Summary of independent expert advice from CSIRO and OGIA
CSIRO advice summary
CSIRO has expertise in groundwater flow and contaminant transport modelling and were engaged to provide advice on:
- Arrow’s assumptions, groundwater modelling and subsequent conclusions
- whether all potential groundwater contamination and gas migration risks associated with the proposed development had been identified
- how the proposed development will influence the mobilisation of contaminants and whether any environmental harm would be caused
- the groundwater monitoring network and if additional groundwater monitoring or contingency measures to manage mobilisation of contaminants.
CSIRO was provided a copy of Arrow’s EA amendment application, modelling, reporting including Arrow’s 2022 Annual Groundwater Report and all monitoring data from the 15 department installed monitoring bores. CSIRO made a number of recommendations and conclusions following their review of this material. In summary, CSIRO found:
- No significant short-term groundwater contamination outside the boundary of the former Linc Energy Site was predicted and gas movement was not predicted under any modelled scenario. However, any model-based prediction of long-term (beyond 2040) groundwater contamination is uncertain and an adaptive management plan that uses ongoing groundwater monitoring data coupled with updates in groundwater modelling is required to predict changes to groundwater water quality to underpin management of contamination.
- The assumptions used for groundwater flow and contaminant transport modelling represent good practice. The highest priority recommended change to the model is to extend the simulation period and density of particle tracking.
- To better characterise the residual contamination source near the gasifiers in the former Linc Energy site, additional monitoring wells should be drilled and cored to analyse cores for residual contamination. This will give a better understanding of the potential for long-term (beyond 2040) release of contaminants.
- Groundwater sampling results collected by the department from the 15 monitoring bores were used by Arrow.
- Additional monitoring bores are recommended to better assess if contamination exists beyond the boundary of the former Linc Energy Site. This would add confidence that Arrow’s proposed 55 wells do not move any contamination beyond the boundary of the former Linc Energy Site.
OGIA advice summary
OGIA has expertise in groundwater flow modelling and were engaged to provide advice on:
- Arrow’s conclusions on risk of mobilisation of contaminants
- whether Arrows modelling is considered to adequately represent current and predicted groundwater movement.
OGIA was provided with a copy of Arrow’s EA amendment application, modelling and reporting including Arrow’s 2022 Annual Groundwater Report. OGIA made a number of recommendations and conclusions following their review of this material. In summary, OGIA found:
- Arrow’s key conclusion that ‘… the potential for this development scenario to significantly affect the site contamination is low’ is reasonably supported by the information and modelling presented by Arrow. There is however room for further improvements to modelling, underlying conceptualisation and the way the outputs are presented in reporting. The modelling, underlying assumptions and conceptualisation could be improved further, and those improvements will affect the groundwater regime in both cases i.e. with the proposed development (the development case) and without it (the base case). Any potential improvements to the base case will also affect the development case and, hence, conclusions about the net change resulting from the proposed development are unlikely to be affected materially.
- Arrow’s modelling forms a good basis, provided that a supporting simple conceptual model is developed and regularly updated as additional monitoring data becomes available. The conceptual model should clearly identify mobilisation pathways and present the groundwater pressure and flow regime around the site, accompanied by a description of how contaminants would migrate over time with and without the proposed development. This should also identify uncertainties in conceptualisation resulting from formation heterogeneity, preferential pathways and structural influences. The numerical groundwater flow model should then be updated with reference to the conceptual model, supported by an uncertainty analysis.