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Geofogtcal Technics Inc Page <br /> ' Groundwater Monitonng Report <br /> Project No 425 2 <br /> December 5, 2002 <br /> ' • For the seventh consecutive event, wells MW-102 and MW-202 did not contain <br /> contaminant concentrations above the laboratory reporting limits <br /> ' • All three of the domestic wells were non-detect for this monitoring event <br /> O Oxidation-Reduction Potential (ORP) was measured (Table 5) The results for the <br /> ' September monitoring are inconclusive ORP values were negative in every monitoring <br /> well, even wells that usually show positive values Instrumentation will be checked and <br /> recalibrated if necessary <br /> I a Dissolved oxygen readings were taken down hole during well purging (Table 5) The <br /> readings show that the water of the site contains fairly high oxygen values, which <br /> should be beneficial to natural attenuation <br /> 3.0 CONCLUSIONS AND RECOMMENDATIONS <br /> ' The following conclusions have been drawn regarding the status of the groundwater at this <br /> site and recommendations for future work <br /> Conclusions <br /> 1 The water table groundwater gradient historically flowed in a northerly direction at <br /> about 0 002 ft/ft prior to May 1998 However, since that time, the gradient has <br /> fluctuated from north to northeast <br /> ' 2 The intermediate depth groundwater has flowed easterly, with two shifts to southeast <br /> during September 2000 & September 2001 The northerly flow direction during the <br /> December 3, 2001 event was anomalous <br /> 3 Vertical groundwater gradients have been found to be flowing upward during winter and <br /> early spring and downward during late spring and summer However, it continued in an <br /> upward direction during this past summer and fall Upward vertical gradients dominate <br /> over downward gradients by a 4 1 ratio <br /> 4 The dominance of upward vertical flow of groundwater may be the primary reason the <br /> contaminants has not impacted the drinking water aquifer <br /> 5 The shallow water table groundwater plume is laterally defined except to the west <br /> However, the data indicate that the contamination does attenuate toward the west <br /> 6 Petroleum hydrocarbon concentrations in the groundwater at the site fluctuate with each <br /> monitoring event The residual contamination in soil up gradient of MW-2 remains a <br /> significant source of impact to the groundwater plume <br /> 7 The deeper groundwater plume is defined vertically since MW-102 and MW-202 <br /> ' remain non-detect for contaminants <br /> 8 The three domestic wells sampled for the event remain non-detect <br />