Two of the most important retention processes for per- and polyfluoroalkyl substances (PFAS) in groundwater likely are sorption and matrix diffusion. The objective of this study was to model concentration and mass discharge of one PFAS, perfluorooctane sulfonate (PFOS), with matrix diffusion processes incorporated using data from a highly chemically- and geologically-characterized site. When matrix diffusion is incorporated into the REMChlor-MD model for PFOS at this research site, it easily reproduces the field data for three key metrics (concentration, mass discharge, and total mass). However, the no-matrix diffusion model produced a much poorer match. Additionally, after about 40 years of groundwater transport, field data and the REMChlor-MD model both showed the majority (80%) of the measured PFOS mass that exited the source zones was located in downgradient low permeability zones due to matrix diffusion. As such, most of the PFOS mass is not available to immediately migrate downgradient via advection in the more permeable sands at this site, which has important implications for monitored natural attenuation (MNA). Plume expansion over the next 50 years is forecasted to be limited, from a 350-m plume length in 2017 to 550 m in 2070, as matrix diffusion will attenuate groundwater plumes by slowing their expansion. This phenomenon is important for constituents that do not degrade, such as PFOS, compared to those susceptible to degradation. Overall, this work shows that matrix diffusion is a relevant process in environmental PFAS persistence and slows the rate of plume expansion over time.

地下水中全氟烷基物质和多氟烷基物质 ( PFAS ) 的两个最重要的保留过程可能是吸附和基质扩散。本研究的目的是模拟一种全氟辛烷磺酸全氟辛烷磺酸的浓度和质量排放（PFOS），使用来自高度化学和地质特征站点的数据结合矩阵扩散过程。当在该研究地点将基质扩散纳入 PFOS 的 REMChlor-MD 模型时，它可以轻松再现三个关键指标（浓度、质量排放和总质量）的现场数据。然而，无矩阵扩散模型产生的匹配要差得多。此外，经过大约 40 年的地下水输送，现场数据和 REMChlor-MD 模型均显示，由于基质扩散，流出源区的 PFOS 质量的大部分（80%）位于下坡度低渗透区。因此，大部分 PFOS 质量无法立即通过平流在该地点的渗透性更强的砂岩中向下迁移，这对监测具有重要意义自然衰减（MNA）。预计未来 50 年的羽流扩张将受到限制，从 2017 年的 350 米羽流长度到 2070 年的 550 米，因为基质扩散将通过减缓其扩张来减弱地下水羽流。与易降解的成分相比，这种现象对于不降解的成分（例如全氟辛烷磺酸）很重要。总体而言，这项工作表明，基质扩散是环境 PFAS 持久性的一个相关过程，并且随着时间的推移减缓了羽流膨胀的速度。