During underground space development, groundwater seepage mostly occurs which may seriously affect the stability of deep excavations as well as retard progress of construction. For smooth progress of work, effective construction and operation of a disposal facility for high level radioactive waste (HLW), it is important to control seepage into excavations by sealing off fractures or fissures and excavation disturbed zones (EDZ) to control groundwater inflow during the construction phase of such a facility. In this study, a series of experiments were conducted on ethanol/bentonite slurries in the laboratory with the aim of determining the effect of a hydrophilic solvent such as ethanol on the hydraulic and injection characteristic of bentonite slurry for the sealing of fissures to control ground water seepage during the construction phase of a repository. Preliminary results revealed ethanol/bentonite slurry as an effective grouting material capable of penetrating micro fractures (100μm or less) and with the permeability of the grouted medium being as low as 10E-7cm/s. The results also show that the effectiveness and efficiency of grouting is dependent on the type of injection and fissure size. Dynamic injection was observed to be efficient as it was able to inject high dense slurry.