Possible building plot - shaft on the property

- the water is over 1.20m deep - exactly how deep, I couldn't find out because my measuring stick was too short (please no jokes )

Laugh! He admitted it invited. Please stop with experts, they cost money here where it is not necessary. In the photos it really looks like an inspection shaft for an underground channel full of water. Whatever causes it. If it was used agriculturally, the suspicion of drainage is obvious. Is it towards Offenbach? Soil experts are also not a bad choice, at least for a free consultation. But in Germany such a structure should be documented somewhere. Of course, not easy in times of Covid.

Could it be that the stream was "tapped"?
Both agriculture and allotment gardens always need water.

That could of course be the case, but it seems unlikely to me. On the one hand, the thing would have to be about 200m long, since the stream really is just a small stream, right? And on the other hand, between the property and the stream (besides the newly built road from 2019) there are still two other properties (one of them an old horse paddock), an older road, and a cemetery (!). If someone had dug up the latter for such a channel, it would presumably also be marked somewhere (although of course you should never say never)?

If necessary, pour concrete in. End of shaft.

But to do that I would have to know how long the thing is, so I know whether I can do it "by hand" with a concrete mixer or if I need 12 truckloads of concrete... Aside from that: is it really that simple? Pour concrete in and that’s it?

In the photos, it actually looks like an inspection shaft for an underground gutter full of water. Whatever causes that. If it was used agriculturally, the assumption of a drainage system is obvious.
Is that towards Offenbach?

No, it’s in the northwest of Frankfurt

A soil expert is also not a bad choice, at least a free consultation. But in Germany, such a structure should be documented somewhere.

If someone built the shaft/channel/gutter/whatever "illegally" who knows how many years ago, I’m not sure if it would really be documented anywhere. In any case, no one at the city was reachable today.

The seller (public authority) mentioned, by the way, that he "assumes it is a well." The thing was already on the property when the state bought it, but it was never really looked at.

I’m thinking of asking a well driller to take a look — even if it’s just to confirm that it definitely isn’t a well. Then at least I could talk to the seller about how we want to handle it. Do you think that makes sense?

Of course, asking questions makes sense, otherwise you wouldn’t be getting anywhere.

Hello BabanaJoe

"Tap the stream" is out due to the distance.
A well is built downwards and not horizontally.
Now just check how deep the water is. If your rod is too short, sound it out. Attach a string, tie on a stone, and throw it in. I would have organized a pump a long time ago. In case it’s not a well. A mobile phone wouldn’t be bad to check either. Attach it to your famous rod and press the video function. That way you could see inside the horizontal shaft.
Crack the riddle!

Steven

Hello

something just occurred to me: ventilation shaft of a bunker. An acquaintance of mine was building a house with a basement. They came across a bunker. It was not recorded.

Steven

A well is built downwards and not horizontally.

I thought so too...

Now go ahead and check how deep the water is. If your rod is too short, test it out. String, a stone attached, and throw it in. I would have long ago arranged a pump. If that’s not a well. A mobile phone wouldn’t be bad to check either. Attach it to your famous rod and press the video function. That way you could view the horizontal shaft. Solve the mystery!

That just shows again that I am practically absolutely unskilled and uncreative. The idea with the stone and string sounds good, and also the one with the phone and the rod. Where do I get such a pump? Can I borrow it at the hardware store? I will try to implement it in the next few days if I manage it alongside work (home office, of course).

Something just came to mind: ventilation shaft of a bunker. A friend of mine was building a house with a basement. They came across a bunker. It was not recorded.

Stop it! Then I can save the house and move straight into the bunker!