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Wastewater Treatment Division (WTD) operations and projects

WTD operations staff remain on the job 24/7 to ensure the region’s wastewater treatment service continues. More information on how to report a problem you believe may be related to the County’s wastewater treatment system is available here:

The King County Wastewater Treatment Division remains committed to sharing information and gathering feedback from community members about its work and projects. WTD staff remain available to answer questions via email and phone during regular business hours. Project information lines remain available and are being monitored for ongoing construction projects.

Project update

May 15, 2020

King County's contractor is completing utility location work this week. On Friday, May 15, crews will complete a location in the sidewalk area by the Upper West Trailhead. They will patch the area and leave a small bridge over it to maintain pedestrian use while it cures over the weekend. View project update .

Starting as early as May 15, crews will close one lane of traffic along Coal Creek Parkway near the Upper West trailhead to verify the location of utilities in the sidewalk using small vacuum excavations.

Design update

King County's Coal Creek Sewer Upgrade Project is in final design. In this phase the team refines the project design, conducts environmental review, and acquires permits and property rights.

We will continue to keep the community up to date, answer questions, hear your input, and address concerns. The Coal Creek team is committed to continuing outreach during the next few months. We will be reaching out to the community to find the best way to keep in touch with you!

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Questions? Concerns? Contact us!

If you would like to discuss the project, ask questions, give input, or share concerns, call Monica Van der Vieren at 206-477-5502 or email:

Project description

King County Wastewater Treatment Division (WTD) will upgrade a regional sewer line that serves Bellevue and Newcastle. The existing pipeline was built between 1966 and 1991 in an area that looked different from today, with a smaller population. The pipeline is nearing its maximum capacity and needs to be upgraded to carry more wastewater and meet the growing needs of your community.

Once installed, the new sewer pipe is designed to serve your community for another 50 years or more.


Timeline for the Coal Creek Sewer Upgrade Project

Protecting the Coal Creek Natural Area

The existing Coal Creek Trunk is approximately 2.5 miles long and primarily follows the banks of Coal Creek in the Coal Creek Natural Area between Newcastle and I-405. The new pipeline alignment will move the active pipeline away from Coal Creek offering better protection to this sensitive environmental area.

The selected pipeline alignment also aims to decrease impacts to both the Natural Area and Coal Creek Parkway SE during construction.

Next steps

The project is in early design phase. Design is expected to be complete in 2022, with construction beginning in 2022. King County will work closely with area neighbors, property owners, community groups, and the Cities of Bellevue and Newscastle to plan for project activities and answer questions or concerns.

Design Phase

Contact us

Contact Monica Van der Vieren at:


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If you are new to the project, you can get up to speed by visiting this Story Map, which covers the project background and early design.

Storymap: Coal Creek Sewer Upgrade

Project location

1711_project-location_600Project location and service area

project area mapProject area map

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