“…Optical sensors (Sivathanu, 2003;Frish et al, 2005;Gao et al, 2006) were also discarded since they lack the accuracy required for detecting and measuring low rate dispersed underground leaks. Gas sensors and acoustic methods (Sivathanu, 2003;Chung and Lee, 2001;Hodgkinson et al, 2006;Millera et al, 1999;Huanga et al, 2007) were neither practical for measuring small leaks disseminated along large distribution networks.…”