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I've got a sinkhole in my back yard of a tear down home (torn down from an old duplex from 1950 and rebuilt). The hole is about 5 feet wide and 4 feet deep. The corner of the deck has sunk in the hole and is temporarily hanging in the hole.

I've had a contractor offer to fill it with concrete for $700. They mentioned the possibility of a drainage issue but my drains are newly and correctly installed. A similar post (without an answer) stated that if this issue persisted into something larger we would have a huge boulder that would need to be removed on top of whatever else may be causing the problem.

I also spoke with a few architectural landscapers and they gave me large price points to JUST examine and determine the cause of the issue. One of them said it may be an old septic tank from the original property. I am located in the Atlanta area and have not heard of this possibility. I've heard of debris pits but not sure that's the issue.

My question is what should I do? Has anyone done this type of work before? Is there a good idea of what causes sinkholes in this part of the country (Atlanta area)? I'd appreciate any help. (I currently have it lifted off the ground with some cinder blocks.

UPDATE: I had a landscape architect come out this afternoon and he is adamant that it is an old well. One from before 1950 most likely. He cited his 20 yrs of experience but in the last 2-3 years he has done about 3-4 of them a year as houses in my area (Atlanta, GA) are getting torn down and rebuilt. His plan would be to dig down deeper, about twelve feet or until water is found, and then cap the well with concrete. After that he would fill with dirt to the top of the sinkhole.

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    first you need to find out if it's a natural sink hole or man-made. If you are in an area with natural sink holes (such as Florida) there may not be a whole lot you can do other than collect insurance and move. Odds are, though, that's it's man-made and an old cess pit is certainly a common possibility. You'd want someone to come look at it to examine it in person. – DA01 Nov 16 '15 at 21:59
  • That seems like a lot of concrete. Is that really an option for a sinkhole rather than just filling with dirt (I don't know, curious)? A 5' round hole at 4' deep would be something like 11 yards of concrete. – JPhi1618 Nov 16 '15 at 22:16
  • I wouldn't fill with concrete unless I was sure nobody would ever want to dig in that area again (no additions to the house, no garden structures, no fences...) What's wrong with filling with sand or soil or something equally normal for the area? – keshlam Nov 16 '15 at 22:37
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    Is the hole continuing to get bigger? Or did appear and the size stabilize? – mikes Nov 16 '15 at 23:26
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    Fill with dirt, not concrete. The only concrete you might need would be to support that post, and there are several options for that, most of which can stay near the surface in your area (shallow frost.) As for "getting deeper" - if it's man-made, you fill it and are done. If the earth is opening up and swallowing your house, you move and fight with insurance. Only in the latter case does the dirt have somewhere to go to. – Ecnerwal Nov 16 '15 at 23:33
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I have filled several of these when I lived in California, abandoned Old redwood septic tanks that finally rotted out, I would check into that. Natural or something like this, I would only use fill dirt / rock . cement would cost way more and wont stop it if it continues to grow. use caution if you do fill it as there may be several feet of the top that has not given way but a person walking on top could be enough for it to let go, a couple of 2"X8"X8' boards laid down to the hole is what we used after I went through 1. the home ones we filled were ~6' round and maybe 6'deep ,the Motel one was close to 20' and at least 8' deep

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