The goal of this research project was to develop a site-specific water quality model to simulate the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) (all nine species) in the Gwinnett County, Georgia water distribution system using a first-order saturation growth model with the distribution system modeling program WaterCAD. These model predictions were compared with measured values from field sampling. The modeling effort produced results with varying success. The results from the HAA modeling appeared to be reasonably successful, having better agreement between predicted and measured concentrations than the THM modeling. While the measured and predicted results were statistically different, the results were of practical value in determining relative changes in water quality that can be expected at various locations throughout the distribution system. The results provided a reasonable indication of the effects of the distribution system on water quality and on the ability to model THMs and HAAs with distribution system hydraulic modeling software. Includes 11 references, tables, figures.