Monitoring moisture dynamics in multi-layer covers for mine tailings remediation using autonomous and remote time-lapse electrical resistivity tomography
Description
The dynamics of moisture content in engineered multi-layer covers constructed on mining wastes were monitored at pilot-scale using 2D autonomous, remote and non-invasive time-lapse electrical resistivity tomography. This innovative monitoring approach was combined with conventional point sensors to assess the hydrogeological behavior of 280 m-long experimental covers under real meteorological conditions at an active mining site. The covers with capillary barrier effects (CCBE) were designed to act as oxygen barriers whereas the covers with low saturated hydraulic conductivity layers (LSHCC) aimed at limiting the water infiltration rate through the covers. A methodology was proposed to process the daily hydrogeophysical datasets from four 23 m-long instrumented sections and estimate the 2D distributions of moisture content daily. Hydrogeophysical monitoring suggested that the CCBE was able to maintain high degrees of saturation (above 85%) in the moisture-retaining layer throughout the 1-year monitoring period and was not significantly affected by the slopes of inclined sections, which would make it an efficient oxygen barrier. Larger spatio-temporal changes in moisture content were identified from hydrogeophysical data in the LSHCC. Most of the low hydraulic conductivity layers remained below 85% of saturation and the estimated moisture content was at the lowest level during August 2022, which was attributed to the combined effect of low precipitation, rapid vegetation development and potential water percolation through the cover. Overall, the methodology proposed in this study allowed to monitor the hydrogeological behavior of the covers, which was helpful to investigate the performance of the covers. This study provided the first "proof-of-concept" at pilot-scale and under real conditions that the geoelectrical method can be used as a complementary monitoring technique to extend spatially the monitoring of moisture dynamics in mining wastes, which might be useful for geochemical and geotechnical monitoring programs in large-scale mining waste storage facilities.