This study presents a method for evaluating the effectiveness of a mine tailing cover. The cover is designed with a 0.5 m layer of clay covered by a 1.5 m layer of glacial till; full water saturation of the clay layer is assumed to be necessary for the maximal reduction of oxygen transport through the cover. The evaluation of cover effectiveness is based on: 1) the reduction of leachate production, and 2) the ability of the clay layer to remain water saturated and avoid cracking. Using 1990 precipitation data, the numerical model SUTRA simulates unsaturated flow in the cover, with results interpreted in terms of pressure head variations and vertical discharge from the cover. The modeling results indicate that this cover design would adequately reduce leachate production from a tailing deposit. In addition, the water saturation of the clay layer remains above its plastic limit during a simulated year of normal recharge conditions; it is therefore not likely that the clay layer would crack. A sensitivity analysis with different hydraulic parameter values is performed, and shows that leachate production is most sensitive to clay hydraulic conductivity, while the water saturation of the clay layer is sensitive to both clay hydraulic conductivity and till porosity.

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