UFA method for site characterization and remediation.

摘要

Direct measurement was made of the unsaturated hydraulic conductivity of soils and sediments using a new experimental method. The experimental method, which uses the Unsaturated Flow Apparatus (UFA(trademark)), employs open-flow centrifugation in a new application. Centrifugation, like gravity, has the effect on a material of a whole-body force exerting equal force at all points within the sample. The equivalent gravitational force exerted throughout the sample is from one to four orders of magnitude higher than earth gravity (from 10 to 10,000 g). The result is an increase in rate of fluid flow equally at all points throughout the sample so that hydraulic steady state is obtained in most geologic materials in a few hours, even at very unsaturated conditions. This extraordinarily short time allows direct measurement of transport parameters, such as hydraulic conductivity, diffusion coefficient, and retardation factors, in any porous media over the complete range of field moisture contents. Traditional techniques and estimation methods require months to years to obtain these data, and cannot provide data for samples at low water contents. Predictive modeling, site restoration strategies, and remediation formulations can be rapidly tested with the UFA method prior to costly and time-consuming field demonstrations. From 8 to 14 measurements of hydraulic conductivity as a function of decreasing volumetric water content were made on each of approximately 50 aridisol samples from a former waste disposal area at Hanford Site in Washington State. This provided over 500 data points to define the characteristic behavior, with respect to Hanford Site vadose zone water for these soils and sediments. The large hydraulic conductivity data set provided information for mapping the subsurface recharge distribution below an area where disposal of large quantities of liquid wastes occurred during a half-century of government weapons research.