Physical-chemical resistances to dissolution from residual multicomponent NAPL mixtures

This research focuses on the dissolution characteristics of NAPL mixtures (chlorinated hydrocarbons and octanol) and aims to elucidate the contribution of mixture non-ideality and intra-NAPL diffusion. The study combines a series of experiments ranging from batch solubility tests to three-dimensional dissolution studies with a numerical modeling investigation. A ternary mixture intra-NAPL diffusion submodel developed here is used to predict aqueous concentrations near the NAPL source and a three-dimensional groundwater transport model (MT3DMS) employs the submodel results to produce field-relevant dissolution scenarios.; Dissolution from the ternary mixture residuals was found to follow similar patterns regardless of the mixture. First, when one or more components were depleted from the source, there was a rise in the aqueous concentration from the remaining component(s). Second, at distances far from the source, there was little variation in aqueous concentrations in response to changes in source geometry.; The modeling work confirmed that slower groundwater flow, non-equilibrium boundary conditions, larger sized sources, and a shrinking source size would lengthen total dissolution time. Furthermore, dissolution times computed using the intra-NAPL diffusion model are highly sensitive to the activity coefficient, although UNIFAC (oft used activity coefficient estimator) was found to be a poor predictor of these values in the multicomponent batch solubility studies.; The implications of this finding are especially relevant at the field scale where plumes of contamination may persist for decades. Plumes that show little change in size and concentrations over extended periods of time may be the result of suppression of aqueous solubility due to non-idealities, and/or non-equilibrium conditions at the boundary. Intra-NAPL diffusion was not found to be the rate-limiting factor for the cases considered. Thus, plumes that continue to grow in size and strength are most likely the result of either continual mixing and/or equilibrium conditions at the source.