NONIDEAL DISSOLUTION BEHAVIOR OF CHLORINATED SOLVENTS FROM FUEL-SOLVENT MIXTURES IN GROUNDWATER

Chlorinated solvents in fuel-based mixtures are a frequent, persistent source of groundwater contamination, and generally toxic at very small concentrations in the organic-phase. The aqueous solubility behavior of hydrocarbon mixtures is often regarded as “ideal” based on approximations determined from Raoult’s Law. Deviations from ideality occur with increased structural and hydrophobic dissimilarity between the components and the bulk mixture, (i.e., equilibrium dissolution behavior does not obey Raoult's Law). Nonideal equilibrium dissolution of chlorinated hydrocarbon-fuel mixtures may be important for low mole fractions because differences between the components and the bulk mixture are the greatest. Small NAPL-phase mole fractions are typically found at many chemical spill sites and waste disposal facilities, thereby emphasizing the importance of understanding nonideality and solubility at realistic NAPL-phase mole fractions. Batch-equilibrium solubility studies are conducted for several multi-component mixtures containing fuels and chlorinated solvents, with NAPL mole fractions of the chlorinated solvent components in the overall mixture less than 0.1. Theoretical expressions are subsequently used to predict nonideal solubilization behavior in terms of the organic-phase activity coefficients. In order to assess the impact of complex NAPL mixtures in groundwater, knowledge of nonideal NAPL-phase dissolution behavior is essential for the development of accurate contaminant-transport simulations, acquiring an enhanced understanding of the movement of contaminant plumes originating from solvent-fuel mixtures, providing appropriate risk-assessment, and the application of effective remedial measures. Data is compared to UNIFAC (universal quasi-chemical functional group activity coefficient) simulations to assess the ability of this model to predict equilibrium dissolution behavior of fuel-solvent mixtures.