Author Topic: Land Conundrum: Shallow Bedrock  (Read 490 times)

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Offline Pallas

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Land Conundrum: Shallow Bedrock
« on: April 25, 2019, 07:45:31 AM »
Hello all, over the past year, I have gotten more serious and active in my land search (expanded my budget, chose a specific area to focus on, got a realtor, etc), and almost closed on 2 lots and experienced a couple heartbreaks after putting tons of time and resources. I can say that buying land has been a slow, grueling, and frustrating experience so far.

After my latest experience, which included shady sellers and multiple lawyers before falling through, I found an off-market piece where the owner is willing to sub-divide a piece of a larger parcel to sell me. It has good access and location; however, I walked the lot with a soil engineer and found that it’s on a bedrock (shale) ledge, with shallow topsoil. The engineer told me there could be deeper pockets where the depth could be slightly deeper, but at best maybe 3 - 4ft to bedrock. The owner confirmed this and said the shale was dig-able and that the dug material could be used on driveway, etc. which I agree with.

HOWEVER, unlike most people who are looking for building lots, I plan to be an active little homesteader/farmer and I’m very concerned about having to bring in heavy machinery every time just to dig a trench or put in a fence pole for my next project. I also want to experiment with earn bermed greenhouse/geothermal/root cellar, all which require lots of soil work.

Although shale is among the easier bedrocks to excavate/flake off for home-building, I’m afraid it may limit what I specifically want to get out of a lot. Am I overreacting? I’d very much appreciate if anyone has had experience with shale and could provide some hope (or a reality check)

Offline Don_P

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Re: Land Conundrum: Shallow Bedrock
« Reply #1 on: April 25, 2019, 05:16:11 PM »
Of the rock to have it could certainly be worse. We are on granite with pockets of shale locally so although I am blessed with rocks we have to buy shale for the roads. My first concern would be perc, can you get in a septic without undue expense. Next, is anyone nearby farming in the way you would like to, visit them. It might be fine for pasture but tough to crop for instance. What is radon like, your soils friend would probably know. Shale does come in many flavors until we call it slate, some is easily dug, others not so much.

Offline ChugiakTinkerer

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Re: Land Conundrum: Shallow Bedrock
« Reply #2 on: April 26, 2019, 08:07:07 AM »
I'll echo Don P's statement that it really varies from one formation to another.  I would ask the landowner to allow you to dig a few test holes with an auger to see what the bedrock is really like.  It could be soft shale that digs easier than gravel, or it could be partially metamorphosed and much harder.  Even then, if it fractures readily it could still be relatively easy to dig.
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Offline NathanS

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Re: Land Conundrum: Shallow Bedrock
« Reply #3 on: April 26, 2019, 09:32:28 AM »
That's a big question. I would look at the websoil survey to see how they classify the soils, and I would look for nearby areas with the same or similar classifications to see what is growing there.

To be successful with fruit trees and other perennials I think you would at a minimum need to create berms to plant into. Recreating what the ground looked like before it was plowed - "pillows and cradles."

Do you still have 18"+ of soil in the more shallow areas? I think that would be my minimum. If the soil engineer finds his 4' area you can be sure he's going to take that for the leach field. If not, they will have to scrape soil from one area to create a 4' deep leach field.

Earth bermed structures are probably not going to economically make sense, the shale also is not going to have much of an insulating property. I think it is important to let the land dictate how you build, and not try to fight against it.

Offline Pallas

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Re: Land Conundrum: Shallow Bedrock
« Reply #4 on: April 26, 2019, 10:16:23 AM »
Thanks very much all for the great replies and good suggestions. The engineer’s initial concern was indeed perc test conditions and he said I could first try to map out a grid of the different pockets with rebar and hammer to test for depth (it’s 15 acres) and narrow down a spot before we do test holes to save money. He thinks we could do a shallow trench system at best and my realtor has been telling me from the start that there are almost no in-ground systems in the county due to the clay (I’m in New York, Hudson Valley).

I’ve been referencing the websoil survey in my general search and unfortunately, the specific area I’m looking in has pretty similar soil. I did a quick google map search on “farms” and “orchards” and sure enough, the results mirror the soil mapper - a few miles east is where the surficial geology changes and is where the farms begin to appear on google.

I guess I was wondering if it was realistic to expect workable pockets on such a large parcel - wanted to come here for an opinion before spending a weekend hammering rebar :) You're right though, the best spot would go to septic first.

Since it’s shale, should I skip to test holes right away just to test for diggability? And what would you all consider “workable” bedrock - is using a pickaxe for a trench the worst thing? Thanks for the permaculture tips Nathan,  I definitely don’t want to spend my time fighting with the land, but knowing how I want to use it, wouldn’t buy land that wasn’t suitable for my needs. 

Offline DaveOrr

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Re: Land Conundrum: Shallow Bedrock
« Reply #5 on: April 26, 2019, 02:32:33 PM »
Shale's gotta be easier than the 4 billion year old granite at my place.   :)

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Offline NathanS

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Re: Land Conundrum: Shallow Bedrock
« Reply #6 on: April 26, 2019, 03:15:24 PM »
"Workable" bedrock would be an excavator can dig it without a hammer attachment. I don't think there is any shale you will want to hack with a pick-axe. For planting, consider the shale impermeable.

I also think it is kind of dubious to say - well the shale will make a nice road base. You're still going to have to truck in small aggregate to make it walkable/comfortable to drive and plow in the winter.

It's hard to give too specific of advice... where I live, we have about 18-24" of ok-draining silt loam, and then 20-50 feet of hardpan, then shale. Our neighbors have the same 18-24" of loam that sits right on the shale. The websoil survey considers the shale to drain better than hardpan, and rates it as a higher quality farm soil for that reason. Either way it doesn't really compare to a valley bottom. As long as you mostly have 1.5'+ of soil, you probably have something you can work with. If you only have a couple inches in most places, there's probably not much you can do other than enjoy what you got.

Offline Don_P

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Re: Land Conundrum: Shallow Bedrock
« Reply #7 on: April 26, 2019, 06:51:00 PM »
Dave you've got me beat by a billion years  :D Is that part of the Canadian shield?
A couple of other good contacts, check with your ag extension agent and see if your plans are compatible with the soils in that area. NRCS would be another set of folks to talk to. A friend picked up some white oak today that we had sawed out for high tunnel skirting and raised bed boxes, that is another way to get good soil in smaller areas.

Offline Pallas

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Re: Land Conundrum: Shallow Bedrock
« Reply #8 on: April 27, 2019, 04:38:36 PM »
Thanks very much all. Very helpful thoughts indeed!

On the gardening, I’m not terribly worried, as I would do raised beds that would build up the soil with compost. My main worry is how limited I would be for typical homesteading projects that would involve digging, like trenching, building posts for a shed, fences, etc. Do I have to coordinate to hire heavy machinery every single time? Or would I be doing that with regular soil anyway? I really have no idea  ???

Specifically, I’d really like a root cellar, and if I put one in 6 feet of shale, that means I can’t just lay some gravel on the floor for drainage, right? Because it will just pool? Would I have to dig a 7 foot trench leading out of any underground structure just to deal with groundwater?

Offline DaveOrr

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Re: Land Conundrum: Shallow Bedrock
« Reply #9 on: April 27, 2019, 06:53:04 PM »
Dave you've got me beat by a billion years  :D Is that part of the Canadian shield?

Yep, sure is It's the oldest section of the shield too.
I can't wait to dig out the basement!!!!   :)
Gonna have to drill a bunch of holes and fill them with non-explosive expanding grout to break up the rock.
I want to end up with a nice level cement floor when I'm done.
It will take a lot of work but it is out of the weather so can be done on even the crappiest of days.
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Offline Dave Sparks

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Re: Land Conundrum: Shallow Bedrock
« Reply #10 on: April 28, 2019, 05:39:44 AM »
Who cares about the weather on a crappy day, go fishing anyway ;)
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Offline MountainDon

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Re: Land Conundrum: Shallow Bedrock
« Reply #11 on: April 28, 2019, 06:19:15 AM »
There's an old saying... Norwegian I think,  "There's no such thing as bad weather, only bad clothes"
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline Don_P

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Re: Land Conundrum: Shallow Bedrock
« Reply #12 on: April 28, 2019, 07:08:47 AM »
 I think ours is the third oldest on the continent. I used Dexpan to dig out a basement a few years ago. The homeowner had dug out most of it through decomposed granite until he hit the solid rock. We used a big Hilti percussion drill for the holes, well, the "we" there was Jack, a strapping young man I hired to ride the drill and sledge, a very good investment. The Dexpan worked well. I had a couple of boxes leftover and stored them in the barn. Last year some guys hit rock and I gave them the leftovers to try. It had lost its oomph, so do be aware it seems to have a shelf life.

Pallas, the only way you'll know is to try digging some, which, you can dig your perc holes by hand to see. A hand dug hole here requires shovel, post hole diggers and a tamping bar, also called a digging bar. The Hilti with a clay spade on it also works as does an electric jackhammer. I dug out another basement in very tight decomposed granite. we used the bobcat forks and bucket until it couldn't penetrate then switched to the hilti to loosen and the bucket on the bobcat to remove, we went down 9'. I always either perimeter drain to daylight, preferred, or to a sump pit with pump if I can't get to daylight. Never assume a pit will self drain, that is a recipe for disappointment.

Offline DaveOrr

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Re: Land Conundrum: Shallow Bedrock
« Reply #13 on: April 28, 2019, 01:57:31 PM »
I think ours is the third oldest on the continent. I used Dexpan to dig out a basement a few years ago. The homeowner had dug out most of it through decomposed granite until he hit the solid rock. We used a big Hilti percussion drill for the holes, well, the "we" there was Jack, a strapping young man I hired to ride the drill and sledge, a very good investment. The Dexpan worked well. I had a couple of boxes leftover and stored them in the barn. Last year some guys hit rock and I gave them the leftovers to try. It had lost its oomph, so do be aware it seems to have a shelf life.

That's the stuff I plan to use.
I can order it online and get free shipping.
Need to wait until I'm ready to use it though as it comes in 3 types with different temp ranges.
I plan to make the rock Swiss cheese and then order for the proper temps at the time and use it all up.
Remove rock and then drill a bunch more. I expect it will take some time to get it all out.
Good thing is I need fill for a driveway from the lake shore up to the cabin for putting the boat in and out as well as running the hovercraft up to the cabin. Truck too in the winter. :)
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Offline Pallas

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Re: Land Conundrum: Shallow Bedrock
« Reply #14 on: April 28, 2019, 03:24:59 PM »
Thanks for the tip on the drainage, Don. Everyone's input has been very encouraging, thank you very much. I think if I plan well and if the rock is indeed "workable" then I can deal with the extra excavation work if it's just a one-time thing to get the pits dug. It certainly looks like others are dealing with much harder rock, so my kudos to you!

My main priority is having as low-maintenance structures as possible, so I think proper water control will be key. The septic issue is a foregone conclusion, so I'll see if I can work on countering the asking price of the land to offset that some.

My planned building is very different from what I think many here are looking to do: I want a BIG passive solar greenhouse with earth tubes providing ground-to-air heat exchange (https://ceresgs.com/climate-control/gaht/), with small living quarters attached next to it, and a root cellar. These will require deep pits in the ground, and if it's all shale bedrock, will likely take longer and more $ than other soils. But hopefully this can be a one-time project?

Regarding the earth tubes, I know there's some controversy surrounding these (I've read almost every site, comment, etc), but I was convinced after reading a few university papers, and am planning on spending a week at the Central Rocky Mountain Permaculture Institute to learn how to build my own (https://crmpi.org/about/the-forest-garden-greenhouse-by-jerome-osentowski/)


Offline Dave Sparks

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Re: Land Conundrum: Shallow Bedrock
« Reply #15 on: April 29, 2019, 08:41:07 AM »
I assume you are near the Rockies? I may have missed it also.  I just want to add that in the old days alot of attention was spent on passive ground to air heating and it was very expensive and alot of labor.

 In my opinion that changed with the advent of the mini-split air to air heat pumps. That was around 2007 when I first started using them for offgrid.

You may want to research that also. I can tell you that I definitely do not use ground source anymore and discourage my 200+ offgrid users early on about going down that road. It can work but the cost of solar and a mini split will probably be 1/10th the cost. You still need to plan a secondary source of heat offgrid and most use pellets, wood, or propane.

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Offline Pallas

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Re: Land Conundrum: Shallow Bedrock
« Reply #16 on: April 29, 2019, 11:40:56 AM »
Hi Dave, the land is actually in upstate NY, but I'm looking to go to Colorado since that's where the passive greenhouse ground to air technology has been honed by a number of organizations (due to their high sun hours).

I'd like to clarify that the ground-to-air exchange would only be for the greenhouse environment, to keep from freezing. Otherwise I will rely on thermal mass and some compost-based heating for the greenhouse. I really like the mini-split idea for the living quarters, especially paired with solar, and that, along with a wood stove, is what I would plan to use for the small attached apartment.

Offline Don_P

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Re: Land Conundrum: Shallow Bedrock
« Reply #17 on: April 29, 2019, 05:27:34 PM »
From my admittedly limited experience with upstate NY, solar isn't going to do much. Also be aware it takes quite a pile of active compost to get the kind of heat you need. In other words plan on using other forms of energy and if those work out great, but don't bet the bank on it. For what you are talking about find a nearby farmers market, hang out and talk to some of the growers. I'd bet once you show an interest you'll be touring their farms and finding out what works locally, and getting a support group of like minded folks who have probably been there, done that.

Offline Dave Sparks

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Re: Land Conundrum: Shallow Bedrock
« Reply #18 on: April 30, 2019, 05:29:41 AM »
Definitely go to Colorado or anyplace in the south west. Look for over 15 inches of rain, an oak wood land nearby, and no worries on the hours of sun except coastal. Watch the elevation over 4,000 feet, too cold.

 Most of the offgrid folks in these areas can build a small greenhouse off the main structure and heat and grow with the house supplying the warmth for winter seed starts. The long growing season in the southwest will amaze you compared to NY. Unless you are thinking of commercial growing, I would still avoid ground source heat.

I live with a master gardener and most counties and states have a Master Gardener program that is state funded. They are an immense source of knowledge on the latest state of the art. As Don said, talk with the locals! The master gardeners are about as local as it gets. They know what farms are doing.
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