Most of the water used to hydraulically fracture a well is not returned to the surface; only about 10% to 30% of it comes back up the well at all. The rest remains in the cracks created by the hydraulic fracturing. The water that does return
contains chemicals from the fracturing fluid as well as brine (salty water), volatile organic compounds (VOCs), and naturally occurring radioactive material (NORM) from the Marcellus formation itself. For more information on the content
and fate of flowback and produced water from Marcellus wells, see Marcellus Shale Issue 8: Water – Out of the Wells.