United States Federal investigators said that engineering errors by an Environmental Protection Agency-contracted team “led directly” to the August, 2015 Gold King Mine spill, which could have been prevented. The much anticipated 132-page report from the Interior Department following the spill of an estimated 3 million gallons of acidic mining sludge into the Animas River, pointed to miscalculations and poor planning.
"It is incorrectly concluded that the water level inside the mine was at the similar elevation, a few feet below the top of the adit roof. This error resulted in development of a plan to open the mine in a matter that appeared to guard against blowout of the mine spoils, instead led directly to the failure of the spoils" the report by the Bureau of Reclamation states.
The investigation revealed that the EPA team should have drilled into the mine from above in order to determine the level of the mine pool. This case should remind all engineers, especially geotechnical engineers, that a thorough site investigation and study is important.
The full report and referenced article says the root causes of the Colorado accident began decades earlier, when mining companies altered the flow of water through a series of interconnected tunnels in the extensively mined Upper Animas River watershed.