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AZURE ENVIRONMENTAL I 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 I 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 0 006 ft/ft ' 3_2 Ground-Water Sampling and Laboratory Analysis ' On May 14, 1996, 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 In addition, the samples from wells MW-9 and MW-10 were analyzed for methyl tertiary-butyl ether (MTBE) 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 IWater-quality data from wells sampled for the second quarter 1996 monitoring event are generally consistent with data presented in previous quarterly monitoring reports 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 underground storage tank locations at the Site (Figure 4) Second quarter monitoring data for well MW-1 indicate concentrations of TPHg (96,000 ppb) and benzene (20,000 ppb) These data indicate a decrease in TPHg concentrations at well MW-1 compared to data collected during the previous sampling event (Table 4) The historical range of petroleum hydrocarbon concentrations ' detected at well MW-1 varies from 170,000 ppb (October 1994) to 64,000 ppb (October 1993) of TPHg, and 42,000 ppb (April 1992) to 19,000 ppb (October 1993) of benzene Benzene concentrations at near source wells MW-3, MW-5 and MW-6 ranged between 3,900 ppb (MW-6) ' and 430 ppb (MW-5) The downgradient extent of petroleum hydrocarbons in ground water is monitored at wells MW-9 and MW-10 Monitoring data collected for wells MW-7, MW-8, MW-9 and MW-10 in May 1996 indicate BTEX compounds were not detected Monitoring data indicated MTBE was not detected in wells MW-9 and MW-10 These data are generally consistent with historical ' monitoring results, which indicate benzene has not been detected at downgradient wells MW-9 since January 1995 (0 6 ppb) and MW-10 since October 1994 (0 6 ppb) TPHg was not detected in monitoring wells MW-8 and MW-9 Relatively low concentrations of TPHg were detected in fmonitoring wells MW-7 (100 ppb) and MW-10 (90 ppb) Ground-water monitoring data continue to indicate the petroleum hydrocarbon plume has stabilized and is restricted to shallow ground water in the area adjacent to the former tank locations at the Site Residual petroleum hydrocarbon concentrations in Site ground water are expected to continue to decrease as a result of biodegradation and/or other attenuation processes I 2