A well is fed by an underground aquifer. No two are alike as far as the rock strata above or below them. It would be impossible to even venture a guess if it would affect them or not because we do not know where your source actually originates, how your ground percolates, what your soil is like. I use spring and also well water for my personal and agricultural needs. I make it a practise not to put anything down on a potential watershed I didn't want to eventually consume.

Cars give off asbestos from brake linings, used moter oil from the engine and emit toxics from the tailpipe. I recently saw the recommendation to not even wash your car at home, because of all the stuff that comes off onto your driveway. I wouldn't be driving anywhere it migh affect my water source, if I could help it. I would be testing my well periodically.

Most drilled wells have the casing grouted to the soil for the top 20 feet to seal out any surface contaminants. There's the question of how much water moves horizontally through the bottom of your well -- how quickly does your well flush itself? The way to check would be to add some sort of dye, wait a period, then draw some water to see how much it's dissapated. But how badly do you want to know?

If things got really bad, and if it was me, I'd salt a little, or more likely, spread my woodstove ashes to help the sun to melt it by increasing absortion of solar heat. I don't know enough about other chemical melters to say, but I think I'd be cautious in the unlikely case that the well caseing grout leaked, and of course my first course of action would be to keep the driveway graded, divert runoff to keep the driveway dry, and plow it out as well as I could.

Dan