New watermain bacteriological samples test procedures

[jimdean]

I am trying to find documentation/clarification on bacteriological testing requirements.

According to AWWA Standards, C651-99, Section 5.1, two consecutive setsof acceptable bacteriological samples are required. I am trying to clarify the requirements on the second day samples. It is my understanding that the second day samples are to be taken from the new water main without any flushing of the main - only flushing prior to
first day samples. Some Chlorination contractors insist that second day samples are to be taken after another flushing of the water main with supply source.

Is there clear documentation on acceptable second day testing procedure.

 

[BobPE]

Typically water mains are flushed one time, where the water is provided by the owner and this is spelled out in the specifications for the project or the owners standard specifications. The idea for the second test is to sample the water that is going to be turned into the system just prior to it going to the system. The intent is to identify if there is something in the main that will cause a positive return, like a dead rabbit stuck to a gate valve. Second flushing as part of the normal process of turning the main to service should be avoided as it will miss these types of occurances.

How the main is disinfected is between the owner and their engineer. AWWA is a guidline for this. You should be upfront with the contractor prior to starting construction so that he knows the deal in advance.

Hope this helped.

Bob Yurick PE

 

[jimdean]

Thanks for your response Bob. I am in total agreement with your reply. Can anybody else provide their input or any documentation requiring a second sample without another flush? Thanks

Jim

 

[Navigator1641]

Jimdean

Bob is right on, the first test is after flushing, and the flushing is actually intended to remove the initial high chlorine levels used to disinfect the pipe. The second sample is a check for what exists in the background of the pipe. Flushing again defeats the purpose, as your testing water from another source, not whats resident in the main you just installed. This check indicates wether the initial cleaning (and or pigging) was sufficient in removal, and if the water itself has sufficient residual to eliminate any background bacterial issues.