August 6, 2001August 2, 2026

Comments on Recently Received Documents Pertaining to Seattle Tacoma International Airport Project Third Runway – Embankment Fill and West MSE Wall

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GeoSyntec Consultants submitted this technical review letter on behalf of the Airport Communities Coalition to the U.S. Army Corps of Engineers and Washington State Department of Ecology, commenting on geotechnical analyses for the Third Runway expansion at Sea-Tac Airport. The letter identifies critical concerns including underestimated seismic risk, incorrectly performed seismic stability analyses, improper representation of liquefiable materials, and overestimated post-earthquake stability. GeoSyntec maintains that the Port of Seattle’s consultants have not demonstrated the project will perform acceptably under anticipated seismic loads.

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As the source for federal transportation grants, the Puget Sound Regional Council was charged with developing a system to meet the growing need for commercial aviation. When the search for a second airport failed, they authorized the Port of Seattle to build the Third Runway, with a mandate to develop a noise abatement and mitigation program. In their effort to stop the Third Runway, the ACC argued over every detail of the Port's efforts--including property buyouts and sound insulation. The dispute was meant to be settled by a three member Expert Arbitration Panel. This is their final report. It finds 2-1, that the Port's program was insufficient in several respects. Despite that, funding for the Third Runway was approved by the PSRC, and the 'Port Package' program, proceeded largely unchanged. Expert Arbitration Panel's final decision finding that the Port of Seattle had not shown sufficient reduction in real on-the-ground noise impacts to satisfy noise reduction conditions required for approval of a third runway at Sea-Tac International Airport. The majority decision concluded the Port's noise abatement programs were insufficient despite being impressive in scope.

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