Groundwater Chemistry at Depth in Granites and Gneisses

摘要

The place considered for a radioactive waste storage is beneath a local water divide along the eastcoast of southern and central Sweden. pH is fixed by the carbonate system and the ground waters can be expected to be saturated with respect to calcite. pH may vary from about 7,2 to about 8,5 with the most probable value around 8. The content of Cl exp - is difficult to asses as it is associated with the presence of relict sea water. Relict sea waters are linked to the postglacial clays and low sections of the terrain. Near local water divides the content of Cl exp - is low approaching the atmospheric contribution or below 10 mg/l. The content of F exp - is restricted by the solubility of fluorspar and may be about 7 mg/l as a maximum, but normally 3,5 mg/l or lower. SO sub 4- seems to be of the same order as the atmospheric contribution or about 15 mg/l. In the deep boreholes sampled so far the contents have been lower. The partial pressure of oxygen in the ground water should be very low. An increasing ironcontent towards depth is likely. Organic substance in the order of a few tenths of mg/l may be present. The local heating of the water close to the storage may bring about precipitation of calcite while the subsequent cooling when the water leaves the storage may result in precipitation of aluminiumsilicates. This may have a sealing effect of the rock. (Atomindex citation 10:431036)