Monitoring of saline‐tracer transport via time‐lapse surface electrical resistivity tomography in a heterogeneous alluvium aquifer at the western part of Bengal Basin

Abstract Electrical resistivity tomography (ERT) has been a valuable tool for subsurface characterization for many decades, particularly in monitoring groundwater flow and solute transport. In this study, the geoelectrical surface imaging system was applied at and around a rural pump house in Kamgachi (Nadia district, West Bengal), a well‐known arsenic‐contaminated region. The sensitivity of subsurface resistivities to the contaminants and their byproducts allows ERT to serve as an effective proxy for visualizing and tracking the movement of solute contaminants through groundwater. The 4‐D (three spatial dimensions with an additional time dimension) ERT technique provided high temporal and spatial resolution in monitoring concentration changes of underground tracer concentration. Time‐lapse profiles were systematically distributed along two 200 m transverse and a 400 m longitudinal survey line in relation to the primary direction of local groundwater flow and the tracer injection well. A computerized mathematical inversion algorithm was employed to process and visualize the ERT data, which revealed zones with up to a 50% decrease in resistivity, indicating increasing saline water concentrations. The ERT results were validated against background tracer concentration data and direct soil samples. Varying flow velocities of the tracer propagation have been observed, suggesting that the area comprises a heterogeneous two‐aquifer system with layered mixtures of sand, silt and clay. The tracer movement predominantly followed the cone of depression towards the water pumping well, with local‐scale heterogeneity also playing a role. This research highlights the significance of integrating advanced imaging techniques like ERT with hydrogeological studies to gain an understanding of contaminant transport from a point source of a heterogeneous alluvial region from the western part of the Bengal Basin.