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Cwtog4uf ncluticslnc Page 5 ' Groundwater Monitoring Report Project No 662 2 January 25, 2006 ' • Figure 6 Deep Well MTBE Concentrations shows that the highest level of MTBE (8 ug/1) is present in well MW-104 The plume attenuates to the down gradient (east) ' locations of wells MW-5 and MW-6 Figure 7 Deep Well TPH-G Concentrations shows that the highest level of TPH-G (86 ug/1) is present in down gradient well MW-6 Additional monitoring is necessary to conclude that the TPH-G plume is displaced from the MTBE containing wells MW-5 and MW-104 ' • Figure 8 MTBE vs Groundwater Elevation in MW-3 illustrates a fairly direct relationship between the concentration of MTBE in groundwater and the elevation of groundwater in well MW-3 A linear trend line has been added to the figure to show a ' general decline in both groundwater elevation and MTBE concentrations over time • Figure 9 MTBE vs Groundwater Elevation in MW-104 does not indicate a clear relationship between groundwater depth and MTBE concentrations The MTBE values ' appear to have a slight increasing trend Table 4 includes Oxidation-Reduction Potential (ORP) and Dissolved Oxygen (DO) measurements for the site's wells The ORP values continue to fluctuate but the ' moderately positive values suggest that the plume may be undergoing some biological activity The DO values are low for all of the sampled wells indicating that the wells are within the halo of reaction depleted water caused by biodegradation 3.0 CONCLUSIONS AND RECOMMENDATIONS ' Conclusions 1 The historical shallow groundwater trend is easterly ' 2 The deeper aquifer direction was anomalous due to a high in well MW-5 The direction has varied for the past four monitoring events but additional monitoring is needed to determine trends It is noted that the three wells used for monitoring this level (MW-5, MW-6 &EW-1) are in a fairly linear geometry that should be viewed with caution 3 Shallow monitoring wells MWA & MW-3 are located adjacent to the former UST ' excavation and contained moderate MTBE (1770 and 2310 ug/l, respectively) for the event Based on previous discrete groundwater sampling, the shallow MTBE groundwater plume does not extend to the down gradient location of MW-5 The CPT-7 boring was advanced adjacent to the MW-5 location and its groundwater sample at 29 feet bgs was free of contamination 4 The deeper aquifer MTBE plume is present in well MW-104 (8 ug/1) and attenuates to the location of MW-5 and MW-6 A sand layer is present at a depth of 38 — 48 feet across the site and it appears to act as a preferential pathway for contaminant migration 5 There are low levels of TPH-G, 50 8 — 82 5 µgh, present in shallow groundwater beneath ' the former UST excavation area The CPT investigation completed in December 2003 revealed high levels of TPH-G beneath the former UST excavation (CPT-4 22,000 µg/1 TPH-G) As with the MTBE, the decrease in TPH-G concentrations may be a result of