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<p>At many petroleum release sites, subsurface contamination and cleanup strategies are significantly affected by the dissolution and migration behaviour of benzene, toluene, ethylbenzene, and xylene (BTEX) in a multi-component oil spill mixture. Designing efficient remediation techniques requires a quantitative understanding of petroleum hydrocarbon fate in the unsaturated zone. This study presents a hydrogeological reactive transport model to investigate multicomponent BTEX dissolution and biodegradation under biostimulation conditions in distributed residual and pooled source configurations. The model couples one-dimensional vertical flow with two-dimensional advection–dispersion–reaction transport using implicit discretization and sequential operator splitting to enhance numerical robustness and computational efficiency. The model explicitly integrates Raoult’s law–governed, composition-dependent dissolution, dual Monod biodegradation kinetics, volatilisation, and sorption processes to assess spatiotemporal transport dynamics under different source compositions and electron acceptor injection scenarios. Simulation results show differential dissolution behaviour of various components, benzene depletes quickly (900&#xa0;mg/L → 444&#xa0;mg/L from binary to quaternary) due to mole-fraction-controlled dissolution, whereas xylene remains because of its low solubility rate and higher retardation (80&#xa0;mg/L → 38&#xa0;mg/L). Composition-dependent dissolution further reduces benzene migration depth in binary mixtures by approximately 1.5 times compared to ternary and quaternary systems. Ternary combinations exhibit 2.5-fold and 2-fold lower ethylbenzene and xylene concentrations, respectively, than binary mixtures after 50 days. Biostimulation analysis indicates that a moderate multi–electron acceptor injection strategy (4&#xa0;mg/L O₂, 82&#xa0;mg/L NO₃⁻, 130&#xa0;mg/L SO₄²⁻) optimally sustains sequential redox-driven degradation. The proposed framework predicts multicomponent BTEX attenuation under varying source configurations in unsaturated systems.</p>

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Hydrogeological Reactive Transport Modeling of Multicomponent BTEX Dissolution under Residual and Pooled Source Configurations in Unsaturated Zone

  • 期刊论文

  • 发表日期：

    2026年7月10日

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  • Akanksha Srivastava,
  • T. I. Eldho,
  • Renu Valsala

摘要

At many petroleum release sites, subsurface contamination and cleanup strategies are significantly affected by the dissolution and migration behaviour of benzene, toluene, ethylbenzene, and xylene (BTEX) in a multi-component oil spill mixture. Designing efficient remediation techniques requires a quantitative understanding of petroleum hydrocarbon fate in the unsaturated zone. This study presents a hydrogeological reactive transport model to investigate multicomponent BTEX dissolution and biodegradation under biostimulation conditions in distributed residual and pooled source configurations. The model couples one-dimensional vertical flow with two-dimensional advection–dispersion–reaction transport using implicit discretization and sequential operator splitting to enhance numerical robustness and computational efficiency. The model explicitly integrates Raoult’s law–governed, composition-dependent dissolution, dual Monod biodegradation kinetics, volatilisation, and sorption processes to assess spatiotemporal transport dynamics under different source compositions and electron acceptor injection scenarios. Simulation results show differential dissolution behaviour of various components, benzene depletes quickly (900 mg/L → 444 mg/L from binary to quaternary) due to mole-fraction-controlled dissolution, whereas xylene remains because of its low solubility rate and higher retardation (80 mg/L → 38 mg/L). Composition-dependent dissolution further reduces benzene migration depth in binary mixtures by approximately 1.5 times compared to ternary and quaternary systems. Ternary combinations exhibit 2.5-fold and 2-fold lower ethylbenzene and xylene concentrations, respectively, than binary mixtures after 50 days. Biostimulation analysis indicates that a moderate multi–electron acceptor injection strategy (4 mg/L O₂, 82 mg/L NO₃⁻, 130 mg/L SO₄²⁻) optimally sustains sequential redox-driven degradation. The proposed framework predicts multicomponent BTEX attenuation under varying source configurations in unsaturated systems.