Notes
Exhibit 464 (AR 022955), prepared by Parametrix, Inc. with Aqua Terra Consultants, Earth Tech, Foster Wheeler Environmental Corporation, HNTB, and Pacific Groundwater Group for Port Of Seattle. December 2001 report analyzing low streamflow impacts and proposing a Flow Impact Offset Facility for Seattle-Tacoma International Airport (STIA) Master Plan Update third runway embankment construction. Uses HSPF (Hydrologic Simulation Program-FORTRAN), Hydrus, and finite-difference Slice model to evaluate hydrologic impacts on Miller Creek, Walker Creek, and Des Moines Creek. Quantifies required flow offsets: 0.11 cfs in Walker Creek and 0.08 cfs in Des Moines Creek over a 92-day low-streamflow mitigation period (late July through October). Proposes stormwater detention vaults of 18.5 acre-ft (Walker Creek) and 13.5 acre-ft (Des Moines Creek) to collect winter runoff for summer release. Submitted in response to Washington State Department of Ecology Water Quality Certification #1996-4-02325 (Amended-1), issued September 21, 2001. Filed in PCHB third-runway-eis administrative record.