Notes
Final meeting notes from October 30, 2001 (8:30–11:30) for 401 Permit post-issuance clarification meeting regarding Sea-Tac International Airport Third Runway low streamflow analysis. Prepared by Kate Snider, Floyd Snider McCarthy, Inc. Attendees included Ann Kenny (Dept. of Ecology), Kelly Whiting and David Masters (King County), Lisa Scott (Corps of Engineers), Keith Smith and Robin Kordick (Port of Seattle), Paul Fendt (Parametrix), Joe Brascher (Aquaterra), Pony Ellingson (Pacific Groundwater Group), Felix Kristanovich (Foster Wheeler). Documents six modeling errors and corrections: (1) 1/24th conversion factor error in HSPF embankment fill input — daily-to-hourly conversion applied twice by modeler and automatically by HSPF program, resulting in embankment flow contribution now 24 times previous value; (2) incorrect AGWO vs. AGWI input files; (3) revised approach to impervious area modeling at embankment filter strips using AGWI and SURO time series; (4) switch from 2-D to 1-D Hydrus model; (5) modeling of discharge from infiltration basins in Miller Creek basin; (6) predeveloped conditions correction for SDS-5, 6 & 7 in Des Moines Creek basin — groundwater incorrectly routed to Des Moines Creek rather than Walker Creek. Also documents QA review by Norm Crawford of Hydrocomp (HSPF model developer) and Port/Ecology/King County decision not to adopt Crawford’s recommendation to route ‘seepage to till’ component directly to stream. Administrative Record number AR022925.