The Monticello Radioactively Contaminated Properties site spans about four square miles in and around Monticello, Utah, and covers 424 private and commercial properties. Radioactive tailings from the nearby Monticello Mill Tailings site were spread across these properties, used as fill, backfill for utilities and foundations, and mixed into concrete, plaster, and mortar for driveways, sidewalks, and other structures. The site was placed on the National Priorities List in June 1986 and was later deleted from that list in February 2000 after cleanup was finished.
Three radioactive contaminants drive the cleanup: radium-226, radon-222, and thorium-230. These were found in solid waste across the original properties area. People can be exposed through ingestion, direct contact, or inhalation of radon gas. EPA assessments show that human exposure is currently under control across the entire site, with no unacceptable exposure pathways remaining.
The U.S. Department of Energy led cleanup under a Federal Facilities Agreement with EPA and the state of Utah. Work focused on excavating and removing contaminated tailings, soil, and construction materials. Contaminated material was disposed of at a repository about one mile south of the former mill. Cleanup was organized into eight operable units covering different geographic areas. Remedial action on the original properties ran from 1984 to January 1997. Work on inclusion, disputed, non-radioactive waste, Hall's Ditch, refusal, site boundary, and supplemental standards properties wrapped up between 1998 and August 1999. Overall construction was complete by September 1999. The site achieved sitewide ready for anticipated reuse status in June 2006, confirming all cleanup goals have been met for current and future land uses.
EPA has conducted five-year reviews regularly to verify the remedy stays protective. The most recent review was completed in June 2022, and the next is estimated between June and August 2027. Today the site includes residential neighborhoods, a commercial district, municipal offices, churches, parks, and schools. As of December 2024, it supported 98 on-site businesses employing 618 people and generating an estimated $44,388,852 in annual sales revenue.
Community members can review site records at the public information repository at 1665 South Main Street in Monticello, Utah. The U.S. Department of Energy's Grand Junction Office also maintains administrative records related to the site.
