1 Hydrogeology and Engineering Geology Group, Department of Geology-Geography, Katholieke Universiteit Leuven, Redingenstraat 16, B-3000 Leuven, Belgium

2 Hydrogeology and Engineering Geology Group, Department of Geology-Geography, Katholieke Universiteit Leuven, Redingenstraat 16, B-3000 Leuven, Belgium
also at Hydrogeology and Environmental Geology, Department of Georesources, Geotechnologies and Building Materials (GEOMAC), Université de Liège, Bât. B52/3,
B-4000 Liège, Belgium

Abstract Most studies that incorporate subsurface heterogeneity in groundwater flow and transport models only analyse and simulate the spatial variability of hydraulic conductivity. Heterogeneity of other flow and transport parameters is usually neglected. This approach is often justified but there are, however, cases in which disregarding the heterogeneity of the other flow and transport parameters can be questionable. In low permeability media, for instance, diffusion is often the dominant transport mechanism. It therefore seems logical to incorporate the spatial variability of the diffusion parameters in the transport model. This study therefore analyses and simulates the spatial variability of the effective diffusion coefficient and the diffusion accessible porosity with geostatistical techniques, and incorporates their heterogeneity in the transport model of a low permeability formation. The calculated output radionuclide fluxes of this model are compared with the fluxes calculated with a homogeneous model and a model with a heterogeneous hydraulic conductivity distribution. This analysis shows that the heterogeneity of the diffusion parameters has a much larger effect on the calculated output radionuclide fluxes than the heterogeneity of hydraulic conductivity.

Keywords diffusion; geostatistics; heterogeneous media; radionuclide transport; waste disposal