A pilot-scale test rig was constructed to simulate intrusion behavior associated with hydraulic transients. Initial tests were conducted using a high-speed datalogger to verify low/negative pressures. Results indicated negative pressures (maximum -12 psi) for 3 to 5 seconds following sudden valve closures. With steady state flow, three orifice diameters (1/8 ″, ¼″ and ½″ ) were overlaid with 3 or 4.5 feet of head to simulate cracks or leak points in a water distribution system. Based on volumetric measurements, average intrusion volumes associated with transients ranged from 47.3 to 550.2 mL. Based on chemical tracer (cesium) measurements, average intrusion volumes ranged from 11.4 to 71.2 mL for 1/8″ and ¼ ″ orifices, respectively. Differences were attributed primarily to dilution of cesium in the test rig. Results also were compared to theoretical and computer model predictions. Findings from this research demonstrate that external water and pathogens potentially can intrude into pipelines during transient events
