Excavating the roadway
As early as March 23, crews will begin work on the 96th Avenue siphon, a sewer pipe that runs under I-90. King County is upgrading this pipe to help sewage flow more efficiently through the system. This work is part of a larger infrastructure project to improve sewer service in your area.
Crews will access the underground pipe at two locations: the intersection of 96th Avenue Southeast and Southeast 35th Street, and on Southeast 36th Street in front of Mercer Island City Hall. They will excavate around the existing maintenance holes to reach the pipe. Crews will use a construction method called open-cut trenching. During open-cut construction, crews sawcut the roadway’s surface, remove asphalt, and dig down to the pipe. Equipment on site will include an excavator, crane and saw cutting tools. This work is a key step in connecting the newly installed sewer pipe under I90 to the rest of the system. You may hear increased noise and experience vibrations during excavation.
96th Ave SE and SE 36th St work and impacts
Work will begin with excavation and installation of a sewer bypass at 96th Ave SE and SE 36th St in front of Mercer Island City Hall. After the bypass is in place, crews will begin upgrades to the 96th Avenue siphon working from north side of SE 36th Street to the south side. This pipe work is expected to take about four months to complete.
For the first few weeks, crews will cover the trench with metal plates and restore two-way traffic outside of work hours. After that, the area will shift to 24-hour single lane alternating traffic for the remainder of the work where crews will install new pipe segments. Driveway access for near neighbors will be maintained at all times.
Please travel slowly through the area and follow all posted signs and crew directions.
 Map of work area at 96th Ave SE and SE 36th St. Single lane alternating traffic will be in place on SE 36th St. Please drive slowly and pay attention to signage and flaggers.
Work and impacts on SE 35th St and 96th Ave SE
Work will begin with excavation to prepare for pipe relining. After excavation, crews will install the pipe casing. During this work, the intersection of SE 35th St and 96th Ave SE will operate with single lane alternating traffic directed by flaggers around. Crews will cover the trench with metal plates and restore two-way traffic outside of work hours. This work is expected to take approximately three months to complete.
Drivers may experience short delays when driving through the intersection.
Driveway access for near neighbors will be maintained at all times. Please travel
slowly through the area and follow all
posted signsand crew directions.
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Map of work area at SE 35th St and 96th Ave SE. Single lane alternating traffic will be in place on SE 35th St and 96th Ave SE. Please drive slowly and pay attention to signage and flaggers.
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Connecting sewer lines
This work is a critical step in connecting the new sewer system. Crews will first open the top of a steel pipe to reach the sewer line inside, remove the old pipe, and pull new pipe sections into place using a cable system. Each section will be secured until the full pipe is installed.
Plans for final restoration
When this work is complete, crews will backfill the roadway and temporarily restore the roadway surface where the pipe was repaired. Then, crews will restore all disturbed areas based on permit conditions agreed upon with the City of Mercer Island.
If you have access concerns, please contact the Community Services team at 425-305-3578 or NMEsewer@kingcounty.gov.
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