Water contamination and remedial measures at the Troya abandoned Pb-Zn mine (The Basque Country, Northern Spain)

This article describes a case of contamination of a karstic aquifer by aban doning an underground mine exploiting sulphide ore body. To exploit the ore , the aquifer was drained and the water level declined about 230 m, drying up the spring that had drained the aquifer up to that moment. When the mini ng activity ceased, the piezometric level recovered and contaminated water began to flow out from a mine adit. The water is high in sulphates and diss olved Fe, although the pH is neutral. When this water reached the nearby cr eek, the fish population was eliminated, principally due to the presence of toxic metals and the precipitation of Fe hydroxides. The contamination ori ginated in an area of the partially flooded mine rooms where the ore is in contact with both air and water. The acidity generated by pyrite oxidation is neutralized by calcite dissolution. Presently, the mine water is diverte d to the old tailings pond which functions as an aerobic wetland. This acti on has allowed the fish population in the creek to be restored.