HISTORICAL ENVIRONMENTAL IMPACT OF URANIUM MINING THROUGH THE GAMMA RAY ANALYSIS OF LIVESTOCK POND SEDIMENTS

In December 1954, Uranium was discovered in Karnes County, 50 miles southeast of San Antonio, Texas. From the mid fifties to the late seventies, Uranium was extracted from more than 60 open pit mines. The region became known as the South Texas Uranium Province. Examples of the health and environmental impact of the mining activity include an episode of livestock poisoning (molybdenosis), as well as chromosomal aberration, and reduced DNA repair in residents of properties located in the direct vicinity of the mining operations. A number of the mines were abandoned and the Railroad Commission of Texas is in the process of decommissioning the sites. While several examples of the impact of the mining activity were documented, a more comprehensive study is yet to be completed.

The goal of this work was to assess if the sediments of a stock pond located near a former Uranium mine could be used to reconstruct the historical impact of the mining activity. The selected pond was located adjacent to an open pit uranium mine, which was later converted to a processing mill tailings waste disposal site near Falls City, Texas. The remediation of the site was completed in 1994 as part of the Uranium Mill Tailings Remedial Action (UMTRA) program managed by the United States Department of Energy (USDOE). Although initially included in the clean up plans, the sediments from the pond were never remediated and should therefore provide a record of the contaminant transport from the mine.

A 115 cm core was extracted from the deepest portion of the stock pond and analyzed for radionuclide contents. The sediments were analyzed for ¹³⁷Cs, ²¹⁴Bi, ²¹⁴Pb, ⁴⁰K, ^234mPa, and ²⁰⁸Th by High Purity Germanium gamma ray spectroscopy. The radiocesium distribution in the core was used to estimate an average sedimentation rate of 2.6 cm/year. The historical variation of the ²²⁶Ra was estimated through the ²¹⁴Bi and ²¹⁴Pb profiles. The sedimentary record indicates that the ²²⁶Ra input to the pond increased three fold from the early sixties to the early seventies. After peaking during the mid seventies the ²²⁶Ra concentration receded to activities close to the pre-mining era, indicating that the environmental impact of the mine to this neighboring property was likely concentrated during mining operations.