Groundwater Contamination May End the Gas-Fracking Boom 
But methane isn't harmful. Also the article doesn't mention the quantities, but another does. [1] It seems that the most that's been found is about 70mg/L, which is not a lot.<p>[1] <a href="http://realclearscience.com/blog/2013/06/theres-methane-in-your-drinking-water-so-what.html" rel="nofollow">http://realclearscience.com/blog/2013/06/theres-methane-in-y...</a>