February 15, 2001August 2, 2026

EXH AR018360: Sheldon & Associates Response to 2000 Public Notice Comments — Water Movement Through Fill and MSE Wall

Notes

Sheldon & Associates letter dated February 15, 2001, responding to public notice comments regarding the Seattle-Tacoma International Airport Masterplan Update Projects Section 404/401 Permits. Addresses movement of water through embankment fill and Mechanically Stabilized Earth (MSE) wall, drainage layer design to prevent excess pore pressures, rock underdrain clogging prevention using Group 1A filter material, shallow groundwater flow maintenance to downslope wetlands (Wetlands 18, 37, 44), Miller Creek hydrology, aquifer compaction under fill, interflow replacement via underdrain collection, and replacement drainage swales. References Pacific Groundwater Group 2000 Sea-Tac Runway Fill Hydrologic Studies Report, Hart Crowser 1999 Geotechnical Report, Parametrix 2000 Wetland Functional Assessment, and Hart Crowser December 9 1998 Sea-Tac Third Runway-Aquifer Compaction letter. AR018360–AR018362.

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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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