August 9, 2000August 2, 2026

EXH AR045601: Evaluation of Perched Zone Interception and Possible Impacts to Wetland Hydrology, Borrow Area 3, Sea-Tac Third Runway

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Hart Crowser draft report prepared for Port of Seattle, August 9, 2000 (J-4978-13), evaluating perched groundwater zone interception and potential wetland hydrology impacts from Borrow Area 3 excavation for the Sea-Tac Third Runway project. Addresses Pacific Groundwater Group (PGG, 2000) concerns commissioned by Washington State Department of Ecology regarding impacts to Wetland 29. Includes ModFlow groundwater modeling, perching layer hydrogeology, seepage face analysis, and revised mine plan preserving wetlands mapped by Parametrix (1999a). Topics include perched water-bearing zone, groundwater flow direction northwest to southeast, Borrow Areas 3 and 4, swale collection of seepage, and drawdown contour mapping.

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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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