2.3.5.1 Methodology

Conceptual models of causal pathways are a specific type of conceptual model which characterises the causal pathways, the logical chain of events ‒ either planned or unplanned ‒ that link coal resource development and potential impacts on water resources and water-dependent assets.

These conceptual models bring together the existing understanding and conceptual models of the key system components, processes and interactions for the geology, hydrogeology, surface water, and surface ecosystems, and consider the most plausible and important impact and their spatial and temporal context. The conceptual modelling draws heavily on companion products from Component 1: Contextual information, which is summarised in Section 2.3.2, Section 2.3.3 and Section 2.3.4.

The causal pathways underpin the construction of groundwater and surface water models, and frame the assessment of the impacts on and risks to water and water-dependent assets. The approach taken in the Hunter subregion has leveraged existing NSW based resources and knowledge of geological, surface water and groundwater conceptual models. The Assessment team summarised the key system components, processes and interactions for the geology, hydrogeology and surface water of the subregion at the ‘Conceptual modelling of causal pathways’ workshop held in Newcastle in August 2015. Discussion with representatives at the workshop focused on the description of the causal pathways, the testing of knowledge gaps and uncertainties identified by the Assessment team, and the identification of potentially impacted landscape classes. Hazards associated specifically with CSG development were not covered in the Hunter hazards workshop, as CSG development is not part of the coal resource development pathway (CRDP) for the Hunter subregion.

In a BA, the identification and definition of causal pathways is supported by a formal hazard analysis, known as Impact Modes and Effects Analysis (IMEA) as outlined in companion submethodology M11 (Ford et al., 2016) and illustrated in Figure 5 (Section 2.3.1). The causal pathways are based on the outcomes of this hazard analysis and current understanding of the way ecosystems and landscape classes in the Hunter subregion work and interact. The IMEA rigorously and systematically identifies potential 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). Only hazards identified through the IMEA process are considered further in the BA. Additionally, the IMEA considers all the possible ways in which activities may lead to effects or impacts, before assessing the severity, likelihood and detectability of such impacts under current controls through structured scoring.

Key to the IMEA for the Hunter subregion was identifying activities, planned events associated with open-cut and underground mining operations. Activities are grouped into components, which are grouped into life-cycle stages. It is important to assign activities to their appropriate life-cycle stage because the scale and duration of similar activities can be different for each life-cycle stage, which is reflected in the scores for severity and/or likelihood of the impacts resulting from these activities.

Activities for open-cut and underground coal mines are separated into five life-cycle stages and four components:

An impact cause is an activity (or aspect of an activity) that initiates a hazardous chain of events. An activity can have undesirable effects (such as water extraction that leads to groundwater drawdown, reduction in baseflows, more frequent episodes of inter-pool connectivity and loss of species richness or abundance) and desirable effects (such as water extraction enabling coal extraction to occur and providing water for other on-site uses).

An impact mode is the manner in which a hazardous chain of events could result in an effect. There might be multiple impact modes for each activity or chain of events. The impact modes may arise through various mechanisms, including anthropogenic activities that are planned and expected to occur as part of operations; unplanned events due to human error or infrastructure failure; or through combination with external factors (e.g. heavy rainfall or floods).

A simple example for open-cut mines is illustrated in Figure 5(a), initiated by ‘dewatering down to coal seam for an open-cut mine’, which is the impact cause. The impact mode (‘intentional dewatering down to coal seam’) leads to the effect (‘change in groundwater quantity (drawdown)’), which in turn may result in an ecological impact, ‘reduced groundwater availability for a groundwater-dependent ecosystem’.

Participants in the Hunter IMEA workshop were invited to identify all plausible hazards and impact modes on an activity-by-activity basis, together with the potential hydrological effects on groundwater and/or surface water. Each hazard is scored with respect to the severity, likelihood and time to detection. The IMEA elicits an interval (upper and lower score) for each hazard that all workshop participants agree upon:

Two overarching hazard ranking scores are calculated:

It is important to emphasise that despite the use of severity scores and likelihood scores, the hazard ranking scores do not provide an absolute or even relative measure of risk. IMEA provides a relative rank of hazards. The value of this analysis lies in the systematic and thorough identification of hazards and in their ranking relative to each other. Hazards with higher scores do not imply that the risks associated with those potential hazards are in some way significant or apply equally across the Hunter subregion at all times, only that it is important that these hazards (along with many others) are considered for inclusion in the BA.

There is considerable structure and hierarchy within these lists of IMEA hazards (Bioregional Assessment Programme, Dataset 1) with the finer-level hazards aggregating to successively coarser resolutions. For example, there are a range of activities that may require the removal of site vegetation (the impact cause), including site clearance prior to construction of pits, storage ponds, site processing plants, water treatment plants, and the construction of access roads and pipeline or infrastructure networks; these may all potentially result in changes to surface water quality from soil erosion following heavy rainfall (impact mode).

The hazards identified by the IMEA represent a conceptual model of the chain of events that begins with an activity and ends with a potential impact on groundwater or surface water; causal pathways include these chains of events and also extend to resulting ecological impacts (see Figure 5). Causal pathways are considered for open-cut and underground coal mines separately, for both the baseline coal resource development (baseline) and the coal resource development pathway (CRDP). A full suite of generic causal pathways for hazards due to coal mining operations is presented in figures in an appendix in companion submethodology M05 (as listed in Table 1) for developing a conceptual model of causal pathways (Henderson et al., 2016). These figures identify activities, impact causes and impact modes as well as those aspects of surface water and groundwater that might be affected. The causal pathways in the submethodology are generally applicable to all subregions or bioregions; Section 2.3.5.3 presents specific results for the Hunter subregion.

Hazards are grouped for the Hunter subregion if they have the same causal pathways, even if those hazards occur because of different activities, at different life-cycle stages, or at different intensities. This smaller set of causal pathway groups provides a useful starting point for summarising and representing the causal pathways associated with coal resource development (e.g. through influence diagrams) and focusing on those causal pathways that are in scope for BA.

The spatial footprint for the identified hazards and causal pathways identified is a core focus of the conceptual modelling, and is arrived at on the basis of existing knowledge, scientific logic and preliminary hydrological modelling results. An important aspect of that is using those same sources to identify which landscape classes and assets may be affected by a potential hydrological change that arises from those causal pathways, and (equally importantly) which landscape classes and assets will not be affected. Throughout the BA, areas that will not be affected are progressively ruled out in order to focus efforts of the Assessment team and ultimately the impact and risk analysis.