Conoco-Phillips Company – Conquista Project

1.0 General Site Information

Site Location: Karnes County near Falls City, TX
Agreement State License Number: R-01634
Agreement State Contact: Hans Weger 512-239-6564
NRC Agreement State Site Monitor: Duncan White
NRC Site Monitor: Martha Poston-Brown

2.0 Site Description

The Conoco Conquista Project is a Title II uranium tailings impoundment located approximately 50 miles southwest of San Antonio near Falls City, Texas in Karnes County.  The Conquista site is near the DOE Falls City Texas Disposal Site (UMTRCA Title I site) and shares similar site characteristics – mesquite dominated woodlands and cleared ranch lands used primarily for agriculture and sparsely populated.   Hydrologically, the Conquista Project is downgradient to the DOE Falls City Disposal site.  The Conquista Project is sited on the Dubose Clay which overlays the Deweeville sandstone.

3.0 Site History

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 materials license was issued to Continental Oil Company (predecessor to Conoco, Inc. and Conoco-Phillips) in September 1971 authorizing the processing into uranium concentrate.  The Project consisted of a mill complex and a tailings impoundment of approximately 250 acres adjacent to the mill complex.  The licensee's impoundment was authorized for mill waste, contaminated solution from the Flatonia municipal water decontamination project, waste from other uranium processing facilities, byproduct material from the Rhone-Poulenc in Freeport, TX  (rare earth extraction) and byproduct from a Conoco Trevino ISL facility near Hebbronville, TX (closed in 1988).

The authorization for processing changed to possession only in 1989, when the licensee decommissioned the mill site. Mill structures and features were dismantled and placed in the tailings impoundment.  The impoundment has been capped and a vegetative cover is in place.  The tailings impoundment is being monitored for performance.

In 2001, Conoco-Phillips submitted a request to the State of Texas to terminate the license.  As part of this termination request, the licensee performed geochemical comparison of the Deweeville sandstone groundwater from the Conquista project and the DOE Falls Creek Disposal site to demonstrate that the groundwater types for the two sites are nearly identical, but the groundwater quality at the Conquista Project site is consistently better.  Then based on the DOE site having been found to meet the required protection criteria for groundwater, the licensee requested that they should also be considered to meet the criteria and be classified as to "not pose a threat to public health, safety and the environment" and not required to submit a request for Alternate Concentration Limits (ACLs).  This approach was rejected by the State.

As of June of 2021, the State of Texas is in the process of processing a major amendment to the license for Conoco-Phillips for the Conquista Project.   The State of Texas is also preparing a Completion Review Report (CRR) for the site.

4.0 Current NRC actions/status

None. NRC will review the CRR when completed by the state. NRC interacts regularly with the state to maintain awareness of the site status.

5.0 Expected Transition to DOE for LTS&M

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

Page Last Reviewed/Updated Friday, October 28, 2022