For years gas drilling companies and regulators have said that decades of hydraulic fracturing had not caused frack fluids to return from depth and reach aquifers. Now a British university study documents why fracking itself (as distinguished from spills at the surface or cementing failures during the drilling phase) has an excellent safety record.
The University of Durham's Energy Institute in the United Kingdom investigated hydraulic fracturing in America, Europe, and Africa by looking at thousands of induced fractures produced by "fracking" and found why hydraulic fracturing has not caused pollution of aquifers. The longest distance for any fracture was 588 meters. meters. http://www.platts.com/RSSFeedDetailedNews/RSSFeed/oil/8221049. Just 1% of the investigated fractures went as much as 350 meters. The lead researcher is Professor Richard J. Davies and the study is published in Marine and Petroleum Geology.
Simply put, fracking for shale gas is happening at such depths that there is next to no danger of polluting groundwater with fluids returning from depth. Fracking for shale gas happens in the USA typically 3,000 to 10,000 feet below any groundwater source, and the induced fractures don't travel anywhere near that distance.
Also it should be noted that this study further confirms that hydraulic fracturing is not a new technology and has been used around the world. As a result the British researchers were able to look at fracking and fractures on three continents. If fracking were causing groundwater contamination, such pollution would have shown up years ago all around the world.
It really is time to focus on the real threats to groundwater--spills and leaks at the surface and cementing errors that allow methane to migrate.