There are environmental concerns about hydraulic fracturing in the Marcellus Shale, in part because
the shales surrounding and including the Marcellus have already experienced natural fracturing, or jointing,
as a part of their geologic history. It has been suggested that stimulating the Marcellus with hydraulic fracturing may cause the pre-existing fractures to connect and create a pathway that leads drilling mud, hydraulic
fracture fluid, formation water, and methane gas to drinking water aquifers or water sources.