Federal, state and local leaders joined community members on Sept. 24, 2025, to cut the ribbon on San Mateo's new Wastewater Treatment Plant, the largest component of the city's $1 billion Clean Water Program.
The upgraded facility replaces 75-year-old infrastructure, eliminates sewer overflows and introduces advanced treatment technologies that protect public health and safeguard San Francisco Bay for generations to come.
Construction by Sundt (contractor), Jacobs (project and construction management) and HDR (design engineer), began in 2019 and was completed while the existing plant was working.
Features include:
• One of the largest BioActiflo systems in the world, enabling treatment of up to 78 million gal. per day during heavy storms.
• A 5.3 million gal. underground flow equalization system (UFES) at the San Mateo Event Center — one of the largest wastewater storage facilities of its kind in California — preventing neighborhood flooding and protecting the bay.
• Five-stage biological nutrient removal and membrane bioreactor systems, making it one of the most advanced treatment facilities in California.
• A LEED Silver-certified administration building, one of the most sustainable treatment plants in the nation, plus new public pathways, landscaping and educational signage.
"This project is first and foremost about clean water and sustainability. By investing in advanced treatment technologies, we're protecting San Francisco Bay, reducing emissions and preparing for a changing climate, said Alex Khokikian, city manager. "At the same time, we wanted this plant to serve our community in more ways than one — not just as a critical piece of infrastructure, but as a public space with walking paths, art and educational features that connect residents to the importance of caring for our environment."
The plant is co-owned by the city of San Mateo and Foster City/EMID and also serves half of Hillsborough, the Crystal Springs County Sanitation District and parts of Belmont and unincorporated San Mateo County — serving more than 170,000 residents.
