2.3.5 Conceptual modelling of causal pathways


Causal pathways are the logical chain of events –either planned or unplanned – that link coal resource development and potential impacts on water resources and water-dependent assets. In the Hunter subregion, the hazards stem from open-cut and underground coal mining operations; there are no existing, approved or planned coal seam gas (CSG) development activities.

Coal mining operations can affect surface water resources through land subsidence, interception of runoff, extraction from and disposal to surface water features, and depressurisation of aquifers. Both water quantity and water quality may be adversely affected by these hazards. Changes in water quantity are the focus of the bioregional assessments (BAs), but implications for stream salinity are considered as part of the analysis in the impact and risk analysis (companion product 3-4 for the Hunter subregion (as listed in Table 2). Groundwater flows and resources can be affected by changes in aquifer connectivity, which enable the movement of water between previously disconnected, or weakly connected, aquifers. Mining voids that are left, or backfilled, may act as sinks for water flows, or as contamination sites for surface water or groundwater resources.

The hazard analysis for the Hunter subregion identified and scored 271 hazards. The top four hazards (listed with the syntax [Activity]:[Impact mode]) identified are in the production life cycle stage and include: (i) Waste rock blasting, excavation and storage: Disruption of natural surface drainage: Pit expansion; (ii) Longwall coal extraction: Subsurface fractures (create new, enlarge or existing); (iii) Mine dewatering, treatment, reuse and disposal (multi-seam mining): Incremental, mine water increase (unplanned) – from old workings; and (iv) Longwall coal extraction: Subsidence, which is related to (ii).

Hazards associated with open-cut and underground mining operations were grouped into four main causal pathway groups that represent the causal pathway via which each hazard potentially impacts water resources and water-dependent assets on and off site. These four causal pathway groups are: ‘Surface water drainage’, ‘Operational water management’, ‘Subsurface depressurisation and dewatering’ and ‘Subsurface physical flow paths’. For the ‘Surface water drainage’ and ‘Operational water management’, hazards associated with open-cut and underground coal mines affect surface water flows primarily through modifications to surface water drainage and water management systems; hazards that impact groundwater flows do so through subsurface depressurisation and dewatering and modification of subsurface physical flow paths.

Last updated:
18 January 2019