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Geological Tecfmics Inc Page 5 ' Groundwater Monitoring Report Project No 425 2 • May 20,2002 o Groundwater levels have previously exhibited a trend of decreasing elevation This situation may have stabilized or reversed since September 2000- see Figure 8 TPH-G and benzene concentrations in MW-1 exhibited a sharp increase to the highest levels recorded in the investigation This well lies in the predominant up gradient 1 direction from the former UST field and the reason for this anomaly is not known See Figure 4 for a graph of Benzene and TPH-G versus time and Figure G for the distribution of TPH-G ' ® BTEX & TPH-G concentrations in MW-2 continue to decrease since the impacted soils in the vicinity of the former USTs were excavated in July 2001 See Figure 5 for graph of Benzene and TPH-G versus time and Figure b for the distribution of TPH-G ' ® Figure 7- Groundwater Elevation vs Time MW-2 demonstrates a general trend of increasing TPH-G concentration with decreasing groundwater elevation a Contaminant concentrations in wells MW-4 and MW-5 exhibit a stable trend o For the sixth consecutive event, wells MW-102 and MW-202 did not contain contaminant concentrations above the laboratory reporting limits G All three of the domestic wells were non-detect for the event o Oxidation-Reduction Potential (ORP) was measured (Table 5 & Figure 9) The results suggest that well MW-2 is in the core of the contamination plume or is immediately down gradient of the plume Negative ORP values indicate that the wells are within the halo of reaction depleted water caused by biodegradation of the contaminants For the February 22, 2002, event, seven water table wells had negative ORP values 1 3.0 CONCLUSIONS AND RECOMMENDATIONS The following conclusions have been drawn regarding the status of the groundwater at this ' site and recommendations for future work Conclusions ' 1 The water table groundwater gradient historically flowed in a northerly direction at about 0 002 ft/ft prior to May 1998 However, since that time, the gradient has fluctuated from north to northeast ' 2 The intermediate depth groundwater has flowed easterly, with two shifts to southeast during September 2000 & September 2001 The direction of north for the December 3 event was anomalous, however the December 21 event was again consistent with the ' historical data showing an easterly flow 3 Vertical groundwater gradients have been found to be flowing upward during winter and early spring and downward during late spring and summer This may be due to the ' annual cycle of the groundwater pumping needs of the community 4 The dominance of upward vertical flow of groundwater may be the primary reason the contaminants have not impacted the drinking water aquifer During periods of heavy