What is shale-gas?
Shale-gas in this text refers to natural gas found in underground formations of shale. In order to extract gas from the shale, holes are normally drilled down within the shale (at whatever direction that requires). The shale is then fractured using pressurized liquid to enhance the permeability of the shale and allow the gas to flow into the well (known as "fracking").
Does fracking impact the groundwater?
While the potential exists for hydraulic fracturing to degrade groundwater quality, a recent USGS study found no groundwater contamination as a result of the Fayetteville Shale exploration. Additional information about water quality and hydraulic fracturing can be found here.
What about earthquakes?
The link between earthquakes and hydraulic fracturing or other deep well injection have been noted in several studies. While fracking is often cited as a cause of earthquakes, if correlations exist, they are normally more easily attributed to deep well injection.
A swarm of earthquakes in central Arkansas were attributed to this type of injection in 2011; after which the Arkansas Oil and Gas Commission placed a permanent moratorium on injection in the area.
See Also
For more information on the USGS Regional Groundwater Studies, please visit the USGS Groundwater Resources Program.