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This survey is about the accessibility of our products, programs, services, and spaces. Please complete the survey by September 30, 2026: here. WTD will use the information shared with us to help identify and prioritize steps to make our system more accessible for all people.
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
Summer/Fall 2026
Project design is moving forward.
In spring 2026, we hired Merlino-Goodfellow Joint Venture (Merlino-Goodfellow) to help us build the project. Now that we have our designers and builders on one team, we are moving the design forward.
We will share more information about the project team's recommendation for upgrading the pipe before the end of 2026.
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
- 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.