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1 Draft . UST2-7 (benzene 39 mg/kg), no detectable concentrations of benzene were encountered in these samples The sample at UST2-7 that contained 14,000 mg/kg TPH- and 39 mg/kg p g g g benzene was collected along the western wall of the UST-2 excavation As ' shown in Figure 3, the western extent of the excavation ended at the footer wall of the facility Therefore, further excavation in this direction was not ' possible Soil samples collected immediately inside the building (HB-11 and HB-12) on the other side of the building footer contained no detectable concentrations of TPH-g or benzene in the vadose zone ' samples TPH-g was detected at HB-11 at a depth of 8 5 feet bgs, however, this detection is likely associated with TPH-g in ground water, not soil because the depth to ground water is approximately 7 feet Therefore, the extent of TPH-g and benzene in soil west of the UST-2 excavation 1s limited ' Samples collected beyond the limits of the excavation (HB-13, HB-14, and HB-20) revealed concentrations of TPH-g ranging from non-detect (HB-20) ' to 85 mg/kg (HB-14) No detectable concentrations of benzene were encountered in these samples, with the exception of HB-14 at 5 feet bgs (0 11 mg/kg) ' 32 GROUND WATER The following subsections present a discussion of the chemical ' compounds detected in ground water at each UST site 321 UST-1 3 2 1 1 Lateral Extent ' The concentration of TPH-g and BTEX compounds downgradient of UST-1 decrease significantly Samples collected from MW-4 in December 1998 contained 120,000 micrograms per liter (µg/1) of TPH-g and 490 µg/1 ' of benzene At MW-1 (approximately 100 feet downgradient), the concentrations decrease an order of magnitude to 4,300 µg/1 of TPH-g and ' 49 µg/1 of benzene 3 2 1 2 Vertical Extent • HB-17 was advanced approximately 20 feet downgradient of MW-4 ' Ground water samples collected at HB-17 revealed concentrations of TPH-g Benzene was not detected above the detection limit of 2 5 mg/l S