Dissolution of monoaromatic hydrocarbons into groundwater from gasoline-oxygenate mixtures

The effects of the "oxygenate" additives methanol and methyl tert-butyl ether (MTBE) on the aqueous solubility of benzene, toluene, ethylbenzene, and xylenes (BTEX) from gasoline were evaluated through equilibrium batch experiments. For a gasoline:water ratio of 1:10 (v/v), up to 15% MTBE or up to 85% methanol in gasoline produced no enhanced BTEX solubility. However, at higher gasoline:water ratios, aqueous methanol concentrations above 10% enhanced BTEX solubility. The initial methanol content of the gasoline and the equilibrating gasoline- to water-phase ratio controlled the aqueous methanol concentration. Partitioning theory and the experimental results were used to calculate aqueous benzene and methanol concentrations m successive batches of fresh groundwater equilibrating with the fuel and subsequent residuals. These successive batches simulated formation of a plume of contaminated groundwater. The front of the plume generated from high-methanol gasoline equilibrating with groundwater at a gasoline:water ratio of more than 1 had high methanol content and elevated BTEX concentrations. Thus, releases of high-methanol fuels could have a more serious, initial impact on groundwater than do releases of methanol-free gasoline.