A study was conducted to determine relationships among physical, mineralogical, and soil hydraulic properties of Ultisols developed in unconsolidated sediments of the Lower Coastal Plain. Soil water retention curves, saturated hydraulic conductivity, bulk density, quantitative mineralogy, surface area, and particle size distribution were determined by horizon for seven pedons and relationships among them were analyzed by regression analysis procedures. Fine sand, sand and clay percentages were highly correlated with saturated hydraulic conductivity, surface area and volumetric water contents at specific pressure heads. Correlation coefficients > 0.95 were obtained for regression equations estimating soil water retention curves from particle size data. These relationships can be useful for quick characterization of soil hydraulic properties from particle size distribution data. No significant correlations were found between soil hydraulic and mineralogical properties of the clay fraction.

Surface contaminant plumes emanating from waste disposal facilities are often denser than the ambient groundwater. Under certain conditions these dense plumes may become unstable, contaminating larger regions of an aquifer. The behavior of contaminant plumes with different densities was examined in three flow containers packed with homogeneous porous media simulating unconfined aquifers. Glass beads and a medium sand were used as the porous media. A horizontal ambient groundwater stream was established in each flow container using deionized water. The contaminant plumes consisted of NaI or NaBr solutions introduced into each flow container from a line source located on top of the porous medium and extending over the total width of the container. Optical tracers were added to the salt solutions to allow flow visualization. Results show that, for a given porous medium, dense plumes were either stable or unstable depending on the magnitude of the horizontal flow velocity, the contaminant leakage rate, and the density difference between the contaminant solution and the ambient groundwater. When a dense plume becomes unstable, lobe‐shaped gravitational instabilities develop which are unsteady and three dimensional. Our experimental results suggest that the behavior of dense contaminant plumes overlying a less dense groundwater stream in a homogeneous porous medium depends on the magnitude of certain nondimensional parameters. It appears that gravitational instabilities begin to develop when the values of these nondimensional parameters exceed certain critical values.

643T techniques may not be applicable at sites where inorganic or radionuclide contaminants in the unsaturated zone are located deeply across a large area. Under these conditions, mobile contaminants might reach the water table at unacceptable concentrations. Desiccation applied to the deep vadose zone has the potential of minimizing downward contaminant migration toward the water table. Th e basic idea of desiccation technology is to inject dry air and to withdraw an equal volume of wet air in an array of wells. In combination with surface fl ux control, the technique can be used to immobilize contamination by reducing aqueous-phase transport.Currently, a soil desiccation pilot test is being prepared at the U.S. Department of Energy's Hanford Site in Washington. The objective of the test is to determine if the mobility of contaminants such as 99 Tc and NO 3 can be signifi cantly lessened by removing sediment pore water, resulting in a reduced threat to the groundwater. Th e test will be conducted in the BC Cribs and Trenches waste site area where the largest vadose zone inventory of mobile 99 Tc contamination on the Hanford Site has been identifi ed.A technical panel, convened at the Hanford Site (Fluor Hanford, Inc., 2006), identifi ed a number of implementation issues to be addressed before desiccation can be deployed. Th ese issues included (i) energy limitations on the volume of water that can be removed, (ii) osmotic eff ects during soil drying, and (iii) potential remobilization of contaminants after cessation of desiccation.Th e fi rst issue is related to the relatively large amount of energy that is needed to evaporate water (~2500 J g −1 ). Th is energy has to be provided by the injected air or the subsurface conducting the air. Th e amount of water that can potentially be removed per unit volume of air, at a given temperature, is the diff erence between the saturated water-vapor density and the water-vapor density of the injected dry air. Since energy has to be provided for water evaporation, however, it is more likely that water-vapor saturation will take place at the lower wet-bulb temperature, yielding a lower saturated water-vapor density. For example, the saturated water-vapor density of 15°C air is 13 g m −3 ; however, the density at the wet-bulb temperature of 5.5°C is only 7 g m −3 . Th e considerable diff erence between these two numbers may result in a slower water removal than the theoretical rate.Th e second issue relates to potential osmotic eff ects, because vapor pressures are lower in zones of increased salt concentrations and lower vapor pressures may reduce the effi ciency and A : PVC, polyvinyl chloride.O R Soil desicca on (drying), involving water evapora on induced by air injec on and extrac on, is a poten ally robust vadose zone remedia on process to limit migra on of inorganic or radionuclide contaminants through the vadose zone. Desicca on also has the poten al to improve gas-phase-based treatments by reducing water satura on and therefore increasing sediment gas-phase permeabil...

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