This is considered the industry standard in overburden casing drilling. This system utilises a drill bit that extends through a casing. The drill bit has a reamer that swings out when the bit is in operation and which in turn drills a hole slightly larger than the casing. The casing in turn is simultaneously advanced by using a percussion force. Cuttings are removed through the casing by compressed air. This is a preferred method for drilling for water near a river bank.
This method is basically the same as reverse circulation but instead of air, a drilling fluid is used. This assist in reducing dust, keeping the drill bit cool and pushing the cuttings to the surface. The fluid selected depends on the formation being drilled.
A solid bit is used which produces rock chips. These chips are removed from the hole through compressed air (or fluid) that is pumped into the hole. At the top the rock chips is recovered by means of a sampler for analysis. This is one of the drilling methods that can be used during exploration for minerals but might be less accurate than diamond bit drilling because of the tendency of heavier metals, like gold, which accumulates at the bottom of the drill hole and in pipe elbows. During reverse circulation the air (or fluid) is pumped down through the annulus and return through the drill stem.