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StateofCaliforniaRegionalWaterQualityControlBoard FormerKastPropertyTankFarmSiteRemediationProjectSCHNo.2014031053 5.2‐1

5.2 GEOLOGY AND SOILS

1. INTRODUCTION

Thissectiondescribesexistinggeologicconditionsat theprojectsiteandapplicableregulationsrelated togeology and soils. The evaluation describes geologic hazards such as liquefaction, unstable soils, lateralspreading,soilerosion,watertableconditionsandactivitiesassociatedwiththeimplementationoftheRAPwithrespect to suchhazards. Theanalysis in this section isbasedon informationprovided in theCityofCarson General Plan, Los Angeles County Building Code, and studies prepared for the Former Kast Site,including the Final Phase I Site Characterization Report, Excavation Pilot Tests, Assessment ofEnvironmental ImpactandFeasibilityofRemovalofResidualConcreteReservoirSlabs,PlumeDelineationReport,andaSubsurfaceDrainageStudy.ThesereportsarereferencedinChapter9ofthisEIRandonfilewiththeRegionalBoard.

2. ENVIRONMENTAL SETTING

Regulatory Framework

Federal Regulations

There are no applicable federal regulations. Geological conditions and soils‐related effects, such asliquefaction,groundshaking,settlement,andearthmovementareaddressedthroughregulationssetforthinStateofCalifornia,LosAngelesCounty,andCityofCarsoncodesandadoptedplans.

State Regulations

Alquist‐Priolo Earthquake Fault Zoning Act

TheAlquist‐PrioloEarthquakeFaultZoningAct (PublicResourcesCodeSection2621)wasenactedby theState of California in 1972 to reduce the risk to life and property from surface fault rupture duringearthquakes.1 The Alquist‐Priolo Earthquake Fault Zoning Act prohibits the location of most types ofstructures intended for human occupancy across the traces of active faults. The act requires thatdevelopment permits for projects in “Earthquake Fault Zones” be withheld until geologic investigationsdemonstrate that the sites are not threatened by surface displacement from future fault rupture. To bezoned under the Alquist‐Priolo Earthquake Fault Zoning Act, a fault must be considered active, or bothsufficientlyactiveandwell‐defined.TheCaliforniaGeologicalSurvey(CGS)definesanactivefaultasonethathashadsurfacedisplacementwithinHolocenetime(about the last11,000years);andasufficientlyactivefault as one that has evidence of Holocene surface displacement along one or more of its segments orbranches.TheCGSconsidersafaulttobewelldefinedifitstraceisclearlydetectableasaphysicalfeatureator justbelowthegroundsurface.2 Thesite isdevelopedwithresidentialusesandwhilenonewhabitable

1 TheActwasoriginallyentitledtheAlquist‐PrioloGeologicHazardsZoneAct.2 California Department of Conservation, California Geological Survey, Special Publication 42, Fault‐Rupture Hazard Zones in

California,Alquist‐PrioloSpecialStudiesZoneActof1972withIndextoSpecialStudiesZonesMaps,2007.

5.2 Geology and Soils November 2014


structures areproposedby theproject, the “EarthquakeFault Zones”mapshelp identify areas in the sitevicinitywherepotentialsurfacefaultrupturehazardsmayexist.

Seismic Hazards Mapping Act

Inordertoaddresstheeffectsofstronggroundshaking,liquefaction,landslides,andothergroundfailuresdue to seismic events, the State of California passed the Seismic Hazards Mapping Act of 1990 (PublicResourcesCodeSection2690‐2699).UndertheSeismicHazardsMappingAct,theStateGeologistisrequiredtodelineate“seismichazardzones.”Citiesandcountiesmustregulatecertaindevelopmentprojectswithinthesezonesuntil thegeologicandsoil conditionsare investigatedandappropriatemitigationmeasures, ifany, are incorporated into development plans. The State Mining and Geology Board provides additionalregulationsandpolicies toassistmunicipalities inpreparing theSafetyElementof theirGeneralPlanandencourageslandusemanagementpoliciesandregulationstoreduceandmitigatethosehazardstoprotectpublichealthandsafety.UnderPublicResourcesCodeSection2697,citiesandcountiesshallrequire,priortotheapprovalofaprojectlocatedinaseismichazardzone,ageotechnicalreportdefininganddelineatingany seismic hazard. Each city or county shall submit one copy of each geotechnical report, includingmitigationmeasures, to the StateGeologistwithin 30 days of its approval. Under Public Resources CodeSection2698,nothingisintendedtopreventcitiesandcountiesfromestablishingpoliciesandcriteriawhicharestricterthanthoseestablishedbytheMiningandGeologyBoard.

Statepublicationssupporting therequirementsof theSeismicHazardsMappingAct include theCaliforniaGeologicalSurveySP117,GuidelinesforEvaluatingandMitigatingSeismicHazardsinCalifornia,andSP118,RecommendedCriteria forDelineatingSeismicHazardZones inCalifornia. Theobjectives of SP117 are toassistintheevaluationandmitigationofearthquake‐relatedhazardsforprojectswithindesignatedzonesofrequired investigations and topromoteuniformandeffective statewide implementationof the evaluationandmitigationelementsof theSeismicHazardsMappingAct. SP118implementstherequirementsof theSeismicHazardsMappingActintheproductionofProbabilisticSeismicHazardMapsfortheState.

TheCaliforniaGeologicalSurvey(CGS)isresponsibleforgeologichazardcharacterization,publiceducation,thedevelopmentofpartnershipsaimedatreducingrisk,andexceptions(basedonscience‐basedrefinementof tsunami inundation zone delineation) to statemandated tsunami zone restrictions. In California, eachearthquake is followed by revisions and improvements in the Building Codes. The 1933 Long BeachEarthquake resulted in theFieldAct, affecting school construction. The1971SylmarEarthquakebroughtanothersetof increasedstructuralstandards. Similarre‐evaluationsoccurredafter the1989LomaPrietaEarthquake and 1994 Northridge Earthquake. These code changes have resulted in stronger and moreearthquakeresistantstructuresstatewide.

In addition to the CGS, the State’s Seismic Safety Commission, the Applied Technology Council, CaliforniaEmergencyManagementAgency,UnitedStatesGeologicalSurvey,CalTech,theCaliforniaGeologicalSurveyaswellasanumberofuniversitiesandprivatefoundationshaveundertakenarigorousprogramtoidentifyseismichazardsandrisks includingactive fault identification,bedrockshaking, tsunami inundationzones,groundmotion amplification, liquefaction, and earthquake induced landslides. Seismic hazardmaps havebeenpublishedandareavailableformanycommunitiesinCaliforniathroughtheCGS.

November 2014 5.2 Geology and Soils


Regional Regulations

Los Angeles County Manual for Preparation of Geotechnical Reports

The Los Angeles County Department of PublicWorks (LACDPW)Manual for Preparation of GeotechnicalReports (“Manual”) (July 1, 2013) presents the requirements for geotechnical work within the County.Geotechnical reports that are required for grading plans must be coordinated with the LACDPW. Thepurpose of theManual is to provide geotechnical consultants with the information necessary to prepareadequate and acceptable reports consistent with the County Code. Geotechnical reports must includerecommendations and conclusions based on soil data, records, geologic conditions, and analysis ofgeotechnicalhazardsinrelationtositedevelopmentorremediation.

Itistheresponsibilityofthesoilsengineertoreviewtheprojectanddeterminewhatitemsmustbecovered(e.g.slopestability,collapsiblesoils, liquefaction,piledesign,constructionconstraints,mitigationofeffectstooffsiteproperty,etcetera)inthepreparationofageotechnicalreport.Thereportmustdemonstratethatproperty and public welfare will be safeguarded in accordance with current County Codes and policies.Provisions of the County Building Code Section 110.2 requires that the building site will be free ofgeotechnical hazards, such as landslide, settlement, or slippage, and that the proposed work will notadverselyaffectoffsiteproperty.CountyBuildingCodeSection111requiresthereportcontainafindingtoshowcompliancewithCountyBuildingCodeSection110.2.TheCountyBuildingCodeSection111statementmust clearlymake a finding regarding the safety of the site against hazard from landslide, settlement orslippageandafindingregardingtheeffectthattheproposedworkwillhaveonthegeotechnicalstabilityoftheareaoutsideoftheproposedwork.Thefindingmustbesubstantiatedbyappropriatedataandanalyses.

TheCountyBuildingCodeSection111statementismandatoryforallgeotechnicalreportsexceptforreportsprepared for tentative subdivisions and environmental impact reports. Although the 111 Statement isoptional for these specific types of reports, there must be sufficient supporting information thatdemonstrates to the satisfaction of the Building Official or Public Works Land Development DivisionSubdivisionMappingSection(SubdivisionMappingSection)that thesiteswillbedevelopableandthattherequiredBuildingCodeSection111Statementcanbeprovidedatalaterstageofdevelopment.

Section3.3.1.2of theManual specifically applies to geotechnical reportsprepared forEIR’s. According tothis section, if a proposed development is identified to have potentially significant impacts and an EIR isrequired, impactsdue to soilsor geology issuesmustbeaddressed in anappropriate report (engineeringgeology,soilsengineering,orgeotechnicalreport).Thereportmustbepreparedtoaddressallgeotechnicalissues that may affect the proposed development and its surroundings, including those identified in theInitial Study. The soils report must have sufficient data and analyses to support the recommendationsprovidedbythesoilsengineer.

ThefindingsinsoilsengineeringandgeotechnicalreportssubmittedtotheLACDPWmustbebasedontheboringlogs,trenches,pits,conepenetrationtestsoundings(CPTs)andothersubsurfaceexplorationsutilizedto characterize the soil data, soil properties, and subsurface conditions. Descriptions of the subsurfaceconditionsshouldbeclearandconsistentwiththesubsurfaceexplorationandsoildatacollected.Thelogsofallsubsurfaceexplorationsandsubsurfacedatashouldbeincludedwithinorappendedtothereport.



Los Angeles County Grading Guidelines

The Los Angeles County Grading Guidelines (“Guidelines”) (January 1, 2008) provide information for thepreparationandprocessingofgradingpermitapplications.Portionsofthegradingcodethatarecommonlyencountered during the planning, permitting, and construction of gradingwork are presented therein inordertoreduceunnecessaryplanreviewtimeandconstructiondelays.Alsoprovidedarereferralstoothergovernmentalagenciesthatmayhaveaninfluenceonthedesignandapprovalofaproject.Theinformationpresented in theGuidelinesdoesnotpresume tocoverall thepossibleCodeandordinancerequirements.TheprospectiveownerandcontractormayfinditnecessarytoconferdirectlywiththestaffofBuildingandSafetyDivisionorLandDevelopmentDivision,oftheLACDPW,foraspecificproject.

Los Angeles County Building Code

The Los Angeles County Building Code (LACBC) (Code of Ordinances Title 26), Appendix J, which isincorporatedby reference in theCity of CarsonMunicipal Code, sets forth regulations specific to grading.Section J101.5, Protection of Utilities, requires protection of utilities and Section J101.6, Protection ofAdjacent Property, requires protection of adjacent property during excavation. Under this provision, noperson shall excavate on land sufficiently close to the property line to endanger any public or privateproperty without taking measures to support such property from settling, cracking, or other damage.SectionJ101.7,StormWaterControlMeasures,requiresthatallprecautionarymeasuresnecessarytoprotectadjacentwatercoursesandpublicorprivatepropertyfromdamagebyerosion,flooding,anddepositionofmud, debris, and construction‐related pollutants originating from the site during grading and relatedconstructionactivitiesshallbeputintoeffectandmaintained.

UnderSectionJ103.1,PermitsRequired,nogradingshallbeperformedwithoutapermitfromtheBuildingOfficial.Aseparatepermitshallbeobtainedforeachsiteandmaycoverbothexcavationsandfillsandmaycoverbothexcavationsand fills. Regulargrading less than5,000cubicyards(CY)mayrequirea licensedcontractoriftheBuildingOfficialdeterminesthatspecialconditionsorhazardsexist.UnderSectionJ103.2,Exemptions,agradingpermit isnot required forexcavations thatdonotexceed2 feet indepthor50CY.Section J104.1, SubmittalRequirements, requires that thegradingplan showexistingand finishedgrades,limits and depths of cut and fill, location of any buildings or structures within 15 feet of the proposedgrading,contours,flowareas,andstormwaterprovisions.

.SectionJ104.2.1requiresthatgradinginexcessof5,000cubicyards(CY)shallbedesignatedas“engineeredgrading.” All engineered grading shall be performed in accordance with an approved grading plan andspecificationspreparedbyacivilengineer,unlessotherwiserequiredbytheBuildingOfficial.SectionJ104.1,SubmittalRequirements,requiresthatthegradingplanshowexistingandfinishedgrades,limitsanddepthsofcutandfill,locationofanybuildingsorstructureswithin15feetoftheproposedgrading,contours,flowareas,andstormwaterprovisions.

Under Section J104.4, Liquefaction Study, a liquefaction study is not requiredwhere the Building Officialdeterminesfromestablishedlocaldatathattheliquefactionpotentialislow.

Sections J105.3, Field Engineer Inspection, and J105.4, Soils Engineer Inspection, require that the fieldengineerorsoilsengineer,respectively,provideon‐site inspectionofthosepartsof thegradingwithintheengineer’sareaoftechnicalspecialty,whichincludesettingofstakes,observationduringgrading,testingfor



requiredcompactionandsafetyof structuresdue toany slippageor settlementof the completedgrading,and ensure that conditions in approved engineering reports are implemented. Under Section J106.1,MaximumCutSlope,theslopeofcutsurfacesshallbenosteeperthansafefortheintendeduse,andshallbeno steeper than 2 units horizontal to 1 unit vertical (50 percent) unless the applicant furnishes a soilsengineering report justifyinga steeper report. Thereportmustcontaina statementby thesoils engineerthatthesitewasinvestigatedandanopinionthatasteeperslopewillbestableandwillnotcauseahazardtopublicorprivateproperty,inconformancewiththerequirementsofSectionJ111.Exceptionsincludeacutsurfaceof 67percentprovided it is not intended to support structures, it is adequatelyprotected againsterosion,itisnomorethan8feetinheight,anditisapprovedbytheBuildingOfficial.

Section J107.4, Fill Material, provides standards for fill material and requires that fill shall not containorganic, frozen, or other deleteriousmaterials. Section 107.5, Compaction, requires that all fillmaterialsmustbecompactedtoamaximumof90percentmaximumdensityasdeterminedbyAmericanSocietyforTestingandMaterials(ASTM)D‐1557,ModifiedProctor,unlessalowerrelativecompaction(notlessthan90percent ofmaximumdry density) is justified by the soils engineer and approved by theBuildingOfficial.WhereASTMD‐1557,ModifiedProctor, isnotapplicable,a testacceptable to theBuildingOfficialshallbeused.Notlessthan10percentoftherequireddensitytests,uniformlydistributed,shallbeobtainedbytheSandCodeMethod.

SectionJ108.1,Setbacks,requiresthatcutandfillslopesbesetbackfromthepropertylines,aminimumof2feet and maximum of 20 feet unless substantiating data is submitted justifying reduced setbacks and ifrecommended in a soils engineering report approved by the Building Official. Under Section J108.4,AlternateSetbacks,theBuildingOfficialmayapprovealternatesetbacksifitisdeterminedthatnohazardtolifeorpropertywillbecreatedorincreased.

UnderSectionJ111,NationalPollutionDischargeEliminationSystem(NPDES)Compliance,plansforallbestmanagement practices (BMPs) shall be provided and BMPs shall be installed before grading begins. Asgradingprogresses,allbestmanagementpracticesshallbeupdatedasnecessarytopreventerosionandtocontrolconstructionrelatedpollutantsfromdischargingfromthesite.SectionJ111.2,StormWaterPollutionPrevention Plan (SWPPP), if required, this plan details best management practices, including temporarydrainage or control measures, or both, as necessary to control construction‐related pollutants. SectionJ111.3, Wet Weather Erosion Control Plans (WWECP) is required if grading is not completed prior toNovember1. TheWWECP shall include specific bestmanagement practices tominimize the transport ofsedimentandprotectpublicandprivatepropertyfromtheeffectsoferosion,flooding,orthedepositionofmud,debrisorconstruction‐relatedpollutants.

Section1805.3.2,FootingSetback fromDescendingSlopeSurface, requires that footingsonoradjacent toslope surfaces shall be founded in firmmaterials with an embedment or setback from the slope surfacesufficient to provide vertical and lateral support for the footingwithout detrimental settlement. Footingshallbeplaces into firmnaturalmaterialand locatedaminimumof5 feet fromtheslopesurface. Section1805.3.5, Alternate Setback and Clearance, allows the Building Official to approve alternate setbacks andclearances if safetyconsistentwith theCode isdemonstratedbyasoilsengineer. Such investigationshallincludethetypeofmaterial,heightofslope,slope‐gradient,loadintensity,anderosioncharacteristicsoftheslope materials. Where adverse geological, soil, and drainage conditions exist, the Building Official mayrequireincreasesinsetbacksandclearances.



Local Regulations

City of Carson Natural Hazards Mitigation Plan

The City of Carson Natural Hazards Mitigation Plan (adopted July 5, 2012) includes resources andinformation to assist City residents, public and private sector organizations, and others interested inparticipatinginplanningfornatural,man‐made,andtechnologicalhazards.TheMitigationPlanprovidesalistofactivities thatmayassist theCityofCarson inreducingriskandpreventing loss fromfuturehazardevents.

The action items addressmulti‐hazard issues, aswell as activities forEarthquake, Flood, andWindstorm.Themission of the City of CarsonMitigation Plan is to promote sound public policy designed to protectcitizens,criticalfacilities,infrastructure,privateproperty,andtheenvironmentfromnaturalhazards. Thiscan be achieved by increasing public awareness, documenting the resources for risk reduction and loss‐prevention,and identifyingactivities toguidetheCity increatingamoresustainablecommunity. PoliciesapplicabletogeologichazardsincludeEQ‐1andEQ‐12,whicharetointegratemappingofexistingandnewearthquakehazardstoandimprovetechnicalanalysisofearthquakehazards.

Implementation through existing programs: The City of Carson addresses statewide planning goals andlegislativerequirementsthroughitsGeneralPlan,CapitalImprovementPlans,andCityBuildingandSafetyCodes. The Natural Hazards Mitigation Plan provides a series of recommendations, many of which arecloselyrelatedtothegoalsandobjectivesofexistingplanningprograms. TheCityofCarsonwillhavetheopportunitytoimplementrecommendedmitigationactionitemsthroughexistingprogramsandprocedures.

SomeofthegoalsandactionitemsintheMitigationPlanmaybeachievedthroughactivitiesrecommendedintheCity'sCapitalImprovementProgram(CIP).VariouscitydepartmentsdeveloptheCIPandreviewitonan annual basis. Upon annual review of the CIP, the Public Safety Commission will work with the citydepartments to identify areas that the Mitigation Plan action items are consistent with CIP goals andintegratethemwhereappropriate.

City of Carson General Plan Safety Element

City of CarsonGeneral Plan Safety Element (adoptedOctober 11, 2004) evaluates natural andman‐madehazardsthathavethepotentialtoendangerthewelfareandsafetyofthegeneralpublicandaimstoreducethepotentialriskofdeath,injuries,propertydamageandtheeconomicandsocialdislocationresultingfromthem.Thepotentialthreatfromnaturalandman‐madehazardscanposesignificantdangertoacommunity.TheSafetyElement identifies flooding, seismic activity, geology, soils andwindasnaturalhazards for theCity. Man‐madehazards involvehazardousmaterials, transportation,oilproduction facilities, civilunrest,nationalsecurityemergenciesandterrorism.TheconcernsidentifiedintheSafetyElementaresubsequentlyincorporated intogoals,policiesandimplementationactions toreducethe impactsofhazards. TheSafetyElementaddressestheexistingconditionsofthesehazardsandprogramscurrentlyinplacetoaddressthem(SafetyElement,page4).



GoalSAF‐1:Minimizetheriskofinjury,lossoflife,andpropertydamagecausedbyearthquakehazards.

PolicySAF‐1.1ContinuetorequireallnewdevelopmenttocomplywiththemostrecentCityBuildingCodeseismicdesignstandards.

PolicySAF‐1.2WorkwiththeCity’sPublicInformationOfficeandPublicSafetyDivisionto:

Educateresidentsinearthquakesafetyathome,

Educatethepublicinself‐sufficiencypracticesnecessaryafteramajorearthquake(e.g.,alternativewatersources, foodstorage, firstaid, familydisasterplans,andthelike),and

Identify locationswhere information is available to thepublic forplanning self‐sufficiency.

PolicySAF‐1.3Examine thepotential tocreateacommercial loanprogramtosubsidizethecostofretro‐fittingbuildingstomeetseismicsafetyregulations.Tothisend,pursueall sources of state and federal funding in order to retro‐fit buildings tomeet seismicrequirements.

ImplementationMeasureSAF‐IM‐1.1:ApplyCityBuildingCodeconsistentlytoalldevelopment.(ImplementsSAF‐1.1)

City of Carson Municipal Code

TheCityofCarsonMunicipalCode(CMC)primarilyincorporatesbyreferencethebuildingrequirementsoftheLosAngelesCountyCode(Title26,AppendixJ)regardinggrading,soils,andgeologicissues. However,additionstoTitle26,AppendixJundertheMunicipalCodearealsoapplicabletogradingoperations.Theseinclude Division 6, Project Grading, Sections 9166.1 and 9166.2. Under these code sections, a projectrequiringtheremovalofmorethan10,000CYofsoilandifmorethan20occupieddwellingunitsarelocatedwithinaparallelcorridor300feetwideoneachsidefromtheedgeofatransportroute,gradingshallnotbepermittedunlesseitherofthefollowingisprovided:

A. AConditionalUsePermitisobtained,or

B. Aplotplanissubmittedtothedirector,whoshallapprovetheplanuponfindingthattheproposedprojectgradingwillcomplywiththerequirementsofthisDivision.

Section9166.2setsforthspecificconditionsforgrading,includingthefollowing:

A. Agradingpermit,whenrequired,shallfirstbeobtainedasprovidedintheBuildingCodebeforethecommencementofanyprojectgrading.

B. The application to the Director or for a Conditional Use Permit, as the casemay be, shall containstatementssettingforththefollowinginformation:



1. Thenamesandaddressesofallpersonsowningalloranypartofthepropertyfromwhichsuchmaterialisproposedtoberemovedandtowhichsuchmaterialisproposedtobetransported.

2. The names and addresses of the person or persons who will be conducting the operationsproposed.

3. Theproposedultimateuseofthelot.

4. Such other information as the Director finds necessary in order to determine whether theapplicationshouldbegranted.

5. InthecaseofanapplicationforaConditionalUsePermit,theinformationrequiredpursuanttoCMC9172.21(A)and9173.1.

C. Theapplicantshallsubmitamapshowinginsufficientdetailthelocationofthesitefromwhichsuchmaterialisproposedtoberemoved,theproposedrouteoverstreets,andthelocationtowhichsuchmaterialistobeimported.

D. AllhaulingasapprovedunderthisSectionshallberestrictedtoarouteapprovedbytheDirectorofPublicWorks.

E. Compliance shall be made with all applicable requirements of the City and other governmentalagencies.

F. IfanyconditionofthisSectionisviolated,orifanylaw,statuteorordinanceisviolated,theprivilegesgrantedhereinshalllapseandsuchapprovalshallbesuspended.

G. Neither the provisions of this Sectionnor the granting of anypermit provided for in thisDivisionauthorizesorlegalizesthemaintenanceofapublicorprivatenuisance.

Existing Conditions

Regional Geological Setting

The City of Carson is situated in the northern part of the physiographic basin known as the Los AngelesBasin,ortheCoastalPlainofLosAngelesandis locatedwithinthenortherlyendofthePeninsularRangesgeomorphic province. The Peninsular Ranges province extends from the Los Angeles Basin south of theSantaMonicaMountainstothetipofBajaCalifornia.

Geologically,theBasinconsistsofaverythicksequenceofunconsolidatedmarineandcontinentalsedimentsoverlying consolidated sedimentary rocks that range in age from a few thousand years to tens ofmillionyears. Geologic units of the northern Peninsula Ranges province consist of Jurassic and Cretaceous agebasementrocksoverlainbyasmuchas32,000feetofmarineandnon‐marinesedimentarystrataranginginage from the late Cretaceous to Holocene epochs. The north, west, and southern portions of Carson isunderlainbystreamQuaternaryNon‐marineTerraceDeposits(Qt).Thecentralandsoutheasternportionofthe City of Carson is directly underlain by Holocene age alluvial (Qal) deposits of the Downey Plain andDominguezGap.Thealluvialdepositsarecomposedofpoorlyconsolidatedsand,silt,clay,andgravel.



Thisgeomorphicprovinceischaracterizedbyelongatednorthwesttrendingmountainrangesseparatedbystraight‐sided sediment floored valleys. Themost prominent landforms features within the City are theDominguezHills,whichrepresentsthecentralportionoftheNewport‐Inglewoodfaultzone(oruplift),andtheDominguezGap,whichcharacterizethearea’snorthwest‐trendingfaultsandfolds.ThelatterincludetheNewport‐Inglewoodfaultzone,theParamountsyncline,theDominguezanticline,theGardenasyncline,theWilmingtonanticline,andtheWilmingtonsyncline.

Earthquake Fault Zones

SeveralmajorfaultsthatcouldaffectthegreaterLosAngelesregionandtheCarsonareaareidentifiedintheCityofCarsonGeneralPlanSafetyElementandNaturalHazardsMitigationPlan. Faultzonesintheregionare illustrated in Figure 5.2‐1, Southern California Earthquake Faults. These include the following faultzones thatare identified in theSafetyElementandNaturalHazardsMitigationPlanashavingthegreatestpotentialeffectontheCityofCarson:

Avalon‐Compton/NewportInglewoodFaultZone

SanAndreasFaultZone

PalosVerdesFaultZone

WhittierFaultZone

SantaMonicaFaultZone

TheAvalon‐ComptonFaultZone,whichispartoftheNewport‐InglewoodFaultZone,istheonlyactivefaultintheCityofCarson.TheAvalon‐ComptonfaultislocatedimmediatelyeastofAvalonBoulevardandnorthof theArtesiaFreeway(SR‐91),approximately fivemiles to thenorthof thesite. Historically, theAvalon‐Compton fault and regional shear zonehasmoderate tohigh seismic activitywithnumerousearthquakesgreaterthanRichtermagnitudefour. TheNewport‐InglewoodfaultextendsfromthesouthernedgeoftheSantaMonicaMountainssoutheastwardtoanareaoffshoreofNewportBeach.ThiszonecommonlyreferredtoastheNewport‐Inglewoodupliftzone,canbetracedatthesurfacebyfollowingalineofgeomorphicallyyounganticlinalhillsandmesas. Thesehillsandmesas includetheBaldwinHills,DominguezHills,SignalHill,HuntingtonBeachMesaandNewportMesa.

Earthquake focal mechanisms (seismic locaters) for 39 small earthquakes (1977 to 1985) show faultingalongthenorthsegment(northofDominguezHills)andalongthesouthsegment(southofDominguezHillstoNewportBeach). The1933LongBeachearthquakehasbeenattributed tomovementon theNewport‐Inglewood fault zone. Based on historic earthquakes, the fault zone is considered active. The Newport‐Inglewood fault zone (outside of the Avalon‐Compton Fault Zone) is considered capable of generating amaximumcredibleearthquakeofamagnitude7.0ontheRichterScale.

The San Andreas Fault Zone is California’s most prominent structural feature, trending in a generalnorthwestdirection foralmost theentire lengthof thestate. Thesouthernsegment isapproximately280miles long. Itextends fromtheMexicanborder into the transverserangeswestofTejonPass. Alongthissegment,thereisnosingletraceablefaultline;rather,thefaultiscomposedofseveralbranches.Thefaultisconsideredcapableofgeneratingamaximumcredibleearthquakeofmagnitude8.25ontheRichterScale.



ThePalosVerdesFault Zone is located southwestof theCityofCarsonand is traceable in the subsurfacealong the northern front of the Palos Verdes Hills. Offshore data, consisting of acoustic and reflectionprofiles,suggestsveryrecentmovementalongthePalosVerdesFault.

TheWhittier Fault Zone (Elysian Park Structure) is the source of the 1987Whittier Narrows earthquake(Richtermagnitude5.9).Theearthquakehasbeenattributedtosubsurfacethrustfaults(alowanglereversefault)thatarereflectedattheearth’ssurfacebyawest‐northwesttrendinganticlineknownastheElysianParkAnticline,ortheElysianParkstructure.Thesubsurfacefaultsthatcreatethestructurearenotexposedatthesurface,anddonotpresentapotentialsurfacerupturehazard.However,asdemonstratedbythe1987earthquakeandtwosmallerearthquakesonJune12,1989,thefaultsareasourceoffutureseismicactivity.Assuch,thestructureshouldbeconsideredanactivefeaturecapableofgeneratingfutureearthquakes.

The Santa Monica Fault Zone is an east‐west trending left reverse fault that extends approximately 24kilometerswithin the immediate vicinity of Pacific Palisades,Westwood, Beverly Hills and SantaMonica.Annualsliprateisestimatedbetween0.27mmand0.39mmperyearalongthefault.Thefaultisconsideredcapableofgeneratinganearthquakebetweena6.0to7.0ontheRichterscale.

TheUniformCaliforniaEarthquakeRuptureForecast(UCERF)published in2007estimatedthatCaliforniahasa99.7percentchanceofhavingamagnitude6.7or largerearthquakeduring thenext30years.3 Thelikelihoodofanevenmorepowerfulquakeofmagnitude7.5orgreater inthenext30years is46percent.BasedontheUCERF,theprobabilityofamagnitude6.7orlargerearthquakeoverthenext30yearsstrikingthe greater Los Angeles area is 67 percent. For the entire California region, the fault with the highestprobabilityofgeneratingatleastonemagnitude6.7quakeorlargeristhesouthernSanAndreasFault.

Secondary Seismic Hazards

Ground shaking, landslides, liquefaction, and amplification are the specific hazards associated withearthquakes.Theseverityofthesehazardsdependsonseveralfactors,includingsoilandslopeconditions,proximitytothefault,earthquakemagnitude,andthetypeofearthquake.Groundshakingisthemotionfelton the earth's surface caused by seismic waves generated by the earthquake and the primary cause ofearthquakedamage. Buildingsonpoorlyconsolidatedandthicksoilswill typicallyseemoredamagethanbuildingsonconsolidatedsoilsandbedrock.

Earthquake‐inducedlandslidesaresecondaryearthquakehazardsthatoccurfromgroundshaking.Theycandestroytheroads,buildings,utilities,andothercriticalfacilitiesnecessarytorespondandrecoverfromanearthquake. Many communities in Southern California have a high likelihood of encountering such risks,especiallyinareaswithsteepslopes.

Liquefactionoccurswhengroundshakingcauseswetgranularsoilstochangefromasolidstatetoaliquidstate. This results in the lossof soil strengthand thesoil'sability tosupportweight. Buildingsand theiroccupants are at risk when the ground can no longer support these buildings and structures. Basicconditions necessary for liquefaction are soil conditions conducive to liquefaction, saturation of thesematerials bywater, and a source of shaking. The Newport‐Inglewood fault zone is a potential source of

3 UnitedStatesGeologicalSurvey,UniformCaliforniaEarthquakeRuptureForecast(UCERF)II,2007.

FIGURESouthern California Earthquake Faults

Former Kast Property Tank Farm Site Remedia on Project 5.2-1Source: General Plan Safety Element, SAF-3, 2002.

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P C R



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groundstress,andliquefactioncouldoccurintheCityofCarsonifthegroundwatertablewerehighenoughduringanearthquake. DuetoexistingconditionsintheCity,particularly inthealluvialandformersloughareas,thereisthepossibilitythatliquefactioncouldimpactbuildingsandotherstructuresintheeventofanearthquake.Figure5.2‐2,LiquefactionAreas‐CityofCarson,showstheareasintheCitywhichhaveshownhistorical occurrence of liquefaction, or areas in which local geological, geotechnical and groundwaterconditionsindicateapotentialforpermanentgrounddisplacements.Liquefactioncanresultintheshiftingoffoundations,settlingofroadwaysandruptureofundergroundpipelinesandcables.Buildingsandotherobjectsonthegroundsurfacecansettle,tiltandcollapseasthefoundationsbeneaththemlosesupport,andlightweightburiedstructuresmayfloattothesurface.AsignificantportionoftheCityhasbeendesignatedas potential liquefaction area and geotechnical investigation reports are required as part of theenvironmentalandbuildingpermitprocessesformostdevelopmentwithintheseareas.

Ground cracking, ground lurching and lateral spreading are secondary features resulting from strong tomoderatelystronggroundshakingandmaybeassociatedwithliquefaction.Groundcrackingusuallyoccursin near‐surface materials, reflecting differential compaction or liquefaction of underlying materials. Thepotential for ground cracking exists especially in those areas of the City that have a moderate to highpotentialforliquefaction.Groundlurchingresultswhensoft,water‐saturatedsurfacesoilsarethrownintoundulatorymotion.Lateralspreading(aformoflandsliding)isreferredtoaslimiteddisplacementgroundfailure,oftenassociatedwithliquefaction.Compactsurfacematerialsmayslideonaliquefiedorlowshearstrengthlayeratashallowdepth,movinglaterallyseveralfeetdownslopesoflessthantwodegrees.Suchaconditionmaybepresentwhereconditionsconductive toshallow liquefactionexist. Because liquefactionhasalowpotentialofoccurrenceattheprojectsite,theseconditionsarenotanticipated.

Amplification can occur when soils and soft sedimentary rocks near the earth's surface modify groundshakingcausedbyearthquakes. Amplification increasesthemagnitudeof theseismicwavesgeneratedbytheearthquake. Theamountofamplificationisinfluencedbythethicknessofgeologicmaterialsandtheirphysical properties. Buildings and structuresbuilt on soft andunconsolidated soils can face greater risk.Amplificationcanalsooccurinareaswithdeepsedimentfilledbasinsandonridgetops.

ThehistoricwithdrawalofoilhasbeenknowntocausesubsidenceinportionsoftheWilmingtonoil field,which is locatedwithin theCityofCarson. Subsidenceextendedalong theNewport‐Inglewood structuralzonebetweenSignalHill and thePortof SanPedroon the southandRedondoBeachon thenorth. Totalsubsidencereachedamaximumof29feetoverthecrestoftheWilmingtonanticline,wheremostoftheoilhadbeenwithdrawn. ThereisnodocumentedgroundsubsidenceassociatedwiththeDominguezoilfield,also located in the City. By the early 1980s, water injection halted subsidence at the oil fields and,subsequently,nofurthersubsidencehasbeendocumented.

Soil Characteristics

OthergeologichazardsthathavethepotentialtooccurinandaroundtheCityofCarsonincludedifferentialsettlement, subsidence, and shrink/swell potential. Differential settlement occurs in loose, cohesionlesssediments where differences in densities in adjacent materials lead to different degrees of compactionduringground shaking. In the caseof saturated cohesionless sediments, post‐earthquake settlementmayoccur when excess pore‐water pressures generated by the earthquake dissipate. Given the lateral andverticalvariationofthealluvialsoilsunderlyingCarson,differentialsettlementcouldoccurasaresultofanearthquakeinareasthoughttohavealowsusceptibilitytosettlement.AccordingtotheEIRpreparedforthe



CityofCarsonGeneralPlan,theunstablesub‐baseofsandysoilinthealluvialdepositsunderlyingthecentralandsoutheasternportionsoftheCity,andQuaternarynon‐marineterracedepositsunderlyingthenorthern,westernandsouthernportionsoftheCity,Carson(aswellastheentireSouthBayarea)isregardedasoneofthemostsevereshockareasintheLosAngelesarea.4 Thesignificanceof thehazardatanyparticularsitewould be determined by soils investigations. Differential compaction resulting from earthquake groundshakingispotentiallydamagingtostructuresandburiedutilitiesandservices.5

Theshrink/swellcharacteristicsofsoilsintheCityofCarsonareanothergeotechnicalconstraint.Soilswithahighclaycontenttypicallyhavehighshrink/swellcharacteristics.Shrinkingandswellingofsoilcancauseoverlyingconcretetocrackandsettle. Inaddition,soilswithhighpercentagesofsandhaveamoderatetohighpotentialforerosion.Table5.2‐1,GeneralPhysicalCharacteristicsofSoilsintheCarsonArea,describesthevarioussoilstypeswithintheCarsonarea.

On‐Site Geologic Setting

Historical Setting

Basedonhistoricalrecords, the formerKastTankFarmthatoccupiedthesiteconsistedof threecrudeoilreservoirs. Oilwaspumped into the reservoirs andwithdrawn from the reservoirs viapipelines that rannorth‐south along the western site property line and east‐west along what is now Lomita Boulevard.

4 CityofCarsonGeneralPlanEnvironmentalImpactReport,Chapter4.6,GeologicandSeismicHazards,October30,2002,page4.6‐6.5 Ibid.

Table 5.2‐1

General Physical Characteristics of Soils in the Carson Area

Soil Association Soil Type Depth Slope Erosion

Potential Shrink‐Swell

Potential

Oceano Sand 60inches

2‐5percent Mod‐High Low

Netz‐Cortina Finesandandfinesandyloam

60inches

0‐5percent Lo‐Mod Low

Hanford Sandyloam

60inches

2‐5percent Low Low

Yolo Siltyloam 60inches

0percent Low‐Mod Mod

Chino(ininclusionsoftheForsterandGrangevilleAssociations)

Clayloam 60inches

0percent Low Mod

Ramona‐Placenta Sandyloam

18‐60inches

2‐5percent Low‐Mod High

Source: City of Caron General Plan Safety Element, Table SAF‐1.

FIGURELiquefac on Areas - City of Carson

Former Kast Property Tank Farm Site Remedia on Project 5.2-2Source: General Plan Safety Element, SAF-3, 2002.

N

P C R

Project Site

Liquefaction Zone



Pipelines are believed to have entered the property from Lomita Boulevard near what is now NeptuneAvenueinanorthwarddirectionandrantothepumphouse.

The reservoirshad reinforcedconcrete‐lined floorswith reinforcedconcrete‐linedearthenberms formingsloped side walls and wood frame roofs supported by wooden posts and/or concrete pedestals. Theconcrete floors of the reservoirs were approximately 7 to 10 feet below current site grade, and thesurroundingearthenwallsweredescribedas “generally about fifteen feet inheight.”6 The reservoirshaddepths of approximately 20 to 25 feet from the top of the berms. The sloped sidewalls of the reservoirberms were approximately 1.5:1 horizontal to vertical. The bottom and sides of the reservoirs werereportedly linedwith a 4 to 5‐inch thick reinforced concrete slab and therewere also 1‐ to 15‐foot highcontainmentbermssurroundingtheproperty.

The concrete bases of the reservoirswere either partially removed from the site or abandoned in place.Followingtheremovalofresidual fluidsfromthereservoirs, trencheswerecut intotheconcretereservoirbases so that the reservoirs would not pond water and adversely affect drainage/infiltration for thesubsequentresidentiallots.Accordingtosoilsreports,78trenchesapproximately8incheswidewerecutorpunchedintotheconcretereservoirbasesinconcentricringsradiatingfromthecenterat15‐footintervals.According to thegeotechnical report for thesoutheasternreservoir (ReservoirNo.6), “nearly6,000 linealfeet of trenchwere punched through the concrete floor using a truckmounted rig.”9 Concrete from thetrencheswas reportedly removed topromote infiltration andmitigatepondingofwater. However, otherdocumentationexiststhatindicatetrenchesinthereservoirbaseswererippedinparallellinesratherthanconcentricrings.10Theconcretefromthereservoirsidewallswasreportedlymixedwithsoilbeforebeingplacedinasinglelayerwithinthelower1footoffilluponthebaseofthereservoirswhereitwaswateredandcompactedinplace.11Asdiscussedinthe1966geotechnicalreportpreparedforLomitaDevelopmentbyPacificSoilsEngineering,theLosAngelesCountyBuildingandSafetyCoderequiredaminimumof7feetoffillsoiltobeplacedovertheconcrete.Thereportrecommendedthat“noconcreteshallbeplacedwithin7feetoffinishedgrade.”12

ThePacificSoilsEngineeringgeotechnicalreportforReservoirNo.5indicatesthatthewesternmostportionof the concrete reservoirbase inTract24836alongMarbellaAvenuewasentirely removed from theSiteduringdemolition.BecausetheeasternedgeofTract24836isalongthebackpropertylineofpropertiesontheeastsideofMarbellaAvenue,theconcretereservoirbaseforReservoirNo.5wouldhavebeenremovedfrombeneathlotsontheeastsideofMarbellaAvenuebutnotbeneathpropertiesontheeasternhalfofthe

6 PacificSoilsEngineering,Inc,1966,quotedinURSCorporation,AssessmentofEnvironmentalImpactandFeasibilityofRemovalof

ResidualConcreteReservoirSlab,FormerKastProperty,Carson,CA,June28,2013,page2‐1.7 Ibid.8 PacificSoilsEngineering,Inc,July31,1967.Re:TractNo.28441,Lots7‐10inclusiveintheCountyofLosAngeles,California9 URSCorporation,AssessmentofEnvironmentalImpactandFeasibilityofRemovalofResidualConcreteReservoirSlab,FormerKast

Property,Carson,CA,June28,2013,page2‐4.10 Ibid.11 Ibid.12 Ibid.



block that frontonNeptuneAvenue. Trencheswere cut in the remainingportionof the concretebaseofReservoirNo.5,similartotheotherreservoirs.13

Testimonyreceivedfromapriorprojectengineerindicated“therewasenoughsoilinthebermstocoverallofthereservoirsandbringthePropertysurfaceuptostreetlevelwithoutimportinganysoil.Therefore,nosoilwasbroughtontothepropertytocoverthethreereservoirs.”14

Existing Geologic Setting

Geophysical and Soils Conditions

The Avalon‐Compton Fault Zone, which is part of the Newport‐Inglewood Fault Zone, is locatedapproximately5milestothenorthof theprojectsite, is theonlyactive fault intheCityofCarsonandthenearest fault zone to the project site. As illustrated in Figure 5.2‐2, the areas designated as having highliquefactionpotentialintheCityarelocatedtotheeastofthesite,totheeastofWilmingtonAvenueandtothewestofthesitetothewestofMainStreetanddonotunderlietheprojectsite.

Thecurrentsitegroundsurfaceelevationrangesfromapproximately44.5feetabovemeansealevel(amsl)attheintersectionofPanamaAvenueand249thStreetinthesoutheastcorneroftheCarouselTractto32.5feetamslneartheintersectionofMarbellaAvenueand244thStreetnearthenorthwestcornerofthetract.Thesitewasgradedtoslopetothenorthwesttopromotedrainageduringroughgradingafterdemolitionofthereservoirs.

Basedonsiteinvestigations,theupper10feetofsoilbeneaththesiteisdominantlyfinegrainedandconsistsofsiltwithlayersorlensesofsiltyfinesand.Soilsbetween10and15feetbgsconsistprimarilyofsiltandsilty finesand. From15to85feetbgssitesoilsconsistof finesandstosilty finesand. Soilsencounteredbetween 85 and approximately 180 feet bgs consist of silt, silty sand, and fine to medium sand. TheshallowestgroundwaterencounteredbeneaththesiteoccurswithintheBellfloweraquitard,anoverallfine‐grainedunitthatlocallyhassandyintervals. Firstgroundwateroccursatadepthofapproximately53feetbeneaththesite,withagroundwaterflowdirectiontothenortheast.

Fieldinvestigationandboringsperformedonthesiteinthe1960sdeterminedthatthesiteisunderlainbyrelativelyuniformsoils.Allsoilswerefoundtobeinadensestateandsuitabletoreceivefill.Generally,thefirst3feetofsoilstendedtobesiltyandclayeysands. Underlyingsoilsrangedfromfinetomediumsands. 15ThegeotechnicalreportdeterminedthatsurfacesoilsinallboringsexceptBorings1and2wereinadensestate and suitable for foundation purposes. The surface soils encountered in Borings 1 and 2were leansandsinasoft,saturatedstateandthegeotechnicalreportstatedthat“similarsoilscanbeexpectedtoexistin the northwest corner of the site due to the presence of an old watercourse as disclosed by aerial

13 PacificSoilsEngineeringquoted inURSCorporation,AssessmentofEnvironmental ImpactandFeasibilityofRemovalofResidual

ConcreteReservoirSlab,FormerKastProperty,Carson,CA,June28,2013,page2‐4.14 Leroy H. Vollmer (Vollmer Engineering) signed Declaration September 9, 2011, quoted in URS Corporation, Assessment of

Environmental ImpactandFeasibilityofRemovalofResidualConcreteReservoirSlab,FormerKastProperty,Carson,CA, June28,2013,page2‐4.

15 PacificSoilsEngineering,Inc,WorkOrder6164,March11,1966,page2.



photographs taken prior to the construction of the reservoirs.”16 In their former state, these soils wereunsuitableforfoundationpurposes.Thegeotechnicalreportrequiredthatsoft,compressiblematerials,suchasthoseencounteredinBorings1and2,beprocessedandcompactedtoadepthoffourfeet.Accordingtothe1966PacificSoilsgeotechnicalreport,theresultingmaterialwouldhaveaminimumrelativecapacityof90percentinaccordancewiththeCountyBuildingCode17

Soilsunderlyingtheleansandsatadepthrangingfrom10to15feetwereclean,denseto finetomediumsands. The moisture content decreased with depth and no groundwater was observed. The soilsencounteredonthetractwerefoundtobenon‐expansivebybothLosAngelesCountyand(FederalHousingAdministration (FHA) criteria. A boring capacity of 1500 lbs/sq. ft. was recommended for structuresfoundedincompactedfillorfirmnaturalgroundtoadepthofonefoot.18

Becausenonewsoilswerebrought to thesitewhen itwasmassgraded in1966(subsequent to the1966geotechnicalreport),itislikelythatsoilspresentin1966werespreadoverthepropertyandarepresentinexisting boring examples. According to 2009 borings, the upper 5 feet of soil encountered in theexplorationswasgenerallyuniform,consistingofdarkgraytodarkgrayishbrownsiltwhichwasmoistandgenerallyincludedshellfragments.Muchoftheupper5feetofsoilwasobservedtohavehydrocarbonodorandstaining.From5to10feetbgs,soilsconsistedprimarilyofsilt,withoccasionallayersorlensesofsiltyfinesand. Hydrocarbonstainingandodorwerealsogenerallyobservedatthisdepthinterval. Basedonareviewoftheboringlogsandconepenetrometertest(CPT)logs,soilsbetween10and15feetbgsconsistedprimarilyoflightolivetoolivesiltsandsiltyfinesand.Lithologyfrom15to85feetbgsconsistedprimarilyof alternating finesands tosilty finesand. Theestimatedpercentageof finesoilsvaried from less than5percenttogreaterthan30percent. Occasionalsiltydepositswereencountered,approximately1 to8 feetthick.Groundwaterwasencounteredbetween53and64feetbgs.Hydrocarbonstainingand/orodorwerenotedintenofthe20locationsdrilledtodepthsbeyond15feetbgs.Thedeepeststainingobservedwasatapproximately65feetbgsintheboringdrilledformonitoringwellMW‐2.19

In the2009study,soilsampleswererecoveredatapproximately3 feet,andevery2.5 to5 feet thereafterwithaModifiedCaliforniasplit‐spoonsoilsampler.Bulksamplesweretakenfromtheupper5feetofeachboring.Representativesampleswereplacedinsealedcontainersandtransportedfortesting.Inboringlogsforthe24612NeptuneAvenuesite,BoringN24612G1,thesubsurfacesoilsconsistofsiltysandandverystiffsandyclayfillsoilstoadepthof8.5feet.Concreteslabsapproximately6‐inchesthickwereencounteredatdepthsof7and8.5feetbgs.Alayerofverystiffleanclaywaspresentbetweentheslabs.Theconcreteslabatadepthof8.5feetwasunderlainbyloosetoverydensesiltysandalluviumtoadepthofapproximately17.5feet.Thislayerisunderlainbyhardleanclaytoapproximately22.5feet.Alayerofdense,siltysandispresent from22.5 feet to themaximumexploreddepthof25.5 feet. InBoringN24612G2, thesubsurfacesoilsconsistofmediumdenseclayeysandfillstoadepthof7.5feet.Aconcreteslabapproximately6inchesthickwas encountered at 7.5 feet. A layer ofmediumdense silty sands andpoorly graded sandwith silt(alluvium)wasencounteredbelowtheconcreteslabtoadepthof16feet,underlainbyhardleanclaytoadepthof22.5feet.Alayerofdense,siltysandispresentfrom22.5feettothemaximumexploreddepthof

16 PacificSoilsEngineering,Inc,WorkOrder6164,January7,1966,page2.17 PacificSoilsEngineering,Inc,WorkOrder6164,January7,1966,page3.18 PacificSoilsEngineering,Inc,WorkOrder6164,January7,1966,page2.19 URSCorporation,FinalPhaseICharacterizationReport,FormerKastProperty,Carson,CA,October15,2009,page4‐1.



25.5 feet. Groundwaterwasnotencountered in anyof theboringsdrilled to themaximumdepthof25.5feet.20

Based on the review of environmental boring logs for the 24533 Ravenna Avenue site, the geotechnicalreportconcludedthatsubsurfacesoilsconsistofsandysiltandsiltysandtotheexploreddepthof10feet.Groundwater was not encountered in the environmental borings drilled to the depth of 10 feet.GroundwatertablemonitoringfromOctoberthroughDecember2011atthesiteindicatedthatgroundwaterwasatanelevationof20feetwhichcorrespondstoapproximately63feetbgs.21

Subsurface Concrete Slabs

Inordertolocateconcreteslabsburiedonsite,morethan2,400soilboringswereperformedat265ofthe285 properties in the Carousel Tract, with an average of approximately nine borings per property. Thetargetcompletiondepthfortheseboringsis10feetbgs,whichistheapproximateupperendofthedepthofburialrangeoftheconcretereservoirslabs.

Figure 5.2‐3, Boring RefusalMap, outlines properties where “refusal”22 was not encountered and showsrefusal depths in increments for locationswhere boringswere terminated due to an encountered object.Front and back yards are shown individually where refusal conditions differed between front and backyards.Thisfigureshowsastrongcorrespondencebetweenboringrefusalatdepthsrangingfrom7.1and10feetbgsandtheoutlinesofthereservoirbases.23

Boringrefusalatdepthsrangingfrom0.1to5feet(shadedgreenandyellowonFigure5.2‐3)isinterpretedtobedue toencountering rocksorotherdebrisandnot the reservoirbase. Locationswhere refusalwasencounteredatdepthsrangingfrom5.1to7feetbgsarehighlightedinorangeonFigure5.2‐3,andlocationswhererefusaloccurredatdepthsof7.1to10feetbgsareshowninlightblue.Atasmallnumberoflocations,refusalwasencounteredatdepthsofgreaterthan10feetbgs;theseareshowninpurple.At133ofthe265propertiesthathavehadresidentialsoilsampling,boringswereadvancedtothetargetdepthof10feetbgsandrefusalwasnotencountered.Thismeansthatrefusalwasencounteredat132propertiesinoneormoreboringsatdepthsrangingfromlessthan1footto12feetbgs.24

In the area of northern Reservoir No. 7, refusal was encountered in borings at more than half of theproperties locatedpartiallyor completelywithin the inner ring interpreted to indicate themarginsof thebaseofthereservoir.Refusalwasmorefrequentinthewesternone‐thirdofthereservoirandlessfrequentin theeasternone‐thirdof thereservoir,consistentwithsitegradeslopingto thenorthwestcornerof thesiteandlowerelevationsinthisarearesultinginshallowerdepthofburial.Atthemajorityoflotswithinthe

20 URSCorporation,GeotechnicalReport,PlannedPilotTestforRemedialExcavationandBackfillPlacement,24612NeptuneAvenue,

Carson,CA,March29,2012,page4‐1.21 URSCorporation,GeotechnicalReport,PlannedPilotTestforRemedialExcavationandBackfillPlacement,24533RavennaAvenue,

Carson,CA,April13,2012,page2‐1.22 “Refusal”isanobstructionofaboring,whichmaybecausedbyconcreteslabsorotherfeatures,suchasstonesorotherrubble.23 URSCorporation,AssessmentofEnvironmentalImpactandFeasibilityofRemovalofResidualConcreteReservoirSlab,FormerKast

Property,Carson,CA,June28,2013,page2‐5.24 URSCorporation,AssessmentofEnvironmentalImpactandFeasibilityofRemovalofResidualConcreteReservoirSlab,FormerKast

Property,Carson,CA,June28,2013,page2‐6.

FIGUREBoring Refusal Map

Former Kast Property Tank Farm Site Remedia on Project 5.2-3Source: URS Corpora on, Assessment of Environmental Impact and Feasibility of Removal of Residual Concrete Reservoir Slabs, 2013.

P C R

0 140 Feet

N



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areaofthefootprintofthenorthernreservoirbase,refusalwasencounteredatdepthsof7.1to10feetbgs.Refusals at the upper end of this depth range are interpreted to be due to the reservoir slab; refusals atshallowerdepthsarepotentiallytheresultofencounteringburiedconcreterubbleorconcretepedestalsthatwereplacedwithinthelowerpartofthefillsectioninthispartofthesiteduringgradingbythedeveloper.25

All of the properties investigated that arewithin the footprint of the base of ReservoirNo. 5, the centralreservoir,encounteredrefusalatdepthsof10feetorless.RefusalwasencounteredatpropertiesalongtheeasternsideofMarbellaAvenue.AtpropertiesalongNeptuneAvenue,refusalwasencounteredatdepthsof10feetorlessinallboringslocatedwithinthefootprintoftheformerreservoirbasedonhistoricaldrawings.Boringrefusalwasencountered less frequently intheareaofsouthernReservoirNo.6,andwhererefusalwasencountereditoccurredinafractionoftheboringsatindividualproperties.Thisisnotunexpected,asthesiteelevationishighestinthisportionoftheTractduetorisingtopographytothenorthwest.26

Theresultsofthesiteassessmentsuggestthatconcreteslabsarepresentwithinthesoilprofile.Duetothepotential adverse effects of the impact of the remaining concrete slabs on waste migration where theconcretefloorsmightstillbepresent,theRAPproposesremovalofsomeoralloftheresidualconcreteslabsifencounteredduringtheimplementationoftheremedialexcavation.

3. METHODOLOGY AND THRESHOLDS

Methodology

Thedeterminationofimpactsisbasedontheevaluationofthepotentialgeologichazardsthatareidentifiedattheprojectsiteunderexistingconditionandtheevaluationofanyhazardscausedbyproposedexcavationorbackfillactivities. Thedeterminationofexistingandpotentialhazards isbasedonbackgroundstudies,including soils analyses, excavationpilot testing, andmappingof seismic or other geologichazards in thearea. These are compared to the activities needed to remove COC‐containing soils around residentialbuildingstotheextentfeasibleandthecontrolsonexcavationimposedunderexistingregulations.Seismicand other geologic hazards are identified according to the location of the site with respect to activeearthquake faults, designated (state‐mapped) liquefaction areas, and the effect of excavation on soilsunderlyingbuildingfoundationsthatwouldremaininplace.

Thresholds of Significance

AppendixGof theStateCEQAGuidelinesprovides a setof screeningquestions that address impactswithregardtogeologyandsoils.Thesequestionsareasfollows:

Wouldtheproject:

a) Exposepeopleorstructurestopotentialsubstantialadverseeffects,includingtheriskofloss,injury,ordeathinvolving:

25 Ibid.26 Ibid.



i. Rupture of a known earthquake fault, as delineated on the most recent Alquist‐PrioloEarthquake Fault Zoning Map issued by the State Geologist for the area based on othersubstantialevidenceofaknownfault;

ii. Strongseismicgroundshaking;

iii. Seismic‐relatedgroundfailure,includingliquefaction;or

iv. Landslides?

b) Resultinsubstantialsoilerosionorthelossoftopsoil?

c) Belocatedonageologicunitorsoilthatisunstable,orthatwouldbecomeunstableasaresultoftheproject,andpotentiallyresult inon‐oroff‐sitelandslide, lateralspreading,subsidence, liquefactionorcollapse?

Be located on expansive soils, as defined by Table 18‐1‐B of the Uniform Building Code (1994),creatingsubstantialriskstolifeorproperty?

d) Have soils incapable of adequately supporting the use of septic tanks or alternative waste waterdisposalsystemswheresewersarenotavailableforthedisposalofwastewater?

AsdeterminedintheInitialStudy,whichiscontainedinAppendixAofthisEIR,theRP’sProposedRemedywouldnotresultinlandslides.AstheprojectistheimplementationoftheRAPinanurbanresidentialareaservicedbythemunicipalsewersystem,theuseofseptictanksisnotapplicable.Assuch,nofurtheranalysisofthesetopicsisnecessary.

Forpurposesofthisanalysis,theprojectwouldhaveasignificantimpactongeologyandsoilsifitwould:

GEO‐1 Exposepeopleorstructurestopotentialsubstantialadverseeffects,includingtheriskofloss,injuryordeath,involving:

Strongseismicgroundshaking,or

Seismic‐relatedgroundfailure,includingliquefaction;

GEO‐2 Be located on a geologic unit or soil that is unstable, or thatwould become unstable as aresultof theproject,andpotentiallyresult inon‐oroff‐site landslide, lateralspreading,subsidence,liquefaction,orcollapse;

GEO‐3 Resultinsubstantialsoilerosionorlossoftopsoil;or

GEO‐4 Belocatedonexpansivesoilcreatingsubstantialriskstolifeorproperty.

4. PROJECT ANALYSIS

Project Design Features

Project Design Features (PDFs) to be implemented as part of the RP’s Proposed Remedy would includegeneralprovisionsforgradinganddesignmeasuresthatanticipatethepreparationofageotechnicalreport



andremedialexcavationgradingplanspriortotheinitiationofgradingactivities. Thegeotechnicalreportand remedial excavation grading planswould be subject to review and approval by the LACDPW,whichrepresentstheCityofCarson.TheproposedPDFsinclude,butarenotlimitedtothefollowing:

PDFGEO‐1 Priortoissuanceofagradingpermit,afinalgeotechnicalinvestigationandremedialexcavation grading plan with final design recommendations applicable to everyexcavated area will be prepared by a California‐registered geotechnical and civilengineer and submitted to the LACDPW and City of Carson for review. Thegeotechnicalreportwilldescribethecharacteristicsofunderlyingnaturalorfillsoils,includingexpansivesoils,potentialdifferentialsettlementandvaryingsoilsstrengthandtheplacementofbackfill.Thegeotechnicalreportwillcontainrecommendationsfor anyneeded cut slopesor compactionof fillmaterials. The remedial excavationgrading plan will detail the excavation and backfill design details based on thefindingsandrecommendationsofthegeotechnicalreport.

PDFGEO‐2 The geotechnical report and remedial excavation grading plans will include site‐specificdesigncriteriarelatedtotheexcavationactivitiesinproximitytofoundationsandfootings.

PDFGEO‐3 Pre‐excavation and post‐excavation surveys of the existing structures andimprovementsatthesiteandatadjacentpropertiesthathavegrantedaccesswillbeconducted to document pre‐excavation conditions and any changes in thoseconditionsfollowingexcavation.Documentationwillconsistofwrittennotes,digitalphotographs, andvideos. Existing cracksor otherdistresspresent in structuresorconcrete will be documented and measured. Cracks will be monitored by directmeasurement using a dial caliper capable ofmeasuring distances to approximately±0.001 inch, or using commercially available crackmonitoring devices installed onthe existing cracks, such that any potential change of crack size duringimplementationoftheRAPcanbemonitoredanddocumented.

PDFGEO‐4 Full time observation should be provided by a licensed engineer during theexcavationoftheverticalslotcuts.Anyconditionsencounteredwithinthefieldthataredifferentthanthoseanticipated(i.e.irrigationwaterseepage,localizedloosesoils,clean sand, etc.) will be brought to the immediate attention of the geotechnicalengineerforcorrectivemeasures.

PDFGEO‐5 Cleansoilwillbeimportedforbackfillofexcavationsfromanoffsitesource. Beforeimporting the backfill soil to the site, samples of the proposed import soil will besubmitted for laboratory geotechnical and chemical characterization analysis.Geotechnical tests include gradation, plasticity index (PI), maximum density andoptimummoisture,andcorrosivitytests.Thegeotechnicalengineerwillapprovethebackfillsoilpriortoitsimport,placement,andcompactionatthesite.

PDFGEO‐6 Upon completion of excavation, concrete removal and environmental sampling (asappropriate), excavated areas will be backfilled as soon as possible. Backfill soilswouldbemoistureconditionedtonearoptimalmoisturecontentandcompactedtoatleast90percentrelativecompaction,orasdeterminedbytheGeotechnicalEngineerandapprovedbyLosAngelesCountyDepartmentofPublicWorks(LACDPW)andtheCity of Carson. Borings from auger excavationwould be backfilledwith controlled



lowstrengthmaterial(CLSM,alsoreferredtoasflowablefillorsand/cementslurry)thesamedaytheyareexcavated.Whereslottrenchingisusedfor5‐footexcavationsor for targeted deeper excavations to 10 feet, the lower part of the slot trencheswould also be backfilled with CLSM. The upper 3 feet of excavations would bebackfilledwithcertifiedcleanimportedsoil.Backfillsoilwouldbefreeofdeleteriousorganicmatter(i.e.,vegetation)andcobbleslargerthanfourinchesindiameter,andwould be approved by the Geotechnical Engineer. The upper foot of soil backfillwouldbetopsoilsuitableforvegetationgrowthandwouldbecompactedtonotmorethan85percentrelativecompaction.

PDFGEO‐7 Landscaping of backfilled properties would be restored to “like conditions” or asagreedtowiththehomeowners.

Analysis of Project Impacts

ThresholdGEO‐1: The project would have a significant impact on geology and soils if it would exposepeople or structures to potential substantial adverse effects, including the risk of loss, injury or death,involvingstrongseismicgroundshakingorseismic‐relatedgroundfailure,includingliquefaction.

Short‐term Impacts

ImpactStatementGEO‐1:Theprojectsiteisnotlocatedwithinaliquefaction‐proneareaandunderlyingsoilsare in a dense state or sufficiently compacted to reduce acceleration effects. Excavationswould besetback frombuildingsandwouldnotaffectunderlyinggeologic structuresor soilsbeneathbuildingfoundations. Protectivesupportwouldbeprovidedforanyencounteredutilitylines. Thus,theprojectwould not increase the exposure of people or structures to potential substantial adverse effects,including the riskof loss, injuryordeath, involving strong seismicground shakingor seismic‐relatedground failure, including liquefaction. The impactoftheRP’sProposedRemedywithrespecttothesegeologichazardswouldbe less than significant. TheExpedited ImplementationOption,whichwouldincrease the intensityofactivityon the site,wouldalso result ina less than significant impactwithrespecttothesegeologichazards.

Fault Rupture

Noknownactiveorpotentiallyactivefaultsunderliethesite,andthesiteisnotlocatedwithinadesignatedearthquakefaultzone.Thus,thepotentialforsurfacegroundruptureisconsideredlow.Therefore,impactsregardingfaultrupturewouldbelessthansignificant,andnomitigationmeasureswouldbenecessary.

Seismic Ground Shaking

The site is locatedwithin a seismically active region of Southern California. Themost likely sources forgroundmotionareknownfaults(e.g.,Newport‐InglewoodFault,AvalonComptonFault),whicharewithinafewmilesofthesite.Moderatetostronggroundmotion(acceleration)couldbecausedbyanearthquakeatthese,oranyofthelocalorregionalfaults.Thelevelofgroundshakingthatwouldbeexperiencedatthesitefrom active, potentially active or blind thrust faults in the region would be a function of several factorsincluding earthquakemagnitude, type of faulting, rupture propagation path, distance from the epicenter,earthquake depth, duration of shaking, project site topography, and project site geology. The site is notlocated within a liquefaction area and, thus, accelerated ground shaking, differential settlement, ground



cracking,ground lurchingand lateralspreadingassociatedwith liquefactionwouldnotoccur. Inaddition,therelativefirmnessandstabilityofon‐sitesoilsanddistancetogroundwaterwouldnotspecificallyamplifygroundmotionorsettlementduringaseismicevent.Existingconcreteslabswithinthesiteareconsideredtobeadensematerialresidingwithinthesoilprofileanddonotcauseinstabilityorgeologichazards.

Project design features, including PDFs Geo‐1 through Geo‐3, which apply to the required geotechnicalreport, would ensure that final grading designs would incorporate adequate support of cuts (if needed),excavationmethods, or setbacks from building foundations during excavation to avoid adverse effects ofseismic ground shaking on adjacent buildings during the site remediation. With adequate structuralprotection during excavation, as determined by the geotechnical engineer, the projectwould not cause aseismic event to result in substantial damage to structures or cause or accelerate geologic hazards thatwouldexposepeopletosubstantialriskofinjury.Excavationactivitieswouldnotaffectsoilsandmaterialsbelow5or10feetbgsorunderlyinggeologicunits.Theimplementationofrequiredsetbacksfromhabitablestructureswould avoid soils that support existing building foundations. It is anticipated that utility lineswouldbelocatedwithintheexcavationdepth. Linesencounteredwouldbeprotectedinplaceorremovedandreplaced.27Thiswouldavoidadditionalstressduringaground‐shakingevent.InaccordancewithPDF‐Geo‐6, borings from auger excavation would be backfilled with CLSM the same day they are excavated.Whereslottrenchingisusedfor5‐footexcavationsorfortargeteddeeperexcavationsto10feet,thelowerpart of the slot trencheswould also be backfilledwith CLSM. The upper 3 feet of excavationswould bebackfilledwithcertifiedclean importedsoil. Backfillsoilwouldbe freeofdeleteriousorganicmatter(i.e.,vegetation) and cobbles larger than four inches in diameter, andwould be approved by theGeotechnicalEngineer.Backfillsoilswouldbecompactedtoatleast90percentrelativecompaction,orasdeterminedbytheGeotechnicalEngineerandapprovedbyLosAngelesCountyDepartmentofPublicWorks(LACDPW)andtheCityofCarsonintheGradingPermit.Becauseexistingstablesoilsremovedduringexcavationwouldbereplaced by stable compacted soils, excavation and backfill activitieswould not cause ground shaking orother seismic hazards to be accelerated compared to existing conditions at the site. Thus, with theimplementationofprojectdesign features, theRP’sProposedRemedywouldnot increase theexposureofpeople or structures to potential substantial adverse effects, including the risk of loss, injury or death,involvingstrongseismicgroundshakingorseismic‐relatedgroundfailure,includingliquefaction.Theshort‐termimpactoftheprojectwithrespecttothesegeologichazardswouldbelessthansignificant.

Long‐term Impacts

Anypotential long‐term impactswouldbeassociatedwith changes thatwould result in increasedgroundshakingduringaseismicevent.Thereplacementofexistingstablesoilswithunconsolidatedorpoorqualitysoils could increase amplification or other geologic hazards. The implementation of PDF‐Geo‐6 providesthat,uponcompletionofexcavation,excavatedareaswouldbebackfilledassoonaspossiblewithmoistureconditionedsoilsandcompactedtoarelativecompactionofatleast90percent,forsoilsplacedfrom3feetbgs toone footbgs. Adequate compactionofbackfillwouldensure that the sitewouldbe returned to itsexistingstableconditionandwouldnotpresentapotentialgeologichazardresultingfromgroundshaking.Inaddition, the implementationPDF‐Geo‐6wouldrequirethatcleansoilwouldbe importedforbackfillofexcavations and that, prior to importation of soil, samples of the proposed soil would be submitted forlaboratory geotechnical and chemical characterization analysis. Geotechnical tests include gradation, PI,

27 Transitewatersupply lines located inthefrontandsideyardsofpropertieswouldbeavoided. Overheadpower linesmayrequire

removalandreplacementforsafetyconsiderations.



maximumdensityandoptimummoisture,andcorrosivitytesting,aswellasinspectionandapprovalbythegeotechnicalengineerwouldensurethatstablesoilconditionswouldbeachievedandmaintained.

The substantial withdrawal of groundwater over a period of time has the potential to result in local orregional subsidence. In the Carson area historical subsidence has been remedied through a regionalseawater injection system. The RAP requires the removal of LNAPL if it is present at a measureablethicknessonthegroundwatersurface.accumulatestoathicknessof0.5feetonthesurfaceoftheBellfloweraquitard,whichunderlies the site. The removal of LNAPLhasbeenongoing for three yearswhere it hasaccumulatesinafewmonitoringwells.BecauseofthelocalizedcharacteroftheLNAPLandrelativelysmallvolumeofLNAPLcomparedtothevolumeoftheaquitard,theremovalofLNAPLdoesnotaffectthesurfacelevelofthewatertable,whichhasremainedstable(between52‐68feetbgs)overaperiodofobservationsince 2009. Therefore, the ongoing removal of LNAPL is not expected to result in localized or generalsubsidence.

Other project design features including PDF‐Geo‐3 would provide a data baseline against which futurestructural changes could be measured. PDF‐Geo‐3 requires an evaluation of pre‐excavation buildingconditionsandpost‐excavationconditionsofbuildingsaswellasevaluationofanystructuralchanges.Thisprojectdesignfeaturewouldprovideforthedetectionofchangesinstructuresfromgradingandexcavationactivities. Existing cracks or other distress present in structures or concrete would be documented andmeasured. Crackswould bemonitored by directmeasurement using a dial caliper capable ofmeasuringdistancestoapproximately±0.001inch,orusingcommerciallyavailablecrackmonitoringdevicesinstalledontheexistingcracks,suchthatanypotentialchangeofcracksizeduringthepilottestscanbemonitoredanddocumented.Thus,withtheimplementationofprojectdesignfeatures,theprojectwouldnotincreasetheexposureofpeopleorstructurestopotentialsubstantialadverseeffects,includingtheriskofloss,injuryordeath, involvingstrongseismicgroundshakingorseismic‐relatedgroundfailure, includingliquefaction.The long‐term impact of the RP’s Proposed Remedy with respect to seismic hazards would be less thansignificant.

Expedited Implementation Option

UndertheExpeditedImplementationOption,thenumberofpropertiesbeingremediatedatonetimecouldincrease from the proposed cluster of up to 8 properties up to 16 properties active at one time. Theremediationcontractorcouldimplementthisoptiononlywhentheconfigurationoflotsandotherconditionsareconducivetoproceedinginthisexpeditedmannersafely. TheOptionwouldresultinagreaterlevelofactivity on the site at one time but would not change the activity at an individual property or the totalactivity(numberoflotsremediated,amountofsoilandothermaterialsremovedfromthesite,etc.).ProjectdesignfeatureswouldbethesameundertheExpeditedImplementationOptionasundertheRP’sProposedRemedy. BecausetheExpedited ImplementationOptionwouldcomplywithCoderequirementsrelatedtoexcavationstability(shoring,etc.),monitoringofcuts,andmaintainingbaselinedatatodetectanydamageorinstabilityatadjacentstructures,andwouldadheretoprojectdesignfeatureswhichfurtherensurestabilityof excavations, theExpedited ImplementationOptionwouldnot cause adverse impacts related to seismichazards, such as ground shaking, ground failure, and liquefaction. Therefore, impacts regarding seismichazardswouldbelessthansignificant.



ThresholdGEO‐2:Theprojectwouldhaveasignificantimpactongeologyandsoilsifitwouldbelocatedona geologic unit or soil that is unstable, or that would become unstable as a result of the project, andpotentiallyresultinon‐oroff‐sitelandslide,lateralspreading,subsidence,liquefaction,orcollapse.

ImpactStatementGEO‐2: Theexcavationof theproject sitewouldnotexposeoralterunderlyinggeologicunits. Surface soilwouldbe removed to5 to10 feetbgsandwouldbe replacedwithappropriatelycompacted backfill. Observation during grading and testing for required compaction and safety ofstructuresduetoanyslippageorsettlementofthecompletedgrading,wouldensurethatconditionsinapprovedengineeringreportsare implemented. With implementationofBuildingCoderequirementsand project design features the projectwould not cause on‐ or off‐site landslide, lateral spreading,subsidence,liquefaction,orcollapse.Therefore,theimpactoftheRP’sProposedRemedywithrespecttothesegeologichazardswouldbe less than significant. TheExpedited ImplementationOptionwouldalsoresultinalessthansignificantimpactwithrespecttothesegeologichazards.


The implementation of theRAPwould require temporarymodifications to the existing grades of the site.Soil would be excavated to a depth of 5 to 10 feet bgs from both landscaped areas and areas currentlycovered by hardscape, including walkways, driveways, patio areas, and hardscape associated withlandscaping. Approximately177,870 CYofsoilwouldberemoved fromtheresidentialpropertieson thesite.Inadditiontotheresidentialsoilexcavation,therewouldbeapproximately8,100CYofsoilexcavatedfor SVE piping installation in the public rights‐of‐way and 725 CY excavated for well installation. Totalexcavation would be approximately 186,945 CY. Final recommendations, including vertical and lateralcapacities of soils, would be developed during final design as required under PDF‐Geo‐1. Soil would beexcavatedfrom219residentialpropertieswhereresultsoftheprevioussiteassessmentsindicatethatRAOsare not met under existing conditions. Residual concrete slabs that formed a portion of the formerreservoirs would be removed from excavation areas, where encountered. If encountered, concreteextendinglaterallybeneathastructureorbeneaththesidewalkwouldbecutattheedgeofthestructureorinneredgeofthesidewalkandtheremainingconcretewouldbeleftinplace.Existingconcreteslabswithinthesiteareconsideredtobeadensematerialresidingwithinthesoilprofileanddonotcauseinstabilityorgeologichazards.

Hardscape and landscapingwould be removed during the initial stage of excavation and restored to likeconditionsfollowingcompletionofexcavationinconsultationwiththehomeowner.Itmaybenecessarytoremovefencesandblockwallsbetweenyardsandornamentalorpartitioningwallsonindividualproperties,as the depth of excavation likelywould exceed fence post and footing depths. Aswith other hardscape,fences and walls would be restored following completion of excavation and prior to restoration oflandscaping. Exceptions to excavationbeneathhardscape includepatios coveredby structures and roofs,swimming pools and pool decking surrounding swimming pools. These hardscape areas would not beexcavated to avoid structural demolition and potential damage to swimming pools and appurtenantequipment. No excavation for the purposes of direct soil removal remediationwould occur beneath Citystreets and sidewalks or beneath houses. However, excavation within City streets would be needed fortrenching as part of the SVE conveyance piping installation process. In addition to treatment by theSVE/bioventingsystemdiscussedbelow,remainingsoilinthesenon‐excavatedareaswouldbeaddressedintheSMPandbyexistingCityregulatoryrequirements.



Excavation would be conducted using rubber track‐mounted excavators or rubber‐tired backhoes. Anapproximately15,000to18,000poundmedium‐sizedexcavatorwouldbeusedforworkinfrontyardsandback yardswhere sufficient access is available, and an approximately3,500‐pound rubber track‐mountedmini‐excavator would be used in back yards with narrow access via side yards. Excavation would beconductedusinga front‐end loaderand/orBobcat skid‐steermini‐loader tomovesoil frombackyards tofrontyardsandviceversatobringincleanfillsoil.

In areaswhere access for equipment is severely limited, hand tools andwheelbarrowswould be used toconductexcavations.

Excavations would be made with side slopes at the horizontal to vertical ratio recommended by thegeotechnical engineer and approved by the LACDPW and City of Carson in the grading permit for theparticular property being excavated.28 The basic excavation protocols would be altered as needed asexcavationsareconductedandtoaddressanypreviouslyunknownutilities,concretedebrisorfoundationsunearthed.Ifpossible,andapprovedbytheLACDPWandtheCity,excavationswouldhaveverticalsidewallstomaximizeremovalofimpactedsoiltothefulldepthofexcavation.29

Geotechnicalreportswerepreparedforthe24612NeptuneAvenueand24533RavennaAvenuepropertiesprior to the pilot test for trenching and excavations. Based on the properties of on‐site soil, the reportconcluded that any construction work within the site would not be subjected to geologic hazards fromlandslides,settlement,orslippage.Theyalsoconcludedthatimplementationoftheremedialactivitieswouldnot adversely affect the geologic stability of surrounding properties. The reports further concluded that,because groundwater was not observed in exploratory borings to a depth of 25.5 feet bgs at the 24612NeptuneAvenuesiteandtoadepthof10feetbgsattheRavennaAvenuesite,thepotentialforgroundwater‐relatedimpactsduringexcavationactivities,includingthepotentialforperchedgroundwaterintrusionintothenear‐surfacezonesduringconstruction,isnotanticipated.30

Excavations to 5 bgs or deeper would require shoring of the cut area, setbacks from structures, slopedexcavation sidewalls, and/or slot trenching in accordance the requirements of the geotechnical report forengineeredgrading. PlacementofcleanfillwouldneedtomeetcompactionrequirementsundertheCode.Because of the shallow depth of excavation (5 to 10 feet) and setbacks from building foundations, theexcavationofsoilwouldnotalterunderlyinggeologicunitsorthecharacterofexistingsoilbeneathexistingfoundations. Surface soil would be replaced by appropriately placed backfill that would meet CountyBuilding Code Section J107.4 to prevent fill material containing organic, frozen, or other deleteriousmaterialsthatcouldcontributetoinstability.ImplementationofPDF‐Geo‐5requiresthatimportedcleansoilwouldbetestedforsuitability(stability,non‐corrosiveproperties,etc.)asfillmaterials. UnderPDF‐Geo‐6,backfillwould begin upon completion of excavation and installation of other remedial elements. Boringsfrom auger excavation would be backfilled with CLSM the same day they are excavated. Where slottrenchingisusedfor5‐footexcavationsorfortargeteddeeperexcavationsto10feet,thelowerpartoftheslottrencheswouldalsobebackfilledwithCLSM.Theupper3feetofexcavationswouldbebackfilledwith28 TheCityofCarson followstheLACDPWGradingGuidelinesand isacontractcity,meaningthattheLACDPWprovidesplancheck

servicesfortheCity.29 TheLACDPWandCitycouldrequiresetbacksfromstructuresinaccordancewithappropriateelementsofSectionsJ101,J104,J106,

andJ108oftheCountyGradingCodeasamendedbytheCityofCarson.30 URSCorporation,GeotechnicalReport,PlannedPilotTestforRemedialExcavationandBackfillPlacement,24612NeptuneAvenue,

Carson,CA,March29,2012,page4‐1.



certifiedcleanimportedsoil. Backfillsoilwouldbefreeofdeleteriousorganicmatter(i.e.,vegetation)andcobbleslargerthanfourinchesindiameter,andwouldbeapprovedbytheGeotechnicalEngineer. Backfillsoilswouldbemoistureconditionedtonearoptimalmoisturecontentandcompactedtoatleast90percentrelativecompaction,orasdeterminedbytheGeotechnicalEngineerandapprovedbyLACDPWandtheCityof Carson in the Grading Permit. The upper foot of soil backfill would be topsoil suitable for vegetationgrowthandwouldbecompactedtonotmorethan85percentrelativecompaction.

Los Angeles County Building Code Sections J105.3, Field Engineer Inspection, and J105.4, Soils EngineerInspection,aswellasPDF‐Geo‐6,requireobservationduringgrading, testing forrequiredcompactionandsafetyofstructuresduetoanyslippageorsettlementofthecompletedgrading,andtoensurethatconditionsin approved engineering reports are implemented. With implementation of County Building Coderequirements and project design features, the RP’s Proposed Remedy would avoid lateral spreading,subsidence, liquefaction, or collapseduring construction. Theproject site is essentially level andno landsliding is anticipated. Therefore, the short‐term impact of the project with respect to landslide, lateralspreading,subsidence,liquefaction,orcollapsewouldbelessthansignificant.


UndertheExpeditedImplementationOption,thetotalamountofexcavatedsoilandimplementationofCoderequirements,suchasprotectionofadjoiningproperties,setbacks,andstabilityofcutswouldbethesameasundertheRP’sProposedRemedy. TheOptionwouldresult inagreater levelofactivityonthesiteatonetime but would not change the activity at an individual property or the total activity (number of lotsremediated,amountofsoilandothermaterialsremovedfromthesite,etc.).ProjectdesignfeatureswouldbethesameundertheExpeditedImplementationOptionasundertheRP’sProposedRemedy.BecausetheExpedited Implementation Option would comply with Code requirements related to excavation stability(shoring, etc.), monitoring of cuts, and maintaining baseline data to detect any damage or instability atadjacent structures, and would adhere to project design features which further ensure stability ofexcavations, the Expedited Implementation Option would not cause adverse impacts related to geologichazards. Therefore, impacts regarding geologic hazards, such as landslide, lateral spreading, subsidence,liquefaction,orcollapsewouldbelessthansignificant.

Long‐term Impacts

Anypotentiallong‐termimpactswouldbeassociatedwithchangesthatwouldcauseorincreaseinstabilityandpotentiallyresultinlateralspreading,subsidence,liquefaction,orcollapse.Thereplacementofexistingstable soilswith unconsolidated or poor quality soils could result in long‐term lateral spreading or othergeologic hazards. As describedunder “Short‐term Impacts,” above the implementation of PDF‐Geo‐5 andPDF‐Geo‐6 would provide for the use of clean soils that meet appropriate geotechnical and chemicalcharacterizationanalysisand forcompactionof soils to least90percent. Adequatecompactionofbackfillwould ensure that the site would be returned to its existing stable condition and would not present apotential long‐term geologic hazard resulting from ground shaking. In addition, project design featureswouldensurethatstablesoilconditionswouldbeachievedandmaintained.

Other project design features including PDF‐Geo‐3 would provide a data baseline against which futurestructural changes could bemeasured. PDF‐Geo‐3 requires an evaluation of pre‐excavation building andfoundation conditions and post‐excavation conditions of buildings and foundations and evaluation of anystructuralchanges.Existingcracksorotherdistresspresentinstructuresorconcretewouldbedocumented



andmeasured.Crackswouldbemonitoredbydirectmeasurementusingadialcalipercapableofmeasuringdistancestoapproximately±0.001inch,orusingcommerciallyavailablecrackmonitoringdevicesinstalledontheexistingcracks,suchthatanypotentialchangeofcracksizeduringthepilottestcanbemonitoredanddocumented.Thisdatabaselinewouldindicateanygeologicinstabilityand,thus,provideameansbywhichpotentialgeologichazardscouldbeaddressed.Thus,withtheimplementationofprojectdesignfeatures,theprojectwouldavoidoraddressadversegeologicconditions,suchaspoorsoilconsolidationthatcouldcauselateral spreading, subsidence, liquefaction, or collapse. The impact of the RP’s Proposed Remedy withrespecttolandslide,lateralspreading,subsidence,liquefaction,orcollapsewouldbelessthansignificant.

ThresholdGEO‐3: Theprojectwouldhavea significant impacton geologyand soils if itwould result insubstantialsoilerosionorlossoftopsoil.

Impact Statement GEO‐3: With the implementation of Code‐required best management practices forexcavation and backfill activities, and immediate loading and covering of cut materials, the RP’sProposed Remedy would not result in substantial soil erosion. In addition, the removal of COC‐containingsoilwouldnotconstitutethesubstantiallossoftopsoil.Therefore,theimpactwithrespectto erosionand lossof top soilwouldbe less than significant. TheExpedited ImplementationOptionwouldalsoresultinalessthansignificantimpactwithrespecttoerosionandlossoftopsoil.


AfunctionoftheRP’sProposedRemedyistoremoveapproximately177,870CYofsoilfromresidentialsites(includinga10percentcontingency),approximately8,100CYfromstreetexcavations,and725CYforwellpreparation,foratotalofapproximately186,945CY.Thesoilwouldbereplacedbybackfill,whichwouldberequired to comply with project design features and Building Code requirements regarding absence oforganicmaterialsorotherdeleteriousmaterials.PDF‐Geo‐6requiresthatcleansoilwouldbeimportedforbackfillwouldbetestedforgradation,plasticity,maximumdensityandoptimummoisture,andcorrosivity.Underexistingconditions,petroleumhydrocarbonsandrelatedVOCsandSVOCsoccurinshallowanddeepsoilsonthesite.Becauseofpotentialhydrocarbonspresentinexistingsoil,underexistingconditionsthesesoilsarenotsuitable forbeneficialuses typicallyassociatedwith topsoil. Althoughsurfacesoilswouldberemovedfromtheresidentialproperties,theremovalofthesematerialswouldnotconstituteasubstantialloss of topsoil. Topsoil in landscaped areas would be replaced in like condition so there would be nosignificantlossoftopsoilassociatedwiththeRP’sProposedRemedy.

Gradingactivitieshavethepotential to increaseerosion, includingerosionofsoilsduringexcavation. TheSWPPPandWWECP,whichwouldbeprepared in accordancewith theCountyBuildingCode,Appendix J,wouldrequirebestmanagementpractices for thecontrolof runoffandpotential transportofsedimentorsoilerosionduringexcavationandbackfilloperations.AsdescribedinChapter2,ProjectDescription,ofthisEIR, generally excavated soil would be loaded directly into an awaiting transport vehicle (i.e., end‐dumptruck,dumptruck,orcoveredsoilbin)usingtheexcavator, front‐end loaderorskid‐steermini‐loader, fortransport to the appropriate recycling or disposal facility. In the unlikely event that it is necessary totemporarily stockpile soil onsite before loading, soil either would be placed upon plastic sheeting andcoveredwith plastic, or theywould be temporarily placed in a covered bin. With the implementation ofCode‐requiredbestmanagementpracticesforexcavationsandbackfill,andimmediateloadingandcoveringofcutmaterials,asneeded,theprojectwouldnotresultinsubstantialsoilerosion.Inaddition,theremoval



ofCOC‐containingsoilwouldnotconstitutethesubstantiallossoftopsoil.Therefore,theshort‐termimpactoftheRP’sProposedRemedywithrespecttoerosionandlossoftopsoilwouldbelessthansignificant.

Long‐term Impacts

Long‐termerosionhasthepotentialtooccurinareasofexposedbackfillsoils.UnderPDF‐Geo‐7,landscaperestoration, including the reconstruction of removed fencing or blockwalls,would be performed to “likeconditions”orasagreed towith thehomeowners. PDF‐Geo‐7requires thatpropertiesberestored to likecondition,includingtopsoilinlandscapedandsoftscapeareas.Withtherestorationoflandscapingandanyremoved hardscape, backfill soils would be covered and the potential for erosionwould be substantiallyreduced. Withthe implementationofprojectdesign features, thesitewouldbereturnedto likeconditionandthelong‐termimpactoftheRP’sProposedRemedywithrespecttoerosionandlossoftopsoilwouldbelessthansignificant.


UndertheExpeditedImplementationOption,thetotalamountofexcavatedsoilwouldbethesameasunderthe RP’s Proposed Remedy. However, because overall activity at any one time would be increased, thequantity of soil exposed to potential erosion forces would be greater. The PDFs and BMPs in the RP’sProposed Remedy would be applicable to all areas where soil is exposed under the ExpeditedImplementationOption therebyminimizingsoilerosion. Thediscussionaboveof impactsassociatedwithlossoftopsoilisthesameasundertheRP’sProposedRemedybecausenoadditionalsurfaceareawouldbedisturbed.Therefore,impactsregardingerosionandlossoftopsoilwouldbelessthansignificant.

ThresholdGEO‐4:Theprojectwouldhaveasignificantimpactongeologyandsoilsifitwouldbelocatedonexpansivesoilcreatingsubstantialriskstolifeorproperty.

ImpactStatementGEO‐4:Theprojectwouldnotremoveexistingsoilsunderresidentialbuildingsorgaragesand, thus,would not change existing conditionswith respect to soils currently supporting habitablestructures. Expansivesoilsdonotnaturallyoccurontheprojectsiteandexpansivesoilswouldnotbeimported to theproject site. Because theRP’sProposedRemedyand theExpedited ImplementationOptionwouldnotchangetheexistingsoilsunderhabitablestructures, itwouldnotcauseachange inexpansivenessofexistingmaterialsthatwouldincreaseriskstolifeorproperty.TheimpactoftheRP’sProposedRemedyand theExpedited ImplementationOptionwithrespect toexpansive soilswouldbelessthansignificant.


Prior geotechnical investigations of the site determined that naturally‐occurring on‐site soils were non‐expansive by both LosAngeles County and FHA criteria. TheRP’s ProposedRemedywould result in theremovalofuptoapproximately186,945CYofsoil fromthesite. Excavatedsoilswouldbebackfilledwithimported materials that must comply with County Building Code Section J107.4 to prevent fill materialcontainingorganic, frozen,orotherdeleteriousmaterials that could contribute to instability. UnderPDF‐Geo‐5,importedbackfillsoiltothesitewouldbetestedforgradationandplasticity,whichwouldensurethathighlevelsofclaythatcouldcontributetoshrinkingandswellingareconsidereddeleteriousandwouldnotbeallowed.Becauseexpansivesoilswouldnotbeimportedtothesite,anyreplacedfencingandhardscapewouldnotbe located in importedexpansivesoils. TheRP’sProposedRemedywouldnotremoveexisting



soilsunderresidentialbuildingsorgaragesand,thus,wouldnotchangeexistingconditionswithrespecttoexisting non‐expansive soils that currently support habitable structures. Because on‐site soils are non‐expansive,andimportedsoilswouldbetestedtoensurethatexpansivesoilswouldnotbeusedinbackfill,theshort‐termimpactoftheprojectwithrespecttoexpansivesoilswouldbelessthansignificant.

Long‐term Impacts

Expansivesoilsdonotnaturallyoccurontheprojectsite.WiththeimplementationofCountyBuildingCoderegulationsthatrequirethatfillmaterialnotcontaindeleteriousmaterialsthatcouldcontributetoinstabilityand PDF‐Geo‐5, which requires that imported backfill soil to the site would be tested for gradation andplasticity,soilsthatcontainhighlevelsofclaythatcouldcontributetoshrinkingandswellingwouldnotbeallowed.TheRP’sProposedRemedywouldnotremoveexistingsoilsunderresidentialbuildingsorgaragesand, thus,wouldnotchangeexistingconditionswithrespecttoexistingnon‐expansivesoils thatcurrentlysupporthabitablestructures.Becauseon‐sitesoilsarenon‐expansive,andimportedsoilswouldbetestedtoensurethatexpansivesoilswouldnotbeusedinbackfill,thelong‐termimpactoftheRP’sProposedRemedywithrespecttoexpansivesoilswouldbelessthansignificant.


UndertheExpeditedImplementationOption,thetotalamountofexcavatedsoilswouldbethesameasunderthe RP’s Proposed Remedy. The Expedited Implementation Option would adhere to all project designfeatures, such as PDF‐Geo‐5, which requires testing of imported backfill soil for gradation and plasticity.This would ensure that high levels of clay that could contribute to shrinking and swelling would not beallowed. Becauseexpansive soilsdonotoccuron the siteorwouldbe imported to the site, any replacedfencing and hardscapewould not be located in imported expansive soils. The Expedited ImplementationOptionwouldnotremoveexistingsoilsunderresidentialbuildingsorgaragesand,thus,wouldnotchangeexistingconditionswithrespecttoexistingnon‐expansivesoilsthatcurrentlysupporthabitablestructures.Becauseon‐sitesoilsarenon‐expansive,andimportedsoilswouldbetestedtoensurethatexpansivesoilswouldnotbeusedinbackfill,theshort‐termimpactoftheExpeditedImplementationOptionwithrespecttoexpansivesoilswouldbelessthansignificant.

5. ALTERNATIVES ANALYSIS

Analysis of Impacts Associated with Alternative 1 (No Project Alternative)

TheNoProjectAlternativewouldnotinvolveanyexcavationofsoilsorchangetoexistinggroundconditionsthat would require grading permits or geotechnical analysis of activities at the site. The No ProjectAlternativewouldavoidanypotentialexcavation‐relatedimpactsassociatedwithsedimentationorerosion,whichweredeterminedtobelessthansignificantundertheRAPwiththeimplementationofprojectdesignfeatures. AlthoughtheNoProjectAlternative,whichwouldnotresult inanygeologiceffects,wouldavoidtheRAP’s less than significant geological effects. However, thisAlternativewouldnotmeet the statutoryrequirementsoftheRAP.



Analysis of Impacts Associated with Alternative 2 (Excavation Beneath Landscape and

Hardscape to 10 Feet Alternative)

Seismic Hazards

Asindicatedpreviously,thesiteisnotlocatedwithinadesignatedearthquakefaultzoneandsurfacegroundruptureisconsideredlow.Becausethesiteislocatedwithinaseismicallyactiveregion,moderatetostrongground motion could be caused by an earthquake. As with the RP’s Proposed Remedy, project designfeatures,suchasPDFsGeo‐1throughGeo‐3,wouldapply.Theserequireageotechnicalreporttoensurethatfinal grading designswould incorporate adequate support of cuts (if needed) and setbacks frombuildingfoundations during excavation to avoid adverse effects of seismic ground shaking on adjacent buildingsduringthesiteremediation.Itisexpectedthat10‐foot‐deepcutswouldbeshoredand/orslottrenchedtoensurestablecuts.Withadequatestructuralprotectionduringexcavation,Alternative2wouldnotcauseaseismic event to result in substantial damage to structures or cause or accelerate geologic hazards thatwouldexposepeopletosubstantialriskofinjury.Excavationactivitieswouldnotaffectsoilsandmaterialsbelow 10 feet bgs or underlying geologic units that could affect seismic activity. Design features wouldrequirebackfillmaterialsfromthebaseofthecuttoonefootbgstobere‐compactedtoatleast90percent,or as required under the grading permit for specific properties. The implementation of project designfeatures,suchasPDF‐Geo‐6,wouldprovidethat,uponcompletionofexcavation,excavatedareaswouldbebackfilledassoonaspossiblewithCLSMinthelowerareasofcutsorboringsandbackfilledwithcertifiedclean imported soil in the upper 3 feet. Thus, with the implementation of project design features andexistinggradingregulationspertinenttoengineeredgrading,Alternative2wouldnotincreasetheexposureof people or structures to potential substantial adverse effects, including the risk of loss, injury or death,involvingstrongseismicgroundshakingorseismic‐relatedgroundfailure, including liquefaction. Impactswithrespecttoseismichazardswouldbelessthansignificant.

Geologic Hazards

UnderAlternative2,allaffectedproperties(241residentialproperties)wouldbeexcavatedtoadepthof10feetbgs.Totalexcavatedquantitieswouldbeapproximately274,700CYfromtheresidentialpropertiesandapproximately43,900CYof impactedsoils fromotherareasonthesite(totalapproximately318,600CY).ThisAlternativewouldentail,onaverage,excavationof1,222CYofsoilperproperty.

AswiththeRP’sProposedRemedy,excavationwouldbeconductedusingexcavatorsorbackhoes.Alimitedaccessbucketaugerdrillingrigwouldbeused inconjunctionwithconventionalexcavationequipment forcuts.Conventionalexcavationusingslot‐trenchingasnecessarytoprotectstructuresorotherfeaturesandopen bulk excavation with appropriate sloping, setbacks, and/or shoring would be used where possible.Augerexcavationusingalimitedaccessrigwouldallowexcavationtobeconductedinrelativelytightspacesadjacent to structures to remove a columnof soil. However, use of auger excavationwould be slow andwouldthereforebeusedinlimitedapplicationinfavorofconventionalexcavationwhereverpossible.

Excavationsto10feetbgswouldrequireshoringofthecutarea,setbacksfromstructures,slopedexcavationsidewalls, and/or slot trenching according to the requirements of the geotechnical report for engineeredgrading.PlacementofcleanfillwouldneedtomeetcompactionrequirementsundertheCode.Geotechnicalreportsattwolocationswithinthesiteconcludedthatanyconstructionworkwithinthesitewouldnotbesubjected to geologic hazards from landslides, settlement, or slippage. The reports also concluded that



implementation of the remedial activitieswouldnot adversely affect the geologic stability of surroundingproperties.31

Los Angeles County Building Code Sections J105.3, Field Engineer Inspection, and J105.4, Soils EngineerInspection,whichareimplementedforallengineeredgrading,aswellas implementationofprojectdesignfeatures,suchasPDF‐Geo‐6,requireobservationduringgrading,testingforrequiredcompactionandsafetyof structures due to any slippage or settlement of the completed grading, and ensure that conditions inapproved engineering reports are implemented. With implementation of County Building Coderequirements and project design features, Alternative 2 would avoid lateral spreading, subsidence,liquefaction,orcollapseduringconstruction.Thesiteisessentiallylevelandnolandslidingisanticipated.Therefore,theshort‐termimpactoftheAlternative2withrespecttolandslide,lateralspreading,subsidence,liquefaction,orcollapsewouldbelessthansignificant.

Erosion Hazards

Alternative2wouldremoveapproximately274,700CYofimpactedsoilsfromtheresidentialpropertiesandapproximately43,900CYofimpactedsoilsfromotherareasonthesiteforatotalof318,600CY.Thesesoilswouldbereplacedbyequivalentvolumesofcleanbackfill.BecausethequantityofexcavatedsoilwouldbegreaterunderthisAlternative,potentialexposuretonaturalforcescouldincreaseerosionpotential.ErosionwouldbeaddressedbytheSWPPPandWWECP,whichwouldbeprepared inaccordancewith theCountyBuildingCode,AppendixJ.Theseprogramsrequirebestmanagementpracticesforthecontrolofrunoffandpotentialtransportofsedimentorsoilerosionduringexcavationandbackfilloperations. AswiththeRP’sProposedRemedy,excavatedsoilswouldbe loadeddirectly intoa transportvehicle (i.e., end‐dumptruck,dumptruck,orcoveredsoilbin).Intheeventthatitisnecessarytotemporarilystockpilesoilonsitebeforeloading,soilseitherwouldbeplaceduponVisqueenplasticsheetingandcoveredwithplastic,ortheywouldbe temporarily placed in a covered bin. Project design features, such as PDF‐Geo‐5,which requires thattopsoilsuitableforplantgrowthintheupper6inchesandunderlainby6‐inch‐thickbackfillscompactedtoarelativecompactionof80to85percent,wouldalsobeimplemented.Theinclusionoftopsoilinthebackfillmaterialsandcompactedunderlyingsoilwithintheupperone‐footwouldpromotethegrowthofvegetation,aswellasreducedeeperosion. WiththeimplementationofCode‐requiredbestmanagementpracticesforexcavations and backfill and project design features, Alternative 2 would not result in substantial soilerosion.TheremovalofexistingCOC‐containingsoilswouldnotconstituteusefultopsoiland,therefore,theimpactofAlternative2withrespecttolossoftopsoilwouldbelessthansignificant.

Expansive Soils Hazards

Prior geotechnical investigations of the site determined that naturally‐occurring on‐site soils were non‐expansive by both Los Angeles County and FHA criteria. Design features, such as PDF‐Geo‐5, would beimplemented,whichrequirethatsoilswithhighlevelsofclaythatcouldcontributetoshrinkingandswellingwouldnotbeallowedasbackfillmaterial. Becauseexpansivesoilswouldnotbe importedtothesite,anyreplacedfencingandhardscapewouldnotbelocatedinimportedexpansivesoils. Alternative2wouldnotremoveexistingsoilsunderresidentialbuildingsorgaragesand,thus,wouldnotchangeexistingconditionswith respect to existing non‐expansive soils that currently support habitable structures. Because on‐site31 URSCorporation,GeotechnicalReport,PlannedPilotTestforRemedialExcavationandBackfillPlacement,24612NeptuneAvenue,

Carson, CA,March 29, 2012, page 4‐1 and Planned Pilot Test forRemedial Excavation andBackfill Placement, 24533RavennaAvenue,Carson,CA,April13,2012,page2‐1.



soilsarenon‐expansive,andimportedsoilswouldbetestedtoensurethatexpansivesoilswouldnotbeusedinbackfill,theimpactofAlternative2withrespecttoexpansivesoilswouldbelessthansignificant.

Analysis of Impacts Associated with Alternative 3 (No Excavation Beneath Hardscape ‐ 5

Feet to Targeted 10‐Feet Alternative)

Seismic Hazards

Asindicatedpreviously,thesiteisnotlocatedwithinadesignatedearthquakefaultzone.Althoughsurfaceground rupture is considered low,moderate to strong groundmotion could be caused by an earthquake.Project design features, such as PDFs Geo‐1 through Geo‐3, would apply, which would ensure that finalgradingdesignswouldincorporateadequatesupportofcutsandsetbacksfrombuildingfoundationsduringexcavationtoavoidadverseeffectsofseismicgroundshakingonadjacentbuildingsduringremediation.Itisexpected that cuts deeper than 5 feet would be shored and/or slot trenched to ensure stability. Withadequatestructuralprotectionduringexcavation,Alternative3wouldnotcauseaseismiceventtoresultinsubstantial damage to structures or cause or accelerate geologic hazards that would expose people tosubstantialriskofinjury.Excavationactivitieswouldnotaffectsoilsandmaterialsdeeperthan10feetbgsor underlying geologic units that could affect seismic activity. PDF‐Geo‐6 would provide that excavatedareaswouldbebackfilledassoonaspossible.Thus,withtheimplementationofprojectdesignfeaturesandexistinggradingregulationspertinenttoengineeredgrading,Alternative3wouldnotincreasetheexposureof people or structures to potential substantial adverse seismic, including ground failure or liquefaction.Impactswithrespecttoseismichazardswouldbelessthansignificant.

Geologic Hazards

Basedontheconclusionsofgeotechnicalreportsfortwolocationswithinthesite,constructionworkwithinthesite isnotconsideredsubjecttogeologichazardsfromlandslides,settlement,orslippage. Thereportsalso concluded that implementation of the remedial activities would not adversely affect the geologicstabilityofsurroundingproperties.32

AswiththeRP’sProposedRemedy,allaffectedproperties(219residentialproperties)wouldbeexcavatedtoadepthof5feet,with targetedareasto10feetbgs. However,becausehardscape(sidewalks,concretepatios,masonrywalls,etc.)andsoilsbeneathhardscapewouldnotberemoved,totalexcavatedsoilswouldbereduced.Itisestimatedthatapproximately92,755CYofsoilwouldbeexportedfromthesite.

Conventionalexcavationusingslot‐trenchingasnecessarytoprotectstructuresorotherfeaturesandopenbulkexcavationwithappropriatesloping,setbacks,and/orshoringwouldbeusedwherepossible.AswiththeRP’sProposedRemedy,mini‐excavators,handtools,orwheelbarrows,whicharelimitedto5‐foot‐deepcuts,couldbeusedtoconductthe5‐foot‐deepexcavations.

Los Angeles County Building Code Sections J105.3, Field Engineer Inspection, and J105.4, Soils EngineerInspection,whichareimplementedforallengineeredgrading,aswellas implementationofprojectdesign

32 URSCorporation,GeotechnicalReport,PlannedPilotTestforRemedialExcavationandBackfillPlacement,24612NeptuneAvenue,

Carson, CA,March 29, 2012, page 4‐1 and Planned Pilot Test forRemedial Excavation andBackfill Placement, 24533RavennaAvenue,Carson,CA,April13,2012,page2‐1.



features,suchasPDF‐Geo‐6,requireobservationduringgrading,testingforrequiredcompactionandsafetyof structures due to any slippage or settlement of the completed grading, and ensure that conditions inapproved engineering reports are implemented. With implementation of County Building Coderequirements and project design features, Alternative 3 would avoid lateral spreading, subsidence,liquefaction,orcollapseduringconstruction. Thesite isessentially levelandno landsliding isanticipated.Therefore, the impact of the Alternative 3 with respect to landslide, lateral spreading, subsidence,liquefaction,orcollapsewouldbelessthansignificant.

Erosion Hazards

Alternative 3 would remove approximately 83,930 CY of impacted soils from the residential properties,includinga10percentcontingency.Inaddition,8,100CYofsoilfromstreettrenchingand725CYfromwellpreparation would be excavated, for a total of 92,755 CY. These soils would be replaced by equivalentvolumesofcleanbackfill. BecausethequantityofexcavatedsoilwouldbelessunderthisAlternativethanunder the RP’s Proposed Remedy, potential exposure to natural forces could decrease erosion potential.Projectdesignfeatures,suchasPDF‐Geo‐5,whichrequiresthattopsoilsuitableforplantgrowthintheupper6 inches and underlain by 6‐inch‐thick backfills compacted to a relative compaction of 80 to 85 percent,wouldalsobeimplemented.Theinclusionoftopsoilinthebackfillmaterialsandcompactedunderlyingsoilwithintheupperone‐footwouldpromotethegrowthofvegetation,aswellasreducedeeperosion.WiththeimplementationofCode‐requiredbestmanagementpracticesforexcavationsandbackfillandprojectdesignfeatures,Alternative3wouldnotresultinsubstantialsoilerosion.TheremovalofexistingCOC‐containingsoilswouldnotconstituteusefultopsoiland,therefore,theimpactofAlternative3withrespecttolossoftopsoilwouldbelessthansignificant.

Expansive Soils Hazards

Prior geotechnical investigations of the site determined that naturally‐occurring on‐site soils were non‐expansive by both Los Angeles County and FHA criteria. Design features, such as PDF‐Geo‐5, would beimplemented,whichrequirethatsoilswithhighlevelsofclaythatcouldcontributetoshrinkingandswellingwouldnotbeallowedasbackfillmaterial. Alternative3wouldnotremoveexistingsoilsunderresidentialbuildings, garages, or hardscape and, thus, would not change conditions with respect to existing non‐expansive soils that currently support habitable structures. Because on‐site soils are non‐expansive, andimportedsoilswouldbe tested toensure thatexpansivesoilswouldnotbeused inbackfill, the impactofAlternative3withrespecttoexpansivesoilswouldbelessthansignificant.

6. CUMULATIVE IMPACTS

Thestudyareaconsideredforthecumulativegeologicimpactsincludes(1)theareathatcouldbeaffectedbytheRAPand(2)theareasaffectedbyotherprojectswhoseactivitiescoulddirectlyor indirectlyaffect thegeologyandsoilsoftheprojectsite.Geologicandsoilimpactsaregenerallysite‐specificandthereislittle,ifany,cumulativerelationshipbetweendevelopmentorremediationprojects.Adherencetoallrelevantplans,codes, and regulationswith respect to project design and constructionwould reduce project‐specific andcumulative geologic impacts to a less‐than significant level. Therefore, since geologic hazards are site‐specific,theRAP,incombinationwithotherpast,present,andreasonablyforeseeablefutureprojects,wouldnotcreateapotentiallysignificantcumulativeimpactongeologicalresources.



Impacts fromerosionand lossof topsoil fromsitedevelopmentandoperationcanbecumulative ineffectwithin awatershed. TheWest Coast Basin of the Los Angeles Coastal Plain encompasses the immediatewatershed region and forms the geographic context for cumulative erosion impacts. DevelopmentthroughoutthewatershedwouldbesubjecttoStateandlocalrunoffanderosionpreventionrequirements,includingtheapplicableprovisionsofthegeneralconstructionpermit,BMPs,andPhasesIandIIofNPDES,as well as implementation of fugitive dust control measures of SCAQMD Rule 403. These measures areimplementedasconditionsofapprovalofprojectdevelopmentandsubjecttocontinuingenforcement.Asaresult, it is anticipated that cumulative impacts on theWest Coast Basin due to runoff and erosion fromcumulativedevelopmentactivitywouldbelessthansignificant.

7. MITIGATION MEASURES

With the implementation of existing regulations and project design features described above, the RP’sProposedRemedynortheExpeditedImplementationOptionwouldresultinsignificantimpactswithrespecttogeologichazards, suchasgroundshaking, slopestability, settlement, liquefaction, erosion,orexpansivesoils.Therefore,nomitigationmeasureswouldbenecessaryfortheRP’sProposedRemedyortheExpeditedImplementationOption.

Withregardtoalternatives, theNoProjectAlternativewouldnot involveanyexcavationorotherphysicalactivity andwould not result in any geologic hazards. Therefore,mitigationmeasureswould also not berequired for thisAlternative. Alternatives2and3wouldnot result in significant impactswith respect togeologichazards,suchasgroundshaking,slopestability,settlement,liquefaction,erosion,orexpansivesoils.Therefore,nomitigationmeasureswouldbenecessaryforAlternatives2and3.

8. LEVEL OF SIGNIFICANCE AFTER MITIGATION

No potentially significant impact with respect to seismic risk or other geologic hazards, such as groundshaking, slope stability, settlement, liquefaction, erosion, or expansive soils have been identified. Nomitigationmeasureswouldbenecessary.BecausetheRP’sProposedRemedy,Alternative2,andAlternative3 would be consistent with the existing regulatory framework relative to seismic hazards, grading,foundations,soils,erosion,andothergeologicalconcerns,mitigationmeasureswouldnotberequired. Nosignificantimpactswithrespecttogeologyandsoilswouldoccur.Alternative1,theNoProjectAlternative,wouldnotinvolveanyphysicalactivityorcauseanygeologiceffects. Therefore,noimpactsareassociatedwiththisAlternative.

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