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Wastewater Treatment Division (WTD) operations and projects

WTD operations staff remain on the job 24/7 to ensure the region’s wastewater treatment service continues. More information on how to report a problem you believe may be related to the County’s wastewater treatment system is available here:

The King County Wastewater Treatment Division remains committed to sharing information and gathering feedback from community members about its work and projects. WTD staff remain available to answer questions via email and phone during regular business hours. Project information lines remain available and are being monitored for ongoing construction projects.


Seattle projects

Chelan combined sewer overflow control – This project will serve West Seattle neighborhoods. It will add capacity to store 4.3 million gallons of stormwater and sewage by constructing a new below-ground storage facility. When the project is complete in 2023, it will prevent a significant amount of harmful sewage overflow from entering our waterways.

Georgetown Wet Weather Treatment Station – King County will continue design on a new combined sewer overflow (CSO) facility in Seattle’s Georgetown neighborhood that will treat up to 70 million gallons of stormwater and sewage that currently flows directly into the Duwamish River during heavy rains.

Interbay sewer and odor control upgrade – King County plans to upgrade an aging sewer pipe in Seattle’s Interbay neighborhood. The existing pipe was built in 1967 and is nearing the end of its service life. New odor control technology will be added to the system while the sewer pipe upgrade is underway. When complete, the sewer will provide reliable service for another 50 years or more.

Jameson Building replacement – King County is replacing buildings that house the West Section Offsite Facilities and North Satellite Construction Management employees. These buildings are located in the Interbay Industrial Area near Fisherman’s Terminal.

Sediment management program – This program enables King County to address sediment contamination near CSO locations in Puget Sound. The county is continuing its efforts to remove historic CSO contamination and restore habitat at locations in Elliott Bay and the Waterway.

Ship Canal water quality  – Seattle Public Utilities and King County are working together to build an underground storage tunnel. During storms, this tunnel will hold polluted water from Ballard, Fremont, Wallingford, and north Queen Anne, preventing it from overflowing into the Lake Washington Ship Canal.

University green stormwater infrastructure - King County is beginning a green stormwater infrastructure project in north Seattle. This project will install facilities to help control a combined sewer overflow in Portage Bay. In 2017-18, the project team will study soil, groundwater, surface water flow, and street conditions in the project area to identify the best locations for facilities to be installed.

West Duwamish CSO control – King County is exploring several alternatives for reducing combined sewer overflows (CSOs) at the Terminal 115 and West Michigan outfalls. There are several options: a 100% “green” solution that could include roadside rain gardens and/or permeable pavement that lets water soak through it, a traditional “gray” infrastructure solution such as an underground storage tank or pipe, or a mix of green and gray.

West Point Treatment Plant improvements  – King County plans a number of improvements at the West Point Treatment Plant. Projects include upgrading and replacing aging equipment to ensure reliable operation and continued compliance with permit conditions.

East King County projects

Coal Creek sewer upgrade – King County is planning to upgrade a regional sewer line that serves Bellevue and Newcastle. The existing pipeline was built between 1966 and 1991, and is nearing its maximum capacity. When complete, the new sewer will provide safe and reliable service for another 50 years or more.

Eastside Interceptor Lining Project – This is part of the conveyance system program created to rehabilitate corroded conveyance pipelines throughout the county’s wastewater system. This project is located in Renton.

Lake Hills and NW Lake Sammamish sewer upgrade – King County is designing an upgrade of approximately 4.5 miles of aging pipeline in Redmond that has been in service for as long as 60 years. The new pipeline will increase system reliability and accommodate population growth.

King County is designing a new vehicle maintenance and staging facility for transporting Loop biosolids. The new facility, expected to be open in 2021-2022, will be located in North Bend (exit 34 off I-90) on County-owned land.

North Mercer Island and Enatai sewer upgrade – King County will continue project planning and design to replace sewer pipelines that have served neighborhoods in North Mercer Island, southwest Bellevue, and the town of Beaux Arts Village since 1970. The new pipeline is being designed to serve these communities for the next 60 years.

Sunset and Heathfield pump stations upgrades – King County plans to upgrade two pump stations in Bellevue as well as connecting sewer pipelines. The project also entails upgrading the Eastgate Trunk structure near I-90, which enables wastewater from these pump stations to get to King County’s South Treatment Plant in Renton.

South King County projects

M Street Trunk Repair – King County will be repairing a section of pipe at the intersection of M Street NE and 2nd Street NE in Auburn. This pipe, called the M Street Trunk, was built around the 1950s and a section has been corroded by the hydrogen sulfide produced from wastewater.

South Treatment Plant improvements – King County has a number of projects at the South Treatment Plant in Renton to replace or upgrade critical treatment plant equipment including pumps motors, and drives, which will improve system reliability, reduce maintenance costs and increase energy efficiency.

Regionwide projects

Conveyance system improvements – the utility is engaging in activities that guide the planning, design, and construction of new pipeline improvements and expansions within the utility’s 420-square-mile service area.

Lower Duwamish Waterway Superfund – King County continues to work on Superfund activities to address historically contaminated sediments in the waterway. King County will also maintain its involvement in the Lower Duwamish Waterway Group in 2016, which is currently working with EPA and the state Department of Ecology to identify a Superfund cleanup strategy.

Conveyance system H2S corrosion rehabilitation – King County will repair and replace sewer pipelines throughout its service area that are deteriorating or damaged as a result of corrosion caused by hydrogen sulfide gas, which commonly occurs in sewage. A current project is the Eastside Interceptor (Section 13) Lining Project.

WTD Resiliency and Recovery Program – King County plans to assess and retrofit sewer infrastructure and buildings in preparation for potential seismic events. The program goal is to protect public safety by avoiding or minimizing critical system damage that could occur during a natural disaster.