After I was done exposing the sewers, I just scratched my head looking at the layout. But with time, I pieced together the intent and figured out how it worked.
At the north end of the building, where the sewer exits toward the street, I have this cast iron piece, which turns out to be a check valve. This valve prevents sewage from backing up into the basement if the city sewer system gets overwhelmed. It is probably also the reason why we found no evidence of flooding in the basement.
Having sewage backing up into the basement is a real issue in Chicago, with its combined sewer system. A combined system basically transports sewage from buildings along with stormwater runoff from building, streets and parking lots in one and the same pipe system.
If it rains really hard, that pipe system may not have enough flow capacity to handle the runoff volume, which can lead to the infamous basement flooding. A check valve can prevent this.
But, once the check valve is closed, how does any sewage leave the building? This is where this other piece of pipe comes into play – the overflow.
With the valve closed, and sewage stacking up in the pipe, it eventually will spill out through the overflow into an ejector pit. I have the ejector pit already removed, but it is basically a round catch basin, 18 inches across and 30 inches deep.
At the bottom of the pit is a sump that picks up any spill over and pumps it under pressure into the street side of the check valve.
A check valve like this needs regular maintenance, such as greasing once a year. Our check valve here hasn’t seen any maintenance in God knows how many years. I am even not sure if it still works.
The sump pump also needs regular checking to make sure that it will work when needed, i.e. during flooding. Flooding usually comes with heavy storms, which may also cause a power outage. In that case, I am still protected from sewage backing up into the building thanks to the check valve, but I can’t use the bathrooms because the pump won’t work - unless I have a battery backup.
Huh! I don’t know about this. Should I keep the system with the check valve and sump, or should I look for another solution?
