Risk of misdiagnosis for vinyl chloride non-conformity

摘要

In drinking water systems, PVC pipes manufactured prior to 1980 can have a wide range of residual content of vinyl chloride. The leaching of this compound into water may lead to exceed the standards for drinking water quality at consumer's taps, in some cases. Diagnoses have been made since 2012 on points where the non-compliance risk is highest. If the measured concentration is below the standard concentration, one or two samples are enough to classify the point as compliant. However, it was observed that the vinyl chloride concentrations measured on a lot of samples at the same point show a huge variability. This variability can't only be explained by the uncertainty of measurement or by the temperature variation, but also by the heterogeneity of the PVC pipes. The contamination level in water fluctuates unpredictably, depending on the unknown residence time and residual level of vinyl chloride in each PVC pipe. It can be figured that packets of water circulates with various levels of contamination. According to this model, the risk of misdiagnosis with a single sample can be estimated. This risk decreases for warmer water, but the probability to classify this point as compliant whereas it is not, is higher than 20%. Thus, the non-compliance management from a single sample can be criticized because it under-evaluates the long-term risk. Vinyl chloride Diagnosis Variability Drinking water system Standard Non-compliance.