When an underground mine is closed, the shaft is blocked and the surface is tidied up. There might be some mounds, which eventually get grassed over, but often that is the only evidence that there was ever a mine there.
But what’s happening underground?
There’s no longer any need to pump the water out of the mine to stop the passageways flooding and with the pumps gone the tunnels and shafts start to fill with water. Water passes through the small holes in the rock and falls into the big holes of the mine.
The water begins to fill the rocks and the holes rising back towards the level that it was at before the mining began. Except the rock underground has been disturbed. Minerals that were locked away in the rocks are now loose and in the path of the water. Chemical reactions can take place, minerals can dissolve in the flow and the water gets contaminated.
Does it matter? Well it does if that water is part of the water supply and is heading for your taps.
Next week we will look at how they are solving this problem in Northumberland.