RPG: Nonionic Organic Pollutant Sorption Mechanisms in Natural Clay-Rich Aquitards

摘要 EAR-9506403 Allen-King 富含粘土的弱透水层和人造粘土衬层为污染物迁移提供了低渗透性屏障，并且由于对底层地下水资源提供了一定程度的保护，因此可用于危险废物处理。透水层基质中的吸附作用会阻碍传输，并为随着时间的推移吸收和释放有机污染物提供一个汇。然而，富含粘土的弱透水层中的吸附机制尚不清楚。例如，最近的观察表明，现有方法明显低估了几种富含粘土且碳相对低碳的弱透水层中全氯乙烯（PCE）的吸附情况。据推测，在天然、低分数有机物含量 (foc) 和富含粘土的弱透水层中，有机质是非离子有机化合物 (NIOC)（例如四氯乙烯）的主要吸附介质。拟议研究的目标是：（1）确定有机碳和/或粘土矿物直接吸附的相对重要性； （2）确定有机物氧化和分布的差异对吸附量和形式的影响；（3）测试相似溶质之间的竞争吸附。利用规划拨款，将使用两个具有相似粘土矿物学和焦点但 PCE 吸附行为明显不同的对比天然弱透水样品来测试该假设。研究结果将为吸附机制提供深入见解，并为建立更全面研究的最佳方法奠定基础。目的是提高对天然低碳地质样品中 NIOC 吸附的机理理解，从而能够更准确地评估污染物迁移，以实现地下水资源保护和修复。

ABSTRACT EAR-9506403 Allen-King Clay-rich aquitards and constructed clay-liners provide low permeability barriers to contaminant migration and are used for hazardous waste disposal because of the margin of protection provided to underlying groundwater resources. Sorption in the aquitard matrix retards transport and provides a sink for uptake and release of organic contaminant mass over time. However, the mechanisms of sorption in clay-rich aquitards are not well understood. Recent observations, for example, have shown that perchloroethene (PCE) sorption in several natural clay-rich and relatively low carbon aquitards is significantly under-predicted by existing methods. It is hypothesized that in natural, low-fraction organic content (foc) and clay-rich aquitards, organic matter is the primary sorbing medium for nonionic organic compounds (NIOCs) such as PCE. The objectives of the proposed research are: (1) to determine the relative importance of organic carbon and/or direct sorption to clay minerals; (2) to determine the effects of differences in oxidation and distribution of organic matter on the magnitude and form of sorptionO and (3) to test for competitive sorption between similar solutes. Using the Planning Grant, the hypothesis will be tested using two contrasting natural aquitard samples with similar clay mineralogy and foc, but markedly different PCE sorption behavior. The results will provide insights into sorption mechanisms and bases for establishing the best methodologies for a more comprehensive study. The objective is to improve mechanistic understanding of NIOC sorption in natural low-carbon geologic samples, thereby allowing more accurate assessments of contaminant transport for groundwater resource protection and remediation.