My background: I have lived my adult life in apartments. This is my first house and it has lots of trees. I have no experience what so ever with caring for trees.
And some of my trees are very sick. 
From Howard's Sick Tree Treatment:
"
1) REMOVE EXCESS SOIL FROM ABOVE ROOT BALL. A very high percentage of trees have been planted too low. Soil on top of the root ball smothers the tree and leads to circling and girdling roots. Soil, or even heavy mulch, on trunks keeps the bark constantly moist which can rot or girdle the tree.
"
I think I understand the whole root ball concept but I am scared of digging around my trees.
My question: When I start removing soil, how do I recognize the root ball? Do I stop digging when I see little roots or big roots? How far out (from the trunk) is a typical root ball? Is this something like a drip line?
Thank You very much!!!
- Emily in Fort Worth