Radionuclide Leaching from Residual Soils: Screening Study

Four soil samples, collected from a National Priorities Listed site contaminated with uranium, thorium, and radium, were leached for two, seven, and 30 days. The nonleached soils, leached soils, and leachates were analyzed using gamma spectroscopy, alpha spectroscopy, and delayed neutron activation. Unleached and leached soils had low radionuclide activities, and four different leaching solutions had no significant observable effect upon the resulting leachate activity. Three of the soils produced leachates with uranium activities below the expected primary drinking water standard of 30 μg/L for uranium, but the leachate from the fourth soil had an unacceptably high concentration of uranium (653 μg/L) despite the low activity of the original, unleached soil. Distribution coefficients calculated for uranium ranged from 100 to 12,000 mL/g, while distribution coefficients for ${}^{226}\mathrm{Ra}\text{,}$ ${}^{228}\mathrm{Ra}\text{,}$ ${}^{228}\mathrm{Th}\text{,}$ ${}^{137}\mathrm{Cs}\text{,}$ and ${}^{40}K$ ranged from 1 to 20 mL/g. The uranium distribution coefficient was strongly correlated to the leachate alkalinity, suggesting that conditions resulting in high alkalinity yield a high potential to leach uranium.