Tree roots

Acc. to this article plumtree roots can go down deep, but don't spread our sideways much:
articles.baltimoresun.com/2007-03-03/features/0703030097_1_plum-tree-tree-species-roots

Thanks for that TriciaF - I'm not sure what it means 'beyond 11/2 time the height of the tree' but it says the roots aren't aggressive so it might support OHs theory they will hit the wall of the tank and be deflected. It's really hard getting advice about this so I appreciate a response. No one on Gardeners World forum answered and the 'experts' won't take questions, the RHS only replies to members and my local garden centre won't commit themselves.

It also depends partly on the age of the setpic tank and what it is made of. If you know you could check with the manufacturer.

We have a reinforced concrete septic tank in our house in France. I doubt if an oak tree could breach that.

It's actually a sewage treatment plant and about two years old so I should think it's pretty tough but I need to be certain now while the tree is still small enough to remove easily. I would have hoped the developer, who also landscaped the garden, would have considered where he put the tree but he's been proven wrong in other important things.

Can you contact the company that made and/or fitted it for their advice?

I'll have to try the manufacturer, i think. I'm not sure of the full reach of the darned thing so I need to know before I start digging holes and planting. Thanks MOnica...