A special gravel filter will be placed in the space between the walls of the borehole and the outer wall of the pump chamber (casing). It consists of gravel, of river origin, smooth, rounded, granulated, washed, free of sand and clay. The silicate composition is predominant and they do not contain brittle quarry gravel.

The installation of the gravel filter will be done with simultaneous circulation of the diluted pulp (mud) outside the pipes. A packer will be used for the best result. In the beginning the circulation is done with a large flow and before the start of the gravel filter the flow is reduced and the pouring is done at a slow pace. The flow will be such that the rate of rise of the fluid (slurry, sludge) will be slightly slower than the “terminal rate of precipitation” of the gravel  into the slurry. In this way the best possible graveling will be achieved.