The U.S. Environmental Protection Agency says a clean-up team accidentally caused about one million gallons of contaminated mine wastewater to spill into a river near the Gold King mine in Colorado.
The EPA said the incident occurred on August 5, 2015, when the clean-up team was conducting an investigation to assess on-going water releases from the mine.
The plan was to excavate the loose material that had collapsed into the cave entry back to the timbering, the EPA said in a statement.
“During the excavation, the loose material gave way, opening the adit (mine tunnel) and spilling the water stored behind the collapsed material into Cement Creek, a tributary of the Animas River,’’ it said.
According to the EPA, initial estimates are that the release contained approximately one million gallons of water that was held behind unconsolidated debris near an abandoned mine portal.
There were several workers at the site at the time of the breach. All were unharmed, the EPA said.
Water quality data from throughout the affected region continues to be collected and evaluated.
Previous analysis of the same mine’s water has shown it to have iron, aluminum, cadmium, zinc and copper in varying concentrations.
The EPA has said the spill does not threaten local sources of drinking water and the main contaminants responsible for the leak’s mustard-like colour are unlikely to be dangerous.