Numerical analysis of periodic transient contaminant-leaching episodes in the unsaturated zone

The concentration of contaminants in groundwater underneath landfills and mine tailing piles and treatment facilities increases when the water table rises sharply due recharge events or the rise of the level rising a negihboor rivers connected to the aquifer. Reactive contaminants may persist for long periods of time due to mineral precipitation and sorption reactions. Here, we present a numerical 2-D flow and solute transport model in a vertical plane to study the leaching of uranium from the unsaturated zone underneath a uranium tailings pile. Model results show that the uranium concentration increases linearly when the leachate flux increases and the upstream flux and the upstream flow of unpolluted groundwater decreases. The concentration of uranium increases in response to the rise of the water table. The peak of uranium concentration takes place about 40 days after the maximum water level in a point located 30 m downstream the uranium source.