"Topsoil" means at least 12 inches of the surface soil layer or a six-inch layer of soil that includes the surface soil and the unconsolidated subsoil immediately below it.
"Underground utility line" means an underground pipeline or conduit of an inside diameter greater than 12 inches or an underground electrical transmission or distribution line of a capacity greater than 115 kilovolts.
Va. Code § 56-257.5