An underground storage tank is, a storage tank, not including any underground piping connected to the tank, that has at least 10 percent of its volume underground

"Underground storage tank" or "UST" means any one or combination of tanks including connected underground pipes that are used to contain regulated substances, and the volume of which including the volume of underground pipes is 10 percent or more beneath the surface of the ground. This does not include, among other things, any farm or residential tank of 1,100 gallons or less capacity used for storing motor fuel for noncommercial purposes, tanks for storing heating oil for consumption on the premises, or septic tanks.