Photograph of part of a septic tank showing the area of sewer gas accumulation How to Cure Sewer Gas Smells from Septic Tanks & Septic Systems

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Sewer & septic gas & odor cures & prevention:

This sewer gas smell article describes how to get rid of or cure odors in buildings including septic or sewage or sewer gas smells or "gas odors" in buildings with a focus on homes with a private onsite septic tank but including tips for owners whose home is connected to a sewer system as well.

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How to Diagnose, Prevent, or Cure Odors and Hazards from Gases in Septic Systems

Photograph of part of a septic tank showing the area of sewer gas accumulationIn a properly constructed drain-waste-vent system and septic tank installation, sewer gases produced in the septic tank find their easiest escape path back up through the scum layer and into the septic tank inlet tee and from there up the drain waste vent (DWV) system to the building plumbing vent stack system where gases are vented above the building roof.

More septic or sewer gases may escape and make their way through the tank's outlet tee top into the soil absorption system where the gases are distributed over a larger (leachfield) area and further filtered and deodorized by the soil.

Where a building is connected to a municipal sewer, the building drain-waste-vent system (DWV) includes traps and vents to be sure that any sewer gases passing back up waste lines are vented safely above the building roof.

Watch out: as we warn in all of our sewer gas articles, because sewer gas contains methane gas (CH4) there is a risk of an explosion hazard or even fatal asphyxiation. Sewer gases also probably contain hydrogen sulfide gas (H2S) In addition some writers opine that there are possible health hazards from sewer gas exposure, such as a bacterial infection of the sinuses (which can occur due to any sinus irritation).

Depending on the sewer gas source and other factors such as humidity and building and weather conditions, mold spores may also be present in sewer gases.

Also see Wet Weather or Cold Weather Septic Odors or Sewage Odor Diagnosis & Repair Guide for additional odor tracing and cure advice for odors occurring during wet or cold weather.

A variety of mistakes or just plain bad luck about site terrain shape and prevailing wind, or something more serious like a failing septic system can, however, produce sewer odors at a property.

Here are some steps to diagnose and correct gas odors at properties served by septic systems. Some of these steps also apply to homes connected to a municipal sewer as well.

What Gases Form in the Septic Tank

At SEPTIC & CESSPOOL SAFETY we've already explained that gases produced in a septic tank are dangerous, as a potential source of explosion and as a cause of death by asphyxiation if someone falls into or deliberately enters a septic tank.

The gases that form in septic tanks are primarily two, methane, CH4, and hydrogen sulfide H2S. It's the H2S (a "rotten egg" smell) that people mostly notice if gases from a sewage system are not properly vented at a building. Other gases produced by the decaying organic matter in the tank are also mixed into this brew as well.

Septic Tank Gas Leak Points Outside

Experts [Burks/Minnis, Kahn et als, Jantrania] will tell readers that septic tanks and their covers and access covers and piping fittings should all be sealed air-tight with proper rubber gaskets.

In nearly 50 years of looking at septic tanks and systems, I've rarely seen a conventional concrete tank which was sealed with gaskets.

Some steel and certainly some of the newer fiberglass septic tanks may be in fact more precisely designed and built, but concrete septic tanks and covers are a bit rough and will be leaky in most installations.

Septic Tank Acidity can Cause Odors

Acidic Septic Tank Problems can also cause odors:  See Acidic septic tanks at SEPTIC or SEWER PIPING LEAKS for the diagnosis and cure of this source of sewage smells.

Septic System Maintenance vs Septic Odors: sewer gas, sulphur odors, rotten egg smells

A review of septic system maintenance advice, particularly from aerobic treatment unit or ATU septic designs makes clear that a system that is not properly maintained may be a source of troubling smells, while a properly operating and maintainted system is not normally a source of complaints. Some examples of septic system maintenance snafus that can result in sewer gas odors at the site or backing up into the building include at least these:

Septic Tank Gases Back Up Into Building

Sewer gases formed in the septic tank can return to a building interior by backing up from the septic tank inlet baffle and pipe to the building drain-waste-vent piping. Inside the building sewer gas (rotten egg or methane) smells may be observed:


Continue reading at SEPTIC / SEWER ODOR SOURCE TABLE or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see SEPTIC ODOR FAQs - diagnostic questions & answers

Or see SEWER GAS ODORS - home



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