EXH0411022130

O seattle,washington98188-3418 vancouver(208)241-6000 - phone edmonton EXHIBIT #_ (206)439-2420- fax www.nho_eb.com seattle _ATE_._ ____- BY: CHERYL j, HNvIME;; January30, 2002 Colonel Ralph H. Graves Ms. Muffy Walker Ms, GaffTerzi U.S. Army Corpsof Engineers SeattleDistrict P.O.Box 3755 Seattle,WA 98124-3755 Dear Colonel Graves,Ms. WalkerandMs. Terzi: Re: CorpsRef. No. 1996-4-02325;Portof SeattleLow StreamflowAnalysis e NorthwestHydraulicConsultants,Inc., (nhc) has beenretainedon behalf of theAirportCommunities Coalition (ACC) to providea technical review of stormwatgrfaciliti_ ands_amflow impactsfrom dovdopment activities at SeaTac airport. The purpose of this Iettoris to commenton theDecember 2001 "Low Streamflow AnalysisandSummerLowFlow ImpactOffset Fadlity Proposal"preparedby Parametrix,Inc.,for thePort of Soattle. The December 2001 Low Streamflow Analysis has numerous flaws, including,but not limited to, being largely unresponsiveto concernswe have raised previously. Forexample,while the reportnow acknowledges poor upper-gage low flow calibrationof the hydrologic models used for the analysis, there does not appear to have been any attemptto improve that calibrationor to address theresultant uncertaintyin the interpretationof model results. Low-flow impactsof IndustrialWastewaterSystem (IWS) improvements and borrow arm developments continue to be ignored. The report fails to provide thedigital data files (as were providedwith previous documents)which wouldgive reviewers the opportunityto independentlyinterpretthePort's simulationresultsand to assess the significanceof apparent modelingerrors. Also, thereappear to be serious fundamentalproblemsin the methodology and assumptions for the third runway embankmentseepage analyses and in the integration of that seepage analysis with the HSPFmodeling used topredict impacts. Each of the three streams consideredby the Low StreamflowAnalysis--Miller, Walker, and Des Moines Creeks--have different sets of unresolvedmodeling/analysis issues. For Miller Creek, the main concern is overembankmentmodeling methods and the way that the embankmentmodelresultsare integrated…

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1904 3rd Avenue, Suite 105, Seattle, WA 98101
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 [...]