A previously proposed microcolumn scale-up procedure is evaluated. Scale-up assumptions dealing with equal capacities in microcolumns and field columns are focused on in an effort to evaluate the effect of preloading carbon with naturally-occurring organic materials (NOM). Reductions in capacity found in the column studies are compared to distilled, groundwater, and pre-adsorbed isotherms. Total organic carbon breakthrough in the field column is presented to explain capacity reductions. A simplified version of a mass transfer model and a more complex mass transfer model are used to predict the pilot column results. For the ground water studied, preloading NOM onto GAC reduced the carbon's capacity for cis- 1,2-dichloroethene. This preloading violated an assumption of a previously presented microcolumn scale-up procedure. Preloading of natural waters was therefore found to render incomplete carbon adsorption models that do not account for the possible reduction in capacity. Of the models that do not take preloading into account, the simple Constant Pattern Homogeneous Surface Diffusion Model gives a comparable prediction to the Dispersed Flow Pore Surface Diffusion Model, which incorporates more kinetic terms.