The salt on the roads can seep down into the aquifer. The salt and other things in the brine drilling fluid are inserted thousands of feet down, way way way below your aquifer. AND that's where they all came from to begin with.

Salt water drilling muds are used any time a well must go through a salt formation. This is made necessary by the fact that fresh water will absorb the salt it comes in to contact with which causes the pH to drop, pipes to corrode, and equivalent down hole pressures to do all kinds of funky things that can cause blow outs or accidental fracking. So, to avoid this, when a drilling operation gets near a salt formation (usually the salt dome that has created the geology that traps the oil) the drilling fluid is switched out to a salt water solution so that it is already saturated with salt, thus preventing dissolution of the surrounding salt into the fluid.

[Linked Image from i30.photobucket.com]