TRANSPORT OF RADIONUCLIDES AT THE BARGMANN URANIUM MINE: ASSESSMENT AND WEPP MODELING

More than 60 former open pit surface uranium mines are located in south Texas. While approximately half of the mines were mined and reclaimed under the Texas Mining and Reclamation Act (1975), there are still 11 unreclaimed pre-law mines. Each of these mines contains Radium-226 rich spoil piles which are often subject to significant weathering and erosion. The former Bargmann Mine in Karnes County is among these and has been unreclaimed for 44 years. The goal of this assessment was twofold: to take field measurements to answer the question of sediment transport and to use the computer modeling program WEPP (Water Erosion Prediction Project) to create a simulation of Bargmann and assess its accuracy. A series of 9 soil cores were taken at the site along a sloped hill gradient which covered 258 m. The cores were sampled in 3 to 5 cm increments and their Radium-226 activities measured by High Purity Germanium Gamma Ray spectroscopy. Activities up to 49000 mBq/g were recorded in the spoil piles and significant activity was recorded until the next to last core. No significant activity was recorded in the last core. While these levels indicate sediment transport, it appears there was not enough movement away from the mine to constitute an environmental or health hazard. The WEPP modeling program was initially created to assess agricultural soil erosion transport by water. A validation study of WEPP for South Texas Uranium mines was conducted by modeling soil material erosion and transport at the Bargmann site. Using such inputs such as soil physical properties, vegetative cover, % slope, and local weather information, the program can predict areas of erosion and deposition along a slope. Surface soil fractions were measured by the ASTM 151H Hydrometer based method and other parameters were obtained from the USDA Natural Resources Conservation Service web soil survey to gather information for the soil input. In this case, the WEPP model results of Bargmann indicate deposition further along the slope than was recorded in the field. Further sensitivity tests need to be conducted with WEPP to determine how inputs such as vegetative cover affect the model results.