United States Nuclear Regulatory Commission - Protecting People and the Environment

Conoco-Phillips Company

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1.0 Site Identification

Type of Site: Unknown
Location: Falls City, TX
License No.: R01634
Docket No.:
License Status:  

2.0 Site Status Summary

The Conquista Project was developed and operated as a mill to process uranium bearing ore from conventional surface mines in the Karnes County area of Texas. A radioactive material license was issued to Continental Oil Company (predecessor to Conoco, Inc. and ConocoPhillips) in September of 1971 authorizing the processing into uranium concentrate. The Conquista Project consisted of a mill complex and a tailings impoundment of approximately 250 acres adjacent to the mill complex. In addition to the waste from the mill operation, the licensee was also authorized to accept and place in the tailings impoundment for disposal up to 10 milligrams of radium-226 per year of contaminated solution from the Flatonia municipal water decontamination project, radioactive waste from other uranium processing facilities, by-product material from Rhone-Poulenc of Freeport, Texas (a rare earth extraction processing facility), and by-product material from Conoco, Inc.'s Trevino Project (an in situ leach uranium extraction project in Texas).

The authorization for processing was changed to (possession) incidental to reclamation activities in 1989 to reflect the licensee's decommissioning of the mill site. The structures and features of the mill complex were dismantled and placed in the tailings impoundment. The tailings impoundment has been capped and a vegetative cover established and is being monitored for performance. Since all structures and equipment have been removed from the site, there will be no release of equipment and materials to unrestricted use. The criteria for release of the site/termination of the license includes demonstration that the tailings impoundment does not exceed the radon flux limit of 20 pCi/m2-sec; gamma levels are indistinguishable from background; radium-226 concentration in soil does not exceed 5 and 15 pCi/g of radium-226 in the first 15 centimeters, and subsequent 15 centimeter soil horizons, respectively; natural uranium in soil does not exceed 30 pCi/g; demonstration that the tailings impoundment and disposal cell have stabilized; and either demonstration that the groundwater does not exceed the limits specified in a table that is comparable to Paragraph 5C in 10 CFR 40, Appendix A, or does not exceed alternate concentration limits, if so established.

3.0 Major Technical or Regulatory Issues

Groundwater contamination remains an outstanding issue.  The licensee is carrying out a groundwater sampling program and a flow and transport modeling effort to better understand the behavior of groundwater beneath and adjacent to the impoundment.  The issue is confounded by the presence of a Title I site in the vicinity that is up-dip of the Conquista Project site and that possible contributor will be built into the model.  The impoundment has experienced some settlement in previous years.  A study to determine the cause of the settlement was conducted. 

During the first quarter of 2015, the Licensee regraded a large area on top of the tailings impoundment to address low areas that had been created by differential settlement. All settlement plates across the tailings impoundment were replaced by new settlement monuments that were flush mounted in concrete at the ground surface of the tailings impoundment cover. The monuments continue to be monitored quarterly for movement.

Page Last Reviewed/Updated Thursday, August 23, 2018