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R CVv �,ATC A S S O C I A T E S I N C =. 4A ANALYTICAL RESULTS 4_1 Soil Analytical Results Soil samples collected from borings MW-4, MW-5, and MW-6 contained no detectable concentrations of TPHg, BTEX, or oxygenate fuel additives. Analytical results of sod samples are summarized in Table 1. 1 4.2 Groundwater Analytical Results The groundwater samples collected from well MW-1 and MW-6 contained no detectable i s= concentrations of TPHg, BTEX or MTBE. The samples from wells MW-4 and MW-5 contained low to nondetectable concentrations of TPHg, toluene, ethylbenzene, and xylenes. None of these rr- constituents exceeded their respective maximum contaminant levels (MCLs). No benzene was detected in either sample. The groundwater samples collected from wells MW-2 and MW-3 contained detectable concentrations of TPHg and benzene. The sample from well MW-2 also contained very low concentrations of toluene, ethylbenzene, and xylenes. Benzene exceeded the MCL in both wells MW-2 and MW-3. Oxygenate fuel additives were not detected in any of the samples submitted for this analysis, wells r-r , MW-4, MW-5, and MW-6. Analytical results of groundwater samples are summarized in Table 2. 5.0 DISCUSSION The objective of this investigation was to obtain current soil and groundwater data in locations north and west of the former USTs where elevated concentrations of petroleum hydrocarbons and free product had previously been detected. Based on the field observations and analytical results obtained during this investigation, soil and groundwater north and west of the location of the former USTs are not adversely impacted by petroleum hydrocarbons. Wells MW-4, MW-5, and MW-6 were placed in locations where elevated concentrations of petroleum hydrocarbons were detected during a subsurface investigation in September 1996. The - very low to nondetectable concentrations of petroleum hydrocarbons currently detected at these locations suggest that intrinsic bioremediation may be occurring in the petroleum hydrocarbon plume beneath the site. This is especially evident in the vicinity of well MW-4 where free product ;? was detected in September 1996. The petroleum hydrocarbon plume beneath the site appears to k = be stable as evidenced by low to nondetectable concentrations in downgradient wells MW-4 and MW-5 and decreasing concentrations in wells MW-2 and MW-3, located in the center of the plume. In the judgment of ATC, no further site investigation is necessary to define the extent of petroleum hydrocarbons in soil and groundwater. ATC recommends performing one additional monitoring event. If petroleum hydrocarbons concentrations remain stable, then ATC ' recommends proceeding with site closure. w:1130991repoAslsumwe1.doc 5 E�_