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Applications of the RATEQ code to field data have yielded several key insights. The simulation results for the Bemidji crude-oil site indicate that the iron chemistry is key to understanding the observed trends in the aqueous geochemistry. In a collaboration with the Colordado District RATEQ was used to simulate the effect of corrosion reactions on the reactivity of the iron particles, pH values, and carbonate precipitation in a reactive barrier of metallic iron particles used to treat a plume of chlorinated hydrocarbons.

Detailed vertical profiles of the microbial population, pore water chemistry, solid phase iron, grain-size distribution, and oil content in the anaerobic portion of the Bemidji crude-oil plume show that the dominant microbial population has evolved from iron reducing to methanogenic conditions in areas of high contaminant flux found both in high permeability layers and in the vicinity of the non-aqueous oil. These results have serious implications for the sustainability of intrinsic bioremediation of petroleum hydrocarbons. Methanogenic conditions are the least efficient at degrading petroleum hydrocarbons and thus lead to the slowest degradation rates. Moreover, it is questionable whether benzene reliably degrades under methanogenic conditions. Our results show that conditions have changed from iron-reducing to methanogenic in the most permeable zones of the aquifer. As the most permeable zones become methanogenic, the combination of high migration velocities and slower degradation rates results in plume growth. This long-term plume growth affects risk analyses at sites where non-aqueous petroleum hydrocarbons provide a sustained flux of contaminants into the groundwater.

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Last modification: August 21, 2003



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