October 25, 2001August 2, 2026

Exhibit 53: Pre Low Flow Meeting Briefing — King County Review of Port Of Seattle HSPF Hydrologic Modeling

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Email from Kelly Whiting (King County Department of Natural Resources, Water and Land Resources Division) to Ann Kenny and Raymond Hellwig, dated October 25, 2001, summarizing a pre-meeting briefing on revised low flow hydrologic modeling related to Port Of Seattle airport embankment impacts. Discusses Hydrocomp (Norm Crawford) independent review findings, HSPF modeling errors including incorrect timestep handling (daily vs. hourly), a factor-of-24 double-application error in HSPF flag defaults, impervious area runoff from runways not infiltrating filter strips (27%), Walker Creek embankment discharges, toe drain routing to active groundwater vs. stream, wet-up period, and concerns that public comments were not being addressed. References Parametrix and embankment model revisions. AR 017663–017664.

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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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