Pre-chillers work, but in my experience, not great.
I think you'd be better off running your wort through a post chiller, rather than trying to cool your ground water which is blasting through at high speed.
Then again though, I'd be thrilled to see anything in the 60's with my tap water. If I can get it to 75, that's pretty good. Lately I've been forced to just let my fermenters chill overnight before I pitch yeast.