The principle objective for rehabilitation of mined land at Liddell Coal is to return the site to a condition where its landforms, soils, hydrology, and flora and fauna are self-sustaining and compatible with the surrounding land uses. The proposed end land use for the site includes a combination of grazing and bushland/wildlife habitat. The post mining landscape will be dominated by a land capability of Class VI grazing land and Class VI and VII bushland habitat. The Liddell Coal rehabilitation strategy includes approaches to landform design and visual impact, slope angles, surface preparation, revegetation and habitat planning. Rehabilitation of disturbed land is carried out in accordance with the Liddell Colliery Mining Operations Plan (MOP).
The post-mining landform design of Liddell has been undertaken in accordance with the Synoptic Plan: Integrated Landscapes for Coal Mine Rehabilitation in the Hunter Valley of NSW developed by the NSW Department of Primary Industries – Mineral Resources (DPI-MR)(1999). Elements such as drainage paths, contour drains, ridgelines, and emplacements are shaped into undulating informal profiles in keeping with natural landforms of the surrounding environment and allowing for a greater diversity of plant species over time.
The drainage characteristics for the site have been developed in accordance with the Draft Guidelines for Designing Stable Drainage Lines on Rehabilitated Mine Sites formulated by the former NSW Department of Land and Water Conservation (1999). The drainage system at Liddell Coal provides for the combination of a connected surface drainage network and distributed storage/infiltration. The system integrates surface storage during periods of high runoff and manages deep infiltration to levels which can be safely tolerated and at the same time reduced size surface drainage conveyances to remove excess water safely from the system.
Sedimentation dams are incorporated into the final landform to collect runoff from rehabilitated areas and allow time for suspended sediment to settle prior to the water leaving the site.
A pre-clearance inspection is undertaken before any clearing can take place. Vegetation is cleared prior to mining using dozers. Stripping of vegetation is kept to a minimum width in advance of operations required for safe working conditions, which minimises dust generation, soil erosion and the risk of deterioration in surface water quality. Topsoil is pushed into windrows by the dozers for removal by loader or excavator and truck to reshaped areas or stockpiling. Long-term topsoil stockpiles are used from time to time during rehabilitation and locations are chosen which will not be subject to disturbance with overburden material. The topsoil stockpiles are seeded until they are required for use in the rehabilitation programme.
Overburden removal is undertaken by excavators and trucks, and shaping of the spoil piles into final landform profiles is undertaken by large dozers. Small dozers spread the topsoil and are used to construct contour drains and conduct final ripping to key in the topsoil. Where necessary, gypsum is applied to the spread topsoil prior to the sowing of pasture and tree areas in order to improve the soil characteristics.
Revegetation commences as soon as possible after topsoil has been placed on the reshaped surfaces. The type of revegetation to be used is assessed at each proposed rehabilitation site to determine the most suitable method for that site. Both tree and pasture species are normally utilised in the revegetation program.
Approximately 30 per cent of all areas requiring revegetation will be sown with native tree seed. The vegetation mix and position is formulated in accordance with the DPI-MR Synoptic Plan and the Liddell Colliery MOP.
Tree seed is applied with a pre-treatment to ensure effective germination. Seed is then mixed and evenly spread on the surface. The tree seeding mix generally contains seven understorey species (mostly Acacia) and nine overstorey (all Eucalypt) species.