Disinfection is a critical process component of drinking water treatment to protect human health. The disinfection performance is highly dependent on the hydraulic efficiency of the disinfection contactor. Accurately evaluating the hydraulic efficiency of the contactor is important to water treatment plant designers and operators. Tracer analysis is the most used approach for evaluating hydraulic efficiency. Many factors that can impact tracer analysis have been well studied, while the monitoring strategy is not. This study investigates the impact of different monitoring strategies, including single point monitoring, multiple point monitoring, and surface average monitoring, for hydraulic efficiency evaluation. It is found that: residence time distribution and characteristic times could be significantly different when monitoring two points near to each other, especially at a location with an uneven velocity distribution; Monitoring a four-point matrix at the target location and using the four-point average could be sufficient to accurate evaluate the hydraulic performance when sampling cannot be done at well mixed locations with a uniform velocity distribution.
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