Intrusion within a Simulated Water Distribution System due to Hydraulic Transients. I: Description of Test Rig and Chemical Tracer Method

A pilot-scale test rig was designed and constructed to simulate intrusion behavior associated with hydraulic transients initiated by sudden events such as rapid valve closure or uncontrolled change in on/off pump status (“pump trip”) in a water distribution system. After establishing steady state flow conditions, intrusion volumes were determined for 3.2 (1/8-in.) and 6.4 mm (1/4-in.) diam orifices overlaid with a column of water that provided 91 mm (3 ft) of external head. Average intrusion volumes associated with hydraulic transient events were determined by mass balance calculations using cesium as the tracer chemical. Average intrusion volumes were 11.4 and 71.2 mL for the two diameters, respectively. Given similar conditions in a water distribution system (i.e., an available pathway and favorable pressures), pathogens in the soil and water surrounding a water main potentially can intrude into the pipe during short-term pressure transient events.