When treating water, we generate waste, also referred to as "residual" streams. Solid materials removed from the river by the treatment process as well as treated drinking water that does not meet water quality standards have been historically released back to the river.
Drinking water contains residual chlorine, added at the treatment plants to disinfect the water. While it is important to ensure a minimum residual of chlorine in the water delivered to all customers for protection of public health, the chlorine residual can be toxic to fish as it damages their gills. We've invested considerable resources to ensure that all water that is returned to the river is dechlorinated first.
Solids produced during treatment processes are managed through the adoption of direct filtration in the fall and winter months. During this time frame, the raw water quality of the North Saskatchewan River is very good and much less alum is required in the treatment process. The switch to direct filtration reduces the amount of solids from the treatment process that is released to the river.
One of the primary objectives of the residuals management strategy is to achieve environmental benefits (reducing solids loading to the river), without compromising the health and safety of drinking water. By optimizing the amount of alum added without compromising drinking water treatment, the amount of solid residuals produced and discharged to the river (especially the amount of chemical residuals) is reduced.