Ionic liquids (ILs) have been studied recently as potential 'green'? solvents due to their negligible vapor pressure. Modeling and measuring their phase behavior with water and organic solvents is vital for evaluating their many potential uses. As a first step towards modeling the phase behavior of IL solutions, we will show how the electrolyte nonrandom two-liquid model can be applied to model activity coefficients of quaternary ammonium salts (potentially interesting ILs) in water. Results indicate that this model is able to capture the nonideal phase behavior of these salts in aqueous solutions up to relatively high concentrations. A particularly important quantity needed for assessment of environmental impact is the octanol/water partition coefficient, Kow. The measurement of this constant for imidazolium based ILs show they do not bioaccumulate. Finally, we will mention some future work to model the Kow using the NRTL model studied in the first part of the project.