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What we do

The Wastewater Treatment Division provides wholesale wastewater treatment services to 17 cities, 17 local sewer districts and more than 1.7 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 sustainable communities, WTD remains focused on resource recycling and renewable energy production as part of its effort to attain carbon neutral operations.

2017 accomplishments

West Point restoration

Dedication to public service was on full display at the West Point Treatment Plant, as employees worked day and night to restore equipment severely damaged by widespread flooding on Feb. 9. In less than two months, workers replaced or repaired all equipment critical for plant operation. West Point resumed full compliance with its water quality permits in May. Repair estimates were reduced from $57 million to under $26 million. Costs will largely be covered by insurance.

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.

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.

In 2017, WTD substantially completed a two-year project to transport biomethane gas produced at South Treatment Plant to seven local filling stations that supply fuel for compressed natural gas vehicles.

Education, outreach, and community services

Environmental education remained a popular feature with the public. More than 17,000 people took part in treatment plant tours, lectures and workshops.

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. 

To help protect water quality, control pollution and build healthy communities, WTD is offering $1.8 million for community-driven projects through its Waterworks Grant Program.

Pollution control and cleanup

WTD continued its engagement with EPA, City of Seattle, Port of Seattle, and Boeing on the Lower Duwamish Superfund Cleanup.

Finance and administration

Infrastructure protecting regional water quality comes with a lower price tag following a credit rating upgrade and bond refinancings that will save $77 million over the next two to three decades.

Financial firm Moody’s Investor’s Service upgraded WTD’s sewer utility bond rating to Aa1 from Aa2, citing its prudent fiscal management and strong financial position. Standard & Poor’s affirmed WTD’s AA+ rating. These ratings are in the second highest rating for each firm. Since 2014, WTD has refinanced almost $2 billion in outstanding debt to save ratepayers more than $446 million over the life of the bonds.

The Washington State Supreme Court upheld a 2013 trial court ruling that awarded King County $14.7 million to cover legal fees stemming from a lawsuit against a Brightwater Project tunneling contractor.

A raw sewage pump replacement project at South Treatment Plant earned an $894,970 grant from Puget Sound Energy. The upgrade will save enough electricity to power 212 homes annually.

Capital projects

In 2017-18, WTD plans to invest over $400 million on a major capital program to build new facilities and upgrade existing infrastructure.

A community celebration in July marked completion of the Fremont Siphon Project, which entailed tunneling twin pipelines beneath the Lake Washington Ship Canal that will push up to 220 million gallons of stormwater and wastewater to the West Point plant each day. The new infrastructure increases system capacity and helps control overflows of stormwater mixed with sewage that sometimes spilled from the old siphon on rainy days.

The division also completed its Murray Combined Sewer Overflow Control Project, which features a 1 million gallon underground tank to hold stormwater and sewage during heavy rains when the treatment system is at capacity. The $47 million project was completed nearly $240,000 under budget.

The division’s use of green infrastructure to keep pollution out of Puget Sound earned honors from the Seattle chapter of the American Society of Civil Engineers. The organization recognized King County’s Barton Combined Sewer Overflow Control Project as a Local Outstanding Civil Engineering Achievement in the water resources category.


In 2018 and beyond, WTD will continue its focus on increased efficiency through Lean, meeting or surpassing permit requirements, exploring new technologies and markets for its recycled products, and investing in its asset management and capital improvement programs. The division will also mark completion of its Rainier Valley Wet Weather Storage and start construction on the Georgetown Wet Weather Treatment Station projects.

2017-dnrp-annual-report-coverEnvironmental Stewardship in King County, 2017

"Environmental Stewardship in King County," the 2017 annual report for King County Department of Natural Resources and Parks, describes the department, what it was tasked to do, and what it accomplished in 2017.

Employees worked around the clock to restore damage caused by flooding at the West Point treatment plant.Employees worked around the clock to restore damage caused by flooding at the West Point treatment plant in February. The plant resumed normal operation in May.

Employees celebrate a $894,970 grant from PSEEmployees celebrate a $894,970 grant from PSE.

Stairs at Murray Wet Weather Storage FacilityPublic art and educational features on the Murray Wet Weather Storage Facility enable people to learn about the facility’s water quality mission.