Notes
Memorandum dated October 26, 2000 from Jim Thomson (HNTB), Mike Bailey (Hart Crowser), and Michael Kenrick (Hart Crowser) to Michael Cheyne, Third Runway Program Leader, regarding Third Runway embankment infiltration at Sea-Tac Airport. AR 021690–021692. The design team concludes that artificially increasing infiltration beyond standard construction practice poses unacceptable risks: increased surficial slope stability problems from seepage and piping, increased risk of subgrade liquefaction of loose to moderately dense native sands beneath the embankment, increased construction complexity and cost (non-silty Group 1 fill material costs approximately 200 percent more than common fill), and long-term maintenance risks including inability to detect or unclog failed infiltration systems deep within the embankment. The memo discusses underdrain design, pore pressure buildup, groundwater level rise, and liquefaction mitigation via densification.