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Geological Teclr�fcs l►u. Page 6 Groundwater Monitoring Report Project No.425.2 October 19,2004 1 The results of the July 2004 event are comparable with the results from previous monitoring events. The following observations are made: a The horizontal groundwater bearing calculated from the Zone A wells, is currently towards the northeast. a The bearing calculated from the Zone B wells is to the northwest. a Vertical groundwater gradients were positive in the Zone A/Zone B and Zone B/Z.one D well pairs. ' a TPH-G concentrations in MW-1 continue to fluctuate within levels usually observed for the site. The concentration of TPH-G in MW-1 measured during the April 2004 event were the lowest recorded at the site in three years. a Contaminant concentrations in well MW-4 exhibit a historically static trend, with TPH-G showing only a slight increase over the last three quarterly groundwater-monitoring- events. ! Contamination in monitoring well MW-5 fluctuates seasonally. The average TPH-G concentrations per season have increased over the past three years. a For the fifteenth consecutive event, well MW-102 did not contain contaminant concentrations above the laboratory reporting limits. e All three of the domestic wells were non-detect for this monitoring event. O Dissolved Oxygen measurements are on the low to moderate end of the scale, ranging between 0.02 and 2.2 ppm(Table 9). ® Oxidation-Reduction Potential (ORP) measurements are mixture of negative and positive ' numbers (Table 9). ' 4.0 CONCLUSIONS AND RECOMMENDATIONS ' Conclusions 1. Zone A groundwater historically flows in a northerly direction. ' 2. Zone B groundwater shows a northwesterly flow over the last three monitoring events. 3. The dominance of upward vertical flow of groundwater may be the primary reason contaminants have not impacted the drinking water aquifer. ' 4. Petroleum hydrocarbon concentrations in the groundwater at the site fluctuate with each monitoring event. The residual contamination in soil, up gradient of MW-2, remains a significant source of impact to the groundwater plume. ' 5. Contamination has been detected in MW-106 (Zone B) and MW-201 (Zone Q. This is an indication of site-specific vertical movement of plume into the deeper zones. 6. Generally the soil and groundwater testing data suggests that the contaminants are t spreading laterally, but not vertically to any extent. 7. The three domestic wells sampled remain non-detect for all analyzed constituents, indicating that the drinking water aquifer has not been impacted.