Environmental recovery of As Pontes mine pit lake

One of the most common solutions for more than 50 years for the recovery of mine holes gener-ated during mining activities is their transformation into lakes. This paper presents the activities carried out from the closure of the As Pontes mine to the total filling of the mining lake. The en-vironmental solution adopted for the recovery of the mining hole and its transformation into a mining lake is described, as well as the methodology followed for its filling, defining the water sources used, its volume and its chemical quality. Perfect mix and stratified lake models were performed to simulate the final chemical quality of the lake. The details of the studies carried out on waves on the shores of the lake and the stability of the slopes of the mine are also presented. The hydraulic works carried out to reintegrate into the lake the watercourses that were diverted during the mining exploitation are also indicated. Water chemical data of the As Pontes lake collected during and after the filling of the lake show the presence of two well-differentiated zones separated by a chemocline. The uppermost layer has a slightly acid pH and oxic conditions, while the deeper layer has very low pH values and anoxic conditions. The methodology used was successful and the forecasts made are in line with the results obtained both in relation to the filling time of the lake and the quality of the overflow waters, which comply with all the established limits.