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CommunityInfrastructureWater Quality

Making life a little bit better during sewer construction

By May 5, 2017September 21st, 2020No Comments

At King County, we know we can’t build essential wastewater infrastructure without some effects on the people we serve. Where we can, we identify ways to make it a little bit better for our communities during construction.

Throughout design and construction, King County’s capital project teams and contractors evaluate our projects to find methods that will work for the site and conditions, and reduce impacts where possible.

The Rainier and North Beach Wet Weather Storage Projects are good examples of how we select construction methods to diminish community impacts. Both of these projects support King County’s goals to reduce untreated discharges of stormwater and wastewater into our waterways. And they both had the potential to impact the communities where they are located.

Rainier Wet Weather Storage

New and reused pipe at S. Bayview St

This project will keep stormwater and wastewater out of the Duwamish River, when heavy rains fill the combined stormwater and wastewater system.

The Rainier Wet Weather Facility will accomplish this two ways. During large storms, a new sewer pipe will transfer flows from one pipe that gets full to another pipe that has more room. A storage tank will hold any remaining extra stormwater and sewage until storms pass and there is room in the system.

Watch the video below to see how the contractor avoided major traffic impacts during installation of the new pipe under busy Rainier Avenue South.

North Beach Wet Weather Storage


The North Beach Wet Weather Storage Facility came online in 2015 to reduce combined sewer overflows to Puget Sound during storms. A tank below the street stores excess flows until storms pass and then pumps the stored flows for treatment when the pipes have more room.

As you can see, the underground tank was built close to homes. The contractor considered this carefully when choosing methods to shore- or support- soils around the excavation while the tank was being built.

Shoring methods are tailored to the soils and groundwater at the site. King County’s contractor proposed a method that had been used only once before in Seattle: soil mix walls.  The soils and groundwater at the North Beach site were well suited to use this method.

The soil mix wall method reduced vibration and noise, the most common shoring effects. In fact, monitors detected more vibration from freight trains traveling along the shoreline than from the shoring activity. Watch this video to see how the method works.


At King County Wastewater Treatment Division, we know that infrastructure construction can cause both inconveniences and concerns, whether it takes place in an industrial area or quiet neighborhood. Our project teams work hard during design to identify ways to keep traffic and people moving, and reduce effects on people and structures nearby.