Considering groundwater dependent ecosystems in closure planning

Authors: Windle, D; Weaver, T; Pawley, H; Tolsma, C Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2415_60

Cite As:
Windle, D, Weaver, T, Pawley, H & Tolsma, C 2024, 'Considering groundwater dependent ecosystems in closure planning', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2024: Proceedings of the 17th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 845-858, https://doi.org/10.36487/ACG_repo/2415_60



Abstract:
Assessment of impacts on potential groundwater dependent ecosystems (GDEs) is a requirement for mine closure in many Australian jurisdictions, but published mapping has recognised limitations. Standard approaches are based on guidance for mine development, and involve consideration of other groundwater data and site-specific information to assess the relevance of mapped potential GDEs. A further step is required to assess the likely impacts on relevant GDEs during mine closure and rehabilitation activities, that includes consideration of historic, current and future conditions. In Australia, GDEs are mapped by the Australian Government Bureau of Meteorology and presented in the GDE Atlas. The Atlas is the first and only national dataset of Australian GDEs available to inform groundwater planning and management. The Atlas lists three types of ecosystems (aquatic, terrestrial and subterranean) and mapping is based on two sources; national assessment, and regional studies – including analysis by state agencies. In Victoria, regional studies include Victorian Government wetland mapping. Mine closure and rehabilitation typically involve activities that are likely to change the local water balance and impact on interactions between groundwater and surface water, and therefore potentially GDEs. Such rehabilitation activities may include the removal of operational water features, creation of pit lake water bodies, and changes to groundwater extraction (increasing or more typically decreasing groundwater pumping). Typically, outputs from the GDE Atlas and wetland mapping are assessed relative to the current conditions at mine sites. In this example from the Latrobe Valley in Victoria, a closure and rehabilitation focused approach has been adopted for the Yallourn Coal Mine. Assessment of potential GDE relevance was undertaken by overlaying topography and groundwater level understanding from current conditions, with consideration of the current operational activities. Assessment of likely impacts to relevant GDEs then conceptually considered future closure conditions to identify where and how groundwater levels were likely to change near these relevant GDEs. Numerical groundwater and surface water modelling could also be undertaken to quantify the potential impacts. A staged approach allows targeted assessment of the likely timing, magnitude and extent of groundwater level changes, and informs ecological assessment for specific, potentially impacted, relevant GDEs as the Yallourn Coal Mine transitions from current operations through to closure and rehabilitation. Depending on the status of closure planning, different approaches are available to assess potential GDEs, inform targeted assessment and support closure planning and approvals.

Keywords: groundwater dependent ecosystems, GDEs, mine closure and rehabilitation, groundwater, aquatic ecosystems, terrestrial ecosystems, subterranean ecosystems, conceptual model, groundwater–surface water interaction

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