Post on 01-Mar-2022
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
[0 105
Miles
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 ©