Determination of water saturation in relatively dry porous media using gas phase tracer tests
Soil desiccation (drying), induced by dry air injection and moist air extraction, is a potentially robust remediation process to slow migration of inorganic or radionuclide contaminants through the vadose zone. The application of gas-phase partitioning tracer tests has been proposed as a means to es...
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Published in | Vadose zone journal Vol. 10; no. 2; pp. 634 - 641 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
Madison
Soil Science Society of America
01.05.2011
Soil Science Society |
Subjects | |
Online Access | Get full text |
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Summary: | Soil desiccation (drying), induced by dry air injection and moist air extraction, is a potentially robust remediation process to slow migration of inorganic or radionuclide contaminants through the vadose zone. The application of gas-phase partitioning tracer tests has been proposed as a means to estimate initial water volumes and to monitor the progress of the desiccation process at pilot tests and field sites. In this study, tracer tests were conducted in porous medium columns with various water saturations using SF6 as the conservative tracer and trichlorofluoromethane and difluoromethane as the water-partitioning tracers. For porous media with minimal silt or organic matter fractions, tracer tests provided reasonable saturation estimates for saturations close to zero. For sediments with significant silt or organic matter fractions, however, tracer tests only provided satisfactory results when the water saturation was greater than 0.1 to 0.2. For drier conditions, the apparent tracer retardation increased due to air-soil sorption, which is not included in traditional retardation coefficients derived from advection-dispersion equations accounting only for air-water partitioning and water-soil sorption. Based on these results, gas-phase partitioning tracer tests may be used to determine initial water volumes in sediments, provided that the initial water saturations are sufficiently large. Tracer tests are not suitable for quantifying moisture content in relatively dry sediments, however, especially if significant amounts of organic matter or silt are present. |
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Bibliography: | Gas‐phase tracers were used in unsaturated porous media tests to evaluate the potential use of tracers to detect and quantify soil moisture during desiccation. Results show these tracers provide reasonable results for water saturations above approximately 0.05, while for smaller saturations solid‐phase tracer sorption reduces applicability of the method. 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. USDOE AC05-76RL01830 PNNL-SA-74637 |
ISSN: | 1539-1663 1539-1663 |
DOI: | 10.2136/vzj2010.0101 |