September 1, 2000August 2, 2026

Analysis of Proposed Mitigation Ratios for Impacts Resulting from the Construction of Sea-Tac Third Runway

Notes

A letter from Azous Environmental Sciences to regulatory agencies analyzing the wetland mitigation plan proposed by the Port of Seattle for impacts from the SeaTac Third Runway construction. The report identifies numerous errors in wetland acreage accounting, inadequate mitigation ratios, and out-of-basin mitigation that fails to meet Washington State Department of Ecology standards for no net loss of wetland functions. The author concludes the Port’s proposal is insufficient to compensate for wetland losses in the Miller, Walker, and Des Moines Creek watersheds.

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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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