InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
How to abandon a septic tank, cesspool, drywell:
This document outlines basic procedures for finding and safely abandoning unused septic systems and cesspools, and provides some safety suggestions for septic system inspectors, septic system inspections, septic pumping contractors, and home owners.
When a septic tank, drywell, or cesspool is no longer to be used, either because a building is connected to a municipal sewer or because the old tank is being left in place and a new septic installed elsewhere, there are very important safety steps that should be taken.
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.
Guide to Proper Abandonment of Un-used Septic Tanks, Drywells, Etc.
Safety Concerns in Abandoning Septic Systems, Seepage Pits, Cesspools, Drywells, even dug wells
Septic tanks, cesspools, and drywells present serious hazards including septic cave-in's or collapses, methane gas explosion hazards, and asphyxiation hazards. Simple precautions which we describe here can help avoid a dangerous septic, cesspool, or drywell hazard.
In addition to having been consulted in fatalities involving humans, we have learned that falling into septic tanks and cesspools is a risk for animals as well. Readers should also see specific warnings about cesspools
at CESSPOOL SAFETY.
Watch out: for unsafe septic tanks and cesspools or drywells and for systems that were not properly abandoned. In 2008 Mark Cramer shared a report from an owner that that their horse fell into a septic tank and died tragically before it could be rescued.
The collapsing septic tank was not in the location which the owners thought it would be found, and clearly it had an unsafe cover. We were consulted in a Long Island death of an adult who fell into and was buried in a collapsing cesspool. And in 2012 we were contacted for comment involving the death of two boys who fell into and perished in an "abandoned" septic tank or cesspool that lacked a safe cover.
See SEPTIC & CESSPOOL SAFETY.
It is important to properly abandon un-used septic tanks, cesspools, or drywells. If an old septic tank, cesspool, or drywell is simply "left alone" there may be very serious cave-in or fall-in safety hazards.
Septic tank, drywell, or cesspool abandonment or tank closure may involve complete tank removal, tank crushing (steel septic tanks), or most common with site-built tanks/cesspools/drywells, and with concrete tanks, the cover is opened and the tank is filled-in with rubble and soil. Details of septic tank, cesspool, drywell abandonment procedures are discussed in this article.
Septic Tank Abandonment Choices
When a septic tank is no longer going to be used, various factors determine what will happen to the old tank:
Cesspools & Drywells: If the old septic system component to be discontinued is a cesspool or drywell, and occasionally with septic tanks, the old tank might be left in place and "daisy chained" to the new one. This was common at country and farm properties that relied on a cesspool for onsite waste disposal.
Owners hoped that the old system might still help a little with wastewater treatment and disposal even though it had stopped working. This approach is dangerous if the old system has an unsafe cover, is in danger of collapse, or is leaking where it should not be.
Steel septic tanks are often removed, crushed, and buried back at the site, possibly below or along side a new septic tank - details are below.
Concrete septic tanks are often filled-in after holes are broken into the tank - details are below.
Plastic or fiberglass septic tanks are a newer item with less experience in abandonment. If such a tank is badly damaged and leaky it needs to be removed and replaced. It may be possible to crush and bury such a tank as in the case of steel tanks.
To avoid the risk of a collapsing septic tank, cesspool, or drywell which is no longer used, it is important to find and properly close out such facilities at any property, residential or commercial. In the photo at the top of this page, the truck "found" an abandoned septic tank by driving over it.
Properly abandoning a septic tank, drywell, or cesspool which is no longer in use involves at least the following steps:
Locate all of the un-used septic tanks, cesspools, drywells on the property. At some properties there may be multiple systems and tanks, such as a chain of old cesspools or one or more septic tanks with a separate drywell. See these articles on finding hidden, lost, buried septic system components:
SEPTIC TANK, HOW TO FIND which offers detailed steps and multiple approaches, including our septic tank and drainfield location videos. An experienced plumber or septic contractor can assist in these steps and may have special equipment that speeds the process. These subtopics are addressed
Pump out the septic tank, cesspool, or drywell - a septic pumping contractor performs this step.
Break open the abandoned septic tank bottom - so that it won't hold surface runoff, forming an un-wanted water or mud reservoir.
Crush & bury old steel septic tanks:
If the septic tank is steel, often the contractor will dig out the tank, crush it, and then bury it back in the original hole. When we installed a new concrete septic tank the contractor pulled out the old steel septic tank, crushed the old steel septic tank into a flat slab of rusty metal by driving his backhoe over it, dropped the new concrete septic tank into the old excavation, slipped the old flat steel septic tank on edge alongside the new concrete tank, and buried it.
Fill in the septic tank, cesspool, or drywell, or hole where the tank was located (if you crushed an old steel tank) with stone, rubble, and soil so that there is on future collapse hazard. If the old septic tank was steel and was crushed (as above), the excavation contractor may decide to clean-up the existing septic tank hole and use it to drop in the new tank in the same location - this is fine, and it simplifies plumbing connections to the new septic tank.
Assure that the septic tank fill is solid & compacted and that a secure cover remains. Otherwise future settlement of the septic tank fill can cause sudden dangerous collapses.
Document the location of the filled-in septic tank, cesspool, drywell, so that future site work or building plans can avoid or at least anticipate these buried obstructions.
If newer septic tanks, cesspools, or drywells remain in use at the property, that is if you're not simply connecting the building to a municipal sewer line, then:
Document remaining septic components: be sure that the remaining septic tank, drywell, or cesspool locations are documented
See SEPTIC TANK LOCATION SKETCH
Safe septic tank covers: Be sure that each remaining septic tank, drywell, cesspool that has not been abandoned has an intact, secure cover that will not cave in nor be easily opened by a child
See SEPTIC TANK COVERS
Keep livestock away from septic tanks and drainfields: We've written elsewhere about the importance of keeping livestock off of septic drainfields and septic tanks. There may be an extra risk of livestock-caused septic tank collapse where old septic tank or cesspool covers or even new fiberglass septic tanks and covers are installed.
Example State Requirements for Septic Tank Abandonment Code
When wastewater disposal systems are abandoned, a septic tank and seepage pit must have the sewage removed by a septic tank pumper, and must be crushed in place or completely filled with compacted soil, concrete, or other approved material, as required by the Uniform Plumbing Code.
Depending on specific site conditions, disinfection may also be required. - Alaska Manual 
Question: how do I abandon a septic tank that remains under the slab of an existing building addition
I have a client with a problem I can't fix YET !
She thinks that a remodel to her living room years ago was built on an abandoned septic.
We have relocated all plumbing and waste lines in the area to start with .
The air still feels bad , the close hanging the closet get mold on them in a short time and she is sick all the time.
If there is a septic under the slab what is keeping it from just drying out and if I jack hammer the slab , how do i remove it all and fill in ?
HELP - B.B. 11/15/2012
Your question is a reminder of the suggestion that it would have been best to properly abandon a septic tank before ever building over it.
I had to deal with this problem at a building whose prior owner built a screened porch atop an old steel septic tank. Luckily the porch had just a wooden floor built on piers, so it was easy to cut an opening in the floor, find the septic tank opening(s), and inspect, pump, clean, and fill the tank. In my case the tank was a steel one that had a rusted-through bottom, had been out of service for decades, and was not particularly smelly.
We filled in the tank with stone, rubble, and clean soil just to make sure that it did not collect water (and produce odors) in the future.
In your case, I'd proceed to locate, inspect, and abandon the under-slab septic tank as follows:
First check that the odor is not coming from somewhere else - such as a dead animal in a wall or other site issues. We'd feel stupid to go to all of the work outlined below only to discover the problem was elsewhere. See ODORS GASES SMELLS, DIAGNOSIS & CURE for suggestions.
Make an opening in the slab over your best guess about exactly where the tank is located. The opening needs to be large enough that if you need to excavate and remove soil to find the septic tank top you can do so - perhaps first cutting a 2' x 2' opening and using a post hole digger to confirm the presence of the septic tank top, then enlarging that opening as needed.
Watch out: old septic tanks may have a rusted steel, rotted wood, or other unsafe cover. Falling into even an abandoned septic tank can mean a quick ugly death. So proceed carefully and don't work alone. See SEPTIC & CESSPOOL SAFETY
Open the septic tank to inspect the interior. If the tank was never pumped it will need to be emptied and cleaned - you may need to add water and work with an experienced septic tank pumper to clean the tank thoroughly.
Wash the tank interior and pump out that wastewater. Sanitizing is optional but in the case of an odor complaint, might be appropriate.
Assure that there is a drainage opening in the tank bottom.
Fill the tank with stone, rubble, sand and add top fill so that the compacted soil slopes away from the septic tank top opening you made.
Restore the floor slab.
That should be sufficient to stop the odor problem and eliminate future hassles with an old septic tank that smells, collects groundwater, collapses, or is in general a possible hazard.
Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: email@example.com
Hankey and Brown home inspectors, Eden Prairie, MN, technical review by Roger Hankey, prior chairman, Standards Committee, American Society of Home Inspectors - ASHI. 952 829-0044 - hankeyandbrown.com 11/06
Arlene Puentes, a licensed home inspector, educator, and building failures researcher in Kingston, NY. 11/29/06
John Francis, Bioworks, Inc., marketing and technical services - editing/proof reading 4/07. "BioWorks provides environmentally responsible, safe and cost-effective solutions to the agriculture industry"
Thanks to Denise Cermola for permission to use the photo above, showing a dump truck collapsed into a seepage pit. (email 11/16/06 to 12/10/06). The contractor drove over this seepage pit connected to septic tank and caused total destruction of the system.
Thanks to George Fielder who points out that methane gas is not toxic, but rather (we add) the hazards of methane gas produced by septic systems include possible explosions or the asphyxiation of someone who enters or even just leans over a septic tank opening. (email 10/20/2007)
Thanks to Donica Ben who points out the danger of digging into buried electrical wires (11/11/07)
 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.)
 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.
 "How to Maintain Your Septic System", Alaska Department of Environmental Conservation, Division of Water, retrieved 8/8/12, original source: http://dec.alaska.gov/water/wwdp/onsite/maintain_septic.htm [copy on file as Alaska_Septic_Care.pdf]
 Installers Manual for Conventional Onsite Domestic Wastewater Treatment and Disposal Systems", Alaska Department of Environmental Conservation, Division of Water, retrieved 1/15/2001, original source: [copy on file as Alaska_Certified_Installer's_Manual.pdf]
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.
US EPA Onsite Wastewater Treatment Systems Manual [online copy, free] 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 Onsite wastewater treatment and disposal systems,
Richard J Otis, published by the US EPA. Although it's more than 20 years old, this book remains a useful reference for septic system designers.
U.S. Environmental Protection Agency, Office of Water Program Operations; Office of Research and Development, Municipal Environmental Research Laboratory; (1980)
"International Private Sewage Disposal Code," 1995, BOCA-708-799-2300, ICBO-310-699-0541, SBCCI 205-591-1853, available from those code associations.
"Manual of Policy, Procedures, and Guidelines for Onsite Sewage Systems," Ontario Reg. 374/81, Part VII of the Environmental
Protection Act (Canada), ISBN 0-7743-7303-2, Ministry of the Environment,135 St. Clair Ave. West, Toronto Ontario M4V 1P5 Canada $24. CDN.
Manual of Septic Tank Practice, US Public Health Service's 1959.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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
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.
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.
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