Immiscible fluid flow in porous media: dielectric properties

Alharthi, A.; Lange, James N.; Whitaker, Emily C.

doi:10.1016/0169-7722(86)90010-0

Cited by 19 publications

(8 citation statements)

References 5 publications

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“…From a physical point of view, α is a geometric factor relating the direction of the effective layering of the different dielectric components to the direction of the applied electrical field (Hilhorst, 1998). It has been widely suggested (Dobson et al, 1985; Alharthi et al, 1986; Roth et al, 1990; Huisman et al, 2003) that α is equal to 0.5 for isotropic and homogeneous soils, but in general it is a fitting parameter and cannot be measured directly or inferred from other soil properties. However, despite this limitation and the apparent simplicity of using the α mixing model, remarkably good agreement was found in modeling the dielectric properties of geological materials (Knight, 2001) and soil–water–NAPL mixtures (Francisca and Montoro, 2012; Comegna et al, 2013a, 2013b).…”

Section: Theoretical Background and Operational Principles Of Tdrmentioning

confidence: 99%

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Estimating Nonaqueous‐Phase Liquid Content in Variably Saturated Soils Using Time Domain Reflectometry

Comegna

Coppola

Dragonetti

et al. 2016

Vadose Zone Journal

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Core Ideas A TDR waveform interpretation method for NAPL content in soils was developed. Correlations between the dielectric response and the NAPL content were determined. The α dielectric mixing model for predicting NAPL presence in soils was expanded. This methodology can be used to obtain predictions of volumetric NAPL content. In recent years, several studies have been conducted in the detection and observation of nonaqueous‐phase liquids (NAPLs) in contaminated soils. Successful remediation of an NAPL‐contaminated site requires appropriate characterization of both the plume extent and the soil volumetric NAPL content (θNAPL). Noninvasive geophysical techniques, such as time domain reflectometry (TDR), may be used to discriminate between θNAPL and soil volumetric water content (θw). Accordingly, the main aim of this work was to develop a TDR waveform interpretation method based on soil dielectric permittivity measurement and observation of the change in the reflected TDR signal amplitude at relatively long times from the waveform source. We demonstrated that the asymptotic value of the reflection signal coefficient can be univocally related with θNAPL in an unsaturated soil. In the procedure adopted, a new formulation of a dielectric mixing model was also derived, introducing a fourth phase that takes the NAPL presence into account. Multiple samples of sandy, silt loam, and loamy soils, at predetermined different θw and θNAPL, were tested, each test consisting in emitting a TDR signal to the soil sample and receiving and analyzing the reflected electromagnetic wave. An empirical dielectric mixing model was calibrated and implemented to estimate the θNAPL. Equipment calibration, measurement accuracy, and error sources, related both to the experimental procedure setup and to the sample preparation conditions, are discussed. The results show that the suggested methodology can be used to obtain predictions of volumetric NAPL content (θNAPL) with acceptable accuracy (R2 = 0.95).

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Section: Theoretical Background and Operational Principles Of Tdrmentioning

confidence: 99%

“…This is because commonly encountered NAPLs have a low dielectric permittivity of 2 to10 vs. 81 for water (Haridy et al, 2004). However, NAPL detection becomes difficult in the case of unsaturated soil at low water content due to the low dielectric permittivity of air (1) and soil mineral grains (3–7) (Alharthi et al, 1986; Ajo‐Franklin et al, 2006).…”

mentioning

confidence: 99%

Estimating Nonaqueous‐Phase Liquid Content in Variably Saturated Soils Using Time Domain Reflectometry

Comegna

Coppola

Dragonetti

et al. 2016

Vadose Zone Journal

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“…(3) where ' is the permittivity of the mixture, i and Vi are the permittivity and volume of the "i" phase respectively, the exponent a is an empirical constant related to the geometry of the grains and their spatial distri- bution (Hilrost, 1998;Coppola et al, 2013). For an homogeneous and isotropic medium, a can be assumed equal to 0.5 (Alharti et al, 1986) and the mixing model is then referred to as the complex refractive index model (CRIM, e.g. Hiusman et al, 2003).…”

Section: Mixing Modelsmentioning

confidence: 99%

Time domain reflectometry-measuring dielectric permittivity to detect soil non-acqeous phase liquids contamination-decontamination processes

Comegna¹,

Coppola²,

Dragonetti³

et al. 2013

J Agricult Engineer

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Contamination of soils with non-aqueous phase liquids (NAPL) constitutes a serious geo-environmental problem, given the toxicity level and high mobility of these organic compounds. To develop effective decontamination methods, characterisation and identification of contaminated soils are needed. The objective of this work is to explore the potential of dielectric permittivity measurements to detect the presence of NAPLs in soils. The dielectric permittivity was measured by Time Domain Reflectometry method (TDR) in soil samples with either different volumetric content of water ( w) and NAPL ( NAPL) or at different stages during immiscible displacement test carried out with two different flushing solutions. A mixing model proposed by Francisca and Montoro, was calibrated to estimate the volume fraction of contaminant present in soil. Obtained results, showed that soil contamination with NAPL and the monitoring of immiscible fluid displacement, during soil remediation processes, can be clearly identified from dielectric measurements. IntroductionSubsurface contamination of soil and groundwater with organic compounds from waste disposal sites, industrial spills, gasoline stations, mine tailings and industrial processes constitutes a serious geoenvironmental problem. The detrimental effects are limited not only to deterioration of chemical, physical and mechanical properties of soils, but also constitute a real risk to human health and the well-being of other living species.Non-aqueous phase liquids (NAPLs), are organic compounds immiscible with water. They have low solubility that may still be several orders of magnitude higher than that of acceptable drinking water standards. NAPLs can be further subdivided into those that are denser than water (DNAPLs) and those that are lighter than water (LNAPLs). Chlorinated solvents such as trichloroethylene (TCE) and tetrachloroethylene (PCE) and polychlorinated biphenyl oils (PCBs) are common examples of DNAPLs. Hydrocarbon fuels such as gasoline, kerosene and jet fuels are common LNAPL contaminants which pollute the environment extensively (Illangasekare, 1998;Jury and Horton, 2004).Following a near-surface release, NAPLs penetrate the subsurface as an immiscible oil phase that migrates in response to gravity and capillary forces. This results in substantial sensitivity to the local distribution of soil and aquifer properties (e.g. permeability and porosity) beneath the source (Gerhard et al., 2007). As a result, the NAPL body (e.g. the source zone) is often expected to exhibit a complex heterogeneous distribution of both mobile pools (i.e. connected-phase accumulations) and immobile residuals (i.e. disconnected blobs and ganglia (Mercer and Cohen, 1990).The remediation of contaminated soil sites requires knowledge of the contaminant distribution in the soil profile and groundwater. Methods commonly used to characterize contaminated sites are coring, soil sampling and the installation of monitoring wells for the collection of groundwater samples (Mercer and Cohen, 1...

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“…Because the models describe precise pressure and saturation distributions, visual observations of frontal positions are insufficient to validate model predictions. Laboratory techniques to determine pressure and saturation distributions are currently being refined (123)(124)(125)(126).…”

Section: Immiscible Phase Flow Modelsmentioning

confidence: 99%

“…The possibility and importance of reversed wettability in groundwater systems has been considered by very few. Alharthi et al explored the importance of wettability to organic phase retention and effective conductivity (126). They examined organic fluid spills in water-wet and completely dry soils.…”

Section: Immiscible Phase Flow Modelsmentioning

confidence: 99%

Modeling multiphase migration of organic chemicals in groundwater systems--a review and assessment.

Abriola

1989

Environ Health Perspect

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Over the past two decades, a number of models have been developed to describe the multiphase migration of organic chemicals in the subsurface. This paper presents the state-of-the-art with regard to such modeling efforts. The mathematical foundations of these models are explored and individual models are presented and discussed. Models are divided into three groups: a) those that assume a sharp interface between the migrating fluids; b) those that incorporate capillarity; and c) those that consider interphase transport of mass. Strengths and weaknesses of each approach are considered along with supporting data for model validation. Future research directions are also highlighted.

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Immiscible fluid flow in porous media: dielectric properties

Cited by 19 publications

References 5 publications

Estimating Nonaqueous‐Phase Liquid Content in Variably Saturated Soils Using Time Domain Reflectometry

Estimating Nonaqueous‐Phase Liquid Content in Variably Saturated Soils Using Time Domain Reflectometry

Time domain reflectometry-measuring dielectric permittivity to detect soil non-acqeous phase liquids contamination-decontamination processes

Modeling multiphase migration of organic chemicals in groundwater systems--a review and assessment.

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