TagStormwater(385)

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

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,

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

A water resources consultant raised concerns in a July 2001 letter to the U.S. Army Corps of Engineers and Washington State Department of Ecology about the Port of Seattle's stormwater management plans for Sea-Tac Airport expansion. The letter challenged the effectiveness of proposed biofiltration swales, noting they can actually increase bacterial levels rather than reduce them, and warned that releasing stored stormwater from detention vaults into nearby Class AA streams could discharge pollutant-laden, oxygen-depleted water into already stressed waterways. The consultant concluded that the Port's plans fell short of providing reasonable assurance that water quality standards would be met.

In a July 18, 2001 memo to Governor Gary Locke, Washington State Department of Ecology Director Tom Fitzsimmons provided an update on the permitting process for the Port of Seattle's proposed Third Runway at Sea-Tac Airport. The department was awaiting final technical data from the Port on stream low-flow mitigation, expected by July 23, 2001, before issuing a 401 Water Quality Certification decision. Provided the information was satisfactory, Ecology planned to render a final decision on the runway project during the week of August 6, 2001.

Water Resources Consulting LLC submitted technical comments in July 2001 on behalf of the Airport Communities Coalition, challenging the Port of Seattle's stormwater management plans for SeaTac Airport expansion. The document disputes Port claims about impervious surface increases, water diversions affecting Miller, Walker, and Des Moines creeks, and the effectiveness of bioswale filtration systems for removing pollutants such as metals from airport runoff.

This table from a July 2001 Comprehensive Stormwater Management Plan summarizes drainage area measurements and changes in impervious surfaces (such as pavement and rooftops) across Miller Creek, Walker Creek, and Des Moines Creek watersheds at Seattle-Tacoma International Airport (STIA). It compares 1994 baseline conditions to projected 2006 future conditions, showing a total increase of approximately 305.7 acres of impervious area across all drainage basins. The data was compiled from GIS coverage to support stormwater management planning for the airport's master plan update.

This section of Sea-Tac International Airport's Comprehensive Stormwater Management Plan outlines proposed Master Plan Update (MPU) improvements and their likely stormwater management requirements. It describes how land use changes — including increases in impervious surfaces across various airport development phases — were analyzed using GIS and hydrologic modeling to assess drainage impacts. The document also notes that projects such as the relocated Airport Surveillance Radar required specific flow controls to manage stormwater runoff on the west side acquisition area.

This document is Table A-3 from the Sea-Tac Airport Master Plan Update, outlining construction projects that require stormwater management. It details activities such as runway safety improvements, taxiway construction, terminal expansions, and embankment work, noting for each whether permanent stormwater detention was provided, the construction timeline, and the type of drainage facility used. Projects are categorized as either new or retrofit stormwater installations, with comments describing impervious surface impacts and drainage routing to temporary or permanent detention facilities.

This document describes the Integrated Water System (IWS) stormwater management configuration at Seattle-Tacoma International Airport (Sea-Tac), detailing storage lagoons totaling 76.9 million gallons and a treatment rate of 4.0 million gallons per day across approximately 435 acres. Simulations over a 50-year period confirmed zero overflow events under proposed conditions, with overflows only beginning to occur if treatment rates dropped below 3.1 million gallons per day. The system experienced only one historical overflow during an extreme rain-on-snow event in December 1996–January 1997, with no petroleum hydrocarbons detected downstream.