EXH0273019513

the determination of impacts to each stream resulting fi'om consmzcrion projects m the Master Plan Update for STIA. The evaluations of the summer Iow-streamflow periods and rates are described in Sections 2.!.2 and 2.1.3. A detailed modeling analysis was used to determine the impacts to stream.flows during the summer Iow-streamflow periods. Modeling tools used include the calibrated Hydrologic Simulation Program - FORTRAN (HSPF; EPA 1997) models for .Miller, Walker, and Des Moines Creeks. HSPF model calibration is described in Section 2.2, and detailed HSPF modelandcalibrationinformationiscontainedinAppendicesA andB (Volumes2 and3)of the SMP (Parametrix 2000a, 2001a). The impacts of the proposed third runway embankraent were modeled using a combination ofHydrus (Simunek et al. 1999) and Slice models. The embankment modeling is described in Section 2.3, and the complete embankment modeling report (Pacific Groundwater Group 2001) is contained in Appendix B. Non-hydrologic impacts, including cessation of water withdrawals and removal of septic tank discharges, are described in Section 2.4. The total net summer low-strearnflow impacts are sunmmrized in Section 2.5. 2.1.2 Determination of Summer Low-Stream/low Period Determinationof thelow-strtamflowperiodforeach streamwas done by analyzingmodeled streamflowfromthecalibratedHSPF modelforeachstream,whichused1994(existing)landuse conditions.Thisdeterrninationissummarizedbelow,and supportinginformationisprovidedin AppendixI. The 7May low-flowperiodforeachyear(using1994flowconditions)m the47-yearperiodof t record(1949to 1995)foreachstreamwas determinedatpointsofcomplianceneartheairport (200 _ Surect in Des Moines Creek, SR 509 m Miller Creek, and at the outlet of the wetland near Des Momes Memorial Drive in Walker Creek). The 7-day low flow was selected as an indicator of persistent dry season flow. For example, summer low streamflows tend to decrease gradually;, therefore, a shorter Iow-streamflow period is unlikely to result…

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Add to CalendarMWednesday Mar 11, 9:00am - 11:35am
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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 [...]