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Project update

May 19, 2022

Check out our latest newsletter!

Our February newsletter provided updates on construction and staging areas for the Coal Creek Sewer Upgrade project. If you did not receive the newsletter in the mail, you can find it in the link below. Translated versions are also available.

King County’s project team is finishing design and applying for permits in spring 2022. Once plans and the County’s permits are finalized, the construction contract will be prepared and advertised for bidding. Construction is expected to start in mid-to-late 2023. This project schedule may change, so watch for updates.

thumbnail of the spring newsletterRead the newsletter for more information.

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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.


Project timeline

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.

Project Elements

This map shows the project work areas and the construction methods King County’s contractor will use in each area. The contractor will install about 10,800 feet of pipe to build the new Coal Creek Trunk Sewer and re-establish connections to the City of Bellevue’s sewer collection system.

King County’s designers work to reduce community impacts and inconveniences where possible. But on large projects like this one, inconveniences are unavoidable. People can expect up to 3-years closure at the Red Cedar trailhead, with a trail detour around the construction site. There will be traffic impacts during work close to the Parkway.

Keep up to date to make sure you have the latest news and information as final design continues.

map of project areaCoal Creek Sewer Upgrade Project Area

Design Phase

Contact us

Contact Monica Van der Vieren at:


If you’d like to receive email or text updates on the Coal Creek sewer upgrade project:

If you are just learning about the Coal Creek project, you can visit online resources to learn more:

Storymap: Coal Creek Sewer UpgradeIntroduction to King County’s regional wastewater service and the history in Bellevue, along with early design.

Photo of exposed maintenance hole cover and riser near Coal Creek. This is an introductory title slide for an open house presentation.Recent updates on project design.

A river with surrounding forest, with a title overlaying the photo: "Welcoming people of all abilities. Options for improving accessibility at the Coal Creek Natural Area"Red Cedar Trailhead Restoration Options - StoryMap and Tour

Project location

project location mapProject location and service area

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