Mercer Slough Nature Park - two pipe projects
Construction on a new pipe is underway. Relining of an old pipe will take place closer to the end of the bigger project.
This StoryMap focuses on the Mercer Slough and Sweyolocken Boat Launch. To learn more about the Mercer Enatai Sewer Upgrade project as a whole, visit the project website .
The blue line on the map shows the new sewer pipeline. King County is also upgrading the North Mercer Pump Station and the City of Mercer Island's Lift Station 11.
Bellevue’s popular Mercer Slough Nature Park centers on the Mercer Slough, which flows under I-90 east of the Enatai neighborhood into Lake Washington.
Looking south where Mercer Slough flows into lake Washington
What are we building?
This project has two parts: a new pipe and the relining of an old pipe.
These two efforts will impact bikers, pedestrians and park users as they travel through and visit:
- The lower end of the slough
- Nearby bike trails
- Sweyolocken Boat Launch
Pipe installation
We will install a new sewer pipe underneath the Enatai hillside between the Sweyolocken Pump Station and Enatai Beach Park.
We are building this pipe to increase the amount of sewage we can carry as the population grows.
Park users will see construction activity at both ends of this pipe - in Enatai Beach Park and at the entrance to the Sweyolocken Boat Launch. Residents and passersby on the hill above the sewer line will not be impacted by construction.
Pipe relining
After we have installed the new pipe under the Enatai hill, we will put a new lining in the existing pipe. This pipe extends east from Enatai Beach Park along the bottom of Lake Washington to the mouth of the Mercer Slough, where it then continues north to the Sweyolocken Pump Station.
Pipe relining allows crews to repair damaged pipes without digging them up. Essentially it creates a new pipe inside the old one, extending the old pipe's life by fifty years or more.
To line the pipe, crews divert wastewater from the pipe and then clean the pipe. Once the pipe is clean, they put a deflated pipe liner into one end of the pipe and pull it through to the other end. Next, they inflate the plastic liner so it fills the pipe. Finally, they use a UV light-curing train to create a chemical reaction that causes the liner to become rigid and impermeable.
What to expect
Construction for the Enatai hillside pipe installation will affect the Sweyolocken boat launch, Enatai Beach Park, and the Mercer Slough trail. This work will begin is underway.
We will be back toward the end of the project, to complete the pipe relining. This will be less impactful and quicker to build but will affect the same areas and the shoreline of Lake Washington and the Mercer Slough.
Impacts during pipe installation under the Enatai hillside
Several trees near the Sweyolocken Boat Launch will be removed to make room for a staging area to store equipment.
Boat launch impacts during pipe installation
The Sweyolocken boat launch will be closed to vehicle, foot and boat traffic for the duration of the pipe installation work.
The access road, which is south of the Sweyolocken Pump Station, will be also closed during construction.
The road to the south of the Swyeolocken Pump Station will be closed during pipe installation
Trail impacts during pipe installation
The Mercer Slough Nature Trail, which connects the I-90 Trail with Bellevue and points north, will be closed during pipe installation work. Bikers and pedestrians will have to detour around this segment of the Mercer Slough Nature Trail.
The I-90 Trail will remain open throughout the installation work.
Use Enatai Beach Park to launch boats during pipe installation
While you won't be able to use the Sweyolocken boat launch, you can still put in at Enatai Beach Park.
Impacts during pipe relining along the Lake Washington Shore
The pipe relining project will have fewer impacts when it begins, toward the end of the project. Sweyolocken boat launch, Mercer Slough, and the surrounding bike trails will generally remain open during this work. Some intermittent closures may be necessary.
The map to the left shows the new pipe in green, and the existing pipe in a black dotted line. The yellow line shows the portion of existing pipe that will be relined.
During pipe relining, the boat launch and trails will generally remain open.
The slough may be temporarily narrowed in work areas, but boats will be able to pass.
Once you are floating on the Slough, you may need to divert around work areas.
We may need to close the Mercer Slough Nature Trail for short periods of time to move construction equipment along the trail. Pedestrians and bikers may have to wait up to 10 minutes to pass.
We will do our best to keep trail closures short.
Schedule and duration
The pipe installation near the Sweyolocken boat launch is underway.
The pipe relining will start closer to the end of the project.
We will provide a more detailed schedule on our website and send it out by email once it is available.
Construction schedules often change. Please sign up to receive information about this section of the project including work and schedule details.
Detour routes
The pipe installation work will close the Mercer Slough Trail between the I-90 Trail and the Sweyolocken Pump Station, located at 3100 Bellevue Way S.E. The I-90 Trail in Bellevue will remain open during this work.
Walkers and bikers will be detoured around the Mercer Slough Trail as shown in the map at the right.
Later, during the pipe relining, the Mercer Slough Trail and the I-90 Trail will have intermittent closures while equipment is moved. Pedestrians and bikers may have to wait up to 10 minutes to pass but will not have to detour.
Detours may be required again during final restoration of the Mercer Slough Nature Trail.
What you'll see when the work is done
At the Mercer Slough, crews will restore affected areas along the slough and bike trails to pre-construction conditions.
Restoration of landscape and paved trails
Restoration includes planting new trees at the end of SE Lake Road, and ecological enhancements in the Mercer Slough Nature Park such as removing invasive species and planting of native vegetation. Crews will repave any sections of the bike paths that were damaged in construction. This will result in better overall bike path condition.
Replanting wetlands
Crews will replant disturbed wetland areas with native vegetation and plant new trees in the areas where existing trees had to be removed.
Repaving
Crews will restore paved areas to their pre-construction conditions or better after the work is completed.
How to reach us
We are committed to working with you during construction.
Here is what you can expect:
If you are a biker or pedestrian, look for:
- Signs along bike trails.
- Sign at the Sweyolocken Boat Launch and Enatai Beach Park.
- Email and/or text announcements - sign up on our webpage .
Parking at the Sweyolocken boat launch will be unavailable during the pipe installation work.
If you are a park user, look for
- Kiosk at Sweyolocken Boat Launch.
- Email and/or text announcements - signup on our webpage.
Talk to us!
For more information or to schedule a virtual meeting, contact the Community Relations Team:
- 425-305-3578
- NMEsewer@kingcounty.gov
Learn more
Visit the project webpage to learn more and sign up for email and/or text alerts: www.kingcounty.gov/MercerEnataiSewer
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