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R604 :UPDATE 9-MARCH, 1992 <br />. INTRODUCTION <br /> This report includes the results of the March, 1992 ground water <br /> quarterly sampling, along with the events that have occurred at <br /> this site since the 8th Update Status Report, that covered events <br /> up through December 17 , 1991 . <br /> As stated in our 8th Update Status report, the first phase of <br /> remediation to the above mentioned site, removing aged gasoline <br /> range hydrocarbons from the soil in the vadose zone beneath the <br /> tank field and pump island areas has been completed. This <br /> finalized the clean-up of contaminated soil at this site . The <br /> following are the conclusions and recommendations from Update <br /> Status Report #8 : <br /> UPDATE #8 <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 a variance, is now temporarily turned off awaiting <br /> the Permit to Operate. During this "off period" two periods of <br /> "re-equilibration" have occurred. Sample results from the vadose <br /> zone wells P1 , P3-Swarm and EX have indicated that these wells and <br /> the surrounding areas are now void of the contaminant. <br /> Vapor extraction has greatly reduced the dissolved contaminant <br /> found in the ground water. The most recent sampling occurred 30 <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 and MW5 likewise has <br /> been reduced; from 31 mg/L TPH to 0 . 19 mg/L TPH. With the <br /> exception of MW1, benzene has been removed from the ground water <br /> beneath the site. The benzene found in MW1 has been greatly <br /> reduced, from 5 , 200 ug/L to 5 . 8 ug/L. <br /> Ground water gradients, corrected for vacuum influence, have shown <br /> potentiometrically low at the wells being used for vapor recovery; <br /> MWI and MW5 . Once the vapor recovery is shut off, normal flow <br /> directions again take place to the east-southeast. <br /> RECOMMENDATIONS <br /> I . Once the Permit to Operate is obtained, restart the <br /> vapor recovery on MW1 and MW5 to continue ground <br /> water remediation. <br /> 2 . Continue to monitor this site on a quarterly bases. <br /> 3 . Obtain depth to ground water and "vacuum influence" <br /> readings, to evaluate the effects of vapor <br /> recovery <br /> page 1 <br />