Question
Hi Jim
I have a approx. 60 foot Spruce tree in my yard and I would like to put a pond in next to it.  I was wondering how close I can excavate wihout hurting the trees root system. The trunk is approx 22 inches wide and the branches hang in a 11 foot radius around the tree. The circular pond would hopefully be under the branches with the closest excavation being 5-6 feet away from the trunk.  Depending upon your response adjustments can be made.
Best regards and thanking you in advance
John

Answer
The roots of a tree extend out about 1 1/2 times the branches. Generally you can cut 25% of a trees roots without causing serious damage to the tree. If you draw a circle around the tree at the outer edge of the branches and then draw the are where the pond and digging  will be and if this cuts more than 25% of the root system you can expect dieback of foliage from the digging. It will survive but the limbs on the side of the trench may die back. I would try to stay as far from the trunk as possible. The closer you dig to the trunk the more damage you will cause to the foliage.