Karlsruhe Institute of Technology (KIT), Institute for Applied Geosciences (AGW), Kaiserstraße 12, 76131 Karlsruhe, Germany.
AECOM Deutschland GmbH, Siemensstraße 10, 63263 Neu-Isenburg, Germany.
J Contam Hydrol. 2021 Mar;238:103757. doi: 10.1016/j.jconhyd.2020.103757. Epub 2021 Jan 5.
The objective of this study is to estimate hydraulic conductivities and biodegradation rate constants in a coal-tar contaminated aquifer by compound-specific isotope analysis (CSIA) and tracer-based (H-He) groundwater dating (TGD). In two observation wells downgradient from the contaminant source in situ biodegradation of o-xylene, toluene and naphthalene under sulfate-reducing redox conditions could be demonstrated using CSIA. Median biodegradation rate constants for o-xylene ranging between 0.08 and 0.22 a were estimated. By using tracer-based groundwater dating in these two wells, hydraulic conductivities could be also estimated, which are in a similar range as k-values derived from sieve analysis, a pumping test and a calibrated groundwater flow model. These results clearly demonstrate the applicability of tracer-based groundwater dating for the determination of in situ hydraulic conductivities in aquifers without pumping contaminated groundwater. Finally, a sensitivity analysis is performed using a Monte Carlo simulation. These results indicate high sensitivities of the assumed effective porosity for the estimation of the hydraulic conductivity and the selected isotope enrichment factor for the biodegradation rate constant, respectively. Conversely, the outcome also evidently demonstrates the main limitations of the novel combined isotope approach for a successful implementation of monitored natural attenuation (MNA) at such field sites.
本研究旨在通过化合物特异性同位素分析（CSIA）和示踪剂（H-He）地下水年代测定（TGD）估算受煤焦油污染含水层的水力传导率和生物降解速率常数。在受污染源下游的两口观测井中，原位硫酸盐还原条件下可证明邻二甲苯、甲苯和萘的生物降解作用，使用 CSIA 对其进行了估算。邻二甲苯的中位生物降解速率常数范围在 0.08 到 0.22a 之间。通过在这两口井中使用示踪剂地下水年代测定法，还可以估算水力传导率，其值与筛析法、抽水试验和校准地下水流动模型得出的 k 值处于相似范围。这些结果清楚地表明，在不抽取受污染地下水的情况下，示踪剂地下水年代测定法可用于确定含水层中的原位水力传导率。最后，使用蒙特卡罗模拟进行了敏感性分析。结果表明，假设的有效孔隙度对水力传导率的估算以及所选同位素富集因子对生物降解速率常数的估算具有较高的敏感性。相反，结果还明显表明，对于在这些现场成功实施监测自然衰减（MNA），新型组合同位素方法存在主要限制。
