Did you know that there is a massive tank under the parking lot at Bayfront Park? The tank is 21,000 m3, or the size of over 8 Olympic swimming pools! It’s a Combined Sewer Overflow (CSO) tank, and its job is to store excess water during storm events to prevent untreated sewage from entering the harbour.
Photo of Royal Avenue CSO tank construction (Photo credit: City of Hamilton)
The Bayfront CSO tank is part of a combined sewer system under the downtown core and older areas of Hamilton. This 600-km network of pipes carries water combined from sanitary sewers and storm sewers. Normally, this water is simply piped to the Woodward Wastewater Treatment Plant for treatment before being released into Hamilton Harbour. However, in the event of a large rainfall or storm, the volume of water can exceed the capacity of the treatment plant. If enough rain falls, the system overflows and untreated sewage and stormwater bypasses treatment and is discharged directly into the Harbour. To prevent these bypass events from happening, Hamilton has constructed nine CSO tanks throughout the city to store the excess sewage water until the treatment plant is able to hold and treat it. These tanks have a capacity of 314,000 m3, or 125 Olympic swimming pools. The CSO tanks have made a huge difference in the number of overflow events, reducing their frequency by 90%! This has helped reduce loadings of suspended solids and phosphorous, and meet initial pollution targets in the harbour. However, overflow events still happen occasionally, and this untreated water is detrimental to the harbour. It contains raw sewage and garbage that people flush down the toilet such as tampon applicators and condoms. It also serves as an introduction for chemicals including caffeine, pharmaceuticals, hormones, nutrients like phosphorus, and bacteria including E. coli. Interestingly, the presence of high concentrations of some of these compounds in the environment can actually be used as an indicator that a CSO event occurred. For example, caffeine is linked to human sources (other animals do not drink coffee!), and can sometimes be detected in concentrations that are 100 times greater than normal. If these times correlate with large storm events, this provides evidence that a CSO event is to blame for the high levels. Climate change means that future storms may be more severe, frequent, and long-lasting, and thus overflow events are a growing concern . Hamilton has a stormwater management plan in order to minimize sewage overflows in the future. Real time control systems have been installed at four locations in the sewer system to control the flow of water during storm events and divert it to tanks that have the capacity to hold the excess water. Additionally, upgrades to the Woodward Wastewater Treatment Plant are currently underway and will increase its capacity to 1300 megaliters per day. Green infrastructure such as permeable pavements, green roofs, bioswales, and rain barrels can all help rainwater infiltrate into soil rather than pooling and running off roadways. Rain gardens are also a wonderful way to collect rainwater, and they provide food and habitat to support many pollinator species. BARC is involved with planting rain gardens at schools throughout the watershed. So what can you do to help prevent untreated water from going into the harbour during a storm? Simply put, less water in the sewage system means less water has a chance to get into the harbour during large storms without being treated. We can all do our part to reduce our water use. On average, Canadians use a lot of water: 250 L per person per day (Statistics Canada, 2016). We can reduce this number through a number of different actions, such as installing low flow toilets and taps, taking shorter showers, and changing what time of day we water our gardens (City of Hamilton, 2017b). Many more water conservation tips can be found on the City of Hamilton’s website here.
BARC, n.d., Rain Gardens (Raingers). http://hamiltonharbour.ca/rain_gardens__raing_
Buerge, I.J. et al., 2006. Combined sewer overflows to surface waters detected by the anthropogenic marker caffeine. Environmental Science and Technology, 40(13), pp.4096–4102.
City of Hamilton, 2014. 2014 Hamilton Water Rate Budget and Services Overview. http://www2.hamilton.ca/NR/rdonlyres/05A31755-677D-4B4E-AA88-075E0F56F11B/0/2014RateBookpart1.pdf
City of Hamilton, 2016. Combined Sewer Overflow Storage Strategy. https://www.hamilton.ca/city-initiatives/our-harbour/combined-sewer-overflow-storage-strategy
City of Hamilton, 2017a. Low Impact Development (LID) - Stormwater Management. https://www.hamilton.ca/home-property-and-development/water-sewer/low-impact-development-lid-stormwater-management
City of Hamilton, 2017b. https://www.hamilton.ca/home-property-and-development/water-sewer/water-conservation-tips City of Hamilton, 2018. Woodward Upgrades Sub-Projects. https://www.hamilton.ca/city-initiatives/our-harbour/woodward-upgrades-sub-projects
Edge, T.A. & Hill, S., 2005. Occurrence of antibiotic resistance in Escherichia coli from surface waters and fecal pollution sources near Hamilton, Ontario. Canadian Journal of Microbiology, 51(6), pp.501–505.
Phillips, P.J. et al., 2012. Combined sewer overflows: An environmental source of hormones and wastewater micropollutants. Environmental Science and Technology, 46(10), pp.5336–5343.
Statistics Canada, 2016. Human Activity and the Environment 2016: Freshwater in Canada https://www150.statcan.gc.ca/n1/pub/16-201-x/16-201-x2017000-eng.htm
Verma, S. et al., 2015. Climate Change Impacts on Flow, Sediment and Nutrient Export in a Great Lakes Watershed Using SWAT. CLEAN - Soil, Air, Water, 43(11), pp.1464–1474.