Contaminant Transport in the Highly Heterogeneous Sedimentary Formation at Canadian Forces Base Borden, Ontario, Canada

Based on results of detailed geostatistical characterization of a sand quarry located two km from the Stanford-Waterloo site at Canadian Forces Base Borden, Ontario, Canada, and evaluation of material properties at this site, we show that the succession is highly heterogeneous with variance of log-conductivity as large as 17.9. The main goal of the present research is to identify key parameters that would impact solute plume transport, and especially tailing, through this formation. The identification, accomplished through modeling, is based on sensitivity analyses. The heterogeneity model adopted here is a special case of a general multi-indicator model, which has been extensively used in the past in stochastic modeling of plume transport and tailing in heterogeneous formations. The present model contains four types of randomly placed 3D oblate ellipsoidal inclusions (e.g. geological lenses) that represent different materials found at the site: gravel, lenticular sands, tabular sands, and clay. Inclusion sizes and volume fractions are determined through indicator geostatistical analysis. A constant hydraulic conductivity and linear sorption distribution coefficient are assigned to each type of inclusion for each simulation. Plume transport and tailing are quantified using break-through curves for a set of equally spaced control planes. Sensitivity analyses of the effect of inclusion sizes, volume fractions and properties on break-through curves are conducted to quantify contaminant tailing and to identify key parameters influencing the tailing. The preliminary results indicate that slow advection and diffusion through clay lenses are the main causes of the plume spreading and can produce plume tailing for several decades or longer.