AWWA ACE93154

Several issues complicate water main disinfection. For example, superchlorination may cause water mains to dissolve, become brittle, or begin to corrode. To improve disinfection of water mains after construction or repair, Philadelphia created new standards for construction and disinfecting the mains before putting them into service; at the same time, it tightened the water quality standards that had to be met to put a water main in service. In a sanitary release survey, water mains are flushed, then filled with distribution water. After 16 hours, samples are collected at 500-foot intervals. The water is then tested, and it must meet or exceed the quality in the distribution system. A study showed that the utility's improved standards for construction and maintenance were offset by the stricter guidelines for sanitary release surveys. Thus, the failure rate of sanitary releases increased 3-fold. There is ample opportunity for microbial contamination during the construction, repair, and replacement of water mains. Sanitary release data confirm that microbial contamination does occur and at times requires considerable effort to fix. Yet the sources and significance of the microbial contamination are unknown, and the adequacy of the disinfection process has not yet been determined.