Below is a great article showing another example of the many ways you can use you a hydro-excavation unit.
BY JOHN RYANHydro-excavation offers another option in rescuing a buried victim in a trench collapse incident. A truck-mounted hydro-excavator system uses a pressurized stream of water to wash the soil away from the victim. The soil and water are then removed simultaneously from the excavation, using a vacuum hose or tube. Although the technique is similar to that of using pneumatic excavators (vacuum trucks), the main difference is that in hydro-excavation, a pressurized water stream replaces a high-pressure air stream.Originally developed as a non destructive excavation method, hydro-excavation uses a highly controlled, variable-pressure stream of water of up to 2,000 psi to reduce the soil to a state in which it can be removed by a high-volume vacuum system. A typical hydro-excavator truck consists of a variable-flow water pressure pump, a vacuum system, and separate holding tanks for water and debris collection.