The objectives of this study were to determine the efficiency of adsorption of powdered activated carbon (PAC) for a typical synthetic organic chemical, to evaluate the importance of particle size and background organics, and to develop a procedure to predict the performance of PAC. Results showed that performance can be significantly improved by using smaller-size PAC but that the rate of adsorption and PAC capacity are markedly reduced when naturally occurring humic substances are present in the groundwater. Accurate predictions of the removal of trace organics by PAC in a continuously stirred tank reactor were made by running equilibrium and closed-batch kinetic tests, determining equilibrium and kinetic constants, and using an equation to determine the removal efficiency of the PAC for any contact time. Includes 33 references, tables, figures.