An unsaturated soil seepage analysis for design of a soil cover system to reduce oxidation of a mine tailings deposit

Abstract

This paper presents a case history of an unsaturated soil seepage analysis for design of a soil cover system to promote saturation within a mine tailings deposit. A gold mine tailings facility in Canada is being closed. The tailings facility consists of perimeter dykes containing tailings with a pond in the central area and a tailings beach along one perimeter dyke. Water quality will be enhanced by reducing the volume of material exposed to oxidation along the tailings beach. An engineered soil cover was considered as an option to maintain tailings saturation and therefore reduce oxidation along the beach. Numerical analyses were conducted to estimate surface water infiltration rates and corresponding saturation and ground water elevations in the tailings. A one-dimensional finite element software, SoilCover, was used to simulate the beach surface infiltration with various cover options. The net infiltration rates obtained from the SoilCover model were then used as input parameters for a subsequent two-dimensional finite element seepage analysis. The 2-D seepage analysis was conducted using a computer software, Seep/W, to determine ground water level and seepage quantities. Transient state analyses were conducted to evaluate ground water levels in response to construction activities and weather condition changes. A practical cover option was selected based on the analysis results. The groundwater levels predicted in the beach and perimeter dyke agreed with the piezometer data, which confirmed the infiltration rate obtained from the SoilCover model and the results from the Seep/W model.