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ATTACHMENT D:MAP AND CROSS SECTIONS OF USDWS Sacramento or San Joaquin rivers,the major rivers that drain the Sacramento and San Joaquin Valleys, and exit the valley at the Delta. Hydrogeology The groundwater system within the Central Valley is subdivided into subbasins,commonly based on surface water drainage that influences the underlying water flow. The STIG-LEC facility is within the Eastern San Joaquin Subbasin portion of the San Joaquin Valley Groundwater Basin (DWR,2006) (Figure D-2). The Eastern San Joaquin Subbasin is bounded by the Mokelumne River on the north and northwest,San Joaquin River on the west, Stanislaus River on the south,and consolidated bedrock of the Sierra Nevada on the east. The Eastern San Joaquin Subbasin is drained by the San Joaquin River and several major tributaries, including the Stanislaus,Mokelumne, and Calaveras rivers. Although groundwater levels in the Eastern San Joaquin Subbasin have shown a steady decline over the past 40 years, groundwater conditions near the STIG-LEC facility have remained fairly stable (Figure D-3). During this period, groundwater levels in other portions of the Eastern San Joaquin Subbasin 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 gpm(DWR,2006). Saltwater intrusion occurring in the Stockton area 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 located southeast of Lodi (DWR,2006). Representative concentrations of typical groundwater constituents are shown in Table D-1. TABLE D-1 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:AFC, 2008 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 direction and magnitude of the hydrologic gradient are controlled by a pumping cone depression around the City of Stockton that persists throughout the year (Figure D-4) (City of Lodi,2006). Locally,groundwater use for irrigation is higher to the east of the STIG-LEC facility project site resulting in a local gradient that is consistently to the D-2 SAC/371322/082550018(ATTACHMENT-D.DOC)