A relative-risk framework for evaluating transient pathogen intrusion in distribution systems

Hydraulic transients generate significant negative pressures in water systems that may cause intrusion of contaminated water from the environment into the pipe. This paper expands the consideration of transient intrusion events from their purely hydraulic aspects by developing a risk-based framework for comparing the relative risk-reduction achieved by alternative transient-intrusion mitigation strategies. Alternative strategies may be any combination of changes to system operation or surge controls that would reduce the potential for intrusion of contaminants from the soil-groundwater environment surrounding the pipe. A reference groundwater contamination is assumed, and intrusion volumes and time-varying pathogen concentrations are computed respectively using hydraulic transient and water quality models. Risk-based measures are proposed to provide quantitative assessments of the relative reduction in the risk of receptor infection achieved by alternative mitigation strategies.