A liquid‐phase granular activated carbon (GAC) pilot plant and a full‐scale GAC adsorber were designed, built, and operated in order to evaluate their performance for treating a groundwater contaminated with several volatile and synthetic organic chemicals. Several empty bed contact times (EBCTs) ranging from 1 to 30 min were used during the pilot‐plant study, and a simple method for evaluating the GAC use rate as a function of EBCT was developed and demonstrated for dichloroethene and trichloroethene (TCE). Pilot‐plant data were compared with the pore surface diffusion model, which considers external and internal mass transfer mechanisms of pore and surface diffusion. Natural organic matter in the water was found to decrease GAC capacity and kinetics for TCE.