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27 September 1999 • AGE-NC Project No. 97-0327 Page 2 of 9 2.2. UNDERGROUND STORAGE TANK REMOVAL On 27 July 1998, one 6,000-gallon diesel UST, one 6,000-gallon gasoline UST, one 10,000-gallon gasoline UST and the associated fuel dispensers and product piping were removed from the site. Laboratory analysis of soil samples collected beneath the former UST and product piping areas detected total petroleum hydrocarbons quantified as gasoline and diesel (TPH-g and TPH-D, respectively) at concentrations ranging as high as 12,000 milligrams per kilogram.(mg/kg). Benzene, toluene, ethylbenzene and xylenes (BTEX compounds) were detected beneath the former UST and product piping areas at concentrations ranging as high as 290 mg/kg; methyl tertiary butyl ether (MTBE) was detected at concentrations ranging as high as 0.80 mg/kg. Analytical results of soil samples collected during tank removal activities are summarized in Table 1. 2.3. PREVIOUS INVESTIGATION On 12 May 1997, five soil borings (P-1 P-5 through were advanced at the site to assess the lateral g ) and vertical extent of impacted soil. A total of five soil samples were submitted to a state-certified laboratory for analysis of TPH-g, TPH-d, BTEX compounds and MTBE. The laboratory analysis did not detect TPH-g, TPH-d,benzene, toluene or ethylbenzene in the soil samples. However,xylene was detected in boring P-4 (30-foot) at a concentration of 0.026 mg/kg; MTBE was detected from Isoil samples collected in probe borings P-3' (25-feet), P-4 (30-feet) and P-5 (25-feet) at concentrations ranging as high as 0.28 mg/kg. Results of the May 1997 investigation were reported in Preliminary Site Assessment dated 06 lune 1997,prepared by AGE. Analytical results of soil ' samples are summarized in Table 2. 2.4. . REGIONAL GEOLOGIC SETTING 1 The property is situated within the Great Valley Geomorphic Province.of California, a large, elongate, northwest trending, asymmetric structural trough. The Great Valley Province has been filled with thick sequences of sediment ranging in age from Jurassic to Recent, creating a nearly flat- lying alluvial plain, extending from the Tehachapi Mountains in the south to the Klamath Mountains in the north. The western and eastern boundaries of this province are comprised of the California Coast Range and the Sierra Nevada, respectively. Rocks composing the basement complex of.the province-have not been-completely defined-but are believed to-be°metamorphic and igneous in origin. The northern and southern portions of the Great Valley Province have been designated the ' Sacramento and San Joaquin Valleys, respectively. . Based on the General Soil Map from the San Joaquin County Soil Survey, published by the United ' States Department.of Agriculture Soil Conservation Service in 1992, the site area is within the Advanced GeoEnvironmental,Inc.