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Rn-220 (Thoron) in ground water and soil gas (Continuation)

English title Rn-220 (Thoron) in ground water and soil gas (Continuation)
Applicant Kipfer Rolf
Number 135513
Funding scheme Project funding (Div. I-III)
Research institution Wasserressourcen und Trinkwasser Eawag
Institution of higher education Swiss Federal Institute of Aquatic Science and Technology - EAWAG
Main discipline Hydrology, Limnology, Glaciology
Start/End 01.04.2011 - 31.07.2012
Approved amount 65'415.00
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Keywords (14)

Rn-220; Rn-222; thoron; radon; emanation; soil gas; groundwater; porous media; Rn-220; Rn-222; thoron; radon; emanation; soil gas

Lay Summary (English)

Lead
Lay summary

Former projects showed the potential of Rn-220 as a tracer to study fluid movement in porous media, in combination with the well-known groundwater tracer Rn-220. The key message of the former project is that subsurface Rn-220 is generally detectable in soil gas but not in groundwater. We presume that soil moisture seems to inhibit the emanation and migration, and therefore the occurrence, of Rn-220 in the subsurface.

These findings set the new conceptual framework for assessing two main research topics in the follow-up project, which aims to understand the release dynamics of Rn-220 in the unsaturated zone in comparison to the release dynamics of Rn-220.

Task I: We intend to verify findings of a field soil-gas experiment in a laboratory experiment, using a sand box. Concentration measurements of Rn-220 & Rn-222 at different water contents up to saturation will give insights into differences in the emanation and transport behavior of the two radon isotopes.

Task II: The experimental data obtained will set the framework for defining a physical transport model of Rn-220 & Rn-222. The model, which will be trimmed to simulate the release of both radon isotopes, is expected to yield a mechanistic prediction of the transport of Rn-220 & Rn-222 under different degrees of wetting.

By assessing these questions, we aim to consolidate and further expand our understanding of Rn-220 emanation in porous media and soil-gas systems.

Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Name Institute

Publications

Publication
220 Rn/ 222 Rn Isotope Pair as a Natural Proxy for Soil Gas Transport
Huxol Stephan, Brennwald Matthias S., Henneberger Ruth, Kipfer Rolf (2013), 220 Rn/ 222 Rn Isotope Pair as a Natural Proxy for Soil Gas Transport, in Environmental Science & Technology, 47(24), 14044-14050.
Processes controlling 220Rn concentrations in the gas and water phases of porous media
Huxol Stephan, Brennwald Matthias S., Kipfer Rolf (2013), Processes controlling 220Rn concentrations in the gas and water phases of porous media, in Chemical Geology, 335, 87-92.
On the fate of 220Rn in soil material in dependence of water content: Implications from field and laboratory experiments
Huxol Stephan, Brennwald Matthias S., Hoehn Eduard, Kipfer Rolf (2012), On the fate of 220Rn in soil material in dependence of water content: Implications from field and laboratory experiments, in Chemical Geology, 298-299, 116-122.
On the fate of Rn-220 in soil material in dependence of water content: Implications from field and laboratory experiments
Huxol S, Brennwald MS, Hoehn E, Kipfer R, On the fate of Rn-220 in soil material in dependence of water content: Implications from field and laboratory experiments, in CHEMICAL GEOLOGY, 298, 116-122.

Associated projects

Number Title Start Funding scheme
119802 Radon-220 (Thoron in ground water) 01.04.2008 Project funding (Div. I-III)
119802 Radon-220 (Thoron in ground water) 01.04.2008 Project funding (Div. I-III)

Abstract

The goal of the ongoing SNF-Project was to study the potential of Rn-220 (also called “thoron”) as a tracer to study fluid movement in porous media, in combination with the well-known groundwater tracer Rn-222 (“radon”). Our ongoing project resulted in three major experimental and scientific results: 1) The conventional detection system (Durridge Rad7), combined with a degassing and sampling unit (RadAQUA), was improved and trimmed for a reliable and robust Rn-220-in-water analysis, by applying an internal Rn-220 calibration procedure using monazite pebbles.2) Having a reliable detection system at hand, we extensively sampled and analyzed ground water in the field. However, no Rn-220 was found in the ground water (except in one special case). In fact, Rn-220 would seem to be generally absent in ground water.3)We therefore concentrated on soil and soil gas, in which Rn-220 is known to occur. We installed an automated Rn-220 and Rn-222 detection system in the unsaturated zone adjacent to a river-fed groundwater body. During dry conditions, Rn-220 and Rn-222 concentration profiles were found to be controlled by the different decay rates of the isotopes, and hence by the effective diffusive path length of the respective radon isotope. Notably, during and after a rain event that caused a local flood Rn-220 in soil gas dropped to virtually zero, whereas Rn-222 concentrations were affected only slightly. The key message from the ongoing project is that subsurface Rn-220 is generally detectable in soil gas but not in groundwater, as the soil moisture seems to inhibit the emanation and migration, and therefore the occurrence, of Rn-220 in the subsurface.These three major results set the new conceptual framework for assessing two main research topics in the follow-up project, which will also lead to the completion of the PhD thesis associated with the ongoing project.The new project aims to understand the release dynamics of Rn-220 in the unsaturated zone.Task I:To achieve this objective, we intend to verify the field soil-gas experiment in a laboratory experiment using a sand box under controlled hydraulic conditions. Concentration measurements of Rn-220 and Rn-222 at different water contents, up to the saturation level of the sand used, will give insights into differences in the emanation and transport behavior of the two radon isotopes.Task II:The experimental data obtained will set the framework for defining a physical transport model of Rn-220 and Rn-222. The model, which will be trimmed to simulate the release of both radon isotopes as a function of soil water content is expected to yield a mechanistic prediction of the transport of Rn-220 and Rn-222 under different degrees of wetting and hydraulic conditions.With these two tasks, we aim to consolidate and further expand our understanding of Rn-220 emanation in porous media and soil-gas systems.
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