Evaluating Vadose Transport Processes Using Centrifugation Methods

摘要

Most subsurface contamination events involve migration through the vadose zone (i.e., unsaturated) before reaching an aquifer; however, research efforts generally focus on processes occurring below the water table, in part, due to the difficulty in mimicking vadose processes in the laboratory. Traditionally, researchers have used vacuum systems to apply tension at the bottom of a soil column as a means of establishing steady flow under unsaturated conditions. Such experimental methods, however, are time consuming, limited to a very narrow range of practical moisture contents, and susceptible to mechanical failure due to long experiment times. The Unsaturated Flow Apparatus (UFA) consists of a centrifuge with a modified rotor and pump system that can apply a controlled stream of tracer solution to the surface of two soil columns while they are spinning. In addition, the UFA can be used to determine the unsaturated hydraulic conductivity and matric potential for porous media much faster than conventional lab techniques, such as pressure plates. The advantages and limitations of such a centrifuge system for evaluating vadose transport processes will be discussed through several relevant environmental examples.