Question
I am planning on digging a trench to place a buried wall made of large cement blocks along a stream on my property to prevent erosion.  The wall will need to pass within 6 feet of a large ponderosa pine that is about 3-4 feet in diameter and 60-80 feet high.  The bottom of wall will be placed about 3-4 feet below grade.  If there is a large root in the area of the proposed wall would cutting the root this close to the tree damage or harm the tree?  Thank you for your thoughtful consideration.

Answer
Since it is a ponderosa pine there should be no problem with the trench. Normally you would not want to cut more than 25 % of the roots system of a tree--this would cause damage to the foliage. Pines have a tap root system and cutting lateral roots is not that big a problem. You should not see any signs of damage from cutting these roots. I do not think there will be a problem with doing this.