Long-term performance of a coarse-grained monolayer Cover on a pre-oxidized mine site

Reclamation of old and sometimes abandoned mine sites can pose significant environmental challenges, due to the pre-oxidized (weathered) nature of tailings and the long-term occurrence of acid mine drainage. The abandoned mine site Aldermac, a legacy of metal mining during the 1930s in the AbitibiTémiscamingue region, Quebec, Canada, was one of the most contaminated mine sites in Quebec prior to its reclamation. The multimillion-dollar reclamation project built in 2011 has subsequently improved site conditions and reduced the environmental impacts. The southern sector was reclaimed using a landfill cell with a high-density polyethylene (HDPE) geomembrane. The selected reclamation method of the northern part of the site consisted of a monolayer cover combined with the elevated water table technique. The elevated water table, positioned above the tailings, was designed to maintain the reactive tailings saturated, thus reducing direct oxidation of sulfides. A monolayer cover composed of coarse-grained (sand and gravel, also known as an evaporation barrier cover) was placed on the reactive tailings to minimize the evaporation while promoting infiltration. In this study, four monitoring stations were installed near observation wells to assess the performance of the cover. Each station was equipped with suction and volumetric water content probes, while pressure sensors were installed in observation wells to continuously monitor water table variations. Field observations indicated that the water table was maintained above the tailings during the monitoring period. This case study demonstrates the capacity of a monolayer cover of coarse-grained materials to effectively reduce evaporation fluxes by enhancing the site water balance. Presented results provide valuable insights for the development of new strategies to enhance climate resilience in reclamation methods using coarse cover.