
COMMISSION AGENDA – Action Item No. 10b Page 2 of 5
Meeting Date: May 10, 2022
Template revised September 22, 2016; format updates October 19, 2016.
DETAILS
King County Wastewater is one of many sewer utilities across the nation under a consent decree
with the Environmental Protection Agency (EPA). In 2013, King County signed an agreement with
the U.S. Department of Justice and the EPA. This agreement known as “Consent Decree” requires
King County to complete its CSO Control Plan by 2030. This plan contains a list of “Protecting Our
Waters” projects with strict timelines. The CSO control project involving construction of a new
CSO facility located at SW. Michigan St./ Terminal 115 is required to meet the critical milestone
of “construction completion by December 31, 2025 ”. Based on the preliminary designs, the
scope of work, and the time needed to construct this CSO facility, King County would like to
acquire this property to ensure meeting the goal and strict timelines set by the Federal Consent
Degree. If King County cannot purchase this property from the Port in an amicable manner, they
will likely use eminent domain to acquire the property.
King County completed an extensive site selection process in 2017 that included careful
evaluation of 17 sites. The result of this process identified the T115 Parcel A property (King
County’s title for subject property) as the ideal site for the tank because the majority of the sewer
overflow volume required is at the W Michigan St. Regulator Station Overflow, which is directly
adjacent to the site and outfall, thus limiting conveyance needs while reducing costs and traffic
and property impacts. The T115 Parcel A site is also the ideal shape and size, allows gravity flow
into the tank, and minimal conveyance. Additionally, it is a large enough site for the tank size
needed with room for on-site landscaping and stormwater treatment and allows for adequate
access to perform routine maintenance.
The site evaluation considered the following criteria:
• Above grade impacts to the existing site use.
• Property acquisition process and ability to acquire.
• Facility configurations that will fit on the site.
• Distance from the W Michigan St. Regulator Station and subsequent conveyance
requirements and potential need to over-size the facility.
• Other considerations such as road closure requirements, construction staging area,
shoreline restrictions, and/or potential to drain the storage facility by gravity.
This process was documented in the Site Selection Technical Memorandum and Alternatives
Analysis Report for the West Duwamish CSO Control Project dated April 21, 2017, prepared by
HDR/King County.
The purpose of the Combined Sewer Overflow storage tank at the T115 Parcel A location is to
control the number of sewage spills from two outfalls (“West Michigan” and “T115”) directly into
the Duwamish River, to fewer than one occurrence per year. Reducing uncontrolled sewage spills
has significant water quality benefits, including the prevention of debris (including plastics),
biodegradable solids, other pollutants and bacteria from entering the Duwamish River. The tank