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Combined Interpretations of the 2003, 2009, and 2016 Standards that apply to Volume 1 of the 2016 TNI Standard


Question:  In Standard Methods there is a requirement to do at least one positive sample verification monthly, in some cases 10% etc.  What if you do not have any positive samples, should you do a positive verification anyway?  I see that for DW (source) even if you do not have any positive samples, a positive verification check is to be done quarterly. How about the other type of waters? For example to check any false negatives? Frequency?

TNI Response:  Questions involving specific methods should be directed to the writer of the method. The requirement for positive controls exists so that the lab can demonstrate that IT isn't the reason there are no positives, i.e., it isn't doing something that causes no growth.