Yet within it there are traces of the past that surface from time to time, yet one past trace that I'm sure those of us who live in the British Isles have all seen are the coastal defences rapidly constructed during World War II.

BBC: The Last Stand

Rather, as a consequence of injecting water and sand into the shale formation to crack the rocks so gas and oil will flow, massive amounts of waste water comes back to the surface with significant amounts of contaminants as a result of leaching out salt, heavy metals and trace amounts of radioactive materials from the rock formation itself.

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