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

Abstract

The magnitude of contaminant mass flux reduction associated with a specific amount of contaminant mass removed is a key consideration for evaluating the effectiveness of a source-zone remediation effort. Thus, there is great interest in characterizing, estimating, and predicting relationships between mass flux reduction and mass removal. Published data collected for several field studies were examined to evaluate relationships between mass flux reduction and sourcezone mass removal. The studies analyzed herein represent a variety of source-zone architectures, immiscible-liquid compositions, and implemented remediation technologies. There are two general approaches to characterizing the mass-flux-reduction/mass-removal relationship, end-point analysis and time-continuous analysis. End-point analysis, based on comparing masses and mass fluxes measured before and after a source-zone remediation effort, was conducted for 21 remediation projects. Mass removals were greater than 60% for all but three of the studies. Mass flux reductions ranging from slightly less than to slightly greater than one-to-one were observed for the majority of the sites. However, these single-snapshot characterizations are limited in that the antecedent behavior is indeterminate. Time-continuous analysis, based on continuous monitoring of mass removal and mass flux, was performed for two sites, both for which data were obtained under water-flushing conditions. The reductions in mass flux were significantly different for the two sites (90% vs. ~8%) for similar mass removals (~40%). These results illustrate the dependence of the mass-flux-reduction/mass-removal relationship on source-zone architecture and associated mass-transfer processes. Minimal mass flux reduction was observed for a system wherein mass removal was relatively efficient (ideal mass transfer and displacement). Conversely, a significant degree of mass flux reduction was observed for a site wherein mass removal was inefficient (nonideal mass transfer and displacement). The mass-flux-reduction/mass-removal relationship for the latter site exhibited a multi-step behavior, which cannot be predicted using some of the available simple estimation functions. KeywordsMass Flux; DNAPL; Source Zone; Remediation INTRODUCTIONThe contamination of groundwater by hazardous organic chemicals and the associated risks to human health and the environment are issues of great importance. One of the most critical issues associated with hazardous waste sites is the potential presence of immiscible-liquid contamination in the subsurface. Immiscible liquids, such as chlorinated solvents, creosote, NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript coal tars, and fuels, once introduced into the subsurface become entrapped, and serve as long-term sources of contamination. The presence of immiscible-liquid contamination at a site can greatly impact the costs and time required for site remediation. It is widely acknowledged that cleaning up sites contaminated with denser-tha...

Effect of Enhanced-Solubilization Agents on Dissolution and Mass Flux from Uniformly Distributed Immiscible Liquid Trichloroethene (TCE) in Homogeneous Porous Media

“…4b). Other researchers have used similar mass removal approaches to investigate source-zone depletion and resulting mass flux behavior for a number of applications (Rao et al 2002;Zhu and Sykes 2004;Falta et al 2005;Jawitz et al 2005;Brusseau et al 2008;DiFilippo and Brusseau 2008). The mass flux reduction results of all five flushing experiments and the overall rate of decline (slope of MFR curves) for each flushing agent are presented in Fig.…”

“…Several studies have examined specific relationships between mass flux reduction and mass removal Rao and Jawitz 2003;Brooks et al 2004;Lemke et al 2004;Parker and Park 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 2007Brusseau et al , 2008Basu et al 2008;DiFilippo and Brusseau 2008;Marble et al 2008;Carroll and Brusseau 2009). Many of these studies have generally categorized mass flux behavior as ideal or nonideal based on the degree of physical heterogeneity of the porous medium (or aquifer) and/or by the distribution of immiscible liquid in the system.…”

“…Evaluating the enhanced-solubilization experiments based on consistent comparison is critical for predicting contaminant transport, conducting risk assessments, and implementing appropriate remediation strategies for sites contaminated by immiscible liquids. Further knowledge, combined from previous studies within more complex systems (e.g., Boving and Brusseau 2000;Brusseau et al 2002;Lemke et al 2004;Fure et al 2006;Basu et al 2008;Brusseau et al 2007Brusseau et al , 2008DiFilippo and Brusseau 2008;Marble et al 2008;Carroll and Brusseau 2009) and newly developed experiments, will allow for a better understanding of the processes that control mass flux behavior, elution behavior, and mass removal from remediation systems utilizing enhanced-solubilization flushing.…”

ZVI-Clay remediation of a chlorinated solvent source zone, Skuldelev, Denmark: 2. Groundwater contaminant mass discharge reduction

“…Established in situ remediation technologies most often only result in partial source mass depletion (DiFilippo and Brusseau, 2008;McGuire et al, 2006). While the in situ remediation technologies may have an immediate impact on contaminant mass in the source zone, the down-gradient response may be less evident.…”

“…The coupling of source mass depletion and downgradient mass discharge has been investigated in a number of studies including mathematical modeling, bench-scale studies and field investigations (e.g., Basu et al, 2006;Brooks et al, 2008;Chambon et al, 2010;Chen and Jawitz, 2009;Christ et al, 2010;DiFilippo and Brusseau, 2008;Falta, 2008;Falta et al, 2005aFalta et al, , 2005bFure et al, 2006;Jawitz et al, 2005;Kaye et al, 2008;Liang and Falta, 2008;Newell and Adamson, 2005;Zhu and Sykes, 2004). Various approaches have been suggested for the assessment of the relationship between the down-gradient mass discharge and the mass depletion in the source zone; one of these approaches is a simple analytical power law model (Basu et al, 2006;Falta et al, 2005a;Zhu and Sykes, 2004).…”