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CL,EARWATER <br /> C R O U o P I N C <br /> 3.4 Groundwater Sample Analytical Results <br /> 3 41 4th Ouarter 1995 <br /> Dissolved TPHg and benzene were detected in concentrations exceeding method <br /> detection limits in samples collected from all wells on October 19, 1995, except those <br /> from the perimeter wells MW-3, MWA, MW-5, MW-6, and MW-7 The highest <br /> detected dissolved hydrocarbon concentrations were noted in the sample from MW- <br /> 2, which contained 31,000 parts per billion (ppb) TPHg and 1,200 ppb benzene <br /> Dissolved MTBE was detected in concentrations exceeding the method detection <br /> limit in samples collected from all wells except the perimeter wells MW-3, MW-4, <br /> MW-5, MW-6, and MW-7 The highest detected concentration of MTBE was 3,400 <br /> ppb in the sample collected from MW-2 Separate phase hydrocarbons (0 07 feet) <br /> were measured in MW-1 <br /> Dissolved hydrocarbon concentrations in groundwater on October 19, 1995 are <br /> displayed on Figure 6 A copy of the laboratory report and chain-of-custody form are <br /> included in Appendix B <br /> 3 4 2 1st Q11arter 1996 <br /> Dissolved TPHg and benzene were detected in concentrations exceeding method <br /> detection limits in samples collected from all wells on January 5, 1996, except those <br /> from the perimeter wells MW-3, MW-4, MW-5, MW-6, and MW-7 and the domestic <br /> well The highest detected dissolved hydrocarbon concentrations were noted in the <br /> sample from MW-2, which contained 6,500 parts per billion (ppb) TPHg and 88 ppb <br /> benzene Dissolved MTBE was detected in concentrations exceeding the method <br /> detection limit in samples collected from all wells except the perimeter wells MW-3, <br /> MW-4, MW-5, MW-6, and MW-7, and the domestic well The highest detected <br /> concentration of MTBE was 1,000 ppb in the sample collected from MW-2 Separate <br /> phase hydrocarbons (0 03 feet) were measured in MW-1 <br /> Dissolved hydrocarbon concentrations in groundwater on January 5, 1996 are <br /> displayed on Figure 7 A copy of the laboratory report and chain-of-custody form are <br /> attached as Appendix B Groundwater analytical results are presented on Table 2 <br /> 4.0 SUMMARY OF CONTAMINATION <br /> 4.1 Summary of Vadose Zone Contamination <br /> The extent of soil contamination was delineated during previous investigative <br /> work by RESNA The horizontal extent of soil contamination is delineated by the <br /> locations of wells MW-3, MW-4, MW-5, MW-6, and MW-7 (see historical soil <br /> sample analytical results on Table 1) The vertical extent of soil contamination <br /> extends from approximately 10 feet below grade to the water table It appears that <br /> contaminants from the former underground storage tanks and associated piping <br /> D-107,PAR RAP <br /> / 6 February 21, 1996 <br /> I <br />