Mill Creek stormwater pond retrofit project

Project overview

King County is making improvements to a stormwater pond near Mill Creek, at S 298th St and 33rd Ave S in south King County, to enhance water quality and reduce pollutants in the wetland that flows to Mill Creek. Improvements to the stormwater pond, built in the 1970s, are critical because most of the stormwater from the neighborhood is running directly into the adjacent wetland.

Improvements will redirect pipes into the stormwater pond which allows pollutants time to settle to the bottom of the pond that are removed by King County maintenance crews. Establishing new native plants and trees in the stormwater pond also helps to filter out pollutants.

The improvements will reduce the flow of stormwater to the wetland during high rainstorms. The community can expect to see standing water in the stormwater pond on a permanent basis.

The project is expected to be constructed during the summer of 2026.

Project goals and benefits

• Improve function of the pond by directing stormwater into the pond.
• Increase the size of the pond.
• Improve water quality treatment.
• Reduce pollutants discharging into the wetland that flows to Mill Creek.

Project schedule

Design and permitting: 2023-2025

Potential grant funding: Summer 2025

Final Design: Fall 2025

Construction: Late Summer 2026

Construction impacts

King County is working to limit the impacts of the construction. Increased truck traffic and noise from construction equipment will occur during work hours. A one lane road closure along S 298th St and 33rd Ave S adjacent to the pond will be necessary during construction. This webpage will be updated through the design, permitting, and construction to provide additional information as it becomes available.

These are changes you can expect to see following construction:

• A deeper pond that is wet year-round
• Changing water levels of up to 2 feet during the rainy season
• Removal of the cedar tree and weeds
• New native wetland vegetation, shrubs, and trees planted in and around the pond
• King County staff on site to monitor and maintain the new vegetation to ensure survival

Project funding

Design work has been funded by:

• Surface Water Management Fees
• Washington State Department of Ecology – Stormwater Grant Program

Language assistance

English

Interpretation and translation services are available to you at no cost. If you need them, please contact us at moshoemaker@kingcounty.gov or 206-263-0697.

Español

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Русский

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