news soon, page-105

Donthat,

the '20 times' figure is one from the UCG industry. Personally I do not believe it is that high in reality as UCG is not carried out in a contiguous fashion over a large areal extent the same way that CSG is.

UCG operates in local area cavities, which are generated along "strings" from the one drilling operation. The placement of additional cavities adjacent to the existing ones is a matter of science to ensure the structural integrity of the overburden is not impacted. I guess I think of it like surface effects from longwall mining if it is not designed properly.

Cheers,

SF