Analyzing variation of the water table level with threedimensional numerical simulations to assess reclamation techniques for an acidic tailings impoundment

Tailings with sulphide mineralsÉxposed to oxygen and water can oxidize and produce acid mine drainage (AMD). This studyÉvaluated the impact of natural conditions and of a thin cover deposition on the water table level, with respect to selecting the reclamation technique to control AMD on theÉlevated portion of an abandoned tailings impoundment. The reactive tailings were partly covered with alkaline tailings transported as a pulp from a nearby mine. A three-dimensional numerical variably saturated groundwater flow model of the tailings impoundment and its surrounding area was built. The simulation results reproduced well the field observations before, during, and after the deposition of a thin layer of tailings. The calibrated model was then used to forecast theÉvolution of the water table position for the next 100 years under various site conditions, including a period of 5 years with dry summers. The results show that the water table levels are on average several metres below the interface between the reactive tailings and the cover, thus failing to meet the target criterion to control the production of AMD determined from previous column tests. The results are analyzed and discussed in terms of the site configuration and atmospheric recharge.