The New Brighton/Arden Hills/TCAAP site covers about 25 square miles in the Minneapolis-St. Paul area of Minnesota. It centers on the former Twin Cities Army Ammunition Plant, which made small-caliber ammunition from 1941 until 2005. Waste dumped at 14 locations over four decades contaminated soil, sediment, and groundwater. The contamination was found spreading beyond the plant boundary into the regional aquifer between 1978 and 1982. The site was added to the National Priorities List in 1983, making it a federal Superfund priority.
Groundwater contamination is the biggest concern. Chlorinated solvents, including trichloroethene, tetrachloroethene, and 1,1,1-trichloroethane, make up the bulk of it, along with benzene, carbon tetrachloride, vinyl chloride, and metals such as arsenic, lead, and mercury. Polychlorinated biphenyls (PCBs) and radionuclides have also been detected in groundwater. Soil and sediment at the former plant contain arsenic, lead, manganese, and other metals. Round Lake, a 123-acre lake southwest of the plant, holds cadmium, chromium, copper, lead, PCBs, and zinc in its sediment. In 2020, EPA added 1,4-dioxane as a contaminant of concern and upgraded treatment systems to handle it.
The U.S. Army is the responsible party and has been conducting cleanup under a 1987 agreement with EPA and the Minnesota Pollution Control Agency. Work is split across multiple operable units. Groundwater in the North and South Plumes is being treated through extraction systems using granular activated carbon and advanced oxidation, while residents with private wells have been given alternative water supplies. Soil remediation at the former plant is complete and in operation. Round Lake is currently in remedial design, with construction estimated to begin around mid-2027. A screening investigation for per- and polyfluoroalkyl substances (PFAS) at the Rice Creek Commons Redevelopment Parcel is underway, and a full PFAS remedial investigation is planned to start in 2026.
EPA assessments show human exposure is currently under control across the entire site, with no unacceptable exposure pathways identified. Contaminated groundwater migration is also stabilized, with no unacceptable discharge to surface water expected. However, physical construction is not complete for the whole site, and it has not yet achieved sitewide readiness for anticipated reuse. A five-year review was completed in August 2024, and the Army is now conducting the sixth five-year review, with EPA's protectiveness determination expected in May 2025.
Community members can get involved through the Restoration Advisory Board, which provides public input on site activities and is scheduled to meet next in September 2026. For questions, community members can contact the EPA Community Involvement Coordinator or Remedial Project Manager. Additional site information is posted on the TCAAP web page.
