In September 2015, Edilmac finished working on a project involving the modernisation of the EDF plant of Passy, in the Upper Savoy region, France. Our company was involved in the process of transferring the penstock from the outside to underground, creating a 190-metre-deep vertical well, with a diameter measuring 3.5 metres. During directional drilling, the cementation of several sections was required, since the high hardness of the rock (gneiss) was interspersed with various fractures. The deviation at the bottom of the well measured only 34cm, which is well below the minimum tolerance of 66cm established in the contract. Boring did not cause problems of any kind, thus allowing us to achieve great performances with an average speed of 75 cm/h. Given the hardness of the rock and its diameter, these are excellent results.