Sewer smell or mold

My rental house's basement has a distinct musty/sewer gas smell, ...I cannot tell which. I suspect it the sewer gas, but would not bet my life on it.

If it is of any help, the smell is distinct when first going down the stairs, but quickly the nose gets used to it, and it is then hard to recognize.

The house is a 40's cape cod with a full basement and cement floor, and cinderblock construction The house has a septic system and a sump pump.

I have opened the windows this summer and put in a fan to air it out. The smell is greatly reduced but not gone.

The basement has a utility sink with a sink pump to bring outflow into the stack. There is one floor drain near the sump and I have capped that. There are no other openings to drains that I can find.

I do not see where septic gas could be coming from except perhaps via the utility sink pump or the sink itself. I do not know if there is a water trap in it to prevent this. So I do not know if it is possible.

There is no such smell anywhere in the house outside of the basement.

Any advice on tracking the source down?

Thanks!

Phil

If the pump pit is not sealed , your smell may be coming from there. I also have seen some homes with overhead sewers going into the septic tank like yours with the tops of the horizontal runs of the drain pipes rotted out, so that is something to look into.

Our basement often smells musty too. If there is a door at the top of the basement stairs keep it open.

I notice that all our rooms (especially those without AC return ducts) can smell quite stale if the door is kept closed, including the basement.

"musty" is a normal basement smell. But it is not mold, and it is not sewer gas. Those are different. Mold may not smell at all, but you can see it. Sewer gas is that rotten egg smell, is rather distinctive, and you should NOT have that odor. If you do, look for an unused sink or floor drain where the trap may have dried out, or if there is an ejector sump, check for bad seals.

The floor drain is normaly trapped and needs water from time to time to prevent it from drying out and allowing sewer gas into the home...how did you cap it...many basements are just damp and have a continuious odor...in cases like this running a dehumidifier 24/7 can work wonders with a hose going from it to the floor drain so the tank does not fill up..

The drain was capped with an adjustable drain plug from HD. I did pour considerable water into the hole before closing, understanding the issue you point out This drain is very close to the sump, so I expect it to drain into the sump.

Is it possible for gas to enter via the graywater system and the sump? This seems very unlikely but I know zero about these systems.

As far as utility sink pumps, are these designed with their own vent which might allow gas into the basement? I thought these were vent-less.

Thanks again,

Phil