Persistent sewer odor in my basement driving me crazy

[pasadena_commut]

Thanks! I think I will get one such detector.

I had one of those on order (my wife's car has a gasoline odor coming from somewhere and we couldn't find it "by nose") which arrived yesterday. After letting it warm up and setting the sensitivity in clean air it did not go off when placed near either a sink or a shower drain for 30 seconds (with working traps and no odor). When the cap was pulled off the clean out in the front yard and the sensor placed just above it, it went off immediately, and there was a sewage odor there. When poked a couple of inches through a hole in a manhole cover over the city's sewer line in the street in a couple of seconds it lit one LED but also stopped ticking. That might be the "sudden change in humidity" effect the manual talks about rather than a true detection. A sewer smell above the manhole cover, if present, was not detectable over the strong "hot asphalt" and "nearby mystery oil spill" smells. (The neighbors must have thought I had lost my mind, kneeling in the street to sniff a manhole cover.)

In conclusion, the device did actually detect sewer gas in the places where I could smell it, and did not detect it where I could not.

Other notes:

It is way too easy to bump the sensitivity dial. Nudge it one way and it screams (in clean air), the other way would give a false negative. The dial should have been recessed or had a cover to avoid that.

The manual says that if the batteries are put in backwards the device will get very hot and be destroyed. Wow. Profit margins so tight that they couldn't add any protective circuitry?

 

[ybnewhomeowner]

You could buy a test plug and seal the drain off with that. Home Depot and Lowes sells them.

You could also get some plastic bags and put a wash cloth in the bags and shove that in the drain real tight.

Once the smell completely goes away for 3-4 days, remove the bag or test plug and see if the smell comes back.

Hi, just a follow-up question. I ended up getting a test plug of the wrong size and Home Depot does not have the correct size for my floor drain. So I am looking at the wash cloth in plastic bags alternative. Does the wash cloth have to be dry or wet for this purpose? Thanks.

 

[Twowaxhack]

Hi, just a follow-up question. I ended up getting a test plug of the wrong size and Home Depot does not have the correct size for my floor drain. So I am looking at the wash cloth in plastic bags alternative. Does the wash cloth have to be dry or wet for this purpose? Thanks.

Dry, the bag does the sealing, the rag is just to get your diameter so that that it fits tight into the drain.

 

[ybnewhomeowner]

I had one of those on order (my wife's car has a gasoline odor coming from somewhere and we couldn't find it "by nose") which arrived yesterday. After letting it warm up and setting the sensitivity in clean air it did not go off when placed near either a sink or a shower drain for 30 seconds (with working traps and no odor). When the cap was pulled off the clean out in the front yard and the sensor placed just above it, it went off immediately, and there was a sewage odor there. When poked a couple of inches through a hole in a manhole cover over the city's sewer line in the street in a couple of seconds it lit one LED but also stopped ticking. That might be the "sudden change in humidity" effect the manual talks about rather than a true detection. A sewer smell above the manhole cover, if present, was not detectable over the strong "hot asphalt" and "nearby mystery oil spill" smells. (The neighbors must have thought I had lost my mind, kneeling in the street to sniff a manhole cover.)

In conclusion, the device did actually detect sewer gas in the places where I could smell it, and did not detect it where I could not.

Other notes:

It is way too easy to bump the sensitivity dial. Nudge it one way and it screams (in clean air), the other way would give a false negative. The dial should have been recessed or had a cover to avoid that.

The manual says that if the batteries are put in backwards the device will get very hot and be destroyed. Wow. Profit margins so tight that they couldn't add any protective circuitry?

Hi, thanks a lot for this. I really appreciate your efforts in testing this on sewer odor!!

My detector arrived 1 week ago, and I have tried it a number of times, by strictly following the instruction manual (including the "warming up" step in clean air, and setting the sensitivity dial at just the right level). But it was not able to detect the sewer smell in my basement even when I pointed the sensor right next to the floor drain. To be sure, I had already made my attempt to seal the floor drain at that time, and I did not open the floor drain to test the detector. But I could still smell the odor in the basement, particularly when I bend down next to the floor drain and sniff.

To be sure, the smell has been reduced after I sealed the drain using a combination and adaptation of the methods suggested here. But it is certainly noticeable to me still. I am still pretty sure that the smell mostly comes from the floor drain.

Now the question is what to do about it. I certainly want the smell to be completely gone.

 

[pasadena_commut]

Hi, thanks a lot for this. I really appreciate your efforts in testing this on sewer odor!!

My detector arrived 1 week ago, and I have tried it a number of times, by strictly following the instruction manual (including the "warming up" step in clean air, and setting the sensitivity dial at just the right level). But it was not able to detect the sewer smell in my basement even when I pointed the sensor right next to the floor drain. To be sure, I had already made my attempt to seal the floor drain at that time, and I did not open the floor drain to test the detector. But I could still smell the odor in the basement, particularly when I bend down next to the floor drain and sniff.

To be sure, the smell has been reduced after I sealed the drain using a combination and adaptation of the methods suggested here. But it is certainly noticeable to me still. I am still pretty sure that the smell mostly comes from the floor drain.

Now the question is what to do about it. I certainly want the smell to be completely gone.

Well, that is both bad and good. Bad because you won't be able to track down the source using that tool. Good because it indicates (assuming the meter isn't broken) that there isn't actually all that much sewer gas in your basement. Always do a positive control, you need to verify that the meter in your hands is actually working. Take off the gas cap on your car and walk towards it slowly (response time isn't fast) with the meter already set up and it should certainly go off when it is near the open gas filler, and will probably go off at quite a distance.

From here:

https://www.forensicsdetectors.com/blogs/articles/sewer-gas-detector

Is my nose more sensitive than a gas detector?

Yes. The human nose is more sensitive than a ppm type of gas leak detector.

Your nose can detect down to 0.001ppm. A detect that costs about $100 bucks detects down to about 1ppm.

The problem however is that the nose changes sensitivity once it smells a rancid smell such as sewer gas in the home. A process called olfactory fatigue reduces its sensitivity, and as such, is not a reliable objective detector.

So in other words, a sewer gas detector is more effective than the human nose for identifying a sewer leak and a much more objective instrument. But, the initial nose sensitivity is much more sensitive than any gas leak detector on the market.

There are lots of different types of molecules in sewer gas and the detectors of this type pick up those that are mostly carbon and can burn. I don't believe that they detect hydrogen sulfide (H2S) at all. Conversely, people easily smell H2s but cannot smell methane. The primary smelly compound in sewer gas is hydrogen sulfide which our noses can detect at less than 1 part per billion. There are special H2S detectors (some are listed on the web site linked above) but unless you spent a lot I don't think you would find one with more sensitivity than the meter you now have.

Maybe have the sewage system smoke tested? There is a description of this here (I didn't have to sign in to read the page, even though it asked me to):

https://www.linkedin.com/pulse/great-stinko-sewer-gas-sarah-gudeman

 

[ybnewhomeowner]

Well, that is both bad and good. Bad because you won't be able to track down the source using that tool. Good because it indicates (assuming the meter isn't broken) that there isn't actually all that much sewer gas in your basement. Always do a positive control, you need to verify that the meter in your hands is actually working. Take off the gas cap on your car and walk towards it slowly (response time isn't fast) with the meter already set up and it should certainly go off when it is near the open gas filler, and will probably go off at quite a distance.

From here:

[link removed]



There are lots of different types of molecules in sewer gas and the detectors of this type pick up those that are mostly carbon and can burn. I don't believe that they detect hydrogen sulfide (H2S) at all. Conversely, people easily smell H2s but cannot smell methane. The primary smelly compound in sewer gas is hydrogen sulfide which our noses can detect at less than 1 part per billion. There are special H2S detectors (some are listed on the web site linked above) but unless you spent a lot I don't think you would find one with more sensitivity than the meter you now have.

Maybe have the sewage system smoke tested? There is a description of this here (I didn't have to sign in to read the page, even though it asked me to):

[link removed]

Okay, so I tried the detector with the gas tank of my car. Yes, it did go off. So this is an indication that this detector is not faulty.

In my own research, I did find this sewer system smoke test. But from what I understand, it can costs thousands of dollars to carry out. I am not even sure the plumbers in my small city are capable of doing this. But even if they are, I am not sure if I am willing to spend all that amount of money to do this test, given what I already believe about the source of the odor:

The smell is restricted to the basement, not the other parts of the house. And I am pretty sure that it is from that floor drain, just by the simple act of squatting and sniffing. Assuming this is correct, what can I do to make that floor drain stop smelling? This is essentially the question I was trying to get an answer to from the start.

I have a plumber coming this Friday for this problem. They only work on weekdays, and I had to take a day off for this, and make an advance appointment. I am hoping to be able to solve this problem before Friday so that I don't have to spend hundreds of dollars, if not more. But if I am not able to eliminate the odor, what can I do in advance to make the Friday plumber appointment as useful as possible?

Thanks!

 

[ybnewhomeowner]

The test will show us the way. Let us not worry.

Okay, so I tried my best to seal off the drain again, using a combination of what you and another commenter suggested (place wash cloths in plastic bags, and stuff those bags in the drain hole). The result is the same as my previous attempt to seal it off. The smell went away, but only for a 1 or 2 days, and then it came back. I am still convinced that it is from the floor drain. I am not sure what more I can do. Should I use those "drain cleaners" even though I don't see any obvious signs of blockage?

I have a plumber appointment this very Friday, for which I had to take time off from work. I was hoping to be able to resolve this issue so that I can cancel that appointment and save hundreds of dollars. I still hope to be able to do that. But if not, what can I do in advance to make the most out of the Friday appointment?

Thanks!!

 

[MicEd69]

The sewer gas that you are smelling is H2S, as others have said. Using a combustible gas detector that you can afford to purchase is/was not a good idea. The odor threshold of H2S is 0.01-1.5 PPM, while the lower explosive range of H2S is 43,000 PPM. So, it takes at least 28,666 times the concentration of H2S that you can smell for it to be combustible. The detectors that you can purchase for a reasonable price will not have the sensitivity to detect odor threshold levels of H2S.

As you have already used soda/vinegar and bleach to clean the drain, I would suspect that there is a crack in your drain if the smell is coming from the drain. Or the gas is bubbling up through the water in the trap. But I would think you would have said something about the water in the trap being disturbed when toilets are being flushed, showers being used, etc. If sewer water is somehow getting into the trap water because of a partially plugged line, the only thing I could suggest is to pour some vegetable oil in the drain. That will float on the water in the drain and seal any smell that is coming from the water in the trap. But it will not stop any bubbling of gas that may be happening or seal any crack in the drain, just something else to try.

 

[Twowaxhack]

Okay, so I tried my best to seal off the drain again, using a combination of what you and another commenter suggested (place wash cloths in plastic bags, and stuff those bags in the drain hole). The result is the same as my previous attempt to seal it off. The smell went away, but only for a 1 or 2 days, and then it came back. I am still convinced that it is from the floor drain. I am not sure what more I can do. Should I use those "drain cleaners" even though I don't see any obvious signs of blockage?

I have a plumber appointment this very Friday, for which I had to take time off from work. I was hoping to be able to resolve this issue so that I can cancel that appointment and save hundreds of dollars. I still hope to be able to do that. But if not, what can I do in advance to make the most out of the Friday appointment?

Thanks!!

If you sealed off the drain and the smell came back with the drain sealed then the smell is coming from some other place.

I can’t smell it from my house so I’m not 100% sure what you’re smelling is sewer gas. I have people mistake all sorts of smells for sewer gas.

 

[Twowaxhack]

You could have someone pour some peppermint oil in the plumbing vents on the roof and then without that person coming inside the house, you could monitor inside for peppermint smell. Turn off all ventilation fans and HVAC systems. Pour a quart of hot water down each vent pipe after the peppermint oil.

This way proves it’s the sewer if you smell peppermint and can help pinpoint the source.

 

[humbolt]

This is just my 2 cents. First I have not read where you called your city department that is responsible for keeping your street sewer lines cleaned. My cities water department is responsible for cleaning the street sewer lines. So now this is my experience for what it is worth. I also, every once in a while smell that sewer odor in my basement. So when that happens, I call my water department and sooner or later I will notice a water department truck show up on my street, remove the man hole cover, and spend some time with equipment placed into the sewer. The staff then tells me that the culprit, as well as what they are doing, could also be my Ptraps as well as their continued cleaning of the street sewer line. They then recommend, for maintenance to help prevent the reappearance of the sewer odor, to pour two capfuls full of Clorex bleach in one gallon of hot water into the drains in my basement at bedtime and to do this for 2 days. They also recommend placing the same in all drains not used every month.

But I must say that it appears you have a very complicated sewer issue and my comment solves a pretty simple sewer oder issuie. Again just my 2 cents.

 

[pasadena_commut]

How would you describe the "sewer gas" smell? H2S smells like rotten eggs, butyric acid (which can form if there is the right mix of organic material and bacteria) smells like "cheesy vomit", skatole or indole produce the "fresh poop" smell, ethyl mercaptan (the odorant from natural gas) has a skunky smell, and the "dead animal" smell is from putrescine, cadaverine, and related compounds. Those are I think the most likely stinkers you are likely to encounter in a situation like this. Some of these are heavier than air and might accumulate in your basement. The nose is very sensitive to all of them.

Sorry the combustible gas detector didn't work for this application. As long as you have it though, you might as well test all your gas appliances in the house, especially at the hose connections.

 

[chinarus]

If the basement drain sole purpose is to serve as an emergency drain I would remove the drain cover, cover it with a freezer bag or similar material, reinstall the vent cover and evaluate the results by sniff testing again.

 

[Twowaxhack]

If the basement drain sole purpose is to serve as an emergency drain I would remove the drain cover, cover it with a freezer bag or similar material, reinstall the vent cover and evaluate the results by sniff testing again.

You’re a little late to the party

 

[ybnewhomeowner]

How would you describe the "sewer gas" smell? H2S smells like rotten eggs, butyric acid (which can form if there is the right mix of organic material and bacteria) smells like "cheesy vomit", skatole or indole produce the "fresh poop" smell, ethyl mercaptan (the odorant from natural gas) has a skunky smell, and the "dead animal" smell is from putrescine, cadaverine, and related compounds. Those are I think the most likely stinkers you are likely to encounter in a situation like this. Some of these are heavier than air and might accumulate in your basement. The nose is very sensitive to all of them.

Sorry the combustible gas detector didn't work for this application. As long as you have it though, you might as well test all your gas appliances in the house, especially at the hose connections.

I honestly don't know how most of things you listed smell like. I can say however, that it does not smell like a dead decomposing body. It does not smell like 'fresh poop' - at least not mine. I am not entirely sure what a rotten egg smells like, but I know sometimes people associate bad breath with a rotten egg. And it can say that the odor in my basement does not smell anything like bad breath. It does not smell like the gas from my car's gas tank. As to natural gas, which I have heard sometimes people mistake for sewer gas. I've smelled natural gas for cooking before, and it did not smell like the odor in my basement. I don't use gas service in the house. However, the pre-purchase inspection home report does note that there is a gas meter at the exterior surface at the side of the home.

 

[ybnewhomeowner]

The sewer gas that you are smelling is H2S, as others have said. Using a combustible gas detector that you can afford to purchase is/was not a good idea. The odor threshold of H2S is 0.01-1.5 PPM, while the lower explosive range of H2S is 43,000 PPM. So, it takes at least 28,666 times the concentration of H2S that you can smell for it to be combustible. The detectors that you can purchase for a reasonable price will not have the sensitivity to detect odor threshold levels of H2S.

As you have already used soda/vinegar and bleach to clean the drain, I would suspect that there is a crack in your drain if the smell is coming from the drain. Or the gas is bubbling up through the water in the trap. But I would think you would have said something about the water in the trap being disturbed when toilets are being flushed, showers being used, etc. If sewer water is somehow getting into the trap water because of a partially plugged line, the only thing I could suggest is to pour some vegetable oil in the drain. That will float on the water in the drain and seal any smell that is coming from the water in the trap. But it will not stop any bubbling of gas that may be happening or seal any crack in the drain, just something else to try.

Thanks.

If it were a crack (which I imagine would be very expensive to fix), would there be any other signs?

And the possibility of blockage: I previously poured a huge mop bucket of water into the floor drain, and the water drained without any problem, and I did not see or hear any bubbles then. Would that rule out any blockage?

 

[pasadena_commut]

I am not entirely sure what a rotten egg smells like,

Really? Not a terrible idea to find out, since even hints of that odor tell you not to eat the food it is coming from. Easy experiment. Hard boil an egg. Punch a small hole in it. Let it sit out for a couple hours at room temperature to pick up some bacteria. (Preceding steps are to limit the amount of decay somewhat, using a fresh egg will result in a stink bomb of epic proportions.) Put it in an airtight container and leave it somewhere warm for a week or so (will vary depending on temperature and the number and types of bacteria that get into it). Take it outside, way outside, open the container and have a small sniff. Then close the container and throw it out.

I don't use gas service in the house. However, the pre-purchase inspection home report does note that there is a gas meter at the exterior surface at the side of the home.

What does the house use for heat in the winter, an electric heat pump? Anyway, if the house really doesn't use any gas then double check that the shutoff valve near the meter is turned off. (Most likely it is.) If the meter exists there are probably gas pipes in the house and there would be no good reason to keep them full of gas. (Assuming this is a standalone house and that the meter doesn't serve any of your neighbors too.)