In total, nearly 3 million tons of uranium ore were blasted out of Midnite Mine. The mined area still contains more than 33 million tons of waste rock and unprocessed or low-grade ore (also known as protore). There are two large open pits on site partially filled with water and several pits backfilled with waste rock. Heavy metals reacting with acidic mine drainage pose an additional potential threat to human health and to the environment. The overall contamination extends to the mining area’s sediment, surface water, soil, and groundwater.
Since Midnite Mine’s closure in 1981, former operator Dawn Mining Company has been required to collect contaminated water flowing from the mined area. An onsite treatment system has been used since 1992 to remove contamination from the water, and is in operation between the months of April and November. This treated water is then piped to a nearby surface drainage that leads to Blue Creek. Dawn then trucks the residual sludge from the water treatment process to Energy Fuels at its White Mesa Mill near Blanding, Utah. While this effort to capture and treat the water has reduced the amount of contamination leaving the site in surface water, some contaminated groundwater still emerges in the lower drainages which flow into Blue Creek.
After a study of the site in 2005, the EPA sought public comment on a proposed cleanup plan. The final cleanup plan for the site was laid forth in a 2006 Record of Decision: it calls for a cap over an area of pits filled with waste during mining; the consolidation and engineered containment of remaining waste in the two open pits; the removal of water entering the pits; and the operation of a treatment system to treat contaminated water from the pits and seeps.
In October 2008, Newmont USA Limited, Dawn Mining Company, and the United States were found liable for the costs associated with the contamination. While negotiating with the EPA to settle their liability, Dawn and Newmont performed the following work required under an Order issued by EPA in November 2008: water treatment and sludge management, site fencing, completion of interim mechanisms to reduce impacts to Blue Creek, and data collection.
In September 2011, the mining companies and the United States signed a settlement agreement (referred to as a Consent Decree), which sets out requirements for design and implementation of the cleanup plan, as well as long-term operations and maintenance. This agreement was finalized in January 2012. Newmont and Dawn will perform the cleanup design and construction, while the Department of Interior will pay a share of the costs. The EPA will oversee the work, in consultation with the Spokane Tribe. Under a separate agreement with the Tribe, the mining companies will fund the Tribe’s continued involvement in overseeing the work.
EPA Cleanup Goals
The cleanup goals are to protect human health and the environment by preventing contact with mine waste, reducing the amount of radon at the ground surface, and lowering the amount of radiation at the ground surface to background levels. Furthermore, cleanup will entail preventing continued groundwater pollution, surface water, sediments, and air, and meeting cleanup standards for soil, sediments, surface water, and groundwater.
The cleanup plan for the site includes moving waste rock and stockpiled ore into the mine pits, under a cover of soil and native plants. Water draining into the pits will be removed, and treated at a new wastewater treatment facility. Treated water will be discharged into the Spokane River arm of Lake Roosevelt. Treated and pressed waste sludge will continue to be transported off site to a licensed hazardous waste facility. Long-term operations (maintenance, monitoring) will occur. The use of land and groundwater will be restricted where waste remains on the site.
Site cleanup activities began in May 2016. So far, the work accomplished includes includes installation of contractor facilities, access road construction, and movement of massive amounts of mine tailings into the open pit areas. The pits will be capped with a 3-foot-thick layer of clean soil and replanted. The cap will reduce human exposure to radon gas and gamma rays - two of the contaminants of concern at the site. Within the next few years, a new water treatment facility will be constructed as part of the cleanup. The Tribe’s monitoring indicates that even with treatment, pollution levels are high enough to kill aquatic insects in Blue Creek.
The tribe wants the water pumped directly into the Spokane River, where the pollution would be diluted in the larger water body. Major cleanup activities are anticipated to be ongoing until 2024. Monitoring for both radon and radiation will continue at the Midnite Mine site after the cleanup is complete.
- Midnite Uranium Mine site:
- Fact sheet:
This project is supported by funds from the Washington State Department of Ecology.