Experimental Research on the Thresholds of Scale-Dependent Dispersivity of Solute Transport

Ruigang Zhang,Dun Wu,Yong Liu,Wenyong Zhang,Mingxi Chu,Zhi Dou

doi:10.2113/2021/7998907

Ruigang Zhang, Dun Wu + Show 4 more

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https://doi.org/10.2113/2021/7998907

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Abstract

Abstract The conventional advection-dispersion equation (ADE) has been widely used to describe the solute transport in porous media. However, it cannot interpret the phenomena of the early arrival and long tailing in breakthrough curves (BTCs). In this study, we aim to experimentally investigate the behaviors of the solute transport in both homogeneous and heterogeneous porous media. The linear-asymptotic model (LAF solution) with scale-dependent dispersivity was used to fit the BTCs, which was compared with the results of the ADE model and the conventional truncated power-law (TPL) model. Results indicate that (1) the LAF model with linear scale-dependent dispersivity could better capture the evolution of BTCs than the ADE model; (2) dispersivity initially increases linearly with the travel distance and is stable at some limited value over a large distance, and a threshold value of the travel distance is provided to reflect the constant dispersivity; and (3) compared with the TPL model, both the LAF and ADE models can capture the behavior of solute transport as a whole. For fitting the early arrival, the LAF model is less than the TPL; however, the LAF model is more concise in mathematics and its application will be studied in the future.

Highlights

Predicting the solute transport in porous or fractured media is essential for groundwater quality control and pollution remediation
Moradi and Mehdinejadiani [10] compared the fractional dispersion coefficient (Df ) in the space fractional advection-dispersion equation (s-FADE) with the dispersion coefficient (D) in the advectiondispersion equation (ADE) by six solute transport experiments at three flow rates, and they concluded that the s
This study mainly focuses on the investigation of 1D solute transport in porous media

Summary

Introduction

Predicting the solute transport in porous or fractured media is essential for groundwater quality control and pollution remediation. The advection-dispersion equation (ADE) with constant dispersivity, typically adopted to model and explain the solute transport process in groundwater system, does not satisfactorily describe the underground solute transport in many cases [1,2,3]. In order to predict solute transport in groundwater system and solve the problem of the scale-dependent dispersivity, many numerical models were developed. Pickens and Grisak [9] used a finite element (linear triangular) solute transport model to handle scale-dependent dispersion, which provided a continuous description of the dispersive process over all travel distances and times. The model was successfully applied to previous tracer test results and exhibited a scale-dependent dispersion in heterogeneous porous media. Moradi and Mehdinejadiani [10] compared the fractional dispersion coefficient (Df ) in the space fractional advection-dispersion equation (s-FADE) with the dispersion coefficient (D) in the advectiondispersion equation (ADE) by six solute transport experiments at three flow rates, and they concluded that the s-

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