San Mateo opens $1 billion advanced wastewater treatment facility

Federal, state and local officials joined community leaders on Sept. 24 to celebrate the completion of San Mateo’s new Wastewater Treatment Plant, the largest component of the city’s $1 billion Clean Water Program. The modernized facility replaces 75-year-old infrastructure, eliminates sewer overflows and introduces advanced nutrient removal and stormwater management technologies to protect public health and safeguard San Francisco Bay.

Designed and built by HDR, Jacobs, and Sundt Construction, the new facility features one of the largest BioActiflo systems in the world, capable of treating up to 78 million gallons per day during major storms. It also includes a 5.3-million-gallon underground flow equalization system (UFES) — one of California’s largest wastewater storage facilities — to prevent neighborhood flooding and manage peak wet-weather flows.

Additional upgrades include five-stage Biological Nutrient Removal and Membrane Bioreactor systems, a LEED Silver–certified administration building and new public amenities such as landscaped pathways and educational signage.

The project received a $277 million low-interest WIFIA loan from the U.S. EPA, which Congressman Kevin Mullin said saved local ratepayers millions. City Manager Alex Khojikian called the project “a model for clean water and sustainability,” while Foster City Mayor Stacy Jimenez emphasized the importance of regional partnership in delivering infrastructure that benefits more than 170,000 residents across multiple jurisdictions.

Construction began in 2019 and was completed while the existing plant remained fully operational.