Terminology Tuesday

Published on October 29th, 2013 | by growwny


Terminology Tuesday: CSO & SSO


There is no doubt that modern infrastructure is affecting our environment. One of the issues that comes up frequently is sewage overflow, specifically the terms CSO and SSO. Combined Sewer Overflows (CSO) and Sanitary Sewer Overflows (SSO) both can cause problems through pollution of local waterways and have features that make them an environmental nightmare.

A Combined Sewer Overflow is when waste/storm water from a combined sewer system is placed directly into a larger body of water. Basically, the separate sections of an area’s sewer system eventually combine into one channel. From there, whatever wastewater is collected is supposed to be taken to a treatment facility where they remove any toxins from the liquid. However, there is a maximum capacity that these treatment facilities can accept from the sewer system. The true controversy occurs when weather conditions, such as heavy rain or snow, cause an excess amount of wastewater to flow through the combined sewer. The amount that can’t be accepted is instead dumped into bodies of water such as lakes, rivers, and oceans. Unfortunately, this excess water is never treated and is therefore high in toxins that can severely pollute local waterways. This discharge of untreated water is known as a CSO. An overflow wall in the pipe is at a specific height that corresponds to the maximum capacity of the local treatment facilities. When the water level is higher than the wall, that surplus amount flows out of the CSO into a waterway. For obvious reasons, the pollution can be detrimental to the surrounding ecosystems as well as the health of the people in the area.

On the other hand, a Sanitary Sewer Overflow refers to anytime that wastewater is released into the water before reaching a treatment facility. According to this definition, a CSO is technically a form of SSO since in both cases the water is not sanitized before exposure to the environment. Although they are similar forms of untreated sewage discharge, an SSO is distinct from a CSO due to the fact that a CSO only occurs with a combined sewer. In regard to an SSO, the overflow can be caused by malfunctions other than just an excess of wastewater. For example, the wastewater can leak due to cracks in sewer lines, power failures at stations, etc. SSO can be particularly dangerous because it is harder to detect than CSO. With an SSO, a crack can be anywhere along a sewer line, whereas the CSO is clearly seen at the edge of a waterway.

Both Combined Sewer Overflows and Sanitary Sewer Overflows pose significant risks to the environment. Their unrestricted disposal of hazardous wastewater into the surrounding environment affects all forms of life depending on that area for resources. Over longer periods of time, the accumulation of larger amounts of toxins can be truly devastating.

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