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Tosco Corporation 2 Tosco Service Station 8671 8606 Thornton Road Stockton CA June 21 2002 • ASSESSMENT ACTIVITIES AND FINDINGS On December 12th through 14'h, 2001, one deep soil boring (SB-1) was drilled to an approximate depth of 63 feet below ground surface (bgs) and three additional groundwater monitoring wells (MW-5, MW-6, and MW-7) were completed at the site by Cascade Drilling of Rancho Cordova, California Each well was installed to a depth of approximately 45 feet bgs Well construction details are provided in Table 1 Boring logs showing subsurface lithology and well completion details are included as Attachment B Field procedures are described in Attachment C The findings of this assessment are discussed below Subsurface Conditions Referring to soil boring SB-1 that was continuously sampled from 7 to 64 feet bgs, the lithology encountered consists of sandy silt and silty sand, with moderate to poorly sorted sand layers encountered at approximately 20 feet bgs, 29 feet bgs, 45 to 54 feet bgs, and 60 to 61 feet bgs Based on the lithology encountered in wells MW-5, MW-6, and MW-7, the sand layers found in SBA at 20 feet bgs and 45 feet bgs appear to have a certain amount of lateral continuity Groundwater was encountered at approximately 34 feet bgs Soil and Groundwater Sampling and Analysis Soil samples from SB-1 were continuously collected, for lithological descriptions, from approximately 8 feet bgs to 63 feet bgs using a split spoon sampler Soil samples from the monitoring wells were collected at five-foot intervals by using a split spoon sampler Selected soil samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg) by EPA Method 8015, benzene, toluene, ethylbenzene, xylenes (collectively BTEX) and methyl tertiary butyl ether (MtBE) by EPA Method 8020, and fuel oxygenates, including MtBE, tertiary amyl methyl ether (TAME), di-isopropyl ether (DIPE), ethyl tertiary butyl ether (EtBE), tertiary butyl alcohol (TBA), ethylene dibromide (EDB), 1,2-dichloroethane (1,2-DCA), and ethanol by EPA Method 8260 Detections of MtBE by EPA Method 8260 were reported in three of 19 soil samples (SB-1 @35', SB-1 @28', and SB-1 @30') at concentrations of 0 53 milligrams per kilogram (mg/kg), 0 89 mg/kg, and 0 94 mg/kg, respectively TBA was reported in one soil sample at a concentration of 0 86 mg/kg (MW-5@30') All other analytes were not detected above laboratory reporting limits Soil analytical data is presented in Table 2 Certified analytical laboratory reports and chain-of-custody documentation are presented as Attachment D Additionally, one grab groundwater sample (SB-1 @64') was collected from SB-1 and analyzed for the same constituents listed above A detection of MtBE by EPA Method . 8260 was reported at a concentration of 130 micrograms per liter (ug/1) Benzene was reported at a concentration of 0 52 ug/l, and total xylenes were reported at a concentration of 074 ug/l All other analytes in sample SB-1 were reported below 077 43791 222/Assessment