Section4.7GeologyandSoils
4.7 GEOLOGYANDSOILS
4.7.1 INTRODUCTION
Thissectiondescribesgeology,soils,andseismicityconditionsinthevicinityoftheprojectsitesand
assessesthepotentialfortheprojecttobeaffectedbyortoincreaserisksassociatedwithidentified
geologicandseismichazards.Thissectionisbasedongeotechnicalreportspreparedfortheproject
(ConverseConsultants2016a,2016b,2016c),andinformationgatheredfromothersourcessuchasthe
U.S.GeologicSurvey,CaliforniaGeologicSurvey,RiversideCountyhazardsmapping,andotherCEQA
documentspreparedforrelevantprojectsintheCoachellaValley.
4.7.2 ENVIRONMENTALSETTING
4.7.2.1 RegionalGeologicSetting
TheprojectstudyareaforgeologyandsoilsextendsthelengthoftheCoachellaValley,fromDesertHot
SpringsinthenorthtotheSaltonSeainthesouth.Italsoincludesthenearbyfaultzonesthathavethe
potentialtogenerateseismiceventsthatcouldaffectprojectfacilities.
TheCoachellaValleyislocatedwithinthenorthernportionoftheSaltonTrough,whichiswithinthe
northernportionoftheColoradoDesertGeomorphicProvinceofSouthernCalifornia.TheSalton
Troughisageologicstructuraldepressionresultingfromlarge-scaleregionalfaultingandrepresentsthe
northwardextensionoftheGulfofCalifornia(CVWD,2015).TheColoradoDesertGeomorphicProvince
isboundedonthenorthbytheTransverseRanges(LittleSanBernardinoandOrocopiaMountains),on
thewestbythePeninsularRanges(SantaRosaandSanJacintoMountains),andontheeastbythe
MojaveDesert.TheValleyfloorrangesinelevationfrom1,600feetabovemeansealevel(MSL)inthe
northwesttoabout230feetbelowMSLattheSaltonSea.Theprovinceisaseismicallyactiveregion
characterizedbyalluviatedbasins,elevatederosionsurfaces,andnorthwest-trendingmountainranges
boundedbynorthwest-trendingstrike-slipfaults.Themostprominentofthenearbyfaultzonesinclude
theSanAndreasandSanJacintofaultzones,bothofwhichhavebeenknowntobeactiveduring
Quaternarytime(themostrecent2.6millionyearsofearth’shistory).
Severalthousandfeetofsediments,includingalluvialdepositsfromtheWhitewaterRiverandaeolian
depositsfromthestrongprevailingwindstypicaloftheregion,underlietheCoachellaValley.Basedon
geologicliteraturereview,thegeologicunitsanticipatedwithintheprojectstudyareaincludealluvial
sandandgravel,loosefinesanddepositedbywind,clayofplayalakes,andquartzdioriteto
granodiorite.
4.7.2.2 RegionalFaultingandSeismicHazards
Faults
ThemajorsourcesofseismicactivityincentralandwesternRiversideCountyaretheSanAndreas,San
Jacinto,andElsinorefaultzones.Figure4-7.1showsthelocationoftheprojectareainrelationtothese
faults,includingtheearthquakeprobabilityforsegmentsofthesefaults.Alloftheprojectfacilitysites
arelocatedwithinadistanceofapproximately1to5mileswestoftheSanAndreasFaultzone,andthe
proposedpipelinetoconveytreatedwaterfromtheID8WBAWaterTreatmentFacilityinDillonRoad
Coachella Valley Water District
Chromium-6 Water Treatment Facilities Project
4.7-1
Draft EIR
April 2016
Section4.7GeologyandSoils
crossesatraceofthisfaultzone(seeFigure4.7-2).TheSanJacintofaultzoneliesapproximately20-25
mileswestoftheprojectarea,andtheElsinorefaultzoneisapproximately40-45mileswestofthe
projectarea.
TheSanAndreasFaultsystemisthemostactivefaultsysteminCalifornia.Initsentirety,itruns
approximately800milesthroughthestate,primarilyalongthecoastlineinthenorthernstretchand
turninginlandforthesouthernstretch.ThefaultformsthetectonicboundarybetweenthePacificand
NorthAmericanplates,anditisalongtheseplatesthatmostseismicactivityoccurs.Inthevicinityof
RiversideCounty,theSanAndreasFaultzoneiscomprisedofthreesegments:1)theSanBernardino
Mountainssegment,2)theCoachellaValleysegment,and3)theMojaveDesertsegment(Earth
ConsultantsInternational,2000).RiversideCountyisbisectedbytheSanBernardinosegmentbetween
theCajonandSanGorgonioPasses.TheCoachellaValleysegmentrunsalongthenortheasternmargin
oftheValley,andextendsfromSanGorgonioPasstotheSaltonSea.Althoughthissegmenthasnot
producedlarge,surface-rupturingearthquakesinhistorictimes,itdoeshaveanestimated22%
probabilityofrupturingbeforetheyear2024,andisestimatedasbeingcapableofproducinga
magnitude7.1earthquake(ontheRichterMagnitudeScale).
TheSanJacintofaultzoneconsistsofcloselyspacedfaultsthatformthewesternmarginoftheSan
JacintoMountains.ThisfaultzoneextendsfromitsjunctionwiththeSanAndreasFaultzoneinSan
Bernardino,southeasterlytowardtheBrawleyarea,whereitcontinuessouthoftheMexicoborderas
theImperialtransformfault.TheSanJacintofaultzonehasahighlevelofhistoricalseismicactivity,
withatleasttendamagingearthquakeshavingoccurredbetween1890and1986.Thesegmentsofthe
SanJacintofaultthatareofmostconcerntocentralRiversideCountyaretheSanBernardino,San
JacintoValley,andAnzasegments.Maximumcredibleearthquakesofmagnitudes6.7,6.9,and7.2are
expectedonthesesegments,respectively.
TheElsinoreFaultzoneparallelstheSanJacintoandispartofthesameright-lateralplatestrainsystem
astheSanAndreasandSanJacintofaults.TherelevantsegmentsoftheElsinoreFaultzoneinwestern
RiversideCountyaretheWhittier,GlenIvy,Temecula,andJuliansegments.Maximumcredible
earthquakesofmagnitude6.7to6.8havebeenassignedforthesesegments.
SeismicHazards
Followingisadescriptionoftheseismichazardsthatcouldaffectprojectfacilitieswithinthestudyarea.
FaultRupture
Surfaceruptureoccurswhenmovementonafaultdeepwithintheearthbreaksthroughtothesurface.
Theevaluationoffaultrupturehazardisgenerallybasedonthehistoricactivityandrecurrenceof
earthquakesalongexistingfaults.Notallearthquakesresultinsurfacerupture.Rupturemayoccur
suddenlyduringanearthquakeorslowlyintheformoffaultcreep.Suddendisplacementsaremore
damagingtostructuresbecausetheycansuddenlydisplacestructuresandareusuallyaccompaniedby
strongshaking.Faultcreepistheslowruptureoftheearth’scrust.Indevelopedareas,faultcreepcan
offsetanddeformcurbs,streets,buildings,andotherstructuresthatlieonthefaulttrace.The
proposedtreatedwaterpipelinealongDillonRoadcrossestheCoachellasegmentoftheSanAndreas
Faultzone,approximately1,000feeteastofLongCanyonRoadand,therefore,isconsideredtobe
susceptibletotheeffectsoffaultrupture.Noneoftheotherprojectsitesarelocatedwithinan
earthquakefaultzone,andpotentialforfaultruptureatthosesitesisconsideredlow.
Coachella Valley Water District
Chromium-6 Water Treatment Facilities Project
4.7-2
Draft EIR
April 2016
Section4.7GeologyandSoils
Groundshaking
Theintensityoftheseismicshaking,orstronggroundmotion,duringanearthquakeisdependentonthe
distancebetweentheprojectareaandtheepicenteroftheearthquake,themagnitudeofthe
earthquake,andthegeologicconditionsunderlyingandsurroundingtheprojectarea.Earthquakes
occurringonfaultsclosesttotheprojectareawouldmostlikelygeneratethelargestgroundmotions.
Theintensityofearthquake-inducedgroundmotionsandthepotentialforcesaffectingstructureswithin
theprojectstudyareacanbedescribedusingpeakgroundaccelerations,whicharerepresentedasa
fractionoftheaccelerationofgravity(g).1Theestimatedpeakgroundaccelerationsforthechromium-6
projectsitesvary,fromalowofapproximately0.56gtoahighof1.14g.Thehighertheacceleration
rate,thestrongerthegroundmotionwillbe.
Liquefaction
Liquefactionisaphenomenoninwhichsaturatedgranularsedimentstemporarilylosetheirshear
strengthduringperiodsofearthquake-inducedstronggroundshaking.Thesusceptibilityofasiteto
liquefactionisafunctionofthedepth,density,andwatercontentofthegranularsedimentsandthe
magnitudeoftheearthquakeslikelytoaffectthesite.Saturated,unconsolidatedsilts,sands,siltysands,
andgravelswithin50feetofthegroundsurfacearemostsusceptibletoliquefaction.Liquefactionrelatedphenomenaincludeverticalsettlementfromdensification,lateralspreading,groundoscillation,
flowfailures,lossofbearingstrength,subsidence,andbuoyancyeffects.
LateralSpreading
Lateralspreadingreferstolandslidesthatcommonlyformongentleslopesandthatcauserapidfluidlikeflowmovement,likewater.Duringlateralspreading,amassmovestowardanunconfinedarea,
suchasadescendingslopeorstream-cutbluff,andcanoccuronslopegradientsasgentleasone
degree.Lateralspreadingischaracterizedbynear-verticalcrackswithpredominantlyhorizontal
movementofthesoilmassoverliquefiedsoils.Alloftheprojectsitesarerelativelyflatanddonot
includesignificantslopes;therefore,theriskoflateralspreadingisconsideredtobelow.
Earthquake-inducedSlopeFailureandLandslides
Earthquakemotioncaninducesubstantialstressesinslopes,causingearthquake-inducedlandslidesor
groundcrackingwhentheslopefails.Earthquake-inducedlandslidescanoccurinareaswithsteep
slopesthataresusceptibletostronggroundmotionduringanearthquake.Exposedrockslopesundergo
rockfalls,rockslides,orrockavalanches,whilesoilslopesexperiencesoilslumps,rapiddebrisflows,and
deep-seatedslides.Slopestabilitycandependonanumberofcomplexvariables,includingthegeology,
soilstructure,andamountofgroundwater,aswellasexternalprocessessuchasclimate,topography,
slopegeometry,andhumanactivity.Landslidescanoccuronslopesof15%orless,buttheprobabilityis
greateronsteeperslopes.Alloftheprojectsitesarerelativelyflatandareconsideredtohavealow
potentialforseismically-inducedslopefailureandlandsliding.
TsunamiandSeiches
Tsunamisareopenseatidalwavesgeneratedbyearthquakes.Tsunamidamageistypicallyconfinedto
low-lyingcoastalareas.DuetothedistanceoftheCoachellaValleyfromtheocean,tsunamisarenota
threattotheprojectstudyarea.Aseicheisaperiodicoscillationor“sloshing”ofwaterinanenclosed
basin(e.g.,lakeorreservoir)causedbyanearthquake.Thenearestenclosedwaterbasin,theSalton
1
Accelerationofgravity(g)=980centimeterspersecondsquared.1.0gaccelerationisarateofincreaseinspeed
equivalenttoacartraveling328feetfromrestin4.5seconds.
Coachella Valley Water District
Chromium-6 Water Treatment Facilities Project
4.7-3
Draft EIR
April 2016
Section4.7GeologyandSoils
Sea,isapproximately10to12milessouthoftheprojectsites;basedonthisdistance,thethreatof
seichesisunlikely.
4.7.2.3 SoilConditions
Problematicsoils,suchasthosethatareexpansiveorcorrosive,candamagestructuresandburied
utilitiesandincreasemaintenancerequirements.Expansivesoilsarecharacterizedbytheirabilityto
undergosignificantvolumechange(i.e.,toshrinkandtoswell)duetovariationsinmoisturecontent.
Changesinsoilmoisturecanresultfromrainfall,landscapeirrigation,utilityleakage,roofdrainage,
and/orperchedgroundwater.Expansivesoilsaretypicallyveryfinegrainedandhaveahightoveryhigh
percentageofclay.Expansionandcontractionofexpansivesoilsinresponsetochangesinmoisture
contentcanleadtodifferentialandcyclicalmovementsthatcancausedamageand/ordistressto
structuresandequipment.Accordingtothegeotechnicalreportspreparedfortheproject,the
expansionpotentialfortheprojectsitesisconsideredtobeverylowtolow.
Thecorrosivityofsoilsiscommonlyrelatedtoseveralkeyparameters,includingsoilresistivity,the
presenceofchloridesandsulfates,oxygencontent,andpH.Typically,themostcorrosivesoilsarethose
withthelowestpHandhighestconcentrationofchloridesandsulfates.Wet/dryconditionscanresultin
aconcentrationofchloridesandsulfates,aswellasmovementinthesoil,bothofwhichtendtobreak
downtheprotectivecorrosionfilmsandcoatingsonthesurfacesofbuildingmaterials.High-sulfatesoils
arealsocorrosivetoconcreteandmaypreventcompletecuring,therebyreducingthestrengthofthe
concreteconsiderably.LowpHand/orlow-resistivitysoilscancorrodeburiedorpartiallyburiedmetal
structures.Dependingonthedegreeofcorrosivityofthesubsurfacesoils,buildingmaterialssuchas
concrete,reinforcingsteelinconcretestructures,andbare-metalstructuresexposedtothesesoilscan
deteriorate,eventuallyleadingtostructuralfailures.Accordingtothegeotechnicalreportspreparedfor
theproject,alloftheprojectsiteshavebeenidentifiedashavingsomesoilcorrosivityexposure,from
mildlycorrosivetoseverelycorrosive.
Table4.7-1providesasummaryofexistinggeologicandsoilsconditionsfortheprojectsites.
Informationinthistableisderivedfromthegeotechnicalreportspreparedfortheproject(Converse
Consultants2016a,2016b,2016c).
4.7.3 REGULATORYFRAMEWORK
4.7.3.1 Federal
Nofederalregulationsareassociatedwithgeology,soilsandseismicityfortheproposedproject.
4.7.3.2 State
Alquist-PrioloEarthquakeFaultZoningAct
TheAlquist-PrioloEarthquakeFaultZoningActwaspassedin1972tomitigatethehazardofsurface
faultingtostructuresforhumanoccupancy.Inaccordancewiththisact,theStateGeologistestablished
regulatoryzones,called“earthquakefaultzones,”aroundthesurfacetracesofactivefaultsand
publishedmapsshowingthesezones.Withinthesezones,buildingsforhumanoccupancycannotbe
constructedacrossthesurfacetraceofactivefaults.Becausemanyactivefaultsarecomplexand
consistofmorethanonebranch,eachearthquakefaultzoneextendsapproximately200to500feeton
eithersideofthemappedfaulttrace.
Coachella Valley Water District
Chromium-6 Water Treatment Facilities Project
4.7-4
Draft EIR
April 2016
Section4.7GeologyandSoils
TABLE4.7-1:SUMMARYOFGEOLOGICANDSOILSCONDITIONSATPROJECTSITES
GeologicUnit
Landslide
/Slope
Failure
Potential
Liquefaction
Susceptibility
Approximate
DistancetoSan
AndreasFaultZone
Loosefinesandoveralluvialsand/gravel
Alluvialsand/gravelofvalleyareas
Alluvialsand/gravelofvalleyareas
Alluvialsand/gravelofvalleyareas
Alluvialsand/gravelofvalleyareas
Loosefinesand-alluvialsand/gravelmargin
Loosefinesandoveralluvialsand/gravel
Loosefinesand-alluvialsand/gravelmargin
Loosefinesandoveralluvialsand/gravel
Loosefinesandoveralluvialsand/gravel
Loosefinesandoveralluvialsand/gravel
Loosefinesand-alluvialsand/gravelmargin
Loosefinesandoveralluvialsand/gravel
Loosefinesandoveralluvialsand/gravel
Loosefinesandoveralluvialsand/gravel
Loosefinesand-alluvialsand/gravelmargin
Alluvialsand/gravelofvalleyareas
Loosefinesand-alluvialsand/gravelmargin
Alluvialsand/gravelofvalleyareas
Alluvialsand/gravelofvalleyareas
Alluvialsand/gravelofvalleyareas
Alluvialsand/gravelofvalleyareas
Alluvialsand/gravelofvalleyareas
Siltysand,siltytosandyclay
Alluvialsand/gravelofvalleyareas
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
Low
High
High
High
High
High
High
High
4milesnortheast
2.5milesnortheast
1.5milesnortheast
1milenortheast
1milenortheast
3milesnortheast
3milesnortheast
3milesnortheast
4milesnortheast
4milesnortheast
4milesnortheast
3milesnortheast
3milesnortheast
3milesnortheast
3milesnortheast
2milesnortheast
1.5milesnortheast
4milesnortheast
3milesnortheast
3milesnortheast
3milesnortheast
5milesnortheast
5milesnortheast
5milesnortheast
5milesnortheast
WBA3408-1
Alluvialsand/gravelofvalleyareas
Low
Low
WBA3409-2
Alluvialsand/gravelofvalleyareas
Low
Low
WBA3410-1
Alluvialsand/gravelofvalleyareas
Low
Low
ID8Treatment
Plant
Alluvialsand/gravelofvalleyareas
Low
Moderate
ID8pipelines
Alluvialsand/gravelofvalleyareas
Low
Moderate
WBA6723-1
WBA6724-1
WBA6725-1
LaQuinta
TreatmentPlant
LaQuinta
pipelines
Alluvialsand/gravelofvalleyareas
Alluvialsand/gravelofvalleyareas
Alluvialsand/gravelofvalleyareas
Low
Low
Low
High
High
High
2milesnorthand1
milesouth
2milesnorthand1
milesouth
2milesnorthand1
milesouth
2milesnorthand1
milesouth
DillonRoadpipeline
crossesfault
7milesnortheast
7milesnortheast
7milesnortheast
Alluvialsand/gravelofvalleyareas
Low
High
7milesnortheast
Alluvialsandandclay
Low
High
7milesnortheast
CVWDSite
Name
SBAFACILITIES
SBA4510-1
SBA4610-1
SBA4720-1
SBA4721-1
SBA4722-1
SBA5632-2
SBA5657-2
SBA5664-1
SBA5676-2
SBA5677-1
SBA5678-1
SBA5679-1
SBA5711-2
SBA5717-1
SBA5718-1
SBA5719-1
SBA5720-1
SBA6701-1
SBA6726-1
SBA6728-1
SBA6734-1
SBA6805-1
SBA6808-1
CRRF
CRRFpipelines
WBAFACILITIES
Coachella Valley Water District
Chromium-6 Water Treatment Facilities Project
4.7-5
Draft EIR
April 2016
Section4.7GeologyandSoils
Title14oftheCaliforniaCodeofRegulations(CCR),Section3601(e),definesbuildingsintendedfor
humanoccupancyasthosethatwouldbeinhabitedformorethan2,000hoursperyear.Theonly
componentoftheprojectthatcrossesafaultzone(SanAndreasFault)istheproposedpipelinethatwill
carrytreatedwaterfromtheID8WBAWaterTreatmentFacilityinDillonRoadtotheexistingCVWD
reservoiratLangloisRoad.Thispipelinedoesnotmeetthecriterionofabuildingusedforhuman
occupancywithinthevicinityofanymappedfaulttrace;therefore,theprovisionsoftheactdonotapply
totheproject.NoneoftheotherprojectfacilitiesarelocatedwithinanAlquist-PrioloEarthquakeFault
Zone.
SeismicHazardsMappingAct
LiketheAlquist-PrioloAct,theSeismicHazardsMappingActof1990(PublicResourcesCodeSections
2690to2699.6)isintendedtoreducedamageresultingfromearthquakes.WhiletheAlquist-PrioloAct
addressessurfacefaultrupture,theSeismicHazardsMappingActaddressesotherearthquake-related
hazards,includingstronggroundshaking,liquefaction,andseismically-inducedlandslides.Itsprovisions
aresimilarinconcepttothoseoftheAlquist-PrioloAct;theStateischargedwithidentifyingand
mappingareasatriskofstronggroundshaking,liquefaction,landslides,andothercorollaryhazards.
CitiesandcountiesarerequiredtoregulatedevelopmentwithinmappedSeismicHazardZones.
UndertheSeismicHazardsMappingAct,permitreviewistheprimarymechanismforlocalregulationof
development.Specifically,citiesandcountiesareprohibitedfromissuingdevelopmentpermitsforsites
withinSeismicHazardZonesuntilappropriatesite-specificgeologicand/orgeotechnicalinvestigations
havebeenconductedandmeasurestoreducepotentialdamagehavebeenincorporatedintothe
developmentplans.Accordingtothepreliminarygeotechnicalreportspreparedfortheproject,the
projectsitesarenotwithinareasdesignatedbyRiversideCountyasSeismicHazardZones.
BuildingCodes
TheCaliforniaBuildingCode(CBC),whichiscodifiedinCCRTitle24,Part2,waspromulgatedto
safeguardthepublichealth,safety,andgeneralwelfarebyestablishingminimumstandardsrelatedto
structuralstrength,egressfacilities,andgeneralbuildingstability.ThepurposeoftheCBCistoregulate
andcontrolthedesign,construction,qualityofmaterials,use/occupancy,location,andmaintenanceof
allbuildingandstructureswithinitsjurisdiction.Title24isadministeredbytheCaliforniaBuilding
StandardsCommissionwhich,bylaw,isresponsibleforcoordinatingallbuildingstandards.The2013
CBCisbasedonthe2006InternationalBuildingCode(IBC)publishedbytheInternationalCode
Conference.Inaddition,theCBCcontainsnecessaryCaliforniaamendmentsthatarebasedonthe
AmericanSocietyofCivilEngineers(ASCE)MinimumDesignStandards7-05.ASCE7-05provides
requirementsforgeneralstructuraldesignandincludesmeansfordeterminingearthquakeloads,as
wellasotherloads(e.g.,flood,snow,wind)forinclusioninbuildingcodes.TheprovisionsoftheCBC
applytotheconstruction,alteration,movement,replacementanddemolitionofeverybuildingor
structureoranyappurtenancesconnectedorattachedtosuchbuildingsorstructuresthroughout
California.
Theearthquakedesignrequirementstakeintoaccounttheoccupancycategoryofthestructure,site
class,soilclassifications,andvariousseismiccoefficients,allofwhichareusedtodetermineaSeismic
DesignCategory(SDC)foraproject.TheSDCisaclassificationsystemthatcombinestheoccupancy
categorieswiththelevelofexpectedgroundmotionsatagivensite,andrangesfromSDCA(verysmall
seismicvulnerability)toSDCE/F(veryhighseismicvulnerabilityandnearamajorfault).Design
specificationsarethendeterminedaccordingtotheSDC.
Coachella Valley Water District
Chromium-6 Water Treatment Facilities Project
4.7-6
Draft EIR
April 2016
Section4.7GeologyandSoils
4.7.3.3 RegionalandLocal
CVWDDevelopmentDesignManual
CVWDhasadoptedtheDevelopmentDesignManual(DDM)toprovidecomprehensiveproceduraland
technicalrequirementsfortheplanning,designandconstructionofCVWDserviceinfrastructure
requiredfornewdevelopment(CVWD2013).TheDDMincludesrequirementsformeetingseismic
designstandards.
RiversideCountyDepartmentofEnvironmentalHealth
TheRiversideCountyDepartmentofEnvironmentalHealthmaintainsatechnicalguidancemanualfor
onsitewastewatertreatmentsystems(RiversideCounty2009).OnsitesanitarydisposalattheID8WBA
WaterTreatmentFacilitysitewouldeitherbeasepticsystem,holdingtank,orportabletoilet.
Installationofanyofthesesystemswouldneedtocomplywiththismanual.
4.7.4 IMPACTSANDMITIGATIONMEASURES
4.7.4.1 SignificanceCriteria
BasedonAppendixGoftheStateCEQAGuidelines,aprojectwouldresultinsignificantimpactsrelated
togeologyandsoilsifitwould:
a. Expose people or structures to potential substantial adverse effects, including the risk of
loss,injury,ordeathinvolving:
•
Rupture of a known earthquake fault, as delineated on the most recent Alquist-Priolo
Earthquake Fault Zoning Map issued by the State Geologist for the area or based on
othersubstantialevidenceofaknownfault.
•
Strongseismicgroundshaking.
•
Seismic-relatedgroundfailure,includingliquefaction.
•
Landslides
b. Resultinsubstantialsoilerosionorthelossoftopsoil.
c. Belocatedonageologicunitorsoilsthatisunstable,orthatwouldbecomeunstableasa
result 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 alternative
wastewaterdisposalsystemswheresewersarenotavailableofthedisposalofwastewater.
4.7.4.2 ApproachtoAnalysis
Thepotentialforimpactsrelatedtogeology,soilsandseismicityareevaluatedaccordingtothe
significancecriterialistedabove.Regionalandlocalgeologicmaps,aswellasproject-specific
preliminarygeotechnicalreports,werereviewedtoidentifygeologicconditionsandgeologichazardsin
Coachella Valley Water District
Chromium-6 Water Treatment Facilities Project
4.7-7
Draft EIR
April 2016
Section4.7GeologyandSoils
thestudyareathat,becauseoftheirproximity,couldbedirectlyorindirectlyaffectedbytheproposed
projectorcouldaffecttheproject.
AreasofNoProjectImpact
Thefollowingthreesignificancecriteriaarenotdiscussedfurtherinthissectionforthefollowing
reasons:
a. Exposepeopleorstructurestosubstantialadverseeffectsrelatedtotherisksofpropertyloss,injury
ordeathduetofaultrupture,seismicgroundshaking,orlandslides.
Thissignificancecriterionisintendedtoaddressfacilitysitinganddesignimpactsanddoesnotapply
totemporaryconstructionimpacts;thereforeitisnotdiscussedintheconstructionimpactsSection
4.7.4.3below.Withregardtolong-termoperationalimpacts,ofthefourhazardslistedinthis
criterion,thepotentialforlandslidestoaffectprojectfacilitiesdoesnotneedfurtherdiscussion
becausealltheprojectsitesarerelativelyflatandconsideredtohavealowpotentialforseismicallyinducedslopefailureandlandsliding.Thepotentialforfaultrupture,stronggroundshakingand
liquefactiondoapplytooperationsofsomeoftheprojectfacilities,andtheyarediscussedin
Section4.7.4.4below.
d.Belocatedonexpansivesoil,asdefinedinTable18-1-BoftheUniformBuildingCode,creating
substantialriskstolifeorproperty.
Asdescribedabove,thesoilexpansionpotentialforalloftheprojectsitesisconsideredtobevery
lowtolow;therefore,thiscriterionisnotdiscussedfurther.
e. Havesoilsincapableofadequatelysupportingtheuseofseptictanksoralternativewastewater
disposalsystemswheresewersarenotavailableforthedisposalofwastewater.
Asnotedabove,theproposedonsitesanitarydisposalmethodfortheID8WBAWaterTreatment
Facilityhasnotyetbeendetermined,butwouldeitherbeasepticsystem,holdingtank,orportable
toilet.InstallationofanyofthesesystemswouldneedtocomplywiththeRiversideCounty
DepartmentofEnvironmentalHealthtechnicalguidancemanualforonsitewastewatertreatment
systems.IfitisdeterminedthatthesoilsattheID8WBAWaterTreatmentFacilitysitearenot
capableofadequatelysupportingtheuseofaseptictankatthissite,oneoftheotherdisposal
systemswouldbeinstalled.CompliancewiththeRiversideCountyguidancemanualwouldensure
thatnoimpactsunderthiscriterionwouldoccur.
4.7.4.3 ConstructionImpactsandMitigationMeasures
ImpactGS-1:Constructionoftheprojectwouldnotresultinsubstantialsoilerosionorthe
lossoftopsoil.(LessthanSignificant)
AlloftheSBAandWBAwellsitesaredevelopedwithexistingCVWDwaterinfrastructureand
havebeenhighlyalteredfromtheiroriginal,naturalstate.Asaresult,thedepthandamountof
gradingandexcavationatthesesiteswouldresultinminimaldisturbancetonativesoils.In
addition,thewellsitesarenearareasofmoderatetointenseurbanuses,suchassurface
streets,residences,andrecreationalandcommercialfacilities.Consequently,nosubstantial
Coachella Valley Water District
Chromium-6 Water Treatment Facilities Project
4.7-8
Draft EIR
April 2016
Section4.7GeologyandSoils
lossoftopsoilduetoerosionorgradingwouldoccurduringconstructionoftheprojectatthese
sites.
TheCRRFandWBAWaterTreatmentFacilitysitesareundevelopedsites.Constructionatthese
siteswouldinvolvegrounddisturbanceincludingsitepreparation,grading,andtrenchingfor
structureandutilityinstallations.Potentialerosionthatmayresultfromgrading,excavation,
pipelinetrenching,andothersoildisturbanceduringconstructionwouldbecontrolledduring
constructionwithimplementationoferosioncontrolplansasrequiredbyCVWD.
Additionally,standardconstructionpracticestopreventandminimizeconstruction-related
erosionwouldbeincludedinconstructiondocumentsandStormWaterPollutionPrevention
Plans(SWPPP)thatarerequiredpursuanttofederalandstateNationalPollutantDischarge
EliminationSystemregulations(seeSection4.10,HydrologyandWaterQuality,forfurther
explanationofSWPPPrequirements).TheSWPPPwouldincludeBestManagementPractices
(BMPs)topreventerosion,suchasuseofsiltfencesorotherbarrierstopreventerosionand
sedimentationintowaterbodies,useofdesiltingbasins,limitationsonworkduringhigh-wind
events,andpost-constructionrevegetationanddrainagerequirements.Implementationofthe
SWPPPandBMPswouldensurethatthisimpactwouldbelessthansignificant.Nomitigation
measuresarerequired.
ImpactGS-2:Constructionofsomeprojectpipelinecomponentswouldbelocatedongeologic
unitsorsoilsthatareunstableorthatmaybecomeunstableduringprojectconstruction,and
potentiallyresultinsoilinstabilityorcollapse;howeverthisexposurewouldnotresultina
substantialrisktopeopleorstructures.(LessthanSignificant)
Thisimpactappliestoinstallationofundergroundpipelineslocatedinareaswithsoilstability
concerns.ConstructionoftherawandtreatedwaterpipelinesthatwouldservetheID8andLa
QuintaWBAWaterTreatmentFacilitiesmayencounterthepotentialforsoilinstabilityor
collapseduringpipelinetrenching.Toaddressthispotential,projectfacilitieswouldbe
designedinaccordancewithrecommendationsofsite-specificgeotechnicalinvestigations
preparedbyaCalifornialicensedgeotechnicalengineer(s).Design-levelgeotechnical
investigationswouldbepreparedforallprojectcomponentstoinformfinaldesignand
constructionthataddressseismichazards.Allrecommendationsofthegeotechnical
investigationswouldbeincorporatedintothefinaldesignandconstructionspecificationsfor
eachprojectcomponent,andwouldbeimplementedasspecifiedbytheconstruction
contractors.Althoughthereisthepotentialforsoilcollapseduringpipelinetrenching,
compliancewiththerequirementsofstateandCVWD’sprofessionalengineeringstandards
wouldensurethatthisimpactwouldbelessthansignificant.Nomitigationmeasuresare
required.
4.7.4.4 OperationImpactsandMitigationMeasures
ImpactGS-3:ThetreatedwaterpipelinetobeinstalledinDillonRoadinDesertHotSprings
wouldcrosstheCoachellaValleysegmentoftheSanAndreasFaultzone,potentiallyexposing
thisprojectfacilitytofaultruptureduringaseismiceventandsubsequentdisruptionofwater
serviceinthisarea;however,thisexposurewouldnotresultinsubstantialrisktopeopleor
structures.(LessthanSignificant)
Coachella Valley Water District
Chromium-6 Water Treatment Facilities Project
4.7-9
Draft EIR
April 2016
Section4.7GeologyandSoils
Theprojectwouldbelocatedinanareaofhighseismicity,andoneoftheprojectpipelines
wouldcrossanactivefaultzone.Potentialdamagecouldincludeabreaktoapipesegmentand
possiblyleakagetothesurroundingarea.Thelocationofthispipelinecrossingofthefaultisin
anareaofverylowdensityresidentialdevelopment,suchthatapipebreakinthislocation
wouldnottypicallybethecauseofsubstantialrisksoflossoflifeorproperty.Intheeventthat
alargeseismiceventdidcauseruptureatthesurface,theruptureareawouldbelocalizedand
anypipelinedamageorleaksimmediatelyrepaired.Inaddition,thepipelinewouldbedesigned
inaccordancewithsite-specificgeotechnicalrecommendationsforthislocation,thereby
reducingthepotentialforsubstantialdamageduringaseismicevent.Implementationofthese
recommendationswouldensurethatthisimpactwouldbelessthansignificant.Nomitigation
measuresarerequired.
ImpactGS-4:Theproposedprojectwouldbesubjecttostronggroundshakingandsome
projectsiteswouldhaveahighliquefactionsusceptibilityduringaseismicevent;however,
thisexposurewouldnotresultinasubstantialrisktopeopleorstructures.(Lessthan
Significant)
Alloftheprojectfacilitieswouldbelocatedwithinaseismicallyactiveregion.Anearthquakeon
localorregionalfaultscouldresultindamagetostructuresandpipelinesduetoseismicshaking
and/orliquefaction.Theintensitywouldbedependentonthemagnitudeoftheearthquakeand
distanceoffacilitiesfromtheearthquakeepicenter.Theprimaryeffectsofgroundshaking
wouldbepotentialdamagetoprojectstructures,includingfoundationsand/orbreaksinwater
pipelines.StructureswouldbedesignedinaccordancewithrequirementsoftheCalifornia
BuildingCoderegardingseismicdesigncriteria,whichwouldhelpminimizedamagesandwould
notresultinsubstantialadverseriskstopeopleorstructures.
Thefollowingprojectsiteshavebeenidentifiedbygeotechnicalreportsashavinghigh
susceptibilitytoliquefaction:SBAwells6726-1,6728-1,6734-1,6805-1,and6808-1;theCRRF
site;WBAwells6723-1,6724-1,and6725-1;andtheLaQuintaWBAWaterTreatmentFacility
anditsrawandtreatedwaterpipelinealignments.Thegeotechnicalreportsforthesefacilities
providespecificdesignrecommendationstoaddressthisliquefactionpotential.Implementation
oftheserecommendationswouldminimizethepotentialfordamagetothesefacilitiesinthe
eventofastrongseismicevent,andthisimpactwouldbelessthansignificant.Nomitigation
measuresarerequired.
ImpactGS-5:Someoftheprojectfacilitieswouldbelocatedonsiteswithcorrosivesoils;
however,thisexposurewouldnotresultinasubstantialrisktopeopleorstructures.(Less
thanSignificant)
Accordingtotheprojectgeotechnicalreports,alloftheprojectsiteshavebeenidentifiedas
havingsomelevelofpotentialexposuretosoilcorrosivity.Thesitesfallintocategoriesthatare
rankedasmildlycorrosivetoseverelycorrosive.Corrosivesoilscould,overtimedeterioratethe
newly-installedprojectfacilities.However,acombinationofprotectivecoatings,pipewrapping,
andpossiblycathodicprotectionwouldbeincludedinfacilities’designandconstructionto
minimizeexposuretothecorrosionprocess.Withincorporationofthesedesignfeatures,
corrosivesoilimpactstolifeandpropertywouldbelessthansignificant.Nomitigation
measuresarerequired.
Coachella Valley Water District
Chromium-6 Water Treatment Facilities Project
4.7-10
Draft EIR
April 2016
Section4.7GeologyandSoils
4.7.5 SIGNIFICANCEAFTERMITIGATION
Nomitigationmeasuresarerequired.
4.7.6 CUMULATIVEIMPACTS
Thegeographicscopeforcumulativeimpactsongeologyandsoilsconsistsofeachproposedprojectsite
andtheimmediatevicinityadjacenttoeachofthesesites(includingtheconstructionarea,facilities,and
thepipelines).Theareaaffectedvariesforeachsite.Geologicandseismicimpactsaregenerallysitespecific,becausetheydependuponthelocalgeologyandsoilconditions.Thisanalysiswasperformed
usingthegrowthprojectionapproachpursuanttoStateCEQAGuidelinesSection15130(b)(1)(B).No
cumulativeprojectshavebeenidentifiedfortheprojectsites,exceptfortheCRRFsite,whichwould
contributetoacumulativegeologyandsoilsimpact.
CVWDisplanningtoconstructtheFillmoreStreetIrrigationDitchprojecttoprotecttheWRP-4sitefrom
floodingandtoconveyoverlandflowsfromnearbyirrigatedlandstotheCoachellaValleyStormwater
Channel.Thisprojectincludesconstructionofafloodplainberm,earthendrainagechannel,and
irrigationditchontheWRP-4parcel.Constructionoftheprojectwouldoccurconcurrentwithorbefore
CRRFconstruction.CVWDwoulddesignandconstructionthisprojectinaccordancewithseismicdesign
standardssuchthatitwouldnotresultinsoilorgeologicinstabilitytotheCRRFparcel,whichiswithin
theWRP-4site.Similarly,theCRRFwouldbeconstructedinaccordancewithgeotechnicaldesign
recommendationsandapplicableseismicdesignstandardssuchthatitwouldnotresultinsoilor
geologicinstabilitytotheFillmoreStreetIrrigationDitchproject.Therefore,theCRRFportionofthe
projectwouldnotcontributetopotentialcumulativegeologyandsoilsimpacts.
4.7.7 REFERENCES
CaliforniaGeologicalSurvey.2007.Fault-RuptureHazardZonesinCalifornia:Alquist-PrioloEarthquake
FaultZoningActwithIndextoEarthquakeFaultZonesMaps.SpecialPublication42,Interim
Revision2007.
ConverseConsultants.2016a.GeotechnicalInvestigationReportforChromium-6TreatmentFacilities:
WellSites.February2016.
ConverseConsultants.2016b.GeotechnicalInvestigationReportforCentralResinRegenerationFacility
andOn-SiteEvaporationPonds.February2016.
ConverseConsultants.2016c.GeotechnicalInvestigationReportforChromium-6WaterTreatment
Facilities:PipelineswithDesertHotSprings/SkyValley,LakeCahuilla(LaQuinta).February
2016.
CVWD.February2015.OasisAreaIrrigationSystemExpansionProjectFinalEIR.PreparedbyDahl
Consultants.
CVWD.July2013.DevelopmentDesignManual.
Coachella Valley Water District
Chromium-6 Water Treatment Facilities Project
4.7-11
Draft EIR
April 2016
Section4.7GeologyandSoils
CVWD.July2011.CoachellaValley2010WaterManagementPlanUpdateDraftSubsequentProgram
EIR.PreparedbyMWH.
EarthConsultantsInternational.2000.NaturalHazardMapping,Analysis,andMitigation:ATechnical
BackgroundReportinSupportoftheSafetyElementoftheNewRiversideCounty2000General
Plan.August.
RiversideCounty.February2015.DraftEnvironmentalImpactReportNo.521forGeneralPlan
AmendmentNo.960.
RiversideCounty.2009.OnsiteWastewaterTreatmentSystemsTechnicalGuidanceManual.VersionA.
Coachella Valley Water District
Chromium-6 Water Treatment Facilities Project
4.7-12
Draft EIR
April 2016
LOS ANGELES
COUNTY
SAN
BERNARDINO
COUNTY
60
Ä
§
¨
¦15
§
¨
¦
215
62
Ä
Ä
60
91
Ä
79
Ä
§¨¦10
Ä
243
74
Ä
§
¨
¦15
Ä
111
74
Ä
§
¨
¦
Ä
ORANGE
COUNTY
215
74
79
Ä
74
Ä
Ä
371
§
¨
¦15
PACIFIC
OCEAN
SAN DIEGO
COUNTY
Source: Riverside County General Plan EIR 2015
Faults Faults
Highways
Waterbodies
Faults
SCALE 0
0
Highways
Waterbodies
December 16, 2013
5
79
Ä
Ä
Chromium-6 Water
Treatment Facilities
86S
Ä
Project Area
111
SALTON
SEA
86
Ä
IMPERIAL
COUNTY
Data Source: California Geological Survey (2003)
17%
Anza Segment
Faults
[
§¨¦10
86
Ä
5
10
Miles
I
Miles
10
17%
Segment occuring
Probability (%)Anza
of an earthquake
on a fault segment in the next 30 years
Figure 4.12.2
Probability (%) of an earthquake occuring
on a fault segment in the next 30 years
Disclaimer: Maps and data are to be used for reference purposes only. Map features are
approximate, and are not necessarily accurate to surveying or engineering standards. The
County of Riverside makes no warranty or guarantee as to the content (the source is often third
party), accuracy, timeliness, or completeness of any of the data provided, and assumes no
legal responsibility for the information contained on this map. Any use of this product with
respect to accuracy and precision shall be the sole responsibility of the user.
EARTHQUAKE
PROBABILITY
Figure 4.7-1
Regional Fault Zone Map
Chromium-6 Water Treatment Facilities Project
Draft EIR
Dillon Road
San Andreas Fault Zone
Source: Converse Consultants 2015 ©
Figure 4.7-2
ID8 WBA Treated Water Pipeline Fault Crossing
Chromium-6 Water Treatment Facilities Project
Draft EIR