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rrealagko,rechn!"Inc Page 8 Groundwater Monitoring Report Project No 723 2 October 25,2005 2 MTBE • None of the wells sampled contained MTBE above the laboratory reporting limits and ' therefore contour diagrams were not produced EPA Method 8260B was utilized for this event • MTBE does not appear to be an issue at this site ' 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 northwest and southwest locations of wells MW-7 and MW-9, respectively Well MW-8 historically has less benzene than MW-5 also ' • 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 centered in well MW-208 and the concentrations attenuate to non-detectable levels in the northwest and southwest locations of wells MW-207 & MW-209, respectively 1 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 deepest well MW-101 intermittently contains BTEX contaminants and it contained low levels TPH-G for the event The TPH-G concentrations in MW-101 have exhibited a slight increasing trend since March 2004 ❑ Deep well MW-201 occasionally contains trace BTEX but was non-detect for the third 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 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 1