The Watermark Coal Project was approved by the NSW Government in January 2015 and by the Australian Government in July 2015, but construction has not yet commenced. The approval allows for the extraction of up to 10 Mt/year ROM coal until June 2046, using open-cut mining methods. ROM coal reserves are estimated to be approximately 268 Mt (). The mine will target the Hoskissons Coal and Melville Coal Member ( ).
Coal extraction will take place from three mining areas. As mining progresses all disturbed areas will be progressively rehabilitated. Tailings and coarse rejects will be co-disposed of in overburden emplacement areas ().
The proposed development includes the construction and operation of a mine access road; administration, workshop and related facilities; a coal handling and preparation plant; and transportation infrastructure. Projectare planned to take place within a disturbance area of approximately 4084 ha ( ).
Water balance modelling was undertaken and showed that, while most site water requirements will be met by reuse of on-siteand , the average net water deficit will be 21 to 162 ML/year.
Table 27 provides a summary of the requirements for the project throughout the mine life.
Where water is required additional to that available from the captured dirtyand water intercepted by mining, the project proposes to draw water from adjoining water sources under water access licences already held or to be purchased. It is proposed to use water pumped from the Mooki River or potentially a borefield.
Table 27 Watermark Coal Project predicted water requirements
aThe volume reported for vehicle washdown represents the losses from the system, which is typically approximately 10% of the total water requirement for vehicle washdown ().
The mine area is located within the Mooki river basin, a tributary of the Namoi River.from the site drains to one of three local drainage lines: Watermark Gully or unnamed flow paths to the north; Native Dog Gully to the south; or west to Lake Goran.
The main parts of the water-related infrastructure for the Watermark Coal Project include:
- sediment dams to collect and treat runoff from the operational areas
- dirty water drains to divert sediment-laden runoff to the sediment dams
- clean water drains to divert runoff from the undisturbed catchment around areas disturbed by mining
- a dirty water storage system to store water pumped out of the mining areas and to collect runoff from the CHPP and coal stockpile area. Mine water dams will be the first priority water source for road watering and CHPP water demands
- raw water storage (the main dam) from the water supply pipeline.
If water collected and treated in the sediment dams is not suitable for release to receiving waters it will be pumped back into the water management system. Runoff water will only be released from site if the quality is acceptable and during a rainfall event that exceeds the design capacity of the sediment control dam system (appropriate licences would be obtained for the release of this water).
The water management system has been modelled over the range of historical rainfall conditions and has been shown to have sufficient capacity to contain all mine water on the site without the need for offsite releases.
With the exception of the Western Mining Area (a portion of which will be the final void), it is planned that mining areas will be progressively rehabilitated as mining advances or concludes. The final void is anticipated to cover approximately 100 ha with a maximum depth of approximately 80 m below the natural ground surface. A mine closure plan will be developed within five years of closure ().
Table 28).seepage into the proposed mining area is predicted to vary throughout the mine life (
Table 28 Predicted Watermark Coal Project groundwater inflows to pit
These are pumpable volumes and so do not include volumes lost to evaporation in the pit, or moisture lost to the mined coal.
Estimated mean groundwater inflow rate
The groundwater seepage from the Permian units into the mining areas averages 180 ML/year over the life of the project. The peak seepage rate to the mining areas is estimated at 756 ML/year in year 23 (). The variability in the seepage rate is due to the different geological conditions that will be encountered in different mine areas.
The groundwater model indicatesin the underlying Permian strata will reduce upward water pressure, and close to the mining areas will induce downward vertical flow from the overlying alluvial in the underlying Permian units.
The modelling quantifies the effects of this depressurisation as follows:
- a reduction in flow to groundwater management zone 3 – 14 ML over life of mine, average rate 0.5 ML/year
- a reduction in flow to groundwater management zone 7 – 1020.8 ML over life of mine, average rate 34 ML/year
- a reduction in flow to groundwater management zone 8 – 35.5 ML over life of mine. However, over the life of the mine, it is reported that the average result is an increase of flow from the Permian to the alluvium at a rate of 1.1 ML/year.
The proponent argues that, although water from the alluvium and the Mooki River (47.5 ML/year or 0.13 ML/day, in year 24) will flow to the Permian units due to depressurisation resulting from the mine, post mining, when the zone of depressurisation has fully retracted, there will be a net increase in flow to the Mooki River of 7.3 ML/year (0.02 ML/day).
Groundwater levels in the final void are predicted to equilibrate at approximately 303 mAHD, after approximately 2000 years. This level remains below theby approximately 1 to 2 m. Consequently the final void will act as a groundwater sink. The water level in the final void is predicted to stabilise well below the crest of the pit, and therefore the pit void is not predicted to spill.
Product Finalisation date
- 2.1.1 Geography
- 2.1.2 Geology
- 2.1.3 Hydrogeology and groundwater quality
- 2.1.4 Surface water hydrology and water quality
- 2.1.5 Surface water – groundwater interactions
- 18.104.22.168 Observed data
- 22.214.171.124 Previous catchment-scale investigations on stream-aquifer interactions
- 126.96.36.199 Overview of controls on surface water – groundwater connectivity based on previous investigations in the Namoi river basin
- 188.8.131.52 Statistical analysis and interpolation
- 184.108.40.206 Gaps
- 2.1.6 Water management for coal resource developments
- 220.127.116.11 Boggabri Coal Mine (baseline) and Boggabri Coal Expansion Project (ACRD)
- 18.104.22.168 Narrabri North Mine (baseline)
- 22.214.171.124 Narrabri South Project (ACRD)
- 126.96.36.199 Rocglen Mine (baseline)
- 188.8.131.52 Sunnyside Mine (baseline)
- 184.108.40.206 Tarrawonga Mine (baseline) and Tarrawonga Coal Expansion Project (ACRD)
- 220.127.116.11 Caroona Coal Project (ACRD)
- 18.104.22.168 Maules Creek Project (ACRD)
- 22.214.171.124 Watermark Coal Project (ACRD)
- 126.96.36.199 Vickery Coal Project (ACRD)
- 188.8.131.52 Narrabri Gas Project (ACRD)
- 184.108.40.206 Mine footprints
- Currency of scientific results
- Contributors to the Technical Programme
- About this technical product