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Tertiary clastic material Late Tertiary to Present Age sediments are exclusively of nonmarine clastic deposition in a variety of alluvial- fluvial environments The present day surface outcrop of geologic units in the Stockton area reflects the Late Tertiary alluvial valley fill derived from the San Joaquin River The fill probably extends to a depth of several hundred feet Site-specific geologic information in the vicinity of the property is ' limited to that which was developed during investigations of the former tank sites Two general soil types were encountered From the ground surface to a depth ranging between approximately 10 and 20 feet below ground surface (bgs), the soils consist of serruconsolidated silts and clays Below this layer and to the maximum depth explored (approximately 25 feet bgs), the soils consist of unconsolidated sand ' with minor amounts of silt and gravel ' HydrogGeology Investigation and tank removal activities indicate the presence of ' confined shallow ground water conditions at Former Tank Sites #1 and #2 During drilling activities performed by ERM and previous investigators, ground water was typically encountered in borings at depths ranging from 3 5 to 19 feet bgs In these borings, ground water was first encountered after drilling through a silt and clay zone into sandy soils. The fine-grained silts and clays appear to confine the ' ground water to the sandy soils The confined nature of the ground water was confirmed after construction and development of monitoring wells at both sites indicated that stabilized water levels ' tended to be higher than initial water levels. In general, the ground water potentiometric surface at the property is at a depth of approximately 4 to 6 feet bgs ' Review ofg round water potentrometric surface maps prepared individually for Sites #1 and #2 indicates that ground water flow ' directions are consistently toward the south-southwest The individual data from both sites provide mutually supporting data interpretations The apparent cause of the flow direction is the ' Stockton Deep Water Channel that lies immediately adjacent to the northern site property line Tidally induced water level fluctuations in the channel appear to be the cause of slight-to-moderate variations in the ground water flow gradient Ground water wells are a common source of potable water in the Great Valley geomorphic province, however, no water supply wells are located within a 2,000-foot radius of Former Tank Sites #1 and #2 2-2