EFFECTS OF FUEL OXYGENATES ON BTEX IN UNDISTURBED COLUMNS OF FINE-GRAINED MATERIALS

The objective of this research is to gain a better understanding of the effects of ethanol and methyl tert-butyl ether (MTBE), common gasoline oxygenates, on the fate and transport of BTEX compounds in fine-grained soils. The BTEX fraction of gasoline (benzene, toluene, ethylbenzene, and xylene) poses the greatest health risk to humans and is the most mobile in the subsurface. MTBE, while not toxic to humans except in high concentrations, imparts a bad taste to water. Studies have shown that MTBE does not affect the biodegradation and transportation of BTEX since it is much more soluble in water and only biodegrades after BTEX compounds have been consumed or eliminated. Ethanol, widely used in the Midwest, is rapidly biodegraded in the environment and poses a minimal risk to humans. The effects of ethanol on the biodegradation and transportation of BTEX in the subsurface are complex and not well understood. Previous studies have used computer modeling or microcosm studies to predict the effects of ethanol with varying results. The hypothesis of this research is that ethanol will increase the amount of time required to biodegrade BTEX as compared to MTBE blended and non-oxygenated fuels. This research uses large diameter, undisturbed soil columns to better simulate the actual subsurface conditions in which an oxygenated gasoline spill would occur. Four, 12-inch diameter soil columns have been constructed to which four different solutions have been added: ethanol and BTEX, MTBE and BTEX, unblended BTEX, and uncontaminated groundwater for a control. The soil used in the columns was extracted from a site near Northern Illinois University at a depth of approximately 2 meters. This soil interval is representative of the soil encountered by a gasoline spill from an underground storage tank. The influent and effluent are analyzed for ethanol, MTBE, and BTEX concentrations as well as pH, DO, Eh, conductivity, and electron acceptors throughout the duration of the experiment. Preliminary results indicate that both ethanol and MTBE are inhibiting the natural attenuation of BTEX to different extents. This information will aid in modeling the fate and transport of oxygenated fuels, especially in the Midwestern United States.