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Project update

April 2021

King County’s Coal Creek Sewer Upgrade Project is in final design. The project team is continuing to collect information in the field to inform design. Beginning April 14, crews will be working within the Natural Area to conduct landscape surveys.

Watch for updates as we continue working on this critical clean water project!

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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.


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.

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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