we fill anything that needs filling: the ground here is very uneven with massive rocks so you need to fill to even, you can empty containers of crap other people give away or pay a fortune.
When we need fill in the US, a big truck comes and dumps actual soil and rock so that lead and other things don’t leach into the groundwater, the construction waste is landfilled after removing the metal for recycling.
If you have well water and have been using construction demolition waste nearby your wellhead, I would suggest an RO filter for drinking water, yikes.