Chlorine dioxide has gained much attention for use as a possible alternative disinfectant in water treatment plants due to concerns regarding trihalomethane formation in drinking waters which utilize chlorine as the primary disinfectant and the strict regulations regarding THM's and THMFP (MCL of 0.080 mg/L for TTHMs) (Pontius, 1993). Although the use of Cl02 as a disinfectant prevents the formation of THM's, concern exists regarding the potential health risks due to the disinfection-by-products of chlorite and chlorate. The main objective of this project was to study the removal of chlorite by reaction with ferrous iron under elevated pH conditions. The stoichiometry of the reaction was evaluated under the following conditions: solution pH of 6.0 to 10.0, 02(aq) concentration of 0.5 to 10 mg/L, and solution DOC concentrations of 0 to 15 mg/L. Mass balances were conducted to define the speciation of the oxychlorine residuals associated with the reduction of Cl02 by Fe(II). / Master of Science