The Arsenic Trioxide Site covers about 568 square miles across Richland and Sargent counties in southeastern North Dakota, near the towns of Lidgerwood, Rutland, and Wyndmere. In the 1930s and early 1940s, farmers spread arsenic-based grasshopper bait across fields in the region. That practice left arsenic trioxide, sodium arsenate, Paris Green, and other arsenic compounds in the groundwater. EPA added the site to the Superfund National Priorities List (NPL) in September 1983 after well testing found unsafe arsenic levels. Arsenic in groundwater is the contaminant of concern. Ingesting or touching contaminated water is the primary health risk.
Cleanup was organized into three operable units. The rural areas water systems unit and the Lidgerwood and Wyndmere unit each received their own investigations, remedy decisions, and construction work. Cleanup actions included expanding three water treatment plants, laying about 300 miles of water pipes, adding storage tanks and reservoirs, and drilling new supply wells. That phase wrapped up in June 1993. When the Safe Drinking Water Act lowered the acceptable arsenic limit to 0.01 milligrams per liter in 2001, Wyndmere and Hankinson were connected to the Southeast Water Users District rural water system. That treatment plant was expanded between 2005 and 2007. By September 2011, about 162 additional users were connected, and bottled water was provided as a bridge until those connections were complete.
EPA deleted the site from the NPL in July 1996. Human exposure is currently under control, meaning no unacceptable exposure pathways exist. Groundwater migration is also under control, with no unacceptable discharge to surface water. Physical construction of the cleanup is complete across the entire site. However, the site has not yet achieved sitewide ready for anticipated reuse status, so monitoring and some land-use controls remain active. EPA conducts five-year reviews to confirm that protections continue to work. The most recent review was completed in September 2023, and the next is estimated between September and November 2028.
One business currently operates on-site, employing 10 people and generating an estimated $1,960,000 in annual sales revenue through EPA's Superfund Redevelopment Program. Community members can review site documents at the Southeast Water Users District office in Mantador, the Lidgerwood Public Library, or the EPA Superfund Records Center in Denver, Colorado. Records can also be requested by calling 303-312-7273 or toll-free at 800-227-8917, extension 312-7273. For questions about the site, residents can contact EPA's Community Involvement Coordinator or Remedial Project Manager directly.
