The city of South San Francisco is constructing a regional storm water capture project that is the first of its kind in northern California. The project captures storm water runoff from Colma Creek, processes and cleans it, reuses it for irrigation and to recharge groundwater, and then returns the water to its path to the San Francisco Bay. The system will clean water for trash, sediment, mercury and polychlorinated biphenyl (PCBs), the latter two of which can cause adverse health effects.
The project was generated in response to regional planning requiring a reduction in mercury and PCBs in storm water runoff flowing to the Bay. The California Department of Transportation (Caltrans) made it feasible through a $15.5 million Cooperative Implementation Agreement.
“This project has been a collaboration between city departments and regional organizations and contributes to more healthy and safe communities,” said South San Francisco Mayor Mark Addiego. “Construction is going well and on schedule.”
This project is the first of two phases as part of the city’s investment for a parks improvement plan, which includes new sports fields and all-weather turf after the completion of the underground storage system.
“Every year, the underground system will clean an equivalent of 150 swimming pools worth of water,” said Bianca Liu, senior engineer for the city of South San Francisco.
Geography of the Colma Creek Watershed
The project processes water from the Colma Creek Watershed. The watershed is a land area bordered by the Santa Cruz mountain range and San Bruno mountain where rainfall is channeled to Colma Creek and travels to the San Francisco Bay. Colma Creek drains more than 6,500 acres of land from six municipalities, including South San Francisco, Colma, Daly City, Pacifica, San Bruno, an unincorporated area and a Caltrans right of way. The Orange Memorial Park Regional Storm Water Capture Project will capture and treat approximately 16% of the annual flow in Colma Creek.
Storm Water Capture Project: How It Works
The Orange Memorial Park Regional Storm Water Capture Project diverts dry-weather flow and the dirty first flush of urban storm water runoff from Colma Creek into an underground system integrated within the park. This system first cleans the water for trash and sediment and then moves it into a cistern, where it processes it for three goals: reuse in irrigation and water trucks; recharging groundwater; and flowing into the San Francisco Bay cleaned. The system will clean water throughout for mercury and PCBs.
Water screened for trash and sediment flows through a pipe to an underground cistern for additional treatment and disinfection. From the cistern, water will be pumped into a water treatment facility to clean the water further and then be used for irrigation in the park and along Centennial Trail, for water trucks, and for other non-potable water use.
“By reusing this water, the system will save over 15 million gallons of potable water per year,” Liu said.
When the cistern is full, water will overflow to an infiltration gallery for groundwater recharge. This groundwater recharge can address overuse of groundwater, which can cause dry wells, sinking land and saltwater intrusion from the ocean and is a beneficial water management practice. Liu said the project will recharge 55 million gallons of groundwater per year.
When the underground storage system is full, or if there is too much water or mud in the system, the cleaned water goes back into the creek. A flow splitter upstream of the storage facilities will discharge the treated overflow.
“The project will provide 130 million gallons of cleaned water back to the creek per year,” Liu said.
In addition to reusing, recharging and cleaning water, the project may reduce localized flooding.
All told, the system will capture 16% of the drainage from the Colma Creek Watershed. Nine percent will flow back to the Bay, 6% will return to groundwater, and 1% will be used for irrigation.
The underground system will be constructed underneath current baseball and softball fields. Once the system is constructed, the park area and sports fields will be rebuilt with improvements, including all-weather turf as part of a separate project. The water system planning was co-located with the 2008 Parks Master Plan.
A Collaborative Vision: City & Regional Planning
The impetus for the project started in 2015, when the San Francisco Regional Water Quality Control Board issued a Municipal Regional Storm Water Permit that required permittees in San Mateo County to regulate their storm water discharges. In particular, the permitting mandated a reduction in PCBs and mercury in water discharging to the San Francisco Bay. The City/County Association of Governments of San Mateo County developed a Storm Water Resource Plan (SRP) to do resource planning for watersheds and storm water runoff. The plan identifies ways to optimize use of storm water and hopes to achieve goals including to “capture and manage storm water more sustainably, reduce flooding and pollution associated with runoff, improve biological functioning of plants, soils and other natural infrastructure, and provide many community benefits, including cleaner air and water and enhanced aesthetic value of local streets and neighborhoods.” The SRP identified the Orange Memorial Park project as a high-priority regional project.
“Many partners were necessary to plan, fund and now construct this innovative storm water solution,” said South San Francisco City Manager Mike Futrell, “and aligning all partners behind a shared vision and acting to execute that vision was key to success.”
Construction of the regional storm water capture system started in March 2021 and is expected to be completed in 2022. The sports fields will be improved and rebuilt in 2022 with the fields set to reopen in 2023.
A Forward-Thinking Project
“This innovative project accomplishes several goals at once to improve our storm water runoff and reuse and recharge our watershed, and the next phase will improve our park. We could not be more excited to build this forward-thinking project,” said Mayor Mark Addiego.
The benefits of the Orange Memorial Park Regional Storm Water Capture Project further the region’s sustainability goals in contributing to a greener bay, reducing potable water usage and recharging groundwater, and will lead to improving functional park spaces for the city of South San Francisco’s residents. It is a project that residents will continue to enjoy well into the future.
About the author:
Mike Futrell is South San Francisco city manager and can be reached at [email protected]. Bianca Liu is South San Francisco senior engineer and can be reached at [email protected].
