Imagine the magnitude of the pollution problem caused by more than half a million people discharging their untreated sewage and industrial waste into the St. Lawrence River. That's the equivalent of more than 15,000 sanitary trucks dumping their load into the river each and every day. The various substances contained in the sewage amount to more than 50 metric tonnes of dry weight a day.

embracing Quebec City and 12 of its suburbs and neighbouring communities, is about to remove 46 of those 50 tonnes. The CUQ is spending $350-million to construct two sewage treatment plants to cover two separate drainage basins with a total surface area of 550 square kilometres.

Using biofiltration, a technology new to North America, as well as more conventional techniques, the plant will remove more than 85 percent of the contaminants from the wastewater. In the summer months, moreover, the plants will get rid of 99.5 percent of the bacteria in the effluent. As a result, the amount of pollution discharged by the CUQ into the St. Lawrence River is expected to be as little as it was at the turn of the century.

The east plant, the larger of the two, is located in Quebec City near its border with Beauport, and will have a capacity of 231,000 cubic metres a day. The west plant, located upstream in Ste-Foy, will handle an estimated daily flow of 157,000 cubic metres.

The two plants will use similar processes. The wastewater entering the plants will pass through bar screens to remove coarse materials which will be compacted and then hauled to the regional incinerator.

Aerated grit chambers will remove sand, gravel and other high- density material. This material will be washed and then trucked away to a sanitary landfill. Scum, such as oil and grease, will be skimmed off, pumped to a concentrator, and then sent by tank truck to the regional incinerator.

A battery of high-rate primary clarifiers will separate most of the suspended solids from the water. Heavy particles will be raked off the bottom of clarifiers, while floating particles will be pumped to the concentrators. Biofiltration will be used to reduce the organic material dissolved in the water.

The biofiltration process works by allowing the clarified water to percolate through a battery of 30 filters, where the filtering material is coated with a bacterial film. The bacteria use the organic material in the solution as food to grow and reproduce, thereby transforming soluble material into suspended material. The suspended material can be removed by backwashing the filters and by separating it from the wash water through clarifiers. No chemical agents are used in this process.

Finally, ultraviolet lamps will be used in the summer to disinfect the effluent before discharging it into the middle of the St. Lawrence.

Sludge from the west plant will be pumped about 12.7 km to the east plant, where it will be thickened along with sludge produced at the east plant. The thickened sludge will then be pumped an additional 1.7 km to a separate sludge treatment plant adjacent to the present regional incinerator.

By the end of the project about 60 major purchase contracts will have been awarded, as well as about 40 construction contracts to about 35 different construction companies.

In considering the scope of the project and the need to complete it in a relatively short period of time, the CUQ divided the work among many engineering and construction firms.

Four engineering firms formed the PCRB consortium to handle the bulk of the engineering work: Piette, Audy, Bertrand, Lemieux Inc., a subsidiary of Lavalin Inc.; Carrier, Trottier et Associes; Roche Ltd. Consulting Group; and Les Consultants BPR. A few other firms come on board late in the project.

This extensive subdivisions of the project has helped to shorten the schedule by alloeing the engineers to produce their drawings at the same time as other construction activities are going on.

To co-ordinate the approximately 3,000 interconnected activities that make up the total project, Rock Merineau, the chief of the planning department, used Open Plan, a PC-based project management package distributed by HMS Software of Montreal.

To plan a project using Open Plan, planners must identify each activity, define its logical relationship with other activities, and specify the duration of that activity. Once all those details are entered, Open Plan can present Gantt charts, PET charts and about 60 other standard project managment reports. These reports allow planners to compare various alternative schedules to find the one that completes the project in the least amount of time.

Merineau needed Open Plan to plot critical path method network diagrams. CPM networks represent the total time spent on a project from start to finish. Time spent on each activity is shown as an arrow, while the completion point of the activity is indicated by a symbol such as a triangle. The critical path, which is the shortest possible time in which the project can be completed, is highlighted on the diagram on the screen.

Merineau's tight scheduling has paid off. The 44-month construction project should be completed by the end of this year - on time and on budget.

For more information on this article or any HMS product or service, contact HMS at 514-695-8122 or via email at info@hmssoftware.ca.