There are currently no nested (multi-level) groundwater observation bore sites in the Richmond river basin and other areas within the Clarence-Moreton bioregion where alluvium, volcanic and sedimentary bedrock aquifers are monitored simultaneously. This means that much of the current understanding of vertical head gradients is based on multiple lines of evidence from hydrochemistry data, interpolation from widely-spaced monitoring bore networks, analogues from other parts of the Clarence-Moreton bioregion where more data exist, or general understanding of the regional geology and recharge processes. In addition, although there are some monitoring time-series data for the alluvial aquifer, the number of observations is relatively small (less than 60 observation bores in the Richmond river basin). There are also only a limited number of observation bores in subcatchments of the Richmond river basin such as the Shannon Brook or Eden Creek catchments, which both flow through the area where CSG development may occur. In order to better understand whether inferred aquitards such as the Maclean Sandstone, Bungawalbin Member and Grafton Formation (or part of the Grafton Formation) form regional seals that hydraulically separate the Walloon Coal Measures from shallower aquifers and thus limit or prevent the influence of CSG activities on shallow water resources, more petrophysical data from these aquitards are required. More work is also needed to determine the impact of tidal-dominated river reaches on groundwater salinity.

Faults were not included in the current version of the three-dimensional geological model and consequently no fault-seal analysis (e.g. determination of shale gouge ratios and juxtaposition values, which assess the vertical offset distances between different layers) could be conducted. Alluvial and coastal sediments were not separated in the three-dimensional geological model; separation of these sediments requires development of a smaller-scale high-resolution three-dimensional geological model of the coastal areas, which was beyond the scope of the Assessment.

Overall, this chapter highlights that the limited amount of actual geological field data in the Clarence-Moreton bioregion, such as wells and seismic lines, introduces considerable uncertainty in the three-dimensional geological model. It is important to note that even after integrating multiple data sources, multiple conceptual hydrogeological models honouring the available data are possible in data-scarce areas with complex geology such as the Richmond river basin. This can influence predictions or assessments based on a given conceptual hydrogeological model.

Last updated:
5 March 2019
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