Dual circulation drilling system

A ground drill system comprising:

• a drill string arranged to form a flushing fluid flow path and a working fluid flow path that are fluidically isolated from each other, the drill string having an up hole end and an opposite down hole end;
• a water hammer coupled to the down hole end of the drill string and in fluid communication with the working fluid flow path wherein the water hammer is operated by a working fluid flowing through the working fluid flow path, wherein the working fluid comprises water or oil or a mixture thereof;
• and
• a flushing fluid outlet in communication with the flushing fluid flow path, the flushing fluid outlet juxtaposed at a fixed location relative to the water hammer and carried by the drill string wherein the flushing fluid outlet advances with the drill string, the flushing fluid outlet being located adjacent to and up hole of the water hammer and capable of directing a flushing fluid flowing through the flushing fluid flow path into a hole being drilled by the ground drilling system;
• and
• wherein the working fluid flow path is a closed flow path and arranged to recirculate working fluid through the water hammer.