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15 April 1999 AGE-NC Project No. 98-0520 Page 2 of 10 UST #3 at a depth of twelve feet bsg. According to a PHS-EHD inspection report petroleum hydrocarbon odors and soil discoloration were noted beneath USTs. Hydrocarbon Impacted Soil TPH-g was detected at the south end of the former UST #3 at a concentration of 4 milligrams per kilogram(mg/Kg). Volatile aromatic compounds (benzene,ethyl-benzene,toluene and total xylene) were detected in the soil samples collected from the south end of the former USTs #2 and #3 at concentrations up to 180 micrograms per kilogram (gglKg). BTEX compounds were also detected in the dispenser samples at concentrations up to 62 /.cg/Kg. Total petroleum hydrocarbons quantified as gasoline (TPH-g) was not detected in the soil samples collected from the dispensers. Total petroleum hydrocarbons quantified as diesel (TPH-d) was not detected in any of the UST floor samples, the dispenser soil samples or the water sample collected from the site. Methyl tertiary butyl ether(MTBE)was detected m€�of the UST floor ands d spe ser soil samples at concentrations up to 320 yg/Kg. Stockpile soil from the UST removal had detectable concentrations of TPH-g, TPH-d and BTEX, as well as MTBE and tertiary-Butanol (TBA). The greatest concentration of TPH-g was 120 mg/Kg and the greatest detection of TPH-d was 790 mg/Kg. BTEX compounds were detected at concentrations up to 6,800 µg/Kg (xylene). MTBE and TBA were detected in the stock pile at concentrations up to 500 yg/Kg and 970 µg/Kg, respectively. Dissolved Petroleum Hydrocarbons TPH-g was detected in the grab ground water sample at a concentration of 37 milligram per liter (mg/L). MTBE was also detected in the grab ground water sample at a concentration of 3,200 micrograms per liter (yg/L). S AID PV's av(nC� x z6vo ,. 2.3. REGIONAL GEOLOGIC/HYDROGEOLOGIC SETTING Based on a Geologic Map of California,published in 1977 by the State of California Department of Mines and Geology,the site is located within the Great Valley Geomorphic Province of California, a large, elongate northwest trending, asymmetric structural trough. The Great Valley Province has been filled to its present elevation 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 advanced GeoEnvironmenial,Inc.