Weldon Spring Ordnance Works (WSOW) was a 17,323-acre (70.10 km²) U.S. Government-owned, contractor-operated (GOCO) facility in St. Charles County, Missouri, 55 km west of St. Louis. The site was originally operated by the Atlas Powder Company during World War II from 1941 to 1945 to produce explosives. The Atomic Energy Commission acquired part of the property in 1955, and Mallinckrodt, Inc. processed uranium ore from 1957 to 1966 under contract. The site has been divided into several parcels, and ownership has transferred over the years. Two portions of the original WSOW property are now Superfund sites that require substantial cleanup efforts. The environmental remediation of the WSOW site is currently designated as a major project of the Defense Environmental Restoration Program of the United States Department of Defense.