Previous modelling studies used a mass balance approach to predict groundwater metal loadings to surface water; however, this approach over-predicted metal loadings when compared to analytical results from samples collected from monitoring wells. In this study, metal attenuation was modelled using United States Geological Survey (USGS)software PHREEQCI in an alluvial aquifer down-gradient of a pit lake and inactive heap leach pile. Sensitivity analyses were completed by varying iron-hydroxide and calcium carbonate concentrations, and groundwater velocity. Model results were calibrated to groundwater analytical results from wells located on the flow path.
The results predict continued metal attenuation, primarily through metal adsorption and co-precipitation, provided groundwater remains buffered against acidic input. Continued acidic input 30 to 40 years post-closure will result in desorption of weakly adsorbed metals (Cd and Co) and potentially result in adverse impacts to the aquatic environment.
For details on the approach, results and modelling interpretation, read the full paper.
For more information, please contact: Gerry Papini
