Controlling Acid Mine Drainage Using an Organic Cover: The Case of the East Sullivan Mine, Abitibi Quebec

Abstract

The East Sullivan site holds 15 million tonnes of tailings which generate significant acid mine drainage. The tailings pond covers a surface area of 150 hectares, and spillage extends over an additional 70 ha. The intersti- tial water at the centre of the pond is characterized as follows : ph= 2.3; Cu= 261 ppm; Zn= 23 ppm; S04= 13 500 ppm; and Fe= 3200 ppm. In order to stop acid drainage from being generated, plans have been made to cover the entire tailings pond with an organic blanket comprised of two metres of softwood and hardwood bark. This type of covering has proven effective in preventing oxygen from reaching the tailings. In fact, oxygen concentrations drop from 16.1 % near the surface to less than 1.5 % some 70 cm below it, while the CO2 concentrations at the same depth rise from 8.2 % to 50.8 %. A grass cover is planted on top of the bark to reduce water seepage. Sludge from a municipal waters treatment plant is incorporated into the first 30 centimetres of the organic material as a conditioner and then seeded. A containment dike will be built around the entire site (6 km) to divert fresh water and carry drainage from the pond to a water treatment system. Studies have shown that some organic contamination results from bark decomposition. Phenol and tannin concentrations of 5.7 ppm and 95 ppm respectively have been mea- sured to date. Tests are under way to determine the best passive treatment system for controlling both organic and mineral contamination caused by the tailings. A multimedia filter was installed a year ago and work will begin this year on experimental wetlands. The ultimate objective of the East-Sullivan mine site reclamation plan is to abandon the site as quickly as possible in an environnemtally benign manner. So far, 30 % of the mine site is under organic cover and the remaining 70 % should be covered within five years at most. The containment dike will be completed within the next three years, and the water treatment system should be operational the following year.