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  • Introduction Developing predictive numerical models of hydrogeochemical systems requires an understanding of the physical and chemical processes affecting the composition of the water. Physical processes like mixing and evaporation can be reasonably well defined using the chemical data but redox sensitive chemical processes are more difficult to quantify. Applying the isotope chemistry of dissolved sulfate to characterise and even quantify these redox processes enhances the capabilities of numerical modelling, in particular those associated with acid mine drainage, acid sulfate soils and sulfide mineral exploration. This work describes how the stable isotopes of sulfur and oxygen in sulfate can be used to better characterise geochemical processees and thereby improve reactive transport models. Discussion Groundwater, pore water and surface water from a number of areas in Australia have been used to determine the sources of sulfur in acid sulfate susceptable systems. Several trends become apparent, sulfate reduction, and sulfide oxidation commonly dominate the chemical processes controlling sulfur in a groundwater system. Bacterial sulfate reduction (BSR) can be recognised by the affect on the 34S and 18O of sulfate. Both ratios increase as the lighter isotope is removed through dissimilatory bacterial reduction, leaving behind the heavier isotopes. Oxidation of sulfides occurs through 2 processes, one involving molecular oxygen (O2) and the other involving oxidised iron (Fe3+). The different pathways result in considerable differences in the oxygen isotopic composition of the product sulfate. Surface water and some groundwater from the Loveday basin in SA show evidence of evaporation and BSR while the near surface pore waters, although similarly evaporated, contain sulfate that predominantly originates from sulfide oxidation. Sulfate in groundwater from several other regions has stable isotopic compositions that indicate sulfide oxidation involving either the O2 or the Fe3+ pathways. The implications of are that the sulfate history can be understood through isotopic analysis and that this can be used in geochemical models to trace

  • Legacy product - no abstract available

  • The Ord Valley Airborne Electromagnetics (AEM) Interpretation Project was undertaken to provide information in relation to groundwater salinity management in the Ord River Irrigation Area (ORIA), and to assess the salinity hazard in areas of potential irrigation expansion. Salinity hazard maps were produced using an informed GIS-based approach. The salinity hazard maps combined AEM-derived maps of the shallow alluvial sediments, salt stored in the unsaturated zone and maps of groundwater salinity, with drilling data and maps of depth to the watertable. Hydrographic analysis showed that under current climate conditions, water tables were rising, and it was therefore assumed for GIS modeling purposes that water levels would continue to rise after land clearing and the onset of irrigation. It was also assumed that if shallow watertables developed at some time in the future, that salt accumulation through capillary rise (if within 2m of the surface) may lead to salinisation. This assumption was informed by prior geochemical modeling that inferred that if relatively modest groundwater salinity levels (>750 mg/l TDS) were evapo-concentrated that it may cause a significant salinity hazard to irrigated agriculture. Salinity hazard was assessed as high where there were significant quantities of salt stored in the alluvium in areas of shallow groundwater, and lowest where there is little or no salt stored in alluvium and groundwater tables are deep. The salinity hazard was forecast to be high to very high in the Mantinea Plain, Carlton Hill, Parry's Lagoon and lower Ord Floodplain areas. In the Knox Creek and Keep River Plains, the hazard was low in the north of the area, but moderate to high in the southern-central and areas of the southern Knox Creek Plain. In the priority development area (Weaber Plain), the salinity hazard was estimated to be highly variable.

  • This Record describes a geophysical survey for Underground water in the Cloncurry River valley, at the request of the Queensland Irrigation and Water Supply Commission, on behalf of the Cloncurry Shire Council. Appreciable differences in ground water level in different sections along the valley suggest the presence of rock bars across the valley. In choosing bore sites it is desirable to know the position of these rock bars. Plate 12 shows the location of rock bars that were indicated by ground water level data. Plate 13 shows the position of rock bars that were indicated by geophysical data. Good agreement exists between the two sets of indications. Sites that were based on geophysical data are suggested for water bores.