A Comparison of Benzene and Toluene Plume Lengths for Sites Contaminated with Regular vs. Ethanol-Amended Gasoline |
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| Authors: | GML Ruiz-Aguilar K O'Reilly PJJ Alvarez |
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| Institution: | Graciela Ruiz-Aguilar;is a post-doctoral fellow in the Department of Civil and Environmental Engineering at the University of Iowa, where she is conducting research on the anaerobic bioremediation of BTEX-ethanol mixtures. She has a Ph.D. in biotechnology and bioengineering from the Institute Politecnico Nacional-CINVESTAV, in Mexico City, Mexico. Her studies focused on fungal technologies for PCB degradation Kirk T. O'Reilly;is a senior environmental specialist with Chevron Texaco's Energy Research and Technology Co. He has a B.S. in biological science from the University of California, Irvine, an M.S. in biology from Portland State University, and a Ph.D. in biochemistry from the University of Idaho. He has 16 years experience investigating the microbial and chemical aspects of the natural attenuation and active remediation of impacted ground water. Since 1996 his research has focused on oxygenate-related issues. Pedro J. Alvarez;is a professor in the Department of Civil and Environmental Engineering at the University of Iowa, where he also serves as associate director for the Center for Biocatalysis and Bioprocessing. He has a B. Eng. in civil engineering from McGill University, and an M.S. and a Ph.D. in environmental engineering from the University of Michigan. His research interests are related to the implications and applications of biological treatment processes to remove hazardous substances from contaminated ground water, waste water and soil. He is a P.E. and a Diplomate of the American Academy of Environmental Engineers. |
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| Abstract: | This article describes various statistical analyses of plume-length data to evaluate the hypothesis that the presence of ethanol in gasoline may hinder the natural attenuation of hydrocarbon releases. Plume dimensions were determined for gasoline-contaminated sites to evaluate the effect of ethanol on benzene and toluene plume lengths. Data from 217 sites in Iowa (without ethanol; set 1) were compared to data from 29 sites in Kansas that were contaminated by ethanol-amended gasoline (10% ethanol by volume; set 2). The data were log-normally distributed, with mean benzene plume lengths (± standard deviation) of 193 ± 135 feet for set 1 and 263 ± 103 feet for set 2 (36% longer). The median lengths were 156 feet and 263 feet (69% longer), respectively. Mean toluene plume lengths were 185± 131 feet for set 1 and 211 ±99 feet for set 2 (14% longer), and the median lengths were 158 feet and 219 feet (39% longer), respectively. Thus, ethanol-containing BTEX plumes were significantly longer for benzene (p < 0.05), but not for toluene. A Wilcoxon signed rank test showed that toluene plumes were generally shorter than benzene plumes, which suggests that toluene was attenuated to a greater extent than benzene. This trend was more pronounced for set 2 (with ethanol), which may reflect that benzene attenuation is more sensitive to the depletion of electron acceptors caused by ethanol degradation. These results support the hypothesis that the presence of ethanol in gasoline can lead to longer benzene plumes. The importance of this effect, however, is probably site-specific, largely depending on the release scenario and the available electron acceptor pool. |
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