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15 5.2 Water Supply from the SFPUC RWS The SFPUC RWS supplies water to both retail and wholesale customers. Retail customers include residents, businesses, and industries located within the boundaries of the City and County of San Francisco. Wholesale customers include 26 cities and water supply agencies in Alameda, San Mateo, and Santa Clara counties, including Redwood City. The City is a member agency of Bay Area Water Supply and Conservation Agency (BAWSCA) and purchases treated water from the SFPUC RWS in accordance with the November 2018 Amended and Restated Water Supply Agreement between the City and County of San Francisco and Wholesale Customers in Alameda, San Mateo, and Santa Clara Counties, which was adopted in 2019. The term of the agreement is 25 years, with a beginning date of July 1, 2009 and an expiration date of June 30, 2034. Per the agreement, the City has an Individual Supply Guarantee (ISG) of 10.93 million gallons per day (mgd), or 12,243 AFY, supplied by the SFPUC RWS. Between 2016 and 2020, the City purchased between 67 percent and 80 percent of its ISG. Additional discussion of the SFPUC RWS water supplies is provided in the City’s 2020 UWMP and SFPUC’s 2020 UWMP. 5.3 Groundwater Supply The City does not rely upon groundwater supplies for its potable water supply since the entirety of the City’s supply is purchased from the SFPUC RWS. However, the City is currently in the early stages of evaluating groundwater as a future emergency and back-up supply. As such, this WSA evaluates groundwater basin conditions pursuant to Section 10910(f). 5.3.1 Groundwater Basin Description The City’s service area overlies the southern end of the San Mateo Plain Subbasin (DWR basin number 2-009.03; “subbasin”) of the Santa Clara Valley Basin. The subbasin is not adjudicated, nor has it been found by the Department of Water Resources (DWR) to be in a condition of overdraft. As part of the implementation of the Sustainable Groundwater Management Act (SGMA), the subbasin was ranked as a “very low priority” basin under the California Statewide Groundwater Elevation Monitoring basin prioritization process. As such, the basin is not subject to the requirements of SGMA. The subbasin is filled with alluvial fan deposits formed by tributaries to San Francisco Bay that drained across the basin and toward the center of the Bay. These alluvial fan deposits are interbedded with thick clay aquitards or confining layers and comprise the main water bearing formations within the subbasin. The major water bearing formation of the subbasin is the Quaternary alluvium, from which all larger yielding wells acquire their water. The Santa Clara Formation underlies the Quaternary alluvium and is the other water bearing formation of the subbasin. In general, the groundwater system is unconfined in the higher elevations, and confined or semiconfined at lower elevations closer to San Francisco Bay. ATTY/RESO.0027/CC RESO WATER SUPPLY ASSESSMENT (920 SHASTA) - EXHIBIT A REV: 04-22-25 VR Page 15 of 42