NAGRA Opalinus Clay (…002 - Version 1
FEP 6.3.1.2 Flow and advective transport

The hydraulic conductivity of the near field is such that porewater flow and advective transport could, in principle, occur in response to a sufficient driving force. A driving force is provided by the (low) ambient hydraulic gradient in the host rock, but the low hydraulic conductivity of the rock means that the resulting flow into and out of the near field is likely to be small. The driving force provided by gas pressure build up must, however, be taken into account.