Abstract: Volatile organic compounds (VOCs) are the most common and critical pollutants in contaminated sites. As representative VOCs, benzene series (BTEX) are characterized by high volatility, strong toxicity, and chemical reactivity. Their multiphase migration and transformation across gas-liquid-non-aqueous phase liquid (NAPL) interfaces significantly increase the complexity of risk assessment and remediation. Enhancing the precision of BTEX multiphase transport models through parameter sensitivity analysis can provide a reference for the treatment of BTEX contaminated sites in China. This study focuses on a typical contaminated site featuring complex loose porous media and selects benzene and ethylbenzene as target pollutants. Numerical simulations of multiphase transport were conducted using the TMVOC model, followed by local and global sensitivity analyses of key parameters. The local sensitivity analyses ranks the key parameters affecting pollutant concentration as follows: leakage rate (Q) > porosity (n) > permeability (k) > molecular diffusion coefficient (D). The three parameters with large sensitivity index, leakage rate, porosity and permeability, are divided into three layers to conduct global sensitivity analysis through uniform design method, and all parameters are respectively analyzed by regression with the total mass fraction of VOCs in the aqueous phase(XVOCW). The sensitivity of the parameters is ranked as Q>n₃>k₂>n₂>n₁>k₃, among which the parameters that have a significant impact on XVOCW are leakage rate Q, gravel permeability k₂, silt porosity n₁, gravel porosity n₂ and mudstone porosity n₃. The result of integrating and sorting according to the parameter categories is Q>n>k, which is consistent with the result of the local sensitivity analysis.

Key words: numerical simulation of multiphase flow, BTEX, sensitivity analysis, TMVOC