Distribution of Fuel‐Grade Ethanol near a Dynamic Water Table

Injections of fuel-grade ethanol (95% v/v ethanol, 5% v/v hydrocarbon mixture as a denaturant) near the water table were conducted in two-dimensional physical models tightly packed with fine sands under varying water-table conditions. As the fuel migrated in the porous media following injection, the denaturant phase separated leaving a residual Light Non-Aqueous Phase Liquid (LNAPL) phase that occupied a region with a volume similar to that of an equal-sized spill of 100% LNAPL without ethanol. When the water table was raised, as may be expected following a catastrophic release that reaches groundwater, most of the ethanol-fuel mixture was mobilized and the vertical distribution of the generated LNAPL was increased. The lower boundary of the residual LNAPL was established during the initial spreading of the fuel and did not change when the water table was raised or lowered. When the water table was raised in increments, the remaining concentrated ethanol/hydrocarbon mixture was mobilized and multiple relatively high LNAPL-saturated lenses were observed in the capillary zone but within the initially LNAPL-impacted zone. The distributions of ethanol and hydrocarbon components in this zone have direct implications for risk evaluation, monitoring strategies, and site management following releases of highly concentrated ethanol fuels.