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24 July 2002 AGE-NC Project No. 02-9048 Page 2 of 5 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).The estimated depth to ground water at the site is approximately 50 to 60 feet below surface grade(bsg)based on information from Lines of Equal Depth of Water Wells Fall 1999,published by the San Joaquin County Flood Control District and Water Conservation District- FCD&WCD. Based on the map titled Lines of Equal Elevation of Groundwater Spring 1999 also published by the San Joaquin County FCD&WCD, estimates the ground water elevation at approximately 10 to 15 feet below sea level and ground water flow generally toward the southwest. However, this may be greatly modified by local recharge and discharge patterns. 2.2. UNDERGROUND STORAGE TANK REMOVAL The following information was obtained from EHD records: One 2,000-gallon unleaded gasoline underground storage tank(UST) and one 500-gallon waste oil UST were removed from the site by Thorpe Oil on 22 May 1987. One soil sample was collected from the floor of each UST excavation. Sample U-2,collected beneath the unleaded UST at a depth of 10 feet,was analyzed by a certified laboratory for total volatile petroleum hydrocarbons(TVPH), benzene, toluene and xylenes (BTX), and sample WO-1, collected beneath the waste oil UST at a depth of 10 feet,was analyzed for TVPH,BTX,polychlorinated bi-phenols(PCBs)and halogenated hydrocarbons(HVOCs);at that time,the soil samples were not analyzed for the fuel additive methyl tert-butyl ether(MTBE).No TVPH,BTX,PCBs or HVOCs were detected in the analyzed samples. Based upon results of soil sample analysis, the site was closed by the EHD with no further investigation. On 18 April 2000,two soil samples were collected by Ground Zero Analysis,Inc. at depths of 6 and 12 feet bsg beneath a 650-gallon gasoline UST,located approximated 10 feet northwest of the former 2,000-gallon gasoline UST; the samples were analyzed for TPH-g, BTEX, total lead, oxygenated additives and volatile organic compounds. The analytical results indicated that total lead concentrations were consistent with naturally occurring background levels;no other target analytes were detected. Based on the analytical results, EHD deemed that no further action was required in a letter dated 30 May 2000, and closed the UST in place. 2.3. PREVIOUS SITE ASSESSMENTS An AGE-prepared Phase I Site Assessment, dated 14 January 2000, identified: 1)two former UST locations and dispenser area, 2) storage locations for batteries, motor oil and other lubricants, 3) hydraulic lifts, 4) a clarifier and 5) a possible former auto paint booth which may be items of Advanced GeoEnvironmental,Inc.