2.2. Time scales of sustainability
It is recognized that time scales over which one averages to confirm
or refute steady-state of a unit operation are vastly different
for, say, a corn-to-ethanol production facility where process
parameters like temperatures, fill levels of tanks, or flow rates fluctuate
on a scale of days or at most months, in contrast to the ‘‘fill
level” of the Ogallala Aquifer in the central Great Plains which declines
over decades and where recharging does apparently not prevent
the decline