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Wastewater Treatment

King County, Washington

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

King Street Center
201 S. Jackson St., Suite 500
Seattle, WA 98104-3855
Phone: 206-477-5371
Fax: 206-684-1741
Telecommunication device for the deaf (TTY): 711

Get Directions to our office location in Seattle, Washington.

Staff Contacts

History of Puget Sound Beach CSO Control Projects

Project Planning Phase (2007-2010)

2014 Update 

The four Puget Sound Beach CSO control projects started construction at the end of 2013.

Learn more about these construction projects on their web pages, listed at right or by clicking on the map below.

Puget Sound Beaches CSO Control Projects

The History of Puget Sound Beach CSO Control Projects web pages cover the Project Planning Phase (CSO control alternatives selection process) for all four beach CSO control projects.

King County presented alternative means for CSO control (2010)

Combined Sewer Overflows (CSO) occur in older parts of King County’s wastewater system that carry both wastewater and stormwater to the treatment plant. When heavy rains fill the pipes, excess stormwater and sewage flow directly into local waterbodies. Historically, CSOs were designed into the system to avoid damage to facilities and sewer backups into homes and businesses and onto streets during storms.

Today, CSOs are a concern because untreated wastewater and stormwater may be discharged to Puget Sound during large storms posing risks to public health and the environment. To meet state regulations, King County's goal is to reduce the number of CSOs each year, with a long-term goal of no more than one untreated discharge per location per year.

In 2010, King County decided on proposals for CSO control in the Barton, Murray, North Beach, and South Magnolia areas. These locations are top priority because people are most likely to come in contact with water during recreational activities such as swimming.

Basin-specific approaches to CSO control

The CSO Control Program assembled a “toolkit” of potential approaches for CSO control. CSO Project teams worked to identify approaches in that toolkit that addressed the problem defined in each project area.

How the public participated

Public participation in the decision processIn fall 2009, the project team evaluated a broad range of alternative means for CSO control using a range of factors. Further refinement and evaluation of these alternatives were carried out in spring 2010. King County decided on a proposal for CSO control in each basin between October and December 2010.

Public input informed the alternatives selection process. Visit the decision process page for King County's decision process and how the public participated.

King County is committed to working with you

King County will work with the public throughout the life of these projects, providing information and opportunities to express comments, questions, and concerns:

  • Work with each basin's community and interested citizens during the decision process
  • Identify potential community and environmental impacts in the environmental and design review processes.
  • Continue an information and involvement program throughout design, construction of the facilities. For more information, view individual project pages below:
  • Provide 24/7 contact information for questions and concerns during operation
North Beach CSO Control Project South Magnolia CSO Control Project Murray CSO Control Project Barton CSO Control Project North Beach CSO control project South Magnolia CSO control project Murray CSO control project Barton CSO control project