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. Fourth Quarter 1996 VES Report - Unocal Station No 6981 <br /> February 7, 1997 <br /> completed " Our concerns regarding installation of the replacement well at this time are <br /> outlined below <br /> • City of Stockton requested the wells be removed to avoid damage or loss during <br /> intersection reconstruction. <br /> • Well MW-11, which has not been destroyed, is situated downgradient of the <br /> dissolved hydrocarbon plume. <br /> • Historical data indicate that concentrations of TPHg have been detected in wells <br /> MW-11, MW-12, and MW-13 during only one of 16 quarterly monitoring event. <br /> After detection of TPHg in these wells during the January 1994 sampling event, the <br /> wells were resampled the following month and TPHg were not detected <br /> • Since construction activities along the eastern side of Pacific Avenue have yet to be <br /> initiated, it seems premature to install a replacement well in this area Past <br /> experience indicates that any construction activities will undoubtedly damage the <br /> wellhead, and could compromise the well to the point it would have to be replaced. <br /> It does not appear fiscally responsible to install a well in areas where there is a <br /> strong likelihood the well will be damaged when other monitoring points (in this <br /> case MW-11) are situated to adequately detect the leading edge of the dissolved <br /> plume <br /> Concentrations of dissolved hydrocarbons in wells MW-1 through MW-8, situated <br /> within the original dissolved hydrocarbon plume, have dropped considerably since <br /> startup of the on-site VES. It appears that in addition to extracting hydrocarbon <br /> vapors from the soil, the VES may also be abating some of the dissolved <br /> hydrocarbons Historical data indicates the dissolved hydrocarbon plume is stable <br /> Based on these points, 76 Products Company will defer consideration of a replacement <br /> downgradient well until after completion of construction activities along the east side of <br /> Pacific Avenue However, if the City of Stockton can delineate an area within the <br /> construction zone where they can guarantee a well will not be damaged or paved over, then <br /> 76 Products Company will install a well in this area prior to completion of construction <br /> activities <br /> 485520-1 3 <br />