Eastern Michaud Flats Contamination

Overview

Eastern Michaud Flats is a 2,530-acre Superfund site near Pocatello, Idaho. It has been on the National Priorities List since 1990. Two phosphate processing facilities operated here starting in the 1940s. The FMC Corporation plant produced elemental phosphorus until it closed in 2001. The J.R. Simplot Company facility still produces solid and liquid fertilizers. Part of the FMC site sits on the Fort Hall Reservation of the Shoshone-Bannock Tribes.

Contaminants affect both groundwater and soil. Metals found at the site include arsenic, lead, cadmium, chromium, mercury, nickel, and zinc. Radioactive substances include radium-226, polonium-210, thorium-230, uranium-238, and radon. Volatile organic compounds such as trichloroethene and tetrachloroethene are present in groundwater. Phosphorus, phosphoric acid, nitrate, fluoride, and several other inorganic compounds have also been detected. Gross alpha and gross beta radiation appear in both soil and groundwater.

EPA divided the site into five operable units and selected a cleanup remedy in 1998, with updates in 2010 and 2012. At the FMC facility, workers finished sitewide grading in 2016 and installed clean soil caps over former operations areas by the end of 2017. Engineered covers sit over areas containing subsurface elemental phosphorus. The main 2024 priority is advancing the groundwater extraction and treatment system design and running pilot tests. At the Simplot facility, a gypsum waste stack was lined in 2018. Extraction wells capture about 65% of phosphorus in the contaminated plume for reuse in fertilizer production. In July 2023, EPA and the Department of Justice settled with Simplot for $1.5 million, requiring nearly $150 million in waste management improvements and $108 million secured for future facility closure.

Human exposure is currently under control across the site. Institutional controls prevent use of contaminated groundwater for drinking, and contaminated soils have been capped. However, groundwater migration is not yet stabilized, and contaminated groundwater continues discharging into the Portneuf River. That river remains impaired under the Clean Water Act due to phosphorus levels. Physical construction is not complete, and the site is not yet ready for unrestricted use. EPA completed a Five-Year Review in September 2025 and found the cleanup remains protective. Despite ongoing contamination challenges, 87 acres of the FMC portion have been cleared for commercial and industrial reuse. As of December 2024, three businesses were operating on-site, employing 89 people and generating about $13.1 million in annual sales.

Community members with questions can contact the EPA Community Involvement Coordinator. Hard copy documents are available at the American Falls Library, Idaho State University Library in Pocatello, the Shoshone-Bannock Library on the Fort Hall reservation, and the EPA Region 10 Superfund Record Center in Seattle.