AWWA WQTC50416

The Montreal distribution system is divided into 6 pressure zones according to elevation. This is done by closing valves, therefore creating dead-end conditions on each side of the valve. The objective of this study was to document the benefits of periodically flushing the dead-end locations. Specific objectives were: to evaluate the short-term variations (24th, 7d) and long term impact (1 yr.) of periodical deadend flushing, and to characterize the loose deposits accumulated in dead-end locations. Two similar sampling sites were chosen on parallel streets in the pressure zone #4. Chlorine is injected during summer at a target level of 0.6-0.9 mg Cl2/L on high-pressure pumps located at the outlet of the Cote-des-Neiges (CDN) storage tank. Mean residence time between the outlet of the tank and the inlet of the dead-end locations is about 7 to 10 hours according to hydraulic simulations. Water quality was sampled on a weekly basis over a 3 month period at the outlet CDN tank and at sampling ports installed directly on the pipes. Routine monitoring included turbidity, total iron, temperature, pH, HPC, coliforms and direct total counts. Includes 10 references, table, figures.