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Project update

October 28, 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 regularly based on updates given by our contractor.

Construction activity in Mercer Island*

At the North Mercer Pump Station: Crews have made progress relocating utilities over the past few weeks. They will begin building a temporary retaining wall and pump station. Some of this work is planned to occur during approved weekend hours on Saturday, November 5. See the notification for details and what to expect .

In north-central Mercer Island: While crews work in the right-of-way, temporary signals or driveway assist devices move traffic through the work area safely. See the notification for details and what to expect .

On 90th PL SE: Construction on 90th Place Southeast began in July 2022. Crews have recently finished moving a City of Mercer Island waterline. While they wait for final permits to connect it, they have begun installing the new sewer line. See the 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 remail remain closed around the clock until it has been repaved. Additionally, you may see crews in orange vests preparing for landscape restoration and tree replanting. See the notification for detours and what to expect .

On Southeast 35th Place: Crews are preparing to install a new sewer line that will run underneath streets and through the wooded area between 97th Ave SE and the cul-de-sac on SE 35th Pl. To support future operations, below-ground structures will be built in the cul-de-sac. Parking will be restricted with resident access maintained. See the notification for details 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:

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North Mercer Island project area

Enatai project area

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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:

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: