The use of Radon (Rn222) isotopes to detect groundwater discharge in streams draining Table Mountain Group (TMG) aquifers
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Date
2021
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Water Research Commission (WRC)
Abstract
Environmental isotopes have been used for decades as natural tracers in studies aimed at understanding
complex hydrogeological processes such as groundwater and surface water interactions. Radon (Rn222)
is a naturally occurring, radioactive isotope which is produced from radium (Ra226) during the radioactive
decay series of uranium (U238). Since U238 is present in most geological substrates, Rn222 is produced in
various lithological structures and subsequently transported with groundwater through fractures and
pore spaces in an aquifer towards surface water discharge points in rivers and springs. This study aimed
to determine (i) the concentration of Rn222 within both surface water and groundwater in Table Mountain
Group (TMG) aquifer systems, and (ii) the feasibility of using Rn222 isotopes as a natural tracer in groundwatersurface water interaction studies. This study was conducted in a highly fractured TMG aquifer system near
Rawsonville, South Africa. Surface water from two perennial rivers (i.e. Gevonden and Molenaars), together
with groundwater from a nearby borehole, were sampled and their corresponding Rn222 concentrations
measured. Our study found median Rn222 concentrations in the Gevonden River of 76.4 Bq∙L-1 and 67.2 Bq∙L-1
in the dry and wet seasons, respectively. Nearly 12% of surface water samples exceeded 100 Bq∙L-1.
Description
Keywords
Environmental isotopes, Headwater streams, Hydrological tracers, Radioactivity, Table Mountain Group
Citation
Strydom, T. et al. (2021). The use of Radon (Rn222) isotopes to detect groundwater discharge in streams draining Table Mountain Group (TMG) aquifers. Water SA, 47(2), 194–199. https://doi.org/10.17159/wsa/2021.v47.i2.10915