Notes
Report prepared by Parametrix, Inc. with Aqua Terra Consultants, Earth Tech, Inc., Foster Wheeler Environmental Corporation, HNTB, and Pacific Groundwater Group for Port Of Seattle regarding Sea-Tac Airport Master Plan Update Improvements. Analyzes summer low streamflow impacts to Walker Creek and Des Moines Creek from planned airport projects and proposes an offset facility using underground stormwater vaults to release stored water during summer low-flow periods (late July through October/November). Documents corrections to HSPF modeling errors involving data transfer (daily/hourly AGWO/AGWI conversion factors), Hydrus 1D/2D embankment flow modeling, infiltration basin simulation, and groundwater routing for SDS5, SDS6, SDS7 basins. References Clean Water Act Section 401 Water Quality Certification #1996-02325 (Amended-1) issued by Washington Department of Ecology on August 10 and September 21, 2001. Coordinates with King County and Ecology on model error resolution.