Homestake

1.0 General Site Identification

Type of Site:	Uranium Recovery Facility
Location:	Grants, NM
License No.:	SUA-1471
Docket No.:	40-8903
License Status:	Decommissioning
Project Manager:	Melanie Wong

2.0 Site Status Summary

The Homestake Mining Company of California (Homestake), Grants Reclamation Project (GRP), located 5.5 miles northeast of Milan, NM, is a conventional uranium mill site under reclamation (Figure 1). Uranium processing started in the late 1950's and continued until 1990. The GRP is in the decommissioning phase with an ongoing restoration program which began in 1997.

Figure 1: Grants Uranium Mill Site Location Map

Tailings generated from the milling operation were placed on two piles, a large tailings pile (approximately 170 acres and approximately 100 feet high) and a small tailing pile (approximately 40 acres and approximately 25 feet high). The facility has a tailings area of 210 acres with a weight of approximately 22 million tons. The large tailings pile is capped currently with an interim soil cover on its top and a radon barrier and a stone erosion cover on the side slopes. The small tailings pile is also capped by an interim soil cover on its southern portion and is the location of evaporation pond (EP) 1 on the northern two-thirds of the pile. Final radon barriers will be constructed after groundwater remediation is completed. Seepage from the tailings piles was noted in 1975.

U.S. NRC Source Materials License No. SUA–1471 (license) was originally issued to Homestake in 1957 by the Atomic Energy Commission. The State of New Mexico was responsible for licensing and regulating uranium milling operations at the site from 1974 to 1986, after it became an NRC Agreement State in 1974, granting it the authority to regulate uranium milling activities. During operations, ore was brought to the site for processing from various mines up to 50 miles away. Homestake deposited uranium tailings into two unlined tailings piles that overlie the San Mateo alluvium. The NRC resumed regulation for the mill from 1986 to present after New Mexico relinquished its authority back to the NRC.

The current effort is a major groundwater remediation corrective action program approved by the NRC, which is also under the oversight of the U.S. Environmental Protection Agency (EPA) through Superfund. A Memorandum of Understanding has been executed between the U.S. Nuclear Regulatory Commission (NRC) and the EPA for the GRP regarding groundwater remediation.

Currently, there are two active large evaporation ponds, two collection ponds, a reverse osmosis treatment building for groundwater remediation, and several administrative and maintenance buildings. The use of lined evaporation ponds began in October 1986 when the first two ponds were constructed. Located on the small tailings pile, EP1 began receiving water in November of 1990, which has been recently been discontinued. Usage of EP2 began in March 1996. A third evaporation pond (EP3) is located to the north of the large tailings pile became operational in 2011. From 1977 to date, more than 800 wells have been installed at the GRP for groundwater injection, collection, and monitoring purposes.

Groundwater restoration activities are being conducted in accordance with the license and a groundwater corrective action program (CAP) that was approved in 1989 and amended in 1998. In 2006, Homestake submitted an updated groundwater CAP. Based on an NRC request for additional information, Homestake submitted revision 2 of the CAP in March 2012 for the NRC review and approval. A third revision to the CAP was submitted by Homestake in December 2019, with an additional update in November 2020. The GRP was subject to an NRC Confirmatory Order on March 28, 2017, that placed sixteen additional requirements into the license to be completed by Homestake. Homestake has satisfied the conditions of the Confirmatory Order, however, several conditions (e.g., training) are ongoing.

Historically, the contaminants resulting from the mining operations and tailing seepage are found in two different aquifer systems. The alluvial system, which averages approximately 100 feet deep, extends generally northeast to southwest encompassing the San Mateo alluvial aquifer. In addition, a second aquifer system is found within the Chinle formation underlying the San Mateo alluvium. It comprises three separate aquifers designated as the Upper, Middle, and Lower Chinle aquifers.

Homestake’s approved groundwater CAP is to restore the groundwater aquifers to background levels with the objective of achieving the concentrations of all constituents listed as the groundwater protection standards (GWPS) in the license, condition 35B. In 1989, NRC established GWPS for the GRP as “background concentrations” from a single alluvial monitoring well. In December 2005, Homestake proposed revising the GWPS in the alluvial aquifer, Chinle mixing zone, and Chinle nonmixing zones. In 2006, NRC, EPA, and the New Mexico Environment Department (NMED) established new GWPS for 10 constituents in the alluvial and Chinle aquifers that are now listed in the license, condition 35B. These GWPS were based upon samples collected at different times and vary with each aquifer.

Homestake continues to operate the groundwater extraction/injection system at the GRP to clean up groundwater contaminated by tailings seepage. A groundwater collection area has been established and is bounded by a downgradient perimeter of injection/infiltration wells and trenches. Alluvial groundwater that flows beneath the tailings enters this collection area. Groundwater in the alluvial aquifer that is within the collection area is captured by the collection well system. Collected groundwater is pumped to the reverse osmosis plant for treatment and reinjected into the aquifers, or to the evaporation ponds. 

In the November 2020 groundwater CAP update, Homestake concluded that extensive groundwater modeling has shown that groundwater remediation to GWPS is unlikely over time due to the amount of contamination remaining in the tailings and contamination from the tailings that has been trapped in fine-grained sediments beneath and downgradient of the tailings that will be a continued source of contamination. Consequently, Homestake is preparing an Alternate Concentration Limit (ACL) application for submission to the NRC in 2025. An ACL application would likely require institutional controls that would restrict access to contaminated groundwater and an expansion of the licensed boundary that would eventually become the long-term care boundary for long-term surveillance and maintenance. The NRC has not made a determination of whether groundwater remediation to the GWPS is practicable at the GRP.

The GRP groundwater remediation effort is also under the oversight of the EPA through Superfund. A Memorandum of Understanding has been executed between NRC and EPA for the GRP regarding groundwater remediation. NMED maintains groundwater discharge permit DP-200 at the GRP. The regulatory agencies, NRC, EPA, and NMED are working cooperatively in the effort to remediate the GRP to levels that are protective of public health, safety and the environment. The GRP will eventually be turned over to the U.S. Department of Energy (DOE) under a General License for long-term surveillance and maintenance.

On July 28, 2023, Homestake completed its application and license amendment request for the large tailings pile evapotranspiration cover design. The application can be found at (ML23222A171). Homestake is proposing to finish the top of the Large Tailings Pile with an evapotranspiration cover in lieu of the currently approved rip rap design.

Additional information and the latest information related to the operations and conditions at the GRP can be found in the Homestake 2024 Annual Monitoring Report and Performance Review for the GRP.

3.0 Major Technical or Regulatory Issues

Site is under US EPA Superfund oversight and has a permit from the State of New Mexico. Upon closure, the site will be transferred to the US DOE under the authority of UMTRCA Title II.

4.0 Estimated Date for Closure

TBD