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Report Second Phue subsurface lnvesLiption <br /> City of Stocks n, Banner Island, Stockon,CA <br /> May 20, 1992 <br /> W06M.1D <br /> channel. Glass, metal and wood were noted in several of the shallow borings drilled during this <br /> phase and in November 1989. Depth to water is approximately 21 feet below grade. The <br /> groundwater flow direction is northerly. <br /> 3.1 Local Groundwater Conditions <br /> A review of data from the California Department of Water Resources (DWR), Regional Water <br /> Quality Control Board (RWQCB), United States Geological Survey (USGS),and the San Joaquin <br /> County Flood Control District (SJCFCD) was undertaken in order to characterize the water <br /> quality and hydrologic setting in the Stockton area. <br /> An investigation conducted by DWR (1967) during the mid-1960's indicated that the <br /> groundwater supply in the greater Stockton area was being slowly infringed upon by the poor <br /> quality waters underlying the Delta. The poor quality waters seemed to be migrating from the <br /> west at a rate governed by certain constant geologic parameters and variable hydnz ulic <br /> parameters, including increased pumping east of Stockton. Appendix B, Figure B-1 shows a <br /> comparison of the chloride content of select wells against time and distance from an arbitrary <br /> baseline (300 parts per million) for the years 1953 and 1963. The largest separation between <br /> the time-chloride lines was in the area of the Deep Water Channel and expanded northeasterly, <br /> rather than the southeasterly direction towards the deepest closing contour of the cone of <br /> r depression (Figure B-2). Stratigraphic conditions in the area may be influencing this direction <br /> of water movement in part; Figure B-3 shows that greater thicknesses of sand were encountered <br /> in wells in the channel area than towards the southeast (DWR, 1967). The major control on the <br /> intrusion pattern, however, has been agricultural and municipal pumping east of downtown <br /> Stockton. Although most of the data used to compute the rate of intrusion are from wells <br /> producing from approximately 150 feet below grade or greater, it is believed that the shallower <br /> R040"I.SAT 4 <br />