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PHOTO of a septic seepage pit collapse when a truck drove over it.Guide to Septic Tank, Drywell & Cesspool Abandonment

  • SEPTIC TANK ABANDONMENT GUIDE - CONTENTS: How to abandon a septic tank cesspool, drywell, seepage pit or in-ground cistern. When & how to fill in or seal/close a septic tank. Fill in the septic tank when connecting to municipal sewer. Why you need a professional to seal an unused septic tankSeptic system, septic tank, & cesspool safety warnings. Septic tank / cesspool collapse warnings. Example regulation describing requirements when a septic system or tank or seepage pit is abandoned
  • POST a QUESTION or READ FAQs about how to discontinue or abandon a septic tank, drywell, cesspool, or seepage pit
  • REFERENCES
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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.



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Guide to Proper Abandonment of Un-used Septic Tanks, Drywells, Etc.

Photograph of Don't fall into a septic tank - it's likely to be fatal.

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:

  1. 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.
  2. 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.
  3. Concrete septic tanks are often filled-in after holes are broken into the tank - details are below.
  4. 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:

  1. 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:

  2. Pump out the septic tank, cesspool, or drywell - a septic pumping contractor performs this step.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. 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 [5]

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

Reply:

BB

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:

  1. 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.
  2. 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.
  3. 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
  4. 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.
  5. Wash the tank interior and pump out that wastewater. Sanitizing is optional but in the case of an odor complaint, might be appropriate.
  6. Assure that there is a drainage opening in the tank bottom.
  7. 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.
  8. 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.

Septic Tank Abandonment Example Regulations

Ohio - ABANDONMENT of SEPTIC TANKS, REGULATIONS [PDF] retrieved 2017/10/20, original source: http://www.odh.ohio.gov/

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Continue reading at SEPTIC & CESSPOOL SAFETY or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see SEPTIC TANK ABANDONMENT PROCEDURE FAQs - questions & answers posted originally at this article

Or see ABANDONED or NEW SEPTIC SYSTEM TESTS

Or see SEPTIC LOCATION VIDEO

Or see SINKHOLE DETECTION, WARNING SIGNS

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