Hydrogeological and geochemical investigations are required when the deep underground environment is explored or when the water from these depths are to be used as a resource. This study demonstrates the methodology on geochemical sampling of groundwater to evaluate the redox condition in a deep borehole with large downward hydraulic gradient. In the case of losses of drilling fluids during drilling, groundwater must be sampled using single or double packer equipment at the time of the fluid loss. When there was no loss of drilling fluids groundwater samples were successfully obtained using a long-term multi-packer system.
