Vertical distribution of H14CO3- transport parameters in Boom Clay in the Mol-1 borehole (Mol, Belgium)

In the range from 191 m to 281 m depth (Below Drilling Table), the Boom Clay Formation can be considered as homogeneous with respect to the hydraulic conductivity and the transport parameters of H14CO3-. The value of the vertical hydraulic conductivity is around 2.5-3 × 10−12 m/s. The average apparent diffusion coefficient Dapp of H14CO3- in the direction perpendicular to the bedding plane is (6 ± 3) × 10−11 m2/s. The product ηR of the diffusion accessible porosity η and the retardation factor R of H14CO3- is 0.26 ± 0.03, lying between the value of iodide (ηR = 0.16) and of HTO (ηR = 0.37). Due to anion exclusion, iodide has a lower porosity than HTO. Because of the lower ηR value of an anion as iodide, a slight sorption of H14CO3- cannot be excluded (R ⩽ 0.26/0.16 ≈ 1.6).