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Thread: Sewer gas from septic tank bubbling through P traps

  1. #1
    DIY Junior Member RickRick's Avatar
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    Default Sewer gas from septic tank bubbling through P traps

    Hi,
    I recently started getting sewer gas bubbling through the P traps in the kitchen and a bath sink. I am guessing that it's because the septic field is not handling the water as this only occurs when we use the washing machine and run many loads back to back and put a lot of water in the system.

    I rebuilt the house maybe eight years ago now and replaced 100% of the plumbing - all the way to the tanks. The work was inspected and met code. The tanks have been pumped regularly and passed inspection each time. Other than this issue, everything still functions as expected.

    There are two septic tanks that drain into a common field and my problem occurs when the washer drains into tank #1 and forces air/gas through tank #2 and bubbles through the bath and kitchen traps. There is nothing common between the tanks on the house side of each tank so the only path to get from the washer drain to the bubbling drains is through the field side of the tanks. I snaked the roof vent for tank #2 and it appears to be clear. I do not have any problems - no slow drains or anything at any other time. Even once the washer is done, I don't have any backups and can use all fixtures without issue. That's not to say the field is not slow but it seems to get by.

    I guess this makes sense if the field is on its last leg and it gets a lot of water but I am puzzled as to why the air does not vent through the roof vent but instead bubbles through two P traps. Could the force be strong enough that it is venting through the roof vent but also the P traps?

    Both the bubbling drains are vented with a studor vent. The kitchen sink is in an island and the bath sink is on an outside wall and due to the way the foundation was built, a pipe could not be run in that wall. There is a roof vent nearby for the toilet and tub.

    The tanks and field are over 40 years old and I am sure are full of roots as there are large trees close to the field.

    Any thoughts? Any suggestions as to what I can do to deal with this until spring (we are in Michigan)? I did put a cleanout between each tank and the house and they are not very deep so I am sure I can do something there if needed - a temporary vent or something until spring.

    Thanks,
    Rick

  2. #2
    In the Trades Jerome2877's Avatar
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    The studor AAV will allow air into the system but not out. So if there is back pressure it has no other place to go. The solution would be to install a proper vent through the roof.

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    DIY Junior Member RickRick's Avatar
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    Thanks for the reply. There is a vent through the roof in the same system where the studor vents are installed because there is also a toilet and tub in the system. I would never use just a studor vent and don't really like to use them at all but since I had a roof vent so close I was not very concerned. It sure seems like the roof vent would be the path of least resistance especially since when this bubbling occurs, there was no water running in any of these drains.

  4. #4
    One who lurks Basement_Lurker's Avatar
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    Have you inspected the roof vent yet?
    Broken promises don't upset me. I just think, why did they believe me? -Jack Handy


    www.blackbirdkitchenandbath.com

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    DIY Junior Member RickRick's Avatar
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    Yes, the roof vent is clear. I ran a snake down passed the bubbling drains. Snake dropped in very easily and was dry so I don't have any standing water in pipes. The vent is a straight shot down the wall to the crawl space so I was able to check that all drain pipe hangers are still in place and nothing is sagging anywhere.

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    DIY Junior Member RickRick's Avatar
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    I had more time this weekend to check this out and it's being caused by a bad drain field. I was able to dig up three clean outs and the problem is obvious. I will need to have a raised engineered field constructed to replace it. I am sure the county will not let me do any work to the old field.

    I am trying to get an idea where I can have the field built before I get someone out this week. Is there a limit as to how far the water can be pumped from the tank to the field? Any rough idea how big would the field need to be?

  7. #7
    General Engineering Contractor ballvalve's Avatar
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    40 years is past its time for a leach field without some upgrades.

    One may often have space to add trenches between the existing ones. If your standard system worked for 40 years why go to the huge expense and shorter life of a pressure dosed raised bed?

    No limit on pumping length.

    Call the septic expert, and OLD one, first, before the county.

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    DIY Junior Member RickRick's Avatar
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    I am quite sure the county will not allow any work on the old field as just about evey neighbor has been through this now and they all have a lovely raised field in their backyards. The water table here is just to high to pass any perc test ( I assume that's what they still do). I will try though. There are a few old companies around including the one that has pumped our tanks for years. I will contact them tomorrow. My only reservation about doing anything with the current field is that there are two 80' tall maple trees vey close to the field (one is within ten feet). But then again, it has worked for years. I assume the trees use a good amount of water at least in the summer. There is no place to put another normal field even if I could. If I need a raised field I would like it to be a couple hundred feet away from the current tanks.

    Anyway, any advice if/when I end up getting a raised field installed?
    Last edited by RickRick; 01-16-2011 at 01:01 PM.

  9. #9
    General Engineering Contractor ballvalve's Avatar
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    Three bids from known companies. Make the county inspect everything in stages before covering it up.

    If they insist on an engineer, you may not need a raised bed, you could possibly do a sand filter flush to the surface, pressure dosed, and then into a short disposal trench, maybe even the old field. Call engineers that do septic, the county should have a list, and you will find many ideas and concepts.
    Last edited by ballvalve; 01-16-2011 at 11:37 PM.

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    DIY Junior Member RickRick's Avatar
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    Thanks for the info again ballvalve. I made a number of calls today and have learned that in our county, the only option is to have a county health dept. engineer design any and all septic field modifications and installations. No one will touch an old field or install a new one without a design from the county. The county offices are closed today so I will check with them tomorrow. I will ask what options I have as far as design.

  11. #11
    General Engineering Contractor ballvalve's Avatar
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    Did you get that information from local independant engineers? Its not legal by any definition, as the "book" of septic solutions runs thousands of pages.

    Here we have 8 engineers to chose from and probably 6 basic varieties of fields for bad areas. Most counties do not want the liability of the design and would much rather take the private engineers stamp as a liability preservative.

    In fact, if you do profile holes, and the inspector is unsure, they check out of the process completely, and the private engineer even does the construction inspection.

    Our health dept. only specs and inspects standard systems, though they do decide trench length, and if chambers or rock.

    The main issue is do you wish to "test" the nature of the official policy, and possibly have them brand you [very falsely] a troublemaker. County workers can be reals devils, or good natured joes.
    Last edited by ballvalve; 01-18-2011 at 09:45 AM.

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    DIY Junior Member RickRick's Avatar
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    I plan to meet with the county tomorrow to ask what all my options would be - including if I can somehow repair the existing field. I am curious to see what they say before I get a perc test. If they don't offer many options, I will do some reaserch with some private engineers who work in nearby counties to see what systems they have installed. We are ony a couple miles from the next county. It sounds like our county is unique compared to nearby counties.
    I completely understand what you mean by testing the nature of the official policy. I went down that road with them when I had a new well drilled...or should I say a couple of expensive holes and then a well. I was pleased to find there was a different person there now so I am hopeful.

  13. #13
    DIY Junior Member RickRick's Avatar
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    I had a perc test today and I need to have a raised engineered field installed. They want me to replace the old tanks and the area where I want to put the field is over 300' from the tanks so it's going to be quite a bill....likely around $18K.

    I was hoping the town would run sewer before the old field got this bad.

    I plan to get started while the ground is still frozen so we will have better access.

    Thanks to everyone for your replies.

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