The overall objective this study was to better understand the chlorination reactions of organic matter by investigating the formation of halogenated DBPs from three molecular size (MS) fractions of GW NOM (greater than 3000, 1000-3000, and less than 1000 daltons). Specifically, in Phase I: to investigate the impact of ozonation and biotreatment on DBP precursors under variable reaction conditions; and in Phase II: to evaluate the chlorination kinetics and reactivity of these fractions under constant organic and inorganic precursors concentrations. The impact of organic and inorganic precursor limitations on the reactivity and kinetics of halogenated DBPs was also evaluated.