Scale‐dependent dispersion in a stratified granular aquifer

Pickens, J. F.; Grisak, G. E.

doi:10.1029/wr017i004p01191

Cited by 442 publications

(263 citation statements)

References 36 publications

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“…This phenomenon, called the dispersion scale effect, has been observed repeatedly in groundwater experiments [Pickens and Grisak, 1981;Sudick32 et al, 1983;Freyberg, 1986].…”

Section: Introductionmentioning

confidence: 96%

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A three‐dimensional field study of solute transport through unsaturated, layered, porous media: 2. Characterization of vertical dispersion

Ellsworth¹,

Jury²

1991

Water Resources Research

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Solute plumes were created in an unsaturated field soil with either flux application or by leaching an initial resident distribution (see Ellsworth et al., this issue). The spatial variance of the plumes initially increased with time between the soil surface and a depth of 2.5 m, within which the soil was a nearly structureless loamy sand. Below this depth, the plumes were observed to compress in the vertical direction as they moved into, and through, a region of subangular blocky structure and loam texture (between 2.5 and 4.0 m depth). As the solute moved below the layer of fine texture, the plume variance again increased with time. Using a transformed advection-dispersion equation description, two constant, field-averaged transport coefficients, V* and D}:, were determined in a scaled coordinate system from the moment equations. These two constant parameters were then used to predict the observed local, or plot scale, transport. Results indicate that the two constant parameters describe transport reasonably well at each plot site and over all sampling depths. INTRODUCTIONThe quest for an adequate description of downward chemical movement through unsaturated soil has been a major priority of soil and environmental scientists for many years. Early efforts at describing the transport process focused on characterizing movement under steady-state water flow through repacked soil columns whose lateral dimension was small compared to the vertical. Under such conditions, the advection-dispersion (or convection-dispersion) equation (ADE) with two constant coefficients (the velocity and longitudinal dispersion coefficient) became generally accepted as the consensus model for describing transport of mobile, nonreactive tracers [Nielsen and Biggar, 1962]. However, the basis for this selection was usually the degree of agreement shown between the model and the effluent concentrations of solute in miscible displacement experiments, which cannot evaluate whether the dispersion parameter in the model is constant without examining concentrations at different distances from the inlet end [Taylor, 1953].Although early field studies of solute movement at the plot scale used the ADE to describe experimental observations The ADE is a scale dependent model, whose representation of the solute dispersion process at the scale of observation is only valid after sufficient time has elapsed for lateral mixing to smooth out differences in concentration caused by advection of solute at different velocities [Taylor, 1953 [1989] indicate that the correlation length scale for saturated hydraulic conductivity may be an order of magnitude less in the vertical direction than in the horizontal, and may be short compared to the depth of interest for modelers of the unsaturated zone. In such cases, the parallel soil column approaches or transfer functions will not be able to estimate transport through the zone of heterogeneity.An example of this failure was reported by Butters and Jury [1989], who observed a linear growth over the first 2 m of ...

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“…This phenomenon, called the dispersion scale effect, has been observed repeatedly in groundwater experiments [Pickens and Grisak, 1981;Sudick32 et al, 1983;Freyberg, 1986].…”

Section: Introductionmentioning

confidence: 96%

“…The dispersion behavior observed in these experiments is usually attributed to heterogeneity in the saturated hydraulic conductivity of the aquifer [Pickens and Grisak, 1981 [Freyberg, 1986].…”

Section: Introductionmentioning

confidence: 99%

A three‐dimensional field study of solute transport through unsaturated, layered, porous media: 2. Characterization of vertical dispersion

Ellsworth¹,

Jury²

1991

Water Resources Research

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“…It has been clearly demonstrated in the literature, both experimentally and theoretically, that dispersivity is positively correlated with the scale of observation [Pickens and Grisak, 1981;Gelhar and Axness, 1983;Neuman, 1990]. One school of thought hypothesizes that a L initially increases linearly with scale of observation and then gradually approaches a constant asymptotic value at an upper bound, which corresponds to the representative elementary volume (smallest volume of a porous medium over which measurements made are representative of the whole) [Gelhar et al, 1992].…”

Section: Hydrodynamic Dispersion and Dispersivitymentioning

confidence: 99%

“…Numerous laboratory and field-scale studies have focused on estimation of either the longitudinal dispersion coefficient [Harleman and Rumer, 1963;Pickens and Grisak, 1981;Koch and Brady, 1985;Han et al, 1985;Chrysikopoulos et al, 1990;Delgado, 2006] or the transverse dispersion coefficient [Delgado and Guedes de Carvalho, 2000;Cirpka et al, 2006;Acharya et al, 2007;Olsson and Grathwohl, 2007]. Transverse dispersion is increasingly recognized as a controlling mass transfer mechanism for contaminant plume migration and NAPL dissolution in aquifers [Chrysikopoulos et al, 1994;Chrysikopoulos and Kim, 2000;Chrysikopoulos et al, 2003;Rahman et al, 2005;Cirpka et al, 2006;Acharya et al, 2007;Rolle et al, 2010].…”

Section: Introductionmentioning

confidence: 99%

Colloid particle size‐dependent dispersivity

Chrysikopoulos,

Katzourakis

2015

Water Resources Research

120

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Laboratory and field studies have demonstrated that dispersion coefficients evaluated by fitting advection-dispersion transport models to nonreactive tracer breakthrough curves do not adequately describe colloid transport under the same flow field conditions. Here an extensive laboratory study was undertaken to assess whether the dispersivity, which traditionally has been considered to be a property of the porous medium, is dependent on colloid particle size and interstitial velocity. A total of 48 colloid transport experiments were performed in columns packed with glass beads under chemically unfavorable colloid attachment conditions. Nine different colloid diameters and various flow velocities were examined. The breakthrough curves were successfully simulated with a mathematical model describing colloid transport in homogeneous, water-saturated porous media. The experimental data set collected in this study demonstrated that the dispersivity is positively correlated with colloid particle size, and increases with increasing velocity. The dispersivity values determined in this laboratory study were compared with 380 dispersivity values from earlier laboratory and field-scale solute, colloid and biocolloid transport studies published in the literature.

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“…Typically, α x = 0.1 * (plume length) or α x = 0.1 * ((plume length) / 2). This approach provides a good general estimate and is consistent with the derivation of the Domenico solution; however, various investigators have shown that calculating a varying α x throughout the plume as a function of x provides a superior match to field data (Pickens and Grisak, 1981;EPA, 2000). Typically α x = 0.1 * (x).…”

Section: Moving Toward a Mass Balance Approachmentioning

confidence: 76%

Mass Balance: a Key to Advancing Monitored and Enhanced Attenuation for Chlorinated Solvents

Looney¹,

Vangelas²,

Adams³

et al. 2006

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Sections 7 and 8 summarize the evaluation in terms of research and development directions and broad goals.Section 9 provides the references for the report.Finally, the appendices provide supplemental information and mathematical derivations to support Sections 4 and 6. The appendices are intended to provide sufficient detail to allow interested readers to better follow and replicate the evaluation and to facilitate technical review and discussion.The process of systematically disassembling and then reassembling a "contaminant plume" -in terms of loading and attenuation capacity -provided useful insights and promising directions to specifically improve implementation of natural attenuation, and generally improve environmental management and legacy management decision-making. source zone aqueous concentration at time zero, mass/volume C (x,y,z,t) concentration at a specific target location and specified time, mass/volume LIST OF TABLES LIST OF CASE STUDIESCase LIST OF ACRONYMS KEY DEFINITIONS Enhancement, Enhanced AttenuationAn enhancement is any type of intervention in a contaminated system that decreases contaminant loading or increases the magnitude of attenuation by natural processes beyond that which occurs without intervention. Enhanced attenuation is the result of applying an enhancement that sustainably manipulates a natural attenuation process leading to an overall reduction in mass flux of contaminants. Integrated Mass Flux (iMF), Loading, DischargeThe integrated mass flux is the total quantity of a migrating substance that moves through a planar transect that is within the system of interest and oriented perpendicular to the direction of movement. If the transect is at the entry point to the system the integrated mass flux is the loading. If the transect is at the exit point from the system, the integrated mass flux is the discharge. Note that these terms have units of mass per time (e.g., Kg/yr, g/day or the like) and they represent an extension of the traditional engineering definition of flux (e.g., Kg/yr/m 2 ) in which the transect area is accounted for to allow mass balance calculation of plume or system scale behavior.Monitored Natural Attenuation "'Monitored natural attenuation' …refers to the reliance on natural attenuation processes (within the context of a carefully controlled and monitored clean-up approach) to achieve sitespecific remedial objectives within a time frame that is reasonable compared to that offered by other more active methods. The 'natural attenuation processes' that are at work in such a remediation approach include a variety of physical, chemical, or biological processes that, under favorable conditions, act without human intervention to reduce mass, toxicity, mobility, volume, or concentration of contaminants in soil or groundwater." (EPA, 1999; pg. 3) Attenuation Capacity (A c )The attenuation capacity is the general term that describes the amount of a contaminant that can be assimilated and attenuated within an identified subsurface system volume. It is the compos...

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Scale‐dependent dispersion in a stratified granular aquifer

Cited by 442 publications

References 36 publications

A three‐dimensional field study of solute transport through unsaturated, layered, porous media: 2. Characterization of vertical dispersion

A three‐dimensional field study of solute transport through unsaturated, layered, porous media: 2. Characterization of vertical dispersion

Colloid particle size‐dependent dispersivity

Mass Balance: a Key to Advancing Monitored and Enhanced Attenuation for Chlorinated Solvents

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