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hydroxyl radicals due to the water matrix, fewer radicals are available to react with the contaminant. These water quality parameters impact various reactors and lamp types differently. • Lamp age. E EO increases as lamps age. That is, more power is required at the end of the lamp life than at the beginning in order to achieve the same effectiveness. This is because the lamp’s UVC electrical efficiency decreases over time. • Flow rate. In general, because E EO is normalized by the flow rate, reactor systems treating different flow rates can be compared. However, such comparisons should be made cautiously as empirical evidence and theoretical analysis have shown that the E EO value decreases to an asymptotic value as flow rate increases. This is due to increases in reactor hydraulic efficiency with increases in turbulence and mixing at higher flow rates. Reactors must be specifically designed for certain conditions, including flow rates. • Hydrogen Peroxide Concentration. E EO is a strong function of H 2 O 2 concentration. The irradiation of H 2 O 2 produces hydroxyl radicals which accelerate the degradation of contaminants in the water. The higher the H 2 O 2 concentration the more UV it absorbs and the more radicals are formed. However, H 2 O 2 itself scavenges hydroxyl radicals. Therefore, the greater the concentration of H 2 O 2 , the greater the scavenging of hydroxyl radicals. Therefore, E EO varies inversely with H2 O 2 concentration but this is not a linear relationship. • Contaminant. Different contaminants will have a different E EO value in the same reactor in water with the same quality. This is due to differences in the quantum yield, molar absorption coefficient, and hydroxyl radical reaction rate (i.e., their fundamental kinetic parameters). 3 PILOT SYSTEM DESIGN 3.1 APPROACH TO THE UV-AOP STUDY While it was the objective of this study to demonstrate the capability of the UV/H 2 O 2 system to treat 1,4-dioxane present in the St. Anthony groundwater, it was decided to inject additional 1,4-dioxane upstream of the UV reactor. This was done to allow the UV/H 2 O 2 pilot system to demonstrate treatment of 1,4-dioxane that exceeds 3-log (i.e., >99.9%) reduction. The primary water quality parameters that influence the efficiency of UV/H 2 O 2 treatment are the UV transmittance (UVT) of the water and its hydroxyl radical scavenging demand. The UVT of the water affects the efficiency of delivering the UV photons to the target chemical (i.e., H 2 O 2 ). Similarly, the hydroxyl radical scavenging capacity quantifies the overall demand for hydroxyl radicals due to all constituents present in the water. Trojan received a water sample from St. Anthony in July 2015. The sample was collected upstream of the GAC filters and is representative of the water that would supply the pilot system. This sample was evaluated for the water quality parameters that potentially impact the efficiency of UV/H 2 O 2 treatment. Figure 1 presents a summary of the data for the St. Anthony water sample. The key conclusions from the water quality analysis are that the UVT is very high at 96.3% and the hydroxyl radical scavenging capacity is moderately high. The moderately high hydroxyl radical scavenging capacity is due to the relatively high alkalinity and resulting bicarbonate ion concentration. These results are consistent with the measurement of pH, alkalinity and DOC and together provide a strong 5