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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

Black Diamond is one of the fastest-growing communities in the Puget Sound region. In 1992, in collaboration with King County, the City built a regional sewer line to serve the area’s much smaller population at the time. Today, we need to upgrade the existing sewer line because it’s reaching capacity. Upgrading the sewer line may include a combination of repairing the existing pipe and installing new pipes

The project will look at options to upgrade 6 miles of sewer pipe in Black Diamond. The option we select will:

  • Serve the community’s wastewater capacity needs through 2070
  • Ensure reliable wastewater service to Black Diamond's homes and businesses
  • Foster a healthy and resilient community with reliable wastewater infrastructure

Project update

August 2025

Your voice matters: Share your thoughts on the Black Diamond Sewer Upgrade Project

We're doing an online survey for people who live in Black Diamond, Covington, Kent, Maple Valley, and unincorporated King County.

The survey will share information about the project. It will also ask for your thoughts on construction impacts, what matters most to the community, and how you like to get updates.

Your feedback will help us plan for construction and keep you informed in the ways that work best for you.

Take our survey!

Find us at a local community event this summer!

The Black Diamond Sewer Upgrade Project team has been actively raising awareness of the project and gathering input from local residents by attending community events and conducting briefings with nearby schools. This summer, we are planning to be back in the community and participating in several community events:

  • Maple Valley Farmers Market on August 23
  • Black Diamond Labor Days on August 31 and September 1

Stop by our booth to learn about the project and ask questions. You can also learn more about the project and share your concerns and priorities with members of the outreach team.

See you there!

A King County representative is sitting behind a table with a green table covering with the King County Logo and "Department of Natural Resources and Parks, Wastewater Treatment Division" underneath. On the table are brochures and communication materials about the Black Diamond Sewer Upgrade project.

Project location

Understanding site conditions and community needs

Our team is in the early stages of design for the project. During the design phase, the project team will:

  • Survey the project area to understand existing conditions in Black Diamond
  • Conduct geotechnical surveys to understand underground conditions
  • Inform community members about the project and upcoming survey work
  • Analyze design alternatives and identify a preferred option to upgrade the sewer
  • Complete 30% design for the project

View fact sheet to learn more.

Working with the community

We’ll share details about specific engagement opportunities as the project progresses

We’re committed to engaging with the community during each stage of the project, and we want to make sure everyone has access to information. We welcome you to take part in the project in the following ways:

  • Contact us to have a one-on-one conversation by phone, video chat, email, or in person. 
  • Invite us to a meeting hosted by your group or organization. 
  • Join our team remotely or in person at future meetings at project milestones. We will post these meetings on our website and email list once they are scheduled.  

Interpretation and translation services are available to you at no cost. If you need them, please contact Annie Plumley, aplumley@kingcounty.gov, 206-263-3203

Los servicios de interpretación y traducción están disponibles para usted sin costo alguno. Si los necesita, comuníquese con Annie Plumley, aplumley@kingcounty.gov, 206-263-3203

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