There was a short piece on Radio 4 this morning and the speaker was briefly explaining it would take 18 months to de-water the 8 million(?) cubic metres of water and process it through an, as yet, un-built treatment plant. Although he did suggest the current market price (about £20,000 per tonne) looked likely to hold for some years, their current plan would aim to produce for a minimum of 8 years.
Just as a comment he said that there were over 1000 old mine shafts in the Poole/Cambourne area.
Jim