Stochastic modelling of the hydrogeological environment in low permeability sediment

In Belgium, the Boom Clay is being considered as a potential host formation for the disposal of nuclear waste. Part of the safety assessment and feasibility studies of a potential nuclear waste disposal consists of hydrogeological modeling. In order to model the groundwater flow and possible radionuclide transport in the clay, the spatial distribution of the hydraulic conductivity of the clay has to be assessed. In this study, geostatistical methods are used to characterize the hydraulic conductivity field. More specific, direct sequential simulation of the hydraulic conductivity is carried out, using measurements of hydraulic conductivity and 4 types of soft data or secondary variables: resistivity logs, gamma ray logs, grain size measurements and descriptions of the lithology. The primary and secondary information is analyzed with geostatistical tools and combined to generate 100 fields of the hydraulic conductivity of the Boom Clay. Next, each field is input to a groundwater flow model to predict the advective travel time of constituents released from the disposed waste in the Boom Clay to the aquifers surrounding the Boom Clay. Statistical analysis of the ensemble of model predictions results in a predictive distribution for the advective travel time. This distribution reflects the uncertainty of the advective travel time that results from the uncertainty of the spatial distribution of the hydraulic conductivity of the Boom Clay