Modelling and field measurements of water percolation through an experimental soil cover on mine tailings

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Abstract
A composite soil cover constructed on acid-producing tailings was evaluated for its ability to retain a high degree of water saturation and low hydraulic conductivity. The cover consisted of a 60 cm thick, compacted, nearly saturated, varved clay placed between two sand layers, each 30 cm thick. A final 10 cm thick gravel layer was placed on the upper sand layer to minimize erosion. The Hydrologic Evaluation of Landfill Performance (HELP) model and a finite-element flow model (SEEP/W) were applied, and the results corroborated with field measurements of percolation and soil-water content. Modelling predictions indicate that 4% of precipitation will percolate through the cover and that the intermediate clay layer will retain a high degree of saturation after a 20 year simulation. Four years of field monitoring also indicate that 4% of precipitation percolates through the cover and that the clay retains its high saturation. These results suggest that a properly designed and constructed soil cover can be effective in reducing acid production in reactive mine tailings. Key words : acid-producing tailings, soil cover, water saturation; capillary barrier, hydrologic processes.