The CSO Control Program

King County's CSO program implements the CSO Control Plan. The program employs various ways to control CSOs, including controlling pollution at its sources, optimizing flow management, monitoring and modeling flows in the system, and constructing CSO control facilities. The program also includes public notification and outreach, sediment management, water quality assessment, plan review and updates, and annual reports.

Projects

The wastewater treatment utility operated by King County has completed several projects to reduce combined sewer overflows since the 1980s. Two projects completed in 2005 include the Henderson/Martin Luther King Jr./Norfolk CSO Control Project and the Denny Way CSO Control Project (a joint project with the City of Seattle).

King County expects to build about 20 CSO control projects during the next 30 years. These projects have been ranked to protect public health, beginning with construction of CSO control projects along Puget Sound beaches (2010-2011) and the east end of the Lake Washington Ship Canal (2015). The final phase of projects will be built along the Duwamish River (2017-2027) and the west end of the Ship Canal (2029-2030).

Notification and Posting

King County has worked jointly with the City of Seattle and the Seattle-King County Health Department in posting warning signs at CSO locations and undertaking public outreach.

The Health Department maintains a CSO information line (206-205-1151) and Web site to answer any health concerns about CSOs.

New! View real-time CSO notification.

Sediment Management

Areas of contaminated sediments exist near some King County CSOs. Most of this contamination is historical, as the county's Industrial Waste Program and CSO Control Program have dramatically reduced pollutants from CSOs. However, the state Department of Ecology has listed several sites in the Duwamish River near CSOs and stormwater outfalls as possible contaminated areas. To deal with sediment issues, King County is partnering with other agencies and organizations to clean up contaminated sites.

More about King County's Sediment Management Program.

CSO Water Quality Assessment

This study was completed in 1998 with help from a large stakeholder group and the Water Environment Research Foundation (external link). The study looked at the following:

• What are the existing sediment and water quality conditions of the Duwamish River and Elliott Bay?
• What are people's values and concerns about the river and the bay?
• How much pollution is contributed by CSOs versus other sources of pollutants?
• What are the impacts of CSOs on human health and aquatic life?

The study found that most risks will be unchanged by the removal of CSOs. That's because most of the risk-related chemicals come from sources other than CSOs. However, removing CSOs will reduce risk of infection from human pathogens, most notably near the Denny Way CSO (which is now controlled). In addition, removing CSOs will reduce risks to sediment-dwelling organisms near the CSO discharges.

Visit the library page for list of final reports.

Annual CSO Report

This report is developed every year and includes an overview and status of the CSO Control Program, and information on annual CSO volumes and number of discharges from each King County CSO. It is submitted to the state Department of Ecology.

CSO Control Program Updates

About every five years as part of the National Pollutant Discharge Elimination System (NPDES) permit for King County's West Point Treatment Plant, King County must provide an update on the CSO control program to the state Department of Ecology. The CSO Control Program Updates include the volume and discharge reduction King County has achieved and estimates will be achieved; information on past and future CSO control projects; and discussion of new regulations, initiatives and technologies affecting the CSO control program.

Note: the next CSO Control Plan Update due date to Ecology has changed in the last NPDES permit to 2008. A CSO Control Program Review report was published in April 2006.

Regional Wastewater Services Plan

King County's Regional Wastewater Services Plan (RWSP) outlines future sewer infrastructure for King County during the next 30 years. Elements include CSO control projects, a third regional treatment plant, biosolids management, water reuse, and inflow and infiltration reduction. Visit the RWSP Web site for more information.

More on CSOs:
Introduction
Controlling CSOs
Reduction and Cost
Being a Good Neighbor
Library
Glossary of Terms

Department of Natural Resources and Parks
Wastewater Treatment Division
201 S. Jackson St., Suite 512
Seattle, WA 98104-3855
Phone: 206-684-1246
Fax: 206-684-2057

Updated: Nov. 30, 2007
 

Related Information:
Duwamish Waterway Programs

Lower Duwamish Waterway Group, consisting of King County, City of Seattle, Port of Seattle and Boeing Co.