DEVELOPMENT OF TENSIOMETRIC BARRIERS FOR CONTAINMENT AND REMEDIATION AT WASTE SITES

This report describes a concept in which dry air is injected into an u nsaturated formation to reduce the soil moisture content, referred to here as a tensiometric (or sometimes dry) barrier. The objective is to reduce the hydraulic conductivity of the unsaturated media to the poi nt where liquid phase transport becomes negligible, thereby achieving containment. The concept could be applied in subsurface formations to provide containment from a leaking facility, or it could be incorporat ed into a cover design to provide redundancy for a capillary barrier. The air injection process could in principle be coupled with a vacuum extraction system to recover soil vapors, which would then provide a r emediation process that would be appropriate if volatile organic compo unds were present. Work to date has consisted of a combined theoretica l, laboratory, and field research investigation. The objective of this research was to demonstrate the technical feasibility of the tensiome tric barrier concept by identifying the parameters which determine its effectiveness. Based on the results obtained for the experimental and theoretical studies, feasibility analyses were prepared as a modifica tion for a landfill cover design to prevent infiltration from atmosphe ric precipitation and for potential application of tensiometric barrie rs to achieve subsurface containment of mobile pollutants and removal of volatile constituents. These analyses considered the technical as w ell as the economic aspects of the tensiometric barrier concept, and f ound that a properly designed and operated tensiometric barrier is com petitive with conventional containment methods. In addition, they bene fit from being able to recover from failure by circulating additional dry air through the formation to re-establish the barrier phenomena.