The Weldon Spring Former Army Ordnance Works covers about 17,232 acres in St. Charles County, Missouri. The U.S. Army used the site from 1941 to 1945 to produce TNT (trinitrotoluene) and DNT (dinitrotoluene) explosives during World War II. Those operations left nitroaromatic compounds in soil and groundwater. The site was listed on the National Priorities List (NPL) in 1990 and is being cleaned up under a Federal Facility Agreement signed in 1991, with the Army Corps of Engineers as the lead federal agency.
EPA identified thirteen contaminants of concern across soil, groundwater, and debris. These include TNT, DNT isomers, nitrobenzene, 1,3-dinitrobenzene, lead, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs). The site is divided into two operable units. Operable Unit 1 (OU1) covers soils and pipelines. Operable Unit 2 (OU2) addresses groundwater.
Cleanup has moved through several major phases. For OU1, excavation and incineration of contaminated soil and pipelines ran from December 1997 through September 2004. Treated soils were placed in a disposal cell at an adjacent facility. For OU2, groundwater remediation actions took place between June and July 2005. The cleanup strategy for groundwater relies on monitored natural attenuation, meaning naturally occurring processes reduce contaminant levels over time while the Army Corps of Engineers samples 17 monitoring wells and 7 springs each year. The site achieved sitewide ready-for-anticipated-reuse status in September 2020.
The most recent five-year review was completed in April 2026. It found that current remedies protect human health and the environment in the short term because access to contaminated areas is controlled through warning signs and land use restrictions. For long-term protection, land use controls need to be formally documented in a Record of Decision Amendment, and soil cleanup goals need review and updates. Those documents are expected by October 2028. An Explanation of Significant Differences for OU1 is estimated for completion between December 2026 and February 2027. The site remains on the NPL and has not been deleted.
Community members can access free technical support through two EPA programs. Technical Assistance Services for Communities (TASC) connects residents with independent scientists and engineers at no cost. Technical Assistance Grants (TAGs) of up to $50,000 are also available so communities can hire their own advisors to review cleanup reports. Site records are available at the Middendorf-Kredell Branch of the St. Charles City/County Library District at 2750 Highway K in O'Fallon, Missouri. For questions, residents can contact the EPA Community Involvement Coordinator or Remedial Project Manager listed in the site contacts.
