4 Discussion

4.1 Hazard identification and analysis

Rigorous, systematic hazard analysis is an essential component of any scientific risk assessment process. In this analysis a proven and well-trusted hazard analysis technique designed for complex industrial systems, Failure Modes and Effects Analysis, has been adapted for CSG and open-cut coal mining operations in the Gloucester subregion, with some small amendments to the scoring process that help communicate and facilitate the process. The modified technique was renamed Impact Modes and Effects Analysis (IMEA). This method has been adapted for the BA Technical Programme; the Gloucester subregion is one case study of the application of this adaptation. The IMEA has been completed for CSG, open-cut and underground coal mines (where each is applicable), for seven other regions.

There are two primary objectives of the IMEA: (i) to identify and rank the water-related hazards associated with CSG and open-cut coal mining operations in the Gloucester subregion and (ii) to identify potentially important stressors, and the balance of deliberate versus accidental events, associated with CSG and open-cut coal mining operations more generally, to inform the scope of the BAs, and thereby determine what should be in and out scope.

CSG extraction and large coal mining operations are complex processes. They involve a large number of activities spanning distinctly different life-cycle periods, and thereby entail a large number of potential environmental hazards. The analysis reported in this submethodology is restricted to potential impacts on water-dependent assets, but nonetheless still identified in excess of 250 and 350 potential hazards for CSG extraction and large coal mining developments respectively.

It is important to emphasise that despite the use of effect severity and effect likelihood scores, this assessment does not provide an absolute or even relative measure of risk. IMEA provides a relative rank of hazards. The value of this assessment lies in the systematic and thorough identification of hazards (impact modes) and in their ranking relative to each other.

The IMEA suggests that potential impacts on aquifers and the effects of production water disposal (CSG), and disruption of, or changes to, natural surface drainage, along with leaching of contaminants (mines) are amongst the most important water-related hazards in the Gloucester subregion. This does not, however, imply that the risks associated with these potential hazards are high or in some way significant, only that it is important that these hazards (along with many others) are considered for inclusion in the BA.

The IMEA also points to the possibility of cumulative impacts associated with vegetation removal and diversion of site drainage lines around CSG plants, mines and pipeline corridors. Individually these hazards are not deemed to be relatively important, but they were in the top five most frequently identified impact causes for open-cut coal mining and CSG operations. These hazards are deliberate and associated with many open-cut coal mining and CSG activities, and are therefore likely to contribute to other stressors in the environment.

Accidental events and stressors that can have detrimental effects on surface water and groundwater quality, particularly TSS, pollutants (metals, trace elements, sulfides and phosphorus), TDS and hydrocarbons, feature prominently in the IMEA.

Quantifying the risks associated with accidental events entails additional calculations over deliberate events, namely the probability that the accidental event will occur over a specified period of time. The historical rates of identical or similar accidents can provide some guidance in this respect so long as the operating conditions during the record period are relevant to modern Australian operating standards.

Quantifying the risks associated with changes in surface water and groundwater quality, as well as quantity, also entails an additional modelling overhead, as described in Chapter 5 in the companion submethodology M06 (as listed in Table 1) for surface water modelling (Viney, 2016).

Finally, whilst the results reported here are specific to the Gloucester subregion, much of the progress and lessons learnt will be applicable to other bioregions and subregions. The list of activities developed for the IMEA for Gloucester subregion (see Appendix B) are generic for similar coal mines and CSG operations, and provide a template for application in other bioregions or subregions. Highly-ranked hazards may vary somewhat between bioregions and subregions, particularly for those with underground mining because this was not relevant for the Gloucester subregion. Accidental events and impacts on water quality are likely to be equally important across all bioregions and subregions.

4.2 Scope

The hazard analysis presented here has provided a systematic consideration of activities associated with all life-cycle stages of coal resource development, their potential causes and pathways to impact, and the possible changes to aspects of surface water or groundwater. A long list of hazards has been generated across both coal mining and CSG. The hazards of primary focus from a BA perspective are those that extend beyond the development site and that may have cumulative impacts, as these are consistent with the regional focus of BA, and are where BA will add value beyond site specific Environmental Impact Statements (EIS). Ultimately, however, BA need to be able to address all identified hazards by considering the scope, modelling, other literature or narratives, and specifying where science gaps may exist.

The following guidelines and analysis categories broadly describe how various hazards may be handled. It is important to note that changes may occur in individual subregions in response to their development or biophysical context. Three categories were considered when determining if the hazards identified by IMEA were in or out of the BA scope: (i) in scope and addressed by the BA modelling, (ii) in scope but addressed by a narrative, (iii) out of scope because the hazard would typically be handled by site-based risk management following an EIS.

In the case of hazards that are deemed to be in scope but handled by a narrative, the hazard priority number and hazard score should be used as a guide to determine the length and detail of the narrative, and may also be used to identify priorities for future research and quantitative analysis.

The following guiding principles were considered in deciding how individual hazards are allocated to each of the three categories:

These categorisations are presented here to provide guidance on which hazards are in and out of the BA scope. How these hazards are carried forward, however, may be altered by local considerations for each subregion (e.g. additional narrative around discharge to a river that may increase the level of the watertable in contributing streams may be warranted) and the availability of data or information to support the modelling (e.g. water extraction from stream for operation needs to be known if it is to be incorporated into the modelling).

4.2.1 Coal seam gas operations

Table 10 categorises the hazards and impact pathways to the water-related effects and changes in surface water or groundwater for CSG operations.

There are a range of other hazards identified that are also covered by site-based risk management but that may be considered to have more negligible potential impacts, for example the effect of ground staff, local watertable reduction from exploration bores, or drill control issues. These hazards should be noted but the extent of the narrative may be more limited to reflect their lower priority.

Table 10 Hazards and impact pathways to the water-related effects and changes in surface water or groundwater for coal seam gas operations

4.2.2 Open-cut and underground coal mines

The following represent categorisations of the hazards and impact pathways to the water-related effects and changes in surface water or groundwater for open-cut and underground coal mines (Table 11).

There are a range of other hazards identified that are also covered by site-based risk management but that may be considered to have more negligible potential impacts, for example the effect of ground staff, spillage, incomplete removal of equipment following mine closure, fire, or dust suppression. Again these hazards should be noted but the extent of the narrative may be more limited to reflect their lower priority.

Table 11 Hazards and impact pathways to the water-related effects and changes in surface water or groundwater for open-cut and underground coal mines

4.3 Connection to causal pathways

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 a water-dependent asset. For BAs, this chain of events is a causal pathway, the logical chain of events ‒ either planned or unplanned ‒ that link coal resource development and potential impacts on water and water-dependent assets (see companion submethodology M05 (as listed in Table 1) for developing a conceptual model of causal pathways (Henderson et al., 2016)).

Grouping hazards by common impact cause – the event that initiates a causal pathway – provides a useful starting point for summarising and representing the causal pathways associated with CSG operations and coal mines, and focusing on those causal pathways that are in scope. The Gloucester subregion case study, for example, identifies more than 20 unique impact causes for CSG operations (see Table 14, Appendix A). However, the most frequently cited impact causes for CSG operations are out of scope for the BAs (see Section 4.2): namely human error, accident (e.g. containment loss, digging, ignition, logging machine fault, formation variation) and litter spills.

Eliminating those initiating events that are out scope allows the impact and risk analysis to identify and focus on the causal pathways that are in scope. Ranking provided by the hazard priority number and/or hazard score provides further guidance on their potential importance. Causal pathways that are deemed within scope can be further distinguished by their likely spatial footprint and the manner in which they are addressed within the BA. For example after human error and accident, the next two most frequently cited impact causes for mining in the Gloucester subregion are corridor or site vegetation removal and diverting site or corridor drain lines (see Table 17, Appendix A). The footprint of both of these causal pathways may be mapped for communication purposes. The first, however, is addressed within the impact and risk analysis via a simple narrative (Section 4.2), whereas the latter is accounted for in the surface water numerical modelling by reducing surface water flows into the rivers and streams of impact catchments, which ultimately feeds through into the quantitative stages of the impact and risk analysis via impacts on surface water-dependent landscape classes in the affected region (Figure 4).

The impact and risk analysis ensures that all causal pathways are accounted for by stepping through each of the unique impact causes, and with reference to the impact modes within common cause categories, determining which are in and out of scope, and how those causal pathways that are in scope are handled. In all cases particular attention should be paid to highly ranked hazards. Highly ranked hazards may be focus points for community concerns, hence it is important to carefully consider the implications of treating these as out of scope or handling them via a simple narrative.