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5 3.1 Gasoline Tank Cavity <br /> Residual gasoline petroleum hydrocarbons remain in place at approximately 13 feet bgs <br /> beneath the former gasoline USTs TPHG concentrations in the soil samples collected <br /> beneath the USTs ranged from 9 5 to 250 ppm, and concentrations of benzene ranged <br /> from 0 63 to 5 4 ppm Soil samples collected from borings drilled near the former tank <br /> cavity (borings B-4, B-5, B-6, and B-9) did not contain residual petroleum hydrocarbons <br /> Based on the results of soil samples collected beneath and adjacent to the former USTs, it <br /> appears that petroleum hydrocarbons do not extend past 20 feet bgs in the vicinity of the <br /> former USTs <br /> 5.3.2 Waste-Oil Tank Cavity <br /> Residual petroleum hydrocarbons remain in place beneath and adjacent to the three former <br /> waste-oil tanks Concentrations of TPHD ranged from below laboratory detection limits to <br /> 4,300 ppm, and concentrations of TOG ranged from below laboratory detection limits to <br /> 500 ppm Concentrations of TPHG ranged from below laboratory detection Limits to <br /> 5,500 ppm The highest concentrations of TPHG, TPHD, and TOG were detected <br /> adjacent to the waste-oil tank east of the station building Volatile organic compounds <br /> were not detected in any of the soil samples collected from the borings <br /> 5.3.3 Product Delivery Lines and Dispenser Islands <br /> Residual petroleum hydrocarbons remain in place beneath the former product delivery <br /> Lines TPHG concentrations range from below laboratory detection limits to 5,700 ppm, <br /> the highest concentration was detected adjacent to the western dispenser island Based on <br /> result-, of soil samples collected beneath and adjacent to the product lines, it appears that <br /> petroleum hydrocarbons extend from below the limit of the excavations to approximately <br /> 55 feet bgs (capillary fringe) <br /> 5.4 Dissolved Petroleum Hydrocarbons in Groundwater <br />' Historical analytical groundwater data for on-site wells, which have been compiled since <br /> quarterly monitoring began in March 1994, are presented in Table 5 TPHG and benzene <br /> concentrations in groundwater from the most recent monitoring event (fourth quarter) are <br /> shown on Figure 9 (EMCON, Quarterly Groundwater Monitoring Report, Second <br /> Quarter 1996) Based on groundwater data obtained to date, low concentrations of <br /> dissolved petroleum hydrocarbons have been detected in groundwater samples from all <br /> three monitoring wells (MW-1 through MW-3) TPHG concentrations have ranged from <br /> below laboratory detection limits to 380 parts per billion (ppb) Benzene concentrations <br /> ranged from below laboratory detection limits to 4 5 ppb Detectable levels of TOG and <br /> SA(-\N\PJ0.0805\08051420 41J5-97\pra 1 Rev 0,3/12/97 <br /> 20805 142 004 5-2 <br />