Column tests to assess water flow and oxygen transport in a monolayer cover placed on acid generating tailings

摘要

This study focuses on the reclamation work being performed on an old acid generating tailings site, located in Quebec, Canada. The tailings are partially oxidised due to extended exposure, so the pore water is already acidic. A monolayer cover, made ofnon acid-generating tailings, is being considered to control acid mine drainage. The goal of the investigation is to assess the behaviour of the tailings-cover system under various conditions, and also, if needed, evaluate alternative reclamation options. To do so, tailings samples were collected in situ and characterised in the laboratory. Large columns have been set up to evaluate the hydrogeological and geochemical response of the tailings and cover following wetting cycles. The instrumented columns were designed to reproduce some of the existing site conditions and provide representative results for long term analyses. Monthly wetting and drying cycles were repeated to simulate climatic conditions. The water content, suction, and oxygen concentration were monitored over time. Experimental data are used to calibrate and to help validate numerical models constructed with Vadose/W (GeoSlope Inc.). Additional simulations are conducted to evaluate the effect of various influence factors, such as depth of the water table and material properties. Alternative cover configurations are also tested. The results presented in this paper focus on unsaturated water flow in the tailings-covers system, and on the diffusive oxygen flux.