EXH2012029274A

SUBJECT: Reviewof "Low FlowAnalysis, Flow Impact OffsetFacilityProposal, Port of Seattle" ParametrixInc., July 2001 This memo is to documentmy reviewof the report, "LowFlowAnalysis,Flow Impact Offset Facility Proposal" preparedfor the Port of Seattleby ParametrixInc., (July2001). This most recent report presentsconsiderableimprovementsin analysisand mitigationfor predictedimpactsof the proposed third runwayon latesummerstreamflows. I alsoread reviewcommentsonthe Port's Low Flow Analysisby KingCountyDepartmentof NaturalResourcessentto Ann by PareBissormette with a cover letter datedAugust3, 2001 (DNR,August3, 2001). An earlierlow flowanalysisprepared for the Port, "Sea-TacAirport Master Plan Update Low StreamflowAnalysis" (EarthTectt December2000), usedthe term"low streamflow"to refer to total flow in localstreamsduringAugustand September,since thosemonthswere considered the most criticalfor minimumstreamflows. ARerre-evaluating47 years ofstreamflow records for Mi'ler, Walker andDes Moinescreeks,this more recentanalysis usesa 3-monthperiod for proposed low-flow augmentation.This provides a marginof safety for futureclimaticaberrationsand, as pointed out by King CountyDNR,constitutessubstantialstreamflowmitigationfor the third runway project. In a special studycommissionedby the 1998 legislature,Pacific GroundwaterGroup de;eloped a "slice mc.del"to quantifythe hydrogeologicbehaviorof the proposedrunwayfill over a characteristic cross-sectionin "Sea-TacRunwayFill HydrologicStudiesReport" (PGG,June2000). The slice model predictedthat infiltrationof precipitationintoperviousareas&the runway fill duringwinter monthswould result in summerdrainagefromthe embankment. Sul';equentlow f_owanalyses, (Earth Tech,December2000), integratedthe results of the PGG slice modeiover the 5,400-footembankment distancealong MillerCreek. Becausethe cross-sectionoft.he June 2000 'slice model"was locatedat an uncharacteristicallythick sectionof the :_11at the proposedMiller Creekretention wall, the groundwaterflowcharacterizedby integratingthe original'slice' along the length of the embankznent adjacentto Miller Creek was thoughtto be unrepresentative.Accordingly,the subject re-ev_luat!_mcf embankmentdrainageandother factorseffectingthe drainage(Parametrix,July 2001) takes several representativeembankment'slices' intoaccount andprovidesmorereasonablefill drainage_stimates for the HSPFstreamflowmc-lels. Exhibit-2012 ECYO0017354 AR 029274.01 Non-Hydrologic Impacts Estimates of non-hydrologic impacts such as influence of importedwater district water,exercise of water rights andon-site…

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Call to order – Roll Call – Quorum Established – Land Acknowledgement We would like to acknowledge that our Agency operates in four present-day counties, which are the traditional lands of the Coast Salish people, past and present. This acknowledgement does not take the place of authentic relationships with indigenous communities in our jurisdiction and [...]