AWWA ACE54377

Blending refers to water suppliers mixing multiple supplies either upstream of treatment works, during treatment, or after treatment. The focus of this study is blending waters containing different secondary disinfectants. Situations that give rise to water suppliers practising or considering blending water of different quality include: one water supplier purchases water from another, where one supplier modifies disinfection practices to respond to changing regulations; connections to adjacent systems are used in emergency situations; and, adjacent systems are joined together to manage growth. Of concern is the ability to manage water quality in the distribution system when distributing water that sometimes contains a free chlorine residual, sometimes a combined chlorine (chloramine) residual, or sometimes a combination or blend of chlorinated and chloraminated water. If blending cannot be avoided, operating strategies and engineering controls can be implemented to minimize the water quality impacts of blending. Case studies are presented to demonstrate the nature of these impacts and to suggest appropriate control measures. Includes 22 references, figures.