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RG04 UPDATE 13 11-24-1992 <br /> INTRODUCTION <br /> ° This report includes the results of the events that have occurred <br /> at this site since the 12th Update Status Report, from September <br /> 11, through November 17, 1992 The following are the conclusions <br /> and recommendations from Update Status Report ##12 . <br /> UPDATE #12 <br /> CONCLUSIONS AND DISCUSSION <br /> Vapor extraction is successfully removing the degraded gasoline <br /> range petroleum hydrocarbons from the soil and ground water for <br /> the most part at this site . The vapor recovery system, operated <br /> under Variance ##91-19 and 91-20 was turned off awaiting the <br /> Permit to Construct, Permit ## AP 91-106 . During this "off period" <br /> two periods of "re-equilibration" have occurred Soil sample <br /> results form SB4 and a vapor sample from the vadose zone well P1 <br /> indicated that the former northeaster pump island area and the <br /> surrounding area is now void of the contaminant <br /> Vapor extraction has removed the lighter fractions of gasoline <br /> range hydrocarbons found in the soil and has greatly reduced the <br /> dissolved contaminant found in the ground water. <br /> Ground water gradients, corrected for vacuum influence, have shown <br /> potenti.ometri.cally lows at the wells being used for vapor <br /> recovery MW1 and MWS Once the vapor recovery is shut off, <br /> normal flow directions again take place to the east-southeast or <br /> northeast , with the exception of the March 5, 1992 gradient, which <br /> flowed to the north northwest and may represent a recharge and/or <br /> a decline in water usage of the municipal wells to the east of the <br /> site <br /> Fecal coliform has been analyzed for monitoring wells MW3 , MW4 , <br /> MW5 and MW6 on a monthly basis from December, 1991 through <br /> February, 1992 Only trace amounts of fecal coliform have been <br /> occasionally detected in any of the wells during those 3 months <br /> This analysis will occur on a quarterly basis starting on the <br /> June, 1992 ground water sampling, see Table 2 <br /> RECOMMENDATIONS <br /> 1 Continue vapor recovery on MWS and the newly <br /> installed vadose wells VSB3 , VSB5, VSB9 and VSB11 . <br /> 2 Continue to monitor this site on a quarterly basis <br /> 3 Obtain depth to ground water, vacuum influent <br /> readings to evaluate the effects of vapor <br /> recovery <br /> 4 . Sample for fecal coliform from MW3 , MW4 , MW5 and MW6 <br /> on a quarterly basis during the quarterly sampling. <br /> page 1 <br />