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How & Why Septic Tank Leaks Cause Septic System Failures
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InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
Septic tank tank leaks are one of the things to check for during a septic tank inspection. Here we explain where and why septic tanks might leak, why surface water or runoff leaking into a septic tank is bad, and why septic effluent leaking out of a septic tank can also be a problem. We explain why pumping a flooded septic tank does not usually fix anything. Leaks in either direction, into the septic tank or out of the septic tank can be a problem.
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Causes, Effects, & Repair of Leaks Out of or Into the Septic Tank
Our page top photo shows water ponding at the connection of a sewer line to a septic tank. Because this sewer line runs downhill from the house to the septic tank it was particularly good at collecting surface water and aiming it all at the septic tank entry port. Because the sewer line was not sealed at the tank, water entered and flooded the septic tank and drainfield. See SEWAGE LEVELS in SEPTIC TANKS for details on normal and abnormal levels and what they mean.
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.
Where do Septic Tank Leaks Occur
 A septic tank can develop a leak at just about any location but here are some common ones.
Our photo shows concrete poured around a waste line entering the septic tank. You can see that just as the concrete pooled in this location, the trench dug for the sewer line would, in wet weather, collect and aim a large volume of water into the septic tank.
- At the sewer line entering the septic tank, or the effluent line leaving the septic tank may leak: if the pipe is not sealed in that location; many older septic tanks provided no sealant unless some home-made system was used. Some installers pour concrete around the waste pipe entering the tank - which can work but it makes future repairs more troublesome.
Modern septic tanks may include a rubber gasket to help seal at the tank entry and exit openings. But if the waste lines entering or the effluent lines leaving the septic tank are at a sharp angle with respect to the tank, the gasket may not seal properly.
- Any damaged sewer piping and even effluent piping might permit ground water or surface runoff to flow into the septic tank or into the drainfield.
- A septic tank cover or cleanout port, especially one that is below ground may permit surface water to enter the septic tank. (Make sure septic tank covers are sound - falling into a septic tank is likely to be fatal).
- Rust damage to a steel septic tank can let effluent out of the tank and water leak in depending on weather conditions.
- Cracks in a concrete septic tank also can let effluent leak out or water leak in - though we have not found these occurring as often as rusted out steel septics
- Damaged fiberglass or plastic septic tanks can also leak at a seam or point of damage - though we heard few reports of this problem.
You can reduce the chances of water leaking into a septic tank by making sure that roof runoff and surface drainage are directed away from the septic tank as well as the drainfield.
Leaks out of the septic tank prevent testing the septic drainfield
Leaks out of the septic tank can occur if the tank has a hole (for example a rusted-out metal septic tank) or if a concrete, fiberglass, or plastic tank is cracked or damaged. A leaky septic tank means that effluent may not be properly treated since it is not reaching the drainfield.
A leaky septic tank also means that a septic loading and dye test to attempt to check on the condition of the drainfield may fail to work. Particularly if the septic system has been unused for some time, and if the leak is near the bottom of the septic tank, the liquid level in the tank will drop very low. The result is that a normal septic dye test volume will simply be filling up the septic tank rather than pushing water out into the drainfield.
In turn this condition means that the septic test could not test the function of the drainfield. The risk is that new owners moving into the property will very quickly discover the bad news that not only has the septic tank got a leak but the drainfield may not really be functional.
A septic tank that is not in use and leaks out may also produce solidified scum and sludge that collect low in the septic tank or on its bottom - making septic tank cleaning extra difficult.
If there is a port to permit safely looking into the septic tank before an inspection or test, be sure to check the sewage level in the tank.
Leaks into a septic tank can flood the tank and drainfield
Leaks into the septic tank can occur if ground water or surface runoff are directed towards the septic tank or pipes that carry sewage into the tank (or effluent out of the tank). Any opening that permits surface runoff to enter the septic tank risks flooding the tank. In rainy weather the result can be a water overload in the septic tank, reducing the level of treatment in the septic tank.
Perhaps more of a problem, the same water running into the tank may also push its way into the drainfield, flooding the septic drainfield. If extra volume of the water entering the septic tank also prevents adequate settling time for sewage entering the tank then an excessive level of suspended solid waste may be forced of the septic tank and into the drainfield, further reducing the life of that component.
Leaks into a septic tank can also occur if the drainfield is so flooded that water is flowing backwards through the drainfield piping and back into the septic tank through its outlet.
Pumping a Flooded Septic Tank - Does that Fix Anything?
Pumping the septic tank won't fix any of these flooded septic tank conditions. A septic tank is normally always "full" to just below the septic tank outlet opening.
But pumping a flooded septic tank might be performed for the following reasons:
- Flooded septic tank needs cleaning: If the septic tank was exposed to area flooding it may have become loaded up with mud and silt and needs to be cleaned in order to work at all. In this case, the septic drainfield piping, distribution boxes, and similar components need to be excavated sufficient to permit their inspection as well.
- Diagnose a flooded septic tank: If the septic tank appears to be filling from surface runoff or ground water leaking into the tank, pumping the tank permits the owner or septic service company to look for these problems by observing the empty tank for signs of effluent or ground water back-flowing into the tank.
- Permit temporary use of a flooded septic tank: if the tank is emptied, and if the building occupants make a maximum effort to minimize unnecessary water usage (showers, laundry, bathing), then the occupants may be able to use the septic system and thus the building and site in a sanitary way, without further contaminating the neighborhood, for a few days to a week, depending on the tank size, number of building occupants, frequency of toilet flushes, etc.
In our OPINION, if the septic tank floods once in 20 years, under exceptional conditions, no design changes or repairs may be needed other than cleaning the septic tank when floodwaters subside. But if this condition happens frequently, the septic system is unsanitary and may be a health risk to the building occupants or its neighbors.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- Special thanks to M & O Sanitation, Dutchess County NY (845) 471-0308 for permitting us to photograph steps during septic system service at our demonstration property.
- Septic System Maintenance Fact Sheet, AEX-740-1, Karen Mancl, Food, Agricultural, and Biological Engineering, Ohio State University Extension, Columbus OH - September 2008
- 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.
- Pennsylvania State Fact Sheets relating to domestic wastewater treatment systems include
- Pennsylvania State Wastewater Treatment Fact Sheet SW-161, Septic System Failure: Diagnosis and Treatment
- Pennsylvania State Wastewater Treatment Fact Sheet SW-162, The Soil Media and the Percolation Test
- Pennsylvania State Wastewater Treatment Fact Sheet SW-l64, Mound Systems for Wastewater Treatment
- Pennsylvania State Wastewater Treatment Fact Sheet SW-165, Septic Tank-Soil Absorption Systems
- Document Sources used for this web page include but are not limited to: Agricultural Fact Sheet #SW-161 "Septic Tank Pumping," by Paul D. Robillard and
Kelli S. Martin. Penn State College of Agriculture - Cooperative Extension, edited and annotated by
Dan Friedman (Thanks: to Bob Mackey for proofreading the original source material.)
- 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). 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 I recommend for professionals--DF.
- 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.
- 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
- ...
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 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.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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