Holiday closure Monday May 28: Most county offices will be closed in observance of Memorial Day.
For questions about the King County CSO Control Program, please contact Karen Huber.

Wastewater Treatment Division
King Street Center
201 S. Jackson St., Suite 505
Seattle, WA 98104-3855

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Real Time CSO Notification

CSO Control Annual Reports

Annual Report

Annual reports are submitted to the state Department of Ecology in accordance with WAC 173-245-090 (external link) and with the requirements for annual CSO reports as established in the National Pollutant Discharge Elimination System (NPDES) Permit, Number WA-002918-1 for the West Point Treatment Plant. These reports include overviews and the status of King County's CSO Control Program, and information on annual CSO volumes and number of discharges from each King County CSO.

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2010 Annual Report (2MB), issued July 2011

Report contents:
Transmittal letter
Section 1. Introduction
Section 2. Programs to Meet EPA’s Nine Minimum Controls
Section 3. Status of Current CSO Control Projects
Section 4. Summary of Rainfall and CSO Events
Section 5. Twenty-Year Moving Average of Event Frequencies
Appendices
A. Untreated CSO Events, January–December 2010
B. Treated CSO Events, January–December 2010
C. Alki CSO Treatment Plant Annual Report
D. Carkeek CSO Treatment Plant Annual Report
E. Mercer/Elliott West CSO Control System Annual Report
F. Henderson/Norfolk CSO Control System Annual Report

Reports for earlier years are listed below:

Changes to annual reporting requirements (beginning with 2008 Annual Report)

The West Point Treatment Plant NPDES Permit was renewed effective July 1, 2009 . Changes in reporting requirements, listed below, have resulted in a different report structure and content from previous years:

  • Submittal deadline of July 31 each year
  • Reporting of information by calendar year
  • "Event-based" data reporting by CSO site
    • Include duration of each CSO event. The duration represents the period from the start until the end of the overflow, as defined by a subsequent 24-hour non-overflow period. The overflow itself may be intermittent within this duration period.
    • Include rainfall data for each CSO event as measured by the nearest King County rain gauge. This event-based rainfall reporting will begin with the August 2009 monthly report and will be compiled in next year's 2009 annual report.
    • Provide event-based data in electronic form along with the report
  • Reporting of the average of the overflow frequency at each CSO site over the last 20 years. Because 20 years of data are not available for all sites, Ecology has specified that missing data from the early years or pre-control project years will be reported from the hydraulic model for those sites identified as having achieved control to the state standard. These modeled data will be provided in the 2009 report.
  • Identification of CSOs considered controlled in both the annual reports and the control plan amendments.