Rio Algom - Ambrosia Lake

1.0 Site Identification

Type of Site: Uranium Recovery Facility
Location: Grants, NM
License No.: SUA-1473
Docket No.: 40-8905
License Status: Reclamation and Decommissioning
Project Manager: Thomas Lancaster

2.0 Site Status Summary

The Ambrosia Lake West site (“the facility”) is a uranium mill tailings site in the Ambrosia Lake uranium district of New Mexico. It is located approximately 25 miles north of Grants, New Mexico (Figure 1). The mill was built by the Kermac Nuclear Fuels Corporation in 1957 and historically consisted of the mill site proper, uranium mill tailings ponds, and associated outlying evaporation ponds. The mill began processing uranium ore in 1958. By 1985, when the mill was placed on standby status following a drop in uranium prices. The tailings impoundment at the facility contains 33 million tons of uranium ore and covers an area of approximately 370 acres.

Figure 1: Map of the Ambrosia Lake Area

Figure 1: Map of the Ambrosia Lake Area

The site was acquired by Rio Algom Mining, LLC (RAML) in 2001. The site status changed from standby status to reclamation status in August 2003 to reflect the licensee's intent to begin full demolition and reclamation of the site leading to termination of the specific license. The mill was demolished and disposed of in the tailings impoundment in late 2003. The demolition was completed in accordance with a mill demolition plan approved by NRC in 2004.

Uranium mill tailings generated during the Facility’s operational period were disposed within the footprint of historical ponds 1 and 2. Disposal cell 1, which overlies historical pond 1, was completed in 1998, and contains approximately 30 million tons of uranium mill tailings covering 260 acres. Disposal cell 2, which overlies historical pond 2, was completed in 2016 and contains approximately 3 million tons of uranium mill tailings covering 90 acres. Additionally, soil affected by windblown uranium mill tailings is expected to be placed into another, yet to be submitted, disposal cell.

Figure 2: Major Features of the Former Ambrosia Lake West Mill

Figure 2: Major Features of the Former Ambrosia Lake West Mill

Former ponds 4–10 have been reclaimed using the Facility’s alternate release criteria (ARC) remedy. The ARC remedy requires the application of clean fill and a rock cover within historical pond footprints to stabilize pond residues and maintain public doses at levels that are both As Low As Reasonably Achievable (ALARA) and less than the dose resulting from exposure to radionuclides at the concentrations stipulated in Criterion 6(6) of 10 CFR 40 Appendix A. The ARC remedy is only applied in parts of the Facility where it is possible to maintain permanent institutional controls.

Former ponds 11–21, referred to as the Section 4 Pond Area, have been reclaimed by the excavation and removal of pond-impacted sediment to disposal cell 2. In 2017, RAML submitted a dose assessment to NRC demonstrating that concentrations of 11e(2) byproduct material within the historical pond footprints are ALARA and would result in a dose to a hypothetical future member of the public less than that received as a result of exposure to the concentrations stipulated in Criterion 6(6) of 10 CFR 40 Appendix A. In the same 2017 submission, RAML requested a partial license termination for former ponds 11-21. The partial site release request was withdrawn in 2020 at a time when EPA actions for mine-affected areas surrounding the RAML site were not yet clarified.

Areas surrounding the disposal cells, possibly including land adjacent to the former Ambrosia Lake West mill, have been affected by windblown tailings. Windblown remedial work has been performed intermittently since 3003 and is on-going. Final status surveys following the 5-point soil sampling grid approach laid out in the 2006 Soil Decommissioning Plan did not meet the required criteria. RAML and NRC held a public meeting on January 23, 2019. RAML proposed an alternative approach based on a Rank Set Sampling (RSS) method to meet the criteria. Submittal and a request for approval of a revised Soil Decommissioning Plan has not yet occurred. The remedy for windblown-affected areas consists of excavation and disposal of affected soil in a disposal cell, the design of which has not yet been submitted to NRC.

The NRC approved a groundwater corrective action program for the Ambrosia Lake West mill in 1989. In 2000, RAML submitted alternate concentration limit (ACL) petitions for the Facility’s alluvial and uppermost bedrock units to NRC. Following approval of the Facility’s ACLs in February of 2006, RAML ceased its groundwater corrective action program and began a groundwater stability monitoring program, which is on-going. Field work based on a 2017 workplan that would support a future supplemental ACL request is ongoing.

Figure 3: Monitoring Well Locations Stipulated in the Ambrosia Lake West Radioactive Material License

Figure 3: Monitoring Well Locations Stipulated in the Ambrosia Lake West Radioactive Material License

In 2017, RAML terminated the site environmental monitoring program with the exception of radon monitoring. The cost for decommissioning is estimated to be approximately $16 million.

3.0 Major Technical or Regulatory Issues

  • Extent of windblown soil contamination, including potentially offsite, and remediation;
  • There are comingled mining and milling related site waste that the NRC and EPA are working together on.

4.0 Estimated Date for Closure

2030

Page Last Reviewed/Updated Wednesday, March 24, 2021