The better approach, the Interior Department’s engineers concluded, would have been to drill a hole from above first to gauge conditions and, if necessary, relieve pressure. In its own review, in August, the E.P.A. argued that a drilling operation would have been too costly and slow. It concluded that the plug would have collapsed eventually, and that a “blowout was likely inevitable.” The Interior Department acknowledged that the plug “may have failed on its own,” but said smarter intervention could have averted that.