Phosphate exploration and mining in southeast Idaho was first conducted in the early-1900s, with mining activities continuing to the present day. Large-scale phosphate mines in the region consist of open pit or contour strip operations. Historic phosphate mining operations involved removal of soils and rock to access the phosphate ore. As ore was excavated, overburden rock and waste shales containing selenium were excavated. This overburden and waste shale were placed adjacent to mine pits, or backfilled into pits. Historic reclamation practices changed throughout the mining period from little to no reclamation requirements to today's more stringent standards.
The historic mines under investigation had varying degrees of reclamation requirements, including regrading of slopes and various revegetation seed mixes. Some of the vegetation planted during reclamation is now known to accumulate selenium at levels that harm or kill livestock. The resultant combination of non-selective waste material placement, in addition to minimal to non-existent reclamation, allowed for infiltration of water into the dumps/pits and oxidation of mine waste.
Selenium is a naturally occurring element in the environment, and an essential micronutrient for humans, plants, and wildlife. However, at too high of concentrations, selenium can be toxic. Mining processes resulting in oxidation of the selenium bearing mine waste results in a selenium oxidation state that makes it highly water soluble, mobile, and toxic. Past mining and reclamation practices have resulted in the interaction of water with selenium-bearing material, leading to selenium contamination of surface and groundwater. Toxic levels of selenium have been detected in water, sediment, vegetation, and animal and fish tissues collected from phosphate mines in southeast Idaho.
Historic and current phosphate mining operations have occurred in southeast Idaho, with most individual mines occurring near the city of Soda Springs, Idaho. Mining impacts have occurred over an approximate 17,000 acre area within portions of Bannock, Bear Lake, Bingham, and Caribou Counties, Idaho. The NRDA Mine Site Project Area contains 16 major open pit phosphate mines and two processing facilities.
In 2015, the Southeast Idaho Phosphate Mine Site Natural Resource Trustee Council (Trustee Council) was formed to develop and coordinate damage assessment activities at the Mine Site and to plan for the restoration of natural resources through the NRDA process. The NRDA process is separate from the CERCLA Remedial Investigation/Feasibility Study process. Under NRDA, the Trustee Council will evaluate if natural resources were harmed over the time that the area has been contaminated and will develop a restoration program to compensate for those losses, if necessary/appropriate.
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The Southeast Idaho Phosphate Mine Site Trustee Council has determined the criteria to perform a NRDA under 43 C.F.R. § 11.23 (e) have been met. The Preassessment Screen outlines the criteria and associated rationale for the Trustee Council's determination to proceed with a NRDA.
- Under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) when there is a release of hazardous substances, natural resource trustees are authorized to conduct a natural resource damage assessment and restoration (NRDAR) to obtain compensation for harm to natural resources. At the Southeast Idaho Phosphate Mine Site, the trustees will pursue the NRDAR process to identify and quantify natural resources injured as a result of the release of hazardous substances at the Mine Site to determine the restoration activities necessary to return the injured natural resources to baseline conditions and compensate the public and the environment for interim losses.
- The Trustee Council currently consists of representatives from the U.S. Department of Interior, U.S. Department of Agriculture, State of Idaho, and Shoshone-Bannock Tribes:
If you have any questions or specific requests regarding documents available on this website, or wish to view a hard copy, please contact Sandi Fisher via email or by phone at 208-237-6975 x 102