November 24, 1999August 2, 2026

Comments on stormwater management plan for proposed 3rd runway development actions at Seattle-Tacoma International Airport

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Northwest Hydraulic Consultants (nhc), retained by the Airport Communities Coalition, submitted technical review comments on the stormwater management plan for the proposed 3rd runway at Sea-Tac Airport. The letter identifies major deficiencies in the analysis, including failure to follow King County Surface Water Design Manual and Washington State Department of Ecology requirements. Key concerns include inadequate flow control performance targets, failure to conduct required offsite analysis, and stormwater facilities that may worsen existing problems in downstream creek systems.

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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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