A constitutive model for air–NAPL–water flow in the vadose zone accounting for immobile, non-occluded (residual) NAPL in strongly water-wet porous media

A hysteretic constitutive model describing relations among relative permeabilities, saturations, and pressures in fluid systems consisting of air, nonaqueous-phase liquid (NAPL), and water is modified to account for NAPL that is postulated to be immobile in small pores and pore wedges and as films o...

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Bibliographic Details
Published in:Journal of contaminant hydrology 2004-07, Vol.71 (1), p.261-282
Main Authors: Lenhard, R.J., Oostrom, M., Dane, J.H.
Format: Article
Language:English
Subjects:
Air
Constitutive theory
Earth sciences
Earth, ocean, space
Engineering and environment geology. Geothermics
Exact sciences and technology
Forecasting
Hydrogeology
Hydrology. Hydrogeology
Models, Theoretical
NAPL flow
Permeability
Pollution, environment geology
Porosity
Relative permeability relations
Residual NAPL
Soil
Soil Pollutants - analysis
Three-phase flow
Water Movements
Water Pollutants - analysis
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Description
Summary:A hysteretic constitutive model describing relations among relative permeabilities, saturations, and pressures in fluid systems consisting of air, nonaqueous-phase liquid (NAPL), and water is modified to account for NAPL that is postulated to be immobile in small pores and pore wedges and as films or lenses on water surfaces. A direct outcome of the model is prediction of the NAPL saturation that remains in the vadose zone after long drainage periods (residual NAPL). Using the modified model, water and NAPL (free, entrapped by water, and residual) saturations can be predicted from the capillary pressures and the water and total-liquid saturation-path histories. Relations between relative permeabilities and saturations are modified to account for the residual NAPL by adjusting the limits of integration in the integral expression used for predicting the NAPL relative permeability. When all of the NAPL is either residual or entrapped (i.e., no free NAPL), then the NAPL relative permeability will be zero. We model residual NAPL using concepts similar to those used to model residual water. As an initial test of the constitutive model, we compare predictions to published measurements of residual NAPL. Furthermore, we present results using the modified constitutive theory for a scenario involving NAPL imbibition and drainage.
ISSN:0169-7722
1873-6009
DOI:10.1016/j.jconhyd.2003.10.014