12 March 2021

Sewer Gas Odor with your Septic System


Do you have a sewer gas odor with your septic system? Wonder what the cause is?  Where on the property are the odors strongest?

  • Downdrafts causing odors?
    • Cold weather can cause downdrafts from a building plumbing vent stack – if this is the case the odors would probably vary by wind conditions and would probably subside as the day warms up; look for nearby plumbing stacks above the area of odor.
  • Long persistent odors?
    • If odors have persisted for some time, and no drains are backing, it’s unlikely that the septic system drain field is blocked. Still if the septic system is in failure, such as a failed leachfield, one common failure mode is that septic effluent is coming to the surface – which will mean outside smells.
  • Look for a wet area
    • This is a clue of sewage effluent coming to the surface, showing signs of a failed leachfield.
  • If a waste line is blocked or partly blocked and the odors are near the house
    • Effluent could be running along the buried pipe but outside it, having leaked from a damaged pipe at the wall, between the wall and the septic tank, or at the tank itself there could be an effluent leak where the line enters the tank, or at the tank cleanout top cover (which could indicate a blocked tank outlet or blocked drainfield.)
  • Effluent will follow a buried pipe because it runs in a trench dug in the soil
    • The pipe and backfill in the trench are less solidly packed than in the surrounding soil – the trench acts as a conduit to bring sewage effluent to the house if the trench is filling with liquid.
  • Broken pipe leaks may be mistaken for groundwater
    • Run a sewer camera to identify leaks or breaks in the sewer pipe.
  • If the drain field is saturated or blocked
    • Expect to find abnormally high sewage level in the septic tank, possibly even backing up and flowing out when the tank is opened.
  • Is the odor inside the house
    • P-traps tend to dry out when the air is dry and they are not used regularly or immediately after having your septic tank pumped. Run water down all drains and the floor drain to eliminate this odor