The Interior Department acknowledged that the plug “may have failed on its own,” but said smarter intervention could have averted that.
The mountains in the region have veins of gold and silver, but also lead, copper and zinc. Mining operations can accelerate the leaching of metals from the soil, add other toxins and create especially concentrated pools of poisoned water. Contaminated water continually seeps from mines into nearby streams, and environmental regulators have tried to slow or stop that process.
But instead of fixing the problem at Gold King, the E.P.A. temporarily made it much worse, incurring the wrath of residents downstream.