For questions about the Wastewater Treatment Division Web site, please send an e-mail message or contact us at:

King Street Center
201 S. Jackson St., Suite 505
Seattle, WA 98104-3855
Phone: 206-684-1280
Fax: 206-684-1741
Telecommunication device for the deaf (TTY): 711

Get Directions to our office location in Seattle, Washington.

Puget Sound shoreline next to the West Point Treatment Plant, Seattle

Puget Sound Beach CSO Control Projects

King County begins planning new projects to protect Puget Sound

Beach CSO map
Click on map location for project details.

As part of its mission to protect public health and the environment, King County is responsible for conveying and treating wastewater collected by 34 local city and sewer agencies, including the City of Seattle.

Reducing combined sewer overflows (CSOs)

Like many cities around the country (external link), the older parts of King County's wastewater system carry both wastewater and stormwater to the treatment plant. When heavy rains fill the pipes, excess stormwater and sewage flow directly into local waterbodies. These discharges are called combined sewer overflows or CSOs. When this happens, about 90 percent of the overflow is stormwater and the rest is dilute sewage. CSOs help avoid sewer backups into homes and businesses and onto streets during storms.

CSOs are a public health and environmental concern because untreated wastewater and storm water may be discharged to Puget Sound during large storms. King County's goal is to reduce the number of CSOs each year, with a long-term goal of less than one untreated discharge per location per year to meet state regulations.

CSO control optionsTo protect Puget Sound and meet our goal, the county is identifying  CSO control options (PDF file) for North Beach, West Seattle, and South Magnolia. These locations are top priority because people are most likely to come in contact with water during recreational activities such as swimming.

North Beach South MagnoliaBarton Pump Station

Your comments and ideas are welcome

  • The county is committed to working with the local communities to evaluate alternatives and address suggestions and concerns. We will work with the public to identify potential community and environmental impacts early in the environmental and design review processes. Our public information and involvement program will continue throughout design, construction and operation of the facilities.
  • For more information about the Puget Sound Beach CSO projects, please contact Martha Tuttle at 206-684-1207 or martha.tuttle@kingcounty.gov.

Related topics