What is Hydraulic Fracturing

Just as a diver:s lungs are compressed by the weight of deep water, Rock layers far below the Earth's surface are compacted by the weight of the rock above them.
That makes it hard for natural gas to escape from small pores in the shale to be harvested for commercial use.
In the late 1990s energy companies began addressing this challenge with a controversial but effective mining method called hydraulic fracturing.
A well is driled to depths of up to a mile below ground, sometimes with a horizontal extension into the rock player.
The well is lined with concrete.
Then workers lower a perforating gun to the location of the trapped gas reservoir; it release and explosive charge that blasts holes in the well casing.
Finally, pumps at the surface push water at extremely high pressure down the well and into the holes, cracking open fissures in the rock.
This allows gas to flow out into the well.
The controversy involves the potential for contamination of ground water.