San Mateo updates Clean Water Program; wastewater plant processes expected online by August 2025

San Mateo city staff on Tuesday updated the City Council on the status, costs and community impacts of the Clean Water Program and the Wastewater Treatment Plant Upgrade and Expansion Project, saying the new treatment processes are expected to be operational by August 2025 with program closeout targeted for December 2026.

The Clean Water Program was launched after a February 2009 cease-and-desist order from the Regional Water Quality Control Board that required elimination of sanitary sewer overflows and upgrades to protect public health and the San Francisco Bay, Deputy Public Works Director Derek Keegan told the council. "This facility will treat wastewater from populations of approximately 150,000 people," Keegan said, describing the plant as serving San Mateo, Foster City, Hillsborough, Crystal Springs County Sanitation District and some properties in Belmont.

The project replaces legacy treatment processes, increases wet-weather capacity from about 60 million gallons per day to roughly 78 million gallons per day, and was designed to be "Title 22 effluent ready" so the effluent meets California recycled‑water standards for nonpotable reuse, Keegan said. He described the new plant as including headworks, primary clarifiers, a bioactive flow facility intended to add wet‑weather capacity, a biological nutrient removal system and a membrane bioreactor (MBR) to produce high‑quality effluent that meets water‑board permits.

Keegan reviewed construction milestones and constraints. Work began in 2019 on the treatment plant; crews have…