COLFAX, Louisiana — Two years ago, the U.S. military had an embarrassment on its hands: A stockpile of aging explosives blew up at a former Army ammunition plant in Minden, Louisiana, sending a cloud of debris 7,000 feet into the sky.

Local residents, alarmed by toxic contaminants from the accident, were nothing short of furious when they learned what the military intended to do with the 18 million of pounds of old explosives still remaining at the depot. The Army was set to dispose of the explosives through what are known as “open burns,” processes that would result in still more releases of pollutants.