Effect of water main repairs on water quality

Sixteen planned repairs of pipe leaks in two distribution systems were investigated in 2004‐2005 to study the occurrence of microbial contamination associated with repair activities in full‐scale distribution systems. Soil and water samples were collected in pipe trenches, and distribution system water was collected at consumers— homes and at flushed hydrants. The frequency of detection of fecal microbial indicators in the soil and water surrounding the mains was low. Evidence of contamination in distribution system water (based on total coliforms, Escherichia coli, and aerobic endospores) was obtained at seven of the sixteen sites. The 17 positive samples (of a total of 424) were almost all collected during flushing; results suggested that adequate pipe flushing after a repair has been completed is an effective way to minimize contamination for this type of repair. Loss of chlorine residuals and turbidity peaks were also observed outside the repair areas.