Remediation of DNAPLs in saturated porous media: Cosolvent flushing and sherwood correlation

Abstract

The contamination of the subsurface by the accidental release of organic contaminants in the form of non-aqueous phase liquids (NAPLs) is a widespread and challenging environmental problem. However, there is lack of cost effective technologies for the remediation of groundwater systems contaminated with NAPLs. A key process influencing the effectiveness of NAPL remediation is the interphase mass transfer which is the transfer of components across the interface separating the aqueous and NAPL phases. This study evaluates the use of cosolvent flushing for the removal of NAPLs from saturated porous media. Intermediate-scale laboratory experiments were conducted to investigate the impact of cosolvent content, flow velocity, and pumping pattern on cosolvent enhanced NAPL dissolution. Results demonstrated the importance of the flushing solution content and the flow characteristics on NAPL removal. The experimental results were also modeled using multiphase flow simulator. The model results highlighted the significance of the interphase mass transfer in NAPL remediation and the need to model this process as a non-equilibrium kinetic process. To further elucidate the factors influencing the interphase mass transfer mechanism, a series of controlled dissolution experiments from pooled NAPL were also conducted. The interpretation of the experiments was performed using a 2D pore network model in addition to a simplified 1D analytical solution. Results showed that the analytical solution which ignores lateral transport, under-estimates the interphase mass transfer coefficient. Based on the estimated mass transfer coefficients, improved non-lumped Sherwood correlations were developed. These correlations can be used in future modeling studies involved pooled NAPL configurations.