High Uniformity versus Low Hydraulic Conductivity for Vertical Barriers in Contaminant Containment Applications

Steady state contaminant transport through vertical barriers is reviewed, and the variability of hydraulic conductivity of barrier materials is discussed. Two important issues for containment systems operated with an inward directed hydraulic gradient across the vertical barrier are that: (1) there is not an advantage to achieving very low values of hydraulic conductivity for the barrier material and (2) the impact of variability in hydraulic conductivity on contaminant flux is to increase contaminant transport out of the contained area compared to an otherwise identical system with uniform hydraulic conductivity. A consequence is that vertical barriers with higher conductivity and greater uniformity are more effective than are vertical barriers with lower conductivity and lower uniformity. For containment systems operated with inward directed hydraulic gradients, it is recommended that more emphasis be placed on achieving and verifying uniform hydraulic conductivity than low hydraulic conductivity.