Dirt was taken from the side yard, no plumbing leaks or problems, putting in a sewer cleanout. Composition is mostly clay/gravel here. Excavated with a backhoe and I assume pushed back it with same. Immediately after being done the pile was 1-1.5 feet higher than surrounding yard. But it was next to my driveway and I found a void under the driveway, about 2 feet under, 1 foot deep, and 5 feet wide. After a couple days of rain the pile shrank to be 1 foot below surrounding grade, still having the void under the driveway. With my topsoil/grass nowhere to be seen (I assume somewhere in the filled hole).