TagStormwater(385)

A August 6, 2001 letter from Water Resources Consulting L.L.C. on behalf of the Airport Communities Coalition critiques the Port of Seattle's 'Low Flow Analysis - Flow Impact Offset Facility Proposal' submitted in support of its Section 404/401 permit application for SeaTac Airport expansion. The letter argues that the Port's plan fails to provide reasonable assurance that the airport's stormwater management will meet water quality standards in Miller Creek, Walker Creek, and Des Moines Creek. Key concerns include an incomplete and unfinished proposal, insufficient stormwater storage capacity, unproven water quality treatment methods, and reliance on vague future 'adaptive management' rather than concrete, enforceable designs.

This August 2001 draft document outlines Water Quality Certification conditions (#1996-4-02325) governing stormwater management at Seattle-Tacoma International Airport (Sea-Tac). It sets requirements for the Port of Seattle to implement and maintain a Comprehensive Stormwater Management Plan, including retrofitting existing impervious surfaces, meeting state water quality standards, and obtaining Ecology approval before discharging stormwater to receiving waters. The document also addresses scheduling, flow control benchmarks, and the use of all known available and reasonable treatment methods (AKART) for runoff from impervious surfaces.

Letter dated August 3, 2001 from Pam Bissonnette, Director of King County Department of Natural Resources, to Ann Kenny, Senior Permit Specialist at Washington Department of Ecology Northwest Regional Office, conveying King County’s technical review findings on the Port Of Seattle’s Comprehensive Stormwater Management Plan (SMP) for Master Plan Update (MPU) Improvements at Seattle-Tacoma International

In August 2001, King County's Department of Natural Resources submitted a technical review letter to the Washington Department of Ecology evaluating the Port of Seattle's Low Flow Impact Analysis and proposed offset facilities for stormwater management near Sea-Tac Airport. The review found the proposal goes well beyond the basic requirements of the King County Surface Water Design Manual and represents substantial mitigation for low flow impacts in affected drainage basins, including Miller and Walker Creeks. Reviewers noted several inconsistencies and data gaps in the documentation and recommended that a final consolidated document be prepared incorporating all corrections and technical memoranda.

This August 2001 draft document outlines Water Quality Certification conditions for Sea-Tac International Airport (STIA), requiring the Port of Seattle to implement a Comprehensive Stormwater Management Plan covering treatment, flow control, and retrofitting of stormwater facilities. Key requirements include obtaining Ecology approval before discharging operational stormwater to state waters, conducting a Water Effects Ratio Study, and ensuring all runoff from impervious surfaces is treated using all known available and reasonable treatment methods. The Port must also retrofit existing stormwater facilities at a rate proportional to new impervious surface construction, with progress documented in quarterly reports.

In August 2001, King County's Department of Natural Resources wrote to the Washington Department of Ecology confirming that the Port of Seattle's Comprehensive Stormwater Management Plan for Sea-Tac International Airport Master Plan improvements met the technical requirements of the 1998 King County Surface Water Design Manual. The review found that the plan demonstrated a feasible conceptual strategy for managing stormwater from proposed airport construction projects. Reviewers noted that while the plan showed compliance with design standards, additional oversight and monitoring would be needed as individual projects moved from planning into construction.

Letter dated August 3, 2001 from King County Department of Natural Resources Director Pam Bissonnette to Ann Kenny, Senior Permit Specialist, Washington Department of Ecology Northwest Regional Office, transmitting King County’s technical review comments on the Port Of Seattle’s Low Flow Impact Analysis – Low Flow Impact Offset Facility Proposal (July 2001). The enclosure provides

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.

Exhibit AR032547 from Washington State Department of Ecology (Ecology), Volume V – Runoff Treatment BMPs, August 2001. Covers phosphorus removal treatment trains (Table 3.1), Enhanced Treatment Menu (Section 3.4) and Basic Treatment Menu (Section 3.5) for stormwater management. Specifies requirements for industrial, commercial, multi-family project sites, arterials and highways discharging to fish-bearing streams or lakes.