Skip to main content

About the Coal Creek Sewer Upgrade Project

Get information about the Coal Creek Sewer Upgrade Project schedule and design elements, including efforts to protect the Coal Creek Natural Area.

Project schedule

project timeline (2018-2028). Construction is anticipated to be late 2023 to early 2028.

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 at least 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 the Coal Creek project area.

Coal Creek Sewer Upgrade Project Area

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