Evaluation of loose deposits in distribution systems through: unidirectional flushing

The objective of this project was to evaluate the extent of loose deposit accumulation in distribution systems in three Canadian cities to determine optimal flushing frequency. Unidirectional flushing was used to remove the deposits. The results obtained were found to be highly system‐dependant. The normalized mass of flushed deposits varied from less than 0.1 g/m (0.03 g/ft) to approximately 40 g/m (12 g/ft). For the range of velocities attained during flushing (0.65–2.3 m/s [2.1–7.6 fps]), the quantity of collected deposits was not a function of velocity. Analysis of the composition of the deposits confirmed the specificity of each water system. In all systems, the major fraction was iron corrosion compounds (38–72%), but organic matter (14–24%) and silicoaluminum compounds (7–16%) were also found to account for an important part of the deposits. Microbiological analyses revealed concentrations of total bacteria of approximately 10 10 bacteria/g, but the presence of total coliforms was limited to 1.2% of the samples (n = 258).