An unusual amount of rainfall has been blamed for the spill August 6 of 40,000 cubic meters of copper sulphate leachate into the Sonora and Bacanuchi Rivers.
The Buenavista del Cobre mine, a subsidiary of Grupo Mexico, said in a statement that the unusual rainfall resulted in an increase in the volume of water and copper sulphate acid solution in a reservoir.
The statement was in response to a criminal complaint filed by Profepa, the federal environmental agency, for environmental offences. The mine said it rejects the punitive legal action being taken by Profepa on the grounds that the spill was the result of natural causes and because the mine’s response had been “prompt and complete.”
The company noted that no environmental incidents had been reported since the mine began operations 23 years ago.
The firm explained that heavier than normal rainfall in July and early August resulted in a significant increase in the volume of liquids contained in a reservoir, which had been almost empty days before.
“The solution,” said the statement, “is raw material for the production of copper, it’s not waste or dangerous residue.”
In earlier reports agencies warned against the consumption of water from the river or nearby wells, and suggested that livestock and other agricultural products were at risk due to high concentrations of heavy metals.
However, National Water Commission head David Korenfeld Federman said two days ago that the most recent tests of the river have revealed that contamination levels are within accepted norms. Three more tests are currently being conducted by two different and independent laboratories. Those results are to be presented tomorrow.
Korenfeld was optimistic that restrictions on use of the river water would soon be lifted. The mine has been ordered to monitor water quality in the river every 15 days during the next five years.
In its statement, the mine also said it had delivered 3.5 million pesos to the affected municipalities to support environmental services and the delivery of water, and had mobilized 877 tanker trucks for the delivery of more than 13 million liters of potable water to homes and schools. It had also installed five water purification plants, the company said.
The Buenavista mine, located in Cananea, Sonora, employs 9,000 people, exports 200,000 tonnes of refined copper and contributes 1.4 billion pesos every month to the local economy, the statement said.