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Basin 4 Collection System Capacity Improvements

Project Type: 

Collection System

Project Schedule/Status: 

  • The pilot study is complete. The results of the study will inform repairs to the sewer system as part of the Basin C Annual Rehabilitation Project.
  • Improvements to increase sewer and pump station capacity are being reviewed to determine which are most effective. The construction schedule for the chosen improvements will be communicated with the public and stakeholders as the projects progress.

Project Location:

Basin 4 is located in southeast San Mateo.

  • The Inflow and Infiltration (I/I) Pilot Project area extends east of Eisenhower Street and Van Buren Street to the lagoon.
  • The Pipeline Improvements are located throughout the Basin 4 area. The number of individual projects and alignments are under review.
  • The Pump Station Improvement Project for the Santa Clara Pump Station is located on Santa Clara Way between Pasadena Drive and Casanova Drive.
Basin 4 Project Area Map

Project Description

How Storm Water Enters the Sewer System
How Storm Water Enters the Sewer System

Inflow and Infiltration Pilot Project

The I/I Pilot Project was designed to help the City of San Mateo (City) better understand how, how much, and where rainwater enters the sewer collection system. The condition of the sewer was determined using video inspection and smoke testing in 2018. The results from the condition assessment will help the City determine the types and locations of repairs, and where to focus rehabilitation efforts, including rehabilitation that’s part of the Basin C project.

Video Inspection

The sewer mains and sewer laterals were video inspected using a camera inside the pipes to determine the location and types of defects that may lead to repairs or replacements. Additionally, some residences have sewer laterals located in their backyards, and these were also mapped.

As part of the assessment process, some neighborhood storm drains were also video inspected. The primary goal was to identify cross-connections between the storm drains and sewer system. Eliminating cross-connections will help prevent storm runoff and lagoon water from entering the sewer system.

Nontoxic Smoke Testing

Smoke testing was performed to help locate cracks and other openings or connections where rainwater might enter the sewer collection system. To perform the test, a nontoxic smoke is blown into parts of the sewer system, and the smoke follows the path of any leak. Observers on the ground record the locations of visible smoke. As shown in the smoke testing figure, potential smoke release locations include:

  • Roof vents
  • Catch basins
  • Clean-outs
  • Roof downspouts
  • Pipe and manhole defects
Planned Repairs

The results from the condition assessment will help the City determine the types and locations of repairs needed, and where to focus rehabilitation efforts, including rehabilitation as part of the Basin C project.

How Non-Toxic Smoke Testing Works

How Non-Toxic Smoke Testing Works

Sewer Pipe Improvement Projects

The Clean Water Program (CWP) staff is conducting an analysis of potential sewer main improvement projects within the Basin 4 area. A computer application is used to create a simulation–known as a hydraulic model–of how the sewer system functions. The hydraulic model will help determine the locations where improvements are needed to reduce the likelihood of sewer overflows. Improvements may include enlarging or rerouting existing sewer mains to increase capacity and more effectively transport wastewater within the sewer system.

Pump Station Improvement Projects

Pump stations lift wastewater so that it can continue flowing by gravity from homes and businesses throughout San Mateo to the wastewater treatment plant. Increasing the pump station capacity to move wastewater is another way to reduce the risk of sewer overflows throughout the community.

The Santa Clara Pump Station does not have adequate capacity to meet projected stormwater flows and is nearing the end of its useful life. The CWP staff is determining the most effective way to increase the capacity of this facility.

If you have additional questions regarding this work, please email: or call (650) 727-6870.