Abstract
Column tests using undisturbed samples of residual sandy soil from the Adamantina Formation (K) were performed to determine the sodium hydrodynamic coefficient by equilibrium and non-equilibrium methods. Analyzing the porosity and soil characteristics, as well as the breakthrough curves, it was possible to note a typical non-equilibrium transport behavior, related to the soil dual-porosity, particularly at early and late time behavior in the breakthrough curve tails. The experimental data were best fitted to the non-equilibrium method than to the equilibrium one, and the sum of the square errors was up to five-fold lower. The conceptual model analysis of the methods led to observations on the limitations of each method and a careful analysis of the obtained values, which are also related to the soil characteristics.
Highlights
The hydrodynamic dispersion coefficient (Dh) is one of the most important solute transport parameters, and its correct quantification is essential to accurately estimate groundwater contamination and, analyze, assess and manage the possible risks related to cont aminated sites
It is well known that undisturbed soil columns are subject to the presence of macroporosity, dual-porosity, and other heterogeneities
The specific weight of the solids was consistent with sandy soil values (26.4 kNm-3)
Summary
The hydrodynamic dispersion coefficient (Dh) is one of the most important solute transport parameters, and its correct quantification is essential to accurately estimate groundwater contamination and, analyze, assess and manage the possible risks related to cont aminated sites. When column tests are performed in soil columns with unpreserved intact structures, these methods work very well (Carmo, Antonino, Netto, & Corrêa, 2010; Magga et al, 2008) since they were developed empirically from tests in homogeneous soils and, often, non-reactive solutes In these conditions, the equilibrium advective-dispersive transport model can represent the regular behavior of the solute. It is well known that undisturbed soil columns are subject to the presence of macroporosity, dual-porosity, and other heterogeneities These characteristics may strongly affect solute transport parameter values by creating non-uniform flow fields with widely different velocities, phenomena often referred to as nonequilibrium transport, i.e. when an immobile (related with micropores) and a mobile (related with macropores) liquid phase is present (van Genuchten & Wierenga, 1976; Brusseau & Rao, 1990; Ray, Ellsworth, Valocchi, & Boast, 1997; Schwartz, Juo, & McInnes, 2000; Lamy, Lassabatere, Bechet, & Andrieu, 2009). For non-equilibrium transport, the CDE is valid in the mobile domain, and diffusion is assumed in the immobile one (van Genuchten and Wierenga, 1976)
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