Simultaneous Monitoring of Water Saturation and Fluid Conductivity in Unconsolidated Sand Columns
- Mostafa Redwan *ab and
- Dieter Rammlmaira
Electrical conductivity can easily be measured, but interpretation is ambiguous since saturation, fluid conductivity, and material properties are interacting parameters. This study aims to indirectly obtain fluid conductivity evolution in time and space in column experiments by repetitively applying two independent non-destructive multi-level methods. Water saturation, is derived from the difference in x-ray attenuation by dry, partially and fully saturated sand filled columns. Also, it is used to calculate fluid conductivity from the electrical conductivity in time intervals for each depth level in the column. The investigated columns show distinct patterns for water saturation, electrical conductivity, and calculated fluid conductivity for individual imbibition and drainage steps at distinct grain-size distributions. During imbibition, the unsaturated capillary fringe head shows a very unusual increase in electrical conductivity gaining with each step of capillary rise. During the drainage cycle, the electrical conductivity peak broadens and moves downward. The calculated fluid conductivities are much higher than expected, but correspond well to conductivity and ion strength of the extracted fluids. The strong increase in electrical conductivity was attributed to the fast rising capillary head fluids, which quickly accumulated all available ions around the particles and moved upward. The slow water was depleted, and showed even a different ion distribution pattern due to slowly reacting minerals. Monitoring of fluid conductivity in time and space by non-destructive methods provides access to enrichment–depletion processes in the critical zone, in the laboratory and in the field. This is essential for understanding the development of hardpans in natural and anthropogenic environments, causing eventually supergene economic enrichment of metals.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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