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Figure 3 shows the physical layout of the investigation site as well as all previous sampling locations. Laboratory results for all samples are included in Appendix A. UST Site 816D Former UST 816D is located along the north wall of Building 816D in the main operation section of the NCS. Although the scope of work (Revision - January 26, 1995) reported that UST 816D contained waste oil, evaluation of analytical results indicates that the tank was probably used to store fuel rather than waste oil. During removal activities in 1989, soil and groundwater samples were collected and analyzed. The analytical results for these samples are reported below. Previous Sampling and Analytical Results Two soil samples were collected during the removal of former UST 816D, one from the north end of the excavation pit and one from the south end. Both samples contained an unidentified hydrocarbon compound within the USEPA 8015 Modified analytical method range at concentrations of between 3,000 mg/kg and 6,000 mg/kg. No other chemical constituents were detected above the detection limit reported. The contracted analytical lab reported the detected limit for BTEX compounds as 2.5 mg/kg, five times the required value, because the sample matrix interfered with the analyte quantitation process when the sample was analyzed undiluted. Dilution was necessary to quantify the concentrations, thus increasing the detection limit to its reported value. In addition to the two soil samples, one groundwater sample was collected at the bottom of the excavation pit. Analytical results indicated the presence of an unidentified hydrocarbon at a concentration of 26,000 µg/l. Benzene and toluene, present at concentrations of 5,300 and 350 µg/l, respectively, were the only other compounds detected above the detection limit. Figure 4 shows the physical layout of the investigation site as well as all previous sampling locations. Laboratory results for all samples are included in Appendix A. 3-2