Hydraulic fracturing, or fracking, involves drilling a long vertical pipe deep into the ground and sucking up petroleum/natural gas (way more complicated than that, but that’s the drift). At issue is the fact that the pipe passes through the water table, the source of our drinking water.
The petroleum deposits in question are way, way below the water table. So the drilling industry constantly, and correctly, points out that it is unlikely for those petrochemicals to migrate through solid bedrock upwards into the water table.
What they don’t point out is the danger of fluids and chemicals used in the pipes leaking into the water table. And apparently that’s happened a few times and they’ve settled in court and essentially covered up.
On the upside, fracking tech has improved. And natural gas (which is what it extracts) is cleaner than some other energy sources.