Soil-gas diffusivity fingerprints of the dual porosity system in fractured limestone

The presence of fractured vadose zones (e.g., limestone or clay tills) may potentially pose significant environmental concerns due to the rapid, preferential migration of gaseous plumes through interconnected pore networks. However, recent modelling studies related to fractured vadose zone processes are mostly limited to hydrogeological (water and solute) transport studies with very poor attention to the gaseous phase
transport studies (Kristensen et al. 2010).
This study characterizes fractured limestone soils for gas diffusion based on three different gas diffusivity fingerprints. The first fingerprint is a two-parameter exponential model, which mainly describes the gas diffusivity in the limestone matrix while taking both fracture connectivity and matrix pore connectivity into account. With the second fingerprint, we make a close observation of the tortuous matrix pore network by means of a modified Buckingham (1904) pore connectivity factor (X*). The third fingerprint of the fracture network involves the average angle of diffusion α (Moldrup et al. 2010), a parameter which characterizes the average angle at which the fractures are penetrating the sample.