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Geological rechAks Ittc Page 5 <br /> Groundwater Momtonng Report <br /> Project No 425 2 <br /> Apn1 18,2003 <br /> For the ninth 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 /> • Oxidation-Reduction Potential (ORP) was measured (Table 5) The results for the <br /> ' December groundwater monitoring were negative in every monitoring well except <br /> MW-6, even wells that historically have shown positive values, suggesting that the site <br /> is under the influence of anaerobic biodegradation of the petroleum hydrocarbon <br /> plume <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 Bowed 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, the gradient is currently N050E at 0 0009 ft/ft <br /> 2 The intermediate depth groundwater has flowed easterly, with three shifts to southeast <br /> during September 2000, September 2001 and December 2002 The northerly flow <br /> direction during the December 3, 2001 event was anomalous The gradient is currently <br /> S620E at 0 0037 ft/ft <br /> 3 Vertical groundwater gradients have been found to be flowing upward, during winter <br /> ' and early spring, and downward during late spring and summer However, it continued <br /> in an upward direction during this past summer and fall Upward vertical gradients <br /> dominate 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 /> Increases in TPH-G concentration in the western monitoring wells indicate that the <br /> plume may be spreading laterally 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 />