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r In addition to the commercial features of the project, establishing the relationship between ORC and MTBE bioremediation, the isotope study will also be fundament to the basic science of MTBE degradation pathways as very little is known about the subject at this time. Another possible explanation for the higher degradation rates is that MTBE- degrading TBE-degrading microorganisms, normally slow to metabolize the substrate, do so at greater efficiency in higher oxygen concentrations. This theory will also be tested in the bioreactor experiments. There are examples in the literature, specifically with PCP degrading fungi, that establish a relationship between high oxygen l concentrations and high rates of degradation. This is important because ORC, as a pure oxygen source, is capable of generating dissolved oxygen levels in excess of 1 those achieved by air saturation. Encouraging results were obtained from a recent data set showing MTBE 1 I degradation outside an area that was source treated with ORC slurry injections. In Wisconsin, after about four months, the degradation rate in a well five feet ' downgradient of the treated area was .0434 (half-life of 25 days). This is presented in Figure 4. Note that these are not measurements from a well with ORC socks; the I well is downgradient from an ORC source injection zone and was exposed to oxygenated groundwater derived from the injection array. Earlier we stated that the biological degradation mechanisms were putative. Several other abiotic explanations must be considered and systematically eliminated; the following dialogue is intended to anticipate the appropriate questions. . _ 1 Q. Is MTBE being absorbed by ORC? Does ORC chemically destroy MTBE? J A. No. Experiments in the laboratory have shown that there is no chemical or a physical reaction between ORC and MTBE. This eliminates the possibility that any type of absorption by ORC or direct chemical oxidation is occurring. i ORC particles are insoluble and, when applied in filter socks, will not migrate from the application well. Groundwater samples were collected by standard purge methods (three to five casing volumes). Any chemical reactions l occurring on the surface of ORC particles in the source well would therefore be diluted out, particularly on the sites in question which have low ground water velocity. Furthermore, the new data show positive results at a distance from the ORC source wells. The fact that oxygen is slowly diffusing from ORC, which in ; turn is stimulating bioremediation of MTBE and competing species such as BTEX, remains the most the likely mechanism of action. 4!8197 6