Notes
Exhibit 329 (AR 020946). GeoSyntec Consultants letter dated February 7, 2002, submitted on behalf of Airport Communities Coalition (ACC) to U.S. Army Corps of Engineers Regulatory Branch (Muffy Walker/Gail Terzi), commenting on the Port of Seattle’s Third Runway Low Flow Analysis for Seattle-Tacoma International Airport. Reviews Pacific Groundwater Group (PGG) November 27, 2001 report ‘Embankment Fill Modeling in Support of Low Streamflow Analysis.’ Key findings: Port’s analysis fails to account for initial years lag time (estimated 1–6 years depending on embankment height of 20 ft, 110 ft, or 150 ft) before water reaches creek drainage layer; Hydrus 2D and SLICE spreadsheet model reliability questioned; embankment hydraulic conductivity overestimated; storage vault volumes likely under-designed; creek low flow mitigation requirements unmet during initial post-construction period. GeoSyntec performed independent Hydrus 2D analyses. References PGG report Figures 5-1, 5-2, 5-3 and Table 5-7; embankment fill lengths of 1600 ft, 3700 ft, and 3200 ft for respective cross-sections.