The Rocglen Mine (formerly known as Belmont Coal Project) is an open-cut mine approximately 28 km north of Gunnedah. The mine was approved in 2008 and mining commenced in the same year. The mine is approved to produce up to 1.5 Mt/year of ROM coal using a truck and excavator method. The mine is anticipated to have a production life of between seven and ten years with a potential resource recovery of up to 15 Mt. Coal is extracted from the Upper Glenroc, Lower Glenroc and Belmont coal members within the Maules Creek Formation. The coal is transported to the Whitehaven CHPP for preparation and distribution to customers. In 2011 approval was given to expand operations by increasing the area of the open-cut pit, to maximise resource recovery, although the rate of production did not increase. The footprint of the open-cut will increase by approximately 50 to 164 ha. The information presented in the rest of this section refers to the approved mine extension.
220.127.116.11.1 Site water use and management
Clean water is managed by diversion away from disturbed areas. Dirty water is managed through the capture and storage of runoff water from disturbed areas across the site, and is treated in a series of sediment basins prior to reuse on-site or discharge at a licensed discharge point. Captured water is reused on-site for dust suppression and around crushing and screening operations. A mine water dam holds water to be pumped to and from the open-cut pit. A bore pump dam stores water to be pumped to and from a groundwater bore.
Most water required on-site will be used for dust suppression, including in the crushing and screening process. A nominal amount of potable water and water for ablutions will be trucked in from an external source.
The annual water requirements of the mine were originally estimated to range between 90 and 109 ML/year (GSS Environmental, 2010). A recent update of the mine water management plan (Whitehaven Coal Pty Ltd, 2015b) reported similar levels of observed usage during operations. Water balance modelling shows the predicted rates of water use and discharge from site. Table 17 shows the modelled water balance results for year 5, being the middle year of the estimated mine life, for three climate scenarios.
Table 17 Water balance model results for year 5 at Rocglen Mine
aA wide scatter of bore water use volumes were predicted, the line of best fit was used to give the values in the table; showing a zero supply requirement for the 10th (dry), 50th (median) and 90th (wet) percentile years, however the modelling also showed that there will be occasional years where a supply of up to 35 ML/year may be required (GSS Environmental, 2010).
bChange in water storage is calculated from other data and may not sum from values above.
Source: Whitehaven Coal Pty Ltd (2015b)
The water balance modelling has predicted a shortfall in water for below average rainfall years, with an excess in wet years. Shortfalls will be supplemented by clean water generated from runoff in the eastern part of the catchment, and harvested in dams on-site. It is expected that discharge from the site will occur infrequently.
The current environment protection licence permits wet weather discharge from two identified discharge points. The operator interprets the licence to mean that in practice they may also discharge (after effective water treatment) during dry periods to dewater dams (Whitehaven Coal Pty Ltd, 2015b, p. 12).
Historical evidence indicates that short periods of high rainfall have previously resulted in discharges and it is considered likely that there will be two to four discharge events per year (Whitehaven Coal Pty Ltd, 2015b).
18.104.22.168.2 Surface water management
The Rocglen Mine is situated in a small valley between the elevated areas of Vickery State Forest to the west and the Community Conservation Area (zone 2) (Aboriginal Areas) Kelvin to the east. The valley ultimately forms part of the Namoi River floodplain.
The mine site is on the valley floor, with elevations ranging between approximately 280 and 300 mAHD. Prior to mining operations, there were several drainage lines that would have entered the site from the east and drained into the two ephemeral creeks within the mine. Due to the topography of the site, a number of drainage lines have been diverted around the site to keep clean water off-site.
The clean water storage dams that will be used for water supply have a combined capacity of 17 ML, which is well within the maximum harvestable right volume for the project site, of 32 ML.
22.214.171.124.3 Groundwater management
Alluvium associated with the Namoi River and tributaries borders the mining lease to the north and also exists approximately 2 km south and south-west of the mining area.
The geology underlying the alluvium near the mine is structurally disrupted by significant folding and faulting. The Hunter-Mooki Thrust Fault System is a few kilometres east of the mine. Several smaller faults, with near vertical displacements of up to 150 m, surround the mine (Whitehaven Coal Pty Ltd, 2015b). Analysis of groundwater samples from the Maules Creek Formation shows that quality is spatially highly variable.
The expected pit depth is to the base of the Belmont coal member of the Maules Creek Formation. The floor of the Belmont Seam is generally at about 240 to 260 mAHD dropping to about 180 to 200 mAHD on the eastern and western sides of the pit (Douglas Partners, 2010).
Inflows to the open-cut pit are estimated by monitoring the volume of water pumped out of the pit (and adjusting for rainfall inflows) and monitoring bore water levels to estimate groundwater gradients towards the pit. Head gradients combined with estimates of strata permeability are used annually to calculate anticipated groundwater flows toward the pit (Whitehaven Coal Pty Ltd, 2015b).
Connectivity with the Namoi River Alluvium is considered to be limited, however there is some uncertainty regarding the leakage which will occur from the Namoi River Alluvium into the Maules Creek Formation due to the mine. Monitoring bores were installed to provide additional data with which to refine the estimates of leakage rates (Douglas Partners, 2010).
Negligible inflows to the mine pit are predicted from future operations (Douglas Partners, 2010). The exception to this is in the eastern extent of the mine where the seams dip more steeply, and hence the pit will be deeper, and pit inflows are estimated to be about 63 ML/year.
A groundwater model was developed (Douglas Partners, 2010) presenting four possible hydrogeological conceptualisations. Case 1 was modelled as having upper bound permeability; Case 1C with a permeable Western Fault; Case 2 was modelled as having a lower bound permeability; and Case 2C with a permeable Western Fault. Table 18 shows the predicted groundwater inflows to the pit for the different modelled conceptualisations.
Site data suggests that Case 2 flows are more likely than Case 1 flows. The Douglas Partners (2010) modelling report does note uncertainty in site conditions, especially to the south-west of the site.
The mean mine inflows are expected to be on the order of 18.8 to 47 ML/year midway through the project (year 5) and between 40.8 and 125 ML/year at the end of mining (approximately 2020) (Douglas Partners, 2010).
Table 18 Modelled pit inflows at Rocglen Mine
aassumes instant excavation and over estimates initial flow rates
bmeasured at constant head boundaries
Data: Douglas Partners (2010)
Most of the predicted impacts in the alluvium will arise from a loss of storage. However, during later years in the life of the mine the impacts on flows to the alluvium increase slightly, with the greatest impact to the southern alluvium. The northern alluvium is up gradient and less hydraulically connected.
Expected final void depth after partial backfilling will be about 250 mAHD, with the exception of an area of about 38 ha in the southern side of the pit where the surface levels will range from 225 to 250 mAHD (Douglas Partners, 2010, p. 60).
It is expected that groundwater inflow and rainfall recharge into the pit will lead to surface water in the southern part of the pit where the ground elevation is locally lower. Inflow to the pit will be offset by evaporation from the area of surface water, and it is therefore unlikely that groundwater levels will recover to pre-development levels. The final water levels are expected to range between 220 and 245 mAHD, which may take 20 to 50 years to occur. It is expected that local increases in salinity are likely within the final void, but would not impact upon the surrounding groundwater and land.
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
- 126.96.36.199 Observed data
- 188.8.131.52 Previous catchment-scale investigations on stream-aquifer interactions
- 184.108.40.206 Overview of controls on surface water – groundwater connectivity based on previous investigations in the Namoi river basin
- 220.127.116.11 Statistical analysis and interpolation
- 18.104.22.168 Gaps
- 2.1.6 Water management for coal resource developments
- 22.214.171.124 Boggabri Coal Mine (baseline) and Boggabri Coal Expansion Project (ACRD)
- 126.96.36.199 Narrabri North Mine (baseline)
- 188.8.131.52 Narrabri South Project (ACRD)
- 184.108.40.206 Rocglen Mine (baseline)
- 220.127.116.11 Sunnyside Mine (baseline)
- 18.104.22.168 Tarrawonga Mine (baseline) and Tarrawonga Coal Expansion Project (ACRD)
- 22.214.171.124 Caroona Coal Project (ACRD)
- 126.96.36.199 Maules Creek Project (ACRD)
- 188.8.131.52 Watermark Coal Project (ACRD)
- 184.108.40.206 Vickery Coal Project (ACRD)
- 220.127.116.11 Narrabri Gas Project (ACRD)
- 18.104.22.168 Mine footprints
- Currency of scientific results
- Contributors to the Technical Programme
- About this technical product