A research program studying the performance of soil covers at the Equity Silver Mine was initiated in 1992. This site is situated in the humid, alpine climate of north central British Columbia. A one-dimensional, fully coupled heat and water transport, soil–atmosphere flux model was developed as part of this research program to simulate the movement of liquid water and water vapour within a soil cover in response to rainfall and evapotranspiration. Predicted and measured conditions in the cover showed good agreement for a five-month period from June to November 1993. The modelling exercise showed that vapour flow was the dominant flow mechanism near the surface of the cover within a few days after the start of drying. This points out the necessity of being able to couple heat and water transport in soil cover analyses and design. The numerical modelling demonstrated that input parameters are readily attainable through field and laboratory measurement. Model predictions of extreme and mean climate conditions indicated that percolation through the cover system would be limited to approximately 2% of the annual precipitation and that oxygen flux through the cover would be reduced by approximately 98% from uncovered conditions.Key words: acid rock drainage, soil covers, unsaturated soils, infiltration, evapotranspiration, matric suction.

The design of soil covers and the prediction of seepage for waste rock facilities are important components of permitting and closure at mines situated in arid climates. This design and prediction require an W1derstanding and application of W1saturated zone hydrology, which, in many respects is CO\lllter-intuitive compared to the saturated conditions that are predominate in grolllldwater hydrology. For example, water llllder saturated conditions prefers to flow through course textured materials, whereas, W1der \lllsaturated conditions, water may prefer to flow through finer textured materials. To ensure accurate and defensible soil cover design and seepage prediction for waste rock facilities, methods must be employed using conceptual models based on \lllsaturated zone hydrology.