LAND AND WATER Environmental Tracers in the Beetaloo Basin Aquifer and groundwater characterization Alec Deslandes, Christoph Gerber, Sebastien Lamontagne, Cornelia Wilske, Axel Suckow November 2019 Cover Photo: Landholder bore with mechanically driven pump and diesel motor – typical setting at landholder sampling sites. ISBN 978‐1‐4863‐1409‐6 (Print) ISBN 978‐1‐4863‐1410‐2 (Online) Citation Deslandes, Alec, Gerber, Christoph, Lamontagne, Sebastien, Wilske, Cornelia, Suckow, Axel (2019): Environmental Tracers in the Beetaloo Basin. Aquifer and groundwater characterization. CSIRO, Australia. Copyright © Commonwealth Scientific and Industrial Research Organisation 2019. To the extent permitted by law, all rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of CSIRO. 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Environmental Tracers in the Beetaloo Basin | i Contents Acknowledgments ............................................................................................................................ vii Executive summary ......................................................................................................................... viii 1 Introduction ......................................................................................................................... 12 1.1 Objectives ............................................................................................................... 13 2 Beetaloo Sub‐Basin .............................................................................................................. 15 2.1 Geological Formations and Structure ...................................................................... 17 2.2 Hydrogeology of the Cambrian Limestone Aquifer ................................................. 18 2.3 Faults ...................................................................................................................... 19 2.4 Recharge and Discharge .......................................................................................... 19 2.5 Climate .................................................................................................................... 20 3 Applied methods .................................................................................................................. 22 3.1 Bore selection ......................................................................................................... 22 3.2 Field sampling ......................................................................................................... 26 3.3 Analytical methods ................................................................................................. 27 3.4 Data evaluation ....................................................................................................... 27 4 Tracer results ....................................................................................................................... 33 4.1 Hydrochemistry ....................................................................................................... 33 4.2 Stable Isotopes of water: 2H & 18O ...................................................................... 39 4.3 Tritium (3H) ............................................................................................................. 40 4.4 Transient Anthropogenic Molecular Gas Tracers .................................................... 43 4.5 Carbon Isotopes ...................................................................................................... 48 4.6 Helium ..................................................................................................................... 51 4.7 Heavy Noble Gases and Nitrogen ............................................................................ 56 5 Discussion ............................................................................................................................ 59 5.1 Groundwater evolution in the Beetaloo Basin ........................................................ 59 5.2 Recharge estimates ................................................................................................. 62 6 Summary .............................................................................................................................. 67 References 69 Appendix A Using environmental tracers to quantify groundwater time scales ........................ 75 ii | Environmental Tracers in the Beetaloo Basin Environmental Tracers in the Beetaloo Basin | iii Figures Figure 2.1 Surface geology of the Cambrian Limestone Aquifer including the Beetaloo Sub‐basin . 16 Figure 2.2 Monthly climate statistics for locations North‐South across the Beetaloo Sub‐basin ..... 21 Figure 3.1 Locations of tracer sampling points and the sampled formation. ................................... 23 Figure 3.2 Hydrogeological map of the Beetaloo Sub Basin including the sampling locations ......... 25 Figure 3.3 Comparison between field titration and laboratory analysis for Total Dissolved Inorganic Carbon (TDIC). .................................................................................................................. 28 Figure 3.4 Specific REE pattern for groundwater of the Tindall Limestone. ..................................... 30 Figure 3.5 Specific REE pattern of the Gum Ridge, Anthony Lagoon Beds Montijinni Formations. .. 31 Figure 4.1 Hierarchical cluster dendrogram based on major and minor ions only (53 samples). ..... 34 Figure 4.2 Map with the spatial distribution of the clusters based on major and minor ions only (54 samples). .................................................................................................................................... 35 Figure 4.3 Boxplots of median and range of electrical conductivity (EC), pH, and concentrations for TDIC, Ca, Li, and Zn for the calculated clusters. .......................................................................... 35 Figure 4.4 Hierarchical cluster dendrogram based on major and minor ions, stable isotopes, and REE (25 samples) .............................................................................................................................. 36 Figure 4.5 Map with spatial distribution of the clusters based on major and minor ions, stable isotopes, and REE (25 samples) ........................................................................................................ 37 Figure 4.6 Boxplots with median and range for Eh, pH, Fe concentration, and ⁸⁷Sr/⁸⁶Sr ratio for the calculated clusters. Outliers are presented as small circles. ...................................................... 38 Figure 4.7 Stable Isotope plot 2H vs. 18O. ..................................................................................... 39 Figure 4.8 Plot of measured tritium (TU) vs. screen depth below groundwater. ............................. 40 Figure 4.9 Map with tritium values at different bores. .................................................................... 42 Figure 4.10 Plot of concentration versus depth below water level for transient gas tracers ........... 44 Figure 4.11 Map of SF6 concentrations ............................................................................................ 45 Figure 4.12 Cross plot of gas tracers versus 3H................................................................................. 46 Figure 4.13 Cross plots of SF6 versus other gas tracers. ................................................................... 47 Figure 4.14 Historical and new 14C data in the Cambrian Limestone aquifer along the flow transect. ........................................................................................................................................... 48 Figure 4.15 Map of historical and new 14C data in the study area. ................................................... 49 13 14 14 Figure 4.16 Cross‐plots of TDIC, C, C and Cabs. .......................................................................... 50 Figure 4.17 Helium ‐Neon cross plot. ............................................................................................... 52 Figure 4.18 Helium isotope plot. ...................................................................................................... 53 Figure 4.19 Map of helium concentrations. ..................................................................................... 54 iv | Environmental Tracers in the Beetaloo Basin Figure 4.20 Helium concentrations along the flow line. ..................................................................