The nation's boom in natural gas production has come with a cost: The technique used to get much of the gas out of the ground, called hydraulic fracturing, or fracking, has contaminated drinking water. But how often and where this contamination is taking place is a matter of much debate and litigation.
Now, a new study has found natural pathways of contamination — but that doesn't mean the drilling industry is off the hook.
When gas drillers frack, they pump millions of gallons of water, mixed with sand and chemicals, down into a layer of rock called the Marcellus Shale of Pennsylvania. That helps free up natural gas that then comes to the surface.
But some Pennsylvanians say that polluted water may be seeping back up. They report a salty brine, sometimes laden with dangerous metals, in their water wells. Industry officials say no: The Marcellus layer is over a mile deep — too deep for water to seep up through all that rock and get into water wells.