That's not entirely true Bear. The Hat has had issues with 'gassy' drinking water going back over 100 years.
"It was common knowledge in the industry that the CPR discovered gas in a water well at Langevin siding in 1883, and drilled a second well in 1884."
Petroleum History Society - preserving history of the petroleum industry in Canada
In today's O/G industry, basically all of the shallow, economic reserves have been tapped. Any new gas plays are generally very deep (thousands of meters). While the fracking fluids are delivered under high pressure, those pressures are no where near high enough to have an impact anywhere close to being able to impact strata and formations so close to the surface. To be honest, I am guessing that the overall impact of the actual frack is within a 30 meter diameter of the perforation(s) of the casing
I'm off to the GPS tomorrow where there will be some big fracking companies. I'll see what kind of answers their techs provide in terms of the kind of diameter that the fracture can have beyond the casing.