Analytical risk-based model of gaseous and liquid-phase radon transport in landfills with radium sources

An analytical model of gaseous and liquid-phase radon transport through soils is derived for environmental modeling of landfills containing uranium mill tailings or Ra-226 sources. Processes include radon diffusion in both the gas and liquid phases, advection of soluble radon in percolating water, radioactive decay, equilibrium partitioning between gas and liquid phases, and emanation from different source terms. A probabilistic framework for the radon-transport model is introduced that provides uncertainty and sensitivity analyses for risk-based assessments. Uncertainty analyses are used to compare simulated performance metrics (e.g., radon surface flux) against regulatory standards. Sensitivity analyses are used to identify key parameters and processes that impact the variability of the simulated results. The models and analyses are illustrated with a probabilistic performance assessment of the Mixed Waste Landfill at Sandia National Laboratories in Albuquerque, NM.