Abstract :
Several transport parameters (as hydraulic conductivity K, apparent diffusion coefficient Dp and diffusion accessible porosity (eta) of HTO and iodide) have been intensively measured in the laboratory on high-quality cores taken at the Mol-1 borehole of the Mol site, in Belgium. The borehole was cored in 1997 from about 145 to 325 m depth, including the whole thickness of the Boom Formation, a Tertiary clay situated between 186 and 288 m depth (ground level), and part of the surrounding layers. The hydraulic conductivity measurements confirm the low permeability of the Boom Clay. An upper 90-m-thick clay layer within this formation can be considered as homogeneous with respect to the hydraulic conductivity. The vertical hydraulic conductivity Kv (i.e. K perpendicular to the bedding) is in the order of magnitude of 10^-12 m s^-1 and the average is 2.3×10 ^-12 m s^-1. This layer comprises from top to bottom the "Transition Zone", the Putte Member, the Terhagen Member and the top of the Belsele-Waas Member of the Boom Formation. The 12 m at the base of the Formation, which corresponds to the lower part of the Belsele-Waas Member is characterised by larger Kv values (ranging between 10^-11 and 9×10^-11 m s^-1). The same thick clay layer can also be considered as homogeneous, regarding the values of the apparent diffusion coefficient and the diffusion accessible porosity (eta) of tritiated water (HTO) and iodide. The average value of the diffusion accessible porosity is 0.37±0.03 for HTO and 0.16±0.02 for iodide. The apparent diffusion coefficient varies from 1.1×10^-10 to 5.5× 10^-10 m^2 s^-1 for HTO and from 9.1×10^-11 to 5.2×10^-10 m^2 s^-1 for iodide.
