Integration of historic groundwater data into the Continent Scale Geochemistry initiative

The groundwater dataset developed by Angela Giblin comprises over 5000 samples across much of Australia and is a useful contribution to the mapping of groundwater chemistry across Australia (the ‘Continental Scale Hydrogeochemistry’ initiative). Sampling and analytical methodology used by Giblin differed from many other protocols. In particular, water samples were not filtered in the field, or indeed prior to analysis. However, given the number of samples and their potential utility, it would be advantageous to modify data from these samples so that they can be readily integrated with other studies. The combined data were initially sorted to ensure consistent detection limits. Data that did not pass a thorough QA/QC assessment were rejected. Correction, and where necessary removal, of data (owing to the analytical artefacts from solids contamination during analysis) was applied. The degree of contamination in bailed samples, and what data therefore to reject, is calculated using an algorithm developed and tested for Western Australian groundwaters. Geochemical changes between sampling and delayed analysis (days or weeks later) cannot be directly quantified. Other research predicted which elements should be most affected by this. This was further tested by comparing overlapping results from Giblin with more recent data from the same sites in Western Australia and Queensland. Results showed good agreement for salinities and major ions, and for the ratio indices (K:Na, etc.) determined from such data. Saturation Index calculations for sulfates gypsum, celestine and barite also closely matched between differing datasets. There was good agreement between datasets for F, HCO₃, Si, V, As, Mo, Ba and U, and moderate agreement for Li, Cr and Au. Weak agreement for pH meant that saturation indices for carbonate minerals such as calcite, dolomite, magnesite, siderite and rhodochrosite did not align, and there was very poor agreement for P, Co, Ni, Cu, Zn, Pb, Mn and Fe. However, in general, these comparisons indicate groundwater to be a robust geochemical medium. Based on this study, this modified data should now be readily usable and ‘seamlessly’ comparable with other datasets. Combining data, across varying sources if necessary, allows hydrogeochemistry to be used to map geology, alteration, prospectivity and geomorphological factors from mine scale to the size of Australia.