AWWA ACE59922

The production of transient low and negative pressures in otherwise pressurized potable water supply distribution systems creates the opportunity for contaminated water to enter the distribution system from external environments. This paper documents the occurrence of transient low and negative pressures in distribution systems as a result of a variety of system features and operations. Fifteen surge events were observed that resulted in a negative pressure, and most of these were caused by the sudden shutdown of all of the pumps at a pump station due to either unintentional (e.g., power outages) or intentional (e.g., pump stoppage/startup tests) circumstances. Smaller but still substantial surges were produced by shutdown of pumps while other pumps remained running, and by other operational events such as flushing, hydrant use, and main breaks. Includes 11 references, tables, figures.