By Mark E. Smith, P.E.
During the heyday of U.S. uranium mining there were more than 50 operating conventional mills. All but one of those is now shut down, with varying degrees of attention to closure. The U.S. Department of Energy (DoE) has published reports1 on at least 43 of those sites, including both Title I and II sites,2 detailing the closure costs, surety levels and other issues. This article summarizes some of that information.
Most of the closure liability comes from securing the tailings storage facilities (TSFs) and addressing control of radon emissions and contamination to groundwater, surface water and land (e.g., dust). In some cases tailings have been completely relocated, such as at Monticello, Utah.3 In others, the tailings were secured on site. About a third of these 43 sites are still the subject of on-going active controls and, to some extent, dispute about whether the sites are secured.4
The accompanying table summarizes key data from the DoE and Robinson reports, which both generally report cost data as of 1994. The costs shown in the table include long-term care where data was available. Those costs have been extrapolated to 2010 using the ENR Construction Cost Index.5 Surety information, where available, has been handled the same way. Costs include both Title I (having operated on or before December 31, 1970, generally producing uranium only for the weapons programs) and Title II (post 1970, generally producing uranium for energy fuel) sites under the Uranium Mill Tailings Radiation Control Act.6 In some cases, alternative sources report different values, in which case either the more credible source was used or a mid-range value was reported herein. For sites that included full, modern capping of the tailings, generally some form of a water balance or evapotranspiration cover has been used.7 In this approach, the cover generally includes high-quality, low-permeability barriers (e.g., geomembrane and clay) for infiltration control in the short term (hundreds of years) and a series of soil layers to provide capillary breaks and absorption-release of season water for the long term (thousands of years). Some form of barrier for rodents (rubble or coarse stone) is also generally included as well as a top vegetative layer. The design life of these systems is generally accepted to be about 1,000 years. As an example, the Monticello tailings closure in southern Utah utilized a 9.5-ft-thick, seven-layer capping system including a combination of a single geomembrane with a drainage layer under an evapotranspirative cover that could be shown to have near zero percolation on a very long-term basis.3
The only operating conventional uranium mill in the U.S., in southern Utah, has been in operation since 1980. The original surety was $5.5 million; the current owner increased this to $11.9 million when they acquired the property. As part of re-licensing, in 2010, the owner has proposed to increase that to $15.8 million.8 This equates to $41,500 per acre, compared with the median and average of all 43 sites of $350,000 and $600,000 per acre, respectively. According to the DoE,9 the cost of this site, before considering the current addition of two tailings cells, will be $36.8 million or $97,000 per acre (2010 dollars). A 2009 U.S. Geological Survey survey of uranium levels in Big Sage Brush beyond the property boundaries has shown elevated levels to the north, east and southeast, suggesting a broader scope for remediation and closure may be required. Modern uranium mills can avoid many of the problems, and liabilities, of the legacy mills by:
- Using modern design for the TSFs incorporating a high level of containment for the liquids;
- Using advanced construction quality control and the use of leak detection systems such as electrical leak location surveys and vadose zone monitoring;
- Implementing well planned water and air monitoring systems;
- Incorporating concurrent closure of facilities as they reach their useful life (e.g., closing tailings cells as they fill, and using small cells to allow them to fill quickly);
- Decommissioning and closing older facilities, especially TSFs with containment systems older than about 20 years; and,
- Aggressively controlling fugitive dust from the tailings, ore stockpiles, truck haulage routes and other areas to limit contamination of adjacent lands.
- Robinson, P., "Uranium Mill Tailings Remediation Performed by the US DOE: An Overview," prepared by the Southwest Research and Information Center, Albuquerque, New Mexico, 2004.
- 10CFR40, Title 10, Ch. I, Part 40, Appendix A, Code of Federal Regulations, "Criteria Relating to the Operation of Uranium Mills and the Disposition of Tailings or Wastes Produced by the Extraction or Concentration of Source Material From Ores Processed Primarily for Their Source Material Content," as amended June 2002.
- U.S. DOE Fact Sheet, "Monticello, Utah, Disposal and Processing Sites," Office of Legacy Management (undated), and supporting documents at www.LM.doe.gov/land/sites/ut/monticello/monticello.htm.
- Native American Times, "EPA to Spent $2.5M Cleaning Uranium on Navajo, Hopi Reservations," Sept. 21, 2010. www.nativetimes.com/index.php?option=com_content&view=article&id=4274:epa-to-spend-25m-cleaninguranium-on-navajo-hopi-reservations&catid=56&Itemid=32.
- Engineering News Record, "Construction Cost Indices," 2010. enr.construction.com/economics.
- UMTRCA, "Uranium Mill Tailings Radiation Control Act of 1978," (P.L. 95 604), 1978.
- U.S. EPA, "Evapotranspiration Landfill Cover Systems Fact Sheet," EPA 542-F-03-015, September 2003.
- Utah DRC, "Renewal Application for Radioactive Materials License (RML) No. UT1900479; Health Physics Interrogatories–Round 2; Engineering Comment Interrogatories–Round 1," Utah Dept. of Radiation Control, DRC2009-006502, submitted November 2009. www.radiationcontrol.utah.gov/Uranium_Mills/IUC/Denison_IUC/reclamation%20plan/reclam_plan_2.pdf
- U.S. DOE, "Decommissioning of U.S. Uranium Production Facilities," DOE/EIA-0592, Dist. Cat. US-950, February 1995.
Mark E. Smith, P.E., R.M. SME, is the founder of Vector Engineering, Inc. and currently president of RRD International Corp. He is a geotechnical and civil engineer with 30 years experience in mine waste management. He has worked on uranium operations in the United States, Australia, South America and Africa. He can be contacted at: [email protected]