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Rifle Mills (Old and New) Mill Sites
Garfield County, Colorado
| Years of Operation |
Status of Mill
or Plant Site |
Uranium Ore
Processed
(Million Short Tons) |
Production
(Million Pounds U3O8) |
| 1924-1932, 1942-1972 |
Decommissioned |
2.70 |
16.54 |
Remediated
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) |
| 166 |
71 |
3.76 |
2,738 |
760 A |
119.17 |
Location: The Rifle (Old and New) Mill sites are located near the town of Rifle in Garfield County, Colorado.
Background: The Old Rifle mill was situated on a 24-acre parcel on the north side of the Colorado River about 0.3 miles east of Rifle, Colorado. The plant was built by the Standard Chemical Company in 1924 and operated until 1928. In the early 1920s the domestic radium industry collapsed, and domestic uranium-vanadium ores were treated mainly for vanadium recovery. The uranium values were discharged along with the mill tailings. The United States Vanadium Company purchased the Rifle plant in 1928 and used it to recover vanadium from roscoelite ore until 1932, when an ore shortage forced its closing. In 1942, Union Carbide Corporation (UCC, which had acquired U.S. Vanadium and the mill) reactivated the mill for vanadium production in support of the war effort. In 1947, the Atomic Energy Commission signed the first of four contracts with UCC for uranium procurement, and the milling process was modified to allow recovery of uranium and vanadium by a sulphuric and hydrochloric-acid leaching process. From October 1947-December 1957, the Old mill processed ore at about 200 tons of ore per day (TPD) and treated nearly 0.7 million tons ore averaging 0.35 percent U3O8 and 1.59 percent V2O5. The mill’s raw ore feed came mainly from company-controlled mines and independent miners in western Colorado. Old vanadium tailings remaining on the site from earlier operations were reprocessed at the mill to recover uranium and residual vanadium. From the combined mill feed materials (ore and tailings), uranium recovery averaged 85 percent and vanadium averaged 69 percent. The AEC purchased all U3O8 produced and 27 percent of the V2O5 during the AEC-contracts period (1947-1957). Of the 0.7 million tons of tailings generated during the AEC uranium contracts period, about 0.4 million tons eventually were moved to the New Rifle mill and reprocessed for uranium and vanadium. The remaining tailings pile, about 0.3 million tons, stood about 33 feet tall and covered 13 acres at the old mill site. In 1967, UCC stabilized the tailings pile in accordance with the State of Colorado regulations. At that time, the pile was reshaped, covered with a 6-inch layer of soil, and seeded with native grasses. The Old Rifle Mill continued to operate during the period of construction of the New Rifle Mill.
The New Rifle Mill was built on a 300-acre parcel located about 2 miles west of Rifle just north of the Colorado River. It began operation in January 1958 at a nominal capacity of 400 TPD. Mill feed consisted primarily of ore from both company-controlled mines and independent miners in western Colorado plus uranium concentrate (slimes and chemical precipitates) from UCC's upgrader plants located at Slick Rock, Colorado, and Green River, Utah (1957-1961), lignite-ash product from the Belfield, North Dakota, ashing facility (1965-1967), and other tailings and residue materials. The new Mill produced uranium concentrate for sale to the AEC through December 1970. During the period of AEC contracts, the mill averaged 400 TPD throughput and treated a total of 1.8 million tons of ore that contained 8.4 million pounds U3O8 and 76.7 million pounds V2O5. Other mill feed, upgrader ore concentrates, lignite ash, tailings, and residues, contained an additional 4.5 million pounds U3O8 and 65.4 million pounds V2O5. Over the years 1958-1970, recovery from the combined mill feed averaged 90 percent or uranium and 83 percent for vanadium. About 96 percent of the uranium concentrate from the mill was purchased by the AEC. All of the mill's vanadium production was delivered to the commercial market. At the termination of UCC's last AEC-procurement contract (December 1970), there were about 2.5 million tons of tailings impounded at the New Rifle Mill site. The mill continued to produce uranium during 1971 and 1972 for the commercial market. At that time, the tailings pile at the new mill site contained about 2.7 million tons of tailings in two piles that covered an area of about 32 acres and stood about 65 feet above the surrounding site. From 1973-1984, the vanadium circuit at the mill was used to treat vanadium solutions trucked from UCC's mill at Uravan, Colorado. This vanadium recovery operation did not result in the addition of tailings to the existing tailings pile. Prior to 1982, UCC had covered the tailings piles with soil and had seeded, fertilized, and irrigated them to stabilize the steep slopes by establishing a vegetative cover. This was only partly successful, and the piles eventually were impacted by wind and water erosion.
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UMTRA Surface Remediation: Both the Old and New Rifle Mill sites were cleaned up as one project by the Department of Energy (DOE). In Phase I (September 1988-September 1989), hazardous materials (asbestos, industrial chemicals, and other materials) were collected and isolated. The unstable and unsafe mill buildings and structures were demolished. The residual vanadium-contaminated materials were shipped for reprocessing at a vanadium refinery. All non-radioactive hazardous materials were relocated to a licensed disposal facility. Phase II (1992-1995) included relocation of the contaminated uranium mill tailings, plant debris, contaminated soil from 113 vicinity properties, and other radioactive materials to the Estes Gulch Disposal Cell site. The cell is located about 6 miles north of the town of Rifle. The former processing sites were backfilled with uncontaminated soil to elevations compatible with the nearby natural surface, recontoured to assure proper surface drainage, and seeded with range grasses.
Disposal Area: In 1994 and 1995, the DOE relocated about 3.8 million cubic yards of mill tailings and other radioactively contaminated materials from the old and New Rifle Mill sites for permanent storage at the newly built Estes Gulch Disposal Cell site. This quantity includes about 193,000 cubic yards of contaminated materials removed from the 113 Rifle vicinity properties. The disposal cell is sited partly below grade. The cell is covered with a 11.5-foot thick multilayered cap. A 1.5-foot thick radon/infiltration barrier consists of a 0.5-foot thick layer of compacted clay placed directly on the radioactive materials; this was next covered by a 1.0-foot thick layer of clay amended with 4 percent bentonite. The radon barrier is covered (in succession) by a 0.5-foot thick frost barrier, a 0.5-foot thick coarse-grained drainage layer, a freeze-thaw layer that averaging 7.5 feet in thickness and consists of compacted silty sand, and a 0.5-foot thick bedding layer of drainage aggregate. A 1-foot thick layer of riprap caps the cell to provide protection against erosion and burrowing. The disposal cell is about 87 feet thick from its highest to lowest points, and it stands nearly 80 feet above the surrounding terrain. Construction on the cell was completed in 1996, and the cell was licensed by the Nuclear Regulatory Commission in 1998. The Estes Gulch Disposal Cell covers 71 acres of a 205-acre tract that was transferred to the DOE in August 1991 by the Bureau of Land Management.
Responsibility for Remediation: U.S. Department of Energy, 90 percent; State of Colorado, 10 percent.
Stewardship: The Rifle (Old and New) Mill sites and the Estes Gulch Disposal Cell site are being managed under the DOE’s Long-Term Surveillance and Monitoring (LTSM) Program in accordance with the approved site specific plans. The former mill sites were deeded to the State of Colorado, which has since transferred ownership to the local government for public use with restrictions. DOE will be responsible in perpetuity for the safety and integrity of the Estes Gulch Disposal Cell site.
Groundwater Program: At the Old Rifle Mill site, processing of uranium and vanadium ores resulted in contamination of groundwater in the alluvial aquifer below the mill site. Contaminated groundwater most likely seeps downgradient via a subsurface discharge area where it enters into the Colorado River water and is dissipated by the natural river flow. Natural flushing action of groundwater will, over time (estimated 100 years), reduce the levels of contaminants, that include arsenic, selenium, uranium, and vanadium. The groundwater at the mill site is not a source of drinking water. The proposed DOE groundwater compliance strategy for the old mill site is to perform verification groundwater monitoring to determine whether natural flushing is reducing the contaminant levels as predicted, perform remediation only for potential health-risk contaminants, and to establish institutional controls in order to discourage use of contaminated groundwater. In 2008, responsibility for groundwater remediation and institutional-control maintenance will transfer from the UMTRA Groundwater Project to DOE’s LTSM Program. Annual groundwater monitoring will be performed by DOE until 2050. In addition, DOE will continue groundwater characterization and modeling studies through 2010 and afterward will conduct routine sampling at 5-year intervals. To the DOE’s knowledge, domestic wells located north and up-gradient from the mill site are not impacted by contamination.
At the New Rifle Mill site, groundwater beneath the site and westward for a distance of about two miles downgradient along the north flood plain of the Colorado River is contaminated with a suite of base metals, including radium, uranium, vanadium, and net gross alpha radiation. Testing has indicated that the Colorado River water has not been impacted. The contamination is attributable to the former processing of uranium and vanadium ores at the mill site. The proposed compliance strategy is similar to that for the Old Rifle Mill site. Groundwater at the site is not a source of drinking water, and natural flushing action will, over time (up to 100 years), reduce the contaminant levels. Thus, DOE anticipates that an active groundwater remediation program will not be required. DOE will seek alternate concentration limits for some constituents. Whether vanadium will be dissipated by natural groundwater flushing or will require remediation will be determined in a pilot study. In 2008, responsibility for groundwater remediation and institutional-control maintenance will transfer from the UMTRA Groundwater Project to DOE's LTSM Program. Annual groundwater monitoring will be performed by DOE through 2050 or until Federal standards are achieved. In addition, DOE will continue groundwater characterization and modeling studies through 2010 and afterward will conduct routine sampling at 5-year intervals.
Under the LTSM Program requirements, DOE conducts annual inspections of the Estes Gulch Disposal Cell and is responsible for monitoring water levels in two standpipes installed in the lower part of the disposal cell. The design of the cell promotes rapid runoff of precipitation and thereby minimizes leachate action. A leachate-collection system was installed at the toe of the cell to intercept any transient pore water discharge from the cell. It is anticipated that the transient drainage volumes will be less than the regulatory thresholds and that no treatment will be required.
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