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.. . <br /> rT� , <br /> 25 May 2001 <br /> AGE-NC Project No. 95-0118 <br /> Page 5 of 6 <br /> induced vacuum (negative pressure) of approximately 20 inches of water was monitored in the <br /> piping between the blower and the extraction.wells. TPH-g was detected in the soil-vapor sample <br /> collected from the soil vapor stream at a concentration of 93 4g/1 and BTEX compounds,were <br /> detected at concentrations of as high as 5.9µg11 (xylene). <br /> The analytical results are summarized in Table 3. The laboratory report (Me Campbell Analytical <br /> Lab M 66526), Quality Assurance and Quality Control(QA/QC)reports and chain-of-custody forms <br /> are included in Appendix B. <br /> 4.0. CONCLUSIONS <br /> Based upon results of ground water monitoring well sampling, AGE concludes: <br /> • The dissolved hydrocarbon-concentrations have decreased to near or below laboratory <br /> method detection limits. <br /> • The only dissolved TPH-g was detected in sample 1AS-2, is 2.38% of the maximum 24,000 <br /> µg11 detected in February 1998, and 13.8 %of the average TPH-g concentration detected in <br /> _t all pervious sampling events. Dissolved TPH-g and BTEX concentrations were at less than <br /> detectable levels in samples from wells MW-2 and MW-3, previously the most intensely <br /> impacted portion of the plume. <br /> • AGE estimates that approximately 0.039 kilograms of gasoline remain dissolved in the <br /> ground water(Appendix P. <br /> • During the soil vapor extraction analysis,the minimal concentration of petroleum as gasoline <br /> detected indicates a low residual of hydrocarbons in soil at the site. The 93 µg/I <br /> concentration of TPH-g detected is only 3.45 % if the maximum 2,690 ggll-detected in <br /> October 1999: <br /> IJ <br /> 5.0. RECOMMENDATIONS <br /> The site should be considered for closure: It is unlikely that additional remediation (soil vapor <br /> extraction) at the site will result in a significant reduction of the residual hydrocarbon mass. <br /> Excluding a very limited volume of the TPH-impactcd ground water around well LAS-2, the ground <br /> water in the former extent of the dissolved plume (UST area)meet drinking water standards set by <br /> i <br /> the DHS - maximum contaminant levels (MCLS) for the contaminantsof concern. <br /> V <br /> } Advanced GeoEnvironmental,Inc. <br /> _:7 <br />