How the Sewer System Works (CSO and Storm Outfalls)
Combined Sewer Overflow Outfalls (CSOs)
The older portions of the City of Hamiton's sewer system collects both domestic sewage (from sink drains and toilets) and storm water runoff in a single pipe called a combined sewer. This mixture, called combined sewage, is sent to the Woodward Avenue Wastewater Treatment Plant (WWTP) for treatment.
During dry weather or small rainstorms, all combined sewage receives full treatment before it is discharged into Hamilton Harbour. During heavy rainstorms however, the excess water can cause excess combined sewage that the sewer system can't handle.
To address this problem, the city has 6 combined sewer outfall tanks. These tanks store the excess combined sewage during rainstorms. The tanks are filled by gravity, and when flows subside after a rainstorm, their liquid contents are drained or pumped back into the combined sewer system and conveyed to the Woodward Avenue WWTP where they are treated.
In some cases, the rainfall will be so heavy that the system and the tanks will become overloaded. When this happens, the excess wastewater will be discharged directly into Hamiton's natural waterways (either at Hamitlon Harbour, Cootes Paradise, Chedoke Creek, or the Red Hill Creek). These discharge points are called Combined Sewer Overflows, and are necessary to minimize system overloads which can result in residential basement flooding.
The storm sewers located on our roadways and in front of our properties is meant for storm water runoff only -- as the materials that go down these drains filter directly into our natural waterways. These discharge points are referred to as storm outfalls.
*Information and pictures taken from the City of Hamilton.