I lived in my current house for five years. Location is Chicago suburbs. I never had an issue until last summer, in a bad summer storm I had my basement flooded due to failed sump pump and failed backup pump. A licensed plumber came in and opened the sealed pit (due to radon) and installed two new pumps, he did not re-sealed the pit. Five months later, one month ago, I noticed a horrible odor, coming out directly from the pit. I flushed the pit with a garden hose and 3 gallons of bleach, the older went away only to come back the following morning. I examined the bottom of the pit, nothing unusual, the water is dark grayish, and some water trickling from the drainage opening into the pit, I collected a sample, it looks clear, does not smell too bad. I bought a new lid and completely sealed the pit, the smell is still there, maybe stronger! two PVC pipes come out on the pit cover, each connected to each pump, they drain outside the house separately, additional galvanized smaller maybe half inch pipe come out, goes into the ceiling then I do not know where, not traceable. I have full finished basement with floor tiles and with radiant hot-water heating, it is working fine, no visible leaks. I have a bathroom next to the pit, it is used often, I also flushed it with Clorox. Next to that I have an ejector pump which is completely sealed, no odor. And the furnace room there is an additional pit with sump pump, it has a cover but not sealed, seems to be working fine, no odor.No leaks no clogging no odor anywhere else in the house. I do not have a septic tank, the village has well maintained main sewer lines. One interesting observation, it is when I disconnected the pumps, the water level filled up above the drain opening inside the pit and covered it, the odor miraculously disappeared for one day, then came right back when I restarted the pumps and the water level sank below the opening!! the check valve is see-through, the water color is grey-ish. The check valve is only installed on the main pump.I placed food coloring on all the sinks and showers and toilets, the color in the check valve remained the same. I do not know how to proceed, any advice? If you need any further clarifications, please ask Thank you in advance.

the water level filled up above the drain opening inside the pit and covered it, the odor miraculously disappeared for one day, then came right back when I restarted
I would say that the odor is coming from the drainage pipes, not the pit. Suggest letting the pit fill with water (up to floor level) and then add bleach and hope that enough bleach will run into the pipes to eradicate the odor. I would use a lot of bleach (couple of gallons) then cover and seal the pit and let it sit for a couple of hours.

I think the problem is you don't have vent for the sealed pit. When pump starts pumping it needs air supply to replace water and air that has been pumped out. If there is inadequate replacement air supply, pump will draw air from where ever it can, including that drain opening.

Each sealed pit should have dedicated vent terminating above the roof. Not sure what that 1/2" pipe is for. If it is meant to be an air vent, than it is way too small to replenish pumped out water and air.

Try to install short piece of 2" pipe as temporary vent on top of the pit with AAV, and to see if that helps

Milo

"he did not re-sealed the pit". Pit should be sealed. Anything totally sealed needs a dedicated vent.

I think the problem is you don't have vent for the sealed pit. When pump starts pumping it needs air supply to replace water and air that has been pumped out. If there is inadequate replacement air supply, pump will draw air from where ever it can, including that drain opening.

Each sealed pit should have dedicated vent terminating above the roof. Not sure what that 1/2" pipe is for. If it is meant to be an air vent, than it is way too small to replenish pumped out water and air.

Try to install short piece of 2" pipe as temporary vent on top of the pit with AAV, and to see if that helps

Milo

I started to have the odor when the pit was not sealed, then I sealed it but that did not solve the issue


I think the problem is you don't have vent for the sealed pit. When pump starts pumping it needs air supply to replace water and air that has been pumped out. If there is inadequate replacement air supply, pump will draw air from where ever it can, including that drain opening.

Each sealed pit should have dedicated vent terminating above the roof. Not sure what that 1/2" pipe is for. If it is meant to be an air vent, than it is way too small to replenish pumped out water and air.

Try to install short piece of 2" pipe as temporary vent on top of the pit with AAV, and to see if that helps

Milo
I will try that, thanks