I have a tree on a 45 degree hill on my property. My goal is to have a nice green yard that surrounds my trees. However, the former home owner had put in a radius of about 4 feet of mulch about 4" high around this tree on the hill. I removed the mulch and discovered car mats under the mulch. After removing the car mats I have found a large rug, among smaller rugs and heavy plastic bags. In between the car mats and the rug(s) there are many rocks, dirt, broken glass, metal fixtures, kitty litter, etc. Also, in the area off the mulched circumference, I have found a lot of broken glass, more metal fixtures, and burnt dirt (is that possible)under a layer of moss. As I am getting to what appears to be the ground, I am afraid I have removed much of the tree's support, but if the tree has to come down, that's ok.
My main concern is what to do with the dirt that has been mixed in with all the metals, glass, and burnt ground. Should this dirt NOT be reused to fill in around the tree? Should it be removed and replaced with clean topsoil? How can I build the ground back up once the old dirt is removed if that is what is necessary? Should the rocks be replaced or keep them out?
Trees generally do not like being backfilled with a landfill. When you get to the native ground level, assuming that is where the tree started from, it should be much happier. I would be more concerned about where to dispose of the pile of refuse someone put down, and surprisingly did not kill the tree. Trees can be planted on fill, but fill should not be placed around established trees. If you need a level area, a retaining wall and new planting are in order. Otherwise, the original ground level is best.