Experimental study of conservative solute transport in heterogeneous aquifers

Preferential flow of phosphorus and nitrogen under steady‐state saturated conditions

“…The two‐region model assumes that the liquid phase is divided into a mobile and an immobile region, and the solute could exchange between those two regions (Nsengumuremyi et al., 2021). Therefore, a conservative non‐sorbing solute is transported by a convective–dispersive process in the mobile domain and enters and leaves the immobile domain as described by a first‐order process (Casey et al., 1997; van Genuchten & Wierenga, 1976): $$$$\begin{equation}{\theta _{\mathrm{m}}}\frac{{\partial {C_{\mathrm{m}}}}}{{\partial t}} + {\theta _{{\mathrm{im}}}}{\mathrm{\;}}\frac{{\partial {C_{{\mathrm{im}}}}}}{{\partial t}} = {\theta _{\mathrm{m}}}{\mathrm{\;}}{D_{\mathrm{m}}}\frac{{{\partial ^2}{C_m}}}{{\partial {x^2}}} - q\frac{{\partial {C_{\mathrm{m}}}}}{{\partial x}}\end{equation}$$$$ $$$$\begin{equation}{\theta _{{\mathrm{im}}}}\;\frac{{\partial {C_{{\mathrm{im}}}}}}{{\partial t}} = {\mathrm{\;}}\alpha \left( {{C_{\mathrm{m}}} - {C_{{\mathrm{im}}}}} \right)\end{equation}$$$$where the subscripts m and im refer to mobile and immobile liquid regions, θ is volumetric water content (cm 3 cm −3 ), C m and C im are the concentrations in mobile and immobile regions, respectively, D m is the hydrodynamic dispersion coefficient of the mobile phase (cm 2 min −1 ), q is the Darcy flux (cm min −1 ), and α is the first‐order mass transfer coefficient for solute exchange between the mobile and immobile regions (min −1 ) (Nsengumuremyi et al., 2021; Zhao et al., 2017).…”

“…where the subscripts m and im refer to mobile and immobile liquid regions, θ is volumetric water content (cm 3 cm −3 ), C m and C im are the concentrations in mobile and immobile regions, respectively, D m is the hydrodynamic dispersion coefficient of the mobile phase (cm 2 min −1 ), q is the Darcy flux (cm min −1 ), and α is the first-order mass transfer coefficient for solute exchange between the mobile and immobile regions (min −1 ) (Nsengumuremyi et al, 2021;Zhao et al, 2017). The Br − BTCs of all the columns were modeled using the CXTFIT 2.0 computer program in inverse mode using both the CDE and MIM models to estimate the solute transport parameters (Toride, 1995).…”