Five radionuclide vadose zone models with different degrees of complexity (CHAIN, MULTIMED(underline)DP, FECTUZ, HYDRUS, and CHAIN2D) were selected for use in soil screening level (SSL) calculations. A benchmarking analysis between the models was conducted for a radionuclide ((sup 99)TC) release scenario at the Las Cruces Trench Site in New Mexico. Sensitivity of three model outputs to the input parameters were evaluation and compared among the models. The three outputs were peak contaminant concentrations, time to peak concentrations at the water table, as well as those of time to exceed the contaminant's maximum critical level at a representative receptor well. Model parameters investigated include soil properties such as bulk density, water content, soil water retention parameters and hydraulic conductivity. Chemical properties examined include distribution coefficient, radionuclide half-life, dispersion coefficient, and molecular diffusion. Other soil characteristics such as recharge rate, was also examined. Model sensitivity was quantified in the form of sensitivity and relative sensitivity coefficients. Relative sensitivities were used to compare the sensitivities of different parameters.