United Nuclear Corp.

Overview

The United Nuclear Corp. site covers about 125 acres near Church Rock and Gallup, New Mexico. It includes a former uranium ore processing mill that ran from 1977 to 1982, leaving behind roughly 3.5 million tons of tailings stored in on-site impoundments. The site was added to the National Priorities List (NPL) in 1983 and has been in active cleanup for over four decades.

Contamination affects both soil and groundwater. Key contaminants in surface soils include radium-226, radon-222, and uranium. Groundwater carries acidic mill tailings seepage along with sulfate, thorium, radium, aluminum, ammonia, iron, and total dissolved solids. Multiple exposure pathways are being monitored, including ingestion and direct contact with contaminated soil and water. Human exposure across the site is currently assessed as under control, though contaminated groundwater continues to migrate beyond the original contamination area. No institutional controls currently restrict use of seepage-impacted groundwater that has moved off the licensed site boundary onto Navajo Trust land to the north.

Cleanup is organized into two main operable units. Operable Unit 1 (OU01) addresses groundwater. A Record of Decision was signed in 1988 calling for extraction wells and evaporation ponds. Several extraction systems were shut down between 1999 and 2000 because they could not sustain pumping or meet cleanup standards. Zone 3 extraction continues at the leading edge of contamination to slow further movement, though those wells foul quickly and last only one to two years. Operable Unit 2 (OU02) addresses surface soils. A Record of Decision was issued in 2013, choosing consolidation of nearby mine waste onto the mill site, excavation, institutional controls, and a soil cover with a bottom liner. Remedial design was completed in 2019, and active surface soil cleanup began on July 2, 2025, under state oversight.

The EPA completed its most recent five-year review on September 29, 2023. That review found the remedy protective of human health and the environment in the short term. The next five-year review is estimated for September through November 2028. Once the Nuclear Regulatory Commission (NRC) Source Materials License is terminated, the Department of Energy will take over long-term care and monitoring. A 1989 Unilateral Administrative Order remains in force, requiring continued groundwater remediation.

Community members can follow site progress through EPA and NRC websites, which host five-year review reports, groundwater corrective action annual reviews, and quality assurance monitoring reports. The EPA held a community meeting on May 9, 2024, at the Gallup Senior Center to discuss the Sixth Five-Year Review results. Site records are available at the Octavia Fellin Public Library in Gallup, the Navajo Nation Navajo Superfund Office in St. Michaels, Arizona, and the New Mexico Environment Department in Santa Fe. Residents with questions can contact EPA staff directly using the information below.