Worth it to dig up asphalt driveway ?

So, I'm stewarding some urban land and I've been given permission from the owner to do what I wanted in the yard. The front yard is pretty large (1/6 of an acre) and has a nice gentle south facing slope which seems ideal for growing things. Problem is there is an asphalt driveway that loops around most of the perimeter and takes up a a lot of space. I'm not sure which approach to take in terms of getting a garden going and have some questions:

Is there value in building soil on top of asphalt ? If so, does the answer change when said asphalt is sloped (~10 degree slope) ?
Is the soil under the asphalt likely to be toxic? (I'm broke at the moment, but if I were to remove the asphalt I would get the newly exposed dirt tested)
If I decide to remove the asphalt, any recommendations for method?
Suggestions for how to use the asphalt chunks ?
I was thinking I might be able to use the asphalt pieces to make small, foot high retaining walls to terrace the slope but I'm not sure how viable that would be.

Thanks for reading and your considerations - any ideas / thoughts / suggestions you care to share will be appreciated!

I think I would look at cost vs return...cost in terms of time and money.  This becomes more problematic if you dont own the land.

A solid driveway in a rural location is gold, so before you assume it's a bad thing, definitely check with the owner.  

Undoing a very expensive asphalt driveway may lower the value of the property.  When all you've got left is slippery mud, it's a nightmare to try to get something back into place.  It would have to be reengineered to stop erosion.  

That kind of a surface is required for big trucks, including fire truck, deliveries of propane, for emptying out septic tanks, any kind of lumber/DIY project deliveries that are too big for one's own vehicle.  It may even have been required by code.    If delivery trucks can't come onto the property on a solid surface, one that won't be slippery or collapse under the trucks from rodent damage (and that is very common for the FedEX/UPS guys), they won't come at all.

The fire department has the last say about such things, because if the fire department can't get to the house, garage, barn or burning landscape, and have a 75-foot turnaround to get out and pass other fire trucks, they could red tag the house.  If the propane truck can't get to the tank, they will notify the fire department, and the fire department will notify the county, and it's not impossible they will be all over the owner about it.  Once the county is able to spot a problem with a piece of property, they can look at everything and find fault with whatever they want.

It's the turning around and passing of fire trucks that is the most important thing, so it's not just about a one-way in and backing up to get out.

But if the owner doesn't mind some portion of the asphalt coming out, the chunks of asphalt are illegal to dump in a landfill.  They may have to be taken to a special hazardous waste dump.  If piled up on the property, then the owner will be required to do something with them, and how happy is he going to be about that?  There will be sand and gravel underneath it that needs to be removed as well.

Probably for the first few years nothing other than landscape - nothing edible -  should be planted there, with very thick compost as a bioremediation remedy.  Then at that point, it probably should get tested before planting food.  You never know what kind of car oil, or car liquids got dumped on that driveway that seeped down below it.  It's a common practice to kill weeds along driveways

What might tone down the look of asphalt on the property is put large pots, raised beds, half barrels in an arrangement that looks like the garden you want.  Shallowly-rooted plants do just fine in a 2-foot raised bed over asphalt.  And it's very clean to walk among the raised beds, the asphalt is sweepable.  Then they can be removed if the property is sold or whatever, and everything is still as it was.

I agree with John. This is a substantial job and may not be worthwhile for you.

Are you sure the owner is okay with this? I would ask specifically. It may have a negative impact on property value. On the other hand, if it's decrepit and needs to be removed, the cost should fall to the property owner. Breaking it up and trucking it out will not be cheap.

As an alternative, what about raised beds with bottoms for the gardens? Sort of oversized planters. These could sit on top of the asphalt but not be in direct contact. And, they can be moved if needed.

EDIT: Cristo beat me to it! Good advice.

As far as using asphalt chunks, once they are detached from the solid bed of sand and gravel they are on, eventually they will crumble, because asphalt crumbles when water gets through the cracks.  That's why roads and driveways are sealed every once in a while.   A wall would be iffy in the long run.  The pieces just aren't weight bearing enough, and there's pressure behind even a small wall, not to mention possible expansion and contraction of soil underneath it.

Ironically, the best thing to do with chunks is put them back down in a walking pathway, over sand and gravel.

:-)

Douglas Alpenstock wrote:I agree with John.  EDIT: Cristo beat me to it! Good advice.

Douglas, been there, done that!    It worked well with cinderblocks stacked on the asphalt, they were solid.

Removing a lengthy stretch of asphalt can be a herculean task. On our previous property we replaced a worn out driveway. The asphalt was a standard 4-inch pour; the attached picture gives an idea of the scale of the removal process. The crew's dump truck made many trips that day.

another issue is what might be under the asphalt. My parents built a house and in order to make the sloping driveway stable before asphalt was put on, a few truckloads of rocks and gravel were put down. You might get the asphalt up and realize you still have a long ways to go to get to soil. Large containers seem like a good option!

Wow! thanks for the replies and insightful discussion!

To add more context - any "real" future development of the property will entail a complete leveling of everything on it. (The lot next door had 20+ mature trees on it one day and zero after the developers were done 'site prep'). The city has already made it very clear that the land will need to be subdivided before any future permits are granted. Given that the house is right on said road and the offending driveway takes up the bulk of what would an entire lot, they will be destroyed. The property has the driveway in the front (as mentioned) and a rear driveway to a carport, so day to day (and emergency) access is accounted for. The front driveway hasn't seen active use in years and is blocked off by a felled tree on one side of the loop and a giant mound of woodchips on the other.

The state of asphalt is pretty poor.. it's 40+ years old and the neighbours' mature trees (RIP) had roots that extended onto my property and pushed up the driveway. I've taken a sledgehammer to part of it to gauge the depth and it's only a 4" pour.

In terms of scope, it does look like a daunting task. I'm currently unemployed so I do have the time for this, though I'm not sure my body could handle doing it with just the sledgehammer.

I have been using the flat part at the top as a platform for a bunch of planters, but once I get to the parts where there is a slope the planters look weird and seem unstable.

Cristo - thanks for the suggestions. I guess I won't use the asphalt as a part of my terracing idea (if terracing ends up being the direction I want to go)

Tereza - the part I removed had dirt underneath. Your comment made me think I should poke around a bit more before I assume the whole underlayer is the same.

Well you could definitely cancel your gym membership for a little while. Win-win!

Ivar,  on the sloping parts of the driveway maybe you could take out strips or holes, chunks here and there?
Work from the edges in and either plant trees or level things out for planters.

I imagine there is some water that collects and runs down the driveway,  strategically placed trees with aggressive roots,  like willows might take advantage of that water.

Tree trunks placed across the drive and staked in place could form terracing.
Break up  the asphalt just above the log on the slope and pile woodchips there, plant berry bushes.  
Break up the asphalt just below the log on the slope, plant trees.

Overall,  I say leverage your labor.
Only break up the asphalt,  don't remove it.
Only break up slopes.
Plant trees and bushes into the holes you make and let the water infiltration and plant roots do the work.

One more idea.
If there is a part of the drive that is in good shape, high underneath it for a root cellar that has 4" of asphalt roof.

Container gardening on the surface?

Funny, I am waiting on a quote to remove about a 25x25 ft flat section of my driveway, to put down wood chips and raised beds.  But I still will have room to park two cars; the flat space just allowed cars to access the garage (which I don't use; I have the driveway set up as workshop).  I guess this might negatively affect the home value at some point, if the owners really want to garage-park their cars, but it could also attract more ecologically-minded folks.  We own and will be here for at least 5 more years, so am not too worried about it.

I tried to do it manually with a jackhammer and gave up after a few hours - way too much work, and not cost-effective with rental fees.

A couple of things came up reading this thread. Cristo covered the access issues nicely.

Before doing anything to property owned by another, I would put together a plan and get their ok IN WRITING with a date of approval. This way it's spelled out clearly to both parties and less chance of misunderstanding. I know it's extra work but it may save you some headache later. And the owner can feel comfortable knowing exactly what you're planning.

Also, even with testing the soil, I would personally not try to grow edibles in the soil beneath asphalt. Asphalt leaches heavy metals and petroleum residue for a long time. The heavy metals will likely not go far due to lack of moisture and just the fact that many are not soluble and won't go with the water (some are and that's a different issue for another thread). One major component of asphalt is the residue from oil refining, so it contains the heavy, long chain organic molecules (called, cleverly enough, asphaltenes and/or polyaromatic hydrocarbons - PAHs which are toxic), metals, and anything else that won't boil off. Making asphalt is a way to use this by product beneficially. But it is really nasty stuff. Do an online search for contaminants in soil beneath asphalt, PAHs, metals, etc. and you will find some good information.

If you still want to build a garden on the soil, I would recommend a barrier put down first then make big tall raised beds to minimize the chance of contaminating the soil you're cultivating.

I've seen gardens made of big and little pots with a variety of plants and they look beautiful.  You can control what you're using for soil so it's safe. Finding an effective way to stabilize them on a slope is a challenge though. This would be my preferred option.

This is not an ideal situation but finding clever ways to get around the problems is what this forum is all about. Good luck!

Robin Katz wrote:
If you still want to build a garden on the soil, I would recommend a barrier put down first then make big tall raised beds to minimize the chance of contaminating the soil you're cultivating.

I was considering that since the driveway isn't super huge, I'm sure if I got a digger out for a couple of days I could remove the driveway and a few inches of dirt. That said, this is likely beyond my current budget of ~zero dollars.  

I'll have to reconsider my plans for the driveway space. A small scale farmer friend of mine swears by container gardening for his tomatoes on a derelict tennis court. He says the surface acts as a heatsink and increases their productivity. I'm going to investigate how I can use this to my advantage - maybe I can break up the asphalt into small terraces.. hmm. If this was for the long haul (10+ years) I would work towards soil remediation, but given that this lot is likely to be developed in that time I'll stick to the basics.

Robin Katz wrote:
This is not an ideal situation but finding clever ways to get around the problems is what this forum is all about. Good luck!

Thanks Robin (and everyone else who contributed) - having people provide food for thought on this is a great relief

containers gave me some surprising results this year- I also didn't expect much, but I got amazing yields from japanese cucumbers, loofas, and cherry tomatoes in 20L containers (which are really not that big). The only downside is you need to keep up on watering or implement some kind of irrigation (I used plastic soda bottles with pinholes in the lids, worked a charm).
Good luck with whatever you decide to do!!

I use containers extensively,  but they are all sub irrigated planters.
One side of my FIL's driveway is lined with whole and halved 55 gallon drum.
Each has a huge reservoir of water in the base.
I generally water twice a season at most.
They are very heavy but the half sized one can be moved via a hand truck.

Unfortunately, the quote for asphalt removal came back at $2500, which is pretty steep.  Might have to wait for the raised beds, or just put my wood chips down directly on top of the asphalt.

We did it in our tiny urban yard (removed 2 parking places worth of asphalt/gravel/remnants of a garage) and it almost doubled our usable space. (Apparently, previous owners hated green things? The whole yard was paved in some manner or other)

However, it required heavy machinery (we were having a drain replaced on our house so it subsidized some of the costs since the machinery was already on site) and we paid something around 500$cad just for the disposal costs. Plus another 300$cad for full-panel testing of the soil underneath, and a couple hundreds to get good soil trucked in (we topped everything with 4-6" of good soil).

It was 100% worth it but it was quite a complex project.

Kena, I think you did very well cost-wise. I would have estimated double that amount, easily.

Kena Landry wrote: Plus another 300$cad for full-panel testing of the soil underneath

Kena - what did you learn from the soil tests? What was your approach to them - did you sample various depths or different parts of the uncovered dirt ?