The Monument 2 upgrader plant was constructed in mid 1955 by VCA and operated until July 1964. The nearby openpit mine supplied all plant feed. Low grade ore ranged from 0.04 to 0.09 percent U₃O₈ and 0.4 to 0.8 percent V₂O₅. The upgrader yielded a shipping-grade product assaying 0.25 to 0.30 percent U₃O₈ and 1.5 to 3.0 percent V₂O₅, depending on the feed grade. The upgrader product was shipped to VCA's Durango, Colorado, mill until it was closed in March 1963, and afterward to VCA's Shiprock, New Mexico, mill. Over the upgrader's life, some 1.1 million tons of low grade ore were treated to produce an estimated 0.1 million tons of "slimes" product. The plant handled about 250 TPD, and recovery of uranium and vanadium was 65 to 70 percent. The upgrader used attrition (grinding) and classification (separation of the fines and sand fractions) to concentrate the uranium and vanadium values. Run-of-mine ore was crushed, finely ground, and then treated in wet classifiers to separate the fines fraction (containing most of the uranium and vanadium) from the "barren" sand fraction. After filtering, the fines formed a wet-cake product that was partly dried before being shipped to the mill.

The "barren" sand tailings from the upgrader plant still retained sufficient uranium and vanadium values to warrant retreatment. A batch-leach plant was constructed in early 1964 to reprocess the tailings. It was operated from October 1964 until November 1967 and treated about 1,000 TPD. The tailings were leached with sulfuric acid in large tanks. Solutions were recycled until the desired uranium and vanadium concentrations were achieved. Uranium and vanadium were precipitated using ammonia. The precipitate was filtered, partially dried, and shipped to the Shiprock mill. Estimated overall recovery was 0.2 million pounds U₃O₈ and 2.0 million pounds V₂O₅.

In 1966, heap-leaching of low grade mine-dump material was begun at the Monument 2 site. Mine dump material was crushed to one inch size and placed on polyethylene sheeting. Sulfuric acid solution flowed onto the top of the heap, percolated downward, and was captured in perforated piping at the bottom of the piles. The pregnant solution was recirculated until concentrations of about 1.5 grams U₃O₈ and 7.0grams V₂O₅ per liter were achieved. Ammonia was added to the leach solution to precipitate the uranium and vanadium. The precipitate was filtered, dried, and shipped to the Shiprock mill. Heap-leaching was continued intermittently until late 1967, when all activities were shut down. It is estimated that about 0.1 million tons of low grade dump material were leached.

In late 1967, the Foote Mineral Company succeeded VCA as the lessee and controller of the site. When the original lease for the mine and plant site expired in 1968, control of the Monument 2 mine, plant, and tailings site reverted to the Navajo Nation.

The upgrader, concentrator, and heap-leaching operations at the Monument 2 site generated about 1.1 million tons of tailings and waste residues. When operations were closed in 1967, the old plant buildings were removed. In the late 1970s, two piles of tailings materials, the contaminated foundations of the upgrader and concentrator plants, other structural debris, and contaminated soil remained at the former ore processing site.

UMTRA Surface Remediation: Contamination at the Monument Valley Site (former Monument 2 ore upgrading site) resulted from past ore-processing operations. When operations ended in late 1967, the site covered about 90 acres. Two on-site tailings piles, one about 10 acres and one about 20 acres in size and some 500 feet apart, remained at the site when remedial action began in May 1989. During the site cleanup project, contaminated surface materials from the process tailings piles, leach areas, evaporation pond, structural debris, and associated contaminated soil and wind blown material from 83 acres at the plant site and four vicinity properties were trucked 17 miles from the Monument 2 site and stabilized in the Mexican Hat Disposal Cell near Mexican Hat, Utah. Following remediation, no residual soil with contamination levels exceeding the U.S. Environmental Protection Agency (EPA) standard remained at the site. Overall, about 1.3 million tons of tailings, structural debris, and contaminated soil were transported to the disposal cell. A funding lapse caused the Monument Valley Site cleanup project to be suspended in February 1990. The project was resumed in September 1992 and completed in May 1994.

Disposal Area: (See the Mexican Hat Mill Site page for a information about of the Mexican Hat Disposal Cell.)

Responsibility for Remediation: U.S. Department of Energy, 100 percent.

Stewardship: The Monument Valley Site is managed under the DOE's Long-Term Surveillance and Monitoring (LTSM) Program in accordance with the approved site specific plan. U.S. Department of Energy is responsible for the long-term stewardship activities and funding at the Monument Valley Site. Under a cooperative agreement initiated in 1983 with the Navajo Nation, which owns the land, the DOE has permanent custodial access to the site and is responsible for all costs of assessment and remediation. The Navajo Nation is responsible for site enforcement under the agreement, with DOE responsible for costs incurred by the Tribe relating to the site.  

Groundwater Program: Groundwater sampling at the Monument Valley Site conducted over many years has identified a plume of contaminated groundwater that extends northeastward for about one mile from the Monument Valley Site. The plume is estimated to be up to one-half mile wide and to contain about 4.5 million gallons of groundwater contaminated with chemical and radioactive agents. Contaminants exceeding the EPA maximum concentration limits occur in the two uppermost bedrock aquifers of the Shinarump Member and a younger alluvial/dune sand aquifer. Included are nitrate, radium, uranium, and possibly net gross alpha. Active remediation of the contaminated groundwater is planned for constituents that pose a potential health risk and/or exceed EPA standards. Monitoring of the groundwater condition is conducted by the DOE to further characterize the groundwater system and the contaminants. DOE assumes that an active remediation program could result in compliance with the EPA's groundwater standards by 2013 at the earliest. Routine groundwater compliance monitoring will be required for an indefinite period of time after the active remediation work is completed, according to the DOE.