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1 increased again in February 1997 after the soil was allowed to relax during the month of January The February rise was followed by a decrease in March At the present time, concentrations measured by PID from both VE-1 "shallow" and VE-2 are in the range of 750-1500 ppm ' Laboratory concentrations in March were 455 and 577 ppm, respectively This represents a 200% increase since December in VE-1 "shallow" and a 15%decrease in VE-2 ' Figure 4 illustrates that concentrations in VE-1 "shallow" leveled off during the fourth quarter of 1996, at about the time VE-2 was installed and Apache personnel reduced the air flow from VE-1 ' "shallow" The curve has not been projected to the end of 1997, but, it appears that there would be little reduction in concentration if the valve on this well remains nearly closed ' Figure 3 indicates that concentrations from the deep zone (below 50 feet) have been low since the end of 1995, when the groundwater level rose above the well opening As long as the water table stays above 60 feet, there will be little or no further reduction in gasoline concentrations in the deep t zone Figure 3 also shows that the installation of VE-2 was successful in removing hydrocarbons that had ' not been previously mobilized from the intermediate zone (35-50 feet) Operation of the well for several weeks lowered the concentrations in December 1996 and again in March 1997, which suggests that concentrations build up after a period of non-operation (e g January 1997) Hence, t1 operating4he extraction unit intermittently for the remainder of 1997 may result in further reduction of gasoline concentrations in this zone 4.2 Weight of VOC's Destroyed Due to the sporadic operation of the extraction unit during the quarter, computation of the weight of ' VOC's extracted would not yield a meaningful number Hence, this calculation is omitted in this report 5.4 GROUNDWATER MONITORING 15.1 Monitoring Procedures ' The depth to groundwater was measured on March 12, 1996-and the results are shown on the Well Monitor Report(Appendix C)and in Table 1 A water sample was collected from MW-5 on that date, after approximately 7 gallons of water were purged and stored in a 55-gallon drum on site At the request of Mr Ron Rowe, the remaining wells were purged and sampled on March 26 Two 40-m1 sample vials were collected from each well and were delivered to Sequoia Analytical in Sacramento The laboratory report and chain-of-custody form are included in Appendix B 5 4 1 �I