This project studies the mechanisms that cause the retardation of Volatile Organic Compounds (VOC) in ground water. Laboratory column and diffusion experiments were run in an effort to determine the contribution of each mechanism to the retarded flow of the VOCs. Retardation factors (Rf), distribution coefficients (Kd) and diffusion coefficients (Dd) were determined for four VOCs commonly found in ground water. Comparison of two separate column experiments at different velocities shows that retardation is independent of flow velocity. The results from the diffusion experiment are presently being analyzed.