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Thunderknight 11-23-2008 01:54 PM

Sump pump smell - not sewer
My house, which is about 25 years old, has a full basement (poured concrete). Every house in the neighborhood has a sump pump that drains in the public storm (not sewer) system via discharge pipe to the street.

In my sump pit, which is lined with a plastic form, there are two corrugated pipes that enter from the slab (not the outside). There is also a 1" wide "trench" cut between the poured walls and the floor slab. This runs all the way around the basement and has a cut that leads to the sump pit. This trench is normally dry. I know my neighbor's house has the same trench.

There are no plumbing drains entering this system as far as I know. I have a seperate sewer drain that runs under the slab front rear to front and out to the public sewer system.

For the 4 years I have lived here, I have had a smell that comes from my sump pit from time to time. It tends to be worse when the water flow is low (i.e. dry weather, frozen winter ground).

The smell does not smell like "sewer" smell (based on what it smells like at sewer treatment plants). It smells more like a sulfur smell. It has an almost bitterish burning smell...I kind of think of wild onions when I smell it.

Looking in the pit, there is an accumulation of reddish - black goop (damp) at the ends of the corrugated pipes, and it is loosely clumped. The water in the pit is discolored a reddish tinge and looks like it could be muddy or sandy.

I do not notice any increase in water flow in the pit relative to sewer water flow in the house (i.e. flushing, showers). For example, right now it has not rained in some time and the pipes are not dripping any water at all in to the pit, nor have I heard the pump run in a while. After heavy rain weather, I can see water dripping in and the pump runs every hour or more.

The pump is in the pit and pumps up to PVC that runs horizontal about 4 feet along the wall, and then downwards for about 4 feet (I assume this is some type of trap) in to a drain pipe that runs out under the foundation to the street. At the point where the pump pipe meets the street pipe, there is a vent pipe that vents up out the side of my house.

I tested my basement for radon about a year ago with a short term test and it was 0.9pCi/L.

The basement is unfinished, but I do have my workshop and trains down there, so I spend perhaps 10 hours a week in the space.

I thought about sealing up the pit tightly to prevent the smell, but I am afraid that could cause a vacuum to form when the pump pumps water out. I also don't know if I should be sealing across where the trench comes in to the pit. I also thought about running a seperate PVC vent from the (then sealed) lid to the outside to provide for make-up air inside the pit. Or I thought about putting a small inline fan in that pipe to draw air from the pit and drains to the outside. I read elsewhere that I need to worry about using an explosion proof fan in that case.

While I can't be sure it's not sewer leakage from my main drain, it doesn't smell or flow like it. I just read on here about using a chlorine test to test the water, and I will be looking for a test kit (It's November in the northeast, so I don't know if I'll find any pool supplies :) )

I imagine that ground water could have a sulfur smell. I know that some remote areas in this region that have wells have to be treated to remove sulfur.

Thunderknight 11-23-2008 05:06 PM

Some updated information:

Between where the sump pump drain enters the slab floor and the outside wall (about 2 feet), there are two cleanout plugs right next to each other. I assume these are the tops of a U shaped trap in the slab.

While cleaning that area today, I found that one of the two cleanout plugs (the street side) was not covering the top. In fact, it doesn't seem to screw down, it's just laying on top. I did push it back over so it's basically covered.

I also found that the top of that cleanout is damp and looks corroded. I did look down the pipe before I put the plug back and it was fairly dry...not backed up. So I assume that plug was loosened by something brushing over it...but the fact that the cap of that pipe appears corroded has me concerned.

The house side plug looks tight and not corroded.

rredogg 11-23-2008 05:31 PM


I would start by cleaning out the bottom of your sump-pump pit. If you've got a shop vac. it would be helpful to you. If not work with a bucket, small shovel and sponge. The residue in the bottom of the pit may be the problem.

Best of luck with the project, rredogg

4just1don 11-23-2008 08:37 PM

put a new plug (is that a brass,iron, or plastic plug??)on the one that doesnt screw down,,,I am somewhat confused,,could THAT be sewer,sanitary type??? IF ya have to,,use an expanding rubber type to get her good and tight,,see if that helps

I used to live in a high sulfur ground water area too,,,that stuff stinks bad. Try bleaching the pit and lines best you can AFTER cleaning as last poster suggested. Once or twice a year bleaching may solve whole issue,,,if so an EASY cheap fix

Could be high Magnesium, think thats what we had,turned fixtures reddish black quickly,,,iced tea black and mixed drinks BITTER!!! Stinks like rotten eggs,,,sorta.But that was a shallow local well water so didnt have a choice!!

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