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EXH 403: GeoSyntec Letter to Army Corps & WA Ecology — Nisqually Earthquake Implications STIA Third Runway MSE Wall & Embankment Fill

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Following the Nisqually earthquake of February 28, 2001, GeoSyntec Consultants wrote to the U.S. Army Corps of Engineers and Washington State Department of Ecology raising serious concerns about the seismic safety of the proposed Third Runway expansion at Seattle-Tacoma International Airport. The letter highlighted that the earthquake caused damage to mechanically stabilized earth (MSE) walls and widespread liquefaction despite being only a moderate event, reinforcing earlier warnings about flaws in the project's seismic design criteria and ground motion analysis. GeoSyntec argued that the airport's role as a regional emergency lifeline demands higher safety standards than those applied to ordinary residential structures.

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Exhibit AR021824. GeoSyntec Consultants letter dated 15 March 2001 to U.S. Army Corps of Engineers (Gail Terzi, Michelle Walker) and Washington State Department of Ecology (Ann Kenny), on behalf of the Airport Communities Coalition, regarding implications of the Nisqually earthquake of 28 February 2001 (magnitude moderate, PGA ~0.19g at SeaTac) for the Seattle-Tacoma International Airport Third Runway embankment fill and West MSE Wall (Mechanically Stabilized Earth wall) expansion project (Reference 1996-4-02325, Port of Seattle applicant). The letter addresses seismic design ground motion criteria, inconsistencies in Hart Crowser Probabilistic Seismic Hazard Analysis (PSHA), FLAC computer program limitations in predicting seismic deformations, liquefaction, lateral spreading, and MSE wall damage observed in the Nisqually earthquake. Sources cited include University of Washington Seismology Laboratory, EERI preliminary reconnaissance report, and PEER preliminary reconnaissance report.

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