Surface and Groundwater Quality Evolution in the Agrio and Guadiamar Rivers After the Aznalcóllar Mine Spill (SW Spain): Lessons Learned

Abstract

The failure of the tailing dam at the Aznalcóllar mine (SW Spain) in 1998 released ≈ 6 million m3 of pyrite sludge and acidic waters, and caused an enormous environmental disaster in the Agrio and Guadiamar rivers. A small aquifer formed by recent alluvial materials deposited by both rivers was also affected. The mine closed as a result of the spill but a new project for its reopening is currently being developed. The area covered by the spill (≈ 60 km long) was later transformed into a protected green corridor, which connects two important natural reserves. This work describes the effectiveness of the remediation measures taken and analyzes the evolution of water quality in the area since 1980 (almost 20 years before the accident occurred). The contaminant levels in both surface and groundwater showed a sharp decrease the first years after the spill, followed by a subsequent stabilization of pollution levels. Nowadays, pollutant concentrations in surface waters are even lower than those recorded before the spill, due to the cessation of mining and the effectiveness of the remediation. Despite this fast and outstanding improvement, the alluvial aquifer close to the mining zone is still polluted, with acidic pH values in some areas, probably due to the slow movement of groundwater together with the existence of some areas with polluted soils. As this aquifer feeds the streams, some pollutants (e.g. Al, Cd, and Zn) reach the surface waters. Remediation of the polluted soils as well as the alluvial aquifer in this sector is strongly recommended to achieve the complete rehabilitation of the affected area.