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depth explored (approximately 25 feet bgs), the soils consist of <br /> unconsolidated sand with minor amounts of silt and gravel Geologic <br /> cross sections for Sites #1 and #2 are provided in Appendix B <br /> 14 GROUND WATER HYDROLOGY <br />' Investigation and tank removal activities indicate the presence of confined <br /> shallow ground water conditions at Former Tank Sites #1 and #2 During <br />' drilling activities performed by ERM and previous investigators, ground <br /> water was typically encountered in borings at depths ranging from 3 5 to <br />' 19 feet bgs In these borings, ground water was first encountered after <br /> drilling through a silt and clay zone into sandy soils The fine-grained <br /> silts and clays appear to confine the ground water to the sandy soils The <br /> confined nature of the ground water was confirmed after construction and <br /> development of monitoring wells at both sites indicated that stabilized <br /> water levels tended to be higher than initial water levels In general,the <br />' ground water potentiometric surface at the property ranges from <br /> approximately 4 to 10 feet bgs <br />' Ground water flow at each tank site was evaluated using the five <br /> monitoring wells constructed at each former tank site Monitoring well <br /> M construction data is summarized in Table 1, and historic water levels <br /> measured in the site wells are summarized in Table 2 Review of the <br /> ground water potentiometric surface maps prepared for Sites #1 and #2 <br />' (Appendix B) indicates that ground water flow directions are consistently <br /> toward the south-southwest The individual data from both sites provide <br /> mutually supporting data interpretations The Stockton Deep Water <br /> Channel, which lies immediately adjacent to the northern site property <br /> line, appears to be influencing the ground water flow direction Tidally <br /> induced water level fluctuations in the channel appear to be the cause of <br /> slight to moderate variations in the ground water flow gradient <br />' Ground water wells are a common source of potable water in the Great <br /> Valley geomorphic province, however, no water supply wells are located <br /> within a 2,000-foot radius of Former Tank Sites #1 and #2 <br /> i <br />' LRXJ 7 CAI ELLUS/2996 10-10/13/99 <br />