Eggs Zachtly wrote:

How much oxygen do you think can get to the roots, more than a
couple feet below the surface, again especially in heavier soils?

I would have thought that water supply was a more important function
for the roots than air supply.

Presumably the roots need air for their own needs, and not to
transport it up into the trunk, branches and leaves - in which case
paving over the roots is of more concern than cutting them (as far as
oxygen goes).

I'm curious as to what kind of fence you're installing

It's a concrete sound wall (about 2-3 inches thick) but it requires a
shallow foundation between posts. The posts have been in place for
several years (6" x 6" spruce, set into 12" concrete piers, spaced 10
feet apart).

IMO, I'd avoid doing any more serious damage to the tree.

I'd really like to not have to cut these roots, but they are too
shallow and I can't form the footing with them there, even if I modify
the design. I wonder if I could tap into the root with a connector
and attach a water line and feed water directly into the root?