Enatai Beach Park

Three pipes connect under this park, making it a critical part of the bigger project. Construction is underway.

King County Wastewater Treatment Division

February 8, 2023

This StoryMap focuses on Enatai Beach Park. To learn more about the Mercer Enatai Sewer Upgrade project as a whole, visit the project website .

This is a map of the entire project area with North Mercer Pump Station on the Left and Sweyolocken Pump Station on the right. There is a line between the two showing the pipe alignment. — 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.

Enatai Beach Park is a critical part of the sewer upgrade project. Three pipes meet here: a new pipeline that will cross under the East Channel from Mercer Island; the existing pipe that follows the shoreline up the Mercer Slough, and the new pipe that will be drilled under the Enatai hillside. These three pipes will help transport wastewater to the Sweyolocken Pump Station about a half-mile east, and from there on to the Renton Treatment Plant.

What are we building?

As the population grows and sewage flows increase, combined sewer and stormwater during heavy rain events will sometimes be too much for the existing Enatai Interceptor (#6) alone. The project is building a brand new, high-capacity sewer line (#3) under the Enatai hillside to the east of the park. This pipe will be drilled under the Enatai hill from Enatai Beach Park to the Sweyolocken Pump Station. In addition to those two sewer lines, we will build a new pipe (#4) across Enatai Beach Park that connects these two lines. The existing pipe (#6) will get a new lining to extend its life.

(in purple) General Staging Under I-90 Bridge: This area will be fenced off and used for staging equipment and materials.
(in red) East Channel Siphon: Pipe will be installed using open-cut and cover trenching construction methods. The shoreline will be restored at the end of the project.
(in light blue) Enatai Siphon: Pipe will be floated out on Lake Washington and then pulled through a predrilled bore hole from Enatai Beach Park to King County's Sweyolocken pump station.
(in green) Structures and Connecting Sewer: New underground pipeline diversion and odor control structures will be installed in this area in addition to a new sewer pipe extending south to the Enatai Interceptor.
(in pink) Swim Beach Sewer Rehabilitation with Temporary Bypass Pumping: Wastewater flows will be diverted around the work area using the Enatai Diversion Sewer during rehabilitation of the existing Enatai Interceptor at the Enatai swim beach.
(in dark blue) Enatai Interceptor Rehabilitation with Temporary Bypass Pumping: Wastewater flows will be diverted to the new Enatai Siphon during rehabilitation of the existing Enatai Interceptor.
(in brown) Access Roadway and Final Restoration: Site restoration and new access road.

Map of Enatai Beach Park showing the work areas.

We will install underground and aboveground equipment under the I-90 bridge to support these new pipes.

Below ground, crews will install a structure to move wastewater between pipes, and an odor control unit. Park users will see electrical cabinets, hatches to the underground equipment, and an odor control stack to release clean air. A new road will allow King County maintenance crews access to the equipment.

This is a map showing where each piece of equipment will be located in the park.

What to expect

Construction is disruptive.

We will send out alerts so you can plan ahead if you live near the active work area.

What to expect during construction

Noise and dust typical of construction
Additional vehicle traffic on surrounding streets
Construction equipment such as excavators, large trucks, backhoe, soil compactors, etc.
Permitted weekday work hours are 7 a.m. to 6 p.m. We will provide advance notification of any weekend or after hours work.
Advance notice of any noisy construction outside of approved hours
Intermittent closures of portions of the park

This photo shows a large piece of construction equipment being used near a park.

In addition to active construction, Enatai Beach Park will be used to stage non-flammable construction materials. This area will be located behind a temporary fence underneath the I-90 bridge.

This image shows a mound covered by a large piece of white plastic. It is meant to represent a staging area for construction.

New pipe installation

When crews are ready to pull the new pipe under the hill, they will assemble up to 3,000 feet of pipe on the Enatai Beach Park shore and then float it out into the water. The pipe will be floated for up to a week. Pulling the pipe through the hole takes up to 48 hours of continuous operations.

This is a photo of a long piece of pipe floating on a lake.

Schedule and duration

The work is underway and will continue intermittently for up to four years.

We will provide a more detailed schedule on our website and by email and/or text once it is available. Construction schedules often change. Please sign up to receive updates about this section of the project.

What you'll see when the work is done

When construction in the park is complete, we will restore disturbed areas to be as good or better than we found them.

As good or better after restoration

All restoration work will be coordinated with the City of Bellevue, and we will return work areas to a condition that is as good as or better than before the work began.

A road for the future too

We have designed the new access road to be compatible with a future phase of park development that may include additional public parking and a hand carry boat launch under the I-90 bridge. This future work will be done by City of Bellevue.

Photo of a tree being planted in the earth.

What you'll see after we are finished under the bridge

On the ground, you’ll see hatches installed to provide access to underground portions of the new system. The new road will provide maintenance staff with access to all the new system equipment.

The only permanent above-ground structures to remain after we are finished the project are the electrical cabinets and pipes to release clean air. These will be located under the I-90 bridge.

Photo of a metal cabinet with electrical equipment in a yard. — Example of an electrical cabinet

Photo of a curved pipe coming out of a concrete slab.

Shoreline restoration - it's not just for the birds

Crews will also improve a section of the shoreline north of the swim area. We will install large logs and return the shoreline to a pebbly surface. This will provide habitat for spawning salmon and other wildlife.