Technical Report NTB 84-24

A liquid chromatography technique was utilized to explore permeability, porosity, and retardation laboratory characteristics of a series of granite samples from 489-670 m depth of the Böttstein borehole, as part of the Nagra deep drilling programme in Northern Switzerland. The samples comprised cores with old healed, mineral/clay-filled fractures and cores of fresh intact rock without filled fractures. These samples revealed no detectable water flow at pressure drops up to 90 bar, i.e., their hydraulic conductivities were smaller than 4·10^-14 m sec^-1.

After artificially fissuring and compressing the samples hydrostatically with pressures approximating the initial rock overburden, the "fresh" and "reopened" fissures exhibit values of 10^-9 to 10^-10 and 10^-11 m sec^-1, respectively, with flow porosities usually smaller than 0.5 %. These fissures displayed a strong tendency to rapid "self-healing" by contact with the relatively HC0₃-rich Säckingen water which was used in the experiments. These results suggest that groundwater transport through unfractured solid Böttstein granite is limited to aqueous phase diffusion in micropores.

Retardation of the sorbing species TcO₄, Sr²⁺, and CO²⁺ was established in an artificially induced fissure in a "fresh" granite sample. The values of 0.16, 0.24, and 0.04, respectively, must be interpreted with great caution, since the applied hydraulic gradient of 2800, and hence the resulting flow rates were unrealistically high.