May 5, 2001August 2, 2026

Exhibit 112: Ecology NWRO Memorandum on Slice Model Integration for Sea-Tac Airport Master Plan Update Low Streamflow Analysis

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Memorandum dated May 5, 2001 from Dave Garland, Ecology NWRO Water Quality Nonpoint Unit, to Ray Hellwig and Ann Kenny, through Kevin Fitzpatrick, documenting an April 20, 2001 meeting with Pony Ellingson and Crispin Prahl of Pacific Groundwater Group (PGG) regarding ‘slice model integration’ for the proposed 3rd runway embankment at Sea-Tac Airport. Discusses Hydrus and Slice modeling tools used to estimate runway embankment drainage, vertical infiltration, shallow and deep recharge components, and horizontal groundwater transport to embankment toe discharge. References Earth Tech December 2000 report ‘Sea-Tac Airport Master Plan Update Low Streamflow Analysis’ and Garland’s March 9, 2001 memo raising accuracy concerns. AR 017889.

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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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