RESISTIVITY IMAGING AND IMAGE ANALYSIS FOR ESTIMATING WATER AND SOLUTE TRANSPORT ACROSS THE CAPILLARY FRINGE IN LABORATORY EXPERIMENTS / Resistivitet mätningar och bildanalys för att uppskatta vatten och partikeltransport genom den kapillära zonen i laboratorieexperiment
This study contains a series of laboratory experiments designed to describe the lateral movement and spatial variability of an infiltrated dye tracer across the capillary fringe of homogenous sand in an aquarium. A combination of image analysis and geoelectrical monitoring was used to track the flow paths of the dye with different hydraulic gradients and infiltration rates. Photographs were taken for image analysis to visualize the flow paths. An ABEM Terrameter LS was used to measure the resistivity data during the experiments with a combination of multiple-gradient array and cross-hole-dipole-dipole array. BERT (Boundless Electrical Resistivity Tomography) was applied to obtain three dimensional models of the resistivity distribution. The results were compared and evaluated in respect to the image analysis. The inverted models gave a clear impression of the dye tracer distribution and movement within the aquarium. All experiments revealed a strong horizontal movement across the capillary fringe. The flow characteristics of the capillary fringe turned out to be more similar to the characteristics of the saturated zone, than to the characteristics of the unsaturated zone. If the results of this laboratory study can be verified under field conditions, it clearly shows that taking measurements and samples only in the saturated zone at contaminated sites can significantly underestimate the actual extent of the contamination plume.