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.

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

These questions on how to abandon a septic tank, cesspool, or drywell were posted originally at SEPTIC TANK ABANDONMENT GUIDE - be sure to review the guidelines and safety advice given there.

Safety Concerns in Abandoning Septic Systems, Seepage Pits, Cesspools, Drywells, even dug wells

Watch out: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.

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.

On 2020-02-11 - by (mod) - how to kill bugs coming out of an abandoned septic tank

Eric,

Just about any pesticide properly employed in the drain would kill the insects that you're concerned about. Or you could even temporarily simply put a rubber plastic cover over the drain. Opening in your building.

However, your question race is a far more serious concern. If the septic tank that was left on your property was not properly abandoned. Then there is a potential fatal safety hazard. If in fact someone should at some future time step over or near the tag and fall into it.

After all we have no idea of the tank age, type, construction materials, nor the most important: the security of its cover.

Proper septic tank abandonment requires that the tank be pumped clean and filled in. You should ask an appropriate excavation or septic contractor to find a tank and uncover the top and check its condition to be sure it has been properly abandoned if it has been the insect problem would be trivial. And a safety questions would have been addressed.

On 2020-02-11 by Eric

We bought a house that has a old septic tank on property -the house was hooked up to city. After we moved in we had a plumber Toto our drain & he went backwards instead of towards the street.

He had to come back & redo it- problem being now we have millions of tiny black bugs that are coming up from the basement drain and dying as soon as the fly out. I’ve tried everything to get rid of the bugs vibrate they just keep on coming.

Please give us any information you might have to kill these bugs I believe are coming up from the septic .

On 2019-11-29 - by (mod) - septic tank decommissioning or abandonment procedure

Harkey

Thank you for an interesting septic tank decommissioning or abandonment procedure question. I would approach it as follows.

First I would have done it by the city and Country where the building or property is located then I would find the septic codes for that jurisdiction. In those codes you will probably find a description of what's required for an acceptable septic tank abandonment.

Usually those requirements are intended to make sure that a tank full of sewage isn't left at the property and that a tank isn't left unprotected such that someone could fall in and be injured or die. So the usual procedure is at the tank is empty and either filled in place or removed.

Ask the health department to be more specific about what they need to know.

Let me know what you find out about your local septic tank abandonment requirements and I may be able to offer more specific suggestions.

On 2019-11-29 by Harley - health department wants a certification of the septic tank as being decommissioned

Prior to building we had the excavation company remove an abandoned septic tank. It was pumped, lid broken and was in pieces by the time they were able to get it out of the ground. I had them take it about 100 yds away into the woods and bury it in pieces.

Now the health department wants a certification of the septic tank as being decommissioned before they will sign off on our new as built an acre away. What are your thoughts? What can I tell them that would satisfy the requirement or their need to require a certification of decommission status?

On 2019-11-09 - by (mod) -

Sure, Doug, assuming the tank has been emptied. Geez though that sounds expensive. What about breaking up a bigger opening and then filling with gravel and sand?

On 2019-11-08 by Doug Thomas

If an old, empty concrete septic tank is partially under a slab on grade home addition, could the abandoned tank be filled with poured concrete?

The existing small access holes would make it nearly impossible to spread and compact sand or dirt.

On 2019-01-26 by MJ

You seem to have misunderstood my question completely. A DRY WELL or drywell is an underground structure that disposes of unwanted water, most commonly surface runoff and stormwater, and in some cases greywater. It is not meant to store it, danjoefriedman, but make it go away without running down a hillside and ponding in other areas. I am questioning the needs of a conversion process, or if it should be done at all.

On 2019-01-26 - by (mod) -

MJ

It's pretty difficult to completely disinfect an old septic tank to make it clean enough to store potable water, but IF you wanted to use the tank to store roof runoff for local plant irrigation that might be more reasonable.

You'll still want the tank to be opened, inspected for structural soundness, safety, and then cleaning.

But for the case you describe it sounds like you want to have your cake and eat it too: running graywater into the septic tank (which itself does NOTHING to properly dispose of that wastewater)

And
Storing rainwater.

In sum it sounds like not the best of ideas to me.

It may be less costly to simply buy a fiberglass or plastic water storage tank that you can use to collect rainwater from roof runoff.

But in any case have the abandoned septic inspected for a safe cover so no one can fall in. See the ARTICLE INDEX above on this page to find our information about SEPTIC TANK ABANDONMENT procedures.

On 2019-01-26 by mjarm67@yahoo.com

CI would like to know about converting an old septic system to be a rainwater dry well. It was "abandoned" over thirty years ago when my parents hooked up to the local sewer system. I remember it being a two section, concrete wall tank about six feet deep, over ten feet from the home. The lid is a foot under ground, and would be level with the basement floor, as it is down a hill from the house.

The original cast pipe is still connected to the basement as a drain for the basement sink, as well as emergency drainage, as we have a very wet basement, and the pump can fail at times. Is this something that gutters could be sent to limit rainwater? I ask because my area will be subject ot a "rain tax" soon, and this would help limit the fees imposed.

On 2018-12-29 - by (mod) -

That's an interesting question, thank you.

My concept of abandoned septic system is specifically defined as one that is intended for no further or future use. That's not the same thing as a system that is in a period of this used but will be returned to operation. So for example a home that stands empty for several years but had a functioning septic system would not be considered abandoned.

The point of Abandonment is that when a septic system is no longer going to be used we don't want to leave an unsafe condition or unsanitary conditions at the property.

On 2018-12-28 by Anonymous

Septic has not had water for 3 years or used. Would it be considered an abandoned septic system?

On 2017-07-24 by (mod) - restore the top on an abandoned septic tank?

I'd restore the top for a couple of reasons:

1. less subsidence of the covering backfill later

2. I want to minimize the water that will still want to run into the septic tank - risking causing a smelly or stagnant or bacteria-laden pond even with the gravel in place. (so seal the top too as best you can)

Some contractors claim they break a hole in the tank bottom before backfill. That'd be nice but not worth killing somebody: it can be fatal to descend into even an old septic tank unless the worker is trained, has proper safety gear, and is working with a support team.

On 2017-07-24 by Norman

After filling should I put the concrete top back on it or bust it up and put in tank with the SB2 gravel

 

On 2017-07-24 by (mod) - groundwater entering an un-used septic tank

Norman,

It's common for ground water to find its way into a septic tank, especially an old one whose pipe seals or access cover seals were probably leaky. Proper abandonment would include just what you say, pump out and fill with stone or rubble.

On 2017-07-24 by Norman

by the way this is a concrete tank

I have an old unused septic tank in my yard that has not been used in at least 20 years or longer,

I have had water standing under my house for awhile now, had a plumber out to look, no leaks in water line or drains, the tank is about 5 feet from my house, he took the top off the tank and it was full to the top with water, I am going to have it pumped out and filled, question will SB2 gravel be a good fill or do I need to use something different.

On 2017-07-09 by (mod) - smelly hole in area of "abandoned" cesspool

D.T.

If the subsidence is in the exact location of the old abandoned Cesspool, septic tank or whatever it was that was to be abandoned and filled in, then it sounds as if additional fill is needed.

On 2017-07-08 by D.T. Gordon

I just had a new pool installed, he was to destroyed the old one, its nine years later and I have a sink hole about two feet in circufence, returned twice and addd dirt,it's still stinking. And hasn't returned

On 2017-07-06 by (mod) - ok to pour a slab over a decommissioned septic tank under a house?

I can't be sure of an OK without knowing what decommissioning was done. A slab on a rusted out steel tank filled with soft soil could settle or crack.

Further investigation of what's there and assurance that there is no hole is needed.

On 2017-07-06 by John Shelby

I'm buying a house in unincorporated town in Northern California. The original septic tank under the house in an un-finished basement, was properly decommissioned with permit, and a new, larger one was installed outside the home's footprint. With the proper decommissioning

, can I now pour slab over the original location during a permitted re-model of the basement?'

On 2017-05-29 by (mod) - put a swimming pool where the septic tank was located

Surfvet

I think what you want to do is reasonable as long as you're not thinking of converting the septic tank itself into an in-ground swimming pool. (No joke, you'll find an article here describing a German couple's conversion of their septic tank into an underground storage facility).

It seems a near-certainty that the excavation for the pool will be larger than the original footprint of a typical residential septic tank. As you're connected to sewer, driving a backhoe over the abandoned drainfield, even if it damages it, isn't a catastrophe, but you will want to know what other buried lines may be present at the site and that need to be avoided or protected such as electrical and water mains.

DO keep heavy equipment well away from the foundations of the home itself - or the foundation could be damaged.

On 2017-05-29 by Surfvet

After converting to the city's sewer system that is very closey located, We'd like to physically remove a property's septic tank and place a pool where the tank is currently located.

So far I've only read about filling in the tank. Is is possible to remove the tank and place a pool in the same spot? Or would that not be advised because if compromise to the area or other structural difficulties?

On 2017-04-24 2 by (mod) - can an abandoned septic tank cause leaks into a building?

Debbie:

Good question.

A septic tank is not usually disposed-of in the sense of physical removal, when it is to be abandoned; rather it is left in place and filled in with rock and soil.

Now some "IF's"

If the septic tank was not filled-in
and
if the septic tank is close to the building,
then

Yes I have encountered cases in which an abandoned tank close to a building foundation wall was a source of water entry into the basement or crawl area. The excavation itself can direct roof spillage or surface runoff into the foundation wall or under the slab.

More likely, though, when a buried septic tank (or oil storage tank) is placed within 10 feet of the foundation wall, the root cause of water entry is not the tank itself but rather the hole into which it was placed.

Roof spillage close to a building from overflowing or absent gutters or for a mis-directed downspout discharge too close to the building that might otherwise run downslope and away from the structure can sometimes find a previously-excavated hole whose backfill is less dense than surrounding soil.

Water then runs into that hole (or pipe trench) and flows towards the foundation.

Start with a close look at roof and surface runoff around the building. Most builders are not so dumb that they put the basement slab below a local high water table. That's why I suspect an above-ground water source.

On 2017-04-24 by Debbie

If a septic tank is not properly disposed of,while hooking up to city sewer lines can it cause under slab leakage?

On 2017-03-20 by (mod) - Rocks + sand would be fine and do not hurt the garter snakes

Rocks + sand would be fine. By the way, garter snakes are harmless and in fact may help you out by eating bugs.

More accurate information about garter snakes is in

Huey, Raymond B., Charles R. Peterson, Stevan J. Arnold, and Warren P. Porter. "Hot rocks and not‐so‐hot rocks: retreat‐site selection by garter snakes and its thermal consequences." Ecology 70, no. 4 (1989): 931-944.
Harvard

Matthews, Kathleen R., Roland A. Knapp, and Karen L. Pope. "Garter snake distributions in high-elevation aquatic ecosystems: is there a link with declining amphibian populations and nonnative trout introductions?." Journal of Herpetology 36, no. 1 (2002): 16-22.

On 2017-03-20 by Carmen

We have an old unused septic tank near our house. We want to fill it and cover it but we also have garter snakes in the area. We know rock or loose substances will attract them . What can we fill it with to avoid this?

On 2016-10-24 by (mod) -

Narender

Sorry I don't have a "how to" for abandoning a septic tank full of sewage. The tank should be emptied, first, then filled with soil and /or rock or equivalent. Trying to fill in and thus safely abandon a septic tank that's full of sewage is going to spill sewage all over the place around the septic tank, on the ground surface - a nasty situation and not one I'd recommend.

On 2016-10-24 by narender

How to close septic tank is fill with soil without cleaning the old septic tank

On 2016-10-09 by (mod) - safety is the first concern when filling sinkholes or septic tanks

Shelley,

The first priority should be taking steps to prevent an avoidable injury or death that you know about. If it were my rental home I'd rope off the suspect area, prevent access to it, then notify the landlord in writing of a dangerous, potentially fatal condition if in fact there's a risk of someone falling into an improperly abandoned septic tank or any other hole or opening including a sinkhole.

There are other, easier to fix sinkholes that develop at properties, not true sinkholes but subsidences caused by poor drainage, improperly abandoned tanks, even rotting buried tree root or debris.

If it were truly a sinkhole, and there are some reported in your state, there may be risks to neighbors as well. In a severe case or with evidence of settling activity it might be appropriate to notify emergency services.

On 2016-10-05 19:10:18.834813 by Shelley

I probably should have stated that I am in twin falls county, Idaho. Since I do not own the property, there is not much I can do to remedy the situation. I feel it is unsafe and not just a hole in the ground that caves in every so often. Am I right in feeling this way because my next step is to demand it be fixed and this could cause me to lose my house that I have rented for 3 years.there are not a lot of tenant protection laws here in Idaho.

On 2016-10-05 by Shelley

I live at a residence that has a sinkhole right outside the back door. Everyone(meaning my boyfriend's family) has told me this is an abandoned septic and go on like it's no big deal.

Ok, obviously it was not filled in, I've been told it was just a hole in the ground with some sort of cover, which has failed. I am alarmed, especially now that his sister and brother in-law want us to purchase the home or sign a lease that states everything is in safe working order.

I guess my question is, is there cause for alarm, and I already know the answer is probably yes. Which brings me to the next question, what the heck should I do about it?

On 2016-09-29 by (mod) - moisture in house walls near abandoned septic tank

Thanks for the interesting question, Scott. If the old septic tank was just filled-in and no holes punched in its sides or bottom, perhaps it's collecting some water from surface runoff or roof spillage, then leaking that water back out at its entry or exit port. Hopefully the tank got filled well enough that it won't serve as an underground pool.

Compacting soil could damage buried downspout lines, footing drains (less likely unless they're near the surface) or might otherwise cause water to be redirected.

A more expert look at the leak locations and patterns, site shape, roof drainage etc. can probably diagnose this trouble. Search InspectApedia.com for BASEMENT WATER ENTRY to see details.

On 2016-09-29 by Scott

A new septic tank was installed before we moved into our house. The old cement tank was filled in.

We are experiencing significant moisture problems in the basement on the wall that borders the old tank. The old tank is located under the patio in the backyard so it is not that far from the house. Is it a possibility that the filling in and compacting of the soil round the old tank has caused an underground waterflow issue in the yard?

On 2016-09-14 by (mod) - do you drill holes in the bottom of an abandoned septic tank?

I prefer to see a drain hole in the bottom of an abandoned concrete septic tank but often a contractor simply fills the tank with soil and rubble.

On 2016-09-14 by Brenda

The wells are dry and made of cement

On 2016-09-14 by Btends

Found abandoned septic tank -2of them in backyard. These are cement and intact. Do you have to drill holes in the bottom and then fill with sand and stone? Is that ok?

On 2016-08-06 by (mod) - hole opens in lot where a septic tank was left

Diane:

Watch out: Besides filling in the abandoned septic tank, depending on the age and location of the property I'd be alert for other older or newer septic tank, drywells, dug wells, abandoned buried oil tanks &c.

Having a plot plan that showed the original house and knowing house age, type of heat, etc. can help sort out those risks.

On 2016-08-05 by diane

Several months ago, we purchase a vacant lot that once had a house on it. The other day a huge hole (that we think is an old septic tank) opened up after someone drove up onto the property (and over the tank).

There is no liquid in the tank, and it is made of concrete. We had no idea it was there because the neighborhood is connected to the city sewer, and there doesn't appear to be any evidence of other parts of the system. Is there anything else we need to look for and fill in other than the tank itself?

On 2016-07-26 by (mod) - basic due diligence and appropriate warnings are important

The main point I think we should emphasize is that some basic due diligence and appropriate warnings are important in these cases as though the chances may seem small, if somebody steps into or falls into a septic tank, even an old one that has been disused for some time, the result could be a quick and ugly fatality.

On 2016-07-26 by Kathy

I would love to know the ans that Carole got we are in the same boat. Been in house 35 yr and no clue now what do we do

On 2016-07-10 by (mod) - watch out for fatal falls into septic tank

Watch out: Considering that a fall into a septic tank through a collapsing tank cover can be fatal and that the materials or even exact location of your septic tank is unknown, we can't eliminate that risk until someone finds the septic tank and either assures that it has already been properly abandoned or does so, taking steps to be sure that there is no safety hazard.

The fact that there is non visible depression is no guarantee whatsoever that the tank cover is safe nor that there can't be a collapse or fatality in the future.

I would either resolve the question immediately or give an allowance rather than risk a fatality, injury, or related liability. Meanwhile, as we don't know the safety of the site it makes sense to take steps to keep anyone from walking over the area where the septic tank is located.

On 2016-07-09 by carole

Buyer did a sweep of our property and found an old septic system (30 years or so) Apparently the entire neighborhood had septic before they brought in public water. There is no sinking and you cannot see where it even was. They say we have to dig it up and inspect it before selling the house. No one in the entire neighborhood has ever had to do this to sell their home. Is the buyer right or just looking for me to give them money at the closing toward it and reducing the price of the sale

On 2016-04-27 by Anonymous

We are planning an extension and the old septic tank is underneath the old septic tank system, which has been partially filled in but sinks a bit during wet weather. The engineer has specified removing the old tank but has said nothing about how to fill in the hole so that we can build over it - any ideas?

On 2016-04-26 by Jerry

I need to retire a non-used aerobic system for about 3 or 4 years. Can this be done and how?

On 2016-04-26 by Cathy

We recently have developed a sink hole and appears it is caused by a very old abandoned septic tank. We live in a relatively new subdivision (9-10 years). We have lived here 8+ years. Should the builder have removed septic tank, before building? We are all on sewer system. Thank You

On 2016-04-04 by (mod) - ok to remove old vent pipe for abandoned septic tank or fields?

Anon: that might make sense to me if I were sure that there would be no reason to return the fields to service later-on.

On 2016-04-04 by Anonymous

after a leach bed has been abandoned for several years, is it alright to remove the vent pipe and fill in the hole?

On 2016-03-13 by (mod) - what to ask the septic inspector

Thanks so much, Jill. We work hard to provide accurate, useful information so I'm thrilled when a reader finds it so. We also will welcome content suggestions, critique, or questions that may arise.

On 2016-03-11 by Jill

Considering purchasing an old house with an equally old septic system and your article has been very informative/helpful. I now know what to do and what questions to ask an inspector. Thanks so much.

Question: is it ok to fill a concrete septic tank with sand?

Can you fill a concrete septic tank in with sand? We are preparing to hook up to city sewer and need to know what the best cost-effective way to handle our septic tank will be. - 8/13/2012

Reply:

Cassandra, the tank gets pumped, cleaned, and filled - sand should be acceptable to your local building department.
If the tank is steel, and recommended even if the tank is concrete, fiberglass, or plastic, the contractor may punch a few bottom holes so that even sand-filled the abandoned septic tank doesn't become a water reservoir.

Question: can I convert an old septic tank into a pond?

I've got an old septic tank in the garden of the house I'm buying. Is it possible to turn it into a pond? I was wondering if I could line it with butyl liner on a cushion of sand (to be more hygienic) - Victoria 9/25/2012

Is it possible to turn an old septic tank into a pond? I was wondering whether I could line it with butyl liner on a cushion of sand. - Victoria

Reply:

Victoria,

While the conversion you describe is technically feasible, it seems a bit deep, unsanitary, and cost-unbalanced an idea to me. To reduce the sanitation hazard you'd need to

1. remove or block off any abandoned sewer lines that drain into or out of the septic tank
2. pump, wash, and sanitize the septic tank
3. provide a security fence or similar measures as one would do around any pool or pond where it may be an attractive nuisance and child hazard
4. provide appropriate water source, aeration, drainage, etc.

Question: foul odors from basement after connection to sewer

(Nov 18, 2012) ray tom said:
The house we have bought about 5 years used to have a septic tank but was converted to public water and sewer before we moved in. But there is a foul sewage smell that comes from the basement. We are almost certain it is because of the old septic tank. How do we properly solve this problem?

Reply:

First Ray we need to know where the old septic tank was located: in a basement would be quite unusual.
See SEPTIC TANK, HOW TO FIND

Next we need to find the source of basement odors: possibly from a plumbing leak, improper venting, or from a prior sewage backup in that area. See SEPTIC SYSTEM ODORS

Question: when abandoning a septic tank what happens to the drainfields or soakbeds or transpiration pits?

(Mar 26, 2014) Anonymous said:
do i leave the leach fields as is or fill outlet with concrete

Reply:

Leave the septic drainfield or soakbed as-is.

Anon, no one should fill a drainfield with concrete. We're talking about 6" perforated pipes buried in gravel trenches or the equivalent; left alone. Only if there were structures in danger of collapse would a fill-in be appropriate. Then one would use rock and soil, not concrete when abandoning such a system.

Question: is it ok to build a structure atop an abandoned septic tank

(May 7, 2014) Anonymous said:
Can you build on top of a septic tank that was filled with slurry?

(Aug 1, 2014) Michele said:
Hi i just wanted to ask can you fill the old transpiration pit and build on top of it . We are connected to sewerage and the septic tank has been crushed and filled in but we want to build a guest accommodation/home office where the old transpiration pit was
Cheers
Michele

Reply:

Anon, if the septic tank was emptied, cleaned, drilled with rubble, it's properly abandoned in my opinion. Building over it should be ok. I'd not bear a structure directly on an abandoned septic tank as a structural support.

At our old Poughkeepsie office the prior owner had constructed a wood-framed porch over an old steel septic tank. He left a trap door in the porch floor to permit tank pumping but no actual tank inspection nor repair. We had the tank emptied, cleaned, and filled with stone and concrete rubble. There were no subsequent odor problems. But none of the porch structure was borne on the tank itself nor on nearby piping trenches.

One of the most common complaints readers report about abandoned septic systems is subsequent subsidence or collapse - not only safety worries but serious problems for anything built atop the septic tank.

Question: How to abandon a septic tank in Australia

(May 25, 2014) Michelle said:
Does anyone know if when a contractor is hired to change a septic system over to a town sewer line is filling the abandon septic tank part of the cost and is it required in ,ma

Reply:

Michelle,

Take a look at Massachusetts Title 5 Septic Regulations for requirements in general. But the contractual obligation of the contractor is another matter. You'll need to review with your attorney the contract that you signed for work to be performed to understand the scope of work that was required.

Generally to be sanitary and safe an abandoned septic tank should be emptied of sewage and then filled-in.

(Aug 1, 2014) Anonymous said:

Typically an abandoned septic tank or similar component is emptied, then filled-in to avoid collapse risk before constructing over the site. Check also with your local building department to determine whether or not there are local requirements.

(Aug 1, 2014) Michelle said:
Thanks for your reply The septic tank has been emptied crushed and filed in I was wondering about the transpiration pit or drainage area where the effluent would drain into from the septic. I live in Australia so maybe our designs are a little different but will call my local council and see if there are and regulations around this. Thanks again Cheers Michele

Reply: transpiration pits

I'm not sure what you really mean by transpiration pit. IF you actually had a seepage pit rather than a drainfield, it too needs to be emptied and filled-in. If you refer to an excavated hole into which was put a pre-cast drywell or cesspool or soakpit structure to dispose of effluent then such devices also need to be filled-in to avoid a future collapse hazard. - Mod.

(Aug 1, 2014) Michele said:
Thanks Dan it would be what you call the drainage area or absorption area
Cheers
Michele

Reply: difference between a transpiration pit and a soakbed or soakaway bed

OK Michele, but a "pit" as opposed to a network of perforated pipes draining effluent into the soil is what we call a drywell, seepage pit, or cesspool. Those methods of disposing of sewage effluent are effective for a limited time as "disposal" methods but ineffective as a treatment method.

Details are at CESSPOOLS

If we were abandoning a conventional soakbed or soakaway bed or drainfield, not a drywall, not a seepage pit, nor other underground cavity, there is nothing to fill-in.

Question: building an above-ground pool over an abandoned septic tank

(Nov 1, 2014) Jo said:
I was interested in purchasing a home and just discovered that the old septic tank was left untouched. My concern is that there is an above ground pool over the old tank. What, if any, concerns should I have.

Reply:

Pool collapse, injury, unsanitary conditions come to mind, Jo. Along with some extra costs to access and properly abandon and fill-in the septic tank

Question: sinking and cave-ins in the yard may be due to old septic tank?

(June 7, 2014) Sue said:
I discovered an area in my backyard slowly (over 2 year time frame) sinking. Then in 3 weeks, the ground started to cave in and a hole is starting to get larger. Most happened after a couple of rains. I have city water but was told that my house had a septic tank system when the house was built. I am assuming the city properly closed the septic system. Is my yard sinking due to the old septic tank? It appears to be in the obvious location for the tank.

Reply:

Sue we hope you roped off the area for safety pending further investigation or fill-in as needed.

Also see SINKHOLE DETECTION, WARNING SIGNS

Question: what is the proper fill to use when abandoning a septic tank

(Dec 8, 2014) ROGER said:
WHAT DO YOU USE TO FILL THE TANK?

Reply:

Roger an abandoned septic tank can be filled with stone rubble or sand. You might use dirt (soil) but I'd watch for future setttlement or compaction problems. Don't toss old tree branches, appliances, or junk into a septic tank to be abandoned as the decay of those items is likeliy to lead to a subsequent collapse.

Question: patio sinking over abandoned septic tank

1/1/2015 Cindi said:
My parents paid a company to fill in the septic tank at their house and hook them up to the sewer. Now, years later, the patio is sinking (right where the tank is) and the sinking is causing structural damage to the house.

The steps leading to the back door are pulling away from the house.

The planter in the backyard has also sunk and the bricks cracked. It is a terrible result especially after my parents paid over 12,000 for the work to be done. Do you think this was mainly a compacting issue?

Reply:

Cindi,

First let's be sure the trouble is due to settlement at the old tank location.

If that's the case then I suspect either poor co paction or poor choice of fill contents. Anotherr possibility is a steel tank rusting out and collapsingg into a void beneath the old tank.

Most likely a large part of the cost you cite was the sewer hookup, so not all of that $ was wasted.

Surely no one built a structure bearing on the old septic tank did they?

In any event if a patio, presumably poured concrete, is settling or tipping towards a building foundation wall I'd expect problems with directing roof spillage or rain or melting snow water against the foundation as well as possible foundation damage from the patio weight against the foundation.

The fix may require removing the patio and proper grading and fill compaction before re-building.

On 2015-10-23 by Andrew

I had a sewer plumbing issue below my slab under an add-on to the house. When the pit was dug, we found the sewer line runs through an old abandoned "coffin" style concrete septic tank 4x10ft and 5ft deep.

It is partially filled with dirt around the new pipe, and is hollow through the rest, with no liquids at all. I'm figuring the folks who constructed the add-on pumped it out, busted out the top corner along the 10ft stretch of the take and installed a new ABS sewer line through the far end of the old tank, running the new pipe out to our "new" tank that is in the backyard.

Then the shoveled as much dirt as they could into the tank around the pipe (likely not compacted well), piled the broken pieces of concrete back on the filled in dirt at the edge of the old tank and backfilled dirt on top, laid the house slab and built the addon. Question, since we've found the tank to be partially hollow, should we worry about trying to back fill it anymore (slurry, dg, sand), or just leave it.

I would still try to shovel as much dirt in as possible, but it won't be compacted as I don't have good access through the 2x2 pit in the house slab.

On 2015-10-10 by Greg

I work in a store evet had a really bad smell.

After a week or so it went away. the boss had people come out and do an inspection of the air quality. I did not get the results.

But they came after the smell had pretty much subsided.

And now I notice that the floor is starting to become really uneven and sloping in different directions.

Not much only an inch or so but it's a cement floor with carpet glued directly onto it... Could this be a septic tank that has broken..?

On 2015-09-14 by (mod) -

No, Barry, not in my opinion; keeping a septic tank means keeping periodic maintenance: pumping and cleaning;

I would abandon the septic tank and install a sewage grinder pump in a pumping station. I'd duplex the pump and include a pump alarm so that I'm confident that we can flush toilets without a backup.

On 2015-09-14 by Barry

We have a working septic tank, but are now being obliged to connect to the main town sewage system. As we live on a hill, it means we will have to install a pump system, to pump sewage around 25 metres in distance and a height of 8 metres.

I expect this to be quite expensive. I think it would be cheaper to install a pumping system to just pump the run off of the waste that exits the septic tank. Is this a viable option?

On 2015-07-21 by Dave

We have a old septic tank which was closed in the late 1950's our above ground pool was installed our the edge of the tank. The pool wall collapsed and the tank filled with water. What should I do? Can I just fill the tank with stone ? Can I fill the tank with stone with water still in the tank?

On 2015-06-1 by (mod) -

Me

A concern with any pump and hose system is that you need first to empty the sewage from the tank and then to fill it with rubble or sand.

If you can pump dry sand and not create or leave a moisture problem (or if it's a steel tank and you can punch holes in the tank bottom so that it wont' hold water after the sewage has been removed) that may work.

Perhaps you can rig up an extended trough such as those used by concrete delivery trucks to move sand or gravel to fill the tanki.

On 2015-06-11 by MeT

I have a customer who has a septic tank under the floor of her house. We are installing a new septic system and I need to fill in the old tank with some sort of material (granular or alternative).

Can you suggest some options? I have to bring it in through the house, by pail, unless I can think of something that will work that can be put in by pump and hose.

On 2015-06-04 by marie

We have a new tank that was installed in a new location. Does my other septic tank NEED to be pumped out before it is crushed/filled with earth & stone Thanks so much!!

On 2015-05-14 by (mod) -

1. Immediately: rope off and protect the area to prevent someone from falling into an opening and being injured

2. Contact an excavator to explore, open, and fill completely as needed the abandoned septic tank.

On 2015-05-14 by Anonymous

Septic tank has not been used for years. On sewers. Now we are getting sink holes where septic tank is. What can we do? I don't think my husband filled in septic tank when sewers put in

On 2015-05-13 by (mod) - we have a cistern well on out property

Smart question, Sandy. Indeed on occasion kids open and fall into such site features. I was drawn to them myself when exploring Goochland County VA as a kid and one Halloween two of us fell into a nasty hole.

A cistern is not a well - it's a water tight reservoir intended to receive and store water. But regardless of whether you're talking about a cistern or an actual dug well, it's common to fill in the opening with stone, stone rubble, and then to cover over the top with enough soil to plant grass.

On 2015-05-12 by sandy

we have a cistern well on out property and were not made aware of it when we purchased the home 11 years ago. Our home is 115 yrs old and it is in town where there is city water/sewer. How can we close it/fill it. I'm concerned that my grandchildren could get it open, and am concerned that it could collapse?

On 2015-05-01 by (mod) - ok to not dig up septic system

"Leave it" does not mean leave a possibly fatal hazard to be encountered in the future. If the tank is emptied and filled that's safest.

If the tank has a solid concrete lid and child safe covers that improves safety until the tank can be emptied and filled.

I would not base your decision on the contractor's advice. Check with your local health and building departments and let me know what they say.

In many jurisdictions local law requires that an abandoned septic be filled-in or removed properly not just "left alone"

On 2015-05-01 by Kathy

I'm hooking up to county sewage system and contractor says it's ok to not dig up septic system I haven't had any problems with it is it ok to leave it

On 2015-04-20 by (mod) -

Sammy

If the tank was water tight and had no water leaking in and none leaking out, it will contain sewage, possibly with some water loss depending on how air-tight was the tank.

If the sewage has solidified too much for pumping your pumping contractor will add water and stir the mix so that it can be removed.

On 2015-04-20 0 by Sammy

Old septic tank has not been used for 15 years due to a new system being installed. Never pumped this tank,what will we find if we dig it up now?

On 2015-01-03 by (mod) - patio is sinking - maybe over the old septic tank

Cindi,

First let's be sure the trouble is due to settlement at the old tank location.

If that's the case then I suspect either poor co paction or poor choice of fill contents. Anotherr possibility is a steel tank rusting out and collapsingg into a void beneath the old tank.

Most likely a large part of the cost you cite was the sewer hookup, so not all of that $ was wasted.

Surely no one built a structure bearing on the old septic tank did they?
In any event if a patio, presumably poured concrete, is settling or tipping towards a building foundation wall I'd expect problems with directing roof spillage or rain or melting snow water against the foundation as well as possible foundation damage from the patio weight against the foundation.

The fix may require removing the patio and proper grading and fill compaction before re-building.

On 2015-01-0 by Cindi

My parents paid a company to fill in the septic tank at their house and hook them up to the sewer. Now, years later, the patio is sinking (right where the tank is) and the sinking is causing structural damage to the house. The steps leading to the back door are pulling away from the house.

The planter in the backyard has also sunk and the bricks cracked. It is a terrible result especially after my parents paid over 12,000 for the work to be done. Do you think this was mainly a compacting issue?

...

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