In WA state it was the law in the late '80s, early '90s to do this testing regularly. Hard to believe it isn't similar in VT.

This is easily testable. There's some goo you can put on the measuring stick that you drop down in the tank to see how full it is. That goo changes color if there is something other than gas (like water) mixed in with it. I used to have to do this weekly and log it when I worked at a grocery/gas store.