Exxonmobil Highlands

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Site Summary

1.0 Site Identification

Type of Site: Uranium Recovery Facility
Location: Converse County, WY
License No.: SUA-1139
Docket No.: 40-8102
License Status: Possession Only License
Project Manager: Ted Carter

2.0 Site Status Summary

The Highland uranium recovery facility included a conventional surface uranium mine with an associated mill. The site also included ore storage pads, four mine pits (two of which have been backfilled), several waste rock piles, one tailings impoundment and an environmental laboratory. Surface mining (beginning in 1970), solution mining (beginning in 1972) and underground mining (beginning in 1977) were used to recover the uranium ore. The first ore was processed at the facility in October 1972.

Approximately 11.3 million tons of ore were processed at the Highland mill using an acid leach circuit between 1972 and the end of operations in mid-1984. The resultant tailings consisted of sand and slimes fractions, which were discharged to the tailings basin around the perimeter of the tailings basin and via causeways built out into the tailings basin. Solution contained in the basin was occasionally recycled to the mill, and pilot aquifer restoration waters were discharged to the tailings basin.

The uranium mill area, including the ore storage pads and the laboratory, has been cleaned up and the tailings buried are under a radon barrier, eliminating nearly all potential for radiation exposures to workers or members of the general public from these sources. However, ExxonMobil reclamation operations may result in minimal exposure of workers to radioactive materials. All windblown material has been reclaimed to unrestricted release standards. The byproduct material exposure is limited to the groundwater pathway. However, there is no current use of groundwater. The water in the pit lake has slightly elevated concentrations of Ra226 + Ra-228 (- 5 pCi/L), gross alpha (- 6 pCi/L), U-nat (-5 mg/L), and selenium (-0.12 mg/L).. All other COCs in the pit lake are below WDEQ Class III standards. The site is fenced with restricted access through Power Resources, Inc.'s (PRI's) gate to the premises. The pit lake has a cliff highwall over more than 50 percent of its circumference, with no fence or berms at the pit rim. The operations of co-located facilities not under ExxonMobil control (PRI facilities) are governed by PRM radiation safety procedures. Exxon Mobil maintains an office in the PRI facility. The HASP assumes that no uranium mill tailings or other radioactive materials will be excavated, exposed, or handled as part of the work. The HASP also assumes that the site meets the radiation-related requirements for unrestricted release.

3.0 Major Technical or Regulatory Issues

A plume of contamination has been detected flowing to the east of the site onto private property. New wells have been installed and samples are being collected to determine the extent of the plume. The pit lake has also been contaminated and has elevated levels of uranium and selenium. These areas of contaminated will delay the closure of the site. No new closure date has been estimated. ExxonMobil has submitted a notice of intent to apply for Alternate Concentration Limits and an expanded long-term care boundary to include the pit lake and property to the east.

4.0 Estimated Date For Closure


Page Last Reviewed/Updated Wednesday, March 24, 2021