Degradation of chlorinated ethenes (CEs) in low conductivity layers of aquifers reduces pollution plume tailing and accelerates natural attenuation timeframes. The degradation pathways involved are often different from those in the higher conductive layers and might go undetected when only highly conductive layers are targeted in site assessments. Reactive transport model simulations (PHT3D in FloPy) were executed to assess the performance of dual carbon and chlorine compound specific stable isotope analysis (CSIA) in degradation pathway identification and quantification in a coupled physical-chemical heterogeneous virtual aquifer. Degradation rate constants were assumed correlated to the hydraulic conductivity: positively for oxidative transformation (higher oxygen availability in coarser sands) and negatively for chemical reduction (higher content of reducing solids in finer sediments). Predicted carbon isotope ratios were highly heterogeneous. They generally increased downgradient of the pollution source but the large variation across depth illustrates that monotonously increasing isotope ratios downgradient, as were associated with the oxidative component, are not necessarily a common situation when degradation is favorable in low conductivity layers. Dual carbon-chlorine CSIA performed well in assessing the occurrence of the spatially separated degradation pathways and the overall degradation, provided appropriate enrichment factors were known and sufficiently different. However, pumping to obtain groundwater samples especially from longer well screens causes a bias towards overestimation of the contribution of oxidative transformation associated with the higher conductive zones. As degradation was less intense in these highly conductive zones under the simulated conditions, overall degradation was underestimated. In contrast, in the usual case of limited CSIA data, dual CSIA plots may rather indicate dominance of chemical reduction, while oxidative transformation could go unnoticed, despite being an equally important degradation pathway.

在低电导率的含水层中氯化乙烯（CEs）的降解减少了污染羽状尾渣并加快了自然衰减的时间框架。所涉及的降解途径通常与较高导电层中的降解途径不同，当在现场评估中仅针对高导电层时，可能无法检测到。进行了反应性运输模型模拟（FloPy中的PHT3D），以评估偶合的物理化学非均质虚拟含水层中降解路径识别和定量分析中的碳和氯化合物双重稳定同位素分析（CSIA）的性能。假定降解速率常数与水力传导率相关：有利于氧化转化（较粗砂中较高的氧气利用率），不利于化学还原（较细的沉积物中还原性固体含量较高）。预测的碳同位素比高度异质。它们通常会增加污染源的下降梯度，但整个深度的较大变化说明，与低氧化层电导率下降有利时，与氧化成分相关的同位素比下降梯度单调增加并不一定是普遍情况。如果已知适当的富集因子并且足够不同，则双碳-氯CSIA在评估空间上分离的降解途径和总体降解的发生方面表现良好。然而，尤其是从较长的井网中抽水获得地下水样品，会导致偏高估计与较高导电区相关的氧化转化的贡献。由于在模拟条件下这些高导电区域的降解不那么强烈，因此总体降解被低估了。相比之下，在CSIA数据有限的通常情况下，双重CSIA图可能表示化学还原占主导地位，而氧化转化尽管是同样重要的降解途径，却可能未被注意到。