Collection System

The Clean Water Program includes a range of capital projects needed to upgrade our aging collection system, improve wet weather capacity to comply with RWQCB requirements, and align with the City’s sustainability goals. The Clean Water Program improves pipes and pump stations, plus the construction of a new underground flow equalization system facility to improve the capacity of the system.

In San Mateo, wastewater from homes and businesses is collected via a network of pipes, manholes, and pump stations. The collection system includes about 240 miles of pipelines, 6032 manholes, and 27 pump stations. This system transports wastewater to the treatment plant for treatment and eventual discharge into the San Francisco Bay.

This existing collection system contains defects and failures that lead to the “inflow and infiltration” of groundwater and rainwater into the system. This increases the volume of wastewater needing to be transported to the wastewater treatment plant. During heavy rains, these flows can reach levels that exceed the system’s capacity.

When the collection system’s hydraulic capacity is exceeded at certain locations in the system, wastewater has nowhere to go except out of manholes or other facilities at the surface, resulting in sanitary sewer overflows (SSOs), as seen in the image below. When SSOs occur, diluted raw sewage overflows onto our streets, then into our storm drains. SSOs negatively impact the water quality of our creeks, lagoon, beaches, and the San Francisco Bay. This sewage contamination is a significant public and environmental health concern. The Regional Water Quality Control Board (RWQCB) issued the City with a Cease and Desist Order mandating the elimination of SSOs.

Sanitary sewer overflow of manhole

Most of San Mateo’s sewer pipes were constructed between 1900 and 1960. Typically, sewer pipes from that time have an average lifespan of 50 to 60 years and are reaching the end of their useful life. Newer pipe materials, technologies, and construction methods are anticipated to have much longer lifespans.

The Clean Water Program map, below, shows the location of 5 “basins” that separate the collection system into areas where capacity improving pipeline and pump station projects, including an underground in-system storage facility, are packaged together. Instead of replacing the entire collection system, these projects have been strategically identified to address the capacity issues and regulatory requirements.

The City also conducts a biennial pump station rehabilitation program, along with an annual sewer pipe CCTV investigation and rehabilitation program. These rehabilitation programs do not increase capacity in the system, but rather ensure the existing collection system components are maintained and operated appropriately.

Map of the collection system