ARCHIVED REPORTS XR0008702 - Laserfiche WebLink

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Tosco Corporation,A Subsidiary of Phillips Petroleum Company 6 Tosco Service Station No 4409,1502 North El Dorado Street,Stockton Cahforma May 29,2002 SUNEWARY OF FINDINGS Site assessment activities identified the following Soils encountered during drilling (maximum explored depth of approximately 80- feet bgs)consisted of interbedded sandy silt, silt, clayey silt, and silty sand • Depth to water in wells MW-8 through MW-10 gauged on October 10, 2001 ranged from approximately 27 feet to 31 feet bgs The direction of groundwater flow within the shallow zone was toward the northeast at a hydraulic gradient of 0 003 foot/foot Groundwater flow direction within the deep zone was toward the northwest and northeast, at hydraulic gradients of 0 045 and 0 136 foot/foot, respectively 0 Soil samples collected from MW-8, MW-9, and MW-10 reported the presence of petroleum hydrocarbons at 60 feet bgs In the boring for well MW-8, and between 60 and 80 feet bgs In the borings for wells MW-9 and MW-10 TPHg was detected in five soil samples at concentrations ranging from 50 mg/kg to 4,400 mg/kg, benzene was detected in four samples at concentrations ranging from 0 22 mg/kg to 77 mg/kg, and methanol was detected in two samples at concentrations of 1,400 mg/kg and 62 mg/kg, respectively MtBE and all other fuel oxygenates were not detected in any soil samples above laboratory reporting limits . • Concentrations of TPHg and BTEX were reported in groundwater samples collected from MW-8 and MW-9 Concentrations of TPHg, ethylbenzene, and xylenes were detected in well MW-10 TPHg and benzene were detected at concentrations up to 22,000µg/1 and 600 µg/1, respectively Concentrations of toluene, ethylbenzene, and xylenes were detected at concentrations up to 260 µg/l, 1,100 µg/1, and 3,600 gg/i, respectively MtBE and other fuel oxygenates were not detected in wells MW-8 through MW-10 above laboratory reporting limits CONCLUSION The presence of petroleum hydrocarbons in soil samples collected at maximum depths of 80 feet and 75 feet bgs in the vicinity of the UST complex and pump islands, respectively, indicates that the vertical extent of petroleum hydrocarbon-impacts have not been defined in these areas Based on the absence of petroleum hydrocarbons in the sample collected at the maximum depth of 80 feet bgs from the boring for well MW-8, the vertical extent of petroleum hydrocarbons in soil has been defined in the downgradient direction Evidenced by the presence of dissolved petroleum hydrocarbons in deep zone wells MW-8 through MW-10, the lateral and vertical extent of the dissolved petroleum hydrocarbon plume has not been delineated SECOR recommends installing additional deep zone groundwater monitoring wells to iinvestigate the lateral and downgradient extent of petroleum hydrocarbons in groundwater Groundwater monitoring wells will continue to be monitored on a quarterly basis to I\Tosco Marketing\4409\ReportAAsmtRpt doe