[en] Tritium transport simulations were conducted to model the mechanisms associated with dilution, dispersion, and radioactive decay that attenuate the 618-11 tritium plume and limit the risk associated with exposure to the Columbia River and Energy Northwest water supply wells. A comparison of simulated and observed tritium concentrations at two downgradient monitoring wells indicated that the model was a reasonable representation of the tritium concentrations immediately downgradient of the site (699-13-3A) and near the leading edge of the plume (699-13-0A). This good match increased confidence in the conceptual model, its numeric implementation, and ultimately, the validity of predictive simulations of tritium fate and transport. Three release scenarios were investigated to measure the impact of the tritium plume at primary receptor locations under different conditions. The three cases were (1) a pulse release of tritium from the burial ground that was the best fit between observed and simulated tritium concentrations; (2) a continuing, decaying source beneath the burial ground through 2015, the milestone for source removal under the River Corridor Closure Contract; and (3) a pulse release as in the best fit case but at twice the concentration. For the best fit case, the model predicts that the maximum tritium concentration will decline to below the drinking water standard by 2031 For the other two release scenarios, maximum tritium concentrations declined to below the drinking water standard by 2040 and 2037, respectively. Tritium from the 618-11 burial ground is not expected to migrate to the Columbia River or to the Energy Northwest water supply wells at concentrations that would pose a significant risk