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Since 1987, King County’s Wastewater Treatment Division (King County) has prepared annual reports on its combined sewer overflow (CSO) control program and submits them to the Washington State Department of Ecology (Ecology).

The annual reports are completed to fulfill requirements under the National Pollutant Discharge Elimination (NPDES) permit for King County’s West Point Treatment Plant in Seattle and requirements in WAC 173-245-090.1

On July 3, 2013 a Consent Decree, Civil Action No. 2:13-cv-677, between the United States Department of Justice (DOJ), United States Environmental Protection Agency (EPA), the Washington State Department of Ecology, and King County was finalized.

Section VIII of the Consent Decree requires submittal of an annual report detailing implementation of the Consent Decree. The first Consent Decree report was submitted at the end of the first calendar quarter after the Consent Decree effective date, October 3, 2013. With the agreement of EPA and Ecology the two annual reports are now being consolidated into one. This report meets the Consent Decree, state, and federal requirements.

Report Contents
1.0 Introduction
2.0 Programs to Meet EPA’s Nine Minimum Controls
3.0 Currently Under Way and Early Action CSO Control Measures
4.0 Summary of Rainfall and CSO Events
5.0 Summary of Consent Decree Violations in 2015
6.0 Twenty-Year Moving Average of Event Frequencies
7.0 Post-Construction Monitoring
A Untreated CSO Events, January–December 2015
B Treated CSO Events, January–December 2015
C Alki CSO Treatment Plant Annual Report, January–December 2015
D Carkeek CSO Treatment Plant Annual Report, January–December 2015
E Mercer/Elliott West CSO Treatment Plant Annual Report, January–December 2015
F Henderson/MLK CSO Control System Annual Report, January–December 2015

Erika Peterson
Water Quality Project Manager