Point sources with contaminants, such as chlorinated solvents, per- and polyfluoroalkyl substances (PFAS), or pesticides, are often located in low-permeability aquitards, where they can act as long-term sources and threaten underlying groundwater resources. We demonstrate the use of a 3D numerical model integrating comprehensive hydrogeological and contamination data to determine the contaminant mass discharge (CMD) from an aquitard into the underlying aquifer. A mature point source with a dissolved chlorinated solvent in a clayey till is used as an example. The quantitative determination is facilitated by model calibration to high-resolution vertical concentration profiles obtained by direct-push sampling techniques in the aquifer downgradient of the contaminant source zone. The concentration profiles showed a plume sinking with distance from the source characteristic for such aquitard/aquifer settings. The sinking is caused by the interplay between infiltrating water and horizontal groundwater flow. The application of 3D solute transport modeling on high-resolution profiles allowed for determining the infiltration rate, the hydraulic conductivity in the aquitard, and, ultimately, the CMD. Different source zone conceptualizations demonstrate the potential effects of fractures and sorption in source zones in aquitards on CMD development. Fractures in the aquitard had a minor influence on the current CMD determined with the presented approach. Still, fractures with hydraulic apertures larger than 10 μm were crucial for the temporal development of the CMD and plume. A thorough characterization of the source zone conditions combined with high-resolution concentration profiles and detailed modeling is valuable for shedding light on the probable future development of groundwater contamination arising from sources in aquitard/aquifer settings and evaluating remedial actions.

含有污染物的点源，例如氯化溶剂、全氟烷基物质和多氟烷基物质 (PFAS) 或农药，通常位于低渗透性的弱透水层中，它们可以作为长期污染源并威胁底层地下水资源。我们演示了如何使用集成综合水文地质和污染数据的 3D 数值模型来确定从弱透水层到底层含水层的污染物质量排放 (CMD)。以在粘土池中溶解有氯化溶剂的成熟点源为例。通过对污染物源区含水层降梯度中的直推采样技术获得的高分辨率垂直浓度剖面进行模型校准，有利于定量测定。浓度分布显示，对于此类弱透水层/含水层设置，羽流随着距源的距离而下沉。下沉是由渗透水和水平地下水流之间的相互作用引起的。在高分辨率剖面上应用 3D 溶质输运模型可以确定渗透率、弱透水层的水力传导率，并最终确定 CMD。不同的源区概念表明了弱水层源区的裂缝和吸附对 CMD 发展的潜在影响。弱透水层的裂缝对用所提出的方法确定的当前 CMD 影响较小。尽管如此，水力孔径大于 10 μm 的裂缝对于 CMD 和羽流的时间发展至关重要。对源区条件的全面表征，结合高分辨率浓度剖面和详细建模，对于揭示弱透水层/含水层环境中源头地下水污染的未来可能发展以及评估补救行动具有重要意义。