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29 December 1999 <br /> AGE-NC Project No 96-0229 , <br /> Page 4 of 5 <br /> samples collected from downgradient well MW-6 and the deeply drowned well MW-1, <br /> demonstrating an elongated, narrow plume oriented toward the northeast <br /> • TBA has consistently been detected in ground water samples collected from well MW-7 at <br />' concentrations as high as 40,ug/l, the remoteness of this well from the former UST area and <br /> its sole hit of TBA during the October 1999 sampling event suggests that TBA detected at <br /> MW-7 may not be from the subject site <br />' • From July 1999 to October 1999, a general decrease in dissolved petroleum hydrocarbon <br /> concentrations was quantified in samples collected from wells MW-4 and MW-6 (Table 2) <br />' Conversely, a general increase was observed in water samples collected from well MW-7 <br /> However, the dissolved petroleum hydrocarbon concentrations detected at wells MW-4, <br /> MW-6 and MW-7 in October 1999 occurred within each wells range established from <br /> previous monitoring events <br /> • Petroleum hydrocarbon concentrations remained below detectable levels in wells MW-5, <br />' MW-9, and MW-10A, demonstrating that the plume is well defined upgradient and <br /> downgradient <br /> • Ground water monitoring data collected in the area of wells MW-1 through MW-10 indicated <br /> a ground water flow direction generally toward the northeast at a gradient of 0 003 ft/ft The <br /> flow direction is close to the norm for the area <br />' • Due to the low gradient at the site, slight variations in ground water measurements or <br /> changes of recharge/discharge of the local ground water could greatly modify ground water <br /> flow direction <br />' • Monitoring wells MW-1 and MW-10B are "drowned", and yield samples more <br /> representative of deeper ground water conditions MW-10B demonstrates the minimum <br /> thickness of the impacted ground water plume Its downgradient position and the periodic - - - - <br />' detection of low concentrations of selected analytes punctuated by periods of non-detection <br /> shows that the downgradient margin of the deeper plume of impacted ground water is in the <br />' vicinity of MW-I OB <br /> • The elevated concentrations of petroleum hydrocarbons detected in samples,collected from <br /> wells MW-1, MW-2, MW-3 and MW-6 indicate that these wells are within or near the <br /> dissoh cd pc iolcurn h' droca.ibon"core arca" of the piurne (Figure 4) <br /> 5.0. RECOMMENDATIONS <br /> Based upon data collected during October 1999, AGE recommends <br /> • <br /> Advanced GeoEnvironmental,Inc <br /> I <br />