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Project update

January 3, 2020 - New year, new phase: the Coal Creek Upgrade project enters final design

King County's Coal Creek Sewer Upgrade Project is entering final design phase. The team will refine the project design, conduct environmental review, and acquire permits. Watch for a January newsletter and opportunities throughout the year to learn about the project, provide input, and meet the team.

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

Please let us know how we can welcome you. Contact Monica Van der Vieren at or 206-477-5502.

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.

Next steps

The project is in early design phase. Design is expected to be complete in 2020,  with construction beginning in 2021. 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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Project location

1711_project-location_600Project location and service area

project area mapProject area map

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