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2.6 GROUND WATER MONITORING <br /> Ground water elevations and samples were collected routinely between <br /> April 1999 and November 2001 from the three wells installed at the site <br />' The ground water samples were analyzed for purgeable hydrocarbons <br /> and BTEX constituents as well as general water quality parameters <br /> Recent sampling events have also included fuel oxygenates, <br /> 1,2-dichloroethane, and organic and total lead A summary of the <br /> quarterly ground water sampling results for the site is included in Table 2 <br />' The only concentrations of TPH-g detected in ground water since the <br /> April 1999 investigation were in monitoring well MW-2 Results of <br /> rquarterly ground water samples at this location are normally below <br /> the reporting limit of 50 µg/1, although concentrations of 57 7, 52 S, and <br /> 135 µg/1 have been detected in this well <br />' 2.7 MASS CALCULATIONS OF TPH-G REMAINING AT THE SITE <br /> As required by Item #13 of the PHS/EHD checklist, a mass balance <br />' calculation of the substance treated versus that remaining must be <br /> presented No treatment has been completed at this site for the residual <br /> impacts of the former UST, however, a calculation has been completed to <br /> approximate the amount of TPH-g remaining at the site based on <br /> investigation and ground water monitoring data As presented below, a <br />' conservative estimate of the residual mass of TPH-g shows that a minimal <br /> amount of gasoline remains in the subsurface <br />' The extent of hydrocarbon release to soil and ground water is estimated <br /> based on the results of site investigations, the calculations are provided in <br /> Appendix B The lateral and vertical extent of TPH-g in the site soil is <br />' limited to a localized area in the vicinity of the former UST, in a zone <br /> between approximately 10 and 35 feet bgs Based on data obtained during <br />' the investigation, the mass of TPH-g remaining in the site soil is estimated <br /> to be approximately 8 04 kilograms (17 7 pounds) This mass would be <br /> equivalent to approximately 2 to 3 gallons of gasoline TPH-g in ground <br /> water is also limited to a localized area and the mass of dissolved TPH-g <br /> remaining is estimated to be approximately 0 91 kilograms (2 01 pounds) <br /> This mass would be equivalent to approximately 2 to 3 pints of gasoline <br />' conservative assumptions, data from soil and ground water suggest <br /> Using consgr gg <br /> that only a very small quantity of gasoline remains at the site Please refer <br /> to Appendix B for a detailed explanation of these calculations <br /> ERM 8 9393 50/UPRR/07/11/02 <br />