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The Chelan Ave. Regulator Station (RS) Overflow is identified under the County's 1999 Sediment Management Plan as posing a potential hazard from contaminated sediments. The plan evaluated remediation strategies for correcting hazards caused by contaminated sediments near seven King County combined sewer overflows (CSOs).
In 2003, EPA issued a “no action” record of decision for the West Waterway operable unit of the Harbor Island Superfund site. They based this decision on the determination that public health and the welfare of the environment were not at risk from contaminants identified in the waterway. The Chelan Ave. outfall is located within but close to the OU boundary. The last 5-year review of the West Waterway OU (September 2020) concluded that no additional evaluations are required at this time. However, post-construction monitoring will occur once the CSO is controlled (see below) to revisit sediment quality and potential need for further action.
Project overview
The Chelan Ave. Regulator Station receives combined flows from the Delridge Trunk in West Seattle and sends them to King County’s West Point Treatment Plant via the West Duwamish Interceptor east of the waterway. The station diverts excess wastewater flows through a City of Seattle storm drain to the Chelan Ave. outfall location in the West Waterway. King County is evaluating options for controlling CSOs at the mouth of the Duwamish River. Read more about the CSO Long-term Control Plan Update process.