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 installed more than 2,000 piles to resist uplift and seismic motion, and the project includes about 33,000 cubic yards of concrete. He said the project team has logged an estimated 1.5 million construction labor hours. The site will include odor‑control facilities intended to capture foul air from the new processes, and an on‑site, state‑accredited laboratory to support process optimization and in‑house testing.

On schedule and costs: the Clean Water Program was originally baselined at $991 million in 2017. Keegan reported a current estimate at completion (EAC) of about $1.028 billion, a variance of roughly $37 million (3.8 percent). For the Upgrade and Expansion construction contract he said the awarded contract amount totals about $430.6 million and the authorized contingency to date is $40.9 million (about 9.5 percent of the construction contract). Staff said they estimate an additional construction contingency of approximately $19.5 million and about $5 million in soft costs related to delays (project management, inspections, insurance, engineering). If the additional contingency were approved now, staff said total contingency would be about $60 million, roughly 14 percent of the construction contract; staff said they will return with a more refined number in the coming fiscal year.

Keegan highlighted how the city financed the program: rate restructuring and multi‑year rate increases established a stable revenue stream that allowed the city to issue $270 million in bonds and obtain federal and state loans, including two WIFIA loans (reported in the presentation as $277 million and $85 million) and a State Revolving Fund loan of about $145 million.

Council members asked about neighborhood restoration and public amenities. A council member said East Side residents were told a temporary parking lot near Mariners Island would be restored to open green space; Keegan said the contractor has removed porta‑potties and vehicle parking and staff are coordinating with the Parks and Recreation Department on final surface restoration. "We intend to restore it with a gravel surface or potentially some other surface of similar nature," Keegan said, adding the fence and any temporary gates will be removed.

The council also asked about lighting and the planned pedestrian and bicycle connection. Keegan said landscaping and screening will be installed along the frontage, and lighting will be provided for safety; lighting seen through screening must remain for 24/7 operations and OSHA safety for plant staff. The improved pathway will provide pedestrian and bicycle connectivity to the J. Hart Clinton Drive crossing and the Bay Trail but will not be reopened for vehicle access, he said.

On odor concerns, Council members and staff said investigations of summertime complaints have pointed to wetlands at Seal Point Park and low‑tide bay emissions as likely sources, not the treatment plant. "We've gone out and made extensive investigations when we've gotten the complaints and have never been able to pinpoint anything coming from the treatment plant," a council member said. Keegan reiterated that the new facilities include odor‑control systems to capture foul air from the new process units.

Council members also asked about long‑term reuse and potable reuse options. Keegan and other staff noted the plant will be able to produce Title 22 recycled water for nonpotable uses but said salinity levels present challenges for local irrigation and that the city is a participant in regional efforts (Peninsula Pure Water) to evaluate advanced purification and regional potable reuse; local distribution of potable‑grade water would require additional treatment and coordination with water purveyors.

Staff described public engagement steps for when the facility is ready: construction and facility tours, school visits, and potential partnerships with College of San Mateo for workforce development. Keegan said clean‑water testing will occur through July 2025, new processes are scheduled to be operational by August 2025 and a ribbon cutting is targeted for September 2025. The presentation closed with staff noting that finishing work on older parts of the existing plant will extend final contract closeout into spring 2026 and that staff will return to council with a refined contingency request when available.

No formal votes or council actions were taken on the item during the meeting; council members directed staff to continue coordination with Parks and Recreation on site restoration, to continue investigations at Seal Point Park related to odor complaints, and to return with a refined request for any additional contingency funding.