2.1.6.8 Maules Creek Project (ACRD)

The Maules Creek Mine is an open-cut coal mine that commenced production in 2015. It is approved to extract up to 13 Mt/year ROM coal over a project life of 20 years. The mine has identified recoverable coal reserves of 381 Mt.

2.1.6.8.1 Mine water use

Water sources for the Maules Creek Mine are:

The water management plan lists the extraction of groundwater from existing or new bores as a measure that may be implemented if water demand on-site looks like exceeding licensed entitlement.

Water balance modelling has been undertaken over the historical climate record, giving 106 ‘realisations’ of the performance of the water management system. The modelling indicated the requirements for water from external sources and examined on-site storage requirements to prevent unlicensed discharges from site. Table 25 presents the modelled site water balance for Maules Creek Mine for the median runoff inflows for the first five years of the mine life.

Table 25 Annual water balance for realisation with median runoff inflows for Maules Creek Mine

^aNote that Maules Creek Mine reports total vehicle wash water requirement, whereas some mines only report the vehicle wash losses. The losses are that part of the water requirement that is not recycled through the system.

CHPP = coal handling and preparation plant

Data: Whitehaven Coal Pty Ltd (2014)

River water (accessed via a pipeline from the Namoi River) will be used in conjunction with water from the mine water dam to supply the CHPP and on-site dust suppression. River water will be the sole water source for vehicle washdown.

On average it is likely that annual volumes of approximately 1000 to 1800 ML will be required. The maximum simulated volume required for any year was 2730 ML. The mine holds high security surface water licences for 3000 ML/year. Additional groundwater licensing will be required (Table 26).

Table 26 Predicted groundwater take versus water access licences

WAL = water access licence

Data: Whitehaven Coal Pty Ltd (2014)

2.1.6.8.2 Surface water management

The Maules Creek Mine is on the southern side of Back Creek, an ephemeral tributary of Maules Creek.

Runoff from undisturbed areas on-site, which would naturally drain toward the open-cut pit, is directed to the highwall dams. Surface water will be discharged off-site from highwall dams into Back Creek. There has been a modelled maximum discharge of 88 ML/year, for the median runoff climate scenario (WRM Water and Environment, 2011).

Runoff from disturbed areas on-site is directed to the network of on-site storages and sediment dams. Excess water in most storages on the site, including the pit, is pumped to the mine water dam (MWD), which has a maximum operating volume of 890 ML. When the MWD is at maximum volume all pumping ceases. Water from the raw water dam is not pumped to MWD.

All other water (in the water balance) will be lost to evaporation, or used on-site in either the CHPP or for dust suppression or vehicle washdown.

Pollutant concentration limits have been specified in the environment protection licence (EPL) for discharge from sediment dams. Where pollutant concentrations in sediment dams after a runoff event are less than the limits specified in the EPL, basins may be dewatered to receiving waters (Whitehaven Coal Pty Ltd, 2014).

Should on-site water storages overflow, discharge from the raw water dam and up to five sediment dams will go into Back Creek. The modelled maximum spill is 20 ML/year, for median rainfall scenario. Modelling showed that proposed operating rules meant that the MWD did not spill under any climate scenarios.

2.1.6.8.3 Groundwater management

Groundwater modelling was undertaken to estimate the impacts of the project on local groundwater systems (AGE Pty Ltd, 2011). The modelling found that the simulated rates of groundwater seepage into the mine pit varied throughout the life of the mine. The seepage rate peaked at about 1460 ML/year in year 14. The mean annual groundwater inflow to the pit is 550 ML/year, over the 21 year mine life.

The Maules Creek Mine will impact on the groundwater in the alluvium in three Upper Namoi groundwater management zones: zone 4, zone 5 and zone 11. The modelling indicates that the mine will intercept flow to the alluvial aquifer at a maximum rate of 128 ML/year at the end of mining. The lowest elevation of the pit floor will be reached in year 14, at 82 mAHD.

A final void is proposed that will be approximately 350 ha and up to a maximum depth of 290 m. Based on simulated inflows and outflows, water will not spill from the final void (water level will equilibrate about 100 m below overflow level).

Long-term modelling shows that final void groundwater inflows will be around 584 ML/year, which represents steady state reached in the 1000 year groundwater model.