This paper addresses the development of a process that is intended to precede and facilitate the biological degradation of trihalomethanes (THMs) in the treatment train by creating conditions that allow nitrifying cultures to flourish in the filters, primarily the destruction of monochloramine using granular activated carbon (GAC). The specific goals of this research are as follows: demonstrate the utility of GAC as a suitable media for the reduction of monochloramine in packed-bed filters under drinking water treatment plant conditions; and, determine GAC surface properties that control reduction of monochloramine. A series of continuous-flow activated carbon column studies was performed for a suite of GAC types, source waters, empty-bed contact times (EBCTs), monochloramine influent concentrations, and pH values. All studies were run until a steady-state condition with respect to monochloramine was achieved. Includes 5 references, tables, figures.