotectthegroundwateratthePOEwhichshouldbelocatedonthefacility'spropertyinthedirectionofgroundwaterflow.
AnevaluationofthegroundwaterconcentrationsatthesourceofthereleaseandatSentryWells(SWs)todeterminewhatgroundwaterCOCconcentrationsareacceptableforprotectionofthewatersupplywellisalsorequired.
Upgradientwatersupplywellsshouldalsobeevaluatedandnamedinthecasethatgroundwaterflowdirectionchangesinthefuture.
Forsiteswheretherearenocurrentwatersupplywells(activeorinactive),aPOEmustbeestablishedatthedowngradientpropertyboundary.
ThePOEmustnotbeahypotheticalwell.
Thisevaluationrequirestheselectionofawell(s)inthesourceareaforcomparisontothetargetlevels.
Theequationsforcomputingtheallowableamountofachemicalinasourcewellandforcomputingthedilution-attenuationfactorarelocatedinAppendixE.
Inadditiontoasourcesentrywell,additionalSWslocatedbetweenthesourceareaandthePOEmustbeselected.
Inmostcases,therewillbemultiplesource-areawellsandnearlyallotherwellswillbedesignatedasSWs.
TheCOCconcentrationsintheseselectedSWsarecomparedtothecalculatedallowablegroundwaterconcentrationsataSW.
TheequationforcomputingtheallowableamountofachemicalinaSWappearsinAppendixE.
Additionally,theDepartmentwillrequirethatconcentrationsintheSWshowadefinitedecreasingtrend.
Theseconditionswillensurethat,intime,thecontaminatedgroundwaterwouldberestoredtoitsappropriatestate.
AnallowablesoilconcentrationinthesourceareamustbecalculatedwhichwillnotallowgroundwateratthePOEtoexceedtheMCLorotheracceptabletargetlevel.
TheequationforcomputingtheallowableamountofachemicalinsourcesoilappearsinAppendixE.
ForRM-1calculations,thedistancestotheSWsandPOEaresite-specificinputvalues.
Fate-and-transportparametersutilizetheRM-1valuesinlocatedintheRSLUser'sGuide.
TheuseofbiodegradationisnotallowedunderRM-1.
ForRM-2calculations,theappropriatedistancestotheSWsandPOEareinputassite-specificvalues.
Site-specificfateandtransportparametersalsoshouldbeutilized.
TheuseofbiodegradationisallowedunderRM-2,butmustbeclearlyjustified.
RefertoAppendixGforcalculatingthesite-specificbiodegradationrateforpetroleumcontaminants.
SeeAppendixBforadetaileddiscussionoftheproperselectionofrepresentativeconcentrations.
Alternatively,insteadofusingtheDomenicomodelinAppendixEtobackcalculatethesoilconcentrationsatthesourcethatareprotectiveofthepointofexposurevialeachingtogroundwater,theARBCAEvaluatorcanutilizetheSyntheticPrecipitateLeachingProcedure(SPLP)EPAMethod1312,ortheToxicityCharacteristicLeachingProcedure(TCLP)EPAMethod1311.
Intheseprocedures,theresulting"leached"materialshouldbecomparedwithalevelprotectiveoftheingestionofgroundwater.
ARBCA(Revision3)20176-266.
10SURFACEWATERPROTECTIONPotentialimpactstostreamsandothersurfacewaterbodiesfromareleasearetobedeterminedutilizingtheprocessdescribedinthissectionandAppendixC.
SamplingforCOCsinsurfacewatermayneedtooccurwhenCOCmigrationisknownorsuspectedtoaffectsurfacewater.
ThisisdiscussedfurtherinSection5.
7.
ThetargetlevelsforsurfacewaterprotectionarecalculatedusingtheequationslocatedinADEMAdminCodech.
335-6-10.
ThesetargetlevelsrepresentsurfacewaterqualitycriteriaforPublicWaterSupplystreams(consumptionoffishandwater)andforFishandWildlifestreams(consumptionoffishonly).
ForanRM-1Evaluation,thesetargetlevelsmustbemetatthedischargepoint.
Atsiteswhereconcentrationsinthegroundwaterdischarging/seepingintothesurfacewaterorstreamcannotbemeasured,theconceptofdilutionattenuationfactors(DAFs)maybeusedtobackcalculatethefollowing:(i)Csoil=Allowablesoil-sourceconcentrations(ii)Cgws=Allowablegroundwater-sourceconcentrations(iii)Csw=AllowableconcentrationsingroundwaterinSentryWells(SWs)atdifferentdistancesbetweenthesurfacewaterandthesourceItems(ii)and(iii)aboveareconsideredSWconcentrationsprotectiveofthesurfacewater.
DetailsofthisprocedurearediscussedinAppendixC.
Theequationstocomputetheallowableconcentrationsofchemicalsofconcerninsourcesoil,insourcegroundwater,andinstreamSWsappearinAppendixE.
IftheRM-1fateand-transportassumptionsarenotrepresentativeofthesite,andifthemeasuredsoilsourceorSWconcentration(s)exceedthecorrespondingtargetlevels,anRM-2SurfaceWaterProtectionEvaluationisnecessary.
ForanRM-2Evaluation,thesurfacewatertargetlevelsascalculatedfollowingtheequationslocatedinADEMAdminCodech.
335-6-10areapplicableatthedownstreamedgeofthemixingzoneformedbythemixingofthedischargeofthecontaminatedgroundwaterintothestream.
SeeAppendixCtocalculateallowableconcentrationsintheSurfaceWaterProtectionEvaluation.
Biodegradation,forpetroleumcompoundsingroundwater,maybeutilizedinanRM-2Evaluationifadequatejustificationisprovided.
IfrepresentativeCOCconcentrationsatthesoilsource,groundwatersource,orSentryWells(SWs)exceedtheRM-1targetlevelsforthestream,thenremediationmayberequiredatthesiteoranRM-2Evaluationmaybeperformed.
UnderanRM-2Evaluation,alternatefate-and-transportmodelsmaybeused.
Also,alternatelow-flowestimatesusedforthedeterminationoftargetlevelsforthestreammaybeused,providedtheprocedureusedisacceptabletotheDepartment.
PriorapprovalofalternateproceduresmustbeobtainedfromtheDepartment.
ARBCA(Revision3)20176-276.
11ESTIMATINGSENTRYWELL(SW)TARGETCONCENTRATIONSFORGROUNDWATERRESOURCEPROTECTIONANDSURFACEWATERPROTECTIONIntheARBCAEvaluation,itisnecessarytodesignateSentryWells(SWs)eitheron-siteand/oroff-sitetoconfirmthattheconcentrationsatthePOEdonotexceedthetargetlevelsinthegroundwaterorinasurfacewaterbody,ifapplicable.
MonitoringofSWsshouldoccur,andthedataobtainedfromthemonitoringofthosewellsshouldbeutilizedasrepresentativeconcentrationstocomparewithcalculatedRM-1orRM-2targetlevels.
MonitoringofSWswillbecontinueduntiltheconcentrationsintheSWsstabilizebelowthecalculatedSWtargetlevels.
TheSWtargetlevelscanbeestimatedusingthefollowingrelationship:SWPOEEWettSWettDAFDAFCC*=argarg(6-1)where,CSWettarg=TargetlevelintheSentryWell(SW)[mg/L]CEWettarg=Targetlevelintheexposurewellorinthewaterdischargingtothestream[mg/L]DAFPOE=Dilution-attenuationfactorforthedistancefromthesourcetotheexposurewellorthepointwheretheplumedischargesintothestreamDAFSW=Dilution-attenuationfactorforthedistancefromthesourcetotheSentryWell(SW)InEquation6-1,theDAFsrepresentthereductioninconcentrationastheCOCstravelfromthesourcetothePOEortheSW.
Thisreductioninconcentrationisduetothecombinedeffectofseveralfactorsincludingadvection,diffusion,dispersion,dilution,adsorption,andbiochemicalprocesses.
Ingeneral,therearetwowaystoestimatetheDAFs.
Thefirstwayistouseafate-and-transportmodelthatcanpredicttheconcentrationatthePOEorSWrelativetotheconcentrationatthesource,asdoneonpageE-14.
ThesecondwayistocalculatetheratioofthemeasuredconcentrationsatthesourcewellandatthePOEorSW.
Thesecondmethodcanbeusedonlyatsiteswheretheplumeisstableandsufficientgroundwater-monitoringdataareavailable.
ForanRM-1Evaluation,theARBCAEvaluatormustcomputedistance-dependentDAFsthatareusedtoestimatetheSWtargetlevels.
RM-1DAFsareestimatedusingtheDomenico'sModel(AppendixE)implementedwithfate-and-transportparameters.
ForanRM-2Evaluation,site-specificDAFsmaybecalculatedusingsite-specificdataoradifferentfate-and-transportmodelmaybeimplementedusingsite-specificdata.
PleaseconsulttheDepartmentbeforeusinganalternatemodel.
ARBCA(Revision3)20176-28Anexamplecalculationispresentedbelow:ThetargetlevelsintheSWsforasitewithaPOEat500feetfromthesourceandaSWlocatedat300feetfromthesource,i.
e.
,200feetupgradientfromthePOE,isestimatedasfollows:300500argargDAFDAFCCEWettSWett*=(6-2)where,CSWtarget=TargetlevelintheSW[mg/L]CEWtarget=Targetlevelintheexposurewell(groundwaterstandard)[mg/L]DAF500=Dilutionattenuationfactorforthedistancefromthesourcetotheexposurewelllocatedat500feetfromthesource(SeeAppendixE)DAF300=DilutionattenuationfactorforthedistancefromthesourcetotheSWlocatedat300feetfromthesource(SeeAppendixE)Inthisexampleforbenzene,usingDAFscomputedwithRM-1fate-and-transportparameters,theequationbecomesasfollowsLmgCSWett/0137.
017.
2336.
63005.
0arg=*=(6-3)Inthisexample,thesoilsourcewidthperpendiculartogroundwaterflow,Y,is1500cm.
Themixing-zonethickness,δgw,is200cm.
TheequationforthedilutionattenuationfactorcanbefoundonpageE-14.
PagesE-15andE-17providetheformulasforcalculatingallowableconcentrationsinsentrywellsfortheGroundwaterResourceProtectionandSurfaceWaterProtectionEvaluations.
ThecalculatedSWtargetlevelof0.
0137mg/LwillbeusedtoestablishSWmonitoringrequirements.
AnidenticalprocedurecanbeusedtodevelopSWtargetlevelsfortheprotectionofsurfacewater.
AtsiteswheretheSWconcentrationsareexceeded,theDepartmentmayrequirecontinuedmonitoringorremediationuntiltheconcentrationsstabilizebelowthecalculatedtargetlevels.
6.
12MANAGEMENTANDCONTROLOFNUISANCECONDITIONSORCONDITIONSREQUIRINGINITIAL-ABATEMENTMEASURESWhiletheARBCAprocessdeterminesthetargetlevelsappropriateforasite,theprocessprimarilyaddressesprotectionofhumanhealthduetochronicexposure.
Thesecalculationsdonottakeintoaccountnuisanceconditionssuchasaestheticconditions,odor,orvisiblestainingofsoils;therefore,theowneroroperatorwillberequiredtomitigateallnuisanceconditionsthataresignificantatasite.
Thesignificanceofthenuisancewillbedeterminedthroughaninvestigationconductedbytheowner/operatorandtheDepartment.
Thepresenceofvaporsinasubsurfacestructuretoincludebasements,buildings,sewers,andotherARBCA(Revision3)20176-29utilityconduitsmustalsobemitigatedtothesatisfactionoftheDepartment.
6.
13ECOLOGICALEXPOSUREExposurestoecologicalreceptorsandhabitatssuchaswetlands,sensitiveenvironments,orthreatenedand/orendangeredspeciesshouldbethoroughlyevaluated.
Abasicscreeningshouldbeperformedforthosesitesthatmayposeathreattoecologicalreceptorsandhabitats.
Whereanecologicalthreatmayexistduetoarelease,aseparateecologicalevaluationshouldbeperformed.
Note,withintheARBCAframework,protectionofsurfacewatersisconsideredindependentoftheecologicalriskevaluation,andtheARBCAEvaluatorshouldrefertoADEMAdmin.
Codech.
335-6-10.
EcologicalriskassessmentguidancemaybefoundinEcologicalRiskAssessmentGuidanceforSuperfund-ProcessforDesigningandConductingEcologicalRiskAssessment.
(U.
S.
EPA,1997).
Thefollowingisamedium-specificlistofecologicalscreeninglevels.
6.
13.
1SurfaceWaterSurfacewaterdatacollectedduringtheassessmentphaseshouldbeevaluatedusingthecriterialocatedinADEMAdmin.
Codech.
335-6-10,usingtheaquaticlifecriteriainTable1ofthatchapter.
IntheabsenceofanADEMWaterQualityCriteriaValue,surfacewaterconcentrationsshouldbecomparedtotheappropriateEPARegion4EcologicalScreeningValue.
Ifavalueisnotlocatedineitheroftheabovereferences,anEPARegion3BiologicalTechnicalAssistanceGroup(BTAG)screeningvalueshouldbeutilized.
Intheabsenceofanecologicalscreeningvalueforsurfacewaterinanyoftheabovereferencedlocations,riskassessorsshouldutilizethescientificliteratureandidentifyanapplicablevalue.
TheselectedvalueshouldbeprovidedtotheDepartmentforreviewwithajustification,includingallreferencesthatwereusedinthedetermination.
6.
13.
2SedimentsSedimentdatacollectedduringtheassessmentphaseshouldbecomparedtotheEPARegion4EcologicalScreeningValuesforsediment.
ThesearelocatedintheRegion4EcologicalRiskAssessmentSupplementalGuidanceInterimDraft.
IntheabsenceofanEPARegion4EcologicalScreeningValueforsediment,anEPARegion3BiologicalTechnicalAssistanceGroup(BTAG)sedimentscreeningvalueshouldbeutilized.
IntheabsenceofanEPARegion3BTAGsedimentscreeningvalue,thesedimentconcentrationsshouldbecomparedtotheFloridaGuidanceManualToSupportTheAssessmentofContaminatedSedimentsinFreshwaterEcosystems.
Theseguidelinescontainvaluesformarine,estuarine,andfreshwatersediments.
Intheabsenceofanecologicalscreeningvalueforsedimentinoneoftheabove-referencedlocations,riskassessorsshouldutilizethescientificliteraturetoidentifyanapplicablevalue.
TheselectedvalueshouldbeprovidedtotheDepartmentforreviewwithajustification,includingallreferencesthatwereusedintheARBCA(Revision3)20176-30determination.
Sedimentthatisnotsaturatedyearroundshouldbeevaluatedassoilandsediment.
6.
13.
3SoilsSoildatacollectedduringtheassessmentphaseshouldbecomparedtotheEPAEcologicalSoilScreeningLevels(EcoSSLs).
Intheabsenceofanecologicalscreeningvalueforsoilsinoneofthereferencedlocations,riskassessorsshouldutilizethescientificliteratureandidentifyanapplicablevalue.
TheselectedvalueshouldbeprovidedtotheDepartmentforreviewwithajustification,includingallreferencesthatwereusedinthedetermination.
Notethatthebenchmarkslistedaresubjecttochange,andthemostcurrentdatashouldbeused.
Ifquestionsariseastowhichsetofbenchmarksshouldbeused,pleasecontacttheDepartmentforadditionalguidance.
6.
14LEADFortheevaluationoflead-contaminatedsurficialsoil,itisnotappropriatetousethemodelslocatedinAppendixEandAppendixJforthedirectcontactexposurepathways.
ThefinalcleanupvaluesusedforleadforthedirectcontactexposurepathwaysshouldbethosevaluespresentedintheRSLTablefor"LeadandCompounds,"orthevaluesshouldbedevelopedusingoneofthefollowingmodelsdependentupontheexposurescenario.
ModelsinAppendixEmaybeusedtogeneratesourcesoilcleanupvaluesforleadintheGroundwaterResourceProtectionEvaluationandintheSurfaceWaterProtectionEvaluation.
TheIntegratedExposureUptakeBiokineticModelforLeadinChildren(IEUBK)maybeusedtoassessriskatsitesduetoleadcontaminatedsoilfortheunrestrictedusescenario.
TheIEUBKattemptstopredictblood-leadconcentrationsforchildrenexposedtoleadintheirenvironment.
Themodelallowstheusertoinputrelevantabsorptionparametersaswellasintakeandexposurerates.
TheAdultLeadModelmaybeusedtoassessriskatsitesduetoleadcontaminatedsoilwherelandusecontrols(LUCs)arerequired,andacommercialscenariowillbeused.
Thismodelusesmethodologyforassessingrisksassociatedwithnon-residential(i.
e.
,commercial)adultexposurestoleadinsoil.
Themethodologyfocusesonestimatingfetalblood-leadconcentrationinwomenexposedtolead-contaminatedsoils.
Thisapproachalsoprovidestoolsthatcanbeusedforevaluatingrisksofelevatedblood-leadconcentrationsamongexposedadults.
BothofthesemodelsarepartofEPA'sRiskAssessmentDatabasesandTools.
FIGURE6-1GRAPHICALDISPLAYOFACONCEPTUALSITEMODELARBCA(Revision3)2017POTENTIALRECEPTORSCURRENTLANDUSEFUTURELANDUSEON-SITEOFF-SITEON-SITEOFF-SITEResidents-ChildResidents-AdultCommercialWorkersConstructionWorkersResidents-ChildResidents-AdultCommercialWorkersConstructionWorkersResidents-ChildResidents-AdultCommercialWorkersConstructionWorkersResidents-ChildResidents-AdultCommercialWorkersConstructionWorkersInhalation(Indoors)Inhalation(Outdoors)WindErosion/Dispersion/Volatilization/VaporMigrationInhalation(vapors&particulates)andDermalContactandIngestionLeachingtoGroundwaterInhalation(Indoors)SubsurfaceSoilsInhalation(Outdoors)DermalContactandIngestionLeachingtoGroundwaterInhalation(Indoors)GroundwaterInhalation(Outdoors)IngestionandinhalationduringdomesticuseNANANANAYESNOFreeProductIndicatespotentiallycompletedpathwaysUtilitiesThreatened(SeeSection5.
6)NANotapplicableaspertheADEMpolicySurfaceWaterswithina500footradiusEcologicalReceptorsFIGURE6-1GRAPHICALDISPLAYOFASITECONCEPTUAL-EXPOSUREMODELAirVaporsSurficialSoilVolatilization/VaporMigrationVolatilization/VaporMigrationTRANSPORTMECHANISMSIMPACTEDMEDIAEXPOSUREROUTESARBCA(Revision3)20177-17.
0REGIONALSCREENINGLEVELEVALUATIONTheobjectiveoftheRegionalScreeningLevel(RSL)EvaluationistoperformapreliminaryriskevaluationtoidentifyconcentrationsofChemicalsofPotentialConcern(COPCs)fromallsourceareasandareasofinterestwithinthesitethatmayneedfurtherevaluation.
TheRSLEvaluationshouldnotbeconfusedwiththePreliminaryInvestigationwhichisaphysicalsiteassessment.
TheRSLEvaluationmaybeperformedatsitesusingdatacollectedduringclosures,environmentalaudits,andpreliminaryinvestigationsandasthefirststageineveryARBCAEvaluation.
TheRSLEvaluationrequiresthecomparisonofthemaximumconcentration(acalculatedrepresentativeconcentrationforsoilsorsedimentsmaybeusedifthereisenoughdatatosupporttheuseofacalculatedvaluesuchasthe95thUpperConfidenceLimit(UCL)aboutthemean)ofCOPCsdetectedwithineachED/DUwiththeRSLsandtheVaporIntrusionScreeningLevels(VISLs).
TheRSLsareupdatedbiannually.
7.
1WHENTOPERFORMAREGIONALSCREENINGLEVELEVALUATIONAnRSLEvaluationrequiresthecomparisonofthemaximumsiteconcentrationstotheRSLsandtheVISLs.
TheRSLEvaluationmaybeperformedattwostagesintheARBCAprocess:(i)asascreeningtoolonclosuredata,preliminaryinvestigations,andenvironmentalaudits,and(ii)aftersiteassessmentiscomplete,asthefirststepineveryriskassessment.
RefertothecurrentAlabamaEnvironmentalInvestigationandRemediationGuidance(AEIRG)fortherequirementsofsitecharacterization.
Ifitisdeterminedthattheindoorvaporinhalationpathwayiscompleteandthatsub-slaborotherappropriatesoil-vaporsamplesneedtobecollectedandanalyzed,thenaplantocollectandanalyzesoilvapordatashouldbesubmittedtotheDepartment.
RefertothecurrentAEIRGandtotheJune2015USEPATechnicalGuideforAssessing&MitigatingtheVaporIntrusionPathwayfromSubsurfaceVaporSourcestoIndoorAirortheJune2015TechnicalGuideforAddressingPetroleumVaporIntrusionatLeakingUndergroundStorageTankSitesforadditionaldetailsforthecollectionofsuchdata.
7.
2COMPARISONOFDATAWITHREGIONALSCREENINGLEVELSThedatacollectedduringtheinitialsiteassessmentandinvestigationshouldbeevaluatedtoensurethefollowing:Arepresentativedatasetofcurrentsoilandgroundwaterconcentrationsareavailable.
SitecharacteristicsarecomparabletoassumptionsusedtodeveloptheRSLsandVISLs.
AnalyticalmethodsusedareconsistentwiththeCOPCsforthesitebasedonsitehistory.
AllQA/QCrequirementsaremet.
DetectionlimitsdonotexceedtheRSLsorVISLs.
Appropriatebackgrounddatahasbeencollected.
Ifthedatasatisfiestheserequirements,themaximumsoilandgroundwaterconcentrationsARBCA(Revision3)20177-2shouldbecomparedwiththeRSLs.
Acalculatedrepresentativeconcentrationforsoilsorsedimentsmaybeusedifthereisenoughdatatosupporttheuseofacalculatedvaluesuchasthe95thUpperConfidenceLimit(UCL)aboutthemean.
TheRSLsarerisk-basedconcentrationsdevelopedwithDOE'sOakRidgeNationalLaboratoryunderanInteragencyAgreement.
RSLsrepresentanupdateandmergeroftheEPARegion3RiskBasedConcentrationTable,EPARegion6HumanHealthMediumSpecificScreeningLevelTable,andtheEPARegion9PreliminaryRemediationGoalsTable.
TheRSLsareusedforscreeningevaluationsasdescribedinSection6.
7.
1.
TheRSLwebsiteisnowthesourceofscreeninglevelsforalltheEPAregions.
TheRSLsarecalculatedusinggenericinputvaluesderivedwithoutsite-specificdataandprovidecomparisonvaluesforresidential(i.
e.
,unrestricteduse)andcommercial/industrialexposurestoair,soil,andtapwater(drinkingwater).
TheVISLslistchemicalsconsideredtobevolatileandsufficientlytoxicthroughthesoilgasintrusionpathway.
Theselevelsalsoprovidegenerallyrecommended,media-specific,risk-basedscreeninglevelconcentrationsforgroundwater,near-sourcesoilgas,sub-slabsoilgas,andindoorair.
Theresultsofrisk-basedscreeningcanhelpthedatareviewteamidentifyareas,buildings,and/orchemicalsthatcanbeeliminatedfromfurtherassessment.
Exceedingasubsurfacescreeninglevelgenerallysuggests,however,thatfurtherevaluationofthevaporintrusionpathwayisappropriate.
IfanacceptablelevelofsiteinvestigationhasbeenperformedasdeterminedbytheDepartment,andthemaximum(or,ifappropriate,acalculatedrepresentativeconcentration),media-specificconcentrationsdonotexceedtheRSLsorVISLs,thenadditionalsiteevaluationmaynotbenecessary.
Ifanyoftheconcentrationsforthechemicalsofpotentialconcern(COPCs)exceedanyoftheRSLsorVISLs,theneitherremediationshouldcommenceoranRM-1oranRM-2EvaluationshouldbeconductedforthoseconstituentswhichexceedtheirrespectiveRSLs.
Theseconstituentsarereferredtoasthechemicalsofconcern(COCs)andareusedtoassessthecumulativeriskwithineachED/DUintheRM-1and/orRM-2Evaluation.
Siteswithadequatesite-specificinformationasdescribedinSection6.
0maymovedirectlyintotheRM-2EvaluationfollowinganRSLEvaluation.
ItispermissibleinmostcasestoadoptRSLsandVISLsascleanupgoals,butthisrequiresthepriorapprovaloftheDepartment.
Sinceasitemaybegrantedano-further-actionorcorrectiveactioncompletestatusunderanRSLEvaluation,itisimportantthatthesiteevaluationidentifythemaximumorrepresentative,media-specificconcentrations.
IfthereisapotentiallycompletepathwaythatdoesnotappeartobeadequatelyaddressedbytheRSLs,anRM-1and/oranRM-2Evaluationshouldbeundertakentoincludeitandallothercompletepathways.
ARBCA(Revision3)20178-18.
0RISKMANAGEMENT-1EVALUATIONTheRM-1EvaluationrequiresthecalculationoftheriskforeachCOC,eachcompleteexposurepathway,andthecumulativerisksforeachreceptor.
IfthecumulativerisksdonotexceedtheDepartment-specifiedtargetrisklevels,therearenogroundwaterresourceprotectionrelatedexceedances,andnosurfacewaterprotectionrelatedexceedances,aNoFurtherActionatthistime(NFA)orCorrectiveActionProcessTerminateddeterminationmaybegrantedbytheDepartment.
ConsistentwiththeassumptionsmadeintheConceptualSiteModel(CSM),certainlandusecontrols(LUCs)maybeneeded.
Ifthecumulativerisksatthesiteexceedthetargetrisklevels,theresponsiblepartymayeithercomputeRM-1targetclean-upconcentrationsforeachCOC,eachcompletepathway,andeachreceptorasidentifiedintheCSM,ortheresponsiblepartymayconductanRM-2evaluation.
TheRM-1andRM-2Evaluationsshouldbedocumented.
AllcomputationsmustbecompletedusingtheequationsandmodelsincludedinAppendixE.
AnRM-1Evaluationrequiresthefollowingsteps:8.
1CHARACTERIZATIONANDCLASSIFICATIONOFTHESITEThisprocesshasbeenpreviouslydescribedinSections4.
0and5.
0.
8.
2DEVELOPMENTOFTHECONCEPTUALSITEMODELThedevelopmentofanCSMhasbeendescribedinSection6.
5.
ThisstepincludesthelocationofthePOEandSentryWells(SW)asperSection6.
6.
Ifanecologicalriskassessmentisneededforthesite,pleaserefertotheguidanceinSection6.
13,anddiscussthesituationwiththeDepartment.
8.
3CALCULATIONOFRISKSANDDEVELOPMENTOFRM-1TARGETLEVELSForeachcompleteexposurepathwayidentifiedintheCSM,theriskshouldbecalculatedusingtheRM-1valuesinthemostcurrentRSLUser'sGuideandappropriatesite-specificdata.
Ifthecumulativerisksexceedthetargetrisklevels,RM-1targetconcentrationsmaybedeveloped,ortheARBCAEvaluatormayproceedtoanRM-2Evaluation.
IftheARBCAEvaluatorchoosestocomputeRM-1targetconcentrations,theequations/modelsinAppendixEmustbeused.
TheusershouldcomparetheRM-1fateandtransportparameterstotheknownsitecharacteristics.
Iftheparametersarenotrepresentativeofthesiteconditions,thenanRM-2Evaluationwillberequired.
Insomecases,modelsotherthanthoselocatedinAppendixEmaybemoresuitableduetosite-specificconditions.
ThemostcurrenttoxicityvaluesrecommendedbytheDepartmentmustbeusedforARBCAEvaluations.
ForCOCsthatmaynothaveaquantitativetoxicityvalue,pleasecontacttheDepartment.
AdditionalinformationregardingtoxicityvaluescanbefoundinSection6.
7.
2.
2.
ARBCA(Revision3)20178-2TheRM-1targetsoilconcentrationsprotectiveofthegroundwaterresourcedependonthedistancetothePOEfromthesource.
Thesetargetsoilconcentrationsshouldbedevelopedassumingnoattenuationintheunsaturatedzoneandnobiodegradationinthesaturatedzone.
Forindirectexposurepathways(wheretheexposureoccursatalocationormediumdifferentthanthesourcemedium,forexample,ingestionofwaterfromadowngradientwellimpactedbyleachingofchemicalsfromthesoil),anRM-1Evaluationrequirestheuseoffateandtransportmodels.
TheDepartmenthasselectedconservativefateandtransportmodelsthathavetobeimplementedwithconservativeandtypicalinputparameters.
DetailsoftheproceduresutilizedtobackcalculatetheRBTLsareshowninAppendicesDandE.
8.
4COMPARISONOFRM-1TARGETLEVELSWITHREPRESENTATIVECONCENTRATIONSIfthecalculatedriskforanyreceptorexceedsthetargetrisklevels,itisnecessarytoeitherdevelopRM-1targetconcentrationsandremediatethesitetotheselevels,withtheapprovaloftheDepartment,orperformanRM-2Evaluation.
IftheARBCAEvaluatordecidestodevelopRM-1targetlevels,theyshouldbecomparedwiththerepresentativeconcentrationsforeachexposurepathwaywithineachED/DUaftertheremediationactivitieshavebeencompleted.
PresenceofproductshouldbenotedandconsideredasdiscussedinAppendixB.
Dependingonthesiteconditions,multiplerepresentativeconcentrationsmayhavetobedevelopedforasite.
Forexample,atasitewhereagroundwaterplumeexistsbelowanon-sitecommercialbuildingandhasmigratedoff-siteunderaresidentialbuilding,representativegroundwaterconcentrationsforon-siteandoff-sitereceptorswouldbedifferent.
RepresentativeconcentrationsshouldbedevelopedforeachED/DU.
AppendixBprovidesdetailedproceduresfordeterminingexposuredomainsandforcalculatingrepresentativeconcentrations.
Followingremediationactivitiesatasite,representativeconcentrationsshouldbeupdatedwithineachED/DU.
Beforeremediationmaybeconsideredcomplete,thetargetcumulativeriskmustbemetforeachreceptorintheCSM.
Insomecases,thismayrequiretheARBCAEvaluatortore-computethecumulativerisksandhazardindicesusingthecurrentrepresentativeconcentrations.
Therepresentativeconcentrationsshouldbeevaluatedasfollows:8.
4.
1SoilsForbothsurficialandsubsurfacesoils,theselectionoftherepresentativeconcentrationassumesthesitehasbeenadequatelyassessed.
Representativesoilsourceconcentrationsrequiredfortheevaluationoftheprotectionofgroundwaterpathwayshouldbecalculatedbasedonthesoildatacollectedwithinthesourcearea.
Thedimensionsforthesourceareausedtocalculatetherepresentativeconcentrationsshouldbeidenticaltothedimensionsusedtodeveloptheconcentrationsprotectiveofthegroundwaterresourcepathway.
Recentaverageandrecentmaximumconcentrationsshouldbedeterminedasnecessarytocalculatetherisksandcomparethemwiththetargetrisklevels.
SeeAppendixBfordetailsoncomputingrepresentativeconcentrations.
Thesoildatafromthemostrecentcomprehensiveinvestigationshouldbeused.
Ifrecent(4yearsold)dataareavailable,themaximumvaluemaybeutilizediftherehavebeennoadditionalreleasessincethedatawascollectedandtheDepartmentconcursthatthedatasetiscomplete.
Ifanewreleasehasoccurred,soilassessmentactivitiesshouldadequatelycharacterizetheextentofthenewrelease.
8.
4.
1.
1SurficialSoilTherepresentativesurficialsoilconcentrationsshouldbedeterminedbasedonrecent(4yearsold)andtheconcentrationsexceedtheRSLs,itmaybeusefultocollectnewdata.
Olddatamaybedisregardedifsufficientnewdataarecollected.
Anewreleasewillalwaysrequirethecollectionofadditionaldata.
Ifthereisasufficientnumberofsoilsampleswithintheexposuredomain/decisionunitthe95%UCLaboutthemeanmaybeusedratherthanusingthemaximumconcentrations.
USEPA'ssoftware,ProUCLmaybeusedtogeneratetherepresentativeconcentration.
PleasenotethatinordernottoviolatetheCentralTendencyTheorem,generally30-50ormoresamplesmustbeavailableforthecalculation.
Non-detectsoilsampleslocatedattheperipheryoftheselectedED/DUshouldnotbeused.
Non-detectsampleswithintheED/DUmaybereplacedbyhalftheirdetectionlimitsifdetectionlimitsarelessthantheappropriateRSL.
IfdetectionlimitsaregreaterthanRSL,theARBCAEvaluatorshouldusethedetectionlimitasthesampleconcentration.
Ifmultiplesurficialsoilsamplesand/ormultiplesubsurfacesoilsamplesareavailablefromthesameborehole,insomecasesitmaybeappropriateforthesetobeaveragedtoestimatetheconcentrationsrepresentativeoftheareaelements.
Priortoaveragingtheconcentrations,theDepartmentshouldbecontactedandthesiteshouldreceiveconcurrenceinthematter.
Surficialandsubsurfacesoilsamplesshouldnotbeaveragedtogether.
B.
4.
2GroundwaterConcentrationsThefollowingstepsarenecessarytodeterminetherepresentativegroundwaterconcentrations:Toaccountforthetemporalvariationingroundwaterconcentrations,theconcentrationinasinglewellmaybeestimatedas:ARBCA(Revision3)2017B-15A.
Forawellwithfluctuatingconcentrations,therepresentativeconcentrationisestimatedasthemaximumconcentrationovertherecenttwoyearsorrecentfourmeasurements.
B.
Forawellwithacleardecreasingtrend,therepresentativeconcentrationisestimatedasthemaximumconcentrationoftherecenttwoyearsofdataorrecentfourmeasurements,whicheverrepresentstheshortertimeduration.
C.
Forawellwithaclearincreasingtrend,therepresentativeconcentrationisestimatedasthemaximumconcentrationoftherecenttwoyearsofdataorrecentfourmeasurements,whicheverrepresentstheshorterduration.
Notethatforwellswithincreasingconcentrationtrends,continuedmonitoring,ataminimum,willberequireduntilthetrendstabilizes.
D.
Non-detectsamplesmaybereplacedbyhalftheirdetectionlimitsifdetectionlimitsarelessthantheappropriateRSL.
IfdetectionlimitsaregreaterthantheRSL,theARBCAEvaluatorshouldusethedetectionlimitasthesampleconcentration.
E.
WellswithconcentrationsconsistentlybelowdetectionlimitsintheperipheryoftheED/DUshouldnotbeused.
Forawellthatcontainedfreeproductduringasamplingevent,therepresentativeconcentrationofthatsamplingeventwouldbetheeffectivesolubilityofthechemicalorthehighestmeasuredconcentrationatthatsite,whicheverishigher.
Notethatwellscurrentlycontainingfreeproductwillberequiredtoundergocorrectiveactionstoremovetheproduct.
Seethe"ChemicalSpecificParameters"tablelocatedinintheRSLGenericTablesforeffectivesolubility.
MoreinformationdescribingthecalculationoftheeffectivesolubilityofachemicalandaneffectivesolubilitycalculatormaybefoundonEPA'sOn-LineToolsforSiteAssessmentCalculationsite.
FIGUREB-1.
CALCULATIONOFGROUNDWATERRESOURCEPROTECTIONTARGETLEVELSCPOESentryWell"Exposure"WellInfiltratingwaterLeachateGroundwaterFlowδGW"mixingzone"GroundsurfaceSubsurfaceimpactedsoilsVadosezoneDistance="XPOE"ft.
Distance="XSW"ft.
163.
3601002003004005006007008009001000DistanceinfeetDAF251.
76AllowablegroundwaterconcentrationatthesourceprotectiveofaPOElocatedatadistanceXPOEfromthesource=CPOExDAFPOEAllowablegroundwaterconcentrationatasentrywell,locatedatadistanceXSWfromthesource,protectiveofaPOElocatedatadistanceXPOEfromthesource=CPOExDAFPOE/DAFSWAllowablesoilconcentrationatthesourceprotectiveofaPOElocatedatadistanceXPOEfromthesource=CPOExDAFPOE/LFSWARBCA(Revision3)2017APPENDIXCCONCENTRATIONSPROTECTIVEOFASTREAMARBCA(Revision3)2017C-1APPENDIXCCONCENTRATIONSPROTECTIVEOFASTREAMC.
1BACKGROUNDWhileperforminganARBCAEvaluationatasite,itisnecessarytoidentifysurfacewaterbodies(lakes,perennialstreams,drainageways,intermittentstreams,wetlands,etc.
)locatednearthesite.
Thesestreamsmaybeaffectedbythedischargeofagroundwaterplumeintothesurfacewaterbody.
Surfacewaterbodieslocatedwithin500feetfromthedowngradientedgeofthegroundwaterplumeshouldbeidentified.
Atsiteswheresuchsurfacewaterbodieshavebeenidentified,theARBCAprocessrequiresthebackcalculationofallowableconcentrationsforthesoilsource,groundwatersource,andstreamsentrywell(s)protectiveofthestream.
Themethodusedtodevelopthesetargetlevelsispresentedinthefollowingsections.
C.
2METHODOLOGYAschematicofthepotentialmigrationofchemicalsofconcern(COCs)fromthesoilsourcetothestreamisshowninFigureC-1.
ResidualCOCconcentrationsatthesoilsourcecouldpotentiallyleachintogroundwaterbelowthesource.
Thisleachatewouldmixwiththeregionalgroundwaterdirectlybelowthesiteandmigrateinthedowngradientdirectiontowardsthestream.
Uponreachingthestream,theplumewoulddischargeintothestreamandmixwiththewaterinthestream.
Atacertaindistancedownstreamofthegroundwaterplumedischargepoint,theCOCsdischargedintothestreamwouldcompletelymixwiththewaterinthestream.
ThemethodusedtocalculateRM-1andRM-2allowablesoilandgroundwaterconcentrationsprotectiveofstreamsisbasedonnumerousconservativeassumptions.
Theseinclude(i)asteady-stategroundwaterplume,(ii)asteady-stateflowinthestream,and(iii)nolossofCOCsinthestreamduetonaturalattenuationprocessessuchasadsorptiontothesediments,volatilizationfromthestream,etc.
Further,inanRM-1Evaluation,surfacewaterstandardsandequationslistedinADEMAdmin.
Codech.
335-6-10mustbemetatthepointofdischarge,i.
e.
,mixingwithinthestreamisnotconsideredintheRM-1calculation.
ARBCA(Revision3)2017C-2Estimationofallowablesoilsourceconcentrationsprotectiveofstreamsarecomputedusingthefollowingsteps:Step1:IdentifystreamspotentiallyaffectedbyCOCsatthesiteTheobjectiveofthisstepistoidentifysurfacewaterbodieslocatednearthesitethatmaybeaffectedbytheCOCsatthesite.
Surfacewaterbodiesincludeintermittentstreams,drainageditches,creeks,ponds,perennialstreams,wetlands,andlakes.
Surfacewaterbodieslocatedwithin500feetofthedowngradientedgeofthesiteshouldbeidentified,unlessotherwiserequiredbytheDepartment.
Thesesurfacewaterbodiesshouldbelocatedonasitemapaswellasatopographicmap.
ThewateruseshouldalsobeidentifiedperADEMAdmin.
Coder.
335-6-10-.
03.
Surfacewaterintakesforpublicwatersupply,locatedwithin1miledownstreamofthesite,shouldalsobeidentified.
Step2:Identifyconcentration(s)upstream(Csu)ofthegroundwaterdischargeThebackgroundconcentrationinastreamshouldbemeasured.
Backgroundconcentrationisdefinedastheconcentrationinthestream,upstreamofthelocationwheretheimpactedgroundwaterplumedischargesintothestream.
Measurementofthisconcentrationmayhelpidentifyanyupstreamsourcesofcontamination.
ThismeasuredconcentrationisrepresentedasCsu.
Step3:EstimatetheallowableconcentrationofeachCOCinthestream(Cstr)TargetsurfacewaterconcentrationsshouldbecalculatedusingthecriteriapresentedinADEMAdmin.
Codech.
335-6-10fortheappropriateuseclassification.
InEquationC-1,theseconcentrationsarerepresentedasCstr.
Step4:Estimatetheallowableconcentrationinthegroundwateratthepointofdischarge(Cgw)ForanRM-1Evaluation,groundwaterconcentrationsatthepointofdischarge,Cgw,aresetequaltotheallowablestreamconcentration,Cstr.
Thus,foranRM-1Evaluation,mixingwithinthestreamisneglected.
ForanRM-2Evaluation,mixingwithinthestreamisused,i.
e.
,theallowablestreamconcentrations,Cstr,havetobemetatthedownstreamedgeofthemixingzonewithinthestream.
Theallowablegroundwaterconcentrationsatthepointofdischargecanbeestimatedusingthefollowingmassbalanceequation:ARBCA(Revision3)2017C-3Where:Qgw=Impactedgroundwaterdischargeintothestream(ft3/day)Cgw=Allowableconcentrationingroundwateratthepointofdischargeintothestream(mg/L)Qsw=Streamflowupstreamofthepointofgroundwaterdischarge(streamflowrate)(ft3/day)Cstr=Allowabledownstreamconcentrationatthedownstreamedgeofthestream'smixingzone(mg/L)Csu=TheCOC'sconcentrationupstreamofthegroundwaterplumedischarge(mg/L)Theimpactedgroundwaterdischarge,Qgw,inEquationC-1,isestimatedasfollows:Where:Ugw=GroundwaterDarcyvelocity(cm/year)K=Hydraulicconductivityofthesaturatedzone(cm/year)i=Hydraulicgradient(cm/cm)Agw=Crosssectionalareaofimpactedgroundwaterflow(ft2)8.
99x10-5=Conversionfactor(cm/yeartoft/day)InEquationC-2,Agwisestimatedas:Where:Lp=Widthofthegroundwaterplumedischargingtothestream(ft)Dp=Thicknessofthegroundwaterplumedischargingtothestream(ft)(C-1)(C-2)(C-4)()+=QQCQQQCCgwswsugwswgwstrgwgwgwgwAUQ***=51099.
8iKUgw*=(C-3)ppgwDLA*=ARBCA(Revision3)2017C-430Xsy=α200Xsz=αForanRM-1Evaluation,thedimensionsoftheplumedischargingintothestreamcanbeestimatedas(DomenicoandPalciauskas,1982):Where:Y=Widthofthesoilsourceperpendiculartotheflowdirection(cm)δgw=Groundwatermixing-zonethickness(cm)Xs=Distancefromthedowngradientedgeofthegroundwatersourcetothestream(ft)αy=Lateraldispersivity(ft)αz=Verticaldispersivity(ft)30.
48=Conversionfactor(cm/ft)InEquationC-5andC-6,αyandαzcanbeestimatedas:ForanRM-2Evaluation,thewidthofthegroundwaterplumemaybeestimatedusingEquationC-5ormeasuredatthesite.
Tomeasurethewidthoftheplumethatdischargesintothestream,monitoringwellsmustbeinstalledalongthestreambank.
OthermeasurementproceduresmaybeutilizedifacceptedbytheDepartment.
ThemethodproposedshouldbeincludedinawrittenplansubmittedtotheDepartment.
ForanRM-2Evaluation,theDepartmentrequiresthatthe7Q10flow(DefinedinEquationC-9)beusedtoestimatetheupstreamflow,Qsw,inEquationC-1.
Whenflowdataisavailable,theDepartmentpreferstheuseoftheRatioMethod.
TheapplicationofflowdatafromUSGSgagesmakestheassumptionthatflowisproportionaltodrainagearea.
Thisisafairlyaccurateassumptionaslongasflowcharacteristicsatthegageandthelocationofinterestaresimilar.
Flowcharacteristicsreferprimarilytotherecessionindicespresentinthewatershedabovethelocationofinterestand,toalesserextent,themeanannualprecipitationinthewatershedabovethelocationofinterest.
ThelongerthesypXYLα248.
30+=szgwpXDαδ+=48.
30(C-5)(C-6)(C-7)(C-8)ARBCA(Revision3)2017C-5periodofrecordforthegage,themoreaccuratetheestimatestendtobe(forthegageitself).
Forstreamsthataregauged,the7Q10canalsobeobtaineddirectlyfromAtkinsandPearman(1994)orbycallingalocalU.
S.
GeologicalSurveyHydrologicaloffice.
ThisisthelesspreferredmethodbutisacceptableiftheRatioMethodisnotfeasible.
ThisflowrateisestimatedusingthemethoddevelopedbyBingham(1982)andconsistsofaregressionequationusingabase-flowrecessionindex,drainagearea,andmeanannualprecipitation.
Thismethodcanbeusedtoestimatelowflowinstreamswithdrainageareasof5to2,460squaremiles.
Iftherearequestionsregardingthedeterminationof7Q10flow,theChiefoftheTechnicalSupportSectionoftheWaterQualityBranchoftheWaterDivisionshouldbecontactedforassistance.
Thespecificregressionequationtakestheform:Where:7Q10=Estimatedstreamflow(ft3/s)G=Streamflowrecessionindex(unitless)(determinedfromgaugedatausingtheGeologicalSurveyofAlabama(GSA)mapsandreferences,inabsenceofGSAgaugedataaslastresort,GmaybedeterminedfromBingham,1982)A=Contributingdrainagearea(squaremiles)P=Meanannualprecipitation(inches)ThemeanannualprecipitationshouldbeobtainedfromtheNOAAwebsiteandtheraindatathatisclosesttotheareaofinterestshouldbeutilized.
Inordertolocatetheannualprecipitationdatagoto"browsedatasets"–"annualsummaries"–thenuseeitherthesearchtooltoquerybylocationortheGISmappingtooltofindastation.
Foraquick,lessaccuratereference,theNorthwestAllianceforComputationalScienceandEngineeringproducesausefulAverageAnnualPrecipitationmapforAlabama.
SeeSection6.
7.
2.
5.
2-Infiltrationrate,"I",foradditionalsourcesofrainfalldata.
Forsituationswherethesiteislocatedinanareawithmorethanonestreamindex,computethe7Q10fortheentiredrainageareausingeachindex,thencalculatetheestimated7Q10basedonaweightedaverage.
Forexample,forasitewithadrainageareaof75squaremilesand55in.
ofannualprecipitation,70%ofthedrainageisinanareawithanindexof50,and30%isinanareawithanindexof100,calculatethe7Q10forbothindicesusingthetotaldrainageareaasshownbelow:(C-9)64.
105.
135.
1530301015.
0107**=PAGQARBCA(Revision3)2017C-6Example:Drainageusingfirstindex7Q10=1.
6cfsDrainageusingsecondindex7Q10=8.
5cfsDeterminetheweightedaveragebasedonthe70and30percentofthebasindrainingeacharea.
1.
6cfs(0.
7)=1.
1cfs8.
5cfs(0.
3)=2.
6cfsWeightedavg=3.
7cfs,thereforethe7Q10=3.
7cfsThe7Q10estimatedfromEquationC-9canbeconvertedtoQswusingthefollowingequation:Where:86400=Conversionfactor(seconds/day)Forstreamswithadrainagearealessthan5squaremiles,streamswithintermittentflow,orwetlands,7Q10isassumedtobezero(C-10)64.
105.
135.
1530557530501015.
0107**=Q64.
105.
135.
15305575301001015.
0107**=Q400,86107*=QQswARBCA(Revision3)2017C-7Step5:Estimatetheallowableconcentrationingroundwateratthesource(Cgws)andthestreamsentrywells(Ccw)Theallowablegroundwaterconcentrationatthesourceprotectiveofthestreamcanbeestimatedusingtheconceptofthedilutionattenuationfactor.
Thus,theallowablegroundwaterconcentrationatthesource,Cgws,canbeestimatedas:Where:Cgws=Allowableconcentrationingroundwaterbelowthesource(mg/L)DAFstream=Dilutionattenuationfactorinthesaturatedzonebetweenthesourceandthestream[unitless]Cgw=Allowablegroundwaterconcentrationatthepointofdischargetothestream,estimatedusingEquationC-1inRM-2(mg/L).
InRM-1,Cgw=CstrThetargetconcentrationinastreamsentrywelllocatedbetweenthesourceandthestream,canbeestimatedasfollows:Where:Csw=Allowableconcentrationatthestream-sentrywell[mg/L]DAFstream=Dilutionattenuationfactorinthesaturatedzonebetweenthesourceandthestream(unitless)DAFsw=Dilutionattenuationfactorinthesaturatedzonebetweenthesourceandthestream-sentrywell(unitless)NotethattheconceptquantifiedbyEquationC-12isalsousedtodevelopthesentry-wellconcentrationsfortheprotectionofthegroundwaterresource(refertoSection6.
11).
ForRM-1andRM-2Evaluations,theDAFstreamandDAFswcanbecalculatedusingthesimplifiedversionofDomenico'smodel,asdiscussedinSection6.
11.
ForthespecificformoftheDomenico'smodel,refertoAppendixE.
gwswstreamswCDAFDAFC*=(C-11)(C-12)streamgwgwsDAFCC*=ARBCA(Revision3)2017C-8Step6:Estimatetheallowablesoil-sourceconcentration(Csoil)Theallowablesoil-sourceconcentrationcanbeconservativelyestimatedassumingnoattenuationintheunsaturatedzone,i.
e.
,theleachateconcentrationatthesoilsourceisidenticaltotheleachateconcentrationreachingthewatertable.
Thesourcesoilconcentrationcanbeestimatedas:Where:Csoil=Allowablesourcesoilconcentration(mg/kg)LFsw=Leachingfactorfromsoiltogroundwater[(mg/L-H2O)/(mg/kg-soil)]SeeAppendixEoftheARBCAguidancedocumentfortheequationtocalculatetheleachingfactor.
C.
3IMPLEMENTATIONOFTHEABOVEMETHODToimplementtheabovemethodinRM-1,theusermustdetermine(i)thedistancefromthesourcetothedowngradientstream,(ii)thelocationofthestreamsentrywells,and(iii)distancefromthesourcetothestreamsentrywells.
Theallowablesoilsourceconcentrationshavetobecomparedwiththerepresentativesoilsourceconcentrationsatasitetodetermineiftherepresentativesoilsourceconcentrationsareprotectiveofthestream.
Inaddition,theallowablegroundwatersourceconcentrationhastobecomparedwiththerepresentativegroundwatersourceconcentrations.
TheRM-1targetgroundwaterconcentrationsinthestreamsentrywellscanbecalculatedusingEquationC-12.
Thestreamsentrywelltargetconcentrationshavetobecomparedwiththerepresentativestreamsentrywellconcentrationstodeterminewhetherthestreamsentrywellconcentrationsareprotectiveofthestream.
RefertoAppendixBforprocedurestodeveloprepresentativestreamsentrywellconcentrations.
TheequationsinAppendixEcanbeusedtocalculatetheallowablesoilandgroundwatersourceconcentrationsandthestreamsentrywellconcentrations.
Thedatarequiredarelistedbelow(parametersinitalicsareusedonlyfortheestimationoftargetlevelsprotectiveofstreams):(C-13)swstreamgwsoilLFDAFCC*=ARBCA(Revision3)2017C-9StreamDataDistancefromthedowngradientedgeof-tocalculateDAFstream,Lp,andDpthegroundwatersourcetothestream(Xs)MeanAnnualprecipitationinthearea(P)-tocalculate7Q10Streamflowrecessionindex(G)-tocalculate7Q10Contributingdrainagearea(A)-tocalculate7Q10Concentrationupstreamoftheplume-tocalculateCgwdischarge(Csu)Allowableconcentrationinthestream(Cstr)-ADEMAdmin.
Codech.
335-6-10ComplianceWellDataDistancefromthedowngradientedgeof-tocalculateDAFswthegroundwatersourcetotheStreamsentrywell(Xssw)ChemicalDataHenry'sLawconstant(H)-RSLChemicalSpecificParametersTableHalf-life(days),whenusingdecay-tocalculateDAFswandDAFstreamOrganiccarbonpartitioncoefficient(Koc)-RSLChemicalSpecificParametersTableAquiferPropertiesHydraulicconductivity(K)-tocalculateDarcyvelocityHydraulicgradient(i)-tocalculateDarcyvelocityGroundwatermixingzonethickness(δgw)-tocalculateLFsw,DAFsw,andDAFstreamInfiltrationrate(I)-tocalculateLFswOrganic-carboncontentinthesaturated-tocalculateretardationfactorinthezone(focs)saturatedzoneSaturated-zoneporosity(θTS)-tocalculateseepagevelocityinthesaturatedzoneSaturated-zonedrybulkdensity(ρss)-tocalculateretardationfactorinthesaturatedzoneVadose-ZoneSoilPropertiesTotalporosity(θΤ)-tocalculateLFswOrganic-carboncontent(foc)-tocalculateLFswWatercontent(θws)-tocalculateLFswDrybulkdensity(ρs)-tocalculateLFswARBCA(Revision3)2017C-10SourceParametersLengthofgroundwatersourceparallelto-tocalculateLFswthegroundwaterflow(W)Groundwatermixing-zonethickness(δgw)-tocalculatethicknessofplumeatthepointofdischargeWidthofgroundwatersourceperpendicular-tocalculateDAFsw,DAFstream,andwidthtothegroundwaterflow(Y)ofplumeatthepointofdischargeThesevaluesareutilizedintheequationslocatedinAppendixEtocalculatetheallowableconcentrationsprotectiveofastreamin(i)soilatthesoilsource,(ii)groundwateratthegroundwatersource,and(iii)groundwateratthestreamsentrywell.
Appropriatejustificationforusingtheselectedvaluesshouldbeprovidedinthefinalreport.
SourcesAtkins,J.
B.
,andPearman,J.
L.
,1994,Low-FlowandFlow-DurationCharacteristicsofAlabamaStreams,U.
S.
GeologicalSurvey,Water-ResourcesInvestigationsReport,93-4186.
Bingham,R.
H.
,1982,Low-FlowCharacteristicsofAlabamaStreams,U.
S.
GeologicalSurveyWater-SupplyPaper2083,U.
S.
GovernmentPrintingOffice,WashingtonD.
C.
Domenico,P.
A.
,andPalciauskas,V.
V.
,1982,AlternativeBoundariesinSolidWasteManagement,Groundwater,vol.
20,no.
3,pp.
303-311.
ARBCA(Revision3)2017Qsw,CsuGroundwaterPlumeCgwDirectionofgroundwaterflowSurfaceWaterQgw+QswPLANVIEWCstrGroundSurfaceSoilSourceVadoseZoneStreamWaterTableGWDischargeDirectionofgroundwaterflowCgwsCgwGroundwaterPlumeCROSS-SECTIONALVIEWExplanationofSymbolsQsw=Streamflowupstreamofthepointofgroundwaterdischarge[ft3/day]Csu=Concentrationupstreamofthegroundwaterdischarge[mg/L]Qgw=Impactedgroundwaterdischargeintothestream[ft3/day]Cstr=Allowabledownstreamconcentrationafteruniformmixing[mg/L]Cgw=Allowableconcentrationinthegroundwaterdischargetothestream[mg/L]Cgws=Allowableconcentrationinthegroundwaterattheedgeofthesoilsource[mg/L]Csoil=Allowablesoilconcentrationatthesource[mg/kg]Lp=Widthofgroundwaterplumedischargingtothestream[ft]Dp=Thicknessofgroundwaterplumedischargingtothestream[ft]Xs=Distancefromthedowngradientedgeofthegroundwatersourcetothestream[ft]XsFigureC-1:SchematicofLeachateMigrationfromtheSoilSourcetotheStreamCsoilGroundwaterSource(Cgws)QgwLpDpCsoilQgwAPPENDIXDBACKCALCULATIONOFRISK-BASEDTARGETLEVELSANDFORWARDCALCULATIONOFRISKSANDHAZARDQUOTIENTSARBCA(Revision3)2017D-1APPENDIXDBACKCALCULATIONOFRISK-BASEDTARGETLEVELSANDFORWARDCALCULATIONOFRISKANDHAZARDQUOTIENTD.
1IntroductionThebackcalculationofrisk-basedtargetlevelsessentiallyprovidestheanswertothequestion,"TowhatlevelmustIremediatemysite"Risk-basedtargetlevels(RBTLs)actasaguidetohelpasitedeterminegoalsforsoiland/orgroundwaterconcentrationcleanupvaluespriortoaremediationactivity.
Theforwardcalculationprocessdeterminesthecumulativeriskatasiteandistheprimaryfactorusedtodetermineifasitehasmettheappropriatecleanupgoals.
Thebackcalculationandforwardcalculationwhenusedtogetherasatoolcanbeusedtoaddressthefollowingsituations:Determinationoftheresidualconcentrationswhichcanbeleftinthesoilsuchthatconcentrationsinanexistingorpotentialdrinkingwaterwellorastreamwillnotexceedthetarget(MCL)valuesfortheCOCs.
Determinationoftheresidualconcentrationsthatcanbeleftinthesoilsuchthattheriskduetoinhalationofvolatileemissionsfromthesoiltoanon-siteoroff-sitereceptordoesnotexceedanacceptablelevel.
Determinationofresidualconcentrationswhichcanbeleftinthesurficialsoilssuchthattheriskduetoaccidentalingestion,directcontact,andinhalationofCOCsdoesnotexceedanacceptablelevel.
RBTLscanbesitespecificdependingonthedatausedinthebackcalculationprocess.
Calculationoftheseconcentrationsdependsonavarietyoffactorsincludingtheacceptablelevelofrisk,sitereceptorcharacteristics(industrialvs.
residentialoradultvs.
child),transportmechanisms,propertiesofthechemical,anddistancebetweenthereceptorandthesource.
Whileperformingthesecalculations,itisimportanttodistinguishbetweendirectandindirectexposurepathways.
Directexposurepathwaysarethoseinwhichthereceptorcomesindirectcontactwiththeaffectedmedia.
Examplesofdirectexposureincludeingestionofsoilanddermalcontactwithsoil.
Indirectpathwaysarethosewheretheexposureoccursawayfromthesource.
Forexample,volatilizationofchemicalsfromsubsurfacesoilmayresultinexposurebyinhalationinsideabuilding,orleachingofchemicalsinthesoiltogroundwatermayresultinexposurefromtheingestionofgroundwateratanearbywell.
Evaluationoftheindirectexposurepathwaysrequirestheuseofchemicalfateandtransportmodels.
Astep-by-stepprocesstobackcalculatetheRBTLsisdescribedinthefollowingsections.
ARBCA(Revision3)2017D-4D.
2Step-by-StepProcedureSTEP1:IDENTIFYACCEPTABLERISKLEVELANDHAZARDQUOTIENTTheacceptableindividualexcesslifetimecancerrisk(IELCR)forcarcinogeniceffectsandtheacceptablehazardquotient(HQ)fornon-carcinogeniceffectsisapolicydecision.
Fortheassessmentandremediationofacontaminatedsite,intheRSLEvaluation,theDepartmentcurrentlyusesavalueof1.
0E-6forlifetimecancerrisks,andtheacceptableHQis0.
1.
IntheRM-1andRM-2Evaluations,theDepartmentcurrentlyusesvaluesof1.
0E-5forlifetimecancerrisks,andtheacceptablehazardindex(HI)is1.
0(HI=ΣHQ).
PleasenotethatsomeMCLsmayhavebeenbasedupondifferenttargetrisksandhazardquotients.
MCLsarepromulgatedvaluesandmustbeusedbeforeacalculatedvalueisused.
Additionally,screeninglevelsforleadaredevelopedusingmethodologiesthatdonotinvolveriskorhazardquotient–seeSection6.
14.
STEP2:ESTIMATETHETOXICITYOFTHECHEMICALSOFCONCERN(COCs)Thetoxicityofchemicalswithcarcinogeniceffectsisquantifiedusingthepotencyvalues-oralslopefactor(SFo)andtheinhalationunitrisk(IUR).
Fornon-carcinogeniceffects,thetoxicityisquantifiedusingtheoralreferencedose(RfDo)andthereferenceconcentration(RfC).
ThesetoxicityvaluesareprovidedintheRSLSummaryTableforeachofthechemicalsofconcern.
Thesevaluesshouldbeutilizedunlessthereisavalidreasontousealternativevalues.
AnyalternativevaluemustbeapprovedbytheDepartment.
ThetoxicityvaluesintheRSLTableareupdatedsemi-annuallyasnewinformationonthetoxicityoftheCOCsismadeavailable.
STEP3:ESTIMATETHEALLOWABLEEXPOSUREPOINTCONCENTRATIONSTheallowableexposurepointconcentrationsareestimatedusingtheuptakeequationsfortherelevantrouteofexposureandappropriateexposurefactors.
TheexposurefactorstheARBCAEvaluatorisexpectedtousetodeveloptheRM-1RBTLsarepresentedintheRegionalScreeningTableUser'sGuide.
DuringanRM-2Evaluation,theDepartmentmayconsiderandapprovealternativeexposurefactorsifjustifiedbysite-specificconditions.
ItistheresponsibilityoftheevaluatorconductingtheanalysistoprovidejustificationfortheuseofthesealternativevaluesandtoobtaintheacceptanceofthesevaluesfromtheDepartment.
Fordirectroutesofexposure,theestimatedconcentrationwillbetherisk-basedtargetlevel.
However,forindirectroutesofexposures,theestimatedtargetlevelsareapplicableatthepointofexposure.
Additionalanalysisaspresentedinthefollowingstepisnecessarytorelatetheexposurepointconcentrationstothesourceconcentrations.
ARBCA(Revision3)2017D-4STEP4:ESTIMATETHEALLOWABLESOURCECONCENTRATIONThisstepvariesdependingonthespecificindirectrouteofexposureandthetransportmechanismfromthesourcetothereceptorpoint.
However,theobjectiveineachcaseistousetheallowableexposureconcentrationestimatedinStep4toestimatethesourceconcentrations.
Example(1)-Estimationofsubsurfacesoilconcentrationsprotectiveofinhalationexposures.
Forthisexposurepathway,theconcentrationsestimatedinStep3wouldbetheconcentrationintheairthatthereceptorisbreathing.
Atwo-stepproceduremaybeusedtoestimateallowablesoilconcentrations.
Initially,ifthereceptorislocatedonsite,aclosed-boxmodelmaybeusedtoestimatetheallowableemissionrate.
Second,usinganemissionmodel,theestimatedallowableemissionrateisrelatedtotheallowablesoilconcentration.
Implementationofthesetwomodels,requiresseveralinputparameters.
ItisimportantthattheresponsiblepartyclearlyidentifythedatausedandprovideadequatejustificationforthespecificvaluesusedfortheRM-1orRM-2Evaluations.
Example(2)-Estimationofsoilconcentrationsprotectiveofingestionofgroundwater.
Forthisexposurepathway,theconcentrationestimatedinStep4wouldbetheconcentrationintheexposurewell.
Theallowableleachateconcentrationatthesourceiscalculatedastheallowableconcentrationattheexposurepointmultipliedbythedilution-attenuationfactor(DAF).
TheDAFistheratiooftheconcentrationatthesourcetotheconcentrationatthereceptor[termedastheconcentrationreductionfactor(CRF),dilutionattenuationfactor(DAF),orthenaturalattenuationfactor(NAF)]andisestimatedusingafateandtransportmodel.
TheDAF(greaterthanorequaltoone)dependsonseveralfactors,suchasthedistancetothewell,groundwatervelocity,chemicalproperties,sizeofthesource,etc.
,thataresite-specificandareaccountedforbythegroundwatermodels.
Severalcoupledmodelsmayberequiredtoestimatethedilution-attenuationfactor,e.
g.
,anunsaturatedzonetransportmodel,asaturatedzonemixingmodel,andasaturatedzonetransportmodel.
Theallowableleachateconcentrationisfinallyconvertedtoanallowablesoilconcentrationeitherbyusingtheresultsofasite-specificleachatetestorbyassumingequilibriumpartitioningbetweenthesoilconcentrationandtheleachateconcentration.
Soilconcentrationsprotectiveofastreamarecalculatedusingthesameprocessasthecalculationofsoilconcentrationsprotectiveofthegroundwaterresource.
TheonlydifferenceisthatthetargetconcentrationsatthePOEwillbedifferentfromthetargetconcentrationinthestream.
AlsorefertoAppendixC.
ARBCA(Revision3)2017D-4D.
3ImplementationThespecificequationsusedtoimplementtheabovelistedstepsforthepreviouslycalculatedRM-1andRM-2RBTLsareshowninAppendixE.
D.
4ForwardModeInforwardmode,theARBCAEvaluatorcalculatestheIELCRsforcarcinogeniceffectsandtheHQsfornon-carcinogeniceffects,addsupalltheIELCRsforareceptor,andaddsupalltheHQsforareceptor.
InRM-1andRM-2,thetotalIELCRforanyreceptor,shouldnotexceed1x10-5.
ThetotalofalltheHQsforareceptor,shouldnotexceedtheHI=1.
0.
TheequationsfortheIELCRsandtheHQsappearinAppendixF.
APPENDIXEMODELS/EQUATIONSFORESTIMATINGRM-1ANDRM-2TARGETLEVELSARBCA(Revision3)2017E-1APPENDIXEMODELS/EQUATIONSFORESTIMATINGRM-1ANDRM-2TARGETLEVELSWITHINTHEARBCAPROCESSThesymbolsusedintheequationspresentedinthisappendixfollowthefollowingthreesources:1.
ASTM,StandardGuideforRisk-BasedCorrectiveActionatPetroleumReleaseSites,1995,Designation:E-1739-95.
ASTM,100BarrHarborDr.
,WestConshohocken,PA19428.
2.
Mid-AtlanticRiskAssessmentUser'sGuide,May2013,http://www.
epa.
gov/reg3hwmd/risk/human/rb-concentration_table/usersguide.
htm.
3.
EnvironmentalQualityManagement,Inc.
,2004,User'sGuideforEvaluatingSubsurfaceVaporIntrusionintoBuildings,Durham,NC,preparedforUSEPA,OfficeofEmergencyandRemedialResponse,Washington,D.
C.
ARBCA(Revision3)2017E-2TableofContentsPageDirectIngestionofGroundwaterE-4IngestionofSoilE-5DermalContactwithSoilE-6InhalationofVaporsandParticulatesfromSurficialSoilandConstructionSoilE-7Ingestionof,DermalContactwith,andInhalationofVaporsandParticulatesfromSurficialSoilandConstructionSoilE-8SubsurfaceSoilConcentrationsProtectiveofLeachingtoGroundwaterE-9LeachingFactorfromSubsurfaceSoiltoGroundwaterE-10SaturationConcentrationinSoilVaporandSoilE-11DomenicoModel:DilutionAttenuationFactor(DAF)intheSaturatedZoneE-12AllowableSoilandGroundwaterConcentrationforGroundwaterResourceProtectionE-13SchematicDescriptionofDomenico'sModelE-14StreamProtection:AllowableGroundwaterConcentrationatPointofDischargeE-15ARBCA(Revision3)2017E-3ThetwoUSEPAVaporIntrusionDocuments,AssessingandMitigatingtheVaporIntrusionPathwayfromSubsurfaceVaporSourcestoIndoorAirandAddressingPetroleumVaporIntrusionatLeakingUndergroundStorageTankSitesshouldbeutilizedastheprimaryreferencefortheIndoorandOutdoorVaporIntrusionpathwayequationsTocalculatetargetconcentrationsatsitesduetothevaporintrusionpathway,itisoftenhelpfultousetheVaporIntrusionScreeningLevel(VISL)Calculator.
Thiscalculatorcontainstablesthatprovidetargetlevels(RBTLs)thatmaybeusedtoaddressaspecificCOCorgroupofCOCs.
Incertaincases,itmaybemoreappropriatetoutilizetheequationsprovidedinoneofthetwoUSEPAVaporIntrusionDocuments,AssessingandMitigatingtheVaporIntrusionPathwayfromSubsurfaceVaporSourcestoIndoorAirandAddressingPetroleumVaporIntrusionatLeakingUndergroundStorageTankSites.
TheDepartmentrecommendsthattargetlevelsfocusonsoilgastargetlevelscollectedatanapproximatedepthof3ftbelowtheareaofconcern(i.
e.
,basement,slab,orcrawlspace).
TheDepartmentpreferstheuseofsoilgastargetlevelsbutitmaybeappropriateincertaincasestoallowtheevaluationtooccurusinganalternatemedia.
Priortoevaluatingthevaporintrusionpathway,thefacilityshouldconsultwiththeDepartment.
ARBCA(Revision3)2017E-4DIRECTINGESTIONOFGROUNDWATERCarcinogenicEffectsowcingwSFRIEFED365ATBWTR=RBTL******Non-carcinogenicEffectswoncingwRIEFEDRfD365ATBWTHQ=RBTL******Source:USEPA,RAGS,Vol.
I,1989,p.
6-35where:RBTLingw=Risk-basedtargetlevelforingestionofwater[mg/L]TR=Targetriskortheincreasedchanceofdevelopingcanceroveralifetimeduetoexposuretoachemical[-]THQ=Targethazardquotientforachemical[-]BW=Bodyweight[kg]ATc=Averagingtimeforcarcinogens[year]ATnc=Averagingtimefornon-carcinogens[year]ED=Exposureduration[year]EF=Exposurefrequency[day/year]IRw=Wateringestionrate[L/day]SFo=Chemical-specificoralcancerslopeorpotencyfactor[(mg/kg-day)-1]RfDo=Chemical-specificoralreferencedose[mg/kg-day]365=ConvertsATc,ATncinyearstodays[day/year]ARBCA(Revision3)2017E-5INGESTIONOFSOIL(CHILDANDADULTRESIDENT,COMMERCIALWORKER,ANDCONSTRUCTIONWORKER)CarcinogenicEffects610365********=oGIsoilcingsSFABSIREFEDATBWTRRBTLNon-carcinogenicEffects610365********=ABSIREFEDRfDATBWTHQRBTLGIsoiloncingsSource:USEPA,RAGSVol.
IPartA,1989where,RBTLings=Risk-basedtargetlevelforingestionofsoil[mg/kg]TR=Targetriskortheincreasedchanceofdevelopingcanceroveralifetimeduetoexposuretoachemical[-]THQ=Targethazardquotientforachemical[-]BW=Bodyweight[kg]ATc=Averagingtimeforcarcinogens[year]ATnc=Averagingtimefornon-carcinogens[year]ED=Exposureduration[year]EF=Exposurefrequency[day/year]IRsoil=Soilingestionrate[mg/day]ABSGI=Oralabsorptionfraction[-]SFo=Chemical-specificoralcancerslopefactor[(mg/kg-day)-1]RfDo=Chemical-specificoralreferencedose[mg/kg-day]365=ConvertsATc,ATncinyearstodays[day/year]10-6=Convertsmgtokg[mg/kg]ARBCA(Revision3)2017E-6DERMALCONTACTWITHSOIL(CHILDANDADULTRESIDENT,COMMERCIALWORKER,ANDCONSTRUCTIONWORKER)CarcinogenicEffects610365**********=ABSdsoilsoilcdsSFABSAFEVSAEFEDATBWTRRBTLNon-carcinogenicEffects610365**********=dsoilsoilABSncdsABSAFEVSAEFEDRfDATBWTHQRBTLSource:USEPA,RAGSVol.
IPartE,2004,Page3-9where,RBTLds=Risk-basedtargetlevelfordermalcontactwithsoil[mg/kg]TR=Targetriskortheincreasedchanceofdevelopingcanceroveralifetimeduetoexposuretoachemical[-]THQ=Targethazardquotientforachemical[-]BW=Bodyweight[kg]ATc=Averagingtimeforcarcinogens[year]ATnc=Averagingtimefornon-carcinogens[year]ED=Exposureduration[year]EF=Exposurefrequency[day/year]SAsoil=Skinsurfaceareaavailableforcontactwithsoil[cm2]EVsoil=Eventfrequency[event/day]AF=Soiltoskinadherencefactor[mg/cm2-event]ABSd=Chemical-specificdermalabsorptionfraction[-]SFABS=Chemical-specificdermalcancerslopefactor[(mg/kg-day)-1]RfDABS=Chemical-specificdermalreferencedose[mg/kg-day]365=ConvertsATc,ATncinyearstodays[day/year]10-6=Convertsmgtokg[kg/mg]ARBCA(Revision3)2017E-7INHALATIONOFVAPORSANDPARTICULATESFROMSURFICIALSOILANDCONSTRUCTIONSOIL(CHILDANDADULTRESIDENT,COMMERCIALWORKER,ANDCONSTRUCTIONWORKER)CarcinogenicEffects1000)(24365*+*******=psoutcinhsVFVFIURETEFEDATTRRBTLNon-carcinogenicEffects)(24365psoutncinhsVFVFETEFEDRfCATTHQRBTL+*******=Source:USEPARegionalScreeningTable–User'sGuide,May2013where,RBTLinhs=Risk-basedtargetlevelofinhalationofvaporsandparticulatesfromsoil[mg/kg]TR=Targetriskortheincreasedchanceofdevelopingcanceroveralifetimeduetoexposuretoachemical[-]THQ=Targethazardquotientforachemical[-]ATc=Averagingtimeforcarcinogens[year]ATnc=Averagingtimefornon-carcinogens[year]ED=Exposureduration[year]EF=Exposurefrequency[day/year]ETout=Outdoorexposuretime[hr/day]IUR=Chemical-specificinhalationunitrisk[(ug/m3)-1]RfC=Chemical-specificinhalationreferencedose[mg/m3]365=ConvertsATc,ATncinyearstodays[day/year]24=Convertsdaystohours[hr/day]1000=Convertsmgtoug[ug/mg]VFs=Volatilizationfactorforvaporemissionsfromsoil[(mg/m3-air)/(mg/kg-soil)]VFp=Volatilizationfactorforparticulateemissionsfromsoil[(mg/m3-air)/(mg/kg-soil)]ARBCA(Revision3)2017E-8INGESTIONOF,DERMALCONTACTWITH,ANDINHALATIONOFVAPORSANDPARTICULATESFROMSURFICIALSOILANDCONSTRUCTIONSOIL(CHILDANDADULTRESIDENT,COMMERCIALWORKER,ANDCONSTRUCTIONWORKER)inhsdsingssRBTLRBTLRBTLRBTL1111++=where,RBTLs=Risk-basedtargetlevelofsoil[mg/kg]RBTLings=Risk-basedtargetlevelforingestionofsoil[mg/kg]RBTLds=Risk-basedtargetlevelfordermalcontactwithsoil[mg/kg]RBTLinhs=Risk-basedtargetlevelofinhalationofvaporsandparticulatesfromsoil[mg/kg]Source:USEPARegionalScreeningTable–User'sGuide,May2013ARBCA(Revision3)2017E-9SUBSURFACESOILCONCENTRATIONSPROTECTIVEOFLEACHINGTOGROUNDWATERSLwSWRBTLRBTLLF=where:RBTLSL=Risk-basedtargetlevelforleachingtogroundwaterfromsubsurfacesoil[mg/kg-soil]RBTLw=Risk-basedtargetlevelforingestionofgroundwater[mg/L-H2O]LFSW=LeachingFactor(fromsubsurfacesoiltogroundwater)[(mg/L-H2O)/(mg/kg-soil)]Source:ASTM,1995,E1739-95GroundsurfaceVadosezoneWaterTableDissolvedcontaminantsLeachateWSubsurfaceimpactedsoilsInfiltration(I)δgwUgwARBCA(Revision3)2017E-10LEACHINGFACTORFROMSUBSURFACESOILTOGROUNDWATER*+**++=IWUHKLFgwgwasssvwssSWδθρθρ1][Source:ASTM,1995,E1739-95where:LFSW=Leachingfactorfromsubsurfacesoiltogroundwater[(mg/L-H2O)/(mg/kg-soil)]ρs=Drysoilbulkdensity[g-soil/cm3-soil]θws=Volumetricwatercontentinvadosezonesoils[cm3-H2O/cm3-soil]Ksv=focv*Koc=Chemical-specificsoil-watersorptioncoefficientfortheunsaturatedzone[cm3-H2O/g-soil]focv=Fractionalorganiccarboncontentintheunsaturatedzone[(g-C)/(g-soil)]H=Chemical-specificHenry'sLawconstant[(L-H2O)/(L-air)]θas=Volumetricaircontentinthevadosezonesoils[cm3-air/cm3-soil]Ugw=GroundwaterDarcyVelocity[cm/year]δgw=Groundwatermixingzonethickness[cm]I=Infiltrationrateofwaterthroughsoil[cm/year]W=Lengthofsourceareaparalleltogroundwaterflow[cm]ARBCA(Revision3)2017E-11SATURATIONCONCENTRATIONINSOILVAPORANDSOILCvSAT:Soilvaporconcentrationatwhichdissolvedphasebecomessaturated[mg/m3-air]CsSAT:Soilconcentrationatwhichdissolvedporewaterandvaporphasesbecomesaturated[(mg/kg-soil)]SingleComponent610***=TRMWPCsSATvMultipleComponents610****=TRMWPxCisiiSATvwhere,CvSAT=Soilvaporconcentrationatwhichvaporphasebecomesaturated[mg/m3-air]Ps=Saturatedvaporpressure[atm]Pis=Effectivevaporpressureofcomponentiinwater=xi*Ps[atm]R=Idealgasconstant[0.
08206atmL/molK]T=Temperature[K]Sei=Effectivesolubilityofcomponentiinwater=xi*S[mg/L-water]xi=Molefractionofcomponenti=(wi*MWavg)/MWi[-]wi=Weightfractionofcomponenti[-]MWavg=Averagemolecularweightofmixture[g/mole]MWi=Molecularweightofcomponenti[g/mole]ρs=Vadosezonedrysoilbulkdensity[g-soil/cm3-soil]106=Conversionfactor[(g/L)/(mg/m3)]Source:ASTM,1995,E1739-95SingleComponent][ρθθρssvwsasssatsKHSC++**=MultipleComponents][ρθθρssvwsasseiSATsKHSC*++**=where:CsSAT=Soilconcentrationatwhichdissolvedporewaterandvaporphasesbecomesaturated[(mg/kg-soil)]S=Purecomponentsolubilityinwater[mg/L-water]Sei=Effectivesolubilityofcomponentiinwater=xi*S[mg/L-water]xi=Molefractionofcomponenti=(wi*MWavg)/MWi[-]wi=Weightfractionofcomponenti[-]MWavg=Averagemolecularweightofmixture[g/mole]MWi=Molecularweightofcomponenti[g/mole]ρs=Vadosezonedrysoilbulkdensity[g-soil/cm3-soil]H=Chemical-specificHenry'sLawconstant[L-water/L-air]θas=Volumetricaircontentinthevadosezonesoils[cm3-air/cm3-soil]θws=Volumetricwatercontentinvadosezonesoils[cm3-water/cm3-soil]Ksv=focv*Kocv=Chemical-specificsoil-watersorptioncoefficientinvadosezone[cm3-water/g-soil]focv=Fractionorganiccarboninvadosezone[g-C/g-soil]Source:ASTM,1995,E1739-95ARBCA(Revision3)2017E-12DOMENICOMODEL:DILUTIONATTENUATIONFACTOR(DAF)INTHESATURATEDZONEDomenicomodelformulti-dimensionaltransportwithdecayandcontinuoussource:()*****x2-zerf-x2+zerfx2Y/2-yerf-x2Y/2+yerftvvvtxerfcvxexpCtzyxCzgwzgwyyoαδαδααααλαλα24+14+1-12)8/1(=),,,(xxxxwhere:C=Dissolved-phaseconcentration[mg/L]Co=Dissolved-phaseconcentrationatthesource(atx=y,0≤z≤δgw)[mg/L]v=Retardedseepagevelocity[cm/year]λ=Firstorderdecayrate[1/year]αx=Longitudinaldispersivity[cm]αy=Lateraldispersivity[cm]αz=Verticaldispersivity[cm]x,y,z=Spatialcoordinates[cm]t=Time[year]x=Distancealongthecenterlinefromthedowngradientedgeofdissolved-plumesourcezoneorsourcewell[cm]Y=Widthofsoilsourceperpendiculartothegroundwaterflowdirection[cm]δgw=Groundwatermixingzonethickness[cm]DAF=Co/C(x)Source:Domenico,P.
A.
andF.
W.
Schwartz,1990,PhysicalandChemicalHydrogeology.
JohnWileyandSons,NY,824p.
(Eqn.
17.
21)Atthecenterline,forsteady-state(afteralongtime)theDAFcanbeobtainedbysettingy=0,z=0,andx<31,whereY=Sw,δgw=Sd,v=u,andCo=CsourceAtthecenterline,forsteady-state,theDAFwithdecaycanbecalculatedusingEquation(1).
InEquation(1),theretardedseepagevelocity(v)iscalculatedas:v=(Ki)/(RsθTS)where:K=Hydraulicconductivity[cm/year]i=Hydraulicgradient[--]θTS=Totalporosityinthesaturatedzone[cm3/cm3-soil]Rs=Retardationfactorinthesaturatedzone[--]ARBCA(Revision3)2017E-13ALLOWABLESOILANDGROUNDWATERCONCENTRATIONFORGROUNDWATERRESOURCEPROTECTIONAllowablesoilconcentrationatthesource=TargetgroundwaterconcentrationattheLFDAFPOESWPOE*Allowablegroundwaterconcentrationatthesource=TargetgroundwaterconcentrationattheDAFPOEPOE*Allowablegroundwaterconcentrationatthesentrywell=TargetgroundwaterconcentrationattheDAFDAFPOESWPOE*where:POE=PointofexposureSW=SentrywellDAFPOE=DilutionAttenuationFactorbetweenthepointofexposureandthesourceDAFSW=DilutionAttenuationFactorbetweenthesentrywellandthesourceLFSW=DrysoilleachingfactorAdditionalrelationshipsusedinthecalculationofallowablesoilandgroundwaterconcentrationwithchemicaldegradation:LifeHalf0.
693ratedecayorderFirst=+=*θρTSsssssKR1)(zonesaturatedintheOrganicsforFactornRetardatioKss=focs*Koc+=*θρTSdsssKR1)(zonesaturatedintheMetalsforFactornRetardatiowhere:ρss=Saturatedzonesoilbulkdensity[g-soil/cm3-soil]Kss=Chemical-specificsoil-watersorptioncoefficientinthesaturatedzone[cm3-H2O/g-soil]Kd=Chemical-specificsoil-waterdistributioncoefficientformetalsinthesaturatedzone[mL/g]θTS=Totalporosityinthesaturatedzone[cm3/cm3-soil]focs=Fractionalorganiccarboncontentinthesaturatedzone[g-C/g-Soil]ARBCA(Revision3)2017E-14SCHEMATICDESCRIPTIONOFDOMENICO'SMODELSoilSourceAreaLeachateYzyxSECTIONUgwYGroundwaterSource(GroundwaterMixingZone)GroundwaterSource(GroundwaterMixingZone)UgwWWCoWaterTableGroundSurfaceCoPLANVadozeZoneDowngradientEdgeoftheGroundwaterSource*Note:(*Assumesonlyverticalleaching,i.
e.
,thereisnohorizontalspreadingintheunsaturatedzone.
)δgwARBCA(Revision3)2017E-15STREAMPROTECTION:ALLOWABLEGROUNDWATERCONCENTRATIONATPOINTOFDISCHARGE()+=gwswsugwswgwstrgwQQCQQQCC()()gwsyszgwUXYXZQ*+*+=αα2where,QgwCgwQswCstrCsuYZαyαzXsUgw===========Impactedgroundwaterdischargeintothestream[ft3/day]Allowableconcentrationingroundwateratthepointofdischargeintothestream[mg/L]Streamflowupstreamofthepointofgroundwaterdischarge(streamflowrate)[ft3/day]Allowableconcentrationatthedownstreamedgeofthestream'smixingzone,i.
e.
,theapplicablestreamwaterqualitycriteria[mg/L]COCconcentrationupstreamofthegroundwaterplumedischarge[mg/L]GWsourcedimensionperpendiculartoGWflowdirection[ft]GWsource(mixingzone)thickness[ft]Lateraldispersivity[ft]Verticaldispersivity[ft]Distancefromthedowngradientedgeofthegroundwatersourcetothestream[ft]Darcyvelocity[ft/day]SeealsoAppendixC,pagesC-3andC-4.
APPENDIXFMODELS/EQUATIONSFORESTIMATINGRISKSARBCA(Revision3)2017F-1APPENDIXFMODELS/EQUATIONSFORESTIMATINGRISKSThesymbolsusedintheequationspresentedinthisappendixfollowthefollowingthreesources:1.
ASTM,StandardGuideforRisk-BasedCorrectiveActionatPetroleumReleaseSites,1995,Designation:E-1739-95.
ASTM,100BarrHarborDr.
,WestConshohocken,PA19428.
2.
Mid-AtlanticRiskAssessmentUser'sGuide,May2013,http://www.
epa.
gov/reg3hwmd/risk/human/rb-concentration_table/usersguide.
htm.
3.
EnvironmentalQualityManagement,Inc.
,2004,User'sGuideforEvaluatingSubsurfaceVaporIntrusionintoBuildings,Durham,NC,preparedforUSEPA,OfficeofEmergencyandRemedialResponse,Washington,D.
C.
ARBCA(Revision3)2017F-2TableofContentPageDirectIngestionofGroundwaterF-4IngestionofSoilF-5DermalContactwithSoilF-6InhalationofVaporsandParticulatesfromSurficialSoilandConstructionSoilF-7Ingestionof,DermalContactwith,andInhalationofVaporsandParticulatesfromSurficialSoilandConstructionSoilF-8SubsurfaceSoilConcentrationsProtectiveofLeachingtoGroundwaterF-9LeachingFactorfromSubsurfaceSoiltoGroundwaterF-10SaturationConcentrationinSoilVaporandSoilF-11DomenicoModel:DilutionAttenuationFactor(DAF)intheSaturatedZoneF-12AllowableSoilandGroundwaterConcentrationforGroundwaterResourceProtectionF-13SchematicDescriptionofDomenico'sModelF-14StreamProtection:SurfaceWaterConcentrationattheEdgeoftheMixingZoneF-15APPENDIXFMODELS/EQUATIONSFORESTIMATINGRISKSARBCA(Revision3)2017F-2APPENDIXFMODELS/EQUATIONSFORESTIMATINGRISKSThesymbolsusedintheequationspresentedinthisappendixfollowthefollowingthreesources:1.
ASTM,StandardGuideforRisk-BasedCorrectiveActionatPetroleumReleaseSites,1995,Designation:E-1739-95.
ASTM,100BarrHarborDr.
,WestConshohocken,PA19428.
2.
Mid-AtlanticRiskAssessmentUser'sGuide,May2013,http://www.
epa.
gov/reg3hwmd/risk/human/rb-concentration_table/usersguide.
htm.
3.
EnvironmentalQualityManagement,Inc.
,2004,User'sGuideforEvaluatingSubsurfaceVaporIntrusionintoBuildings,Durham,NC,preparedforUSEPA,OfficeofEmergencyandRemedialResponse,Washington,D.
C.
ARBCA(Revision3)2017F-3TableofContentsPageDirectIngestionofGroundwaterF-4IngestionofSoilF-5DermalContactwithSoilF-6InhalationofVaporsandParticulatesfromSurficialSoilandConstructionSoilF-7Ingestionof,DermalContactwith,andInhalationofVaporsandParticulatesfromSurficialSoilandConstructionSoilF-8GroundwaterSourceConcentrationforGroundwaterResourceProtectionF-9LeachingFactorfromSubsurfaceSoiltoGroundwaterF-10SaturationConcentrationinSoilVaporandSoilF-11DomenicoModel:DilutionAttenuationFactor(DAF)intheSaturatedZoneF-12Soil&GroundwaterSourceConcentrationsatSentryWell&POEforGroundwaterResourceProtectionF-13SchematicDescriptionofDomenico'sModelF-14SurfaceWaterConcentrationattheEdgeoftheMixingZoneF-15ARBCA(Revision3)2017F-3ThetwoUSEPAvaporintrusiondocuments,AssessingandMitigatingtheVaporIntrusionPathwayfromSubsurfaceVaporSourcestoIndoorAirandAddressingPetroleumVaporIntrusionatLeakingUndergroundStorageTankSitesshouldbeutilizedastheprimaryreferencefortheIndoorandOutdoorVaporIntrusionpathwayequationsTocalculateriskatsitesduetothevaporintrusionpathway,itisoftenhelpfultousetheVaporIntrusionScreeningLevel(VISL)CalculatortocalculatetheriskduetoaspecificCOC.
Incertaincases,itmaybeappropriatetosumtheriskcalculatedfortheindividualconstituentscalculatedusingtheVISLCalculatortodeterminethecumulativeriskforthevaporintrusionpathway.
TheDepartmentrecommendstheuseofsoilgascollectedatanapproximatedepthof3ftbelowtheareaofconcern(i.
e.
,basement,slab,orcrawlspace)anduseofthe"SG_IA_calc"worksheet.
The"SG_IA_calc"worksheetallowstheusertoenterthescenario,riskinformation,soilgasconcentrations,andselectchemicalstocalculateindoorairconcentrationandindoorairriskassociatedwiththecontaminatedmedia.
The"GW_IA_calc"maybeusedtocalculatetheriskfromagroundwaterconcentration,butduetothemanyvariablesthattypicallyexistbetweenthegroundwatersurfaceandthebasement,slab,orcrawlspace,theDepartmentpreferstheuseofsoilgassamples.
PriortoevaluatingthevaporintrusionpathwayusingtheVISLCalculator,thefacilityshouldconsultwiththeDepartment.
ARBCA(Revision3)2017F-4DIRECTINGESTIONOFGROUNDWATERCarcinogenicEffects365ATBWSFIREFEDC=IELCRcowwingw******Non-carcinogenicEffectsoncwwingwRfD365ATBWIREFEDC=HQ******Source:U.
S.
EPA,RAGS,Vol.
I,1989,p.
6-35where:IELCRingw=Individual'sexcesslifetimecancerriskortheincreasedchanceofdevelopingcanceroveralifetimeduetoexposuretoachemicalindrinkingwater[-]HQingw=Hazardquotientforachemicalindrinkingwater[-]Cw=Contaminantconcentrationindrinkingwater[mg/L]BW=Bodyweight[kg]ATc=Averagingtimeforcarcinogens[year]ATnc=Averagingtimefornon-carcinogens[year]ED=Exposureduration[year]EF=Exposurefrequency[day/year]IRw=Wateringestionrate[L/day]SFo=Chemical-specificoralcancerslopeorpotencyfactor[(mg/kg-day)-1]RfDo=Chemical-specificoralreferencedose[mg/kg-day]365=ConvertsATc,ATncinyearstodays[day/year]ARBCA(Revision3)2017F-5INGESTIONOFSOIL(CHILDANDADULTRESIDENT,COMMERCIALWORKER,ANDCONSTRUCTIONWORKER)CarcinogenicEffects365106********=ATBWSFABSIREFEDCIELCRcoGIsoilsingsNon-carcinogenicEffectsoncGIsoilsingsRfDATBWABSIREFEDCHQ********=365106Source:U.
S.
EPA,RAGSVol.
IPartA,1989where,IELCRings=Individual'sexcesslifetimecancerriskortheincreasedchanceofdevelopingcanceroveralifetimeduetoexposuretoachemicalinsoilthroughingestion[-]HQings=Hazardquotientforachemicalinsoil[-]Cs=Contaminantconcentrationinsoil[mg/kg]BW=Bodyweight[kg]ATc=Averagingtimeforcarcinogens[year]ATnc=Averagingtimefornon-carcinogens[year]ED=Exposureduration[year]EF=Exposurefrequency[day/year]IRsoil=Soilingestionrate[mg/day]ABSGI=Oralabsorptionfraction[-]SFo=Chemical-specificoralcancerslopefactor[(mg/kg-day)-1]RfDo=Chemical-specificoralreferencedose[mg/kg-day]365=ConvertsATc,ATncinyearstodays[day/year]10-6=Convertsmgtokg[mg/kg]ARBCA(Revision3)2017F-6DERMALCONTACTWITHSOIL(CHILDANDADULTRESIDENT,COMMERCIALWORKER,ANDCONSTRUCTIONWORKER)CarcinogenicEffects365106**********=ATBWSFABSAFEVSAEFEDCIELCRcABSdsoilsoilsdsNon-carcinogenicEffectsABSncdsoilsoilsdsRfDATBWABSAFEVSAEFEDCHQ**********=365106Source:U.
S.
EPA,RAGSVol.
IPartE,2004,Page3-9where,IELCRds=Individual'sexcesslifetimecancerriskortheincreasedchanceofdevelopingcanceroveralifetimeduetoexposuretoachemicalinsoilthroughdermalabsorption[-]HQds=Hazardquotientforachemicalinsoilduetodermalabsorption[-]Cs=Contaminantconcentrationinsoil[mg/kg]BW=Bodyweight[kg]ATc=Averagingtimeforcarcinogens[year]ATnc=Averagingtimefornon-carcinogens[year]ED=Exposureduration[year]EF=Exposurefrequency[day/year]SAsoil=Skinsurfaceareaavailableforcontactwithsoil[cm2]EVsoil=Eventfrequency[event/day]AF=Soiltoskinadherencefactor[mg/cm2-event]ABSd=Chemical-specificdermalabsorptionfraction[-]SFABS=Chemical-specificdermalcancerslopefactor[(mg/kg-day)-1]RfDABS=Chemical-specificdermalreferencedose[mg/kg-day]365=ConvertsATc,ATncinyearstodays[day/year]10-6=Convertsmgtokg[kg/mg]ARBCA(Revision3)2017F-7INHALATIONOFVAPORSANDPARTICULATESFROMSURFICIALSOILANDCONSTRUCTIONSOIL(CHILDANDADULTRESIDENT,COMMERCIALWORKER,ANDCONSTRUCTIONWORKER)Carcinogeniceffects()243651000***+*****=cpsoutsoilinhsATVFVFIURETEFEDCIELCRNon-carcinogeniceffects()RfCATVFVFETEFEDCHQncpsoutsoilinhs***+****=24365Source:U.
S.
EPARegionalScreeningTable–User'sGuide,May,2013where:IELCRinhs=Individual'sexcesslifetimecancerriskortheincreasedchanceofdevelopingcanceroveralifetimeduetoexposuretovaporsandparticulatesfromsoil[-]HQinhs=Hazardquotientduetoexposuretovaporsandparticulatesfromsoil[-]Csoil=Contaminantconcentrationinsoil[mg/kg]ATc=Averagingtimeforcarcinogens[year]ATnc=Averagingtimefornon-carcinogens[year]ED=Exposureduration[year]EF=Exposurefrequency[day/year]ETout=OutdoorExposuretime[hr/day]IUR=Chemical-specificinhalationunitrisk[(ug/m3)-1]RfC=Chemical-specificinhalationreferenceconcentration[mg/m3]365=ConvertsATc,ATncinyearstodays[day/year]24=Convertsdaystohours[hr/day]1000=Convertsmicrogramstomilligrams[g/mg]VFs=Volatilizationfactorforvaporemissionsfromsoil[(mg/m3-air)/(mg/kg-soil)]VFp=Volatilizationfactorforparticulateemissionsfromsoil[(mg/m3-air)/(mg/kg-soil)]Note:Thedepthtosurficialsoilforaconstructionworkerisuptothetypicalconstructiondepth.
ARBCA(Revision3)2017F-8INGESTIONOF,DERMALCONTACTWITH,ANDINHALATIONOFVAPORSANDPARTICULATESFROMSURFICIALSOILANDCONSTRUCTIONSOIL(CHILDANDADULTRESIDENT,COMMERCIALWORKER,ANDCONSTRUCTIONWORKER)CarcinogeniceffectsinhsdsingssIELCRIELCRIELCRIELCR++=Non-carcinogeniceffectsinhsdsingssHQHQHQHI++=where,IELCRs=Cumulativeindividualexcesslifetimecancerriskortheincreasedchanceofdevelopingcanceroveralifetimeduetoexposuretoachemicalinsoil[-]HIs=Hazardindexforachemicalinsoil[-]IELCRings=Individual'sexcesslifetimecancerriskforachemicalbyingestionofachemicalinsoil[-]IELCRds=Individual'sexcesslifetimecancerriskforachemicalbydermalexposuretoachemicalinsoil[-]IELCRinhs=Individual'sexcesslifetimecancerriskforachemicalbyinhalationofachemicalinsoil[-]HQings=HQforachemicalbyingestionofachemicalinsoil[-]HQds=HQforachemicalbydermalexposuretoachemicalinsoil[-]HQinhs=HQforachemicalbyinhalationofachemicalinsoil[-]Source:U.
S.
EPARegionalScreeningTable–User'sGuide,May2013ARBCA(Revision3)2017F-9GROUNDWATERSOURCECONCENTRATIONFORGROUNDWATERRESOURCEPROTECTIONSWsswLFCC*=where:Cw=Groundwatersourceconcentrationforgroundwaterresourceprotection[mg/L-water]Css=Subsurfacesoilconcentrationforgroundwaterresourceprotection[mg/kg-soil]LFSW=LeachingFactor(fromsubsurfacesoiltogroundwater)[(mg/L-H2O)/(mg/kg-soil)]Source:ASTM,1995,E1739-95GroundsurfaceVadosezoneWaterTableDissolvedcontaminantsLeachateWSubsurfaceimpactedsoilsInfiltration(I)δgwUgwARBCA(Revision3)2017F-10LEACHINGFACTORFROMSUBSURFACESOILTOGROUNDWATER*+**++=IWUHKLFgwgwasssvwssSWδθρθρ1][Source:ASTM,1995,E1739-95where:LFSW=Leachingfactorfromsubsurfacesoiltogroundwater[(mg/L-H2O)/(mg/kg-soil)]ρs=Drysoilbulkdensity[g-soil/cm3-soil]θws=Volumetricwatercontentinvadosezonesoils[cm3-H2O/cm3-soil]Ksv=focv*Koc=Chemical-specificsoil-watersorptioncoefficientfortheunsaturatedzone[cm3-H2O/g-soil]focv=Fractionalorganiccarboncontentintheunsaturatedzone[(g-C)/(g-soil)]H=Chemical-specificHenry'sLawconstant[(L-H2O)/(L-air)]θas=Volumetricaircontentinthevadosezonesoils[cm3-air/cm3-soil]Ugw=GroundwaterDarcyVelocity[cm/year]δgw=Groundwatermixingzonethickness[cm]I=Infiltrationrateofwaterthroughsoil[cm/year]W=Lengthofsourceareaparalleltogroundwaterflow[cm]ARBCA(Revision3)2017F-11SATURATIONCONCENTRATIONINSOILVAPORANDSOILCvSAT:Soilvaporconcentrationatwhichdissolvedphasebecomessaturated[mg/m3-air]CsSAT:Soilconcentrationatwhichdissolvedporewaterandvaporphasesbecomesaturated[(mg/kg-soil)]SingleComponent610***=TRMWPCsSATvMultipleComponents610****=TRMWPxCisiiSATvwhere,CvSAT=Soilvaporconcentrationatwhichvaporphasebecomesaturated[mg/m3-air]Ps=Saturatedvaporpressure[atm]Pis=Effectivevaporpressureofcomponentiinwater=xi*Ps[atm]R=Idealgasconstant[0.
08206atmL/molK]T=Temperature[K]Sei=Effectivesolubilityofcomponentiinwater=xi*S[mg/L-water]xi=Molefractionofcomponenti=(wi*MWavg)/MWi[-]wi=Weightfractionofcomponenti[-]MWavg=Averagemolecularweightofmixture[g/mole]MWi=Molecularweightofcomponenti[g/mole]ρs=Vadosezonedrysoilbulkdensity[g-soil/cm3-soil]106=Conversionfactor[(g/L)/(mg/m3)]Source:ASTM,1995,E1739-95SingleComponent][ρθθρssvwsasssatsKHSC++**=MultipleComponents][ρθθρssvwsasseiSATsKHSC*++**=where:CsSAT=Soilconcentrationatwhichdissolvedporewaterandvaporphasesbecomesaturated[(mg/kg-soil)]S=Purecomponentsolubilityinwater[mg/L-water]Sei=Effectivesolubilityofcomponentiinwater=xi*S[mg/L-water]xi=Molefractionofcomponenti=(wi*MWavg)/MWi[-]wi=Weightfractionofcomponenti[-]MWavg=Averagemolecularweightofmixture[g/mole]MWi=Molecularweightofcomponenti[g/mole]ρs=Vadosezonedrysoilbulkdensity[g-soil/cm3-soil]H=Chemical-specificHenry'sLawconstant[L-water/L-air]θas=Volumetricaircontentinthevadosezonesoils[cm3-air/cm3-soil]θws=Volumetricwatercontentinvadosezonesoils[cm3-water/cm3-soil]Ksv=focv*Kocv=Chemical-specificsoil-watersorptioncoefficientinvadosezone[cm3-water/g-soil]focv=Fractionorganiccarboninvadosezone[g-C/g-soil]Source:ASTM,1995,E1739-95ARBCA(Revision3)2017F-12DOMENICOMODEL:DILUTIONATTENUATIONFACTOR(DAF)INTHESATURATEDZONEDomenicomodelformulti-dimensionaltransportwithdecayandcontinuoussource:()*****x2-zerf-x2+zerfx2Y/2-yerf-x2Y/2+yerftvvvtxerfcvxexpCtzyxCzgwzgwyyoαδαδααααλαλα24+14+1-12)8/1(=),,,(xxxxwhere:C=Dissolved-phaseconcentration[mg/L]Co=Dissolved-phaseconcentrationatthesource(atx=y,0≤z≤δgw)[mg/L]v=Retardedseepagevelocity[cm/year]λ=Firstorderdecayrate[1/year]αx=Longitudinaldispersivity[cm]αy=Lateraldispersivity[cm]αz=Verticaldispersivity[cm]x,y,z=Spatialcoordinates[cm]t=Time[year]x=Distancealongthecenterlinefromthedowngradientedgeofdissolved-plumesourcezoneorsourcewell[cm]Y=Widthofsoilsourceperpendiculartothegroundwaterflowdirection[cm]δgw=Groundwatermixingzonethickness[cm]DAF=Co/C(x)Source:Domenico,P.
A.
andF.
W.
Schwartz,1990,PhysicalandChemicalHydrogeology.
JohnWileyandSons,NY,824p.
(Eqn.
17.
21)Atthecenterline,forsteady-state(afteralongtime)theDAFcanbeobtainedbysettingy=0,z=0,andx<31,whereY=Sw,δgw=Sd,v=u,andCo=CsourceAtthecenterline,forsteady-state,theDAFwithdecaycanbecalculatedusingEquation(1).
InEquation(1),theretardedseepagevelocity(v)iscalculatedas:v=(Ki)/(RsθTS)where:K=Hydraulicconductivity[cm/year]i=Hydraulicgradient[--]θTS=Totalporosityinthesaturatedzone[cm3/cm3-soil]Rs=Retardationfactorinthesaturatedzone[--]ARBCA(Revision3)2017F-13SOILANDGROUNDWATERSOURCECONCENTRATIONSATSENTRYWELLANDPOEFORGROUNDWATERRESOURCEPROTECTIONGroundwaterconcentrationatthesentrywell=GroundwatersourceconcentrationattheSWDAFPOE*GroundwaterconcentrationatthePOE=GroundwatersourceconcentrationatthePOEDAFPOE*where:POE=PointofexposureSW=SentrywellDAFPOE=DilutionAttenuationFactorbetweenthepointofexposureandthesourceDAFSW=DilutionAttenuationFactorbetweenthesentrywellandthesourceAdditionalrelationshipsusedinthecalculationofallowablesoilandgroundwaterconcentrationwithchemicaldegradation:LifeHalf0.
693ratedecayorderFirst=+=*θρTSsssssKR1)(zonesaturatedintheOrganicsforFactornRetardatioKss=focs*Koc+=*θρTSdsssKR1)(zonesaturatedintheMetalsforFactornRetardatiowhere:ρss=Saturatedzonesoilbulkdensity[g-soil/cm3-soil]Kss=Chemical-specificsoil-watersorptioncoefficientinthesaturatedzone[cm3-H2O/g-soil]Kd=Chemical-specificsoil-waterdistributioncoefficientformetalsinthesaturatedzone[mL/g]θTS=Totalporosityinthesaturatedzone[cm3/cm3-soil]focs=Fractionalorganiccarboncontentinthesaturatedzone[g-C/g-Soil]ARBCA(Revision3)2017F-14SCHEMATICDESCRIPTIONOFDOMENICO'SMODELSoilSourceAreaLeachateYzyxSECTIONUgwYGroundwaterSource(GroundwaterMixingZone)GroundwaterSource(GroundwaterMixingZone)UgwWWCoWaterTableGroundSurfaceCoPLANVadozeZoneDowngradientEdgeoftheGroundwaterSource*Note:(*Assumesonlyverticalleaching,i.
e.
,thereisnohorizontalspreadingintheunsaturatedzone.
)δgwARBCA(Revision3)2017F-15SURFACEWATERCONCENTRATIONATTHEEDGEOFTHEMIXINGZONE()swgwswsugwgwstrQQQCQCC++=()()gwsyszgwUXYXZQ*+*+=αα2where,QgwQswCstrCgwCsuYZαyαzXsUgw===========Impactedgroundwaterdischargeintothestream[ft3/day]Streamflowupstreamofthepointofgroundwaterdischarge(streamflowrate)[ft3/day)Concentrationatthedownstreamedgeofthestream'smixingzone,i.
e.
,theapplicablestreamwaterqualitycriteria[mg/L]Groundwaterconcentrationatthepointofdischargeintothestream[mg/L]COCconcentrationupstreamofthegroundwaterplumedischarge[mg/L]GWsourcedimensionperpendiculartoGWflowdirection[ft]GWsource(mixingzone)thickness[ft]Lateraldispersivity[ft]Verticaldispersivity[ft]Distancefromthedowngradientedgeofthegroundwatersourcetothestream[ft]Darcyvelocity[ft/day]ARBCA(Revision3)2017G-1APPENDIXGDEVELOPMENTOFASITE-SPECIFICBIODECAYRATEARBCA(Revision3)2017G-2APPENDIXGDEVELOPMENTOFASITE-SPECIFICBIODECAYRATEG.
1BACKGROUNDTheapplicationoftheARBCAprocessatpetroleum-impactedsitesinAlabamaultimatelyresultsinremedialand/orrisk-managementdecisionsbasedonthecumulativeriskdeterminedforallofthecompleteroutesofexposure.
Atallsites,ifthecumulativeriskisexceeded,theARBCAprocesssuggeststhedevelopmentofRBTLsprotectiveofalldirectandindirectpathways.
Thesetargetlevelsmaybedevelopedusingsite-specificbiodegradationratesprovidedthatthereissufficientsite-specificevidencetoconfirmthatbiodegradationisoccurringandthatsufficientdataisavailabletoestimateasite-specificbiodegradationrate.
Thisappendixprovidesthemethodologyfordeterminingsite-specificbiodecayrates.
Pleasenotethatthetermsbiodecayandbiodegradationareusedinterchangeablyinthisdocument.
TheuseofbiodecayisnotallowedinanRM-1Evaluation.
Thisappendixcontainsguidanceonthedevelopmentofasite-specificbiodegradationrateforuseinestimatingsoilandgroundwaterRBTLsprotectiveofgroundwaterresources.
Theestimationofsite-specificbiodegradationratesisanevolvingscienceandtheARBCAEvaluatorisencouragedtoreviewpubliclyavailableliteratureforcurrentapproachestoestimatesite-specificbiodegradationrates.
Thesoilandgroundwaterconcentrationsprotectiveofthegroundwaterresourcecanbeestimatedusingeitheroftwoways.
Onewayiswithoutbiodegradation-usingadilutionattenuationfactor(DAF)inthesaturatedzonethatdoesnotconsiderbiodegradationofthechemicalofconcern.
Thesecondwayiswithbiodegradation,whichallowstheuseofasaturated-zoneDAFthatincorporatesuser-specified,site-specific,chemicalspecific,biodegradationrates.
ThechoicetoutilizebiodecayincalculatingGroundwaterResourceProtectionRBTLsmustbejustified.
Atasitewithlittletonoevidenceofbiodegradation,theARBCAEvaluatorshouldnotusethisoptiontocalculatetheconcentrationsprotectiveofthegroundwaterresource.
Whenproperlyjustified,asite-specificbiodecayrateisanappropriatechoice.
ARBCA(Revision3)2017G-3TheDepartmentwillacceptARBCAEvaluationsusingthebiodegradationrateonlyif(1)adequateevidenceispresentedthatindicatesthatbiodegradationisoccurringatthesite,and(2)thecalculatedbiodegradationrateistechnicallycorrect.
EvenatsiteswheretheARBCAEvaluatorproposestheapplicationofthebiodegradationrate,anevaluationwithouttheapplicationofthebiodegradationrateshouldbepresentedintheeventtheevaluationutilizingthebiodegradationrateisnotacceptable.
Thefollowingtwosectionscontaininformationandproceduresforapplyingasite-specificbiodegradationrate.
Thefirstsectioncontainsinformationonhowthesitedataitselfmustbeevaluatedtodetermineifbiodecayisasignificantprocessatthesite.
Thesecondsectioncontainsaproceduretocalculatethesite-specificbiodecayrate.
SectionG.
2presentsadiscussionofthetypeofinformationthatshouldbeevaluatedtodemonstratethatbiodegradationisoccurringatthesite.
SectionG.
3discussesthemethodusedtocalculateasite-specificbiodecayrateforuseintheequationsinAppendixEonpageE-14.
G.
2HOWTOJUSTIFYNATURALATTENUATIONWITHBIODEGRADATIONSeveralparameters(hydrocarbons,electronacceptors,microorganisms,nutrients,andcarbondioxide)maybemeasuredtodemonstratetheoccurrenceofbiodegradation.
Thesemeasurementsaretypicallydividedintothreetiers,or"linesofevidence",todemonstrateNaturalAttenuation(NA).
Theseinclude:(i)primary,(ii)secondary,and(iii)tertiarylinesofevidence.
Datacollectedundereachlineofevidencecanbeevaluatedqualitativelyorquantitativelyasdiscussedinthefollowingsections.
AdiscussionoftheinterpretationofthemostcommonprimaryandsecondarylinesofevidencefortheoccurrenceofnaturalattenuationisgivenintheASTMStandardonthetopic(1999).
G.
2.
1PrimaryLinesofEvidenceTheprimarylineofevidencefortheoccurrenceofNA,notspecificallybiodegradation,isdatademonstratingthelossofchemicalmassthroughevaluationofmeasuredpetroleumhydrocarbonconcentrations.
OfallthemethodsavailabletodemonstratetheoccurrenceofNA,thisisperhapsthesimplestandmostusefultodemonstratereductioninsite-specificrisks.
Site-specificapplicationoftheprimarylinesofevidencerequires:(i)anadequateARBCA(Revision3)2017G-4numberofcorrectlyinstalledsamplingpoints(monitoringwells),(ii)adequatedurationandfrequencyofchemicaldatacollectedfromthesepoints,and(iii)properevaluationofthisdata.
Althoughtheprimarylineofevidencecanshowwhetheracontaminantplumeisattenuatingbasedonchemicalconcentrations,itdoesnotdemonstratewhetherthedecreaseinconcentrations,orattenuation,isduetodestructivemechanisms,e.
g.
,biodegradationordilution.
Asecondarylineofevidenceisnecessarytodeterminewhetherthedecreaseisduetobiodegradation.
Statisticaltestsmaybeusedtoestablishandcharacterizethetrendinconcentrationsovertime.
Thesetestscanbeusedtotestanullhypothesisvs.
analternativehypothesis.
Anexampleofanullhypothesisisthatthereisnotrendintheconcentrationsvs.
distance.
Thealternatehypothesisisthatthereisadownwardorupwardtrend.
Applicationofastatisticaltestwouldthenresultintheacceptanceorrejectionofthenullhypothesisataspecifiedlevelofsignificance.
Iftheconcentrationvs.
timeorconcentrationvs.
distancedataindicatesadecreasingorincreasingtrend,aregressionanalysismaybeusedtoestimatetheslopeofthebest-fitlineanddeterminewhetherornotthetrendissignificant.
Theslopeofthebest-fitlineforthedatacanbeusedtoestimatethenaturalattenuationorthebiodegradationrate.
Foradditionalinformationonregressionanalysis,refertoanystatisticstextbook.
G.
2.
2SecondaryLinesofEvidenceSecondarylinesofevidenceoftheoccurrenceofbiodegradationrefertothemeasurementsofelectronacceptorsandproductsofmetabolismandtheircomparisonwithconcentrationsintheunimpactedareaoftheaquifer,wherenobiodegradationactivitywouldbeexpectedtooccur.
Theseparametersarealsoreferredtoasgeochemicalindicatorsorintrinsicindicatorsofbiodegradation.
Parametersthataretypicallymeasuredinthefieldinclude:(i)dissolvedoxygen,(ii)carbondioxide,(iii)dissolvednitrates,(iv)manganese,(v)ferrousiron,(vi)sulfate,and(vii)methane.
Theseparametersshouldbemeasuredatupgradientlocations,insidetheplumenearthesource,andinthedowngradientlocations.
ThedistributionandoccurrenceoftheseparametersthatisindicativeofbiodegradationisdiscussedintheASTMstandardonthetopic(1999).
ARBCA(Revision3)2017G-5Aschemicalsareconsumedbymicroorganisms,thereisacorrespondingdecreaseofthecompoundsthatserveaselectronacceptors.
Thus,theconcentrationofthesecompoundsdecreasesintheportionoftheplumewherebiodegradationisoccurring.
Forexample,underaerobicbiodegradation,theconcentrationofoxygenwoulddecrease,assumingoxygenisnotbeingaddedtotheplume.
Similarly,underanaerobicconditions,adepletionofnitrate,ferric(III)iron,sulfate,andcarbondioxidemaybeanticipated.
Itshouldbenotedthatthesecondarylinesofevidencedemonstratetheoccurrenceofbiodegradationonly.
ItdoesnotprovideanydataontheoccurrenceofotherNAprocesses.
G.
2.
3TertiaryorOptionalLinesofEvidenceTertiaryoroptionallinesofevidenceinvolvetheperformanceofmicrobiologicalstudiessuchastheidentificationandcountingofthemicroorganismspresentintheformation.
Thus,theobjectivesofthemeasurementofsecondaryandtertiarylinesofevidencearesimilar.
Althoughpetroleum-degradingmicrobesareubiquitousinsoilandgroundwater,microbesatasitemaynotbeabletodegradecertaincompounds,forexampleMTBE.
Intheportionoftheplumewherebiodegradationisoccurring,theratioofpetroleumdegradingbacteriatothetotalnumberofbacteriaisexpectedtobehigher.
Tertiarylinesofevidenceareseldomrequiredatpetroleumhydrocarbonimpactedsites,hence,theyarenotdiscussedfurtherhere.
G.
2.
4DocumentationofBiodegradationintheARBCAReportIfthesecondaryortertiary(rarelymeasured)linesofevidenceindicatethatbiodegradationisoccurring,ataminimum,thefollowinginformationshouldbesubmittedasjustification:1.
Tableofhistoricalintrinsicindicatorsofbiodegradation2.
Graphsofhistoricalvaluesofintrinsicindicatorsofbiodegradationplottedastimevs.
concentrationperwell3.
Aseriesofcontourmap(s)illustratingtrendsofpertinentindicatorsofbiodegradationovertime4.
IncludecomparisonsofsiteconcentrationswithRBTLswithandwithoutbiodegradation5.
Tableofdecayrateinput/outputvalues6.
Tableofcalculatedattenuationandbiodecayratesincludingrangesandaverages7.
Copyofthecomputationalsoftwareinputandoutput,ifsoftwarewasusedARBCA(Revision3)2017G-6G.
3ESTIMATIONOFSITE-SPECIFICCHEMICALHALF-LIVESThefollowingstep-by-stepproceduremaybeusedtodevelopasite-specificbiodegradationrateorhalflifeforuseintheGroundwaterResourceProtectionEvaluation.
Note,theprocedureshouldberepeatedforeachchemicalofconcernthatexceedsanyGroundwaterResourceProtectionorSurfaceWaterProtectionsite-specifictargetlevel(SSTL).
ItisnotnecessarytocomputehalflivesforchemicalsthatdonotexceedGroundwaterResourceProtectionorSurfaceWaterProtectionSSTLs.
Step1:Determinethegroundwaterflowdirectionsbasedonthewaterlevelmeasurementsforeachmonitoringevent.
Step2:Foreachmonitoringevent,identifythewellslocatedalongthedirectionsofflow,i.
e.
,alongtheplumecenterline(s).
Note,sincetheflowdirectionmayvary,differentwellsmaybeusedfordifferentmonitoringevents.
Step3:Tabulatetheconcentrationsofthechemicalsofconcernandcalculatethenaturallogoftheconcentrations.
Step4:Foreachmonitoringevent,plotthenaturallogoftheconcentrationsontheY-axisandthedistancealongtheX-axis.
Aseparateplotshouldbemadeforeachevent.
Step5:Foreachplot,calculatetheslopeofthebest-fitlineandtestwhetherornotthenullhypothesiscanberejectedatthe.
05levelofsignificance.
Thenullhypothesisinthiscaseisthattheslopeoftheregressionlineiszero,indicatingnorelationshipbetweenthenaturallogofconcentrationanddistance.
Step6:Estimatetheretardedgroundwaterseepagevelocityandthelongitudinaldispersivity.
Step7:Multiplytheslopeofthebest-fitlinecalculatedinStep5bytheseepagevelocitytoestimatek(seeBuscheckandAlcantar,1995).
TheresultwouldrepresenttheoverallNArate.
ThisNAraterepresentsthereductioninconcentrationduetothecombinedinfluenceofthevariousNAprocessesmentionedinSectionG.
2.
NotethatthisoverallNArate(k)shouldnotbeconfusedwiththebiodegradationrate(λ)thatisaninputtotheGroundwaterResourceProtectionmodelusedinARBCA(seepageE-14).
ARBCA(Revision3)2017G-7Step8:Estimatethebiodegradationrate(λ)usingEquationI.
1derivedbyBuscheckandAlcantar(1995,equation9)basedonthesolutionoftheone-dimensionaltransportequationwithbiodegradation.
(I.
1)Where:λ=Biodegradationrate(1/year)αx=Longitudinaldispersivity(x/10)(cm)x=DistancefromthesourcetothePOE(cm)k=AttenuationRate(unitless)v=Seepagevelocity(retarded)(cm/year)(Kxi)/(θTSxRs)Rs=+=*θρTSsssssKR1)(zonesaturatedintheOrganicsforFactornRetardatioKss=focs*KocRs=+=*θρTSdsssKR1)(zonesaturatedtheinforMetalsFactornRetardatiowhere:ρss=Saturatedzonesoilbulkdensity(g-soil/cm3-soil)Kss=Chemical-specificsoil-watersorptioncoefficientinthesaturatedzone(cm3-H2O/g-soil)Kd=Chemical-specificsoil-waterdistributioncoefficientformetalsinthesaturatedzone(mL/g)θTS=Totalporosityinthesaturatedzone(cm3/cm3-soil)Steps1through8shouldbecompletedforeachrelevantgroundwatermonitoringevent,forexample,allthosewithintheperiodoverwhichrepresentativeconcentrationshavebeencalculated.
TheresultsshouldbepresentedasarangeofNAandbiodecayrates,kandλ,respectively.
ThelatterisusedasaninputtotheDomenicomodeltoestimatethesaturatedzonedilution-attenuationfactor.
Duetoconfoundingfactorssuchasseasonalvariationsingroundwatervelocity,water-levelfluctuations,errorsinsamplingandanalysismethods,theNAandbiodegradationratesmayvarysignificantlybetweenevents.
Therefore,itisbesttopresenttherangeaswellastheaveragerates.
Professionaljudgementmustbeusedtodeterminethemostrepresentativeλforuseinthecalculationofthechemicalhalf-lives.
()[]+=12142vkααvλxxARBCA(Revision3)2017G-8Step9:Calculateahalf-lifeforeachchemicalusingtheequation,λ=.
693/half-life.
λshouldbewrittenas1/daysforthiscalculation.
EquationI.
1occasionallyproducesnegativehalf-lives.
Negativehalf-livesareartifactualandshouldnotbeused.
Youmayaveragethehalf-livesforonechemical.
Utilizethederivedsite-specifichalf-livestocalculatetheGroundwaterResourceProtectionwithBiodegradationRBTLsforsoilandgroundwater.
Thehalf-livesforeachchemicalofconcernthatexceedsatargetlevelwithoutbiodegradationshouldbestatedinthereport.
Usingtheaveragehalf-lifeforaCOC(notusinganynegativehalf-lives),theARBCAEvaluatorshouldcomputenewDAFsandnewsoilandgroundwaterconcentrationstomeetinthesourceareaandinanysentrywellsthatexceededSSTLswithoutbiodegradation.
ThenewRBTLsshouldbestatedinthereport.
Forcomparison,thecorrespondingRBTLswithoutbiodegradationshouldalsobelisted.
G.
4REFERENCESASTM,1999,DesignationE1943-98StandardGuideforRemediationofGroundWaterbyNaturalAttenuationatPetroleumReleaseSites,in:ASTMStandardsonAssessmentandRemediationofPetroleumReleaseSites,ASTMCommitteeE-50onEnvironmentalAssessment,AmericanSocietyforTestingandMaterials,100BarrHarborDrive,WestConshohocken,Pennsylvania,19428-2959,pages82-123.
Buscheck,T.
E.
,andC.
M.
Alcantar,1995.
RegressionTechniquesandAnalyticalSolutionstoDemonstrateIntrinsicBioremediation,inHinchee,R.
E.
,J.
T.
Wilson,andD.
C.
Downey,editors,1995,IntrinsicBioremediation,BattellePress,Columbus,Ohio,pages109-116.