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R604 :UPDATE 9-MARCH, 1992 <br /> CONCLUSIONS AND DISCUSSION <br /> Vapor extraction has been successful in removing the degraded <br /> gasoline range petroleum hydrocarbons from the soil and for the <br /> most part ground water at this site. The vapor recovery system, <br /> operated under Variances #91-19 and 91-20 was turned off awaiting <br /> the Permit to Construct, Permit # AP 91-106 . During this "off <br /> period" two periods of "re-equilibration" have occurred. Sample <br /> results from the vadose zone wells P1, P3-Swarm and EX have <br /> indicated that these wells and the surrounding areas are now void <br /> of the contaminant. <br /> Upon start-up for the Permit to Construct P1 , P3-Swarm and EX <br /> exhibited minor vapor recovery, 0 . 04, 0 . 07 and 0 . 01 lbs/day <br /> respectively. As of April 14, 1992 no detectable hydrocarbon <br /> vapors are being produced from these wells . <br /> Vapor extraction has greatly reduced the dissolved contaminant <br /> found in the ground water. The most recent sampling occurred 80 <br /> days after the vapor recovery system was shut down and showed that <br /> since vapor recovery has been used at this site, MW1 has been <br /> reduced from 2 mg/L TPH to <0 . 05 mg/L TPH. MW5 , likewise has been <br /> reduced from 31 mg/L TPH to 0 . 08 mg/L TPH. The BTEX' s have also <br /> been removed from the ground water beneath the site to below the <br /> detection limits . <br /> . Ground water gradients, corrected for vacuum influence, have shown <br /> potentiometrically low at the wells being used for vapor recovery; <br /> MW1 and MW5 . Once the vapor recovery is shut off, normal flow <br /> directions again take place to the east-southeast; with the <br /> exception of the March 5, 1992 gradient, which flowed to the north <br /> northwest and may represent a recharge and/or a decline in water <br /> usage of the municipal wells to the east of the site. <br /> Fecal coloform 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 coloform 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 . The Permit to Construct has been obtained. As <br /> requested in the permit, twice weekly sampling of <br /> the effluent is to occur for the first month then <br /> monthly thereafter. Continue vapor recovery on MW1 <br /> and MW5 to continue ground water remediation. <br /> 2 . Continue to monitor this site on a quarterly bases. <br /> . 3 . Obtain depth to ground water, vacuum influent <br /> readings to evaluate the effects of vapor <br /> recovery. <br /> page 10 <br />