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King County Washington home

Sammamish Plateau Diversion

The Sammamish Plateau Diversion Project will build new wastewater infrastructure to serve the growing East Lake Sammamish area.

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Project description

The project includes new underground pipes in the East Lake Sammamish area and upgrades to the York Pump Station near Redmond.

This project will help WTD to expand its services and meet future wastewater needs.

Project update

This section includes project updates. For more details about these updates, read our latest project email. Sign up for our listserv to stay up to date.

June 10, 2026

Survey work continues in the project corridor

Project crews will continue collecting survey data along East Lake Sammamish Parkway NE and on NE Inglewood Hill Road. This information will help inform the pipe location within the corridor and construction methods. To learn more about the project corridor, visit the project’s Online Open House and click on the “Project Corridor” tab.

Saturday survey work

When: Morning of Saturday, June 13

Where: East Lake Sammamish Parkway between NE 28th Place and NE 18th Place

What to expect:

  • Work hours are from 6 to 9 a.m.
  • Temporary single-lane closures
  • Traffic signs, flaggers, and a truck with flashing lights
  • Minor delays
  • People on bikes will need to merge with traffic.

A satellite image of East Lake Sammamish Parkway Northeast with a yellow box including Northeast 28th Place down to Northeast 18th place with an approximate survey area callout box

Marking utilities along East Lake Sammamish Parkway Northeast

Crews are working in the shoulder, which does not affect traffic. Work is taking place Monday through Friday, between 7 a.m. and 3:30 p.m.

Please watch for survey crews and use caution when driving or biking in the area.

Surveying trees

Crews will be surveying and assessing larger trees along the project corridor. You may see numbered tags on some trees. These tags assist with tree assessments and do not indicate future impacts. If any trees may be affected by the project, the project team will work with the appropriate public or private property owners. Tree survey activities will not affect traffic.

We’ve added community questions to our website!

Over the course of this project, we’ve heard from community members about your questions, concerns, and what’s important to you in this area. We’re documenting and tracking what we’re hearing and learning with the project team.

As we compile community questions, we’re adding some of them to a new Community Questions webpage on our project website. We will update this webpage throughout the project.

Check out the new Community Questions webpage here!

Thank you for visiting us at Bike Everywhere Day on May 13!

Our project team hosted a station as a part of Cascade Bicycle Club’s Bike Everywhere Day event on Wednesday, May 13. We enjoyed speaking with you and hearing your feedback! We’ll be out at more events this summer and fall. Stay tuned as we share more details in future updates!

Cyclists stop at a King County Wastewater Treatment information booth under a canopy on a rainy day along a paved trail

A King County WTD representative discusses the project with two community members at Bike Everywhere Day, 2026.

Previous project updates

Project timeline

2023-2025 2026-2031 2031-2035
Pre-design Design Construction

Project schedules may change due to a number of factors. We will provide updates on our progress and schedule throughout the project.

Project location