EXH0108017883

TO: '/Ann Kenny, Ecology NWROShorelines and EnvironmentalAssessment Kevin Fitzpatrick,Ecology NWRO WaterQuality Section Manager Ray Hellwig, Ecology NorthwestRegional Director V" SUBJECT: Review of"Low Flow Analysis, Flow Impact Offset Facility Proposal, Port of Seattle" Parametrix Inc.. July 2001 This memois to document my review of the repork "Low Flow Analysis. Flow Impact Offset Facility Proposal" prepare/for the Portof Seattleby ParamctrixInc, (July 2001). This most recent report ' presents considerableimprovements in analysisandmitigationfor predicted impactsof the proposed third runwayon late summcrstreamflows. Ialso readreview commentson the Port's Low Flow Analysis by King County Dcparunentof NaturalResources sent to Ann by Pam Bissonnette witha cover letter datedAugust 3, 2001 (DNI_ August3, 2001). An earlierlow flow analysis preparedfor the Port, "Sea-Tat Airport Master Plan Update Low Streamflow Analysis" ('EarthTech. December 2000), used the term"low streamflow" to referto total flowinlocalstreamsduringAugustandSeptember,sincethosemonthswereconsideredthemost criticalforminimumsUeamflows.Aiderre-evaluating47yearsofsU'eamflowrecordsforMiller, WalkerandDesMoinescreeks,thismorerecentanalysisusesa3-monthperiodforproposedlow-flow augmentation.Thisprovidesamarginofsafetyforfutureclimaticaberrationsand,aspoir_tedoutby KingCountyDNR, constitutessubstantialstrcamflowmitigationforthethirdrunwayproject Inaspecialstudycommissionedbythe1998legislature,PacificGroundwa_'rGroupdevelopeda "slicemodel"toquantifythehydrogaologicbehavioroftheproposedrunwayfillovera characteristic cross-section in "Sea-Tac Rtmway Fill Hydrologic Studies Report" (PGG, June 2000). The slice modelpredicted that infiltrationof precipitationinto pervious areasof the runwayfill duringwinter monthswould result in summerdrainagefrom the embankment. Subsequentlow flow analyses, (Earth Tech. December 2000), integratedthe resultsof the PGG slice modelover the 5,400-foot embankment distancealong Miller Creei_ Because the cross-section of the June 2000 'slice model' was locatedat an uncharacteristicallythick section of the fill atthe proposed MillerCreek retentionwail, the groundwaterflow characterizedby integratingthe original 'slice' alongthe length oftha embankment adjacentto Miller Creekwas thought to be um'eprc'_ntative.Accordingly, the subject re-evaluationof embankmentdrainageandother factorseffecting the drainage 0Parametrix,July 2001) takes several representativeembankment'slices' into accountand provides more reasonablefill drainageestimates .. for the HSPF strcamflowmodels. l DOE$,|3;0i 0193…

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PSCAA Advisory Council Meeting Agenda
Add to CalendarMWednesday Mar 11, 9:00am - 11:35am
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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 [...]