You need to understand a bit of geology for this. Aquifers are layers of rock with tears around them. Same as oil reservoirs but with water instead of oil. If you see the earth from the side you would see many layers on top of each other folding and warping and going up and down, etc. Aquifers can for many any many miles and the layer ends up hitting the surface. That's the collection zone rain water is collected here and percolate through the aquifer until it reaches hundreds of feet underground and miles upon miles in a direction. What he means is that everywhere is basically a collection zone for an aquifer somewhere. But where you're standing next to an oil well with an aquifer on the way, you're most likely NOT standing in the collection zone of that aquifer.

What he meant from his comment is that a sales aquifer (layer of shale, sandstone, shale for example) holds water in the middle where the trap rock (shale) won't allow fluid to pass through it this will be a few hundred feet underground.

An oil well drills waaaaaaay pass that many many thousands of feet (7-9k in Barnett shale, even more in marcellus and sometimes even more than 15k feet in other parts of the world) this goes past many many many layers of different kinds of rock, including many layers of trap rock like shale.

What he ultimately means is that you drill a well in Barnett shale where the horizontal Frac section is like 7500ft underground. Then the Frac is from a couple ft long to around 30-40 ft long in the most extreme cases at most braking through a couple layers of the engineer was really really bad. The aquifers are still thousands of feet away from that.

Obviously spilling a bunch of chemicals in the ground is going to contaminate an aquifer somewhere maybe, but spilling some chemicals on the ground is horrible and illegal to start with and surface negligence from operators and workers SHOULD be punished.