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Wastewater Treatment

King County, Washington

For questions about the Wastewater Treatment Division website, please send an e-mail message or contact us at:

King Street Center
201 S. Jackson St., Suite 500
Seattle, WA 98104-3855
Phone: 206-477-5371
Fax: 206-684-1741
Telecommunication device for the deaf (TTY): 711

Get Directions to our office location in Seattle, Washington.

Staff Contacts

Resource Recovery South Plant demonstration projects

Groco demonstration garden | CitySoil Farm | Research and reports | AwardsResources | Volunteer | Tours, field trips, community partnerships

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GroCo demonstration garden

Demonstrating the beauty, effectiveness and safety of using recycled nutrients on your garden.

Currently, the beds are amended with GroCo compost made with Loop, Cedar Grove Compost, and organic fertilizer. Beds are planted with a variety of flowers, food crops, annuals and perennials.

CitySoil Farm

King County, Seattle University and the Salvation Army Renton Food Bank have partnered on a 5-year community farm project (external link) located on one acre of the South Treatment Plant facility in Renton, WA.

This project was designed and permitted to benefit the wastewater utility and the public by:

  • Demonstrating the use of GroCo compost made with Loop® biosolids and increasing public understanding of the benefits of recycling carbon and nutrients.
  • Providing an active learning site for the Seattle University Environmental Studies Urban Agriculture students.
  • Creating a locally grown supply of fresh produce for the Renton Food Bank.
  • Providing community education opportunities to expand knowledge of local water and food system challenges and solutions.
  • Demonstrating the benefits of diversified and collaborative urban land use and the potential for material and resource sharing and conservation. Since start up in 2011, large quantities of lansdscaping waste and surplus building materials have been repurposed and recycled on site; reducing transportation and disposal costs to the utility and providing a cost effective source of materials and supplies for the farm.  

Research and reports



Volunteer and Support

  • Volunteer opportunities available throughout the week. Children are welcome with parent/guardian present.
  • Service learning projects for schools and organizations can be scheduled between March and November.
  • Donations of plants (herbs, fruit trees, perennial flowers), expertise, new or gently used materials and tools, and financial donations are always welcome. Seattle University is a 501c3 institution and your donations are tax deductible.  
  • If you are an individual or small group interested in volunteering on a regular basis please contact Allison Mountjoy at

Tours, field trips and community partnerships

  • Site tours: contact Allison Mountjoy at 
  • High school: a food systems program with Seattle University City Soil Farm can be combined with a wastewater systems tour of South Treatment Plant. Learn more.
  • SeaMar Renacer Youth Program and Renton Area Youth Services teen program partner regularly for environment, health, education and art programing.

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CitySoil Farm

A partnership community farm with Seattle University and King County Wastewater Treatment Division. Contact for more information.

Education program questions: contact Casey Plank at 206-477-5448 or

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