Characterization and quantification of aquifer heterogeneity using outcrop analogs at the Canadian Forces Base Borden, Ontario, Canada

Abstract

Accurate characterization of internal structures and geometries of aquifers is critical for evaluation of plume migration and dispersion of contaminants. For this reason, high-resolution transport study field sites, such as the Waterloo Groundwater Research Site at the Canadian Forces Base Borden, Ontario, Canada, have been established. However, geological characterization at this site is based primarily on cores and shallow geophysical data. Outcrop analog studies offer detailed horizontal data that can help to build quantified models of aquifer heterogeneity. We used a combination of ground-based light detection and ranging (LiDAR) and high-resolution photographs at a sand quarry cut into Borden aquifer sediment to evaluate and quantify the distribution of lithofacies and hydrofacies that control flow properties in the Borden aquifer. We exposed sixteen ∼20 m × 1.5 m outcrops, LiDAR surveyed, photographed, and field mapped lithofacies at each exposure, and segmented the lithofacies from photographs to produce maps of facies distributions. We grouped different lithofacies into hydrofacies based on overall facies geometry and estimated hydraulic properties. We used LiDAR scans and the segmented facies maps to produce a digital outcrop model (DOM) of the site. The resultant DOM combines lithofacies and hydrofacies derived from field observations with high-resolution (5 mm) LiDAR data to reconstruct hydrofacies distributions in a three-dimensional (3-D) geomodel. The DOM offers a relatively complete horizontal correlation structure that was used in transition probability geostatistical modeling to create realizations of hydrofacies distributions in the aquifer at the study site.