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1 ' 15 March 2000 AGE-NC Project No 96-0229 ' Page 4 of 5 ' The highest MTBE concentrations were encountered in ground water samples collected from the deeply drowned well MW-1 (screened 48 to 53 feet bsg) and from the downgradient well MW-7 (screened 20 to 40 feet bsg), implying that MTBE-impact may be present ' crossgradient to downgradient of the site at deeper depths • The highest BTEX concentrations were encountered in ground water samples collected from ' the deep screened well MW-1 and downgradient well MW-6, demonstrating an elongated, narrow plume (Figure 3), BTEX-impact may also be present at deeper depths • From October 1999 to January 2000, a general decrease in dissolved petroleum hydrocarbon concentrations was quantified in samples collected from well MW-3 (Table 2) Conversely, a general increase was observed in water samples collected from wells MW-2, MW-6, and MW-7, demonstrating a potential shift in the plume towards the north-northeast The dissolved petroleum hydrocarbon concentrations detected at wells MW-2,MW-3,MW-6 and MW-7 in January 2000 occurred within the range of hydrocarbon concentrations previously detected in ground water samples from each well • Monitoring wells MW-1 and MW-10B are "drowned", and yield samples more representative of deeper ground water conditions MW-10B demonstrates the minimum thickness of the impacted ground water plume Its downgradient position and the periodic detection of low concentrations of selected analytes punctuated by penods of non-detection shows that the downgradient margin of the deeper plume of impacted ground water is in the vicinity of MW-10B • The elevated concentrations of petroleum hydrocarbons detected in samples collected from wells MW-1, MW-2, MW-3 and MW-6 indicate that these wells are within or near the dissolved petroleum hydrocarbon "core area" of the plume (Figure 4) • The horizontal extent of petroleum hydrocarbon-impacted ground water has not been delineated to the northwest • The vertical extent of MTBE-impacted ground water has not been delineated in the area of MW-6 and MW-7 I 5.0 RECONDIENDATIONS Based upon data collected during January 2000, AGE recommends I Preparation of a work plan for the installation of deeper ground water monitoring wells located adjacent MW-6 and MW-7 and one shallow ground water monitonng well located approximately 150 feet west of MW-6 to further assess the extent of the crossgradient dissolved petroleum hydrocarbon plume toward the northwest IAdvanced GeoEnl,iron rix ntaI Inc i