Soilatmosphere modelling of an engineered soil cover for acid generating mine waste in a humid, alpine climate

Abstract

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.