Notes
Exhibit 411 (AR 022130–022132), dated January 30, 2002. Letter from Northwest Hydraulic Consultants, Inc. (nhc) to Colonel Ralph H. Graves, Ms. Muffy Walker, and Ms. Gail Terzi of the U.S. Army Corps of Engineers, Seattle District, on behalf of the Airport Communities Coalition (ACC). Corps Ref. No. 1996-4-02325. Technical review of the December 2001 ‘Low Streamflow Analysis and Summer Low Flow Impact Offset Facility Proposal’ prepared by Parametrix, Inc. for the Port Of Seattle. Identifies specific errors and inadequacies in the Miller Creek low flow analysis including: double-counting of groundwater discharges from embankment areas due to HSPF PERLND 80 input error; flawed PGG (Pacific Groundwater Group) embankment seepage methodology that examines only post-construction conditions without baseline current-conditions comparison; failure to update embankment fill modeling for subgrade over-excavation and wetland soil removal per Hart Crowser November 2, 2001 Geotechnical Summary Report; and overestimation of seepage flow delivered to Miller Creek at the SR509 compliance point by two to three times versus PGG June 2000 Sea-Tac Runway Fill Hydrologic Studies Report. Also addresses Walker Creek IWS (Industrial Wastewater System) baseflow reductions exceeding 30% and Des Moines Creek upper-gage calibration discrepancy of nearly 100%. HSPF modeling, PGG Hydrus and Slice models, and Sea-Tac third runway embankment discussed.