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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 f1/ft in the area of wells MW-6 and MW-9 ' 3_2 Ground-Water Sampling and Laboratory Analysis ' On June 15, 1999, ground-water samples were collected from eight momtonng wells at the Site The samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg) and benzene, toluene, ethylbenzene, and xylenes (BTEX) compounds Historical laboratory analysis results are ' summanzed in Table 3, laboratory certificates are included in Appendix A and field sampling data sheets are included in Appendix B Most recent benzene analysis data are illustrated in Figure 4 ' Petroleum hydrocarbon data from wells sampled for the second quarter 1999 monitoring event are generally consistent to previous results for wells at the perimeter of the ground-water plume, while concentrations were generally lower at wells near the former UST locations compared with ' data from the previous sampling events The highest concentrations of petroleum hydrocarbons in ground water are detected at monitoring wells MW-1, MW-3 and MW-6, which are located adjacent to the area of the former UST locations at the Site (Figure 4) Benzene concentrations at near source wells MW-1 and MW-3 ranged between 19,000 ppb (MW-1) and 6,000 ppb (MW-3) These data indicate lower benzene concentrations at each well compared to data collected during the previous sampling event (Table 3) Second quarter monitoring data for well MW-6 indicate concentrations of TPHg (17,000 ppb) and benzene (1,600 ppb), which are lower compared to data collected during the previous sampling event (Table 3) 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 1,600 ppb (June 1999) of benzene Benzene concentrations were essentially unchanged in well MW-5 in June 1999 (4 10 ppb) compared to the previous quarterly sampling result (400 ppb) Fluctuations in concentrations of benzene and other 1 petroleum hydrocarbons in the near-source wells are likely the result of changes in ground-water levels, dissolution of hydrocarbons from capillary zone soils, and the effects of natural attenuation mechanisms The downgradient extent of petroleum hydrocarbons in ground water is monitored at perimeter wells MW-7 through MW-10 Morutoring data collected for perimeter wells in June 1999 ' indicate benzene was not detected and TPHg was detected at a trace concentration (65 ppb) only in well MW-7 Historical data indicate benzene has not been detected at concentrations greater than 0 5 ppb in downgradient wells MW-9 since January 1995 (0 6 ppb) and MW-10 since ' October 1994 (0 6 ppb) These data continue to indicate the petroleum hydrocarbon plume is . stable and is restricted to shallow ground water in the area adjacent to the former tank locations at the Site 2