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Sewer Improvement Projects

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The Clean Water Program includes a range of capital projects needed to upgrade our aging wastewater system, improve wet weather capacity and reduce inflow and infiltration to comply with Regional Water Quality Control Board (RWQCB) requirements, and align with the City’s sustainability goals. The Clean Water Program will make improvements to the wastewater treatment plant, sewer pipes, pump stations, and construct 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, 6,032 manholes, and 27 pump stations. This system transports wastewater to the treatment plant for treatment and eventual discharge into the San Francisco Bay.

Our 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. The Clean Water Program has several collection system rehabilitation projects that specifically help to reduce “inflow and infiltration” into the system.

When the collection system’s hydraulic capacity is exceeded at certain bottleneck 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. 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 RWQCB issued the City with a Cease and Desist Order mandating the elimination of SSOs. Specific upgrades at the wastewater treatment plant and the collection system’s pipes and pump stations, plus the construction of the new underground flow equalization system project, provide the additional capacity needed to comply with the Cease and Desist Order requirements.