Efficient natural attenuation of acidic contaminants in a confined aquifer

As the demand for energy grows steadily and fossil fuels are depleted gradually, nuclear power will continue to play an important role in meeting energy needs in the future. Uranium, as the fuel for nuclear power generation, has experienced the increase in production in recent years. Acid in situ leach uranium mining is an effective and popular technique to extract uranium without exposure of workers to radioactive ore deposits. Despite this advantage, this technique causes extremely high concentrations of contaminants in confined aquifers after mining is completed. These contaminants will undergo natural attenuation while migrating downgradient with regional groundwater. Mounting concerns have been raised regarding widespread groundwater contamination due to concentrations of contaminants and lack of published studies for comparison. In this study, the fate of various contaminants was examined to infer the extent of natural attenuation in a confined aquifer in northwest China. Results indicate the efficiency of natural attenuation in the confined aquifer. In addition, the contaminant plume migrated much slower than regional groundwater. The dual-domain theory has been invoked to aid in the interpretation of the decoupling of the plume migration with the regional groundwater flow. This study also implies that widespread contamination in confined aquifers is more likely to be caused by external factors (e.g., mechanical failure, human errors) than post-mining spreading of contaminants. To be always safe, strict monitoring schemes must still be established and operated.