The Green River disposal site is about 0.5 mile east of the Green River and 1.5 miles southeast of the city of Green River, Utah.

History

Union Carbide Corporation constructed a uranium mill at the site in 1957 and operated it from March 1958 through January 1961. During its three years of operation, the mill processed 183,000 tons of ore and generated an estimated 114,000 cubic yards of radioactive tailings that covered about 9 acres to an average depth of 7 feet.

The U.S. Department of Energy cleaned up the mill site from November 1988 through September 1989, and all mill tailings and other contaminated materials were contained in an on-site disposal cell. The cell also received material from 17 contaminated area properties.

Geology

In the north-central part of the Colorado Plateau, the Green River disposal site is underlain by the Cedar Mountain Formation of Early Cretaceous age. This bedrock consists of sandstone, conglomerate, and shale. Overlying the Cedar Mountain Formation are a few remnants around the site of Dakota Sandstone of Late Cretaceous age that contain minor coaly material and fossil wood.

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The Mexican Hat disposal site is located on the Navajo Nation in southeast Utah, 1.5 miles southwest of the town of Mexican Hat and 1 mile south of the San Juan River. 

History

Texas-Zinc Minerals Corporation constructed the Mexican Hat mill on land leased from the Navajo Nation and operated the facility from 1957 to 1963. Atlas Corporation purchased the mill in 1963 and operated it until it closed in 1965. A sulfuric acid manufacturing plant operated at the site from 1957 to 1970. Control of the site was returned to the Navajo Nation after the lease expired in 1970.

Much of the ore (rock or sediment that contains valuable minerals) brought to the mill contained a large amount of copper sulfide and other sulfide minerals and was processed to recover both copper and uranium. The milling process produced radioactive tailings that were mixed with process water and pumped through a pipeline to two on-site tailings piles — the former lower tailings pile and the former upper tailings pile.

The U.S. Department of Energy cleaned up the surface of the site in 1995. Radioactive materials from the former upper tailings pile, demolished mill structures, and 11 area properties that had become contaminated by mill tailings, were placed in a disposal cell.

Geology

Near the center of the Colorado Plateau, the Mexican Hat disposal site sits on the Halgaito Formation of Early Permian age. This formation consists of reddish-brown sandstone and siltstone deposited in a floodplain environment. Less than 200 feet beneath the site are limestone beds deposited in a marine environment. On the skyline to the east is the Raplee Anticline, an upwarp formed 40 to 70 million years ago, where colorful red and gray beds of the Halgaito and Honaker Trail formations are exposed.

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The Monticello, Utah, Disposal and Processing Sites are located in and near the city of Monticello, in the southeastern corner of the state, about 250 miles southeast of Salt Lake City, Utah.

History

In 1942, the U.S. government, through the Defense Plant Corporation (DPC), provided funding for a mill to be constructed at an ore-buying station that had been built in 1940. The Vanadium Corporation of America (VCA) operated the mill from 1942 into early 1944 to produce vanadium, a steel-hardening element, during World War II. VCA reopened the mill from 1945 to 1946 under lease from DPC. The U.S. Atomic Energy Commission (AEC), predecessor of the U.S. Department of Energy (DOE), obtained the mill in 1948 and it was modified to process ore for uranium. Although government-owned, it continued to be operated by private entities until ore milling was terminated in January 1960. The mill was modified in the early 1950s to process ore for uranium. Milling continued intermittently until the early 1960s, when the mill was dismantled.

Waste gathered through remedial actions is encapsulated in an engineered disposal cell (or waste repository) on DOE property approximately 1 mile south of the former mill site. Disposal of waste was completed in June 2000.

Federal Lands-to-Parks

In 1995, the Monticello Site Specific Advisory Board (SSAB), with the concurrence of the Mayor of the City of Monticello, requested that DOE transfer the former mill site property to the City of Monticello for expansion of the existing nine-hole municipal golf course and other recreational uses. DOE began working through the Federal Lands-to-Parks Program to transfer the former mill site and some adjacent government-owned properties. This program allows state and local agencies to acquire land and facilities provided that they are open to the public and used exclusively for park and recreational activities. Properties transferred under the program must be used according to the terms of the transfer in perpetuity, although the actual terms and conditions may be amended by mutual agreement.

DOE and the City of Monticello signed a Cooperative Agreement in 1998 that established their responsibilities to complete restoration of the transferred property. This agreement required the City of Monticello to complete restoration of the property in accordance with a design that included construction of wetlands, final grading, reconstruction and realignment of Montezuma Creek, revegetation of the entire mill site, and erosion control of steep upland areas. DOE, EPA, and the Utah Department of Environmental Quality approved the design.

In April 2000, the National Park Service approved a use plan for the Monticello property for recreational open space that includes a walking trail and picnic areas. The following June, DOE completed the transfer of the 383.24-acre parcel of land to the City of Monticello through the Federal Lands-to-Parks Program. Today, the former mill site is an open space park open to the public.

Ecology

The disposal cell at the Monticello site is a unique example of ecological engineering. The cell’s cover was designed to be sustainable, working with, rather than against, Mother Nature. It was designed to store moisture in a fine-textured soil “sponge” layer. Moisture is removed from the soil sponge during the growing season by soil evaporation and plant transpiration — which is the movement of water through a plant and its evaporation from leaves, stems, and flowers. A layer of coarse sand placed below the soil sponge increases the water storage capacity of the sponge. Gravel and soil layers help plants to grow and protects the cell from large roots and burrowing animals, such as prairie dogs.

The cell cover was seeded with native plants such as sagebrush, rabbitbrush, wheatgrass, smooth brome, squirreltail, and numerous wildflower species. Wildlife openings in the fence encourage browsing by mule deer and elk. Coyotes, fox, and birds of prey also commonly visit the site, as it is home to small mammals such as voles, mice, and rabbits.

Geology

The Monticello sites sit at the east foot of the majestic Abajo (or Blue) Mountains. The processing and disposal sites are within the central part of the Colorado Plateau. The sites are on the Great Sage Plain subprovince of the Paradox Basin, a low-relief surface that is covered mainly by fine-grained windblown sediments of Pleistocene age. Also covering the Sage Plain surface at the disposal site is coarse fan material shed off the nearby Abajo Mountains to the west in Late Tertiary to Pleistocene time.

East-flowing drainages such as Montezuma Creek at the processing site have cut through the Mancos Shale and into the underlying Dakota Sandstone of Early Cretaceous age that contains some thin coal beds. In the east part of the disposal site in the area of the extraction wells, Montezuma Creek has cut into the Burro Canyon Formation of Early Cretaceous age, and it cuts increasingly older rocks eastward as the canyon deepens.

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