EPA Superfund Program: UNITED NUCLEAR CORP., CHURCH ROCK, NM

Superfund Site Profile

The 125-acre United Nuclear Corp. site is located near Gallup, New Mexico. The site includes a former uranium ore processing mill and tailings disposal area. Two underground uranium mines formerly operated near the site. United Nuclear Corporation (UNC) operated the former Northeast Church Rock mine, located northwest of the site. Quivira (formerly Kerr-McGee) operated a mine north of the site. The uranium mill on site operated from 1977 to 1982. The facility processed uranium ore using a combination of crushing, grinding and acid-leach solvent extraction methods. Milling produced acidic slurry of ground rock and fluid tailings. Disposal of about 3.5 million tons of tailings took place in on-site impoundments. Facility operations contaminated soil and groundwater. Cleanup activities and monitoring are ongoing.

Current Status
Ground Water Operable Unit (OU01)
Groundwater remedial activities are being conducted by the United Nuclear Corporation (UNC) in accordance with an EPA Unilateral Administrative Order under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA).

The groundwater remedial activities were designed to control tailings seepage in three shallow ground-water zones at the UNC Church Rock Superfund site (Site); the alluvium (referred to as the Southwest Alluvium) and Zones 1 and 3 of the Upper Gallup Sandstone Formation.

The remedy consists of extraction wells to pump contaminated ground water and evaporation ponds for water disposal. Currently, groundwater migration is not under control. The only ground-water extraction system being operated is for Zone 3. The extraction systems for Zone 1 and the Southwest Alluvium are shut off. The Zone 1 extraction system was shut down in 1999 because it had reached its limit of effectiveness in achieving the cleanup levels established by EPA in its 1988 EPA Record of Decision (ROD). Operational results for Zone 1 demonstrated significant declines in pumping rates over time due to insufficient natural recharge of the aquifers. The loss in saturation reached levels that did not support pumping and the systems were shut down. For the Southwest Alluvium, the extraction system provided partial hydraulic containment to tailing-seepage migration, but there was little progress in achieving some Site cleanup standards over time and the system was temporarily shut-off to perform a natural attenuation test.

The Zone 3 system was shut down in 2000 for the same reasons as Zone 1 and because it was accelerating the movement of the contaminated water rather than containing it. However, over the last few years, UNC conducted other tests to enhance the performance of the extraction system for Zone 3 and stop the migration of the tailing seepage-impacted ground water. Those tests were unsuccessful, but operation of extraction wells at the leading edge of the seepage-impacted front was found to slow its advancement. Hence, UNC has continued to operate those wells and, in 2008, drilled new wells further down-gradient to continue to slow the seepage-impacted ground water, to the extent possible.

Due to the dysfunction of the remedy, in 2006, UNC was required to complete a Site Wide Supplemental Feasibility Study (SWSFS). As an interim measure, while the remedy was under re-evaluation, additional extraction wells were installed in 2010 at the leading edge of the advancing seepage-impacted front to continue to collect contaminated water and slow contaminant migration to the maximum extent practicable. Alkalinity amended Mill water was injected in one of the new wells to neutralize tailings seepage fluid. Three of the seven new Zone 3 Extraction wells were taken off line during this latest five-year period due to fouling. Four extraction wells and one Plume Boundary well were operational in 2012. The remedy enhancements in Zone 3 are meant to buffer, intercept, slow down, direct, and extract impacted ground water. The configuration and pumping scheme of the injection-extraction well arrays tries to minimize the withdrawal of background water and the tendency to draw it westward while maximizing the volume of impacted water that is extracted. Extraction wells in Zone 3 have a life expectancy of one to two years due to fouling and extremely low yield (less than one gallon per minute (gpm)).

Background

The United Nuclear Corporation National Priority List Site (UNC Site) is located 17 miles northeast of Gallup, on the southern border of the Navajo Indian Reservation in Church Rock, McKinley County, New Mexico. The Site includes a former uranium ore processing mill (25 acres) and tailings disposal area (100 acres). The tailings disposal area is subdivided into three cells identified as the South Cell, Central Cell, and North Cell. The surrounding lands include Indian Tribal Land, Indian Allotment Land and UNC-owned property. There are two operable units within the UNC Site: the ground water operable unit (OU01) and the surface soil operable unit (OU02). The area is sparsely populated, with the nearest residence located 1.5 miles north of the Site. The land use near the Site is primarily grazing for sheep, cattle and horses.

Four water wells are within a 4-mile radius, the nearest being 1.7 miles northeast of the Site; however, nearby residents generally have used bottled water.

Ground Water Operable Unit (OU01)

EPA signed the Record of Decision for the ground water operable unit (OU01) on September 30, 1988. The contaminants of concern in ground water are acidic mill tailings seepage, total dissolved solids, sulfate, thorium, radium, aluminum, ammonia, and iron. The selected remedy included: containment and removal of contaminated ground water in three shallow ground-water zones utilizing existing and additional wells, evaporation of ground water removed from aquifers, and implementation of performance monitoring and evaluation programs. The tailings cells have been capped with an interim radon barrier cover as part of the reclamation activities directed by the Nuclear Regulatory Commission. Two evaporation ponds have been constructed on top of the cells as part of the EPA’s ground-water remedy.

Background
The United Nuclear Corporation National Priority List Site (UNC Site) is located 17 miles northeast of Gallup, on the southern border of the Navajo Indian Reservation in Church Rock, McKinley County, New Mexico. The Site includes a former uranium ore processing mill (25 acres) and tailings disposal area (100 acres). The tailings disposal area is subdivided into three cells identified as the South Cell, Central Cell, and North Cell. The surrounding lands include Indian Tribal Land, Indian Allotment Land and UNC-owned property. There are two operable units within the UNC Site: the ground water operable unit (OU01) and the surface soil operable unit (OU02). The area is sparsely populated, with the nearest residence located 1.5 miles north of the Site. The land use near the Site is primarily grazing for sheep, cattle and horses.
Four water wells are within a 4-mile radius, the nearest being 1.7 miles northeast of the Site; however, nearby residents generally have used bottled water.

Ground Water Operable Unit (OU01)
EPA signed the Record of Decision for the ground water operable unit (OU01) on September 30, 1988. The contaminants of concern in ground water are acidic mill tailings seepage, total dissolved solids, sulfate, thorium, radium, aluminum, ammonia, and iron. The selected remedy included: containment and removal of contaminated ground water in three shallow ground-water zones utilizing existing and additional wells, evaporation of ground water removed from aquifers, and implementation of performance monitoring and evaluation programs. The tailings cells have been capped with an interim radon barrier cover as part of the reclamation activities directed by the Nuclear Regulatory Commission. Two evaporation ponds have been constructed on top of the cells as part of the EPA’s ground-water remedy.

National Priorities Listing (NPL) History
NPL Proposed Date: 12/30/82
NPL Final Date: 9/08/ 



SITE STATUS

Construction
Complete?
Yes (09/29/1998)
Human Exposure
Status

Under Control
Contaminated Ground
Water Status
Not Under Control
Site-Wide Ready for
Anticipated Use?
No