Laboratory Experiments of Desiccation as a Method for Contaminant Transport Reduction

Desiccation (soil drying) applied to the unsaturated zone has the potential of reducing vertical contaminant migration towards the groundwater. The basic idea of desiccation is to inject dry air and to withdraw wet air through a series of wells. Typically, in combination with surface flux control, the technique can be used to reduce mobilization of contaminants. Currently, a soil desiccation pilot test is being prepared at the Hanford Site in Washington with the objective to determine if the mobility of contaminants such as Tc-99 and nitrate can be significantly lessened by reducing sediment moisture content. A number of implementation issues need to be addressed before desiccation can be deployed: (1) energy limitations on the volume of water that can be removed, (2) osmotic effects, and (3) potential remobilization of contaminants after cessation of desiccation. A series of intermediate-scale flow cell experiments were conducted in homogeneous and simple heterogeneous porous medium systems to demonstrate the soil desiccation process for different boundary conditions, to develop temperature and relative humidity data sets to test and verify numerical simulators, and to investigate the effect of salt concentration on the desiccation process.