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Creologaal Tech/ "14C Page 7 Groundwater Monitoring Report Project No 723 2 August 31,2004 ' 2 MTBE * The MTBE concentrations were not confirmed utilizing EPA Method 8260 and ' therefore contour diagrams were not produced When Method 8260 is utilized the wells are non-detect for MTBE ' a MTBE appears not 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 southwest, west and northwest locations of wells MW-9, MW-4 & MW-7, respectively The plume also attenuates ' to the east in the location of MW-8 * 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, west and northwest locations of MW-209, MW-101 & 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 ❑ 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) ❑ Intermediate well MW-101 did not contain petroleum hydrocarbon contaminants above the laboratory reporting limits for the first time during the previous March 2004 monitoring event The previous contamination is probably a drilling artifact 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 did not contain contaminant concentrations above the laboratory ' reporting limit The previously noted 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 direct relationship between 1