Characteristics of radioactivity contamination of soil at the Nevada test site

For 35 years the Nevada Test Site Complex has been contaminated by a combination of transuranic elements, fission products, and activation products. Within the nuclear detonation sites the initial radionuclide distribution depended upon the different types of nuclear tests (airburst, surface, or underground) and meteorological conditions at the time of each test. Results of this study show that the present distribution is the result of wind and water erosion, whereas site specific geomorphic features and pedogenic processes played secondary roles. The high temperatures of the detonations resulted in most of the radionuclides being incorporated into fused soil and rock materials which have very low solubilities in aqueous media. The glassy silicate contaminants vary in size, but most (91%) are greater than 0.1 mm in diameter. Therefore, the radioactivity contributed by the resuspendible (< 0.1 mm) and respirable (< 0.005 mm) particles in the soils is less than 9% of the total soil radioactivity, indicating that the site has a very low potential for off-site environmental and health hazards under natural conditions. Nevertheless, the contaminants are expected to have faster physical and chemical weathering rates than those of soil minerals because they are mostly porous glass rather than crystalline in form. From the results of the characterization studies, suggestions are made to consider pretreatment of the contaminated soils in order to reduce the volume to be removed and to maintain a stable nonerodible surface in the treated area.