TagDes Moines Creek(169)

An email dated February 8, 2002, from Peter Willing to John Strand reports turbidity measurements taken during a site visit at Sea-Tac on January 28, 2002, between 11:45 and 12:08. Two samples were recorded: Sample #1 showed tank farm outfall at 281 NTU and DM Creek at 31 NTU, while Sample #2 showed tank farm outfall at 299 NTU and DM Creek at 31.2 NTU. The data indicates significantly elevated turbidity levels at the tank farm outfall compared to the creek reference point.

Declaration of Kelly Whiting, Senior Engineer at King County Department of Natural Resources, filed before the Pollution Control Hearings Board (PCHB No. 01-133) in Airport Communities Coalition v. State of Washington Department of Ecology and Port Of Seattle. Whiting reviewed the Port Of Seattle’s Comprehensive Stormwater Management Plan (SMP) for Master Plan Update Improvements at

Memorandum dated December 12, 2001 from Michael Kenrick and Reese Hastings of Hart Crowser Inc. to Jim Thomson of HNTB, project number 4978-62, analyzing pre-construction and post-construction hydrologic conditions at Borrow Area 1 associated with the Port of Seattle Master Plan Update for Sea-Tac International Airport (STIA). Covers surface water and groundwater impacts, wetland hydrology,

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 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.

Report prepared by Parametrix, Inc. with Aqua Terra Consultants, Earth Tech, Inc., Foster Wheeler Environmental Corporation, HNTB, and Pacific Groundwater Group for Port Of Seattle regarding Sea-Tac Airport Master Plan Update Improvements. Analyzes summer low streamflow impacts to Walker Creek and Des Moines Creek from planned airport projects and proposes an offset facility using underground

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.

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

A November 2001 letter from Northwest Hydraulic Consultants, written on behalf of the Airport Communities Coalition, raises serious technical objections to the Port of Seattle's proposed plan to manage low streamflow impacts from SeaTac Airport's third runway construction on Miller, Walker, and Des Moines Creeks. The letter argues that the Port's analysis contains critical flaws, including an incorrect assumption that virtually all runway runoff infiltrates into adjacent grassed filter strips, and that the use of hourly rather than shorter time intervals in hydrological modeling causes stream impacts to be underestimated and mitigation storage facilities to be undersized. The consultants also express concern that the Port was not adequately addressing outstanding public comments or certification requirements set by regulatory agencies such as the Washington Department of Ecology.

A 2001 technical memo from Hydrocomp, Inc.'s Norm Crawford outlines recommendations for hydrological modeling of Miller, Walker, and Des Moines Creeks near Sea-Tac Airport's new runways and taxiways. The document describes how surface runoff and groundwater flow from both impervious runway surfaces and surrounding pervious grasslands should be calculated and linked across three modeling tools: HSPF, Hydrus, and the Slice model. Key recommendations include properly accounting for infiltration, reducing till seepage by 33% for inactive groundwater recharge, and reconciling discrepancies in land area calculations between the different models.