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.