Prevention of bacterial contamination of stored hydrants: Utility recommendations for hydrant inlet orientation and capping

Abstract

To avoid contamination of the drinking water distribution system and obtain reliable bacteriological testing results, a rigorous and protective hygiene approach must be followed when storing, repairing or installing hydrants. However, in North America strategies to avoid or eliminate microbial contamination of hydrants during storage, transport and installation are often insufficiently defined in utility standards and manuals. In the summer of 2015, Edmonton (Alberta, Canada) utility field crews encountered several instances where water samples collected from newly installed hydrants were total coliform (TC) positive and thus did not meet the regulatory requirements to be put into service. The present study evaluated whether stored hydrants were contaminated with TC. The study also evaluated the efficacy of an intervention targeting two common hydrant storage practices at preventing microbiological contamination: pointing the hydrant inlet downwards and capping hydrants by the manufacturer. We swabbed 24 hydrant inlets and recorded inlet orientation and capping status prior and after the intervention. The swabs were processed using IDEXX Colilert tests for total coliform and E. coli detection. Positive samples were further identified by Biomerieux 20E API testing. Out of the 24 tested hydrants, twenty were oriented with the inlet pointing downward. Ninety percent of the downward pointing hydrants were TC negative, while the remaining 10% were TC positive. Seventy five percent of the hydrants not pointing downward were TC positive, while the remaining 25% were not contaminated. The results showed that hydrant inlet orientation had a statistically significant effect on hydrant contamination with TC (Fisher Exact Test two-tailed p-value=0.018). The results also highlighted that capping, while efficacious in protecting water mains from contamination in the field, did not have a statistically significant impact on bacterial contamination of hydrants as capped and uncapped hydrants were TC negative 86% and 70% of the time, respectively. All TC were identified as Pantoea spp. indicating that the most likely source of contamination was environmental not fecal in nature. We were unable to identify the source of the bacterial contamination but recommend that hydrant disinfection practices related to new mains be expanded upon in standards in the future, as the cost of a failed bacteriological test can be exorbitant (>US$10,000). Results highlighted that contamination of distribution system network components with environmental TC interferes with detection of real point source contamination resulting from actual system failures. It can also result in delayed appropriate remedial actions and an impairment in the evaluation of risk to the public. Results also highlight the importance of educating field crews about bacterial contamination and its sources to benefit utilities, reduce false positives, improve performance and empower crews to make informed decisions.