A Retardation Factor Considering Solute Transfer Between Mobile and Immobile Water in Porous Media
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A Retardation Factor Considering Solute Transfer Between Mobile and Immobile Water in Porous Media Nobuyuki Egusa 1
&
Kei Nakagawa 2 & Tatemasa Hirata 3
Received: 23 May 2019 / Accepted: 5 August 2020 # Springer Nature Switzerland AG 2020
Abstract In advective-dispersive simulations of aquifers, retardation factors using linear adsorption isotherms are commonly employed to represent the adsorption-desorption process for solutes in soil. In particular, the retardation factors that use entire pore space (total porosity) or effective pore space (effective porosity) are widely used. Although another retardation factor that describes solute transfer between mobile and immobile water in porous media has been developed, characteristics of the model have not been examined extensively. This retardation factor retains the ease of use and characteristics of the first two models; for example, its breakthrough curve is similar to those generated by models that employ total porosity for aquifers in which groundwater flow is fast and solute transport by advection and mechanical dispersion is predominant, as well as models that employ effective porosity for aquifers in which groundwater flow is slow, solute transport by molecular diffusion is predominant, and a large amount of adsorption-desorption occurs. It is therefore expected that when performing advective-dispersive simulations of aquifers with complex structures (e.g., aquifers in which sand and clay layers alternate), the reproducibility of the simulation results will be improved by using the retardation factor of this latter model, which considers solute transfer between mobile and immobile water. Keywords Advective-dispersive simulations . Adsorption-desorption process . Retardation factor . Aquifer . Total porosity . Effective porosity . Mobile water . Immobile water
1 Introduction In advective-dispersive simulations of aquifers, retardation factors using linear adsorption isotherms have been employed extensively to represent the adsorption-desorption process for solutes in soil (e.g., Bear [2]; Freeze & Cherry [8]; Kinzelbach [10]; Domenico & Schwartz [5]; Bear and Cheng [3]). The retardation factors are also adopted in widely used advective-
* Nobuyuki Egusa [email protected] Kei Nakagawa [email protected] Tatemasa Hirata [email protected] 1
Department of Systems Engineering, Wakayama University, 930 Sakaedani, Wakayama 640-8510, Japan
2
Institute of Integrated Science and Technology, Nagasaki University, 1-14 Bunkyomachi, Nagasaki 852-8521, Japan
3
Wakayama Study Center, The Open University of Japan, 1-7-20 Nishitakamatsu, Wakayama 641-0051, Japan
dispersive simulation codes, such as MT3D, RT3D, and HYDRUS2D/3D. The retardation factors can easily be applied to actual sites because they can be elucidated if the distribution coefficient is known and are thus well suited to practical advective-dispersive simulations. However, these retardation factors are those based on models that consider total porosity and those models based on effective po
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