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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 the RGSR project, surface water will be used instead of groundwater in wet years, allowing the groundwater to recharge through rainfall and decreased pumping. This will create a savings account of up to 20 billion gallons of groundwater that will be stored in the aquifer.
In dry years, when less surface water is available, the saved water will be pumped from the new groundwater well recovery facilities at a rate of up to 7.2 million gallons per day. To put this into context, that amount of water could serve up to 24,000 homes. The RGSR project is designed to help diversify our water supply for drought protection and will ensure we are even more resilient during and after an earthquake or other emergency. The water quality from this stored supply will meet the California Department of Public Health requirements for drinking water supplies.
A Regional Approach to Groundwater Protection
A landmark agreement between the SFPUC and three San Mateo County organizations was finalized and signed in December 2014 to ensure long-term management and sustainability of the South Westside Groundwater Basin. The partnership with SFPUC, City of Daly City, City of San Bruno and California Water Service Company allows these agencies to operate the basin sustainably and provide us with a new 20-billion-gallon regional dry year groundwater supply. These San Mateo County agencies provide drinking water from two sources, local groundwater from the South Westside Groundwater Basin and surface water supplies from the SFPUC.
Groundwater Storage Around the Bay
In the Bay Area alone, similar conjunctive water management programs are being implemented by the 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), the Alameda County Water District (serving Fremont, Newark, and Union City) and the Zone 7 Water Services Agency (serving Livermore, Pleasanton and Dublin). These programs have been operating successfully for decades.
The original project design included the construction of up to 16 groundwater wells and well stations to be connected to three wholesale customers on the Upper Peninsula and the SFPUC transmission system to achieve the water supply goal. Phase 1 included the installation of 13 well stations to produce approximately 6.2 mgd, and the original scope of Phase 2 included construction of 2 to 3 additional well stations, based upon well yield.
Due to difficulties with siting well stations in the central portion of the groundwater basin, Phase 2 has been modified to install up to 3 test wells (Ludeman North, Ludeman South and Centennial Trail), complete the South San Francisco Main well and pipeline, and complete other Phase 1 scope items, including chemical system monitoring, sampling and storage at various sites. The Phase 2 test wells will not be converted to production wells at this time, but will allow for determination as to whether the identified sites could be viable future production wells, and will provide valuable information related to water quality and potential pumping capacities that can be used for future planning and decision making.