I have a couple of specific suggestions but first a general one: relax, don't worry, have a homebrew.
40-50 gallons to get 6 down to 80 seems really really high. are you stirring or otherwise moving your wort while chilling? if not you should be able to cut your chill time in half just with that.
Getting it below 80 quickly is great but if you can't do it so it goes. get it as cool as you are willing to waste water on and then put it in the fermenter and let your fridge or the cool night air get it the rest of the way down to pitching temp.
Don't pitch the yeast into the wort until it's at or below 65* if that takes 12 hours so be it.
Airborne contamination while chilling is unlikely, contamination while chilling in the fermenter is unlikely. as you learned when your bottle of chilling ice opened in the wort, contamination is harder than we think.
I live in northern california and my ground water in summer is... pleasant for bathing let's say. I chill 11 gallon batches to ~90 in 20-30 minutes with a 50" copper IC. I run the water full bore because as long as the water is coming out hot, it's getting all the heat it can out. when the output water starts to feel cooler I stir. when stirring doesn't make the output water feel much warmer I call it quits, pull the ic, whirlpool, let settle and run off into the fermenters. those go into the fridge and I aerate and pitch in the morning.
I use about 35 gallons of water for 11 gallons of wort this way.