DNAPL migration through interbedded clay-sand sequences

摘要

This paper examines the migration of DNAPL and the associated aqueous phase plume through clay-sand sequences. Numerical simulations are carried out examining contaminant distribution and migration rates in single fractures, simple layered clay-sand sequences, and spatially-correlated random fields where all low permeability lenses are assigned fractures. The results of this work illustrate that matrix diffusion does not significantly affect the rate of DNAPL migration in fractured clay, and that fracture aperture is the most influential parameter governing the rate of migration through fractures. In all simulations, the arrival of the aqueous phase plume at depth was approximately coincident with the arrival of DNAPL. Time periods for redistribution to residual were in excess of 15 years in the spatially correlated random field. Factors influencing the vertical and horizontal degree of spreading include the variance of the permeability field, the mean permeability, and the percentage of fractures assigned. In general, the role of fractures was more pronounced in the simple layered systems as compared to the spatially correlated random fields.