EXH0402021820

Subject: Correction to Comment #7 of our I6 February, 2001, letterregarding the Third Runway Project GeoSyntec Consultants (GeoSyntec) recently submitted a technical reviewletter dated 16February, 2001, to you on behalf of the Airport Communities Coalition regarding the Third Runway project at Seattle Tacoma InternationalAirport. The Ietter containedan error in the caption for comment #7, which read as follows: Comment7: The methodology used in performing pseudo-static (seismic) stability analysis is incorrect and may seriously the ability of the wall to withstand seismic loads. The word "underestimate" is incorreeL The correct word is "overestimate." Our concern is that the Hart Cmwser methodology, wherein the yield acceleration was calculated only for the failure surface with the lowest static factor of safety rather than systematically searching for the failure surface with the lowest yield acceleration, may seriously overestimate the seismic resistance of the wall. The corrected comment is attached to this letter. ,14b 'I Ull • ,',e MillsCourt_a0caaer/= MAR9 20G1 R_',,,_ora¢== USACE Labor_o,'_= Atl=t=,GX.Au==,,TX•So,:=R=o,.FL._ic,,_. r,. REGULATORY BRM_H OA.xt_=. ax Columbia.MD • HuntingtonBeak, CA • WalnutCreek,CA BocaR,_on,Ft. - - AR 021820 GzoS_c Co_T_ Freeximan/Kenny March2001 Page 2 We apologize forany confusion this correctionmay.have caused. Sincerely, Edward Kavazanjian, Jr., Ph.D.,P.E.,G.E. Principal Principal Enclosures: RcvisM Comment#7 cc: PeterEglick, HelsellFettermanl.l.p Kimbedy Lockard,AirportCommunities Coalition l:WR0380_ubmittal_SeaTacConuntntLetterCorrtction.doc A AR 021821 G£oS_rr_ Co_t_T_-rs Freedman/Kenny March 2001 Page 3 Comment7: The methodology u_ed in pe.ffqrmin_pseudo-static(seismic) stability analysis is incqrrectand mayseriouslyoverestimate the abilityof the wall to withstand seismic loads. According to Hart Crowser, "We typically apply the seismic coefficient to the most critical failure…

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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 [...]