PhD defence: Field investigations and reactive transport modelling of biodegrading coal tar compounds at a complex former manufactured gas plant

Groundwater contamination by coal tar and other aromatic hydrocarbon mixtures is a global issue with significant environmental and public health implications. Coal tar, a dense liquid, can persist as a long-term source of groundwater pollution when it infiltrates the subsurface after being deposited on the ground's surface. Hydrocarbons dissolve from the coal tar into the groundwater, where they undergo complex physical, biological and chemical transformations that depend on site-specific conditions.

This study focuses on the Griftpark, a former gas manufacturing site in Utrecht, that is severely contaminated with coal tar. The site features numerous chemical and physical complexities, that lead to a lack of comprehensive field data. Our research seeks to provide valuable knowledge for risk assessments and remediation strategies for such complex sites that are common in the real world, but not often studied in the academically. 

The findings of this thesis demonstrate that employing conventional investigation techniques yields valuable information about physical, chemical and biological conditions at the site. Subsequently, we developed a numerical reactive transport model that effectively captures and qualitatively describes significant subsurface processes. The model highlights the potential effectiveness of monitored natural attenuation, a method that relies on naturally occurring processes (including degradation facilitated by microbes) to reduce contaminant concentrations, as a management option for Griftpark. Success depends on factors like the volume of contaminated soil and degradation rates.

This study underscores the value of combining field research and numerical modeling to gain insights into complex sites like Griftpark. Such insights support the transition from active management to natural attenuation, contributing to more sustainable and cost-effective groundwater remediation strategies.