$552 million San Mateo wastewater upgrade expands underground treatment capacity
SAN MATEO, Calif. — A five-year, $552 million upgrade to the San Mateo Wastewater Treatment Plant is now complete, marking one of the largest infrastructure investments in the region’s history. The expanded system will help prevent sewer overflows, improve treatment performance, and better protect San Francisco Bay.
The project, funded in part by the State Water Resources Control Board, increased the facility’s hydraulic capacity to handle heavy storm flows and added new underground treatment components, including headworks, primary clarifiers, biological nutrient reactors, and an odor-control system.
“Upgrading our wastewater infrastructure to withstand extreme weather is a critical part of adapting to climate change for most towns and cities,” said State Water Board Member Sean Maguire. “Infrastructure improvements are a major undertaking that require years of planning and extensive financing. We at the board are proud to partner with cities like San Mateo to provide grants and loans that make large-scale projects more affordable and, ultimately, achievable for municipalities and their customers.”
The State Water Board provided more than $137 million in low-interest funding through the Clean Water State Revolving Fund, saving ratepayers an estimated $22 million. Since 2022, the board has distributed $3.5 billion statewide for wastewater upgrades.
The San Mateo project modernized primary treatment facilities, added nitrification and denitrification systems to improve effluent quality, and expanded capacity to reduce nutrient discharges linked to harmful algae blooms.
“Protecting our Bay and providing clean water for our community is at the heart of this project,” said San Mateo City Manager Alex Khojikian. “We built one of the most sustainable treatment plants in the nation — a facility that not only safeguards public health and prepares us for climate change, but also welcomes residents with new walking paths, landscaping and educational features. This is an investment in both our environment and our quality of life for generations to come.”
The upgrade also received federal funding through the U.S. EPA’s Water Infrastructure Finance and Innovation Act (WIFIA) program.
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