Is Methane Produced from a Fuel-Ethanol Spill Predictable?

Abstract

With an increase in the use, production, and transportation of fuel-ethanol, the likelihood of a release increases. Under anaerobic conditions, ethanol biodegrades to acetate, which then biodegrades to methane. This methane has been shown to get to explosive levels. The purpose of this study was to examine the predictability of methane produced from fuel-ethanol spills. A conceptual mass budget model was constructed and compared to measured data collected from two E95 fuel-ethanol spill sites. The model consistently predicted higher concentrations of dissolved methane than what was measured and consistently predicted lower concentrations of soil gas methane than what was measured. This difference is likely due to the many assumptions of the model. Based on chi square analyses, there was no significant agreement between the models and the measured data. Calculated ethanol decay rates fell within the range of findings from other studies. In order to further inspect the measured data, correlation coefficients were calculated. Correlation analysis showed a significant, positive correlation between acetate and dissolved methane for both sites and significant, positive correlation between dissolved methane and soil gas methane for one site. Overall, the model contains useful concepts and is a starting point for understanding the complex degradation process. The results demonstrate how site physical characteristics play a role in contaminant fate and transport. The model is useful in that it gives us an idea of the sensitivity of the resulting concentrations to the inputted rate constants and coefficients. The correlation calculations are useful, in that there is a significant pattern in constituent increase. Finally, because the model only encompasses biological decay and spreading from groundwater flow, the results show the environmental process is not that simple.