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Project update

March 5, 2019

Survey work in the Coal Creek Natural Area beginning March 11 

Surveyors will be working in the Coal Creek Natural Area beginning March 11 to collect additional information for King County’s Coal Creek Sewer Upgrade Project. As project design continues, some additional field work will be needed to inform design. We will let you know when field work is scheduled. View Project Update .

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.

Online version of the January 2019 project newsletter providing an overview of the project. View online version of January 2019 project newsletter to learn more about the project.


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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