The Forest Service, with the assistance of the U.S. Environmental Protection Agency and the State of South Dakota, has developed and is implementing a cleanup plan for the Riley Pass Abandoned Uranium Mines in the North Cave Hills. This website provides background information and documentation associated with the site and updates regarding ongoing reclamation efforts.
Mine Site Overview
Riley Pass is located on the Custer National Forest’s Sioux Ranger District, about 25 miles north of Buffalo, SD. Uranium mining started at Riley Pass in 1954 as authorized by the General Mining Law and Public Law 357. Strip mining to reach uranium contained in the underlying Tertiary Fort Union formation coal seams removed up to 80 feet of overburden, which was piled on the outer edges of the rimrock. No reclamation was required as directed by PL 357.
Approximately 250 acres of disturbed highwall, pit floor, and spoils areas have been identified for reclamation and clean-up. Hazards within the Riley Pass area include high walls, pit floor, unstable overburden, elevated radioactive materials, and heavy metals. Onsite mine wastes are fine-grained particles readily dispersed by wind and surface water erosion. Contaminants of concern include arsenic, molybdenum, thorium, and uranium. Concentrations range from below established background to ten times higher for sediment samples in impacted drainages and several hundred times higher for mine waste samples.
Reclamation
The Forest Service has been working at the Riley Pass site under Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) authority since 1996. A 2007 Action Memorandum and 2007 Administrative Settlement Agreement and Order on Consent with Tronox LLC initiated CERCLA removal efforts to contain, consolidate, stabilize, and revegetate historic mine impacts. Of the 12 bluffs at the site, labeled A-K, Tronox is responsible for cleanup of six bluffs (B, C, D, E, G, and H, and associated retention ponds). The remaining Non–Tronox bluffs (A, F, I, J, K, and L) have no viable Potentially Responsible Party (PRP). Due to a lack of PRP, the Forest Service plans to conduct the removal actions on the Non-Tronox bluffs.
Newsletters
Documents, Maps, and Photos
Documents, maps, and photos regarding the clean-up work at Riley Pass will soon be available for download from this website. To request any of the following items prior to them being posted, please contact us at the number below. Documents include:
- April 2010 Action Memorandum for the Riley Pass Uranium Mines Site Non-Tronox Bluffs Removal Action
- April 2007 North Cave Hills Abandoned Uranium Mines Impact Investigation Final Report
- February 2007 Action Memorandum Riley Pass Uranium Mines Site Removal Action for Tronox Bluffs
- November 2006 Final Engineering Evaluation and Cost Analysis (EE/CA), Riley Pass Abandoned Uranium Mine
- 2006 Regional Geology and Uranium Deposition PowerPoint
- Riley Pass Vicinity Map
- Riley Pass Bluff Identification Map
Contact Us
For more information on Riley Pass, to request documents not yet posted to this website, or to be added to the Riley Pass Newsletter mailing list, please contact Mary Beth Marks, On-Scene Coordinator, at 406-587-6701.
