How to control tree root depth

[SamArborista]

So there is an open park, contaminated soil was covered with a 1m layer of clean material (mostly clayey silt, some sand/gravel, moist). Nothing can be planted that will potentially grow roots deeper than 1 metre (3.28').
Been looking into root deflectors but they all seem to be vertical for roots growing horizontal - looking for something that is the opposite.
Any suggestions? Ways to contain the roots in the upper surface of the soil? I am feeling that no matter what is put down to deflect the roots there is always the chance that they deflect horizontally along the deflector, get to the edge and grow vertical again... so maybe trees shouldn't be planted on the site.... Just looking for some thoughts.
Cheers!

 

[JustinK]

Most tree roots go horizontally anyway, not vertically.... but red maples seem to be shallow rooted, more than most.

 

[JD3000]

Yeah I second that, most growth will be within your 1 m.

Soil contaminated with what?

 

[SamArborista]

It doesn't really matter what the contamination is, risk management measures in a report state that no human or ecological receptors may come into contact with the contaminated soil. So no roots can go there. And yes I also agree most roots are shallow, but the more reading I do, the more I see that there can always be variations to that. So basically I haven't come across a blanket statement for any species that assures me that the root could not grow deeper than 1 metre. Planting on mounds/berms might be an option if the client is willing to spend on importing soil... but how high should they be?

 

[JD3000]

Yeah, raised bed and fill grading may be needed.

 

[mrtree]

You need to hire a consulting arborist and ecologist

 

[cerviarborist]

I just hope all the plant material in the Ontario area read the report too. What's to be done if a squirrel plants an acorn or a bird drops a seed? Plants are going to do what plants do.

The only thing, which comes to my mind right now in the way of a solution is taking off the top.66 meters of clean soil, mechanically compacting the remaining .33, then replacing the remaining .66 back on top in a de-compacted condition. Once sufficiently compacted, neither air, water or tree roots should penetrate the bottom layer of clean/compacted soil. You might need to also install drains to keep the area from becoming saturated with water.

It sounds like an interesting challenge to surmount!