Wet Weather or Cold Weather Sewage or Septic Odors: Diagnosis and Repair Guide InspectAPedia® -
How to diagnose sewer odors 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
Questions & answers about diagnosing the source of septic or sewer odors in cold weather
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.
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Some of the diagnostic steps pertain to all seasons. The photograph provides a lot of septic odor diagnostic information if you look closely: there is a home made septic tank nearly touching the
building wall (by those steps), and in the foreground is a pony pump that the owner was using to try to move septic effluent uphill to his
drainfield. This system would not work reliably: the tank is too small for normal use and the pump is exposed to freezing.
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. Also see Backdrafting & Sewer/Septic Odors This article describes sewer odors due to a combination of wet weather and building back-drafting. Also see ODORS & SMELLS DIAGNOSIS & CURE for procedures to diagnose and cure all kinds of odors in and around buildings.
Also see our broad-scope article on diagnosis and cure of sewer gas and septic odors: Sewer Gas Odors diagnosing, finding, and curing septic tank and sewer line smells.
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. Technical reviewers are welcome and are listed at "References."
This is a chapter of Inspecting, Testing, & Maintaining Residential Septic Systems an online book on septic systems.
Other Sources of Sewer Gas or Methane Gas Odors in buildings
Others with whom we have worked on tracking down sewer gas odor problems have
had a plumber pressure test the drain waste vent piping to find sewer gas leaks
found sewer gas leaks at a toilet with a bad seal
found sewer gas leaks where plastic pipes had never been properly glued in a wall
found sewer gas leaks where drain waste vent pipes had been perforated by a nail from flooring or in one case from hanging a picture on the wall
found sewer gas leaks outside due to a failing septic drainfield and/or blocked sewer piping causing backups that leaked outdoors. In a case where odors were traced to leaks at a septic tank, odors from the septic tank were strongest at the front entry door to the home, perhaps in part because the system was in failure and backing up.
found sewer gas odors at plumbing fixture traps whose water trap was lost due to trap siphonage due in turn to missing, improperly installed (too distant), or blocked plumbing vent piping. Where dry plumbing traps pass sewer gases back into a building the problem may be worse in cold weather or when building vent fans are decreasing the in-building air pressure, drawing gases out of drain piping
tracked indoor sewer gas odors to a combination of wet weather, flooding sewer and storm drains, and backdrafting in the building due to improper bathroom exhaust fan vent installation - see Backdrafting & Sewer/Septic Odors This article describes sewer odors due to a combination of wet weather and building back-drafting.
found methane gas in the building water supply from public or private wells - see METHANE GAS SOURCES
CONTACT us to add other sewer gas odor sources you've found - it will help others
The Short Answer to Diagnosing Bad Smells: Septic Odors in Cold Weather
Locate the outdoor septic components - septic tank and fields, or their probable location. Melted areas of snow can be helpful
as they often mark the location of even properly-working septic system components - the soil is warmer at the septic tank
and at the drainfield lines.
As in the two photographs of snow over septic fields (left) and over a septic tank (right),
if you see snowmelt, the system is probably not frozen. Warm effluent is entering from the septic
tank and bacterial action is progressing in the soils.
If you do not see septic effluent coming to the surface of
the yard and if drains are not backing up inside the outdoor parts of the septic system appear to be working.
But how do we know if the septic system is frozen and not accepting waste from the building? What if we think the
septic system is blocked by freezing? See Septic Inspection Testing for details.
Before doing anything costly it's important to do your best to properly diagnose the problem. Do NOT hire a company to "rejuvenate" your septic field nor to install or flush or use any other magic product. It would be a better investment to take the cash you'd have paid them and rip it into small pieces and flush it down the drain.
Frozen septic fields: A septic system can become frozen in prolonged very cold weather if the system is also not in regular use. If the septic field froze and stopped accepting effluent, or if it were totally blocked and in failure (see below), your entire septic system would back up as you used the building drains, and you'd see drains backing up into the lowest areas of the home like a basement toilet or sink. I don't mean odors, I mean sewage backup.
Partial septic blockage: If a building drain or septic system or system drainfield is partially blocked, it's possible for that condition to generate odors in or out of the building. In this case odors often correspond to surges in system use, and odors should not correspond particularly to cold weather, except insofar as cold still air may permit gases to fall (from a plumbing vent stack, for example) , or different seasonal wind patterns may cause gases to move to areas where they're not noticed in warmer weather.
Cold Weather Sewer/Septic Odor Clues that do Not Point to a Frozen Drainfield
If you're using the building plumbing, drain, and septic system and it's not backing up it's not so likely that the problem is a frozen septic field.
There could be a drain vent line problem such as a frozen vent line (frost from moisture moving up the vent line above the roof from use of that drain for laundry or showering).
Be sure the traps in the lower bath are not dry as a dry trap will often send sewer gases into a building.
Cold Weather Sewer or Septic Gas Odor Sources
Check out the above items first. But take a look at these cold weather sewer gas or septic gas sources that may show up more noticeably when temperatures outside are falling or when the outdoor air is still such as in evenings.
Blocked septic systems::
The photo shows red septic dye in the snow during our test of the septic system shown in the photo at the very top of this page.
This septic system was in failure, as indicated first by the septic loading and dye test (with less than 50 gallons
of water run into the septic system in this case. The septic absorption field would not accept any effluent not due to freezing but because it had become
saturated and clogged.
In fact the combination of home-made too-small septic tank, no working effluent distribution system,
a septic effluent pump that sprayed effluent on anyone nearby when it operated, and sewage flowing to the yard surface, this
unfortunate property had no working septic system at all.
If a septic tank is blocked, outdoor drain lines are blocked, broken, or clogged, or if a drainfield has failed and won't accept septic effluent,
the system may partially back up when loaded (extra visitors, doing laundry), and is well on the way to a complete failure requiring further
diagnosis, drain repair, tank repairs, or field replacement.
A sluggish septic system can also cause septic gas backups in buildings. If the septic tank is blocked because of a failing drainfield, pumping the septic tank may give temporary relief - and a false sense that the problem has been fixed.
A blocked septic tank outlet baffle can cause sewer gases to back up into the building drain system any time, cold weather or not. Pumping the septic tank may "cure" this problem by removing the blockage at the tank outlet, but we suspect the building also has a leaky or defective vent piping system or leaky defective toilets or fixture traps as well
Sewer/Storm Drain Flooding: Tracked indoor sewer gas odors to a combination of wet weather, flooding sewer and storm drains, and backdrafting in the building due to improper bathroom exhaust fan vent installation - see Backdrafting & Sewer/Septic Odors This article describes sewer odors due to a combination of wet weather and building back-drafting.
Frequently Asked Questions (FAQs) on tracking down cool weather and night time sewer gas / septic tank smells
Question: on cool summer nights we smell septic gas, always at the same place, how do we fix this odor?
Have septic system in mountain area of NC. Only on COOL summer nights do we smell septic gas (always in same place) at rear of house. Also noted that either dishwasher or bathtub or washing machine is emptying into system when smell is detected.
The roof vent pipe is located on backside of house roof where we detect the smell below. Have concluded that smell is associated with vent gas being displaced by emptying water from an appliance and since outside air is COOL the gas "falls" to ground level where it is detected.
Do you have any thoughts on what might be causing problem? If agree with my conclusion there are vent mounted activated carbon filters that mount on top of vent pipe that are claimed to solve the problem, any comments will be appreciated.
- S.T.
[Our photo at left shows a common source of septic gas odors at an older home. This add-on plumbing vent may be a bit too close to that bedroom window, and also in cool weather its exhaust may be noticed by people on the ground below or on a nearby deck.]
Reply: Cause and Cure Suggestions for Septic Tank Smells in cool evening hours
A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem in the septic tank, drainfield, or plumbing venting system. That said, here are some things to consider:
A basic tenet of tracking down odors is just what you have done - relate the smell to other conditions like time of day, weather, etc. Without knowing details about your home I am just speculating:
If you have a slow plumbing drain, a sluggish drainfield that is failing, or a plumbing vent defect, pushing water into a drain at high rate can in turn result in an increase in the level of sewer gases (or septic tank gases) that are back-venting up the drain/waste/vent piping. Those gases should vent through the roof and should not be noticeable to building occupants.
But in the cool of evening not only do temperatures fall, but typically wind velocity falls as well. Under those conditions even a modest smell problem can become more noticeable because the gases are not being dissipated by air movement, and may even be falling towards ground level as escaping plumbing gases are cooled in the night air and, counter intuitively, might even ride descending air currents that during warmer daylight hours, would instead be rising air currents.
Your suggestion of adding a filter to try to reduce odors is a band-aid approach that has some risks: you might be better off to track down the odor source to see what it means. For example, improper plumbing venting can be unsanitary or even dangerous; and obtaining an early warning that the septic drainfield is failing may be useful in planning for repair or replacement of the system.
Tracking Down Sewer Odors Outside
Because you notice the odor at a particular location - at the rear of the house, and at a particular time - in evenings, that's a good time and place to start tracking the odor to its source.
If by "rear of the house" you mean outdoors, sniff towards the septic tank, drainfield, or any sewer line vents (see our photo at above left) or sewer line cleanouts that might be installed between house and septic tank.
Tracking Down Sewer Odors Inside
If you meant that the odors are noted inside the house, see if you can track the smell to a particular room or plumbing fixture or drain. Sometimes we find that sewer odors are traced to a leaky plumbing drain, loose toilet, or even a poorly connected dry plumbing vent running through the ceiling.
In both old and new construction we also occasionally come across an orphaned drain or waste vent line that was just chopped off and forgotten (photo at left).
A plumber can pressure-test your drain-waste-vent piping if that step becomes needed in tracking down the odor.
Also remember to have an expert take a look into the septic tank to see if it's sewage level is normal, if the baffles are intact, etc.
See SEWER GAS ODORS for our checklist of sewer gas or septic smell odor track-down details.
Questions & Answers regarding this article
Questions & answers about diagnosing the source of septic or sewer odors in cold weather
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Herb Reed County Extension Director, Agricultural and Natural Resources Educator, Calvert County Maryland - private email to DF 9/5/2006 adding comments about odors and partial blockages.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Advanced Onsite Wastewater Systems Technologies, Anish R. Jantrania, Mark A. Gross. Anish Jantrania, Ph.D., P.E., M.B.A., is a Consulting Engineer, in Mechanicsville VA, 804-550-0389
(2006), Advanced Onsite Wastewater Systems Technologies.
Outstanding technical reference especially on alternative septic system design alternatives. Written for designers and engineers, this book is not at all easy going
for homeowners but is a text we recommend for professionals--DF.
AEROBIC SEPTIC SYSTEMS
Builder's Guide to Wells and Septic Systems, Woodson, R. Dodge: $ 24.95; MCGRAW HILL B; TP;
Quoting from Amazon's description: For the homebuilder, one mistake in estimating or installing wells and septic systems can cost thousands of dollars. This comprehensive guide filled with case studies can prevent that. Master plumber R. Dodge Woodson packs this reader-friendly guide with guidance and information, including details on new techniques and materials that can economize and expedite jobs and advice on how to avoid mistakes in both estimating and construction. Chapters cover virtually every aspect of wells and septic systems, including on-site evaluations; site limitations; bidding; soil studies, septic designs, and code-related issues; drilled and dug wells, gravel and pipe, chamber-type, and gravity septic systems; pump stations; common problems with well installation; and remedies for poor septic situations. Woodson also discusses ways to increase profits by avoiding cost overruns.
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.
Onsite Wastewater Disposal Books
Onsite Wastewater Disposal, R. J. Perkins;
Quoting from Amazon: This practical book, co-published with the National Environmental Health Association,
describes the step-by-step procedures needed to avoid common pitfalls in septic system technology.
Valuable in matching the septic system to the site-specific conditions, this useful book will help you install a reliable system in
both suitable and difficult environments. Septic tank installers, planners, state and local regulators, civil and sanitary engineers,
consulting engineers, architects, homeowners, academics, and land developers will find this publication valuable.
Onsite Wastewater Treatment Systems, Bennette D. Burks, Mary Margaret Minnis, Hogarth House 1994 - one of the best septic system books around, suffering a bit from small fonts and a weak index. While it contains some material more technical than needed by homeowners, Burks/Minnis book on onsite wastewater treatment systems a very useful reference for both property owners and septic system designers.
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
Planting Over Septic System Component", Daniel Friedman (author/editor, InspectAPedia.com), The Innovator, Winter/Spring 2008, BCOSSA, British Columbia OnSite Sewage Association, 201-3542 Blansard St., Victoria BC V8X 1W3 Canada
Septic System Owner's Manual, Lloyd Kahn, Blair Allen, Julie Jones, Shelter Publications, 2000 $14.95 U.S. - easy to understand, well illustrated, one of the best practical references around on septic design basics including some advanced systems; a little short on safety and maintenance. Both new and used (low priced copies are available, and we think the authors are working on an updated edition--DF.
Quoting from one of several Amazon reviews: The basics of septic systems, from underground systems and failures to what the owner can do to promote and maintain a healthy system, is revealed in an excellent guide essential for any who reside on a septic system. Rural residents receive a primer on not only the basics; but how to conduct period inspections and what to do when things go wrong. History also figures into the fine coverage.
Test Pit Preparation for Onsite Sewage Evaluations, State of Oregon Department of Environmental Quality, Portland OR, 800 452-4011. PDF document. We recommend this excellent document that offers detail about soil perc tests, deep hole tests, safety, and septic design. Readers should also see Soil Percolation Tests and for testing an existing septic system, also see Dye Tests
Grass is Always Greener Over the Septic Tank, Bombeck, Erma: $ 5.99; FAWCETT; MM;
This septic system classic whose title helps avoid intimidating readers new to septic systems, is available new or used at very low prices.
It's more entertainment than a serious "how to" book on septic systems design, maintenance, or repair. Not recommended -- DF.
US EPA Onsite Wastewater Treatment Systems Manual Top Reference: US EPA's Design Manual for Onsite Wastewater Treatment and Disposal, 1980, available from the US EPA, the US GPO Superintendent of Documents (Pueblo CO), and from the National Small Flows Clearinghouse. Original source http://www.epa.gov/ORD/NRMRL/Pubs/625R00008/625R00008.htm
Water Wells and Septic Systems Handbook, R. Dodge Woodson. This book is in the upper price range, but is worth the cost for serious septic installers and designers.
Quoting Amazon: Each year, thousands upon thousands of Americans install water wells and septic systems on their properties. But with a maze of codes governing their use along with a host of design requirements that ensure their functionality where can someone turn for comprehensive, one-stop guidance? Enter the Water Wells and Septic Systems Handbook from McGraw-Hill.
Written in language any property owner can understand yet detailed enough for professionals and technical students this easy-to-use volume delivers the latest techniques and code requirements for designing, building, rehabilitating, and maintaining private water wells and septic systems. Bolstered by a wealth of informative charts, tables, and illustrations, this book delivers:
* Current construction, maintenance, and repair methods
* New International Private Sewage Disposal Code
* Up-to-date standards from the American Water Works Association
Wells and Septic Systems, Alth, Max and Charlet, Rev. by S. Blackwell Duncan, $ 18.95; Tab Books 1992. We have found this text very useful for conventional well and septic systems design and maintenance --DF.
Quoting an Amazon description:Here's all the information you need to build a well or septic system yourself - and save a lot of time, money, and frustration. S. Blackwell Duncan has thoroughly revised and updated this second edition of Wells and Septic Systems to conform to current codes and requirements. He also has expanded this national bestseller to include new material on well and septic installation, water storage and distribution, water treatment, ecological considerations, and septic systems for problem building sites.
The NSFC Products List has an excellent list of design manuals/modules available from their website or by telephone 800-624-8301
Submissions welcome. send us a suggested document link or request an exchange of website links
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