NAGRA Opalinus Clay (…002 - Version 1
FEP 12.4.2 Influx of oxidising water​

Oxidising porewater may have an adverse effect on the retention of some radionuclides. In their oxidised form radionuclides may be better soluble and have lower sorption constants (examples: U, Tc). The pyrite in the host rock may be oxidised leading to higher sulphate concentrations in the porewater. The pH value may also decrease but Opalinus Clay is well buffered by its calcite content. The low hydraulic conductivity of Opalinus Clay and the strong buffering by pyrite and organic matter prevent oxidising water from entering from overlying or underlying rocks.