September 24, 1999August 2, 2026

EXH AR042987: Subsurface Conditions Data Report, Borrow Areas 1, 3, and 4, Sea-Tac Airport Third Runway

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Hart Crowser subsurface conditions data report (project J-4978.02) prepared for HNTB and Port Of Seattle, dated September 24, 1999, covering Borrow Areas 1, 3, and 4 for the Sea-Tac Airport Third Runway project. Report includes generalized geologic conditions, subsurface soil conditions, hydrogeologic regime, groundwater elevation data, and perched water-bearing zone analysis. Field explorations used dual-wall percussion hammer drilling with reverse circulation; laboratory testing included grain size analysis, water content determinations, and Unified Soil Classification. Tables provide water level data for Borrow Areas 1, 3, and 4; figures include geologic cross sections, groundwater elevation contour maps, and exploration plan maps. AR042987.

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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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