December 23, 1998August 2, 2026

EXH AR041907: Memorandum — Summary of Hydrologic Issues, Borrow Areas 1, 3, and 4, Third Runway Project, Sea-Tac Airport

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Hart Crowser memorandum (J-4978-03) dated December 23, 1998, from Michael Bailey P.E. and Michael Kenrick P.E. to Barbara Hinkle, Port Of Seattle, addressing hydrologic impacts of Borrow Areas 1, 3, and 4 for the Third Runway Project at Seattle-Tacoma International Airport. Discusses impacts on baseflow to Des Moines Creek and riparian wetlands, including runoff reduction, infiltration increases, and groundwater recharge from removal of glacial till soils exposing high-permeability outwash deposits. AGI (1996) estimates cited: 188,471 gpd increase for Area 1, 23,849 gpd for Area 4; Hart Crowser estimates 70,000 gpd increase for Area 3. Document covers Shallow Regional Aquifer, perched water zones, stormwater pollution prevention, erosion and sedimentation control, and long-term hydrologic benefits post-reclamation.

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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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