Numerical simulations of water flow and contaminants transport near mining wastes disposed in fractured rock mass
Produced mining wastes can be placed in open pits or underground excavations. The adjacent rock mass is often fractured and the discontinuities may control the flow of water and transport of contaminants from the wastes. Numerical simulations have been carried out to assess the influence of joints on underground flow and mass transport in and around a surface mine opening. The influence of a regional hydraulic gradient was also analyzed. To conduct these investigations, contaminant transport and unsaturated flow modelling was performed using the HydroGeosphere numerical model. Analyses including the vadose zone were conducted by simulating various 2D cases using experimentally obtained material properties and controlled boundary conditions. The effects of material hydrogeological properties (i.e., the water retention curve and hydraulic conductivity function), fracture network characteristics and joint conductivity were also investigated. The simulations show that water flow and contaminant transport are significantly affected by the type of filling material (tailings or waste rock material), the nature of initial and boundary conditions and the degree of rock mass fracture (vertical fractures or an orthogonal fracture network). Fractures significantly influence the water flow network and contaminant concentrations. In fact, the presence of joints induces a more rapid migration of contaminants from mining wastes, and the contaminant plume can reach greater distances that can increase the risk of surface and ground water contamination. The effect of the regional hydraulic gradient can be additional to that of the fracture network. Thus, the level of fracture of the rock mass must be characterized to better predict contaminant migration from open pits.