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' AZURE ENVIRONMENTAL November 1997 The ground-water level at MW-2 increased approximately 0 1 feet during the ' quarterly period from September to November 1997 ' 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 ' 332 Ground-Water Sampling and Laboratory Analysis ' On November 13, 1997, ground-water samples were collected from nine monitoring wells at the Site (MW-1, MW-2, 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 xylenes (BTEX) compounds In addition, the samples were analyzed for oxygenates, including methyl tertiary-butyl ether (MTBE), using EPA Method 8260 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 monitoring data of benzene concentrations in ground water are illustrated in Figure 4 '• Water-quality data from wells sampled for the fourth quarter 1997 monitoring event are generally consistent with concentrations detected for previous quarterly sampling events The highest ' concentrations of petroleum hydrocarbons in ground water are detected at monitoring wells MW- 1, MW-2, 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)- Fourth quarter monitoring data for ' well MW-1 indicate concentrations of TPHg (94,000 ppb) and benzene (22,000 ppb) These data indicate an increase in TPHg concentrations at well MW-1 compared to data collected during the previous sampling event (Table 4) The histoncal range of petroleum hydrocarbon concentrations ' detected at well MW'1 vanes 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-2, MW-3, MW-5 and MW-6 ranged between 2,800 ppb (MW-3) and 560 ppb (MW-5) MTBE was not detected in any monitoring well samples The downgradient extent of petroleum hydrocarbons in ground water is monitored at wells MW-9 I and MW-10, the lateral extent is monitored at perimeter wells MW-7 and MW-8 Monitoring data for wells MW-7 and MW-8 in November 1997 indicate BTEX compounds were not detected Trace concentrations of toluene (1 6 ppb) were detected in well MW-9, and trace concentrations of BTEX compounds (up to 3 ppb) were detected in well MW-10 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) Relatively low concentrations of TPHg were detected in monitoring wells MW-7 (90 ppb) and MW-10 (160 ppb) ` 2