Sewer Gas Odor in Basement

D107

Over the past few years every month or so, sometimes more often, we get the smell of sewer gas in our basement. 1924 house. (Prior to 1955, house waste was diverted to the house rear towards a septic tank; so stack plus runout, cleanout , house trap and sewer line are all about 65 years old.)

We've had people over to look but usually they say call us when the smell is there so we can figure it out. We've had our sewer line videoed but no blockage shows. There is root intrusion but RootX takes care of that. My knowledgeable neighbor says they can smell sewer gas sometimes coming from the manhole in front of their house--depending on prevailing winds-- but not in their basement; feels it could be pitch of sewer main or blockages that happen time to time. The smell usually doesn't last for more than an hour or two. I've had our DPW come out and check the sewers and they couldn't find anything--by the time they came smell was gone.

We have been trying to figure out if smell is from the street or our own system. Yesterday it definitely had the street smell. When I've checked the main trap other times, it's full of water as it should be. Our house is also about 55 feet of 4 and 5 inch clay and transite pipe from street connection, goes from about 6 to 7 below the ground. Our house is on about a 2-3ft hill, so sewage would have a bit of a climb--we've never had a backup into our basement, but before we started using RootX we have had root blockages that required snaking and cutting. We have the two trap plugs, another basement cleanout plug and a slop sink that would the first to show seepage.

In trying to figure out what conditions could cause the odor I wondered if it was worth looking at a crack in vertical air inlet pipe which is just on the house side of the main trap. The inlet terminates with a drain cover on the outside wall of the house but the vertical portion is inside the foundation, covered with sheetrock. Of course if there was water in the trap then no sewer gas from the street should get past the trap to enter the air inlet. Seems to me that either sewage is entering the trap or the trap has to have no water for there to be such a smell.

Perhaps a blockage within the main stack from debris or an errant spaldeen? The diagram below is a good example of our house piping. Love to install a back-flow preventer but not sure where we'd fit it in.

Intplm.

@D107 If the trap is full of water and does not have a leak draining it past the trap weir then the smell is most likely coming from the house side of the drain. This of course can be located on the vent or the drain.

You mention that you have clay pipe. I usually ask folks if they have had any work done , road construction or anything of that nature that could cause the clay pipe to move allowing for the sewer gas smell? This could be a cause of the smell put one that is not obvious.

If the trap is buried as pictured, it could have a leak that stops at a height that looks like it is full but is not and may have lost its prime. Draining ever so slightly below the traps weir, or the traps water height, and causing that smell.

"Orangeburg", or clay pipe can become very brittle and crack easily over its lifespan.

Smells are always a head scratcher. This smell is intermittent? Leading me to believe that the smell only occurs when the drainage system is used and is not a constant smell.
Be on the lookout for when it is used to investigate further.

An indoor brake at the trap or the pipe near the drain serving the trap is the place to continue looking.

This is one reason why DWV systems are terminated through the roof rather then as shown in your drawing.

D107

@Intplm.
You wrote:

Intplm. said:

@D107 If the trap is full of water and does not have a leak draining it past the trap weir then the smell is most likely coming from the house side of the drain. This of course can be located on the vent or the drain.
I guess to see this closely at all I'd have to tear away the sheetrock--see photo.

You mention that you have clay pipe. I usually ask folks if they have had any work done , road construction or anything of that nature that could cause the clay pipe to move allowing for the sewer gas smell? This could be a cause of the smell put one that is not obvious.
The line is 4in cast iron from the trap down six feet, then transitions to 4in transite, then at 34ft transitions to 5in orangeburg. Added problem is that transite has issues and doesn't last forever either.
There is heavy root entry between 34-41st in the clay and has been for years. Could not the gas escape from the breakage and 'hug' the line up towards the house? I knoW I have found roots entering the trap pit in the past

If the trap is buried as pictured, it could have a leak that stops at a height that looks like it is full but is not and may have lost its prime. Draining ever so slightly below the traps weir, or the traps water height, and causing that smell.

"Orangeburg", or clay pipe can become very brittle and crack easily over its lifespan.

Smells are always a head scratcher. This smell is intermittent? Leading me to believe that the smell only occurs when the drainage system is used and is not a constant smell.
Be on the lookout for when it is used to investigate further.
Not sure about smell only apparent when drainage system used but worth checking out. I do know that it does not appear every time system is used.
An indoor break at the trap or the pipe near the drain serving the trap is the place to continue looking.
Yes and to do that I guess it might be worthwhile to remove the sheetrock--see photo--around the vent pipe and thoroughly check everything.

This is one reason why DWV systems are terminated through the roof rather then as shown in your drawing.

Hmm...Well the main stack does terminate through the roof but you're referring to the DWV. I guess roof exit would tend to keep smells distant, but some of the conditions you've speculated upon might not be solved by the roof exit. Thanks so much for your excellent suggestions.

Also in the photo you will see a small grille at the top, which is above the vent and when I removed it and looked inside it was full of plaster debris possibly from construction of finished basement and others have suggested it is a mere handhole for access. I checked and haven't noticed any smell coming from that.

Intplm.

That grill on the wall should not be part of the plumbing system.

Do you have any of these installed anywhere on your system?


They can, at times emit sewer gas .

Intplm.

DWV is drainage waste and vent. The vent in your drawing shows the vent penetrating through the wall and not through the roof.

If it becomes enough of a bother, yes you will need to remove the sheet rock. I hope you find the issue there after going to all of that trouble.

D107

@Intplm. Yes we have one mini-vent in the basement slop sink and also in the first floor half-bath sink. Yeah I guess wise to check the low-hanging fruit first. Do they get stuck open after the water drains? Do they need to be serviced or replaced? Not sure whether to call a sewer man or plumber to help suss this out.

I also thought if the air inlet vent was blocked, or the first floor toilet vent was blocked that might cause issues. Probably easy to open the main trap air inlet cover on the outside wall--not an upside down U as in the photo--and verify there's no debris in there.

Zman

If you put smoke in the pipe you will figure this out quickly. There a machines available that work very well. In your case, a simple smoke bomb would probably do the trick.
Combustible gas detectors can be useful for pinning down the origin of sewer smells as well.

Intplm.

Yes. Checking the sure/studor vents are a good idea. The problem with finding a smell that isn't always there is they are so good at migrating from a place other then from where they originate.
@Zman suggests using smoke. That is a very good idea.
I would do the smoke test first before anything else. Use harmless smoke like theatrical smoke. Safety first!
I haven't used smoke in over 35+ years but I think it's a good idea before taking walls down.

Afterword , if you still can't find the leak It's probably the the intermittent issue of a studor/sure vent failing. And possibly the house trap issue I mentioned earlier.

D107

@Intplm. @Zman My sewer guy snaked and videoed my line last year. His thoughts:

Roots - my thought is that you have the beginnings of a backup just because we know you have relentless root intrusion - and it's not quite completely stopped up yet. But as the water rises in the pipe and it gets as high as your vent line - it in effect cuts off your vent - because it's full of water. It's then going to force out odors other places - But it's just an educated guess.

Attached are links to the two videos he made from last year--in case you're really short on entertainment-- one before snaking and one after. He may be right above, but even in the 'before' tape, you can see that it's not until he reaches 24 feet in that the water gets an inch or so deep and it does get deeper going forward. So not sure if water that far down in the pipe is going to cut off venting. On the other hand, he had a limited flow going with a hose--it wasn't a toilet flush or wash cycle's worth of water. He didn't come there specifically because we were backing up but to help a sewer installer give an esimate for replacement. He does say that the intermittency can be caused by the water rising then receding as it drains back it no longer blocks the vent. For the past 8 years or so annual treatment with RootX has kept us free of backups.

Before https://www.dropbox.com/s/ipjlsoofpz1zmp9/2019-05-17-16-30-28.mp4?dl=0

After https://www.dropbox.com/s/tasvoi8q8ljlpk3/2019-05-17-17-38-40.mp4?dl=0

Zman

Assuming you have vents on the plumbing branches in the house, I can't imagine a flooded house vent causing the smell.
Were they able to cut the roots and worm out at 38'? I could see that being a serious issue down the road.

D107

@Zman He spent quite a lot of time with different size blades etc and went in and out a few times on that second video but there were some portions that would not come out. Not sure why; I always assumed that snaking would remove everything. Perhaps we need to Hydrojet? Overall pipe looked much better after snaking with spots at 34 and 38ft still not fully clean. We were going to install a new line but the Transite gives me pause in how to deal with such material. One contractor wanted to leave the existing trap and the initial cast iron run, replace the transite and clay up to a few feet from the cityline connection; others replace it all the way to connection.

Intplm.

Something else comes to mind.

Do you have any plumbing fixtures or floor drains that have lost there trap prime. Any of those could be the cause of this. Has there been a floor drain that was covered over by new flooring installed?

Your drain seems to be fine now. Eventually those roots that have been left in the drain will be a clog problem.

MikeL_2

We like to use oil of peppermint to test DWV systems. It's easy, effective, pleasant to track / trace, and, you can control it. Sanitary sewers don't usually have the same odor produced by festering septic tanks; is it possible a decaying animal, battery, or natural gas leak is causing the scent?

D107

@Intplm wrote:

Intplm. said:

Something else comes to mind.

Do you have any plumbing fixtures or floor drains that have lost there trap prime. Any of those could be the cause of this. Has there been a floor drain that was covered over by new flooring installed?
Not as far as we know. Small house, 2 bathroom sinks, two toilets, 1 kitchen sink, 1 basement slop sink, all with primed traps. There is a basement cleanout between the bottom of main stack and house trap that may just be straight pipe, will have to check. But the smoke test should also tell me if any of the vents including the trap air inlet or main stack are blocked or are leaking.
Your drain seems to be fine now. Eventually those roots that have been left in the drain will be a clog problem.

Note that those videos are from a year ago. I applied RootX early May.
As a layman, I can easily understand how the gases could enter if:
1. Loss of prime of main or other traps;
2. Blockages of vents or main stack.

What I don't see is--agreeing with @Zman --how, if the water in the line from the street rose in level due to either root blockage or street backup how that could cause odor except if the smell out of the broken clay 'hugged' the outside of the line and entered the house trap.

Since Saturday there is no smell and we have used the water as usual except we haven't used washing machine yet.

Aside from getting a smoke test, which will tell us about the house side, we're also trying to figure out how we can know if the odors are coming from the street side, whether from temporary blockages, or bad main pitch, etc.

D107

@MikeL_2 Don't think decaying animal, battery or natural gas leak pertains here. I'm very familiar with natural gas smell. How do you disperse the oil of peppermint?

MikeL_2

D107,
We like to identify all possible contributors and do an orderly & documented process of elimination. I've been involved in scores of offensive odor investigations; about 25% of the time it's related to a DWV system.
Stored fertilizer, pool chemicals, acid / drain cleaner, lawn equipment, generators, evaporator or drain pans under freezers/ icemakers / refrigerators / ac equipment / dehumidifiers /, etc have all put up a stink.
Don't open the bottle of peppermint oil until you're on the roof, and definitely
don't bring it indoors. Dedicate someone to pour it into a rooftop plumbing vent and don't let that person inside the house. The vent should be capped afterwards - peppermint oil expands rapidly and will find a leak.....

mattmia2

Does the odor by any chance track the uh...type of waste you have put in the sewer system inside the building? If the vent system inside the house is leaking somewhere, it is only going to stink if the effluent in the inside of the house at the time stinks.

Could be a small leak in one of the fittings leading from the toilet as well.

D107

@mattmia2 yes I had tried to ascertain that. The possible 'inside' odor you describe does seem a bit less than the 'full-on' street sewer smell we had Saturday. And after looking at videos of smoke tests, I can easily imagine any number of old cast iron joints, toilet fittings, even the body of the house trap as intplm. suggested, having pinholes.

If the house trap air inlet was leaking that might be subject to prevailing winds––especially a downdraft into the roof stack(?) But the air inlet is on the house side of the trap, so if the trap's full, supposedly odors could not pass. It's been three days and no odors at all. I think a smoke test is the smartest way to go.

However having just looked at some old photos of renovations where we uncovered some of the plumbing vents done by the previous owners in the 1980s, I'm going to check those out. I suspect venting was done very poorly which could account for some issues.

Intplm.

@D107
Years ago I had a similar issue that turned out to be that someone had covered vent stacks with a matching cap. This was done on a commercial building during a renovation.
A year later the caps were found and the sewer gas smell went away.
I suspect that you have either a cracked fitting. Your fixture vents are faulty, or your main vent(s) are plugged or partially plugged.
look to those few things first.The process of elimination should show some results.

mattmia2

it is possible the studor vents are stuck closed or even clogged with lint or something and causing the water to get sucked out of the trap in say the laundry sink too.

D107

@mattmia2 Had a plumber out and he verified that vents seem to be working. Most parsimonious explanation is that weeks ago when I used a plunger on the slop sink to speed up drainage, it exercised the mini-vent, which may have been stuck open after doing the laundry. since that time there has been no smell. It could have been that mini-vent or the 1st floor bathroom sink. I've rinsed out both mini-vents and will keep a nostril open....