A pilot plant study was conducted in Newport News, Virginia to investigate the effectiveness of powdered activated carbon [PAC] and granular activated carbon [GAC], with and without preoxidation, for reducing trihalomethane [THM] precursor concentrations in Harwood's Mill Reservoir water. Preoxidation with ozone followed by GAC is referred to as the "biological activated carbon" [BAC] process. This study showed that the GAC and BAC processes obtained the same level of organic removal; however, BAC would provide longer bed life and require less carbon than the GAC process. PAC treatment of alum coagulated water provided significantly higher TOC and THMFP removals than alum coagulation alone. The use of a preoxidant (ozone) with PAC slightly improved the organic removal efficiency. While treatment by PAC increased THMFP removals, it was not as efficient as the GAC and BAC processes. UV absorbance measured at 254 nm and TOC were found to be good surrogates for THMFP in the GAC column, but not in the BAC column. / Master of Science