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I �I 24 October 2001 AGE-NC Project No. 01 -0877 Page 2 of 7 collected from stockpiled soil removed from the excavation (SP1 -W and SP1 -E). Petroleum hydrocarbons were detected in each soil sample collected. Total petroleum hydrocarbons as gasoline (TPH-g) was detected in the soil samples collected beneath the USTs and fuel dispensers at concentrations as high as 4,300 milligrams per kilogram (mg/kg). Total petroleum hydrocarbons as diesel and motor oil (TPH-d and TPH-mo) were detected in samples collected beneath the former waste oil UST and fill port and from the stockpile soil samples at concentrations as high as 1 , 800 mg/kg. Oil and grease was detected in the soil sample collected beneath the former waste oil UST ata concentration of 3,900 mg/kg. Soil samples collected beneath the faeIUSTS and dispensers were not analyzed for TPH-d, TPH-mo and Oil and Grease. Toluene was detected in all UST and dispenser samples at concentrations as high as 99 mg/kg (T3-E). Ethylbenzene and total xylenes were detected in the soil samples collected beneath the USTs at concentrations as high 200 mg/kg and 1 , 100 mg/kg, respectively. Total lead was detected in all .of the soil samples at concentrations as high as 39 mg/kg. Chromium, nickel and zinc were detected in the soil samples collected beneath the waste oil UST, fill location and the stockpile at concentrations as high as 40 mg/kg 34 mg/kg and 330 mg/kg, respectively. Metal concentrations are not outside the background, natural range of metals concentrations in California soils. Hexavalent chromium and PCB ' s were not detected at or above laboratory reporting limits in the soil samples analyzed. 2.2. REGIONAL GEOLOGICMYDROGEOLOGIC SETTING The site is located within the northern San Joaquin Valley which comprises part of the Great Valley geomorphic province of California. The San Joaquin Valley is formed by the Great Valley geosyncline, which is a large, elongate, northwest-trending asymmetrical structural trough (basin). It is bordered by the Coast Ranges to the west, the Klamath Mountains and Cascade Range to the north, and the Siena Nevada to the east. This trough has been filled with sediments derived from i both marine and continental sources. Thickness of the sedimentary fill ranges from thin veneers along the valley edges to more than 20,000 feet in the south central portion of the valley. The sedimentary formations range in age with the older deposits being primarily marine in origin and the younger deposits being primarily continental. Continental-derived sediments were primarily deposited in lacustrine, fluvial, and alluvial environments with sediment sources being the mountain ranges surrounding the valley (Ohnsted and Davis, 1961). The site is located on unconsolidated and semi-consolidated alluvium, lake, playa and terrace deposits of Quaternary age (California Division of Mines and Geology, 1977). The Modesto, Riverbank and Turlock Lake Formations and overlying Recent alluvium are the principal sources of domestic ground water in the 13,500-square mile San Joaquin Valley Ground Advanced CeaEnvironmental, Inc.