Need guidance for tiling - home renovation

Hey all, My family is getting our home renovated and we are in process of getting the tiling done. The floor currently has chips and we have the following options as per the contractor: * Get tiles pasted on top of chips using some chemical * Problem: the chips floor is never levelled, so pasting tiles on top of chips may not be evenly put and may break easily if something falls * Get the chips removed and get tiling done as fresh work * Problem: This may disturb the underground sewage/water pipeline and create unwanted problems Do you have any experience with the same and can share any suggestions? Is there any other option we have, someone suggested getting the chips floor levelled somehow using some floor grinding tool. Does that work?