Characterisation of vadose zone processes in a tailings facility

Abstract

The undisclosed mining company in Limpopo Province, where the study is undertaken, is one of the world’s most accomplished copper mines. The waste dumps onsite (tailings storage facilities in particular) are known to provide ideal conditions for oxidation. An extensive investigation into the groundwater sulphate levels has indicated that only a small percentage of the sulphate load that reaches a nearby river, is contributed by groundwater. It was subsequently speculated that a significant sulphate load may result from sporadic rainfall-induced discharges, in the surface and near surface/vadose zone, potentially moving seepage water from the impoundments and the return water dams into the river. A study of surface and near-surface water and solute fluxes was proposed, for which this assessment will aid in quantifying water fluxes throughout the tailings storage facility on-site. This study aims at predicting, by means of a conceptual and a physically based model, the water fluxes that result in surface and near-surface sulphate loads. In order to develop reliable predictions, the waste materials need to be characterised. The material characterisation has included in-situ measurements of hydraulic characteristics as well as laboratory testing of the tailings storage facility material as well as the cover material overlaying the latter mentioned. In-situ observations include waste volumetric water content, runoff processes as well as meteorological observations. Before parameterising the HYDRUS-2D programme, a conceptual model was developed to define water flows and potential pathways through the tailings storage facility.