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09 June 2000 AGE-NC Project No. 98-0497 Page 2 of 10 samples collected beneath the diesel USTs/dispenser island area and product piping detected total - petroleum hydrocarbons quantified as diesel (TPH-d) lat concentrations as high as 5,100 mg/kg (milligrams per-kilogram). ` 2.3. PRELIMINARY SUBSURFACE INVESTIGATION. On 29 September 1999,two soil probe borings(P=1 and -2)were advanced at the site. Soil samples were.collected at approximate 5-foot intervals. Faint t' moderate hydrocarbon odor was noted in duplicate soil samples collected from P-1 at depths between 15 feet bsg and-65 feet bsg. Organic vapor was detected at concentrations as high as 400 parts per million-(ppm) using a PID in soil sample duplicates.collected from P-1. Total petroleum hydrocarbons quantified as gasoline(T- PH-;g)-were detected in soil samples collected from probe boring P-l at concentrations as high as 1,900mg/kg;TPH-d was detected in soil samples collected from P-1 at concentrations as high as 10,000 g/kg. However, further laboratory review of the gasoline=and diesel-range chromatograms indic, ted the sample chromatograms to be more- . indicative of a diesel impact. Volatile aromatic compounds(benzene, toluene, ethyl benzene and xylenes;BTEX)were detected in,soil samples collected from'P-I and were quantified at concentrations ranging as high as 8.3 mg/kg;benzene was detected in the P-I sample at 65 fee bsg,and was quantified at a concentration of 0.047,mg/kg: Methyl tertiary-butyl ether.(MTBE)was detected in'soil samples collected from-P-I utilizing EPA Method 8260 Modified at concentrations ranging as-high as 0.055 mg/kg.No other fuel oxygenated• compounds were detected during the laboratory analysis of selected soil samples. Details of the initial investigation were included m1he.Preliminary Investigation and Evaluation 'Report dated 12 October 1999, prepared by.AGE. 2.4. REGIONAL GEOLOGIC SETTING The property is situated within the Great Valley•Ge. morphic Province of California, a large, elongate, northwest.trending, asymmetric structural trough. The Great Valley Province has been . 'filled with thick se4iiences of sediment ranging in age frm Jurassic to Recent,creating a nearly flat- dying alluvial plain,extending from the Tehachapi Moun ains in the south to the Klamath Mountains in the north. The western and eastern boundaries ofthi province are comprised of the California Coast Range and the Sierra Nevada, respectively. Roc s composing the basement complex of the Advanced GeoEnvironmental,Inc.