Monticello Mill Tailings (USDOE)

Overview

From 1942 to 1960, a uranium and vanadium mill in Monticello, Utah processed material for the U.S. nuclear weapons program. That milling work contaminated soil, surface water, and groundwater across the site and nearby properties. The site was added to the National Priorities List on November 21, 1989, and EPA, the U.S. Department of Energy (DOE), and the Utah Department of Environmental Quality (UDEQ) work together under a Federal Facilities Agreement to carry out cleanup.

EPA identified 33 contaminants of concern at the site. These include radioactive substances such as uranium isotopes, radium-226, and radon, along with heavy metals including arsenic, lead, selenium, and vanadium. Groundwater and surface water hold dissolved metals and salts such as arsenic, manganese, molybdenum, nitrate, selenium, sodium, sulfate, uranium, and vanadium. Solid waste at the mill site contains several of those same materials plus copper and zinc.

Cleanup is organized into four operable units covering the mill site, peripheral properties, groundwater and surface water, and sitewide coordination. Workers excavated contaminated soil and debris and placed them in an on-site repository between 1991 and 2004. Peripheral properties were partially deleted from the National Priorities List in October 2003. For groundwater, a permeable reactive barrier was installed to stop contamination from spreading beyond the mill-site boundary. Groundwater extraction and treatment, monitored natural attenuation, hydraulic control, and institutional controls restricting groundwater use and zoning round out that part of the remedy. Final remedial action for the groundwater and surface water unit ran from May 2014 to June 2016.

As of the most recent five-year review, completed in June 2022, human exposure to contamination is under control and contaminated groundwater migration is stabilized. Physical construction across the site is complete, but the site is not yet ready for full anticipated reuse. Land-use restrictions and cleanup goals still need to be fully achieved in some areas. DOE transferred 383 acres of the former mill site to the City of Monticello in June 2000 through the federal Lands-to-Parks program for use as a public park. By 2004, DOE and the city had also restored three backwater wetlands along Montezuma Creek. The site is estimated to reach anticipated reuse between September and November 2027, when the next five-year review is also scheduled.

Community members with questions can contact the EPA Remedial Project Manager. For state-related questions, contact UDEQ. DOE inquiries can go to the Monticello Area Project Manager. Site documents are available at a public repository at 1665 South Main Street in Monticello, at the DOE Grand Junction Office, or at the EPA Superfund Records Center in Denver.