Underground Mine

A high production mining method is required due to the size of the resource, the large depth of cover and the corresponding high cost of surface to underground access. Longwall mining provides the best option in terms of:

• workplace safety;
• financial viability;
• production capacity;
• environmental considerations; and
• resource recovery.

The Wallarah seam, averaging around 6m thick will be mined by a longwall system, with the coal conveyed to the surface via a drift conveyor system (this can be thought of as being similar to a moving walkway commonly seen in large shopping centres). The coal will be processed to produce up to 5 Million tonnes per annum of product coal from the mine.

The mine layout will incorporate a variety of longwall panel widths and extraction heights in order to optimise economic reserve recovery taking into account environmental and subsidence constraints, including:

• Special subsidence limitation to protect structures in the Hue Hue Mine Subsidence District;
• Existing flood prone valleys and structures;
• Management of surface water and groundwater, including water catchment functions.

The mine will operate 24 hours per day, seven days per week.

Product and Market

The mine will produce a single 14-18% ash product to be marketed for export and domestic electricity generation.

Gas is a normal by-product of coal mining while providing safe and well ventilated working areas. It will be extracted from the mine and brought to the surface facilities by underground pipeline and used either on site to generate power or transferred into the general gas grid.

Subsidence Design Considerations

Surface subsidence is a lowering of the ground surface level in an area above underground extraction. The degree of subsidence is dependent on a variety of complex factors, including the width of the longwall panel, the extraction height (the thickness of coal to be mined) and depth of cover (how deep underground the coal is extracted from). By decreasing panel width and/or extraction height, lower levels of surface subsidence would be expected.

In 1998 the Hue Hue Mine Subsidence District, which overlies the initial mining zone, was proclaimed. The outcome of this proclamation is that mining induced ground movement limits are:

• Maximum ground strain 3 mm/m
• Maximum ground tilt 4 mm/m

The Wyong Mine Subsidence District has no real ground movement limits applied. Rather, building methods within the district are required to be modified to cater for the levels of mine subsidence that would be likely upon extraction of the seam utilizing 250 m wide longwall panels with an extraction height of up to 5 m.

An additional consideration is that the Dooralong and Yarramalong valleys are subject to flooding. Mine plans have been created which reduce the amount of subsidence within the flood plain area, which will minimize the increase of flood impacts.

Coal Processing

The coal processing consists of crushing only. No tailings or reject will be produced as the mine will not require a coal washing plant. Water generated by the mine will be recycled and reused in the process, and any surplus water will be treated before being made available for other water uses or purposes.

Site Water Management

An on-site sewage treatment plant is planned for the Tooheys Road and Buttonderry sites. This would service the offices and bathhouses.

Holding and settling ponds for mine water and surface runoff are integrated into the mine pit top design in order to protect the environment and provide water for surface usage.

Water and Mine Water Disposal

Studies to date indicate that the mine will make up to 3 ML per day (after 20 years of mining). In the early years there is likely to be a slight water deficit, but a surplus will occur in later years. Water will come from the coal seam ifself, not surface aquifers or streams.

As the underground water produced is expected to be moderately saline it is proposed to construct a treatment plant to improve water quality that can then be used in the mine for cooling, dust suppression and underground equipment purposes. Surplus water will be treated to an appropriate standard that would be available for a range of other beneficial uses so that the community and environment can potentially gain benefits from this mining water source. For example, the water could be available for industry or, for example, for discharge into the Wyong water supply catchment while enhancing environmental flows in the local waterways.

It is envisaged that potable water for drinking and amenities would at first be trucked on-site before eventually connecting the site to town supply.

Gas Regimes

Results from gas testing have been compiled and a comprehensive assessment undertaken. The following conclusions have been made and incorporated in the mine plan:

• Gas content is generally restricted to the coal seam and consists of greater than 95% methane;
   
• Gas content for areas not affected by intrusions can be predicted confidently from depth, ash content, and volatile matter;
   
• The regional gas content gradient is determined by depth below sea level, with gas contents in-seam ranging from 6.0 to 8.9 m³/t;
   
  
• Gas drainage or gas capture from the coal seam, underground workings and ventilation system will be required to achieve satisfactory gas levels with high production rates and acceptable ventilation levels;

• The gas will be brought to the surface by an underground pipeline running through the underground mine workings to the surface at the Tooheys Road site. The gas will then be processed and used either on site to generate power or transfered to the general gas grid.

Transportation

All coal produced will be transported to the north by rail either to the Port of Newcastle or Power Stations along the route.

The project will primarily generate road traffic movements from the construction phase that will last up to three years. After the mine becomes operational, traffic generation will primarily consist of workforce movements and stores deliveries.

Greenhouse Gas

The W2CP embraces the concept of reducing its carbon footprint and has incorporated energy efficiencies throughout the design of the mining and processing operations, buildings and transport systems.  The project includes the capture and reuse of methane and will actively participate in any future carbon trading scheme.

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