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Our regional wastewater collection and treatment system

Find information about King County's regional wastewater conveyance and treatment system.

The Wastewater Treatment Division (WTD) protects water quality and public health in the central Puget Sound region by providing high quality and effective treatment to wastewater collected from our local sewer agencies.

WTD serves about 2 million people within a 424-square-mile service area, which includes most urban areas of King County and parts of south Snohomish County and northeast Pierce County.

King County's wastewater system includes:

  • 3 large regional wastewater treatment plants (the West Point plant in the City of Seattle, the South plant in the City of Renton, and the Brightwater plant near Woodinville),
  • 2 small wastewater treatment plants (one on Vashon Island and one in the City of Carnation),
  • one community septic system (Beulah Park and Cove on Vashon Island),
  • 5 combined sewer overflow (CSO) treatment facilities (Alki, Carkeek, Georgetown, Mercer/Elliott West, and Henderson/Norfolk—all in the City of Seattle),
  • about 383 miles sewer lines (and 15 miles reclaimed water lines),
  • 26 regulator stations,
  • 48 pump stations, and
  • 38 CSO outfalls.
  • View more facts about our system.

Service area and treatment plants

King County wastewater service area map displaying wastewater pipes, treatment plants and wet weather treatment plants 

View service area maps at King County GIS Center. Select "+" next to "King County Wastewater Treatment Service Area Maps" to view and download maps.