Client has us taking out an old garage and putting in a new one about half again as large. The home was built in 1909. It’s clear that the original ‘garage’ (probably a carriage house) was torn down and replaced with a larger structure. The original slab had a second slab poured on top of it, extending off of the edges, by significant amounts on two sides.
In taking out the original slab in preparation for the new, we uncovered what is in the attached pictures. As opposed to the standard 4″-or-so slab, the slab was about 7″ thick on top of this. It looks like concrete was formed around this to seal water flow in one direction or another. The pipe into the ground looks to be about 5″. The cast iron looks 1.5″ to 2″. It does not look as though the cast iron ever went any further than what you see in the picture.
Just found this today, so haven’t had time to try to look for any other pipes, etc.
Note that this ground percolates pretty well…it’s pretty sandy soil.
Is this just an ancient and abandoned septic tank?
Replies
Interior French drain?
Thanks.
Could be a dry well. There isn't anywhere that I can see a drain into it in the garage.
I suspect you want to dig a little more and find out what kind of a cavity may be there.
Could be anything from a cistern for rain or other fresh water to a waste tank for human or other waste.
As I am sure you are well aware, you would not want to rely on whatever this is as support for a new garage floor without knowing what is there.
There's a sewer drain guy locally who might have a camera we could put down there. I've got a call in to him.
Further...I dug a hole right next to the pipe, past its bottom end. The pipe does not appear to go into any sort of vessel, as far as I can tell. Unless whatever was there just disintegrated. which is, of course, possible if it is some sort of clay or earthenware.
My house was built in 1911. My detached garage is that old too. The interior slab there is pitched to the middle to a drain that Im almost 100% sure is just a french drain.
Where was your"drain" located?
No penetrations in the slab. I suppose it could have been a replacement slab.
I finally had what I call an 'epiphany of the terminally slow.'
I taped my phone onto the business end of a digging bar, ran it down the hole, and took a video. There was a cavity at the end about 6" deep and 18" in diameter. It looks like this was indeed a crude drain (not even a dry well) and the drainage of whatever it was over however long it was had caused the subsidence that created the cavity.
Anyway, I dug it out to undisturbed dirt, which gave me a hole about 54" deep from grade. I'll line it with geotex and compact gravel into it before I start building up for my slab.
Here is a link to the video (https://photos.app.goo.gl/xoWuUQ6QV9zxAXyV7) if you have any interest. There appears to be some wood of some type in the cavity, and I found a little totally rusted iron, but nothing that seemed to indicate that there was any 'vessel' down there.
any oil residue in the dirt you dug out.?
No.