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22 November 1999 <br /> i AGE-NC Project No 95-0103 <br /> Page 4 of 5 <br /> • Morutoring wells MW-1,MW-2,MW-3, and MW-4 had ground water approximately three <br /> ' to four feet above the top of the screened Interval, potentially reducing the effectiveness of <br /> these ground water monitoring wells to characterize the dissolved-phase hydrocarbon plume <br /> in the shallowest ground water <br /> • The greatest concentrations of petroleum hydrocarbons as gasoline were detected in samples <br /> ' collected from well MW-4 and vapor wells VE-1 and VE-6 The highest concentration of <br /> benzene was detected in the sample collected from monitoring well MW-4 and vapor well <br /> VE-6 at 1,700 ygll <br /> MTBE was detected in the ground water sample from well MW-1 at a concentration of 13 <br /> ,ugll <br /> • A reduction of the dissolved-phase hydrocarbon p1w-ne concentrations`on the site has <br /> occurred However, the dissolved hydrocarbon concentrations, specifically the benzene <br /> concentrations dissolved in ground water have increased The static level of ground water <br /> decreased contemporaneously with the Increase of dissolved benzene concentrations <br /> Additional soil impacted with benzene may have been exposed to the upper most water table <br /> • with desorption of benzene from soil possibly occurring - <br /> • The current concentrations of benzene in samples MW-1, MW-3 and MW-4 are graphically <br /> presented in Appendix C t <br /> 5.0. RECOMMENDATIONS <br /> Based on data collected over the quarter at the site, AGE recommends <br /> • Continued monthly and 'quarterly ground water monitoring The next ground water <br /> monitoring event is scheduled for December During the next quarterly sampling event, <br /> ' collect water samples from selected wells to provide for the most representative ground water <br /> data (I e all vapor wells with screens in the current water table level) <br /> a <br /> a <br /> 1 ' <br /> Advanced GeoEmironmental,Inc <br /> i <br /> t <br />