Computational fluid dynamics (CFD) modeling is a useful tool for studying the spillage, dispersion, and related safety issues of liquefied natural gas (LNG). This paper presents a CFD code that directly models the complete spill and pool formation process (direct CFD simulation method), taking into consideration heat and mass transfer governing equations and the Monin-Obukhov similarity theory for atmospheric stability. The model was validated against experimental data from the Burro test series under atmospheric conditions which allowed the LNG dispersion to be predominately gravity-driven. The direct CFD simulation method clearly provides better predictions than the conventional approach, which simply estimates the pool size from natural gas inlet conditions and uses a fixed vaporization rate. The direct CFD simulation method was further applied to investigate the effect of an impoundment on LNG spill and dispersion mitigation. It was clearly shown that an impoundment can confine the LNG spill and control the dispersion by both increasing air flow turbulence and generating a swirl/recirculation at the upwind walls, resulting in reduction of vapor cloud dispersion by up to 55%.