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i r AZURE ENVIRONMENTAL Water table elevation data collected at the Site indicate the general direction of ground-water flow IS toward the northeast, with local variations of flow direction in the area adjacent to the former tank locations at the Site(Figure 3) These data are generally consistent with potentiometric data and interpretations of ground-water flow direction at the Site presented in previous investigation reports Shallow ground water in the site vicinity flows toward the northeast under a hydraulic gradient of approximately 0 002 ft/ft 3.2Ground-Water er t Sampling and Laboratory Analysis On May 11, 1998, ground-water samples were collected from eight monitoring wells at the Site (MW-1, MW-3, MW-5, MW-6, MW-7, MW-8, MW-9 and MW-10) The samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg) and benzene, toluene, ethylbenzene, and xylene (BTEX) compounds Historical laboratory analysis results are summarized in Table 3, laboratory certificates are included in Appendix A and field sampling data sheets are included in Appendix B Most recent ground-water monitoring data of benzene concentrations in ground water are illustrated in Figure 4 Petroleum hydrocarbon data from wells sampled for the second quarter 1998 monitoring event are generally consistent to previous results for wells at the perimeter of the ground-water plume, while concentrations are generally higher at wells near the former UST locations compared with data from the previous quarterly sampling event The highest concentrations of petroleum hydrocarbons in ground water are detected at monitoring wells MW-1, MW-3, MW-5 and MW-6 which are located adjacent to the area of the former UST locations at the Site (Figure 4) Second quarter monitoring data for well MW-6 indicate concentrations of TPHg (83,000 ppb) and benzene(25,000 ppb) These data indicate an increase-in petroleum hydrocarbon concentrations at well MW-6 compared to data collected during the previous sampling event (Table 4) The historical range of petroleum hydrocarbon concentrations detected at well MW-6 vanes from 120,000 ppb (October 1994) to 15,000 ppb (November 1996) of TPHg, and 25,000 ppb (May 1998)to 2,200 ppb (October 1995) of benzene Benzene concentrations at near source wells MW-1, MW-3, and MW-5 ranged between 22,000 ppb (MW-1) and 2,000 ppb (MW-5) These data indicate a similar or an increase in benzene concentrations at each well compared to data collected during the previous sampling event (Table 4) The increase of benzene and other petroleum hydrocarbons in the near-source wells are likely I the result of the rise in ground-water levels and dissolution of hydrocarbons from capillary zone soils The downgradient extent of petroleum hydrocarbons in ground water is monitored at perimeter wells MW-7 through MW-10 Monitoring data collected for perimeter wells in May 1998 indicate BTEX was not detected and TPHg was detected at a trace concentration (50 ppb) only in well MW-7 Historical data indicate benzene has not been detected at concentrations greater than 0 5 ppb in downgradient well MW-9 since January 1995 (0 6 ppb) and well MW-10 since October • 1994 (0 6 ppb) 2 r