Notes
Exhibit 247 (AR 019085–019087). Letter dated November 26, 2001, from Northwest Hydraulic Consultants to Colonel Ralph H. Graves, Ms. Muffy Walker, and Ms. Gail Terzi, U.S. Army Corps of Engineers Seattle District, on behalf of Airport Communities Coalition (ACC), Corps Ref. No. 1996-4-02325. Identifies serious flaws in Port Of Seattle’s HSPF low-flow analysis for Miller Creek, Walker Creek, and Des Moines Creek related to Sea-Tac Airport third runway. Critiques Pacific Groundwater Group August 2001 embankment fill modeling report for incorrectly assuming all runway and taxiway impervious surface runoff infiltrates into grassed filter strips, contradicting Earth Tech December 2000 ‘Seattle-Tacoma Airport Master Plan Update Low Streamflow Analysis.’ Argues embankment recharge volumes are overstated, stream low-flow impacts understated, and reserve storage mitigation volumes undersized. Also criticizes use of hourly HSPF time step (should be 15-minute per 1998 King County Surface Water Design Manual) and Port’s failure to respond to King County 401 certification conditions and outstanding public comments by Hydrocomp consultant Norm Crawford.