Diffusion Coefficients and Hydraulic Conductivity in Unsaturated Hanford Soils and Sediments

by Judith Wright, Pacific Northwest Lab, United States,

Document Type: Proceeding Paper

Part of: High Level Radioactive Waste Management 1990


Two groundwater transport parameters of some Hanford formation materials, the hydraulic conductivity and the diffusion coefficient, were measured to aid in predicting contaminant migration. The hydraulic conductivities and diffusion coefficients for five soil types were determined as functions of the water content for the aqueous phase. The degree of saturation (or the volumetric water content) in the soil was fixed at desired levels by use of a high-speed core ultracentrifuge with an ultralow constant-rate flow pump feeding water into the sample through a rotating seal. After the water content was fixed and the soil was at hydraulic steady-state (within two to four hours), the electrical conductivity was measured using a 1 kHz conductivity bridge. Diffusion coefficient values were calculated from the measured electrical conductivity values using the Nernst-Einstein equation. Hanford formation soils exhibit great heterogeneity regarding hydraulic conductivity in subunit soils.

Subject Headings: Water content | Soil water | Diffusion (porous media) | Hydraulic conductivity | Unsaturated soils | Sediment | Saturated soils | Water sampling

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