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December 2025
 South Plant Construction, early 1960's. The original treatment facility (completed in 1965) was treating an average of 24 million gallons a day.
This year, South Treatment Plant celebrates 60 years of protecting public health and the environment by collecting and cleaning wastewater. But our story didn't start as a celebration – it began to address a critical problem.
In the 1950s, small local treatment facilities couldn’t keep up with Seattle-King County's rapidly growing population. Sewage and partially treated wastewater flowed into Lake Washington, Puget Sound, and nearby rivers and lakes, contaminating water across the region. Beaches closed, algae blooms clouded the water, and fish and wildlife suffered.
Communities knew something had to change. In 1958, voters created Metro and developed a regional wastewater treatment system based on watersheds rather than political boundaries. Construction on South Treatment Plant followed soon after.
When the Plant opened in 1965 as the region's first wastewater treatment plant, it helped turn the tide for water quality in the Puget Sound, contributed to the dramatic recovery of Lake Washington, and set a new standard for clean water protection for the entire region.
 Left: A past when water pollution closed swimming spots. Right: Today’s restored waterways where families can safely swim.
Six decades later, we're proud to carry that work forward. Over the years, we've expanded treatment processes, upgraded equipment, strengthened odor control, streamlined operations, and deepened our connections with the community.
Today, South Plant treats an average of 90 million gallons of wastewater per day from communities including Auburn, Bellevue, Issaquah, Kent, and Renton—serving more than 860,000 residents across 240 square miles. Our operators work around the clock, 365 days a year, to keep the system running safely and reliably.
And, we do more than treat wastewater, too! We generate renewable energy, create Loop® biosolids for farms and forests, produce recycled water, and support community amenities like CitySoil Farm, Waterworks Gardens, and hands-on K-12 learning opportunities.
While a lot has changed in 60 years, our mission and commitment to protecting public health and the environment remains the same. As we mark this anniversary, we're grateful for the communities we serve, our partners, volunteers, and staff who make this work possible—and we’re excited for what comes next.
To learn more about our past, present and future, dive into our interactive South Plant StoryMap.
 South Plant Community Services Team connect with neighbors at events in Renton.
Highlights from 2025 community engagement
As we celebrated 60 years of South Treatment Plant, we also focused on the ongoing work of building relationships with the people we serve.
This summer and fall, the South Treatment Plant Community Services team hosted booths at four Renton events, connecting with nearly 1,000 community members who stopped by to learn about wastewater treatment, resource recovery, sustainability, and the amenities available at South Plant.
Some of the most common questions we heard were:
- Do you offer plant tours? Yes, we do!
- How does wastewater travel through the system?
- What does South Plant do to manage odors?
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Are "flushable" wipes really flushable? (They aren't—thank you for asking!)
How can students and adults get involved at South Treatment Plant?
While this year’s tabling season may be over, our tours, programs, and community opportunities continue all year round. Learn more by visiting our website or contacting our Community Services team at SouthPlantCS@kingcounty.gov or call 206-477-5552.
You can dig deeper into this year's conversations and find answers to the most common questions in our 2025 Community Engagement Summary.
We're hiring!
Our award-winning agency offers careers in a wide range of fields. Find your career, with competitive pay, benefits, and a pension plan. We also offer internship programs and opportunities for entry-level candidates, including the Operator-in-Training Program.
Ready to start your career in wastewater treatment operations? Apply for the 2026 Operator-in-Training Program today!
 We are hiring for multiple Operator-In-Training (OIT) positions for 2026. This hands-on, paid training program can lead to a rewarding career in clean water services. During your first six months, you'll learn the skills needed to operate essential wastewater treatment equipment and work toward earning a Washington State certification. As an OIT, you’ll play an important role in protecting the health of our communities and the environment.
Please note, you must have a high school diploma or GED to apply.
Applications are open until 11:59 p.m. on Monday, December 22!
Please follow this link to learn more about this opportunity and apply:
Visit our treatment plant website to sign up for email updates and learn more: kingcounty.gov/southplant
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