PRZMGW:-Implementation and Case StudiesPresentation to theEnvironmental Modeling Public MeetingMarch 19 2013March19,2013Reuben BarisU S EPA Office of Pesticide ProgramsU.S.EPA,OfficeofPesticidePrograms,Environmental Fate and Effects Division1Presentation OutlinePresentationOutline•Purpose•Background and Milestones•Implementation of PRZMGW in OPPImplementationofPRZM-GWinOPP•One year evaluation period•Case Studies2Purpose•N-methyl Carbamate Cumulative assessment–Groundwater modeling approach was developed torefine Tier I estimates•Provide efficient refinements of Tier I estimates•Provide healthprotective estimatedconcentrations for vulnerable private wells•Advance the scienceAdvancethescience•Address SAP comments on current Tier Imodeling approach for groundwatermodelingapproachforgroundwater3Background: NAFTA ProjectBackground:NAFTAProject•Developed a harmonized conceptual modelDevelopedaharmonizedconceptualmodel•Reviewed 19 models•Intensel e al ated PRZM LEACHM andIntenselyevaluatedPRZM,LEACHM,andPEARLC l d d th t PRZM i b t f NAFTA t•ConcludedthatPRZMisbestforNAFTApartners•Evaluated PRZM-GW with monitoring data•Completed final report and harmonized guidancedocuments4Milestones•February 2005 SAP•A t 2005 SAPAugust2005SAP–Proposed refined GW modeling approach•2006 PRZM-GW used in N-methyl carbamatecumulative assessment•2006-2012 NAFTA Project–Harmonized GW modelingaroach with PMRApp•January 2013 implementation5Expectations•Tier I screening level estimates may be higherTierIscreeninglevelestimatesmaybehigherthan previous GW concentrations•Fewer chemicals will pass the initial screenFewerchemicalswillpasstheinitialscreen•Tier II refinements based on actual practicesdd i kmayaress riskconcerns•Spatial refinements focus on areas vulnerableto GW contamination (soils, weather, aquiferdepth)6NAFTA Conceptual ModelPotable wellDepth toifrDecliningaerobicdegradationwith depth1 mHydrolysisor otherrelevantaquiferWellWater Tableprocessesbelow 1mScreenLength7Theconceptualmodelrepresentsknowndrinkingwatersources(i.e.,thereisanidentifiablepopulationthatusesvulnerablegroundwaterwellsassourcedrinkingwater)Standard Scenarios Locations8Implementation Strategy•One year evaluation periodImplementationStrategy•Use PRZM-GW as Tier 1 and Tier 2 tool•Continue toreport SCIGROW 2 3 as part of theContinuetoreportSCI-GROW2.3aspartoftheTier 1 analysis during a 1 year evaluation period•Recommend the highest DW concentrations forTier 19Tier1Tier 2 Refinement StrategiesTier2RefinementStrategies•Sensitivity analysisSensitivityanalysis–Usage info from BEAD and/or FOCUS meetingsImpact of well setbacks–mpactofwellsetbacks–Fate inputs (e.g., half-life, Koc, subsurfacedegradation)•Modeling additional scenariodi l di f•Exposuredurations relevant toduration ofconcern (e.g., annual, 90-day, time series data,)etc.10Evaluation Period•Collect data on refinements and outcomes–How often do we have to refine?Howoftendowehavetorefine?–What refinements are effective?–Risk assessment and management outcomes?•What is being tracked?Ti I t ti (SG PRZM)–TierIconcentration(SGorPRZM)–Inputs–Reported concentration and scenario–Maximum concentration from monitoring (whereavailable)–Refinements Tier II concentration and how theRefinements,TierIIconcentration,andhowtherefinement(s) impacted the assessment11Case Studies•Three chemicals: moderately persistent toCaseStudiesThreechemicals:moderatelypersistenttopersistent•Stable to hydrolysisStabletohydrolysis•Moderately mobile (Koc’s range from 392-1730)•Refinements were explored12Chemical 1Chemical1•Low throughputs for 30-year simulation•Ran extended weather file for 100 yearsl db kh h( )13•Delayedbreakthrough(~88 years)•Scenario: WisconsinChemical 1 ContinuedChemical1Continued•15 years of consecutive applicationsPeriodofapplication14Chemical 2Chemical2•Reduce number of # of applications to 1/yearReducenumberof#ofapplicationsto1/year•Increasing organic carbon content in the toplayer(s) of the soil increased hold up in the top15layer(s)ofthesoilincreasedholdupinthetopmeter of the soil profileChemical 316Questions?17Chem1 Chem2 Chem3Applicationrate(lbsa.i./A;#offapplications)0.022(2)0.08(1)0.75(1)d lblblblHyroysisStae Stae StaeAerobicSoilMetabolism 1730days 1298days†392.4days†,‡Sorptioncoefficient Koc=1760L/goc Kfoc=481L/goc 336L/gocPeakTierIconcentration8.8μg/22.4μg/L 107μg/Lconcentration2L(PRZM‐GW)22.4μg/L(PRZM‐GW)107μg/L(PRZM‐GW)Post‐breakthroughAverageconcentration7.2μg/L(approx.80years)19.3μg/L(approx.26years)94.2μg/LSimulationAverage 2.11μg/L(100years)5.5μg/L(30years)75.8μg/L(30years)Drinkingwaterconcern? No Yes Yes,cancerendpointRefinementsNA1)Reducednumber1)RefinedhydrolysisRefinementsReducedofapplicationsonlabel;2) refinementsrelatedtosoil1)Refinedhydrolysisdegradationrate;2) removed3xuncertaintyfactorfromASMrelatedtosoiltyperestrictionsfromASM18TierIIpeakconcentration NA 19.4μg/L 1)65.6μg/L,51.3μg/L2)32.6μg/L,26μg/LImplementation:TierIProcessDiagramRun the six standardRunthesixstandardscenarios using PRZMGW 30 year simulationIf a standard scenariodoesn’t represent usemove to Tier IIRun SCI-GROW2 3Report EDWC(s) forall model runs;movetoTierIIReport EDWCs forscenarios wherebreakthrough wasWas breakthroughobserved for all2.3.allmodelruns;recommend the mostconservativeEDWC(s) for use inHED assessment(i.e., highest of allYesobserved.observedforallscenarios?PRZM-GW scenariosand SCI-GROW 2.3.If EDWC(s) exceedlevel of concernRun 100 yearsimulation forscenarios thatbreakthrough wastb dNolevelofconcernmove to Tier IInotobserved.Report EDWCs for100 year simulation.19Implementation:TierIIProcessDiagramConsider refinement options including:Incorporate usage info from BEAD;Report EDWC(s) and recommend thet ti fi d EDWC( ) fConsider impact of well setbacks;Develop representative scenario;Consider additional fate inputs (e.g., subsurfacedegradation); andmostconservative refinedEDWC(s)foruse in HED assessment.YesDetermine exposure durationsrelevant to duration ofconcern (e.g., annual, 90-day, time series data, etc.)Run PRZM-GW representativescenarios with refinedinput parameters.Run 100 year simulation forscenarios where breakthroughtb dNoWas breakthrough observed for all scenarios?was notobserved.Report EDWCs for 100 yearsimulations.20Tier 1 PRZM-GW Results Compared toHuman Health BenchmarksHumanHealthBenchmarks•19% exceed theacuteHHBP (of those19%exceedtheHHBP(ofthosechemicals with a HHBP†)•23% exceed thechronic††HHBP (of those23%exceedthechronic††HHBP(ofthosechemicals with a HHBP‡)71% dMCL(5 f th 7 h i l th t•exceed(5ofthe7chemicalsthathave an MCL established)http://iaspub.epa.gov/apex/pesticides/f?p=HHBP:homep pg p p p†41 of 66 NAWQA chemicals list anAcuteHHBP††Assumes 100% Relative Source Contribution‡51 of 66 NAWQA chemicals list aChronicHHBP211 Year IP Summary Compared toSCIGROW 2 3‐GROW2.3100001000001001000

p pb0.1110

[PRZM-GW] p0.0010.01All Chemicals Evaulatedone to one lineSCI-GROW0.00010.0001 0.001 0.01 0.1 1 10 100 1000 10000[NAWQA] ppbNote:The“IP”(ImplementationPlan)plottedvalue(blackdiamonds)isthelargerofthePRZM‐GWhybridandSCI‐GROW2.3values.Comparisonsaremadetotheall‐timemaximumofallsamplesfromallwellsinNAWQAregardlessofwelltypeandcharacteristics.22