Many organic compounds in water supplies are resistant to conventional treatment, and many others are toxic or nuisances. Low concentrations of organic contaminants are not readily removed by conventional treatment methods, but activated carbon has an affinity for various organics, and its use for organic contaminant removal from water supplies has been widely studied. The U.S. EPA has initiated a series of field studies to evaluate the performance of granular activated carbon (GAC). The studies involve the construction and operation of GAC systems under 'field-scale' conditions.