InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
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.
We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.
Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved
to the author.
How to Diagnose, Prevent, or Cure Odors and Hazards from Gases in Septic Systems
In 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.
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:
Aerobic treatment unit septic system parts failure: an aerator pump or control valve failure can cause the ATU to emit septic smells and risks system damage or even failure - by the discharge of inadequately treated wastewater into the effluent disposal bed.
Drain backups & sewage odors: blocked drain lines or vent pipes resulting in trap siphonage or sewer gas backups into the building can have as a component or even primary cause a failed septic system drainfield. A drainfield or soakaway bed failure in turn may be due to inadequate maintenance such as failure to pump or clean out the septic tank on schedule.
Septic tank or sewer line leaks at any point in the system can discharge effluent or, depending on the leak location, may be a source of sewer gas leaks & odors. Sewer lines within a building may corrode at the top of the piping or may be cracked or damaged at a position hard to see but one that can be located by careful inspection and odor tracking.
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:
A blockage at the septic tank can cause sewer gases to back up into the building. Blockages at the tank range from very costly (a failing drainfield) to less costly (a blocked or damaged sewer line between the septic tank and the distribution box or drainfield), to least costly and repaired by normal maintenance (pumping the septic tank). How can pumping the septic tank cure a sewer gas odor?
If the septic tank outlet baffle has become blocked by a too-thick floating scum layer or "pillow" then sewer gases may be backing up into the building through the incoming sewer line to the tank.
Still, if the building vent system and traps are in good condition, this odor should not appear indoors so look for additional problems we list next:
At loose toilets that are not properly sealed to waste lines, often appearing at lowest floor toilets first but possibly appearing at any toilet that is not well sealed.
Even a toilet that does not "rock" on the floor may have a crushed leaky wax ring sealing the toilet base to the waste pipe. If smells are worst around a particular toilet we suggest having your plumber remove and re-seal the toilet.
At leaky or defective plumbing traps or plumbing vent lines - links below point to detailed articles on these topics.
Thanks to Slade Franklin
for the reminder that a leaky wax ring at a toilet can lead to septic odors in bathrooms. 11/2007
Thanks to J.V. (privacy protected) for the reminder to make a detailed inspection of the plumbing vent system when sewer gas odors are present. 07/2008
Thanks to Roger Hankey & Cheryll Brown, www.hankeyandbrown.com, ASHI home inspectors in Minnesota, for the deteriorated transite pipe gas flue vent photograph and comments. Mr. Hankey is a past chairman of the ASHI Technical Committee, serves as co-chairman of ASHI legislative committee, and has served in other ASHI professional and leadership roles. 7/2007
PLUMBING DRAIN NOISE DIAGNOSIS: may indicate defective or clogged plumbing: how to diagnose and cure drain soundscalculating septic tank volume from size measurements
Septic Tank/Soil-Absorption Systems: How to Operate & Maintain [ copy on file as /septic/Septic_Operation_USDA.pdf ] - , Equipment Tips, U.S. Department of Agriculture, 8271 1302, 7100 Engineering, 2300 Recreation, September 1982, web search 08/28/2010, original source: http://www.fs.fed.us/t-d/pubs/pdfimage/82711302.pdf.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Country Plumbing: Living with a Septic System, Hartigan, Gerry: $ 9.95; ALAN C HOOD & TP;
Quoting an Amazon reviewer's comment, with which we agree--DF:This book is informative as far as it goes and might be most useful for someone with an older system. But it was written in the early 1980s. A lot has changed since then. In particular, the book doesn't cover any of the newer systems that are used more and more nowadays in some parts of the country -- sand mounds, aeration systems, lagoons, etc.
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: firstname.lastname@example.org. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones