A sewer overflow is an event that can have a profound and damaging impact on our local ecosystems and public health. While they may seem like a distant or minor problem, these events are a serious concern that affects every community with a connected sewer system.
What Are Sewer Overflows?
A sewer overflow occurs when a sewer system’s capacity is exceeded, causing untreated or partially treated wastewater to discharge into the environment. There are two primary types of these events. In older urban areas, Combined Sewer Overflows (CSOs) are common; these systems collect both stormwater runoff and sanitary sewage from homes and businesses in a single pipe. During heavy rainfall or snowmelt, the combined volume of water can overwhelm the system, causing the untreated mixture to be discharged directly into nearby water bodies. In contrast, Sanitary Sewer Overflows (SSOs) occur in systems with separate pipes for stormwater and sanitary waste. SSOs happen when blockages, aging infrastructure, or excessive inflow of groundwater and stormwater into the sewer lines during wet weather cause a backup, forcing raw sewage to overflow from manholes, pump stations, or cracked pipes and into the environment.
Why Do Sewer Overflows Happen?
Sewer overflows are not random events; they are typically caused by a combination of factors. Heavy rainfall is the most common cause, especially for CSOs, as the sheer volume of water overwhelms the system’s capacity. Additionally, aging infrastructure is a significant factor. Many sewer systems are decades, if not a century, old, and over time, pipes can crack, break, or collapse, creating leaks that allow groundwater to infiltrate and increase the system’s volume. Blockages are a major cause of SSOs, often from common culprits like tree roots invading pipes through cracks, or the improper disposal of fats, oils, and grease (FOG) and so-called “flushable” wipes that do not break down and form solid blockages. Finally, as urban areas grow, the original systems may not have adequate capacity to handle the increased population and wastewater volume, making overflows more likely during even moderate storms.
The Damaging Impact on Waterways
When a sewer overflows, it releases a potent mix of pollutants into our waterways, with severe consequences for both the environment and human health. The environmental damage is particularly acute. The untreated sewage contains high levels of organic matter, which can cause a rapid depletion of dissolved oxygen in the water as it decomposes. This can lead to massive fish kills and disrupt the entire aquatic ecosystem. Overflows can also contain heavy metals, chemicals, and other toxins from industrial or household waste, which can contaminate sediments and poison aquatic life over time. Furthermore, the high levels of phosphorus and nitrogen in sewage act as a powerful fertilizer, leading to excessive algae growth, which can further deplete oxygen, block sunlight, and disrupt the natural balance of the waterway.
In addition to environmental harm, there are serious public health risks. Untreated sewage is a breeding ground for harmful pathogens, including bacteria like E. coli and Salmonella, viruses like Hepatitis A, and parasites like Giardia. These can cause a wide range of illnesses, from mild gastrointestinal issues to severe, life-threatening diseases. As a result, overflows can close beaches, rivers, and lakes to swimming, fishing, and other recreational activities, as direct contact with or accidental ingestion of contaminated water poses a significant risk. In some cases, sewer overflows can even contaminate public drinking water sources, posing a widespread health risk to communities.
Solutions and Prevention
Addressing sewer overflows is a complex challenge that requires a multi-faceted approach involving municipalities, businesses, and individual homeowners. Cities are working to modernize infrastructure by separating combined sewer systems and replacing aging, cracked pipes with modern, durable materials. This “gray infrastructure” is the backbone of a reliable system. At the same time, communities are increasingly turning to “green” infrastructure to manage stormwater. Projects like rain gardens, permeable pavement, green roofs, and urban tree canopies help to absorb rainwater where it falls, reducing the amount of runoff that enters the sewer system. Public awareness is also critical, as educating people on what not to flush, as well as the proper disposal of fats, oils, and grease, is essential to preventing blockages. Finally, regular maintenance for both municipal and private sewer lines, such as with CCTV drain cameras and high-pressure jetting, is crucial to prevent the buildup of debris and detect problems before they lead to an overflow.
Sewer overflows are a direct reminder of our connection to the environment. By understanding the causes and consequences, we can all play a part in advocating for better infrastructure, adopting smarter habits, and working toward cleaner, healthier waterways for our communities.