REAL–TIME CONTROL OF COLLECTION SYSTEM TO REDUCE COST OF COMBINED SEWER OVERFLOW LONG–TERM PLAN : A CASE STUDY

In 1988, the Quebec Urban Community (QUC) has undergone a Combined Sewer Overflow (CSO) long-term control plan to reduce overflows in the St-Lawrence river and the St-Charles river to a level that will permits a safe use of these two water bodies for recreational activities during the summer period. The CSO control plan is divided in 5 main phases : (1) the characterization of the QUC CSO pollution problem, (2) the modeling of the QUC watersheds and sewer networks, (3) the study of different interventions needed to comply with the environmental objectives, (4) the implementation of a Global Predictive Control (GPC) scheme and (5) the construction of retention facilities. At this time, the first 4 phases have been completed. The implementation of a Global Predictive Real Time Control (GP-RTC) strategy on the Westerly Sewer Network has been a success in terms of proven efficiency. RTC will permit to build only 4 storage facilities instead of the 7 needed if QUC did not implement GP-RTC, resulting in savings in the long-term CSO control plan of approximately 9 M (22% of the cost of the plan without GP-RTC).