November 7, 2001August 2, 2026

Exhibit AR026126: Notes on HSPF Modeling of Miller, Walker and Des Moines Creeks — Linkages Between HSPF and Hydrus/Slice

Notes

A technical memorandum authored by Norm Crawford of Hydrocomp, Inc., dated November 7, 2001, presenting notes and recommendations on HSPF hydrological modeling of Miller, Walker, and Des Moines Creeks in relation to Sea-Tac Airport’s new runway and taxiway construction. The document describes linkages between the HSPF, Hydrus, and Slice models for simulating groundwater, surface runoff, and infiltration through fill and Vashon till layers. It includes eight numbered modeling recommendations and three additional issues regarding area discrepancies and base flow handling in the HSPF model.

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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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