Plumbing vent beginning to clog with snow (C) Daniel FriedmanCold or Wet Weather Sewage or Septic Odors
Diagnosis and Repair Guide

  • SEWER GAS ODORS in COLD WEATHER - CONTENTS: How to diagnose & cure sewer odors that occur in wet or cold weather. Causes and cures for sewer gas odors related to wet or cold weather. Questions & Answers on tracking down cool weather and night time sewer gas / septic tank smells. How to find and cure bad smells in buildings
  • POST a QUESTION or READ FAQs about diagnosing the source of septic or sewer odors in cold weather
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Cold-weather-related sewer or septic system odors:

This article describes how to diagnose and correct sewer gas or septic odors (and other building smells and odors with focus on diagnosing odor sources and causes in cold weather. This article on diagnosing sewer gas or septic odors is a special cold-weather edition of our more general advice on finding and curing sewage odor problems.

Here we focus on sewage or septic odor problems that occur during cold weather or wet weather.

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Sewer Gas Odor Tracking by Site Location and Season or Weather

Photograph of melting snow indicating septic tank locationArticle Series Contents

Where on the property are odors strongest? you may be able to point to a waste line, building exit piping, leaks at a septic tank, drainfield failure, or even a neighbor's septic system problem.

  • 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.
  • Frozen septic systems causing odors?: If a septic system is backing up due to a failed (or frozen solid) drainfield, sewer gases may be pushed back into the home even before there is an actual sewage backup (this is unusual but possible. usually a sewage backup is not far off.)

    If the system is clogged, such as a clogged waste line, blocked septic tank inlet or outlet line or baffle (in the tank), or failed drainfield, and if the system is in common daily use by one or more people, you'd expect that the system would soon backup, forcing drains to back up with sewage, starting at the lowest drain in the building - look there.
  • Long persistent odors? If odors have persisted for some time, and no drains are backing up, it's unlikely that the septic system drain field is blocked. Still if the septic system is in failure, such as a failed drainfield, one common failure mode is that septic effluent is coming to the surface - which will mean outside smells.

Look for a wet area, possibly covered by snow in northern climates - kick the snow aside in a grid pattern over the septic system components (don't' fall into a collapsing septic system - it can be fatal).

Look for areas where snow has melted to a thinner cover. This can occur in a normal system (bacterial action in the soil over the septic system and warm septic effluent carry heat out of the septic tank). But it can also be a clue of sewage effluent coming to the surface. Check such areas for effluent.

If a waste line is blocked or partly blocked and the odors are near the house, such as at the house wall at the waste line exit point, 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 would 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 sewer pipe (C) Daniel FriedmanBroken pipe leaks may be mistaken for ground water leaks:

At left we show a broken sewer pipe found by lifting a section of sidewalk in a soft smelly area of the yard.

At a different property where basement paneling was removed following "a history of basement water entry from 'rising ground water' (according to the basement de-watering company)" a company had installed an expensive interior trench and drain system and sump pump to pump the "ground water" away.

We saw an inverted "vee" of leak stains on the basemen wall extending from below the main waste line where it exited the building.

It was obvious that the water entry had been not from rising ground water but from a broken leaking waste line outside the wall. Sure enough, our septic dye appeared in the new basement trench and drain system in just a few minutes.

The basement de-watering system had not been needed at this home, and the owner still needed to have the broken waste line excavated and repaired.

Look for leaks at a waste line, perhaps first by having a plumber snake the line from inside the building to see if s/he feels evidence of a broken or collapsing or damaged pipe between the house and the septic tank.
See How to Find Distance to Drain Blockage

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, and possibly also evident at the distribution box.

Sewer gases occurring in wet weather:

Any of the following articles will offer helpful suggestions for finding the source of odors that seem to appear only in wet or cold weather:

Plumbing Vent Blockage Problems as a Source of Building Smells, Septic or Sewage Odors

This topic has moved to PLUMBING VENT BLOCKAGE ODORS - separate article

PlumbingTrap Siphonage, Dry Plumbing Traps, Sewer Gas Leaks & Freezing Weather-Related Plumbing Vent Problems

This discussion is now at TRAP SIPHONAGE & SEWER GAS

How to Find & Fix Sources of Septic Odors that Occur in Cold Weather

This topic moved to TRACK DOWN COLD WEATHER SEWER ODORS - separate article

Tips for Tracking Down Hard-to-Find Sewer Gas Odors in buildings

Please see SEWAGE ODOR SOURCE LOCATION - other Sources of Sewer Gas or Methane Gas Odors in buildings


Continue reading at SEWER GAS ODOR REMEDIES or select a topic from the More Reading links shown below.


Or see TRACK SEPTIC ODORS to SOURCE - weather independent

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SEWER GAS ODORS in COLD WEATHER at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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