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12 March 1999 AGE-NC Project No. 98-0432 Page 2 of 6 • During the removal of the UST hydrocarbon-impacted soil was encountered. The soil stockpiled on the site was sampled for laboratory analysis during the UST removal. The locations of these features are depicted on Figure 2. • The soil was impacted by low concentrations of total petroleum hydrocarbons quantified as diesel and gasoline (TPH-d and TPH-g). See Table 1 for soil sample concentrations. Additionally, the soil at a depth of seven feet, three feet below the invert of the UST was impacted with solvents and PCBs. • The soil was placed back in the excavation and then covered with clean pea-gravel fill and concrete. 2.2. REGIONAL GEOLOGICIHYDROGEOLOGIC SETTING The site is located within the northern San Joaquin Valley which comprises part of the Great Valley geomorphic province of California. The San Joaquin Valley is formed by the Great Valley geosyncline, which is a large, elongate, northwest-trending asymmetrical structural trough (basin). It is bordered by the Coast Ranges to the west, the Klamath Mountains and Cascade Range to the north, and the Sierra Nevada to the east. This trough has been filled with sediments derived from both marine and continental sources. Thickness of the sedimentary fill ranges from thin veneers along the valley edges to greater than 2.0,000 feet in the south central portion of the valley. The sedimentary fon-nations 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). 2.3. REGIONAL GROUNDWATER DEPTH AND FLOW DIRECTION The estimated depth to ground water at the properties is approximately 50 feet below surface grade (bsg), based on the neap titled Lines of Equal Depth to Groundwater Spring 1996 published by the San Joaquin County Flood Control District and Water Conservation District(FCD&WCD). The map titled Lines of Equal Elevation of Groundtivater Spring 1996, also published by the FCD&WCD, shows ground water flows toward the southwest in the general area of the site, but this may be