2.3.5 Conceptual modelling of causal pathways

Summary

This section discusses the causal pathways for open-cut coal mines and coal seam gas (CSG) operations to impact water quantity and quality, and to affect water-dependent assets in the Gloucester preliminary assessment extent (PAE).

A hazard analysis was used to systematically identify activities that occur as part of coal resource development in the Gloucester subregion and which may initiate hazards, defined as events, or chains of events, that might result in an effect (change in the quality and/or quantity of surface water or groundwater). A large number of hazards were identified; some of these are beyond the scope of bioregional assessments (BAs), such as accidents, and others are adequately addressed by site-based risk management processes and regulation. While individual hazards constitute causal pathways, many of these hazards can be grouped by common impact cause and impact mode and represented by a smaller number of aggregated causal pathways for consideration in the BA.

CSG operations have their immediate impact deep below ground. Aquifer depressurisation, enhanced inter-aquifer connectivity, and the storage and disposal of co-produced water are the main impact modes. Open-cut mines most directly affect surface water flows and aquifers, with disruption of natural surface drainage, inter-aquifer connectivity, and the storage and disposal of rainfall the main impact modes.

The baseline coal resource development (baseline) includes only open-cut mines (as of December 2012), while the coal resource development pathway (CRDP) includes the baseline as well as expansions to the open-cut mines (as of December 2012), a new open-cut mine, and a CSG project.

Linkages between impact modes and affected landscape classes are inferred, with most of the landscape cleared for agriculture. Both the perennial streams of Mammy Johnsons River and the intermittent streams of Avon River are potentially impacted by coal mines and CSG operations. The spatial and temporal scale of impacts are summarised, with most effects only local but with unknown fault and fracture zone behaviour making this speculative. Time scales of impact include the full life of mine plus potentially decades into the future as drawdown cones spread slowly and mine-site rehabilitation is established.