WPC  V~~X1fﺋE`aM3vH>xȴpf^Kzj&Dw}=R̞Ol@Nc`k7F9YK-Mb2(>m"5T4kzݻI G;hOK;Ab\5wYMaYʻ3feJq2l,B"#,ƺD4ÇoCTV)#aNr+J ' TJ(0 ..j|s0VN)&WE<)LO^ :(4ŗ8I'W`%=PJ0ڒ;z,B*2YT KύfV#ԹhݫO&XC*ny\bȼnu8!Z;w.*c7 QjLŵ/T(^ײ}\6$jFzǡGfH-SS*T+ 0jZU\< 0HU*H 0%Tr 0 0 W 0L- 0Wy |  L 0CV  0C~"d Cfa Bu* Bfafa~)"fa BUN  %ZN` 0(b mw@4#!6x4Heading 1  @  Q\  `$Times NewRomanQ     &&&Q\  `$Times NewRomanQ \  `$Times NewRoman6p4Heading 2  @XXX?%2A`Arial?    &&&Q\  `$Times NewRomanQ %2A`Arial6m4Heading 3  @XXXQ\  `$Times NewRomanQ   &&&Q\  `$Times NewRomanQ <jj:Default ParaQ\  `$Times NewRomanQ&&&Q\  `$Times NewRomanQ0.Footer !(#&&&Q\  `$Times NewRomanQ;1R Z bj #;&&&Q\  `$Times NewRomanQ:j8Page NumberQ\  `$Times NewRomanQ>4,JR Z bj #>&&&Q\  `$Times NewRomanQ0.Header !(#&&&Q\  `$Times NewRomanQ;1R Z bj #;&&&Q\  `$Times NewRomanQ' NATURAL ATTENUATION DEMONSTRATION x x y 0 .      b*  _ &6/%X X&6/%% &6/! !(#X!&6/%%&6/&6/%%&6/    %&6/    1  &6/%݌  Ќ! X!(#!&6/%%&6/&6/%%&6/  %&6/ ,! !(#X!&6/%&6/%%&6/     ݌̌! X!(#!%&6/  ,E14 <DL!T$XE(2b$ #!    b)  _ &6/%X X&6/%% &6/! !(#X!&6/%%&6/&6/%%&6/    %&6/    1  &6/%݌  Ќ! X!(#!&6/%%&6/&6/%%&6/  %&6/ ,! !(#X!&6/%&6/%%&6/     ݌̌! X!(#!%&6/  ,E14 <DL!T$XE(2b$ #!   t    \R'3\      dTable_A&0 d d dTable_BTable_C t    \R3'\     Table_DK Kd3|xw(hH  Z 6Times New Roman Regular X($U lEmnEoEpqDr sDvDwU]i%Acrobat PDFWriter,,,,,,0 #!  _  XBXX X     NATURALATTENUATIONSTUDY  INWISCONSINANDILLINOIS     XiaopingYang,HowardGlasser,andRay_Stoelting_Ԁ(AmocoCorporation)Mike_Barden_Ԁ(FormerlywithWisconsinDepartmentofNaturalResources)̀George_Mickelson_ԀandJim_Delwiche_Ԁ(WisconsinDepartmentofNaturalResources)Eric_Portz_ԀandCraig_Steinhermer_Ԁ(IllinoisEnvironmentalProtectionAgency) @4 _Gilberto_ԀAlvarez(UnitedStatesEnvironmentalProtectionAgencyRegion5) @4 Debra_Hagerty_,Susan_Petrofske_,andDavid_Misky_Ԁ(DeltaEnvironmentalConsultants,Inc.)  @(  )ABSTRACT: AnaturalattenuationfieldstudyhasbeenconductedjointlybytheU.S.   EnvironmentalProtectionAgency(U.S.EPA)Region5,WisconsinDepartmentofNaturalResources(_WDNR_),theIllinoisEnvironmentalProtectionAgency(_IEPA_),andAmocoCorporation(Amoco)sinceOctober1994.Projectgoalsincludeddeterminingtheeffectivenessofnaturalattenuationanddevelopingacosteffectivewaytoevaluateit.Fourleakingundergroundstoragetank(LUST)sitesinWisconsinandthreeinIllinoiswereselected,andpetroleumhydrocarboncompounds,suchasbenzene,toluene,_ethylbenzene_,andtotal_xylenes_Ԁ(_BTEX_)),aswellasselected_bioparameters_,weremeasuredatthesesitesfortwoormoreyears.Methyltertiarybutylether(_MTBE_)wasalsomeasuredattheWisconsinsites.Dataobtainedfromthisfieldstudyindicate,withtheexceptionofonesitewhichappearstohavebeenimpactedbyareleasefromupgradientofthesite,thattheplumeshavebeenstableorshrinkingandthereisstrongevidencethatnatural_biodegradation_Ԁhasbeenoccurring.Althoughseveral_bioparameters_couldbeusedtodemonstrate_biodegradation_,thetrendofthe_BTEX_Ԁcompoundsovertimeordistancewasfoundtobethebestindicatorfordemonstratingtheappropriatenessandeffectivenessofnaturalattenuation.  x`   4 "l! @XBXXXBXBXXXB    |   INTRODUCTION|     @ӌ "l  ЌXBXXXBXBXXXB   4 In1988,whentheFederalLUSTprogramtookeffect,fewstateprogramsanticipatedthelargenumbersofLUSTsitesgeneratedasaresultoftherules.Inmanyways,theincreaseddemandforoversightcreatedinnovativeapproachestoenvironmentalregulatorymanagement.Forexample,traditionalriskassessmentand P)8#* _evaluationapproacheshavebeenmodifiedandstreamlinedintowhatisnowknownasriskbasedcorrectiveaction(_RBCA_)programs._RBCA_Ԁprogramsallowstatesandresponsiblepartiestomanagethelargeworkloadssothosesitesposingthegreatestrisktothehumanhealthandtheenvironmentareaddressedfirstandwiththenecessaryresources. 4 Inthepastdecade,significantadvancementshavebeennotedintheareasofsiteinvestigationmethodsandcorrectiveactiontechnologies.Earlyon,somestudiesseemedtoindicatethatcertainLUSTsiteswereundergoingconstituentconcentrationreductionwithouttheuseofactivetechnologies.Eventually,theuseofnaturalattenuation,whichistheprocesswherenaturallyoccurringphysical,chemical,andbiologicalprocesseswilleffectivelyachieveremedialgoalsandcanbedemonstratedthroughmonitoring,wasbeingconsideredbystateregulatoryprogramsasaviable_remediation_Ԁalternative. 4 Manystateswereunfamiliarwithand,therefore,unwillingtoconsiderapprovingcorrectiveactionplansinwhichnaturalattenuationwasbeingproposedasanalternative.Althoughseveralenvironmentalconsultantshadconductedsimilartypesofstudies,somestateregulatorssuggestedthatresultscouldbeviewedasmorecredibleifthestatesandtheU.S.EPAhadparticipatedinthestudy.Ifaregulatoryagencyhadparticipatedandsupportedtheresultsofastudy,stateLUSTprogramsmightbemorewillingtomodifyexistingorcreatenewpolicieswithrespecttonaturalattenuation. 4 Earlyin1994,U.S.EPARegion5approachedLUSTmanagerswithinthe_WDNR_ԀandscientistswithinAmocotodeterminethefeasibilityofconductinganaturalattenuationfieldstudyatanumberofLUSTsitesinWisconsin.Atthetime,Wisconsin hadcompletedanaturalattenuationpolicyguidancedocumentandwasevaluatingthe (!2 conceptfurther.Soonafter,staffwiththe_IEPA_Ԁagreedtoparticipate,andadditionalsitesinIllinoiswereincludedinthestudy.  4 Thegoalofthisprojectwastogainabetterunderstandingofnaturalattenuationatseveralpetroleumimpactedsites,todetermineeffectivenessandcosteffectivemonitoringstrategies.Anothergoaloftheprojectwastoselectsiteswithvariedlithologyinsteadofonlyfocusingonhomogeneoussandysoilswhichmostotherstudieswerebasedon. 4 Thebasicpremisewastoconductasiteselectionprocess,agreeonspecificnaturalattenuationindicatorparameterstobestudied,establishamonitoringschedule,andmonitorthesitesovertime.Thepurposeofmonitoringthesitesovertimewastodetermineifanycontaminantreductiontrendscouldbeestablished,andifso,couldthetrendsbeattributedtonaturalattenuationprocesses.ThestudyoftheseparticularsiteswouldbeconductedoutsideoftheformalLUSToversightprocessstateregulatorsoftenfollow.Ingeneral,theeffectivenessofnaturalattenuationwasdeterminedonthebasisofwhethertheindividualplumeswereexpanding,stable,orshrinking,andwhetherornotthedatacollectedfromthesitesadequatelymadethecaseforanyofthosescenarios.PersonnelfromtheRegulatoryagencies,Amoco,andconsultants(mainlyfromDeltaEnvironmental)metatleasttwiceayeartoevaluateprogressandmonitoringstrategies."H!0 @XBXXXBXBXXXB    O  MATERIALSANDMETHODSO  @ӌ "( ЌXBXXXBXBXXXB  4$l#T @XBXXXBXBXXXB      SiteGeologyand_Hydrogeology_H 0 @ӌ 4$* ЌXBXXXBXBXXXB   4 Followingthesiteselectionprocess,fourLUSTsitesfromWisconsinandthree %x, fromIllinoiswerechosentoparticipateinthestudy.TheselectedsitesinWisconsin werelocatedinConcord,Milwaukee,HalesCorners,and_Marshfield_.Theselectedsites H(0"0 inIllinoiswerelocatedinHighlandPark,Broadview,andChicago(Table1summarizesthegeology,_hydrogeology_,andbackgroundinformationoftheselectedstudysites).  4 ThenearsurfacegeologybeneaththeConcord,Wisconsinsiteispredominantlysiltyandsandyclayunderlainbybedrock.Thedepthtowateratthesiterangesfrom8to11feetbelowgroundsurface(_bgs_)withacalculatedhydraulicconductivityof3.1x103centimeterspersecond(cm/sec).#bbddԀThegroundwatervelocityisestimatedtobe @(  approximately10feetperyear(ft/yr).#ddbb    4 BeneaththeMilwaukee,Wisconsinsite,thenearsurfacegeologyispredominantlyclayandsiltyclay.Thedepthtowateratthesiterangesfrom11to16feet_bgs_Ԁwithacalculatedhydraulicconductivityof9.5x105cm/sec.Thegroundwater   velocityiscalculatedtobeapproximately3ft/yr. 4 ThegeologybeneaththeHalesCorners,Wisconsinsiteispredominantlyclayunderlainbybedrockatapproximately12feet_bgs_.Thesiteappearstohavethreeseparate_hydrogeologic_Ԁsystemswithaperchedwatertable(upperaquifer),underlainbyaanothershallowaquifer(loweraquifer),andabedrockaquifer.Thedepthstowaterrangefrom5to7,13to16,and39to43feet_bgs_,intherespective_hydrogeologic_systems.Acalculatedhydraulicconductivityof8.2x105cm/secwasestablishedfor & theupperaquifer.Thegroundwatervelocityfortheupperaquiferiscalculatedtobeapproximately1.5ft/yr. 4 Thegeologybeneaththe_Marshfield_,Wisconsinsiteispredominantlysandyclay.Thedepthtowateratthesiterangesfrom24to29feet_bgs_Ԁwithacalculatedhydraulicconductivityof7.9x105cm/sec.Thegroundwatervelocityiscalculatedtobe (!2 approximately7.5ft/yr. p)X#4 Ї 4 BeneaththeHighlandPark,Illinoissite,thenearsurfacegeologyconsistsofpredominantlyclayandsiltyclay.Thedepthtowateratthesiterangesfrom2to6feet_bgs_Ԁwithacalculatedhydraulicconductivityof1.4x106cm/sec.Thegroundwater  velocityiscalculatedtobeapproximately0.2ft/yr. 4 ThenearsurfacegeologybeneaththeBroadview,Illinoissiteisalsosiltyclaywithtracesofsandandgravel.Thedepthtowateratthesiterangesfrom3to6feet_bgs_withacalculatedhydraulicconductivityof5.2x105cm/sec.Thegroundwater   velocityiscalculatedtobeapproximately1.2ft/yr. 4 ThenearsurfacegeologybeneaththeChicago,Illinoissiteispredominantlybackfilltoapproximately7feet_bgs_,underlainbysandto12feet_bgs_,andthensiltyclay.Thedepthtowateratthesiterangesfrom5to9feet_bgs_Ԁwithacalculatedhydraulicconductivityof5.2x104cm/sec.Thegroundwatervelocityiscalculatedtobe  approximately7ft/yr. 4 Asummaryofthegeologyand_hydrogeology_ԀfortheselectedsitesispresentedonTable1.X@x @XBXXXBXBXXXB    /  GroundWaterSamplingandAnalyticalMethods// }/ @ӌ X@$ ЌXBXXXBXBXXXB   4 Tomeasurepetroleumhydrocarbonconstituentsingroundwater,wellswerepurgedoffivewellvolumesoruntildryusingasubmersiblepump.Groundwatersampleswerecollectedwithadisposablebailerandcontainerizedin40millilitervialscontaininghydrochloricacid(_HCl_)preservative.#bbddGroundwatersamplesfromthe $& . WisconsinsitesweresubmittedtoPaceAnalyticalServices,Inc.(Pace)andanalyzedforpetroleumvolatileorganiccompounds(_PVOCs_)byEPAMethod8020andgasolinerange ("2 _organics_Ԁ(_GRO_)bythe_WDNR_ԀModified_GRO_ԀMethod8015.GroundwatersamplesfromtheIllinoissitesweresubmittedtoIndustrial&EnvironmentalAnalysts,Inc.(_IEA_)andanalyzedfor_BTEX_ԀbyEPAMethod8020.#ddbb   ,  @XBXXXBXBXXXB    4  _Biodegradation_ԀParametersinGroundWater4B5 *5 @ӌ   ЌXBXXXBXBXXXB   4 Toevaluatetheoccurrenceandrateofnatural_biodegradation_,themeasurement P 8 ofsitespecificenvironmentalparametersisessential.Duringthestudy,variousgroundwaterparametersweremeasured,includingpetroleumhydrocarbonconstituents,dissolvedoxygen(DO),oxidationreductionpotential(_ORP_),pH,temperature,andconductivity.Followingcollectionofthegroundwatersamplethatweresentforlaboratoryanalysis,_bioparameters_Ԁweremeasureddirectlyinthewells.DOandtemperatureweremeasuredbya_YSI_ԀMODEL57meterwithMODEL5739probes,pHbyaCOLE_PARMER_Ԁ_DIGISENSE_Ԁmeter,_ORP_ԀbyanORION_ORP_Ԁprobe,oran_OAKTON_ԀMODEL35650tester,andconductivitybya_YSI_ԀMODEL33meter.T<t @XBXXXBXBXXXB    j:  SoilGas_Bioparameters_ j:: : @ӌ T< ЌXBXXXBXBXXXB  ݀ 4 Other_bioparameters_Ԁsuchasoxygen(O2)andcarbondioxide(CO2)insoilwere  alsomeasuredforallsevensites.Inaddition,vaporphasemethane(CH4)andvolatile   organiccompounds(_VOCs_)weremeasuredforthethreesitesinIllinoisandforonesiteinWisconsin(_Marshfield_)duringseveralsamplingevents.Similartomeasurementof_bioparameters_Ԁingroundwater,soilgas_bioparameters_Ԁweremeasureddirectlyinthewells.,soilgasesO2,CO2,CH4,and_VOCs_Ԁweremeasuredforselectedsites.A |!d& polyvinylchloride(PVC)capwithanattachedsamplingtubewasplacedonamonitoringwell,alowvolumepneumaticdiaphragmpumpwasusedtopurgethe_headspace_Ԁforapproximatelyfiveminutes,andsoilgaswasthencollectedintoa_tedlar_ԀbagwhichwaslatermeasuredforO2andCO2byusinga_GASTECH_Ԁ32500X.IfO2wasdepleted,a & . 10:1airtosampledilutionwasusedforthetotal_VOCs_Ԁ(includingCH4)reading.Soil H(0"0 gasesCH4and_VOCs_Ԁweremeasuredbya_FOXBORO_ԀOVA128meter.Theactual )#2 _VOCs_Ԁwerecalculatedbythedifferencebetweenthetotal_VOCs_ԀandCH4.ForCH4  analysis,acarbonfilterwasusedtoadsorballhydrocarbonsexceptCH4. t\   @XBXXXBXBXXXB    LC  SITESELECTIONCRITERIAFORUSINGNATURALATTENUATION LCC C @ӌ   ЌXBXXXBXBXXXB   4 Todeterminewhetherthesesevensiteswereappropriatefornaturalattenuation,aworkplanwasdevelopedbasedonliteratureinformation(3,4,5,6,9,10,12,&14)aswellas    fieldscreeningexperiences.Siteswereselectedbasedon(1)pasthistoryof_BTEX_compounds,(2)potentialrisktoreceptors,and(3)availabilityofdissolvedoxygeninbackground. 4 Thedataonthe_BTEX_Ԁconcentrationsaddressesthequestionofwhetherthesesiteshadapotentialfornaturalattenuation.AccordingtotheASTMStandardGuidefor_Remediation_ԀofGroundWaterbyNaturalAttenuationatPetroleumSites2andU.S.EPA 0 Directive9200.41713,trendsestablishedfromhistoricaldataaretheprimarylineof t evidencefornaturalattenuation,andmeasuredpetroleumhydrocarbonconcentrationsovertimeformthebasisfordefiningtheplumeasshrinking,stableorexpanding.Forthepurposeofthisstudy,aninitialpoolofpotentialsiteswasestablishedwhichmetadditionalcriteriasuchaswhetherthesitewasaninactiveoractiveservicestation(amixturewaspreferred),ifdissolved_BTEX_Ԁconcentrationswereatasufficientbaselineleveltotrackanydecreaseandwhetheranyofthesiteswereundergoingregulatoryenforcementaction.Severalsitesintheavailablepoolwereconsideredsuitablefornaturalattenuationbecauseplumeswerereasonablyexpectedtocontinuetoremain lowrisksitesandnotadverselyimpactsensitivereceptors.BackgroundinformationontheselectedsitesissummarizedinTable1.  'h!0  4 _Remediation_Ԁbynaturalattenuationdependsuponnotonly_biodegradation_Ԁbut alsonaturalprocessessuchasdilution,dispersion,sorption,volatilization,andsoon.Duetothenumerousprocessesinvolved,itwasnotpracticaltoquantifytherelativecontributionof_biodegradation_Ԁwithrespecttoothernaturalattenuationprocesses.Theprimaryconcernforsiteselectionwastheattenuationstatusandbehaviorofplumeandthesecondaryconcernwaswhetherornotfavorableattenuationconditionsexistedatthesites.Nevertheless,naturalattenuationislookeduponmorefavorablyiftheappropriateconditionsfor_biodegradation_Ԁexistinthesubsurface. 4 Availabilityofdissolvedoxygeninbackgroundwasconsideredasoneofthemostimportantconditionsforrapid_biodegradation_Ԁofcompoundsofconcern.Thestabilizationandeventualshrinkingoftheplumeedgecanbeanticipatedduetorelativelyfast_biodegradation_Ԁratesunderaerobicconditionsascomparedtoanaerobicconditions.SinceDOinbackgroundwellswasabove0.7milligramsperliter(mg/L)atallsevenselectedsites,anaerobicconditionaroundtheedgeoftheplumeswasindicated.Anoxygenlevelofabove0.7mg/Lhasbeenselectedasanindicatorofaerobiccondition,basedonthestudybyBarkeretal.(3),inwhichbenzene,toluene,and_xylenes_Ԁwere   observedto_biodegrade_ԀataninitialDOof0.5mg/Lorhigher.ThelevelofDOinthecenteroftheplumewasnotconsideredtobeascriticalsinceanaerobic_biodegradation_willtakeplaceviaotheravailableelectronacceptors,suchasnitrate,sulfate,ferrousiron,andcarbonates,whenoxygenisabsent(14). H!0(  4 TheresultsfromtheDOreadingsindicatedthat_bioremediation_ԀwasalreadyoccurringsincetheDOlevelsobservedintheimpactedwellsweremuchlowerthanthoseinbackground,upgradient,ornonimpactedwells(5).Figure1indicatesthe & 0  relationshipbetweenaverageDOreadingsingroundwaterandawellslocationtothe (!2 plumecenter.Exceptatthe_Marshfield_,Wisconsinsitewheretheremaybeanoffsiteimpact,aconsistentcorrelationbetweenDOandwelllocationexists.  4 Otherterminalelectronacceptorsordegradationindicatorssuchasnitrate,sulfate,andiron,werenotanalyzedsincetheDOlevelsinbackgroundwellswereabove0.7mg/L,suggestinganaerobiczonearoundtheedgeoftheplumeswhichaidinstabilizingandeventuallyshrinkingtheplumes.Nutrientssuchasnitrogenandphosphoruswerenotmeasuredsinceadditionofnutrientswouldnotbeexpectedtoincreaseinsitu_biodegradation_Ԁrates(1,7,8,9,&11).Althoughbacterialcountswereinitially   performed,thisparameterisviewedasunnecessaryforfuturesitesbecausealmostallpetroleumreleasesitesexhibitadequatebacterialcounts.ThepHmeasurementwasperformedatthesesitesbutisconsideredasanoptionalparametersincepHinapetroleumreleasesiteisgenerallybetween5.5and8.5whichisconsideredastheoptimalpHrange(9).   4 Inshort,theselectedsevenstudysitesweredeterminedtobesuitablefornaturalattenuationmainlybasedonreceptorsurveys,historicdatatrendsonthecompoundsofconcern,theavailabilityofDOinbackgroundwells,andthefactthattheprimarysourcesofimpact(tanks,dispensers,and/orlines)wereremovedandfreeproduct,ifpresent,continuedtoberecovereduntilitwasnolongerpresent.  & <$t\ @XBXXXBXBXXXB    [  PARAMETERSUSEDTOMONITORNATURALATTENUATION[`\ H\ @ӌ <$ ЌXBXXXBXBXXXB   4 Todeterminealongtermcosteffectivemonitoringplanfornaturalattenuation,various_bioparameters_Ԁ(inadditiontocompoundsofconcernandDO)weremeasuredtoevaluatetheiraddedbenefitsfordemonstratingnaturalattenuation.Thegroundwater_bioparameters_ԀmeasuredforselectedsitesincludedpH,_ORP_,temperature,andconductivity,andthesoil_bioparameters_Ԁmeasuredforselectedsitesincludedbacterialcounts,soilgasO2,CO2,CH4,and_VOCs_.Itshouldalsobenotedthatadditionalsite   characterizationtookplaceatseveralsitesduringthecourseoftheprojecttobetterdefinetheextentofcontamination.Thisincludedtheadvancementofsoil_borings_,installationofmonitoringwellsandperformanceofvaporsurveysinnearbyutilities. 4 Analysisofbacterialcountswasestablishedinitiallyandsubsequentlydroppedasaroutineparametersinceotherresearchersinthefieldbegantodiscounttheusefulnessofroutinemeasurementsduetoabundanceofbacteriaobservedatpetroleumhydrocarbonsites.Asfarassoilgasdata(O2,CO2,CH4,and_VOCs_)areconcerned,   theresultsdidestablishconsistenttrends,anditwasdeterminedbytheprojectteamthatfurthercollectionofthesedatawasnotwarranted.Similarly,otherparameters(suchaspH,temperature,conductivity,andredoxpotential.)discussedabove,althoughinformative,didnotprovidesignificantinsighttotheeffectivenessofnaturalattenuationatthesesites.Theimportantlearningfromthisprojectwasthatanumberofparametersmeasuredinitiallydidnotprovetobemuchvalueadded. 4 Thebestevidencethatnaturalattenuationwasappropriateandsufficientatthesesitesandthat_biodegradation_Ԁwasoccurringwasprovidedbyanevaluationofthe ("2 differenceoftheDOlevelsbetweenimpactedandbackgroundwells,changeintheconcentrationsofchemicalsofconcernovertime,decreaseintheconcentrationofchemicalsofconcernalongthegroundwaterdirection,andthelocationoftheplumeedgeinrelationtoreceptors.ConsistentwiththeASTMStandardGuidefor_Remediation_ԀofGroundWaterbyNaturalAttenuationatPetroleumSites2andU.S.EPADirective  p 9200.41713,thisnaturalattenuationstudyresultssuggestthatplumestatusisthe    primarylineofevidenceforreductionofconstituents. 4 Overtheyears,otherresearchhasindicatedthatotherterminalelectronacceptors(_TEAs_)suchasnitrate,iron,sulfate,manganese,etc.contributetothe_biodegradation_processandatsomesitestheseother_TEAs_ԀmaybemoresignificantthanDO.UsersofthisreportshoulddetermineifonlymeasuringDOisadequateoriftheyneedtoalsosampleandanalyzeforother_TEAs_Ԁorotherbiologicalindicators.  @XBXXXBXBXXXB    mj  TRENDSANDCORRELATIONmjj j @ӌ  ЌXBXXXBXBXXXB   4 Concord,Wisconsinsitehasbeenaninactiveservicestationsince1988withthe_USTs_ԀexcavatedinMay1989.Atthattime,approximately300cubicyards(yds3)of " petroleumimpactedsoilwasexcavatedandtreatedonsitebythinspreading.TheoccurrenceofnaturalattenuationattheConcord,Wisconsinsite(AppendixA,FigureA1)wasevidentastheplumewasreducedtotheacceptablelevelswithinthreeyears.Toillustratethis,estimatedbenzene_isoconcentration_ԀmapsforMay1993andApril1996sampleeventsarepresentedonFigureA2.Inaddition,benzeneconcentrationsvs.timewereplottedonasemiloggraphandtheresultis#bbddԀpresentedasFigureA3.Historicaldata $& . indicatesthatbenzeneconcentrationshavenotbeendetectedsinceFebruary1995.O#ddbbffsite 'h!0 monitoringwellsanda_piezometer_Ԁwellwereinstalledandmonitored.Theresults ("2 indicatedthatplumeadequatelyattenuatedanddidnotmigrateoffsiteand/orvertically.Closureofthesitehasbeenapprovedbythe_WDNR_Ԁ(July17,1996).#bbddԀAsummaryofthe t\ groundwateranalyticalresultsand_bioparameter_ԀmeasurementsispresentedinTableA1.#ddbbԀ   4 AttheMilwaukee,Wisconsinsite(AppendixB,FigureB1),theservicestationdiscontinuedoperationsin1992aftertheremovalofthe_USTs_.Atthattime,nopetroleumimpactedsoilwasexcavated.Historicaldataindicatesthebenzeneconcentrationshavedecreasedovertime.MonitoringwellOW4,locatedadjacenttotheformertankbasin,istheonlywellofsignificantconcernwithrelativelyhighconcentrationsofbenzene(FigureB4).An_MTBE_Ԁplumehasproceededaheadofthe_BTEX_ԀplumeasindicatedbytheanalyticaldatafromdowngradientmonitoringwellsMW13andMW14.Since_MTBE_ԀlevelsareonlyslightlyaboveWisconsinGroundWaterStandards,additionalwellswerenotinstalledtoassessplumemigration.Estimatedbenzene_isoconcentration_ԀmapsarepresentedasFigureB2andanestimated_MTBE_Ԁ_isoconcentration_ԀmapispresentedasFigureB3.G#bbddroundwateranalyticalresults   and_bioparameter_ԀmeasurementsaresummarizedinTableB1.#ddbb |d  4 Beforestartingtheuseofnatural_remediation_ԀattheactiveHalesCorners,Wisconsinsite(AppendixC,FigureC1),thesitehadundergoneactive_remediation_Ԁwithsoilvaporextractionandgroundwaterrecoveryandtreatment.However,becauseofthecomplexgeologyofthesite,thesystemprovedtobeineffectiveandwasdiscontinued.Thenaturalattenuationprogressaftershuttingdownsoilvaporextractionwasmostevidentbythebenzeneconcentrationchangeovertime,indicatingastableorshrinkingplume(FigureC2).Theplumeisconcentratedpredominantlyintheupperaquiferwhichiscomposedofclayandwillgreatlylimitmigrationofgroundwaterimpactstopotentialreceptors.FigureC3illustratesbenzeneconcentrationchangeovertimeatthesite.#bbddԀAsummaryofgroundwateranalyticaland_bioparameter_ԀresultsareinTableC1.#ddbb p)X#4 Ї 4 Atthe_Marshfield_,Wisconsinsite(AppendixD,FigureD1),theeffectivenessofnaturalattenuationcouldnotbeadequatelyassessedduetothepossibilityofimpactbyanoffsitesource.TheservicestationdiscontinuedoperationsinDecember1988andtheremovalofthe_USTs_ԀoccurredinJune1989.Atthattime,approximately400yds3of ,  petroleumimpactedsoilwasexcavatedandtreatedonsitebythinspreading.Negotiationshaveoccurredbetweenthe_WDNR_ԀandtheneighboringresponsiblepartytoallowAmocoaccesstotheoffsitepropertytocollectindicatordata.G#bbddroundwater @(  analyticalresultsand_bioparameter_ԀmeasurementsaresummarizedinTableD1andTableD2.#ddbbԀ      4 TheeffectivenessofnaturalattenuationattheactiveHighlandPark,Illinoissite(AppendixE,FigureE1)wasapparentbythebenzeneconcentrationchangeovertime(FigureE2).Astabilizedplumeisevidentatthesite.Adowngradient,offsitemonitoringwell(MW17)verifiesthattheplumestabilizesduetonaturalattenuationandnotoffsiteand/orverticalmigration.Toillustratethis,estimatedbenzene_isoconcentration_ԀmapsarepresentedonFigureE3#bbdd._Bioparameter_Ԁresultsandgroundwateranalyticalresultsare |d summarizedinTableE1andTableE2,respectively.#ddbb    4 AstableplumeisalsoevidentattheBroadview,Illinoissite(AppendixF,FiguresF1andF2)whichdiscontinuedoperationasaservicestationinNovember1987.The_USTs_ԀwereexcavatedinFebruary1988.SinceJanuary1993,benzeneconcentrationshaveremainedstableorslightlydecreased.However,aminorimpactappearedoffsite.To#bbddԀlocate "* andassessthepotentialofpetroleumhydrocarbonsinoffsiteutilities,manholes,andgrates,#ddbbԀa $, receptorsurveywasperformed.#bbddHydrocarbonswerenotdetectedinanyoftheutilities \%D. surroundingthesite.#ddbbFigureF3illustratesbenzeneconcentrationchangeovertimeatthe & 0 site.#bbddԀ_Bioparameter_ԀmeasurementsandgroundwateranalyticalresultsaresummarizedinTable (!2 F1andTableF2,respectively.#ddbb p)X#4 Ї 4 AttheChicago,Illinoissite(AppendixG,FigureG1),benzenehasbeenstableatlowconcentrations.Minorimpactsexistadjacenttotheformerandexisting_UST_Ԁbasins,asindicatedonFigureG2.Semilogplotsofbenzeneconcentrationsovertimearepresented  #bbddonFigureG3.#ddbbԀThetrendof_BTEX_Ԁcompoundsovertimewasfoundtobethebestevidence ,  fordemonstratingtheappropriatenessandeffectivenessofnaturalattenuation._Bioparameter_measurementsandg#bbddroundwateranalyticalresultsand_bioparameter_Ԁmeasurementsare    summarizedinTableG1andTableG2.Thissitewassomewhatcomplicatedbythefactthatitisanactiveservicestationandsomeoftheconcentrationfluctuationscouldbeattributedtosmallspillsnearthedispenserislandsfrommotoristsrefuelingtheirvehicles.Atothersiteswherenaturalattenuationisbeingconsideredinthefuture,thisaspectshouldbeconsidered.#ddbb 4 Tofurtherassesstheoccurrenceandappropriatenessofnaturalattenuation,anumberofcorrelationwereattemptedtoderivepossibleconnectionsbetween_bioparameters_Ԁ(suchasDO,_ORP_,pHetc.)and_BTEX_Ԁconcentrations(AppendixH)._Bioparameters_Ԁwerealsoplottedagainstother_bioparameters_Ԁ(e.g.DOvs._ORP_).Inaddition,waterelevationsandtheeffecttheymayhaveon_BTEX_Ԁconcentrationsor_bioparameter_Ԁmeasurementswasanalyzed. 4 Nosignificanttrendsorcorrelationswerederivedwhencomparing_bioparameters_DO,_ORP_,andpHwith_BTEX_Ԁconcentrations(SeeFiguresinAppendixH).Further,nothingsignificantwasderivedfrom_ORP_ԀandDOcomparison. 4 Aspreviouslymentioned,thetrendof_BTEX_Ԁcompoundsovertimewasfoundtobethebestevidencefordemonstratingtheappropriatenessandeffectivenessofnaturalattenuation.Table2isasummaryofwhetherbenzeneconcentrationsinindividualmonitoringwellsareincreasing,decreasing,orstable.Asseenfromthetable,thebenzeneconcentrationindowngradientandsidewellsstabledordecreasingwhilethebenzene p)X#4 concentrationintheimpactedwellsdeclined.Ingeneral,itcanbeconcludedthatthebenzeneplumesinallsevensitesareeitherstableorshrinking,providingevidenceofnaturalattenuation. 4 Table3isasummaryofthefirstorderbenzenenaturalattenuationratesestimatedusinganalyticaldatafromselectedmonitoringwells.Asseenfromthetable,thefirstorderbenzeneattenuationratesrangedfrom0.05%to0.82%. 4 TheWisconsin_DNR_Ԁhashadgroundwaterstandardsfor_MTBE_Ԁforseveralyearsandhasrequiredthatthisparameterbemeasured.Since_MTBE_ԀhasnotbeenaddedtopetroleumbasedfuelsathighlevelsinWisconsin,_MTBE_Ԁingroundwaterhasnotbeenaseriousissueinthestate.Forexample,theMilwaukeesitemayhavealowlevel_MTBE_plumeextendingoffsite.Sincethe_MTBE_ԀlevelareonlyslightlyaboveWisconsinStandardsin_downgradient_Ԁwells,benzeneconcentrationsinthesourceareaatthatsiteisamuchgreaterconcernthanlowlevel_MTBE_Ԁthatmaymigrateoffsite._MTBE_snaturalattenuationcharacteristicsmaybequitedifferentthannaturalattenuationcharacteristicsforother_BTEX_Ԁcompounds.Thereforetheconclusionsinthisreportmaynotbeapplicabletositesinotherstatewhere_MTBE_Ԁispresentathighlevels.X@x @XBXXXBXBXXXB      CONCLUSIONSQ 9 @ӌ X@$ ЌXBXXXBXBXXXB   4 Withoutanyeffectiveactiveremedialsystems,petroleumhydrocarbonplumesattheselectedservicestationshavedecreased,stabilized,ordissipatedduetonaturalattenuationprocesses.Asindicatedbythedifferentvaluesofbiologicalparametersfoundintheimpactedareacomparedtobackgroundmeasurements,theplumesshrinking,stabilizing,ordisappearingcouldbeattributedinparttobiologicaldegradation. ("2  4 Onewaytodemonstratetheoccurrenceandappropriatenessofnaturalattenuationwithrespecttotheadequateprotectiontohumanhealthandtheenvironmentistoexaminetheplumestatuscombinedwithareceptorsurvey.Amongvariousbiologicalindicators,thedissolvedoxygenmeasurementalonemaybesufficientatmostsitessincethepurposeofmonitoringisnottoidentifyandquantifyallthebiologicalmechanismsunderneathasite,butrathertoverifythatbiologicaldegradationiscontributingtotheoverallnaturalattenuationofaplume.Asindicatedabove,whenthenumberofthe_bioparameters_measuredincreases,costeffectivenessofnaturalattenuationmaybereduced.   @XBXXXBXBXXXB    ǜ  ACKNOWLEDGMENTSǜY A @ӌ   ЌXBXXXBXBXXXB   4 Overthepastyears,anumberofconsultantsandmanyindividualshavecontributedtothesuccessofthisproject.WearealsothankfultothecommentsandsupportbyLaurie_Egre_,Wendell_Wojner_,andCarol_Hefferan_Ԁfromthe_WDNR_,George_Halloran_,Andrew_Tschampa_,andGerryPhillipsfromU.S.EPARegion5,Linda_Curran_ԀandJoe_Murzyn_ԀfromAmocoCorporation.̀ DISCLAIMER    ThenaturalattenuationstudythatisthesubjectofthisreportwasconductedasacooperativeeffortinvolvingtheU.S.EnvironmentalProtectionAgency,theWisconsinDepartmentofNaturalResources,theIllinoisEnvironmentalProtectionAgencyandAmocoCorporation.However,theopinionsandinterpretationscontainedinthisreportaresolelythoseoftheauthors,anddonotnecessarilyreflectthepoliciesorproceduresofthecooperatingagencies.Ifreadersofthereporthavequestionsregardingspecificrules,regulationsorstatutesthatapplytothisorsimilarprojects,theyshouldcontacttheappropriateregulatoryagencyandshouldnotrelayonstatementsfoundinthisreport.ww ("2  @XBXXXBXBXXXB      REFERENCES3  @ӌ  ЌXBXXXBXBXXXB  1.AirForceCenterforEnvironmentalExcellence(1994)._Bioventing_ԀPerformanceandCostSummary.?+ 4 <DL!X?2.ASTM(1997).StandardGuidefor_Remediation_ԀbyNaturalAttenuationatPetroleumReleaseSites.B.4 <DL!XB3.Barker,_J.F._,Patrick,_G.C._,&D.Mayor(1987).NaturalAttenuationofAromaticHydrocarbonsinaShallowSandAquifer.GroundWaterMonitoringReview,pp.6471.   4._Buscheck_,_T.E._,_OReily_,_K.T._,&S.N.Nelson(1993).EvaluationofIntrinsic_Bioremediation_ԀatFieldSites.InProceedingsofPetroleumHydrocarbonsandOrganicChemicalsinGroundwater:Prevention,Detection,andRestoration.NationalGroundWaterAssociation,pp.367381.5.Caldwell,_K.R._,_Tarbox_,D.L.,Barr,_K.D._,_Fiorenze_,S.,_Dunlap_,_L.E._,&S.B.Thomas(1992).AssessmentofNatural_Bioremediation_ԀasanAlternativetoTraditionalActive_Remediation_ԀatSelectedAmocoOilCompanySites,Florida.NationalGroundWaterAssociation,pp.509525.6.Chiang,_C.Y._,_Salanitro_,J.P.,_Chai_,_E.Y._,_Colthart_,J.D.,&_J.L._ԀKlein(1989).Aerobic_Biodegradation_ԀofBenzene,Toluene,andXyleneinaSandyAquifer:DataAnalysisandComputerModeling.GroundWater,27,pp.823834. $& .   'h!0 7.Downey,D.C.(1993).FullScale_Bioventing_ԀinLowPermeabilitySoilProves Successful.TheHazardousWasteConsultant. t\ 8.Dupont,R.R.,_Doucette_,W.,&R.E._Hinchee_Ԁ(1991).Assessmentofinsitu_bioremediation_Ԁpotentialandtheapplicationof_bioventing_Ԁatafuelcontaminatedsite.InSituandOnSitu_Bioreclamation_,R.E._Hinchee_ԀandR.F._Olfenbuttel_,_Eds_.,_Butterworth_Ԅ_Heineman_,_Stoneham_,MA,pp.262282.9._WDNR_ԀGuidanceMemorandum(1993).Natural_Biodegradation_ԀasaRemedialActionOptionInterimGuidance.WisconsinReleaseNews3(1). T<  10._McAllister_,P.M.,&C.Y.Chiang(1994).APracticalApproachtoEvaluatingNaturalAttenuationofContaminantsinGroundWater.GroundWaterMonitoringReview,pp.161 hP 173.11.Miller,R.N.(1991).AFieldScaleInvestigationofEnhancedPetroleumHydrocarbon_Biodegradation_Ԁinthe_Vadose_ԀZoneEnhancedbySoilVentingatTyndallAirForceBase,Florida.InSituandOnSitu_Bioreclamation_,R.E._Hinchee_ԀandR.F._Olfenbuttel_,_Eds_.,_Butterworth_Ԁ_Heineman_,_Stoneham_,MA,pp.283302.12._Salanitro_,J.P.(1993).TheRoleof_Bioattenuation_ԀintheManagementofAromaticHydrocarbonPlumesinAquifers.GroundWaterMonitoringReview,pp.150161. "* o X?+ 4 <DL!X? o13.l 4 lmmU.S.EPADirective9200.417(1997).UseofMonitoredNaturalAttenuationatSuperfund,_RCRA_ԀCorrectiveAction,andUndergroundStorageTankSites. n  XB.4 <DL!XBn (!2 14.ppq 4 q_Wiedemeier_,_T.H._,Wilson,_J.T._,Miller,R.N.,&D.H._Kambell_Ԁ(1994).UnitedStates AirForceGuidelinesforSuccessfullySupportingIntrinsic_Remediation_ԀwithanExamplefromHillAirForceBase.NationalGroundWaterAssociation.  n Xn  ?+ 4 <DL!X?n n15._Wiedemeier_,_T.H._,Wilson,_J.T._,_Kambell_,D.H.,&_J.E._ԀHansen(1995).TechnicalProtocolforImplementingIntrinsic_Remediation_ԀwithLongTermMonitoringforNaturalAttenuationofFuelContaminationDissolvedinGroundwater.AirForceCenterForEnvironmentalExcellence,TechnologyTransferDivision,BrooksAirForceBase,San_Antonio,TX_.    hP     TRO'33''3 Letter Landscape3'T    o oN:` hp x (#%'0*,XN Table1.@..Geology,_Hydrogeology_,andbackgroundInformationoftheSelectedStudySites.    8\  *q ddd Xdd Xdd Xx-x-q,91,,,t,D1,,=,=,:,M,,1+  7(  Xd7q Xqm#4 <DL!T$&JR Z bj #r%'"*z,XZXXB) ZSite  No. G8' "d dGLocation K8'"d dKReportedReleaseDate K8'D h "d dKGeology K8' "d dKDepthtoWater K8' "d dKAverageHydraulicConductivity K8'D h"d dKAverageHydraulicGradient K8'D h"d dKGroundWaterVelocity K8'D h"d dK_LPH_Present K8'D h"d dKHighestHistoricBenzeneConcentration K8' "d dKHighestBenzeneConcentration(1996) K8'  "d dKPotentialReceptors aP2 "" X  d 8da 1* I8' #"d dIConcord,WI K8' $"d dK2/89 K8' %"d dKSiltyandsandyclay K8' '"d dK8to11feet_bgs_ K8' ("d dK3.1x103  ) cm/sec K8' *"d dK0.0014ft/ft K8' +"d dK10ft/yr K8' ,"d dKNo K8' -"d dK300_g_/L(9/93) K8' /"d dK<1.0_g_/L(4/96) K8' 1"d dKNo aP2 2" 8  d 8da2 I8't 3"d dIMilwaukee,WI K8' D5"d dK2/92 K8't 6"d dKClayandsiltyclay K8' D8"d dK11to16feet_bgs_ K8't 9"d dK9.5x105 t : cm/sec K8' D;"d dK0.03ft/ft K8't <"d dK3ft/yr K8't ="d dKNo K8't >"d dK24,000_g_/L(11/94) K8' D@"d dK17,000_g_/L(3/96) K8' DB"d dKNo aP2t C" 8  d 8da3 I8'8 D"d dIHalesCorners,WI K8' F"d dK11/89 K8'8 G"d dKClayunderlainbybedrockatapprox.12feet_bgs_ K8'< K"d dKUpperaquifer:57ft_bgs_ԀLoweraquifer:1316ft_bgs_ԀBedrockaquifer:3943ft_bgs_ K8'< O"d dK8.2x105 8 P cm/sec(upperaquifer) K8'< S"d dK0.017ft/ftπ(upperaquifer) K8'l V"d dK1.5ft/yr(upperaquifer) K8'l Y"d dKSeenotes** K8' ["d dK8,600_g_/L(2/91) K8' ]"d dK1,800_g_/L(3/96) K8' _"d dKNo _P28 `" 8  d 8d_4 G8' 0 a"d dG_Marshfield_,WI K8' c"d dK6/89 K8' 0 d"d dKSandyclay K8' 0 e"d dK24to29feet_bgs_ K8' 0 f"d dK7.9x105  0 g cm/sec K8' h"d dK0.03ft/ft K8' 0 i"d dK7.5ft/yr K8' 0 j"d dKNo K8' 0 k"d dK12,000_g_/L(5/94) K8' m"d dK10,000_g_/L(6/96) K8' o"d dKNo aP2 0 p" 8  d 8da5 I8' q"d dIHighlandPark,IL K8'Hls"d dK9/89 K8' t"d dKClayandsiltyclay K8'Hlv"d dK2to6feet_bgs_ K8' w"d dK1.4x106  x cm/sec K8'Hly"d dK0.10ft/ft K8' z"d dK0.2ft/yr K8' {"d dKNo K8' |"d dK4,070_g_/L(1/90) K8'Hl~"d dK3,200_g_/L(12/96) K8'Hl"d dKNo aP2 " 8  d 8da6 I8'<`"d dIBroadview,IL K8'<`"d dK6/91 K8'<`"d dKSiltyclaywithtracesofsandandgravel K8'"d dK3to6feet_bgs_ K8'<`"d dK5.2x105 <` cm/sec K8' "d dK0.08ft/ft K8'<`"d dK1.2ft/yr K8'<`"d dKNo K8'<`"d dK5,600_g_/L(10/93) K8' "d dK3,600_g_/L(12/96) K8' "d dKNo WF2<`" 8  d (W7 =,!x" =Chicago,IL ?,!x" ?6/92 ?,!x" ?07ft:backfillπ712ft:sandπ1214ft:siltyclay ?,!|" ?5to9feet_bgs_ ?,!x" ?5.2x104 x cm/sec ?,!$H" ?0.004ft/ft ?,!x" ?7ft/yr ?,!x" ?No ?,!x" ?2,000_g_/L(11/92) ?,!$H" ?96_g_/Lπ(3/96) ?,!$H" ?NorND,x" (0   (Nrr LB*(L" (0   (Lr '(3 'ss '(3 ' '(3 ' '(3 ' '(3 ' '(3 ' '(3 ' '(3 ' '( 3 ' '( 3 ' '( 3 ' J;( 3 ( XdJ Notes: </, d d< E8',3d dE E8',3d dE K8',3d dK <2',3d < ',3 ' ',3 ' ',3 ' ',3 ' ',3 ' ',3 ' H9,3 X (H_bgs_Ԁ=belowgroundsurface  B/$0 B 6,!3 6 '3 ' '3 ' '3 ' '3 ' ' 3 ' '!3 ' H9"3 ( (Hcm/sec=centimeterpersecond  B/$ ,$0 B 6,!\ %3 6 '\ &3 ' '\ '3 ' '\ (3 ' '\ )3 ' '\ *3 ' '\ +3 ' H9\ ,3 ( (Hft/ft=feetperfoot  9/$ .0 9 ' /3 ' 0 03 0 6,! 13 6 ' 23 ' ' 33 ' ' 43 ' ' 53 ' ' 63 ' ' 73 ' H9 83 ( (Hft/yr=feetperyear  9/$ ,:0 9 '\ ;3 ' 0\ <3 0 6,!\ =3 6 '\ >3 ' '\ ?3 ' '\ @3 ' '\ A3 ' '\ B3 ' '\ C3 ' H9\ D3 ( (H_LPH_Ԁ=liquidphasehydrocarbons  B/$F0 B 6,! G3 6 ' H3 ' ' I3 ' ' J3 ' ' K3 ' ' L3 ' ' M3 ' H9 N3 ( (H_g_/L=microgramsperliter  9/$, P0 9 0\ Q3 0 6,!\ R3 6 '\ S3 ' '\ T3 ' '\ U3 ' '\ V3 ' '\ W3 ' '\ X3 ' H9\ Y3 ( (H*=SiteclosedbyStateofWisconsin  B/$ [0 B 6,! \3 6 ' ]3 ' ' ^3 ' ' _3 ' ' `3 ' ' a3 ' ' b3 ' H9 c3 ( (H**=Liquidphasehydrocarbonspresentin_GMOW_Ԅ1Son6/8/95and9/14/95.  9/$, e0 9 '\ f3 ' '\ g3 ' '\ h3 ' '\ i3 ' B1\ j3 ( (B]@,JR Z bj #r%'"*z,XJX] =,!k3 =m#4 <DL!T$&JR Z bj #r%'"*z,,JX =,!l3 = =,!m3 = ?,!n3 ? 6,!o3 6 'p3 ' 'q3 ' 'r3 ' 's3 ' 't3 ' 'u3 '-#!v3 (0  -  v  XW:` hp x (#%'0*,XJXW & % )&6/% %& Table2.StabilityofBenzeneConcentrationsinIndividualMonitoringWells.    D  *  'd d91tD1==:M1x-x- ,1,,,y,s 1+  7( d 'Xd7 Xm#4 <DL!T$&JR Z bj #r%'"*z,X& %%&6/ K8'3d dKUpgradientWells K8'"d dKSidegradientWells K8'"d dKImpactedWells K8'"d dKDowngradientWells _P2 " X ' d Xd_Concord,WI B/  d dBMW1(0),MW9(0),MW13(0) K8'  "d dKMW5(0),MW8(0),MW11(0),MW12(0) K8' "d dKMW3(0),MW4(),MW6(0) K8' "d dKMW7(0),MW10(0),MW14(0) aP2 " X  d 8daMilwaukee,WI B/ d dBOW1(0),OW5(0),_GMOW_Ԅ12(0) K8' "d dKOW10(0) K8' "d dKOW4(0) K8' "d dKOW6(0),OW7(0),_GMOW_Ԅ8(0),_GMOW_Ԅ9(0),_GMOW_Ԅ11(0),MW13(0),MW14(0) aP2\" 8  d 8daHalesCorners,WI B/| d dBOW1(0),OW6(0),_GMOW_Ԅ2S(0),_GMOW_Ԅ6D(0) K8',P "d dKOW5(0),_GMOW_Ԅ2S(0),_GMOW_Ԅ5D(0) K8',P ""d dK_GMOW_Ԅ1S(),_GMOW_Ԅ1D() K8'Tx $"d dKOW2(),_GMOW_Ԅ3S(),_GMOW_Ԅ3D(0),_GMOW_Ԅ4D(0),_GMOW_Ԅ8D(0) aP2,P '" 8  d 8da_Marshfield_,WI B/Lp (d dBMW10(0) K8'Lp )"d dKMW4(0) K8'Lp *"d dKMW8(0),MW9(0),MW12(0),MW13(0) K8'$H ,"d dKMW6(0),MW14* aP2Lp -" 8  d 8daHighlandPark,IL B/Dh.d dBMW7(0),MW9(0),MW10(0), K8'@0"d dKMW16(0) K8'Dh1"d dKMW1(0),MW3(),MW14(0),MW15(),_SVE_Ԁ() K8'4"d dKMW4(0),MW17(0) aP2Dh5" 8  d 8daBroadview,IL B/86d dBMW6(0),MW8(0),MW9(0) K8'8"d dKMW3(0),MW10(),MW11(0) K8':"d dKMW2(0),MW5(),MW7(0) K8'<"d dKMW12(0) ]L28=" 8  d 8d]]@,JR Z bj #r%'"*z,XJX]Chicago,IL B/ 0>d dBm#4 <DL!T$&JR Z bj #r%'"*z,,JXMW1(0),MW2(),MW6(0) K8'@"d dKMW5(0),_RW_Ԅ2(),_RW_Ԅ3() K8'B"d dKMW3(),_RW_Ԅ1(0) K8' 0C"d dKMW4(0)B86 0D" 80   d B X  W:` hp x (#%'0*,XJXW &6/% %& D    0TF * 'd'd1ys 1x-x-,1,1+  7(  Xd7 Xm#4 <DL!T$&JR Z bj #r%'"*z,X& %%&6/Notes: B/4Xd dB aN24X3 X d (a+=increasing  ^K/ 00 (  (^Ѐ=decreasing  ^K/ 0 (  (^0=nochange  ^K/ 0 (  (^*=only1samplingevent  TC/  0 (  (T]@,JR Z bj #r%'"*z,XJX] ?,! 3 ?m#4 <DL!T$&JR Z bj #r%'"*z,,JX<20 3 (0   < XW:` hp x (#%'0*,XJXW &6/% %&            TRX3'O'33' Letter'3 Letter LandscapeT    _v   vs   TRY$3'P'33' Letter'3 Letter LandscapeT  s   ?+ 4 <DL!X?Table3.SummaryofFirstOrderNaturalAttenuationRateEstimateforBenzene      \D  *` d'd114!4!`, D4,rD4,rD4,DD+  9(  8Kd9 XB.4 <DL!XBSourceofData I8'"d dIFirstOrderRateConstantEstimated I8' "d dIHalfLives(days) K8'  "d dKRsquareofFit TE- " 8K d (TMW3inConcordWI ;,!g O  ;0.16% ;,!g O" ;430 ?,!g O" ?65.0% N?'g O" (  8NMW4inConcordWI* ;,!w _ ;0.20% ;,!w _" ;350 ?,!w _" ?44.6% N?'w _" 8  8N_GMOW_Ԅ1SinHalesCornersWI* ;,! o ;0.11% ;,! o" ;630 ?,! o" ?30.0% N?' o" 8  8N_GMOW_Ԅ3SinHalesCornersWI ;,! ;0.13% ;,!" ;580 ?,!" ?24.3% N?'" 8  8NOW6inHalesCornersWI ;,!  ;0.16% ;,! " ;430 ?,! " ?23.0% N?' " 8  8NMW3inBroadviewIL ;,! ! ;0.17% ;,! "" ;410 ?,! #" ?36.5% N?' $" 8  8NMW5inBroadviewIL ;,! % ;0.28% ;,! &" ;250 ?,! '" ?40.0% N?' (" 8  8NMW10inBroadviewIL ;,! ) ;0.12% ;,! *" ;560 ?,! +" ?16.1% N?' ," 8  8NMW2inChicagoIL ;,! - ;0.82% ;,! ." ;85 ?,! /" ?53.2% N?' 0" 8  8NMW3inChicagoIL* ;,!1 ;0.20% ;,!2" ;350 ?,!3" ?61.8% N?'4" 8  8N_RW_Ԅ3inChicagoIL ;,!5 ;0.17% ;,!6" ;410 ?,!7" ?46.2% N?'8" 8  8NMW14inHighlandParkIL ;,!9 ;0.27% ;,!:" ;260 ?,!;" ?33.9% N?'<" 8  8NMW15inHighlandParkIL* ;,!'= ;0.05% ;,!'>" ;1390 ?,!'?" ?35.9% P?''@" 8  8PE1,v&~ .6>!XEMW16inHighlandParkIL =,!7A =E.4 <DL!,vXE0.13% =,!7B" =530 ?,!7C" ?49.4%7-+7D" 8   7 X?+ 4 <DL!X?  D Note: 4  cKF (1). 4 Wellsmarkedwithanasterisk(*)aresourceareawells. H (2). 4 Nodataareincludedintheabovetableforwellsthatindicatednegativedegradationrates. J (3). 4 GraphsthatillustratetheestimationforthesefirstorderratesareincludedinAppendixI. /L