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i I 2.2 Project History On October 1 , 1992 three underground storage tanks were removed by Crisp } Construction from the Derickson Trucking property in Escalon, California as follows: One (1) 12,000.Gallon Diesel Tank One (1) 2,000 Gallon Gasoline Tank One (1) 2,000 Gallon Waste Oil Tank Soil samples were collected from beneath the ends of the 2,000 gallon tanks and beneath the ends and center of the :12,000 gallon tank. The 12,000 gallon diesel tank samples were analyzed for the-Volatile aromatics benzene, toluene, ethylbenzene, and xylenes (BTEX) and Total P.etroleumn°Hydrocarbons (TPH) referenced to diesel. The 2,000 gallon gasoline tank samples were analyzed for BTEX, TPH as gasoline, ethylene dibromide (EDB) and Total Lead. The 2,000 gallon waste oil tank samples were analyzed for BTEX, TPH (diesel), TPH(gasoline), polychlorinated biphenyls 3 (PCBs) and the metals listed in Title 22 of the California Code of Regulations (CAM metals). The samples were collected and analyzed by FGL Environmental. Slightly elevated diesel concentrations were detected in the samples retrieved from beneath =. - the north and center.of the former diesel tank. Following a review of these analytical j. results, the San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) required a full assessment to determine the extent of the soil and/or groundwater impaction related to the diesel tank. AGI was retained to conduct the Site Assessment. During March 15-16, 1993 four borings were-drilled adjacent to the open diesel tank excavation. The borings were advanced to a maximum depth of 40 feet to delineate the vertical and lateral limits of impacted soils. Drilling operations, :soil sampling and field screening were conducted according to standard protocols. _` Selected samples were submitted to certified laboratories for chemical analysis.. Hydrocarbons were encountered only by Boring D- 1', angle drilled under the former diesel tank from the north end of the excavation. Based on the field and analytical results; an area of 550 square feet was thought to be impacted by diesel hydrocarbons. The plume was interpreted to extend to a depth of at least 33 feet. The highest TPH(diesel) concentrations reported were 4100 ppm. In addition, a fifth boring was advanced to 10 feet at the site of the former 2,000 gallon = waste oil tank to obtain a sample for Nickel and Chromium analysis. The metal concentrations detected were well below regulatory limits and .appear to represent background concentrations. The water level in a domestic water well located on the property occurs at approximately 90 feet and historically a water table as high as 50 feet has been reported in the Escalon area. A Leaching Potential'Analysis as described in the 3 of 9 {