AWWA JAW65236

A significant knowledge gap exists for utility managers struggling to comply with the Stage 2 Disinfectants/Disinfection Byproducts Rule and other water quality objectives. This is particularly true for utility managers who have switched to or are considering switching from free chlorine to combined chlorine disinfection. Water chemistry and temperature can significantly affect chlorine demand and residual chlorine in distribution systems. Galvanized-iron and unlined cast-iron pipes are most likely to experience the lowest chlorine residuals, particularly under low-flow to stagnant-flow conditions. This article provides a simplified approach for combined chlorine modeling, similar to that used for free chlorine dissipation modeling. Knowledge of the mechanisms, rates/kinetics, and a simplified approach to modeling and predicting total chlorine residuals will enable utility managers to be more comfortable and confident in decisions they make about switching to chloramines. Includes 14 references, tables, figures.