Granular activated carbon (GAC) has been shown to be a viable treatment technique for the removal of a broad spectrum of organic contaminants. To accurately model effluent concentrations from a GAC column, the effects of background organics must be taken into account. Background organics can affect adsorption by either competing directly with the target compound, or by restricting adsorption by loading onto the carbon ahead of the target compound. Recently, there has been substantial progress in evaluating the effects of preloading on adsorption. In the study, cis 1,2-dichloroethene (DCE) was spiked into water from the Great Miami aquifer (GMA) and fed to pilot columns which were preloaded with unspiked GMA water for various lengths of time. The objectives of the study, therefore, were to: (a) evaluate how preloading of a natural groundwater affects the capacity and rate kinetics of adsorption in pilot columns; (b) evaluate the microcolumn scale-up procedure developed by Crittenden, et al; and (c) determine if different isotherm techniques have any effect on the final capacity of preloaded carbon.