|
Edgemont Mill Site
Fall River County, South Dakota
| Years of Operation |
Status of Mill
or Plant Site |
Uranium Ore
Processed
(Million Short Tons) |
Production
(Million Pounds U3O8) |
| 1956-1974 |
Decommissioned |
1.98 |
6.86 |
Mill/Plant Area
(Acres) |
Disposal Cell
Area
(Acres) |
Disposal Cell
Radioactive
Waste
Volume
(Million Cubic Yards) |
Disposal Cell
Total Radioactivity
(Ci, 226Ra) |
Disposal Cell
Average Tailings
Radioactivity
(pCi/g, 226Ra) |
UMTRA Project
Final Cost
(Million Dollars) |
| 360 |
100 |
3.00 |
527 |
NA |
5.41 |
Location: The former mill site mill is located immediately east of Edgemont, Fall River County in southwestern South Dakota.
Background: Sandstone-type uranium ores were discovered in the Black Hills area north of Edgemont, South Dakota, in mid 1951 and north of Carlile, Wyoming, in early 1952. Exploration by the Government and private firms developed sufficient ore reserves by 1955 to justify a mill. Mines Development, Inc. (MDI), began construction of the uranium mill in 1955 on a site adjacent to an ore buying station operated by the U.S. Atomic Energy Commission (AEC). At startup in July 1956, the mill’s initial throughput capacity was 250 tons of ore per day (TPD); this was increased to 500 TPD by mid 1957. In early 1955, MDI had contracted to produce uranium for the AEC, and the mill supplied uranium under additional contracts through December 1968. In July 1956, MDI purchased the AEC ore buying station with its accumulated stockpile of uranium ore. From 1956 to 1960, the mill did not recover vanadium (from the carnotite-type ore), and vanadium slime tailings from the mill were impounded in a pond separate from the mill’s coarse tailings pond. In 1960 and afterward, MDI recovered both uranium and vanadium. Recovery of other metals at the mill was unimportant. During the period of AEC deliveries, about 500 TPD of ore averaging 0.20 percent U3O8 was processed, and the total of ore treated was more than 1.6 million tons. About 99 percent of the uranium production in that period was purchased by the Government. All of the vanadium production was sold in the commercial market. From 1969 to 1974, the mill produced uranium and vanadium for commercial market sales. The old vanadium slime tailings also were reprocessed beginning in 1972 for their vanadium values. In mid 1974, the Tennessee Valley Authority (TVA) acquired the mill site and plant from Susquehanna-Western, Inc., parent firm of MDI, along with rights to several uranium properties. TVA, based on economic and other factors, decided to not restart the mill. It permanently closed the mill in August 1974.
Ore feed for the mill, which operated mainly as a “custom” mill, came largely from independently operated mines in the Black Hills area of South Dakota and Wyoming. Carnotite-type ores (shallower, oxidized zone) and uraninite-coffinite ores (deeper, reduced zone), were the primary uranium minerals. In the early years, some ore was shipped from mines in the Powder River Basin area of Wyoming and from Washington State, and uraniferous ash from open-field burning of lignite ore was also fed to the mill. At first, the burning of lignite ore was done in the mining area near Slim Buttes, South Dakota. Later, stockpiled lignite ore was shipped to the Edgemont mill site and burned there in linear heap piles.
|
|
In 1979, decommissioning plan was prepared by TVA for the Title II mill site. The U.S. Nuclear Regulatory Commission (NRC) issued a Draft Environmental Statement (DES) for the facility in September 1981. NRC, under the National Environmental Policy Act of 1969, permitted the decommissioning to proceed, subject to conditions as specified in the DES. In March 1983, TVA adopted the final environmental impact statement for decommissioning of the mill site. Decommissioning work began at the mill site in 1986 and reclamation was completed by 1989. TVA removed or decontaminated uranium mill buildings, removed tailings sands and slimes, and removed the contaminated soil from the mill site. Surficial soil was also removed from a nearby forest and open area found to be contaminated by windblown tailings. The areas excavated during mill-site cleanup were backfilled with clean soil, graded for proper drainage, and revegetated. All reclaimed radioactive materials, including mill debris, tailings, and soil, were impounded in an engineered disposal cell constructed to ensure containment of the low level radioactive wastes. TVA estimated that the cost of its decommissioning project was about $33 million. (This amount is not included in the “Decommissioning Final Costs” item in the accompanying summary table.)
UMTRA Surface Remediation: In January 1983, the UMTRCA legislation was amended to authorize the DOE to perform remediation of identified vicinity properties in Edgemont, South Dakota. In late 1984, the State of South Dakota and the U.S. Department of Energy(DOE) began a project to cleanup 137 vicinity properties at Edgemont. These properties included residences, commercial buildings, and open land identified in the DOE radiometric survey as contaminated with residual radioactive materials from the mill site. The radioactive materials were excavated and relocated to the Edgemont Disposal Cell for permanent stabilization. No further reclamation of the former Edgemont mill site was done by the DOE under the UMTRA Program. The site has since been released for general use.
Disposal Area: The Title II Edgemont disposal cell was built by TVA in 1989 to encapsulate uranium mill tailings and other contaminated waste material from the mill site. The base of the cell is in a thick impermeable shale sequence. The NRC-approved disposal cell is located about 2 miles southeast of former mill site. An estimated total of 5.4 million tons of contaminated material was moved to the disposal cell during in the TVA-funded decommissioning project. This includes some 2.5 million tons of uranium mill tailings from the 11 separate tailings impoundment ponds that covered about 125 acres at the original 213-acre mill site. Residual radioactive materials removed from the Edgemont vicinity properties during the DOE-State cleanup project were co-located with the uranium mill tailings and other contaminated materials removed from the mill site and stabilized in the Edgemont disposal cell. In 1996, the disposal cell, with NRC approval, was placed under authority of the general license for long-term custody and care. The engineered disposal cell has a 9-foot thick cap built up of the following layers: a 3-foot thick layer of compacted clay covers the radioactive materials and serves as the radon barrier and minimizes percolation of rainwater through the cell; a 5-foot thick layer of compacted soil provides frost protection; and a 1-foot thick layer of topsoil. Native grass species were planted on the cell cap to prevent soil erosion. When work on the cell was completed, the cell site became eligible for transfer to DOE for custody and long-term care. TVA made a one-time payment to the U.S. Treasury to cover monitoring and maintenance costs, and in June 1996, the Edgemont disposal cell was transferred for long-term stewardship activities.
Responsibility for Remediation: U.S. Government, 90 percent, and State of South Dakota, 10 percent.
Stewardship: The Edgemont disposal cell is being managed under the U.S. Department of Energy’s Long-Term Surveillance and Monitoring Program in accordance with the approved site specific plan.
Groundwater Program: The disposal cell site is subject to Title II of UMTRCA, and the Government is responsible for the site’s long-term care and monitoring. In the vicinity of the disposal cell, the uppermost groundwater aquifer is located below a 300-foot thick sequence of impermeable shale strata. This precludes the need for groundwater monitoring at the site. Long-term stewardship activities include annual site inspections and maintenance as needed. Grazing of the site is permitted to promote growth of a healthy cover of vegetation.
Historical Note: On June 27, 1996, the Nuclear Regulatory Commission staff terminated the site-specific license for the Tennessee Valley Authority's (TVA's) Edgemont, South Dakota uranium mill tailings site. This is the first license terminated for a Uranium Mill Tailings Radiation Control Act, Title II facility.
|
|
