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• the building (JLM-9-29' and JLM-10-30') All five of the water-table samples that were tested for TPH as diesel exceeded the detection limit, and those concentrations were higher than the gasoline concentration in four of the five samples Whether diesel is actually present however, is uncertain, because the detected hydrocarbons span the transition from gasoline to kerosene to diesel and the laboratory noted that the samples may represent aged (weathered) gasoline Most samples contained no detectable concentrations of BTEX compounds, which testifies to the weathered nature of the gasoline Toluene was detected at 12 and 0 83 µg/l in the two samples below the building, and one of these also contained ethylbenzene and xylene at concentrations of 1 7 and 0 06 µg/1 Other gasoline compounds that were detected included three oxygenates (MTBE, DIPE, and TBA) and the lead scavenger 1,2- DCA Concentrations of these compounds were also low, mostly near 1 pg/l but ranging up to 24 µg/l for 1,2-DCA in JLM-9 The laboratory also detected hydrocarbons in the two samples that were collected from the lower portion of the first aquifer A TPH-g concentration of 77 µg/1 was detected in JLM-6-36', and a TPH-d concentration of 84 µg/1 was detected in JLM-11-38' No BTEX compounds were detected in either sample, but 1,2-DCA and MTBE were detected in both and DIPE was detected in JLM-11-38' The presence of these gasoline compounds suggests that the hydrocarbons reported as TPH-d may again represent weathered gasoline It is also worth noting that even though the sum of gasoline compounds detected in JLM-11-3 8' by EPA method 8260 exceeds the 50 µg/1 detection i limit for TPH-g (55 pg/l [1,2-DCA] +28 µg/l [DIPE] + 4 8 µg/l {MTBE] = 85 8 µg/l), the laboratory did not detect TPH-g above this limit using EPA method 8015 The fact that this sum is within 2 µg/1 of the reported TPH-d concentration further suggests that all of the reported TPH-d actually consists of lead scavengers and gasoline oxygenates rather than diesel fuel In addition, the fact that the 1,2-DCA concentration exceeded the MTBE concentration in most samples further suggests that the gasoline is old Figures 5-8 illustrate the distribution of gasoline-range hydrocarbons in groundwater as interpreted from the available samples These maps include older data from JLM-1 and JLM-2, as well as the most recent (January 2003) data from JLM-4 through JLM-6, so they do not represent a single monitoring event, but rather a general picture of the impacted area The maps for TPH-g, total oxygenates, and 1,2-DCA are all quite similar, and depict an elliptical contaminant plume that trends generally northwest-southeast The plume is quite similar iri shape to the shape of the impacted soil (Figure 4), although the groundwater impact is more extensive BTEX compounds appear to be more uniformly distributed in the groundwater, although there is a slight north-south elongation as presently mapped The groundwater plume appears to originate between JLM-5 and the former tank cavity and become wider to the southeast, parallel to the groundwater flow direction that has been observed during the past three calendar quarters This suggests downgradient dispersion of petroleum molecules As discussed above, the laboratory detected extractable hydrocarbons in six samples using the EPA method 8015/3550 method and reported them as TPH-d These 6