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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
May 2026
Our team is growing: We've hired a builder to help us with construction
King County has hired Merlino-Goodfellow Joint Venture (MGJV) to help build the sewer upgrade project. Construction is still a few years away. Until then, MGJV will help us plan for construction and shape the design.
Read our latest email update for more information.
Leer este correo electrónico en Español.
Where should we meet next? Share your ideas!
Thanks to everyone that talked with us from March to May at our Library Chats. We want to keep meeting with you in person as design continues. If you have ideas for places or events we should visit, send them to our project email. Our Community Services team will do our best to meet you where you are.
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
- 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.