Physical-Model Simulations of Spills of Ethanol- and Methanol-Blended Fuels and Pore Water Impacts

To assess source formation, phase separation, capillary zone depression, alcohol transport and potential pore-water impacts, unsaturated zone releases of ethanol- and methanol-blended fuels were compared in two-dimensional continuous flow experiments. Experiments were conducted with blends of varying alcohol content (15, 25, 50 and 85 vol. %). Visualization and image analysis of the releases showed decreases in residual NAPL saturation and increases in area impacted by NAPL with increasing alcohol content for blends of both alcohols. Comparing equivalent alcohol-content fuels, spill areas were less for the methanol blends than for the corresponding ethanol blends while residual saturations were greater for the methanol blends. Aqueous methanol and hydrocarbon concentrations were measured downstream of an M15 release and compared with a source dissolution and transport model. Source depletion of hydrocarbons was significantly faster than that predicted for equilibrium dissolution of the NAPL, suggesting flow bypassing of a portion of the NAPL source.