GSI Environmental Inc., Houston, TX, United States.
Naval Facilities Engineering and Expeditionary Warfare Center, Port Hueneme, CA 93041, USA.
J Contam Hydrol. 2022 May;247:103986. doi: 10.1016/j.jconhyd.2022.103986. Epub 2022 Mar 5.
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.
对于地下水而言，全氟和多氟烷基物质（PFAS）最重要的两个保留过程可能是吸附和基质扩散。本研究的目的是使用高度化学和地质特征化的地点的数据，通过包含基质扩散过程来模拟一种 PFAS（全氟辛烷磺酸，PFOS）的浓度和质量排放量。当将基质扩散纳入到研究点的 REMChlor-MD 模型中用于 PFOS 时，它可以轻松再现三个关键指标（浓度、质量排放量和总质量）的现场数据。然而，没有基质扩散的模型匹配效果则差得多。此外，在地下水迁移大约 40 年后，现场数据和 REMChlor-MD 模型都表明，从源区排出的测量 PFOS 质量的大部分（80％）位于由于基质扩散而处于下游低渗透性区域。因此，在该地点，大部分 PFOS 质量由于基质扩散而无法通过更具渗透性的砂层立即向下游迁移，这对监测自然衰减（MNA）具有重要意义。预计在未来 50 年内，由于基质扩散会减缓地下水羽流的扩展，羽流的扩展将受到限制，羽流长度从 2017 年的 350 米扩展到 2070 年的 550 米。与易降解的物质相比，对于不易降解的物质（如 PFOS），这种现象非常重要。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，并随着时间的推移减缓了羽流扩展的速度。
