What can you dump in a combined sewer?

The phrase “Only rain down the drain” is a saying people have been hearing for quite a while. The catchy little rhyme is a way to educate people about the illegal dumping of waste products down sewer drains and stormwater drains. The idea that waste should not be dumped down drains is so intertwined with clean water that youth groups have been stenciling these messages on roadways for decades. “Dump no waste!”, in some incarnation, is even cast in iron on nearly all new sewer grates.

Before we continue let’s review the difference between separate sewers and combined sewers. In newer communities the sanitary waste sewers and the stormwater runoff are conveyed in different sewer pipes; this is called a separate sewer. Waste materials are conveyed to a treatments plant while stormwater runoff is conveyed to a nearby stream, river, or lake. Alternatively, combined sewer systems convey both the sanitary/industrial waste and stormwater runoff in the same pipe. Combined sewer systems are typically seen in central cities and inner ring suburbs. Under normal circumstance the entire combined flow is conveyed to a wastewater treatment plant for processing. However, during severe rain events the combined sewer system becomes overwhelmed and the mixed waste water is discharged to the environment untreated.

How does this relate to the dumping of waste materials down drains? In a separate sewer area the consequences are obviously bad. Waste materials such as oil, paint, solvents, soaps, feces, etc. dumped down the storm drains in streets will end up polluting our water and causing adverse health impacts. In a combined sewer area the multiple negative consequences of dumping waste materials are less understood. The thought is since a combined sewer flows to a treatment plant anything can be dumped down the drain and it will be processed. As you will read shortly there are serious consequences to human health and infrastructure when illegal dumping occurs. Both the City of Cleveland and the Northeast Ohio Reginal Sewer District have regulations controlling what can be discharged into their sewer systems; these codes identify "unacceptable discharges". The remainder of this blog will list some common items that are deemed an unacceptable discharge and how they can be detrimental to even a sanitary/industrial waste sewer.

Fats, Oils, Grease: These materials either dumped in the street or down the kitchen sink combine with wet wipes, condoms, sanitary napkins, and other debris to create a congealed fatberg. Fatbergs impede the flow of the sewer and can cause sanitary waste back-ups in to the street or even your home. Major metropolitan areas such as London and New York City especially have issues with this.

Paints, Solvents, Soap, Chemicals: These materials have the ability to mix with other chemicals that are in the sewer either by permit or illegally dumped. Run away chemical reactions can create hazardous gasses and even explosions in extreme circumstances. In 1953 a mile long stretch of W. 117th Street in Cleveland exploded leaving 1 woman dead, 60 injured, and massive property damage.

Concrete wash water, Saw cut slurry: These materials will harden in the sewer pipe creating surface roughness which will snag solid debris leading to clogs and back-ups.

Soil, Grass Clippings, Leaves: These materials will partially decompose into a slow moving sludge that can create clogs and cause back-ups.

The bottom line is that regardless of where a sewer flows; be it to the environment or to a wastewater treatment plant, it's only rain down the drain.

Keep an eye out for illegal dumping and report issues to your local service department.

Blog Author: Brent Eysenbach, Stormwater Program Manager

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