Temporal and spatial variation of hydrochemical contamination in a former radium-uranium tailing dam as a result of environmental remediation field works

Abstract The main objective of this work was to understand the evolution of water quality within a tailings dam of a former radium-uranium mining site as a response to environmental remediation works. For this, results of numerical groundwater modeling were combined with multivariate hydrochemical trend analysis derived multivariate Principal Component Analysis and K-means clustering analysis. Numerical groundwater models were developed with the aim of detecting the main flow paths inside the tailings dam and across its bordering. These models allowed the identification of the hydrodynamic flows in the area that are most likely to be directly responsible for relevant hydrochemical exchanges in time. The spatial evolution of the contamination plume in time was mapped considering a cumulative interpretation that integrates all the hydrochemical indicators simultaneously through multivariate and clustering analysis. Resulting hydrochemical maps were superposed with the flow paths identified from modelling allowing to conclude that the contamination plume migrates within the tailings in the dependence of the main water flow paths that percolates within the tailings dam due to the existence of old shafts and old pre-existing streamlines located underneath the tailings dam. The methodology adopted allowed the verification of a general improvement in groundwater quality with a spatial reduction of the contamination plume within the tailings dam.