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Vashon Treatment Plant

Vashon Treatment Plant

The Vashon Treatment System plays a critical role in wastewater treatment services on Vashon Island. Many homes and businesses on the island are connected to the Vashon Treatment Plant, which is located just northeast of the Town Center. The Vashon Treatment Plant can treat up to 1.4 million gallons per day during storm season, and it is consistently recognized for award-winning compliance with state and federal effluent permit limits

Vashon Treatment Plant nestled amongst trees and green grassVashon Treatment Plant

At Vashon, we treat wastewater through standard biological treatment processes. The Vashon Treatment Plant collects wastewater from pipes owned and maintained by the Vashon Sewer District . We cycle that wastewater through oxidation and clarification tanks and disinfect the water with ultraviolet light. It is then released into the Puget Sound. Any excess solids are sent to South Treatment Plant in Renton for further treatment.

King County also operates the Beulah Park Treatment Facility, which is a community septic system in Beulah Park and Cove Beach. This is not connected to the Vashon Treatment Plant. Instead, wastewater is treated using a series of septic tanks, sand filters, and ultraviolet disinfection. The water is then pumped to the Beulah Park drain field. Learn more about how to protect the drain field here.

Learn more:

  • See how Vashon’s Treatment System works here
  • Learn how to take care of the Beulah Park septic system and drain field here
  • Get the facts on the Vashon Treatment System’s operations here
  • Learn how Vashon contributes to a sustainable future for the surrounding community and environment
  • Explore educational opportunities here

Please report odor concerns and sewer-related incidents right away to support timely investigation. Where to report:

  • 24-hour emergency and odor reporting: 206-263-1760
  • Vashon Treatment Plant Administration: 206-463-7318
  • Vashon Sewer District (for vacuum collection system problems): 206-463-9219
Contact us

24 hour emergency and odor reporting:   206-263-1760
Administration:  206-463-7318 

9615 S.W. 171st St.
Vashon, WA 98070

Directions and map

Related content

Public treatment plant tours (available but limited)

Education resources for schools and community groups

View NPDES permit

Service area 

Overflows and emergencies

Odor reporting