Influence of alternative dissolution models and subsurface heterogeneity on DNAPL disappearance times

The numerical model CompFlowC++ is used to examine the relative importance of different formulations of a forward dissolution rate model, within the range of parameters measured from laboratory and field studies, for predicting the mean and uncertainty in dense nonaqueous phase liquids (DNAPL) dissolution times in heterogeneous sandy aquifers. We also investigate whether uncertainty in the DNAPL distribution due to imprecise knowledge of the form of the nonaqueous phase relative permeability curves and the variance of the heterogeneous permeability field are more important factors affecting the dissolution of a DNAPL source zone than the formulation and parameter values of the forward dissolution rate. Results indicate that the mean dissolution time is particularly sensitive to the exponent associated with the nonaqueous phase saturation term, in the kinetic formulation of the forward dissolution rate expression, while the uncertainty is sensitive to the Reynolds number associated with aqueous phase flow. Uncertainty in the DNAPL distribution due to imperfect knowledge of parameters controlling multiphase flow or the geostatistical nature of the aquifer exert less influence on the dissolution behaviour of the DNAPL source zone than the formulation of, or parameters associated with, the forward dissolution rate.