Between 1932 and 1934, engineer Harold Kingsmill, Cerro de Pasco Copper Corporation official, ordered the construction of a tunnel with the objective that would serve for the drainage of underground mines in the area.
The tunnel is located at a depth of 500 meters and covers an area of 11 (sq?)km. Its path begins in Morococha and passes through the district and the communities of Pucara and Yauli until it flows into the Yauli River, where it has deposited acid run-off at a rate of 1100 liters per second for more than 70 years.
The waters of the Kingsmill tunnel have high content of metals, particularly iron, manganese, zinc, lead, arsenic, aluminum, and cadmium. To treat this effluent, Minera Chinalco Peru has built a plant that employs a high density sludge process (HDS), which is considered to be the best technology for the treatment acidic effluents in the world.
The treatment process permits an increase of the River water’s pH, by increasing the density of the metals with lime which enables their removal. At the end of the process, the clarified water is neutralized and pours into the Yauli River. This has significant advantages because it reduces the volume of sludge by more than 95 per cent, does not contaminate the surrounding groundwater, resulting in lowering the costs of the elimination of sludge, among other contaminants.
Fully complying with the commitment made by Minera Chinalco Peru in 2006 and within the parameters approved by the Ministry of Energy and Mines, the plant began operations in the second half of 2010.