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Capital projects

Find information on King County’s wastewater capital projects, including project descriptions, locations, and status, and sign up for project updates.

Current and planned projects

Alki standby generator

This project will provide reliable power supply to ensure our sewer system keeps working during outages and helps protect water quality in Puget Sound.

Black Diamond sewer upgrade

The Black Diamond Sewer Upgrade Project will increase capacity for 6 miles of regional sewer pipe in Black Diamond. The project will help us treat more wastewater to meet the needs of the growing Black Diamond community.

Coal Creek sewer upgrade

The Coal Creek Sewer Upgrade Project will install new sewer pipes to carry more wastewater and meet the growing needs of Bellevue and Newcastle.

Eastside Interceptor Section 8 rehabilitation

The Eastside Interceptor Section 8 Rehabilitation Project will repair 4,800 square feet of a 90- to 96-inch wastewater tunnel in Bellevue that is nearing the end of its useful life. 

Elliott West Wet Weather Treatment Station upgrade

King County is planning to upgrade the Elliott West Wet Weather Treatment Station to ensure compliance with stricter environmental regulations, meet the demands of a growing population, and handle a changing climate.

Georgetown Wet Weather Treatment Station

The Georgetown Wet Weather Treatment Station reduces water pollution and improves aquatic habitat and overall water quality of the Duwamish River. The station is currently operational and a ribbon cutting celebration is scheduled in 2023 after artwork installation is complete.

Interbay sewer and odor control upgrade

The Interbay Sewer and Odor Control Upgrade Project will replace aging sewer pipes in Seattle’s Interbay neighborhood and add new odor control technology.

Lake Hills and NW Lake Sammamish sewer upgrade

The Lake Hills and NW Lake Sammamish Sewer Upgrade Project will upgrade 4.5 miles of sewer pipes serving the growing Redmond and Bellevue area.

Lake Hills sewer relining

The Lake Hills Sewer Relining Project will install pipe lining along existing concrete pipe to prevent corrosion and extend the life of the pipe another 50 years.

Lakeland Hills Pump Station replacement

The Lakeland Hills Pump Station Replacement Project will replace the aging Lakeland Hills Pump Station and build a new facility in Auburn to upgrade sewer services in south King County.

M Street Trunk rehabilitation

The M Street Trunk Rehabilitation Project will repair about 2.6 miles of deteriorated sewer pipes in the City of Auburn. 

North Mercer Island/Enatai sewer upgrade

The North Mercer Island/Enatai Sewer Upgrade Project will replace aging pipes serving areas in North Mercer Island and Bellevue near Enatai Beach, and the Town of Beaux Arts Village.

Sammamish Plateau Diversion

The Sammamish Plateau Diversion Project will build new wastewater infrastructure to serve the growing East Lake Sammamish area.

Ship Canal water quality (joint project with Seattle Public Utilities)

Seattle Public Utilities and King County Wastewater Treatment Division are building an underground storage tunnel to significantly reduce the amount of polluted stormwater (from rain) and sewage that flows into the Lake Washington Ship Canal, Salmon Bay, and Lake Union from our sewer system.

South Park wastewater backup protection

King County is working on short-term and long-term solutions to reduce the risk of wastewater backups in South Park.

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.

West Duwamish Wet Weather Storage

King County’s plans to build a wet weather storage facility to hold stormwater and wastewater that currently overflows into the Duwamish River during large storms.

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.

Capital project map

Recently completed capital projects

View list of projects by title, region and date completed.