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7 <br /> 3. SITE HYDROLOGYGEOLOGY AND HYDROGEOLOGY <br /> 3.1 REGIONAL HYDROLOGIC SETTING AND HISTORY <br /> Stockton hes in the northern portion of California's San Joaquin Valley within the San <br /> ' Joaquin River Hydrologic Region The San Joaquin River drams the entire region which is <br /> bordered on the west by the Sacramento-San Joaquin Delta and on the East by the Sierra <br /> ' Nevada Mountain range The regional groundwater basin consists of sediments that have <br /> eroded from the surrounding mountains and washed into the valley by streams <br /> ' Mar to the Sacramento-San Joa um Delta, the Stockton area is only sever feet <br /> l� q a, Y � <br /> above sea level and surrounding water bodies experience tidal flows from the Pacific Ocean <br /> r <br /> The Stockton area has experienced tidal flows from the Pacific Ocean The Stockton area has <br /> also experienced heavy groundwater pumping for agriculture and urban use since initial <br /> settlement (Department of Water Resources 1994) This heavy pumping led to a significant <br /> decline in groundwater elevation centered at Stockton during the latter half of the century The <br /> Stockton groundwater depression was highlighted in Groundwater Monitonng (L Everett, <br /> 1980) (Figure 3-1) <br /> x' The heavy pumping in concert with the delta margin location have led to a saline <br /> groundwater front that intrudes from the west and runs north-south beneath Stockton Since <br /> ' 1971, the San Joaquin County Flood Control and Water Conservation District has monitored <br /> groundwater levels and groundwater quality along this front and encouraged better <br /> management practices The comparison of Fall 1997 Flood Control_$ Watei_,..Conservation..: <br /> ' District Groundwater Report, to a 1970 groundwater neap, shows that the groundwater at the <br /> center of the depression has risen approximately 30 feet and that the large depression centered <br /> ' on Stockton no longer exists The report, however, also shows that the aline front aced on_ <br /> 300 p -m-cHoride) has generally moved further inland (east) than in 1980 throughout the <br /> ' Stockton area.(Figure 3-2) <br />