SSSAJ: Volume 74: Number 5 • September–October 2010 1457 Soil Sci. Soc. Am. J. 74:1457–1468 Published online 4 Aug. 2010 doi:10.2136/sssaj2009.0398 Received 24 Oct. 2009. *Corresponding author (mostafa.redwan@ymail.com). © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Simultaneous Monitoring of Water Saturation and Fluid Conductivity in Unconsolidated Sand Columns Soil Physics M onitoring changes related to water content and electrical conductivity are very important aspects in soil science. Tey are required for understanding transport, mobilization of ions, and precipitation mechanisms, especially in the unsaturated part of the soil. Electrical conductivity measurements are used both in the feld and in the laboratory to obtain information on rock, sediment, or soil conductivities. Tey are used either for estimating sulphide or graphite mineralized zones, zones of alteration, fresh water/salt water boundaries or for humidity levels in soils, sedi- ments, and tailings (Katsube and Mareschal, 1993; Jones et al., 1997; Collins and Easley, 1999; Airo and Loukola-Ruskeeniemi, 2004; Logsdon and Laird, 2004; Hofmann-Rothe et al., 2004; Harinarayana et al., 2006). Electrical conductivity depends on a number of factors such as the electrical conductivity of the rock, sediment, or soil itself, as well as the conductivity of the fuid expressed by the salinity of the pore water and the level of water saturation (Archie, 1942; Chinh, 2000), and tortuosity of the current fow paths (Glover et al., 1996). Terefore, electrical conductivity measurements are not unambiguous for interpretation. Single profles obtained by feld measurements provide eventually Mostafa Redwan* Bundesanstalt fuer Geowissenschaften und Rohstoffe (BGR) Stilleweg 2 30655 Hannover, Germany and Geology Dep. Faculty of Science Sohag Univ. 82524 Sohag, Egypt. Dieter Rammlmair Bundesanstalt fuer Geowissenschaften und Rohstoffe (BGR) Stilleweg 2 30655 Hannover, Germany Electrical conductivity can easily be measured, but interpretation is ambiguous since saturation, fuid conductivity, and material properties are interacting parameters. Tis study aims to indirectly obtain fuid 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 diference in x-ray attenuation by dry, partially and fully saturated sand flled columns. Also, it is used to calculate fuid conductivity from the electrical conductivity in time intervals for each depth level in the column. Te investigated columns show distinct patterns for water saturation, electrical conductivity, and calculated fuid 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. Te calculated fuid conductivities are much higher than expected, but correspond well to conductivity and ion strength of the extracted fuids. Te strong increase in electrical conductivity was attributed to the fast rising capillary head fuids, which quickly accumulated all available ions around the particles and moved upward. Te slow water was depleted, and showed even a diferent ion distribution pattern due to slowly reacting minerals. Monitoring of fuid 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 feld. Tis is essential for understanding the development of hardpans in natural and anthropogenic environments, causing eventually supergene economic enrichment of metals. Abbreviations: C, coarse grain size, CM, coarse-medium grain size; CMF, coarse plus medium plus fne grain size; CT, computed tomography; EDXRF, energy dispersive x-ray fuorescence; F, fne; ICP–MS, inductively coupled plasma–mass spectrometry; ICP–OES, inductively coupled plasma– optical emission spectrometry; LREE, light rare earth elements; M, medium; MF, medium fne; NMR, nuclear magnetic resonance; PVC, polyvinyl chloride; REE, rare earth element. Published September, 2010