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{� The calculated water table elevations were used to construct the groundwater gradient map in <br /> Figure 3 There is an east-trending depression in the water table that trends toward well GT-10 <br /> However, the static water level is slightly elevated in this well, forming a slight mound in the center <br /> of the depression The predominant flow direction appears to be eastward <br /> In comparison to most other sites, the groundwater gradient beneath the Gillies Trucking facility <br /> has been highly variable during the seven years during which we have constructed gradient maps <br /> This subject was addressed in the First Quarter 1999 Report, in which several different <br /> interpretations of the groundwater flow direction were illustrated Over the years, there have been <br /> substantial seasonal variations in both flow direction and gradient, making it difficult to identify the <br /> predominant flow direction or the primary controls on groundwater flow <br /> 3.2 Analytical Results <br /> Diesel was detected in three of the monitoring wells and in the Gillies domestic well (G-1) (Table <br /> 2) The,concentration has increased since December 2000 in GT-I and GT-10,but declined in GT- <br /> 6 This continues a pattern of fluctuating concentrations from quarter to quarter The increase in <br /> GT-10 follows a sharp decrease in December In the Fourth Quarter 2000 Report, we hypothesized <br /> that the December decrease was probably not sustainable, and the March results confirm this The <br /> results also confirm our suggestion in an earlier report that purged wells do not necessarily yield <br /> contaminant concentrations that are greater or more valid than non-purged wells This is probably <br /> especially true of diesel, which has low volatility However, it is also notable that the benzene, <br /> Ethylbenzene, and xylene concentrations in GT-10 also increased in March All of these <br /> compounds are more volatile than diesel, yet they did not degrade to lower concentrations than <br /> were detected after purging the wells in December It is particularly significant that diesel was <br /> detected in G-1, even though we did not purge the holding tank before cQllecting a sample <br /> 4.0 CONCLUSIONS <br /> The groundwater gradtent and flow direction continue to fluctuate over a large range of compass <br /> directions A northward flow direction has been measured during the first quarter in more than one <br /> year, but this was not the case during the first quarter of 2001, when an eastward or northeastward <br /> direction was apparent The flow pattern is complex and variable, and the main factors controlling it <br /> are ambiguous - <br /> In the 3rd Quarter 2000 Report, we concluded that purging has little effect on contaminant <br /> concentrations, because concentrations were quite similar to those during the second quarter, even <br /> though the wells were not purged in the tlurd quarter, In the fourth quarter, a slight increase from <br /> non.-detect to 100 parts per billion was noted in GT-1 and GT-5 that might have been attributable to <br /> the effects of purging in the fourth quarter The results from the first quarter of 2001, however, <br /> show that purging has little, if any, effect on contaminant concentrations Therefore, we recommend <br /> reducing the frequency of purging in the future This will reduce equipment, manpower, and <br /> disposal costs but will not adversely affect the laboratory results Purging could be done on an <br /> 3 <br />