King County's regional wastewater conveyance and treatment system
The county's Wastewater Treatment Division (WTD) serves about 1.8 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:
- three 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),
- two 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),
- four combined sewer overflow (CSO) treatment facilities (Alki, Carkeek, Mercer/Elliott West, and Henderson/Norfolk—all in the City of Seattle),
- over 391 miles of sewer pipelines,
- 25 regulator stations,
- 48 pump stations, and
- 39 CSO outfalls.
- View more facts about our system.
Service area and treatment plants
King County wastewater treatment service area maps (GIS center)