Preventing Acid Mine Drainage with an Elevated Water Table: Long-Term Column Experiments and Parameter Analysis

The elevated water table (EWT) technique for preventing acid mine drainage (AMD) was tested using instrumented laboratory columns containing reactive tailings from the Louvicourt and Sigma mines, Abitibi, Quebec. The tests were performed in short (0.4 m) and long (1.4-1.7 m) columns over 400-500 days and included periodic surface recharge and subsequent monitoring of the leached drainage water. In each column, the water table depth was adjusted relative to the air entry value (AEV or psi(a)) of the tailings. The influence of different water table elevations was evaluated by measuring the effluent pH, as well as the concentrations of major ions including sulphate, iron, zinc, copper and lead. Provided the water table depth below the tailings surface remained less than one half of the tailings' AEV, the observed data showed that an EWT can be very effective in reducing acid mine drainage. The principal factors controlling drainage quality were the saturated hydraulic conductivity (k (sat)) and the air entry value (psi(a)) of the tailings. A lower k (sat) and a higher psi(a) in the tailings tend to increase the performance of an elevated water table by limiting drainage-induced desaturation. Mineralogical composition had relatively little effect on the hydrogeochemical evolution provided the tailings remained highly saturated (S (r) a parts per thousand yenaEuro parts per thousand 90%). The results presented here indicate that an elevated water table can be an effective means for controlling the production of AMD when the design conditions are properly selected and applied.