eastern michaud flats contamination


The Eastern Michaud Flats (EMF) Superfund Site is located in Southeast Idaho, approximately 3 miles northwest of Pocatello, Idaho. Within the site boundaries are two adjacent phosphate ore processing facilities, the FMC Corporation and the J.R. Simplot Company, began operation since the 1940s. The J.R. Simplot Don Plant (Simplot) is still an active facility; the FMC Corporation Elemental Phosphorus Plant (FMC) ceased operations in December 2001 and was subsequently demolished. The main portion of the site is roughly 2,475 acres in size, which is 1,450 acres for the FMC Operable Unit and 1,025 for the Simplot Operable Unit). The EMF Superfund Site also includes the Off-Plant Operable Unit, which encompasses the areal extent of contamination at or from both plants outside of the previously defined operable units. The J.R. Simplot facility produces 12 principle products, including five grades of solid fertilizer and four grades of liquid fertilizers. The raw materials for their processes are phosphate ore (transported to the plant via a slurry pipeline from the Smoky Canyon Mine), sulfur, air and natural gas. The primary waste by-product from the Simplot plant is phosphogypsum, which is pumped as a thick slurry to large unlined stacks south of the processing plant. The FMC plant produced approximately 250 million pounds of elemental phosphorus per year from two million tons of shale, silica, and coke; the elemental phosphorus was sold and used in a variety of products from cleaning compounds to foods. Ore was shipped to the plant in railcars and stockpiled at the plant. The primary by-products from the production process were slag (stored on-site), ferrous-phosphate residuals, carbon monoxide and several aqueous streams (such as phossy water/solids, precipitator slurry, calciner water/solids, and industrial wastewater). Most of the aqueous streams were managed in lined surface impoundments some of which were subject to regulation under the federal Resource Conservation and Recovery Act. FMC shut down operations in December 2001. In 1976, the Idaho Department of Health and Welfare conducted a groundwater monitoring study down gradient from the plants. The investigation showed elevated levels of arsenic, lead and cadmium above Federal Drinking Water Standards. Further sampling during the 1980s confirmed these results, and the site was listed on the National Priorities List on August 30, 1990. The Michaud Flats are on the Snake River Plain and are bordered by the American Falls Reservoir, the Portneuf River, Rock Creek, and on the south by the foothills of the Deep Creek Mountains and Bannock Range. The Portneuf River, which is located 1/4 mile from the site, is used for fishing, recreation, and irrigation downstream from the site. The Portneuf River flows back onto the Fort Hall Reservation 1 mile downstream of Batiste Spring, an area where contaminated groundwater flows into the surface waters of the river. The river flows through the "Bottoms" area of Fort Hall, a wetland that is sacred to the Shoshone-Bannock Tribes, then into the American Falls Reservoir. Site Responsibility: This site is being addressed through federal and potentially responsible parties' actions.

Hazardous Ranking Score

58 / 100

A score of 28.5 or higher qualifies a site for the Superfund National Priority List.

Regional Contact

Region 10
Phone: (800) 424-4372

Contact Region



Site Inspection
Preliminary Assessment
Final Listing On NPL

Contaminants & Health Effects

      Endocrine Disrupter
      Reproductive Toxin
      Persistent, bioaccumulative and toxic


        African American
        American Indian and Alaska Native
        Native Hawaiian


        People living
        within a 1 mile radius


        Average Income


        Occupied homes

        Potentially Responsible Parties

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