Originally Posted By: Fleetmon
for those following this and for Hokiefyd, the answer is around 1/4". 1/4" in a TYPICAL 12000 gallon UST equals about 40 gallons, give or take.
Again, it would depend on the dimensions.
Clawson Tank is a mainline supplier of fiberglass USTs; you can see on
their website that they offer more than one configuration for most sizes. They offer two 12,000 gallon UST sizes, one is 32'x8', and one is 18.5'x10.5'.
For the 32'x8' tank, 40 gallons would be close to 1-1/2", and 600 gallons of free-phase water would be over 9" on the bottom.
For the 18.5'x10.5' tank, 40 gallons would be 2", and 600 gallons of free-phase water would over 12" on the bottom.
I would consider 600 gallons of free-phase water to be a lot; that's something we just never have in our tanks. There is some volume of water that will be adsorbed into the alcohol in the fuel, but this is generally a pretty small amount, at least in my experience.
I do appreciate this discussion; it's always good to hear of other perspectives on this (or any) issue.
Oh, and we're thinking of you guys in the upper mid Atlantic and northeast. I've seen forecasts of multiple feet of snow for some; hope it's not too disruptive and pray that everyone stays safe.