2.1.6.9 Watermark Coal Project (ACRD)

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 (Hansen Bailey, 2013). The mine will target the Hoskissons Coal and Melville Coal Member (Hansen Bailey, 2013).

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 (Hansen Bailey, 2013).

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. Project activities are planned to take place within a disturbance area of approximately 4084 ha (Shenhua Watermark Coal, 2013).

2.1.6.9.1 Mine water use

Water balance modelling was undertaken and showed that, while most site water requirements will be met by reuse of on-site runoff and groundwater inflows, the average net water deficit will be 21 to 162 ML/year.

Table 27 provides a summary of the water use requirements for the project throughout the mine life.

Where water is required additional to that available from the captured dirty surface water and 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 (Hansen Bailey, 2013).

Data: after WRM Water and Environment (2013)

2.1.6.9.2 Surface water management

The mine area is located within the Mooki river basin, a tributary of the Namoi River. Runoff 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:

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 (Hansen Bailey, 2013).

2.1.6.9.3 Groundwater management

Groundwater seepage into the proposed mining area is predicted to vary throughout the mine life (Table 28).

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.

Data: WRM Water and Environment (2013)

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 (AGE Pty Ltd, 2013). The variability in the seepage rate is due to the different geological conditions that will be encountered in different mine areas.

The groundwater model indicates depressurisation in the underlying Permian strata will reduce upward water pressure, and close to the mining areas will induce downward vertical flow from the overlying alluvial aquifers in the underlying Permian units.

The modelling quantifies the effects of this depressurisation as follows:

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 the regional watertable by 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.