Ann: Testing of Canadian Oil Shale , page-7

it is all fine to work under the 'watertable' but what do you do with gap you leave after you're done?

you would have to fill it with something, simply to prevent 'caving in' of the top part...

...usualy thats done with water (i think saudis are pumping sea water into cavities)...

please feel free to correct me if im wrong...

now...it is that water that is contaminated by remainder of coal that is a potential problem for future...