What are the harmful impacts of underground coal gassification?

Dermot - It's very important to do it at depths where all of the water has been formally classified as permanently unusable. These are very, very salty water deposits at depths of a kilometre or thereabouts. Nobody would ever extract those kind of waters, the very fact that they are heavily salty means they're poisonous anyway. You have to be operating at the kind of depths where nobody would ever bring that water to the surface as a water supply. Then no matter what happens, you're not going to cause contamination that causes any problems.