Leaching of contaminants through fractured aquitards such as clayey tills may occur due to typically slow matrix advection and diffusion, or it can be dramatically enhanced in the presence of preferential flow through fractures and macropores. Sorption also plays a crucial role since it can significantly impact contaminant leaching and residence times. These different mass‐transfer mechanisms imply a distinct transport behavior and very different time scales for contaminant leaching toward underlying aquifer systems. However, the prevalent controls on contaminant transport and their effects are difficult to assess. This paper shows a detailed characterization of flow and transport processes under water‐saturated conditions in two large undisturbed columns (LUCs) collected from two visually similar fractured/macroporous clayey tills typical for the Northern hemisphere. Flow‐through tracer and pesticide experiments revealed a contrasting transport behavior. In one column, transport through fractures/macropores was dominant, whereas matrix advection and diffusion had a distinct influence on solute transport in the other column. Detailed 3D discrete‐fracture‐matrix models were developed to illuminate prevalent controls on contaminant transport and to quantitatively interpret the flow‐through experiments with a minimal number of fitting parameters. Nonequilibrium sorption kinetics were included to reproduce the transport behavior of the considered pesticide. The parameters determined from the two LUC experiments were integrated in a vertical cross‐section model to investigate the influence of varying fracture properties on vertical solute transport through surficial clayey till aquitards. The analysis showed that small fracture apertures in deeper parts of the aquitard could substantially prolong solute migration times and control solute fluxes.

中文翻译：

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示踪剂和农药通过破裂的黏土耕层的运输：大型原状柱实验和基于模型的解释

通过典型的缓慢的基质对流和扩散，可能发生通过裂缝的阿奎塔德（例如黏土小块）的污染物浸出，或者在存在优先通过裂缝和大孔的流动的情况下，污染物的浸出可能会大大增强。吸附也起着至关重要的作用，因为它会显着影响污染物的浸出和停留时间。这些不同的传质机制意味着不同的传输行为和非常不同的时间尺度，污染物朝着下面的含水层系统渗出。但是，对污染物迁移及其影响的普遍控制措施很难评估。本文显示了在水饱和条件下从两个视觉上相似的北半球典型裂缝/巨孔黏土层中收集的两个大型无扰动色谱柱（LUC）中的流动和输运过程的详细特征。流通式示踪剂和农药实验显示出相反的运输行为。在一个色谱柱中，主要通过裂缝/大孔输送，而在另一色谱柱中，基质的对流和扩散对溶质的输​​送有明显的影响。开发了详细的3D离散断裂矩阵模型，以阐明对污染物传输的普遍控制，并以最少数量的拟合参数来定量解释流通实验。包括非平衡吸附动力学来重现所考虑农药的运输行为。将两个LUC实验确定的参数整合到垂直横截面模型中，以研究不同的裂缝性质对垂直溶质从表层黏土直到阿奎塔德的迁移的影响。分析表明，在阿奎塔尔较深部分的小裂隙孔可以大大延长溶质的迁移时间并控制溶质通量。