Over a decade ago I was searching for a dissertation topic and a self-reporting fracking site had come online (only CO and TX were required to track IIRC) that showed promise for helping to assess impact.
Before jumping blindly into the data, I interviewed several former field workers and engineering professors. The consistent narrative was that water spills with the fracking chemicals where extremely common and only had to be reported under a very limited set of situations, if they were even reported at all.
To the person, the field hands were personally worried about future cancers and other health conditions. All the field hands had since moved on to graduate school themselves, several in medicine.
Further, not all the chemicals being leaked, spilled, or entered into the water supply via bad casings were reported, as any that had trade secrets (at the time and to the best of my recollection) were excluded.
EDIT: https://archive.is/gaQ5x