a brief summary from a layman, page-21

UCG and GTL must have a smaller carbon footprint as it requires less process. Burning underground does not require conventional mining and as such, very little associated energy is needed. If the coal is mined and burnt conventionally, you would expect around 99% of the available carbon to end up in the atmosphere. With the UCG and GTL process you expect one way or another the same (ie. 99% of coal’s carbon would also end up in the atmosphere), the difference however, is that using the underground UCG process you save all the energy costs of mining, so UCG and GTL must have a smaller carbon footprint than conventional coal use.

To put this in perspective at Chinchilla there is around 140m of overburden, the energy cost of moving that amount of material is not insignificant. Then you have the energy cost of transporting the coal to the power station, or another energy conversion process. Then there are all the other associated costs of mining, large numbers of people getting to work, construction and maintenance of mining equipment, supplying goods and services ……. and the list goes on.