A number of things can cause sewage spills, potentially leading to serious health risks and environmental damage. In many regions of the world, sewage treatment facilities must notify authorities in the event of a spill, so that citizens can be warned and cleanup actions can be initiated. There are also a number of safeguards in place to reduce the risk of spills.
There are three main areas where a sewage spill can occur. The first is in the inflow and outflow pipes which lead to individual homes and businesses. It is also possible for a spill to appear somewhere along municipal sewage lines as they travel through a city to reach the sewage treatment plant. Finally, problems at a sewage treatment plan can lead to a spill.
In the case of sewage spills around the home, a common cause of spills is clogging of the pipes with things like grease, tree roots which grow through the line, and other materials. When this happens, the pipe backs up, potentially forcing sewage out of the drains of a home. It is also possible for water to flood the pipes if they are broken or damaged, overloading their capacity and leading to a sewage back up. In most cities, individual citizens are held responsible for maintenance of the sewage lines leading to their homes.
When sewage spills are caused by problems with the municipal sewage system, the most common cause is flooding of the lines. In areas where sewage lines are not isolated from storm drains, heavy rains can cause flooding and a spill; in some cases, sewage may even bubble up through manholes, which is not a pleasant sight. Spills can also be caused by blockages in the pipes.
At sewage treatment plants, sewage spills are often caused by flooding of holding ponds of sewage. In some cases, these ponds simply overflow, spilling sewage at various stages of the treatment process onto the ground around them, where it seeps into the groundwater and surrounding rivers. In other instances, a plant may make a calculated decision to release sewage to avert the risk of more serious flooding and damage.
The obvious risk of sewage spills is that sewage contains pathogens which are dangerous to human health. Sewage pollution can also kill fish, if it enters a waterway, and it can pose health risks to other animals. Spills may also lead to algae blooms, as organisms feed on the sewage and reproduce in large numbers. Once sewage enters a waterway or the groundwater, getting rid of it can be a very costly endeavor.