Solute Transport in Boom Clay

This report compiles and discusses information from various research projects concerning the nature of the transport processes occurring in the Boom Clay in NE-Belgium. These multiple lines of evidence were investigated in order to come to a consistent view on the mechanisms of solute transport in Boom Clay under past and present conditions. Relevant Boom Clay properties related to solute transport discussed in the report are porosity and hydraulic conductivity. The considered elements of the hydrogeological context that have influence on the mechanisms of solute transport are the hydraulic gradient and the velocity, from which the Péclet number was calculated, indicating the dominant transport mechanism in the Boom Clay. Another independent line of evidence describing the main transport mechanism in Boom Clay was given by the modelling interpretation of a large scale in situ experiment and of natural tracer profiles in the Boom Clay. Finally, the influence of possible preferential flow paths (fractures and layers containing septarian concretions) on solute transport in Boom Clay was described. It was found that - with the current knowledge - these multiple lines of evidence all indicate diffusion–dominated transport through Boom Clay under past and present conditions. However, some unresolved issues still remain.