In heap leaching, how can we determine if the ore at the middle and bottom of the heap has been fully leached?

The recommendation for a rectangular heap is to improve water permeability. To determine whether all the ore has been fully permeated, small barriers can be created on the surface of the heap, similar to paddy fields, and the water level in each barrier can be observed to assess the quality of permeation. In the initial stages, excavators can be used to turn over the heap to avoid this issue.