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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)

Barton CSO Control Project

March 2012 Update
Design on the Barton CSO Control project began in 2011.
>> For current information on this project, view HERE.

Learn more about the decision process and recommended proposal completed in 2010.

Why are CSOs a problem at Barton?

Like many cities around the country, 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 Puget Sound near the Barton Pump Station. These events, called combined sewer overflows, or CSOs, help to avoid sewer backups into homes and businesses and onto streets during storms, but they are a public health and environmental concern. When a CSO happens, about 90 percent of the overflow is stormwater and the rest is dilute sewage.

In 2008, King County reported that the Barton CSO facility has four overflows per year on average that discharge a total of four million gallons into Puget Sound off Fauntleroy.

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 on a long term average to meet state regulations.

Proposed project

Barton CSO basin project area - green stormwater infrastructure (GSI) King County recommends a “Green” proposal for combined sewer overflow (CSO) control in Barton

King County plans to design and build green stormwater infrastructure (GSI) to control combined sewer overflows (CSOs) in the Barton basin. The GSI project will consist of planted areas between sidewalks and curbs in the Sunrise Heights and Westwood neighborhoods in West Seattle. Also known as “raingardens,” GSI refers to engineered infrastructure used to manage stormwater. GSI uses soils and vegetation, in combination with other decentralized storage and infiltration approaches to infiltrate, evaporate, capture, and reuse stormwater. In the Barton basin, raingardens, plantings, and street trees in the City of Seattle-owned right-of-way will be designed to capture and reduce the amount of peak stormwater  flows that would enter the combined sewer system to reach the control target of no more than one overflow per year on a long-term average. This is the first “green” project King County Wastewater Treatment Division will implement for flow control in the conveyance system. King County will work closely with project neighbors and the West Seattle community throughout design, construction, and into operations.


Learn more about the project schedule.

New project web page

News releases 

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Related information

Upgrades needed to Barton Street Pump Station
Barton Street Pump Station
Upgrading the Barton Street Pump Station will help alleviate some CSO volumes. King County has operated the Barton Street Pump Station and sewer facilities for more than 40 years. This pump station is no longer considered reliable. It lacks backup generators to keep the pumps working during power outages, and it has no odor control. If equipment fails, raw sewage could flow onto the beach and into Puget Sound. Moreover, capacity may be inadequate for future demand. Learn more about the Barton Street Pump Station Upgrade project.