Anderson Katelyn A, Garza-Rubalcava Uriel, Widdowson Mark A, Suchomel Eric J, Cápiro Natalie L, Pennell Kurt D
School of Engineering, Brown University, Providence, RI 02912, USA.
Charles E. Via Jr. Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA 24061, USA.
J Hazard Mater. 2025 Aug 15;494:138500. doi: 10.1016/j.jhazmat.2025.138500. Epub 2025 May 5.
Monitored natural attenuation (MNA) is widely used to manage groundwater plumes with persistent chlorinated solvents exceeding regulatory standards. In heterogeneous aquifers, accumulation and release of these contaminants can impact MNA's effectiveness. Research often focuses on tetrachloroethene (PCE) and trichloroethene (TCE), but incomplete reductive dichlorination can lead to cis-1,2-dichloroethene (DCE) accumulation. This study investigates rate-limited sorption-desorption processes governing DCE release from lower-permeability media. Batch reactor studies with two soils established equilibrium linear distribution coefficients (K) of 0.15 mL/g and 0.25 mL/g. Column transport studies were then completed using the same soils at two flow rates with flow interruptions to assess rate-limited desorption. A numerical simulator with a "two-site" sorption model was used to fit the effluent concentration data, yielding parameters for the fraction of sorption sites at instantaneous equilibrium (f) and the rate of sorption for time-dependent sites (k) ranging from 0.2 to 0.6 and 0.4-2 1/day, respectively. Soils with small f and k exhibit prolonged DCE release, which can benefit MNA at sites with an active DCE-to-ethene dechlorinating microbial community. These persistent, low concentrations of DCE can support microbial reductive dichlorination by providing sufficient residence time for the complete biodegradation to non-toxic ethene. This work emphasizes the importance of developing conceptual site models that capture sorption-desorption processes contributing to natural attenuation of chlorinated solvents in heterogeneous aquifers.
监测自然衰减（MNA）被广泛用于管理含有超过监管标准的持久性氯化溶剂的地下水羽流。在非均质含水层中，这些污染物的积累和释放会影响MNA的有效性。研究通常集中在四氯乙烯（PCE）和三氯乙烯（TCE）上，但不完全还原脱氯会导致顺式1,2 - 二氯乙烯（DCE）积累。本研究调查了控制DCE从低渗透介质中释放的限速吸附 - 解吸过程。对两种土壤进行的间歇式反应器研究确定了平衡线性分配系数（K）分别为0.15 mL/g和0.25 mL/g。然后使用相同的土壤在两种流速下并设置流量中断来完成柱体传输研究，以评估限速解吸。使用具有“双位点”吸附模型的数值模拟器来拟合流出物浓度数据，得出瞬时平衡时吸附位点分数（f）和随时间变化位点的吸附速率（k）的参数，范围分别为0.2至0.6和0.4 - 2 1/天。具有小f和k的土壤表现出DCE的长时间释放，这对于具有活跃的DCE - 乙烯脱氯微生物群落的场地的MNA可能有益。这些持续存在的低浓度DCE可以通过为完全生物降解为无毒乙烯提供足够的停留时间来支持微生物还原脱氯。这项工作强调了开发概念性场地模型的重要性，该模型能够捕捉有助于非均质含水层中氯化溶剂自然衰减的吸附 - 解吸过程。
