HPC dilution dups

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HPC dilution dups

Postby lschantz2 » Fri May 11, 2012 7:08 am

For our last inspection we had a deficiency for not running HPC dilutions in duplicate. We justify this departure from standard procedures in our Quality Manual, and we base it on the very low HPC recovery rates for the water tested, which is chlorinated filtered water. In our Quality Manual I state that since 90% of our HPC test results are <1 cfu/mL, and 97% <30 cfu/mL, duplicates provide little to no statistical value. This is especially true when one considers the fact that 500cfu/mL is the level of interest in the drinking water industry. Therefore, running duplicates on our Finished Water samples is a waste of materials and time. However, we do run duplicate dilutions for our Raw Water samples, which represents untreated water. For previous inspections, this reasoning had been acceptable, but not this time (always the same inspector).
Anyone care to comment on our logic for not running dups. This isn’t the biggest problem I have but I just hate wasting time and supplies for what I see as a pracatice that adds no value to the quality of the data. The other point that irks me is that I know for a fact other water utilities do not run duplicate dilutions, but they have never been challenged about it. It is the “old” audit consistency issue, again.
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