ARCHIVED REPORTS XR0009493 (2) - Laserfiche WebLink

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i 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 to previous investigation reports Shallow ground water to the site vicinity flows toward the northeast under a hydraulic gradient of approximately 0 002 ft/ft 3._2 Ground-Water Sampling and Laboratory Analysis On May 27, 1997, 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) and methyl tertiary-butyl ether(MTBE) compounds Historical laboratory analysts 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 to ground water are illustrated to Figure 4 Water-quality data from wells sampled for the second quarter 1997 monitoring event are generally consistent or higher than concentrations detected for previous quarterly sampling events The lughest 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) MTBE was not detected to any monitoring well samples Second quarter monitoring data for well MW-1 indicate concentrations of TPHg (85,000 ppb) and benzene(21,000 ppb) These data indicate an increase in petroleum hydrocarbon 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 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-3, MW-5 and MW-6 ranged between 22,000 ppb (MW-6) and 1,300 ppb (MW-5) These data indicate 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 the result of the seasonal rise to ground-water levels and dissolution of hydrocarbons from capillary zone soils 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 1997 indicate BTEX and MTBE compounds were not detected 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 monitoring wells MW-7 (70 ppb) and MW-10 (70 ppb)