Question
My neighbor is considering replacing the sewer line from her house to the street (main) pipe as she has had some backups.  This new line would run about 15 feet from a large, very established maple tree.
Although the tree is likely causing the problem, my neighbor wants to preserve it.
Would digging the new sewer pipe damage enough roots to endanger the tree?

Answer
Trenching 15 feet from a tree should not damage the tree. I would however make sure the equipment is not driven under or around the tree. This can compact the soil and damage the roots and cause more damage than the digging. Newer sewer pipes are sealed and the tree roots can not enter them compared to the old clay pipes that were not sealed. So the newer sewer line should not have any problems with the trees root system.