Evaluation of monitored natural attenuation as a bioremediation technique of benzene in the "Bois Saint-Jean" site

This study explores the applicability of Monitored Natural Attenuation (MNA) as a groundwater remediation approach in a hydrogeologically complex area contaminated with benzene. Situated in Bois Saint-Jean, this site has witnessed various remediation strategies over time, including In Situ Chemical Oxidation (ISCO), which has significantly influenced its hydrogeochemistry. The primary objective is to evaluate MNA's potential to mitigate benzene contamination, utilizing a multi-faceted approach involving major ion analysis, isotopic assessment, and microbial profiling. Encouragingly, the results reveal the presence of substantial biodegradation potential, corroborated by evidence from diverse analytical perspectives. Nevertheless, the intricate history of the site and the application of diverse remediation methods render result interpretation a multifaceted challenge. Although multiple lines of evidence collectively suggest biodegradation potential, they do not uniformly converge toward definitive conclusions. This underscores the nuanced nature of data interpretation within a dynamic subsurface environment. Sulphate-reducing conditions are identified within the aquifer, but their robustness for dissimilatory sulphate reduction-based MNA remains uncertain. Conversely, compelling evidence consistently supports benzene biodegradation via nitrate reduction, particularly through the dissimilatory nitrate reduction pathway. However, the low nitrate concentrations present in the contaminated area raise questions about the feasibility of relying solely on MNA for achieving benzene levels below regulatory thresholds. To address this challenge, a proposed enhanced bioremediation strategy involves bio-stimulation through the injection of nitrate-rich nutrients, aiming to stimulate indigenous microorganism growth and facilitate benzene degradation.