INFLUENCE OF ALTERNATIVE DISSOLUTION MODELS AND SUBSURFACE HETEROGENEITY ON DNAPL DISAPPEARANCE TIMES

The numerical model CompFlowC + + is used to examine the relative impo rtance of different formulations of a forward dissolution rate model, within the range of parameters measured from laboratory and field stud ies, 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 perm eability curves and the variance of the heterogeneous permeability fie ld are more important factors affecting the dissolution of a DNAPL sou rce zone than the formulation and parameter values of the forward diss olution rate. Results indicate that the mean dissolution time is parti cularly sensitive to the exponent associated with the nonaqueous phase saturation term, in the kinetic formulation of the forward dissolutio n rate expression, while the uncertainty is sensitive to the Reynolds number associated with aqueous phase flow. Uncertainty in the DNAPL di stribution due to imperfect knowledge of parameters controlling multip hase flow or the geostatistical nature of the aquifer exert less influ ence on the dissolution behaviour of the DNAPL source zone than the fo rmulation of, or parameters associated with, the forward dissolution r ate. (C) 1998 Elsevier Science B.V.