Groundwater is contaminated with 2-Chlorofenol (C= 150 mg/L). The best way to treat the groundwater before supplying to the town is oxidizing using hydroxyl radical. Acceptable concentration is 5 mg/L, in Turkish Drinking Water Directive. So, what would be the reaction time for this reaction to provide acceptable water quality? The reactor system provides 1010 mol/L hydroxyl radical (OH.) continuously, which has a 1.2x1010 L/mol.s reaction rate constant with 2-Chlorofenol