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1 INTRODUCTION This document describes the work performed to demonstrate the ultraviolet/hydrogen peroxide (UV/H 2 O 2 ) advanced oxidation process (AOP) for treating various 1,4-dioxane present in the potable groundwater well of The City of St. Anthony Village, Minnesota water treatment plant. The primary goals of the study were to demonstrate the ability of the UV/H 2 O 2 process to treat the contaminants in question and provide the basis to determine the economic costs of implementing and maintaining a full-scale system. To facilitate these goals Trojan Technologies has supplied, installed and operated a small pilot-scale UV/H 2 O 2 system. The tests were performed on August 26th and 27th, 2015. This document provides a brief description of the procedures and results of these tests. The treatment process at the St. Anthony water treatment plant comprises greensand filtration for iron, manganese and turbidity removal followed by GAC for 1,4-dioxane and VOC removal. 1,4-dioxane is very poorly adsorbed by GAC and the required change-out frequency makes it prohibitively expensive to operate. It is proposed to locate UV/H 2 O 2 AOP upstream of the GAC contactors to allow the oxidation process to treat 1,4-dioxane and many of the VOCs and allow the GAC to quench the residual H 2 O 2 leaving the UV reactor and provide a second barrier to VOCs. 2 UV-OXIDATION FUNDAMENTALS 2.1 TREATMENT MECHANISMS UV-based advanced oxidation processes rely upon the simultaneous mechanisms of direct UV photolysis and UV oxidation to degrade chemical contaminants in water. UV-photolysis is the process by which chemical bonds of the contaminants are broken by the energy associated with UV light. UV- photolysis does not require the addition of H2 O 2. UV-Oxidation systems rely on the in-situ generation of hydroxyl radicals (•OH) by way of the UV-photolysis of H 2O2 and the subsequent oxidation of chemical contaminants by those hydroxyl radicals. Hydrogen peroxide is commercially available as aqueous solutions of varying strength. The solutions most commonly employed in UV oxidation processes for water treatment are either 35% or 50% by weight and are certified to meet NSF/ANSI Standard 60 requirements. Hydrogen peroxide is a relatively weak absorber of UV light having a molar absorption coefficient at 254 nm of 19.6 L mole-1 cm-1. Nevertheless, the quantum yield of hydrogen peroxide UV photolysis is relatively high. Therefore, the UV/H 2O2 process is one of the most efficient advanced oxidation processes. Hydroxyl radicals are extremely reactive, short lived and unselective transient species. The mean lifetime of hydroxyl radicals in natural water in the presence of natural organic matter (NOM) and alkalinity is estimated to be in the order of 10 μs (Oppenlander 2002). Therefore, the high reactivity and short life of these chemical species result in the requirement of in-situ generation of these oxidants. They will not exist beyond the boundaries of the UV reactor volume. Hydroxyl radicals can oxidize organic and inorganic compounds by various types of reactions, comprising electron transfer reactions, hydrogen abstraction and electrophilic addition. In UV oxidation treatment processes the desired reactions are the oxidation of specific contaminant molecules. 2