The Weldon Spring Quarry/Plant/Pits site sits in St. Charles County, Missouri, about 30 miles west of St. Louis. The U.S. Department of Energy leads cleanup, with the U.S. Army also involved in site management. The Army produced explosives there starting in 1941, and uranium ore and thorium processing began in 1956. Those activities released radioactive and chemical contaminants into soil, groundwater, and surface water. The site was placed on the National Priorities List in 1987 and 1989.
More than 80 contaminants of concern have been identified across the site. These include explosives like TNT (trinitrotoluene) and dinitrotoluene, radioactive substances such as uranium-235, uranium-238, thorium-230, and thorium-232, heavy metals including arsenic, lead, chromium, and mercury, and solvents like trichloroethene (also called trichloroethylene). PCBs (polychlorinated biphenyls), PAHs (polycyclic aromatic hydrocarbons), nitrates, and fluoride are also present. Contamination is spread across soil, sediment, sludge, solid waste, and groundwater.
Physical construction of cleanup work finished in August 2005. The site received a Sitewide Ready for Anticipated Use designation in 2013. The main work still underway is long-term groundwater restoration at both the chemical plant and quarry locations. Groundwater migration is stabilized, and EPA assessments indicate human exposure is under control with no unacceptable exposure pathways currently identified. A five-year review was completed in September 2021, with the next review estimated between September and November 2026. The site has not yet been deleted from the National Priorities List.
Institutional controls protect public health while the site remains in long-term monitoring. Zoning restrictions prevent residential development. Covenants with the Missouri Department of Conservation and Missouri Department of Transportation/St. Charles County limit groundwater use and land use in sensitive areas like the Southeast Drainage area and the Quarry site. These areas are visually inspected every year to confirm restrictions remain effective. Soil and groundwater contamination still exceeds levels that would allow unrestricted use, but recreational use is acceptable under the controls in place.
The public can visit the site's Interpretive Center, located south of the disposal cell, to learn about the site's history and cleanup. The center draws between roughly 21,500 and 27,000 visitors per year. A hiking and biking trail built from a former haul road and wildlife habitat restoration areas are also open. Community members with questions can contact EPA's Community Involvement Coordinator or Remedial Project Manager, or reach out to the Department of Energy's Office of Legacy Management representative. Contact details are listed separately.
