A PRIVATE mining firm endangered thousands by failing to promptly report a massive acid spill at its Buenavista mine, a regional civil defence chief claimed today.

The delay allowed acid to flow into a river that supplies water to tens of thousands of people, said Sonora state civil defence director Carlos Arias.

As well as faulting the company for the delay, he said that the spill at the copper mine had been caused by defects in newly constructed leaching ponds.

A pipe failed on August 7, allowing 10 million gallons of acid to escape.

“It was an error” in design or construction of a retaining pond, Mr Arias added.

The sulphuric acid spill contained high levels of pollutants like arsenic. 

Water supplies have been cut to about 20,000 people.

Environmental inspector Arturo Rodriguez said lax supervision at the mine, along with construction defects, appeared to have caused the spill.