The Safe Drinking Water Act (SDWA) Amendments of 1986 and the proposed Disinfectants/Disinfection Byproducts Rule (D/DBPR) impose somewhat conflicting disinfection regulations whereby the finished water level of disinfection must be increased while the disinfectant and disinfection byproduct residuals must be lowered. The aim of this research project was to evaluate a method for maximizing the hydraulic efficiency of contactors in order to reduce required disinfectant concentrations and subsequently, the disinfection byproduct formation can be controlled and/or minimized. Effective design of new basins and retrofitting of existing basins play an important role in disinfection regulation compliance. The hydraulic performance of a contactor can be influenced by internal baffling and inlet and outlet location. To understand the effects of the basin configuration on hydraulics and disinfection, empirical data obtained from tracer tests performed on full scale or pilot scale basins are usually analyzed. An attractive alternative to these expensive experimental tracer testing methods, is the use of computational fluid dynamics (CFD) modeling to simulate tracer studies. In addition to determining concentration profiles as obtained from tracer tests, CFD modeling offers insight on the internal flow patterns including velocity, energy, and pressure. The goals of this research project were to evaluate the ability of simulated tracer tests to reproduce data from tracer experiments, and to analyze the influence of baffling arrangements and inlet and outlet positions on the performance of the contactor. Various configurations of disinfection contactors were modeled using a commercially available finite element CFD software package called FIDAP(R). The hydraulics and concentration distribution were used to determine optimal basin designs. Tracer studies were simulated using the CFD software and ultimately compared to empirical data to validate this approach. Includes 22 references, tables, figures.