Influence of hydraulic property correlation on predicted dense nonaqueous phase liquid source zone architecture, mass recovery and contaminant flux

Abstract

[1] Organic liquid saturation distributions resulting from a simulated tetrachloroethene (PCE) spill were generated with alternative models of spatially varying aquifer properties for a statistically homogeneous, nonuniform sand aquifer. The distributions were analyzed to quantify DNAPL source zone characteristics and then incorporated as initial conditions for simulated PCE recovery using surfactant-enhanced aquifer remediation (SEAR). The predicted evolution of the spatial distribution of DNAPL saturations or source zone ''architectures'' and associated remediation efficiencies are strongly influenced by the spatial correlation of aquifer parameters and multiphase flow constitutive relationships. Model predictions suggest that removal of 60 to 99% of entrapped PCE can reduce dissolved contaminant concentration and mass flux under natural gradient conditions by approximately two orders of magnitude. Aqueous phase contaminant flux, however, does not vary consistently as a function of the percentage of DNAPL removed, and notable differences in flux evolution were observed for models incorporating correlated versus uncorrelated capillary entry pressure and permeability fields. Simulation results demonstrate that the application of alternative models of aquifer parameter spatial variability can influence predicted DNAPL infiltration, entrapment, and recovery, even for relatively homogeneous aquifers of the type investigated here. Results also demonstrate potential benefits, in the form of reduced mass flux, accruing from partial mass removal that may not be readily predicted from analyses relying on simplified conceptual models for DNAPL source zone architecture or aquifer flow fields.

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

“…One example is the ganglia-to-pool ratio (e.g., Lemke et al, 2004;SERDP, 2006). The ganglia-to-pool ratio provides some qualitative measure of immiscible-liquid accessibility with respect to the degree of contact between flowing water and the immiscible liquid, under the assumption that immiscible liquid in regions comprising primarily "ganglia" (residual saturation) would generally be more accessible than immiscible liquid associated with pools.…”

“…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).…”

“…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). The specific relationship between mass flux reduction and mass removal has since been examined and discussed in a number of studies (e.g., Enfield et al, 2002;Rao et al, 2002;Rao and Jawitz, 2003;Stroo et al, 2003;Brooks et al, 2004;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;NRC, 2005;Fure et al, 2006;Lemke and Abriola, 2006;Brusseau et al, 2007).…”

Relationship between mass-flux reduction and source-zone mass removal: Analysis of field data

“…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). The specific relationship between mass flux reduction and mass removal has since been examined and discussed in a number of studies , Rao et al, 2002, Rao and Jawitz, 2003Stroo et al, 2003;Brooks et al, 2004; Jayanti and Pope, 2004;Lemke et al, 2004;Parker and Park, 2004;Phelan et al, 2004;Soga et al, 2004;Jawitz et al, 2005; NRC, 2005;Fure et al, 2006;Lemke and Abriola, 2006;Brusseau et al, 2007Brusseau et al, , 2008.Three simplified, prototypical relationships between mass flux reduction and mass removal, representative of systems for which the source zone is undergoing continuous water flushing, which are useful for comparative discussion are presented in Figure 1a. These relationships can be readily developed by employing a simple limiting-case analysis of the temporal contaminant-elution/mass-removal function for immiscible-liquid systems (as shown in Figure 1b), from which the mass-flux-reduction/mass-removal relationship can be Figure 1a represents the relationship for a system for which the flushing process (mass-transfer and displacement) is relatively ideal, wherein immiscible-liquid dissolution and other mass-transfer processes are under equilibrium conditions and all contaminant mass is accessible to flowing groundwater.…”

“…The fundamental concept of contaminant mass flux, its relationship to mass-removal processes and source-zone properties, and its impact on risk has long been established (e.g., Fried et al, 1979;Pfannkuch, 1984). The impact of subsurface heterogeneity, immiscibleliquid distribution, and mass-transfer dynamics on mass-removal behavior and aqueous concentration profiles (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;Powers et al, 1998;Unger et al, 1998;Broholm et al, 1999;Brusseau et al, 1999a;Frind et al, 1999;Zhang and Brusseau, 1999;Nambi and Powers, 2000;Zhu and Sykes, 2000;Brusseau et al, 2000Brusseau et al, , 2002 Saba and Illangasekare, 2000;Sale and McWhorter, 2001;Rivett et al, 2001;Enfield et al, 2002;Rao et al, 2002;Rao and Jawitz, 2003; Jayanti and Pope, 2004;Lemke et al, 2004;Parker and Park, 2004;Phelan et al, 2004;Soga et al, 2004; Falta et al, 2005a, b ;Jawitz et al, 2005; Feenstra, 2005, Fure et al, 2006;Lemke and Abriola, 2006;Suchomel and Pennell, 2006;Brusseau et al, 2007Brusseau et al, , 2008). 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 (1...…”