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CTeologic01 T"/inla I" Page 8 Groundwater Monitoring Report Project No 723 2 June 21,2006 • Figure 8 illustrates the distribution of Benzene in the intermediate wells A localized high is centered in well MW-3 that attenuates to the west, northwest, northeast and ' southwest locations of wells MW-1, MW-107, MW-108 &MW-109, respectively • Figure 9 illustrates the distribution of Benzene in the deep wells A localized high is present in well MW-2.08 and the concentrations attenuate to non-detectable levels in ' the northwest and southwest locations of wells MW-207 &MW-209, respectively The results of the groundwater sample analysis show the following ' ❑ Review of the historic groundwater elevations show that groundwater levels experience seasonal fluctuations from the mid 1990s to spring 2000 but have been decreasing steadily with each seasonal cycle since spring 2000 However, this trend ' may be slowed by the higher than average precipitation experienced in the spring seasons of 2005 & 2006 ' ❑ The shallow aquifer gradient for the event was to the northeast that is consistent with the previous events It is noted that an anomalous low was present in well MW-6 for this monitoring episode This is why the direction arrow in Figure 2A is located up gradient of the release to show the regional trend ❑ The vertical gradient is predominately downward, which has contributed to the depth below the water table that this contaminant plume has migrated ❑ The concentrations of BTEX and TPH-G continue to fluctuate in individual monitoring wells from one sampling event to the next However, there is a general trend of concentrations tracking the groundwater elevations ' ❑ The main mass of contaminants appears to have migrated to the depth of the intermediate well screen interval (43 to 70 ft bgs) ❑ On site deep well MW-101 intermittently contains BTEX contaminants and it usually ' contains low levels of TPH-G The well did not contain contaminant concentrations above the laboratory reporting limits for the second time in the investigation ❑ The site's deepest well MW-201 occasionally contains trace BTEX and again it contained toluene and xylene for the event (1 2 and 2 4 ug/l, respectively) The intermittent contamination is probably a drilling artifact created by the use of mud rotary drilling The contaminant concentration decline since the first monitoring ' event in December 2001 supports the conclusion that the initial high concentrations were from a drilling artifact ' ❑ Figure 10 illustrates TPH-G and Benzene concentrations versus elevation in well MW-3, which lies near the core of the plume There appears to be a fairly direct relationship between the water table and the TPH-G concentrations Benzene ' concentrations have stabilized in the well The graph shows the significant rise in the water table over the last two years- over 9 feet since October 2004 ❑ Figure 11 illustrates TPH-G and Benzene concentrations versus elevation in well ' MW-4, which lies up gradient of the core of the plume The contaminant concentrations exhibit a decreasing trend in this well ❑ Figure 12 illustrates TPH-G and Benzene concentrations versus elevation in deep well MW-101, which lies near the core of the plume The TPH-G concentrations 1