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Basins 2 & 3 Pipe Capacity Improvements

Project Type: 

Collection System

Approximate Construction Start & End Dates:

January 2020 to July 2021

Project Location:

  • El Camino Real: El Camino Real from 36th Ave to Delaware St
  • Hillsdale Blvd: Hillsdale Blvd from Hacienda to El Camino Real
  • El Camino Real: El Camino Real from 38th Ave to 42nd Ave
  • 28th Ave: 28th Ave from Flores St to Juniper St
  • Colegrove St: 36th Ave from El Camino Real to Colegrove St, and Colegrove St from 36th Ave to 39th Ave
  • Flores St: Flores St from 25th Ave to 28th Ave, and 25th Ave at El Camino Real
  • Delaware St: Delaware St from 25th Ave to Pacific Blvd
  • 41st Ave: Pacific Blvd from 41st Ave to Delaware St.

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.

This package of conveyance improvements includes eight independent pipe upgrades that total approximately 16,000 feet of pipe reliefs, extensions, and upsizes. The upgrades will reinforce the system, helping to reduce sewer overflows. Project locations are shown on the maps below.

Condition assessments and site investigations at each location are nearing completion, and final design is in progress. Most of the new pipelines will be in City streets, including some in high-traffic areas. Others will be in existing utility easements on private property. Several different methods of construction, such as open-cut trenching or different trenchless technologies, will be used based on the current conditions of each site and to reduce potential impacts on the public.

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:

Caltrans Encroachment Permit; Caltrain Third Party Access; State of California, Division of Occupational Safety and Health-Mining – Tunneling; Final Programmatic Environmental Impact Report.

Engineer Firm Name:


Constructor Name:


Map of project location.

W. Hillsdale Relief Extension (SST-X3): 2,426 ft of 18-inch pipe to replace 10-inch sewer, and 149 ft of deeper 8-inch gravity sewer to replace an existing siphon

Map of project location.

Hacienda/Flores Relief Sewer (SST-5): 1,206 ft of 24-inch pipe

Map of project location.
El Camino Relief Extension (SST-X2): 377 ft of 24-inch CIPP, and 815 ft of 24-inch pipe and 486 ft of 30-inch pipe to replace 15-inch through 24-inch sewer

Map of project location.
El Camino Relief (SST-12): 1,563 ft of 8-inch and 10-inch pipe upsized to 12-inch pipe

Map of project location.
28th Ave Relief (SST-9): 1,249 ft of 15-inch pipe to replace 6-inch through 10-inch sewer, and a diversion structure to connect to the Hacienda/Flores Relief Sewer

Map of project location.
Colegrove Relief Extension (SST-X1): 454 ft of 18-inch pipe, 635 ft of 15-inch pipe, and 435 ft of 12-inch pipe to replace 6-inch through 15-inch sewers

Map of project location.
Delaware Relief (SST-3): Upsize 3,137 ft of 24-inch pipe to 36-inch pipe

Map of project location.
41st Ave Pump Station Force Main (SST-13): 3,400 ft of new 14-inch force main, and 82 ft of 24-inch gravity sewer