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R603 UPDATE-11 11/19/92 4. 0 DISCUSSION AND CONCLUSIONS As stated in earlier reports, the soil is contaminated with gasoline range hydrocarbons beneath the tank field (MW10 ) and along the capillary fringe of the ground water, (MW1, MW2, MW3 and MW10) , see Figure 6 . Ground water beneath the site contains the dissolved constituents of gasoline range hydrocarbons and has spread out from beneath the site to the north (MW-6 ) , to the south (MW-7 ) to the west (MW-9 ) and to the east (MW-8 ) . The latest ground water sampling, September 22 , 1992 , has shown a decline in the lateral extent of the plume, see Figure 5 ( 9-22-92 ) . Vapor extraction commenced on October 17, 1991 and up until November 17 , 1992 has operated for 5388 hours out of a possible 8821. 5 for a 61% run time, destroying 39 , 542 pounds of gasoline range hydrocarbons. Since the last status report, October 16 , 1992, a total of 5176 pounds of gasoline range hydrocarbons have been removed/destroyed in 524 hours of operation ( 9 . 88 pounds per hour or 237 pounds per day of operation) . DCE, TCE and PCE screening indicates that these compounds are not present an the vapor stream at this site. . Ground water elevation measurements show that the ground water is still in a discharge cycle with a valley forming from MW10 towards MW1 , whale the overall flow direction is to the southeast from the tank area towards newly installed monitoring well MW12 . Ground water sample results obtained on December 17 , 1991, approximately 1473 hours after commencement of vapor extraction, compared to the ground water sample results obtained on September 22, 1992, 7486 hours after commencement of vapor extraction, show a decline an the extent of the dissolved constituents an all of the monitoring wells except MW3 and MW10 . These wells have floating product, see Table 1 . It is felt that once the air dilute has been completely closed and all vacuum recovery can be directed to MW1, MW2 , MW3 , MW10 and EX-- 4" , an increase in the vacuum influence will be obtained and a more substantial reduction in the contaminants, found an the other ,,ells, Si7a11 be noted. The permit to dump treated ground water to the sewer has been received and once the ground water recovery - treatment system has been completed, pumping will occur from monitor wells MW1 and MW3 . Non 4er l.11lel.l rGs111 Ls S llOw 411aL pulling fresh air across 1.i:c iFluidt air interface within the Convault (tank) strips the hydrocarbons from the water that are presently stored an the tank. The increased active air spargeang that will occur an the tank should greatly reduce contaminant levels of the water that will be pumped PAGE 9