The influence of mass transfer characteristics and porous media heterogeneity on nonaqueous phase dissolution

Abstract

A two‐dimensional multiphase flow and species transport model was developed and applied to the case of nonaqueous phase liquid (NAPL) emplacement and dissolution in both homogeneous and heterogeneous porous media systems. Simulations were performed to observe dissolution rate variations and the degree of NAPL‐aqueous phase nonequilibrium as a function of two aqueous phase velocities and five forms of the NAPL‐aqueous phase mass transfer formulation. An integrated form of the Damkohler number was introduced to analyze the degree of NAPL‐aqueous phase nonequilibrium. Mass removal rates for homogeneous media were insensitive to the form of the NAPL‐aqueous phase mass transfer formulation, yielding results similar to a local equilibrium approach for all but one mass transfer formulation. This latter formulation was most sensitive to NAPL saturation and yielded significant nonequilibrium behavior, which was manifested as a decrease in NAPL dissolution rates as the NAPL volume fraction decreased. Variations in mass elution rates between homogeneous and heterogeneous media were observed, with more significant variations found for variances in porous media properties than for horizontal correlation lengths. In heterogeneous media, decreases in dissolution rates were attributed to the existence of relatively immobile regions of NAPL with saturations greater than the residual saturation of the media, so‐called NAPL pools. These results illustrate the importance of the statistical characteristics of heterogeneous porous media on NAPL distribution and dissolution processes.

STOMP Subsurface Transport Over Multiple Phases Version 2.0 Theory Guide

“…Several theoretical and experimental studies have shown that the aqueous-phase concentrations of dissolved oil can be significantly lower than equilibrium conditions for relatively large entrapped NAPL ganglia, high groundwater velocities, or low NAPL saturations [e.g., Mayer and Miller 1996]. These studies often yield formulations for mass transfer 4.60 correlations between the NAPL and aqueous phases, that relate the mass transfer coefficient, in dimensionless form as the Sherwood number Sh, to other system properties.…”

Mass-removal and mass-flux-reduction behavior for idealized source zones with hydraulically poorly-accessible immiscible liquid

“…The impact of subsurface heterogeneity and non-uniform immiscibleliquid distribution on mass-removal behavior and associated aqueous-phase concentrations (mass flux) has been examined for some time through laboratory, modeling, and field studies (e.g., Schwille, 1988;Dorgarten, 1989;Guiguer, 1991;Anderson et al, 1992;Brusseau, 1992;Guarnaccia and Pinder, 1992;Mayer and Miller, 1996;Berglund, 1997;Nelson and Brusseau, 1997;Blue et al, 1998;Powers et al, 1998;Unger et al 1998;Broholm et al, 1999;Brusseau et al, 1999;Frind et al, 1999;Zhang and Brusseau, 1999;Brusseau et al, 2000;Nambi and Powers, 2000;Saba and Illangasekare, 2000;Zhu and Sykes, 2000;Rivett et al, 2001;Sale and McWhorter, 2001;Brusseau et al, 2002;Jayanti and Pope, 2004;Lemke et al, 2004;Parker and Park, 2004;Phelan et al, 2004;Soga et al, 2004;Falta et al, 2005;Jawitz et al, 2005;Rivett and Feenstra, 2005;Fure et al, 2006;Lemke and Abriola, 2006;Brusseau et al, 2007). An early effort to quantify the relationship between contaminant mass flux reduction and mass removal, and the resultant reduction in risk, was presented by Freeze and McWhorter (1997).…”

Non–aqueous phase liquid dissolution in heterogeneous systems: Mechanisms and a local equilibrium modeling approach

“…They observed Several researchers have recently used numerical models to predict NAPL dissolution in heterogeneous media described by random distributions of the hydraulic conductivity fields [Mayer and Miller, 1996;Dekker, 1996;Berglund, 1997]. In general, increases in the variance describing the distribution of hydraulic conductivities resulted in the increased time for remediation.…”

“…Application of these relationships [e.g., Miller et al, 1990; Powers et al, 1994a] often required an extrapolation to NAPL saturations much higher than the values used in their development. Mayer and Miller [1996] noted that small differences among the various relations describing mass transfer coefficients developed from experiments with homogeneous media resulted in more significant differences in predicted aqueous phase concentrations when applied to heterogeneous systems.…”