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18 November 1999 AGE-NC Project No. 97-0327 Page 2 of 9 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 SUBSURFACE INVESTIGATION On 12 May 1997, five soil borings (P-1 through P-5) were advanced at the site to assess the lateral and vertical extent of impacted soil as part of a preliminary site assessment. Results of the May 1997 investigation were reported in Preliminary Site Assessment, dated 06 June 1997, prepared by AGE. 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 feet bsg) at a concentration of 0.026 mg/kg; MTBE was detected from soil samples collected in probe borings P-3 (25 feet bsg), P-4 (30 feet bsg) and P-5 (25 feet bsg) at concentrations ranging as high as 0.28 mg/kg. Analytical results of soil samples are summarized in Table 2. On 21 June 1999, four soil probe borings (P-6 through P-9) were advanced at the site to assess petroleum hydrocarbon-impact encountered during UST removal activities. Results of the June 1999 investigation were reported in Preliminary Irn�estigation and Evaluation Report,dated 27 September 1999, prepared by AGE. Analytical results of soil and grab ground water samples collected are summarized in Tables 2 and 3. The estimated extent of petroleum hydrocarbon-impacted soil is — depicted in cross sectional view A -A ' in Figure 3. Based on Figure 3, the horizontal and vertical extent of petroleum hydrocarbon-impacted soil has not been fully delineated toward the south, southeast and southwest of the UST area; the horizontal and vertical extent of petroleum hydrocarbon-impacted ground Nvater has not been fully delineated in any direction. — 2.4. REGIONAL GEOLOGIC SETTING The property is situated within the Great Valley Geomorphic Province of California, a large, elongate, north-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 Advanced GeoEnvironmental,Inc.