Acoustic monitoring of terrorist intrusion in a drinking water network

In collaboration with Kiwa Water Research, TNO (Netherlands Organisation for Applied Scientific Research) has investigated the possibilities to detect and classify aberrant sounds in water networks, using acoustic sensors. Amongst the sources of such sounds are pumps, drills, mechanical impacts, which could indicate, for instance, a terrorist's attempt to inject a toxicant into the water mains. In parallel, an important spin-off is recognised in the detection of other sounds, such as those caused by leaks in water pipes and leaking valves. The acoustic water pipe monitoring project was carried out between 2003 and 2007 in three distinct phases: • The first phase was carried out in 2003-2004 to gain knowledge on the subject. Models were developed for the sound propagation in water pipes and computer simulations were carried out to specify detection ranges. • In the second phase, in 2005-2006, the knowledge created in phase 1 was applied for detection of leakage and terrorist attacks. To this end, a number of field experiments were carried out to characterise background noise and suspicious sounds. It was shown that both leakage and intrusion sounds could be detected up to a range of 100 m in regular 110-mm diameter PVC pipes. At this point, Kiwa Water Research and TNO decided to focus their efforts on terrorist detection in the third and last phase of the project. • In the third phase, carried out in 2006-2007, a demonstrator was developed for the detection and classification of aberrant sounds and tested on an operational water supply system. Overall, the TNO acoustic monitoring demonstrator, equipped with two sensors fixed on fire hydrants and two on service taps, has proven to be a suitable and promising system for protection of buildings: it is capable of working in real time and detected about 90% of terrorist intrusion sounds within a range of 110 m (a range suitable for building protection). Using the techniques developed for leakage detection in phase 2, and a similar acoustic demonstrator, the performance of operational systems could further be assessed to detect leakage