EXH1115041914

'_ Re: SeaTac Third Runway - Aquifer Compaction Dear Ms. Hinlde: in response to your request, this letter addresses the question of potential compaction of aquifers beneath the proposed Third Runway embankment. We understand that you will us_ this information in responding to questions raised by U.S. Army Corps of Engineers on potential hydrogeologic impacts related to construction. SUMMARY Construction of the Third Runway at SeaTac will involve placement of up to about 160 feet of soil fill to create an embankment to support the new runway on the west side o_:the current airport. A question has been raised on whether the weight of this fill will compress the underlying aquifers and possibly diminish their resource value. Three aquifers have been identified below the proposed embankment; the Shallow Aquifer which contributes to base flow of Miller Creek, and the underlying Intermediate and Deep Aquifers which provide part of the regionat water supply (ACI, 1996). . 4no_'_e o#ont,_O• I.ongBea_J)• Der,_r. O_ago ..l_ey Oty AR 041914 1115 DEC-2'?-_I _:_ _ O_DWSER L:_6624367S =.03 M Port of Seattte J-4978-03 December 9, 1998 Page 2 Hart Crowser's calculations, based on worst-case assumptions, indicate that void ratio within the Shallow, Intermediate, and Deep Aquifers within the area immediately underlying and adiacent to the embankment would be reduced by roughly 1 to 3 percent due to the maximum weight of the embankment. For perspective, this corresponds to about a 4-inch maximum change in thickness for the 50-foot.thick Shallow Aquifer. The magnitude of the changein void ratio…

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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 [...]