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The Shiprock uranium mill was a uranium mill on the Navajo Nation in Shiprock, New Mexico operated by Kerr-McGee from 1954 until 1963 and by the Vanadium Corporation of America until the mill closed in 1968. The mill, ore storage area, tailings ponds, and tailings piles occupied approximately 230 acres leased from the Navajo Nation. The mill's operations created process-related wastes and uranium tailings, and in 1983, the U.S. Department of Energy and the Navajo Nation entered into an agreement for site cleanup. By September 1986, all tailings and associated materials, including contaminated materials from offsite vicinity properties, were contained in a disposal cell built on top of the existing tailings piles.

The disposal cell and adjacent former mill site sit on a terrace that is trisected by two minor drainages, Bob Lee Wash and Many Devils Wash. At the northeast edge of the terrace, a steep escarpment 50 to 60 feet high forms the boundary between the San Juan River floodplain and the terrace area. The horizontal distance from the disposal cell to the San Juan River is about 600 feet. Groundwater in the terrace area is thought to be a result of human activities. Past milling operations and irrigation in the terrace area are believed to have contributed most of the water in the terrace groundwater system. The floodplain alluvial aquifer is north of the disposal cell in the floodplain area between the San Juan River and the base of the escarpment. In 1961 a test hole was drilled on the terrace about 0.5 mile northwest of the disposal cell area. This hole, drilled to a depth of 1,850 feet, was not capped. Artesian flow from this hole, now known as site well 0648, has continued since 1961 and is currently flowing at a rate of about 64 gallons per minute across the terrace into Bob Lee Wash, which drains to the floodplain and eventually to the San Juan River. Inflow from well 0648 supplies more than half the volume of groundwater in the floodplain. The floodplain aquifer also receives inflow from the San Juan River and from the terrace groundwater system. Past milling operations have left contaminants in the terrace groundwater system and in the floodplain alluvial aquifer. Contaminated groundwater from the terrace has infiltrated the upper few feet of the underlying weathered Mancos Shale bedrock and has migrated into the alluvial aquifer on the floodplain. Terrace groundwater has also surfaced in several places as seeps at the edge of the escarpment and in Bob Lee and Many Devils Washes. The contaminants of concern are ammonia, manganese, nitrate, selenium, strontium, sulfate, and uranium.

The Shiprock UMTRA site is in the Navajo Nation in San Juan County in the northwest corner of New Mexico, approximately 28 miles (mi) west of Farmington (Figure 2–1). The UMTRA site is accessible by Uranium Boulevard, which extends from U.S. Highway 666 eastward about 0.5 mi to the Navajo Engineering and Construction Authority (NECA) facility. The site of the former uranium mill is on the NECA facility. The UMTRA disposal cell, which covers 76 acres, is immediately east of the NECA facility. From the center of the town of Shiprock (junction of U.S. Highways 64 and 666), the disposal cell on the site is about 1 mi to the south, on an elevated, gravel and cobble-covered terrace overlooking the northwest-flowing San Juan River and its floodplain. The site area is south of the San Juan River and extends from the disposal cell about 1 mi to the southeast and 1.5 mi to the northwest.

The disposal cell and adjacent former millsite area sit on an elevated terrace overlooking the floodplain of the San Juan River. The terrace is trisected by two minor north-northeast drainages, Bob Lee Wash and Many Devils Wash. At the northeast edge of the terrace, an escarpment 50 to 60 ft high forms the boundary between the San Juan River floodplain and the terrace area to the south. The crescent-shaped floodplain area immediately north of the disposal cell extends southeast upstream from the U.S. Highway 666 bridge to a point about 1,500 ft downstream from Many Devils Wash confluence. The horizontal distance from the disposal cell to the San Juan River is about 600 ft.

A layer of gray Mancos Shale of Cretaceous age forms the bedrock underlying the entire site. Ground water in the floodplain is hydrologically connected to the San Juan River and receives inflow from an artificial ground water system in the terrace. In the northwest part of the site west of U.S. Highway 666, a distributary channel (former river channel) of the San Juan River is adjacent to the escarpment. The south edge of the site area is marked by the appearance of weathered Mancos Shale that forms a subtle upland area. In the subsurface, this boundary is abrupt in the form of a buried bedrock escarpment that marks the south edge of terrace alluvial material deposited by the ancestral San Juan River.

In this high desert environment, vegetation is sparse in the nonirrigated areas of the terrace and in the upland, and sparse to thick in the riparian environment in the San Juan River floodplain. Some agriculture occurs on the terrace in the northwest part of the site where irrigation is supplied by the Helium Lateral Canal system.

Several thousand people live in the site area south of the San Juan River in the south part of the sprawling unincorporated community of Shiprock. Land use is varied across the site area. Grazing of a few sheep, goats, and cows occurs in the open lands southeast of the NECA gravel pit and in the upland area south of the disposal cell. The only perennial source of surface water available for these animals is the San Juan River. Grazing of some cows and horses also occurs in the fields irrigated by water from the Helium Lateral Canal in the northwest part of the site. No grazing is allowed in the floodplain area immediately north of the disposal cell. Commercial and administrative developments and various housing areas are about 0.5 to 1 mi west of the disposal cell. An elementary school, a high school, and a new site for Diné College (under construction) are just more than 1 mi to the west. No ground water from the floodplain is being used in the site area. The only known ground water use from the terrace area is at the high school property where a well is used for irrigating the school grounds, and about 0.5 mi northwest of the disposal cell where water from a deep artesian well is infrequently used for livestock watering.

The uranium-vanadium mill, known as the Navajo Mill, operated from 1954 to 1968. The site had been leased from the Navajo Nation, and control reverted to the Navajo Nation when the leases expired in 1973. During its operating lifetime, the mill processed about 1.5 million tons of ore, producing about 7.9 million pounds of U3O8 and 35.4 million pounds of V2O5. The mill was initially designed for an acid cure process, in which ore was allowed to “cure” by soaking in a sulfuric acid solution for 12 hours or longer. The acid cure process is designed primarily to recover vanadium. A decrease in the vanadium market about 1 year after the plant opened led to its conversion to an agitation leach process, with recovery of uranium only. Shortly thereafter, a solvent extraction process was added to supplement, and eventually to replace, the original fixed- bed ion exchange process. By 1957, the solvent extraction process had been modified into a two- stage process that included vanadium recovery with a strong acid solution. The two solvent extraction processes used di(2-ethylhexl) phosphoric acid (EHPA) and tributyl phosphate (TBP) in a base of high flash-point kerosene. Alcohol was probably added as a modifying agent, nitrate and ammonium complexes were added as ion exchange strippers to concentrate uranium, and ammonia was used for pH adjustment of the slurry.

Tailings from the washing circuit were pumped to ponds on two tailings piles just to the east. Raffinate from the solvent extraction operation was allowed to evaporate in up to ten unlined raffinate ponds that covered approximately 20 acres just south and southwest of the tailings piles. Water for the milling process was pumped from the San Juan River at an intake about 0.6 mi east-southeast of the mill.

The Shiprock mill was shut down in 1968. Between 1968 and 1973, when the lease on the millsite reverted to the Navajo Nation, some of the mill buildings and most of the equipment were dismantled and placed in the west tailings pile. Shortly after the Navajo Nation assumed control of the site in 1973, the Navajo Tribal Chairman asked officials from the Environmental Protection Agency and other federal agencies for assistance in stabilizing the tailings piles. EPA subsequently surveyed the site and recommended decontaminating the site and stabilizing the tailings. Decontamination work under EPA guidance began in January 1975 and continued until 1980.

Uranium Mill Tailings Radiation Control Act legislation in 1978 specified significant changes to remedial action criteria for former uranium millsites compared with the decommissioning work that had already taken place at the Shiprock site. A series of surface and ground water characterization studies were performed in the early 1980s for preparation of the RAP in 1985. The DOE conducted surface remedial actions in late 1985 and 1986 consisting of removing windblown and water-transported contaminated soils from the area surrounding the millsite and tailings piles and placing this material in an engineered disposal cell on site. The two tailings piles were consolidated and encapsulated to form the disposal cell. A long-term surveillance plan was prepared for the disposal site in 1994. After this plan was approved, the U.S. Nuclear Regulatory Commission issued a license in September 1996 to the DOE–Grand Junction Office for the long-term care of the site; the license also deferred site ground water cleanup to the UMTRA Ground Water Project.

The contaminants of concern (COCs) that have been identified for the Shiprock site are ammonium, manganese, nitrate, selenium, strontium, sulfate, and uranium. During active uranium and vanadium milling, water with tailings from the washing circuit and from yellow-cake filtration was pumped to the disposal area. Although excess solutions were recycled to the plant during the winter months, raffinate was also disposed of by evaporation in separate holding ponds. The milling operations, as noted above, used large amounts of sulfuric acid and ammonia, as well as smaller amounts of organic solvents, which were transported to the tailings and raffinate ponds. Ground water contamination at the site is believed to have resulted from infiltration of the milling fluids, and leaching of ore and uranium mill tailings constituents by mill water and rainwater. Using data from Merritt (1971) for the average flow to the tailings ponds, site evaporation rates calculated from pan evaporation data to estimate losses from the ponds to evaporation, and an estimate of total runoff to the floodplain alluvium from a U.S. Department of Health, Education, and Welfare (1962) study, the SOWP estimated that the cumulative volume of water infiltrated into the terrace alluvium during the 14 years of milling operations was approximately 308 million gallons.

Water has been added to the terrace area of the site from sources other than the Navajo Mill. From 1944 through the 1950s, water was used in a helium-processing plant built by the U.S. Bureau of Mines at the present site of the Shiprock Shopping Center. Starting in the late 1950s, irrigation water was brought to the terrace west area by a siphon from the Hogback Canal, which diverts water from the San Juan River; this siphoned water was distributed into the Helium Lateral Canal system for agricultural use. In 1961 a test hole was drilled on the terrace about 0.5 mi northwest of the disposal cell area. This hole, drilled to a depth of 1,850 ft into the Morrison Formation, was not capped. Artesian flow from this hole, now known as site well 648, has continued since 1961 and is currently flowing at a rate of about 64 gpm across the terrace into Bob Lee Wash, which drains to the floodplain and eventually to the San Juan River. This flow has been beneficial in flushing milling-related contamination from the northwest part of the floodplain.

By 1986, all tailings and waste left by the companies were stored in a "highly engineered disposal cell," which sits on a natural terrace 600 feet away from the San Juan River and a few yards above the water table. In 2000, DOE added fencing and engineered structures to capture contamination, Gil added. The pit is covered with compacted soil and riprap, but is unlined, and monitoring wells show that groundwater contamination from the site is extensive. "The groundwater contaminations include the entire flood plain and terrace areas within the Shiprock UMTRA site," said Madeline Roanhorse, Navajo UMTRA manager, during her presentation. "Water contamination is down to the Mancos Shale aquifer." Roanhorse, whose office provides oversight and technical assistance to DOE, said Shiprock gets drinking water from Farmington Lake, a reservoir of the San Juan River located east of Farmington. The drinking water supply is not affected by the mill site, she explained. To date, DOE has implemented a pump-and-evaporate system to capture groundwater contamination and has partnered with Diné College to research phytoremediation - the use of plants to remove contaminants - at the site.

Former uranium-mill workers and their survivors are now eligible for government compensation due to radiation exposure. A U.S. Energy Department ruling has increased a list from 3 to 20 mill tailings plants where workers may have suffered illness from the job. Newly entitled workers from four uranium mill tailings plants in the Four Corners area can now apply for compensation and medical benefits. According to a news release, the U.S. Department of Labor is notifying newly eligible workers at seventeen plants nationwide about potential benefits. The action follows a decision last month that the Uranium Mill at Shiprock New Mexico falls under the Energy Employees Occupational Illness Compensation Program Act. A subsequent survey identified other plants that met the statutory definition of a controlled radiation facility, dating back to 1942. Three others in Utah, Colorado and Pennsylvania are also due additional benefits for illness claims up to the year 2000. Closest to home, workers at the following Four Corners plants now qualify under the Uranium Mill Tailings Radiation Control Act: In Utah, the Uranium Mills in Monticello, Mexican Hat and Monument Valley. In Colorado, nine plants including Western Slope uranium mills at Gunnison, Naturita, Maybell, Rifle, Slick Rock and Durango, and the Climx Uranium Mill in Grand Junction. In New Mexico, the Shiprock plant and uranium mill at Ambrosia Lake.

According to unofficial estimates of Shiprock's population in 1980, there were 90 people living within .5 mi (.8km) of the site and 2,200 within 1 mi (1.6 km). In 1983, the population of Shiprock was estimated at 8,000. A mix of commerical and residential development exists near the site. A U.S. Public Health Service building, Navajo Engineering and Construction Authority buildings, Abandoned Mine Land Program office buildings, and fairgrounds are immediately west of the former mill site.

VCA later merged with Foote Mineral Company.