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K H Jensen - One of the best experts on this subject based on the ideXlab platform.

  • flow and transport processes in a macroporous subsurface drained Glacial Till soil ii model analysis
    Journal of Hydrology, 1998
    Co-Authors: Karen G Villholth, K H Jensen
    Abstract:

    Abstract The experimental results from a field-scale tracer experiment in a subsurface-drained Glacial Till soil were analyzed by the application of a single/dual porosity model (MACRO), optionally accounting for concurrent and interacting flow and transport in the bulk soil porosity as well as in the macropores. The model analysis showed that macropore flow is essential in describing the observed transport phenomenon on a short as well as a longer time scale. The diffusive exchange of solute between the matrix and the macropores was very sensitive and critical for the model prediction of the drainage concentration. The exchange was overpredicted and too rapid when the soil aggregate size (distance between macropores) obtained from an image analysis of soil cores was used in the model. On this basis, the model assumption of instant equilibration of the solute across the matrix porosity, disregarding small-scale concentration gradients, is questioned. Decreasing the domain exchange resulted in an improved model correspondence with the drainage chemograph. The drainage flow pattern was altered between drainage seasons owing to the changes in hydraulic efficiency of surface-vented macropores influenced by the physical disturbance and compaction of the soil surface. Hypothetically introducing fully surface-connected macropores into the calibrated model resulted in a 22% increase in the loss of solute to the drain, indicating the significance of the hydraulic conditions at the soil surface and the model specification thereof.

  • flow and transport processes in a macroporous subsurface drained Glacial Till soil i field investigations
    Journal of Hydrology, 1998
    Co-Authors: Karen G Villholth, K H Jensen, J Fredericia
    Abstract:

    Abstract The qualitative and quantitative effects of macropore flow and transport in an agricultural subsurface-drained Glacial Till soil in eastern Denmark have been investigated. Three controlled tracer experiments on individual field plots (each approximately 1000 m 2 ) were carried out by surface application of the conservative chloride ion under different application conditions. The subsequent continuous long-term monitoring of the rate and chloride concentration of the drainage discharge represented an integrated and large-scale approach to the problem. In addition, point-scale determination of macropore structure and hydraulic efficiency, using image analysis and tension infiltration, and of soil water content, level of groundwater table, and chloride content of soil water within the soil profile yielded insights into small-scale processes and their associated variability. Macropore flow was evidenced directly by the rapid (within 10 mm of water input) and abrupt chloride break-through in the drainage water at 1.2 m depth in two of the tracer experiments. In the third experiment, the effect of macropore transport was obvious from the rapid and relatively deep penetration of the tracer into the soil profile. Dye infiltration experiments in the field as well as in the laboratory supported the recognition of the dominant contribution of macropores to the infiltration and transport process. The soil matrix significantly influenced the tracer distribution by acting as a source or sink for continuous solute exchange with the macropores. An average field-determined active macroporosity constituted 0.2% of the total porosity, or approximately 10% of the total macroporosity.

Karen G Villholth - One of the best experts on this subject based on the ideXlab platform.

  • flow and transport processes in a macroporous subsurface drained Glacial Till soil ii model analysis
    Journal of Hydrology, 1998
    Co-Authors: Karen G Villholth, K H Jensen
    Abstract:

    Abstract The experimental results from a field-scale tracer experiment in a subsurface-drained Glacial Till soil were analyzed by the application of a single/dual porosity model (MACRO), optionally accounting for concurrent and interacting flow and transport in the bulk soil porosity as well as in the macropores. The model analysis showed that macropore flow is essential in describing the observed transport phenomenon on a short as well as a longer time scale. The diffusive exchange of solute between the matrix and the macropores was very sensitive and critical for the model prediction of the drainage concentration. The exchange was overpredicted and too rapid when the soil aggregate size (distance between macropores) obtained from an image analysis of soil cores was used in the model. On this basis, the model assumption of instant equilibration of the solute across the matrix porosity, disregarding small-scale concentration gradients, is questioned. Decreasing the domain exchange resulted in an improved model correspondence with the drainage chemograph. The drainage flow pattern was altered between drainage seasons owing to the changes in hydraulic efficiency of surface-vented macropores influenced by the physical disturbance and compaction of the soil surface. Hypothetically introducing fully surface-connected macropores into the calibrated model resulted in a 22% increase in the loss of solute to the drain, indicating the significance of the hydraulic conditions at the soil surface and the model specification thereof.

  • flow and transport processes in a macroporous subsurface drained Glacial Till soil i field investigations
    Journal of Hydrology, 1998
    Co-Authors: Karen G Villholth, K H Jensen, J Fredericia
    Abstract:

    Abstract The qualitative and quantitative effects of macropore flow and transport in an agricultural subsurface-drained Glacial Till soil in eastern Denmark have been investigated. Three controlled tracer experiments on individual field plots (each approximately 1000 m 2 ) were carried out by surface application of the conservative chloride ion under different application conditions. The subsequent continuous long-term monitoring of the rate and chloride concentration of the drainage discharge represented an integrated and large-scale approach to the problem. In addition, point-scale determination of macropore structure and hydraulic efficiency, using image analysis and tension infiltration, and of soil water content, level of groundwater table, and chloride content of soil water within the soil profile yielded insights into small-scale processes and their associated variability. Macropore flow was evidenced directly by the rapid (within 10 mm of water input) and abrupt chloride break-through in the drainage water at 1.2 m depth in two of the tracer experiments. In the third experiment, the effect of macropore transport was obvious from the rapid and relatively deep penetration of the tracer into the soil profile. Dye infiltration experiments in the field as well as in the laboratory supported the recognition of the dominant contribution of macropores to the infiltration and transport process. The soil matrix significantly influenced the tracer distribution by acting as a source or sink for continuous solute exchange with the macropores. An average field-determined active macroporosity constituted 0.2% of the total porosity, or approximately 10% of the total macroporosity.

Krishna R Reddy - One of the best experts on this subject based on the ideXlab platform.

  • geochemical assessment of metal transport in Glacial Till during electrokinetic remediation
    Environmental Monitoring and Assessment, 2008
    Co-Authors: Ashraf Z Alhamdan, Krishna R Reddy
    Abstract:

    This paper presents the chemical speciation and retention behavior of chromium (Cr), nickel (Ni), and cadmium (Cd) prior to and after the electrokinetic remediation in Glacial Till soil. The speciation of the metals was predicted using the chemical speciation program MINEQL(+). The simulations were performed for single-contaminant with only Cr(VI) or Ni, and multi-contaminants consisting of: (1) Cr(VI), Ni, and Cd; (2) Cr(III), Ni and Cd; (3) Cr(VI), Cr(III), Ni and Cd; (4) Cr(VI), Ni, and Cd with reducing agents; and (5) Cr(III), Ni, and Cd with oxidizing agent (Mn). The results showed that the speciation and distribution of cationic metals [Ni, Cd, and Cr(III)] in Glacial Till soil remain unaffected or slightly affected during electrokinetics. This is attributed to the high pH buffering capacity of the Glacial Till, leading the metals to precipitate in the soil prior to and after electrokinetics. This study showed that during electrokinetics, Cr(VI) existed as anionic complex and migrated towards the anode and the migration is maximum in case of a single-contaminant system. The study also showed that near the anode in the absence of any reducing and oxidizing agent, Cr(VI) mostly adsorbed, and some of Cr(VI) reduced to Cr(III) and migrated towards the cathode and finally precipitated due to high pH conditions. Ni and Cd remain adsorbed or precipitated due to the high pH conditions throughout the soil. Among the reducing agents, the sulfide had significant effect on the migration of metals compared to ferrous ions. While in the presence of oxidizing agent (Mn), no noticeable Cr(VI) was found in the soil sample indicating the reduction of Cr(VI) to Cr(III) and the predominance of reducing conditions due to the presence of naturally occurring iron in the Glacial Till soil. Overall, this study provides a reasonable explanation of the speciation and distribution of chromium, nickel and cadmium during the electrokinetic remediation of Glacial Till soil.

  • adsorption of heavy metals in Glacial Till soil
    Geotechnical and Geological Engineering, 2006
    Co-Authors: Ashraf Z Alhamdan, Krishna R Reddy
    Abstract:

    The charged sites on soil particles are important for the retention/adsorption of metals. Metallic counterions can neutralize the intrinsic charges on the surfaces of soil particles by forming complexes. In this study, efforts have been made to determine the effect of surface potential, pH, and ionic strength on the adsorption of four metal ions, hexavalent chromium Cr(VI), trivalent chromium Cr(III), nickel Ni(II) and cadmium Cd(II), in Glacial Till soil. Batch tests were performed to determine the effect of pH (2–12) and ionic strength (0.001–0.1 M KCl) on zeta potential of the Glacial Till soil. The point of zero charge (pH PZC ) of Glacial Till was found to be 7.0±2.5. Surface charge experiments revealed the high buffering capacity of the Glacial Till. Batch adsorption experiments were conducted at natural pH (8.2) using various concentrations of selected metals. The adsorption data was described by the Freundlich adsorption model. Overall Glacial Till shows lower adsorption affinity to Cr(VI) as compared to cationic metals, Cr(III), Ni(II) and Cd(II).

  • enhanced electrokinetic remediation of heavy metals in Glacial Till soils using different electrolyte solutions
    Journal of Environmental Engineering, 2004
    Co-Authors: Krishna R Reddy, Supraja Chinthamreddy
    Abstract:

    Previous electrokinetic remediation studies involving the geochemical characterization of heavy metals in high acid buffering soils, such as Glacial Till soil, revealed significant hexavalent chromium migration towards the anode. The migration of cationic contami- nants, such as nickel and cadmium, towards the cathode was insignificant due to their precipitation under the high pH conditions that result when the soil has a high acid buffering capacity. Therefore the present laboratory study was undertaken to investigate the performance of different electrolyte ~or purging! solutions, which were introduced to either dissolve the metal precipitates and/or form soluble metal complexes. Tests were conducted on a Glacial Till soil that was spiked with Cr~VI! ,N i~II!, and Cd~II! in concentrations of 1,000, 500, and 250 mg/kg, respectively, under the application of a 1.0 VDC/cm voltage gradient. The electrolyte solutions tested were 0.1M EDTA ~ethylenediaminetetraacetic acid!, 1.0M acetic acid, 1.0M citric acid, 0.1M NaCl/0.1M EDTA, and 0.05M sulfuric acid/0.5 M sulfuric acid. The results showed that 46 - 82% of the Cr~VI! was removed from the soil, depending on the purging solution used. The highest removal of Ni~II! and Cd~II! was 48 and 26%, respectively, and this removal was achieved using 1.0M acetic acid. Although cationic contaminant removal was low, the use of 0.1M NaCl as an anode purging solution and 0.1M EDTA as a cathode purging solution resulted in significant contaminant migration towards the soil regions adjacent to the electrodes. Compared to low buffering capacity soils, such as kaolin, the removal of heavy metals from the Glacial Till soil was low, and this was attributed to the more complex composition of Glacial Till. Overall, this study showed that the selection of the purging solutions for the enhanced removal of heavy metals from soils should be primarily based upon the contaminant characteristics and the soil composition.

Hans Rönnqvist - One of the best experts on this subject based on the ideXlab platform.

Bengt Espeby - One of the best experts on this subject based on the ideXlab platform.

  • preferential water flow in a Glacial Till soil
    Hydrology Research, 2005
    Co-Authors: Christer Jansson, Bengt Espeby, Pererik Jansson
    Abstract:

    Measured and simulated response of runoff during snowmelt has suggested that preferential water flow occurs as part of the infiltration process in Glacial Till. However, only a few quantitative studies have been presented. TDR measurements of soil water content were performed during the growing period in a Till slope (7-10%) outside Stockholm. Soil cores were used to determine the water retention curve and the saturated hydraulic conductivity. A physically based one-dimensional model was used to simulate soil water dynamics in the slope. Two simulation approaches were used: a strict one-domain Darcian approach and a two-domain approach accounting for a bypass of the matrix flow system. The measured response of soil water content occurred within the first few hours after rainfall. This was best represented by the two-domain approach, while the response for the one-domain approach was significantly delayed with time and depth. The general behaviour of the soil water content throughout the season was, however, best simulated with a one-domain approach. The results indicated that preferential flow patterns through the unsaturated zone does not need to be considered to describe the seasonal pattern in Glacial Till soil. However, the results also point out that the purpose of the simulation is decisive when choosing a simulation approach, depending on whether the general soil water content over the season or the instant behaviour immediately after rainfall is of major interest.

  • tracing the origin of natural waters in a Glacial Till slope during snowmelt
    Journal of Hydrology, 1990
    Co-Authors: Bengt Espeby
    Abstract:

    Abstract A study of the origin of water sampled at a set of sampling points in the discharging area of a sloping forested Glacial Till, was performed during the two snowmelts of 1986 and 1987. Analyses of a limited number of chemical components and the 18 O content were performed of the sampled water from the snowmelt of 1986. On the basis of the findings from these analyses, a tracer experiment was performed during the snowmelt of 1987, when potassium iodide (KI) was sprayed on top of the snow cover at two surfaces in the discharging area of the slope. The results from both snowmelt studies indicate that macropore channels of old root remains can conduct water rapidly through an unsaturated and frozen matrix without displacing the soil-bound water. Alkalinity and pH values of the sampled water from a macropore were similar to the alkalinity and pH values of sampled snow cores. Even the deeper ground water from a spring site was affected by the acid surge during the peak snowmelt of 1986, giving proof that macrostructures present in the Till were promoting preferential water movement through the soil matrix. The surge was also detected with the 18 O technique but was not as pronounced as in the values of the chemical components. The iodide tracer experiment during the snowmelt of 1987 also indicated the above-mentioned findings despite the large amount of tracer that was retained in the unsaturated soil matrix. The otherwise conservative tracer subsequently gave no distinguished breakthrough in the discharging water at the V-notch, where the runoff from the slope was measured. It was therefore not possible to determine the tracer turnover time during this snowmelt. However, one very important conclusion from this experiment is that iodide should be injected below the humus and the leaching horizons of podsols in order to get good saturated conditions and thereby prevent retention in the matrix.

  • an analysis of saturated hydraulic conductivity in a forested Glacial Till slope
    Soil Science, 1990
    Co-Authors: Bengt Espeby
    Abstract:

    The author made a statistical analysis of 100 soil core samples taken from six soil pits in a forested Glacial Till slope in south central Sweden to determine the spatial variability of the saturated hydraulic conductivity, K{sub 8}. He also analyzed correlations to other soil properties. Analysis of variance (ANOVA) determined whether the K{sub 8} values were significantly dependent upon the position in the slope and the sampling depth below soil surface. A multifactor analysis of variance (MANOVA) tested the interaction effect between position in the slope (elevation level) and soil depth (horizon level) on K{sub 8}.