Final voids in floodplains – are they really that bad? | Chris Gimber, ERM7 September 2020
There are many examples of situations where final voids on floodplains have resulted in problems, manifesting in large water inventories, poor quality water, migration of contaminants and ongoing erosion issues. This has led to an increasing focus from industry and regulators on whether final voids should be permitted in floodplains, and if they are to exist, how they should be designed and operated.
The exclusion of floodwater into mining voids usually minimises the risk of erosion, loss of catchment runoff and maintains catchment hydrologic processes. This has led mine planners to try to sequence mining so that final voids are located outside the floodplain, or construct landforms around mine voids using overburden with the primary purpose of isolating final voids from the floodplain.
While it is generally true that water resource risks are reduced if final voids are located outside floodplains, this is not always the case. There are valid arguments that for some sites the siting of a final void on a floodplain may improve long term environmental and social outcomes, for example by providing a water storage, ecological habitat, mitigating groundwater drawdown or limiting oxidation of sulfides.
This presentation gives an overview of the risk factors that apply in different situations across a range of commodities. It also highlights a decision making framework for weighing up costs and benefits associated with different design approaches that could be applied by both miners and regulators to determine the merits of a range of final void scenarios. All of which will be explored in more detail at the Life of Mine Conference 2021.
Chris Gimber, Partner – ERM
Chris Gimber is a Partner with ERM and provides specialist expertise in the areas of mine rehabilitation and closure, water management, hydrogeochemistry, catchment management and soils. His experience covers all stages of resource project planning and execution, including feasibility studies, impact assessment, concept and detailed engineering, operations and auditing, decommissioning, rehabilitation and monitoring. He has over 20 years consulting experience in the environmental sector across a range of geographies including Australia, Thailand, Indonesia, PNG, India, Brazil and New Zealand.