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Construction of the Carnation plant began in 2006 and the plant began operation in May 2008.


  • Before 2002 – All residents and businesses in Carnation had septic systems for their wastewater. The Carnation City Council voted that a wastewater treatment system would be beneficial for economic and environmental welfare in Carnation.
  • July 2002 – The Carnation City Council approved an agreement with King County to build a treatment plant. In the agreement, the city would design and build a local wastewater collection system while the county would design, build, operate and maintain a new treatment plant and associated discharge facilities.
  • December 2004 – The site for the treatment plant was selected and analysis of alternatives for wetland enhancement and river discharge moved forward.
  • Summer 2006 – Construction of the treatment plant began.
  • Spring 2007 – Construction of the conveyance system began.
  • February 2008 – Construction of the sewer pipe conveyance system was completed. 
  • May 5, 2008 – First day of operations for the City of Carnation collection system and the King County wastewater treatment plant. 

Regional system history

In 1958 voters approved the creation of a regional wastewater treatment system to clean the wastewater being generated from the developing cities. Metro was formed as the organization to build and manage this system and was later merged with King County. More regional wastewater system history.

project dignitaries with hard hats and shovels at Ground Breaking eventGround breaking, July 6, 2006

View more photos on our Flickr site  .

Contact us

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

4405 Larson Ave.
Carnation, WA 98041

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