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

CSO Control 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, and amends the plan for any proposed changes.

Current CSO Control Program update

A 2018 CSO Long-term Control Plan Update is underway.

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 in March 2013.

The 2018 CSO Long-term Control Plan Update: will reflect environmental, social, and financial goals to meet current needs, including Consent Decree requirements. It will reflect current interested parties’ and community values and interests. It will explore a variety of technical solutions, including separating stormwater and sewer systems, green stormwater infrastructure, offline storage, and wet weather treatment. It will also consider the possibility of collaborative projects with the City of Seattle.

The results of the water quality assessment study, to be completed early in the timeframe, will provide guidance for projects that follow. 

CSO Control Project Sequencing

Erika Peterson
Water Quality Project Manager

206-477-5525