The processes impacting solute transport through unsaturated porous media have been receiving renewed attention due to their relevance to the transport of emerging contaminants. A set of well-monitored and highly controlled experiments in sand columns were conducted to determine the effect of partial saturation on conservative solute breakthrough in porous media. The results suggest traditional transport parameter estimation methods inadequately account for the pore-scale processes of mass transfer to the immobile zones and the effects of partial saturation on advective transport, even for conservative tracers. Accurate estimation of these basic transport parameters is critical to evaluate the multi-phase partitioning of nonconservative solutes, as any errors in these parameters would bias the estimates of multi-phase partitioning parameters. Herein, we introduced the Mass Transfer Index (MTI), a semi-empirical approach for quantifying the impact of non-Fickian elements of pore-scale unsaturated solute transport (i.e. immobile water, tortuous flow paths, and non-uniform solute distribution), which become increasingly important as the wetting fluid saturation decreases. Importantly, this MTI was determined independently of chemically driven phase partitioning and is supported by experimental data. Based on this conceptualization, the 1-D equilibrium advection dispersion equation was modified to incorporate the MTI as a lumped parameter which quantifies resistance to (MTI > 1) or promotion of (MTI < 1) of advective solute flux. Analytical solutions to the modified advection-dispersion-reaction equation for pulse and step inputs were developed. Conservative tracer experiments were conducted in variably saturated sand columns to validate both the MTI conceptualization and the inversion method used to estimate the MTI. These experiments involved the use of X-ray absorption spectroscopy integrated with sensor-based measurements of soil moisture, temperature, and electrical conductivity for tracer breakthrough. The mathematical model developed herein adapts traditional macroscopic models of solute transport to account for the non-Fickian pore-scale transport behaviors observed in unsaturated porous media with significant advective flux.

影响溶质通过不饱和多孔介质传输的过程因其与新兴污染物传输的相关性而受到新的关注。在砂柱中进行了一系列监控良好和高度控制的实验，以确定部分饱和对多孔介质中保守溶质突破的影响。结果表明，传统的传输参数估计方法不能充分考虑质量转移到固定区域的孔隙尺度过程以及部分饱和对对流运输，即使对于保守示踪剂。这些基本传输参数的准确估计对于评估非保守溶质的多相分配至关重要，因为这些参数中的任何错误都会使多相分配参数的估计产生偏差。在此，我们介绍了传质指数 (MTI)，这是一种用于量化非菲克元素对孔隙尺度不饱和溶质传输（即固定水、曲折流径和非均匀溶质分布）影响的半经验方法，随着润湿流体饱和度的降低，这变得越来越重要。重要的是，该 MTI 独立于化学驱动的相分配而确定，并得到实验数据的支持。基于这个概念，修改一维平衡平流分散方程，将 MTI 作为集总参数，量化对 (MTI > 1) 或促进 (MTI < 1) 对流溶质通量的阻力。改进了脉冲和阶跃输入的对流-弥散-反应方程的解析解。保守示踪剂实验在可变饱和砂柱中进行，以验证 MTI 概念化和用于估计 MTI 的反演方法。这些实验涉及使用 X 射线吸收 保守示踪剂实验在可变饱和砂柱中进行，以验证 MTI 概念化和用于估计 MTI 的反演方法。这些实验涉及使用 X 射线吸收 保守示踪剂实验在可变饱和砂柱中进行，以验证 MTI 概念化和用于估计 MTI 的反演方法。这些实验涉及使用 X 射线吸收光谱与基于传感器的土壤湿度、温度和电导率测量相结合，以实现示踪剂突破。本文开发的数学模型采用传统的溶质运移宏观模型来解释在具有显着平流通量的不饱和多孔介质中观察到的非菲克孔隙尺度运移行为。