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30 July 1999 AGE-NC Project No. 97-0300 Page 2 of 5 630 ,ug/kg, 610 ,ug/kg ethylbenzene, 7,300 ,ug/kg total xylenes and 3,500 ,ug/kg MTBE. The soil sample from the west wall of tank#3 had 5.8,ug/kg total xylenes. The soil samples for tank#1 tested below the minimum reporting limits. All associated piping had detectable concentrations of motor oil and diesel. 2.2. REGIONAL GEOLOGIC SETTING The site is located in the eastern portion of the Great Valley geomorphic province of California. The valley is a nearly flat,elongate trough trending northwest and southeast for approximately 450 miles. The valley is enclosed by the granitic Sierra Nevada on the east and the sedimentary and metamorphic Coast Ranges on the west. The surficial and upper several hundred feet of subsurface layers consist primarily of unconsolidated alluvial and floodplain deposits(predominantly sand, silt, and clay)of Quaternary age, which were derived from the mountains of the Sierra Nevada. Beneath the upper sedimentary deposits lie a thick sequence of marine deposits of Mesozoic age, which in turn are underlain by a pre-Jurassic complex of igneous and metamorphic basement rock. 2.3. GROUND WATER DEPTH AND FLOW DIRECTION N ?S The estimated depth to ground water at the site is between 60 and 70 feet below surface grade (bsg) based on information from Lines of Equal Depth of Water Wells Fall 1997, published by the San Joaquin County Flood Control District and Water Conservation District. The prevailing ground water flow direction in eastern Stockton is generally toward the northeast, although flow directions may be both locally and seasonably variable. 3.0. SCOPE OF WORK Based upon analytical results of soil samples collected upon removal of the three USTs in February 1999, the PHS-EHD is requiring investigation to determine the lateral and vertical extent of hydrocarbon-impacted soil. Initially,AGE proposes to drill and sample six soil probe borings at the site.However, additional probe borings may be required to adequately define the lateral and vertical extent of hydrocarbon-impacted soil and/or ground water. The investigation will consist of the following tasks: • Permitting and pre-field work activities; Advanced GeoEnvironmental,Inc.