The E.P.A. said it was reviewing the report and offered no immediate response to the specifics in it. The accident occurred in a remote area, at an elevation of 11,500 feet, where a mine entrance had been plugged with rocks and soil that held back the water. The E.P.A., working with the state Department of Natural Resources, pushed a pipe horizontally through the top of the plug, expecting to find a pocket of air. Instead, water began to gush out.