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GeologfcalTeclucicsl�cc Page 8 Groundwater Monitoring Report Project No 723 2 June 20,2005 ' 3 Benzene ' • Figure 7 illustrates the distribution of Benzene in the shallow wells A localized high is centered in well MW-5 that attenuates to the southwest, northwest and east locations of wells MW-9,MW-7 and MW-8, respectively ' • Figure 8 illustrates the distribution of Benzene in the intermediate wells A localized high is centered in well MW-3 that attenuates to the southwest, west and northwest locations of wells MW-109, MW-1 & MW-107, respectively The plume also ' attenuates to the east in the location of MW-108 • Figure 9 illustrates the distribution of Benzene in the deep wells A localized high is centered in well MW-208 and the concentrations attenuate to non-detectable levels in ' the southwest and northwest locations of wells MW-209 &MW-207, 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 reversed ' by the higher than average precipitation experienced this spring of 2005 ❑ 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 contaminants and it contained low levels TPH-G for the event It is noted that the contaminant concentrations in MW-101 ' have continuously declined since it's installation in contrast to the shallow wells that do not show a similar contaminant decline ❑ Deep well MW-201 occasionally contains trace BTEX but was non-detect for the second consecutive event 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 ❑ Figure I 1 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 and benzene concentrations have displayed a decreasing trend, although a slight increasing trend is evident for the past year The steep decline in the initial concentrations suggests that the contaminants detected in the well were initially a drilling artifact 1