Seattle and King County to expand wastewater treatment

June 27, 2024
Seattle and King County will expand wastewater treatment in new agreement with EPA, DOJ and Ecology.

The U.S. Department of Justice (DOJ), the U.S. Environmental Protection Agency (EPA), and the Washington Department of Ecology announced on June 26, 2024, that they have reached an agreement in principle with King County and the City of Seattle that commits the local governments to significant expansion of the work they agreed to perform in 2013.

The work is to reduce discharges of untreated combined sewage and stormwater into Lake Washington, Lake Union, the Duwamish River and Puget Sound.

In 2013, Ecology and EPA found that the city and county’s interconnected combined sewer system regularly violated the state and federal clean water laws by sending hundreds of millions of untreated or undertreated wastewater into local waterways each year, and allowing sewage to back up into homes in some low-lying communities such as Duwamish Valley.

At that time, both the city and county signed consent decrees with Ecology and the United States committing to major infrastructure investments to reduce the wastewater entering local waterways and people’s homes.

Citing increasing rainfall intensity and other impacts of climate change, supply-chain disruptions, and the increased costs of construction in the Seattle area, in 2019 the city and county requested modifications to the 2013 consent decrees to allow for more time to control combined sewer overflows.

The new agreements extend the completion date for some of the projects from 2030 to 2037 and commit the city and county to significant increases in wastewater storage and treatment capacity.

The additional time also enables closer coordination between the city and county, projects to reduce stormwater volumes, and additional planning and design work to ensure that new wet-weather control facilities are more resilient to a changing climate.

Generally, this means that these facilities will be capable of handling larger volumes of combined sewage that will result from changing rainfall patterns in the Seattle area.

The agreed-to modifications include significant improvements to major projects including King County’s Mouth of the Duwamish Wet Weather Treatment Facility, West Duwamish/Terminal 115 CSO Control Project, Ship Canal Water Quality Project, and Montlake and University.

The agreement provides the city and county with a certain amount of flexibility to revise projects as they meet or exceed the original performance criteria.

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