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06 June 2000 <br /> ' AGE-NC Project No. 95-0197 <br /> Page 2 of 7 <br /> B6 were advanced to a depth of 30 feet below surface grade (bsg). Probe boring B3 was <br /> advanced to a depth of 35 feet bsg. Total petroleum hydrocarbons quantified as gasoline and <br /> diesel (TPH-g and TPH-d, respectively) and volatile aromatics (benzene, toluene, <br /> ethylbenzene and xylenes:BTE&X)were detected in soil samples collected from B1. TPH-d <br /> was detected in soil samples collected from B3 and B5 and BTEX compounds were detected <br /> in soil samples collected from B6. TPH-g, TPH-d, and BTEX compounds were detected in <br /> ' the grab ground water sample collected from B3,benzene was detected in the ground water <br /> sample from B5, and TPH-d was detected in the ground water sample collected from B6. <br /> ' o On 08 &09 April 1999 four borings were advanced at the site to maximum depths of 35 feet <br /> bsg. Borings MW-1 through MW-4 were converted into 2-inch diameter PVC ground water <br /> monitoring wells. The soil and ground water samples were analyzed for TPH-g, TPH-d, <br /> ' BTEX compounds,methyl tertiary butyl ether(MTBE), and the suite of five fuel oxygenated <br /> compounds. No target analytes were detected above laboratory reporting limits in any of the <br /> soil samples selected for analysis. Ground water samples were collected on 12 April 1999, <br /> TPH-d was detected in the ground water sample collected from MW-1 at a concentration of <br /> 130 Fcg/l and MTBE was detected in the ground water samples collected from MW-2 and <br /> MW-3 at concentrations of 2.5 jcg/l and 0.71 ug/l. <br /> The lateral and vertical extent of the petroleum hydrocarbon impacted soil has not yet been <br /> delineated northwest and southeast of the former southwest fuel dispensers (Figures 5,6 and <br /> ' 7). The lateral extent of dissolved MTBE has also not been fully characterized to the <br /> northeast and east of monitoring well MW2. <br /> 2.2. REGIONAL GEOLOGIC/HYDROGEOLOGIC SETTING <br /> ' The site is located within the northern San Joaquin Valley which comprises part of the Great Valley <br /> geomorphic province of California. The San Joaquin Valley is a large, elongate, northwest-trending <br /> ' asymmetrical structural trough (basin). It is bordered by the Coast Ranges to the west, the Klamath <br /> Mountains and Cascade Range to the north, and the Sierra Nevada to the east. This trough has been <br /> filled with sediments derived from both marine and continental sources. Thickness of the <br /> sedimentary fill ranges from thin veneers along the valley edges to more than 20,000 feet in the south <br /> central portion of the valley. The sedimentary formations range in age with the older deposits being <br /> primarily marine in origin and the younger deposits being primarily continental. The younger <br /> continental-derived sediments were primarily deposited in lacustrine, fluvial, and alluvial <br /> environments with sediment sources being the mountain ranges surrounding the valley(Olmsted and <br /> Davis, 1961). The site is located on unconsolidated and semi-consolidated alluvium, lake,playa and <br /> terrace deposits of Quaternary age (California Division of Mines and Geology, 1977). <br /> The Modesto, Riverbank and Turlock Lake Formations and overlying Recent alluvium are the <br /> Advanced GeoEnvi ron mental,Inc. <br /> 1 <br />