Booster chlorination is an approach to residual maintenance in which chlori
ne is applied at strategic locations within the distribution system. Situat
ions in which booster chlorination may be most effective for maintaining a
residual are explained informally in the context of a conceptual distributi
on system. To form the basis of a quantitative analysis of booster chlorina
tion, experiments simulated chlorine decay under booster conditions. These
experiments suggested a conceptual model for bulk chlorine decay, which is
used to analyze an example representing a header pipe serving two distinct
zones in a distribution system. The chlorine mass savings associated with b
ooster chlorination in this example are derived and used to show the influe
nce of flow rates, residence times, and decay kinetics on the effectiveness
of booster chlorination. The role of booster chlorination is also discusse
d as part of coordinated treatment efforts meant to manage the risks associ
ated with biological regrowth and disinfection by-products.