2.3.5 Conceptual model of causal pathways


This section describes the causal pathways by which open-cut coal mines and coal seam gas (CSG) operations impact water quantity and quality, and affect water-dependent assets in the Maranoa-Balonne-Condamine preliminary assessment extent (PAE). The coal resource development pathway (CRDP) includes five baseline CSG operations, five baseline open-cut coal mines and two additional open-cut coal mines (New Acland Coal Mine Stage 3 and The Range).

A hazard analysis systematically identifies activities that occur as part of coal resource development in the Maranoa-Balonne-Condamine subregion and which may initiate hazards, defined as events, or chains of events, that might result in an effect (change in the quality or quantity of surface water or groundwater). A large number of hazards are 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. Hazards associated with CSG operations and open-cut coal mines that are considered to be in scope for BA in the Maranoa-Balonne-Condamine subregion are grouped into four main causal pathway groups: (i) ‘Subsurface depressurisation and dewatering’; (ii) ‘Subsurface physical flow paths’; (iii) ‘Surface water drainage’; and (iv) ‘Operational water management’.

‘Subsurface depressurisation and dewatering’ causal pathway group associated with the CRDP has the potential to directly affect the regional groundwater system, and indirectly affect surface water – groundwater interactions and depth to the watertable. For the ‘Subsurface physical flow paths’ causal pathway group, subsurface physical flow paths can be affected by hydraulic fracturing, changes to well integrity and surface water – groundwater interactions associated with coal resource development. The extent of these changes is likely to be restricted to aquifer or aquifer outcrop areas within tenements, but can affect connected watercourses within and downstream of tenements. Incomplete knowledge of the location of subterranean faults and fractures of the geological layers means that uncertainty exists in the precise spatial extent of groundwater level decline due to CSG operations.

‘Surface water drainage’ is the most common causal pathway group for CSG operations and open-cut coal mines. Subsidence, diverting site drain lines, rainwater and runoff diversion, levee bunds and creek crossings can change, or disrupt, surface water drainage. Effects on surface water direction, volume and quality can have medium-term (5 to 10 years) to long-term (10 to 100 years) cumulative effects on watercourses within and downstream of tenements. The ‘Operational water management’ causal pathway group involves the modification of water management systems and may have cumulative effects on surface water catchments and stream networks, surface water – groundwater interactions and groundwater conditions. Effects are likely to be in the medium to long term and include the alluvium and watercourses in aquifer outcrop areas that are within and downstream of tenements. The availability of long-term, consistent water quality and water quantity data measurements of surface water and groundwater systems limits the value of developing a coupled surface water-groundwater numerical model in the Maranoa-Balonne-Condamine subregion at this time.

Last updated:
16 October 2018
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