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Climate Change and Toronto's Aging Sewage System

For this week, The Pristine Blue Initiative will be looking at an issue that is occurring more frequently every year in Toronto, Mass flooding and Toronto’s aging sewage infrastructure

Flooding in Toronto and climate change

In the summer of 2018, Toronto saw some of its heaviest rainfalls with flash floods overwhelming sewage systems across the city. Social media and news articles captured the stunning images of partially submerged streetcars and cars in flooded underpasses across the city. Major intersections were underwater, causing dire traffic conditions, with the TTC subway forced to shut down due to the high volume of water. The flood in one instance had almost become life-threatening for some; people were trapped in flooded elevators, with just inches of air leftover before being rescued.

Over the years, Toronto has been the subject of many floods but what has changed is its vulnerability to flooding. According to the Insurance Bureau of Canada (IBC), Toronto floods in 2013 reportedly led to damages worth $1 billion, ranking as the “most costly insured severe weather” on record in Ontario. Just last year, the August 8 flooding in Toronto alone incurred insured damages worth $80 million. From population density to land use change under increased urbanization coupled with antique infrastructure particularly the sewage system, not to mention the underlying design of the city and its construction activities near waterways, Toronto is vulnerable to flooding. The city is faced with the grim reality of devastating potential for flooding and a precarious future in terms of flood risk as severe weather such as flash flooding with its frequency and intensity are expected to increase under climate change.

Why focus on aging sewage infrastructure?

With the need for a comprehensive response strategy to better manage and mitigate the flood risk facing our city, one of the key areas of intervention is understanding the role of aging sewage structure during flooding. Flash floods with combined sewer overflows (CSOs) due to aging infrastructures are the culprit of significant property damages costing tax payers and insurers, endangering Toronto’s water quality among others.

During a typical storm, high volumes of rainfall are generated within a short period of time. The water reaches the ground surface, with some infiltrating into the subsurface while others result in runoff which eventually ends up in Lake Ontario through a series a pipes managing stormwater. The urban landscape of Toronto with paved surfaces however allows for reduced infiltration, resulting in a larger runoff that enters the drains and complex system of pipes and waterways underlining the city. Toronto’s century old sewage system in older parts of the city combine sewer system with storm water management. A typical combined sewage system is characterized by a single pipe system that carries both sewage and storm water, meant to be sent to wastewater treatment plants; which under heavy rainfall events gets diverted to Toronto’s water ways when the system is past its capacity to handle the deluge of combined sewer flow.

As it happens, Toronto’s antiquated sewage infrastructures are inadequately prepared to accommodate the influx of high volume of stormwater, resulting in the flash floods and combined sewer overflows that have been witnessed around the city. During heavy rainfall, waste content gets backed up from wastewater treatment; with rain water responsible for creating the overwhelming volume of combined sewer overflows during flash floods carrying sewage with all of its harmful microorganisms and chemicals. Aside from the devastating damages of a flash flood, the city is confronted with precarious water quality during and after flooding. The basement flooding damages from these floods not only make for expensive repairs but the sewer backup events flood homes with the accompanying waste materials and pathogens which can be harmful for health with disease-causing agents. The combined sewer overflows affecting the quality of the water that is released into the city and its water systems has yet to be adequately addressed.

Geographical distribution and implications of combined sewage structure on water quality:

Figure 1. Map of Toronto by type of sewage system. 2009.

On one hand, the combined sewer overflows are like our last-resort valves - they open up and expel untreated water directly into the lake or river when the system is overwhelmed. On the other hand, without the outlet, a large part of Toronto with its pre-1940 combined sewage system cannot handle the outbound torrential storm water combined with the cumulative output of waste materials from the neighbourhoods. We are forced between the two evils: flash floods, or contamination of the precious Lake Ontario. The combined sewage system is a problem in 25% of Toronto. The older areas in central south of Toronto (Figure 1) tend to have the combined system, making them prone to flash floods. Our neighbours in the Greater Toronto Area, such as York, Durham, and Peel regions, all have zero combined sewage system.

In response to these flash floods, the City of Toronto has initiated basement flooding protection subsidy program that helps households retrofit their homes against flooding. Moreover, the City has committed about $3.1 billion for stormwater management which will help fund basement flooding protection programs as well as target storm water quality released into the city’s waterways and the Lake. Although these initiatives are promising, there is more to be done.The debate around flooding issues rarely includes the larger public on the impact of these flooding events, the aging sewage infrastructure, on the state of the city’s water systems from human to marine ecosystem health issues.We can only imagine, from toilet bowls to dish washers, whatever content there is in sewage, it is indiscriminately expelled into the lakewater when we resort to combined sewer overflows.

In a report by the Former Environmental Commissioner Dianne Saxe, sewage from 60 aging municipal sewer systems were released into Southern Ontario waterways from April 2017 to March 2018 notwithstanding the issue of runoffs with fertilizers and winter road salts contaminating our waterways. Lake water contamination with sewage contents such as fecal matter is a public health concern. The Lake Ontario Waterkeeper which monitors water quality in Lake Ontario, found that the city reported a total of 38 sewage bypasses into Lake Ontario in 2013 to the Ministry of the environment and the municipality under provincial laws but failed to inform residents on the precarious water quality. Upon conducting water sample test in the aftermath of the July 12, 2013 storm, the Lake Ontario Waterkeeper revealed E. coli contamination in Humber River and the Toronto Harbour near Sugar Beach, well beyond the approved provincial standards. As such, public transparency on the extent of CSOs entering Ontario waterways and its impact on water quality is an important issue as it concerns public health and the health of the environment. The City’s discourse on reducing flood risk and flood damage must address the issue of stormwater management systems in depth including the combined sewage system and infrastructure design to better protect not only the flood damages against property but also the health of the City’s waterways and the Lake. At the very heart of Toronto’s flooding crises, climate change is brought up each time flooding events such as the 2018 one overwhelms the city with exorbitant amount in property damages and flood damage clean up. With the grim forecast on climate change and its effects on flooding events across the City, we need to develop a long term strategy including infrastructure development and preparedness that takes into account the role of climate change instead of expedient solutions that may leave us ill-prepared in long run.


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