This kind of drilling is like solid stem, except the Claw Bit is attached to a hollow stem, instead of a solid one. Once the bore hole reaches the desired depth, the hollow stem acts as a temporary casing, keeping the sides of the bore hole from caving in. The drilling crew can take samples through the hollow stem, or use it for setting a groundwater monitoring well into place.

The advantages of Hollow Stem Auger drilling include the following:

• It allows for uncontaminated sampling in formations of unconsolidated soils.

• Rapid drilling into clay-filled soils is easy and cost-effective.

Hollow stem auger drilling has disadvantages though. Drilling is not effective when boulders or large cobble stones are encountered. Also, auger refusal can occur when a large consolidated igneous formations are encountered. Its use is limited in loose, sandy soils where water table infiltration can contaminate sampling. Sampling in loose soils requires alternate sampling equipment like split spoon or continuous coring. The depth is limited to 150 feet or less.