The hole size can be from 4 to 12 inches in diameter and can be from 1 to 20 feet deep.
Exercising Valves: How? Why?
Water distribution valves of all sizes spend their lives sitting underground mostly open so that water is available to everyone on the system. If left unattended those valves will rust, suffer cathodic damage, get stuck in place, become covered in dirt and silt from the street above, get paved over, or even shift with freezing and thawing conditions if you are in a northern climate.