When performing calculations or numerical simulations for the fate and transport of PFAS and other surface-active solutes in the vadose zone, accurately representing the relationship between the area of the air-water interfaces (A_aw) as a function of water saturation (S_w), and changes in that relationship resulting from changes in soil texture, are equally important as accurately characterizing interfacial adsorption coefficients and the concentration dependence for PFAS solutes. This is true because the magnitude of the A_aw directly governs the degree of air-water interfacial adsorption, which contributes to the transport retardation of these solutes within unsaturated porous media. Herein, a well-known thermodynamic-based model for predicting the A_aw-S_w relationship is evaluated through comparisons to literature data collected using various measurement techniques for model sands and a limited number of soils using data collected from the current published literature. This predictive model, herein termed the Leverett thermodynamic model (LTM), relies on the characterization of the soil-water retention curve (SWRC) for a given soil, using the van Genuchten (VG) equation for the pressure head-vs-S_w relationship. Therefore, methods to estimate the VG equation parameters are also compared as to the A_aw-S_w relationships predicted. Comparisons suggest that the LTM provides the best estimate of the actual A_aw-S_w relationships for water containing non-surface-active solutes. Because PFAS solutes are also surface-active, A_aw measurement methods utilizing surface-active tracers are considered to provide the most accurate representation of the A_aw-S_w relationship for these solutes. Differences between A_aw-S_w relationships derived from tracer methods and the LTM are described in relation to media surface roughness effects. Based on the available literature data, a practical empirical model is proposed to adjust the LTM prediction to account for the effects of surface roughness on the magnitude of the A_aw for surface-active solutes. Finally, example retention calculations are performed to demonstrate the sensitivity of the predicted A_aw-S_w relationship on the vadose zone transport of of a representative PFAS, perfluorooctane sulfonate.

在对渗流区 PFAS 和其他表面活性溶质的归宿和迁移进行计算或数值模拟时，准确地表示空气-水界面面积 ( A _aw ) 与水饱和度 (S _w的函数) 之间的关系)，以及由土壤质地变化引起的这种关系的变化，与准确表征界面吸附系数和 PFAS 溶质的浓度依赖性同样重要。这是真的，因为A _aw的幅度直接控制空气-水界面吸附的程度，这有助于这些溶质在不饱和多孔介质中的传输延迟。在此，通过与使用从当前出版文献中收集的数据收集的模型沙子和有限数量的土壤的各种测量技术收集的文献数据进行比较，评估了一种众所周知的基于热力学的模型，用于预测A _aw -S _w关系。这种预测模型，在此称为 Leverett 热力学模型 (LTM)，依赖于给定土壤的土壤保水曲线 (SWRC) 的表征，使用 van Genuchten (VG) 方程来计算压头-vs- S _w关系。因此，估计 VG 方程参数的方法也与预测的A _aw -S _w关系进行了比较。比较表明，对于含有非表面活性溶质的水，LTM 提供了对实际A _aw -S _{w关系的最佳估计。}由于 PFAS 溶质也是表面活性的，因此使用表面活性示踪剂的A _aw测量方法被认为可以最准确地表示这些溶质的A _aw -S _w关系。A _aw -S _w之间的差异从示踪剂方法和 LTM 导出的关系与介质表面粗糙度效应有关。基于现有的文献数据，提出了一个实用的经验模型来调整 LTM 预测，以解释表面粗糙度对表面活性溶质A _{aw大小的影响。}最后，执行示例保留计算以证明预测的 A _aw -S _w关系对代表性 PFAS、全氟辛烷磺酸的渗流区传输的敏感性。