Yes, there's a rather significant amount of groundwater contamination due to poorly operated and/or improperly abandoned wells.
However, the vast majority of the contamination has nothing to do with whether or not hydrofracturing was applied. It's far more frequently due to bad casing jobs, etc.
In other words, most of the contamination is due to sloppy work. It would happen regardless of whether it was a convention or unconventional well.
There are situations where fracking can directly lead to contamination. After all, you're deliberately creating permeability in an aquitard. However, these are not anywhere near as common as the cases where a bad casing job, etc can lead to groundwater contamination (every well).
In a nutshell, we're seeing an increase in groundwater contamination because of the spike in the number of wells drilled in the areas. It's not directly related to the completion method used in the well (e.g. fracking).
However, it doesn't help that there are highly variable state/local regulations and a huge number of sloppy operators.