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EXH 240A: Preliminary Comments Set 2 on Aug 2000 Stormwater Management Plan STIA Master Plan Update

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A September 2000 letter from Northwest Hydraulic Consultants raises concerns that the Seattle-Tacoma International Airport's Stormwater Management Plan fails to adequately assess or mitigate the third runway embankment's impact on stream base flows and seepage flows to nearby wetlands. The consultants argue that the Port of Seattle's own data contradicts its claims that the embankment fill would maintain groundwater recharge, and that independent re-analysis suggests summer groundwater reductions to Miller Creek could be roughly twice what the Port reported. The letter calls for more rigorous and consistent hydrologic modeling before construction commitments are made.

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Letter dated September 25, 2000 from Northwest Hydraulic Consultants Inc. (Bill Rozeboom) to Gordon White, Program Director, Shorelands and Environmental Assistance Program, Washington State Department of Ecology. Second installment of preliminary review comments on the August 2000 Stormwater Management Plan (SMP) for the Sea-Tac Airport Master Plan Update third runway embankment. Addresses project impacts to stream base flows and seepage flows to wetlands, citing the SeaTac Runway Fill Hydrologic Studies Report (Ecology, 2000), HSPF model analysis of subbasins SDW1A and SDW1B, Miller Creek groundwater reductions, and the Industrial Wastewater System (IWS). Challenges Port of Seattle’s commitment to preserving seepage flows, critiques Elizabeth Leavitt Technical Memorandum of September 5, 2000, and identifies inconsistencies in Appendix F base flow impact analysis versus Table A-4 calibrated model parameters. Exhibit 240A, AR018988.

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