Electrical resistivity imaging to monitor water infiltration and contamination risk assessment in tailings ponds

Abstract

This study investigates the internal structure and water content variations of the abandoned tailings ponds in the Hiendelaencina Ag-mining district, Spain, using Electrical Resistivity Imaging (ERI). The objectives were to delineate the geometry of the tailings deposits and to assess the spatial and temporal changes in water content within the ponds and the underlying geological units. The pollution risk assessment was evaluated as well. Six resistivity profiles were obtained during two separate field campaigns in September 2020 and May 2021, allowing for a comparison of resistivity data under different moisture conditions.

The results revealed three distinct resistivity zones corresponding to the tailings, Cenozoic sedimentary deposits, and the underlying metamorphic basement, respectively. Temporal variations in resistivity indicates significant changes in water content between the two field campaigns, with increased water infiltration following spring rainfall. While no direct soil moisture measurements were available for calibration, the ERI results provide robust qualitative insights into relative water content changes and infiltration pathways.

Notably, the fractured metamorphic basement showed higher water saturation, indicating vertical and lateral water flow from the tailings. These findings suggest that the tailings ponds are not impermeable, with water infiltrating into deeper layers, potentially transferring pollutants into the groundwater system. The study highlights the effectiveness of ERI as a non-invasive tool for investigating mining sites and provides important insights into the hydrological behavior of mine tailings, which is critical for environmental monitoring and risk assessment.