I recently had a tree in my back yard cut down, it still has a massive stump protruding from the ground so I was digging around to expose more of it. While digging I hit something hard, turned out there are 20"X20" pavers buried a few inches under the dirt.

So I exposed them and removed all the 20X20 pavers, only to find another layer of 20x10 pavers under them.



So I lifted one of the 20X10 pavers, and found a hole under it.

After more digging and clearing the area a bit more, I discovered the 20X10 pavers are sitting over a piece of thin metal, the edge is about 28" long.



Aren't septic tanks supposed to be bigger? I thought a cover is supposed to be concrete or plastic not steel?





When I lifted one of the pavers quite a bit of sand and dirt fell into the hole. A quick measure it's 18" to the bottom. The inside walls seem to be concrete although I am not sure there are roots crawling up the inside of the walls.



What am I looking at? Is this an abandoned septic tank? It is all the way on the other side of the house where the bathrooms are.

In addition, what is this round thing on the lower left corner? It is very deeply buried it is at least 10" deep.





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Is it located in the back of the property? You should be able to see the baffles if it is a septic, and if it is abandoned anything it should be back filled with crushed stone in case of a collapse nobody falls in especially if it is a rental property

I do not see a baffle tee, but I didn't stick my head into the hole to look all around.

I removed all the pavers over the metal lid. There are a bunch of holes big and small, round and square. The lid is 40" long and 28" wide, and the concrete wall inside is only slightly bigger.













If this is indeed a septic tank, then does it mean there are another tank near by? I looked on the internet and most septic tank has two compartments one where the sewage flows into and there is an overflow for fluids to run into another compartment?

All of this is research for you and guesswork:
* The necessary components of a septic system are an inlet pipe, a tank and an outlet to the leech field. YOu haven't mentioned an inlet or outlet pipe yet.
* Most modern septic tanks have 2 or more chambers (mine have a third pump chamber) and baffles or half walls. Can you see any structures like those?
* What's under the round lid?
* Another uncommon possibility is a cesspool. Google "cesspool vs septic tank" for details.
* Here are some images of septic tank and cesspool covers: [www.google.com]
* Here are a bunch of images of other cesspool and septic tank covers [www.dreamstime.com]

Bsipps mentioned that unused pits should be filled for safety. It sure looks like a previous owner covered yours with large pavers for that reason. Or just to hide it.

Thank you, I do have some additional information but no where close to any real answers.

"* The necessary components of a septic system are an inlet pipe, a tank and an outlet to the leech field. YOu haven't mentioned an inlet or outlet pipe yet."

I do not see any pipes by shining a flashlight into the hole on the metal cover. I didn't see ANY pipe or any plumbing fitting but I wasn't able to see every angle, I am a bit uneasy sticking my head into that hole. The cover does not come off, not sure how it is attached to the structure.

"* Most modern septic tanks have 2 or more chambers (mine have a third pump chamber) and baffles or half walls. Can you see any structures like those?"

All I can see inside are vertical walls on four sides, it seems to be the same size as the rectangular cover. 28"X40" and it's about 16" deep. The bottom looks to be dirt, or poo, not sure, I am not sure what the true depth is because may be it's partially filled with collapsed dirt.

"* What's under the round lid?"

Well, funny you asked that. It's not a lid, or if it's a lid it's an 18" thick lid. Solid concrete. It is the size almost the same as a five gallon bucket. I am curious if this round concrete cylinder is a component of the rectangular tank, or is it something else entirely unrelated?



One thing, I have uncovered another concrete cylinder like this about six months ago, in the same general area. At the time I thought it was some sort of an anchor for a post or gate, but now I found another one.

"Bsipps mentioned that unused pits should be filled for safety. It sure looks like a previous owner covered yours with large pavers for that reason. Or just to hide it."

Well here is the thing, I went to the city permit office and look through old permit records. The house switched from septic to city sewer in 2008, there was a permit in 2008 for abandon existing septic tank. But no location information. All I got is an ISO diagram. This ISO does show an "existing septic" but it's not correct, the tank I found is on the other side of the building.



Since the owner got a permit for abandoning the septic tank, and passed the inspection. I know the city requires old septic to be filled, then how can this tank be not filled? Unless this is not the same septic tank? The house was built in 1941, may be there is a newer septic tank (which I haven't yet found) that was abandoned in the 2008 permit.

The tank is 28"X40" and about 16" deep. If I assume it's 24" deep, still the volume is less than 120 gallons. This is small for a septic isn't it? I thought septic tanks are 1000 gallons, 2000 gallons?

What is the smallest septic tank ever seen?

I was able to remove the metal cover.

What I see is a rectangular box 28" X 40". It is lined with 2" thick pavers, not concrete blocks.



As you can see, there is no pipe entering the rectangular box. Unless it is much lower.







At the bottom of the box seems to be a cementitious bottom, with a smaller rectangular hole. I tried to rinse the bottom out and the water stay in the hole for a long while.





Also, the round concrete thing is not attached to the box so it may be completely unrelated. It is the size of a five gallon bucket, may have been a pier or anchor for something.



Any idea as to what I am looking at here? Even guesses?

No one knows what this is?

I still think this "box" can't be a septic tank because it's just too small.

but what is the smaller rectangular hole at the bottom of this thing?





Not sure if it's easy to see, here is the same picture with a red outline of what I am talking about.





Any idea what that is?


Is it possible that is the real opening to a large septic tank below? That we are merely looking at a cavity reserved for a 16-18" deep riser from a deep septic tank? Any chance of that? But most of these risers are round and not rectangular right?

How deep is a septic tank usually buried?

I am thinking I should just fill it in. I agree, but before I do that I want to make sure of two things.


(1) That I am not dealing with a sealed/closed bottom, because if that's the case, then if and when it get rained on it will just be a large bucket with dirt and water can't escape.


(2) I am installing gutters on that side of the house, and have been looking for a place to drain the runoff. My thought was to dig a big hole for a storm runoff drain field. I wonder since I have a hole here, whether I can fill it with gravel instead and pipe my gutter runoff to this hole instead.

That concrete pillar almost resembles a footing for a parking lot light

it may be an anchor for a post for something? A bird house, a cloth hanging line or some such things?

But is it safe to say the concrete pillar thing has nothing to do with the hole next to it?

Can the hole be the top portion of a well? is there a septic tank at the bottom of this hole?

The round pier sure looks like a base for something but it's the most perfect cylinder I've ever seen buried...had to have been formed with a caisson or sono tube like thing....strange, obviously wasn't a dug hole filled w conc

I agree the box is too small for septic and lacking inlet/outlet

I think he buried his money there and just too bad he didn't forget to retrieve before he moved

Now that we can see the sides, it does not look like structure was designed to hold water. As you say, it is too small to be a septic tank.

It appears to be built out of pavers laid into a dirt hole, then covered with more pavers. That would make a great place to hide a large bag of cash. That doesn't explain the metal cover however.

Everybody agrees that concrete cylinder looks like a pre-cast post footing. If I were digging a hidey hole, I would bury it under a few inches of dirt, right by one of the posts in the back yard, so I would never forget where it was.

Are you going to try to dig through the bottom?



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Buying a home might be the largest investment you will ever make. An important thing to do before you close the deal is to hire a septic inspector to give you an honest and full assessment of the septic system. This will help you to know the condition of the septic system and what to expect.

Septic inspection level 1: This is a visual inspection that involves running water from various drains and flushing toilets in the home. The septic tank inspector is looking at how well everything is draining. The visual inspection also includes looking for septic leakage to the top of the drain field area. We also check for sewage odors in the area of the septic tank and the leach field. This inspection can help identify problems but a level two can give our septic inspectors a better idea on issues with your septic system.

Septic inspection level 2: Have the septic tank pumped. they remove the cover of the septic tank. This allows the septic tank inspector to check the water level. Water levels determine whether water is properly draining. To make sure the water is properly flowing, the septic inspector will run water in the home. This is done to determine if the water level rises when more water is introduced. Next, they will check if your septic system has backflow from the absorption area. Backflow will let them know if there is a problem with the leach field.

After this is done, the septic inspector will pump your tank. Next, they will check if your septic system has backflow from the absorption area. Backflow will let them know if there is a problem with the drain field.



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