Regional changes inand flows due to could potentially lead to changes in surface water and groundwater quality. While water quality was not modelled as part of this , the implications for water quality in the are considered here in light of the modelled hydrological changes due to additional coal resource development.
- Relevant factors for assessing the potential for changes in regional groundwater and surface water quality due to additional coal resource development in the Namoi subregion are:
- Coal resource developments in the subregion are required to manage discharges according to volumes, quality and discharge windows specified in environment protection licences (EPL), which are a condition of their approval to operate.
- There is one CSG development being modelled, the Narrabri Gas Project. However, potential water quality issues from use of hydraulic fracturing chemicals have not been considered here as there are no plans to use hydraulic fracturing in the Project (Santos, n.d.).
- None of the additional coal resource developments propose to re-inject co-produced water into depressurised aquifers.
The following sections identify the groundwater and surface waterthat could potentially lead to regional , and assess the of impact. The extent of influence and existing regulation and management practices are used to inform the assessment of risk.
Changes inquality due to coal resource development can occur as an indirect result of and of and changes to subsurface physical pathways between aquifers, which enhance leakage between aquifers of different quality water. Changes in groundwater quality can also occur as a direct result of coal resource development and operational water management, such as when water is deliberately injected into an aquifer or coal seam to manage surplus water or counter the effects of groundwater depressurisation. Unless hydrologically isolated from their surroundings, the creation of coal stockpiles, rock dumps and tailings dams on coal mine sites can result in leaching of contaminants to groundwater. 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 mining operations are in close proximity.
Table 13 lists potential causes of changes in groundwater quality from coal resource development in the and identifies the potential for off-site . In NSW, a water supply work approval is needed under NSW’s Water Management Act 2000 for a new . Construction of a bore must be undertaken by a licensed driller and drillers are expected to meet minimum requirements set out in guidelines outlined in the National Uniform Drillers Licensing Committee (). These guidelines detail mandatory requirements and good industry practice for all aspects of the bore life cycle from bore design, bore siting, drilling fluids, casing, maximising bore efficiency, sealing and bore completion. While some leakage from older bores is considered likely, these bores are not part of the potential impact due to and are not within the scope of this BA. Three of the four in Table 13 could potentially have off-site impacts. In the remainder of this section, the of impacts is considered in the of existing regulatory controls.
The potential impacts on level, water pressure and groundwater quality from environmentally relevant activities, such as coal mining, are managed through the NSW Aquifer Interference Policy (). This policy requires that all water taken from an aquifer is properly accounted for; minimal impact considerations on the watertable, water pressure and water quality are addressed; and remedial measures are planned for in the event that actual impacts are greater than predicted. For aquifers in the Namoi subregion, no change in the beneficial use category of a groundwater source further than 40 m from the activity is permitted, unless studies can demonstrate that the change in groundwater quality will not affect the long‑term viability of any water sharing plan, , culturally significant site or water supply work. An increase of more than 1% per activity of the long-term average salinity is not permitted in a highly connected water source at the nearest point to the activity. As part of their groundwater monitoring and modelling plans, mining companies must demonstrate to the satisfaction of the NSW Department of Primary Industries Water that the proposed development is undertaken in accordance with the policy. Given this, the potential for significant changes in regional groundwater quality are likely to be low.
Table 13 Potential causes of changes in groundwater quality and potential for off-site impacts in the Namoi subregion
Changes in tensile and compression forces in the overburden above longwall panels following their collapse can lead to fracturing above longwall panels and hydraulic enhancement of the, with the potential for freer movement of water between aquifers of potentially different water quality. Hydraulic enhancement was modelled in the Namoi groundwater model (companion product 2.6.2 for the Namoi subregion ( )) and was shown to affect the extent of and – groundwater exchanges, but implications for groundwater quality were not modelled. Sometimes groundwater assessments undertaken by mines represent changes in hydraulic properties above longwall panels in their modelling, but sometimes these changes are ignored because the scale of influence is deemed too local to affect larger-scale drawdown predictions. If hydraulic enhancement of the goaf is ignored, the hydraulic properties of the interburden may be overestimated to compensate for the lack of groundwater flowing into the mine. Invariably, the groundwater models do not represent changes in groundwater quality or surface water quality due to changes in hydraulic properties. The effect of coal resource development on the water quality of nearby aquifers and streams in the Namoi subregion remains largely a knowledge gap.
In relation to leaching of contaminants from mining-related contaminant sources, the Department of Industry Resources and Energy (DIRE), under NSW’s Mining Act 1992, requires mines to have an approved mining operations plan (MOP). The MOP provides details of how the mining operation will be carried out, including details of management of stockpiles, rock dumps and tailings dams. Mining companies, as part of best practice management, are required to design storages that are secure and stable over their life and have a low risk of spills.
Changes inquality from coal resource development can occur as a result of 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. Disturbed soil due to mining and bare surfaces as a result of vegetation removal increase the of erosion, with potential to increase total suspended solids (TSS) in waterways. There is the potential for ecological imbalance in receiving waterways due to the mine water into the stream network as part of operational water management, if the quality of the discharged water lowers the quality of the receiving water below its current beneficial use level. pumping and subsurface fracturing and above longwall panels can lead to changes in surface flow and to streams and potentially affect the water quality of the stream.
Table 14 lists potential causes of changes in surface water quality due to coal resource development and identifies the potential for off-site in the , having regard to the likely scale of the effect and existing management. The ‘Altering surface water system’ is considered unlikely to lead to noticeable off-site water quality impacts; the remaining three could potentially have off-site impacts on water quality.
Table 14 Potential causes of changes in surface water quality and potential for off-site impacts
Due to highly strict mine operating licencing conditions, theof off-site water quality impacts from altering the surface water system on the mine sites is considered low. There is a long history of soil erosion management in NSW, which has its origins in the agricultural sector, but has been extended to minimise the generation and mobilisation of sediments in all developments where disturbance of the soil occurs. NSW Resources and Energy (NRE) requires mines to provide details of how the mining operation proposes to minimise soil loss at all life stages of the mine and post-mining as part of an approved mining operations plan. Environmental protection licences, issued by NRE under NSW’s Protection of the Environment Operations Act 1997, may also specify erosion control conditions. Furthermore, DIRE requires authorised mines to develop, implement and report on environmental monitoring programs. In annual environmental management reports (AEMR), the coal mining companies must publish their monitoring data in order to demonstrate that they are meeting their environmental objectives under their licence to operate.
184.108.40.206.1 Stream salinity
220.127.116.11.1.1 Discharges to regulated and unregulated rivers
There are many competing demands on water resources in the rivers of theand water needs to be of a quality to support a diverse range of agricultural uses, town water supply and environment. Background salt levels are naturally high in some parts of the subregion such as the Coxs Creek and Mooki and Peel rivers, which are the major contributors of salts to the Namoi River. Salinity in these areas are thought to be caused by the presence of salt in underlying soil or bedrock released by weathering, salt deposited during past marine inundation of an area, or salt particles being carried over the land surface from the ocean ( ).
These coal mines are required to hold an environment protection licence (EPL), which specifies conditions attaching to the mine’s licence to operate, including those relating to the management of mine water.of mine and CSG-related water to streams are authorised only if the quality of discharged water is the same or better than the quality of receiving waters. For example, in the Boggabri Coal Mine, water dams will be constructed to store contaminated water, including saline water, and water will be reused if the water quality is unsuitable to be discharged to Nagero Creek. Discharges may also be permitted during high-flow windows when the natural salinity of the river decreases and the river can accommodate extra salt from industrial discharges without exceeding salinity thresholds.
Table 15 shows that there are no flow thresholds stipulated for streams in the Namoi subregion above which mine water is allowed to be discharged. All mine projects have proposed to fully utilise the mine water for mine operation purposes or contain it within the mine site, except in the case of an extended wet season. Modelling studies carried out using historical rainfall conditions for the environmental impact assessments of respective mines suggest that there should be sufficient capacity to contain all mine water.
Table 15 Discharge arrangements of the different mine projects and effect of additional coal resource development (ACRD)
aCaroona Coal Project was ceased and exploration licence cancelled. Not much information available at the time of writing (June 2017).
na = not applicable; NA = not available
In conclusion, due to a high level of regulation and monitoring of discharges of mine water to the surface drainage network in the Namoi subregion, theto stream water quality from this is considered to be minimal.
18.104.22.168.1.2 Depressurisation, dewatering and hydraulic enhancement
Theto regional stream water quality caused by changes in following and of mines and/or changes in subsurface physical flow paths (e.g. from hydraulic enhancement of the ) 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 . Modelling of the hydrological changes due to in the predicts a probable reduction in baseflows to Namoi subregion streams. If, as is usually the case, the salinity of the groundwater is higher than that of the stream into which it discharges, a reduction in baseflow would be expected to lead to a reduction in stream salinity.
Companion product 1.5 () for the Namoi subregion provides details on groundwater and quality. In all the streams identified from the regional-scale modelling as at risk of potentially large changes in flow regime, the on local stream salinity will depend on the relative reductions in catchment and baseflow over time. Reductions in catchment runoff are more likely to affect runoff peaks, while baseflow reductions have a more noticeable effect on low flows. The implications for stream salinity at any given time will depend on how the relative contributions from the quick and slower flow pathways change over time. In streams, such as Back Creek, Merrygowen Creek and Ballol Creek, Tulla Mullen Creek and Mooki River near the Maules Creek, located near Boggabri, Tarrawonga, Vickery and Watermark coal mines respectively, where modelling results suggest increasing numbers of , it is likely that channel pools will be subject to longer periods of salt concentration by evaporation and less efficient flushing. These are conditions that favour increasing the salinity of these water bodies.
Increases in baseflow, potentially leading to increases in alluvialand stream salinity, cannot be ruled out, however, this is not an outcome that has been reported in the literature and remains an area for further investigation. The magnitude and extent of water quality changes cannot be determined without specifically representing water quality parameters in the modelling. This remains a knowledge gap.
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 'Floodplain or lowland riverine' (non-Pilliga) landscape group
- 3.4.4 'Non-floodplain or upland riverine' (non-Pilliga) landscape group
- 3.4.5 Pilliga riverine (upland and lowland)
- 3.4.6 Potentially impacted landscape classes lacking quantitative ecological modelling
- 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