Numerical models for simulating tritiated water (HTO) transport in unsaturated soil were developed to assess the migration of HTO from contaminated groundwater to terrestrial biosphere. Column experiments using sandy soil and deuterated water (D2O) were performed and a scenario of HTO transport from contaminated aquifer to atmosphere through an unsaturated soil zone was investigated. The results obtained by both model calculations and column experiments indicated that hydraulic conductivity of soil is an important soil parameter characterizing D2O transport speed and that dispersion and advection are dominant elemental transport processes in unsaturated soil.