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Protecting Our Waters projects are planned and prioritized years – even decades – in advance.

CSO Long-term Control Plan Update process 

King County submits an update to the CSO Long-term Control Plan every five years as a part of the application for renewal of the West Point Treatment Plant's National Pollutant Discharge Elimination System (NPDES) permit from the Washington State Department of Ecology (Ecology).

Under Ecology's CSO regulation (WAC 173-245 ) King County’s CSO Long-term Control Plan Update reviews the achievements of the CSO program over the past five years, commits to the next phase of projects for CSO control for the next NPDES permit phase.

In 2012, the King County Council and Executive approved the 2012 King County Long-term CSO Control Plan Amendment. This authorized nine capital projects to control CSO overflows, using both storage and treatment infrastructure and natural drainage methods, as well as a water quality assessment study. The plan was approved by the United States Environmental Protection Agency and Washington Department of Ecology in March 2013.

Current CSO Control Program update

King County submitted a CSO Program Update to Ecology in 2019 with the NPDES permit renewal for West Point Treatment Plant.

The results of the water quality assessment study provide guidance for projects that follow. 

Faon O'Connor
CSO Control Program

206-477-4499