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What we do

The Wastewater Treatment Division (WTD) provides wholesale wastewater treatment services to 17 cities, 17 local sewer districts and more than 1.8 million residents across a 420-square-mile area in King, Snohomish and Pierce counties.

The division’s 700 employees plan and design new facilities, regulate the disposal of industrial waste, educate the public about pollution prevention, and manage a regional system of treatment plants, pipelines and pump stations that operate around the-clock. Guided by a commitment to clean water and healthy habitat, WTD remains focused on resource recycling and renewable energy production as part of its effort to attain carbon neutral operations.

2019 accomplishments, looking forward to 2020

Operations and planning

WTD treated over 59 billion gallons of wastewater in 2019. A Flows and Loads Study completed this year indicated facility upgrades at our treatment plants are coming due faster than expected. As the region’s population grows rapidly, WTD is prioritizing projects to improve capacity. 

Resource recovery and recycling

One-hundred percent of the division’s Loop® biosolids were recycled for use in forestry, agriculture and commercial composting applications, and demand for this nutrient-rich resource remained strong. A Class A biosolids pilot project at the South Plant is being considered for 2020.

The division continued supplying recycled water to customers near its Brightwater and South treatment plants. Customers include Willows Run Golf Course, the Lake Washington Youth Soccer Association’s playfields at 60 Acres Park, Starfire Sports Fields in Tukwila, and the City of Kirkland.

Education, outreach, and community services

A robust public engagement effort for the Clean Water Plan , that included an online open house, workshops, and public events sparked conversations across the region. The community voiced their clean water priorities to help guide future wastewater plans. Opportunities for community members to engage with the planning team will continue throughout the planning process.

Through partnerships with schools, labor organizations and nonprofits, WTD worked to attract more youth and people of color to job opportunities in the clean-water field. The Operator in Training Program successfully trained and hired 15 new wastewater treatment plant operators. WTD provided high school and college internships for young people interested in exploring a wastewater career that supports the environment and furthers social justice.  

To help protect water quality, control pollution and build healthy communities, WTD awarded nearly $2 million over the last 2 years for a variety of community-driven projects through its Waterworks Grant Program.

Finance and administration

Infrastructure protecting regional water quality will with a lower price tag following credit refinancing that will save $41 million over the next 15 years.

King County expanded the Capacity Charge rate affordability classification, reducing the cost burden of connecting to the public sewer system for low-income housing and providing assistance to those experiencing financial hardship. 

Capital projects

In 2019, WTD invested $211 million on major capital programs to build new facilities and upgrade existing infrastructure, including 21 major maintenance projects at West Point and South Treatment Plants.

WTD completed the East Side Interceptor relining of 3700 feet of sewer pipe, with the largest bypass King County has ever used. 45 million gallons of wastewater per day was routed through temporary facilities to upgrade nearly 50 year old pipes.


In 2020 and beyond, WTD will continue its focus on protecting public health, affirming our dedication to clean water and healthy habitat, meeting or surpassing permit requirements, exploring new technologies and markets for its recycled products, and investing in its asset management and capital improvement programs.

Seattle Public Utilities and King County Wastewater Treatment Division are building an underground storage tunnel, as part of the Ship Canal water quality project , to significantly reduce the amount of polluted stormwater (from rain) and sewage that flows into the Lake Washington Ship Canal, Salmon Bay and Lake Union from our sewer system. 

2020 will mark the completion of the Georgetown Wet Weather Treatment Station, which won the coveted “Platinum” rating from the Institute for Sustainable Infrastructure’s Envision rating system. North Mercer Island and Enatai Interceptors Upgrade project construction will begin, as will progress toward a Loop vehicle maintenance facility in North Bend.

Over the next few decades, the Puget Sound region will collectively spend billions of dollars on protecting water quality. In 2020, the Clean Water Plan will begin to emerge, and King County’s wastewater plan will be updated to make the right investments at the right time, for the best water quality outcomes.

Clean Water Healthy Habitat bannerKing County is developing a Clean Water Plan which will address issues like aging wastewater pipes, pumps and treatment plants, stormwater pollution, climate impacts and changing regulations. This planning effort will help the us create a long-term strategy for wastewater treatment that brings the best outcomes for water quality and health and meets the needs of our ratepayers.

sewer pipe placed in trenchIn 2019, WTD invested $211 million on major capital programs to build new facilities and upgrade existing infrastructure.

"Environmental Stewardship in King County," the Annual Report for King County Department of Natural Resources and Parks, describes the department, what it was tasked to do and what it accomplished annually. The report provides maps, facts and figures to convey the breadth of department responsibilities and includes overviews of executive initiatives, performance measures and results, and awards won by the department on an annual basis.