Our client extracts groundwater that is elevated in metals and organics and is required to treat this groundwater to meet both industrial and environmental end uses. It is a regulatory requirement under the Environmental Protection Act 1986 that some of this extracted groundwater must be returned to the aquifer after it is treated.
To support the safe implementation of aquifer recharge, EHS Support completed detailed geochemical modelling to assess how introduced water would interact with the receiving groundwater system and host geology.
The study evaluated mixing scenarios between treated water and groundwater within the aquifer, focusing on mineral stability, dissolution potential, and water chemistry evolution. Modelling incorporated site-specific mineralogy and groundwater chemistry data to simulate realistic subsurface conditions.
Results showed that introducing low-mineralised water can initially cause minor dissolution of carbonate minerals, particularly calcite, before equilibrium conditions are established. This process was quantified across a range of mixing scenarios, demonstrating that, while some dissolution occurs, it is limited in magnitude and manageable from a design perspective.
Further analysis confirmed that the risk of trace metal mobilisation is low under typical conditions, with only minor sensitivities identified at depth where reducing conditions are present.
Overall, the modelling provides confidence that aquifer recharge can be implemented with appropriate controls, supporting sustainable water reuse while managing geochemical risks.