TagThird Runway(1098)

This December 2001 report, prepared by Parametrix, Inc. and several partner firms for the Port of Seattle, analyzes low streamflow conditions and proposes a Summer Low Flow Impact Offset Facility as part of the Seattle-Tacoma International Airport Master Plan Update Improvements. The study examines how planned airport expansion may affect seasonal low-flow water resources in the surrounding area and outlines mitigation measures to offset those impacts. The report is organized across multiple volumes, with Volume 1 containing the main text and Appendices B through J.

This technical report analyzes low streamflow conditions in three creeks near Seattle-Tacoma International Airport (Miller, Walker, and Des Moines Creeks) to assess the potential impacts of airport construction projects on summer water flows. Using a 47-year record of streamflow data and computer modeling tools, analysts determined target streamflow levels for each creek and evaluated how proposed runway and infrastructure improvements might affect seasonal low-flow periods critical to salmon habitat. The study found existing summer low streamflow targets of 0.33 cfs for Des Moines Creek, 0.77 cfs for Walker Creek, and 0.73 cfs for Miller Creek, which were used to guide mitigation planning.

This technical document compares observed and model-predicted 7-day low streamflows for Walker Creek and Des Moines Creek near Seattle-Tacoma Airport for water years 1991–1996. Results show that calibrated (simulated) flows generally underestimated observed flows at most gage locations, with the exception of 1995, when the model overpredicted flows. Discrepancies at upstream gage locations are attributed to uncertain groundwater conditions within the watersheds.

This December 2001 technical report, prepared for the Port of Seattle, analyzes low streamflow conditions around Seattle-Tacoma International Airport and proposes a facility to offset the impact of airport Master Plan construction on summer low flows in nearby creeks. It includes hydrologic modeling, water quality design considerations, and an operation and monitoring plan for a stormwater storage and release system intended to maintain stream levels during dry summer months. Note that while archived alongside airport planning documents, this report focuses on water resources and stream impact mitigation rather than noise policy.

This December 2001 technical report analyzes low streamflow conditions in Miller, Walker, and Des Moines Creeks near Seattle-Tacoma International Airport, assessing the hydrologic impacts of the proposed third runway embankment as part of the airport's Master Plan Update. The study found that the runway construction would reduce summer stream flows, requiring mitigation of 0.11 cfs in Walker Creek and 0.08 cfs in Des Moines Creek during the annual low-flow period (late July through October). To offset these impacts, the Port of Seattle proposed collecting and storing excess winter stormwater in underground vaults—approximately 18.5 acre-feet for Walker Creek and 13.5 acre-feet for Des Moines Creek—for controlled release during dry-season low-flow periods.

Declaration by Brett Fish, President of Citizens Against Sea-Tac Expansion (CASE), filed in PCHB No. 01-160 (Airport Communities Coalition v. Washington State Department of Ecology and Port Of Seattle). Fish declares CASE’s interest in intervening in the ACC’s appeal of Ecology’s 401 Certification for the proposed third runway and master plan update at Sea-Tac Airport.

Third declaration of William A. Rozeboom, professional civil engineer with Northwest Hydraulic Consultants, filed before the Pollution Control Hearings Board (PCHB), Case No. 01-160, Airport Communities Coalition (ACC) v. State of Washington Department of Ecology and Port Of Seattle. Declaration concerns Section 401 Certification No. 1996-4-02325 and CZMA concurrency statement. Rozeboom identifies significant technical deficiencies

Report by Pacific Groundwater Group (project JE0105) prepared for Port Of Seattle, dated November 27, 2001, analyzing embankment fill modeling in support of low streamflow analysis for the Sea-Tac Third Runway. Uses HYDRUS-SLICE modeling to assess vertical infiltration through embankment fill materials (General Fill and Type 1 Fill), saturated flow beneath the fill, and effective

Letter dated November 26, 2001, from Northwest Hydraulic Consultants (on behalf of ACC, Airport Communities Coalition) to Colonel Ralph H. Graves, Ms. Muffy Walker, and Ms. Gail Terzi of U.S. Army Corps of Engineers, Seattle District, Corps Ref. No. 1996-4-02325. Identifies serious flaws in Port Of Seattle’s low flow mitigation analysis for Miller Creek, Walker

This 2001 legal declaration by civil engineer William Rozeboom, submitted to Washington's Pollution Control Hearings Board, challenges the Port of Seattle's stormwater and low-flow mitigation plans for the proposed third runway at Sea-Tac Airport. Rozeboom argues that the Port's analysis underestimates low-flow impacts on local streams and that the proposed underground storage vaults—equivalent in volume to more than seven Olympic-size swimming pools—are undersized. The declaration also disputes claims by Port engineer Paul Fendt that the water volumes involved are small and that mitigation can be easily adjusted.