The revision (ANSI/AWWA C651-14) is the result of multiple years of review, research, and discussion by the committee. The update also takes into account a recent project from the Water Research Foundation (Project No. 4307, Effective Microbial Control Strategies for Main Breaks and Depressurization). The major revisions included in this important update of the standard include the following:
Expanded guidance for disinfecting existing water mains after repair. This includes a rationale for evaluating risk during pipe repairs, and the level of disinfection and sampling needed under each of those conditions. The revision also clarifies differences in the requirements between new and repaired mains.
- Added a spray disinfection method for large transmission mains.
- Changed the requirement for bacteriological sampling in new mains from two sets of samples 24 hours apart to add two options for two sets of samples: Option A samples are 16 hours apart and Option B samples are 15 minutes apart after a 16 hour rest period.
- The flushing rate of 2.5 ft/sec has been increased to 3.0 ft/sec for a scour flush based on testing performed under Water Research Foundation Project No. 4307, which indicates the threshold velocity of 2.5 to 3.0 ft/sec for successful flushing (2.5 to 3.0 log removal) of sand particles. Since this is a threshold velocity, 3.0 ft/sec was chosen for this edition of the standard.
- References to new standard ANSI/AWWA C655 are included for dechlorination and disposing of heavily chlorinated water.
These updates provide improved guidance and requirements for disinfecting newly installed and existing repaired water mains.
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