EXH0160018360

• Sea-Tac Runway Fill Hydrologic Studies Report (Pacific Groundwater Group 2000). This report was funded by the Washington State Department of Ecology • Geotechnical Report (Hart Crowser 1999) • WetlandFunctionalAssessmentand ImpactReport(Parametrix,Inc.2000) • Seattle-TacomaAirportMaster Plan Update-Low StreamflowAnalysis(Pacific GroundwaterGroup2000) _." Wetlands located downslope of the embankn_nt are maintained by groundwater discharge seeps ._.r _I._ locatedbeneaththenandattheirmargins,seasonalperiodsofshallowinterflow,and(inthecase of Wetland 18, 37, and 44 some channelized flow). .s,_ _ 2. The primary purpose of the drainage layer at the base of the embankment fill is to prevent _ _ _t__,_' the build-up of excess pore pressures in the overlying fill material by preventing the development _?o_. _ of fully sanu'ated conditions at the base of the fill. It does this by providing a high-permeability,_"/_ pathway that allows drainage to occur to the toe of the embankment if the rate of infiltration and_ !_ _,_ seepage through the embankment exceeds the permeability of the underlying native soils. . _ w-.[ The primary hydrologic source for the wetlands (groundwater discharging through a shallow "'_[,,_L#_r _aquifer) will remain in place. Groundwater will continue to recharge the shallow aquifer located beneath and-east of the embanlanent and pass beneath the embankment before discharging to the soil structure beneath iL the resulting reductions in porosity, void ratio, and permeability are conservatively estimated to be less than 5% under the maximum height of the fill (Sea-Tac Third _ Runway-Aquifer Compaction, letter, to Port of Seattle from Hart Crowser, December 9, 1998) and C/_ so the groundwater flow will continue largely unimpeded. _/l_'_'_,_,,_e.L…

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PSCAA Advisory Council Meeting Agenda
Add to CalendarMWednesday Mar 11, 9:00am - 11:35am
1904 3rd Avenue, Suite 105, Seattle, WA 98101
Call to order – Roll Call – Quorum Established – Land Acknowledgement We would like to acknowledge that our Agency operates in four present-day counties, which are the traditional lands of the Coast Salish people, past and present. This acknowledgement does not take the place of authentic relationships with indigenous communities in our jurisdiction and [...]