Transport of nonreactive and volatile Solutes in unsaturated porous media under wetting and draining conditions

Persistent Link:
http://hdl.handle.net/10150/191230
Title:
Transport of nonreactive and volatile Solutes in unsaturated porous media under wetting and draining conditions
Author:
Padilla, Ingrid Yamill, 1964-
Issue Date:
1998
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The effect of water content and soil-water hysteresis on transport of unreactive water-tracers and volatile organic compounds (VOCs) in porous media is investigated under steady-state water-flow conditions. Specifically, this research addresses the effect on dispersive and mass transfer processes affecting the movement of NaC1 and trichloroethene (ICE) and how these processes influence the approach to Fickian flux conditions. Transport experiments were conducted in a 25-cm column packed with silica sand. Based on the results, it is concluded that water content (0), pore-water velocity, and flow history affect the average movement and spread of water-tracers and VOCs. It is suggested that non-volatile solutes in unsaturated media travel longer distances or times to achieve a Fickian state. Consequently, a greater number of averaged heterogeneities are encountered and solute flux is characterized by a greater dispersion coefficient (D). A power (n) law relationship (D(m) = η(v(m)/ θ(m))ⁿ), found between mobile dispersion coefficients (D(m_), pore-water velocity (v(m)), and water content (θ(m)) for different porous media, indicates that dispersivity (η) is not only a function of the media, but also of θ(w). TCE transport is controlled by advection processes for Ow greater than 50% saturation. Lower θ(w) result in greater TCE dispersion, retardation, mass-transfer resistance, vapor diffusion, and spreading. Consequently, VOCs reach the Fickian regime at shorter distances than unreactive solutes in water. Although VOC transport is influenced by multiple rate-limited mass transfer, the mechanisms controlling the overall mass-transfer resistance vary as a function of θ(w). The hysteretic behavior of solute transport parameters is attributed to a greater degree of irregular flow paths and entrapped air, higher air-water interfacial areas, and thicker water-films for wetting than draining scenarios. Consequently, wetting conditions result in slower mixing (up to 98% lower mass-transfer coefficients) of dissolved solutes. Since TCE transport at low water contents and wetting conditions is dominated by diffusion and dispersion mechanisms, the TCE velocity distribution in the liquid phase is normalized by velocity distributions in the gas-phase and becomes closer to Fickian conditions.
Type:
Dissertation-Reproduction (electronic); text
Keywords:
Hydrology.; Porous materials -- Fluid dynamics.
Degree Name:
Ph. D.
Degree Level:
doctoral
Degree Program:
Hydrology and Water Resources; Graduate College
Degree Grantor:
University of Arizona
Committee Chair:
Conklin, Martha

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleTransport of nonreactive and volatile Solutes in unsaturated porous media under wetting and draining conditionsen_US
dc.creatorPadilla, Ingrid Yamill, 1964-en_US
dc.contributor.authorPadilla, Ingrid Yamill, 1964-en_US
dc.date.issued1998en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThe effect of water content and soil-water hysteresis on transport of unreactive water-tracers and volatile organic compounds (VOCs) in porous media is investigated under steady-state water-flow conditions. Specifically, this research addresses the effect on dispersive and mass transfer processes affecting the movement of NaC1 and trichloroethene (ICE) and how these processes influence the approach to Fickian flux conditions. Transport experiments were conducted in a 25-cm column packed with silica sand. Based on the results, it is concluded that water content (0), pore-water velocity, and flow history affect the average movement and spread of water-tracers and VOCs. It is suggested that non-volatile solutes in unsaturated media travel longer distances or times to achieve a Fickian state. Consequently, a greater number of averaged heterogeneities are encountered and solute flux is characterized by a greater dispersion coefficient (D). A power (n) law relationship (D(m) = η(v(m)/ θ(m))ⁿ), found between mobile dispersion coefficients (D(m_), pore-water velocity (v(m)), and water content (θ(m)) for different porous media, indicates that dispersivity (η) is not only a function of the media, but also of θ(w). TCE transport is controlled by advection processes for Ow greater than 50% saturation. Lower θ(w) result in greater TCE dispersion, retardation, mass-transfer resistance, vapor diffusion, and spreading. Consequently, VOCs reach the Fickian regime at shorter distances than unreactive solutes in water. Although VOC transport is influenced by multiple rate-limited mass transfer, the mechanisms controlling the overall mass-transfer resistance vary as a function of θ(w). The hysteretic behavior of solute transport parameters is attributed to a greater degree of irregular flow paths and entrapped air, higher air-water interfacial areas, and thicker water-films for wetting than draining scenarios. Consequently, wetting conditions result in slower mixing (up to 98% lower mass-transfer coefficients) of dissolved solutes. Since TCE transport at low water contents and wetting conditions is dominated by diffusion and dispersion mechanisms, the TCE velocity distribution in the liquid phase is normalized by velocity distributions in the gas-phase and becomes closer to Fickian conditions.en_US
dc.description.notehydrology collectionen_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.typetexten_US
dc.subjectHydrology.en_US
dc.subjectPorous materials -- Fluid dynamics.en_US
thesis.degree.namePh. D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineHydrology and Water Resourcesen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.chairConklin, Marthaen_US
dc.identifier.oclc218664036en_US
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