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HomeMy WebLinkAboutSWARR-GEOTECH REPORT updated 8-10-17GolderAssociatesMay12,2017ProjectNo.1777638DavidJenness,PMPSeniorProjectManagerPugetSoundEnergy10885N.E.4thStreetBellevue,WA98004RE:CRITICALAREASSTUDYD.W.SWARRPROPANE-AIRPLANT(KINGCO.PARCELNO.202305-9071)2100BENSONDRIVESOUTHRENTON,WASHINGTON98055DearMr.Jenness:ThisletterpresentstheresultsofGolderAssociatesInc.’s(Golder’s)criticalareasstudyforPugetSoundEnergy’s(PSE’s)D.W.Swarrpropane-airplant(KingCo.ParcelNo.202305-9071)locatedat2100BensonDriveSouth,Renton,Washington,98055.ThisstudywasperformedinaccordancewiththescopeofworkpresentedinourproposaldatedMarch29,2017andtheAgreementforProfessionalServicesNo.4600005182,AmendmentNo.12,datedApril19,2017.TheSwarrsiteislocatedinaSensitiveAreaasdefinedandmappedbytheCityofRenton(COR)MunicipalCodeduetothefollowinggeologichazarddesignations:aSteepSlopes—Thesiteisdesignatedashavingsteepslopesgreaterthan40%•ErosionHazard—ThesiteissituatedinanareadesignatedashavingahigherosionhazardseverityaLandslideHazard—ThesiteissituatedinanareadesignatedashavingahighlandslidehazardseverityaCoalMineHazard—ThesiteissituatedinanareadesignatedashavingamoderatetohighcoalminehazardPSEisplanningroutinesitemaintenanceandminorfacilityworkattheSwarrfacility.TheCityofRentonnotedthemappedgeologiccriticalareasandrequestedPSEprepareacriticalareasreporttosupporttheplannedwork.BasedontheresultsofourreviewofPSE’splannedworkandtheCORmunicipalcodeweconcludethattheplannedactivitiesareinareasthatdonotmeetthedesignationcriteriaforthemappedcriticalareasorthehazardislow.Therefore,werecommendthatCORgrantanexemptionfortheplannedactivitiescurrentlylocatedinmappedcriticalareas.1.0PROJECTBACKGROUNDTheSwarrfacilityisa17acrepropane-airinjectionplantconstructedin1965andretrofittedin1996locatedinasmallravineinRenton,Washington.TheplantisborderedbySouthPugetDrivetotheeast,BensonDriveSouthtothewest,andresidentialpropertytothesouth(Figure1-1).Thefacilityhas39undergroundpropanestoragetanks,processequipmentthatproducesamixtureofpropaneandair,andaone-storybuildingthathousesprocessequipmentandcontroloperations.1777638-I-swarr-cñticalarea-revl-2017-05-12.docxGolderAssociatesInc.18300NEUnionHillRoad,Suite200Redmond,WA98052USATel:(425)883-0777Fax:(425)882-5498www.golder.comGolderAssociates:OperationsinAfrica,Asia,Australasia,Europe,NorthAmericaandSouthAmericaGolder,GolderAssociatesandtheGAglobedesignaretrademarksofGolderAssociatesCorporation DavidJennessPugetSoundEnergy2May12,20171777638Theundergroundtanklayoutincludestwogroupsoftanks,thewesttankgroupincludes19tanksandtheeasttankgroupincludes20tanks.Itisestimatedthatthetopsofthetanksareapproximately2to3feetbelowtheexistinggroundsurface(bgs).Constructionoftheplantsiteincludedtheplacementofimportedfillmaterialtobringthesitetograde;however,fillthicknessesareunknownatthistime.BasedondiscussionswithPSE,itisestimatedthatthelowerportionsofthetanksareburiedinnativematerialwiththeupperportionsburiedunderimportedfill.PSEisanticipatingcompletingthefollowingsiteworktoperformroutinemaintenanceandrepairoftheplantfacilities:BEvaluationofTankNos.7,8,and9and15through19inthewestportionofthesiteandTanks27,28,38and39intheeast.Theevaluationwillrequireexcavationstoamaximumdepthof7feetbgstoproperlyinspectthetanks.Excavationisplannedtobeaccomplishedusingavactortruck,andwilloccurneartheendofthetanksandbetweenthetanks(refertoAttachment1).Excavatedareaswillbebackfilledwithnativematerialifsuitable,orimportedgranularmaterial,followingcompletionoftheevaluation.•TofacilitateevaluationofTanks15through19,15treeslocatedadjacenttothesetanksareproposedtoberemovedastheymayposeasafetyhazardduringtheexcavationrequiredfortankevaluation.PSEisalsoconcernedthatrootsfromthenearbytreeshavepossiblygrownonoraroundthetanksandmaycausedisruptiontothetankcoatingprotectionsystem.Thetreeswillbecutandthestumpsleftinplacepriortoexcavationtoexaminethetanks.Followingcompletionoftheevaluation,thestumpsmayberemovedifdoingsowillnotimpacttheintegrityofthetanks.NotreeremovalisanticipatedforinspectionofTankNos.7,8,9,27,28,38,and39.BThetankinvestigationworkistheinitialphaseofanoverallupgradeoftheSwarrStation.Additionalworkidentifiedtodatewillbelimitedtotheimprovedportionofthesiteandwillincludeminorgradingandreplacingequipmentsuchasgeneratorsandthevaporizer.Noadditionalimpervioussurfacesareanticipatedaspartoftheupgrade.ThiscriticalareasstudywasperformedtomeetCORrequirementsastreeremovalandexcavationisnotallowedincriticalareaswithoutareview.Thisstudyhasbeencompletedtoreviewtheplannedrepairandmaintenanceasitrelatestothecriticalareasandwillbeutilizedtoassessthebestpathforwardforpermittingthesitework,whetherthatpathwillbefilingforacriticalareaexemptionordefinepotentialmitigationtoallowtheworktooccur.oiier-AssociatesFigure1-1.ApproximateSwarrFacilityPropertyBoundary.ImagecourtesyofGoogleEarth(2013).1777638-I-swarr-criticalarea-revl-2017-05-12doc DavidJennessMay12,2017PugetSoundEnergy317776382.0SITERECONNAISSANCEAsitereconnaissancewasperformedonApril18,2017byGolder’sgeologist,JohnHennessy.Mostoftheproposedtankexcavationareasexhibitedlittletonoslopereliefwithin50feetoftheplannedexcavationlocations.However,theslopestothewestandnorthofthewesterntankpadexhibitedthegreatestverticalriseneattheproposedexcavationlocationsforTanks15through19.ThesetanksarelocatedeastofadrainagethatrunsalongthetoeoftheslopeontheeastsideofBensonDriveSouth.Thisslopeisabout20to25feethighandiswithin50feetoftheproposedexcavations.AstaffgaugeandclinometerwereusedtodetermineslopeheightsimmediatelywestofTanks14and17andnorthandnorthwestofTank19(Attachment1).ABruntoncompasswasusedtomeasuretheapproximateangleofslopeateachlocation.Table2-1liststheslopeparametersdeterminedforeachlocation.Table2-1:DimensionsforSlopesAdjacenttothePlannedWorkAreaApproximateApproximateApproximateApproximateApproximateLocationSlopeRiseHorizontalRunSlopeAngleSlopePercentofMeasurement(ft)1(ft)3(Degrees)2(%)WestofTank147.112.33058WestofTank178.418.02547NorthwestofTank199.422.22542NorthofTank19(westend)10.625.12542NorthofTank19(eastend)11.928.22542Notes:1)Sloperise(verticalheight)measuredfrombasetocrestofslope.2)SlopeanglemeasuredfromhorizontalusingaBruntoncompass.3)Sloperun(horizontaldistance)frombasetocrestofslopecalculatedfromslopeheightandslopeangle.4)Slopepercentcalculatedfromsloperiseandrunfrombasetocrestofslope.TreeshavegrownwithinthesitedevelopmentareaattheendsoftheTanks15through19andaresituatedadjacenttotheplannedexcavationareas.Twopotholesweredugtoanapproximatedepthof0.5feetusingashoveltoobservetheshallowsubsurfacematerials.OnepotholedugmidwayonthewesternslopebetweenTanks16and17yieldedathincoverofforestduff(sandyloamofdecayedplantmatter)overlyingolivegray,finetomediumgrainedsandwithsomesilt(SP-SM).Thesecondpotholewasdugmidwayonthenorthwest-facingslopetothenorthwestofTank19andyieldedathincoverofforestduffoverlyingbrown,silty,finetomediumgrainedsand(SM).Basedonourunderstandingofsiteconstruction,thesesoilsarelikelyfillmaterial.3.0CRITICALAREASREVIEW3.1SteepSlopesTheCORMunicipalCode(RMC)definessteepslopesincriticalareasunderSection4-3-050-B.1.basslopeswithaminimumverticalriseof15feet.AslistedinTable2-1,theslopeheightsintheimmediatevicinityoftheproposedexcavationswerefoundtobelessthan15feet;therefore,nobufferorsetbackisrequiredfortheseslopesaspertheCORcriticalareasrequirement.3.2ErosionHazardsThesiteisdesignatedbytheCORashavingHigherosionhazardseverity.TheCORMunicipalCodedefinesHigherosionhazardunderSection4-3-050-G.5.c:GolderAssociatesI777638-I-swarr-cñticalarea-revl-2017-05-12dacx DavidJennessMay12,2017PugetSoundEnergy41777638HighErosionHazard—AreaswithsoilscharacterizedbytheNaturalResourceConservationService(NRCS;formerlyU.S.SoilConservationService)ashavingsevereorverysevereerosionpotential,andaslopemotethanfifteenpercent(15%)Thesoilsobservedintheupper0.5footappearedtobeimportedfillandarenotincludedintheNRCScharacterization.Erosionpotentialofafillmaterialisbasedonthesoiltypeandotherfactors.Aspreviouslystated,thefillwasusedtobringthesitetogradeduringconstruction;however,fillthicknesseswerenotdeterminedduringthefieldreconnaissance.Theobservedsoilswereloosenearthesurfacebuttherewasverylittleevidenceofsurfaceerosionobserved.Ashallowerosionchannelabout4inchesdeepbyabout8incheswidewasobservedonthenorthernslopeofthewesttankpad.Nootherevidenceoferosionwasobservedinthevicinityoftheproposedtankexcavationsandnosignificanterosionhazardscouldbeidentifiedwithregardtotheplannedworkactivity.3.3LandslideHazardsThesiteisdesignatedbytheCORashavingHighlandslidehazardseverity.TheCORMunicipalCodedefinesHighlandslidehazardunderSection4-3-050-G.5.b:•HighLandslideHazard—Areaswithslopesgreaterthanfortypercent(40%),andareaswithslopesbetweenfifteenpercent(15%)andfortypercent(40%)andunderlainbysoilsconsistinglargelyofsiltandclay.Thesteepslopesadjacenttotheplannedworkareaaregreaterthan40%andarenotunderlainbysoilsconsistinglargelyofsiltandclay.Inaddition,noevidenceoflandslidemorphologywasobservedinthevicinityoftheproposedexcavations.Furthermore,noseeps,orevidencethereof,wereobservedalonganyoftheslopesinthevicinityoftheproposedexcavations.Thepotentialforlandslidestooccurasaresultoftheplannedworkactivityisverylowbasedontheproximitytoapplicableslopesandnon-cohesivesoilsobservedonsite.3.4CoalMineHazardsThesiteisdesignatedbytheCORashavingMediumtoHighcoalminehazardseverity.TheCORMunicipalCodedefinesHighlandslidehazardunderSection4-3-050-G.5.b:•MediumCoalMineHazards—Areaswheremineworkingsaredeeperthantwohundredfeet(200’)forsteeplydippingseams,ordeeperthanfifteen(15)timesthethicknessoftheseamorworkingsforgentlydippingseams.Theseareasmaybeaffectedbysubsidence.•HighCoalMineHazard—Areaswithabandonedandimproperlysealedmineopeningsandareasunderlainbymineworkingsshallowerthantwohundredfeet(200’)indepthforsteeplydippingseams,orshallowerthanfifteen(15)timesthethicknessoftheseamorworkingsforgentlydippingseams.Theseareasmaybeaffectedbycollapseorothersubsidence.Golderpreparedaminehazardevaluationoftheprojectsite(MineHazardEvaluationAddendumtothePSESwarrSafety-BasedQualitativeRiskAssessmentReport,Renton,Washington,preparedforPSE,datedMarch18,2015).Basedontheresultsofthisevaluation,mine-relatedsubsidenceandcollapsecanbequalitativelycharacterizedasalowrisk.Theplannedworkactivityinvolvesroutinemaintenanceandrepairofexistingfacilitiesanditisouropinionthattheplannedworkwillnotengage,affect,oralterdesignatedcoalminehazardspresentatthesite.4.0CONCLUSIONOurreviewofthecriticalareasdesignationindicatesthatalthoughtheplannedworkareasaremappedwithincriticalareas,theplannedworkisnotlocatedinareasthatmeetcriticalareadesignationrequirementsorthehazardposedbythecriticalareadesignationislow,asisthecasefortheCoalMineGo14er1777638-Iswarrcntjcalarearevi201705-12docxAsSociates DavidJennessMay12,2017PugetSoundEnergy51777638Hazard.Therefore,werecommendthatPSErequestaLetterofExemptionfromtheAdministratorfortheplannedworkactivityrequiredformaintenanceandrepairofexistingfacilities.WehopethislettersatisfiestheCORrequirementstopermittheproposedworkactivity.Ifyouhaveanyquestionsorcomments,pleasecontactusat(425)883-0777.GOLDERASSOCIATESINC..ogoeongGogsl943c’prnsonMargaretPryorJamesG.Johnson,LG,LEGSeniorProjectGeotechnicalEngineerPrincipalAttachments:AttachmentI-PSEPartialSitePlan,CoatingInvestigationMP/JGJ/tpGolderI777638-I-swarr-cricaIarea-revI-2Ol7-05-12docxASSociates ATTACHMENTIPSEPARTIALSITEPLAN,COATINGINVESTIGATION c}rpROP1STORAGE)RONONMARANONONONAlSWAIN015101$.At(ON)ONA00000MM.NAILSONRNP00WONAMINOIWO10000001010OMIT000010001010ON0000001110RION.ANOINtONAMINO0010ONMAIOUMAINURWAMONIMNMIWONAN001AMIOU!A001MIONMIONOONMAlIONWON10110010POWOAMIIRWOMWIAP00001001000010111.MtMARSMt0001010IONONMONJANAPANMAIN.©srrnogySYSrEMS,(NC.WINPUGET‘YSOUNDSAGPsoNRyENERGYftTWINS10ACINSPECTEDIAVOiDNOTESIl—lI-IlIPRELIMINARYN-Il-ANA.OIL!!rnhitZat”‘0501111.SIltPLAN.COATINGNISESTIORTANILL10—17—10WESTTANKGROUP(BURIEOPROPANESTORAGE)(13503—10—17113—C—2LNONE