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Black Diamond sewer upgrade
The Black Diamond Sewer Upgrade Project will increase capacity for 6 miles of regional sewer pipe in Black Diamond. The project will help us treat more wastewater to meet the needs of the growing Black Diamond community.
Project update
Fall 2026
Temporary lane closures to start in Black Diamond as early as Nov. 2
Temporary lane closures will allow crews to safely check soil conditions and underground utilities. Crews will work between SE Covington Sawyer Road and SE Sawyer Ridge Way / SE 312th Street. Expect delays when you walk, bike, or drive on these roads.
- 216th Avenue SE
- SE 296th Street
- 224th Avenue SE
- 228th Avenue SE
What the crew will do
Crews will dig small holes in or next to the road. Each hole will be about 12 inches wide. They will collect soil and utility data. When they finish in each spot, they will fill the hole and re-open the traffic lane and sidewalk.
What to expect
- Work hours are between 7:30 a.m. and 4 p.m.
- Temporary lane closures will begin as early as November 2.
- Flaggers will help people walk, bike, and drive around the closures.
- We will maintain access for emergency and service vehicles.
- There will be increased noise and vibrations while machines dig holes.
For more information, please read our latest project email update.
Stay up to date
Sign up for project updates (email) to get the latest news and event information.
Interested in a project briefing for your community group?
We can meet with you to share updates and answer questions. Contact Annie Plumley at 206-263-3203 or BDSewerUpgrade@kingcounty.gov for more information.
Previous project updates
- Our team is growing: We’ve hired a builder to help us with construction, May 2026
- Septic or sewer: Your questions matter. Updated April dates for library chats., March 2026
- Come see how WTD’s Sewer Superheroes keep pipes clean and flowing!, February 2026
- 6 miles of sewer upgrades: What we heard and what’s next, January 2025
- Lane closure on 224th Ave SE planned for December 11 and 12, December 2025
- Your voice matters: Share your thoughts on the Black Diamond Sewer Upgrade Project, July 2025
- Wetland sampling along the regional sewer pipeline planned for April 10 through April 15, April 9, 2025
- Traffic control and lane shifts along King County pipeline planned for February 19, February 14, 2025
- Exploratory surveys for an upcoming King County project starting in your area, August 2024
Project description
Upgrading the sewer pipe to meet Black Diamond's growth
The City of Black Diamond built the Black Diamond Trunk sewer pipe in 1992 with help from King County. Now the pipe is almost full. King County plans to upgrade it to serve the growing community.
We may repair the pipe, expand it, or add new pipes. The Black Diamond Trunk Sewer carries wastewater from the City of Black Diamond. The pipe runs north of the city between Black Diamond and Covington.