Mud-Rotary Drilling techniques use a tri-cone bit connected to a string of drill rod. A casing is placed as the hole is advanced, and the soil is transported to the top of the hole by use of re-circulated bentonite/water slurry – or mud. Undisturbed samples can be advanced from the bottom of the hole, and temporary or permanent wells can be set. The drill bits used with mud-rotary drilling are best for use in areas with shallow groundwater levels free of hard rock drilling conditions. Often rigs equipped with mud-rotary can be changed over to rock coring with little effort if needed.