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Administrative Draft Environmental Impact Report Gill Medical Center Project Impact 4.12-4: The proposed project would use groundwater for its water supply, which could decrease groundwater supplies, impeded sustainable management of the groundwater basin, and conflict with the local groundwater sustainability plan. Impact Determination:no impact Threshold: Substantially decrease groundwater supplies or interfere substantially with groundwater recharge such that the project may impede sustainable groundwater management of the basin. and Conflict with or obstruct implementation of a water quality control plan or sustainable groundwater management plan. The potable water supply for the Project will be provided by onsite groundwater wells. In accordance with the requirements of Senate Bill 610 and California Water Code Sections 10910-10915, a Water Supply Assessment (WSA) (ECORP 2021) was prepared to evaluate the adequacy of the groundwater supplies for the Project. Water for the existing vineyards on the Project site are provided by an old natural gas well that has been converted to a water well. The Project will replace approximately 32 acres of vineyards. For the proposed Project, water would be supplied by a new recently installed well near the center of the Project site. The information presented below is summarized from the WSA. The proposed Gill Medical Center is located within the Eastern San Joaquin Subbasin within the larger San Joaquin Valley Groundwater Basin. In general, groundwater levels within the East San Joaquin Valley Subbasin exhibit minor seasonal fluctuations of a few feet due to increased pumping demand in the summer and increased recharge during the winter and spring. The more significant trend has been a persistent decline in groundwater levels ranging from 20 feet to more than 60 feet in most areas of the Subbasin since the 1960s. However, groundwater levels have remained relatively stable within the City of Stockton, potentially because municipal water demands tend to be appreciably lower than agricultural water use on a per-acre basis. The current volume of fresh (i.e., non-saline) groundwater in storage in the Eastern San Joaquin Subbasin is estimated to be 53 million acre-feet. The amount of groundwater in storage has decreased by approximately 0.01 percent per year, or about 5,300 acre-feet per year, between 1995 and 2015. However, a reduction in beneficial uses, which is an undesirable result under the Sustainable Groundwater Management Act, would not occur until the volume of water in storage is reduced by 23 million acre-feet, to a total of 30 million acre-feet. Under the current rate of decrease in water storage, it would take several thousand years to reduce the volume in storage to that level. As such, it is highly unlikely the Subbasin will experience conditions under which the volume of stored groundwater poses a concern, although the depth to access that groundwater will increase over time, potentially requiring the deepening of many wells resulting in increasing drilling and pumping costs, and higher energy demand. As discussed in Section 4.12.1.3, above, and shown in Table 4.12-1, during wet and normal years, which have occurred for 24 of the past 50 years, there is a net increase in groundwater in storage in the Subbasin, ranging from an average of 20,000 acre-feet per year under normal hydrologic conditions to an average of 185,000 acre-feet per year during wet hydrologic conditions. During below normal, dry, and critically dry hydrologic conditions, which have occurred for 26 of the past 50 years, there is a net Hydrology and Water Quality 4.12-25 October 2021