Estimating lead and copper transport parameters from unsaturated clay soil column

ABSTRACT: The predictive accuracy of using the one-dimensional advection-dispersion equation to evaluate the fate and transport of solute in a soil column is usually dependent on the proper determination of transport parameters, dispersion coefficient (D) and retardation factor (R), which need to be quantified before the equation can be used for actual prediction purposes. Estimation for these two parameters is often obtained by analyzing experimental column effluent curves. In these paper data sets of adsorbing contaminants Pb and Cu transport in short unsaturated homogeneous soil columns were used to estimate the transport parameters by the (i) breakthrough curve (BTC) method and (ii) error function (Erfc) method under the conditions of step input and steady state flow. Results indicated that both the BTC and Erfc methods are capable of calculating precisely retardation factor (R) and dispersion coefficient (D) and the concentration simulated by Erfc method agreed well with the measured data. The rate of metal transport in clay soil is: Cu > Pb. The retardation factors of lead and copper for unsaturated homogeneous clay soils increased with distance. The regression analysis specified that the relationship between the retardation factor and the distance can be best described with a power-law function.