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i 26 October 2001 I AGE-NC Project No 01-0839 Page 2 of 8 feet bsg and from the stockpiled soil excavated from the UST excavation Soil samples were analyzed for total petroleum hydrocarbons quantified as gasoline (TPH-g), volatile aromatic compounds - benzene, toluene, ethylbenzene and total xylenes (BTEX), and fuel oxygenates - di-Isopropyl ether (DIPE), ethyl-tertiary butyl ether (ETBE), methyl-tertiary butyl ether (MTBE), tertiary-amyl methyl ether (TAME) and tertiary butanol (TBA) The three USTs were located at the southeast end of the site During the UST removals, a total of seven soil samples (1T through 3T), two from beneath each 10,000-gallon UST and three from I beneath the 12,000-gallon UST were collected from the floor of the UST excavation A total of nine soil samples, one from beneath each product dispenser(D 1 through D-5) and one beneath every 20 linear feet of product piping(P 1 through P4)were collected Also,four two-part composite samples (SP-1 through SP-4) were collected from the soil stockpile TPH-g was detected in three of the seven soil samples collected beneath the former USTs at I concentrations of 1 0 mg/kg {].TC-15 5), 2,300 mg/kg (2TW-15 5) and 1 1 mg/kg (3TW-15 5) ` TPH-g was also detected in one of the five soil sample collected beneath the product dispensers at a concentration of 17 mg/kg (D2-3) and in one of the four samples from the stockpiled soil at a I concentration of 1 0 mg/kg(SP-1) Toluene, ethylbenzene and total xylenes were detected in UST sample 2TW-15 5 at concentrations of 1 1 mg/kg, 8 4 mg/kg and 70 mg/kg, respectively Toluene and total xylenes were detected in soil sample P44 at concentrations of 0 005 mg/kg and 0 016 mg/kg, respectively MTBE was detected in 15 of the 20 soil samples collected during the UST removals at Econcentrations as high as 17 mg/kg (132-3) Every Soil sample collected under the dispensers contained detectable concentrations of MTBE TBA was detected in soil sample 1TE-15 5 at a concentration of 1 3 mg/kg and in all four stockpile soil samples at concentrations as high as 0 67 mg/kg A summary of soil analytical results are presented in Table 1 23 REGIONAL GEOLOGIC/HYDROGEOLOGIC SETTING I The site is located within the southern 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) I It is bordered by the Coast Ranges to the west, the Klamath Mountains and Cascade Range to the north, and the Sierra Nevada to the east This trough has been filled with sediments derived from 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 manne in origin and the younger deposits being primarily continental Continental-derived sediments were primarily Advanced GeoEnvironmental,Inc