SITE INFORMATION AND CORRESPONDENCE

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5.15 WATER RESOURCES Groundwater levels in the Eastern San Joaquin Subbasin have shown a continuous decline over the past 40 years. During this period, groundwater levels have declined at an average rate of 1.7 feet per year and have dropped as much as 100 feet in some areas (DWR, 2006). Well yields in the fresh water-bearing formation underlying the subbasin range from approximately 650 to 1,500 gallons per minute (DWR,2006). Saltwater intrusion,occurring as a result of declining groundwater levels,has caused water quality to deteriorate eastward along a 16-mile front on the east side of the Delta. In addition, large areas of elevated nitrate levels exist in groundwater supplies within the subbasin southeast of Lodi. The majority of groundwater in the Eastern San Joaquin Subbasin is characterized by calcium-magnesium bicarbonate or calcium-sodium bicarbonate types. Bicarbonate is predominant in the eastern part of the subbasin. Large areas of chloride type water occur along the western margin of the subbasin along the San Joaquin River. Based on the analyses of 174 water supply wells in the subbasin, total dissolved solids (TDS) concentration ranges from 30 to 1,632 milligrams per liter,with an average TDS of approximately 310 milligrams per liter (DWR,2006). Table 15.5-5 presents groundwater quality from a well near the LEC project site. TABLE 5.15-5 Groundwater Quality in the Vicinity of the LEC Project Site Constituent Quantity Total Dissolved Solids 600-700 mg/L Calcium, Magnesium 40 mg/L Chlorine 10-20 mg/L Sulfate 5 mg/L Sodium, Potassium 60-70 mg/L Bicarbonate, Carbonate 60-70 mg/L Source: Lowney-Kaldveer Associates, 1975 Domestic wells in the Eastern San Joaquin Subbasin range from approximately 25 to 993 feet in depth, averaging approximately 242 feet (DWR,2006). Irrigation wells in the subbasin range from approximately 75 to 780 feet in depth, averaging approximately 349 feet (DWR, 2006). Regionally, the hydrologic gradient and groundwater movement are controlled by a pumping cone depression around the City of Stockton that persists throughout the year, and the groundwater moves in an east-southeasterly direction (City of Lodi,2006). Groundwater use for irrigation is higher to the east of the LEC project site resulting in a local gradient that is consistently to the east (City of Lodi,2006). As a result, groundwater in the vicinity of the LEC project site flows generally from west to east (City of Lodi,2006). Groundwater elevations in the vicinity of the LEC project site fluctuate seasonally and in response to variations in precipitation from year to year (City of Lodi,2006).Groundwater fluctuations are lowest to the west of the LEC project site because the Delta is subject to less pumping and more uniform recharge throughout the year. Groundwater elevations at production wells in the vicinity of the LEC project site typically fluctuate by up to SAC1371322/082340005(LEC_5.15_WATER_RESOURCES.DOC) 5.15-9