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z CENET Evaluation 1 Introduction and growth without the addition of air or oxygen. Oxygen levels in the reactors fell, but never completely reached zero. Several test results confirm that this microbial process does not include methanogenesis. No significant population of anaerobic microbes were found in the anaerobic plate counts, no significant amount of gas was ever produced, and the pH of the reactors remained on the high side of neutral. There is some evidence that nitrate conversion or some other non- oxygen transformation may be acting as the energy source for the microbes. Nitrate and phosphate concentrations decreased over the course of the evaluation, while nitrite levels increased. It is probable that some nitrate is being used by the bacteria as an energy source in place of supplimental oxygen, although a mass balance was not possible due to funding limitations. Additional energy sources can, therefore, not be ruled out. Whatever the energy source is, results sugrgOst that no tilling for oxygenation purposes would be necessary to promote aerobic metabolism in the field, which could lower bioremediation costs and decrease the likelihood of VOC emissions. The process was found to be most effective in the diesel reactors, with later TPH test results showing signs of"alternative organics" which may be metabolic byproducts of diesel bioconversion. The organics yielded were implied by the increasing difference between TPH tests that either had or hadn't been subjected to EPA procedures to separate non petroleum organics from the samples. This separation was performed, using EPA procedures, to remove interfering compounds (false positives). Selective microbial activity was also seen in the TOE and DDT reactors, although the microbial populations were not as high as in the diesel reactors, partially due to lower contaminanVsubstrate concentrations. In addition it was shown that lunger time frames were necessary to establish microbial growth in the TOE reautots. In conclusion, while the process did show degradation in all reactors, the process effectiveness for contaminant removal could not be well established by this evaluation. Several factors interfered with an accurate calculation of the rate of removal, including: (1) soil heterogeneity, (2) active bacterial populations in the control bioreactors similar to JI=T-1 TM, and (3) possible evaporation of volatile compounds during soil sampling. which could not be monitored with results from the control reactors due to the presence of degrading bacteria in the controls. 1-4