New simplified design methods for engineering barriers around contaminated sites with Cauchy boundaries.

Since the 1980s, low-permeability slurry trench cutoff walls have been widely constructed as barriers to retard the migration of contaminants. The thickness of the cutoff walls is a key determinant of the wall service life. Through a series of theoretical derivations, simplified methods for determining the flux limit and concentration limit were proposed to determine the thickness of cutoff walls for contaminated sites with constant pollutant flux. The relative errors of both the flux-based and concentration-based methods increase as the breakthrough criterion of the ratio between the specified limit concentration of the contaminant to the source concentration (C*) and the ratio of the limited value of contaminant flux to the constant source flux (F*) increases, with a given Peclet number PL. The maximum relative error reaches 4% and 6% when C* and F* are both 0.1, which covers most practical situations in cutoff wall design. Good agreements of wall thickness were obtained between the proposed simplified methods and analytical solutions via a clear example. The proposed method can efficiently simplify the design process of cutoff walls with high accuracy, providing a basis for containing contaminated sites.

Measurement of contaminant adsorption on soils using cycling modified column tests.

An innovative cycled column test with supporting batch equilibrium and kinetic analysis for adsorption or desorption were developed for evaluation of adsorption behavior of soils. Non-equilibrium adsorption was observed in the cycled column tests as the traditional testing methods. The isotherm of local equilibrium of the soil was conducted based on the testing results within a relatively short duration with simple analysis. The concentration curves of influent and effluent of the cycled column tests were simulated by dual-porosity (DP) model with a modified inlet boundary. Based on the modeling results, the isotherm of local equilibrium is close to that of the mobile phase adsorption capacity, whereas the immobile phase of the soil is nearly inactive in the retardation of the contaminants. The testing results from cycled column tests are hardly interfered by desorption or the sorption rate according to the modeling for corresponding scenarios. The cycled column test can be used as an alternative or supplementary method to the traditional column test for the determination of local equilibrium isotherm, with advantages of shorter testing duration and easier data analysis.