Septic smell

[LAL426]

I moved into my newly built house at the end of last year. We have a four bedroom house with a 1250 gallon spetic tank. We have two children who are still too young to use the toilet (in diapers). Both of us work so we do not use the toilet all that often here. For at least the last couple of months whenever it rains heavy we have a very distinct septic odor smell in the house. The smell goes away completely about 2 days after it starts raining. It only smells in a really heavy rain. Any ideas as to what this is? Could it be a major issue? I would think that the system does not need to be pumped yet. Thanks for any replies

[LazyPup]

In order for the sewer gases to enter the house there must be a problem with one or more traps on the drainage system.

After a rain the ground is saturated which slows the leaching action in the leach field, resulting in a rise in the tank liquid level. The rise in tank level increases the back pressure on the gases in the tank which then temporarily increases the amount of gasses present in the drain, waste and vent system throughout the house.

I would suspect that a four bedroom house has two or more bathrooms, and as you stated there are only two adults in the household, consequently the second bath lavatory and tub/shower are seldom if ever used. No doubt the water in the traps has evaporated out leaving the drain lines open to the house.

Solution: at least once every couple months run some water in all sinks, lavatories, tub/showers and drains to insure there is an adequate level of water in the traps. If you have a basement with floor drains pour a couple quarts of water into each drain. That would be a sufficient amount to insure the traps are full, and the excess will simply drain away.

After you have run the water in the traps you might elect to pour a small amount (1/4 cup) of liquid cooking oil in all the unused drains. The oil will float on top of the water in the traps and prevent the water from evaporating out.

[LAL426]

As soon as it cleared up today (about 5 hours after it stopped raining heavy) the smell went away completely. My wife is convinced that the smell has to do with gasses in the atmosphere when the cloud cover is low. But for now I will try solving it by running the water unless anyone else has another possible cause/solution.

[LazyPup]

You wife may be correct. In some rare instances when the atmospheric pressure is high and a roof vent is in the vicinity of an open window sewer gasses can get back into the structure in the same manner as would smoke from a chimney. It is for that reason that the codes list minimum distances a roof vent opening may be from a window.

You may examine the problem from both viewpoints. First, make sure all the traps have and adequate supply of water, then examine the location of the roof vents and see if there are any windows or other openings in the vincinity where the gases could get back into the structure.

[Hube]

In many situations like yours, the smell is emitting from the Plumbing vent on the roof. With a LOW barometric pressure such as rainy days etc,this odor can "drift" downward and enter the home thru any other openings. There are no specific codes for locating ROOF vent locations(for sidewalls ,yes) but the remedy would be to ADD a couple of feet of vent pipe to the existing pipe, and see if that eliminates any "down-draughting " odors. Good luck Hube