Methane is going to move way faster through the subsurface than will many other compounds, particularly those used in fracking fluids. So, if methane is diffusing or otherwise traveling through the subsurface, other compounds may very well follow, but a far slower rate, possibly taking years or even decades before they show up.
There’s a lot of press about the recent Duke study showing high incidence of elevated methane levels in well water near hydrofracturing operations, but also
They did not find evidence of well-water contamination from fracking fluids or from the flow-back water…
There’s a big need to keep up the monitoring, now that they’ve established a network of monitoring sites, testing for a broad spectrum of organic and inorganic compounds. No doubt the gas industry would welcome this approach, to aid understanding of their methods and to help develope various methods of tracking the transport and fate of fracking compounds. (One good way to save money: composite samples.)