Uranium-series isotopes transport in surface, vadose and ground waters at San Marcos uranium bearing basin, Chihuahua, Mexico

In the U deposit area at San Marcos in Chihuahua, Mexico, hydrogeological and climatic conditions are very similar to the Nopal I, Pena Blanca U deposit, 50 km away. The physicochemical parameters and activity concentrations of several U-238-series isotopes have been determined in surface, vadose and ground waters at San Marcos. The application of some published models to activity ratios of these isotopes has allowed assessing the order of magnitude of transport parameters in the area. Resulting retardation factors in San Marcos area are R-f238 approximate to 250-14,000 for the unsaturated zone and approximate to 110-1100 for the saturated zone. The results confirm that the mobility of U in San Marcos is also similar to that of the Nopal I U deposit and this area can be considered as a natural analog of areas suitable for geologic repositories of high-level nuclear waste. (C) 2012 Elsevier Ltd. All rights reserved.