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Mr. Lloyd Gums A91701.OIB January 15, 1996 Page 10 6.0 EVALUATION 6.1.1 Soil Characterization, Northwestern Dispenser Island: The result of the field screening of soil sample from soil boring B-8 with the PID indicated the possible presence of PPCs in the sample collected at approximately 15 feet. The laboratory analytical results did not confirm the presence of PPCs in this sample. In view of the fact that the PID will register the presence of volatile organic compounds which are not PPCs, these findings are not anomalous. These findings indicate that PPCs are not present above the detection limits in the soil sample collected from soil boring B-8 at approximately 15 feet BSG. L The laboratory analytical results for the soil sample collected at approximately 35 feet in soil boring B-1 indicated the presence of TPH-D at a concentration of 13 milligram per kilogram (mg/kg). In view of the fact that TPH-D has a low percentage of volatile organic compounds, it is not unusual for field screening with the PID to fail to detect TPH-D. This data suggest that the soil cuttings and decontamination rinsate from soil boring B-1 may contain concentrations of TPH-D. Previous work suggest that TPH-D,TPH-G,benzene,toluene, ethylbenzene and xylenes are present beneath and on the north side of the northwestern dispenser island (corresponding L to sample locations #3 and #4, Drawing 2) in subsurface soil at a depth of approximately 5 feet BSG. PPCs were not detected at concentrations above the detection limits from the soil samples collected at sample locations #1 and #2 on the south side of the northwestern dispenser island at 5 feet BSG. Findings from this work suggest that TPH-D is present in soil beneath the northwester dispenser island at a depth of approximately 35 feet BSG in a location corresponding to the 35-foot BSG sample location of soil boring B-1. (Note: Because soil boring B-1 was drilled on an angle from vertical, the lateral locations of soil samples varied as the depth of the samples varied as shown on Drawing 4). The analytical results and PID reading findings do not indicate the presence of PPCs in the soil samples collected from soil borings B-2, B=8 at depths of 10, 20, 30, or 35 feet BSG or the soil samples collected in soil boring B-1 at 10, `- 20, and 30 feet BSG. The foregoing data suggest that PPC migration is limited to the area i• around soil sample locations #3 and #4 at 5 feet BSG and the location of the 35-foot BSG soil sample from soil boring B-1. Soil borings were not advanced beyond approximately 35 feet BSG due to the lack of field indications of PPCs at that depth; the anticipated presence of groundwater at approximately } 45 feet BSG; and by limitations of the authorized work scope. Based on standards of ` practice, two consecutive five-foot samples with no detectable constituents of concern can demonstrate the vertical extent of impact. Therefore the vertical extent of TPH-D migration beneath the northwester dispenser island has not been delimited.