Northeast Mercer Island

We are building two underground structures in the cul-de-sac on SE 35th Place:

1. An underground diversion structure: a box where the gravity pipe changes to a siphon.
2. An odor control structure. Odors are often created at the beginning and end of sewer siphons. We will install an activated carbon scrubber at this location to manage odors.

To learn more about how we manage odors in the sewer system, read our   fact sheet  .

We will install equipment above the ground in the 35th PL SE cul-de-sac to support the underground structures. This will include electrical cabinets, an air stack to release clean air from the odor control equipment, and a vent for air intake.

Lift Station 11, in Fruitland Landing, connects the City of Mercer Island’s wastewater system to King County’s regional sewer system.

As part of this project, we will relocate the King County pipe, shown in yellow on the diagram. Currently, the pipe runs down 97th Ave SE and along the lake bottom, as shown on the left-hand image. After construction, the pipe will cross under 97th Avenue SE at the top of the hill near the I-90 trail, as shown in the right-hand image.

We will put a new lining in the pipe that runs down the lower half of 97th Ave SE, near Fruitland Landing. This will extend its service life. This pipe will connect to the new pipe that is being installed halfway up the street. The new pipe will connect to the pipe being installed underneath the I-90 Trail.

After we have installed the new pipes, Lift Station 11 will need to pump wastewater flows further up the hill. As a result, we will install bigger pumps and an upgraded electrical system in the station. The City of Mercer Island recently installed a generator in the park to maintain service during power outages.

• We will dig a pit at the intersection of 97th and 34th. We will secure the pit to prevent public access.
• Flaggers will help keep traffic moving safely during active work hours. 
• When we put a new lining in the pipe, we will need to divert wastewater into temporary piping for about a month. This temporary piping will run down the east side of the street. We will place ramps over the pipe so that residents can get in and out of their driveways.  
• Emergency vehicles will have access to the homes on the street at all times.

Like any construction project, there will be noise, dust, traffic impacts and other inconveniences.

• Permitted weekday work hours are 7 a.m. to 7 p.m. We will provide advance notification of any weekend or after hours work.
• We will detour regular through traffic around these streets. Residents will have access to their homes.
• Residential streets will be reduced to one lane.
• Flaggers will direct traffic.
• Homeowners may need to work with crews for driveway access during certain work elements.
• Emergency vehicles will always be able to access homes on streets under construction.

School bus stops may move temporarily. King County is working with the Mercer Island School District. They will communicate changes to you in advance of any moved bus stops.

Services such as garbage, recycling, package delivery and mail will continue. Residents may need to move garbage bins to a new location during active construction. King County will provide advance notification of any changes to bin locations.

The work we are doing will take place in the public right-of-way. We may be working in the green spaces at the side of the road, often called parking strips. We know that many residents have improved these right-of-way areas with landscaping. Before we begin our work, a surveyor will stake the property boundaries to ensure all work is being done in the right-of-way.

In areas where we need to dig up the public right-of-way, we will give neighbors advance notice so they can remove any landscaping improvements they have made for use in other places.  Crews will survey the right-of-way limits, and you may see flags or stakes indicating the property boundary.

To meet City of Mercer Island code requirements, if your plantings do extend into the public right-of-way we will not replace them after the project.

We will close Fruitland Landing to the public for the duration of the Lift Station 11 construction. It’s a small park, and there simply won’t be room to safely retain public access around the workers, equipment and materials that will be located there.

• Materials stacked up for later use.
• Temporary pumps - you may hear noise coming from the pumps.
• Pipes on the ground that are actively being used to divert wastewater.
• A pit at the park entrance that will be used when we reline the pipe. We will secure the pit to prevent public access.

Crews will install pipe in the wooded area between 97th Ave SE and the cul-de-sac on SE 35th Place.

To install the pipe, they will build a temporary dirt construction road and remove approximately 30 trees.

See the "when we're done section to learn about tree restoration".

During construction work on the 96th Ave siphon pipe, crews will excavate around the existing maintenance holes near the intersection of 96th Ave SE and SE 35th St.

They will store equipment nearby and you will see a temporary sewer pipe that will carry wastewater flows during the work.

The other end of the pipe is in the HOV lane in front of Mercer Island City Hall. Crews will excavate around the existing maintenance holes on SE 36th St in front of Mercer Island City Hall.

The cul-de-sac on SE 35th Place will look different when work is complete.

There will be access hatches for the underground equipment, an electrical cabinet, an air stack to release clean air, and a vent for the air intake.

The image on the right shows approximate locations for the below and above-ground equipment.

Fruitland Landing will have an above ground generator and electrical cabinet, and the existing vaults will be updated.

We will plant vegetation to replace what is removed for construction.