Although I respect the civility of your answer, it does sound a bit like the company koolaid. Could you discuss how often you personally (not some dude in a truck with a clipboard) revisited the well sites, and what tests were run to assess environmental impact? I don't mean that to spike you; I just want to make the point that your perspective is skewed, because you guys are run hard. You go to a job, knock it out, and move to the next one. You won't be asked to knock on doors 5 years later and ask if anyone has any problems... you'll be off fracking another well that day.
Also, although I know the literature implies that fractures will travel linearly through the formation, doesn't that run counter to almost all rock stress data in geology? If you're an engineer you may have taken structural geology at some point; remember Mohr's circle? I make this point because if the fractures travel upwards through formations, it creates a path for the chemicals *and* oil and gas to travel outside the formation. I'm not familiar with concrete research (man, this would be expensive) that tests continuity between producing and non-producing water-saturated layers in the area of a well. Simulations are out there, sure... I play a simulation where I'm an elf druid that kills orcs, and just because you have a lot of unknowns about my life, you can't say it provides an approximation of my life.
I think a lot of the concerns expressed here follow a similar vein: we are seeing problems with the water supply in areas where hydraulic well fracturing is predominant. Although that does not create causation, it leaves a lot of room for doubt. Evidence either way will build up over time, but people are concerned *now* if something will hurt them or their family in 10 years.