Characterization of Contaminant Evolution in DNAPL Source Zone

This technical report presents a high-resolution hydrogeochemical characterization of a fractured sedimentary rock aquifer that has been contaminated for over 50 years by a dense non-aqueous phase liquid (DNAPL). The study indicates significant temporal and vertical variability in contaminant composition within the source zone, with samples revealing a homogeneous mixture of chlorinated ethenes, ethanes, methanes, ketones, and aromatic hydrocarbons. The primary objective was to elucidate the influence of degradation and mass transfer processes on natural source zone depletion (NSZD). The research involved quantifying volatile organic compound (VOC) concentrations from depth-discrete rock core samples and comparing these with groundwater concentrations to assess contaminant mass distribution. Results indicate an 80 to 95% reduction in total mass since 2002, with a notable persistence of ketones in certain depth intervals. The findings highlight the role of microbial activity and degradation pathways in contaminant dynamics, which are critical for informing remediation strategies.