Methodology and Preliminary Results of Unsaturated-Flow Studies for a Proposed Low-Level Radioactive Waste Disposal Facility, Texas

Site characterization studies are being conducted for low-level radioactive waste disposal in an area 35 miles (65 km) southeast of El Paso, Texas. An important factor in the evaluation of site suitability for waste disposal is estimating the direction and rate of moisture movement through the thick unsaturated zone. Physical and chemical approaches were used to evaluate moisture movement in the unsaturated zone. Physical methods include monitoring moisture content with a neutron probe and monitoring water potential with psychrometers. Chemical tracers such as bomb ^36Cl were used to evaluate recharge rates over a longer period (approximately 30 years). The lack of temporal variations in moisture content and the low water potentials indicate that water movement through the unsaturated zone is minimal and is primarily restricted to upward vapor movement, probably controlled by evapotranspiration. Recharge estimates from the chemical tracers are also minimal, less than 1% of the mean annual precipitation rate.