The Transport and Fate of Ethanol and BTEX in Groundwater Contaminated by Gasohol

Abstract

Ethanol is used a component in all gasoline in Brazil, and its use could increase significantly in the U.S. to meet the requirements of the Clean Air Act Amendments. Recent problems with ground water contamination by methyl tert-butyl ether (MTBE) have made policymakers more cognizant of the need to consider the overall impact of gasoline oxygenates in the environment. Therefore, a thorough understanding of the impact of incorporating ethanol as a gasoline component on the fate and transport of gasoline releases is required. This article provides a comprehensive review of the transport of ethanol and monoaromatic hydrocarbons (BTEX) in the subsurface following a gasohol spill. Two mechanisms related to the presence of ethanol are generally considered to impact BTEX transport. Ethanol can increase the aqueous concentration of BTEX compounds due to a cosolvent effect, and it can inhibit BTEX biodegradation by preferentially consuming electron acceptors and nutrients. Our review illustrates that cosolvent effects should be minor at the ethanol concentrations expected from gasohol spills. Nevertheless, the inhibition of BTEX biodegradation and the possible decrease in sorption-related retardation suggests that ethanol is likely to increase BTEX plume lengths. The net effect of ethanol on natural attenuation of BTEX is likely to be system specific, depending largely on the release scenario and the assimilative capacity of the aquifer.