Clean Water Program LogoCity of San Mateo LogoCity of Foster City LogoCity of San Mateo Public Works Logo


Basin 2 & 3 Pipe Capacity Improvements – Delaware Street Relief Sewer Project

Map of Delaware St. Project LocationProject Type: 


Approximate Construction Start & End Dates:

June 2022 – June 2023

Project Status:

Construction is underway and is expected to be complete in June 2023.

Project Location:

In the Caltrain right-of-way between the north end of the Hillsdale Caltrain Station parking lot near 28th Avenue to the junction of Pacific Blvd and Delaware Street.

Project Description:

The purpose of the Basin 2 & 3 Collection System Upgrade is to improve the ability of the overall wastewater collection system to manage heavy seasonal rainfall. These improvements will help prevent sewer overflows, as well as help the City comply with regulatory requirements. During heavy rains, the wastewater collection system capacity is overwhelmed by the amount of rainwater that enters the system through infiltration and inflow. This causes sewer overflows at locations around San Mateo, such as manholes and at the wastewater treatment plant. These overflows contaminate city streets, creeks, lagoons, beaches, and San Francisco Bay.

The Basin 2 & 3 package of conveyance improvements includes four independent pipe upgrades that total approximately 16,000 feet of pipe, including new relief sewers and extensions and size increases to existing lines. The upgrades will reinforce the system, helping to reduce sewer overflows.

This Delaware Street Relief Sewer Project will construct approximately 3,100 feet of new high-flow relief gravity sewer line that generally parallels the existing gravity sewer along Delaware Avenue. The project will be constructed using several construction methods, such as open-cut trenching and open cut and trenchless (micro tunneling) technologies will be used based on the current conditions of the site and to reduce potential impacts on the public.

Most of the new pipelines will be installed in City streets, including some in high-traffic areas. Other pipelines will be installed in existing utility easements on private property. Key aspects of the project will be constructed in the Joint Powers Board right-of-way. The crews will be in close coordination with the Joint Project Board to interface building the pipeline concurrently with grade separation projects.

Mitigation measures will be in place to minimize the effects of the project on residents, businesses, commuters, and others. Notifications will be sent ahead of construction to alert property owners and occupants when the work will be conducted.

Environmental and Permitting Documents:

In Progress

Engineer Firm Name:


Constructor Name: