That suggests that leaking wells are likely the source of such methane contamination, rather than any migration upward from the deep. (scientificamerican.com)
In aquifers overlying the Marcellus and Utica shale formations of northeastern Pennsylvania and upstate New York, we document systematic evidence for methane contamination of drinking water associated with shale - gas extraction. (dotearth.blogs.nytimes.com)
Our results show evidence for methane contamination of shallow drinking - water systems in at least three areas of the region and suggest important environmental risks accompanying shale - gas exploration worldwide. (pnas.org)