I live very close to the Tresavean site and know it very well. The photos of a bat castle during construction, is not the one that is seen later on standing alone with a few saplings planted around it.
The only large scale works on the site was at Man Engine Shaft, where a grilled bat castle with a viewing platform 5 metres below ground level was installed. This large construction was to preserve the features at the side of the shaft for posterity, it being the site of the first Man Engine in Cornwall. There is also a grille to enable you to view this feature, behind the bat castle.
The other Bat castle looks like it may be part of Penstruthal sett, but it's difficult to tell from the picture.
All the shafts up there are hellish deep so any waste would have to be in small packages to ensure it went down deep. If any at all was dumped they would have had to remove the grilles off the bat castles or, as is being suggested by them, removal of the castle, dump stuff and then make good afterwards with a small vent pipe inside a cairn. I wonder where this story originated?
"You Chinese think of everything!"
"But I''m not Chinese!"
"Then you must have forgotten something!"