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South Treatment Plant
Find information and facts about South Treatment Plant located in Renton, including the treatment process, capital and improvement projects, and visiting the facility and grounds.
October 2025
New South Plant Fact Sheet Available!
Learn how King County’s South Treatment Plant supports clean water, sustainability, and education in your community. The fact sheet includes highlights on wastewater treatment, resource recovery, and free learning opportunities for students and visitors.
- You can view the fact sheet in English by clicking here: English
- You can view the fact sheet in Spanish by clicking here: Espanol
Investing in Tomorrow: What’s Ahead at South Plant
Explore the latest updates in our Spring/Summer 2025 newsletter.
We’re gearing up for major improvements at South Treatment Plant to boost efficiency and resilience. Two key projects—the Influent Pump Building Seismic Upgrade (2027) and the Dissolved Air Flotation Tank Rehabilitation (2028)—are on the horizon.
Check out our newsletter for details, plus tips on protecting our regional wastewater system. Available in English and Español (Spanish).
Aerial view of South Treatment Plant in Renton.
Located in Renton, South Treatment Plant (South Plant) began operating in 1965. South Plant features a 1.5-acre demonstration farm, CitySoil, that produces more than 5,000 pounds of food for a local foodbank. South Plant is our most visited facility, hosting robust on-site educational programming for school groups and plant tours. The facility is also host to a septage disposal facility for commercial haulers. South Plant treats an average of 90 million gallons of wastewater per day from communities in Auburn, Bellevue, Issaquah, Kent, Renton, and Sammamish.
South Plant StoryMap
Are you a wastewater nerd like us? Itching to learn about all the ins and outs of how South Plant operates and benefits the community? We have put together an interactive tool that allows you to do just that.
Visit the South Plant StoryMap to learn about the history of our plant, the workforce that runs it, the way the plant interacts with the community, and more!
Learn more
- See how South Plant's Treatment System works.
- Get the facts on the South Treatment Plant System’s operations here.
- Learn how South Plant contributes to a sustainable future for the surrounding community and environment.
- Explore educational opportunities.