Adsorption studies were conducted to determine how preloading a natural groundwater onto granular activated carbon affects the adsorption of cis-1,2-dichloroethene in small-scale and pilot-scale columns. Capacities were determined from batch-isotherm tests, microcolumns, and pilot columns, which were preloaded for various lengths of time. Breakthrough profiles from short-bed adsorbers and pilot columns provided information regarding the kinetics of adsorption. Some of the results are: adsorption capacity and kinetic rate decreased with increasing time of preloading, the preloaded microcolumns showed capacity reductions similar to that of the preloaded pilot columns, and preloaded column capacities were represented well by preloaded isotherms. The reduction in pilot-column capacity due to preloading for cis-1,2-dichloroethene was shown to be partially off-set by using columns in series where the columns were only added when needed to contain the mass-transfer zone. For cis-1,2-dichloroethene, the increased run time due to adding columns may not be worthwhile in field applications. However, for stronger adsorbing compounds, or columns which are preloaded before the contaminant of interest arrives, a significant improvement in carbon performance may result.