Xenobiotic organic compounds can be discharged from contaminated groundwater inflow and may seep into streams from multiple pathways with very different dynamics, some not fully understood. In this study, we investigated the spatio‐temporal variation of chlorinated ethenes discharging from a former industrial site (with two main contaminant sources, A and B) into a stream system in a heterogeneous clay till setting in eastern Denmark. The investigated reach and near‐stream surroundings are representative of peri‐urban settings, with a mix of high channel alteration and more natural stream environment. We therefore propose an approach for risk assessing impacts arising from such complex contamination patterns, accounting for potential spatio‐temporal fluctuations and presence of multiple pathways. Our study revealed substantial variations in pathway contributions and overall contaminant mass discharge to the stream. Variable contaminant contributions arising from both groundwater seepage and urban drains were identified in the channelized part of the north stream, primarily from source A. Furthermore, variations in the hyporheic and shallow groundwater flows were found to enhance contaminant transport from source B. These processes result in an increase of the overall mass of contaminant discharged, correlating with the channels' flow. Thus, an in‐stream control plane approach was found to be an effective method for integrating multiple and variable discharge contributions quantitatively, although information on specific contaminant sources is lost. This study highlights the complexity and variability of contaminant fluxes occurring at the interface between groundwater and peri‐urban streams, and calls for the consideration of these variations when designing monitoring programs and remedial actions for contaminated sites with the potential to impact streams.

中文翻译：

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排放到周边城市河流的污染物时空变化的证据

异源生物有机化合物可从受污染的地下水流入中排出，并可能以多种不同的动力学方式从多种途径渗入流中，其中有些尚未完全了解。在这项研究中，我们调查了从以前的工业场所（具有两个主要污染源，A和B）排放到异质粘土中的流系统中的氯乙烯的时空变化，直至丹麦东部。所调查的河段和近溪流环境代表了城市周边环境，其中包括高水道变化和更自然的溪流环境。因此，我们提出了一种风险评估方法，用于评估这种复杂的污染模式所产生的影响，并考虑潜在的时空波动和多种途径的存在。我们的研究表明，途径贡献和向河流排放的污染物总量有很大变化。在北流的渠道化部分中，主要是源A识别出了由地下水渗漏和城市排水所引起的可变污染物贡献。此外，发现流变和浅层地下水流量的变化会增强源B的污染物迁移。这些过程的结果排放污染物总量的增加，与通道流量相关。因此，尽管丢失了有关特定污染物源的信息，但在流控制平面方法被认为是定量地综合多个排放变量的有效方法。