Application of VLEACH to Vadose Zone Transport of VOCs at an Arizona Superfund Site

Rosenbloom, Jeff; Mock, Peter; Lawson, Peter W.; Brown, James G.; Turin, H.

doi:10.1111/j.1745-6592.1993.tb00085.x

Cited by 22 publications

(15 citation statements)

References 8 publications

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“…The use of contaminant-mass-discharge or mass-flux measurements to characterize site conditions and assess remediation performance is becoming more widespread (Rosenbloom et al, 1993; Butcher and Gauthier, 1994; Freeze and McWhorter, 1997; DiGiulio et al, 1999; Einarson and Mackay, 2001; Rao et al, 2002; Newell et al, 2003; Bockelmann et al, 2003; Stroo et al, 2003; Brooks et al, 2004; Soga et al, 2004; NRC, 2005; SERDP, 2006; Brusseau et al, 2007; Basu et al, 2009; ITRC, 2010; Brusseau et al, 2011a, 2011b). Almost all applications to date have been based on obtaining one or two discrete measurements of contaminant mass discharge (e.g., collected before and after a remedial action), using multi-point transects or short-term pumping tests that are often applied within the contaminant plume.…”

Section: Introductionmentioning

confidence: 99%

Characterizing long-term contaminant mass discharge and the relationship between reductions in discharge and reductions in mass for DNAPL source areas

Brusseau

Matthieu

Carroll

et al. 2013

Journal of Contaminant Hydrology

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The objective of this study was to characterize the temporal behavior of contaminant mass discharge, and the relationship between reductions in contaminant mass discharge and reductions in contaminant mass, for a very heterogeneous, highly contaminated source-zone field site. Trichloroethene is the primary contaminant of concern, and several lines of evidence indicate the presence of organic liquid in the subsurface. The site is undergoing groundwater extraction for source control, and contaminant mass discharge has been monitored since system startup. The results show a significant reduction in contaminant mass discharge with time, decreasing from approximately 1 to 0.15 kg/d. Two methods were used to estimate the mass of contaminant present in the source area at the initiation of the remediation project. One was based on a comparison of two sets of core data, collected 3.5 years apart, which suggests that a significant (~80%) reduction in aggregate sediment-phase TCE concentrations occurred between sampling events. The second method was based on fitting the temporal contaminant mass discharge data with a simple exponential source-depletion function. Relatively similar estimates, 784 and 993 kg, respectively, were obtained with the two methods. These data were used to characterize the relationship between reductions in contaminant mass discharge (CMDR) and reductions in contaminant mass (MR). The observed curvilinear relationship exhibits a reduction in contaminant mass discharge essentially immediately upon initiation of mass reduction. This behavior is consistent with a system wherein significant quantities of mass are present in hydraulically poorly accessible domains for which mass removal is influenced by rate-limited mass transfer. The results obtained from the present study are compared to those obtained from other field studies to evaluate the impact of system properties and conditions on mass-discharge and mass-removal behavior. The results indicated that factors such as domain scale, hydraulic-gradient status (induced or natural), and flushing-solution composition had insignificant impact on the CMDR-MR profiles and thus on underlying mass-removal behavior. Conversely, source-zone age, through its impact on contaminant distribution and accessibility, was implicated as a critical factor influencing the nature of the CMDR-MR relationship.

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Section: Introductionmentioning

confidence: 99%

Characterizing long-term contaminant mass discharge and the relationship between reductions in discharge and reductions in mass for DNAPL source areas

Brusseau

Matthieu

Carroll

et al. 2013

Journal of Contaminant Hydrology

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“…These two issues are typically the primary risk drivers for decisions regarding remediation of vadose-zone systems. Hence, the development and assessment of cleanup objectives for vadose-zone sources is typically based on evaluating the impact of vapor discharge from the vadose zone on groundwater quality or vapor intrusion (e.g., Rosenbloom et al, 1993; DiGiulio et al, 1999; EPA, 2001; USACE, 2002; Carroll et al, 2012; Brusseau et al, 2013a). …”

Section: 0 Introductionmentioning

confidence: 99%

“…The standard approach for characterizing vapor-phase mass discharge is to measure static vapor and/or sediment concentrations, and to use them as input for a mathematical screening model to estimate contaminant mass discharge (e.g., Johnson and Ettinger, 1991; Rosenbloom et al, 1993; DiGiulio et al, 1999; Hers et al, 2002). This approach has become widely used to evaluate the impact of vadose-zone sources on groundwater or vapor intrusion.…”

Section: 0 Introductionmentioning

confidence: 99%

The vapor-phase multi-stage CMD test for characterizing contaminant mass discharge associated with VOC sources in the vadose zone: Application to three sites in different lifecycle stages of SVE operations

Brusseau

Mainhagu

Morrison

et al. 2015

Journal of Contaminant Hydrology

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Vapor-phase multi-stage contaminant mass discharge (CMD) tests were conducted at three field sites to measure mass discharge associated with contaminant sources located in the vadose zone. The three sites represent the three primary stages along the soil vapor extraction (SVE) operations lifecycle- pre/initial-SVE, mid-lifecycle, and near-closure. A CMD of 32 g/d was obtained for a site at which soil vapor SVE has been in operation for approximately 6 years, and for which mass removal is currently in the asymptotic stage. The contaminant removal behavior exhibited for the vapor extractions conducted at this site suggests that there is unlikely to be a significant mass of non-vapor-phase contaminant (e.g., DNAPL, sorbed phase) remaining in the advective domains, and that most remaining mass is likely located in poorly accessible domains. Given the conditions for this site, this remaining mass is hypothesized to be associated with the low-permeability (and higher water saturation) region in the vicinity of the saturated zone and capillary fringe. A CMD of 25 g/d was obtained for a site wherein SVE has been in operation for several years but concentrations and mass-removal rates are still relatively high. A CMD of 270 g/d was obtained for a site for which there were no prior SVE operations. The behavior exhibited for the vapor extractions conducted at this site suggest that non-vapor-phase contaminant mass (e.g., DNAPL) may be present in the advective domains. Hence, the asymptotic conditions observed for this site most likely derive from a combination of rate-limited mass transfer from DNAPL (and sorbed) phases present in the advective domain as well as mass residing in lower-permeability (“non-advective”) regions. The CMD values obtained from the tests were used in conjunction with a recently developed vapor-discharge tool to evaluate the impact of the measured CMDs on groundwater quality.

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“…Despite its widespread application, there are few documented cases testing VLEACH against experimental or field data. Rosenbloom et al (1993) compared VLEACH simulation results with measured field concentrations of freon 11 and freon 12 at a site in Texas. Model simulations were found to be in close agreement with the field data.…”

Section: Validation Of the Modelmentioning

confidence: 98%

“…The model simulating processes include liquid phase advection, vapor phase diffusion, and adsorption. A detailed description of mathematics and numerical solutions of the model can be seen in Rosenbloom et al (1993), Ravi and Johnson (1994), and Rong (1995). Rong (1995) discussed assumptions and limitations of VLEACH, conducted sensitivity analysis, and uncertainty analysis for model parameters.…”

Section: Introductionmentioning

confidence: 99%

A Study of Vadose Zone Transport Model VLEACH

Rong¹

1999

Journal of Soil Contamination

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Application of vadose zone transport models has been hampered by lack of model validation. Difficulties to validate vadose zone models using field data not only come from model assumptions that are uncertain to the subsurface transport processes but also from the uncertainties associated with soil contaminants' release time and quantity, soil sampling, sample transport, and analytical procedures. This article first conducts a test of a popularly used vadose zone transport VLEACH by comparing model results with a set of laboratory soil column infiltration and volatilization study data. The comparison shows a close agreement between the VLEACH model results and the laboratory data. Second, the sorption coefficient K d calculated in VLEACH is compared with field data. The comparison indicates that VLEACH may overestimate the mass leached from soil to groundwater. The article also discusses the selection of the model simulation timestep, the vertical dimension increment, the Courant criterion, and the lower boundary condition using the sensitivity analysis method based on a case study of soil remediation for trichloroethylene. The procedures presented in this paper are important to practical model application and modification. This level of work should be routinely conducted for any new or modified version of vadose zone models.

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Application of VLEACH to Vadose Zone Transport of VOCs at an Arizona Superfund Site

Cited by 22 publications

References 8 publications

Characterizing long-term contaminant mass discharge and the relationship between reductions in discharge and reductions in mass for DNAPL source areas

Characterizing long-term contaminant mass discharge and the relationship between reductions in discharge and reductions in mass for DNAPL source areas

The vapor-phase multi-stage CMD test for characterizing contaminant mass discharge associated with VOC sources in the vadose zone: Application to three sites in different lifecycle stages of SVE operations

A Study of Vadose Zone Transport Model VLEACH

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