Assessment of environmental risk of reclaimed mining ponds using geophysics and geochemical techniques

• Properties of dumped material promoted the natural plants colonization.
• Total Pb, Cd, Zn concentrations in dumped materials exceed the allowed values.
• Metals mobility has been reduced by the presence of dumped materials.
• Erosion and runoff are taking place in areas uncovered by dumped materials.
• Bedrock did´t present discontinuities that promote metals transport to deep layers.

This study aims to evaluate the environmental risk of three reclaimed mining ponds using geophysics and geochemical techniques. The reclamation works were based in the use of some materials for covering the tailing layer in order to reduce its erosion and transport. Samples from dumped materials and tailing layers were analyzed for their properties and total, diethylene triamine pentaacetic (DTPA) extractable and water soluble metals. Electrical resistivity imaging (ERI) method helped to identify erosion processes and the thickness of dumped materials and their contact with tailing layers. Properties within dumped material promoted the colonization of natural plants on these tailings. However, total Pb, Cd, and Zn concentrations exceed the maximum admissible concentration allowed by legislation. Risk of mobility of these metals from the surface layer through plant uptake and leaching or runoff water has been significantly reduced. The concentration of some metals in dumped materials was higher than that reported in tailing layers: their immobilization is therefore recommended. According to ERI method, two ponds experienced erosion by water action. Efforts need to be focused to re-cover these areas to reduce the erosion and metal mobility from the tailing layers. The bedrock did not present any discontinuity that could allow the transport of heavy metals to deeper horizons.