SCALE DEPENDENCE OF SOIL PERMEABILITY TO AIR - MEASUREMENT METHOD ANDFIELD INVESTIGATION

This work investigates the dependence of soil permeability to air on s ampling scale in near-surface unsaturated soils. A new dual-probe dyna mic pressure technique was developed to measure permeability in situ o ver different length scales and different spatial orientations in the soil. Soils at three sites were studied using the new technique. Each soil was found to have higher horizontal than vertical permeability. S ignificant scale dependence of permeability was also observed at each site. Permeability increased by a factor of 20 as sampling scale incre ased from 0.1 to 2 m in a sand soil vegetated with dry grass, and by a factor of 15 as sampling scale increased from 0.1 to 3.5 m in a Sandy loam with mature Coast Live Oak trees (Quercus agrifolia). The result s indicate that standard methods of permeability assessment can grossl y underestimate advective transport of gas phase contaminants through soils.