Septic gas belching past full p-traps/ Septic tank drainfield failing? Venting issue?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by ryan100, Dec 7, 2007.

  1. ryan100

    ryan100 New Member

    Split level house in the country--approximately 30 years old
    Septic system--1500 gallon tank
    I've lived in house while renovating for about 2 years. My parents owned it previously. House was unoccupied for approximately 5 years to me moving in and renovating.

    First noticed very strong septic gas smell from lower level bath vanity (vessel bowl.) Happens only when water is run and gas immediately breaks or "belches" past p-trap seal. This is where the worst gas problem occurs.

    Later noticed this was happening in kitchen sink on main level of house. Gas is not as strong, but still very evident.

    Finally checked main bath on upper level (two basins on vanity) and smell is very faint. Same belching condition.

    There is no siphoning of water from p-traps. Bubbles "belch" through p-trap when water is run from fixture and runs into drain.

    The home never previously had problem to my knowledge prior to the 5-year period house sat unoccupied. My parents lived here and I grew up in the home. The original homeowner (who my parents purchased house from in early 1980's) also built the home primarily himself. While most construction was outstanding, I question his understanding of plumbing. None of the individual fixtures in house have their own vent branch into the main stack with the exception of the kitchen sink, which actually has its own vent (through roof.) The main stack actually serves as a long wet vent into which most of the waste lines drain into. Neither vent through the roof is clogged...they have both had a hose run down and verified water runs freely through. In the crawlspace below the kitchen I opened a cleanout which is directly below the sink and water from the kitchen sink vent was very visibly running clean through.

    I had a plumber out. He had no answers other than "most fixtures were not properly vented." He could not explain why kitchen sink emitted the gas because it did seem to be vented.

    But wait, there's more: I had the septic tank pumped about 3 months ago. I learned later that the tank probably had 3 access points (1500-gallon concrete tank) but we only dug down to the center. Therefore, the inlet and outlet were not inspected. This was the first time in 30 years the tank was pumped. The "pumper" said that it seemed surprisingly not overfilled with solids. Additives like Rid-X were used throughout the years, including recently.

    This septic tank is buried right behind the home, and to my knowledge is attached to the usual drainfield. However, one unique (and probably unlawful) feature is that several hundred feet away in a small primarily dry creek an overflow pipe peeks out which I'm told is an overflow from the septic system. When excessive rains came, it was uncapped to provide a release point for an apparently overtaxed drainfield. This has been uncapped since I've lived here (2 years) and probably a number of years prior. There doesn't appear to be much dampness coming from it, however I haven't tested it by running massive amounts of water in the tank and seeing if there is any "overflow" from this drainpipe.

    The lower bath (where gas odor is worst from sink) is the last stop on the main waste line that runs out towards septic system. I removed the toilet (the very last fixture draining into the waste line before heading out towards the septic tank.) I had someone run water from the kitchen sink (main level of house) and a massive amount of gas was emitted from the toilet pipe (as waste water ran down main stack and down towards this line on its way towards septic tank.)

    So...barbaric septic gas seems to be creeping up into the main stack and the various waste lines to fixtures, and most of the sink p-traps appear to fail to keep it in check.

    As I mentioned, this was not problem in the past to my knowledge. Therefore, although I recognize the system is not properly vented, why did it become a problem at some point? The septic odor is unbelievably rank. By the way, I worked as a licensed embalmer for a number of years, so I know a bad smell when I'm exposed to it!

    Could the septic drainfield be failing/clogged to some extent and not absorbing gases? There has been no problem with waste water backing up.

    Obviously it's as if the gas is trapped throughout the stack and doesn't fully release through the roof vent(s).

    Anyone? Anyone?

    Many thanks in advance. I'd be glad to answer any specific follow up questions. I'm starting to lose sleep over this after having nightmares about trying to re-vent the system, only to learn the septic tank (drainfield) is the culprit. Or how about vice versa? Either way, I know I'm talking about a decent sized investment to rectify this.
    Last edited: Dec 7, 2007
  2. cwhyu2

    cwhyu2 Consultant

    Cincinnati OH
    Have you had the tank pumped recently?Have the baffel on the incoming
    side of tank checked.
  3. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Central Florida
    Have you checked the roof vent(s) for obstructions? Could be critter nest(s).
  4. leejosepho

    leejosepho DIY scratch-pad engineer

    Yes, and improving the venting at individual fixtures would likely not affect the bottleneck, wherever it is.

    Checking the inlet of the septic tank *might* reveal some kind of partial blockage that lets sewage build up in the line before forcing its way into the septic tank and causing an unusual backup of gas that then overpowers the system venting through the roof once it gets to moving, and I would actually look into that possibility at both ends of the tank. Then, maybe some roots have your distribution box (just past the outlet of the tank) partially blocked. The inspection ports in the top of that tank are only going to be a couple of feet away from the center port you have already located, so you should not have any trouble finding them. Personally, I would also vent either the distribution box or the line between it and the tank so your overall system can breathe someplace other than inside your house while on its way to the roof.
  5. chel_in_IL

    chel_in_IL New Member

    Northern IL (bbrrrr!!!)
    I have a bi-level house (like a raised ranch), and the septic runs out the bottom of the house and into the septic tank. From there, it runs into a lift-station with a pump, which draws the liquids up and out to the distribution box, which then goes to the field lines.

    Last winter (stuff like this always happens when there is snow on the ground and it's harder to work on), the lower level toilet started burbling whenever water was run elsewhere. A week after, the septic backed up through the basement drain. I had the smelly gases from the drains as well.

    The septic company found that the rear baffle was gone, which allowed solids to go into the lift station, and clogged up the line from the lift to the dist box. Soon after I had this replaced, the lift pump went, so again the house stunk and the septic backed up.

    With my experience, I'd wonder if your system had some sort of blockage down the line from your tank which is causing it to drain slower.
  6. hj

    hj Moderator & Master Plumber Staff Member

    Cave Creek, Arizona

    What you call "belching" is probably the air trapped in the drain coming up through the overflow passage, and if so it is bringing the odors from that passage. Pour some liquid drain cleaner into the overflow opening to kill any growths in the overflow and that should eliminate your odors.
  7. ryan100

    ryan100 New Member

    Follow up to responses

    cwhyu2: I did have the tank pumped about 3 months ago, and didn't have the access hatches near the outlet and inlet uncovered and opened. I learned later (and especially now) that this was critical.

    Mikey: The roof vents are all clear. I had a hose (fast stream of water) and auger down them.

    leejosepho: Thanks, I do believe you are right in thinking that something is not right with the flow through the septic system. I'll be starting with digging it out again (all three ports/hatches and probably the distribution box, this time) and having everything inspected and investigate the flow of wastewater into and through the system. I'm pretty sure there are no tree roots in this area after digging and trenching for other projects nearby and not running into any (there are no trees in the backyard, either.)

    chel_in_IL: I'm in Illinois, too! Thanks for sharing your experience, although you're septic is engineered differently, I think the partial blockage theory should be investigated next. I'll have to wait until better weather. I'm in southern Illinois, between Carbondale and St. Louis, MO.

    hj: Thanks, although there is NO overflow on two of the sinks (a glass vessel bowl in the lower bath and the stainless kitchen sink. The gas is emitted from both of these drains (the lower bath vanity-vessel bowl is the worst fixture in the house.) I have used a flashlight below the vessel bowl vanity to shine through the white plastic p-trap and can see large bubbles move upwards breaking through as water first begins to run down the drain. All the drains have been bleached several times, and I've eliminated that this is the smell of hot water (anode rods removed from hot water heater and hot water tank bleached out 2 years ago...this was necessary because I use a water softener which contributed to the sulfur-bacteria smell problem inside the hot water tank.)
  8. You should have your septic tank pumped and inspected at least every five years. I have my 1977 system tank pumped each year that ends in a 0 or 5 to keep it simple.
    If you have no vents on your sinks, I would at least install an air admittance valve as high as possible under each sink after the trap.
    Cap off that illegal septic overflow drain into the creek. If you have to have any repairs done to the system, they should get a permit and inspection from your Health Department, and there might be a fine involved for that violation.
    The solution to your problem may be adding another drainfield line due to the others becoming sluggish.
    Good Luck!
  9. Cass

    Cass Plumber

    The frequency of pumping is determined by 2 things the size of the tank and the # of people using the house.

    Generally I recommend every 2-3 years for a family of 5 or 6.

    The cost of pumping in comparrison to a field replacement in nothing.
  10. Yep. It costs only $225 to pump a tank here, and a whole lot more to replace drainfield lines. All NC septic permits now require a "repair area" that doubles the layout size of the drainfield area so that the homeowner can replace the entire field if and when necessary.
    The "pump-the-tank-out at least every five years" is the minimum recommendation by NC State University, which has conducted extensive septic system studies for many years. If usage is above average, then more frequent pumping is needed, as Cass says.
    NCSU studies have also concluded that all of those septic system additives are unnecessary and a waste of money. Normal usage will provide all of the bacteria needed for a system to function properly.
    I've been on a septic system for 31 years now, and I've never used additives, but due to the drainfield having shrubbery planted over it, I flush a cup or two of copper sulphate crystals down about three times per year to prevent roots in the lines. No problems.
  11. ryan100

    ryan100 New Member

    It's time for springtime septic digging

    Hello, everybody, I'm coming out of hibernation. Better weather is right around the corner here in Illinois and my father and I will be digging out all 3 access portals to my septic tank and also uncovering the distribution box to inspect the system to see if anything is evident that might be causing the odd gas back pressure in this 30-year old septic system. I suspect there may be a problem with the tank inlet tee or maybe the outlet, so maybe that will help solve my problem quickly.

    Two additional questions that I've been thinking about:

    I have heard of creating a running trap between the house and the inlet to the septic tank. In fact, I have read that some installers put them on all septic systems. Does anybody have any caveats about this? I'm not really sure it would help if there is such a back pressure problem in the tank. Although I don't seem to ever get the back pressure of septic gas through the shower drain trap in the lower level bathroom nor any toilets, but it does come out most of the sink drain p-traps, so maybe this helps predict that a large 4" running trap outside between the back of the garage and the septic tank (this is a fairly small run) would help block the pressure.

    Venting the septic tank or distribution box is the possibility previously discussed here which I agree may be necessary. What is the best type of vent for this and how far does it have to rise from the ground? This is going to be very evident in the back yard of the house.

    Thanks for all the ideas so far. I'm just about ready to get shoveling.
  12. leejosepho

    leejosepho DIY scratch-pad engineer

    My vents are flush with the ground. You should be able to find a green, plastic 4" grate that fits inside a PVC coupling at the top of the vent pipe.

    I live just a little east of you, and yesterday a septic contractor reported digging through 39" of frost. My guess is another month before our shovels will be useful!
  13. got_nailed

    got_nailed DIY Senior Member

    I do know that in some parts of PA that you have to have a dedicated septic vent that can tie in into other vents but only in the roof. With concrete floors and a finished house you would need to go out side and run it up the house (this is an off the wall I just woke up thought).

    As far as a sluggish drain field unless the pipes have collapsed I would think they would be fine after 5 years. Don’t quote me on this but I did read (a few places) somewhere that if the lines have 6 months of no use to dry out that most of the time they will work fairly well after words. I would think it might be more on the side of tree roots for your being sluggish.

    I don’t deal too much with septic systems (we have the septic people for it). But can’t they test them after the tank fills back up by watching how fast the water goes out of the last chamber?
  14. ryan100

    ryan100 New Member

    Okay to install elbow at septic tank inlet baffle?

    If I could revise the title of this thread it would be appended to say: The Nightmare Continues.

    I'd like to report that I have just installed 2 vents on my septic tank (just outside the tank at the inlet and outlet) and still have noxious gas breaking through certain household sink traps when water is run down them. After calling out various plumbers and listening to countless free "coffee shop opinions" there is still no resolution.

    My septic tank is still completely uncovered (it is buried almost 2' deep) and I'm now thinking about two other alternatives to solve this ongoing headache:

    1. A whole house running trap. This is going to be a pain because the septic is only a few feet from the back of my garage and I've already chopped into the line to install one of the vents. Also, a french drain runs along the back of the garage and over the main line out to the septic, so I have very little room to work to put in a running trap.

    2. Inside the septic tank at the inlet, putting a 90 degree elbow on the inlet and running a bit of pipe down below the surface of the tank's contents, thus preventing the gas inside the tank from entering into the inlet and back into the house. Currently there is no tee on the inlet. This concrete tank is over 30 years old and was built with baffles. I did put a tee on the outlet because the concrete baffle on the discharge side of the tank is starting to deteriorate.

    Is there a problem with putting an elbow (not a tee which would be open at the top) at the inlet and running a short length of pipe down into the tank in an attempt to stop gas from coming back in the house?
  15. leejosepho

    leejosepho DIY scratch-pad engineer

    One of my tanks was originally made with an inlet box that was essentially like an elbow down into just below the tank's fluid level, but I do not believe something like that would solve your problem. Wherever your obstruction or defective plumbing might be, your problem is like trying to pour water into a slender neck on a large bottle.

    Since you have vented your septic tank and your burp problem still persists, my guess is your "bottle neck" is somewhere ahead of your septic tank; for whatever reason(s), your drain plumbing is not allowing an immediate escape (venting) of air whenever something is drained into it.

    Maybe those few feet of pipe between your last fixture and your septic tank are partially clogged and draining far more slowly than they should?

    If you can, you might try placing a temporary "test vent" right after your last fixture ... and I bet it fills with water when you drain that sink.
  16. Redwood

    Redwood Master Plumber

    Absolutely Amazing!
    I wish I had seen this earlier.

    One of the first things I would have looked into is the condition of the line to the tank. This is exhibiting classic symptoms of a partial blockage or, a belly in the line.

    With the tank inlet cover open have someone flush a toilet and listen at the cover. You should hear water rumbling as it falls down the drop to the line. Then maybe you will hear it slosh as it comes through the horizontal pipe, then it will pour out into the tank.

    If you do not hear the rumble of the water falling I guarantee that is your problem. Even if you do hear it it may still be a problem and a camera inspection will reveal for sure.
  17. ryan100

    ryan100 New Member

    Yes, some water is standing in discharge line out to septic.

    Hmm, based on what you've both said I guess you might be interested to know one detail I left out of my update. When we uncovered the tank fully this time, the backhoe operator and my father immediately noticed that the line running into the tank was angling slightly upward into the tank. Not a downslope into the tank. Some water is standing in the main pipe. The straight main pipe is about 25' from the lower bath (fixtures draining directly into the main pipe at the lowest level) and maybe 35' from the stack drop which collects from the other house drains on the upper levels. We did flush an upstairs toilet a few times to see what was happening and it did appear some minor solids were getting hung up in water the main line. Nobody thought that this water standing in the pipe would be enough to cause any problem.

    My father thinks the septic was installed this way. (That the installer dropped the septic tank in the excavation and realized that somebody should have dug the hole a little deeper, but didn't do it.) I wondered if the tank had heaved in some way over time to cause the line to angle upwards, thus creating this venting/gas problem only over recent years.

    Many thanks for your replies, do you have additional thoughts based on what I added...perhaps confirming your insightful suspicions? You are saying that this condition will absolutely need to be corrected?
  18. Redwood

    Redwood Master Plumber

    It is with no doubt in my mind the source of your problem.
    The line from the house to the tank needs to be properly pitched at 1/4" per foot to allow proper venting. lowering it at the tank, raising it at the house, or, just redoing it in the middle to have proper pitch is essential.
    Whatever it takes!
    This recommendation requires on site measurement to uncover the best option in your case.
  19. ryan100

    ryan100 New Member

    Inspecting the line

    That's what I was afraid you were going to say (regarding fixing the pitch of the line.) That entire length of pipe (30' or so) is under a poured slab. Ouch. I guess getting somebody out with a camera to inspect the line will be the next logical step.
  20. Redwood

    Redwood Master Plumber

    That would be. as well as checking elevation at the tank and inside to see if proper pitch is possible.
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