Boom Clay Hydraulic Conductivity A synthesis of 30 years of research

The hydraulic conductivity of the Boom Clay has been measured using various techniques since the beginning of the research programme on the possibility of radioactive waste disposal in this geological layer. Most of the K values are derived at the Mol site from hydraulic tests conducted on clay samples from the HADES URF and from the Mol-1 borehole or from in situ tests in the HADES URF. Nearly all the K values measured for the Putte and Terhagen Members are in the order of 10-12 m/s. The geometric mean of the vertical and horizontal hydraulic conductivities for the Putte and Terhagen Members at the Mol site are 1.7×10-12 m/s and 4.4×10-12 m/s, respectively with an anisotropic ratio about 2.5 (based on orientation distinguishable test results including laboratory tests and interference tests). A regional analysis of vertical K variability in the northeast of Belgium based on test results at five boreholes shows an increase in hydraulic conductivity from the east towards the west. Such a regional variation in K was demonstrated to be attributed in part to the variable content of coarse material (i.e. sand), and in part to porosity which is related to the burial depth of the clay.