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.� CONFIDENTIAL 12686 E*.49cke Rd.,Lockeford,California AWS Project No.0041 4.0 AREA GEOLOGY& GYDROGEOLOGY 4.1 Geoloev The Site is located on the United States Geological Survey 15 minute Lockeford, California Topographic Map Quadrangle, dated 1968 (photo-revised 1979), at an approximate elevation of 100 feet above sea level. The ground surface at the Site has a gently southwesterly slope, and the Site is situated approximately 4 miles north-northwest of Mokelumne River. The Property lies within the San Joaquin Valley region consisting of Quaternary alluvial deposits consisting of uncondolidated gravel, sand, silt, and clay originating from the Sierra Mountains. Alluvial soil generally consist of silty medium to fine grained sands with occasional gravels 4.2 Hvdroeeoloav According to Mr. Ted Norgard of San Joaquin County Environmental Health Division, ground water in the area is reported at approximately 100 feet below grade. According to the Lockeford Community Services District, the nearest community ground water well is located approximately 2,000 feet to the west. 5.0 CONCLUSIONS The following conclusions are based on analysis results for soil samples, on field observations, and on our experience with similar projects: • Soil beneath the storm pond does not appear to have been adversely impacted by petroleum hydrocarbons and Title 22 (CAM) metals. • Low concentrations of petroleum hydrocarbons were detected in soil samples collected from the NW and SW dry wells. Only Toluene and Total Petroleum Hydrocarbons (as gasoline) (TPHg) were detected above the laboratory detection limits. The registered levels for the NW dry well was 1.4 ppm for Toluene, and 2.0 ppm for TPHg. The registered levels for the SW dry well was 0.034 ppm for Toluene, while no TPHg was detected in the SW dry well. No TPHd (diesel)was detected in the four dry wells, and the CAM 17 metal results for the four dry wells were within the normal average for background levels. 6.0 PROJECT DISCUSSION Based on Site reconnaissance, field observations and laboratory chemical analysis results, it appears that minor gasoline releases on the paved parking lot migrated into the holding pond. ` The outfalls from the storm drain system that discharge storm water into the holding pond are located on the northwestern and southwestern portions of the holding pond. Based on these facts, a reasonable assumption can be made that gasoline leaks from parked vehicles migrated ` into the storm drain system and were deposited in the holding pond through both outfalls. Both 5