• Email
  • Print

Wet Weather Equalization Basin

Wet Weather Equalization Basin (EQ Basin)


Storm Event Memo 11-5-2021


Project Overview  UPDATED 11/3/20

The City of Pacifica constructed a 2.1 million gallon wet weather flow equalization basin (EQ Basin) in order to comply with the San Francisco Regional Water Quality Control Board's Cease and Desist Order (CDO) to eliminate capacity related sanitary sewer overflows by January 1, 2019. The project consists of buried multi-cell tank that was constructed with a two part wall system including a slurry wall and cast-in-place liner wall. Wet weather flows are diverted to the equalization basin through a system of overflow weirs that passively divert excessive flows from the City's existing collection system into an influent conveyance pipeline. The 2.1 million gallon basin was constructed within the parking lot of the City's community center located immediately adjacent to single family homes. The diversion structures and conveyance pipeline were constructed within residential, established neighborhood with numerous existing utilities requiring detail design investigation and coordination. Pipeline installation methods included bore and jack as well as open trench.  

The successful completion of the project was a result of close collaboration between the City, design team, and construction management team members. The EQ Basin project is a key component to the City’s overall management of its wastewater collection and treatment system in order to provide reliable sanitary sewer service to the community while protecting the environment and water quality. The EQ Basin completion is the result of more than a decade of planning, design, and construction efforts to meet the terms of the CDO.


2020 American Public Works Association- Silicon Valley Section, Project of the Year - Wet Weather Equalization Basin (EQ Basin)

2020 American Society of Civil Engineers -  San Francisco Section, Environmental Project of the Year - Wet Weather Equalization Basin (EQ Basin)


For More Information on the EQ Basin Project:

Quick Fact Sheet on EQ Basin project

EQ Basin Project Overview Information Sheet

12/12/2016 Presentation to City Council on the EQ Basin Project - a project update on the EQ Basin Project as presented at the City of Pacifica Council Meeting on December 12, 2016.

In accordance with the California Environmental Quality Act (CEQA), the City of Pacifica prepared and released a Draft Mitigated Negative Declaration/Initial Study (MND/IS) for public review. Hardcopies of the document can be reviewed at the City of Pacifica Planning Department, 1800 Francisco Blvd.

Fact Sheet for more information on CEQA Public Comment Period for EQ Basin Project

Wet Weather Equalization Basin Site Feasibility Evaluation - Final
Addendum to Wet Weather Equalization Basin Site Feasibility Evaluation