Innovative Technologies For Stormwater And Combined Sewer Management

By Martin Couture and Gianfranco Maragno, Veolia Water Technologies

Stormwater flows have historically been considered as harmless by the general public and system designers. Recent studies have shown that these flows cannot be dismissed as easily. Chebbo (1992), Marsalek (1997) and Valiron (1992) have shown that stormwater is a source of diffuse pollution with a high source of suspended solids (SS), adsorbed hydrocarbons (HC), nutrient loads (N, P, etc.) and heavy metals (Pb, Cr, etc.), which ultimately influence the quality of the receiving body of water. Since 1994, the USEPA has enforced stringent new rules concerning stormwater management (USEPA, 1994). In Canada, the same tendency toward legislation is felt. Some municipalities require controlling their stormwater flowrates and perhaps even treating them. This article presents novel technologies for the management of stormwater flows and how they can mitigate the impact on the collection system.

Problem
Municipal managers and operators of urban drainage systems are recognizing the importance of controlling and managing stormwater flows in order to limit the damages of a rapid and important stormwater runoff (Brière, 1994). In delaying or reducing the speed of stormwater flows, it becomes possible to free additional volumes in the system and consequently limit sewage overflow during storms. When stormwater flows exceed the outlet capacity of a combined sewer system, the exceeding water overflows directly into a receiving medium (rivers, lakes, creeks, etc.). It is estimated that 95% of sanitary overflows occur during storm events. (WPCF, 1989). These flows pollute the vegetation, beaches/coasts and banks of the receiving body of water.