The United States is set to destroy what remains of its declared stockpile of chemical weapons in a major milestone for international arms control efforts. Under the Chemical Weapons Convention, the U.S. has until Sept. 30 to eradicate the remnants of its stockpile, which, at the end of the Cold War, amounted to 30,000 tons. Workers at the Blue Grass Army Depot in Kentucky are about to destroy the last of 51,000 M55 rockets filled with the GB nerve agent—also known as sarin—that have been kept at the site since the 1940s. And in Colorado, staff at the Army Pueblo Chemical Depot finished destroying a cache of around 2,600 tons of mustard blister agent. “One thing that we’re really proud of is how we’re finishing the mission. We’re finishing it for good for the United States of America,” Kim Jackson, the manager of the Pueblo Chemical Agent-Destruction Pilot Plant, told the Associated Press.