Notes
Hart Crowser letter (project J-4978-03) to Barbara Hinkle, Health Safety & Environmental Services, Port Of Seattle, dated December 9, 1998, addressing aquifer compaction beneath the proposed Third Runway embankment at Sea-Tac Airport in response to U.S. Army Corps of Engineers questions on hydrogeologic impacts. Analysis covers the Shallow Aquifer (contributing to Miller Creek base flow), Intermediate Aquifer, and Deep Aquifer (regional water supply). Worst-case calculations indicate 1–3 percent reduction in void ratio, ~4-inch maximum thickness change in the 50-foot Shallow Aquifer, and 2–5 percent permeability reduction. Embankment fill estimated at up to 160 feet; deformation modulus range 3,000,000–7,000,000 psf; glacial preload ~185,000 psf. No impacts to drinking water wells anticipated within the 500-foot affected zone.