Transport phenomena in contaminated water from waste disposal sites deposited into deep mines are analysed in the paper. Critical transport path for pollutant migration by diusion of contaminants and buoyancy-driven convection of contaminated water is assumed to be in a vertical cylindrical enclosure. In the ®rst approximation, both transport phenomena are modeled and then numerically simulated separately. The models presented describe ion diusion and axisymmetric turbulent convection in a vertical cylinder with the radius R 3 . 5 m heated from the sidewalls. One-dimensional diusion equation is used for simulating the ion diusion in an enclosure of height H 1000 m. Three low-Reynolds number twoequation turbulence models contained in the FIDAP 7 . 5 software package were tested in our computational simulations of the natural convection. Two typical case studies of buoyancy-driven convection represent the aspect ratios H/R 14 . 3 and H/R 286. The former corresponds to the initial state just after deposition of the surplus water, the latter to the whole height of the cylindrical enclosure ®lled by the underground water. The numerical results obtained show that ion diusion is not dangerous as far as the contamination of subsurface water is concerned. On the other hand, it is concluded that the buoyancy-driven convection in the enclosures with the above aspect ratios can lead to the transport of contaminants into subsurface water and hence the protection of receiving waters from contamination must be designed.