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 (³H–³He) 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⁻¹ 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.

这项研究的目的是通过化合物特异性同位素分析（CSIA）和基于示踪剂的（³ H – ³ He）地下水测年（TGD）估算煤焦油污染含水层的水力传导率和生物降解速率常数。在两个观察井中，可以使用CSIA证明在硫酸盐还原氧化还原条件下邻源二甲苯，甲苯和萘的生物降解是由污染物源引起的。邻二甲苯的生物降解率中位数常数在0.08至0.22 a ^-1之间被估计。通过在这两个井中使用基于示踪剂的地下水测年，还可以估算水力传导率，其范围与筛分分析，抽水试验和校准的地下水流模型得出的k值相近。这些结果清楚地证明了基于示踪剂的地下水测年法在不泵送被污染的地下水的情况下确定含水层中原位水力传导率的适用性。最后，使用蒙特卡洛模拟进行灵敏度分析。这些结果表明，假定的有效孔隙度对水力传导率的估计具有很高的敏感性，而对于生物降解速率常数而言，则选择了同位素富集因子。反过来，