Superfund Site: MIDNITE MINE, WELLPINIT, WA
Superfund Site Profile
Midnite Mine is an inactive former uranium mine in the Selkirk Mountains of eastern Washington. Located within the reservation of the Spokane Tribe of Indians, the mine was operated from 1955 until 1981.
Two open pits, backfilled pits, a number of waste rock piles, and several ore/protore stockpiles remain on site. In addition to elevated levels of radioactivity, heavy metals mobilized in acid mine drainage pose a potential threat to human health and the environment. The site drains to Blue Creek, which enters the Spokane Arm of Franklin D. Roosevelt Lake. Contaminated water emerging below the waste rock and ore piles is currently captured for treatment in an on-site treatment system.
After a study of the site, EPA sought public comment on a proposed cleanup plan in September 2005. The final cleanup plan for the site is described in the Record of Decision issued September 29, 2006.
The Record of Decision calls for a cap over an area of pits filled with waste during mining, consolidation and engineered containment of remaining waste in the two open pits, removal of water entering the pits, and operation of a treatment system to treat contaminated water from the pits and seeps.
Who pays for the cleanup?
EPA's policy is to have the responsible parties - also called Potentially Responsible Parties, or PRPs - pay for cleaning up pollution. Responsible parties can be past or present operators and land owners.
Under a legal agreement called a consent decree (finalized in January 2012), Dawn Mining Company, LLC, and Newmont USA Limited will complete the cleanup work, and the United States will contribute a share of the cleanup costs. EPA will oversee the cleanup work in coordination with the Spokane Tribe.
Dawn and Newmont (the mining companies involved with Midnite Mine) completed the final 100% Basis of Design Report in October 2015.
- Fact Sheet: 100% Basis of Design Report (PDF) (4 pp, 1MB) – November 2015
- Full Report: 100% Basis of Design Report and Supporting Documents - October 2015
The cleanup at the site includes the following:
- Earthwork: Prepare the two open pits for consolidation of mine waste rock by removing contaminated water and sediments and placing a layer of drain rock and liner in the pit bottoms.
- Excavation: Excavate mine waste rock, protore, and contaminated soils and sediments from the waste rock piles, access roads, and drainages.
- Backfill: Consolidate the mine waste rock, protore, and contaminated soils and sediments in the lined pits.
- Cover: Cover the consolidated waste rock, protore, and contaminated soils and sediments to limit water infiltration and migration of contaminants.
Some components of the remedial design are still ongoing. The design of the new Water Treatment Plant is on hold pending completion of WTP investigations and studies, and the reissuance of the NPDES permit for the WTP. Once complete, treated water from the new WTP will be discharged through a new pipeline to the Spokane Arm of Lake Roosevelt.