In the first Summer RAIN Blog , we learned a little bit about the hydrologic cycle, and how it can change in urbanized areas. We explored some of the basic causes for an increased risk of flooding, and decreased water and habitat quality. This should have highlighted the need for stormwater management, which is one of the most important parts of planning any urban area.
The City of Hamilton provides several resources to learn about the methods used to manage surface water, including stormwater management ponds, municipal drains, and cross culverts.
In this blog, we’ll be focusing on how homes, buildings, and other impervious surfaces interact with the city’s sewer systems.
Separated vs. Combined Sewer Systems
Newer areas of Hamilton typically have separated sewer systems, meaning that there are two different underground pipes. Sewage from your home flows into the sanitary sewer, and is kept separate from surface runoff entering storm drains into the storm sewer. Sanitary sewers are directed to the wastewater treatment plant to be cleaned before being released into Hamilton Harbour, while storm sewers lead directly to the environment.
Simplified diagram of separated versus combined sewer systems. (Copyright © City of Hamilton)
Combined sewer systems collect wastewater from homes, and lead into one pipe that also collects stormwater runoff. This was the standard setup for over 100 years across Canada. Since Hamilton is an older city, parts that were built before 1970 still have combined sewer systems. Combined sewers are also directed to the wastewater treatment plant for cleaning before being released into Hamilton Harbour. But what happens when the amount of runoff exceeds the amount that can be held at the wastewater treatment plants?
Map of lower Hamilton, indicating the areas serviced by a combined sewer system. (Copyright © City of Hamilton)
This is where Combined Sewer Overflow (CSO) Tanks come in. These are large storage tanks that will hold excess wastewater until the storm event is over and it can be pumped back into the sewer system to the wastewater treatment plant. There are nine CSO Tanks strategically located in Hamilton, which are prepared to store up to 125 Olympic-size swimming pools worth of excess wastewater from combined sewers during heavy rainfall events.
The 2018 Chedoke Creek Spill resulted from an undetected malfunction at a CSO Tank, and brought a lot of attention to the combined sewer system and these tanks. What may not have been clear to many in the news of this spill however, is that CSO Tanks are designed with an overflow to release untreated, diluted wastewater directly into our waterways once they reach capacity—and these events occur more often than you might think. However, without this option to overflow into Hamilton Harbour for example, large areas of Hamilton would experience flooding, impacting homes, businesses, and public infrastructure.
To get an idea of how often wastewater overflows occur, and to learn more about the different types of overflows and bypasses, visit: www.hamilton.ca/wastewaterbypass. This page is updated weekly with the duration and volume of any overflow events.
The Importance of Prevention
Hamilton’s CSO Tanks are critical in limiting untreated sewage from reaching our waterways. Though as we’ve seen, these systems can and do overflow and malfunction. As Hamilton continues to experience more intense rainstorms more frequently due to climate change, CSO Tank overflows could happen more often in the not-so-distant future.
A growing number of people and organizations are realizing the need for innovative ways to maintain the natural water cycle in cities. Preventing the system from becoming overwhelmed during storm events starts by soaking up more rain where it falls. Source control measures are physical solutions located at the beginning of a drainage system. Since a lot of Hamilton is privately-owned property, opportunities for source control measures are often on residential, commercial, industrial, and institutional properties. This means there is great potential for wide-ranging improvements to the health of our city if enough people are made aware, and get involved by making small changes. Next week, we will explore the ways in which we can prevent these overflow events, and how action starts at home.
This should emphasize the importance of ONLY flushing the 3P’s—pee, poo, and toiler paper, and keeping litter where it belongs. Anything that doesn’t make it to the wastewater treatment plant or can’t be broken down safely, can clog pipes or end up as floating waste in Hamilton Harbour!