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AWWA RSP64387
- Understanding the Sources, Fate and Transport of Coliform Bacteria in Distribution Systems
- Conference Proceeding by American Water Works Association, 03/01/2007
- Publisher: AWWA
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This paper presents a review of research conducted at the Ecole Polytechnique NSERC IndustrialChair on Drinking Water to address several questions relating to the contamination of full scaledistribution systems during normal operations. Results of various projects are presented toprovide insight into microbial methodological detection limitations, the relationshipbetween positive coliform samples and distribution system operations, and specificcontamination sources and events. The use of molecular methods such as FISH probes was foundto increase the number of positive Enterobacteriaceae detected in treated and distributed water.The occurrence of 140 positive coliform samples was investigated in five systems; 48 heterotrophic plate counts (HPC)events were evaluated in four systems; and 217 customer complaints were investigated in threesystems. The integrating of all available data into an geographic information system (GIS) query based model revealed that theimpact of operation and maintenance (O&M) activities on the occurrence of coliforms in distribution systems varies from onesystem to another, explaining a minimum of 9% and up to 45% of the number of coliform casesinvestigated in each system. About a third of the customer complaints investigated in each of thenetworks studied could be associated with O&M work, while its association with HPC eventswas negligible in three systems out of four. Although O&M activities are beneficial for waterquality on a long-term basis, their short-term negative impacts should be understood for betterprevention and control of potential water quality degradation. Event based investigations alsoshowed that, in the distribution system studied, operations (pipe repairs, flushing, fire drills, etc.) were notassociated with an increased presence of indicators of microbial contamination such as totalcoliform bacteria, E. coli, aerobic spores and other water quality indicators. Further workdocumenting contamination by intrusion is ongoing but preliminary results did not revealcontamination during or after negative pressure events. Includes 80 references, tables, figures.
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