Integrated Modeling of Transient Biogeochemical and Isotopic Signatures in a Complex DNAPL Contaminated Aquifer

Dense non-aqueous phase liquid (DNAPL) contaminations commonly pose a long-term threat to the environment and human health. The frequently reported low cost-benefits of active remediation strategies make passive approaches, i.e., monitored natural attenuation (MNA), an attractive option to deal with DNAPL impacted sites. In such cases modeling of reactive transport can be a crucial element for assessing case-specific natural attenuation potentials but also to develop generic process understanding. In this study a comprehensive quantitative framework that integrates all key physical and chemical processes that affect the fate of typical coal tar compounds in ground water systems was developed. The model was then applied for the simulation and integrated interpretation of observed hydrochemical and compound specific isotope data from a well documented coal-tar contamination, which originated over 60 years ago at a former wood treatment plant in Germany. The modeling outcomes illustrate how diverse and transient the fate of individual compounds can evolve as a result of the source depletion dynamics and the widely varying physico-chemical properties of coal-tar constituents. This modeling study suggests that a holistic understanding of the governing processes that control the effectiveness of natural attenuation is required before it is implemented as a remediation strategy.