Help! I've hired some local 'independent' interlockers to do some interlocking out front. Upon coming home today, I noticed they cut off some pretty thick roots (about 3 veins or so each about 5 inches wide) that were about a foot under. These thick roots are about 3 ft out from the base of the tree. I believe the tree is a silver maple and it seems really old. Diameter of trunk is about 3 ft wide. Is this safe?