EXH0453022838

I"l' " RECEIVED WORKING,4FEB- 8 2002 ! COPYL, RTENBROWI',IINC: A GeoSyntec Consultants 7February2002 U.S. Army Corps of Engineers RegulatoryBranch P.O.Box 3755 Seattle,WA 98124 ATTN: Muffy Walker/GallTerzi Subject: Commentson RecentlyReceived DocumentsPertainingto SeattleTacomaInternationalAh'portProject ThirdRunway- Low Flow Analysis GeoSy_tec Consultants (GeoSymec) has been retained on behalf of the Airport CommunitiesCoalition (ACC) to provide a technicalreview of investigation,analysis and design relating to geotechnicaiandhydrogeoiogicalelements of theproposedThird RunwayExpansion Projectat the SeattleTacoma InternationalAirport, GeoSyn.tec has previouslycommentedon seismic and geotcchnicalaspects of the embankmentfill and MechanicallyStabilizedEarthWall. Inmy October2001 declarationin supportof ACC's motion for stay, I raised numerousconcerns relatingto the Fort's Low Flow hmalysis. This letterpresentsan expansionon the issues raised in the declarationbased largelyon reviewof the November27, 2001reportby Pacific GroundwaterGroup(PGG)titled"Port of"Seattle - Sea-Tac ThirdRunway - EmbankmentFill Modelingin Supportof Low Su'eanfflowAnalysis." Introduction The purposeof the low flow analysis is to evaluate the impact thatconstructionof the Third Runway Embankmentwill have on the rate at which runoff and infiltration rechargethecreeks. The impactoftheembankmentisthatitstoresinfiltratingwater and subsequentlyreleases it to rechargethe low streamflows at differenttimes thanif the embankmentwere not in place. To mitigatethe impactof theembankment,excess watermust be storedandreleased to the creeksto maintainconditionsthatexisted prior to the constructionof the embankment.The analysis must be able to predict the magnitudeof the impactof the embankmentand providea soundbasis forcalculating I:WRO380(S_Tzc)_$ubmi,'_;_Syn_cSc_l'a¢Commc__ #3._ __ _..a_hy_r, ,:_,CourtRepolV'_tness'-_=_'="""_er AR 022838 b | WalkerFl'emi _ GeoSyntccCm_ultan_ February2002 Page 2 ' the requiredstorage to maintain flows in the creeks. Like any work of this type, the analyses must reliability analytical method and the results of the consider the of the uncertainty of the parametersinput into the analyses. If the…

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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 [...]