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Regional Groundwater Storage and Recovery (WSIP)

A Water Savings Account for Protection Against Drought
The proposed Regional Groundwater Storage and Recovery (GSR) project is part of our Water System Improvement Program (WSIP) and would benefit over 2.6 million people and businesses in the Bay Area by providing a local supply of water for use in times of drought. By storing water in wet years, when water supply is sufficient, this project builds a water savings account that can be tapped during dry years or in emergency situations such as an earthquake. The project is needed to meet our dry year water supply needs. Without the project, we cannot fulfill the region's dry year water supply needs for its residents and would need to increase mandatory rationing above currently projected levels.

A Regional Approach to Drought Protection
The GSR project is a partnership between SFPUC and three San Mateo County agencies: the California Water Services Company (serving South San Francisco and Colma), the City of Daly City and the City of San Bruno. Every drop of water stored by this project helps our region during times of drought. The project would balance the use of both groundwater and surface water to increase dry-year water supplies. During years of normal or heavy rainfall, the project would provide additional surface water to the partner agencies in San Mateo County in order to reduce the amount of groundwater pumped from the South Westside Groundwater Basin. Over time, the reduced pumping would result in a water savings account of up to 60,500 acre-feet of water — a volume equivalent to that of Crystal Springs Reservoir. The water would be stored underground in the South Westside Groundwater Basin aquifer in San Mateo County.

To extract the stored groundwater, 16 recovery wells, well stations, pumps and piping would be installed as part of the GSR project. The wells could extract the stored groundwater at a rate of up to 7.2 million gallons per day which would serve up to 24,000 households. The project is designed to protect against drought, and will provide enough of a water savings account to provide protection through a multi-year dry spell lasting up to seven and a half years. The water quality from this stored supply would meet California Department of Public Health requirements for drinking water supplies.

                   Regional Groundwater Map
The proposed project would include installation of up to 16 new recovery well facilities in northern San Mateo County.


How Would the Proposed Project Work?
The concept of groundwater storage and recovery, also known as “conjunctive water management”, consists of storing water in wet years and recovering that water for use during dry years. As part of this proposed project, surface water would be used instead of groundwater in wet years. This would create a savings account of groundwater stored in the aquifer by allowing it to recharge through rainfall and decreased pumping. In dry years, when less surface water is available, the saved water would be pumped from the new groundwater well recovery facilities. This local savings account of water would be made available during drought conditions or emergencies such as an earthquake. The GSR project would increase the water supply reliability for over 2.6 million Bay Area residents and businesses that rely on the Hetch Hetchy Regional Water System for all or part of their water supply.

In wet years, municipal pumping is decreased and groundwater fills the available aquifer storage space.
In dry years, groundwater is pumped from storage – the “water savings account”.


Groundwater Storage Around the Bay
In the Bay Area alone, such programs are being implemented by Santa Clara Valley Water District (serving Campbell, Cupertino, Gilroy, Los Altos Hills, Milpitas, Monte Sereno, Morgan Hill, Mt. View, Palo Alto, San Jose, Santa Clara, Saratoga and Sunnyvale, and the towns of Los Altos and Los Gatos), Alameda County Water District (serving Fremont, Newark, and Union City) and Zone 7 Water Services Agency, (serving Livermore, Pleasanton and Dublin). These programs have been operating successfully for decades.