Air Permeability in Undisturbed Volcanic Ash Soils

Soil air permeability (ka) governs convective air and gas transport in soil. The increased use of soil venting systems during vadose zone remediation at polluted soil sites has created a renewed interest in ka and its dependency on soil type and soil air‐filled porosity (ε). Predictive ka(ε) models have only been tested within limited ranges of pore‐size distribution and total porosity. Andisols (volcanic ash soils) exhibit unusually high porosities and water retention properties. In this study, measurements of ka(ε) on 16 undisturbed Andisols from three locations in Japan were carried out in the soil matric potential interval from −10 cm H2O (near water saturation) to −15000 cm H2O (wilting point). Two simple power‐function ka(ε) models, both with measured ka at −100 cm H2O as a reference point, gave similar and good predictions of ka(ε) between −10 and −1000 cm H2O. For one location comprising finely textured and humic Andisols, both models largely underpredicted ka(ε) in dry soil (