Vashon Wastewater Treatment Plant

Welcome to the Vashon Treatment Plant, located at 9615 SW 171st St., on Vashon Island in Puget Sound southwest of Seattle, Washington.

The plant serves the Vashon Sewer District as part of King County's regional system that treats wastewater for about 1.4 million people in the Puget Sound region. The collection system, owned and maintained by the Vashon Sewer District, delivers sewage to the plant from about 425 residential and commercial customers in and around the island's main business area.

History

Vashon Sewer District contracted with King County in 1999 to treat the wastewater of its customers. Then, the system was experiencing many violations. King County’s expertise in wastewater treatment and financing was needed to solve serious problems.

After taking over treatment plant operations in November 1999, the county carried out many interim steps to improve the plant. While the old plant was doing an adequate job, it was at capacity for the amount of incoming waste and flows. The old plant lacked backup systems.

In addition to the treatment plant upgrades, the County advanced funds to the sewer district to build facilities to deal with health hazard areas at Bunker Trail and Beulah Park/Cove.

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Vashon Treatment Plant
9615 SW 171st St.,
Vashon, Washington
View driving directions and map

The Plant (upgraded in 2006)

King County began building a new plant in 2004. Moving the marine outfall further out in the Puget Sound was completed in October 2004. Construction was completed in 2006 and an open house for the community was held in May 2007.

The new plant and improvements were needed to meet regulatory requirements and to protect human health and the environment. This project was funded in part by loans from the Public Works Trust Fund, Washington State Department of Ecology and the US Environmental Protection Agency.

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Plant entrance

More plant photos
(from May 2007 Open House)

The Process

The Vashon Plant serves the Vashon Sewer District. The average normal flow is 90,000 gallons a day and the average wet weather flow is 180,000 gallons a day. The maximum plant flow capacity is 1.4 million gallons a day.

Wastewater coming into the plant undergoes a series of treatments, including the following:

• Preliminary treatment: where trash is removed from the wastewater.
• Biological treatment: next, the water goes to an oxidation ditch where hungry "bugs" eat up contaminants. The water then flows to a clarifier which acts like a giant bathtub and the solids fall to the bottom. The clean water is ready to move to disinfection.
• Disinfection: (ultraviolet light) destroys most remaining pathogens, or disease-causing bacteria before the final effluent is released through an outfall pipe and diffuser into Puget Sound.
• Solids removal: the solids are stored, settled and loaded into tanker trucks and taken to the South Treatment Plant in Renton for solids handling. They are ultimately recycled into various beneficial ways.

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Wastewater Treatment Process
How is wastewater treated at King County's Vashon Treatment Plant?
(.PDF file, 289KB)

The Vashon Plant discharges treated wastewater under permits issued by the Washington State Department of Ecology.

The People

The Vashon Treatment Plant runs 24 hours a day, seven days a week.

At the plant, a state-licensed operator is responsible for the daily operations, performing analysis on processes and optimizing the plant's operations. Crews of mechanics and electrical and instrumentation staff, stationed at the South Treatment Plant in Renton, maintain and repair equipment.

Our goal is to provide the region with the best wastewater treatment service available while operating as efficiently and effectively as possible.

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Greg Burnham, a state-licensed operator at the Vashon Treatment Plant

Address and Contacts

Administration: 206-463-7318
     Monday through Friday, during business hours
Odor Control Hotline: 206-684-2404
     24 hours a day

9615 SW 171st Street
Vashon, WA 98070

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More about Vashon :

Links to .pdf files require the free Adobe Acrobat Reader to view.

  Plant Tours

  Treatment plant upgrade project and brochure

• Treatment Plant Project Update, Spring 2007 (1.3 MB, PDF)
• Plant upgrade project, completed Fall 2006

  You can also find out about:

• South Treatment Plant, in Renton
• West Point Treatment Plant, in Seattle
• Brightwater, a third regional treatment plant under construction
• Biosolids recycling and application
• Odor control in wastewater facilities
• Public involvement and community relations
• King County Wastewater (NPDES) Permits
• Speaker's Bureau
• Let's Talk Trash -- protecting water quality starts with all of us

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Updated: April 15, 2008