Inhalation Exposure from Tritium for Intrusion Scenarios at Low Level Waste Disposal Sites

P.D. Rittmann (Fluor Government Group, Inc.)

Low level waste disposal sites must evaluate potential direct exposures to buried waste due to inadvertent intrusion by humans after site closure. The intrusion scenario usually depicts an individual who drills a well that passes through the disposal site. The borehole cuttings include some low level waste, which then becomes part of a garden or cow pasture. While most radionuclides behave in the environment as inorganic compounds, tritium readily becomes part of water molecules which are far more mobile. Inhalation dose from inorganic compounds in the surface soil is based on dust resuspension rates. Inhalation dose from tritiated compounds in the surface soil is based on water evaporation rates. The tritium is represented as tritiated water that emanates from the surface soil due to normal evaporation during the year following intrusion. Dilution in the ambient air is represented using a simple box model with a time dependence that accounts for loss from the surface layer. The new tritium model is compared with the soil screening guidance from the USEPA (United States Environmental Protection Agency) to show that the tritium model gives similar results for the air concentrations above contaminated soil. The new tritium model is also compared with models currently in the RESRAD and GENII software. Finally, the uncertainties associated with the tritium model parameters are discussed.

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