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- 01 March 1999 <br /> AGE-NC Project No. 95-0103 <br /> Page 7 of 8 <br /> • The current concentration of benzene in well MW-4 is 2.4 % of the initial and highest <br /> concentration of benzene detected in the monitoring well. <br /> • DIPE, MTBE, TBA were detected in water samples collected from wells MWA, MW-3, <br /> MW-5 and VE-6. The MTBE was detected in ground water samples at concentrations as high <br /> as 33 ppb (MW-1). <br /> • The concentrations of benzene exceeds the state maximum contaminant level (MCL) of 1 <br /> ppb in four of the monitoring wells sampled. <br /> • Between September and December 1998, the SVE system extracted an estimated 1.2 gallons <br /> of gasoline from the site. Since initiation of the SVE system an estimated total of 409 gallons <br /> of gasoline have been removed. <br /> • It is likely, based on the soil gas/vapor samples that the SVE system has removed most of <br /> the hydrocarbons from the vadose soil zone, in the SVE system's area of influence. It is <br /> likely that soil contamination remains within the saturated soil in portions of the dissolved <br /> hydrocarbon plume. <br /> • Benzene concentrations in the extracted soil-vapor have been reduced to less than the <br /> detection limit of the soil vapor analytical method 8020 (Table 4). <br /> • On-site, a population of biodegrading micro-organisms exists that may promote degradation <br /> of the hydrocarbons on the site. In the off-site sample analyzed, these organisms were not <br /> detected. These populations may be encouraged due to the addition of oxygen through the <br /> ground water sparging, but are not seen off-site due to the lack of added oxygen. Due to the <br /> lack of significant petroleum biodegrading microorganisms off site, natural attenuation of <br /> the petroleum hydrocarbons through biologic activities may not be occurring. <br /> rldranced GeoEnvironmental,Inc. <br />