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02 May 2013 AGE-NC Project No. 04-1168 Page 7 of 10 • It is not likely that soils from depths of 25 and 35 feet bsg will be excavated and exposed, which would threaten public health. • Based on documented deeper soil impact and the flow and depth of groundwater (48 feet bsg; toward to the southeast/southwest), it appears that the remaining soil impact at the site would not pose a significant threat to human heath in buildings directly adjacent to the site or to future development of the site. /5.0. ASSESSMENT OF HYDROCARBON-IMPACTED GROUNDWATER Between August 2005 and December 2010, nine (9)groundwater monitoring events were conducted at the site to monitor dissolved petroleum hydrocarbon concentrations in groundwater and to characterize groundwaterflow direction and gradient at the site. Based on the above historical groundwater monitoring results, TPH-g, BTEX and MTBE compounds have been established as the main contaminants of concern at the site and to a lesser extent TAME and 1,2-DCA. Laboratory analysis of groundwater samples typically detected TPH-g, BTEX and MTBE from all three wells (MW-1 through MW-3). Maximum TPH-g, MTBE and BTEX concentrations were generally reported in samples collected from well MW-1 at concentrations of 2,600 pg/I (TPH-g), 2,200 pg/I (MTBE), 8.9 pg/I (toluene), 4.1 pg/I (ethylbenzene) and 31.5 pg/I (total xylenes); benzene was reported during one sampling event from MW-3 at a concentration of 4 pg/l. Groundwater analytical data is summarized in Table 3. Based on the most recent groundwater monitoring data collected at the site (December 2012), the dissolved TPH-g plume is located directly beneath the former underground storage area, in the location of well MW-1. The dissolved plume appears to radiate surrounding the wells location, but is currently defined to the northwest and west by wells MW-1 and MW-2. The plume is undefined to the north to the east and the south of well MW-1's location. However, low concentrations reported in all three wells suggests that the plume is laterally limited to the areas surrounding the well network.Vertically,groundwater samples have not been collected at depths deeper than the installed well network at 70 feet bsg (Tables 3; Figure 6). Based on plots of TPH-g and MTBE versus time (Appendix F), a trend of decreasing dissolved concentrations is evident in site wells MW-2 and MW-3. Further,TPH-g appears to be slightly increasing in well MW-1,while MTBE is decreasing. Considering the residual mass of adsorbed petroleum at the site, any estimated time to groundwater quality compliance is tempered by changes to site conditions and regional stability. Trend graphs are presented in Appendix F. Advanced GeoEnvironmentaf,Inc. v