INTERFACIAL TENSION OF MULTICOMPONENT DNAPLS AS A FUNCTION OF ORGANIC COMPOSITION

Dense nonaqueous phase liquids (DNAPLs), such as chlorinated hydrocarbons, are known to pose a significant threat to groundwater quality. The interfacial tension between water and DNAPLs is a very important factor for determination of capillary-pressure relationships as well as for interphase mass transfer theory. Most DNAPL assessments have treated the organic phase as a single, pure compound. However, most DNAPLs at actual sites contain more than one organic-liquid component, and the composition of the mixture (e.g., the NAPL-phase mole fraction) changes as the DNAPL mixture dissolves or volatilizes. The purpose of this research is to investigate the impact of varying NAPL-phase mole fraction on the interfacial tension of a chlorinated DNAPL mixture. Twenty-nine DNAPL mixtures were prepared for use in the experiments. The mixtures included various combinations of tetrachloroethylene (PCE), trichloroethylene (TCE), and 1,2-dichloroethylene (DCE), and water. Binary, ternary, and quaternary mixtures of DNAPL and water (using two- and three-component DNAL mixtures) are used in the experiments. The interfacial tension measurements were performed using a duNouy interfacial tensiomenter. The measured values of NAPL mixtures were compared with values predicted by theory (e.g., Fu et al., 1986). To our knowledge, this is the first such comparison for thee-component DNAPL mixtures in water. A computer code for universal inverse modeling (Poeter and Hill, 1998) has been used to calibrate theoretical parameters that are difficult to measure. Simple linear mixing rule has been applied to extend the theory from binary NAPL-water mixtures to the more complex mixtures used here. The theoretical model can predict the experimental results very well for the quaternary mixture (three-component DNAPL) and also for the ternary mixtures of TCE-DCE-water and PCE-DCE-water (measured values are within 2% of predicted values). The results are satisfactory for the PCE-TCE-water mixtures (predicted within 10% of measured). Implications of these results for development of DNAPL transport and dissolution models are also presented.