Notes
Exhibit 231 (AR 018920–018922), dated May 3, 2000, is a follow-up technical comment letter from Northwest Hydraulic Consultants (nhc) on behalf of the Airport Communities Coalition (ACC), addressed to U.S. Army Corps of Engineers project manager Jonathan Freedman and Washington State Department of Ecology environmental specialist Tom R. Luster. The letter responds to the Port of Seattle’s March 10, 2000 reply to nhc’s November 24, 1999 comments on the Stormwater Management Plan (SMP) for the Sea-Tac Airport Master Plan Update third runway development. nhc identifies major inconsistencies in hydrologic model input files for the Miller Creek and Walker Creek basins, including contradictory soil type assumptions (till vs. outwash) between performance target models and detention facility models, four inconsistent parameter sets for airport fill runoff, and flawed Level 1 and Level 2 flow regime analyses linked to the Regional Detention Facility (RDF). The letter calls for a complete overhaul of the SMP hydrologic modeling, calibration to recorded streamflow data, independent technical review, and clarification of applicable King County Surface Water Design Manual (KCSWDM) version (1990 vs. 1998) under the 09/04/97 Interlocal Agreement (ILA) with the City of SeaTac.