Integrating Small-scall Electrical Resistivity with Multi-compartment Sampler Techniques to Monitor Solute Fluxes

Abstract

Understanding water and contaminant transport in the unsaturated zone is highly challenging due to spatial variability. Sufficient characterization of spatial and temporal distribution of contaminant transport requires measurements of solute fluxes at multiple locations with high temporal resolution. Solute monitoring is often limited to observations of resident concentrations, while flux concentrations govern the movement of solutes in soils. We developed a new instrument, which combines multi-compartment sampling with electrical resistivity techniques, to monitor solute fluxes. The multi-compartment electrical resistivity sampler (MCERS) is capable of measuring downward solute fluxes at a high spatio-temporal resolution under natural conditions. The instrument consists of 100 cells (each 31.5 by 31.5 mm). For each cell, the amount of drops passing through every 5 min is recorded, monitoring directly water fluxes. Electrodes are mounted at each corner of each cell, making it possible to perform small-scale ERT measurements above each cell while water percolates through, thereby monitoring solute fluxes. By using different electrode couples, the setup can also be used to image above the MCERS. The percolate is collected from each cell and can be repeatedly extracted for additional chemical analysis while leaving the instrument buried in situ, facilitating prolonged operation times.