Mladen Antonov/AFP/Getty Images A water tank truck is seen on
the main street in Waynesburg, Pa., on April 13. Scientists say
naturally polluted water can rise to the surface of the
Marcellus Shale; that finding suggests that frack water could
seep out, too. 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