Umetco Minerals Corporation – Gas Hills East

1.0 General Site Information

Site Location: Gas Hills Mining District, WY
Former NRC License No.: SUA-648
NRC Docket No.: 40-0299
Agreement State Contact: Brandi O'Brien 307-777-6435
NRC Agreement State Site Monitor: Stephen Poy Stephen.Poy@nrc.gov
NRC Site Monitor: Thomas Lancaster Thomas.Lancaster@nrc.gov

2.0 Site Description

The Umetco site is located in Fremont and Natrona Counties in Wyoming, approximately 60 miles east of Riverton in a remote area of central Wyoming (Figure 1). The site is located within the Gas Hills Uranium District of the Wind River Basin, in portions of Sections 10, 15, 16, and 22, Township 33 North, Range 89 West.

Figure 1. Umetco-Gas Hills Project Site Location Map
Source: U.S. Department of Energy. “Long-Term Surveillance Plan for the Gas Hills East (UMTRCA Title II) Disposal Site, Fremont and Natrona Counties, Wyoming.” Grand Junction, Colorado: U.S. Department of Energy. 2009.
Figure 1. Umetco-Gas Hills Project Site Location Map Source: U.S. Department of Energy. “Long-Term Surveillance Plan for the Gas Hills East (UMTRCA Title II) Disposal Site, Fremont and Natrona Counties, Wyoming.” Grand Junction, Colorado: U.S. Department of Energy. 2009.

3.0 Site History

The facility was constructed in 1959, and operations began in 1960. Heap leach activities at the site began in 1963. Mill operations were put into standby status in 1984 and later shut down in 1987. Reclamation was completed in 2006.

The Umetco site consists of 3 primary tailings disposal areas on the 1,920 acre parcel – the 170 acre Above Grade Tailings Impoundment (AGTI), the 55 acre A-9 repository and the 60 acre Heap Leach area.  In addition, GHP-2 adjacent to the AGTI also contains waste from the heap leach operations.  NRC approved the Final Status Survey for the site in 2005.  In 2009 erosion was detected on the slopes of the AGTI and A-9 covers and in 2010 Umetco submitted an erosion protection enhancement plan to the NRC.  The plan was approved in 2011 and Umetco completed the erosion enhancements in 2012.

Tailings Management and Disposal

The former facility site is on the Wind River Formation, which comprises a sequence of alternating and discontinuous layers of sandstone, siltstone, claystone, and conglomerate. Groundwater beneath the site occurs in two flow regimes separated by a mudstone unit.

The shallower Southwestern Flow Regime (Figure 2) includes the upper portion of the Wind River Formation and is characterized by more oxidizing conditions. The deeper Western Flow Regime includes the lower portion of the Wind River Formation, but is still part of the shallower aquifer. This aquifer is characterized by more reducing conditions. Groundwater flows toward the Pathfinder Lucky Mc Uranium Mill site (Source Materials License SUA-672), which is located 5 miles from the Umetco site. Mining-related activities have affected groundwater quality as oxygenated surface water has percolated through open-pit mines, mine spoils, and backfill materials, dissolving previously reduced minerals such as uranium and radium. Groundwater reclamation was completed in 2006.

Figure 2. Umetco-Gas Hills Site Layout
Figure 2. Umetco-Gas Hills Site Layout

Reclamation of the Heap Leach and Above-Grade Tailings Impoundment (AGTI) areas was completed in 2002. The cover for these areas included a radon barrier, filter layer, frost protection layer, and topsoil (Figure 3). The sides of the Heap Leach area also incorporated a radon cover and a frost protection layer. Riprap erosion protection covers the Heap Leach and AGTI areas. Reclamation of the A-9 Repository, C-18 Pit, and Gas Hills Pond No. 2 (GHP2) areas was completed in 2006. Reclamation activities at the A-9 Repository included placing a liner and regrading the slopes for the North and South Evaporation Pond. The A-9 Repository cover for these areas included a radon barrier, filter layer, frost protection layer, and riprap erosion protection. The C-18 Pit was backfilled with soil and regraded to promote soil drainage. At the GHP2 area, Umetco constructed a radon barrier and frost protection layer and placed riprap on top of the cover to limit erosion effects.


Figure 3. Schematic Cross-Section of Covers for the Heap Leach, Above-Grade Tailings Impoundment, A-9 Repository, C-18 Pit and Gas Hills Pond No. 2 Areas
Source: U.S. Department of Energy. “Long-Term Surveillance Plan for the Gas Hills East (UMTRCA Title II) Disposal Site, Fremont and Natrona Counties, Wyoming.” Grand Junction, Colorado: U.S. Department of Energy. 2009.

4.0 Current NRC actions/status

The U.S. Nuclear Regulatory Commission (NRC) has approved Umetco's Construction Completion Report. The U.S. Department of Energy (DOE) has submitted a draft Long-Term Surveillance Plan for technical review by NRC. Before license termination, DOE must arrange to transfer BLM land that is within the long-term care boundary.

NRC currently has no actions for the site until the CRR is submitted by the State of Wyoming.

5.0 Expected Transition to DOE for LTS&M

2026 (See DOE LM Site Management Guide, March 2022)

Page Last Reviewed/Updated Thursday, May 19, 2022