Notes
Letter dated August 6, 2001 from Northwest Hydraulic Consultants (NHC) to Gordon White, Program Director, Shorelands and Environmental Assistance Program, Washington State Department of Ecology, on behalf of Airport Communities Coalition (ACC). Reviews the Port Of Seattle July 23, 2001 two-volume document ‘Low Flow Analysis Flow Offset Facility Proposal’ related to the third runway embankment at Sea-Tac Airport. Identifies six major deficiencies: (1) incomplete draft missing key sections including Determination of Impacts to Streamflow and preliminary facility drawings; (2) failure to address low-flow impacts from post-1994 Industrial Wastewater System expansion and future airport business park development at proposed borrow pits in upper Des Moines Creek Basin; (3) inconsistency between proposed reserve storage vaults (NEPL, Cargo, SDN2X/4X, SDN3X for Miller Creek; SDS3, SDS4 for Des Moines Creek; Vault F for Walker Creek) and Stormwater Management Plan (SMP) vaults C1, C2, G1; (4) unexamined dry-period transit losses via evaporation, transpiration, seepage in open ditches and infiltration systems; (5) no assurance constant flow release orifices (as small as 0.5 inches diameter) are feasible without plugging; (6) poor HSPF calibration for Walker Creek low flows, with actual lowest flows occurring June/July rather than model-predicted October, suggesting low flow period should extend July 1–October 31. AR 023086–023088. Exhibit filed in PCHB Third Runway EIS administrative record.