[Johnny555]

What about the ground water near popular general aviation airports? Granted, there aren't nearly as many airplanes as cars, but over years, contamination can accumulate.

I remember a small lake in San Francisco that had to be decontaminated due to lead pollution from cars:

https://www.sfgate.com/bayarea/article/Workers-pour-poison-i...

"Lead from car emissions seeped into the water for decades until leaded gasoline was phased out beginning in the 1970s. The lead combined with pesticides flowing in from the golf course to form a toxic stew."