AWWA WQTC59012

This AwwaRF project was conceived primarily to test certain assumptions about low-pressure transients in drinking water distribution systems. The basic assumptions tested were that low and negative pressure transients actually occur in real distribution systems (not just within large transmission mains) and that they can cause liquid external to the pipe to be intruded into a drinking water main through a leaking pipe barrel, pipe joint, or other orifice. Pressure transients can result in contamination when the pressure of water surrounding the water main exceeds the internal pressure. Under these conditions, water external to the main may flow into the main through leakage points, submerged air-vacuum valves, cross connections, and faulty seals or joints. Pressure transients can travel throughout a distribution system and cause significant pressure fluctuations in some portions of the system. Many of the causes of pressure transients are a part of regular water distribution system operations, and therefore, pressure transients may occur frequently in certain water distribution systems. The overall aim of pilot testing was to verify the occurrence of intrusion during surge events in the distribution system by constructing and operating a pilot-scale test rig apparatus (test rig) at Tulane University. A second objective was to quantify intrusion volume under various test conditions. Hydraulic transients were induced in the test rig by closing a valve quickly. Intrusion was facilitated by applying an external column of water on the plate of a blind flange with a pre-drilled orifice that was mounted on the test rig. Experiments were conducted near maximum attainable velocity conditions to enhance hydraulic responses in the test rig. The field study phase of this research included three primary objectives: Locational and Event Monitoring - determine the frequency and location of low and negative pressures in representative distribution systems under normal operating conditions and during specific operational events such as flushing, fire flow tests, valve operation, and pump starts and stoppages; Comparison of Different Monitoring Technologies - document differences in pressure monitoring equipment capabilities to measure instantaneous pressure transient occurrences in distribution systems (i.e., compare electronic monitors to conventional mechanical pen and chart recorders); and, Verification of Model Predictions - compare field monitoring results to surge model findings in order to verify the ability of such models to accurately simulate low and negative pressure occurrences in distribution systems. Pressure monitoring was performed both long-term to record any and all pressure variations at a specific location ("locational monitoring"; two weeks to 1.6 years), and short-term to monitor effects from a specific type of distribution system operation ("event monitoring"; hours). For the long-term locational monitoring, high-speed electronic pressure data loggers were connected to distribution system piping at a minimum of three different locations in each of the seven participating distribution systems studied, typically for a period of at least two weeks each. The monitoring was intended to capture events of any origin, known or unknown. In two of the systems the monitors were left in place continuously for over a year and a half. Short-term event monitoring was performed to detect pressure changes during the following types of scheduled operational events: pump tests (including starts/stoppages); high demand periods (e.g., system flushing, fire fighting practices, tank filling, and high-demand consumers); valve operation (e.g., butterfly and pressure reducing valves); and, surge tank operations. The primary electronic pressure monitor used was a high-speed single-channel pressure transient datalogger (Model RDL 1071L/3 Pressure Transient Logger; Radcom Technologies, Inc., Woburn, MA). In some cases a slightly older model of the