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1 � V • , <br /> 4 <br /> therefore analyzed to check the results from MW-3 However, no contaminants were detected in either <br /> duplicate sample Therefore, MW-3 was resampled on June 21 No contaminants were detected in the <br /> repeat sample, confirnung that the May 23 result for MW-3 was probably erroneous (Table 2) <br /> 6.0 CONCLUSIONS AND RECOMMENDATIONS <br /> 1 <br /> Approximately 3,430,000 cu ft of vapors were withdrawn and combusted between April I and June <br /> 30, 1996 VOC concentrations (as measured by PID) in the shallow well vapor stream generally <br /> increased during this period, whereas concentrations in the deep well decreased The laboratory result <br /> for a vapor sample collected during the quarter did not approximate the PID reading on the same date, _ <br />' causing uncertainty regarding the accuracy of both the laboratory and field measurement techruques <br /> Ignoring this uncertainty, the mean VOC concentration measured m the shallow well during the 12 <br /> monitoring events was 1364 ppm Using this value, we calculate that 1224 pounds of hydrocarbons <br />' were destroyed <br /> i <br /> Contaminant concentrations in the groundwater sample from MW-5 were higher in the second quarter <br />' than in the first quarter of the year, repeating the pattern seen in 1995 This is probably due to the <br /> seasonal rise in the static water level, placing groundwater in contact with residual gasoline in the <br /> capillary fringe and basal vadose zone As the static water level drops during the coming months, the <br />' capillary fringe and "smear zone" will probably be exposed, and vapor concentrations are likely to <br /> increase again as dissolved concentrations decline <br /> In contrast, contaminant concentrations in the water sample from VE-1 were lower than in the first <br /> quarter of 1996 Continued monitoring of this well may help to identify a trend in contaminant levels <br /> and determine the reasons for concentrations vanations <br /> At the present time, regulatory policies and cleanup guidelines for underground tank sites are being re- <br /> evaluated by the State Water Quality Control Board What changes might be proposed, and how such <br />' changes might affect the Apache Plastics site, are uncertain at this time Based on the current policy, it <br /> is unlikely that the site can be certified for closure with the existing benzene concentrations, however, <br />' this option should be reconsidered in the coming months as changes in policy become more clear <br /> 1 f <br /> 1 <br /> , <br /> 6 <br /> 1 <br />