AWWA ACE90068

The objectives of this study were to: (1) conduct tracer studies at full-scale water treatment plants to determine T10 values for the various process units exposed to disinfectants (T10 is the time it takes 10% of the tracer to pass through a mixing basin, storage tank, or other vessel); (2) calculate the contact time (CT) allowed by the Surface Water Treatment Rule (SWTR) for each water system; (3) develop residence time distributions (RTDs) for the various process units at each plant and calculate an "effective CT" based on the RTD and the kinetics of chlorine decay, and compare these to the CT allowed by the SWTR. Three full-scale water treatment plants using surface water sources were evaluated. Two plants were located in Maryland; the other was located in North Carolina. Tracer tests were conducted using both the step-input method and the pulse-input method. Fluoride was the primary tracer chemical. All three plants use chlorine as the primary disinfectant.