AWWA WQTC56958

This paper presents the results obtained from the application of an "integrated approach" that combines the use of water quality, system operation and maintenance data, hydraulic model and geographical information systems to identify the main causes of total positive coliform samples collected in the distribution system of the city of Laval (Quebec, Canada), from 1997 to 2000. Using this approach, almost half (43%) of the coliform cases had one (or more) highly probable cause identified. Among those causes are distribution system types of events such as pipe flushing, localized low pressures, and valve and hydrant operation. Water treatment plant events such as measured coliforms at the outlet of the plant were also associated to positive coliform samples in the distribution system (DS). Peaks in water consumption typically observed during summertime (with the outcome of potentially degraded water quality out of the treatment plant (WTP) because of increased "pressure" on the treatment processes and/or hydraulic disturbances in the DS causing sediment resuspension) also constitute a factor that could play a major role in the occurrence of coliforms in this DS. Includes 13 references, tables, figures.