The driver was not seriously injured, but about 9 cubic yards of sludge spilled into the water, officials said.
Gold King Mine
The EPA chose 26 mining sites for interim work to reduce human and environmental risks while a long-term solution is studied.
Pruitt has been under close scrutiny for his spending and relationships with industry representatives.
Jonathan Thompson places the Gold King Mine spill within the long history of mining and pollution in Southwest Colorado.
A mining company accused the agency of letting untreated mine wastewater get into the Animas River.
The allegation was made by Sunnyside Gold Corp., which is fighting the EPA over who should pay for a potentially costly groundwater study.
The EPA is considering using robots and other sophisticated technology to help prevent mine "blowouts" or clean them up if they happen.
The UN Environment Program report tallied 40 significant mine waste accidents in the past decade. Most involved dams or other storage areas that failed.
The EPA is installing a barrier at the mine outside Silverton to prevent another spill like the one in 2015 that sent 3 million gallons of toxic water into rivers.