EXH1204046044

FROM: Michael A.P. Kenrick, P.E.,and Michael J.Bailey, P.E.,Hart Crowser RE: Sea-Tac Third Runway - Borrow Area 3 c,.,c_g. Preservation of Wetlands J-4978-06 Oelt ve¢ As requested by the Port of Seattle, this memo and the attached figures provide conceptual designand supporting information for the proposed drainage swale to protect wetlands in Borrow Area 3. We also provide a brief explanation of the hydrolo_/that supports the wetlands, including why excavation of Borrow Area 3 will not drain these wetlands. Figure F_,_,-_,,.,_. shows the location of Borrow Area 3 to the south of Sea-TacAirport. REVIEW OF BORROW AREA 3 WETLAND HYDROLOGY . _ .... :,:_ The first section of this memo provides a review and explanation of the hydrology' that currently supports and sustainswetlands in Borrow Area 3. Understanding these hydrologic factors is important in ensuring the long-term preservation of the wetlands during and after excavation of the fill materials contained in Borrow Area 3. _"_ Factors Promoting Preservation of the Wetlands Existingwetlands and current topography in Borrow Area 3 are shown on Figure 2; the ,._,-,a_a_ proposed area of mining and resulting contours for final excavation are shown on Figure 3. The seriesof wetlands mapped in Borrow Area 3 follow a line of shallow depressionsin the southcentral part of the site, extending to the southeast from Wetland 29 through Wetlands _,,,_ B9, 30, B7, B6, and BS. These wetlands exist in an area of relatively permeable subsoils where the main groundwater table is at a depth of 10 to 15 feet…

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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 [...]