Ethanol-Enhanced Dissolution of a Residually Trapped Synthetic Gasoline Source

Batch partitioning and column experiments were conducted to assess the effect of ethanol on the enhancement of BTX (benzene, toluene, and xylenes) concentrations in groundwater near existing sources of NAPL (nonaqueous phase liquid, i.e., gasoline) contamination. The experiments were conducted to approximate a possible worst case scenario in which highly concentrated ethanol (e. g., fuel-grade ethanol) becomes in direct contact with pre-existing gasoline in water-saturated conditions such as near the ground water table. The enhancements of BTX, 1,2,4-trimethylbenzene (TMB), and n-octane concentrations in the aqueous phase by ethanol were investigated. Significant enhancements in the BTX and TMB concentrations occurred with injections of highly concentrated ethanol. For example, when a pulse of 97% ethanol, equivalent to one source pore volume, passed through the source region containing trapped NAPL, the enhancements in the effluent peak concentrations over the solvent-free water concentrations ranged from factors of 1.7 (for benzene) to 3.0 (for m-xylene). When the ethanol pulse size was doubled, the enhancements in peak effluent concentrations increased by factors of 10 (for benzene) to 125 (for m-xylene). Experimental results were consistent with equilibrium dissolution model simulations.