Mobility of aqueous contaminants at abandoned mining sites: insights from case studies in Sardinia with implications for remediation

Public awareness of environmental health issues has increased significantly in recent years, creating the need for detailed scientific studies that can identify potential environmental problems. This paper reports the results of hydrogeochemical surveys carried out in Sardinia, an Italian region with a long mining history. When mining operations in Sardinia ceased, actions for limiting the potential adverse effects of mine closure on the water system were not undertaken. Drainages from flooded mines and seeps from mining residues left on the ground are the main mining-related sources of contamination in Sardinia. Due to the proximity of mining sites to water resources and land that is within reach of animals and humans, the major risks to human health are associated with the direct discharge of contaminated waters into the streams and soils located down-gradient of the abandoned mines. Results of hydrogeochemical surveys carried out under different seasonal conditions showed that the dispersion of toxic and harmful elements (As, Cd, Ni, Pb, Sb and Zn) increases during the rainy season, especially under high runoff conditions. These results should help regional and national authorities to address present environmental regulations, particularly those regarding the quality of water resources. Furthermore, the results might be useful elsewhere for planning remediation actions at abandoned mining sites. Lessons learned by past mining in Sardinia indicate that correct disposal and management of mining residues should be mandatory from the beginning of exploitation and processing at each active mine. This would allow reduction of the environmental risks as well as the cost of remediation.