What is a combined sewer overflow (CSO)? The City of Ottawa has three types of sewers: wastewater, stormwater, and combined. Wastewater sewers: Collect wastewater from homes, businesses and industries, and transport the wastewater through a network of sewers, pumping stations and forcemains to main or trunk sewers, and direct it to the Robert O. Pickard Environmental Centre for treatment. Stormwater sewers: Carry rainfall and other surface water run-off directly to the nearest creek, stream or river, generally without treatment. Combined sewers: Collect and transport both sanitary wastewater and stormwater runoff in a single pipe. This type of collection system was typically installed from 1880 to 1960 and is still in operation in older areas of most Canadian cities. During dry weather, wastewater is collected and carried from the combined sewer to a wastewater treatment plant. During heavy rain storms or snow melts, the combined sewer may not be able to handle the high volume of stormwater runoff entering the system. Most of the wastewater is transported to treatment plants via the wastewater pipe, but to prevent flooding and sewer backups, some of the rain and wastewater mixture is diverted as overflow into the river. The practice of discharging overflows during the normal operation of combined sewer systems is accepted by the Ministry of the Environment. In Ottawa, these events are monitored and reported to the Ministry of Environment and downstream users such as water purification plants and special interest groups. The Above Information was Written and Provided by the City of Ottawa Location ID #OT0002
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