Fix old landfill tiles to be removable in Patch 2.0. You can remove the mod after making changes and saving. It just fixes your map. You don't need it after that!

Use with /fix-old-landfill

Works by using map generation to figure out what the missing data in your 1.1 landfill tiles was, and filling it in. Specifically, it creates a new surface that matches map generation settings of your surface, creates chunks and checks their tiles, and copies missing data from those tiles to your landfill's memory of which tile is "hidden" under it. This temporary surface is then discarded. Nothing is added to your map, and nothing is changed except data on landfill tiles that should be there anyway.