Skip to main content
King County logo

Project update

September 23, 2022

*Please note that construction schedules often change due to weather, staffing, and other unforeseen things. Dates on email notices may differ from the dates posted on the web. The dates below will be updated weekly based on updates given by our contractor.

Construction activity in Mercer Island*

Construction equipment and material storage coming to South Parking Lot in Luther Burbank Park. The back half of the South Parking Lot will be closed for parking starting Thursday, October 6th. See notification for details and what to expect .

At the North Mercer Pump Station: Crews will begin building a temporary retaining wall at the North Mercer Pump Station as early as October 4th. Before the temporary wall is constructed crews will grade and level the western edge of the pump station property. They will also relocate some utilities. See notification for details and what to expect .

In north-central Mercer Island: Crews are installing an upgraded sewer pipe using an “open-cut” trenching construction technique. Crews will work west-to-east from SE 22nd St to 78th Ave SE and then to SE 24th St. See notification for details and what to expect .

On 90th PL SE: Water and sewer line relocation is underway. For this work to occur, the cul-de-sac at 90th PL SE is closed while crews excavate and relocate utilities. Crews will restore the right-of-way once work is complete. See notification for details and what to expect .

On the I-90 Trail: Crews are installing pipe using an “open cut” trenching construction technique. The trail is closed from Shorewood Dr to SE 35th PL. The trail will remain closed around the clock until it has been repaved. See notification for detours and what to expect .

Construction activity in Bellevue*

At Enatai Beach Park: Crews are preparing for Enatai Siphon construction. Crews are staging materials, fusing pipe, and preparing for Horizontal Directional Drilling (HDD) behind a temporary fence underneath the I-90 bridge. See notification for details and what to expect .

At the Sweyolocken Boat Launch: Crews continue to drill a new sewer pileline under the Enatai hillside. See notification about additional noise and vibration . Additionally, to make space for construction crews and activities, the access road from Bellevue Way SE to the Sweyolocken Boat Launch is closed. The area south of the pump station is closed as well. See notification for detours and what to expect .

Recent notifications:

Sign up for email and text updates 

Sign up for general project updates in two geographic areas:

North Mercer Island project area

Enatai project area

Click on a project area number to learn more and sign up to receive email or text updates.

Project areas: 1 | 2 | 3 | 4 | 5| 6 | 7 | 8

The construction route has been divided into 8 areas. You can sign up to receive updates for one or all of these areas.

View Construction Reference Guide.

Project description

With over four hundred miles of pipes moving wastewater to one of our award-winning treatment plants, King County WTD works hard to maintain our system. We inspect and monitor our regional system and update plans for needed upgrades.

King County WTD needs to replace sewer pipes that serve areas in North Mercer Island, the southwest portion of Bellevue near Enatai Beach, and the Town of Beaux Arts Village. This pipeline carries wastewater from the North Mercer Island Pump Station to the Sweyolocken Pump Station in Bellevue.

To learn more about what we are building, construction, and what to expect, click on the StoryMap below.

Aerial view of Lake Washington. Click Storymap: learn more about the North Mercer/Enatai Sewer Upgrade Project.


Project design began in 2016 and was completed in 2021. Construction began in early 2022 and will extend until 2025. View March 2022 project newsletter for latest schedule .


Contact us

Contact Kristine Cramer, community services lead at:

24-hour construction hotline: 206-263-1915

Project location

The project area spans from the North Mercer Pump Station to the Sweyolocken Pump Station (Mercer Slough)

Back to the capital projects overview map .

Lets Talk Mercer Island!

The City of Mercer Island and King County are collaborating to ensure Mercer Island residents get timely, accurate construction information. In addition to the County’s website, Let’s Talk Mercer Island will feature the project with monthly updates and will monitor for resident questions and comments. 

Related information

System planning

Local municipalities: