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18 November 1996 <br /> AGE-NC-Project No 95-0134 <br /> IPage 7 of 8 <br /> I3 0. CONCLUSIONS AND RECOMMENDATIONS <br /> 31 CONCLUSIONS <br /> IBased upon the existing data and the modeling results, the following conclusions are offered <br /> • A soil interval containing concentrations of hydrocarbons was encountered between 30 to <br /> 40 feet in the confirmatory borings drilled on 14 June 1994, TPH-g was detected in borings <br /> CB-1 and CB-2 at concentrations of up to 2,200 ppm <br /> • Mass balance calculations based on analytical results of soil samples collected from borings <br /> CB-1 and CB-1, indicate that approximately 94% of hydrocarbons released to the soil have <br /> been remediated <br /> • Benzene was not detected in any of the samples analyzed from the confirmatory borings, and <br /> only low concentrations of toluene, ethylbeiizene and xylenes were detected Therefoie, the <br /> more volatile and concurrently more toxic spectrum of hydrocarbons has been successfully <br /> remediated <br /> • The results of a fate and transport modeling program indicate that the remaining hydrocarbon <br /> compounds are not likely to pose a threat to ground water and would naturally degrade over <br /> I time <br /> • Petroleum hydrocarbons were not detected in water samples collected during the last four <br /> monitoring events indicating that the hydrocarbon impact in ground water has been reduced <br /> to below detectable concentrations <br /> • The results of vapor extraction activities are postulated to have positively influenced ground <br /> I water in the vicinity of the extraction wells, as well Combined with natural degradation, this <br /> aspect is considered likely to decrease petroleum hydrocarbon concentrations to below <br /> detectable limits in the ground water <br /> I3 2 RECOMMENDATIONS <br /> Based upon the above-mentioned conclusions, AGE recommends the following <br /> I • Consideration for site closure No further action for soil and ground water monitoring and <br /> remediation should be required at the site <br /> • Proper abandonment of existing wells Upon site closure certification, all monitoring and <br /> extractions wells associated with the site should be abandoned in accordance with local <br /> regulations <br /> I <br />