King County's Combined Sewer Overflow Control ProgramThank you for visiting the Web site for King County's Combined Sewer Overflow (CSO) Control Program Web site. Here, we share information on what a CSO is, why they occur, and where they are found in the King County system. And we explain what we're doing to control them.
By reducing combined sewer overflows into local water bodies, King County is protecting public health and the environment. What are CSOs?CSOs are discharges of untreated sewage and stormwater released directly into marine waters, lakes and rivers during heavy rainfall, when the sewers have reached their capacity. Although the sewage in CSOs is greatly diluted by stormwater, both CSOs and stormwater may be harmful to public health and aquatic life because they carry chemicals and disease-causing pathogens. Why do we have CSOs?From the late 1800s through the 1940s, engineers designed combined sewers (sewers that carry sewage and stormwater runoff in a single pipe) to convey sewage, horse manure, street and rooftop runoff, and garbage from city streets to the nearest receiving body of water.
Around the 1950s, most sewer systems were built as separated systems (sewage in one pipe; stormwater in another pipe). In the late 1950s, treating wastewater became the standard. Interceptor pipes were built to transport all wastewater (from either combined or separated systems) to treatment plants.
Where are King County CSOs?
More on CSOs:
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If you have questions about the CSO Control Program, contact Karen Huber. Department of Natural Resources and Parks
Updated: Nov. 30, 2007 |
Related Information: Regional Wastewater Services Plan
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King County | Natural Resources & Parks | Wastewater Treatment Division Links to external sites do not constitute endorsements by King County. |