Disinfection detention time, one of the key factors in determining compliance with the Surface Water Treatment Rule, was evaluated in this study to determine: whether typical water plant basins can be modified with intrabasin baffles to improve detention time; and whether model basins can simulate full-scale systems. The results of the work show that both a rectangular and a circular basin can be modeled quite accurately by small-scale basins. Tracer tests showed that T10 detention time can be improved with simple intrabasin baffle walls to approximately 60 percent of theoretical detention time. Includes 9 references, tables, figures.