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R603 UPDATE-11 11/19/92 • Ground water elevation measurements show that the ground water ,is still in a discharge cycle with a valley forming from MW2 towards MW1, while 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 in the extent of the dissolved constituents in all of the monitoring wells except MW3 and MW10. These wells have floating product. NW11 and MW12 were sampled for the first time on September 22 , 1992, see Table 1 and Figures 5A and 5B. 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- 411 , an increase an the vacuum influence will be obtained and a more substantial reduction in the contaminants, found in the other wells, will 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 certified results show that pulling fresh air across the fluid air interface within the Convault (tank) straps the hydrocarbons from the water that are presently stored in the tank. The increased active air spargeing that will occur an the tank should greatly reduce contaminant levels of the water that will be pumped from MWl and MW3 for treatment. Treatment will be tank strapping, utilizing the "Convault" as a 1000 gallon tank strapper to batch treat approximately 300 gallons every 5 hours. All vapors driven off by the air strapping from the tank will be processed into the thermal oxidizing unit for destruction. The activities described in the work plan, Lo place and sample two offsite ground water monitoring wells, have been completed, see Appendix C. RECOMMENDATIONS 1. Perform ground water sampling for gasoline range hydrocarbons and fecal coliform on a quarterly basis. 2 . Until the REMOX unit is stabilized, no air dilution, ccntlnue eekil' ad_ust.-nents and •iiivnthl iTiGisitoring using the lOS50 PID-GC. • 3 . Provide monthly update status reports of vapor recovery/destruction. PAGE 2