Region 8

Monticello Mill Tailings (USDOE)

Site location map Site Type: Federal Facility Final NPL
City: Monticello
County: San Juan
Street Address: T33S-R23E Sec 36% T33S-R24E Sec 31
ZIP Code: 84535
EPA ID: UT3890090035
SSID: 08E4
Site Aliases: AEC Millsite
Congressional District: 3

Site Status & Updates

The cleanup is being addressed through a Federal Facilities Agreement. The US Department of Energy (DOE) is the lead federal agency. EPA placed the site on the National Priorities List (NPL) in 1989.

Soil contamination has been removed from the former mill site and peripheral properties, except where supplemental standards have been applied. Restoration of the mill site was completed in 2001. The final remedy for surface and groundwater was selected in 2004.

This site, except for the surface- and groundwater operable unit, was transferred to DOE's Long-Term Surveillance and Maintenance (LTSM) program in 2001. Under the LTSM program, the repository and properties granted supplemental standards will be monitored and maintained to make certain that the selected remedies remain protective. The most recent five-year review of the remedies was completed in 2012.

Site Description

The Monticello Mill Tailings site, a former U.S. Department of Energy (DOE) processing facility, lies in the Montezuma Creek Valley, east of the Abajo Mountains in southeastern Utah. The former mill site, on 78 acres of land, is bordered by the City of Monticello.

The mill was constructed by the Vanadium Corporation of America in 1942. In 1944 the mill began production of a uranium/vanadium sludge for the Manhattan Engineering District. In 1948, the US federal government bought the site. Mill operations stopped and tailings were stabilized in1960. In1964, the mill was dismantled.

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Site Risk

The groundwater and surface water are contaminated with uranium, as well as its radioactive decay products, thorium 230, radium 226, radon 222 and heavy metals from tailings deposited on the site, including arsenic, selenium, vanadium, molybdenum, manganese, etc. Exposure to uranium through contact with groundwater may be a potential threat to the health of individuals in the vicinity.

The City of Monticello has its own water system, supplied by water from springs located on the flanks of the Abajo Mountains. The domestic water source for those people living outside the city limits is groundwater drawn from wells completed in the Burro Canyon Formation. There is no known contamination of the domestic water supplies attributable to contamination from the site.

Media Affected Contaminants Source of Contamination
soils, surface water, groundwater, sediment, sediment, solid waste uranium, thorium 230, radium 226, radon 222 and heavy metals including arsenic, selenium, vanadium, molybdenum, manganese uranium milling operations

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Cleanup Progress

Former Mill Site and Tailings Piles

Construction of the repository was initiated in 1995, and the excavation, transportation and placement of contaminated material began in 1997. An evapo-transpiration cover was constructed on the repository and revegetated.

DOE completed the transfer of 383 acres of land to the City of Monticello in 2000. DOE has also entered into a Cooperative Agreement with the City of Monticello, as the city will be responsible for final restoration of the mill site. Restoration of one mile of Montezuma Creek and five acres of wetland was completed in September 2001. About 150 acres, including the former mill site, were reseeded.

Peripheral Properties

Thirty-four peripheral properties with contamination have been identified. Contractors excavated contaminated materials, moved them to the repository, and revegetated disturbed areas. In October 2003, 22 of the peripheral properties were deleted from the NPL.

Surface Water and Groundwater

In 1998, the DOE completed an investigation of surface water and groundwater and the impact to human health and the environment from contaminated soils and sediments that have been transported downstream by Montezuma Creek. An interim remedial action Record of Decision was signed in September 1998. The interim remedial action includes:

  • Institutional controls to restrict the use of contaminated groundwater
  • Treatment of contaminated surface and groundwater during source removal
  • Monitoring of the contaminated ground-water system
  • Construction of a permeable reactive-treatment wall for groundwater at the mill-site boundary

A removal action of hot-spot contamination in the Montezuma Creek flood plain has been completed downstream from the mill site. Supplemental standards are in place, and the Utah state engineer has placed a restriction on the construction of any groundwater wells within the contaminated plume. In 1999, a PeRT wall (permeable reactive treatment wall) was complete down-gradient of the mill site. This is a full-scale treatability study to determine the effectiveness of the reactive barrier to remove contaminants from the groundwater.

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Site Documents

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Fourth Five-Year Review Report (PDF), June 2012 (144 pp, 5.6 MB)

Fact Sheet: Monticello, Utah, Disposal and Processing Sites (PDF), April 2009 (4 pp, 517 K)

Fact Sheet: Partial Deletion of Monticello Mill Tailings Site From the National Priorities List (PDF), July 2003 (3 pp, 587 K)

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Vera Moritz
Remedial Project Manager
U.S. Environmental Protection Agency, Region 8
1595 Wynkoop Street (EPR-F)
Denver, Colorado 80202-1129
800-227-8917 ext. 312-6981 (toll free Region 8 only)


Jalena Dayvault
Monticello Area Project Manager
U.S. Department of Energy
Grand Junction Office
2597 B-3/4 Road
Grand Junction, CO 81503
970-248-6023 FAX

Site Information Repositories:

Information Repository
Monticello Site
1665 South Main Street
Monticello UT 84535
801-587-2272 FAX

Administrative Record
U.S. Department of Energy
Grand Junction Office
2597 B-3/4 Road
Grand Junction CO 81502
970-248-6040 FAX

EPA Superfund Records Center
1595 Wynkoop Street
Denver, CO 80202-1129
To request copies of administrative record documents call:
800-227-8917 ext. 312-7273 (toll free Region 8 only)


Michael Storck
State Project Manager
Utah Department of Environmental Quality
Environmental Response and Remediation Division
195 North 1950 West
Salt Lake City, UT 84116
801-536-4242 FAX

Dave Allison
Community Involvement Specialist
Utah Department of Environmental Quality
Environmental Response and Remediation Division
195 North 1950 West
Salt Lake City, UT 84116

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U.S. Department of Energy Office of Legacy Management: Monticello, Utah, Disposal and Processing Sites

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