Maybe I read this wrong and you are grading 40" on your property.
Or maybe I wrote it wrong........LOL! Yes, we had to take out 40" of ground in order to get a level 15x30 surface. So now we have an embankment basically of almost 4 feet. Picture this.............15 feet from our house is a
48" dropoff in land. Then about 3 feet in starts the pool. We are putting gravel around the pool about 18" from the wall I think. We are using railroad ties to build a retaining wall for the drop off. The top part will be landscaping only so no grass to mow up there. I hope this makes sense. Actually, here is a picture.......