King County Sewerline Upgrade

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North Mercer - Enatai Sewer Upgrade Project

King County is upgrading four miles of sewer pipeline across north Mercer Island and south Bellevue. In addition to the new sewer pipeline, King County will upgrade the County’s North Mercer Pump Station, as well as the City of Mercer Island’s Lift Station 11 at Fruitland Landing. The pipes, installed in the 1970s, are aging and reaching capacity. They serve north Mercer Island, southwest Bellevue near Enatai Beach Park, and the town of Beaux Arts. (Click map for a larger version)

The sewer upgrade is a big project that’s been years in the making and will involve years of construction. We expect construction to begin in early 2022 and be complete in 2025. Some of the work will be in heavily used public spaces, and some will be in residential areas. The end product will provide great public benefit, but the work to get there will involve inconveniences to residents and users of public spaces. The City of Mercer Island and King County are committed to keeping you informed about what’s happening and why.

Get a visual look at the project by taking an interactive tour online.

To learn even more, visit King County’s website at www.kingcounty.gov/mercerenataisewer

North Mercer - Enatai Sewer Upgrade Project

King County is upgrading four miles of sewer pipeline across north Mercer Island and south Bellevue. In addition to the new sewer pipeline, King County will upgrade the County’s North Mercer Pump Station, as well as the City of Mercer Island’s Lift Station 11 at Fruitland Landing. The pipes, installed in the 1970s, are aging and reaching capacity. They serve north Mercer Island, southwest Bellevue near Enatai Beach Park, and the town of Beaux Arts. (Click map for a larger version)

The sewer upgrade is a big project that’s been years in the making and will involve years of construction. We expect construction to begin in early 2022 and be complete in 2025. Some of the work will be in heavily used public spaces, and some will be in residential areas. The end product will provide great public benefit, but the work to get there will involve inconveniences to residents and users of public spaces. The City of Mercer Island and King County are committed to keeping you informed about what’s happening and why.

Get a visual look at the project by taking an interactive tour online.

To learn even more, visit King County’s website at www.kingcounty.gov/mercerenataisewer

  • Enatai Siphon Pipe Installation Complete

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    The County's contractor finished installing the pipe between Enatai Beach Park and the Sweyolocken Pump Station ahead of schedule on December 19.

    What to expect for the remainder of the year:

    • At Enatai Beach Park: Crews will work during typical permitted hours (7:00am - 5:00pm) to temporarily restore and winterize the site.
    • At Sweyolocken Pump Station/Boat Launch: Crews will continue 24-hour work until the site is temporarily restored and winterized. The boat launch will remain closed until further notice.
    • At both sites, for the remainder of the year: the County expects minimal construction activities, vibrations, and noise. Crews will monitor and maintain both construction sites.


  • Enatai Siphon Pipe Installation Planned to Begin as Early as December 15

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    King County's contractor will begin the final process to install a new pipe under the Enatai Hillside between Enatai Beach Park and the Sweyolocken Pump Station as early as December 15. The first step will be to fuse and then float the fused pipe on Lake Washington. Then, crews will install the pipe around the clock until the pipe is installed. This work is anticipated to take approximately 10 days of continuous work to complete.

    The pipe will be in the East Channel of Lake Washington for about one week before the final installation. The pipe will not be anchored to the lakebed. Multiple workboats will orient the pipe and maintain a navigable channel 24 hours a day.

    Neighbors living on Lake Washington will see increased lights on the lake while the pipe is floating. Each workboat will have spotlights to illuminate the pipe and work areas to ensure safety. Boat captains will minimize pointing these spotlights toward shore. Neighbors may also notice increased noise at night coming from Enatai Beach Park once the pipe pull starts.


  • Construction Hotline is Transitioning to 425-305-3578

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    The County's project outreach team staffs a 24-hour construction hotline every day to answer any questions you may have about the North Mercer Island/Enatai Sewer Upgrade Project. They are switching to a new service that will allow you to get in touch with the team in new ways, including texting the project team.

    The new hotline number is 425-305-3578

    The County will continue to monitor the existing hotline (206-263-1915) through February 2023.

    For more information or to schedule a virtual meeting, contact the Community Relations Team using the 24-hour construction hotline or email the County at NMEsewer@kingcounty.gov.


  • Construction on Southeast 35th Place Beginning Next Week

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    King County is preparing to install a new sewer line that will run underneath streets, the I-90 Trail, and through the wooded area between 97th Ave SE and the cul-de-sac on SE 35th PL. In this cul-de-sac, the pipe changes from a gravity pipe to a siphon (a pipe that uses pressure to move wastewater flows). To support this transition, the County will build above and below-ground structures supporting future operations.

    Parking will be restricted in the cul-de-sac on SE 35th PL while County crews work in this area. Crews will partially close SE 35th PL between E Mercer Way and Frontage Road, however residents will still be able to access their homes. They will also build temporary access roads for construction machinery - the roads will connect to the western work area on 97th Avenue SE and the eastern staging area at the Mercer Island Boat Launch.

    Pedestrian and bike access to the Mercer Island Boat Launch will be closed during construction on SE 35th PL. The I-90 Trail will remain open to the south of SE 35th PL.

    Planned construction activities and schedule:

    Starting as early as Monday, October 31, the County's contractor will begin work by surveying the work area, removing and storing existing signage, and installing erosion control and tree protection.

    As early as Monday, November 7, crews will partially close SE 35th PL between E Mercer Way and Frontage Road (see map on reverse) and install the access road from the Boat Launch to the cul-de-sac at 35th PL SE. The partial closure on SE 35th PL will be used to lay down and store materials for the above and below-ground structures in the cul-de-sac. Then as work progresses, this will be the location of the new sewer pipe.

    Beginning in mid-November, crews will begin to excavate and install the above and below-ground structures in the cul-de-sac.

    The County has received requests for a neighborhood walk to help residents better understand construction and discuss potential impacts. They are working with the contractor to schedule a visit and will follow up with neighbors once a date and time have been selected.

    What to expect:

    • All work will be performed in the public right-of-way.
    • We will not access private property during this work unless we have a signed agreement.
    • Permitted work hours are 7 a.m. to 7 p.m. Monday to Friday and 9 a.m. to 6 p.m. on Saturday.
    • Work outside these hours will be done as approved by the City of Mercer Island.
    • Some homes may be subject to temporary daytime driveway access interruptions.
    • Access to residences should always be maintained during construction. If access is denied, please call the 24-hour hotline at 425-305-3578. We will speak with the on-site construction inspector and contractor and resolve the issue as quickly as possible.
    • Crews will lay metal plates over excavations to restore access as needed. It may take crews up to 15 minutes to set up a safe surface for you to cross.
    • There will be noise, dust, and vibrations typical of an active construction project.
    • Vibration monitors are onsite collecting data during construction to ensure that vibration levels do not exceed allowable limits set by the City of Mercer Island.
    • If vibration levels exceed the allowable limits, crews will temporarily stop work to address vibration levels as needed.
    • Emergency vehicle access will be maintained during construction.
    • Services such as garbage, recycling, composting, and mail will not be interrupted.

    Read about work on SE 35th PL by visiting the project website.

  • July 2022 Update

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    Construction and Activity Starting on 90th Place Southeast

    As early as August 1, King County crews will begin preparing 90th PL SE for construction as part of the North Mercer Island/Enatai Sewer Upgrade project. Construction will include parking revisions, temporary driveway impacts, and service interruptions for everyone who lives or travels on this street. See our email update for more information.

    Sewer Line Construction Begins in North-Central Mercer Island

    King County crews will install an upgraded sewer pipe on SE 22nd St, 78th Ave SE, and SE 24th in Mercer Island residential neighborhoods using an “open-cut” trenching construction technique. During open-cut construction, crews will saw cut the roadway’s surface, remove asphalt, and dig from the surface to the pipe depth. Expect increased noise, vibrations, and some driveway access interruptions on SE 22nd St, 78th Ave SE, and SE 24th.

    Meet the Project Team at the Mercer Island Farmers Market

    The County’s community relations team will set up a booth at the Mercer Island Farmers Market on the following dates: August 21 and Sept 18. Staff will share project updates, have informational materials, and answer your questions.

    Please Follow Detour and Closure Signage

    Construction crews have reported people ignoring posted closure and detour signage around active construction areas. While the coast may look clear, construction is complex - do not enter areas that are closed for your own safety, and follow detour signs to protect yourself and construction workers.

    Learn more about this project on the County's website and view the latest newsletter mailed to homes on the Island.

  • An Update on I-90 Trail Construction Work

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    Last week, King County shared plans to close the I-90 trail between Shorewood Drive and Southeast 35th Street as early as June 8. They are now planning to start the closure as early as June 17. Before the closure starts, crews will install a pedestrian detour and will maintain trail access during installation.

    Here's what to expect:

    Work to install new sewer pipes as part of the North Mercer / Enatai sewer upgrade project will impact everyone who lives near or travels on the I-90 trail. On Mercer Island, the County will close the I-90 trail in sections to complete the work. During each closure, crews will use a construction technique called “open-cut” trenching to bury the new pipe where it needs to go.

    The County expects to close the trail in this section around the clock for about six months until the trail has been restored.

    What to expect during trail closures:

    • The I-90 trail will close 24/7 between Shorewood Drive and SE 35th St, starting as early as June 17.
    • Permitted weekday work hours are from 7 a.m. to 7 p.m.
    • Please note that construction schedules often change due to weather, staffing, and other unforeseen things.
    • Bicycle and pedestrian traffic will detour off the I-90 trail (see maps on reverse).
    • The detour will merge bicycles and cars along North Mercer Way.
    • We will paint sharrows on the road to remind drivers to look for bicycles.
    • Pedestrians will be directed to use a separate path on the north side of North Mercer Way.
    • Speed limits on North Mercer Way will reduce to 20 MPH near the construction area.
    • Trenches for open-cut construction will be covered with steel plates at the end of each workday.
  • Construction Work on the I-90 Trail Will Begin as Early as June 8

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    King County will close the I-90 trail corridor between Shorewood Drive and Southeast 35th Street as part of the North Mercer Sewer Upgrade Project. This is the first section of the I-90 trail that will close for construction. Work will impact those who live near or travel on the trail. Learn more on the County's website.

  • Surveying Continues, Utility Locates Beginning in May

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    Expect increased noise and vibration in neighborhoods, public parks, and along the I-90 trail.

    Starting as early as May 16, crews will locate utilities in north Mercer Island and Bellevue to prepare for major construction activities beginning later this Spring. Surveying and utility location will take place in neighborhoods, public parks, and along the I-90 trail. Most work will take place in the public right of way. King County will notify property owners ahead of any work on private property.

    Utility location helps crews avoid service disruptions during construction work. To locate utilities, crews will use a jackhammer break-up pavement. Next, they use a vacuum excavation truck to remove dirt and locate buried utilities. Once the utilities have been located and documented, the roadway will be restored with asphalt.

    What to expect while crews are locating utilities:

    • Permitted hours are 7 a.m. to 7 p.m. Monday to Friday and 9 a.m. to 6 p.m. on Saturday.
    • The County will provide advance notice of any weekend or after-hours work.
    • Utility location is expected to take approximately one month to complete.
    • Please note, construction schedules often change due to weather, staffing, and other unforeseen things.
    • Flaggers will direct vehicle, pedestrian, and bicycle traffic around the work site, as necessary.
    • Expect intermittent loud noise during jackhammering and saw cutting.
    • Expect increased continuous noise while the vacuum truck is in use.

    King County will share additional information about impacts and schedule via the location-specific email lists, as needed. Learn how to sign up for targeted construction notifications here.

    For your safety, and the safety of our crews, please drive slowly and obey signs near active work areas.

  • April 2022 Update

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    Construction is starting across north Mercer Island and southwest Bellevue. This project has been years in the making and will involve four years of construction - project work will be in heavily-used public spaces and residential areas. Check out King County's latest storymap below to learn about:

    • What is being built
    • What to expect
    • Schedule and duration
    • Detour routes
    • What it will look like when the project is done
    • How to reach King County about this project
  • March 2022 Update

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    Construction will begin this spring to upgrade four miles of sewer pipeline across north Mercer Island and southwest Bellevue. In addition to the new sewer pipeline, King County will upgrade the County’s North Mercer Pump Station and the City of Mercer Island’s Lift Station 11 at Fruitland Landing. The pipes, installed in the 1970s, are aging and reaching capacity. The sewer upgrade is a big project that will involve years of construction.

    Before major construction starts, the crews will be surveying, setting up construction trailers, and preparing work areas for active construction. King County is committed to being a good neighbor and keeping you informed about what is happening to minimize impacts whenever possible - the City of Mercer Island will share their updates here on Let's Talk.

    You can learn more by reading King County's latest newsletter on the project's website.

    If you’d like to receive email or text updates, you can easily sign up online.

Page last updated: 27 Dec 2022, 10:59 AM