EXH1259051729

SUBJECT: Low Stmamflow Analysis, Summer Low Flow Impact Offset Facility Proposal, Seattle-Tacoma International Airport This letter summarizes the Portof Seattle's evaluation of summer low stzeamflow impacts in Des Moines, Miller, and Walker Creeks calculated to result from proposed airport Master Plan Update projects. This letter also _ the Port's proposalto offset these impacts to maintain existing summer low streamflow conditions in these creeks post project. The methodology used to determine the effects and the plan to offset the impacts was developed and discussed in a series of meetings between the Port of Seattle (Port), Deparunent of Ecology (Ecology), and King County, with staff from Floyd Snide="McCarthy, Inc., acting as facilitators. The evaluation and low streamflow impact offset proposal is final, subject to potential conditions associated with your review during 401 prauiit deliberations. The Port plans to submit final ) documentation of the low streamflow evaluation and operational plan for mitigation facilities in the form of a detailed Low Streamflow Analysis Report and Summer Low Flow Impact Offset Facility Operational Plan, outlines of which are included as an attachment to this letter. Summary The Port's proposal b to detain stormwater in underground vaults and release the detained water continuously into each creek during the summer low streamflow period at a rate equal to the calculated summer low streamflow impact to that creek from planned Port projects. The summer low streamflow impacts in each creek were determined through detailed modeling analysis. The summer low streamflow periods were determined through statistical analyses of…

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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 [...]