Regional hydrological changes due to could potentially impact and quality. Although water quality was not modelled as part of this , the implications for water quality in the are briefly considered in this section, in light of the previously discussed modelled changes due to additional coal resource development.
Relevant factors for assessing the potential for changes in regional groundwater and surface water quality from the seven additional coal resource developments in the Galilee subregion are:
- Natural streamflow in the Galilee subregion varies considerably, with long periods of little to no streamflow during times of low rainfall. This is likely to affect surface water quality (e.g. variations in salinity and turbidity) between wet and dry seasons.
- Approval conditions for off-site discharge of mine-related water are yet to be finalised (as of December 2017).
- No groundwater off site is envisaged (e.g. it is not proposed as part of environmental impact statement (EIS) documentation), with most groundwater extracted as part of routine mine operations expected to be utilised on site for various mining and processing applications (see Section 2.5.2 in companion product 2.5 for the Galilee subregion () for further information). Therefore, it is possible that salts derived from this groundwater will need to remain contained on site.
- Source of external water supplies for mines is yet to be finalised. Transferrals of large volumes of water will include dissolved solutes and may influence distribution of salt within the catchment, or possibly in other (nearby) catchments.
- Surface water salinity data are patchy, with large gaps (both spatial and temporal) between measurements in most of the streams in and near to the zone.
- Other than salinity information, there is very little available analytical data for minor, trace and organic analytes from groundwater and surface water in the .
- None of the additional coal resource developments propose to re-inject co-produced water into depressurised .
- Water quality from non-modelled developments (see Section 3.6) will be additional to any potential water quality changes derived from modelled development areas, but are not further assessed here.
In the following sections the groundwater and surface water that could potentially lead to regional water quality impacts are identified and the of impact is qualitatively assessed. The extent of influence and existing regulation and management practices are used to inform this assessment of risk.
quality in the is covered by the Environmental Protection (Water) Policy 2009 (EPP (Water)), which achieves the objectives of Queensland’s Environmental Protection Act 1994. The groundwater modelling results presented in companion product 2.6.2 () indicate that any potential groundwater will be confined to hydrostratigraphic units assigned to the Galilee Basin (primarily the upper Permian coal measures, Rewan Group, and to a lesser extent the Clematis Group ) and in areas where alluvium and Cenozoic sediments overlie the Galilee Basin aquifers. These conditions largely occur around the central-eastern margin of the Galilee Basin in the vicinity of the modelled .
Changes in groundwater quality from coal resource development can occur as an indirect result of and of aquifers and changes to subsurface physical pathways between aquifers, which may enhance leakage between aquifers that contain groundwater of different qualities. Changes in groundwater quality can also occur as a direct result of coal resource development and its associated operational water management practices, such as when water is deliberately injected into an aquifer or coal seam to manage surplus water, counter the effects of groundwater depressurisation or to facilitate the process of CSG extraction. Unless hydrologically isolated from their surroundings, the creation of coal stockpiles, rock dumps and tailings dams on coal mine sites can also result in leaching of contaminants to shallow . In all these cases, a arises when the quality of the receiving water is changed such that it reduces its beneficial use value. are concerned with the from non-accidental changes to water quality off site, which may be cumulative where different mining operations occur in proximity.
Table 17 lists potential causes of changes in groundwater quality from coal resource development in the Galilee subregion and identifies the potential for off-site impacts. Groundwater quality (including aquifer properties and groundwater composition) is potentially affected by up to eight in the Galilee subregion. Effects on groundwater quality are localised within , downstream watercourses and irrigated areas or target aquifers used to dispose of co‑produced water. Risks will mainly be addressed by future mine water management and monitoring plans within tenements. In some areas of Queensland (e.g. around the Surat Basin), Healthy Waters Management Plans may also exist for potentially affected downstream watercourses. In the remainder of this section, the risk to water quality off site is considered in the of the scale of the effect and existing regulatory controls.
Coal mines have the potential to change – groundwater interactions. These changes are likely to be within tens of metres of a watercourse and so are not represented in the regional groundwater model developed for the Galilee subregion. Preferential flow paths can also be affected by changes to surface water – groundwater interactions (including changes to aquifer interconnectivity, mine expansion close to a river or lake, preferential drainage and associated with post-closure water filling the pit). Mine developments that link aquifers and lead to preferential drainage can affect groundwater quality, but may be limited to the vicinity of open-cut pits. Changes to surface water – groundwater interactions can also change the timing and volume of contributions to streams, which can affect the stream within and downstream of tenements. These changes are likely to be restricted to areas where direct interactions between watercourses and are possible.
While not specifically identified for each development, monitoring and dewatering bores are required for coal resource developments. The code of practice for constructing and abandoning coal seam gas and associated bores in Queensland () was developed to ensure that all CSG wells and CSG water bores are constructed and abandoned to a minimum acceptable standard resulting in long-term well integrity, containment of gas and the protection of groundwater resources.
Fracturing above underground longwall panels due to removal of coal and hydraulic enhancement (of aquifers and ) above the potentially affects the rate, volume and timing of groundwater flow between aquifers. Enhanced aquifer has the potential to lead to mixing between different quality groundwater sources, or to locally enhance recharge of surface water to shallow aquifers. However, the degree of change in connectivity is dependent on site-specific conditions at each underground operation, and requires substantially more local-scale studies than what has been possible to undertake for this BA.
Dam construction and other water management structures that change natural surface drainage and have the potential to affect patterns, in turn affecting groundwater quality and quantity/volume. However, this is likely to be limited to watercourses within and downstream of tenements.
Table 17 Potential causes of changes in groundwater quality and potential for off-site impacts in the Galilee subregion
quality in the is covered by the Environmental Protection (Water) Policy 2009 (EPP (Water)), which achieves the objectives of Queensland’s Environmental Protection Act 1994. The is situated in the headwaters of the Burdekin river basin. Draft environmental values and water quality guidelines for the Burdekin river basin were released for consultation in March 2017 (). These built on work undertaken as part of the Burdekin Region Water Quality Improvement Plan 2016 (). also provides background information on water quality issues in the Burdekin river basin.
Changes in surface water quality from coal resource development can occur following disruptions to surface drainage from the removal of vegetation and disturbance of soil in construction of roads, site facilities, excavation of open-cut pits and landscaping of the site during production and rehabilitation. Bare surfaces increase the of erosion with potential to increase loads of total suspended solids in waterways. Consequently, adequate controls are an important component of managing enhanced erosion risks due to coal mining developments. In addition, the discharge of mine water into the stream network as part of operational water management is a potentially hazardous activity, especially if the quality of the discharged water lowers the quality of the receiving water below its current beneficial-use level. Similarly, any unintentional releases of mine water off site could also be considered as a potential to surface water quality. However, such unintended release events are typically rare (e.g. potentially caused during major floods or in the event of unexpected dam failure), with approved design and containment strategies required to be developed in order to adequately address such aspects of mine site water management.
and of and changes to subsurface physical pathways between aquifers can lead to a change in to streams and potentially affect the water quality of the stream. Table 18 lists potential causes of changes in surface water quality from coal resource development in the Galilee subregion and identifies the potential for off-site , having regard to the relevance of the in the subregion and the likely scale of the effect.
Table 18 Potential causes of changes in surface water quality and potential for off-site impacts
The of off-site water quality impacts to broader surface water systems is reduced through the capture of surface water on mine sites, which is then utilised for various on-site and processes. As of December 2017, conditions for off-site discharge of any excess water are yet to be finalised for the . Site-specific discharge conditions will form part of future mine approval conditions.
All of the modelled coal mining projects in the Galilee subregion are situated in the headwaters of the Belyando river basin. From the perspective of the greater Burdekin river basin, the mean annual stream from the Belyando River accounts for about 10% of the total discharge volume of the Burdekin River (). During the period 2005 to 2010, Bainbridge et al. (2014) estimated that the mean annual discharge contribution from the Belyando River was about 780 GL/year. In comparison, for the other main rivers above the Burdekin Falls Dam, the mean annual discharge was estimated as 740 GL/year for the Cape River, 820 GL/year for the Suttor River and 4500 GL/year for the Burdekin River ().
Sediment loads in the Belyando and Burdekin river basins vary significantly from year to year and are in part dependent on streamflow volumes (). Sediment loads increase in wetter years or during large cyclone events. For the 2005 to 2010 period, estimated that the average sediment load contribution from the Belyando River to Lake Dalrymple (Burdekin Falls Dam) was 0.16 Mt/year. In comparison, the sediment contributions from the other main rivers were estimated to be: Cape River (0.27 Mt/year), Suttor River (0.25 Mt/year) and the Upper Burdekin River (5.23 Mt/yr). Thus, the Upper Burdekin River is clearly the main contributor to the overall sediment budget in the Burdekin river basin (above Lake Dalrymple).
It is estimated that the Burdekin Falls Dam (Lake Dalrymple) traps around 65% of the sediment and nutrient load from the combined input of the Upper Burdekin, Belyando, Suttor and Cape rivers (). The trapping efficiency and effectiveness of the Burdekin Falls Dam has implications for the downstream dispersion of any extra sediment load that may occur due to future coal mining in the Belyando river basin.
The risk to regional surface water quality caused by changes in baseflow following depressurisation and dewatering of mines and/or changes in subsurface physical flow paths (e.g. from hydraulic enhancement above the in longwall mines) will depend on the magnitude of the hydrological changes and the salinity of the relative to the salinity of the water in the stream into which it discharges. Modelling of the hydrological changes due to additional coal resource development in the Galilee subregion suggests some reduction in baseflow is likely to occur within the , thereby potentially leading to changes in water quality.
The magnitude and extent of water quality changes cannot be determined without specifically representing the key water quality parameters in the modelling. This remains an important knowledge gap for the Galilee subregion, particularly in the of multiple large-scale mining developments that may potentially result in to water quality (see Section 3.7.4 for further discussion about gaps and limitations relevant to this ).
Product Finalisation date
- 3.1 Overview
- 3.2 Methods
- 3.3 Potential hydrological changes
- 3.4 Impacts on and risks to landscape classes
- 3.4.1 Overview
- 3.4.2 Landscape classes that are unlikely to be impacted
- 3.4.3 'Springs' landscape group
- 3.4.4 'Streams, GDE' landscape group
- 3.4.5 'Streams, non-GDE' landscape group
- 3.4.6 'Floodplain, terrestrial GDE' landscape group
- 3.4.7 'Non-floodplain, terrestrial GDE' landscape group
- 3.5 Impacts on and risks to water-dependent assets
- 3.6 Commentary for coal resource developments that are not modelled
- 3.7 Conclusion
- Contributors to the Technical Programme
- About this technical product