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CSO Control Program reviews and plan updates

King County's CSO control program issues two documents for a comprehensive review of program successes, updates, and future projects. The reviews and updates are done in approximately five-year intervals.

CSO Control Program Review

Program Reviews are submitted to the King County Executive and Council. The Program Review analyzes the need for CSO control, public involvement, and the relationship of the CSO control program to other county priorities. The control project schedule is verified and, if necessary, reprioritized based on any new information or data.

CSO Control Plan

As a part of the application for renewal of the county's West Point Treatment Plant's National Pollutant Discharge Elimination System (NPDES) permit from the Washington State Department of Ecology, King County submits an update to the CSO Control Plan about every 5 years.

Under Ecology's CSO regulation (WAC 173-245) CSO Control Plan Updates include a review of the achievements of the program over the past five years, commits to the next phase of projects for CSO control for the next NPDES permit phase, and amends the plan for any proposed changes.

The West Point Treatment Plant’s NPDES permit was administratively extended in 2020. The next CSO Control Program Update will coincide with the upcoming permit application renewal.  

2018 CSO Control Program Update

The 2018 CSO Control Program Update reflects an evaluation of the program and the status of Long-term Control Plan implementation. Based on a review of the CSO program, the Wastewater Treatment Division (WTD) of the Department of Natural Resources and Parks does not recommend any changes or amendment to the CSO Long-term Control Plan (LTCP) at this time.


2018 CSO Control Program Update (1.9 MB)