In 2010 a store and release cover (the cover) was constructed on the south waste rock dump (SWRD) at Century mine (the mine). The purpose of the cover is to reduce seepage (percolation) into the potentially acid forming (PAF) waste rock by maintaining a compacted reduced permeability layer (RPL) at near-saturated conditions. This is achieved by overlaying the RPL with a 1.5 to 2 m thickness of dolomite rock and soil-mulch (the soil-mulch). The RPL is the trafficked surface of the SWRD. The soil-mulch has a hummocky final surface that captures rainfall so it does not runoff, allowing it in part to infiltrate, with excess water removed by evaporation and transpiration. The unsaturated behaviour of the cover is being monitored by instrumentation including volumetric water content sensors and a weather station capable of estimating potential evapotranspiration. The instrumentation allows for the calculation of storage of rainfall in the cover, seepage (or percolation) through the base of the cover and in situ soil water characteristic curves (SWCC). The paper presents the results of three years of monitoring. It shows that seepage is about 6% of the total rainfall over the monitoring period and that the majority of the infiltration is going into storage within the cover before being removed by evapotranspiration. The paper presents a preliminary water balance for the cover by calibrating a Vadose/w model (the model) using in situ SWCCs and calculating actual evapotranspiration.
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