INSTRUMENTATION AND MONITORING OF COVERS USED TO CONTROL ACID MINE DRAINAGE
CIM Montreal 2007
Bruno Bussière, Mamert Mbonimpa, Michel Aubertin, Ward Wilson,
Different management options and rehabilitation strategies are available for mine wastes that can produce acid mine drainage (AMD). One of them consists in building layered soil covers over the mine wastes to limit the availability of oxygen and/or water, two essential components of the chemical reactions leading to the generation of AMD. Recent projects have shown that a cover with capillary barrier effects (CCBE) can be used to control AMD production. In a humid climate, CCBEs are mainly used to create an oxygen barrier (especially on relatively flat areas). In this case, a high degree of saturation must be maintained in one (or more) of the cover layers to prevent oxygen migration. Under arid and semi-arid climates, where it is more difficult to maintain a high degree of saturation in soils near the surface, CCBEs are rather used as a Store, Divert and Release (SDR) cover, which mainly aims at controlling water infiltration into the waste disposal sites. The objective of a SDR cover is to promote runoff, evapotranspiration, storage, and (in the case of an inclined cover) lateral diversion to avoid deep water percolation into the wastes.
Prior to cover construction, a monitoring strategy must be established to evaluate the response and performance of the layered systems, with a particular emphasis on its ability to limit AMD production. At this early stage, it is important to choose the adequate parameters to be monitored and the corresponding instruments that will be installed in (and beneath) the cover. The main parameters to monitor typically include matric suction, volumetric water content, oxygen flux (and/or oxygen concentration), hydraulic conductivity, meteorological parameters, and water percolation and quality.
In this paper, the main concepts behind CCBE for both wet and dry climates are first recalled. The different techniques available to measure the key monitoring parameters are then described and compared. Examples are also shown to illustrate typical results obtained on various sites. Finally, recommendations (based on existing cases) on the location and the number of monitoring stations and on the measurement frequency for each monitored parameters are presented.
Mine site rehabilitation, Instrumentation, Performance evaluation, covers, Monitoring