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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 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.

Project update

February 2026

Learn how WTD’s Sewer Superheroes keep pipes clean and flowing!

Join the Black Diamond Sewer Upgrade team at the City of Covington’s Superhero Social on March 7! At the social, you can:

  • Meet the project team
  • Learn about our sewer project
  • Meet our “Sewer Superheroes” who serve King County every day

Our “Sewer Superheroes” will bring our new sewer cleaning truck to the event.

Read the full project notice (web version). It has more information about the event.

For more information and event registration, please visit City of Covington’s website.

Black Diamond Sewer Upgrade - Library Chats

If you cannot come to the event, our Community Services team can still help you.

Starting in March our Community Services team will be at the Covington and Black Diamond libraries twice a month. Visit us to ask questions and learn more about the project.

Dates and times below:

March 2026

  • Friday, March 13
    • Location: Covington Library
    • Time: 11 am – 3 pm
  • Friday, March 20
    • Location: Black Diamond Library
    • Time: 10 am – 2 pm

April 2026

  • Monday, April 13
    • Location: Covington Library
    • Time: 3 – 6 pm
  • Saturday, April 11
  • Location: Black Diamond Library
  • Time: 12 – 4 pm

May 2026

  • Saturday, May 9
    • Location: Covington Library
    • Time: 11 am – 3 pm
  • Tuesday, May 12
    • Location: Black Diamond Library
    • Time: 4 – 7 pm

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.

Project location