Objective
The Underground Flow Equalization System (UFES) was designed to address a critical infrastructure need in San Mateo: the elimination of sanitary sewer overflows (SSOs) during heavy rainfall events. In response to a Cease and Desist Order from the San Francisco Bay Regional Water Quality Control Board, the City launched this project as part of its broader $1 billion Clean Water Program. The UFES consists of a 5.3-million-gallon underground holding facility located beneath the San Mateo County Event Center parking lot. Its purpose is to temporarily store excess wastewater during storms, preventing overflows into streets, creeks, and the Bay, thereby protecting public health and the environment.
Challenge
Executing the UFES project involved navigating a complex set of engineering, environmental, and community challenges. The underground structure required a deep excavation and the installation of approximately 270 micro piles extending 40 feet below the basin floor. Construction had to be staged in six phases over several years, with concurrent pipeline work along Saratoga Drive and South Delaware Street. The project team faced concerns from nearby residents about noise, vibration, dust, and traffic disruptions. Despite these hurdles, the team maintained rigorous monitoring and communication protocols to minimize impacts and maintain public trust.
Results
The UFES project reached substantial completion in 2024, marking a major milestone for the City of San Mateo.
