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T f 19 March 1999 AGE-NC Project No. 98-0471 Page 2 of 12 sedimentary formations range in age with the older deposits being primarily marine in origin and the younger deposits being primarily continental. Continental-derived sediments were primarily deposited in lacustrine, fluvial, and alluvial environments with sources being the mountain ranges surrounding the valley (Olmsted and Davis, 1961). The site is located on unconsolidated and semi- consolidated alluvium, lake, playa and terrace deposits of Quaternary age (California Division of Mines and Geology, 1977). The Modesto, Riverbank and Turlock Lake Formations and overlying Recent alluvium are the principal sources of domestic ground water in the 13,500-square mile San Joaquin Valley Ground Water Basin (Basin 5-22). Ground water occurs in a generally sandy clay layer extending from approximately 6 feet bsg to an unknown depth. 2.2. GROUND WATER DEPTH AND FLOW DIRECTION Based on the San Joaquin County Flood Control District and Water Conservation District Lines of Equal Depth of Water Wells Fall 1996 map no relative information to estimated depth to ground water is available for the site area in western most Stockton, except that ground water elevation contours are less than 10 feet below surface grade(bsg). Based upon information obtained from the AST assessment, ground water is currently at a depth of approximately 5 feet below surface grade (bsg). Ground water flow direction is unknown and may be highly variable. 2.3. REGIONAL HYDROLOGIC SETTING The Middle River is the nearest surface water feature to the property, located approximately 500 feet south of the site. Water from the channel drains into the San Joaquin River and is primarily used for commercial and recreational boating, with agricultural as a secondary use. The channel contains water continually and potentially has a tidal effect upon ground water depth or flow direction in the area. 2.4. ON-SITE RECONNAISSANCE In June 1998, AGE personnel visited the site at the request of Herum, Crabtree et al, to identify locations on the property that potentially have subsurface impacts resulting from past and current site usage and related environmental concern area. Three area,of concern were noted: a large (7,500- gallon)diesel AST which appeared to be leaking fuel from the dispensing location onto the dispenser pad;a smaller operating (approximately 1,000-gallon)AST with a portion of its system lines buried; and an area used for waste oil handling and possibly disposal. Advanced GeoEnvironmental,Inc.