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KLEINFELDER <br /> _ 1 <br /> 5 CONCLUSIONS AND RECOMMENDATIONS <br /> The underground fuel tank which appears to be the source of soil and ground water <br /> contamination identified at the site was removed in 1985. A VES was installed in 1987 and <br /> operated for 15 months. Measurements made on the emissions during the period of VES <br /> operation indicated that the system was effectively removing hydrocarbons from the vadose <br /> zone. <br /> Based on soil sampling and analysis performed in January 1988, it appears that over the <br /> period of VES operation,TPH concentrations in the most contaminated area of the vadose <br /> zone have been reduced significantly (from a range of 1,100 to 4,400 mg/kg down to 43 <br /> mg/kg). Additionally, i,' appears that benzene, toluene, ethylbenzene, and xylene <br /> concentrations have been reduced to below detection Iimits, based on a soil sample <br /> collected from the most contaminated zone identified in previous investigations. <br /> Based on ground water monitoring performed at the site, (data presented in Table 3), it <br /> appears that concentrations of benzene, toluene, ethylbenzene, and xylene in the ground <br /> water have dropped substantially over the period of VES operation. Benzene has not been <br /> detected in ground water samples since March 1987. In the last sampling round, toluene <br /> was detected in MW-2 at a concentration just over the detection limit. No other BTEX <br /> constituents were detected in samples collected from the eight monitoring wells in May <br /> 1988. This observed decrease in BTEX concentrations may be the result of natural or VES <br /> enhanced biodegradation of the hydrocarbons. The increased flow of oxygen during <br /> operation of the VES may have increased the rate of biological activity in the vadose zone <br /> and the ground water. <br /> { <br /> Low concentrations of TPH (less than 1 mg/1), reported as an unidentified hydrocarbon <br /> mixture and quantified as either gasoline or diesel,were detected in ground water samples <br /> collected from MW-I, MW-2, MW-3, MW-5, and MW-7 during May 1988. However, <br /> analytical results for triplicate samples collected from MW-1 for quality assurance/quality <br /> control did-not---have-detectable--TPH-concentrations;-----Chemwest reported--TPH ---- <br /> concentrations of .87 and .3 mg/I in blind duplicate samples from MW-1, and Enseco <br /> reported no TPH concentrations over the detection limit of.1 mg/1 in a triplicate sample. . <br /> This may be.a function of the difference in extraction solvents used by the two laboratories. <br /> '"" 113-88-908 12 <br />