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Title: SENSITIVITY ANALYSIS OF PHYSICAL AND CHEMICAL PROPERTIES AFFECTING FIELD-SCALE CADMIUM TRANSPORT IN A HETEROGENEOUS SOIL PROFILE

Author
item SEUNTJENS, P - FLEMISH INST TECH RES,BEL
item MALLANTS, D - BEL NUC RES CTR,BEL
item SIMUNEK, J - UC, RIVERSIDE, CA
item PATYN, J - FLEMISH INST TECH RES,BEL
item JACQUES, D - BEL NUC RES CTR,BEL

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: Transport of reactive chemicals in soils is affected by complex interactions involving biological, chemical and physical processes. These micro-scale processes act simultaneously and include biodegradation, chemical reactions between soluble and solid constituents of the soil (e.g., sorption/desorption, complexation, precipitation/dissolution) and physical transport of solutes. Field-scale transport of reactive solutes through the vadose zone depends on spatially variable physical and chemical soil properties. The importance of physical and chemical parameters required for field-scale solute flux predictions is generally unknown, as is the level of detail and accuracy at which the parameters must be determined. This paper presents a sensitivity analysis that ranks the importance of spatially variable water flow and solute transport parameters affecting field-scale Cd flux through a heterogeneous soil profile.

Technical Abstract: This paper presents a sensitivity analysis that ranks the importance of spatially variable water flow and solute transport parameters affecting field-scale Cd flux through a heterogeneous soil profile. Data on the heterogeneity of flow and transport parameters of a layered sandy soil were collected from a 180-m-long and 1-m-deep transect. Each soil layer was described in terms of the probability density function (pdf) of five model parameters: shape parameters a and n of van Genuchten's water retention curve, the saturated hydraulic conductivity Ks, the dispersivity l and the Cd soil-water distribution coefficient Kd. Uncertainty about the contaminant source (i.e., atmospheric Cd deposition originating from a metallurgical industry) was incorporated into the inlet condition of a one-dimensional reactive solute transport model. Cd redistribution in the profile following a 100-year deposition was calculated using a Monte-Carlo simulation approach. Partial rank correlation coefficients (PRCC) were used to quantify the effect of variations in the model parameter and in the deposition rate on the field-scale Cd flux. The results show that the steady-state field-scale Cd flux is most sensitive to the contaminant deposition rate and the soil-water distribution coefficient Kd. The maximum Cd concentration in the drainage water was affected by variability in Ks of the humus-rich top layers, but not by the other layers. The effect of the spatial variability in water retention curve shape parameters a and n on field-scale Cd flux was insignificant. Variations in the dispersivity l of the deeper soil layers had a significant influence on field-scale Cd flux at the beginning and at the end of the Cd breakthrough. Additional Monte-Carlo simulations involving nonlinear Cd sorption, in which the Freundlich exponent is treated as a deterministic parameter show that nonlinearity strongly influenced Cd migration at the early and final stages of the breakthrough.