Potential for pathogen intrusion during pressure transients

Pressure transients in drinking water pipelines (i.e., surges) may cause hydraulic pressure gradients, resulting in the potential for intrusion of pathogens present in the external environment into the distribution system. The objectives of this study were to determine the occurrence of indicator microorganisms and pathogens in the vicinity of potable water pipelines and assess the potential for intrusion attributable to transient distribution system pressure changes. As part of an earlier study (Kirmeyer et al, 2001), soil and water samples were collected at sites immediately exterior to drinking water pipelines at eight locations in six states. Samples were then tested for occurrence of total and fecal coliforms, Clostridium perfringens, Bacillus subtilis, coliphage, and enteric viruses. Indicator microorganisms and enteric viruses were detected in more than 50% of the samples examined. Monitoring of pressure transients at a large distribution system indicated that pressure transients occurred frequently, although negative pressures were detected on only one occasion. The results of this study suggest that during negative- or low-pressure events, microorganisms may enter the treated drinking water through pipeline leaks.