Scenario-based modelling of mass transfer mechanisms at a petroleum contaminated field site-numerical implications

• Published in: Journal of environmental management 2016-06, Vol.175, p.9-19
• Main Authors: Vasudevan, M., Nambi, Indumathi M., Suresh Kumar, G.
• Format: Article
• Language: English
• Subjects: Biodegradation; Biodegradation, Environmental; Environmental Pollution - analysis; Fuel composition; Groundwater - chemistry; Groundwater pollution; India; Mass transfer; Models, Theoretical; Petroleum; Petroleum - analysis; Petroleum hydrocarbons; Polycyclic aromatic hydrocarbons; Polycyclic Aromatic Hydrocarbons - chemistry; Raoult's law; Residual saturation; Risk assessment; Simulation; Water Movements; Water Pollutants, Chemical - analysis; Water Pollutants, Chemical - chemistry
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2016.03.009

Knowledge about distribution of dissolved plumes and their influencing factors is essential for risk assessment and remediation of light non-aqueous phase liquid contamination in groundwater. Present study deals with the applicability of numerical model for simulating various hydro-geological scenarios considering non-uniform source distribution at a petroleum contaminated site in Chennai, India. The complexity associated with the hydrogeology of the site has limited scope for on-site quantification of petroleum pipeline spillage. The change in fuel composition under mass-transfer limited conditions was predicted by simultaneously comparing deviations in aqueous concentrations and activity coefficients (between Raoult's law and analytical approaches). The effects of source migration and weathering on the dissolution of major soluble fractions of petroleum fuel were also studied in relation to the apparent change in their activity coefficients and molar fractions. The model results were compared with field observations and found that field conditions were favourable for biodegradation, especially for the aromatic fraction (benzene and toluene (nearly 95% removal), polycyclic aromatic hydrocarbons (up to 65% removal) and xylene (nearly 45% removal). The results help to differentiate the effect of compositional non-ideality from rate-limited dissolution towards tailing of less soluble compounds (alkanes and trimethylbenzene). Although the effect of non-ideality decreased with distance from the source, the assumption of spatially varying residual saturation could effectively illustrate post-spill scenario by estimating the consequent decrease in mass transfer rate. •Differentiating rate-limited dissolution from the effect of change in composition.•Effect of non-ideal dissolution decreased with distance from the source.•Modification in mass transfer by including spatially varying residual saturation.•Effect of source migration and weathering related to apparent change in composition.