Two processes for hydraulic drilling of rock are dry drilling and wet drilling. In a dry hole, compressed air is forced down the drill rods to flush the cuttings and drive the
hammer. In a wet hole, water is forced down. As part of an analysis to determine the
cost of drilling a hole, an experiment was conducted in the Great-Karoo near Graaff-
Reinet to determine whether the time it takes to dry drill a distance of 5 meters in rock
increases with the depth at which drilling begins. The results for one portion of the
experiment are shown in Table 1.