Is there a giant chalk deposit in my Berkeley garden?
July 23, 2017 12:09 PM Subscribe
I am slowly reclaiming a corner of my yard where a shed once stood and I keep digging up big hunks of chalky white stuff. Can you help me figure out what it could be?
Either there is a giant chalk deposit in my back yard or someone buried a great cake of … ? Chalk? Lime?? Rat poison? I'm leaving towards lime, but I don't know how to figure it out.
Pictures at:
http://amandabees.tumblr.com/post/163334970631/either-there-is-a-giant-chalk-deposit-in-my-back
The back corner of our yard used to have a shed of some kind that was torn out but there is a bit of rubble left from it. In addition, about 3" below the soil there is a 6" deep deposit is some kind of white chalky stuff that holds together in chunks but crumbles very easily. I haven't found the edges of it the deposit, but I keep hitting it when I dig. The whole area is probably 5'x10'. It is odorless, though since it is pretty powdery I haven't really stuck my nose right in it. It might have a scent of I tried hard to smell it but I don't really want to inhale random powders.
The soil here is looser than in the rest of the yard, which is solid clay, so I suspect that the chalk and the soil on top of it were put here by the last gardener. Our immediate predecessor was an artist who didn't really take care of the garden. He was a painter, as far as I know but may have done some sculpture work. Not sure if that is relevant or not.
So it could be something he used and left behind, it could be that someone was storing chemicals in the old shed. Possible that it is just here naturally. So I guess my question is: how should I go about figuring out what this is? I'd especially like to confirm that it isn't some kind of toxic thing. I wouldn't be surprised if a cache of rat poison was hidden out here.
Any ideas about what it could be or how I can start ruling out possibilities? Thanks!
Either there is a giant chalk deposit in my back yard or someone buried a great cake of … ? Chalk? Lime?? Rat poison? I'm leaving towards lime, but I don't know how to figure it out.
Pictures at:
http://amandabees.tumblr.com/post/163334970631/either-there-is-a-giant-chalk-deposit-in-my-back
The back corner of our yard used to have a shed of some kind that was torn out but there is a bit of rubble left from it. In addition, about 3" below the soil there is a 6" deep deposit is some kind of white chalky stuff that holds together in chunks but crumbles very easily. I haven't found the edges of it the deposit, but I keep hitting it when I dig. The whole area is probably 5'x10'. It is odorless, though since it is pretty powdery I haven't really stuck my nose right in it. It might have a scent of I tried hard to smell it but I don't really want to inhale random powders.
The soil here is looser than in the rest of the yard, which is solid clay, so I suspect that the chalk and the soil on top of it were put here by the last gardener. Our immediate predecessor was an artist who didn't really take care of the garden. He was a painter, as far as I know but may have done some sculpture work. Not sure if that is relevant or not.
So it could be something he used and left behind, it could be that someone was storing chemicals in the old shed. Possible that it is just here naturally. So I guess my question is: how should I go about figuring out what this is? I'd especially like to confirm that it isn't some kind of toxic thing. I wouldn't be surprised if a cache of rat poison was hidden out here.
Any ideas about what it could be or how I can start ruling out possibilities? Thanks!
Could be chunks of gyproc; especially if it appears in layers about 1/2" thick.
posted by Mitheral at 12:37 PM on July 23, 2017 [1 favorite]
posted by Mitheral at 12:37 PM on July 23, 2017 [1 favorite]
Drywall texture and joint compound or stuff for patching drywall can be bought in bulk bags. Some might look like that when dried.
posted by slidell at 12:42 PM on July 23, 2017
posted by slidell at 12:42 PM on July 23, 2017
Caliche is a carbonate deposit that is present in Bay Area hills, subsurface, often exposed by eroding. If you drop a small chunk of it in vinegar, and it disappears, leaving a little silt or sand, then it was calcium carbonate, and probably naturally occurring.
It could also be plaster, or plaster of paris, calcium sulfate, leftover from plastering your walls of your turn-of-the-century home. Similarly, it could be discarded drywall compound. Check that stratum for other construction debris or artifacts that may be contemporaneous with the white chunks. Do I see scrap lumber in that photo? A hose bib handle? What's that green thing?
posted by the Real Dan at 1:19 PM on July 23, 2017
It could also be plaster, or plaster of paris, calcium sulfate, leftover from plastering your walls of your turn-of-the-century home. Similarly, it could be discarded drywall compound. Check that stratum for other construction debris or artifacts that may be contemporaneous with the white chunks. Do I see scrap lumber in that photo? A hose bib handle? What's that green thing?
posted by the Real Dan at 1:19 PM on July 23, 2017
Old eroded septic tile looks a lot like that too. So seconding the outhouse idea.
posted by scruss at 2:15 PM on July 23, 2017
posted by scruss at 2:15 PM on July 23, 2017
Response by poster: Direct link to image: 📸
Some answers:
* I think the green thing is a scrap of green insulated ground wire.
* All the white that you see in that photo is more of the chalky stuff.
* There is other rubble back there but is mostly chunks of brick and cinderblock. Most of the wood from the old shed was shoved into a little space between the garage and the fence where it's been breeding spiders and rot. But there is indeed a bit of 2x2 in the bottom of the photo.
* I dropped a peach-pit sized piece in small glass of vinegar and it immediately began fizzing dramatically, and then slowed down. The chalk hunk dissolved a bit, but most of it is still there, fizzing gently 30 min later.
posted by amandabee at 6:15 PM on July 23, 2017
Some answers:
* I think the green thing is a scrap of green insulated ground wire.
* All the white that you see in that photo is more of the chalky stuff.
* There is other rubble back there but is mostly chunks of brick and cinderblock. Most of the wood from the old shed was shoved into a little space between the garage and the fence where it's been breeding spiders and rot. But there is indeed a bit of 2x2 in the bottom of the photo.
* I dropped a peach-pit sized piece in small glass of vinegar and it immediately began fizzing dramatically, and then slowed down. The chalk hunk dissolved a bit, but most of it is still there, fizzing gently 30 min later.
posted by amandabee at 6:15 PM on July 23, 2017
I'll bet on calcium carbonate, then.
Might be the climax stage of an extremely heavy application of lime, perhaps for a large buried animal like a horse. Might be an old limecrete floor, long buried and forgotten, from a shed. How old is your house?
posted by the Real Dan at 9:52 PM on July 23, 2017
Might be the climax stage of an extremely heavy application of lime, perhaps for a large buried animal like a horse. Might be an old limecrete floor, long buried and forgotten, from a shed. How old is your house?
posted by the Real Dan at 9:52 PM on July 23, 2017
Response by poster: I've more or less decided it is rubble from the shed. Drywall or something that was stored there. But I'll let you know if I dig up a horse.
posted by amandabee at 2:19 PM on November 22, 2017
posted by amandabee at 2:19 PM on November 22, 2017
This thread is closed to new comments.
posted by tizzie at 12:35 PM on July 23, 2017 [4 favorites]