TagDes Moines Creek(169)

This November 2001 document from Parametrix, Inc. contains responses to U.S. Army Corps of Engineers questions regarding the Sea-Tac International Airport (STIA) Master Plan Update's natural resource mitigation project. It addresses technical questions about wetland mapping, watershed basin sizes, low-flow analysis, and cumulative wetland impacts across the Miller Creek, Walker Creek, and Des Moines Creek basins, showing projected wetland acreage reductions of approximately 3-4% with the project. The document also covers mitigation measures including wetland restoration sites and performance standards for invasive species control.

This technical memo from Hydrocomp, Inc. (authored by Norm Crawford) outlines recommendations for improving hydrological computer modeling of Miller, Walker, and Des Moines Creeks near Seattle-Tacoma International Airport's new runway construction. It describes how rainfall and runoff from the new impervious runway and taxiway surfaces and surrounding pervious grasslands are tracked through a linked series of models (HSPF, Hydrus, and Slice) to estimate groundwater movement and seepage through underlying soil layers. The document identifies several discrepancies in the existing model setup and recommends corrections to better account for water flow paths, drainage areas, and groundwater recharge in the fill areas created by airport expansion.

A biological scientist hired by the Airport Communities Coalition reviewed the Port of Seattle's plan to store airport stormwater in detention vaults and release it into Miller, Walker, and Des Moines Creeks during summer low-flow periods. The review found that the plan could worsen water quality in those creeks, because stored sediments may release toxic levels of copper and zinc, and potentially harbor human pathogens from airplane wastewater. The scientist concluded that regulators lacked sufficient information to approve the proposal without further testing, modeling, and independent scientific review.

A water resources consultant, writing on behalf of the Airport Communities Coalition, argues that the Port of Seattle's July 2001 Low Flow Analysis for Sea-Tac Airport expansion fails to provide reasonable assurance that the project will meet water quality standards in Miller, Walker, and Des Moines Creeks. The letter criticizes the submission as incomplete and rushed, noting missing figures, unfinished sections, and an unresolved plan to store the required 46 acre-feet of stormwater across the three watersheds. The consultant contends that the Port's proposed water quality protections—including filtration, aeration, and biofiltration swales—are unproven, inadequately designed, and fall short of the regulatory standard required for Section 401/404 permit approval.

This August 2001 King County review evaluates the Port of Seattle's Low Flow Impact Analysis and proposed Flow Impact Offset Facility, which aims to mitigate reductions in stream flows in local creeks—including Des Moines, Miller, and Walker creeks—caused by future airport development. The review finds that while the proposed water storage and augmentation measures substantially offset low-flow impacts during the critical late-summer period, there are significant gaps in documentation, biological assessment, and design details that need to be addressed. Recommendations include professional engineering certification, enhanced biological monitoring, improved calibration documentation, and refinements to the reserve storage facility designs.

Parametrix, Inc. report prepared for Port Of Seattle on cumulative impacts to wetlands and streams from Seattle-Tacoma International Airport Master Plan Update improvements, August 2001 (AR 050792, Exhibit 1267). Covers land use changes in Miller Creek and Des Moines Creek watersheds, wetland inventories, soil survey maps, aerial photograph analysis, stream conditions and fish habitat in

Letter dated July 23, 2001 from Port Of Seattle to Ann E. Kenny at Washington State Department of Ecology Northwest Regional Office regarding Low Streamflow Analysis and Summer Low Flow Impact Offset Facility Proposal for Seattle-Tacoma International Airport. Covers summer low streamflow impacts in Des Moines Creek, Miller Creek, and Walker Creek from airport Master

Parametrix, Inc. report prepared for Port Of Seattle assessing the existing (1994) and future (2006) hydrologic divide of Miller Creek, Walker Creek, and Des Moines Creek following Master Plan Update (MPU) construction at Seattle-Tacoma International Airport (STIA). Analyzes compliance with Governor’s Certification requirement that the third runway project will not cause changes in the location

Port of Seattle letter dated July 23, 2001 to Ann E. Kenny, Washington State Department of Ecology, Northwest Regional Office, summarizing low streamflow impact analysis and flow impact offset facility proposal for Seattle-Tacoma International Airport Master Plan Update projects. Prepared by Parametrix, Inc. Analysis covers summer low streamflow impacts to Des Moines Creek, Miller Creek,

In a July 2001 letter to the Washington State Department of Ecology, Northwest Hydraulic Consultants raised concerns on behalf of the Airport Community Coalition that the Port of Seattle's ongoing low streamflow analyses for Des Moines, Walker, and Miller Creeks near Sea-Tac Airport were likely underestimating the airport's impact on local waterways. The consultants argued that the models were poorly calibrated for upper-basin conditions and failed to account for post-1994 improvements to the Industrial Wastewater System or the future loss of forested areas due to planned airport development. They requested that a final report on the streamflow analysis and any proposed mitigation measures be made available for public comment before Ecology used it to make its 401 Certification decision.