Section4.7GeologyandSoils

Coachella Valley Water District 4.7-1 Draft EIR Chromium-6 Water Treatment Facilities Project April 2016

4.7 GEOLOGYANDSOILS

4.7.1 INTRODUCTIONThissectiondescribesgeology,soils,andseismicityconditionsinthevicinityoftheprojectsitesandassessesthepotentialfortheprojecttobeaffectedbyortoincreaserisksassociatedwithidentifiedgeologicandseismichazards.Thissectionisbasedongeotechnicalreportspreparedfortheproject(ConverseConsultants2016a,2016b,2016c),andinformationgatheredfromothersourcessuchastheU.S.GeologicSurvey,CaliforniaGeologicSurvey,RiversideCountyhazardsmapping,andotherCEQAdocumentspreparedforrelevantprojectsintheCoachellaValley.4.7.2 ENVIRONMENTALSETTING4.7.2.1 RegionalGeologicSettingTheprojectstudyareaforgeologyandsoilsextendsthelengthoftheCoachellaValley,fromDesertHotSpringsinthenorthtotheSaltonSeainthesouth.Italsoincludesthenearbyfaultzonesthathavethepotentialtogenerateseismiceventsthatcouldaffectprojectfacilities.TheCoachellaValleyislocatedwithinthenorthernportionoftheSaltonTrough,whichiswithinthenorthernportionoftheColoradoDesertGeomorphicProvinceofSouthernCalifornia.TheSaltonTroughisageologicstructuraldepressionresultingfromlarge-scaleregionalfaultingandrepresentsthenorthwardextensionoftheGulfofCalifornia(CVWD,2015).TheColoradoDesertGeomorphicProvinceisboundedonthenorthbytheTransverseRanges(LittleSanBernardinoandOrocopiaMountains),onthewestbythePeninsularRanges(SantaRosaandSanJacintoMountains),andontheeastbytheMojaveDesert.TheValleyfloorrangesinelevationfrom1,600feetabovemeansealevel(MSL)inthenorthwesttoabout230feetbelowMSLattheSaltonSea.Theprovinceisaseismicallyactiveregioncharacterizedbyalluviatedbasins,elevatederosionsurfaces,andnorthwest-trendingmountainrangesboundedbynorthwest-trendingstrike-slipfaults.ThemostprominentofthenearbyfaultzonesincludetheSanAndreasandSanJacintofaultzones,bothofwhichhavebeenknowntobeactiveduringQuaternarytime(themostrecent2.6millionyearsofearth’shistory).Severalthousandfeetofsediments,includingalluvialdepositsfromtheWhitewaterRiverandaeoliandepositsfromthestrongprevailingwindstypicaloftheregion,underlietheCoachellaValley.Basedongeologicliteraturereview,thegeologicunitsanticipatedwithintheprojectstudyareaincludealluvialsandandgravel,loosefinesanddepositedbywind,clayofplayalakes,andquartzdioritetogranodiorite.4.7.2.2 RegionalFaultingandSeismicHazardsFaultsThemajorsourcesofseismicactivityincentralandwesternRiversideCountyaretheSanAndreas,SanJacinto,andElsinorefaultzones.Figure4-7.1showsthelocationoftheprojectareainrelationtothesefaults,includingtheearthquakeprobabilityforsegmentsofthesefaults.Alloftheprojectfacilitysitesarelocatedwithinadistanceofapproximately1to5mileswestoftheSanAndreasFaultzone,andtheproposedpipelinetoconveytreatedwaterfromtheID8WBAWaterTreatmentFacilityinDillonRoad

Section4.7GeologyandSoils

Coachella Valley Water District 4.7-2 Draft EIR Chromium-6 Water Treatment Facilities Project April 2016

crossesatraceofthisfaultzone(seeFigure4.7-2).TheSanJacintofaultzoneliesapproximately20-25mileswestoftheprojectarea,andtheElsinorefaultzoneisapproximately40-45mileswestoftheprojectarea.TheSanAndreasFaultsystemisthemostactivefaultsysteminCalifornia.Initsentirety,itrunsapproximately800milesthroughthestate,primarilyalongthecoastlineinthenorthernstretchandturninginlandforthesouthernstretch.ThefaultformsthetectonicboundarybetweenthePacificandNorthAmericanplates,anditisalongtheseplatesthatmostseismicactivityoccurs.InthevicinityofRiversideCounty,theSanAndreasFaultzoneiscomprisedofthreesegments:1)theSanBernardinoMountainssegment,2)theCoachellaValleysegment,and3)theMojaveDesertsegment(EarthConsultantsInternational,2000).RiversideCountyisbisectedbytheSanBernardinosegmentbetweentheCajonandSanGorgonioPasses.TheCoachellaValleysegmentrunsalongthenortheasternmarginoftheValley,andextendsfromSanGorgonioPasstotheSaltonSea.Althoughthissegmenthasnotproducedlarge,surface-rupturingearthquakesinhistorictimes,itdoeshaveanestimated22%probabilityofrupturingbeforetheyear2024,andisestimatedasbeingcapableofproducingamagnitude7.1earthquake(ontheRichterMagnitudeScale).TheSanJacintofaultzoneconsistsofcloselyspacedfaultsthatformthewesternmarginoftheSanJacintoMountains.ThisfaultzoneextendsfromitsjunctionwiththeSanAndreasFaultzoneinSanBernardino,southeasterlytowardtheBrawleyarea,whereitcontinuessouthoftheMexicoborderastheImperialtransformfault.TheSanJacintofaultzonehasahighlevelofhistoricalseismicactivity,withatleasttendamagingearthquakeshavingoccurredbetween1890and1986.ThesegmentsoftheSanJacintofaultthatareofmostconcerntocentralRiversideCountyaretheSanBernardino,SanJacintoValley,andAnzasegments.Maximumcredibleearthquakesofmagnitudes6.7,6.9,and7.2areexpectedonthesesegments,respectively.TheElsinoreFaultzoneparallelstheSanJacintoandispartofthesameright-lateralplatestrainsystemastheSanAndreasandSanJacintofaults.TherelevantsegmentsoftheElsinoreFaultzoneinwesternRiversideCountyaretheWhittier,GlenIvy,Temecula,andJuliansegments.Maximumcredibleearthquakesofmagnitude6.7to6.8havebeenassignedforthesesegments.SeismicHazardsFollowingisadescriptionoftheseismichazardsthatcouldaffectprojectfacilitieswithinthestudyarea.FaultRuptureSurfaceruptureoccurswhenmovementonafaultdeepwithintheearthbreaksthroughtothesurface.Theevaluationoffaultrupturehazardisgenerallybasedonthehistoricactivityandrecurrenceofearthquakesalongexistingfaults.Notallearthquakesresultinsurfacerupture.Rupturemayoccursuddenlyduringanearthquakeorslowlyintheformoffaultcreep.Suddendisplacementsaremoredamagingtostructuresbecausetheycansuddenlydisplacestructuresandareusuallyaccompaniedbystrongshaking.Faultcreepistheslowruptureoftheearth’scrust.Indevelopedareas,faultcreepcanoffsetanddeformcurbs,streets,buildings,andotherstructuresthatlieonthefaulttrace.TheproposedtreatedwaterpipelinealongDillonRoadcrossestheCoachellasegmentoftheSanAndreasFaultzone,approximately1,000feeteastofLongCanyonRoadand,therefore,isconsideredtobesusceptibletotheeffectsoffaultrupture.Noneoftheotherprojectsitesarelocatedwithinanearthquakefaultzone,andpotentialforfaultruptureatthosesitesisconsideredlow.

Section4.7GeologyandSoils

Coachella Valley Water District 4.7-3 Draft EIR Chromium-6 Water Treatment Facilities Project April 2016

GroundshakingTheintensityoftheseismicshaking,orstronggroundmotion,duringanearthquakeisdependentonthedistancebetweentheprojectareaandtheepicenteroftheearthquake,themagnitudeoftheearthquake,andthegeologicconditionsunderlyingandsurroundingtheprojectarea.Earthquakesoccurringonfaultsclosesttotheprojectareawouldmostlikelygeneratethelargestgroundmotions.Theintensityofearthquake-inducedgroundmotionsandthepotentialforcesaffectingstructureswithintheprojectstudyareacanbedescribedusingpeakgroundaccelerations,whicharerepresentedasafractionoftheaccelerationofgravity(g).1Theestimatedpeakgroundaccelerationsforthechromium-6projectsitesvary,fromalowofapproximately0.56gtoahighof1.14g.Thehighertheaccelerationrate,thestrongerthegroundmotionwillbe.LiquefactionLiquefactionisaphenomenoninwhichsaturatedgranularsedimentstemporarilylosetheirshearstrengthduringperiodsofearthquake-inducedstronggroundshaking.Thesusceptibilityofasitetoliquefactionisafunctionofthedepth,density,andwatercontentofthegranularsedimentsandthemagnitudeoftheearthquakeslikelytoaffectthesite.Saturated,unconsolidatedsilts,sands,siltysands,andgravelswithin50feetofthegroundsurfacearemostsusceptibletoliquefaction.Liquefaction-relatedphenomenaincludeverticalsettlementfromdensification,lateralspreading,groundoscillation,flowfailures,lossofbearingstrength,subsidence,andbuoyancyeffects.LateralSpreadingLateralspreadingreferstolandslidesthatcommonlyformongentleslopesandthatcauserapidfluid-likeflowmovement,likewater.Duringlateralspreading,amassmovestowardanunconfinedarea,suchasadescendingslopeorstream-cutbluff,andcanoccuronslopegradientsasgentleasonedegree.Lateralspreadingischaracterizedbynear-verticalcrackswithpredominantlyhorizontalmovementofthesoilmassoverliquefiedsoils.Alloftheprojectsitesarerelativelyflatanddonotincludesignificantslopes;therefore,theriskoflateralspreadingisconsideredtobelow.Earthquake-inducedSlopeFailureandLandslidesEarthquakemotioncaninducesubstantialstressesinslopes,causingearthquake-inducedlandslidesorgroundcrackingwhentheslopefails.Earthquake-inducedlandslidescanoccurinareaswithsteepslopesthataresusceptibletostronggroundmotionduringanearthquake.Exposedrockslopesundergorockfalls,rockslides,orrockavalanches,whilesoilslopesexperiencesoilslumps,rapiddebrisflows,anddeep-seatedslides.Slopestabilitycandependonanumberofcomplexvariables,includingthegeology,soilstructure,andamountofgroundwater,aswellasexternalprocessessuchasclimate,topography,slopegeometry,andhumanactivity.Landslidescanoccuronslopesof15%orless,buttheprobabilityisgreateronsteeperslopes.Alloftheprojectsitesarerelativelyflatandareconsideredtohavealowpotentialforseismically-inducedslopefailureandlandsliding.TsunamiandSeichesTsunamisareopenseatidalwavesgeneratedbyearthquakes.Tsunamidamageistypicallyconfinedtolow-lyingcoastalareas.DuetothedistanceoftheCoachellaValleyfromtheocean,tsunamisarenotathreattotheprojectstudyarea.Aseicheisaperiodicoscillationor“sloshing”ofwaterinanenclosedbasin(e.g.,lakeorreservoir)causedbyanearthquake.Thenearestenclosedwaterbasin,theSalton

1Accelerationofgravity(g)=980centimeterspersecondsquared.1.0gaccelerationisarateofincreaseinspeedequivalenttoacartraveling328feetfromrestin4.5seconds.

Section4.7GeologyandSoils

Coachella Valley Water District 4.7-4 Draft EIR Chromium-6 Water Treatment Facilities Project April 2016

Sea,isapproximately10to12milessouthoftheprojectsites;basedonthisdistance,thethreatofseichesisunlikely.4.7.2.3 SoilConditionsProblematicsoils,suchasthosethatareexpansiveorcorrosive,candamagestructuresandburiedutilitiesandincreasemaintenancerequirements.Expansivesoilsarecharacterizedbytheirabilitytoundergosignificantvolumechange(i.e.,toshrinkandtoswell)duetovariationsinmoisturecontent.Changesinsoilmoisturecanresultfromrainfall,landscapeirrigation,utilityleakage,roofdrainage,and/orperchedgroundwater.Expansivesoilsaretypicallyveryfinegrainedandhaveahightoveryhighpercentageofclay.Expansionandcontractionofexpansivesoilsinresponsetochangesinmoisturecontentcanleadtodifferentialandcyclicalmovementsthatcancausedamageand/ordistresstostructuresandequipment.Accordingtothegeotechnicalreportspreparedfortheproject,theexpansionpotentialfortheprojectsitesisconsideredtobeverylowtolow.Thecorrosivityofsoilsiscommonlyrelatedtoseveralkeyparameters,includingsoilresistivity,thepresenceofchloridesandsulfates,oxygencontent,andpH.Typically,themostcorrosivesoilsarethosewiththelowestpHandhighestconcentrationofchloridesandsulfates.Wet/dryconditionscanresultinaconcentrationofchloridesandsulfates,aswellasmovementinthesoil,bothofwhichtendtobreakdowntheprotectivecorrosionfilmsandcoatingsonthesurfacesofbuildingmaterials.High-sulfatesoilsarealsocorrosivetoconcreteandmaypreventcompletecuring,therebyreducingthestrengthoftheconcreteconsiderably.LowpHand/orlow-resistivitysoilscancorrodeburiedorpartiallyburiedmetalstructures.Dependingonthedegreeofcorrosivityofthesubsurfacesoils,buildingmaterialssuchasconcrete,reinforcingsteelinconcretestructures,andbare-metalstructuresexposedtothesesoilscandeteriorate,eventuallyleadingtostructuralfailures.Accordingtothegeotechnicalreportspreparedfortheproject,alloftheprojectsiteshavebeenidentifiedashavingsomesoilcorrosivityexposure,frommildlycorrosivetoseverelycorrosive.Table4.7-1providesasummaryofexistinggeologicandsoilsconditionsfortheprojectsites.Informationinthistableisderivedfromthegeotechnicalreportspreparedfortheproject(ConverseConsultants2016a,2016b,2016c).4.7.3 REGULATORYFRAMEWORK4.7.3.1 FederalNofederalregulationsareassociatedwithgeology,soilsandseismicityfortheproposedproject.4.7.3.2 StateAlquist-PrioloEarthquakeFaultZoningActTheAlquist-PrioloEarthquakeFaultZoningActwaspassedin1972tomitigatethehazardofsurfacefaultingtostructuresforhumanoccupancy.Inaccordancewiththisact,theStateGeologistestablishedregulatoryzones,called“earthquakefaultzones,”aroundthesurfacetracesofactivefaultsandpublishedmapsshowingthesezones.Withinthesezones,buildingsforhumanoccupancycannotbeconstructedacrossthesurfacetraceofactivefaults.Becausemanyactivefaultsarecomplexandconsistofmorethanonebranch,eachearthquakefaultzoneextendsapproximately200to500feetoneithersideofthemappedfaulttrace.

Section4.7GeologyandSoils

Coachella Valley Water District 4.7-5 Draft EIR Chromium-6 Water Treatment Facilities Project April 2016

TABLE4.7-1:SUMMARYOFGEOLOGICANDSOILSCONDITIONSATPROJECTSITES

CVWDSiteName

GeologicUnit

Landslide/SlopeFailurePotential

LiquefactionSusceptibility

ApproximateDistancetoSan

AndreasFaultZone

SBAFACILITIESSBA4510-1 Loosefinesandoveralluvialsand/gravel Low Low 4milesnortheastSBA4610-1 Alluvialsand/gravelofvalleyareas Low Low 2.5milesnortheastSBA4720-1 Alluvialsand/gravelofvalleyareas Low Low 1.5milesnortheastSBA4721-1 Alluvialsand/gravelofvalleyareas Low Low 1milenortheastSBA4722-1 Alluvialsand/gravelofvalleyareas Low Low 1milenortheastSBA5632-2 Loosefinesand-alluvialsand/gravelmargin Low Low 3milesnortheastSBA5657-2 Loosefinesandoveralluvialsand/gravel Low Low 3milesnortheastSBA5664-1 Loosefinesand-alluvialsand/gravelmargin Low Low 3milesnortheastSBA5676-2 Loosefinesandoveralluvialsand/gravel Low Low 4milesnortheastSBA5677-1 Loosefinesandoveralluvialsand/gravel Low Low 4milesnortheastSBA5678-1 Loosefinesandoveralluvialsand/gravel Low Low 4milesnortheastSBA5679-1 Loosefinesand-alluvialsand/gravelmargin Low Low 3milesnortheastSBA5711-2 Loosefinesandoveralluvialsand/gravel Low Low 3milesnortheastSBA5717-1 Loosefinesandoveralluvialsand/gravel Low Low 3milesnortheastSBA5718-1 Loosefinesandoveralluvialsand/gravel Low Low 3milesnortheastSBA5719-1 Loosefinesand-alluvialsand/gravelmargin Low Low 2milesnortheastSBA5720-1 Alluvialsand/gravelofvalleyareas Low Low 1.5milesnortheastSBA6701-1 Loosefinesand-alluvialsand/gravelmargin Low Low 4milesnortheastSBA6726-1 Alluvialsand/gravelofvalleyareas Low High 3milesnortheastSBA6728-1 Alluvialsand/gravelofvalleyareas Low High 3milesnortheastSBA6734-1 Alluvialsand/gravelofvalleyareas Low High 3milesnortheastSBA6805-1 Alluvialsand/gravelofvalleyareas Low High 5milesnortheastSBA6808-1 Alluvialsand/gravelofvalleyareas Low High 5milesnortheast

CRRF Siltysand,siltytosandyclay Low High 5milesnortheastCRRFpipelines Alluvialsand/gravelofvalleyareas Low High 5milesnortheastWBAFACILITIES

WBA3408-1 Alluvialsand/gravelofvalleyareas Low Low 2milesnorthand1milesouth

WBA3409-2 Alluvialsand/gravelofvalleyareas Low Low 2milesnorthand1milesouth

WBA3410-1 Alluvialsand/gravelofvalleyareas Low Low2milesnorthand1

milesouthID8Treatment

Plant Alluvialsand/gravelofvalleyareas Low Moderate2milesnorthand1

milesouth

ID8pipelines Alluvialsand/gravelofvalleyareas Low Moderate DillonRoadpipelinecrossesfault

WBA6723-1 Alluvialsand/gravelofvalleyareas Low High 7milesnortheastWBA6724-1 Alluvialsand/gravelofvalleyareas Low High 7milesnortheastWBA6725-1 Alluvialsand/gravelofvalleyareas Low High 7milesnortheastLaQuinta

TreatmentPlantAlluvialsand/gravelofvalleyareas Low High 7milesnortheast

LaQuintapipelines Alluvialsandandclay Low High 7milesnortheast

Section4.7GeologyandSoils

Coachella Valley Water District 4.7-6 Draft EIR Chromium-6 Water Treatment Facilities Project April 2016

Title14oftheCaliforniaCodeofRegulations(CCR),Section3601(e),definesbuildingsintendedforhumanoccupancyasthosethatwouldbeinhabitedformorethan2,000hoursperyear.Theonlycomponentoftheprojectthatcrossesafaultzone(SanAndreasFault)istheproposedpipelinethatwillcarrytreatedwaterfromtheID8WBAWaterTreatmentFacilityinDillonRoadtotheexistingCVWDreservoiratLangloisRoad.Thispipelinedoesnotmeetthecriterionofabuildingusedforhumanoccupancywithinthevicinityofanymappedfaulttrace;therefore,theprovisionsoftheactdonotapplytotheproject.NoneoftheotherprojectfacilitiesarelocatedwithinanAlquist-PrioloEarthquakeFaultZone.SeismicHazardsMappingActLiketheAlquist-PrioloAct,theSeismicHazardsMappingActof1990(PublicResourcesCodeSections2690to2699.6)isintendedtoreducedamageresultingfromearthquakes.WhiletheAlquist-PrioloActaddressessurfacefaultrupture,theSeismicHazardsMappingActaddressesotherearthquake-relatedhazards,includingstronggroundshaking,liquefaction,andseismically-inducedlandslides.ItsprovisionsaresimilarinconcepttothoseoftheAlquist-PrioloAct;theStateischargedwithidentifyingandmappingareasatriskofstronggroundshaking,liquefaction,landslides,andothercorollaryhazards.CitiesandcountiesarerequiredtoregulatedevelopmentwithinmappedSeismicHazardZones.UndertheSeismicHazardsMappingAct,permitreviewistheprimarymechanismforlocalregulationofdevelopment.Specifically,citiesandcountiesareprohibitedfromissuingdevelopmentpermitsforsiteswithinSeismicHazardZonesuntilappropriatesite-specificgeologicand/orgeotechnicalinvestigationshavebeenconductedandmeasurestoreducepotentialdamagehavebeenincorporatedintothedevelopmentplans.Accordingtothepreliminarygeotechnicalreportspreparedfortheproject,theprojectsitesarenotwithinareasdesignatedbyRiversideCountyasSeismicHazardZones.BuildingCodesTheCaliforniaBuildingCode(CBC),whichiscodifiedinCCRTitle24,Part2,waspromulgatedtosafeguardthepublichealth,safety,andgeneralwelfarebyestablishingminimumstandardsrelatedtostructuralstrength,egressfacilities,andgeneralbuildingstability.ThepurposeoftheCBCistoregulateandcontrolthedesign,construction,qualityofmaterials,use/occupancy,location,andmaintenanceofallbuildingandstructureswithinitsjurisdiction.Title24isadministeredbytheCaliforniaBuildingStandardsCommissionwhich,bylaw,isresponsibleforcoordinatingallbuildingstandards.The2013CBCisbasedonthe2006InternationalBuildingCode(IBC)publishedbytheInternationalCodeConference.Inaddition,theCBCcontainsnecessaryCaliforniaamendmentsthatarebasedontheAmericanSocietyofCivilEngineers(ASCE)MinimumDesignStandards7-05.ASCE7-05providesrequirementsforgeneralstructuraldesignandincludesmeansfordeterminingearthquakeloads,aswellasotherloads(e.g.,flood,snow,wind)forinclusioninbuildingcodes.TheprovisionsoftheCBCapplytotheconstruction,alteration,movement,replacementanddemolitionofeverybuildingorstructureoranyappurtenancesconnectedorattachedtosuchbuildingsorstructuresthroughoutCalifornia.Theearthquakedesignrequirementstakeintoaccounttheoccupancycategoryofthestructure,siteclass,soilclassifications,andvariousseismiccoefficients,allofwhichareusedtodetermineaSeismicDesignCategory(SDC)foraproject.TheSDCisaclassificationsystemthatcombinestheoccupancycategorieswiththelevelofexpectedgroundmotionsatagivensite,andrangesfromSDCA(verysmallseismicvulnerability)toSDCE/F(veryhighseismicvulnerabilityandnearamajorfault).DesignspecificationsarethendeterminedaccordingtotheSDC.

Section4.7GeologyandSoils

Coachella Valley Water District 4.7-7 Draft EIR Chromium-6 Water Treatment Facilities Project April 2016

4.7.3.3 RegionalandLocalCVWDDevelopmentDesignManualCVWDhasadoptedtheDevelopmentDesignManual(DDM)toprovidecomprehensiveproceduralandtechnicalrequirementsfortheplanning,designandconstructionofCVWDserviceinfrastructurerequiredfornewdevelopment(CVWD2013).TheDDMincludesrequirementsformeetingseismicdesignstandards.

RiversideCountyDepartmentofEnvironmentalHealthTheRiversideCountyDepartmentofEnvironmentalHealthmaintainsatechnicalguidancemanualforonsitewastewatertreatmentsystems(RiversideCounty2009).OnsitesanitarydisposalattheID8WBAWaterTreatmentFacilitysitewouldeitherbeasepticsystem,holdingtank,orportabletoilet.Installationofanyofthesesystemswouldneedtocomplywiththismanual.4.7.4 IMPACTSANDMITIGATIONMEASURES4.7.4.1 SignificanceCriteriaBasedonAppendixGoftheStateCEQAGuidelines,aprojectwouldresultinsignificantimpactsrelatedtogeologyandsoilsifitwould:

a. Expose people or structures to potential substantial adverse effects, including the risk ofloss,injury,ordeathinvolving:

• Ruptureof a knownearthquake fault, asdelineatedon themost recentAlquist-PrioloEarthquake Fault ZoningMap issued by the State Geologist for the area or based onothersubstantialevidenceofaknownfault.

• Strongseismicgroundshaking.

• Seismic-relatedgroundfailure,includingliquefaction.

• Landslides

b. Resultinsubstantialsoilerosionorthelossoftopsoil.

c. Belocatedonageologicunitorsoilsthat isunstable,orthatwouldbecomeunstableasaresult of the project, and potentially result in on- or off-site landslide, lateral spreading,subsidence,liquefactionorcollapsecreatingsubstantialriskstolifeorproperty.

d. Be located on expansive soil, as defined in Table 18-1-B of the Uniform Building Code,creatingsubstantialriskstolifeorproperty.

e. Have soils incapable of adequately supporting the use of septic tanks or alternativewastewaterdisposalsystemswheresewersarenotavailableofthedisposalofwastewater.

4.7.4.2 ApproachtoAnalysisThepotentialforimpactsrelatedtogeology,soilsandseismicityareevaluatedaccordingtothesignificancecriterialistedabove.Regionalandlocalgeologicmaps,aswellasproject-specificpreliminarygeotechnicalreports,werereviewedtoidentifygeologicconditionsandgeologichazardsin

Section4.7GeologyandSoils

Coachella Valley Water District 4.7-8 Draft EIR Chromium-6 Water Treatment Facilities Project April 2016

thestudyareathat,becauseoftheirproximity,couldbedirectlyorindirectlyaffectedbytheproposedprojectorcouldaffecttheproject.AreasofNoProjectImpactThefollowingthreesignificancecriteriaarenotdiscussedfurtherinthissectionforthefollowingreasons:a. Exposepeopleorstructurestosubstantialadverseeffectsrelatedtotherisksofpropertyloss,injury

ordeathduetofaultrupture,seismicgroundshaking,orlandslides.

Thissignificancecriterionisintendedtoaddressfacilitysitinganddesignimpactsanddoesnotapplytotemporaryconstructionimpacts;thereforeitisnotdiscussedintheconstructionimpactsSection4.7.4.3below.Withregardtolong-termoperationalimpacts,ofthefourhazardslistedinthiscriterion,thepotentialforlandslidestoaffectprojectfacilitiesdoesnotneedfurtherdiscussionbecausealltheprojectsitesarerelativelyflatandconsideredtohavealowpotentialforseismically-inducedslopefailureandlandsliding.Thepotentialforfaultrupture,stronggroundshakingandliquefactiondoapplytooperationsofsomeoftheprojectfacilities,andtheyarediscussedinSection4.7.4.4below.

d.Belocatedonexpansivesoil,asdefinedinTable18-1-BoftheUniformBuildingCode,creatingsubstantialriskstolifeorproperty.

Asdescribedabove,thesoilexpansionpotentialforalloftheprojectsitesisconsideredtobeverylowtolow;therefore,thiscriterionisnotdiscussedfurther.

e. Havesoilsincapableofadequatelysupportingtheuseofseptictanksoralternativewastewaterdisposalsystemswheresewersarenotavailableforthedisposalofwastewater.

Asnotedabove,theproposedonsitesanitarydisposalmethodfortheID8WBAWaterTreatmentFacilityhasnotyetbeendetermined,butwouldeitherbeasepticsystem,holdingtank,orportabletoilet.InstallationofanyofthesesystemswouldneedtocomplywiththeRiversideCountyDepartmentofEnvironmentalHealthtechnicalguidancemanualforonsitewastewatertreatmentsystems.IfitisdeterminedthatthesoilsattheID8WBAWaterTreatmentFacilitysitearenotcapableofadequatelysupportingtheuseofaseptictankatthissite,oneoftheotherdisposalsystemswouldbeinstalled.CompliancewiththeRiversideCountyguidancemanualwouldensurethatnoimpactsunderthiscriterionwouldoccur.

4.7.4.3 ConstructionImpactsandMitigationMeasures

ImpactGS-1:Constructionoftheprojectwouldnotresultinsubstantialsoilerosionorthelossoftopsoil.(LessthanSignificant)AlloftheSBAandWBAwellsitesaredevelopedwithexistingCVWDwaterinfrastructureandhavebeenhighlyalteredfromtheiroriginal,naturalstate.Asaresult,thedepthandamountofgradingandexcavationatthesesiteswouldresultinminimaldisturbancetonativesoils.Inaddition,thewellsitesarenearareasofmoderatetointenseurbanuses,suchassurfacestreets,residences,andrecreationalandcommercialfacilities.Consequently,nosubstantial

Section4.7GeologyandSoils

Coachella Valley Water District 4.7-9 Draft EIR Chromium-6 Water Treatment Facilities Project April 2016

lossoftopsoilduetoerosionorgradingwouldoccurduringconstructionoftheprojectatthesesites.TheCRRFandWBAWaterTreatmentFacilitysitesareundevelopedsites.Constructionatthesesiteswouldinvolvegrounddisturbanceincludingsitepreparation,grading,andtrenchingforstructureandutilityinstallations.Potentialerosionthatmayresultfromgrading,excavation,pipelinetrenching,andothersoildisturbanceduringconstructionwouldbecontrolledduringconstructionwithimplementationoferosioncontrolplansasrequiredbyCVWD.Additionally,standardconstructionpracticestopreventandminimizeconstruction-relatederosionwouldbeincludedinconstructiondocumentsandStormWaterPollutionPreventionPlans(SWPPP)thatarerequiredpursuanttofederalandstateNationalPollutantDischargeEliminationSystemregulations(seeSection4.10,HydrologyandWaterQuality,forfurtherexplanationofSWPPPrequirements).TheSWPPPwouldincludeBestManagementPractices(BMPs)topreventerosion,suchasuseofsiltfencesorotherbarrierstopreventerosionandsedimentationintowaterbodies,useofdesiltingbasins,limitationsonworkduringhigh-windevents,andpost-constructionrevegetationanddrainagerequirements.ImplementationoftheSWPPPandBMPswouldensurethatthisimpactwouldbelessthansignificant.Nomitigationmeasuresarerequired.ImpactGS-2:Constructionofsomeprojectpipelinecomponentswouldbelocatedongeologicunitsorsoilsthatareunstableorthatmaybecomeunstableduringprojectconstruction,andpotentiallyresultinsoilinstabilityorcollapse;howeverthisexposurewouldnotresultinasubstantialrisktopeopleorstructures.(LessthanSignificant)Thisimpactappliestoinstallationofundergroundpipelineslocatedinareaswithsoilstabilityconcerns.ConstructionoftherawandtreatedwaterpipelinesthatwouldservetheID8andLaQuintaWBAWaterTreatmentFacilitiesmayencounterthepotentialforsoilinstabilityorcollapseduringpipelinetrenching.Toaddressthispotential,projectfacilitieswouldbedesignedinaccordancewithrecommendationsofsite-specificgeotechnicalinvestigationspreparedbyaCalifornialicensedgeotechnicalengineer(s).Design-levelgeotechnicalinvestigationswouldbepreparedforallprojectcomponentstoinformfinaldesignandconstructionthataddressseismichazards.Allrecommendationsofthegeotechnicalinvestigationswouldbeincorporatedintothefinaldesignandconstructionspecificationsforeachprojectcomponent,andwouldbeimplementedasspecifiedbytheconstructioncontractors.Althoughthereisthepotentialforsoilcollapseduringpipelinetrenching,compliancewiththerequirementsofstateandCVWD’sprofessionalengineeringstandardswouldensurethatthisimpactwouldbelessthansignificant.Nomitigationmeasuresarerequired.

4.7.4.4 OperationImpactsandMitigationMeasures

ImpactGS-3:ThetreatedwaterpipelinetobeinstalledinDillonRoadinDesertHotSpringswouldcrosstheCoachellaValleysegmentoftheSanAndreasFaultzone,potentiallyexposingthisprojectfacilitytofaultruptureduringaseismiceventandsubsequentdisruptionofwaterserviceinthisarea;however,thisexposurewouldnotresultinsubstantialrisktopeopleorstructures.(LessthanSignificant)

Section4.7GeologyandSoils

Coachella Valley Water District 4.7-10 Draft EIR Chromium-6 Water Treatment Facilities Project April 2016

Theprojectwouldbelocatedinanareaofhighseismicity,andoneoftheprojectpipelineswouldcrossanactivefaultzone.Potentialdamagecouldincludeabreaktoapipesegmentandpossiblyleakagetothesurroundingarea.Thelocationofthispipelinecrossingofthefaultisinanareaofverylowdensityresidentialdevelopment,suchthatapipebreakinthislocationwouldnottypicallybethecauseofsubstantialrisksoflossoflifeorproperty.Intheeventthatalargeseismiceventdidcauseruptureatthesurface,theruptureareawouldbelocalizedandanypipelinedamageorleaksimmediatelyrepaired.Inaddition,thepipelinewouldbedesignedinaccordancewithsite-specificgeotechnicalrecommendationsforthislocation,therebyreducingthepotentialforsubstantialdamageduringaseismicevent.Implementationoftheserecommendationswouldensurethatthisimpactwouldbelessthansignificant.Nomitigationmeasuresarerequired.ImpactGS-4:Theproposedprojectwouldbesubjecttostronggroundshakingandsomeprojectsiteswouldhaveahighliquefactionsusceptibilityduringaseismicevent;however,thisexposurewouldnotresultinasubstantialrisktopeopleorstructures.(LessthanSignificant)Alloftheprojectfacilitieswouldbelocatedwithinaseismicallyactiveregion.Anearthquakeonlocalorregionalfaultscouldresultindamagetostructuresandpipelinesduetoseismicshakingand/orliquefaction.Theintensitywouldbedependentonthemagnitudeoftheearthquakeanddistanceoffacilitiesfromtheearthquakeepicenter.Theprimaryeffectsofgroundshakingwouldbepotentialdamagetoprojectstructures,includingfoundationsand/orbreaksinwaterpipelines.StructureswouldbedesignedinaccordancewithrequirementsoftheCaliforniaBuildingCoderegardingseismicdesigncriteria,whichwouldhelpminimizedamagesandwouldnotresultinsubstantialadverseriskstopeopleorstructures.Thefollowingprojectsiteshavebeenidentifiedbygeotechnicalreportsashavinghighsusceptibilitytoliquefaction:SBAwells6726-1,6728-1,6734-1,6805-1,and6808-1;theCRRFsite;WBAwells6723-1,6724-1,and6725-1;andtheLaQuintaWBAWaterTreatmentFacilityanditsrawandtreatedwaterpipelinealignments.Thegeotechnicalreportsforthesefacilitiesprovidespecificdesignrecommendationstoaddressthisliquefactionpotential.Implementationoftheserecommendationswouldminimizethepotentialfordamagetothesefacilitiesintheeventofastrongseismicevent,andthisimpactwouldbelessthansignificant.Nomitigationmeasuresarerequired.ImpactGS-5:Someoftheprojectfacilitieswouldbelocatedonsiteswithcorrosivesoils;however,thisexposurewouldnotresultinasubstantialrisktopeopleorstructures.(LessthanSignificant)Accordingtotheprojectgeotechnicalreports,alloftheprojectsiteshavebeenidentifiedashavingsomelevelofpotentialexposuretosoilcorrosivity.Thesitesfallintocategoriesthatarerankedasmildlycorrosivetoseverelycorrosive.Corrosivesoilscould,overtimedeterioratethenewly-installedprojectfacilities.However,acombinationofprotectivecoatings,pipewrapping,andpossiblycathodicprotectionwouldbeincludedinfacilities’designandconstructiontominimizeexposuretothecorrosionprocess.Withincorporationofthesedesignfeatures,corrosivesoilimpactstolifeandpropertywouldbelessthansignificant.Nomitigationmeasuresarerequired.

Section4.7GeologyandSoils

Coachella Valley Water District 4.7-11 Draft EIR Chromium-6 Water Treatment Facilities Project April 2016

4.7.5 SIGNIFICANCEAFTERMITIGATIONNomitigationmeasuresarerequired.4.7.6 CUMULATIVEIMPACTSThegeographicscopeforcumulativeimpactsongeologyandsoilsconsistsofeachproposedprojectsiteandtheimmediatevicinityadjacenttoeachofthesesites(includingtheconstructionarea,facilities,andthepipelines).Theareaaffectedvariesforeachsite.Geologicandseismicimpactsaregenerallysite-specific,becausetheydependuponthelocalgeologyandsoilconditions.ThisanalysiswasperformedusingthegrowthprojectionapproachpursuanttoStateCEQAGuidelinesSection15130(b)(1)(B).Nocumulativeprojectshavebeenidentifiedfortheprojectsites,exceptfortheCRRFsite,whichwouldcontributetoacumulativegeologyandsoilsimpact.CVWDisplanningtoconstructtheFillmoreStreetIrrigationDitchprojecttoprotecttheWRP-4sitefromfloodingandtoconveyoverlandflowsfromnearbyirrigatedlandstotheCoachellaValleyStormwaterChannel.Thisprojectincludesconstructionofafloodplainberm,earthendrainagechannel,andirrigationditchontheWRP-4parcel.ConstructionoftheprojectwouldoccurconcurrentwithorbeforeCRRFconstruction.CVWDwoulddesignandconstructionthisprojectinaccordancewithseismicdesignstandardssuchthatitwouldnotresultinsoilorgeologicinstabilitytotheCRRFparcel,whichiswithintheWRP-4site.Similarly,theCRRFwouldbeconstructedinaccordancewithgeotechnicaldesignrecommendationsandapplicableseismicdesignstandardssuchthatitwouldnotresultinsoilorgeologicinstabilitytotheFillmoreStreetIrrigationDitchproject.Therefore,theCRRFportionoftheprojectwouldnotcontributetopotentialcumulativegeologyandsoilsimpacts.4.7.7 REFERENCESCaliforniaGeologicalSurvey.2007.Fault-RuptureHazardZonesinCalifornia:Alquist-PrioloEarthquake

FaultZoningActwithIndextoEarthquakeFaultZonesMaps.SpecialPublication42,InterimRevision2007.

ConverseConsultants.2016a.GeotechnicalInvestigationReportforChromium-6TreatmentFacilities:

WellSites.February2016.ConverseConsultants.2016b.GeotechnicalInvestigationReportforCentralResinRegenerationFacility

andOn-SiteEvaporationPonds.February2016.ConverseConsultants.2016c.GeotechnicalInvestigationReportforChromium-6WaterTreatment

Facilities:PipelineswithDesertHotSprings/SkyValley,LakeCahuilla(LaQuinta).February2016.

CVWD.February2015.OasisAreaIrrigationSystemExpansionProjectFinalEIR.PreparedbyDahl

Consultants.CVWD.July2013.DevelopmentDesignManual.

Section4.7GeologyandSoils

Coachella Valley Water District 4.7-12 Draft EIR Chromium-6 Water Treatment Facilities Project April 2016

CVWD.July2011.CoachellaValley2010WaterManagementPlanUpdateDraftSubsequentProgramEIR.PreparedbyMWH.

EarthConsultantsInternational.2000.NaturalHazardMapping,Analysis,andMitigation:ATechnical

BackgroundReportinSupportoftheSafetyElementoftheNewRiversideCounty2000GeneralPlan.August.

RiversideCounty.February2015.DraftEnvironmentalImpactReportNo.521forGeneralPlan

AmendmentNo.960.RiversideCounty.2009.OnsiteWastewaterTreatmentSystemsTechnicalGuidanceManual.VersionA.

Chromium-6 Water Treatment Facilities ProjectDraft EIR

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Figure 4.12.2

EARTHQUAKEPROBABILITY

Faults Highways

Waterbodies

Faults

Data Source: California Geological Survey (2003)

17%Anza Segment

Probability (%) of an earthquake occuringon a fault segment in the next 30 years

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December 16, 2013 Disclaimer: Maps and data are to be used for reference purposes only. Map features areapproximate, and are not necessarily accurate to surveying or engineering standards. TheCounty of Riverside makes no warranty or guarantee as to the content (the source is often thirdparty), accuracy, timeliness, or completeness of any of the data provided, and assumes nolegal responsibility for the information contained on this map. Any use of this product withrespect to accuracy and precision shall be the sole responsibility of the user.

Faults Highways

Waterbodies

Faults

Source: Riverside County General Plan EIR 2015

17%Anza Segment

Probability (%) of an earthquake occuringon a fault segment in the next 30 years

Regional Fault Zone Map

Chromium-6 Water Treatment Facilities Project Area

San Andreas Fault Zone

Dillon Road

Chromium-6 Water Treatment Facilities ProjectDraft EIR

Figure 4.7-2ID8 WBA Treated Water Pipeline Fault Crossing

Source: Converse Consultants 2015 ©