Spatial Scale Dependence of In Situ Solute Transport

Wesenbeeck, I. J. van; Kachanoski, R. G.

doi:10.2136/sssaj1991.03615995005500010001x

Cited by 64 publications

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“…However, such studies have been limited mostly to laboratory flow cells and numerical experiments. Large-scale infiltration experiments are useful to characterize field-scale spatial variability of hydraulic properties (van Wesenbeeck and Kachanoski 1991;Youngs 1991). Important vadose zone transport processes have been identified in the few large-scale transport studies conducted internationally during the last decade.…”

Section: Technical Backgroundmentioning

confidence: 99%

Vadose Zone Transport Field Study: Summary Report

Ward¹,

Conrad²,

Daily³

et al. 2006

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SummaryA series of field studies were conducted at the Hanford Site, near Richland, Washington, from FY 2000 through FY 2003 at two different locations to develop data sets to test models of flow and transport in the vadose zone. The field studies were also done to investigate advanced monitoring techniques for evaluating flow-and-transport mechanisms and delineating contaminant plumes in the vadose zone at the Hanford Site. The studies were conducted as part of the Groundwater/Vadose Zone Integration Project Science and Technology Project, now known as the Remediation and Closure Science Project, managed by the Pacific Northwest National Laboratory (PNNL) and supported by the U.S. Department of Energy, Richland Operations Office. This report summarizes the key findings from the field studies and demonstrates how data collected from these studies are being used to improve conceptual models and develop numerical models of flow and transport in Hanford's vadose zone. Results from the field studies and associated analysis have appeared in more than 46 publications generated over the past 4 years. These publications include test plans and status reports in addition to numerous technical notes and papers.Two major field campaigns were performed, one at a well injection test site and a second at a clastic dike test site. Both field studies have resulted in field-scale transport parameters for Hanford conditions, which are useful for improving predictions of subsurface flow and transport at the Hanford Site. In addition, advanced geophysical methods, including high resolution electrical resistivity measurements, were successfully tested and are now being deployed at Hanford for subsurface investigations and tank retrieval detection. The most useful information gained from these studies has been a better understanding of flow and transport in the vadose zone, and this has been specifically related to the impact of small-scale stratigraphic features (e.g., sediment layering) on water flow and contaminant transport. Conceptual models have been developed that take into account the lateral spreading of water and contaminants observed in the field studies. Numerical models of unsaturated flow and transport have been revised to account for lateral spreading of subsurface contaminant plumes.The key results from these studies include: 1) Greater understanding of the complexity of plume migration in the vadose zone at Hanford. Finescale geologic heterogeneities, including grain fabric and lamination, were observed to have a strong effect on the large-scale behavior of contaminant plumes, primarily through increased lateral spreading resulting from anisotropy.2) Observations of anion exclusion in Hanford sediments. Anion exclusion is a mechanism by which negatively charged ions are repelled from the surfaces of negatively charged soil particles, thereby increasing their velocity. Thus, the travel time of ions like pertechnetate, the stable form of 99 Tc found in oxidized environments, may decrease over that of unsaturated water f...

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Section: Technical Backgroundmentioning

confidence: 99%

Vadose Zone Transport Field Study: Summary Report

Ward¹,

Conrad²,

Daily³

et al. 2006

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“…Several studies have concentrated on the collection of field tracer data for this purpose (Jury 1982;Schulin et al 1987a;Jaynes et al 1988;Butters et al 1989;Köhne and Gerke 2005). Solute transport at the field-scale, however, is known to be complicated by several processes, such as the presence of variable horizon thicknesses or tonguing (Van Wesenbeeck and Kackanoski 1991), and preferential flow (Roth et al 1991;Zehe and Flühler 2001;Jarvis 2007). Furthermore, calibration and validation of theoretical models requires data collected from displacement experiments with well-controlled boundary conditions, which are often difficult to establish in field soils.…”

Section: Introductionmentioning

confidence: 99%

Field-scale solute transport parameters derived from tracer tests in large undisturbed soil columns

Mallants¹

2014

Soil Res.

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Abstract. Transport parameters obtained from laboratory tracer experiments were used to evaluate the stochastic form of the equilibrium convection-dispersion equation (CDE) in describing the transition of scale, i.e. from the column or local scale to a larger field scale. Local-scale solute breakthrough curves (BTCs) were measured in 1-m-long and 0.3-m-diameter undisturbed soil columns by means of time-domain reflectometry at six depths for a 79-h input pulse of chloride. The localscale data were analysed in terms of the equilibrium CDE and the mobile-immobile non-equilibrium transport model (MIM). At the local scale, the MIM transport model better described the observed early breakthrough and the tailing of the BTC than did the CDE. A linear regression analysis indicated that the relationship between the hydrodynamic dispersion D and pore-water velocity v was of the form D = 31v l.92 (correlation r v,D = 0.74). Averaging of the local-scale BTCs across the field produced a large-scale or field-scale mean BTC; at the greatest observation depth (0.8 m) the fieldscale dispersivity / = l equals 0.656 m. The results further showed that for large values of the mean dispersion coefficient, , local-scale dispersion is an important mechanism for field-scale solute spreading, whereas the standard deviation, s D , and the correlation between v and D, r vD , have negligible effects on field-scale transport. Stochastic stream tube models supplemented with statistical properties of local-scale transport parameters provide a practical and computationally efficient tool to describe heterogeneous solute transport at large spatial scales.

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“…Ellsworth and Boast (1996) interpreted the change in the correlation length of concentrations as a change in lateral solute mixing at or above the depth of observation, although a certain correlation length can also be obtained without any lateral mixing if a heterogeneous flow field is present. Van Wesenbeeck and Kachanoski (1991) found the presence of spatial correlation lengths for solute transport in both a forested and a cultivated site, likely because of pedogenesis and/or soil past management practices. Furthermore, the correlation length also provides a measure of the minimum plot size necessary to include the full range of horizontal variability in the local pore‐water velocity, which can then be compared with spatial distributions of soil properties affecting solute transport (Van Wesenbeeck and Kachanoski, 1991).…”

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confidence: 95%

Characterization of Field Tracer Transport Using High-Resolution Images

Kasteel¹,

Burkhardt²,

Giesa³

et al. 2005

Vadose Zone Journal

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Flow and transport in soils and groundwater are greatly affected by subsurface heterogeneity. We present results from infiltration experiments on four heterogeneous field plots (Orthic Luvisol) for plowed and nonplowed conditions. A 2‐mm pulse of Br− was applied, followed by a 40‐mm application of a 5 g L−1 solution of the food dye Brilliant Blue FCF (Color Index 42090) in a 6‐h period. Horizontal cross sections were photographed at 0.05‐ and 0.10‐m depth intervals, representing the Ap and Bt horizons, respectively, either immediately or 90 d after the tracer application. High‐resolution spatial maps of Brilliant Blue concentration were derived from the scanned photographs using one single calibration relationship between Brilliant Blue concentration and the color spectra for all plots and depths. No significant or consistent directional dependence was observed in the spatial correlation structure of the dye concentration for the horizontal cross sections. However, the integral scale showed a distinct depth dependency, partially caused by horizonation, with a larger value in the Ap than in the Bt horizon. Disturbed soil samples were taken at 15 locations for each cross section and analyzed for Br− Although Brilliant Blue was retarded in the soil matrix with respect to Br−, both tracer concentrations showed an exponential decay with depth because of preferential flow enhanced by plowing. Only a small fraction of the dye was subjected to fast transport. The plot‐scale information of the dye distribution revealed that our 15 sampling locations at each depth were sufficient to identify the averaged plot‐scale transport behavior in the soil matrix, but failed to represent the conducting preferential flow pathways.

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Spatial Scale Dependence of In Situ Solute Transport

Cited by 64 publications

References 0 publications

Vadose Zone Transport Field Study: Summary Report

Vadose Zone Transport Field Study: Summary Report

Field-scale solute transport parameters derived from tracer tests in large undisturbed soil columns

Characterization of Field Tracer Transport Using High-Resolution Images

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